Synthesis and novel reactivity of halomethyldimethylsulfonium salts

Iodomethyl-, chloromethyl-, and fluoromethyldimethylsulfonium salts, 4b-d, have been synthesized and are observed to be highly reactive molecules that exhibit extraordinary diversity with respect to the nature of their reactivity, undergoing facile direct substitution (S(N)2) reactions, but also being highly susceptible to electron-transfer reactions. Cyclic voltametry experiments indicated that the iodomethyldimethylsulfonium compound, 4b, is a potent electron acceptor, even surpassing the reactivity of perfluoro-n-alkyl iodides in that capacity. The iodo- and chloromethyldimethylsulfonium salts, 4b,c, as well as the analogous iodomethyltrimethylammonium salt, 3a, are shown to be reactive SET acceptors.     

Extended DLVO calculations expose the role of the structural nature of the adsorbent beads during chromatography

Protein adsorption onto hydrophobic interaction chromatography supports was studied by a surface-thermodynamics approach. To gather relevant experimental information, contact angle measurements and zeta potential determinations were performed on three different commercial adsorbent beads, Phenyl Sepharose 6 Fast Flow, Toyopearl Phenyl 650-C and Source 15 Phenyl, having soft to rigid backbone structure. Similar information was obtained for a collection of model proteins, lysozyme, bovine serum albumin (BSA), polygalacturonase, aminopeptidase, chymosin, aspartic protease, beta-galactosidase, human immunoglobulin G, and lactoferrin, were evaluated in the hydrated and in the dehydrated state. Based on the mentioned experimental data, calculations were performed to obtain the (interfacial) energy versus distance profiles of nine individual (model) proteins on (commercial) beads of three different types. All of these beads harbored the phenyl-ligand onto a matrix of differentiated chemical nature. Extended Derjaguin, Landau, Verwey, and Overbeek (DLVO) calculations were correlated with actual chromatographic behavior. Typical chromatography conditions were employed. The population of model proteins utilized in this study could be segregated into two groups, according to the minimum values observed for the resulting interaction energy pockets and the corresponding retention volumes (or times) during chromatography. Moreover, trends were also identified as a function of the type of adsorbent bead under consideration. This has revealed the influence of the physicochemical nature of the bead structure on the adsorption process and consequently, on the expected separation behavior.     

Development of a simultaneous liquid-liquid extraction and chiral derivatization method for stereospecific GC-MS analysis of amphetamine-type stimulants in human urine using fractional factorial design

A stereospecific gas chromatography-mass spectrometry analysis method for amphetamine-type stimulants in human urine was recently developed. For maximum efficiency, liquid-liquid extraction and chiral derivatization of the analytes using (R)-(-)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl chloride were performed simultaneously. The effects of (1) use of saturated sodium chloride in 2.0 m sodium hydroxide, (2) extraction solvent volume, (3) percentage of triethylamine, (4) derivatization reagent volume, (5) sample mixing time, (6) incubation temperature and (7) incubation time on method sensitivity and variability were assessed using a two-level, eight-run Plackett-Burman design followed by a fold-over design. The use of saturated sodium chloride solution and the derivatization reagent volume were significant factors (ANOVA, p < 0.01). The saturated sodium chloride solution decreased sensitivity whereas an increased volume of derivatization reagent increased sensitivity. Calibration curves for all analytes were linear between 5 and 500 microg/L, with correlation coefficients of >0.99. Detection limits were 相似文献   

α-Glucosidase, α-Amylase and Antioxidant Evaluations of Isolated Bioactives from Wild Strawberry

Diabetes mellitus is a metabolic disorder and is a global challenge to the current medicinal chemists and pharmacologists. This research has been designed to isolate and evaluate antidiabetic bioactives from Fragaria indica. The crude extracts, semi-purified and pure bioactives have been used in all in vitro assays. The in vitro α-glucosidase, α-amylase and DPPH free radical activities have been performed on all plant samples. The initial activities showed that ethyl acetate (Fi.EtAc) was the potent fraction in all the assays. This fraction was initially semi-purified to obtain Fi.EtAc 1–3. Among the semi-purified fractions, Fi.EtAc 2 was dominant, exhibiting potent IC₅₀ values in all the in vitro assays. Based on the potency and availability of materials, Fi.EtAc 2 was subjected to further purification to obtain compounds 1 (2,4-dichloro-6-hydroxy-3,5-dimethoxytoluene) and 2 (2-methyl-6-(4-methylphenyl)-2-hepten-4-one). The two isolated compounds were characterized by mass and NMR analyses. The compounds 1 and 2 showed excellent inhibitions against α-glucosidase (21.45 for 1 and 15.03 for 2 μg/mL), α-amylase (17.65 and 16.56 μg/mL) and DPPH free radicals (7.62 and 14.30 μg/mL). Our study provides baseline research for the antidiabetic bioactives exploration from Fragaria indica. The bioactive compounds can be evaluated in animals-based antidiabetic activity in future.     

A Simple and Fast Aqueous‐Phase Synthesis of Ultra‐Highly Concentrated Silver Nanoparticles and Their Catalytic Properties

A simple and fast synthetic route to ultra‐highly concentrated silver nanoparticles with long‐term stability by reducing AgNO₃ with ascorbic acid in the presence of polyethyleneimine (PEI) as a stabilizer in an aqueous phase is reported. The concentration of silver precursor was as high as 2000 mm (200 g of Ag nanoparticle per liter of water) and the reaction time was less than 10 min. The resulting silver nanoparticles show long‐term stability after two months of storage at room temperature without any signs of particle aggregation or precipitation in an aqueous phase. The successful ligand exchange of PEI‐stabilized silver nanoparticles to polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) without particle aggregation is also demonstrated. In addition, the catalytic activities of silver nanoparticles stabilized by various stabilizers prepared by the ligand exchange method was investigated. The PEI‐stabilized silver nanoparticles exhibited a higher stability than those of PEG‐ and PVP‐stabilized silver nanoparticles in the diffusion‐controlled catalytic reduction of 4‐nitrophenol to 4‐aminophenol by NaBH₄.     

Synthesis of new boswellic acid derivatives as potential antiproliferative agents

Abstract

In the current investigation, a series of heterocyclic derivatives of boswellic acids were prepared along with new monomers of 3-O-acetyl-11-keto-β-boswellic acid (AKBA, 1) 11-keto-β-boswellic acid (KBA, 2) and several new bis-AKBA and KBA homodimers and AKBA-KBA heterodimers. The effects of these compounds on the proliferation of different human cancer cell lines, viz., FaDu (pharynx carcinoma), A2780 (ovarian carcinoma), HT29 (colon adenocarcinoma), and A375 (malignant melanoma), have been evaluated. Thus, KBA homodimer 21 effectively inhibited the growth of FaDu, A2780, HT29, and A375 cells with EC₅₀ values below 9?μM. In addition, compounds 7, 8, 11, 12, 15, 16, and 17 also exhibited cytotoxic effects for A2780, HT29, and A375 cancer cells. In particular, the pyrazine analog 8 was highly cytotoxic for A375 cancer cells with an EC₅₀ value of 2.1?μM.     

The single-mode rate equations for semiconductor lasers with thermal effects

A mathematical model describing the coupling of electrical,optical and thermal effects in semiconductor lasers is introduced.Numerical and asymptotic solutions are derived, including expressionsfor key physical quantities such as the initial time delay,the frequency of spike oscillation and the temperature rise,together with its influence on the photon density, the electronconcentration and the threshold current. The consequences ofthermal effects in reducing efficiency are thus quantified.     

On <Emphasis Type="Italic">g</Emphasis>-functions for Laguerre function expansions of Hermite type

We examine weighted L ^p boundedness of g-functions based on semigroups related to multi-dimensional Laguerre function expansions of Hermite type. A technique of vector-valued Calderón–Zygmund operators is used.