The photodissociation of aldehydes such as formaldehyde (CH2O) and acetaldehyde (CH3CHO) results in the formation of either radical species ( H + HCO) or molecular species (H2 + CO). The near threshold photodissociation of propanal via the HCO + C2H5 channel on the triplet surface was studied by means of direct PM3-SRP classical trajectory calculations. The initial conditions for the trajectories were specified either by a quasi-classical or a Wigner distribution function. The HCO translational energy and rotational distributions were in good agreement with experimental data. While the results obtained with the Wigner distribution showed a better agreement with the observed experimental HCO translational energy distribution, in general both sampling methods resulted in similar product energy partitioning.

The near threshold photodissociation of propanal via the HCO + C2H5 channel on the triplet surface is studied by direct PM3-SRP classical trajectory calculations. The initial conditions for the trajectories are selected by either the quasi-classical or the Wigner distribution function. The HCO translational energy and rotational distributions obtained in this study are in good agreement with experiment. Even though the results obtained with the Wigner distribution showed a better agreement with the observed experimental HCO translational energy distribution, in general both sampling methods lead to similar product energy partitioning.

Molecular dynamics simulations of the water-isooctane interface are performed to sort out the effect of temperature on the properties of liquid-liquid interfaces. Reliable interaction potential models are applied to describe the interactions, including the treatment of long-range electrostatic forces. It is shown that the increase in temperature has little effect on the basic structural features of the interface, i.e. its sharpness and corrugation. Other interfacial properties, such as the density profile, specific solvent orientations or hydrogen-bonding characteristics are nearly identical for the range of temperatures considered (from 277 to 323 K). However, the liquid-liquid interfacial tension of the water/isooctane system has a non-monotonic behaviour, presenting a maximum at a specific temperature, in contrast to the monotonic decay found for the liquid-vapour case. This behaviour is similar to the one observed for binary mixtures of partially miscible Lennard-Jones fluids.

Three newly formed pigments were detected and isolated from a 2-year-old Port wine through TSK Toyopearl HW-40(S) gel column chromatography and characterized by UV-visible spectrophotometry, NMR, and mass spectrometry (ESI/MS). H-1 NMR and C-13 NMR data for these pigments obtained using 1D and 2D NMR techniques (COSY, NOESY, gHSQC, and gHMBC) are reported for the first time. The structure of the pigments was found to correspond to the vinyl cycloadducts of malvidin 3-coumaroylglucoside bearing either a procyanidin dimer or a flavanol monomer ((+)-catechin or (-)-epicatechin). Additionally, conformational analysis was performed for one of these newly formed pigment using computer-assisted model building and molecular mechanics. A chemical nomenclature is proposed to unambiguously name this new family of anthocyanin-derived pigments.

Azidoacetonitrile (N3CH2CN) and azidoacetone (N3CH2COCH3) are studied by matrix-isolation FTIR spectroscopy in solid neon, argon, and nitrogen. The IR spectra calculated using the density-fuctional theoretical method are discussed in comparison with the experimental data. Significant broadening of the recorded azide bands indicate an awkward fit of these compounds into the solid environment. The strongest absorption is observed for both compounds in the regions of asymmetric and symmetric stretches of the N-3 azide group. Strong band splittings in the N-3 asymmetric stretch region can be most likely explained by very strong Fermi resonances with the CN stretch and combinations and overtones of the numerous lower-frequency vibrational modes. (C) 2003 American Institute of Physics.

Azidoacetonitrile (N3CH2CN) and azidoacetone (N 3CH2COCH3) were studied by matrix-isolation FTIR spectroscopy in solid neon, argon and nitrogen. The IR spectra calculated using the density fuctional theoretical method are discussed in comparison with the experimental data. Significant broadening of the recorded azide bands indicate an awkward fit of these compounds into the solid environment. The strongest absorption is observed for both compounds in the regions of asymmetric and symmetric stretches of the N3 azide group. Strong band splittings in the N3 asymmetric stretch region can be most likely explained by very strong Fermi resonances with the CN stretch and combinations and overtones of the numerous lower frequency vibrational modes.

Cytochrome P450 (CYP) is a family of enzymes responsible for organism detoxification. However, some of the members of the CYP1A subfamily also catalyse the activation of heterocyclic amines (HAs), present in cooked meat, to carcinogenic compounds which have been shown to increase the risk of breast, colorectal and lung cancer. In humans, CYP1A2 is the enzyme with the most significant action in HA metabolism but in rodents CYP1A1 is also important in this biotransformation. Understanding the metabolic action of these enzymes is essential to predict the factors that enable the formation of the carcinogenic products. We have built two models of CYP1A2, one for the human enzyme and one for the rat homologue. The templates chosen include the only X-ray structure published to date for a mammal CYP, a quimeric C2A5 from rabbit, as well as CYPs belonging to Bacillus megaterium (CYPBm-3), Pseudomonas putida (CYPcam), Pseudomonas sp. (CYPterp), and Saccharopolyspora erythraea (CYPeryf). Two HAs, MeIQ (2-amino-3,4-dimethylimidazo[4,5-f] quinoline) and MeIQx (2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline), known substrates of human and rat CYPIA2, were docked in the active site of the models, providing information regarding the different catalytic rates associated with the metabolisms in both enzymes. This is important for analysing the behaviour of animal models concerning the testing of anticancer drugs.

C(alpha)-C(alpha)dialkylglycines, sarcosine, O-methyltyrosine and beta-(imidazol-1-yl)-alanine are noncoded amino acids with a large pharmaceutical potential. We have developed a set of parameters for these amino acids, consistent with the AMBER force field. Several dipeptide and tripeptide models were built to simulate the different possibilities for insertion of the noncoded amino acids in a peptide backbone. Bonding parameters were obtained from both existing force fields and quantum calculations. The Coulombic parameters have been determined using a multiconformational weighted approach and a restricted electrostatic potential fitting, at a 6-31G* ab initio level. Molecular dynamics simulations have been carried out on the model peptides to validate the parameters obtained. The characteristic geometry features such as the planarity of peptide bonds have been conserved on these models. The peptide models, which included monosubstituted residues, have revealed considerable backbone flexibility. The conformational flexibility of the peptides containing disubstituted residues has been significantly restricted by the length and volume of their side chains.