Photoinduced Proton Transfer as a Possible Mechanism for Highly Efficient Excited-State Deactivation in Proteins

CASSCF//CASPT2 pathways for a two-glycine minimal model system show that photoinduced electron-driven forward and backward proton transfer could play an important role for the stability of proteins against damage by UV radiation, when a hydrogen bond is located between the two amino acids. The overall photoinduced process involves two electron and proton transfer processes (forward and backward) and results in the reformation of the initial closed-shell electronic structure of the system.Ministerio de Educación y CienciaUniversidad de Alcal

Structural Substituent Effect in the Excitation Energy of aChromophore: Quantitative Determination and Application toS-Nitrosothiols

A methodology for the prediction of excitation energies for substituted chromophores on the basis of ground state structures has been developed. The formalism introduces the concept of ?structural substituent excitation energy effect? for the rational prediction and quantification of the substituent effect in the excitation energy of a chromophore to an excited electronic state. This effect quantifies exclusively the excitation energy variation due to the structural changes of the chromophore induced by the substituent. Therefore, excitation bathochromic and hypsochromic shifts of substituted chromophores can be predicted on the basis of known ground and excited potential energy surfaces of a reference unsubstituted chromophore, together with the ground state minimum energy structure of the substituted chromophore. This formalism can be applied if the chemical substitution does not affect the nature of the electronic excitation, where the substituent effect can be understood as a force acting on the chromophore and provoking a structural change on it. The developed formalism provides a useful tool for quantitative and qualitative determination of the excitation energy of substituted chromophores and also for the analysis and determination of the structural changes affecting this energy. The proposed methodology has been applied to the prediction of the excitation energy to the first bright state of several S-nitrosothiols using the potential energy surfaces of methyl-S-nitrosothiol as a reference unsubstituted chromophore.Ministerio de Ciencia e InnovaciónUniversidad de Alcal

Azonia derivatives of the γ-carboline system. A new class of DNA intercalators

1-Methyl-γ-carboline derivatives were transformed into the corresponding N-aminoazinium salts, which were condensed with 1,2-dicarbonyl compounds (Westphal reaction) to afford azonia derivatives with a bridgehead quaternary nitrogen atom. Some of them show DNA intercalating properties.Instituto de Qulmica Computaciona

Pyrrolodiazines. 4. Structure and chemistry of 3,4-dihydropyrrolo[1,2-a]pyrazine

The structure of 3,4-dihydropyrrolo[1,2-a]pyrazine and its N-protonated form is studied by ab initio calculations. Examples of the reactivity of this poorly studied system are presented in which it is shown that the imino moiety does not react with dienes but does undergo inter- and intramolecular 1,3-dipolar cycloadditions by reaction of azomethine ylides of this bicyclic system with suitable dipolarophiles.Ministerio de Educación y CienciaCentro de Computación de Galixia (CESGA