Simultaneous determination by GC-MS-SIM of o-, m-, p-hydroxyphenylacetic acid, 3:4-dihydroxyphenylacetic acid and homovanillic acid in biological samples using a common selected ion

A GC-MS-SIM method is described for the simultaneous determination of five acid metabolites, o-, m-, and p-hydroxyphenylacetic acid, 3:4-dihydroxyphenylacetic acid and homovanillic acid in biological samples using a common selected ion for all the acids. The TMS ethers of methyl or ethyl esters of these compounds have a common ion at m/e 179 which is used for their quantitation by selected ion monitoring. The molecular ion at m/e 238 of the three monohydroxy phenylacetic acids, which is also the M-30 ion for homovanillic acid, is also used for their quantitation. The GC conditions for their separation, the relative sensitivities and some advantages of TMS ethers over other derivatives are described. The application of this method to biological samples is illustrated by data on human urine and plasma.     

Ti掺杂对α″-Fe16N2相稳定性的影响

研究了掺杂Ti对α″-Fe₁₆N₂相稳定性的影响，发现适量Ti掺杂有利于α″-Fe₁₆N₂相的形成．理论分析表明，掺杂适量Ti元素后含Ti的α″-(Fe,Ti)₁₆N₂相的生成焓降低，使α″相的稳定性提高，也使α″相更易制备．Ti浓度为3—15at％的(FeTi)-N薄膜具有高饱和磁化强度，μ₀M_s=2.3—2.5T． 关键词：     

Ionic strength and solvent control over the physical structure, electronic properties and superquenching of conjugated polyelectrolytes

In this paper, we investigate the photophysical properties of the conjugated poly electrolyte poly(2-methoxy-5-propyloxy sulfonate phenylene vinylene) (MPS-PPV), dissolved in both water and DMSO as a function of the solution ionic strength. Dynamic light scattering indicates that MPS-PPV chains exist in a highly agglomerated conformation in both solvents, and that the size of the agglomerates depends on both the ionic strength and the charge of the counter-ion. Even though the degree of agglomeration is similar in the two solvents, we find that the fluorescence quantum yield of MPS-PPV in DMSO is nearly 100-times greater than that in water. Moreover, intensity-dependent femtosecond pump-probe experiments show that there is a significant degree of exciton-exciton annihilation in water but not in DMSO, suggesting that the MPS-PPV chromophores interact to form interchain electronic species that quench the emission in water. Given that the emission quenching properties depend sensitively on the chain conformation and degree of chromophore contact, we also explore the superquenching may be either enhanced or diminished in either of the solvents via addition of simple salts, and we present a molecular picture to rationalize how the conformational properties of conjugated polyelectrolytes can be tuned to enhance their emissive behavior for sensing applications.     

Hydrogel microparticles from lithographic processes: novel materials for fundamental and applied colloid science

In recent years there has been a surge in methods to synthesize geometrically and chemically complex microparticles. Analogous to atoms, the concept of a "periodic table" of particles has emerged and continues to be expanded upon. Complementing the natural intellectual curiosity that drives the creation of increasingly intricate particles is the pull from applications that take advantage of such high-value materials. Complex particles are now being used in fields ranging from diagnostics and catalysis to self-assembly and rheology, where material composition and microstructure are closely linked with particle function. This is especially true of polymer hydrogels, which offer an attractive and broad class of base materials for synthesis. Lithography affords the ability to engineer particle properties a priori and leads to the production of homogenous ensembles of particles. This review summarizes recent advances in synthesizing hydrogel microparticles using lithographic processes and highlight a number of emerging applications. We discuss advantages and limitations of current strategies, and conclude with an outlook on future trends in the field.     

Controlled nucleation from solution using polymer microgels

Despite its widespread occurrence in nature and broad application in industrial practice, nucleation of crystalline materials remains largely unpredictable and therefore difficult to control. In this work, we demonstrate a new method to control nucleation with polymer microgels by tuning their microstructure to vary systematically the degree of nanoscopic confinement and its effects on nucleation. We find that the polymer microstructure has a significant impact on nucleation kinetics. Moreover, there exists an optimum polymer mesh size at which the rate of nucleation is dramatically enhanced, the degree to which depends on the extent of polymer-solute interactions. With easily tunable microstructure and chemistry, polymer microgels offer a promising approach for the rational design of materials for controlling nucleation from solution.     

Colloidal interactions mediated by end-adsorbing polymer-like micelles

We derive a statistical mechanical model for colloidal interactions mediated by polymer-like micelles (PLMs) that adsorb at the colloid surface. The model considers the end-adsorption and reversible scission of ideal chains, and is based on experimentally measurable parameters relevant to PLMs. The model predicts interparticle attractions due to micellar bridging that are stronger and longer-range than those encountered in ordinary telechelic polymers. Mapping the analytical potential onto the more familiar Double Yukawa potential allows, for the first time, accurate, a priori prediction of suspension microstructure and phase behavior when compared to experimental data for model nanoparticles dispersed in wormlike micelles over a range of solution conditions.     

Studies of some iron dithiolate complexes by the ESCA,Mössbauer and extended Hückel methods

Iron dithiolate complexes have been studied by Mössbauer and ESCA spectroscopy. Atomic charges and iron atom populations have been evaluated. Molecular orbital calculations have been made using the iterative extended Hückel method. The theoretical results are compared with the experimentally obtained charge distributions.     

The electronic structure of a series of tin complexes studied by XPS and Mössbauer spectroscopy

The isomer shift and 3d_5/2 core electron binding energy shift have been measured for a series of complexes. By using a simple model for the interpretation of these shifts in terms of occupation numbers of valence orbitals an estimate of the electronic structure is obtained.