Biocomposites of covalently linked glucose oxidase on carbon nanotubes for glucose biosensor

The formation of covalently linked composites of multi–walled carbon nanotubes (MWCNT) and glucose oxidase (GOD) with high-function density for use as a biosensing interface is described. The reaction intermediates and the final product were characterized by using FT–IR spectroscopy, and the MWCNT-coated GOD nanocomposites were examined by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Interestingly, it was found that the GOD–MWCNT composites are highly water soluble. Electrochemical characterization of the GOD–MWCNT composites that were modified on a glassy carbon electrode shows that the covalently linked GOD retains its bioactivity and can specifically catalyze the oxidation of glucose. The oxidation current shows a linear dependence on the glucose concentration in the solution in the range of 0.5–40 mM with a detection limit of 30 μM and a detection sensitivity of 11.3 μA/mMcm². The present method may provide a way to synthesize MWCNT related composites with other biomolecules and for the construction of enzymatic reaction-based biofuel cells and biosensors. Supported by grants from the National Natural Science Foundation of China (NSFC, No. 20125515; 90206037; 20375016) and the Natural Science Foundation of Jiangsu Province (Grant No. BK 2004210)     

EPR study of spin adducts of silyl and phosphonyl radicals with higher internal perfluoroalkenes

The EPR method was used to study the structure of spin adducts of silyl and phosphonyl radicals with higher internal perfluoroalkenes. The capacity for spin adducts to split off hydrogen atoms is determined by the degree of steric screening of the free radical center. The preparative photochemical reaction of hydrosilanes and dialkyl phosphites with perfluoro-4-methylpent-2-ene leads to regiospecific hydrosilylation and hydrophosphorylation products with yields up to 80%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1018–1023, May, 1991.     

Determination of the thiol redox state of organisms: new oxidative stress indicators

This study describes a new methodology by which the concentrations of non-protein (NP) thiols glutathione (GSH), cysteine (CSH), N-acetylcysteine (AcCSH), and protein (P) thiols (PSH), as well as the contribution of these components to symmetric and mixed disulfides (NPSSR, NPSSC, NPSSCAc, PSSR, PSSC, PSSCAc, PSSP) can reliably be measured. The methodology consists of a strict sequence of methods which are applied to every sample. Free thiols at any given state of the procedure are measured by Ellmans assay, the CSH fraction is measured by its unique response in the ninhydrin assay, AcCSH is selectively measured with ninhydrin after enzymatic deacylation, proteins are separated from non-protein thiols/disulfides by precipitation with trichloroacetic or perchloric acid, disulfides are reduced into free thiols with borohydride, mixed disulfides between a protein and a non-protein component are measured by extracting the non-protein thiol from the protein pellet after borohydride treatment, and protein thiols/disulfides are measured after resolubilization of the protein pellet.When this method was applied to animal and fungal tissue, new molecular indicators of the thiol redox state of living cells were identified. The findings of the present study clearly show that the new parameters are very sensitive indicators of redox state, while at the same time the traditional parameters GSH and GSSG often remain constant even upon dramatic changes in the overall redox state of biological tissue. Therefore, unbiased assessment of the redox state also requires explicit measurement of its most sensitive thiol indicators.Electronic Supplementary Material Supplementary material is available in the online version of this article at . A link in the frame on the left on that page takes you directly to the supplementary material.     

Synthetic diamond electrodes: Photoelectrochemical behavior of vacuum-annealed undoped polycrystalline diamond films

The photocurrent and photopotential for undoped polycrystalline diamond film electrodes prepared by chemical vapor deposition and annealed in vacuum at 1500–1640°C are measured. The metal-like samples (annealed at 1630°C) have a negligible photosensitivity. Judging from the positive sign of the photopotential and the cathodic direction of the photocurrent, the material under study formally behaves as a p-type semiconductor. The photoeffects are presumably caused by structure defects, in particular, the dislocations in diamond crystallites formed close to intercrystalline boundaries during the high-temperature annealing.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 343–349.Original Russian Text Copyright © 2005 by Pleskov, Krotova, Ralchenko, Khomich, Khmelnitskii.     

Preparative synthesis of the stable α-fluorosulfatotetrafluoro-ethylbis(perfluoroisopropyl)methyl radical

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2450–2451, October, 1990.     

Stereoselective hydroboration of 5-dimethylaminomethyl-2-methyl-4,5-dihydrofuran: A simple way to (±)-muscarine

Conclusions A fundamentally new scheme was found for the synthesis of (±)-muscarine, in which the required arrangement of all the substituents is achieved in a single step, involving the hydroboration of 5-dimethylaminomethyl-2-methyl-4,5-dihydrofuran.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1383–1386, June, 1989.     

Skeletal Isomerization of <Emphasis Type="Italic">n</Emphasis>-butenes over Solid Acid Catalysts

Conversion reactions of n-butenes over zeolites and amorphous catalysts have been investigated to deduce the factor that determines the selectivity for the skeletal isomerization producing isobutene. The effects of pore structure and acid site concentration on the selectivity for the skeletal isomerization are discussed on various catalysts. The pore structures of FER and CLI zeolites induce the distant locations of butene molecules, accelerating monomolecular skeletal isomerization. On the other hand, acid site concentration determines the preferred reaction path of n-butenes on amorphous catalysts. Oligomerization followed by cracking that produces various hydrocarbons is suppressed on the catalyst with low acid site concentration, resulting in high selectivity for isobutene. The feasibility of monomolecular skeletal isomerization on zeolites and amorphous catalysts is confirmed by its reversibility with high selectivity.     

Enzymatic kinetic of cellulose hydrolysis

The ethanol effect on the Trichoderma reesei cellulases was studied to quantify and clarify this inhibition type. To determine inhibition parameters of crude cellulase and purified exoglucanase Cel7A, integrated Michaelis-Menten equations were used assuming the presence of two inhibitors: cellobiose as the reaction product and ethanol as a possible bioproduct of cellulose fermentation. It was found that hydrolysis of cellulose by crude enzyme follows a model that considers noncompetitive inhibition by ethanol, whereas Cel7A is very slightly competitively inhibited. Crude cellulase is much more inhibited (K _iul=K _icl=151.9 mM) than exoglucanase Cel7A (K _icl=1.6 × 10¹⁵ mM). Also, calculated inhibition constants showed that cellobiose inhibition is more potent than ethanol inhibition both for the crude enzyme as well as exoglucanase Cel7A.     

Voltage-Height Spectroscopy in the <Emphasis Type="Italic">Ex Situ</Emphasis> Configuration of a Scanning Tunneling Microscope

Basic regularities of electrochemical processes in the gap of an ex situ scanning tunneling microscope in conditions of condensation of air moisture at the sample surface are considered on a qualitative level. A layer of condensed moisture is viewed as an electrolyte in a two-electrode cell. The depolarizers present in this layer may experience electrochemical conversions on the tip and in an area of the sample surface near the tip. As a result, the recorded “tunneling” current includes electrochemical constituents. Depending on the electrochemical processes in the gap, various dependences of the tip-sample distance on the current and applied voltage can be expected. For preliminary diagnostics of processes in the gap it is suggested to use voltage-height spectra, whose shape and characteristic heights are sensitive to the nature and location of redox active species. Experimental data for various films on conducting supports (quasi-two-dimensional adsorbed layers of hemin and peroxidase, electrodeposited nonstoichiometric tungsten oxides, doped tin dioxide, solid electrolyte with ionic conduction) are presented as an examples.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 583–595.Original Russian Text Copyright © 2005 by Yusipovich, Vassiliev.     

Trace analysis of rapamycin in human blood by micellar electrokinetic chromatography

A capillary electrophoretic method with UV detection at 278 nm has been developed for analysis of the immunosuppressant rapamycin (sirolimus) in human blood at low microgram per liter levels. Separation has been achieved in an acidic carrier electrolyte containing sodium dodecylsulfate and 30% (v/v) acetonitrile. For sample clean-up and preconcentration, an off-line solid-phase extraction step using a silica-based reversed-phase material and an on-capillary focussing technique were employed. The latter allows the injection of increased sample volumes without excessive band broadening. Although this new method is less sensitive than existing liquid chromatographic procedures combined with mass spectrometry, it is fully suited to routine analysis of rapamycin in blood from patients treated with this drug. Last but not least the low costs make it an attractive alternative to established methods.