8-Hydroxyquinoline derivatives (BQOH and BQClOH) were synthesized as fluorescent chemosensors for metal ions. BQOH and BQClOH hardly show fluorescence themselves, but they showed strong fluorescence with the addition of zinc or cadmium ions. The order of the maximum values of fluorescence intensity (If,max) was BQClOH-Zn2+ > BQClOH-Cd2+ >> BQOH-Cd2+ > BQOH-Zn2+. Therefore, the ab initio calculations (by Gaussian 98) using the time-dependent density functional method with 6-31+G(d) basis set were carried out on the Zn2+ complexes of quinoline chromophore, BQOH and BQClOH, in order to investigate the cause of the difference in the fluorescent intensity (BQClOH-M2+ >> BQOH-M2+, M2+ = Zn2+ or Cd2+). The results of the calculations showed that the T2 state of the [ZnBQO]+ lay just below its S1 state, while that was not the case for [ZnBQClO]+.
This study presents a method and algorithms for calculation of 3D similarity between pairs of chemical structures represented as 3D molecular graphs. Similarity searching in chemical databases is widely used for virtual screening, lead discovery and optimization, and most recently protein amino-acid sequences studies to discover and determine the functionality of a new isolated protein. This method has obvious advantages over other known methods due to the following: (i) the superposition method does not depend on the preliminary alignments of the chemical structures; (ii) entire conformational space is searched without generation of each conformer; (iii) excellent discrimination between geometrical isomers. Although it is a computationally demanding method, recent implementation of maximum clique algorithm and bound smoothing algorithm made possible the optimization of this method and application to similarity searching in chemical databases of non trivial size.
The canonical ensemble partition function is obtained for a two-molecule system with the repulsive step function outside the hard sphere wall in a spherical cell. Fluid-fluid phase transition-like behavior is evident at low temperatures. The spinodal line is obtained in the (V, T) domain and a negative expansion coefficient is found in the stable state. The theoretical pVT relationship is confirmed through Monte Carlo simulations. The periodic 108-molecule system examined by Monte Carlo simulations also provides a qualitatively similar pVT relationship to the two-molecule system.