Designing a Useful Lipid Raft Model Membrane for Electrochemical and Surface Analytical Studies

A model biomimetic system for the study of protein reconstitution or drug interactions should include lipid rafts in the mixed lipid monolayer, since they are usually the domains embedding membrane proteins and peptides. Four model lipid films composed of three components: 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), cholesterol (Chol) and sphingomyelin (SM) mixed in different molar ratios were proposed and investigated using surface pressure measurements and thermodynamic analysis of the monolayers at the air–water interface and imaged by Brewster angle microscopy. The ternary monolayers were transferred from the air–water onto the gold electrodes to form bilayer films and were studied for the first time by electrochemical methods: alternative current voltammetry and electrochemical impedance spectroscopy and imaged by atomic force microscopy. In excess of DOPC, the ternary systems remained too liquid for the raft region to be stable, while in the excess of cholesterol the layers were too solid. The layers with SM in excess lead to the formation of Chol:SM complexes but the amount of the fluid matrix was very low. The equimolar content of the three components lead to the formation of a stable and well-organized assembly with well-developed raft microdomains of larger thickness, surrounded by the more fluid part of the bilayer. The latter is proposed as a convenient raft model membrane for further physicochemical studies of interactions with drugs or pollutants or incorporation of membrane proteins.     

Control of Luminescence by Tuning of Crystal Symmetry and Local Structure in Mn4+‐Activated Narrow Band Fluoride Phosphors

Mn⁴⁺‐doped fluoride phosphors have been widely used in wide‐gamut backlighting devices because of their extremely narrow emission band. Solid solutions of Na₂(Si_xGe_1?x)F₆:Mn⁴⁺ and Na₂(Ge_yTi_1?y)F₆:Mn⁴⁺ were successfully synthesized to elucidate the behavior of the zero‐phonon line (ZPL) in different structures. The ratio between ZPL and the highest emission intensity υ₆ phonon sideband exhibits a strong relationship with luminescent decay rate. First‐principles calculations are conducted to model the variation in the structural and electronic properties of the prepared solid solutions as a function of the composition. To compensate for the limitations of the Rietveld refinement, electron paramagnetic resonance and high‐resolution steady‐state emission spectra are used to confirm the diverse local environment for Mn⁴⁺ in the structure. Finally, the spectral luminous efficacy of radiation (LER) is used to reveal the important role of ZPL in practical applications.     

Application of the additive increments method to the calculation of chemical shift of olefinic protons in aromatic olefines: Additive increments for para and meta substituents in the aromatic ring

Additive increments for para and meta substituents in the aromatic ring were calculated on the basis of 332 examples of chemical shifts and were correlated with Hammett's constants. Examples of calculation of chemical shifts of olefinic protons in substituted aromatic olefines by means of the increments are given.     

Organosulphur compounds—XVIII: A new and general synthesis of ketene s,s- and o,s-thioacetals based on the horner-wittig reaction

A new and general synthesis of ketene S,S-thioacetals (1) and ketene O.S-thioacetals (6) which involves the Horner-Wittig reaction of carbonyl compounds with the metallated S,S- and O,S-thioacetals of formyl-phosphonates (4 and 5) is described. The Horner-Wittig reaction of 4 with aromatic aldehydes can be carried out under two-phase conditions. The generation of the carbanions from 4 and 5 as well as the course of their reaction with carbonyl compounds were studied by the low temperature ³¹P NMR spectroscopy. It was found that S,S-thioacetals of formylphospbonates (4) are very easily metallated in contrast to O,S-thioacetals of formyl-phosphonates (5) which form the lithium derivatives only on treatment with t-butyllitnium. No evidence was obtained from ³¹P NMR spectra supporting the formation of the lithium derivatives of 0,0-acetals of formyl-phosphonates (12).     

Fingerprints of damped quantum rotation observed in solid-state proton NMR spectra.

(1)H NMR spectra of the methyl group in an oriented crystal sample of methylmalonic acid with all three non-methyl protons replaced by deuterons are interpreted in terms of the damped quantum rotation (DQR) theory of NMR line shapes. The DQR approach offers a perfect theoretical reproduction of the observed spectra while the conventional Alexander-Binsch line-shape model shows evident defects in the present case. The temperature trends of the quantities characterizing the coherent and incoherent dynamics of the methyl group in the DQR approach (the effective tunnelling frequency and two coherence-damping rates) derived from the spectra are fairly reproduced using a model reported previously. The present findings provide further evidence of limitations to the validity of the common belief that molecular rate processes in condensed phases are necessarily classical.     

Synthesis and Structural Analysis of Higher Analogs of Sucrose

ABSTRACT

Three sucrose monoalcohols with free hydroxyl groups at C-1', C-6, and C-6' (1, 4, and 6) were prepared selectively and in good yield from 2,3,3',4,4'-penta-O-benzylsucrose. These compounds were oxidized to aldehydes and reacted with stabilized ylide, Ph₃P=CHCO₂Me to afford appropriate α,β-unsaturated esters 10, 11, and 12. Each olefin was cis-hydroxylated with OsO₄/NMO to stereoisomeric diols 13/14, 15/16, and 17/18, configurations of which were assigned by chemical correlation and CD evaluation. Stereoselectivity of the osmylation reaction was surprisingly low (ca 3:2), especially as compared to a similar process performed on simple derivatives of 6,7-unsaturated methyl glycosides for which the ratio of isomeric diols was assigned as 10:1. The osmylation of 11 (derivative homologated by a C₂-unit at the glucose part) did not obey Kishi's rule. Horner-Emmons reaction of sucrose aldehyde 7 with a sugar-derived phosphonate 22 afforded α,β-unsaturated derivative 24, homologated by a C₇-unit at the glucose end.     

DMEA: a direction-based multiobjective evolutionary algorithm

A novel direction-based multi-objective evolutionary algorithm (DMEA) is proposed, in which a population evolves over time along some directions of improvement. We distinguish two types of direction: (1) the convergence direction between a non-dominated solution (stored in an archive) and a dominated solution from the current population; and, (2) the spread direction between two non-dominated solutions in the archive. At each generation, these directions are used to perturb the current parental population from which offspring are produced. The combined population of offspring and archived solutions forms the basis for the creation of both the next-generation archive and parental pools. The rule governing the formation of the next-generation parental pool is as follows: the first half is populated by non-dominated solutions whose spread is aided by a niching criterion applied in the decision space. The second half is filled with both non-dominated and dominated solutions from the sorted remainder of the combined population. The selection of non-dominated solutions for the next-generation archive is also assisted by a mechanism, in which neighborhoods of rays in objective space serve as niches. These rays originate from the current estimate of the Pareto optimal front??s (POF??s) ideal point and emit randomly into the hyperquadrant that contains the current POF estimate. Experiments on two well-known benchmark sets, namely ZDT and DTLZ have been carried out to investigate the performance and the behavior of the DMEA. We validated its performance by comparing it with four well-known existing algorithms. With respect to convergence and spread performance, DMEA turns out to be very competitive.     

119Sn NMR Spectra of Some Carbohydrate Organotin Derivatives

Abstract

The ¹¹⁹Sn NMR spectra of several sugar-tin derivatives were recorded. The geometric and steric isomers of all of the organotin derivatives studied were easily differentiated by ¹¹⁹Sn NMR. The appropriate ¹¹⁹Sn resonances are: ca - 50 ppm for trans and ?60 ppm for cis vinyltin derivatives (1-3), ca 16 ppm for allyltins 4-6, and ca ?32 ppm for tin-carbinols 9 and 11. When the hydroxyl group in carbinol 9 was converted to an O-acetyl group, the chemical shift of ¹¹⁹Sn was shifted to ?22 ppm.