Computers & chemistry最新文献

The cyclic voltammetry reduction process of the reaction series of substituted iodobenzenes X–C₆H₄–I where X=H, p-Cl, p-Br, p-I, p-CH₃, m-CF₃ was investigated in 0.3 M TBAP in DMF. A numerical model of the process consistent with the ECE mechanism of mono-iodobenzenes reduction and consecutive ECE–ECE reduction of p-diiodobenzene was applied. On the basis of α_i vs. E_p,i dependence, the value of ∂α_i/∂E was found to be 0.37±0.07 for first electron transfer (Eq. (10). The ECE–ECE system seems to be an another example of elementary α kinetic discrimination between two identical two-electron processes analogous to that described in a previous paper (Sanecki, P., Kaczmarski, K. (1999). J. Electroanal. Chem. 471, 14 and erratum to it (2001)). A method of simultaneous treatment of the substrate and all electroactive intermediates, i.e. the transformation of any experimental consecutive CV reduction curves (e.g. ECE or ECE–ECE) into curves corresponding to reduction of the multi-component systems is presented and discussed.

A program in Maple V is developed that allows for the calculation of polarizabilities of both anions and cations on the basis of a new method and of the extension of the one developed previously. Furthermore, an alternative way of evaluation of ∂r_i/∂p is given. Values of ∂α_total/∂p can be evaluated for a given salt even when experimental data at high pressures are not available.

Three-dimensional (3D) convex hulls are computed for theoretically generated structures of a group of 18 bioactive tachykinin peptides. The number of peptides treated as a training set is 14, whereas that treated as a test set is four. The frequency of atoms of the same atomic type lying at the vertices of all the hulls computed for all the structures in a structural set is counted. Vertex atoms with non-zero frequency counted are collected together as a set of commonly exposed groups. These commonly exposed atoms are then treated as a set of correspondences for aligning all the other 13 structures in a structural set against a common template, which is the structure of the most potent peptide in the set using the FIT module of the sybyl 6.6 program. Each aligned structural set is then analyzed by the comparative molecular field analysis (CoMFA) module using the C.3 probe having a charge of +1.0. The corresponding cross-validated r² values range from −0.99 to 0.57 for a number of 73 structural sets studied. The comparative molecular similarity indices analysis (CoMSIA) module within the sybyl 6.6 package is also used to analyze some of these aligned structural sets. Although the CoMSIA results are in accord with those of CoMFA, it is also found that the CoMFA results of several structural sets can be improved somewhat for conformations of the structures in the sets that are adjusted by constraint energy minimization and then constraint molecular dynamics simulation runs using distance constraints derived from some commonly exposed groups determined for them. This result further implies that the convex hull–CoMFA is a feasible approach to screen the bioactive conformations for molecules of this class.

The simultaneous polarographic determination of the ternary mixture of captan-captafol and folpet is studied. The polarographic signals of these compounds in their mixture show a high overlapping. For this reason different chemometric methods such as PLS, PCR and artificial neuronal network (ANN) have been utilized for the simultaneous determination of these compounds in mixtures. The calibration model is built from solutions containing river water of known pesticide concentrations and the signals obtained by Sampled DC and DPP (differential pulse polarography) have been used. The analysis of both synthetic and real samples (river water) has been carried out by PLS with satisfactory results in most cases. It is possible to determine 0.25 ppm of each pesticide in river water samples after a preconcentration step by extraction into diethyl ether. ANN has also been applied to improve the results obtained by the PLS tool when the sampled DC current is recorded or when liquid–solid extraction with C₁₈ cartridges is performed.

A fast and accurate (to any required precision) numerical method is presented to calculate the vapour-liquid equilibrium for any subcritical temperature from a given equation of state. The calculations are made using the popular program mathematica, and we think that this method could be very useful in chemical physics and chemical engineering applications, as well as for teaching purposes.