Studies of the g factors and zero-field splitting for the trigonal Ti(2+)(Ga)-S(p) defect center in GaP crystal

The EPR g factors g(parallel), g(perpendicular) and zero-field splitting D suggested to be caused by a donor-acceptor nearest-neighbour pair defect [Ti(Ga)(2+)-Sp] in GaP:Ti(2+) co-doped with sulphur are calculated from the high-order perturbation formulas based on a two spin-orbit coupling parameter model for the EPR parameters of 3d(2) ion in trigonal symmetry. The calculated results are close to the observed values. The suggestion of [Ti(Ga)(2+)-Sp] pair defect in GaP:Ti co-doped with sulphur is also confirmed from this calculation.     

Solvent effects on infrared spectra of methyl 4-hydroxybenzoate in pure organic solvents and in ethanol/CCl4 binary solvents

Infrared spectroscopy studies of methyl 4-hydroxybenzoate (MHB) in 17 different organic solvents and in ethanol/CCl4 binary solvent were undertaken to investigate the solvent-solute interactions. The frequencies of carbonyl stretching vibration nu(C=O) of MHB in single solvents were correlated with the solvent acceptor number (AN) and the linear solvation energy relationships (LSER). The assignments of the two bands of nu(C=O) of MHB in alcohols and the single one of that in non-alcoholic solvents were discussed. The shifts of nu(C=O) of MHB in ethanol/CCl4 binary solvents showed that several kinds of solute-solvent hydrogen bonding interactions coexisted in the mixture solvents, with a change in the mole fraction of ethanol in the binary solvents.     

Effect of PEG on the crystallization of PPDO/PEG blends

A new biodegradable polymer system, poly(p-dioxanone) (PPDO)/poly(ethylene glycol) (PEG) blend was prepared by a solvent casting method using chloroform as a co-solvent. The PPDO/PEG blends have different weight ratios of 95/5, 90/10, 80/20 and 70/30. Crystallization of homopolymers and blends were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). When 5% of PEG was blended, the crystallization exothermal peaks (T_c) of PPDO increased sharply and the crystallization exothermal peaks (T_c) of PEG decreased slightly compared with the homopolymers. The crystallization rates of both components increased, and caused greater relative crystallization degree (X_t%). But when the content of PEG was more than 5%, the crystalline behaviors of blends had no more significant changes accordingly. The melting points of each sample varied little over the entire composition range in this study. The nonisothermal crystallization of PPDO homopolymer and blend (PPDO/PEG = 70/30) were also studied by DSC. The crystallization began at a higher temperature when the cooling rates were slower. The nonisothermal crystallization kinetics of blends was analyzed by Ozawa equation. The results showed that the Ozawa equation failed to describe the whole crystallization of the blend, but Mo equation could depict the nonisothermal crystallization perfectly.     

Near-infrared fluorimetric determination of nucleic acids by shifting the ion-association equilibrium between heptamethylene cyanine and Alcian blue 8GX

A new method based on near-infrared (near-IR) fluorescence recovery, employing a two-reagent system which is composed of an anionic heptamethylene cyanine (HMC) and a polycationic phthalocyanine dye, Alcian blue 8GX, is presented for the determination of nucleic acids. With a maximum excitation wavelength at 766 nm and a maximum emission wavelength at 796 nm, the fluorescence recovery is linear with the concentration of nucleic acids added. Factors including the acidity of the medium, the reaction time, the optimal ratio of the two reagents, as well as the influence of foreign substance were all investigated. Meanwhile, the mechanism of fluorescence recovery was also studied. Under the optimal conditions, the linear ranges of the calibration curves were 10-250 ng ml⁻¹ for calf thymus DNA (CT DNA) and 10-200 ng ml⁻¹ for yeast RNA. The detection limits were 6.8 ng ml⁻¹ for CT DNA and 6.3 ng ml⁻¹ for yeast RNA, respectively. The method has been applied to the analysis of practical samples and the recovery results were satisfactory.     

Study on the interaction of platinum(IV), gold(III) and silver(I) ions with DNA

Fluorescence, absorption spectra have been produced by the interaction of platinum(IV), silver(I) and gold(III) ions with the berberine–DNA system (berberine, Scheme 1). Platinum(IV) and gold(III) ions show different effects from that of silver(I) ion on the spectral characteristics of the berberine–DNA system. Quenching fluorescence is seen with platinum(IV) and gold(III) ions addition, whereas increasing fluorescence is observed for silver(I) ions. The addition of gold(III) and silver(I) ions cause an increase in absorption of the berberine–DNA system. The above results suggest that different metal ions exhibit different affinities when binding to DNA correlates well with the ions’ charge, structure and the coordination ability.     

Rational principles of compound selection for combinatorial library design

It is practically impossible in a short period of time to synthesize and test all compounds in any large exhaustive chemical library. We discuss rational approaches to selecting representative subsets of virtual libraries that help direct experimental synthetic efforts for both targeted and diverse library design. For targeted library design, we consider principles based on the similarity to lead molecules. In the case of diverse library design, we discuss algorithms aimed at the selection of both diverse and representative subsets of the entire chemical library space. We illustrate methodologies with several practical examples.     

DFT study on the geometric, electronic structure and Raman spectra of 5,15-diphenylporphine

The ground state geometric, electronic structure and Raman spectra of 5,15-diphenylporphine (H(2)DPP) have been studied using B3LYP/6-31G(d) method and compared with that of well-studied free base porphine (H(2)P) and meso-tetraphenylporphine (H(2)TPP). Calculation shows that 5,15-substitution causes remarkable in-plane distortion, whereas the resulting out-of-plane distortion is negligible. The calculated electronic structure of H(2)DPP is consistent with the absorption spectra compared with H(2)P and H(2)TPP. The calculated vibrational frequencies of H(2)DPP scaled with a single factor of 0.971 agree well with experimental data (the rms error is 8.0 cm(-1)). The assignment of experimental Raman bands of H(2)DPP was discussed on the basis of theoretical calculation and the comparison with that of H(2)P and H(2)TPP. The splitting of some vibrational modes involving the motion of C(m) atom, such as nu(1), nu(8), and nu(10), was observed and was attributed to the diversification of the environment around C(m) atoms. As the shift of absorption peaks, the shift of some structure-sensitive Raman bands of H(2)DPP form that of H(2)TPP and H(2)P was attributed to the in-plane nuclear reorganization (IPNR) induced by phenyl-substitution, though the contribution of nonplanarity mechanism could not be excluded completely.     

Synthesis of new 1,3-bis（phenylethynyl）disilazanes

Three new 1,3-bis(phenylethynyl)disilazanes were synthesized from the reaction of 1,3-dichlorodisilazanes with (phenylethy- nyl)lithium,and characterized by infrared (IR) spectra,nuclear magnetic resonance (NMR) and mass spectrometry (MS).     

Theoretical formalism and experimental verification of line shapes of NMR intermolecular multiple-quantum coherence spectra

Although the theories and potential applications of intermolecular multiple-quantum coherences (iMQCs) have been under active investigations for over a decade, discussion of iMQC NMR signal formation was mainly confined in the time domain. In this paper, a full line-shape theory was developed to describe iMQC signals in the frequency domain. Relevant features of the line shape, such as peak height, linewidth, and phase, were investigated in detail. Predictions based on the theory agree well with experimental and simulated results. Since radiation-damping effects always couple with iMQCs in highly polarized liquid-state NMR systems, and strongly radiation-damped signals have many spectral characteristics similar to those of iMQCs, a detailed comparison was also made between them from different spectral aspects. With detailed comparison of peak height, linewidth, and phase, this work demonstrates that the iMQC and radiation-damping phenomena result from two completely different physical mechanisms despite that both present similar signal features and coexist in highly polarized liquid-state NMR systems.