OXIDATIVE DEPROTECTION OF TRIMETHYLSILYL ETHERS TO CARBONYL COMPOUNDS WITH PdCI2(PhCN)2-CrO3 AND CLAY-BIS(TRIMETHYLSILYL) CHROMATE IN SOLVENTLESS SYSTEM

Abstract

A simple and selective oxidative deprotection of trimethylsilyl ethers to carbony1 compounds is described that occurs on PdCl₂(PhCN)₂-CrO₃ and bis(trimethylsily1) chromate under solvent free conditions and is expedited by microwave irradiation.     

An Efficient One‐pot Access to Substituted Dihydropyrrol‐2‐one Derivatives Using Sucrose as Natural,Biodegradable and Inexpensive Catalyst

An efficient and simple procedure for the synthesis of highly substituted dihydropyrrol‐2‐ones has been developed via one‐pot four‐component condensation of amines, dialkyl acetylenedicarboxyaltes and formaldehyde in the presence of sucrose as an organocatalyst. The salient advantages of this method are using a natural, biodegradable and commercial available catalyst, good yields, short reaction times, simple work‐up and lack of need for column chromatography.     

DSC and elastic moduli studies on tellurite-vanadate glasses containing antimony oxide

xSb₂O₃-40TeO₂-(60 − x) V₂O₅ glasses with 0 ≤ x ≤ 10 (in mol%) have been prepared by rapid- melt quenching method. DSC curves of these ternary glasses have been investigated. The glass transition properties that have been measured and reported in this paper, include the glass transition temperature (T _g ), glass transition width (ΔT _g ), heat capacity change at glass transition (ΔC _P ) and fragility (F). Thermal stability, Poisson’s ratio, fragility and glass forming tendency of these glasses have been estimated, to determine relationship between chemical composition and the thermal stability or to interpret the structure of glass. In addition, Makishima and Makenzie’s theory was applied for determination of Young’s modulus, bulk modulus and shear modulus, indicating a strong relation between elastic properties and structure of glass. Generally, results of this work show that glass with x = 0 has the highest shear, bulk and Young’s moduli which make it as suitable candidate for the manufacture of strong glass fibers in technological applications; but it should be mentioned that glass with x = 8 has higher handling temperature and super resistance against thermal attack.     

Boronic acid hydrogen bonding in encapsulation complexes

Hydrogen bonding is a key determinant of much macromolecular structure in nature, but individual donor and acceptor pairs are rarely observed in solution. Their weak interactions result in nanosecond lifetimes and rapid exchange of partners. Reversible encapsulation isolates molecules in very small spaces for milliseconds to hours and allows their characterization by NMR methods. Here we report a competitive study of hydrogen-bonding functions--carboxylic acids, primary amides, and boronic acids--within a multicomponent capsular assembly. The pairwise co-encapsulation of these molecules allows the direct observation of homodimeric boronic acids and their heterodimeric complexes with carboxylic acids and primary amides. The efficiency of boronic acids as hydrogen-bonding partners derives from their adaptable structures rather than from their intrinsic acid/base properties.     

A nickel hydride complex in the active site of methyl-coenzyme m reductase: implications for the catalytic cycle

Methanogenic archaea utilize a specific pathway in their metabolism, converting C1 substrates (i.e., CO2) or acetate to methane and thereby providing energy for the cell. Methyl-coenzyme M reductase (MCR) catalyzes the key step in the process, namely methyl-coenzyme M (CH3-S-CoM) plus coenzyme B (HS-CoB) to methane and CoM-S-S-CoB. The active site of MCR contains the nickel porphinoid F430. We report here on the coordinated ligands of the two paramagnetic MCR red2 states, induced when HS-CoM (a reversible competitive inhibitor) and the second substrate HS-CoB or its analogue CH3-S-CoB are added to the enzyme in the active MCR red1 state (Ni(I)F430). Continuous wave and pulse EPR spectroscopy are used to show that the MCR red2a state exhibits a very large proton hyperfine interaction with principal values A((1)H) = [-43,-42,-5] MHz and thus represents formally a Ni(III)F430 hydride complex formed by oxidative addition to Ni(I). In view of the known ability of nickel hydrides to activate methane, and the growing body of evidence for the involvement of MCR in "reverse" methanogenesis (anaerobic oxidation of methane), we believe that the nickel hydride complex reported here could play a key role in helping to understand both the mechanism of "reverse" and "forward" methanogenesis.     

Exploring the Loading Capacity of Generation Six to Eight Dendronized Polymers in Aqueous Solution

Aspects of size, structural (im)perfection, inner density, and guest molecule loading capacity of dendronized polymers (DPs) of high generation (6≤g≤8) in aqueous solution are studied using electron paramagnetic resonance spectroscopy on amphiphilic, spin‐labeled guest molecules. The results show that the interior of the charged DPs is strongly polar, especially in comparison to their lower generation (1–4) analogues. This is a direct sign that large amounts of water penetrate the DP surface, reflecting the structural (im)perfections of these high‐generation DPs and much lower segmental densities than theoretically achievable. Images obtained with atomic force microscopy reveal that the high‐generation DPs do not aggregate and give further insights into the structural imperfections. Electron paramagnetic resonance spectroscopic data further show that despite their structural imperfections, these DPs can bind and release large numbers of amphiphilic molecules. It is concluded that attention should be paid to their synthesis, for which a protocol needs to be developed that avoids the relatively large amount of defects generated in the direct conversion of a generation g=4 DP to a generation g=6 DP, which had to be used here.     

Optimization of an HPLC method for determination of gabapentin in dosage forms through derivatization with 1-fluoro-2,4-dinitrobenzene

A rapid, sensitive and accurate high performance liquid chromatography with UV detection method was developed and validated for the quantification of gabapentin in dosage forms. Gabapentin was quantified after pre-column derivatization with 1-fluoro-2,4-dinitrobenzene. Amlodipine was used as an internal standard. The chromatographic separation was carried out on a Nova-Pak C(18) column using a mixture of acetonitrile-sodium dihydrogenphosphate (pH 2.5; 0.05 M) (70:30, v/v) as mobile phase with UV detection at 360 nm. The method was linear over the range of 10-500 microg/ml of gabapentin (r(2)>0.999). The within-day and between-day precision values were in the range of 0.86-1.11%. The method was successfully used for quantitative determination and dissolution rate study of Neurontin capsules.     

The effect of electrospinning parameters on the compliance behavior of electrospun polyurethane tube for artificial common bile duct

The present research introduced a method to produce an artificial common bile duct using electrospinning technique. Also, the effect of electrospinning variables on the mechanical properties of produced prostheses is investigated. Using electrospinning of polyurethane nanofibres, cylindrical prostheses were produced on a rotating mandrel considering the different controllable factors such as the mandrel rotational speed, the applied voltage, and the flow rate of polymer solution. Taguchi method was used to investigate the effect of mentioned factors on the compliance of circular prostheses. MTT assay was performed to study the cytotoxicity of prostheses. The results of the signal-to-noise analysis showed that the mandrel rotational speed factor has the strongest effect on the compliance values. The flow rate was the second factor and it was followed by electrospinning voltage. In addition, the optimum conditions to reach the highest compliance value were determined. The results of MTT assay indicated no cytotoxic effects of prostheses on the cells. The compliance of optimum prosthesis was found close to the compliance value of a native common bile duct.