1
|
BECERRA-HERRERA MERCEDES, SAYAGO ANA, BELTRÁN RAFAEL. Exploring antioxidant reactivity and molecular structure of phenols by means of two coupled assays using fluorescence probe (2,3-diazabicyclo[2.2.2]oct-2-ene, DBO) and free radical (2,2-diphenyl-1-picrylhydrazyl, $$\hbox {DPPH}^{\cdot }$$ DPPH · ). J CHEM SCI 2017. [DOI: 10.1007/s12039-017-1331-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
|
2
|
Arnold WA, Oueis Y, O'Connor M, Rinaman JE, Taggart MG, McCarthy RE, Foster KA, Latch DE. QSARs for phenols and phenolates: oxidation potential as a predictor of reaction rate constants with photochemically produced oxidants. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2017; 19:324-338. [PMID: 27942650 DOI: 10.1039/c6em00580b] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Quantitative structure-activity relationships (QSARs) for prediction of the reaction rate constants of phenols and phenolates with three photochemically produced oxidants, singlet oxygen, carbonate radical, and triplet excited state sensitizers/organic matter, are developed. The predictive variable is the one-electron oxidation potential (E1), which is calculated for each species using density functional theory. The reaction rate constants are obtained from the literature, and for singlet oxygen, are augmented with new experimental data. Calculated E1 values have a mean unsigned error compared to literature values of 0.04-0.06 V. For singlet oxygen, a single linear QSAR that includes both phenols and phenolates is developed that predicts experimental rate constants, on average, to within a factor of three. Predictions for only 6 out of 87 compounds are off by more than a factor of 10. A more limited data set for carbonate radical reactions with phenols and phenolates also gives a single linear QSAR with prediction of rate constant being accurate to within a factor of three. The data for the reactions of phenols with triplet state sensitizers demonstrate that two sensitizers, 2-acetonaphthone and methylene blue, most closely predict the reactivity trend of triplet excited state organic matter with phenols. Using sensitizers with stronger reduction potentials could lead to overestimation of rate constants and thus underestimation of phenolic pollutant persistence.
Collapse
Affiliation(s)
- William A Arnold
- Department of Civil, Environmental, and Geo- Engineering, University of Minnesota, 500 Pillsbury Drive SE, Minneapolis, Minnesota 55455-0116, USA.
| | - Yan Oueis
- Department of Civil, Environmental, and Geo- Engineering, University of Minnesota, 500 Pillsbury Drive SE, Minneapolis, Minnesota 55455-0116, USA.
| | - Meghan O'Connor
- Department of Civil, Environmental, and Geo- Engineering, University of Minnesota, 500 Pillsbury Drive SE, Minneapolis, Minnesota 55455-0116, USA.
| | - Johanna E Rinaman
- Department of Chemistry, Seattle University, 901 12th Avenue, Seattle, WA 98122, USA.
| | - Miranda G Taggart
- Department of Chemistry, Seattle University, 901 12th Avenue, Seattle, WA 98122, USA.
| | - Rachel E McCarthy
- Department of Chemistry, Seattle University, 901 12th Avenue, Seattle, WA 98122, USA.
| | - Kimberley A Foster
- Department of Chemistry, Seattle University, 901 12th Avenue, Seattle, WA 98122, USA.
| | - Douglas E Latch
- Department of Chemistry, Seattle University, 901 12th Avenue, Seattle, WA 98122, USA.
| |
Collapse
|
3
|
Liu Y, Wang Q, Lei J, Hao Q, Wang W, Ju H. Anodic electrochemiluminescence of graphitic-phase C₃N₄ nanosheets for sensitive biosensing. Talanta 2014; 122:130-4. [PMID: 24720973 DOI: 10.1016/j.talanta.2014.01.018] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Revised: 01/13/2014] [Accepted: 01/17/2014] [Indexed: 01/22/2023]
Abstract
This work observed the anodic electrochemiluminescence (ECL) of C₃N₄ nanosheets (CNNS) for the first time. The ECL emission was 40 times stronger than that from bulk g-C₃N₄ in the presence of triethylamine (Et₃N) as a coreactant due to large surface-to-volume ratio, which enhanced the sensitivity for biosensing. At pH 7.0, the CNNS modified electrode prepared with 0.75 mg mL(-1) CNNS in 0.025% chitosan solution possesses good stability and acceptable reproducibility in the presence of 30 mM Et₃N. The ECL mechanism of CNNS/Et₃N system was proposed to be emitted from the excited CNNS, which was produced during the reaction between the electro-oxidation products of CNNS and coreactant Et₃N. Based on the annihilation between the oxidation product of dopamine (DA(+)) and Et₃N radical, a quenching-based method was established for sensitive and specific detection of dopamine ranging from 1.0 nM to 100 nM with a detection limit of 96 pM by using the CNNS nanosheets as an ECL emitter. The proposed method showed excellent specificity, high sensitivity and low detection limit, and could be applied in analysis of real samples.
Collapse
Affiliation(s)
- Yueting Liu
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
| | - Quanbo Wang
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
| | - Jianping Lei
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
| | - Qing Hao
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
| | - Wei Wang
- Institute of Basic Medicine Shangdong Academy of Medical Science, Jinan 250062, PR China
| | - Huangxian Ju
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China.
| |
Collapse
|
4
|
Mouslmani M, Patra D. Revoking excited state intra-molecular hydrogen transfer by size dependent tailor-made hierarchically ordered nanocapsules. RSC Adv 2014. [DOI: 10.1039/c3ra45095c] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
|
5
|
|
6
|
El-Sheshtawy HS, Pischel U, Nau WM. Solvent Polarity Affects H Atom Abstractions from C–H Donors. Org Lett 2011; 13:2694-7. [DOI: 10.1021/ol2007956] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Hamdy S. El-Sheshtawy
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany, and Centro de Investigación en Química Sostenible (CIQSO) and Departamento de Ingeniería Química, Química Física y Química Orgánica, Universidad de Huelva, Campus de El Carmen, E-21071 Huelva, Spain
| | - Uwe Pischel
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany, and Centro de Investigación en Química Sostenible (CIQSO) and Departamento de Ingeniería Química, Química Física y Química Orgánica, Universidad de Huelva, Campus de El Carmen, E-21071 Huelva, Spain
| | - Werner M. Nau
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany, and Centro de Investigación en Química Sostenible (CIQSO) and Departamento de Ingeniería Química, Química Física y Química Orgánica, Universidad de Huelva, Campus de El Carmen, E-21071 Huelva, Spain
| |
Collapse
|
7
|
Lewandowska A, Hug GL, Hörner G, Pogocki D, Kazmierczak F, Marciniak B. Intramolecular H-atom transfer reactions in rigid peptides — Correlated solvent and structural effects. CAN J CHEM 2011. [DOI: 10.1139/v10-110] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The rates and the mechanism of intramolecular hydrogen-atom transfer across the rigid diketopiperazine spacer in two epimeric benzophenone–tyrosine dyads were studied by nanosecond laser flash photolysis in 12 non-protic and protic solvents. Effects of the stereochemistry on the ground-state structures and conformational equilibria and dynamics have been addressed by means of NMR-based population analysis and long-term molecular-dynamics simulations. The excited triplet state of the benzophenone is found to be quenched intramolecularly by the remote phenol moiety with rates that are highly dependent on the solvent and on the relative benzophenone–phenol orientation. In agreement with previous studies, the kinetic diversity, with rates ranging from <105 s−1 to 2 × 107 s−1, can be attributed to retarding effects of the bulk viscosity and to effects of specific solvation, which can be both rate retarding and rate accelerating. As an extension of the previous knowledge, however, the phenomenology of the kinetic solvent effects, that is, the nature of the predominating solvent parameter and its absolute impact on the reactivity, is found to be highly correlated with structural effects.
Collapse
Affiliation(s)
- Anna Lewandowska
- Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
- Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Faculty of Biology and Agriculture, University of Rzeszow, 35-601 Rzeszow, Poland
- Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland
| | - Gordon L. Hug
- Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
- Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Faculty of Biology and Agriculture, University of Rzeszow, 35-601 Rzeszow, Poland
- Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland
| | - Gerald Hörner
- Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
- Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Faculty of Biology and Agriculture, University of Rzeszow, 35-601 Rzeszow, Poland
- Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland
| | - Dariusz Pogocki
- Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
- Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Faculty of Biology and Agriculture, University of Rzeszow, 35-601 Rzeszow, Poland
- Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland
| | - Franciszek Kazmierczak
- Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
- Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Faculty of Biology and Agriculture, University of Rzeszow, 35-601 Rzeszow, Poland
- Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland
| | - Bronislaw Marciniak
- Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
- Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA
- Faculty of Biology and Agriculture, University of Rzeszow, 35-601 Rzeszow, Poland
- Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany
- Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland
| |
Collapse
|
8
|
Lewandowska A, Hug GL, Hörner G, Pedzinski T, Filipiak P, Marciniak B. Efficient photochemical oxidation of anisole in protic solvents: electron transfer driven by specific solvent-solute interactions. Chemphyschem 2010; 11:2108-17. [PMID: 20540143 DOI: 10.1002/cphc.201000196] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The dynamics of the bimolecular quenching of triplet excited benzophenone by anisole was studied by nanosecond flash photolysis. We carried out a detailed study of the solvent dependence of the reaction rates and efficiencies in a number of protic and non-protic solvents. These studies were augmented by theoretical modelling and experimental investigation of solute/solvent interactions in the triplet excited and the ground state, respectively. The triplet quenching that follows Stern-Volmer kinetics in all cases is profoundly dependent on the nature of the solvent, with the highest reactivity being consistently found in protic solvents. The results in non-protic solvents are compatible with unproductive quenching via a charge-transfer state, whereas the generally fast quenching in protic solvents is accompanied by efficient formation of free-radical products. Analysis of the solvent dependence in terms of Marcus theory reveals the impact of specific solvation of benzophenone by protic solvents on the ET driving force and kinetics. Specific solvation is found to support efficient free radical ion formation in media of moderate and low polarity as well.
Collapse
Affiliation(s)
- Anna Lewandowska
- Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, Poznan 60-780, Poland
| | | | | | | | | | | |
Collapse
|
9
|
Meyer R, Zhang X, Nau WM. Effect of bridgehead substitution on the fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-enes by solvents and antioxidants. Photochem Photobiol Sci 2009; 8:1694-700. [PMID: 20024166 DOI: 10.1039/b9pp00081j] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Azoalkanes of the 2,3-diazabicyclo[2.2.2]-oct-2-ene type have been introduced as probes for antioxidants in homogeneous solution as well as in liposomes and micelles. The bimolecular fluorescence quenching of the bridgehead dichloro-substituted 1,4-dichloro-2,3-diazabicyclo[2.2.2]-oct-2-ene (3) was compared with that of the parent compound 2,3-diazabicyclo[2.2.2]-oct-2-ene (1) and the bridgehead-dialkylated compound 4-methyl-1-isopropyl-2,3-diazabicyclo[2.2.2]-oct-2-ene (2). Compound 3 showed a more efficient fluorescence quenching in C-H containing solvents (e.g., in n-hexane: 30 ns for 3 versus 340 ns for 1 and 770 ns for 2), but a less efficient quenching in aqueous solution (e.g., in deaerated H(2)O: 485 ns for 3 versus 420 ns for 1 and 340 ns for 2), and also by molecular oxygen (k(q)/10(9) M(-1) s(-1) = 0.32 for versus 2.5 for 1 and 1.9 for 2). Towards low-molecular weight antioxidants, compound 3 showed a significantly higher reactivity (e.g., for reduced glutathione: k(q)/10(9) M(-1) s(-1) = 1.8 for 3 versus 0.82 for 1 and 0.39 for 2), at the expense of a lower differentiation between the investigated antioxidants (lower selectivity). The increased reactivity of 3 and lower, as well as qualitatively different, selectivity is attributed to a combination of factors, most importantly the slightly increased excitation energy of 3 and its lower excited-state nucleophilicity. The latter was independently corroborated, besides its longer fluorescence lifetime in aqueous solution, through the trends in quenching rate constants of the azoalkanes 1-3 towards electron-deficient versus electron-rich lactone antioxidants of the benzofuranone type. While common inorganic buffer constituents caused no fluorescence quenching, significant quenching was observed, as a curiosity, for hydrogencarbonate (k(q)/10(6) M(-1) s(-1) = 1.7 for 3 versus 2.4 for 1 and 0.45 for 2), with a fully manifested kinetic deuterium isotope effect (k(q)(H(2)O)/k(q)(D(2)O) = 12) for 3.
Collapse
Affiliation(s)
- Roland Meyer
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759, Bremen, Germany
| | | | | |
Collapse
|
10
|
Dondi D, Ravelli D, Fagnoni M, Mella M, Molinari A, Maldotti A, Albini A. Regio- and Stereoselectivity in the Decatungstate Photocatalyzed Alkylation of Alkenes by Alkylcyclohexanes. Chemistry 2009; 15:7949-7957. [DOI: 10.1002/chem.200900810] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
11
|
In-vitro antioxidant activities of an ethanolic extract of the oyster mushroom, Pleurotus ostreatus. INNOV FOOD SCI EMERG 2009. [DOI: 10.1016/j.ifset.2008.07.002] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
12
|
Hörner G, Hug G, Pogocki D, Filipiak P, Bauer W, Grohmann A, Lämmermann A, Pedzinski T, Marciniak B. Head-to-Tail Interactions in Tyrosine/Benzophenone Dyads in the Ground and the Excited State: NMR and Laser Flash Photolysis Studies. Chemistry 2008; 14:7913-29. [DOI: 10.1002/chem.200800315] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
13
|
Investigations on the fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene by certain flavonoids. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2008; 91:143-50. [DOI: 10.1016/j.jphotobiol.2008.03.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2007] [Revised: 03/08/2008] [Accepted: 03/11/2008] [Indexed: 11/22/2022]
|
14
|
Anbazhagan V, Kandavelu V, Kathiravan A, Renganathan R. Investigation on the fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by certain estrogens and catechols. J Photochem Photobiol A Chem 2008. [DOI: 10.1016/j.jphotochem.2007.06.026] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
|
15
|
Sahoo H, Hennig A, Florea M, Roth D, Enderle T, Nau WM. Single-label kinase and phosphatase assays for tyrosine phosphorylation using nanosecond time-resolved fluorescence detection. J Am Chem Soc 2007; 129:15927-34. [PMID: 18044894 DOI: 10.1021/ja074975w] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The collision-induced fluorescence quenching of a 2,3-diazabicyclo[2.2.2]oct-2-ene-labeled asparagine (Dbo) by hydrogen atom abstraction from the tyrosine residue in peptide substrates was introduced as a single-labeling strategy to assay the activity of tyrosine kinases and phosphatases. The assays were tested for 12 different combinations of Dbo-labeled substrates and with the enzymes p60c-Src Src kinase, EGFR kinase, YOP protein tyrosine phosphatase, as well as acid and alkaline phosphatases, thereby demonstrating a broad application potential. The steady-state fluorescence changed by a factor of up to 7 in the course of the enzymatic reaction, which allowed for a sufficient sensitivity of continuous monitoring in steady-state experiments. The fluorescence lifetimes (and intensities) were found to be rather constant for the phosphotyrosine peptides (ca. 300 ns in aerated water), while those of the unphosphorylated peptides were as short as 40 ns (at pH 7) and 7 ns (at pH 13) as a result of intramolecular quenching. Owing to the exceptionally long fluorescence lifetime of Dbo, the assays were alternatively performed by using nanosecond time-resolved fluorescence (Nano-TRF) detection, which leads to an improved discrimination of background fluorescence and an increased sensitivity. The potential for inhibitor screening was demonstrated through the inhibition of acid and alkaline phosphatases by molybdate.
Collapse
Affiliation(s)
- Harekrushna Sahoo
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany
| | | | | | | | | | | |
Collapse
|
16
|
Nam TG, Rector CL, Kim HY, Sonnen AFP, Meyer R, Nau WM, Atkinson J, Rintoul J, Pratt DA, Porter NA. Tetrahydro-1,8-naphthyridinol Analogues of α-Tocopherol as Antioxidants in Lipid Membranes and Low-Density Lipoproteins. J Am Chem Soc 2007; 129:10211-9. [PMID: 17655300 DOI: 10.1021/ja072371m] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Recently we demonstrated that the C(7)-unsubstituted tetrahydro-1,8-naphthyridin-3-ol has more than an order of magnitude better peroxyl radical trapping activity than alpha-tocopherol (alpha-TOH) in inhibited autoxidations in benzene. In order to prepare analogues more structurally related to alpha-TOH for further studies in vitro and in vivo, we developed synthetic approaches to C(7)-monoalkyl and C(7)-dialkyl analogues using a sequence involving (1) AgNO3-mediated hydroxymethyl radical addition to 1,8-naphthyridine, (2) regioselective alkyllithium addition by cyclic chelation in a nonpolar solvent, (3) iodination of the naphthyridine at C(3), and (4) CuI-medidated benzyloxylation of the aryl iodide followed by catalytic hydrogenolysis. An alpha-TOH isostere was prepared by a Wittig coupling of a C16 side chain identical to that of alpha-TOH to the naphthyridinols. The C(7)-mono- and dialkyl analogues exhibited more than an order of magnitude higher antioxidant activity (k(inh) = (5.3-6.1) x 10(7) M(-1) s(-1)) than alpha-TOH (k(inh) = 0.35 x 10(7) M(-) s(-1)) in benzene, as determined by a newly developed peroxyl radical clock. In addition to the strong antioxidant activity in benzene, the closest alpha-TOH analogue (naphthyridinol-based tocopherol, N-TOH) showed excellent inhibition of the oxidation of cholesteryl esters in human low-density lipoprotein and spared endogenous alpha-TOH in these experiments. Lateral diffusion of N-TOH in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine liposomes was comparable to that of alpha-TOH, suggesting that it will have good antioxidant characteristics in both membranes and lipoproteins. Furthermore, a binding assay using a fluorescent tocopherol analogue showed that N-TOH binds to recombinant human tocopherol transfer protein better than alpha-TOH itself, suggesting that distribution of unnatural antioxidants such as N-TOH in vivo is possible.
Collapse
Affiliation(s)
- Tae-gyu Nam
- Center in Molecular Toxicology and Vanderbilt Institute of Chemical Biology, Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
17
|
Koner AL, Pischel U, Nau WM. Kinetic Solvent Effects on Hydrogen Abstraction Reactions. Org Lett 2007; 9:2899-902. [PMID: 17580891 DOI: 10.1021/ol071165g] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Kinetic solvent effects on hydrogen abstractions, namely, acceleration in nonpolar solvents, have been presumed to be restricted to O-H hydrogen donors. We demonstrate that also abstractions from C-H and even Sn-H bonds by cumyloxyl radicals and n,pi*-excited 2,3-diazabicyclo[2.2.2]oct-2-ene are fastest in the gas phase and nonpolar solvents but slowest in acetonitrile. Accordingly, solvent effects on hydrogen abstractions are more general, presumably due to stabilization of the reactive oxygen or nitrogen species in polar solvents.
Collapse
Affiliation(s)
- Apurba L Koner
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany
| | | | | |
Collapse
|
18
|
Abad S, Bosca F, Domingo LR, Gil S, Pischel U, Miranda MA. Triplet Reactivity and Regio-/Stereoselectivity in the Macrocyclization of Diastereomeric Ketoprofen−Quencher Conjugates via Remote Hydrogen Abstractions. J Am Chem Soc 2007; 129:7407-20. [PMID: 17508750 DOI: 10.1021/ja0712827] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Intramolecular excited triplet state interactions in diastereomeric compounds composed of a benzophenone chromophore (ketoprofen) and various hydrogen donor moieties (tetrahydrofuran, isopropylbenzene) have been investigated by laser flash photolysis. The rate constants for hydrogen abstraction by excited triplet benzophenone are in the order of 10(4)-10(5) s(-1), with the highest reactivity for the tetrahydrofuran residue. A remarkable diastereodifferentiation, expressed in the triplet lifetimes of the carbonyl chromophore (e.g., 1.6 versus 2.7 micros), has been found for these compounds. With an alkylaromatic moiety as donor, related effects have been observed, albeit strongly dependent on the length of the spacer. The reactivity trend for the initial hydrogen transfer step is paralleled by the quantum yields of the overall photoreaction. The biradicals, formed via remote hydrogen abstraction, undergo intramolecular recombination to macrocyclic ring systems. The new photoproducts have been isolated and characterized by NMR spectroscopy. The stereochemistry of the macrocycles, which contain up to four asymmetric carbons, has been unambiguously assigned on the basis of single-crystal structures and/or NOE effects. Interestingly, a highly regio- and stereoselective macrocyclization has been found for the ketoprofen-tetrahydrofuran conjugates, where hydrogen abstraction from the less substituted carbon is exclusive; cisoid ring junction is always preferred over the transoid junction. The photoreaction is less regioselective for compounds with an isopropylbenzene residue. The reactivity and selectivity trends have been rationalized by DFT (B3LYP/6-31G*) calculations.
Collapse
Affiliation(s)
- Sergio Abad
- Instituto de Tecnología Química, UPV-CSIC, Universidad Politécnica de Valencia, Av. de los Naranjos s/n, E-46022 Valencia, Spain
| | | | | | | | | | | |
Collapse
|
19
|
Hennig A, Florea M, Roth D, Enderle T, Nau WM. Design of peptide substrates for nanosecond time-resolved fluorescence assays of proteases: 2,3-Diazabicyclo[2.2.2]oct-2-ene as a noninvasive fluorophore. Anal Biochem 2007; 360:255-65. [PMID: 17134673 DOI: 10.1016/j.ab.2006.09.015] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2006] [Revised: 09/15/2006] [Accepted: 09/17/2006] [Indexed: 11/26/2022]
Abstract
Fluorescence protease assays were investigated with peptide substrates containing a 2,3-diazabicyclo[2.2.2]oct-2-ene-labeled asparagine (Dbo) as a fluorescent amino acid. The special characteristic of the fluorophore Dbo is its exceedingly long fluorescence lifetime (ca. 300 ns in water under air), which allows the use of nanosecond time-resolved fluorescence (Nano-TRF) detection to efficiently suppress shorter-lived background emission. In addition, the natural amino acids tryptophan and tyrosine can be employed as intramolecular fluorescence quenchers, which facilitates substrate design. Fourteen synthetic peptide substrates (composed of 2-19 amino acids) and five enzymes (trypsin, pepsin, carboxypeptidase A, leucine aminopeptidase, and chymotrypsin) were investigated and, in all 28 examined combinations, enzymatic activity was detected by monitoring the increase in steady state fluorescence with time and determining the reaction rates as kcat/Km values, which ranged from 0.2 to 80x10(6) M-1 min-1. The results suggest an excellent compatibility of the very small and hydrophilic fluorescent probe Dbo with solid-phase peptide synthesis and the investigated proteases. For all 14 peptides the fluorescence lifetimes before and after enzymatic cleavage were measured and Nano-TRF measurements were performed in 384-well microplates. The fluorescence lifetimes of the different peptides provide the basis for the rational design of Dbo-based fluorescent substrates for protease assays. Measurements in Nano-TRF mode revealed, in addition to efficient suppression of background fluorescence, an increased differentiation between cleaved and uncleaved substrate. The Dbo-based assays can be adapted for high-throughput screening.
Collapse
Affiliation(s)
- Andreas Hennig
- School of Engineering and Science, International University Bremen, Campus Ring 1, D-28759 Bremen, Germany
| | | | | | | | | |
Collapse
|
20
|
Lundgren CV, Koner AL, Tinkl M, Pischel U, Nau WM. Reaction of Singlet-Excited 2,3-Diazabicyclo[2.2.2]oct-2-ene andtert-Butoxyl Radicals with Aryl-Substituted Benzofuranones. J Org Chem 2006; 71:1977-83. [PMID: 16496983 DOI: 10.1021/jo052440k] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
5,7-Di-tert-butyl-3-aryl-3H-benzofuran-2-ones are lactones with potential antioxidant activity, owing to their abstractable benzylic C-H hydrogens. The fluorescence quenching of the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), an established probe for the hydrogen-donor propensity of chain-breaking antioxidants, was investigated for 16 aryl-substituted benzofuranone derivatives [m,m-(CF3)2, p-CN, m-CN, p-CF3, p-COOCH3, m-CF3, p-Cl, p-F, H, m-CH3, p-CH3, m,p-(CH3)2, p-OCH3, o-CH3, o-CF3, o,m-(CH3)2]. Analysis of the rate data in terms of a linear free energy relationship yielded a reaction constant of rho = +0.35. This implies that n,pi*-excited DBO acts as nucleophilic species. In contrast, hydrogen abstraction of tert-butoxyl radicals from the benzofuranones was accelerated by electron-donating substituents (rho = -0.23), in conformity with the electrophilic character of oxygen-centered alkoxyl radicals. Possible implications for the optimization of the hydrogen-donor propensity of antioxidants through structural variation are discussed.
Collapse
Affiliation(s)
- Cecilia Vannesjö Lundgren
- School of Engineering and Science, International University Bremen, Campus Ring 1, D-28759 Bremen, Germany
| | | | | | | | | |
Collapse
|