The precipitation of silica by tannin

The precipitation of silica by tannin from chloride solution has been examined. Precipitation was never complete, the maximum being 96 % from a solution 0.075 N in ammonia.Separations of zirconium and tin from silica in acid chloride solution and of tin from acid oxalate solution were shown to be clean only if the initial acidity was higher than 0.4 N. Separations of titanium from silica in both acid chloride and acid oxalate solution were never clean, as titanium, required a very low acidity before precipitation was complete.     

Investigations into the chromatographic behaviour of silica gels produced from ester silicates

Summary Silica gels produced from ester silicates (ES-gels) are excellent chromatographic supports. In comparison with other silica gels the RP-materials obtained from them show little peak tailing even with polar, and, in particular, with basic compounds. Gels produced by various manufacturing processes have been classified by adsorption with methyl pyridinium chloride. ES-gels yield very low methyl pyridinium chloride values and small asymmetry parameters. The results indicate that there are strongly acidic, structurally-related surface centres which cause peak tailing on most commercial gels. It was shown that surface silanols on silica gels do not, in themselves, lead to peak tailing.     

Periodic precipitation of lanthanum molybdate crystals in silica gel

Formation of Liesegang rings on the growth of La₂(MoO₄)₃·XH₂O in silica gel by single diffusion technique is discussed. The nature of the periodic precipitation is found to depend on the concentration of inner and outer electrolytes, gel medium and its pH. The ‘time law’, ‘spacing law’ and ‘the law relating diffusion depth and width’ are found obeyed in this system. The one-dimensional Liesegang phenomena is thus investigated quantitatively making use of the simple laws of diffusion.     

Investigations into the utility of high-surface area silica pellets as potential solid-phase synthesis supports

Grace-Davidson silica pellets (SMR-057-015) are found to be optimal for surface grafting of (RO)₃Si(CH₂)₃FG reagents. While loadings of up to 2.1 mmol g⁻¹ can be attained (ca. 0.05 mmol per pellet) access of further reagents to the graft sites is problematic above loadings of 0.8 mmol g⁻¹. ¹³C CPMAS NMR studies may be carried out on individual pellets (using natural abundance substrates) and the resulting spectra are diagnostic in identifying successful subsequent coupling reactions.     

Multi-objective dynamic optimization of semi-batch polymerization processes

An improved evolutionary algorithm is proposed to perform multi-objective dynamic optimization of a semi-batch styrene polymerization process. The target is to determine the optimal feeding trajectories and the reactor operating temperature, which maximize the monomer conversion rate and minimize the initiator residue concentration in the final product. The optimization problem has been formulated as a multi-objective mixed-integer nonlinear problem (MOMINLP). The proposed approach allows the effective computation of the optimal operating strategies for the production of polymers with the average molecular weight and the polydispersity index required.     

Investigations on the silica gel supported form of microcrystalline zirconium phosphate ion exchanger and its applications in chemical separations

The ion exchanger Si-ZrP in the form of particles of high mechanical stability and good ion exchange performance was prepared by precipitating silicic acid in the slurry of crystalline zirconium phosphate. The conditions of preparation were optimally chosen. The stability of Si-ZrP ion exchanger particles in acidic and basic solutions, the ion exchange properties and kinetics of Si-ZrP were investigated.     

Hydrolysis of a two-membered silica ring on the amorphous silica surface

We have combined density functional theory (DFT) with classical interatomic potential functions to model hydrolysis of amorphous silica surfaces. The water-silica interaction is described by DFT with incorporation of a long-range elastic field described by classical interatomic potentials. Both physisorption and chemisorption of water on a surface site, known as the two-membered silica ring, are studied in detail. The hybrid quantum-mechanical and classical mechanical method enables more realistic treatment of chemical processes on an extended surface than previous methods. We have studied cooperative events in the hydrolytic reactions and discovered a new reaction pathway that involves a double proton transfer process. In addition, the evaluation of the total energy in a hybrid quantum-mechanical and classical mechanical system is discussed.     

Investigations on lactams

3-Ethoxy-3,4-dehydrothiazane has been synthesized by the reaction of 3-thiazanone with triethyloxonium fluoroborate. The condensation of 3-ethoxy-3,4-dehydrothiazane with-amino--cyanoacetamide has given 3-amino-2-carbamoylimidazo [2,1-c]thiazane, which is the key compound for the synthesis of a new series of heterocyclic compounds, 4-substituted thiazano[4,3-e]purines.Investigation carried out in the chemical laboratory of Cambridge University, England.     

Investigations on benzodiazines

The luminescence properties of 6-methoxy-2-phenyl-4-piperidino-quinazoline and 6-methoxy-4-morpholino-2-phenylquinazoline, synthesized for the first time, have been studied.For part IX, see [1].     

噻吩光解反应机理的理论研究

使用密度泛函理论(DFT)中的B3LYP方法, 采用6-31G**和6-31＋＋G**基组, 对噻吩的光解反应进行了理论研究. 对照实验结果, 我们研究了五个光解通道, 包括生成C₄H₄＋S, C₂H₂＋C₂H₂S和CS＋C₃H₄的三个闭壳层分子解离通道与生成HCS＋C₃H₃和HS＋C₄H₃的自由基解离通道. 各个可能的反应通道的产物碎片的具体形式得到了确认. 研究发现在基态生成C₂H₂＋C₂H₂S和在最低三态生成C₄H₄＋S的反应从能量上考虑最为有利, 而实验上观测到的主要产物C₂H₂＋C₂H₂S主要是在基态上产生的. 通过对比实验结果与计算结果, 我们认为噻吩光解反应机理与所用激发光波长有关.     

Estimation of diffusion coefficient of Ba++ ions in silica gel from periodic precipitation of BaMoO4

Formation of Liesegang rings on the growth of BaMoO₄ crystals in silica gel by single diffusion is discussed. The rhythmic precipitation is found to be influenced profoundly by (a) the molarity of inner and outerelectrolytes (b) the age of gel and (c) the pH of the gel medium. The time law, spacing law and the law relating diffusion depth and width are verified. A method to estimate the diffusion coefficient of the outer electrolyte in the gel medium is developed and calculated for Ba⁺⁺ions.     

单细胞分析研究

单细胞分析是一个令分析化学家十分感兴趣和重视的领域.本实验室近年来在以下方面开展了研究工作.