Rosa M.S. Álvarez

Singlet oxygen quenching and radical scavenging capacities of structurally-related flavonoids present in Zuccagnia punctata Cav.

The singlet oxygen (1O2) quenching and free radical (DPPH•, ABTS• + and O2• −) scavenging ability of three structurally-related flavonoids (7-hydroxyflavanone HF, 2′,4′-dihydroxychalcone DHC and 3,7-dihydroxyflavone DHF) present in the Argentinean native shrub Zuccagnia punctata Cav. were studied in solution by combining electrochemical and kinetic measurements, mass spectroscopy, end-point antioxidant assays and computational calculations. The results showed that the antioxidant properties of these flavonoids depend on several factors, such as their electron- and hydrogen atom donor capacity, the ionization degree of the more acidic group, solvatation effects and electrostatic interactions with the oxidant species. The theoretical calculations for both the gas and solution phases at the B3LYP level of theory for the Osanger reaction field model agreed with the experimental findings, thus supporting the characterization of the antioxidant mechanism of the Z. punctata flavonoids.

Spectroscopic and theoretical studies of sulfamoil fluoride, FSO2NH2 and N-(fluorosulfonyl) imidosulfuryl fluoride, FSO2NS(O)F2

Abstract FT-IR and Raman spectra of sulfamoil fluoride, FSO 2 NH 2 , and N-(fluorosulfonyl) imidosulfuryl fluoride, FSO 2 NS(O)F 2 , were obtained. The experimental data are compared to results of ab initio and density functional theory (DFT) calculations. According to the theoretical studies the main conformer of FSO 2 NH 2 possesses anti conformation (F–S single bond in anti position with respect to the nitrogen lone pair). The vibrational spectra do not confirm the presence of a second conformer in the gas and liquid phases. They have been interpreted on the basis of C S symmetry. The Raman spectra of the liquid and the gas infrared spectra of FSO 2 NS(O)F 2 have been interpreted in the terms of the existence of a single conformation possessing C 1 symmetry, as determined previously by gas electron diffraction (GED). An assignment of the observed bands is proposed for both molecules.

VIBRATIONAL STUDIES OF FLUOROFORMYLIMINOSULFUR DIFLUORIDE : FC(O)NSF2

Abstract The Raman spectrum of liquid fluoroformyliminosulfur difluoride. FC(O)NSF2, and its IR spectrum of the vapor phase were obtained. The observed features and the polarized Raman spectra are consistent with the existence of only one conformer possessing Cs symmetry both in the vapor and liquid phases. Assignment of 13 of the 15 fundamental vibrations are reported. The UV-visible spectrum was recorded and its bands assigned. The preresonance Raman effect was not detected. A theoretical ab initio vibrational spectrum was also obtained using a 6-31G∗ basis set. Symmetry force constants arising from experimental data were determined for the A′ species.

Conformational and bond properties of chlorosulfonyl isocyanate, CISO2NCO

Abstract The Raman and IR spectra of chlorosulfonyl isocyanate in the liquid phase are reinvestigated, and the IR spectra of the vapour phase are recorded. A complete assignment of the observed bands is proposed. Subsequently a normal coordinate analysis is performed. Vibrational data confirm that CISO 2 NCO exists only in one single conformation in both phases. The presence of depolarized bands in the Raman spectra of the liquid phase is consistent with either C 1 symmetry and a very low rotational barrier between the two equivalent optic isomers or with a C S symmetry. This interpretation allows the rationalization of data obtained from several spectroscopic techniques. An unusual force constant-bond length relationship is found for the S-Cl moiety.

Raman spectroscopic study of the conformational changes of thyroxine induced by interactions with phospholipid.

Abstract. Comparison of the Raman spectra of thyroxine (L-3,3′,5,5′-tetraiodothyronine) in the pure state and in a 1:5 mixture with phosphatidylcholine reveals spectral differences that reflect structural changes of thyroxine induced by interactions with the phospholipid. These structural changes could be localized in specific parts of the thyroxine molecule on the basis of a vibrational analysis that was carried out by density functional calculations with the B3LYP hybrid functional applying the SDD effective core potential basis set. The calculated (and subsequently scaled) frequencies reveal a good agreement with the experimental data, which together with calculated IR and Raman intensities allow a plausible assignment of most of the IR and Raman bands. Thus, it is found that modes localized in the aromatic β-ring and in the ether group as well as the C-I stretching modes of ring α are affected upon lipid interactions, indicating that thyroxine interacts with the phosphatidylcholine bilayer via penetration of the hydrophobic part of the molecule.

Vibrational and conformational study of FSO2NCO: FT-IR, preresonance Raman effect, force field and theoretical calculations

Abstract Starting with ClSO 2 NCO and SbF 3 , fluorosulphuryl isocyanate, FSO 2 NCO, was prepared. FT-IR data for the vapour and Raman spectra for the liquid were obtained. The observed features and the pre-resonance Raman data are consistent with the existence of only one conformer possessing C 1 symmetry both in the vapour and liquid phase. For all but the torsional mode of this rotamer, experimental wavenumbers are reported. Symmetry force constants were calculated using a torsional frequency taken from ClSO 2 NCO. The experimental studies were augmented by ab initio calculations at various levels of sophistication (HF/3-21G*, HF/6-31G*, MP2/6-31G*). The predicted conformational properties for FSO 2 NCO are in good agreement with the experimental data.

Vibrational spectra and theoretical calculations of N-(trifluoromethyl)iminosulphur dichloride: CF3NSCl2

Abstract The Raman spectrum of liquid N -(trifluoromethyl)iminosulphur dichloride, CF 3 NSCl 2 and the infrared spectrum of its vapour phase were recorded. The observed features were consistent with the existence of only one conformer with Cs symmetry, as derived by the reported electron-diffraction analysis. Theoretical vibrational spectra were also determined using ab initio and Density Functional Theory (DFT) calculations at different levels of approximation. For all except one of the torsional modes, experimental wavenumbers were obtained. A subsequent normal coordinate analysis was performed using a torsional wavenumber calculated by theoretical methods.

Vibrational Spectra of Trifluoromethanesulfonyl Isocyanate, CF3SO2NCO

CF3SO2NCO was prepared by reaction of ClSO2NCO and CF3SO2NH2. Fourier transform IR data for the vapour and Raman spectra for the liquid were obtained and compared with those of other isocyanates. Vibrational assignments were made for all but one of the torsional fundamental modes. The observed features and the polarization measurements of the Raman lines in the spectra of the liquid are consistent with the existence of only one conformer possessing C1 symmetry, in both the gas and liquid phases.

Vibrational spectra, assignments and ab initio calculations of sulfur difluoride chlorosulfonyl imide (ClSO2NSF2)

Abstract The gas FTIR (4000-400 cm−1) and the liquid Raman spectra (2000-50 cm−1) of sulfur difluoride chlorosulfonyl imide have been recorded. Assignment of 16 of the 18 fundamental vibrational modes were performed based on group frequencies and normal coordinate analysis. The fundamental vibrational frequencies are compared with those obtained from ab initio calculation employing the HF/6-31G∗ basis set and the corresponding values observed from related molecules. According to the computational approaches HF/3-21G∗, HF/3-31G∗ and BPW/916-31G∗, a conformation with ClSNS dihedral angle of 114.0°, 103.3° and 102.2°, respectively, represents the only conformer in the gas phase.

Vibrational and theoretical studies of N-(fluorosulfonyl)imidosulfurous difluoride, FSO2N=SF2.

The Raman spectrum of liquid N-(fluorosulfonyl)imidosulfurous difluoride FSO2N = SF2 and the IR spectrum of its vapour phase were recorded. The observed features in combination with the theoretical studies indicate the existence at room temperature of only one conformer. In accord with previous results obtained by electron-diffraction analysis, this single conformer possesses C1 symmetry in which the SF2 group is oriented syn with respect to the N-S single bond. Theoretical vibrational spectra were also determined using ab initio and density functional theory (DFT) calculations at different levels of approximation. For all except one of the torsional modes, experimental wavenumbers were obtained. A subsequent normal coordinate analysis was performed using a torsional wavenumber calculated by theoretical methods.