A minimalist NMR approach for the structural revision of mucoxin

In an attempt to revise the structural assignment of mucoxin, and faced with 64 diastereomeric possibilities, we resorted to the synthesis of truncated structures that contained the core stereochemical sites. Twelve stereochemical analogues were synthesized, their (1)H and (13)C NMR spectra were analyzed and four recurring stereochemical trends were distilled from the data. Applying the observed trends to the diastereomeric population pared the possible choices for the correct structure of mucoxin from 64 to 4. Synthesis of these analogues led to the identification of the correct structure of mucoxin.     

Selective oxidation of sulfides to sulfoxides using 30% hydrogen peroxide catalyzed with a recoverable silica-based tungstate interphase catalyst

Various types of aromatic and aliphatic sulfides are selectively oxidized to sulfoxides and sulfones in good to excellent yields using 30% H2O2 in the presence of catalytic amounts of a novel recoverable silica-based tungstate interphase catalyst at room temperature. The catalyst can be recovered and reused for at least eight reaction cycles under the described reaction conditions without considerable loss of reactivity. [reaction: see text]     

Aqueous solutions of ionic liquids: study of the solution/vapor interface using molecular dynamics simulations

We performed a detailed molecular dynamics study of the interfacial structure of aqueous solutions of 1-butyl-3-methylimidazolium tetrafluoroborate in order to explain the anomalous dependence of the surface tension on concentration. At low concentrations the surface tension decreases with concentration. At higher concentrations the surface becomes saturated; a plateau is observed in simulations with a non-polarizable force field while a possible increase is detected in simulations with a polarizable force field. The structure is characterized by a surplus of cations at the surface (with hydrophobic butyl chains pointing toward vacuum) which at low concentrations is only partly compensated by the anions because of asymmetric solvation. A more hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate is also simulated for comparison.     

A Proline-Based Aminophosphinic Acid Ligand and It’s Vanadyl Complex: Synthesis,Characterization and In Vitro Inhibitory Effects on α-Amylase And α-Glucosidase

Abstract

A proline-based aminophosphinic acid ligand and it's vanadium complex have been synthesized and characterized by spectroscopic techniques. The inhibitory activity on pancreatic α-amylase and Baker's yeast α-glucosidase has been examined in vitro. The novel complex showed more inhibitory potency against pancreatic α-amylase and Baker's yeast α-glucosidase compared to acarbose as an antidiabetic drug.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Defect capture under rapid solidification of the melt induced by the action of femtosecond laser pulses and formation of periodic surface structures on a semiconductor surface

A theory of defect-strain instability with formation of periodic surface relief in semiconductors irradiated by ultra-short (τ_p=10^-13 s) powerful laser pulses is developed. The period and time of formation of surface relief are calculated. Regimes of multi-pulse laser ablation leading to formation of either a smooth surface or arrays of surface-relief spikes are pointed out and corresponding experimental results are interpreted from the viewpoint of the developed theory. Received: 4 December 2000 / Accepted: 23 July 2001 / Published online: 11 February 2002     

2, 4, 6-Trichloro-1, 3, 5-triazine/dimethylformamide as an efficient reagent for one-pot conversion of alcohols into N-alkylphthalimides

<正>An efficient and mild method for the direct conversion of alcohols into N-alkylphthalimides using 2,4,6-trichloro-1,3,5-triazine and dimethylformamide was described.The reaction was preceded via(alcoxymethylene) dimethylammonium chloride intermediate and produced corresponding N-alkylphthalimides in good-to-excellent yields.     

A novel and simple method for the preparation of (R)- and (S)-pyrrolidine-2-phosphonic acids: phosphonic acid analogues of proline

A simple and convenient method has been developed for the preparation of (R)- and (S)-pyrrolidine-2-phosphonic acids. The thermal reaction of proline with diethyl phosphite in the presence of benzaldehyde gave an N-benzyl derivative of diethyl pyrrolidine-2-phosphonate, which was transformed into two diastereomeric amides by sequential debenzylation and acylation with (+)-dibenzoyl-l-tartaric anhydride. The two diastereomeric amides were separated by column chromatography and the structure of one of them was determined by X-ray crystallographic analysis. Hydrolysis of the amides in the usual manner afforded (R)- and (S)-pyrrolidine-2-phosphonic acids. The advantages of the present method are that it is easy, rapid, and prepares both enantiomers of pyrrolidine-2-phosphonic acids.     

β-Cyclodextrin as an efficient catalyst for the one-pot synthesis of 1-aminophosphonic esters in water

A simple, efficient, and general method has been developed for the one-pot synthesis of α-aminophosphonic esters in water using β-cyclodextrin as an efficient catalyst. α-Aminophosphonic esters were obtained in good yields (45-82%) and purity under mild conditions by the reaction of diethyl phosphite with a mixture of aldehyde and amine in water at reflux.     

Separation performance of foils from Pd—In(6%)—Ru(0.5%), Pd—Ru(6%), and Pd—Ru(10%) alloys and influence of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript>, and water vapor on the H<Subscript>2</Subscript> flow rate through the test membranes

The H₂ flow rate through the 30-μm thick foil from Pd—Ru(6%) and Pd—Ru(10%) alloys at 673 and 773 K was found to be controlled by the diffusion of H atoms in the foil bulk. The interrelation between hydrogen permeability through the Pd—In(6%)—Ru(0.5%), Pd—Ru(10%), Pd—Ru(6%), and Pd—Ag(23%) membranes and the permeability pre-exponential factors in the Sieverts equation in the 573—773 K temperature interval indicated that the hydrogen permeability depended on the structural characteristics of palladium alloys. The influence of the CO₂, CH₄, and water vapor impurities on the H₂ flow rate through the studied membranes depended on the driving force nature (the sweep gas or transmembrane pressure) used for the development of the partial hydrogen pressure difference across the membrane. The negative influence of CH₄ and CO₂ was observed only when using a transmembrane pressure and at the impurity content of 20% or more. This effect increased with increasing temperature in the 573—773 K range, with the influence of CO₂ being more pronounced due to its reaction with hydrogen leading to the formation of CO. The influence of water vapor was studied at its 11—23% content in hydrogen and at 573 and 773 K of temperature. The negative influence of water vapor was found to subside as its content in the hydrogen mixture decreased and the temperature increased. It was shown that water vapor can be used as a sweep gas and at T = 773 K its influence on the H₂ flow rate through the membrane was almost the same as that of N₂.     

Kinetics of the Initial Stage of Gelation in Chitosan Solutions Containing Glutaric Aldehyde: Viscometric Study

The effects of glutaric aldehyde concentration C _GA(in the range from 0.07 to 0.2 wt %) and temperature T(from 20 to 65°C) on the kinetics of an increase in the effective viscosity _effof aqueous solutions of chitosans (C _CH= 2.4 wt %, pH 3.6, and ionic strength I= 0.05) with molecular masses equal to 33 × 10⁴and 55 × 10⁴and the degrees of substitution at N-acetyl and amino groups of 0.08 and 0.90, respectively were studied. The kinetic curves _eff(t) exhibited the induction periods of a relatively slight increase in the viscosity of chitosan–glutaric aldehyde mixed solutions with time followed by the periods of a drastic increase in the viscosity. The former periods correspond to the formation of gel clusters; the latter periods, to the gelation over the whole volume of a solution. Optimal ranges of the parameters C _GAand Twere determined for the preparation of spherical gel particles of slightly cross-linked chitosan, which are used for the sorption of heavy metals from low-concentrated solutions.