RESUMO
B3LYP/6-31G* and 6-311++G** calculations have been carried out in order to study the hydration of phosphates in aqueous media. Optimized geometries and relative stabilities for PO4(-3), HPO(4)-2, H2PO4(-1) have been calculated considering the interaction with one, two, three, four and five discrete water molecules and taking into account the solvent effect by using the self-consistent reaction field theory (Onsager and PCM methods). The role of specific and bulk contributions of solvent effect on the observable properties of phosphate compounds is analysed. Good agreement between theoretical and available experimental results of harmonic vibration frequencies is found. Significant effects on the geometrical and vibrational frequencies are found for those studied phosphate anions. The results presented here provide a first step toward the understanding of the phosphate group as a hydration sensor in lipid bilayers.
Assuntos
Modelos Químicos , Fosfatos/química , Água/química , Cristalografia por Raios X , Soluções , Espectroscopia de Infravermelho com Transformada de Fourier , Termodinâmica , VibraçãoRESUMO
Ethyl methanesulfonate, CH3SO2OCH2CH3, is well-known as an alkylating agent in mutagenic and carcinogenic processes. Its electronic structure and that of the methanesulfonate anion (CH3SO3-) were determined using optimization methods based on density functional theory and Moller-Plesset second-order perturbation theory. For CH3SO2OCH2CH3, two conformations with symmetries C(s) and C1 are obtained, the former being more stable than the latter. Natural bond orbital (NBO) calculations show the C(s) conformation provides a more favorable geometry of the lone pairs of the oxygen atom linking the ethyl group. The NBO technique also reveals the characteristics of the methanesulfonate anion as a leaving group due to the rearrangement of the excess electronic charge after alkylation. Furthermore, the infrared spectra of CH3SO2OCH2CH3 are reported for the liquid and solid states as well as the Raman spectrum of the liquid. Comparison to experiment of the conformationally averaged IR spectrum of C(s) and C1 provides evidence of the predicted conformations in the solid IR spectrum. These experimental data along with the calculated theoretical force constants are used to define a scaled quantum mechanical force field for the target molecule, which allowed the measured frequencies to be reproduced with a final root-mean-square deviation of 9 cm(-1) and, thus, a reliable assignment of the vibrational spectrum.
RESUMO
The infrared spectra of 2,2,2-trifluoroethyl trifluoromethanesulfonate (CF3SO2OCH2CF3) were obtained in the gaseous, liquid and solid states as well as the Raman spectrum of the liquid. Quantum chemistry calculations using the density functional theory were used to predict the most stable geometry and conformation of the studied molecule. Subsequently, the harmonic vibrational frequencies and force field were calculated. An assignment of the observed spectral features made after comparison with the related molecules and with the predicted frequencies was used as the basis of a scaling of the original force field in order to reproduce as well as possible the experimental frequencies. With this purpose a set of scale factors was calculated by a least square procedure, leading to a final root mean square deviation (RMSD) of 9.7 cm(-1).