1,721,036 research outputs found
Chiral Discrimination in the formation of diastereomeric pairs. A thermodynamic and Conformational investigation.
No full textStereoselective effects in reactions between optically active compounds: a kinetic approach
No full textChiral discrimination in the energetics of formation of diastereomeric adducts involving polypeptides
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Photoinduced Electron Transfer in alfa-helical Poly(L-Lysine) carrying Randomly Distributed Donor-Acceptor pairs. A kinetic and Conformational Statistics Investigation
No full textStereoselective Electron-Transfer Between Chiral Substrates and Metal Chelates Anchored to Polypeptides.
No full textMolecular Modeling of a Functionalized Aib-based Octapeptide by Molecular Mechanics calculations restrained by NMR and Fluorescence Data in DMSO
No full textThe structural features of the sequential octapeptide Boc-(Leu)2-Lys(P)-(Aib)2-(Leu)2-Lys(N)-OtBu, where P is protoporphyrin IX and N is naphthalene, were investigated in DMSO by NMR and fluorescence spectroscopy. Earlier IR, CD, and fluorescence results showed that this compound attains a 310-helical conformation in methanol or water/methanol (75/25, v/v). By contrast, the backbone structure in DMSO is destroyed, but the high helix propencity of the Aib residues forces the peptide to attain locally ordered arrangements, reminiscent of β-turn features. Both NMR coupling constant and NOE connectivity data allowed us to compute the structural features of part of the molecule, but only their combination with fluorescence results allowed us to build up the whole molecular model. Implications of fluorescence data on the dynamics of internal rotation of the chromophores are briefly discussed
Association complexes between Fe (III) or Cu (II) ions and chitosan denvatives: a thermodynamic and spectroscopic investigation
No full textAssociation complexes between iron(III) or copper(II) ions and deoxylactit-1-yl (1), 2-substituted pentanedioic acid (2), or 2-substituted propanoic acid (3) derivatives of chitosan were prepared and characterized by thermodynamic and spectroscopic measurements. Complex solutions did not show any precipitate or even opalescence, owing to the hydrolysis of free metal ions, within a wide range of [Me(n+)]/[P] molar ratio, even al a pH as high as 10.5 (Me(n+) = Fe3+ or Cu2+). Both equilibrium dialysis and Job plot experiments suggest that the functional groups in each monomeric residue are an effective site of binding for one metal ion. Reduction potentials, as obtained by cyclic voltammetric measurements, indicate that (i) coordination of the aforementioned polymeric ligands to Cu2+ ions stabilizes the oxidized species, and (ii) iron complexes have an oxidation power definitely higher than that of the corresponding copper compounds. Electron paramagnetic resonances (100 or 6 K) and Mossbauer (r.t.) spectra suggest that the order of increasing distortion from idealized geometry is Me(n+)-chitosan almost-equal-to Me(n+) -(3) < Me(n+) -(2) less-than-or-equal-to Me(n+) -(1). These results are discussed briefly in the light of a few general considerations concerning the structural features of association complexes between macromolecules and transition metal ions
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