The structures of (PbS)n (n = 1-9) clusters are investigated with density functional theory at the B3LYP level. Various pseudopotential basis sets on lead and the 6-31+G basis set on sulfur were employed. Full geometry optimization and extensive searches of the potential energy surface were carried out for clusters with n = 1-6. We find that even small PbS clusters (n > 2) start to take on the characteristic features of the rock salt structure of solid-state PbS (galena). The origin of some of the structural aspects of these crystals is shown to be associated with the partial covalent nature of the Pb-S bond. The magnitude of the HOMO-LUMO gap oscillates with increasing size of the clusters, in agreement with the observed behavior of the corresponding UV absorption bands of ultrasmall PbS quantum dots. Direct conformation of this oscillation was found by CIS(D) calculations, for which the absorption with the largest oscillator strength oscillates as the clusters grow from PbS to (PbS)9.

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Theory C 1000 Density Functional Study of the Structures of Lead Sulfide Clusters (PbS) n (n = 1-9). -(ZENG, H.; SCHELLY*, Z. A.; UENO-NOTO, K.; MARYNICK, D. S.; J. Phys. Chem. A 109 (2005) 8, 1616-1620; Dep. Chem. Biochem., Univ. Tex., Arlington, TX 76019, USA; Eng.) -Schramke 21-003

The DNA-binding ability of the zinc-finger (ZF) protein and the modulation of its affinity to DNA through amino acid mutations were theoretically investigated. Classical molecular dynamics and energy decomposition analysis based on large-scale ab initio fragment molecular orbital calculations were used to obtain the DNA binding affinities of wild-type and three mutant ZFs. Calculated binding free energies qualitatively well explained the DNA binding affinity modulation experimentally observed by Dhanasekaran et al. [Dhanasekaran, M.; et al., Biochemistry 2007, 46, 7506-7513]. It had been considered that only the α-helix domain in the ZF plays an important role in DNA recognition; however, our results clearly show that the N-terminal regions, BR1 and BR2, also play important roles in DNA recognition.