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Beutick SE, Vermeeren P, Hamlin TA. The 1,3-Dipolar Cycloaddition From Conception to Quantum Chemical Design. Chem Asian J 2022; 17:e202200553. [PMID: 35822651 PMCID: PMC9539489 DOI: 10.1002/asia.202200553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Revised: 07/08/2022] [Indexed: 11/12/2022]
Abstract
The 1,3‐dipolar cycloaddition (1,3‐DCA) reaction, conceptualized by Rolf Huisgen in 1960, has proven immensely useful in organic, material, and biological chemistry. The uncatalyzed, thermal transformation is generally sluggish and unselective, but the reactivity can be enhanced by means of metal catalysis or by the introduction of either predistortion or electronic tuning of the dipolarophile. These promoted reactions generally go with a much higher reactivity, selectivity, and yields, often at ambient temperatures. The rapid orthogonal reactivity and compatibility with aqueous and physiological conditions positions the 1,3‐DCA as an excellent bioorthogonal reaction. Quantum chemical calculations have been critical for providing an understanding of the physical factors that control the reactivity and selectivity of 1,3‐DCAs. In silico derived design principles have proven invaluable for the design of new dipolarophiles with tailored reactivity. This review discusses everything from the conception of the 1,3‐DCA all the way to the state‐of‐the‐art methods and models used for the quantum chemical design of novel (bioorthogonal) reagents.
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Blokker E, van Zeist WJ, Sun X, Poater J, van der Schuur JM, Hamlin TA, Bickelhaupt FM. Methyl Substitution Destabilizes Alkyl Radicals. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202207477] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Abstract
We have quantum chemically explored the competition between the SN2 and SN2' pathways for X- + H2C═CHCH2Y (X, Y = F, Cl, Br, I) using a combined relativistic density functional theory and coupled-cluster theory approach. Bimolecular nucleophilic substitution reactions at allylic systems, i.e., Cγ═Cβ-Cα-Y, bearing a leaving-group at the α-position, proceed either via a direct attack at the α-carbon (SN2) or via an attack at the γ-carbon, involving a concerted allylic rearrangement (SN2'), in both cases leading to the expulsion of the leaving-group. Herein, we provide a physically sound model to rationalize under which circumstances a nucleophile will follow either the aliphatic SN2 or allylic SN2' pathway. Our activation strain analyses expose the underlying physical factors that steer the SN2/SN2' competition and, again, demonstrate that the concepts of a reaction's "characteristic distortivity" and "transition state acidity" provide explanations and design tools for understanding and predicting reactivity trends in organic synthesis.
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Moloto BP, Vermeeren P, Dalla Tiezza M, Esterhuysen C, Bickelhaupt FM, Hamlin TA. Palladium‐Catalyzed Activation of Carbon–Halogen Bonds: Electrostatics‐Controlled Reactivity. European J Org Chem 2022. [DOI: 10.1002/ejoc.202200722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Svatunek D, Houszka N, Hamlin TA, Bickelhaupt FM, Mikula H. Corrigendum: Chemoselectivity of Tertiary Azides in Strain‐Promoted Alkyne–Azide Cycloadditions. Chemistry 2022; 28:e202200414. [DOI: 10.1002/chem.202200414] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Nieuwland C, Hamlin TA, Fonseca Guerra C, Barone G, Bickelhaupt FM. B-DNA Structure and Stability: The Role of Nucleotide Composition and Order. Chemistry 2022; 11:e202200013. [PMID: 35103418 DOI: 10.1002/open.202200013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Invited for this month's cover are the groups of Célia Fonseca Guerra at the Vrije Universiteit Amsterdam and Leiden University, Giampaolo Barone from the Università degli Studi di Palermo, and F. Matthias Bickelhaupt at Vrije Universiteit Amsterdam and Radboud University Nijmegen. The cover picture shows the four primary interaction components (hydrogen bonding, cross-terms, base stacking, and solvation) that determine the stability of B-DNA duplexes. Quantum chemical analyses identify an interplay between the stabilizing hydrogen bonds between nucleotides that drive the formation of the DNA double-strand, and the destabilizing loss of stacking interactions within individual strands combined with partial desolvation. The sequence-dependence in the duplex stability originates mainly from the cross-terms, which can be attractive or repulsive. Read the full text of their Research Article at 10.1002/open.202100231.
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Nieuwland C, Hamlin TA, Fonseca Guerra C, Barone G, Bickelhaupt FM. B-DNA Structure and Stability: The Role of Nucleotide Composition and Order. ChemistryOpen 2022; 11:e202100231. [PMID: 35083880 PMCID: PMC8805170 DOI: 10.1002/open.202100231] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Revised: 12/10/2021] [Indexed: 11/08/2022] Open
Abstract
We have quantum chemically analyzed the influence of nucleotide composition and sequence (that is, order) on the stability of double-stranded B-DNA triplets in aqueous solution. To this end, we have investigated the structure and bonding of all 32 possible DNA duplexes with Watson-Crick base pairing, using dispersion-corrected DFT at the BLYP-D3(BJ)/TZ2P level and COSMO for simulating aqueous solvation. We find enhanced stabilities for duplexes possessing a higher GC base pair content. Our activation strain analyses unexpectedly identify the loss of stacking interactions within individual strands as a destabilizing factor in the duplex formation, in addition to the better-known effects of partial desolvation. Furthermore, we show that the sequence-dependent differences in the interaction energy for duplexes of the same overall base pair composition result from the so-called "diagonal interactions" or "cross terms". Whether cross terms are stabilizing or destabilizing depends on the nature of the electrostatic interaction between polar functional groups in the pertinent nucleobases.
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Nieuwland C, Hamlin TA, Fonseca Guerra C, Barone G, Bickelhaupt FM. Front Cover: B‐DNA Structure and Stability: The Role of Nucleotide Composition and Order (ChemistryOpen 2/2022). Chemistry 2022. [DOI: 10.1002/open.202200014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Rozsar D, Formica M, Yamazaki K, Hamlin TA, Dixon DJ. Bifunctional Iminophosphorane-Catalyzed Enantioselective Sulfa-Michael Addition to Unactivated α,β-Unsaturated Amides. J Am Chem Soc 2022; 144:1006-1015. [PMID: 34990142 PMCID: PMC8793149 DOI: 10.1021/jacs.1c11898] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
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The
first metal-free catalytic intermolecular enantioselective
Michael addition to unactivated α,β-unsaturated amides
is described. Consistently high enantiomeric excesses and yields were
obtained over a wide range of alkyl thiol pronucleophiles and electrophiles
under mild reaction conditions, enabled by a novel squaramide-based
bifunctional iminophosphorane catalyst. Low catalyst loadings (2.0
mol %) were achieved on a decagram scale, demonstrating the scalability
of the reaction. Computational analysis revealed the origin of the
high enantiofacial selectivity via analysis of relevant transition
structures and provided substantial support for specific noncovalent
activation of the carbonyl group of the α,β-unsaturated
amide by the catalyst.
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Shiomi S, Shennan BDA, Yamazaki K, Fuentes de Arriba ÁL, Vasu D, Hamlin TA, Dixon DJ. A New Organocatalytic Desymmetrization Reaction Enables the Enantioselective Total Synthesis of Madangamine E. J Am Chem Soc 2022; 144:1407-1415. [PMID: 35037758 PMCID: PMC8796237 DOI: 10.1021/jacs.1c12040] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
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The
enantioselective total synthesis of madangamine E has been
completed in 30 steps, enabled by a new catalytic and highly enantioselective
desymmetrizing intramolecular Michael addition reaction of a prochiral
ketone to a tethered β,β′-disubstituted
nitroolefin. This key carbon–carbon bond forming reaction efficiently
constructed a chiral bicyclic core in near-perfect enantio- and diastereo-selectivity,
concurrently established three stereogenic centers, including a quaternary
carbon, and proved highly scalable. Furthermore, the pathway and origins
of enantioselectivity in this catalytic cyclization were probed using
density functional theory (DFT) calculations, which revealed the crucial
substrate/catalyst interactions in the enantio-determining step. Following
construction of the bicyclic core, the total synthesis of madangamine
E could be completed, with key steps including a mild one-pot oxidative
lactamization of an amino alcohol, a two-step Z-selective
olefination of a sterically hindered ketone, and ring-closing metatheses
to install the two macrocyclic rings.
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Hansen T, Vermeeren P, Bickelhaupt FM, Hamlin TA. Stability of alkyl carbocations. Chem Commun (Camb) 2022; 58:12050-12053. [DOI: 10.1039/d2cc04034d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The traditional and widespread rationale behind the stability trend of alkyl-substituted carbocations is incomplete.
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Hansen T, Sun X, Dalla Tiezza M, van Zeist WJ, Poater J, Hamlin TA, Bickelhaupt FM. C(spn)-X (n = 1-3) Bond Activation by Palladium. Chemistry 2021; 28:e202103953. [PMID: 34958486 PMCID: PMC9306469 DOI: 10.1002/chem.202103953] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Indexed: 11/09/2022]
Abstract
We have studied the palladium-mediated activation of C( sp n )-X bonds (n = 1-3 and X = H, CH 3 , Cl) in archetypal model substrates H 3 C-CH 2 -X, H 2 C=CH-X and HC≡C-X by catalysts PdL n with L n = no ligand, Cl - , and (PH 3 ) 2 , using relativistic density functional theory at ZORA-BLYP/TZ2P. The oxidative addition barrier decreases along this series, even though the strength of the bonds increases going from C( sp 3 )-X, to C( sp 2 )-X, to C( sp )-X. Activation strain and matching energy decomposition analyses reveal that the decreased oxidative addition barrier going from sp 3 to sp 2 to sp , originates from a reduction in the destabilizing steric (Pauli) repulsion between catalyst and substrate. This is the direct consequence of the decreasing coordination number of the carbon atom in C( sp n )-X, which goes from four, to three, to two along this series. The associated net stabilization of the catalyst-substrate interaction dominates the trend in strain energy which indeed becomes more destabilizing along this same series as the bond becomes stronger from C( sp 3 )-X to C( sp )-X.
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Hansen T, Roozee JC, Bickelhaupt FM, Hamlin TA. How Solvation Influences the S N2 versus E2 Competition. J Org Chem 2021; 87:1805-1813. [PMID: 34932346 PMCID: PMC8822482 DOI: 10.1021/acs.joc.1c02354] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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We have quantum chemically
investigated how solvation influences
the competition between the SN2 and E2 pathways of the
model F– + C2H5Cl reaction.
The system is solvated in a stepwise manner by going from the gas
phase, then via microsolvation of one to three explicit solvent molecules,
then last to bulk solvation using relativistic density functional
theory at (COSMO)-ZORA-OLYP/QZ4P. We explain how and why the mechanistic
pathway of the system shifts from E2 in the gas phase to SN2 upon strong solvation of the Lewis base (i.e., nucleophile/protophile).
The E2 pathway is preferred under weak solvation of the system by
dichloromethane, whereas a switch in reactivity from E2 to SN2 is observed under strong solvation by water. Our activation strain
and Kohn–Sham molecular orbital analyses reveal that solvation
of the Lewis base has a significant impact on the strength of the
Lewis base. We show how strong solvation furnishes a weaker Lewis
base that is unable to overcome the high characteristic distortivity
associated with the E2 pathway, and thus the SN2 pathway
becomes viable.
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Zaccaria F, van der Lubbe SCC, Nieuwland C, Hamlin TA, Fonseca Guerra C. How Divalent Cations Interact with the Internal Channel Site of Guanine Quadruplexes. Chemphyschem 2021; 22:2265-2266. [PMID: 34791760 DOI: 10.1002/cphc.202100761] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The front cover artwork is provided by the TheoCheM group of the Vrije Universiteit Amsterdam. The image shows that guanine quadruplexes have a stronger binding affinity for divalent cations than monovalent cations. Read the full text of the Article at 10.1002/cphc.202100529.
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Blokker E, Sun X, Poater J, van der Schuur JM, Hamlin TA, Bickelhaupt FM. The Chemical Bond: When Atom Size Instead of Electronegativity Difference Determines Trend in Bond Strength. Chemistry 2021; 27:15616-15622. [PMID: 34609774 PMCID: PMC9298008 DOI: 10.1002/chem.202103544] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Indexed: 11/28/2022]
Abstract
We have quantum chemically analyzed element−element bonds of archetypal HnX−YHn molecules (X, Y=C, N, O, F, Si, P, S, Cl, Br, I), using density functional theory. One purpose is to obtain a set of consistent homolytic bond dissociation energies (BDE) for establishing accurate trends across the periodic table. The main objective is to elucidate the underlying physical factors behind these chemical bonding trends. On one hand, we confirm that, along a period (e. g., from C−C to C−F), bonds strengthen because the electronegativity difference across the bond increases. But, down a period, our findings constitute a paradigm shift. From C−F to C−I, for example, bonds do become weaker, however, not because of the decreasing electronegativity difference. Instead, we show that the effective atom size (via steric Pauli repulsion) is the causal factor behind bond weakening in this series, and behind the weakening in orbital interactions at the equilibrium distance. We discuss the actual bonding mechanism and the importance of analyzing this mechanism as a function of the bond distance.
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Maitland JAP, Leitch JA, Yamazaki K, Christensen KE, Cassar DJ, Hamlin TA, Dixon DJ. Switchable, Reagent‐Controlled Diastereodivergent Photocatalytic Carbocyclisation of Imine‐Derived α‐Amino Radicals. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202107253] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Maitland JAP, Leitch JA, Yamazaki K, Christensen KE, Cassar DJ, Hamlin TA, Dixon DJ. Switchable, Reagent-Controlled Diastereodivergent Photocatalytic Carbocyclisation of Imine-Derived α-Amino Radicals. Angew Chem Int Ed Engl 2021; 60:24116-24123. [PMID: 34449968 PMCID: PMC8597041 DOI: 10.1002/anie.202107253] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Revised: 08/13/2021] [Indexed: 12/15/2022]
Abstract
A reagent‐controlled stereodivergent carbocyclisation of aryl aldimine‐derived, photocatalytically generated, α‐amino radicals possessing adjacent conjugated alkenes, affording either bicyclic or tetracyclic products, is described. Under net reductive conditions using commercial Hantzsch ester, the α‐amino radical species underwent a single stereoselective cyclisation to give trans‐configured amino‐indane structures in good yield, whereas using a substituted Hantzsch ester as a milder reductant afforded cis‐fused tetracyclic tetrahydroquinoline frameworks, resulting from two consecutive radical cyclisations. Judicious choice of the reaction conditions allowed libraries of both single and dual cyclisation products to be synthesised with high selectivity, notable predictability, and good‐to‐excellent yields. Computational analysis employing DFT revealed the reaction pathway and mechanistic rationale behind this finely balanced yet readily controlled photocatalytic system.
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Tiekink EH, Vermeeren P, Bickelhaupt FM, Hamlin TA. How Lewis Acids Catalyze Ene Reactions. European J Org Chem 2021. [DOI: 10.1002/ejoc.202101107] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Rodrigues Silva D, de Azevedo Santos L, Hamlin TA, Bickelhaupt FM, P Freitas M, Fonseca Guerra C. Dipolar repulsion in α-halocarbonyl compounds revisited. Phys Chem Chem Phys 2021; 23:20883-20891. [PMID: 34528039 PMCID: PMC8479779 DOI: 10.1039/d1cp02502c] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The concept of dipolar repulsion has been widely used to explain several phenomena in organic chemistry, including the conformational preferences of carbonyl compounds. This model, in which atoms and bonds are viewed as point charges and dipole moment vectors, respectively, is however oversimplified. To provide a causal model rooted in quantitative molecular orbital theory, we have analyzed the rotational isomerism of haloacetaldehydes OHC–CH2X (X = F, Cl, Br, I), using relativistic density functional theory. We have found that the overall trend in the rotational energy profiles is set by the combined effects of Pauli repulsion (introducing a barrier around gauche that separates minima at syn and anti), orbital interactions (which can pull the anti minimum towards anticlinal to maximize hyperconjugation), and electrostatic interactions. Only for X = F, not for X = Cl–I, electrostatic interactions push the preference from syn to anti. Our bonding analyses show how this trend is related to the compact nature of F versus the more diffuse nature of the heavier halogens. Beyond point charges! The point charge concept within dipolar repulsion model is valid for compact atoms like fluorine. This model breaks down for larger halogens, for which the electrostatic attraction between nuclei and charge densities dominates.![]()
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Vermeeren P, Hamlin TA, Bickelhaupt FM. Origin of asynchronicity in Diels-Alder reactions. Phys Chem Chem Phys 2021; 23:20095-20106. [PMID: 34499069 PMCID: PMC8457343 DOI: 10.1039/d1cp02456f] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 09/02/2021] [Indexed: 02/02/2023]
Abstract
Asynchronicity in Diels-Alder reactions plays a crucial role in determining the height of the reaction barrier. Currently, the origin of asynchronicity is ascribed to the stronger orbital interaction between the diene and the terminal carbon of an asymmetric dienophile, which shortens the corresponding newly formed C-C bond and hence induces asynchronicity in the reaction. Here, we show, using the activation strain model and Kohn-Sham molecular orbital theory at ZORA-BP86/TZ2P, that this rationale behind asynchronicity is incorrect. We, in fact, found that following a more asynchronous reaction mode costs favorable HOMO-LUMO orbital overlap and, therefore, weakens (not strengthens) these orbital interactions. Instead, it is the Pauli repulsion that induces asynchronicity in Diels-Alder reactions. An asynchronous reaction pathway also lowers repulsive occupied-occupied orbital overlap which, therefore, reduces the unfavorable Pauli repulsion. As soon as this mechanism of reducing Pauli repulsion dominates, the reaction begins to deviate from synchronicity and adopts an asynchronous mode. The eventual degree of asynchronicity, as observed in the transition state of a Diels-Alder reaction, is ultimately achieved when the gain in stability, as a response to the reduced Pauli repulsion, balances with the loss of favorable orbital interactions.
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Dalla Tiezza M, Hamlin TA, Bickelhaupt FM, Orian L. Radical Scavenging Potential of the Phenothiazine Scaffold: A Computational Analysis. ChemMedChem 2021; 16:3763-3771. [PMID: 34536069 PMCID: PMC9292796 DOI: 10.1002/cmdc.202100546] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2021] [Revised: 09/05/2021] [Indexed: 01/05/2023]
Abstract
The reactivity of phenothiazine (PS), phenoselenazine (PSE), and phenotellurazine (PTE) with different reactive oxygen species (ROS) has been studied using density functional theory (DFT) in combination with the QM‐ORSA (Quantum Mechanics‐based Test for Overall Free Radical Scavenging Activity) protocol for an accurate kinetic rate calculation. Four radical scavenging mechanisms have been screened, namely hydrogen atom transfer (HAT), radical adduct formation (RAF), single electron transfer (SET), and the direct oxidation of the chalcogen atom. The chosen ROS are HO., HOO., and CH3OO.. PS, PSE, and PTE exhibit an excellent antioxidant activity in water regardless of the ROS due to their characteristic diffusion‐controlled regime processes. For the HO. radical, the primary active reaction mechanism is, for all antioxidants, RAF. But, for HOO. and CH3OO., the dominant mechanism strongly depends on the antioxidant: HAT for PS and PSE, and SET for PTE. The scavenging efficiency decreases dramatically in lipid environment and remains only significant (via RAF) for the most reactive radical (HO.). Therefore, PS, PSE, and PTE are excellent antioxidant molecules, especially in aqueous, physiological environments where they are active against a broad spectrum of harmful radicals. There is no advantage or significant difference in the scavenging efficiency when changing the chalcogen since the reactivity mainly derives from the amino hydrogen and the aromatic sites.
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Hansen T, Vermeeren P, Bickelhaupt FM, Hamlin TA. Innenrücktitelbild: Origin of the α‐Effect in S
N
2 Reactions (Angew. Chem. 38/2021). Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202108477] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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48
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Hansen T, Vermeeren P, Bickelhaupt FM, Hamlin TA. Origin of the α‐Effect in S
N
2 Reactions. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202106053] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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49
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Hansen T, Vermeeren P, Bickelhaupt FM, Hamlin TA. Origin of the α-Effect in S N 2 Reactions. Angew Chem Int Ed Engl 2021; 60:20840-20848. [PMID: 34087047 PMCID: PMC8518820 DOI: 10.1002/anie.202106053] [Citation(s) in RCA: 43] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Revised: 05/27/2021] [Indexed: 11/07/2022]
Abstract
The α-effect is a term used to explain the dramatically enhanced reactivity of α-nucleophiles (R-Y-X:- ) compared to their parent normal nucleophile (R-X:- ) by deviating from the classical Brønsted-type reactivity-basicity relationship. The exact origin of this effect is, however, still heavily under debate. In this work, we have quantum chemically analyzed the α-effect of a set of anionic nucleophiles, including O-, N- and S-based normal and α-nucleophiles, participating in an SN 2 reaction with ethyl chloride using relativistic density functional theory at ZORA-OLYP/QZ4P. Our activation strain and Kohn-Sham molecular orbital analyses identified two criteria an α-nucleophile needs to fulfill in order to show α-effect: (i) a small HOMO lobe on the nucleophilic center, pointing towards the substrate, to reduce the repulsive occupied-occupied orbital overlap and hence (steric) Pauli repulsion with the substrate; and (ii) a sufficiently high energy HOMO to overcome the loss of favorable HOMO-LUMO orbital overlap with the substrate, as a consequence of the first criterion, by reducing the HOMO-LUMO orbital energy gap. If one of these two criteria is not fulfilled, one can expect no α-effect or inverse α-effect.
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Zaccaria F, van der Lubbe SCC, Nieuwland C, Hamlin TA, Fonseca Guerra C. How Divalent Cations Interact with the Internal Channel Site of Guanine Quadruplexes. Chemphyschem 2021; 22:2286-2296. [PMID: 34435425 PMCID: PMC9293024 DOI: 10.1002/cphc.202100529] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 08/24/2021] [Indexed: 11/06/2022]
Abstract
The formation of guanine quadruplexes (GQ) in DNA is crucial in telomere homeostasis and regulation of gene expression. Pollution metals can interfere with these DNA superstructures upon coordination. In this work, we study the affinity of the internal GQ channel site towards alkaline earth metal (Mg2+, Ca2+, Sr2+, and Ba2+), and (post‐)transition metal (Zn2+, Cd2+, Hg2+, and Pb2+) cations using density functional theory computations. We find that divalent cations generally bind to the GQ cavity with a higher affinity than conventional monovalent cations (e. g. K+). Importantly, we establish the nature of the cation‐GQ interaction and highlight the relationship between ionic and nuclear charge, and the electrostatic and covalent interactions. The covalent interaction strength plays an important role in the cation affinity and can be traced back to the relative stabilization of cations’ unoccupied atomic orbitals. Overall, our findings contribute to a deeper understanding of how pollution metals could induce genomic instability.
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