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Vennelakanti V, Jeon M, Kulik HJ. How Do Differences in Electronic Structure Affect the Use of Vanadium Intermediates as Mimics in Nonheme Iron Hydroxylases? Inorg Chem 2024; 63:4997-5011. [PMID: 38428015 DOI: 10.1021/acs.inorgchem.3c04421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/03/2024]
Abstract
We study active-site models of nonheme iron hydroxylases and their vanadium-based mimics using density functional theory to determine if vanadyl is a faithful structural mimic. We identify crucial structural and energetic differences between ferryl and vanadyl isomers owing to the differences in their ground electronic states, i.e., high spin (HS) for Fe and low spin (LS) for V. For the succinate cofactor bound to the ferryl intermediate, we predict facile interconversion between monodentate and bidentate coordination isomers for ferryl species but difficult rearrangement for vanadyl mimics. We study isomerization of the oxo intermediate between axial and equatorial positions and find the ferryl potential energy surface to be characterized by a large barrier of ca. 10 kcal/mol that is completely absent for the vanadyl mimic. This analysis reveals even starker contrasts between Fe and V in hydroxylases than those observed for this metal substitution in nonheme halogenases. Analysis of the relative bond strengths of coordinating carboxylate ligands for Fe and V reveals that all of the ligands show stronger binding to V than Fe owing to the LS ground state of V in contrast to the HS ground state of Fe, highlighting the limitations of vanadyl mimics of native nonheme iron hydroxylases.
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Affiliation(s)
- Vyshnavi Vennelakanti
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Mugyeom Jeon
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Heather J Kulik
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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2
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Xiang J, Pan Y, Liu LL, Wang LX, Yang H, Cheng SC, Yiu SM, Leung CF, Ko CC, Lau KC, Lau TC. Visible Light-Induced Oxidation of Alcohols by a Luminescent Osmium(VI) Nitrido Complex: Evidence for the Generation of PhIO + as a Highly Active Oxidant in the Presence of PhIO. J Am Chem Soc 2023; 145:9129-9135. [PMID: 37053567 DOI: 10.1021/jacs.3c00760] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/15/2023]
Abstract
Although alcohols are readily oxidized by a variety of oxidants, their oxidation by metal nitrido complexes is yet to be studied. We report herein visible-light-induced oxidation of primary and secondary alcohols to carbonyl compounds by a strongly luminescent osmium(VI) nitrido complex (OsN). The proposed mechanism involves initial rate-limiting hydrogen-atom transfer (HAT) from the α-carbon of the alcohol to OsN*. Attempts to develop catalytic oxidation of alcohols by OsN* using PhIO as the terminal oxidant resulted in the formation of novel osmium(IV) iminato complexes in which the nitrido ligand is bonded to a δ-carbon of the alcohol. Experimental and theoretical studies suggest that OsN* is reductively quenched by PhIO to generate PhIO+, which is a highly active oxidant that readily undergoes α- and δ-C-H activation of alcohols.
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Affiliation(s)
- Jing Xiang
- Key Laboratory of Optoelectronic Chemical Materials and Devices, Ministry of Education, Jianghan University, Wuhan 430056, China
- College of Chemistry and Environmental Engineering, Yangtze University, Jingzhou, Hubei 434020, China
| | - Yi Pan
- Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong 999077, China
| | - Lu-Lu Liu
- College of Chemistry and Environmental Engineering, Yangtze University, Jingzhou, Hubei 434020, China
| | - Li-Xin Wang
- College of Chemistry and Environmental Engineering, Yangtze University, Jingzhou, Hubei 434020, China
| | - Huan Yang
- College of Chemistry and Environmental Engineering, Yangtze University, Jingzhou, Hubei 434020, China
| | - Shun-Cheung Cheng
- Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong 999077, China
| | - Shek-Man Yiu
- Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong 999077, China
| | - Chi-Fai Leung
- Department of Science and Environmental Studies, The Education University of Hong Kong, Tai Po N. T., Hong Kong 00000, China
| | - Chi-Chiu Ko
- Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong 999077, China
| | - Kai-Chung Lau
- Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong 999077, China
| | - Tai-Chu Lau
- Research Center for Eco-Environmental Engineering, Dongguan University of Technology, Dongguan, Guangdong 523808, China
- Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong 999077, China
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3
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Zhao H, Yuan X, Bai F, Wang Y, Zhao L. Colorimetric determination of cholesterol based on the peroxidase-like activity of Cu-Salt-Fe nanozyme with multiple active sites. Mikrochim Acta 2023; 190:140. [PMID: 36932288 DOI: 10.1007/s00604-023-05697-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Accepted: 02/09/2023] [Indexed: 03/19/2023]
Abstract
A strategy to enhance the peroxidase-like activity of the hemin composite is presented. The Cu-Salt-Fe with enhanced activity was synthesized by one-step heat treatment and applied to the colorimetric determination of free cholesterol in human serum. Phosphate can act in complexing Cu2+ to form a carrier Cu-Floc with a large specific surface area. The coordination effect of Cu-Floc with hemin was used to disperse and load hemin to form Cu-Floc-Hemin from which Cu-Salt-Fe was prepared. The Cu-Salt-Fe exhibits a synergistic catalytic effect of Cu-Salt, Fe2+, Fe3+, or Fe-Nx active sites in amplification of H2O2 oxidation. As expected, Cu-Salt-Fe triggered H2O2-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), resulting in H2O2-dependent absorbance changes at 652 nm. A cholesterol oxidase (ChOx)/Cu-Salt-Fe-TMB colorimetric sensing system exhibited excellent cholesterol determination performance in the range 5-1200 μM with a detection limit of 2.73 μM. Cholesterol recoveries from the three-level spiked serum ranged from 92.2 to 98.9% (RSD ≤ 5.4). This colorimetric sensing system not only provided a strategy for the determination of endogenous substances with H2O2 as an intermediate, but also provided a new design idea (carrier selection, activity enhancement method) for the development of other artificial enzymes with the same catalytic core.
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Affiliation(s)
- Hanqing Zhao
- Department of Pharmacy, Shenyang Pharmaceutical University, Shenyang, 110016, Liaoning, People's Republic of China
| | - Xucan Yuan
- Department of Pharmacy, Shenyang Pharmaceutical University, Shenyang, 110016, Liaoning, People's Republic of China
| | - Fujuan Bai
- Department of Pharmacy, Shenyang Pharmaceutical University, Shenyang, 110016, Liaoning, People's Republic of China
| | - Yang Wang
- Department of Pharmacy, Shenyang Pharmaceutical University, Shenyang, 110016, Liaoning, People's Republic of China.
| | - Longshan Zhao
- Department of Pharmacy, Shenyang Pharmaceutical University, Shenyang, 110016, Liaoning, People's Republic of China.
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4
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Vennelakanti V, Mehmood R, Kulik HJ. Are Vanadium Intermediates Suitable Mimics in Non-Heme Iron Enzymes? An Electronic Structure Analysis. ACS Catal 2022. [DOI: 10.1021/acscatal.2c01143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Vyshnavi Vennelakanti
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Rimsha Mehmood
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Heather J. Kulik
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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5
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Carrascoza F, Surducan M, Eriksson LA, Silaghi-Dumitrescu R. Interaction of cobalt and iron hydroperoxo bleomycin with deoxyribonucleic acid (DNA): Dynamic vs. electronic structure considerations. Inorganica Chim Acta 2020. [DOI: 10.1016/j.ica.2020.119682] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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6
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Monika, Ansari A. Mechanistic insights into the allylic oxidation of aliphatic compounds by tetraamido iron( v) species: A C–H vs. O–H bond activation. NEW J CHEM 2020. [DOI: 10.1039/d0nj03095c] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This work is based on a deep insight into a comparative study of C–H vs. O–H bond activation of allylic compound by the high valent iron complex. Our theoretical findings can help to design catalysts with better efficiency for catalytic reactions.
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Affiliation(s)
- Monika
- Department of Chemistry
- Central University of Haryana
- Mahendergarh-123031
- India
| | - Azaj Ansari
- Department of Chemistry
- Central University of Haryana
- Mahendergarh-123031
- India
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7
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Anderson CM, Aboelenen AM, Jensen MP. Competitive Intramolecular Amination as a Clock for Iron-Catalyzed Nitrene Transfer. Inorg Chem 2019; 58:1107-1119. [DOI: 10.1021/acs.inorgchem.8b02284] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Caitlin M. Anderson
- Department of Chemistry and Biochemistry, Ohio University, Athens, Ohio 45701, United States
| | - Ahmed M. Aboelenen
- Department of Chemistry and Biochemistry, Ohio University, Athens, Ohio 45701, United States
| | - Michael P. Jensen
- Department of Chemistry and Biochemistry, Ohio University, Athens, Ohio 45701, United States
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8
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Pattanayak S, Jasniewski AJ, Rana A, Draksharapu A, Singh KK, Weitz A, Hendrich M, Que L, Dey A, Sen Gupta S. Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with Fe V═O and Fe IV═O Units. Inorg Chem 2017; 56:6352-6361. [PMID: 28481521 DOI: 10.1021/acs.inorgchem.7b00448] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
In this report we compare the geometric and electronic structures and reactivities of [FeV(O)]- and [FeIV(O)]2- species supported by the same ancillary nonheme biuret tetraamido macrocyclic ligand (bTAML). Resonance Raman studies show that the Fe═O vibration of the [FeIV(O)]2- complex 2 is at 798 cm-1, compared to 862 cm-1 for the corresponding [FeV(O)]- species 3, a 64 cm-1 frequency difference reasonably reproduced by density functional theory calculations. These values are, respectively, the lowest and the highest frequencies observed thus far for nonheme high-valent Fe═O complexes. Extended X-ray absorption fine structure analysis of 3 reveals an Fe═O bond length of 1.59 Å, which is 0.05 Å shorter than that found in complex 2. The redox potentials of 2 and 3 are 0.44 V (measured at pH 12) and 1.19 V (measured at pH 7) versus normal hydrogen electrode, respectively, corresponding to the [FeIV(O)]2-/[FeIII(OH)]2- and [FeV(O)]-/[FeIV(O)]2- couples. Consistent with its higher potential (even after correcting for the pH difference), 3 oxidizes benzyl alcohol at pH 7 with a second-order rate constant that is 2500-fold bigger than that for 2 at pH 12. Furthermore, 2 exhibits a classical kinteic isotope effect (KIE) of 3 in the oxidation of benzyl alcohol to benzaldehyde versus a nonclassical KIE of 12 for 3, emphasizing the reactivity differences between 2 and 3.
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Affiliation(s)
- Santanu Pattanayak
- Chemical Engineering Division, CSIR-National Chemical Laboratory , Pune 411008, India
| | - Andrew J Jasniewski
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States
| | - Atanu Rana
- Department of Inorganic Chemistry, Indian Association for the Cultivation of Science , Kolkata 700032, India
| | - Apparao Draksharapu
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States
| | - Kundan K Singh
- Chemical Engineering Division, CSIR-National Chemical Laboratory , Pune 411008, India
| | - Andrew Weitz
- Department of Chemistry, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States
| | - Michael Hendrich
- Department of Chemistry, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States
| | - Lawrence Que
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States
| | - Abhishek Dey
- Department of Inorganic Chemistry, Indian Association for the Cultivation of Science , Kolkata 700032, India
| | - Sayam Sen Gupta
- Department of Chemical Sciences, Indian Institute of Science Education and Research-Kolkata , Mohanpur, West Bengal 741246, India
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9
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Leto DF, Massie AA, Rice DB, Jackson TA. Spectroscopic and Computational Investigations of a Mononuclear Manganese(IV)-Oxo Complex Reveal Electronic Structure Contributions to Reactivity. J Am Chem Soc 2016; 138:15413-15424. [PMID: 27802057 DOI: 10.1021/jacs.6b08661] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The mononuclear Mn(IV)-oxo complex [MnIV(O)(N4py)]2+, where N4py is the pentadentate ligand N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine, has been proposed to attack C-H bonds by an excited-state reactivity pattern [ Cho, K.-B.; Shaik, S.; Nam, W. J. Phys. Chem. Lett. 2012 , 3 , 2851 - 2856 (DOI: 10.1021/jz301241z )]. In this model, a 4E excited state is utilized to provide a lower-energy barrier for hydrogen-atom transfer. This proposal is intriguing, as it offers both a rationale for the relatively high hydrogen-atom-transfer reactivity of [MnIV(O)(N4py)]2+ and a guideline for creating more reactive complexes through ligand modification. Here we employ a combination of electronic absorption and variable-temperature magnetic circular dichroism (MCD) spectroscopy to experimentally evaluate this excited-state reactivity model. Using these spectroscopic methods, in conjunction with time-dependent density functional theory (TD-DFT) and complete-active space self-consistent-field calculations (CASSCF), we define the ligand-field and charge-transfer excited states of [MnIV(O)(N4py)]2+. Through a graphical analysis of the signs of the experimental C-term MCD signals, we unambiguously assign a low-energy MCD feature of [MnIV(O)(N4py)]2+ as the 4E excited state predicted to be involved in hydrogen-atom-transfer reactivity. The CASSCF calculations predict enhanced MnIII-oxyl character on the excited-state 4E surface, consistent with previous DFT calculations. Potential-energy surfaces, developed using the CASSCF methods, are used to determine how the energies and wave functions of the ground and excited states evolved as a function of Mn═O distance. The unique insights into ground- and excited-state electronic structure offered by these spectroscopic and computational studies are harmonized with a thermodynamic model of hydrogen-atom-transfer reactivity, which predicts a correlation between transition-state barriers and driving force.
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Affiliation(s)
- Domenick F Leto
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , Lawrence, Kansas 66045, United States
| | - Allyssa A Massie
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , Lawrence, Kansas 66045, United States
| | - Derek B Rice
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , Lawrence, Kansas 66045, United States
| | - Timothy A Jackson
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , Lawrence, Kansas 66045, United States
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10
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Tang Z, Wang Y, Cui X, Yang Y, Tian J, Fei X, Lv S. Theoretical study of the effect of ligand topology on Fe(IV)O and Ru(IV)O complex reactivities. Inorganica Chim Acta 2016. [DOI: 10.1016/j.ica.2016.01.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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11
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Ansari A, Rajaraman G. ortho-Hydroxylation of aromatic acids by a non-heme Fe(V)=O species: how important is the ligand design? Phys Chem Chem Phys 2015; 16:14601-13. [PMID: 24812659 DOI: 10.1039/c3cp55430a] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
There is a growing interest in probing the mechanism of catalytic transformations effected by non-heme iron-oxo complexes as these reactions set a platform for understanding the relevant enzymatic reactions. The ortho-hydroxylation of aromatic compounds is one such reaction catalysed by iron-oxo complexes. Experimentally [Fe(II)(BPMEN)(CH3CN)2](2+) (1) and [Fe(II)(TPA)(CH3CN)2](2+) (2) (where TPA = tris(2-pyridylmethyl)amine and BPMEN = N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine) complexes containing amino pyridine ligands along with H2O2 are employed to carry out these transformations where complex 1 is found to be more reactive than complex 2. Herein, using density functional methods employing B3LYP and dispersion corrected B3LYP (B3LYP-D) functionals, we have explored the mechanism of this reaction to reason out the importance of ligand design in fine-tuning the reactivity of such catalytic transformations. Dispersion corrected B3LYP is found to be superior to B3LYP in predicting the correct ground state of these species and also yields lower barrier heights than the B3LYP functional. Starting the reaction from the Fe(III)–OOH species, both homolytic and heterolytic cleavage of the O···O bond is explored leading to the formation of the transient Fe(IV)=O and Fe(V)=O species. For both the ligand systems, heterolytic cleavage was energetically preferable and our calculations suggest that both the reactions are catalyzed by an elusive high-valent Fe(V)=O species. The Fe(V)=O species undergoes the reaction via an electrophilic attack of the benzene ring to effect the ortho-hydroxylation reaction. The reactivity pattern observed for 1 and 2 are reflected in the computed barrier heights for the ortho-hydroxylation reaction. Electronic structure analysis reveals that the difference in reactivity between the ligand architectures described in complex 1 and 2 arise due to orientation of the pyridine ring(s) parallel or perpendicular to the Fe(V)=O bond. The parallel orientation of the pyridine ring is found to mix with the (πFe(dyz)–O(py))* orbital of the Fe-oxo bond leading to a reduction in the electrophilicity of the ferryl oxygen atom. Our calculations highlight the importance of ligand design in this chemistry and suggest that this concept can be used to (i) stabilize high-valent intermediates which can be trapped and thoroughly characterized (ii) enhance the reactivity and efficiency of the oxidants by increasing the electrophilicity of the ferryl oxygen containing FeVO species. Our computed results are in general agreement with the experimental results.
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Affiliation(s)
- Azaj Ansari
- Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai, India.
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12
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Surducan M, Makarov SV, Silaghi-Dumitrescu R. O-S Bond Activation in Structures Isoelectronic with Ferric Peroxide Species Known in O-O-Activating Enzymes: Relevance for Sulfide Activation and Sulfite Reductases. Eur J Inorg Chem 2014. [DOI: 10.1002/ejic.201402657] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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13
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Sun X, Sun X, Geng C, Zhao H, Li J. Benchmark study on methanol C-H and O-H bond activation by bare [Fe(IV)O](2+). J Phys Chem A 2014; 118:7146-58. [PMID: 25091205 DOI: 10.1021/jp505662x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
We present a high-level computational study on methanol C-H and O-H bond cleavages by bare [Fe(IV)O](2+), as well as benchmarks of various density functional theory (DFT) methods. We considered direct and concerted hydrogen transfer (DHT and CHT) pathways, respectively. The potential energy surfaces were constructed at the CCSD(T)/def2-TZVPP//B3LYP/def2-TZVP level of theory. Mechanistically, (1) the C-H bond cleavage is dominant and the O-H activation only plays minor role on the PESs; (2) the DHT from methyl should be the most practical channel; and (3) electronic structure analysis demonstrates the proton and electron transfer coupling behavior along the reaction coordinates. The solvent effect is evident and plays distinct roles in regulating the two bond activations in different mechanisms during the catalysis. The effect of optimizing the geometries using different density functionals was also studied, showing that it is not meaningful to discuss which DFT method could give the accurate prediction of the geometries, especially for transition structures. Furthermore, the gold-standard CCSD(T) method was used to benchmark 19 different density functionals with different Hartree-Fock exchange fractions. The results revealed that (i) the structural factor plays a minor role in the single point energy (SPE) calculations; (ii) reaction energy prediction is quite challenging for DFT methods; (iii) the mean absolute deviations (MADs) reflect the problematic description of the DFs when dealing with metal oxidation state change, giving a strong correlation on the HF exchange in the DFs. Knowledge from this study should be of great value for computational chemistry, especially for the de novo design of transition metal catalysts.
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Affiliation(s)
- Xianhui Sun
- State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University , Changchun 130023, P.R. China
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14
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Hirao H, Thellamurege N, Zhang X. Applications of density functional theory to iron-containing molecules of bioinorganic interest. Front Chem 2014; 2:14. [PMID: 24809043 PMCID: PMC4010748 DOI: 10.3389/fchem.2014.00014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Accepted: 03/10/2014] [Indexed: 12/29/2022] Open
Abstract
The past decades have seen an explosive growth in the application of density functional theory (DFT) methods to molecular systems that are of interest in a variety of scientific fields. Owing to its balanced accuracy and efficiency, DFT plays particularly useful roles in the theoretical investigation of large molecules. Even for biological molecules such as proteins, DFT finds application in the form of, e.g., hybrid quantum mechanics and molecular mechanics (QM/MM), in which DFT may be used as a QM method to describe a higher prioritized region in the system, while a MM force field may be used to describe remaining atoms. Iron-containing molecules are particularly important targets of DFT calculations. From the viewpoint of chemistry, this is mainly because iron is abundant on earth, iron plays powerful (and often enigmatic) roles in enzyme catalysis, and iron thus has the great potential for biomimetic catalysis of chemically difficult transformations. In this paper, we present a brief overview of several recent applications of DFT to iron-containing non-heme synthetic complexes, heme-type cytochrome P450 enzymes, and non-heme iron enzymes, all of which are of particular interest in the field of bioinorganic chemistry. Emphasis will be placed on our own work.
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Affiliation(s)
- Hajime Hirao
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological UniversitySingapore, Singapore
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15
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Poater A, Chaitanya Vummaleti SV, Cavallo L. The "innocent" role of Sc(3+) on a non-heme Fe catalyst in an O2 environment. Dalton Trans 2014; 43:11190-4. [PMID: 24740434 DOI: 10.1039/c4dt00321g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Density functional theory calculations have been used to investigate the reaction mechanism proposed for the formation of an oxoiron(iv) complex [Fe(IV)(TMC)O](2+) (P) (TMC = 1,4,8,11-tetramethylcyclam) starting from a non-heme reactant complex [Fe(II)(TMC)](2+) (R) and O2 in the presence of acid H(+) and reductant BPh4(-). We also addressed the possible role of redox-inactive Sc(3+) as a replacement for H(+) acid in this reaction to trigger the formation of P. Our computational results substantially confirm the proposed mechanism and, more importantly, support that Sc(3+) could trigger the O2 activation, mainly dictated by the availability of two electrons from BPh4(-), by forming a thermodynamically stable Sc(3+)-peroxo-Fe(3+) core that facilitates O-O bond cleavage to generate P by reducing the energy barrier. These insights may pave the way to improve the catalytic reactivity of metal-oxo complexes in O2 activation at non-heme centers.
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Affiliation(s)
- Albert Poater
- Institut de Química Computacional i Catàlisi, Departament de Química, Universitat de Girona, Campus de Montilivi, E-17071 Girona, Catalonia, Spain.
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16
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Hunter SC, Podlesnyak AA, Xue ZL. Magnetic Excitations in Metalloporphyrins by Inelastic Neutron Scattering: Determination of Zero-Field Splittings in Iron, Manganese, and Chromium Complexes. Inorg Chem 2014; 53:1955-61. [DOI: 10.1021/ic4028354] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Seth C. Hunter
- Department
of Chemistry, The University of Tennessee, 1420 Circle Drive, Knoxville, Tennessee 37996, United States
| | - Andrey A. Podlesnyak
- Quantum
Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Zi-Ling Xue
- Department
of Chemistry, The University of Tennessee, 1420 Circle Drive, Knoxville, Tennessee 37996, United States
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17
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Gelalcha FG. Biomimetic Iron-Catalyzed Asymmetric Epoxidations: Fundamental Concepts, Challenges and Opportunities. Adv Synth Catal 2014. [DOI: 10.1002/adsc.201300716] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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18
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Coggins MK, Toledo S, Kovacs JA. Isolation and characterization of a dihydroxo-bridged iron(III,III)(μ-OH)2 diamond core derived from dioxygen. Inorg Chem 2013; 52:13325-31. [PMID: 24229319 PMCID: PMC3885352 DOI: 10.1021/ic4010906] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Dioxygen addition to coordinatively unsaturated [Fe(II)(O(Me2)N4(6-Me-DPEN))](PF6) (1) is shown to afford a complex containing a dihydroxo-bridged Fe(III)2(μ-OH)2 diamond core, [Fe(III)(O(Me2)N4(6-Me-DPEN))]2(μ-OH)2(PF6)2·(CH3CH2CN)2 (2). The diamond core of 2 resembles the oxidized methane monooxygenase (MMOox) resting state, as well as the active site product formed following H-atom abstraction from Tyr-OH by ribonucleotide reductase (RNR). The Fe-OH bond lengths of 2 are comparable with those of the MMOHox suggesting that MMOHox contains a Fe(III)2(μ-OH)2 as opposed to Fe(III)2(μ-OH)(μ-OH2) diamond core as had been suggested. Isotopic labeling experiments with (18)O2 and CD3CN indicate that the oxygen and proton of the μ-OH bridges of 2 are derived from dioxygen and acetonitrile. Deuterium incorporation (from CD3CN) suggests that an unobserved intermediate capable of abstracting a H-atom from CH3CN forms en route to 2. Given the high C-H bond dissociation energy (BDE = 97 kcal/mol) of acetonitrile, this indicates that this intermediate is a potent oxidant, possibly a high-valent iron oxo. Consistent with this, iodosylbenzene (PhIO) also reacts with 1 in CD3CN to afford the deuterated Fe(III)2(μ-OD)2 derivative of 2. Intermediates are not spectroscopically observed in either reaction (O2 and PhIO) even at low-temperatures (-80 °C), indicating that this intermediate has a very short lifetime, likely due to its highly reactive nature. Hydroxo-bridged 2 was found to stoichiometrically abstract hydrogen atoms from 9,10-dihydroanthracene (C-H BDE = 76 kcal/mol) at ambient temperatures.
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Affiliation(s)
| | | | - Julie A. Kovacs
- The Department of Chemistry, University of Washington: Box 351700 Seattle, WA 98195-1700
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Ansari A, Kaushik A, Rajaraman G. Mechanistic Insights on the ortho-Hydroxylation of Aromatic Compounds by Non-heme Iron Complex: A Computational Case Study on the Comparative Oxidative Ability of Ferric-Hydroperoxo and High-Valent FeIV═O and FeV═O Intermediates. J Am Chem Soc 2013; 135:4235-49. [DOI: 10.1021/ja307077f] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Azaj Ansari
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Abhishek Kaushik
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Gopalan Rajaraman
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
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20
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Sharma VK. Ferrate(VI) and ferrate(V) oxidation of organic compounds: Kinetics and mechanism. Coord Chem Rev 2013. [DOI: 10.1016/j.ccr.2012.04.014] [Citation(s) in RCA: 221] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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21
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Jaccob M, Rajaraman G. A computational examination on the structure, spin-state energetics and spectroscopic parameters of high-valent FeIVNTs species. Dalton Trans 2012; 41:10430-9. [DOI: 10.1039/c2dt31071f] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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22
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Corban GJ, Hadjikakou SK, Tsipis AC, Kubicki M, Bakas T, Hadjiliadis N. Inhibition of peroxidase-catalyzed iodination by thioamides: experimental and theoretical study of the antithyroid activity of thioamides. NEW J CHEM 2011. [DOI: 10.1039/c0nj00626b] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Chattopadhyay S, Geiger RA, Yin G, Busch DH, Jackson TA. Oxo- and hydroxomanganese(IV) adducts: a comparative spectroscopic and computational study. Inorg Chem 2010; 49:7530-5. [PMID: 20690762 DOI: 10.1021/ic101014g] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The electronic structures of the bis(hydroxo)manganese(IV) and oxohydroxomanganese(IV) complexes [Mn(IV)(OH)(2)(Me(2)EBC)](2+) and [Mn(IV)(O)(OH)(Me(2)EBC)](+) were probed using electronic absorption, magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD spectroscopies. The d-d transitions of [Mn(IV)(OH)(2)(Me(2)EBC)](2+) were assigned using a group theory analysis coupled with the results of time-dependent density functional theory computations. These assignments permit the development of an experimentally validated description for the pi and sigma interactions in this complex. A similar analysis performed for [Mn(IV)(O)(OH)(Me(2)EBC)](+) reveals that there is a significant increase in the ligand character in the Mn pi* orbitals for the Mn(IV)=O complex relative to the bis(hydroxo)manganese(IV) complex, whereas the compositions of the Mn sigma* orbitals are less affected. Because of the steric features of the Me(2)EBC ligand, we propose that H-atom transfer by these reagents proceeds via the sigma* orbitals, which, because of their similar compositions among these two compounds, leads to modest rate enhancements for the Mn(IV)=O versus Mn(IV)OH species.
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Affiliation(s)
- Swarup Chattopadhyay
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, USA
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Hocking RK, DeBeer George S, Gross Z, Walker FA, Hodgson KO, Hedman B, Solomon EI. Fe L- and K-edge XAS of low-spin ferric corrole: bonding and reactivity relative to low-spin ferric porphyrin. Inorg Chem 2010; 48:1678-88. [PMID: 19149467 DOI: 10.1021/ic802248t] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Corrole is a tetrapyrrolic macrocycle that has one carbon atom less than a porphyrin. The ring contraction reduces the symmetry from D(4h) to C(2v), changes the electronic structure of the heterocycle, and leads to a smaller central cavity with three protons rather than the two of a porphyrin. The differences between ferric corroles and porphyrins lead to a number of differences in reactivity including increased axial ligand lability and a tendency to form 5-coordinate complexes. The electronic structure origin of these differences has been difficult to study experimentally as the dominant porphyrin/corrole pi --> pi* transitions obscure the electronic transitions of the metal. Recently, we have developed a methodology that allows for the interpretation of the multiplet structure of Fe L-edges in terms of differential orbital covalency (i.e., the differences in mixing of the metal d orbitals with the ligand valence orbitals) using a valence bond configuration interaction model. Herein, we apply this methodology, combined with a ligand field analysis of the Fe K pre-edge to a low-spin ferric corrole, and compare it to a low-spin ferric porphyrin. The experimental results combined with DFT calculations show that the contracted corrole is both a stronger sigma donor and a very anisotropic pi donor. These differences decrease the bonding interactions with axial ligands and contribute to the increased axial ligand lability and reactivity of ferric corroles relative to ferric porphyrins.
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Affiliation(s)
- Rosalie K Hocking
- Department of Chemistry, Stanford University, Stanford, California 94305, USA
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Wang Y, Han K. Steric hindrance effect of the equatorial ligand on Fe(IV)O and Ru(IV)O complexes: a density functional study. J Biol Inorg Chem 2010; 15:351-9. [PMID: 19916032 DOI: 10.1007/s00775-009-0607-4] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2009] [Accepted: 11/04/2009] [Indexed: 10/20/2022]
Abstract
The geometric structures and mechanisms for hydrogen abstraction from cyclohexane for four high-valent complexes, [Fe IV(O)(TMC)(NCMe)]2+ (where TMC is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane; 1-NCMe), the inverted isomer [Fe IV(NCMe)(TMC)(O)]2+ (2-NCMe), [Ru IV(O)(TMC)(NCMe)]2+ (the ruthenium analogue of 1-NCMe; 3-NCMe), and the inverted isomer [Ru IV(NCMe)(TMC)(O)]2+ (4-NCMe), were investigated using density functional theory. The axial NCMe ligand was found to be sterically more hindered in 2-NCMe than in 1-NCMe, which is in accord with the calculated results that the Fe-L axial distance is longer in the former. Both 1-NCMe and 2-NCMe are capable of hydrogen abstraction from cyclohexane via two-state reactivity patterns. In contrast, 3-NCMe and 4-NCMe react with cyclohexane by a single-state mechanism. The reaction pathways computed reveal that 2-NCMe is more reactive than 1-NCMe, in agreement with experimental results, whereas the reactivity of 3-NCMe and 4-NCMe shows little dependence on whether the oxo unit is syn or anti to the four N-methyl groups. Our analysis shows that along the reaction pathway for 2-NCMe in the triplet spin state, the NCMe ligand moves away from the iron center, and therefore the energy of the sigma *2 z (alpha-spin) orbital decreases and an electron is transferred to this orbital. Finally, we calculated the kinetic isotope effect and investigated the relationship between this effect and reaction barriers.
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Affiliation(s)
- Yi Wang
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 116023 Dalian, People's Republic of China
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Rosa A, Ricciardi G, Baerends EJ. Is [FeO]2+ the Active Center Also in Iron Containing Zeolites? A Density Functional Theory Study of Methane Hydroxylation Catalysis by Fe-ZSM-5 Zeolite. Inorg Chem 2010; 49:3866-80. [DOI: 10.1021/ic1000073] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Angela Rosa
- Dipartimento di Chimica, Università della Basilica, Via N. Sauro 85, 85100 Potenza, Italy
| | - Giampaolo Ricciardi
- Dipartimento di Chimica, Università della Basilica, Via N. Sauro 85, 85100 Potenza, Italy
| | - Evert Jan Baerends
- Dep. of Chemistry, Pohang Univ. of Science and Technology, Pohang 790-784, South-Korea
- Theoretische Chemie, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
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Balcells D, Clot E, Eisenstein O. C—H Bond Activation in Transition Metal Species from a Computational Perspective. Chem Rev 2010; 110:749-823. [PMID: 20067255 DOI: 10.1021/cr900315k] [Citation(s) in RCA: 843] [Impact Index Per Article: 60.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- David Balcells
- Institut Charles Gerhardt, Université Montpellier 2, CNRS 5253, cc 1501, Place Eugène Bataillon, 34000 Montpellier, France
| | - Eric Clot
- Institut Charles Gerhardt, Université Montpellier 2, CNRS 5253, cc 1501, Place Eugène Bataillon, 34000 Montpellier, France
| | - Odile Eisenstein
- Institut Charles Gerhardt, Université Montpellier 2, CNRS 5253, cc 1501, Place Eugène Bataillon, 34000 Montpellier, France
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Latifi R, Bagherzadeh M, de Visser SP. Origin of the correlation of the rate constant of substrate hydroxylation by nonheme iron(IV)-oxo complexes with the bond-dissociation energy of the C-H bond of the substrate. Chemistry 2009; 15:6651-62. [PMID: 19472231 DOI: 10.1002/chem.200900211] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Mononuclear nonheme iron containing systems are versatile and vital oxidants of substrate hydroxylation reactions in many biosystems, whereby the rate constant of hydroxylation correlates with the strength of the C-H bond that is broken in the process. The thermodynamic reason behind these correlations, however, has never been established. In this work results of a series of density functional theory calculations of substrate hydroxylation by a mononuclear nonheme iron(IV)-oxo oxidant with a 2 His/1 Asp structural motif analogous to alpha-ketoglutarate dependent dioxygenases are presented. The calculations show that these oxidants are very efficient and able to hydroxylate strong C-H bonds, whereby the hydrogen abstraction barriers correlate linearly with the strength of the C-H bond of the substrate that is broken. These trends have been rationalized using a valence bond (VB) curve-crossing diagram, which explains the correlation using electron transfer mechanisms in the hydrogen abstraction processes. We also rationalized the subsequent reaction step for radical rebound and show that the barrier is proportional to the electron affinity of the iron(III)-hydroxo intermediate complex. It is shown that nonheme iron(IV)-hydroxo complexes have a larger electron affinity than heme iron(IV)-hydroxo complexes and therefore also experience larger radical rebound barriers, which may have implications for product distributions and rearrangement reactions. Thus, detailed comparisons between heme and nonheme iron(IV)-oxo oxidants reveal the fundamental differences in monoxygenation capabilities of these important classes of oxidants in biosystems and synthetic analogues for the first time and enable us to make predictions of experimental processes.
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Affiliation(s)
- Reza Latifi
- The Manchester Interdisciplinary Biocentre and the School of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester M1 7DN, UK
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Martinho M, Xue G, Fiedler AT, Que L, Bominaar EL, Münck E. Mössbauer and DFT study of the ferromagnetically coupled diiron(IV) precursor to a complex with an Fe(IV)(2)O(2) diamond core. J Am Chem Soc 2009; 131:5823-30. [PMID: 19338307 DOI: 10.1021/ja8098917] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Recently, we reported the reaction of the (mu-oxo)diiron(III) complex 1 ([Fe(III)(2)(mu-O)(mu-O(2)H(3))(L)(2)](3+), L = tris(3,5-dimethyl-4-methoxypyridyl-2-methyl)amine) with 1 equiv of H(2)O(2) to yield a diiron(IV) intermediate, 2 (Xue, G.; Fiedler, A. T.; Martinho, M.; Munck, E.; Que, L., Jr. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 20615-20). Upon treatment with HClO(4), complex 2 converted to a species with an Fe(IV)(2)(mu-O)(2) diamond core that serves as the only synthetic model to date for the diiron(IV) core proposed for intermediate Q of soluble methane monooxygenase. Here we report detailed Mossbauer and density functional theory (DFT) studies of 2. The Mossbauer studies reveal that 2 has distinct Fe(IV) sites, a and b. Studies in applied magnetic fields show that the spins of sites a and b (S(a) = S(b) = 1) are ferromagnetically coupled to yield a ground multiplet with S = 2. Analysis of the applied field spectra of the exchange-coupled system yields for site b a set of parameters that matches those obtained for the mononuclear [LFe(IV)(O)(NCMe)](2+) complex, showing that site b (labeled Fe(O)) has a terminal oxo group. Using the zero-field splitting parameters of [LFe(IV)(O)(NCMe)](2+) for our analysis of 2, we obtained parameters for site a that closely resemble those reported for the nonoxo Fe(IV) complex [(beta-BPMCN)Fe(IV)(OH)(OO(t)Bu)](2+), suggesting that a (labeled Fe(OH)) coordinates a hydroxo group. A DFT optimization performed on 2 yielded an Fe-Fe distance of 3.39 A and an Fe-(mu-O)-Fe angle of 131 degrees , in good agreement with the results of our previous EXAFS study. The DFT calculations reproduce the Mossbauer parameters (A-tensors, electric field gradient, and isomer shift) of 2 quite well, including the observation that the largest components of the electric field gradients of Fe(O) and Fe(OH) are perpendicular. The ferromagnetic behavior of 2 seems puzzling given that the Fe-(mu-O)-Fe angle is large but can be explained by noting that the orbital structures of Fe(O) and Fe(OH) are such that the unpaired electrons at the two sites delocalize into orthogonal orbitals at the bridging oxygen, rationalizing the ferromagnetic behavior of 2. Thus, inequivalent coordinations at Fe(O) and Fe(OH) define magnetic orbitals favorable for ferromagnetic ineractions.
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Affiliation(s)
- Marlène Martinho
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
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Wang Y, Wang Y, Han K. Theoretical study of cyclohexane hydroxylation by three possible isomers of [FeIV(O)(R-TPEN)] 2+: does the pentadentate ligand wrapping around the metal center differently lead to the different stability and reactivity? J Biol Inorg Chem 2009; 14:533-45. [PMID: 19172312 DOI: 10.1007/s00775-009-0468-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2008] [Accepted: 12/31/2008] [Indexed: 11/26/2022]
Abstract
Density functional theory calculations have been carried out to elucidate the mechanism of cyclohexane hydroxylation by three possible isomers of [Fe(IV)(O)(N-R-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine)](2+) (R is methyl or benzyl) (Klinker et al. in Angew Chem Int Ed 44:3690-3694, 2005). The calculations offer a mechanistic view and reveal the following features: (a) all the three isomers possess triplet ground states and low-lying quintet excited states, (b) the relative stability follows the order isomer A > isomer B > isomer C, in agreement with the conclusions of Klinker et al., (c) the theoretical investigations provide a rationale to explain the interconversion of the three isomers, (d) the reaction pathways of the C-H hydroxylation are initiated by a hydrogen-abstraction step, and (e) the three isomers react with cyclohexane via two-state-reactivity patterns on competing triplet and quintet spin-state surfaces. As such, in the gas phase, the relative reactivity exhibits the trend isomer B > isomer A, while at the highest level, B2//B1 with zero point energy and solvation corrections, the relative reactivity follows the order isomer B > isomer A > isomer C. Thus, the calculated reaction pathway shows that pyridine rings perpendicular to the Fe-O axis result in more reactive species, and a pyridine ring coordinated trans to the oxygen atom leads to the least reactive isomer.
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Affiliation(s)
- Yi Wang
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, People's Republic of China
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31
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Lu CC, DeBeer George S, Weyhermüller T, Bill E, Bothe E, Wieghardt K. An electron-transfer series of high-valent chromium complexes with redox non-innocent, non-heme ligands. Angew Chem Int Ed Engl 2008; 47:6384-7. [PMID: 18618881 DOI: 10.1002/anie.200800669] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Connie C Lu
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany.
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Jackson TA, Rohde JU, Seo MS, Sastri CV, DeHont R, Stubna A, Ohta T, Kitagawa T, Münck E, Nam W, Que L. Axial ligand effects on the geometric and electronic structures of nonheme oxoiron(IV) complexes. J Am Chem Soc 2008; 130:12394-407. [PMID: 18712873 DOI: 10.1021/ja8022576] [Citation(s) in RCA: 157] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A series of complexes [Fe(IV)(O)(TMC)(X)](+) (where X = OH(-), CF3CO2(-), N3(-), NCS(-), NCO(-), and CN(-)) were obtained by treatment of the well-characterized nonheme oxoiron(IV) complex [Fe(IV)(O)(TMC)(NCMe)](2+) (TMC = tetramethylcyclam) with the appropriate NR4X salts. Because of the topology of the TMC macrocycle, the [Fe(IV)(O)(TMC)(X)](+) series represents an extensive collection of S = 1 oxoiron(IV) complexes that only differ with respect to the ligand trans to the oxo unit. Electronic absorption, Fe K-edge X-ray absorption, resonance Raman, and Mossbauer data collected for these complexes conclusively demonstrate that the characteristic spectroscopic features of the S = 1 Fe(IV)=O unit, namely, (i) the near-IR absorption properties, (ii) X-ray absorption pre-edge intensities, and (iii) quadrupole splitting parameters, are strongly dependent on the identity of the trans ligand. However, on the basis of extended X-ray absorption fine structure data, most [Fe(IV)(O)(TMC)(X)](+) species have Fe=O bond lengths similar to that of [Fe(IV)(O)(TMC)(NCMe)](2+) (1.66 +/- 0.02 A). The mechanisms by which the trans ligands perturb the Fe(IV)=O unit were probed using density functional theory (DFT) computations, yielding geometric and electronic structures in good agreement with our experimental data. These calculations revealed that the trans ligands modulate the energies of the Fe=O sigma- and pi-antibonding molecular orbitals, causing the observed spectroscopic changes. Time-dependent DFT methods were used to aid in the assignment of the intense near-UV absorption bands found for the oxoiron(IV) complexes with trans N3(-), NCS(-), and NCO(-) ligands as X(-)-to-Fe(IV)=O charge-transfer transitions, thereby rationalizing the resonance enhancement of the nu(Fe=O) mode upon excitation of these chromophores.
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Affiliation(s)
- Timothy A Jackson
- Department of Chemistry and Center for Metals in Biocatalysis, 207 Pleasant Street S.E., University of Minnesota, Minneapolis, Minnesota 55455, USA
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Tong GSM, Wong ELM, Che CM. Density functional theory study of trans-dioxo complexes of iron, ruthenium, and osmium with saturated amine ligands, trans-[M(O)2(NH3)2(NMeH2)2]2+ (M=Fe, Ru, Os), and detection of [Fe(qpy)(O)2]n+ (n=1, 2) by high-resolution ESI mass spectrometry. Chemistry 2008; 14:5495-506. [PMID: 18478515 DOI: 10.1002/chem.200701563] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Density functional theory (DFT) calculations on trans-dioxo metal complexes containing saturated amine ligands, trans-[M(O)2(NH3)2(NMeH2)2]2+ (M=Fe, Ru, Os), were performed with different types of density functionals (DFs): 1) pure generalized gradient approximations (pure GGAs): PW91, BP86, and OLYP; 2) meta-GGAs: VSXC and HCTH407; and 3) hybrid DFs: B3LYP and PBE1PBE. With pure GGAs and meta-GGAs, a singlet d2 ground state for trans-[Fe(O)2(NH3)2(NMeH2)2]2+ was obtained, but a quintet ground state was predicted by the hybrid DFs B3LYP and PBE1PBE. The lowest transition energies in water were calculated to be at lambda approximately 509 and 515 nm in the respective ground-state geometries from PW91 and B3LYP calculations. The nature of this transition is dependent on the DFs used: a ligand-to-metal charge-transfer (LMCT) transition with PW91, but a pi(Fe-O)-->pi*(Fe-O) transition with B3LYP, in which pi and pi* are the bonding and antibonding combinations between the dpi(Fe) and ppi(O(2-)) orbitals. The FeVI/V reduction potential of trans-[Fe(O)2(NH3)2NMeH2)2]2+ was estimated to be +1.30 V versus NHE based on PW91 results. The [Fe(qpy)(O)2](n+) (qpy=2,2':6',2'':6'',2''':6''',2''''-quinquepyridine; n=1 and 2) ions, tentatively assigned to dioxo iron(V) and dioxo iron(VI), respectively, were detected in the gas phase by high-resolution ESI-MS spectroscopy.
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Affiliation(s)
- Glenna So Ming Tong
- Department of Chemistry and Open Laboratory of Chemical Biology of the Institute of Molecular Technology for Drug Discovery and Synthesis, The University of Hong Kong, Pokfulam Road, Hong Kong
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Lu C, DeBeer George S, Weyhermüller T, Bill E, Bothe E, Wieghardt K. An Electron-Transfer Series of High-Valent Chromium Complexes with Redox Non-Innocent, Non-Heme Ligands. Angew Chem Int Ed Engl 2008. [DOI: 10.1002/ange.200800669] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Chanda A, Shan X, Chakrabarti M, Ellis WC, Popescu DL, Tiago de Oliveira F, Wang D, Que L, Collins TJ, Münck E, Bominaar EL. (TAML)FeIV O complex in aqueous solution: synthesis and spectroscopic and computational characterization. Inorg Chem 2008; 47:3669-78. [PMID: 18380453 DOI: 10.1021/ic7022902] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Recently, we reported the characterization of the S = (1)/ 2 complex [Fe (V)(O)B*] (-), where B* belongs to a family of tetraamido macrocyclic ligands (TAMLs) whose iron complexes activate peroxides for environmentally useful applications. The corresponding one-electron reduced species, [Fe (IV)(O)B*] (2-) ( 2), has now been prepared in >95% yield in aqueous solution at pH > 12 by oxidation of [Fe (III)(H 2O)B*] (-) ( 1), with tert-butyl hydroperoxide. At room temperature, the monomeric species 2 is in a reversible, pH-dependent equilibrium with dimeric species [B*Fe (IV)-O-Fe (IV)B*] (2-) ( 3), with a p K a near 10. In zero field, the Mössbauer spectrum of 2 exhibits a quadrupole doublet with Delta E Q = 3.95(3) mm/s and delta = -0.19(2) mm/s, parameters consistent with a S = 1 Fe (IV) state. Studies in applied magnetic fields yielded the zero-field splitting parameter D = 24(3) cm (-1) together with the magnetic hyperfine tensor A/ g nbeta n = (-27, -27, +2) T. Fe K-edge EXAFS analysis of 2 shows a scatterer at 1.69 (2) A, a distance consistent with a Fe (IV)O bond. DFT calculations for [Fe (IV)(O)B*] (2-) reproduce the experimental data quite well. Further significant improvement was achieved by introducing hydrogen bonding of the axial oxygen with two solvent-water molecules. It is shown, using DFT, that the (57)Fe hyperfine parameters of complex 2 give evidence for strong electron donation from B* to iron.
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Affiliation(s)
- Arani Chanda
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA
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Shokhireva TK, Berry RE, Zhang H, Shokhirev NV, Walker FA. Assignment of Ferriheme Resonances for High- and Low-Spin Forms of Nitrophorin 3 by H and C NMR Spectroscopy and Comparison to Nitrophorin 2: Heme Pocket Structural Similarities and Differences. Inorganica Chim Acta 2008; 361:925-940. [PMID: 19262680 PMCID: PMC2390817 DOI: 10.1016/j.ica.2007.05.044] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Nitrophorin 3 (NP3) is the only one of the four major NO-binding heme proteins found in the saliva of the blood-sucking insect Rhodnius prolixus (also called the Kissing Bug) for which it has not been possible to obtain crystals of diffraction quality for structure determination by X-ray crystallography. Thus we have used NMR spectroscopy, mainly of the hyperfine-shifted ferriheme substituent resonances, to learn about the similarities and differences in the heme pocket and the iron active site of NP3 as compared to NP2, which has previously been well-characterized by both X-ray crystallography and NMR spectroscopy. Only one residue in the heme pocket differs between the two, F27 of NP2 is Y27 for NP3; in both cases this residue is expected to interact strongly with the 2-vinyl side chain of the B heme rotational isomer or the 4-vinyl of the A heme rotational isomer. Both the high-spin (S = 5/2) aquo complex, NP3-H(2)O, and the low-spin (S = 1/2) N-methylimidazole (NMeIm) complex of NP3 have been studied. It is found that the chemical shifts of the protons of both forms are similar to those of the corresponding NP2 complexes, but with minor differences that indicate a slightly different angle for the proximal histidine (H57) ligand plane. The B heme rotational isomer is preferred by both NP3 and NP2 in both spin states, but to a greater extent when phenylalanine is present at position 27 (A:B = 1:8 for NP2, 1:6 for NP3-Y27F, 1:4 for NP3, and 1:3 for NP2-F27Y). Careful analysis of the 5Me and 8Me shifts of the A and B isomers of the two high-spin nitrophorins leads to the conclusion that the heme environment for the two isomers differs in some way that cannot be explained at the present time. The kinetics of deprotonation of the high-spin complexes of NP2 and NP3 are very different, with NP2 giving well-resolved high-spin aquo and "low-spin" hydroxo proton NMR spectra until close to the end of the titration, while NP3 exhibits broadened (1)H NMR spectra indicative of an intermediate rate of exchange on the NMR timescale between the two forms throughout the titration. The heme methyl shifts of NP2-OH are similar in magnitude and spread to those of NP2-CN, while those of metmyoglobin-hydroxo complexes are much larger in magnitude but not spread. It is concluded that the hydroxo complex of NP2 is likely S = 1/2 with a mixed (d(XY))(2)(d(XZ),d(YZ))(3)/(d(xy))(1)(d(xz),d(yz))(4) electron configuration, while those of met-Mb-OH are likely S = 1/2,3/2 mixed spin systems.
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Affiliation(s)
- Tatiana Kh Shokhireva
- Contribution from the Department of Chemistry, The University of Arizona, Tucson, AZ 85721-0041
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37
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Reactivity of ferrate(V) with aminopolycarboxylates in alkaline medium: A premix pulse radiolysis. Inorganica Chim Acta 2008. [DOI: 10.1016/j.ica.2007.07.019] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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38
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Zhou Y, Shan X, Mas-Ballesté R, Bukowski M, Stubna A, Chakrabarti M, Slominski L, Halfen J, Münck E, Que L. Contrastingcis andtrans Effects on the Reactivity of Nonheme Oxoiron(IV) Complexes. Angew Chem Int Ed Engl 2008. [DOI: 10.1002/ange.200704228] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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39
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Zhou Y, Shan X, Mas-Ballesté R, Bukowski M, Stubna A, Chakrabarti M, Slominski L, Halfen J, Münck E, Que L. Contrastingcis andtrans Effects on the Reactivity of Nonheme Oxoiron(IV) Complexes. Angew Chem Int Ed Engl 2008; 47:1896-9. [DOI: 10.1002/anie.200704228] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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40
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Hirao H, Que L, Nam W, Shaik S. A Two-State Reactivity Rationale for Counterintuitive Axial Ligand Effects on the CH Activation Reactivity of Nonheme FeIVO Oxidants. Chemistry 2008; 14:1740-56. [DOI: 10.1002/chem.200701739] [Citation(s) in RCA: 180] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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41
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Louwerse MJ, Vassilev P, Baerends EJ. Oxidation of Methanol by FeO2+ in Water: DFT Calculations in the Gas Phase and Ab Initio MD Simulations in Water Solution. J Phys Chem A 2008; 112:1000-12. [DOI: 10.1021/jp075914n] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Manuel J. Louwerse
- Theoretical Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
| | - Peter Vassilev
- Theoretical Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
| | - Evert Jan Baerends
- Theoretical Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
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42
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Decker A, Rohde JU, Klinker EJ, Wong SD, Que L, Solomon EI. Spectroscopic and quantum chemical studies on low-spin FeIV=O complexes: Fe-O bonding and its contributions to reactivity. J Am Chem Soc 2007; 129:15983-96. [PMID: 18052249 DOI: 10.1021/ja074900s] [Citation(s) in RCA: 191] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
High-valent FeIV=O species are key intermediates in the catalytic cycles of many mononuclear non-heme iron enzymes and have been structurally defined in model systems. Variable-temperature magnetic circular dichroism (VT-MCD) spectroscopy has been used to evaluate the electronic structures and in particular the Fe-O bonds of three FeIV=O (S = 1) model complexes, [FeIV(O)(TMC)(NCMe)]2+, [FeIV(O)(TMC)(OC(O)CF3)]+, and [FeIV(O)(N4Py)]2+. These complexes are characterized by their strong and covalent Fe-O pi-bonds. The MCD spectra show a vibronic progression in the nonbonding --> pi* excited state, providing the Fe-O stretching frequency and the Fe-O bond length in this excited state and quantifying the pi-contribution to the total Fe-O bond. Correlation of these experimental data to reactivity shows that the [FeIV(O)(N4Py)]2+ complex, with the highest reactivity toward hydrogen-atom abstraction among the three, has the strongest Fe-O pi-bond. Density functional calculations were correlated to the data and support the experimental analysis. The strength and covalency of the Fe-O pi-bond result in high oxygen character in the important frontier molecular orbitals (FMOs) for this reaction, the unoccupied beta-spin d(xz/yz) orbitals, that activates these for electrophilic attack. An extension to biologically relevant FeIV=O (S = 2) enzyme intermediates shows that these can perform electrophilic attack reactions along the same mechanistic pathway (pi-FMO pathway) with similar reactivity but also have an additional reaction channel involving the unoccupied alpha-spin d(z2) orbital (sigma-FMO pathway). These studies experimentally probe the FMOs involved in the reactivity of FeIV=O (S = 1) model complexes resulting in a detailed understanding of the Fe-O bond and its contributions to reactivity.
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Affiliation(s)
- Andrea Decker
- Department of Chemistry, Stanford University, Stanford, California 94305, USA
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43
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Spiegel DA, Schroeder FC, Duvall JR, Schreiber SL. An oligomer-based approach to skeletal diversity in small-molecule synthesis. J Am Chem Soc 2007; 128:14766-7. [PMID: 17105261 DOI: 10.1021/ja065724a] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Access to small molecules of widely varying molecular shapes has been identified as an enabling step in the discovery of biologically active materials. In this communication we introduce an approach to the systematic development of architecturally distinct chemical compounds based upon the assembly of reactive monomers into linear oligomers, each of which encodes a unique molecular framework under a common set of reaction conditions. Certain products of the initial chemical transformation (Ru-catalyzed metathesis reaction) encode additional skeletons upon treatment with a second common set of reagents (Diels-Alder dienophiles). Application of this oligomerization approach has led to the discovery of a previously unreported tandem ene-yne-yne metathesis-6pi-electrocyclization-1,5-hydride migration that converts a linear substrate into a complex tricyclic 1,3-diene in a single step. Thus, the reported strategy might serve not only as a generator of skeletally diverse small molecules but also as a discovery platform for the identification of novel chemical transformations.
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Affiliation(s)
- David A Spiegel
- Howard Hughes Medical Institute, Broad Institute of Harvard and MIT, Chemical Biology Program, Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
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44
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Sicking W, Korth HG, Jansen G, de Groot H, Sustmann R. Hydrogen Peroxide Decomposition by a Non-Heme Iron(III) Catalase Mimic: A DFT Study. Chemistry 2007; 13:4230-45. [PMID: 17323385 DOI: 10.1002/chem.200601209] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Non-heme iron(III) complexes of 14-membered tetraaza macrocycles have previously been found to catalytically decompose hydrogen peroxide to water and molecular oxygen, like the native enzyme catalase. Here the mechanism of this reaction is theoretically investigated by DFT calculations at the (U)B3LYP/6-31G* level, with focus on the reactivity of the possible spin states of the FeIII complexes. The computations suggest that H2O2 decomposition follows a homolytic route with intermediate formation of an iron(IV) oxo radical cation species (L.+FeIV==O) that resembles Compound I of natural iron porphyrin systems. Along the whole catalytic cycle, no significant energetic differences were found for the reaction proceeding on the doublet (S=1/2) or on the quartet (S=3/2) hypersurface, with the single exception of the rate-determining O--O bond cleavage of the first associated hydrogen peroxide molecule, for which reaction via the doublet state is preferred. The sextet (S=5/2) state of the FeIII complexes appears to be unreactive in catalase-like reactions.
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Affiliation(s)
- Willi Sicking
- Institut für Organische Chemie, Universität Duisburg-Essen, Campus Essen, Universitätsstrasse 5, 45117 Essen, Germany
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45
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Rohde JU, Stubna A, Bominaar EL, Münck E, Nam W, Que L. Nonheme oxoiron(IV) complexes of tris(2-pyridylmethyl)amine with cis-monoanionic ligands. Inorg Chem 2007; 45:6435-45. [PMID: 16878956 DOI: 10.1021/ic060740u] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Treatment of [Fe(IV)(O)(TPA)(NCMe)](CF3SO3)2 [TPA, N,N,N-tris(2-pyridylmethyl)amine] with 3 equiv of NR4X (X = CF3CO2, Cl, or Br) in MeCN at -40 degrees C affords a series of metastable [Fe(IV)(O)(TPA)(X)]+ complexes. Some characteristic features of the S = 1 oxoiron(IV) unit are quite insensitive to the ligand substitution in the equatorial plane, namely, the Fe-O distances (1.65-1.66 A), the energy ( approximately 7114.5 eV) and intensity [25(2) units] of the 1s-to-3d transition in the X-ray absorption spectra, and the Mössbauer isomer shifts (0.01-0.06 mm.s(-1)) and quadrupole splittings (0.92-0.95 mm.s(-1)). The coordination of the anionic X ligand, however, is evidenced by red shifts of the characteristic near-IR ligand-field bands (720-800 nm) and spectroscopic observation of the bound anion by (19)F NMR for X = CF3CO2 and by EXAFS analysis for X = Cl (r(Fe-Cl) = 2.29 A) and Br (r(Fe-Br) = 2.43 A). Density functional theory calculations yield Mössbauer parameters and bond lengths in good agreement with the experimental data and produce excited-state energies that follow the trend observed in the ligand-field bands. Despite mitigating the high effective charge of the iron(IV) center, the substitution of the MeCN ligand with monoanionic ligands X- decreases the thermal stability of [Fe(IV)(O)(TPA)]2+ complexes. These anion-substituted complexes model the cis-X-Fe(IV)=O units proposed in the mechanisms of oxygen-activating nonheme iron enzymes.
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Affiliation(s)
- Jan-Uwe Rohde
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455, USA
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46
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Sinnecker S, Svensen N, Barr EW, Ye S, Bollinger JM, Neese F, Krebs C. Spectroscopic and Computational Evaluation of the Structure of the High-Spin Fe(IV)-Oxo Intermediates in Taurine: α-Ketoglutarate Dioxygenase fromEscherichia coliand Its His99Ala Ligand Variant. J Am Chem Soc 2007; 129:6168-79. [PMID: 17451240 DOI: 10.1021/ja067899q] [Citation(s) in RCA: 166] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The Fe(II)- and alpha-ketoglutarate (alphaKG)-dependent dioxygenases activate O2 for cleavage of unactivated C-H bonds in their substrates. The key intermediate that abstracts hydrogen in the reaction of taurine:alphaKG dioxygenase (TauD), a member of this enzyme family, was recently characterized. The intermediate, denoted J, was shown to contain an iron(IV)-oxo unit. Other important structural features of J, such as the number, identity, and disposition of ligands in the Fe(IV) coordination sphere, are not yet understood. To probe these important structural features, a series of models for J with the Fe(IV) ion coordinated by the expected two imidazole (from His99 and His255), two carboxylate (succinate and Asp101), and oxo ligands have been generated by density functional theory (DFT) calculations, and spectroscopic parameters (Mössbauer isomer shift, quadrupole splitting, and asymmetry parameter, 57Fe hyperfine coupling tensor, and zero field splitting parameters, D and E/D) have been calculated for each model. The calculated parameters of distorted octahedral models for J, in which one of the carboxylates serves as a monodentate ligand and the other as a bidentate ligand, and a trigonal bipyramidal model, in which both carboxylates serve as monodentate ligands, agree well with the experimental parameters, whereas the calculated parameters of a square pyramidal model, in which the oxo ligand is in the equatorial plane, are inconsistent with the data. Similar analysis of the Fe(IV) complex generated in the variant protein with His99, the residue that contributes the imidazole ligand cis to the oxo group, replaced by alanine suggests that the deleted imidazole is replaced by a water ligand. This work lends credence to the idea that the combination of Mössbauer spectroscopy and DFT calculations can provide detailed structural information for reactive intermediates in the catalytic cycles of iron enzymes.
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Affiliation(s)
- Sebastian Sinnecker
- Max-Planck Institut für Bioanorganische Chemie, D-45470 Mülheim an der Ruhr, Germany
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47
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Ma Y, Balbuena PB. Catalytic Activity Tuning of a Biomimetic HO−FeVO Oxidant for Methane Hydroxylation by Substituents on Aromatic Rings: Theoretical Study. J Phys Chem B 2007; 111:2711-8. [PMID: 17315920 DOI: 10.1021/jp067429i] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
HO-(TPA)FeV=O (TPA = tris(2-pyridylmethyl)amine) has been proposed in the literature as the key high-valent iron-oxo intermediate involved in alkane hydroxylation. Here the structure of this species is investigated theoretically in the framework of density functional theory (DFT). A detailed electronic structure analysis leads to the presumption that the properties of the FeV=O bond can be modified by introducing substituents to the aromatic rings of TPA and thus the reactivity of HO-(TPA)FeV=O for the hydrogen atom abstraction of methane hydroxylation can be tuned on the quartet potential energy surface. The validity of our presumption is verified by DFT calculations. According to the rebound mechanism, the H-abstraction step is examined by using five complexes with TPA and TPA-derivative ligands and the corresponding reaction energies and energy barriers are obtained and compared with each other. The results are fully in agreement with our qualitative model, showing that electron-withdrawing groups are able to lower the barrier and facilitate the reaction, whereas the electron-donating groups increase the barrier and reduce the reactivity.
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Affiliation(s)
- Yuguang Ma
- Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843, USA
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48
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Kumar D, Hirao H, Shaik S, Kozlowski PM. Proton-shuffle mechanism of O-O activation for formation of a high-valent oxo-iron species of bleomycin. J Am Chem Soc 2007; 128:16148-58. [PMID: 17165768 DOI: 10.1021/ja064611o] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Bleomycins (BLMs) can utilize H2O2 to cleave DNA in the presence of ferric ions. DFT calculations were used to study the mechanism of O-O bond cleavage in the low-spin FeIII-hydroperoxo complex of BLM. The following alternative hypotheses were investigated using realistic structural models: (a) heterolytic cleavage of the O-O bond, generating a Compound I (Cpd I) like intermediate, formally BLM-FeV=O; (b) homolytic O-O cleavage, leading to a BLM-FeIV=O species and an OH* radical; and (c) a direct O-O cleavage/H-abstraction mechanism by ABLM. The calculations showed that (a) is a facile and viable mechanism; it involves acid-base proton reshuffle mediated by the side-chain linkers of BLM, causing thereby heterolytic cleavage of the O-O bond and generation of Cpd I. Formation of Cpd I is found to involve a barrier of 13.3 kcal/mol, which is lower than the barriers in the alternative mechanisms (b and c) that possess respective barriers of 31 and 17 kcal/mol. The so-formed Cpd I species with a radical on the side-chain linker, methylvalerate (V), adjacent to the BLM-FeIV=O complex, resembles the formation of the active species of cytochrome c peroxidase in the Poulos-Kraut proton-shuffle mechanism in heme peroxidases (Poulos, T. L.; Kraut, J. J. Biol. Chem. 1980, 255, 8199-8205). Experimental data are discussed and shown to be in accord with this proposal. It suggests that the high-valence Cpd I species of BLM participates in the DNA cleavage. This is an alternative mechanistic hypothesis to the exclusive reactivity scenario based on ABLM (FeIII-OOH).
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Affiliation(s)
- Devesh Kumar
- Department of Organic Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University, Jerusalem 91904, Israel
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49
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Hocking RK, Wasinger EC, Yan YL, Degroot FMF, Walker FA, Hodgson KO, Hedman B, Solomon EI. Fe L-edge X-ray absorption spectroscopy of low-spin heme relative to non-heme Fe complexes: delocalization of Fe d-electrons into the porphyrin ligand. J Am Chem Soc 2007; 129:113-25. [PMID: 17199290 PMCID: PMC2890250 DOI: 10.1021/ja065627h] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Hemes (iron porphyrins) are involved in a range of functions in biology, including electron transfer, small-molecule binding and transport, and O2 activation. The delocalization of the Fe d-electrons into the porphyrin ring and its effect on the redox chemistry and reactivity of these systems has been difficult to study by optical spectroscopies due to the dominant porphyrin pi-->pi(*) transitions, which obscure the metal center. Recently, we have developed a methodology that allows for the interpretation of the multiplet structure of Fe L-edges in terms of differential orbital covalency (i.e., differences in mixing of the d-orbitals with ligand orbitals) using a valence bond configuration interaction (VBCI) model. Applied to low-spin heme systems, this methodology allows experimental determination of the delocalization of the Fe d-electrons into the porphyrin (P) ring in terms of both P-->Fe sigma and pi-donation and Fe-->P pi back-bonding. We find that pi-donation to Fe(III) is much larger than pi back-bonding from Fe(II), indicating that a hole superexchange pathway dominates electron transfer. The implications of the results are also discussed in terms of the differences between heme and non-heme oxygen activation chemistry.
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Affiliation(s)
- Rosalie K Hocking
- Department of Chemistry, Stanford University, Stanford, California 94305, USA
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50
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Louwerse MJ, Jan Baerends E. Oxidative properties of FeO2+: electronic structure and solvation effects. Phys Chem Chem Phys 2007; 9:156-66. [PMID: 17164898 DOI: 10.1039/b613182d] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
An electronic structure analysis is provided of the action of solvated FeO(2+), [FeO(H(2)O)(5)](2+), as a hydroxylation catalyst. It is emphasized that the oxo end of FeO(2+) does not form hydrogen bonds (as electron donor and H-bond acceptor) with H-bond donors nor with aliphatic C-H bonds, but it activates C-H bonds as an electron acceptor. It is extremely electrophilic, to the extent that it can activate even such poor electron donors as aliphatic C-H bonds, the C-H bond orbital acting as electron donor in a charge transfer type of interaction. Lower lying O-H bonding orbitals are less easily activated. The primary electron accepting orbital in a water environment is the 3sigma*alpha orbital, an antibonding combination of Fe-3d(z(2)) and O-2p(z), which is very low-lying relative to the pi*alpha compared with, for example, the sigma* orbital in O(2) relative to its pi*. This is ascribed to relatively small Fe-3d(z(2)) with O-2p(z) overlap, due to the nodal structure of the 3d(z(2)).The H-abstraction barrier is very low in the gas phase, but it is considerably enhanced in water solvent. This is shown to be due to strong screening effects of the dielectric medium, leading to relative destabilization of the levels of the charged [FeO(H(2)O)(5)](2+) species compared to those of the neutral substrate molecules, making it a less effective electron acceptor. The solvent directly affects the orbital interactions responsible for the catalytic reaction.
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Affiliation(s)
- Manuel J Louwerse
- Theoretical Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV, Amsterdam, The Netherlands
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