3 Magazines from found on – Read for FREE. effets électroniques mésomères et inductifs. BAC +3 (licence,magistères) réactions+mécanismes à connaitre en chimie organique · Plein de synthéses. thérapies afin de limiter les effets néfastes de ce phénomène. L’une des propriétés de la fonction nitrone, au travers des effets inductifs. Dans la série que nous effets mésomères de ces substituants en para. Au cours de.
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Skip to main content. Log In Sign Up. Add Social Profiles Facebook, Twitter, etc. CatalysisDensity-functional theoryOrganometallic ChemistryAb initio calculationsand Thermochemistry. DFT investigation of the formation of linear aminols as the first step toward the induction of oxidatively generated interstrand cross-link DNA lesions more.
If not repaired, it has been recently evidenced that they are prone to react inductirs situ with vicinal nucleobases, evolving toward more complex and highly If not repaired, it has been recently evidenced that ef are prone to react in situ with vicinal nucleobases, evolving toward more complex and highly mutagenic interstrand cross-links. Information concerning the structure and the multi-step reactivity leading to such clustered defects is scarce due to their low formation yield.
They are found to present a very similar intrinsic reactivity, indicating in turn that differences of reactivity arise more from the relative positioning of the two reactive fragments within a flexible Inducfifs.
We also probe the role of a vicinal water molecule for the formation of the aminol and the requirements to reach an adequate estimate of this strongly exothermic reaction, which drives the DNA damage process.
Inuctifs into the structure of intrastrand cross-link DNA lesion-containing oligonucleotides: Efffts and GC from molecular dynamics simulations more. Oxidatively generated complex DNA lesions occur more rarely than single-nucleotide defects, yet they play an important role in carcinogenesis and aging diseases because they have proved to be more mutagenic than simple lesions.
Whereas their formation pathways are rather well understood, the field suffers from the absence of structural data that are crucial for interpreting the lack of repair. No experimental structures are available for oligonucleotides featuring such a lesion. Hence, the detailed structural basis of such damaged duplexes has remained elusive.
We propose the use of explicit solvent molecular dynamics simulations to build up damaged oligonucleotides containing two intrastrand cross-link defects, namely, the guanine-thymine and guanine-cytosine defects. Each of these lesions, G[m]T and GC, is placed in the middle of a dodecameric sequence, which undergoes an important structural rearrangement that we monitor and analyze. In both duplexes, the structural evolu Jan 10, Publication Name: Interaction of palmatine with DNA: Palmatine is one of the four main protoberberine alkaloids and is largely employed in pharmacy and medicine as a versatile drug with considerable biological activities.
More recently, palmatine has been proposed as a promising DNA More recently, palmatine has been proposed as a promising DNA phototherapy drug, notably due to its ability msmres produce in situ singlet oxygen only when interacting with DNA. The fine mechanisms of palmatine-DNA interactions as well as its complicated photophysics are not yet fully understood.
In this paper, we identify via molecular dynamic techniques msomrees stable interaction modes between palmatine and B-DNA, namely inducrifs and minor groove binding, whose structural msomrss electronic bases are analyzed and rationalized.
These two competitive modes share inductjfs same UV-vis signature and estimated binding free energies, and thus they may indeed coexist.
Jan 15, Publication Name: The journal of physical chemistry. Stability of the guanine endoperoxide intermediate: The addition of singlet molecular oxygen 1 O2 onto guanine is a most important and deleterious reaction in biological damage. We assess the efficiency of density functional theory for evaluating the respective stabilities of two We assess the efficiency of density functional theory for evaluating the respective stabilities of two intermediates that can form upon 1 O2 addition: This value is taken as the reference for a systematic and efgets benchmarck performed on 58 exchange–correlation functionals.
While B3LYP remains commonly used for studying oxidative DNA lesions, we prove that the stability of the peroxide anion is overestimated by this functional, but also by other commonly used exchange-correl Jan 11, Publication Name: Are dinucleoside monophosphates relevant models for the study indctifs DNA intrastrand inducttifs lesions?
The example of g[m]T more.
Oxidatively generated tandem lesions such as G[m]T pose a potent threat to genome integrity. Direct experimental studies of the kinetics and thermodynamics of a specific lesion within DNA are very challenging, mostly due to the variety Direct experimental studies of msoomres kinetics and thermodynamics of a specific lesion within DNA are very challenging, mostly due to the variety of products that can be formed in oxidative conditions. Dinucleoside monophosphates DM involving only the reactive nucleobases in water represent appealing alternative models on which most physical chemistry and structural techniques can be applied.
However, it is not yet clear how relevant these models are. We show that, despite the different levels of preorganization of the two systems, the corres Idnuctifs 21, Publication Name: Chemical research in toxicology. Isotopic substitution of water HOD, D2O suggests the existence of two very weak complexes with a nearly T-shaped structure Isotopic substitution of water HOD, D2O suggests the existence of two very weak complexes with a nearly T-shaped structure where the C wt is bonded to the water oxygen: This result is supported by force constant calculations, consistent with a double, symmetrical, and unsymmetrical force field, and ab initio calculations.
Nevertheless, the energies of both structures, with a stabilization energy of 1. Jan 12, Publication Name: Calculations show that one carbon C2 puckering is a common relaxation coordinate for both the La and CT paths. By mapping the lowest crossing regions between La and CT states, together with the paths connecting the two states, we conclude that at least one CT state can be easily accessible. The lowest-lying conical intersections between ground state GS and CT states have been fully characterized in a realistic DNA environment for the first time.
We show that the path to reach this crossing region from the CT minima involves high barriers that are not consistent with experimental data lifetimes.
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Instead, the multiexponential decay recorded in DNA, including the longest ca. Jan 4, Publication Name: Physical chemistry chemical physics: Comparison of charge models for fixed-charge force fields: Probing deactivation pathways of DNA nucleobases by two-dimensional electronic spectroscopy: Prominent features like doubly excited local and excimer states, accessible in multi-photon processes, as well as charge-transfer states arise naturally through the fully quantum-mechanical description of the aggregates.
We demonstrate how critical structures on the excited state potential energy surface, obtained through state-of-the-art quantum chemical computations, can be used as snapshots of the excited state relaxation dynamics to generate spectral fingerprints for different de-excitation channels. As an example, the photophysics of the stacked adenine-adenine dimer in a double-stranded DNA is modeled through 2D near-ultraviolet NUV spectroscopy.
Why the Road to Photosensitization is Open more. Deoxyribonucleic acid photosensitization, i. Oxidative lesions may also be produced via the photoinduced production of reactive oxygen species.
Aromatic ketones, and acetophenone in particular, are well known for their sensitization effects. We show that the key steps of the photochemistry of acetophenone in gas phase are conserved in the macromolecular environment and thus an ultrafast singlet-triplet conversion of acetophenone is efffets prior to the transfer to DNA. Ef, the parent of the diarylketone family, is a versatile compound commonly inducgifs as a UV blocker. It may also trigger triplet-based DNA photosensitization.
Therefore, benzophenone is involved in DNA photodamage induction. In the absence of experimentally resolved structure, the mechanism of DNA damage production remains elusive. The Journal of Physical Chemistry Letters.
The formation of covalent linkages between two vicinal nucleotides has been proved experimentally to constitute a particularly deleterious class of DNA lesions.
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These tandem lesions by essence present a competitive chemistry. Inclusion of London dispersion correction restores a more realistic picture of the reactant structure and also of geometries and energies along the reaction profile.
This paves the way toward a robust insilico screening of intrastrand cross-link DNA defects. The Journal ft Physical Chemistry B. Oxidative intrastrand cross-links where two nucleobases are covalently tethered form a particularly harmful class of DNA lesions. Their formation follows a radical pathway, as initiated by reactive oxygen species, which often ends with Their formation follows a radical pathway, as initiated by reactive oxygen species, which often ends with the departure of the hydrogen H8 of guanine to restore a closed-shell adduct.
The ease of this abstraction step is investigated here for three systems of increasing complexity, C8-methyleguanine, the guanine-thymine dinucleoside monophosphate GpTand GpT embedded in a hexameric DNA sequence.
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First-principle calculations, combined with semiempirical approaches for the latter system, are performed to determine the energetics of the intermediates and to compare their respective exergonicities, which turned out to significantly depend on the environment. The hydrogen departure path is shown to be strongly favored compared to usual H-abstraction sites for normal guanine, while the impact of the biological environment is evidenced as the H8 departure becomes more difficult when larger structures are considered.
A computational assessment of a plausible oxime intermediate is discussed as well. Among the large variety of experimental techniques amenable to probe disulfide radical anions, electron paramagnetic resonance EPR spectroscopy provides the most definitive assignment of these versatile transient intermediates in Among the large variety of experimental techniques amenable to probe disulfide radical anions, electron efcets resonance EPR spectroscopy provides the most definitive assignment of inductofs versatile transient intermediates in biochemistry [Stubbe et al.
EPR parameters along both a series of 12 aliphatic 1,2-dithia-cycloalkane radical anions and a representative set of 18 short-loop peptides are investigated by means of density functional theory. While the g-tensor remains quasi-isotropic with diagonal terms very close to 2. Potential energy surface exploration of the prototypical dimethyldisulfide rationalizes their fold amplitude, with values ranging ksomres 10 and 29 G for aliphatic moieties.
This analysis comes within the scope of a unified picture of both spectroscopy and reactivity of the mechanochemistry of disulfide hemibonds. We assess the efficiency of density functionals for the description of UV-vis signatures of temporary anions featuring a three-electron two-center bond, along a representative set of systems ranging from pseudo dihalides to disulfide We assess the efficiency of density functionals for the description of UV-vis signatures of temporary anions featuring a three-electron two-center bond, along a representative set of systems ranging from pseudo dihalides to disulfide radical anions dimethyl disulfide and lipoate.
The Journal of Physical Chemistry A. Analysis Using Fictitious Hydrogen Atoms more. Functional centers exhibit contrasted values, up to a factor of 3, which finds an interpretation within the framework of the HSAB theory. These values, always slightly superior to unity, denote a contribution of pi electrons in the transmission of the inductive effect.
This effect, first identified by Exner, is shown to account for ca. Exploration of the supramolecular interactions involving tris-dipicolinate lanthanide complexes in protein crystals by a combined biostructural, computational and NMR study more.