Application of explicitly correlated Gaussian functions for calculations of the ground state of the beryllium atom

The electronic energy of atoms and molecules may be evaluated accurately by the use of wave functions where the interelectronic distances are explicitly present. In particular, explicitly correlated Gaussian-type functions make these types of calculations feasible and computationally tractable even for more extended systems. The resulting multielectron integrals may be reduced to standard one- and two-electron integrals that are readily evaluated. Initial calculations have been made for the Be atom where all four electrons were correlated at the same time. The preliminary results show that accurate results may be obtained. © 1993 John Wiley & Sons, Inc.     

Quantum mechanical models correlating structure with selectivity: predicting the enantioselectivity of beta-amino alcohol catalysts in aldehyde alkylation

Quantitative structure selectivity relationship (QSSR) models are described that provide consistently reliable predictions for the asymmetric addition of Et2Zn to PhCHO catalyzed by beta-amino alcohols. Statistically valid two-variable linear regression models that correlate the structures of the chiral catalysts with their enantioselectivities are obtained from three-dimensional physical property grids. The strength of the present method is that statistical models obtained from a small set of experimentally determined selectivities and relatively simple theoretical calculations yield selectivity predictions that are as accurate as those derived from higher-level calculations of transition-structure energies. Only minutes of computing time are required. Simple models are obtained which permit straightforward physical interpretation and generate realistic predictions.     

Identification of a novel high affinity copper binding site in the APP(145-155) fragment of amyloid precursor protein

The copper(II) binding features of the APP(145-155) and APP(145-157) fragments of the amyloid precursor protein, Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-NH2 and Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-Glu-Thr-NH2 were studied by NMR spectroscopy and NMR findings were supported by UV-vis, CD and EPR spectra. Potentiometric measurements were performed only for the more soluble Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-Glu-Thr-NH2 peptide fragment. The following was shown: (i) the imidazole rings of all the three His residues are involved in metal coordination; (ii) metal binding induces ionisation of Leu-148 and His-149 amide nitrogens that complete the donor set to copper(II) in the species dominant at neutral pH; (iii) the unusual coordination scheme of the His-Xxx-His-Xxx-His consensus sequence justifies the high specificity for Cu(II) when compared to SOD-like or albumin-like peptides or even in amyloid Abeta fragments. The present findings may represent the key for interpreting the observed requirement of His residues conservation for the redox cycling between Cu(II) and Cu(I) by soluble APP.     

Polarographic studies on the complexation of cobalt(II), nickel(II) and copper(II) withd-glucosamine andd-galactosamine

D.c. polarography was used to establish the equilibria existing in Cu(II), Ni(II) and Co(II) systems with d-glucosamine and d-galactosamine. The results clearly indicated the formation of 1:1 complexes, ML, and allowed calculation of the stability constants of some complexes. The present results completed very well the potentiometric and spectroscopic data obtained earlier. The reduction mechanisms and the electrochemical behaviour of the formed complexes were also established.     

Surface Deformation and Walls in the Conduction Regime of Nematic Liquid Crystals

Reflection of a laser beam from the free surface of a nematic liquid crystal shows that the surface is periodically deformed when a high electric field (conduction regime) is continuously applied. Walls which appear to be of the alignment-inversion type have also been observed for these fields. These results are associated with flow cells that were discussed earlier.     

Dynamic job assignment: A column generation approach with an application to surgery allocation

We consider the assignment of jobs to heterogeneous agents in a dynamic system with a rolling time horizon. An example is a hospital operating theatre where the jobs are surgeries and the agents are the surgeons. The paper is presented in the context of surgery allocation and the system is characterized as follows: Patients are grouped into categories and they arrive continually following a stochastic process. Patients in each group have specific time limits within which they need treatment and if it cannot be accommodated then the patients are outsourced. The service level is the percentage of patients in each group treated within the time limit. Surgery durations are stochastic and depend on the surgeon conducting the surgeries. Each surgeon has limited time available and expected overtime is penalized by a non-decreasing convex function. We develop a column generation approach for the assignment of already arrived patients and tentative future patients to surgeons on specific days. It balances the conflicting objectives of including as many arrived patients as possible within their time limits, maximizing the service level of future patients, and minimizing the expected overtime of surgeons. A computational study is conducted with the model embedded in a rolling time horizon frame. The study indicates that the assignment of patients based on our model increases system performance in terms of service level and reduced overtime compared to a First-Come-First-Served (FCFS) policy when the arrival rates of patients are medium to high compared to the capacity of the system.     

Performance of DFT in modeling electronic and structural properties of cobalamins

Computational modeling of the enzymatic activity of B12-dependent enzymes requires a detailed understanding of the factors that influence the strength of the Co--C bond and the limits associated with a particular level of theory. To address this issue, a systematic analysis of the electronic and structural properties of coenzyme B12 models has been performed to establish the performance of three different functionals including B3LYP, BP86, and revPBE. In particular the cobalt-carbon bond dissociation energies, axial bond lengths, and selected stretching frequencies have been analyzed in detail. Current analysis shows that widely used B3LYP functional significantly underestimates the strength of the Co--C bond while the nonhybrid BP86 functional produces very consistent results in comparison to experimental data. To explain such different performance of these functionals molecular orbital analysis associated with axial bonds has been performed to show differences in axial bonding provided by hybrid and nonhybrid functionals.