Performance of Becke's half-and-half functional for non-covalent interactions: energetics, geometries and electron densities.

The performance of Becke's half-and-half functional, BHandH, for description of non-covalent interactions is reported, using high-level ab initio results as benchmarks. Binding energies are found to be well reproduced for complexes that are bound predominantly by dispersion, whereas significant and consistent overestimation is observed for hydrogen bonded complexes. Overall, the mean average error is around 2 kcal mol(-1), for all basis sets considered. The effect of changing the proportion of exact and Slater exchange in the functional is shown to alter the balance of description of hydrogen bonded and dispersion bound complexes, but does not improve the overall performance. However, a simple multiplicative scaling of binding energies is possible, and reduces the mean average error to less than 1 kcal mol(-1). The performance of the BHandH functional for geometry optimization was also studied, and in almost all cases the difference from ab initio geometries is small, with root mean square deviations of between 0.05 and 0.20 A. Harmonic frequency calculation allow us to check whether optimized geometries are true minima at this level, and to estimate the zero point vibrational energy change on binding.

Calculation of lipophilicity of a large, diverse dataset of anticancer platinum complexes and the relation to cellular uptake.

A quantitative structure--property relationship (QPSR) for the octanol--water partition of platinum complexes was constructed using molecular descriptors derived from density functional (DFT) calculations. A dataset of partition data for 64 complexes, consisting of 43 square-planar platinum(II) and 21 octahedral platinum(IV) complexes, was drawn from literature sources. Not only does this dataset include considerable structural diversity of complexes considered but also a variety of techniques for the measurement of partition coefficients. These data were modeled using descriptors drawn from electrostatic potentials and hardness/softness indices projected onto molecular surfaces. This required initial descriptor selection using a genetic algorithm approach, followed by partial least-squares regression against log Po/w data. In this way, a statistically robust model was constructed, with errors of similar size to the variation in log Po/w from multiple experimental measurements. Implications of lipophilicity for cellular accumulation of Pt-based drugs, and hence for design of new drugs, are discussed, as is the uptake of metabolites of cisplatin.

The RP-HPLC measurement and QSPR analysis of logP(o/w) values of several Pt(II) complexes.

The n-octanol/water partition coefficient, logP(o/w), for a set of 24 Pt(II)-complexes was estimated by means of reversed-phase high performance liquid chromatography (RP-HPLC) technique using a C18 (ODS, octadecyl silane) column as a stationary phase and water/methanol mixtures as mobile phases. Based on the known logP(o/w) of several Pt(II)-complexes, we set a method to correlate the partition coefficient of this kind of complexes with the corresponding retention parameters. The best result was obtained from extrapolation to 0% of the organic modifier (MeOH) of the aqueous eluant. A quantitative structure-property relationship (QSPR) was constructed using molecular descriptors derived from density functional theory (DFT) calculations, which was found to correlate and predict these values with good accuracy. The use of DFT calculations is required because group-additive methods fail due to lack of values for appropriate fragments for many Pt(II)-complexes.

The aromaticity and Möbius characteristics of carbeno[8]heteroannulenes and triplet state annulenes.

Two types of annulene which may show significant Möbius aromatic character and bond and twist delocalisation are proposed; triplet states with 4n + 2 occupancy of the p pi array of atomic orbitals and a novel 8-pi carbeno[8]heteroannulene ring system 1 where the Hückel highly antiaromatic nature as a planar system can be attenuated or even reversed by the C2 symmetric Möbius distortion.