Roberto Improta

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By combining quantum-mechanical analysis and statistical survey of peptide/protein structure databases we here report a thorough investigation of the conformational dependence of the geometry of peptide bond, the basic element of protein structures. Different peptide model systems have been studied by an integrated quantum mechanical approach, employing(More)
During the last ten years, intense experimental and theoretical work has proven the existence of ultrafast non-radiative decay routes for UV-excited monomeric nucleic acid bases explaining their high photostability. This mechanism has been explained by the occurrence of easily accessible conical intersections connecting the first excited * state with the(More)
The conformational behavior of the title compounds has been investigated by Hartree-Fock, MP2, and DFT computations on the most significant structures related to variations of the backbone dihedral angles, cis/trans isomerism around the peptide bond, and diastereoisomeric puckering of the pyrrolidine ring. In vacuum the reversed gamma turn (gammal),(More)
By using calculations rooted in the time dependent density functional theory (TD-DFT) we have investigated how the lowest energy excited states of a face-to-face pi-stacked cytosine dimer vary with the intermonomer distance (R). The perfomances of different density functionals have been compared, focussing mainly on the lowest energy single excited state of(More)
A general formalism for the calculation of cavitation energies in the framework of the scaled particle theory has been implemented in the Polarizable Continuum Model (PCM), contributing to the nonelectrostatic part of the molecular free energy in solution. The solute cavity and the solvent molecules are described as hard spherocylinders, whose radius and(More)
The role of intraresidue interactions in determining the conformational behavior of polypeptides is analyzed by means of density functional and post-Hartree-Fock computations on the alanine dipeptide analog and other model compounds. Our computations show that the accuracy of current density functionals is sufficient for H-bond, electrostatic, inductive,(More)
The conformational behavior of a dipeptide analogue of tyrosine (TDA) has been investigated by density functional methods using the polarizable continuum model (PCM) for the description of solvent effects. Our study points out the interplay of backbone and side chain contributions in determining the relative stabilities of energy minima. In particular,(More)
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