Quantum chemical calculations of stability constants: study of ligand effects on the relative stability of Pd(II)�Cpeptide complexes

Replacement of [Pd(H₂O)₄]²⁺ by cis-[Pd(en)(H₂O)₂]²⁺, [PdCl₄]^2?, and [Pd(NH₃)₄]²⁺ on the hydrolytic cleavage of the Ace-Ala-Lys-Tyr-Gly?CGly-Met-Ala-Ala-Arg-Ala peptide is theoretically investigated by using different quantum chemical methods both in the gas phase an in water solution. First, we carry out a series of validation calculations on small Pd(II) complexes by computing high-level ab initio [MP2 and CCSD(T)] and Density Functional Theory (B3LYP) electronic energies while solvent effects are taken into account by means of a Poisson-Boltzmann continuum model coupled with the B3LYP method. After having assessed the actual performance of the DFT calculations in predicting the stability constants for selected Pd(II)-complexes, we compute the relative free energies in solution of several Pd(II)?Cpeptide model complexes. By assuming that the reaction of the peptide with cis-[Pd(en)(H₂O)₂]²⁺, [Pd(Cl)₄]^2?, and [Pd(NH₃)₄]²⁺ would lead to the initial formation of the respective peptide-bound complexes, which in turn would evolve to afford a hydrolytically active complex [Pd(peptide)(H₂O)₂]²⁺ through the displacement of the en, Cl^?, and NH₃ ligands by water, our calculations of the relative stability of these complexes allow us to rationalize why [Pd(H₂O)₄]²⁺ and [Pd(NH₃)₄]²⁺ are more reactive than cis-[Pd(en)(H₂O)₂]²⁺ and [PdCl₄]^2? as experimentally found.     

An improved construction of progression-free sets

The problem of constructing dense subsets S of {1, 2, ..., n} that contain no three-term arithmetic progression was introduced by Erdős and Turán in 1936. They have presented a construction with |S| = W(n^log₃2)|S| = \Omega ({n^{{{\log }_3}2}}) elements. Their construction was improved by Salem and Spencer, and further improved by Behrend in 1946. The lower bound of Behrend is

Nanometer-precision contour-measurement technique for the diagnostics of multilayer nanostructures

A new technique of contour measurements with nanometer precision for the diagnostics of multilayer structures and other samples applied in optical and silicon technologies, and metal processing is proposed. This paper describes the development of two main technical solutions to achieve and verify nanometer resolution of the contour measuring instrument—single-crystal-silicon guide and test plates. The use of a crystal as a linear guide gives the possibility to achieve long-term stability of its bearing surface within a few nanometers. A test sample of a multilayer structure is developed and its parameters are controlled by means of transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). The results of measuring test samples with a step height of 100 and 200 nm by means of the contour measurement technique are presented.     

Construction of almost integral manifolds of affine control systems

We consider the problem of constructing manifolds of a special form, which are said to be almost integral, lie in the state space of an affine control system, and have the following property: the restriction of the control system to such a manifold is an almost trivial control system defining the part of trajectories of the original system lying on that manifold.     

富钇混合稀土对AM60镁合金显微组织与力学性能的影响

在AM60镁合金的基础上添加不同质量分数的富Y混合稀土(分别为0.5%,1.0%,1.5%,2.0%),研究了富钇混合稀土对AM60镁合金显微组织与力学性能的影响。结果表明:富Y稀土的加入使AM60镁合金的显微组织明显细化,并能显著提高合金的抗拉强度、屈服强度及延伸率。加入混合稀土后,合金中形成块状的铝钇化合物Al2Y,Al6Mn6Y,β-Mg17Al12相数量减少。当稀土加入量为1%时,合金的各方面性能达到最好。     

Cross-docking of inhibitors into CDK2 structures. 2

In the preceding paper (Duca, J. S.; Madison, V. S.; Voigt, J. H. J. Chem. Inf. Model. 2008, 48, 659-668), the accuracy of docking and affinity predictions of the Gold and Glide programs were investigated using single protein conformations spanning 150 CDK2/inhibitor crystallographic complexes. High docking accuracy was observed with both methods; furthermore, Glide showed modest log(IC50)/score correlations. In this part of the study, the effect of combining docking results from multiple protein conformations in a consensus fashion was probed. This approach enhanced docking accuracy only for Glide, which was attributed to the nature of its scoring function. For log(IC50)/score correlations, particular emphasis was placed on considering only scores from correctly docked poses. Using multiple instead of single protein structures showed an improvement in the correlations. Validation sets and scrambling experiments were used to examine the statistical significance and predictivity of these correlations. Rather than actual improvements in scoring accuracy, docking to multiple protein conformations produced overfitting artifacts.     

On hamiltonicity of <Emphasis Type="Italic">P</Emphasis><Subscript>3</Subscript>-dominated graphs

We introduce a new class of graphs which we call P ₃-dominated graphs. This class properly contains all quasi-claw-free graphs, and hence all claw-free graphs. Let G be a 2-connected P ₃-dominated graph. We prove that G is hamiltonian if α(G ²) ≤ κ(G), with two exceptions: K _2,3 and K _1,1,3. We also prove that G is hamiltonian, if G is 3-connected and |V(G)| ≤ 5δ(G) − 5. These results extend known results on (quasi-)claw-free graphs. This paper was completed when both authors visited the Center for Combinatorics, Nankai University, Tianjin. They gratefully acknowledge the hospitality and support of the Center for Combinatorics and Nankai University. The work of E.Vumar is sponsored by SRF for ROCS, REM.