“Statistical” symmetry with applications to phase transitions

Hermann proposed that mesomorphic media should be classified by assigning certain statistical symmetry groups to each possible partially ordered array. Two translational groups introduced were called superordinate and subordinate. We find that the average density in such a partially ordered medium has the superordinate symmetry ₁, while the pair correlation function has the subordinate symmetry ₂. A complete listing is made of all compatible combinations of ₁ and ₂ in two and three dimensions. This leads to more possible symmetries than Hermann obtained, e.g., also to nonstoichiometric crystals. The order parameter space for the systems is found to be the quotient space ₁/₂. In most cases it is identical to the order parameter space of low-dimensionalXY spin systems. The Landau free energy is expanded as functional of the two-particle correlation functionK; the translation group is found to be ₁×₂. A Landau mean-field theory can then be carried out by expanding the system free energy into a series of invariants of the active irreducible representations ofK and mapping the free energy onto that for anXY planar spin system. We predict novel critical behavior for transitions between mesomorphic phases and go nogo selection rules for continuous transitions. We give the structure factors for X-ray scattering so changes in all such phase transitions are observable. The statistical symmetry groups, which describe point and translational symmetries of the mesophases, are classified. Proposals are made to include quasi-long-range or topological order in the classification scheme.This work supported in part by National Science Foundation (Division of International Programs), the PSC-BHE—Faculty Research Award CUNY and Deutsche Forschungsgemeinschaft.     

Chemical applications of group theory and topology

The following procedure is described for investigating the qualitative dynamics of simple chemical systems: 1) A so-called influence diagram is generated representing the relationships between the reference reactants (phase-determining intermediates); 2) This influence diagram is used to generate a truth table indicating possible transitions between state vectors representing the signs of the time derivatives of of the reference reactant concentrations; 3) The truth table is used to determine a state transition diagram representing the flow topology around unstable equilibrium points; 4) The characteristic equation of the adjacency matrix of the influence diagram is solved in order to determine the presence of such unstable equilibrium points. The two types of qualitative dynamics possible for chemical systems containing two reference reactants and one feedback circuit are bifurcation between two attracting regions (bistability) and limit cycle oscillation. However, in two reference reactant systems oscillation requires an additional self-activating loop to generate the unstable equilibrium point required for its realization. Bistability and limit cycle oscillation are also two of the possible types of qualitative dynamics for chemical systems containing three reference reactants. However, chemical systems with three reference reactants and two or more feedback circuits can also contain interlocking limit cycles, which can lead to toroidal oscillations or chaos. The influence diagrams are given for the systems exhibiting these various types of dynamic behavior along with a summary of the important properties of all 729 possible influences for simple chemical systems containing three reference reactants.     

一种新型的表面声波阻抗传感器及其在液相体系中的应用

一种新型的表面声波阻抗传感器及其在液相体系中的应用姚守拙，陈康，刘德忠，聂利华（湖南大学化学化工系，长沙，４１００８２）关键词表面声波，阻抗传感器，液相应用表面声波传感器（ＳＡＷＳ）具有较高的灵敏度和检测精度，已广泛应用于气体微量组分分析、色谱检测和...     

Solid Phase Synthesis of 4H-Pyrimido[2,1-b] Benzothiazol-4-ones from Resin-Bound Cyclic Malonic Ester

The solid phase synthesis of 4H-pyrimido[2,1-6] benzothizaol-4-ones has been reported.     

Two-dimensional commensurate soliton structures

A phase diagram of pinned soliton structures in two dimensions has been found for a repulsive interactionU(x) between solitons withU(x)>0. The critical fugacity of the commensurate soliton structure is shown to be proportional toU(l), wherel is the period of this structure.     

相转移催化元素硫的歧化反应

本工作将相转移催化(PTC)应用于元素硫歧化反应,大大降低了反应温度,提高了反应速度。该反应被证实与熔态硫在水溶液中的歧化相同,即4S+6OH~-=2S~(2-)+S_2O_3~(2-)+3H_2O。比较了四乙基铵、四丁基铵、十六烷基三甲基铵和三辛基甲基铵四种相转移催化剂及四氯乙烯、二甲苯和四氯乙烷三种溶剂的影响。讨论了本体系相转移催化的证据。为改进以元素硫歧化反应为基础的提取冶金过程提供了依据。     

Dominant Factors Affecting the Chromatographic Behaviour of Bile Acids

With the aim of optimizing the chromatographic process by avoiding any preliminary derivatizing step, we examined the chromatographic behaviour of a selected set of unconjugated bile acids looking at the dominant factors that affect the performances of three different stationary phases: RP-8, RP-18 and RP-18 Base Deactivated (RP-18-BD). Accordingly to its structural peculiarity, the RP-18-BD column combined with a specific mobile phase has proved to be the most suitable one, in enhancing both separation factor α and resolution R _S within the selected set of analytes. Pronounced changes in the chromatographic profiles by only slightly changing the mobile phase composition (pH, buffer concentration, percentage and kind of organic modifier) prompted us to achieve satisfactory results in the separation and resolution of the selected set of bile acids.Presented at: CE in the Biotechnology & Pharmaceutical Industries: 7th symposium on the practical applications for the analysis of proteins, nucleotides and small molecules, Montreal, Canada, August 12–16, 2005.An erratum to this article can be found at     

N-Nosyl-α-amino acids in solution phase peptide synthesis

A highly efficient and practical synthesis of peptides in solution phase has been developed. The procedure is based on the use of p-nitrobenzenesulfonyl (nosyl) group for the protection of the amino function of α-amino acids. Every step of the procedure, protection of the amino function by the nosyl group, formation of the peptide bond, and removal of the sulfonamide group, is characterized by high yields and excellent purity of the final products. The described strategy allows the preparation of short peptide sequences keeping the chiral integrity of amino acid precursors. Compatibility of nosyl group with the side-chain protecting groups used in Fmoc-based strategy is demonstrated. The method here presented is an alternative strategy that could provide advantages for future peptide synthesis.     

HPLC Analysis of Cotinine in Urine After SPE with a Cholesterol-Modified Adsorbent

A one-step solid-phase extraction procedure, based on a new silica gel adsorbent modified with cholesterol groups, has been investigated for measurement of cotinine in urine. Cotinine is the main metabolite of nicotine in the human body and is analyzed as a biomarker for assessment of direct or passive exposure to tobacco smoke. New cholesterol-modified adsorbents have been obtained by chemical modification of silica gel of different porosity with cholesterol ligands. Although recovery by this extraction procedure were optimum over a relatively broad range of sample pH (3.1–8.0), analytical conditions such as sample loading, washing and elution conditions, concentration of cotinine to be extracted, and the type of adsorbent used for extraction were found to affect the efficiency of the procedure and had to be controlled for optimum recovery. When these conditions were controlled, recovery of cotinine from spiked human urine was reproducible and depended on compound ionization. Quantitative analysis of cotinine was performed by reversed-phase high-performance liquid chromatography with UV detection. Presented at: Conference of the Hyphenation of Liquid Chromatography–Nuclear Magnetic Resonance Spectroscopy, Liquid Chromatography–Mass Spectrometry and Related Topics, Tuebingen, Germany, March 25–29, 2006.     

Optical spectra of Yb and Yb–Nd interaction in Cs2NaNd0,4Yb0,6Cl6

Interaction between octahedrally coordinated Nd³⁺ and Yd³⁺ in Cs₂NaNd_0,4Yb_0,6Cl₆ reduces the Nd³⁺ luminescence lifetime by roughly two orders of magnitude with respect to that found in Cs₂NaNdCl_{6– · –} Analysis of low temperature absorption and emission spectra reveals that the nonradiative Nd³⁺–Yb³⁺ energy transfer has to be assisted by lattice phonon emission, nevertheless the rate of the transfer is high in the 4–300 K temperature region and attains 5.8×10⁵s^-1 at room temperature. A phase transition of Cs₂NaNd_0,4Yb_0,6Cl₆ between 12 and 13 K is evidenced by abrupt change of both the spectra and lifetimes of Yb³⁺. Reduction of Yb³⁺ lifetime from 5.3 ms to 150 μs is at the transition from low symmetry phase to high symmetry phase is supposed to be associated with a three ion interaction which occurs in ordered lattice and disappears in low temperature disordered structure.