Thermal decomposition of iron(II) sulphate heptahydrate in air in the presence of basic magnesium carbonate

Results on the thermal decomposition of iron(II) sulphate heptahydrate in the presence of basic magnesium carbonate are presented and discussed. These results are compared with those for the mixture of iron(II) sulphate heptahydrate with basic beryllium carbonate. While no reaction occurs between the components in the case of basic beryllium carbonate, basic magnesium carbonate reacts readily with iron(II) sulphate heptahydrate.

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Zusammenfassung Bei der in Gegenwart von basischem Magnesiumcarbonat erfolgten thermischen Zersetzung von Eisen(II)-sulfat-Heptahydrat erhaltene Ergebnisse werden beschrieben, diskutiert und mit denen verglichen, die in Gegenwart von Berylliumcarbonat erhalten wurden. Im Gegensatz zu basischem Berylliumcarbonat reagiert basisches Magnesiumcarbonat mit Eisen(II) sulfat-Heptahydrat.

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The author gratefully acknowledges the support extended by Professor P. K. Jena, Director of this laboratory, and the permission to publish the results.     

Attracting cavities for docking. Replacing the rough energy landscape of the protein by a smooth attracting landscape

Molecular docking is a computational approach for predicting the most probable position of ligands in the binding sites of macromolecules and constitutes the cornerstone of structure‐based computer‐aided drug design. Here, we present a new algorithm called Attracting Cavities that allows molecular docking to be performed by simple energy minimizations only. The approach consists in transiently replacing the rough potential energy hypersurface of the protein by a smooth attracting potential driving the ligands into protein cavities. The actual protein energy landscape is reintroduced in a second step to refine the ligand position. The scoring function of Attracting Cavities is based on the CHARMM force field and the FACTS solvation model. The approach was tested on the 85 experimental ligand–protein structures included in the Astex diverse set and achieved a success rate of 80% in reproducing the experimental binding mode starting from a completely randomized ligand conformer. The algorithm thus compares favorably with current state‐of‐the‐art docking programs. © 2015 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.     

In vitro hydrolytic degradation of poly(?-caprolactone) grafted dextran fibers and films

We studied the hydrolytic degradation of poly(?-caprolactone) grafted dextran (PGD) fibers and films (matrices) prepared by electrospinning and solvent evaporation methods, respectively. In vitro degradation and erosion experiments were carried out in phosphate buffered saline (pH 7.4 ± 0.1) at 37 ± 1 °C for 150 days. Changes in molecular weights and morphologies of the PGD matrices were monitored as a function of degradation time. The extent of degradation was measured by physical weight loss, scanning electron microscopic (SEM) observations, Fourier transform-infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). During the progress of hydrolysis, GPC chromatograms appeared bi modal for fibers and bi and trimodal for the films. The crystallization temperature (T_c) and heat of fusion were significantly increased in both matrices; this indicated preferential hydrolytic degradation in amorphous regions followed by cleavage-induced crystallization. The biodegradation rates were faster for the films (28%) than fibers (23%). After 150 days of degradation, the pH was steady at 5.8 ± 0.3 for fibers and 6.1 ± 0.3 for films. The faster degradation of the films could be probably due to autocatalysis in the interior of the films and the degraded oligomers are hard to diffuse out into the surrounding solution due to its compact physical geometry. Thus, our preliminary results about the degradation of matrices suggested that PGD nanofibers could be excellent matrices in tissue engineering over the films.     

Stereoselective functionalisation of SuperQuat enamides: asymmetric synthesis of homochiral 1,2-diols and α-benzyloxy carbonyl compounds

Homochiral (E)- and (Z)-enamides derived from SuperQuat (S)-4-phenyl-5,5-dimethyl-oxazolidin-2-one undergo highly diastereoselective epoxidation upon treatment with dimethyldioxirane. Subsequent epoxide opening with meta-chlorobenzoic acid proceeds via a stereoselective S_N1-type process, with retention of configuration, to give the corresponding 1′-m-chlorobenzoyl-2′-hydroxy derivatives. Treatment of the SuperQuat enamides with mCPBA effects this two-step transformation in one pot. Reductive cleavage of the isolated 1′-m-chlorobenzoyl-2′-hydroxy derivatives (≥96% de) generates homochiral 1,2-diols in ≥96% ee. Alternatively, regioselective lithiation of the enamide at C(1′) with ^tBuLi followed by reaction with an aromatic aldehyde and in situ O-benzylation generates a 1′-(benzyloxy-aryl-methyl) substituted enamide with high diastereoselectivity. Subsequent oxidative cleavage of the enamide CC bond with NaIO₄/RuCl₃ followed by methanolysis of the resultant N-acyl fragment furnishes an O-benzyl protected α-hydroxy methyl ester in high ee.     

Application of microwave method to the solid phase synthesis of pseudopeptides containing ester bond

A new procedure was developed for reducing the reaction time and improving the yield of esterification reaction in solid phase synthesis of pseudopeptides containing an ester bond by utilizing microwave irradiation. We selected a pseudodipeptide (Fmoc-LysΨ[COO]Leu-NH₂) and optimized the microwave-assisted esterification reaction in solid phase synthesis using Fmoc chemistry. For this, microwave-assisted esterification reactions with different reaction time, temperature, and solvents were performed using 1,3-diisopropylcarbodiimide (DIC) as the coupling reagent. We synthesized several pseudodipeptides containing an ester bond by using the optimized microwave irradiation method. The purity and yield of the pseudodipeptides synthesized in this way were better than those obtained without microwave irradiation. Furthermore, we applied this methodology for synthesizing pseudopeptides (6- and 12-mer) corresponding to the α helical peptide. The microwave-assisted esterification reaction afforded the target pseudopeptides with high yield (∼80%) and purity within 12 min, whereas the reaction without microwave irradiation afforded the target compound with poor yield (∼45%) and low purity.     

Microwave-assisted, Mo(CO)6-mediated, palladium-catalyzed amino-carbonylation of aryl halides using allylamine: from exploration to scale-up

Palladium-catalyzed aminocarbonylations of various (hetero)aryl halides with allylamine using Mo(CO)₆ as a solid, in situ CO source, were explored. Microwave-enhanced conditions proved to be highly useful in promoting the conversions in a mere 10-20 min with various (hetero)aryl iodides, bromides and chlorides. The scale-up of a microwave-enhanced aminocarbonylation to 25 mmol scale was performed successfully.     

Fatty Acid Profiling During Microbial Lipid Production Under Varying pO2 and Impeller Tip Speeds

The fatty acid profile study was undertaken to study the effect of impeller tip speed-associated shear stress and dissolved oxygen saturation (DO) on the fatty acid composition variation and on total lipid content of the cells. The study was undertaken in a 5-l stirred tank bioreactor using Mucor sp. RRL001. To study the interaction of parameters and their effects, a central composite design was used. The fatty acid profiling during the course of study suggested that oleic acid and palmitic acid were two major components with their composition varying between 34-47% and 29-39.1%, respectively, of the total lipid content. The GLA content varied between 3% and 9% of the total lipid. The lipid profile study also revealed the presence of a minor amount of fatty acids of chain length C:12, C:20, C:22, and C:24. The modeling of lipid accumulation suggested that it follows a quadratic model with both impeller tip speed (p = 0.0166) and dissolved oxygen concentration (p = 0.0098) following the quadratic order of effect. The fermenter run based on the optimum production zone in response surface plot resulted in the maximum 4.8 g l(-1) lipid compared with the model-predicted value of 4.49 g l(-1). The present study suggests that dissolved oxygen saturation is a more significant contributor to total lipid accumulation. However, the study also suggests that the fatty acid profile of fungal lipid is not directly associated with the shear stress or oxygen availability in Mucor sp. RRL001.     

Mechanistic study of samarium diiodide-HMPA initiated 5-exo-trig Ketyl-Olefin coupling: the role of HMPA in post-electron transfer steps

The mechanistic importance of HMPA and proton donors (methanol, 2-methyl-2-propanol, and 2,2,2-trifluoroethanol) on SmI2-initiated 5-exo-trig ketyl-olefin cyclizations has been examined using stopped-flow spectrophotometric studies. In the presence of HMPA, the rate order of proton donors was zero and product studies showed that they had no impact on the diastereoselectivity of the reaction. Conversely, reactions were first-order in HMPA, and the additive displayed saturation kinetics at high concentrations. These results were consistent with HMPA being involved in a rate-limiting step before cyclization, where coordination of the intermediate ketyl to the sterically congested Sm(III)HMPA both stabilizes the intermediate and inhibits cyclization. Liberation of the contact ion pair through displacement by an equivalent of HMPA provides a solvent-separated ion pair releasing the steric constraint to ketyl-olefin cyclization. The mechanism derived from rate studies shows that HMPA is important not only in increasing the reduction potential of Sm(II) but also in enhancing the inherent reactivity of the radical anion intermediate formed after electron transfer through conversion of a sterically congested contact ion pair to a solvent-separated ion pair. The mechanistic complexity of the SmI2-HMPA-initiated ketyl-olefin cyclization is driven by the high affinity of HMPA for Sm(III), and these results suggest that simple empirical models describing the role of HMPA in more complex systems are likely to be fraught with a high degree of uncertainty.     

Dielectrophoresis and AC-induced assembly in binary colloidal suspensions

Dielectrophoretic behaviors and assembly of a binary suspension in aqueous media are examined in the presence of nonuniform alternating current (AC) electric field. A peculiar low-frequency threshold and dielectrophoresis (DEP) crossover frequency determine the applicable frequency window for binary assembly under positive DEP, which can be effectively tuned by medium conductivity and particle size, suggesting that the dynamic double-layer effect is responsible for the interfacial polarization of micrometer to submicrometer-sized particles in aqueous suspensions. Strong effects of AC-field frequency, medium conductivity, and size ratio on binary assembly morphology have been observed. A frequency-medium conductivity phase diagram is obtained to illustrate the morphological transition of assembled colloidal aggregates from segregated, ordered assemblies to inverted segregation with the appearance of amorphous phases upon increasing frequency and/or medium conductivity, which is a direct consequence of the competition between DEP and hydrodynamic mobility. Significantly, our results demonstrate a rapid method to form hybrid nanostructured materials.