Nickel(II)-Mediated Reversible Thiolate/Disulfide Conversion as a Mimic for a Key Step of the Catalytic Cycle of Methyl-Coenzyme M Reductase

According to the well-accepted mechanism, methyl-coenzyme M reductase (MCR) involves Ni-mediated thiolate-to-disulfide conversion that sustains its catalytic cycle of methane formation in the energy saving pathways of methanotrophic microbes. Model complexes that illustrate Ni-ion mediated reversible thiolate/disulfide transformation are unknown. In this paper we report the synthesis, crystal structure, spectroscopic properties and redox interconversions of a set of Ni^II complexes comprising a tridentate N₂S donor thiol and its analogous N₄S₂ donor disulfide ligands. These complexes demonstrate reversible Ni^II-thiolate/Ni^II-disulfide (both bound and unbound disulfide-S to Ni^II) transformations via thiyl and disulfide monoradical anions that resemble a primary step of MCR's catalytic cycle.     

Unusual Surface Latent Heat Flux Variations and Their Critical Dynamics Revealed before Strong Earthquakes

We focus on the possible thermal channel of the well-known Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) mechanism to identify the behavior of thermal anomalies during and prior to strong seismic events. For this, we investigate the variation of Surface Latent Heat Flux (SLHF) as resulting from satellite observables. We demonstrate a spatio-temporal variation in the SLHF before and after a set of strong seismic events occurred in Kathmandu, Nepal, and Kumamoto, Japan, having magnitudes of 7.8, 7.3, and 7.0, respectively. Before the studied earthquake cases, significant enhancements in the SLHF were identified near the epicenters. Additionally, in order to check whether critical dynamics, as the signature of a complex phenomenon such as earthquake preparation, are reflected in the SLHF data, we performed a criticality analysis using the natural time analysis method. The approach to criticality was detected within one week before each mainshock.     

Electro‐optical cells using a cellulose derivative and cholesteric liquid crystals

A cellulose derivative/liquid crystal composite‐type electro‐optical cell using a commercial cholesteric liquid crystal (CLC) was investigated. The electro‐optical properties of the system were examined, i.e. the dependence on applied voltage of the reflected wavelength and the minimum and maximum transmissions. A thin film of the CLC was dispersed with a cross‐linked cellulose film of 25 µm thickness. In the voltage dependence of the reflected wavelength it was verified that there is a hysteresis in the reflected wavelength. The variation of the reflected wavelength with temperature was also determined. The results are analysed in the framework of similar systems described in the literature for CLC dispersed in a polymer matrix.     

Magnesium-induced regiospecific C-silylation of suitably substituted enoates and dienoates

The β-aryl-β-silyl and β,β-disilyl propionates have been synthesized from cinnamates and β-silyl acrylates by a regiospecific reductive C-silylation using Mg/silyl chloride/DMF system at room temperature. These reductive C-silylation conditions have also been applied to δ-aryl substituted dienoates wherein silylation took place at the δ-position leading to the synthesis of single regioisomeric allylsilanes with very high stereoselectivity.     

A study of self-quenching of lyoluminescence yield from gamma-irradiated saccharides and amino acids

Tissue equivalent (TE) lyoluminescence (LL) dosimetry requires practical amount of phosphor for dissolution, typically 5-30 mg. Pronounced mass quenching effect has been observed even in the region of 5 mg, in the cases of LL of lactose-monohydrate, d-glucose, d-mannose, raffinose, sucrose and 1-glutamine. Ordinary concentration-quenching is non-existent but yield per mg falls rapidly with increasing mass of the phosphor. The curves have been fitted with a self-absorption type formula. A well-recognised dose effect is present in quenching curves. The role of free radicals at high radiation doses has been discussed in the contribution of dose effect in quenching.     

Investigation of the solid phase synthesis of tyrosine‐derived diphenol monomers with resin‐bound carbodiimide coupling reagents

Tyrosine‐derived pseudo‐polypeptides have recently been established as potential biomaterials. The bulk production of these polymers is dependant upon the convenient synthesis of tyrosine‐derived diphenolic monomers. Suitable solution phase methods for the synthesis of such monomers, with transient activated esters, have been reported previously by Kohn, J.; Langer, R. In Biomaterials Science: An Introduction to Materials in Medicine; Ratner, B. D.; Hoffman, A. S.; Schoen, F. J.; Lemons, J. E., Eds.; Academic Press: New York, 1996; pp 64–72. However, for all the methods reported by them, purification and isolation of the diphenol monomer involves rigorous extraction, column purification, or an extensive aqueous workup. These may lead to the incorporation of solvent‐based as well as inorganic impurities and also may lead to difficulties in the process scale‐up. In this article, an alternate and relatively more convenient method for the synthesis of tyrosine‐based diphenol monomers is reported. This involved the investigation of polymer resin‐bound carbodiimide in the solid‐phase synthesis of L‐tyrosine‐based diphenolic monomers. This method was found to eliminate the need for rigorous purification processes and was found to maintain reasonable yield as well as maintain purity of the final monomer product. The monomer was able to produce polymers of a reasonably high‐molecular‐weight and a narrow polydispersity. The amide bond formation by such a polymer‐tethered reagent can be described to follow a reverse‐Merrifield sense and the method is relatively convenient to scale up. The L‐tyrosine‐based diphenolic monomeric compound formed by this method was analyzed by NMR, Fourier transform infrared, and elemental microanalysis techniques for chemical structure and composition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4906–4915, 2004