0000000000524737
AUTHOR
Francisco J. Ramírez
showing 6 related works from this author
Amino Acid Chemistry in Solution: Structural Study and Vibrational Dynamics of Glutamine in Solution. An ab Initio Reaction Field Model
1998
The self-consistent reaction field (SCRF) theory was used to study structural and vibrational features of the amino acid L-glutamine in solution. Raman and infrared spectra of this molecule in solutions of H 2O and D2O were recorded and measured. The bands were firstly assigned on the basis of the isotopic shifts. An ab initio quadratic force field at the 6-31 +G* level was achieved. The calculation simulated a polar solvent by placing the molecule in an ellipsoidal cavity surrounded by a continuum dielectric. The theoretical results, in terms of structural parameters, vibrational frequencies and descriptions, and infrared intensities, were in satisfactory agreement with the experimental da…
On the handedness of helical aggregates of C3 tricarboxamides: a multichiroptical characterization
2015
A complete chiroptical characterization of the supramolecular polymers formed by tricarboxamides (S)-1 and (R)-1 is performed using ECD, VCD and CPL dichroic techniques. The helical aggregates show an intense CPL signal and their absolute P- or M-configuration is assigned with the help of theoretical calculations.
Amino acid chemistry in solution: structural properties and vibrational dynamics of serine using density functional theory and a continuum solvent mo…
2004
A structural and vibrational study of amino acid serine in aqueous solution has been carried out using Fourier transform spectroscopies and quantum mechanical calculations. FT-IR and FT-Raman spectra of serine in H2O and D2O solutions were recorded and a general assignment of the observed bands was proposed on the basis of a zwitterionic structure for serine. Main criteria were the observed wavenumber shifts upon deuteration and previous assignments for other amino acids. A quadratic force field was computed using ab initio methodology at the 6-31+G** level and the hybrid functional B3LYP. The solvent effect was simulated by placing the serine molecule into an ellipsoidal cavity surrounded …
Vibrational Dynamics of Histamine Monocation in Solution: An Experimental (FT-IR, FT-Raman) and Theoretical (SCRF-DFT) Study
2000
spectra of histamine monocation in solution, based on the isotopic shifts and a previous vibrational study in solid state. Force field and normal coordinate calculations were computed to support these assignments. The ab initio force constants were transformed into a set of locally symmetrized internal coordinates and subsequently scaled to the experimental frequencies by using one specific and two generic scaling factors. The comparison in terms of vibrational frequencies and normal coordinate descriptions supported most of the proposed assignments. The theoretical infrared spectra for the two isotopomers on the basis of the ab initio intensities also showed a good correlation with the exp…
FT-Raman and QM/MM study of the interaction between histamine and DNA
2006
The interaction between histamine and highly polymerized calf-thymus DNA has been investigated using FT-Raman spectroscopy and the hybrid QM/MM (quantum mechanics/molecular mechanics) methodology. Raman spectra of solutions containing histamine and calf-thymus DNA, at different molar ratios, were recorded. Solutions were prepared at physiological settings of pH and ionic strength, using both natural and heavy water as the solvent. The analysis of the spectral changes on the DNA Raman spectra when adding different concentrations of histamine allowed us to identify the reactive sites of DNA and histamine, which were used to built two minor groove and one intercalated binding models. They were…
Aminoacid zwitterions in solution : Geometric, energetic, and vibrational analysis using density functional theory-continuum model calculations
1998
Glycine and alanine aminoacids chemistry in solution is explored using a hybrid three parameters density functional (B3PW91) together with a continuum model. Geometries, energies, and vibrational spectra of glycine and alanine zwitterions are studied at the B3PW91/6-31+G∗∗ level and the results compared with those obtained at the HF and MP2/6-31+G∗∗ levels. Solvents effects are incorporated by means of an ellipsoidal cavity model with a multipolar expansion (up to sixth order) of the solute’s electrostatic potential. Our results confirm the validity of the B3PW91 functional for studying aminoacid chemistry in solution. Taking into account the more favorable scaling behavior of density funct…