Pore assembled multilayers of charged polypeptides in microporous membranes for ion separation

In this study, highly permeable ion-selective membranes are prepared via immobilization of polyelectrolyte multilayer networks within the inner pore structure of a microporous (pore size = 0.2 microm) support. Electrostatic layer-by-layer assembly is achieved through alternate adsorption of cationic and anionic polyelectrolytes under convective flow conditions. To initiate pore assembly, the first layer consists of covalently bound charged polypeptides (poly(L-glutamic acid) (PLGA) or poly(L-lysine) (PLL)) establishing a charged support for subsequent adsorption. Nonstoichiometric immobilization of charged multilayers within a confined pore geometry leads to an enhanced volume density of ionizable groups in the membrane phase. This overall increase in the effective charge density allows for Donnan exclusion of ionic species (especially divalent co-ions) using microporous materials characterized by permeability values that exceed conventional membrane processes. Multilayer assemblies are fabricated using both PLGA/PLL and synthetic polyelectrolytes (poly(styrenesulfonate)/poly(allylamine)) in an attempt to compare the level of adsorption and separation properties of the resulting materials. The role of salt concentration in the carrier solvent on overall polyelectrolyte adsorption was examined to determine its effect on both solute (Cl-, SO4(2-), As(V)) and water transport. Constriction of the pore size induced by multilayer propagation was monitored through permeability measurements and dextran rejection studies at each stage of the deposition process.     

Monomeric, dimeric and polymeric [Cp2MoH2] complexes with Ag---S bonds

The reaction of [Cp₂MoH₂] and AgBF₄ with the dithio ligands Na(S₂CPh) and K(S₂COⁱPr) afforded the complexes [(Cp₂MoH₂AgS₂CPh)₂] (1) and [(Cp₂MoH₂AgS₂COⁱPr)₂] (2). Using the monothio ligands Na(SC(O)Ph), K(SC(O)CH₃) and Na(S(NHPh)C=C(CN)₂) the complexes [(Cp₂MoH₂AgSC(O)Ph)₂] (3), [((Cp₂MoH₂)₂(AgSC(O)CH₃)₃)_n] (4) and [(Cp₂MoH₂)₂AgS(NHPh)C=C(CN)₂] (6) were formed. The reaction of thiobenzamide and [(Cp₂MoH₂)₂AgCl] gave the complex [(Cp₂MoH₂Ag(Cl)S(NH₂)CPh)₂] (5). Complexes 1 and 2 have a dimeric structure with the two dithio ligands bridging the two silver atoms. Complex 3 is also a dimer, however, the monothio ligands are coordinated with their single sulphur atoms to the silver atoms. In the polymer 4 the thioacetate ligand has the same bonding mode as in 3. The three-dimensional structure of 4 is built-up of parallel strings. In the dimer 5 the thiobenzamide ligands bind with the sulphur atom to a silver atom each. Complex 6 has a monomeric structure in which the silver atom is coordinated to two [Cp₂MoH₂] ligands and to the sulphur atom of the S(NHPh)C=C(CN)₂ ligand. Compounds 1–6 were characterised analytically and spectroscopically and the structures were determined by single crystal X-ray analyses.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

The benzene+OH potential energy surface: intermediates and transition states

The potential energy surface for the interaction between benzene and hydroxyl radical is studied in detail using quantum mechanical methods, with a particular focus on the hydrogen abstraction pathway. Geometric parameters are optimized using a variety of density functional methods as well as perturbation theory. Energies are refined using coupled cluster singles and doubles with perturbative triples [CCSD(T)] extrapolated to the complete basis set limit. At our most reliable level of theory, complexation energies are found to be (with zero-point corrected energies in parentheses) 3.7 (2.8) kcal/mol for the benzene-hydroxyl radical complex and 2.9 (-1.7) kcal/mol for the phenyl radical-water complex. The barrier to H abstraction lies 6.5 (4.2) kcal/mol above the infinitely separated benzene and hydroxyl radical monomers.     

Development of food reference materials for nutritional analysis

Summary The development of five reference materials for major nutritional properties, whole milk powder, pork muscle, wheat and rye flour, and haricots verts beans is described. Homogeneity and stability of these materials proved to be adequate. A preliminary intercomparison of methods showed that results for total fat and total dietary fibre were method dependent. Evaluation of methods used for available carbohydrates revealed poor solubilisation and hydrolysis of starch in some laboratories. This intercomparison has given valuable information for the final certification of these materials.     

Tetragermacyclobutadiene: Energetically Disfavored with Respect to Its Structural Isomers

Germanium has been a central feature in the renaissance of main‐group inorganic chemistry. Herein, we present the stationary‐point geometries of tetragermacyclobutadiene and its related isomers on the singlet potential energy surface at the CCSD(T)/cc‐pVTZ level of theory. Three of these 12 structures are reported for the first time and one of them is predicted to lie only 0.4 kcal mol^?1 above the previously reported global minimum. Focal‐point analyses has provided electronic energies at the CCSD(T) level of theory, which are extrapolated to the complete basis‐set limit and demonstrate the convergence behavior of the electronic energies with improving levels of theory and increasing basis‐set size. The lowest‐energy structure is the bicyclic structure, which lies 35 kcal mol^?1 below the “all‐Ge” cyclobutadiene structure. The reaction energies for the association of known Ge hydrides (e.g., digermene) to form Ge₄H₄ indicate that Ge₄H₄ could be observed experimentally. We investigate the bonding patterns by examining the frontier molecular orbitals. Our results demonstrate that: 1) the cyclic isomers of (GeH)₄ distort to maximize the mixing of the p orbitals that are involved in the π system of tetragermacyclobutadiene and 2) the lowest‐energy isomers exhibit unusual bonding arrangements (e.g., bridging H bonds) that maximize the nonbonding electron density at the Ge centers.     

Results of the eurofoods trial on between-laboratory variation in the analysis of macronutrients in foods

Summary In order to determine the influence of laboratory procedures on nutrient values in different food tables and data banks, an interlaboratory study was set up. Nineteen laboratories participated, and received well-homogenized samples of egg powder, full-fat milk powder, whole rye and wheat meal, biscuits and french beans to perform analyses of macronutrients by their own routine methods. For dry weight the results agreed very well; the results for ash agreed rather well. For protein the coefficient of variation between laboratories (CV_between) ranged from 2.8% to 6.4%. The CV_between for total fat ranged from 5.4% to 54%. For available carbohydrates the CV_between ranged from 9% to 27%. The CV_between for total dietary fiber ranged from 23% to 84%. It is concluded that leading laboratories produce widely different values for macronutrients in common foods. Reference materials of certified nutrient concentration are needed.     

Interference of flavonoids with enzymatic assays for the determination of free fatty acid and triglyceride levels

Flavonoids are bioactive food compounds with potential lipid-lowering effects. Commercially available enzymatic assays are widely used to determine free fatty acid (FFA) and triglyceride (TG) levels both in vivo in plasma or serum and in vitro in cell culture medium or cell lysate. However, we have observed that various flavonoids interfere with peroxidases used in these enzymatic assays, resulting in incorrect lower FFA and TG levels than actually present. Furthermore, addition of isorhamnetin or the major metabolite of the flavonoid quercetin in human and rat plasma, quercetin-3-O-glucuronide, to murine serum also resulted in a significant reduction of the detected TG levels, while a trend was seen for FFA levels. It is concluded that when applying these assays, vigilance is needed and alternative analytical methods, directly assessing FFA or TG levels, should be used for studying the biological effects of flavonoids on FFA and TG levels.     

Cr(VI) Oxidation of Cholesterol—A Kinetic Study Using N-Cetylpicolinium Dichromates,A Class of Novel Phase Transfer Oxidants

Kinetics and Catalysis - Kinetic study of cholesterol oxidation has been studied using a series of N-cetylpicolinium dichromates (CPDC), a class of phase transfer oxidants, in acetic acid medium...