DNA-modified electrodes; part 4: optimization of covalent immobilization of DNA on self-assembled monolayers

The covalent immobilization of DNA onto self-assembled monolayer (SAM) modified gold electrodes (SAM/Au) was studied by X-ray photoelectron spectrometry and electrochemical method so as to optimize its covalent immobilization on SAMs. Three types of SAMs with hydroxyl, amino, and carboxyl terminal groups, respectively, were examined. Results obtained by both X-ray photoelectron spectrometry and cyclic voltammetry show that the largest covalent immobilization amount of dsDNA could be gained on hydroxyl-terminated SAM/Au. The ratio of amount of dsDNA immobilized on hydroxyl-terminated SAMs to that on carboxyl-terminated SAMs and to that on amino-terminated SAMs is (3-3.5): (1-1.5): 1. The dsDNA immobilized covalently on hydroxyl-terminated SAMs accounts for 82.8-87.6% of its total surface amount (including small amount of dsDNA adsorbed). So the hydroxyl-terminated SAM is a good substrate for the covalent immobilization of dsDNA on gold surfaces.     

Sensitive high-performance liquid chromatographic determination of famotidine in plasma. Application to pharmacokinetic study.

A sensitive high-performance liquid chromatographic (HPLC) method for the quantitation of famotidine in human plasma is described. Clopamide was used as the internal standard. Plasma samples were extracted with diethyl ether to eliminate endogenous interferences. Plasma samples were then extracted at alkaline pH with ethyl acetate. Famotidine and the internal standard were readily extracted into the organic solvent. After evaporation of ethyl acetate, the residue was analysed by HPLC. The chromatographic separation was accomplished with an isocratic mobile phase consisting of acetonitrile-water (12:88, v/v) containing 20 mM disodium hydrogenphosphate and 50 mM sodium dodecyl sulphate, adjusted to pH 3. The HPLC microbore column was packed with 5 microns ODS Hypersil. Using ultraviolet detection at 267 nm, the detection limit for plasma famotidine was 5 ng/ml. The calibration curve was linear over the concentration range 5-500 ng/ml. The inter- and intra-assay coefficients of variation were found to be less than 10%. Applicability of the method was demonstrated by a bioavailability/pharmacokinetic study in normal volunteers who received 80 mg famotidine orally.     

ANION AND SOLVENT EFFECTS ON THE RATE OF REDUCTION OF TRIPLET EXCITED THIAZINE DYES BY FERROUS IONS

Abstract— The lifetimes of the triplet excited states of thionine and methylene blue were measured in aqueous and 50 v/v% aqueous acetonitrile solutions acidified with 0.01 N sulfuric or trifluoromethyl-sulfonic acid. The rate constants for reaction of the triplet excited dyes with ferrous ions were measured in the same solutions. The triplet lifetimes in the absence of added quenchers were insensitive to a change in acid from trifluoromethylsulfonic to sulfuric or to a change in solvent from water to 50v/v% aqueous acetonitrile (τ for triplet thionine ˜7.5 μs, τ for triplet methylene blue ˜4.5 μs). In contrast, the rate constant for reaction of the triplet dyes with ferrous ions increased by nearly a factor of 10 with a change in acid from trifluoromethylsulfonic to sulfuric. In solutions containing sulfate ions this reaction rate constant increased with increasing sulfate concentration and with a change in solvent from water to 50 v/v% aqueous acetonitrile. The results are discussed in terms of the possibility of association of the positively charged reactive ions with sulfate anions. Quenching of the triplet excited dyes by ferric ions or by ground state dye molecules was shown to be negligible at the concentration used for the ferrous ion quenching study.     

Phytoecdysteroids of plants of the genusSilene. VII. Sileneoside D — ecdysterone 3-O-α-D-galactopyranoside fromSilene brahuica

A phytoecdysteroid, sileneoside D, has been isolated from the roots ofSilene brahuica Boiss. and it has been shown to be ecdysterone 3-O-α-D-galactopyranoside.     

Crystal structure of the stoichiometric compound Cs2W3O10 with a fractional number of atoms in the unit cell

The crystal structure of Cs₂W₃O₁₀ (a=16.103, c=10.169 Å, $I\bar 4$ , Z=120/11) was determined from three-dimensional X-ray diffraction data (CAD-4 automatic diffractometer, 1612 reflections, R=0.044). The structure has an AB₂O₆ defective pyrochlore motif in which some of the groups consisting of four WO₆ octahedra have been subtracted from the tungsten-oxygen framework and substituted by Cs⁺. The crystal has no vacancies in the substitution site (as confirmed by the occupancy refinement), and the composition of the crystal is strictly stoichiometric with a fractional number of atoms in the unit cell. A similar composition is suggested for the isostructural rubidium compound, which was earlier considered nonstoichiometric.     

Coumarins of three species of the genusHaplophyllum

The results are given of an investigation of three species of the genusHaplophyllum: H. villosum, H. kowalenskyi, andH. tenue, fromwhich five substances of coumarin nature have been isolated. Of them, two substances (I and II) have been identified as scopoletin and lomatin isovalerate, respectively, while suitable structures have been established for the new compounds tenuidin, villosin, and tenudiol. It has been shown that the coumarin composition of the plants changes with the growth site.     

Algorithms for high-level data processing in gas chromatography

Computer processing of gas chromatographic data is discussed, with special emphasis on the numerical operations needed. The CHADIC program is described. This program enables optimal separation conditions to be determined and isothermal gas chromatograms to be processed for qualitative and quantitative analysis.     

Claisen rearrangement taking place in the mass spectrometer

Conclusions The Claisen rearrangement of bucharaine and of the aldehyde bucharainal takes place under the conditions of mass spectrometry. At low temperatures inversion predominates and at high temperatures the anomalous rearrangement.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 577–583, September–October, 1970.     

Volumetric determination of Pt(IV) in the presence of Ir,Pd, and Rh with ferrous ammonium sulfate in alkaline mannitol medium

A potentiometric reductimetric method for the determination of platinum (Pt(IV)Pt(II)) with a standard Fe(II) solution in an alkaline medium of mannitol is described. The method, the error of which does not exceed 2%, can be used in the presence of palladium, iridium, and rhodium.     

Preparation of arylphosphonates by the reaction of aryl halides with tris(trimethylsilyl) phosphite under homogeneous catalysis conditions

The reaction of tris(trimethylsilyl) phosphite with aryl bromides under homogeneous catalysis conditions gives bis(trimethylsilyl)arylphosphonates. The desilylation of these phosphonate products with methanol leads to arylphosphonic acids.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1461–1462, June, 1991.