Electrochemical grafting by reduction of 4-aminoethylbenzenediazonium salt: Application to the immobilization of (bio)molecules

We propose in this study a simple and rapid way to produce stable amino-derivatized conductive surfaces for the subsequent immobilization of (bio)molecules. This was achieved through the use of (4-aminoethyl)benzenediazonium salt (AEBD), which was immobilized on glassy carbon and gold electrodes by its electrochemical reduction. The presence of terminal grafted amino functions was evidenced with XPS by analyzing N1s core level. Besides this conventional surface characterisation, an electrochemical strategy is proposed here to evidence the presence of immobilized amines, in which the chemical reactivity of amines towards 2,4,6-trinitrobenzenesulfonic acid (TNBS) is used. Surface-bound TNBS served as an electrochemical marker and was detected by cyclic voltammetry. Additionally, pre-modified gold electrodes with amino functions can be derivatized with biomolecules such as glutathione (GSH). Glutathione attachment was evidenced by studying the electrochemical behaviour of ferri/ferrocyanide redox before and after its immobilization. The functionalized electrodes were then used for the detection of copper ions in neutral aqueous solutions.     

Structure and intermolecular interactions of <Emphasis Type="Italic">N</Emphasis>-(3,5-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-4-hydroxybenzyl)thioureas

The molecular and crystal structure and the hydrogen bonding in crystal and in solutions of N-phenyl-N-(3,5-di-tert-butyl-4-hydroxybenzyl)thiourea and N-(3,5-di-tert-butyl-4- hydroxybenzyl)thiourea were studied by single crystal X-ray diffraction and IR spectroscopy. The intermolecular interactions of these compounds are essentially different.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1864–1870.Original Russian Text Copyright © 2004 by Bukharov, Litvinov, Gubaidullin, Chernova, Shagidullin, Nugumanova, Mukmeneva.This revised version was published online in April 2005 with a corrected cover date.     

Synthesis, structure, and electrochemical properties of 12,42-dioxo-21,31-diphenyl-7,10,13-trioxa-1,4(3,1)-diquinoxalina-2(2,3),3(3,2)-diindolizinacyclopentadecaphane

The oxidative dehydrocyclization of the 3-(indolizin-2′-yl)-2-oxoquinoxaline monopodand performed either electrochemically or under the action of molecular iodine affords new redox-active heterocyclophane consisting of the redox-switchable biindolizine fragment combined with the polyether-bridged π-deficient quinoxaline systems. The single-crystal X-ray diffraction study showed that the trioxaundecane chain of heterocyclophane adopts an extended conformation, and one of the phenyl substituents of the molecule closes the pseudocavity formed by the spacer from one of the sides. The cyclic voltammetric study of heterocyclophane in MeCN and DMF showed the three-step oxidation of the indolizine fragments accompanied by the single-electron transfer in each step. The first and third steps are reversible, and the second step is irreversible. The oxidation at potentials of the first peak gives rise to stable radical cations detected by the ESR method (g = 2.0024, a _2N = 0.26 mT). Dedicated to Professor E. A. Berdnikov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1991–2003, October, 2007.     

Stereoselective transformation of 1,3-dithia-4-cyclohexene enaminonitriles into substituted 3,4-trans-1,2,3,4-tetrahydropyridine-6-thiolates with pyridinium ylides

4-Amino-6-aryl-2,2-dialkyl-5-cyano-1,3-dithia-4-cyclohexenes react with pyridinium ylides in thermodynamically controlled conditions with the formation of 4-aryl-2-oxo-thioxo)-3-(1-pyridino)-5-cyano-3,4-trans-1,2,3,4-tetrahydropyridine-6-thiolates. Arylidenecyanothioacetamides act as intermediates of this recyclization, and the corresponding pyridine-6-thiolates were obtained from them by an independent method. The synthesized hydrogenated pyridine-6-thiolates are in the half-chair conformation with a trans-diaxial position of the 3-H and 4-H hydrogen atoms.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1082–1086, August, 1991.     

Interplay between Auger and ionization processes in nanocrystal quantum dots

We study the interplay between Auger effects and ionization processes in the limit of strong electronic confinement in core/shell CdSe/ZnS semiconductor nanocrystal quantum dots. Spectrally resolved fluorescence decay measurements reveal a monotonic increase of the photoluminescence decay rate on excitation density. Our results suggest that Auger recombination accelerates ionization processes that lead to the occupation of dark, nonemissive nanocrystal states. A model is proposed in the quantized Auger regime describing these experimental observations and providing an estimate of the Auger assisted ionization rates.     

Reaction of 3,3-dichloropentane-2,4-dione with aromatic aldehydes under the conditions of Darzens reaction

3,3-Dichloropentane-2,4-dione reacts with aromatic aldehydes under the conditions of Darzens reaction to give 4-acetoxy-4-aryl-3,3-dichlorobutan-2-ones, the products of insertion into the -C-C bond. The reaction of ethyl dichloroacetylacetate with benzaldehyde yields a derivative of tricyclo[5.1.0.0^3,5]octane, rather than 2,6-bis(1-chlorobenzylidene)cyclohexane-1,4-dione, as the by-product.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1294–1298, July, 1995.     

On the convergence of the exponential multiplier method for convex programming

In this paper, we analyze the exponential method of multipliers for convex constrained minimization problems, which operates like the usual Augmented Lagrangian method, except that it uses an exponential penalty function in place of the usual quadratic. We also analyze a dual counterpart, the entropy minimization algorithm, which operates like the proximal minimization algorithm, except that it uses a logarithmic/entropy proximal term in place of a quadratic. We strengthen substantially the available convergence results for these methods, and we derive the convergence rate of these methods when applied to linear programs.Research supported by the National Science Foundation under Grant DDM-8903385, and the Army Research Office under Grant DAAL03-86-K-0171.     

Effects of concentrated matrices on the determination of trace levels of platinum and gold in aqueous samples using solvent extraction—Zeeman effect graphite furnace atomic absorption spectrometry and inductively coupled plasma—mass spectrometry

Two methods of determining trace levels of platinum and gold in aqueous solutions with high concents of total dissolved solids were investigated. The first involves preconcentration and separation of the precious metals from the interfering matrix by solvent extraction, followed by graphite furnace atomic absorption spectrometry (GFAAS) with Zeeman effect background correction. The direct determination of Pt and Au in solutions of high ionic strength by GFAAS is not desirable because of interference between elements in the matrix and the analyte, increased imprecision of analysis, greatly increased background absorbance leading to increased detection limits and rapid deterioration of the graphite tube. All the extraction methods for gold examined in this study resulted in decreased imprecision, increased sensitivity and lower background absorbance compared with direct measurements on the aqueous solution. All techniques also exhibited good recoveries (> 8%) and reproducibilities (relative standard deviation < 10%). The highest sensitivities for gold extraction from distilled water were obtained for dibutyl sulfide (DBS)—toluene and the lowest for cyanide—dibutyl ketone. The degree of extraction of Au was, however, dependent on the composition of the solution, indicating that standard and sample matrices should be closely matched even when employing solvent extraction. Solvent extraction was generally less successful for Pt. In order to obtain an acceptable imprecision in the Pt extractions, it was found that the use of SnCl₂ as a labilizing agent is essential for most of the techniques investigated.The second method was direct measurement by inductively coupled plasma mass spectrometry (ICP—MS). ICP—MS offers the advantages of a very low detection limit (100 ng l^?1 or better) without preconcentration and a large dynamic range. However, severe matrix effects can occur in concentrated solutions. Whereas high concentrations in solution of both sodium perchlorate and sodium chloride decrease the sensitivity, the presence of sulfide and natural organic (fulvic) acid increase the sensitivity for Pt and Au by a factor of up to 4. Sulfate, on the other hand, decreases the sensitivity of ICP-MS for Pt. The method of standard additions or isotope dilution is recommended for routine use to circumvent this problem, especially when the nature of the matrix is unknown or cannot be easily matched in the standards.     

Synthesis and molecular structure of 3,7-dimethyl-2-[N-(4-methylpyridyl-2)-4-hydroxy-3-methyl-5-oxopyrrolen-3-yl-2]imidazo[1,2-a]pyridine

Heterocyclization of 2-chloroepoxy-1,1-diethoxy-2.3-butane with 2-amino-4-methylpyridine occurred with participation of all three potential electrophilic centers to give 3,7-dimethyl-2-[N-(4-methylpyridyl-2)-4-hydroxy-3-methyl-5-oxopyrrolen-3-yl]imidazo[1,2-a]pyridine, the structure of which was determined by X-ray crystallography. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, 1089–1094, July 2006.