Marcello F. Costa

An experimental and theoretical vibrational study of interaction of adenine and thymine with artificial seawaters: A prebiotic chemistry experiment.

Nucleic acid bases play important roles in living beings. Thus, their interaction with salts the prebiotic Earth could be an important issue for the understanding of origin of life. In this study, the effect of pH and artificial seawaters on the structure of adenine and thymine was studied via parallel determinations using FT-IR, Raman spectroscopy and theoretical calculations. Thymine and adenine lyophilized in solutions at basic and acidic conditions showed characteristic bands of the enol-imino tautomer due to the deprotonation and the hydrochloride form due to protonation, respectively. The interaction of thymine and adenine with different seawaters representative of different geological periods on Earth was also studied. In the case of thymine a strong interaction with Sr(2+) promoted changes in the Raman and infrared spectra. For adenine changes in infrared and Raman spectra were observed in the presence of salts from all seawaters tested. The experimental results were compared to theoretical calculations, which showed structural changes due to the presence of ions Na(+), Mg(2+), Ca(2+) and Sr(2+) of artificial seawaters. For thymine the bands arising from C4=C5 and C6=O stretching were shifted to lower values, and for adenine, a new band at 1310cm(-1) was observed. The reactivity of adenine and thymine was studied by comparing changes in nucleophilicity and energy of the HOMO orbital.

ESR and calculations on electronic structure of phenalenyl and phenalenyl derivative radicals

Calculations on electronic structure of the perinaphthenyl radical and phenalenyl derivative radicals responsible for the composition of the ESR spectrum of marine diesel under heating were performed to obtain support for the experimental ESR results. The parameters calculated were the hyperfine coupling constants (A), which were then used for comparison with the experimental data. The energy‐minimized structures were obtained using the density functional theory method. In all cases, the symmetry system was taken into account in theoretical calculations. The differences between experimental and theoretical values were below 7% for nearest hydrogens in molecules, named hyperfine coupling constant A (first neighbors) and 18% for farthest hydrogens atoms named hyperfine coupling constants A′ (second neighbors), for all structures analyzed. Copyright

Gaussian basis sets for ab initio calculation of NLO properties of polyatomic molecules

In this paper, basis sets for H, C, N and O atoms were adjusted to obtain electric properties of diatomic molecules. The dipole moment, polarizability and first-order hyperpolarizability were calculated for H

Visible light production of superoxide anion with MCarboxyphenylporphyrins (M = H, Fe, Co, Ni, Cu, and Zn) free and anchored on TiO2: EPR characterization

_{2}

Ab initio calculation of electric properties for the BH, CO, CS and N2 molecules

, CH

The ALOS Kyoto & Carbon Initiative Science Plan

^{+}

NLO-X (X = I–III): New Gaussian basis sets for prediction of linear and nonlinear electric properties

, CN

Estudo teórico do 1,4-bis (3-carboxi-oxo-prop-1-enil) benzene I.

^{-}

Exploring the experimental photoluminescence, Raman and infrared responses and density functional theory results for TFB polymer

and CO molecules and the basis sets modified to reproduce the reference data available. A sequential methodology was used, where the basis set for H is firstly adjusted and then used to fit the basis set for C in the CH

Estudo Computacional do Phenalenyl (Computational Study of Phenalenyl)

^{+}