Manganese complexes as models for manganese-containing pseudocatalase enzymes: Synthesis,structural and catalytic activity studies

Manganese complexes of the type [TpMn(X)] and [TpMn(μ-N₃)(μ-X)MnTp] (X = acetylacetonate, acac; picolinate, pic and Tp = Tp^Ph,Me for acac, Tp = Tp^ipr2 for pic complexes) having Tp^Ph,Me (hydrotris(3-phenyl,5-methyl-pyrazol-1-yl)borate)/Tp^ipr2 (hydrotris(3,5-diisopropyl-pyrazol-1-yl)borate) as a supporting ligand have been synthesized and structurally characterized. IR and X-ray structures suggest that complexes 7 and 9 are binuclear with azido and bidentate ligands (acac/pic) bridging, whereas complexes 6 and 8 are mononuclear with a 5-coordinated metal center. In complex 9 the picolinate is coordinated as tridentate in a η₃-fashion, but in complex 7 acac behaves as bidentate, whereas azide is coordinated in a bridging bidentate μ-1,3-manner in both 7 and 9. Since the coordination geometry of the manganese ions in complex 9 is very similar to the active site structure of manganese-containing pseudocatalase, we have tested the catalytic activity of the same towards the disproportionation of hydrogen peroxide. The catalytic results indicated that complex 9 has reasonably good catalase activity and may be suitable, structurally as well as functionally, as a model for the pseudocatalase enzyme.     

Load Extraction from Photoelastic Images Using Neural Networks

Photoelastic materials develop colored fringes under white light when subjected to mechanical stresses, which can be viewed through a polariscope. This technique has traditionally been used for stress analysis of loaded components, however, this can also be potentially used in sensing applications where the requirement may be measurement of the stimulating forces causing the generation of fringes. This leads to inverse photoelastic problem where the developed image can be analyzed for the input forces. However, there could be infinite number of possible solutions which cannot be determined by conventional techniques. This paper presents neural networks based approach to solve this problem. Experiments conducted to prove the principle have been verified with theoretical results and finite element analysis of loaded specimens. The developed technique, if generalized, can be implemented for whole-field analysis of the stress patterns involving complex fringes under different loading conditions. This can also provide direct visualization of the stress field, which may find application in a variety of specialized areas including biomedical engineering and robotics.

Experimental study on isotope fractionation of evaporating water of different initial isotopic composition

The studies of evaporative isotopic fractionation in controlled conditions are of particular importance for understanding the mechanism of evaporation fractionation in natural conditions. We present the measurements of the average isotopic fractionation factors during the evaporation of water having different initial isotopic compositions at constant temperature. The results show that the isotopic composition of residual water become more enriched over the time and the initial isotopic composition of evaporating water has considerable effect on the average isotopic fractionation factors. The average isotopic fractionation factors in evaporation of Water A and Water B under the present experimental conditions were found to be 0.9817 ± 0.0044 and 0.9887 ± 0.0031 for oxygen and 0.9178 ± 0.0182 and 0.9437 ± 0.0169 for hydrogen, respectively. The findings of this work should lead to a better understanding and use of stable isotope techniques in isotope hydrology by using a simple technique of evaporation pan.     

1,8‐Diazabicyclo[5.4.0]undec‐7‐ene: A Highly Efficient Catalyst for One‐Pot Synthesis of Substituted Tetrahydro‐4H‐chromenes,Tetrahydro[b]pyrans,Pyrano[d]pyrimidines,and 4H‐Pyrans in Aqueous Medium

We have reported 1,8‐diazabicyclo[5.4.0]undec‐7‐ene catalyzed one‐pot synthesis of tetrahydro‐4H‐chromenes, tetrahydro[b]pyrans, pyrano[d]pyrimidines and 4H‐pyrans from aldehydes, active methylene compounds malononitrile/ethyl cyanocacetate and activated C–H acids such as dimedone, 1,3‐cyclohexanedione, 1,3‐cyclopentanedione, 1,3‐dimethylbarbituric acid, and ethyl acetoacetate in water under reflux. The attractive features of this process are mild reaction conditions, reusability of the reaction media, short reaction times, easy isolation of products, and excellent yields. Copyright © 2013 HeteroCorporation     

Lanthanum Triflate–Catalyzed Rapid Oxidation of Secondary Alcohols Using Hydrogen Peroxide Urea Adduct (UHP) in Ionic Liquid

A convenient and efficient protocol for the oxidation of secondary hydroxyl group to ketone using hydrogen peroxide–urea adduct and catalytic (CF₃SO₃)₃La in ionic liquid has been developed. A number of 1,2-diols, α-hydroxyketones, and other aromatic and aliphatic secondary alcohols have been successfully oxidized to the corresponding ketones using this protocol in good yields and short reaction times.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

High-pressure behaviour and elastic properties of heavy rare-earth Gd monopnictides

Pressure-induced structural phase transition of gadolinium monopnictides GdX (X=As and Sb) has been studied theoretically using an inter-ionic potential theory. This method has been found quite satisfactory in case of the pnictides of rare-earth and describes the crystal properties in the framework of rigid-ion model. We have modified the ionic charge so that it may include the Coulomb-screening effect by the delocalization of f electron of the rare-earth ion. The anomalous structural properties of these compounds with many f electrons have been interpreted in terms of the hybridization of f electrons with the conduction band and strong mixing of f states of Gd ion with the p orbital of neighbouring pnictogen ion. Both the compounds are found to undergo from their initial NaCl (B₁) structure to body centered tetragonal (BCT) structure at high pressure and agree well with the experimental results. The BCT structure is viewed as distorted CsCl structure and is highly anisotropic with c/a=0.82–0.85. The nature of bonds between the ions is predicted by simulating the ion–ion (Gd–Gd and Gd–X) distance at high pressure. Elastic properties of these compounds have also been studied with their second-order elastic constants.