Electrochemical amination. Ti(IV)/Ti(III) mediator system in aqueous solutions of sulfuric acid

As a result of polarographic and spectrophotometric studies, and mathematical modeling, the dependence of electrochemical properties of the Ti(IV)/Ti(III) pair on the composition of the Ti(IV) complexes is established in sulfuric acid solutions. It is found that Ti(IV) in 1-17 M H2SO 4 at the metal ion concentrations used in the process of amination of aromatic compounds can exist in the form of twelve basic complex forms, of which seven, including the binuclear and two tetranuclear ones, are observed for the first time. Ten forms are electrochemically active. An increase in the overall amount of reversibly reducing cationic mononuclear hydrosulfate complexes of Ti(IV) among these at a growing H2SO4 concentration results in an increase in the redox potential of the Ti(IV)/Ti(III) mediator system and therefore in an increase in the yield of the electrochemical amination products. © Pleiades Publishing, Ltd., 2010

Amperometric DNA biosensor for the determination of auto-antibodies using DNA interaction with Pt(II) complex

A method of denatured DNA immobilisation on cellulose nitrate film has been developed. A modified film of uniform and stable surface has been used as a bio-sensitive part of amperometric DNA biosensor based on the stationary mercury-film covered silver electrode. The biosensor has been used to devise a new variant of solid-phase immunoassay of auto-antibodies (Ab) in blood serum without separation of components. The content of auto-Ab was monitored by measuring the currents of catalytic hydrogen evolution (with potentials of -1.2 and -1.4V) resulting from the complexing of Pt(II) with DNA or auto-Ab respectively. The determination has been performed within a wide concentration area of 5.0×10-10 to 7.0×10-8M. The limit of detection is 3.0×10-10M. The affinity constants for the immunoreaction of DNA-antibodies have been found to be 1.25×10 9 and 2.50×108M-1, which confirms the specificity of the interaction. The protocol of the immunoassay has been proposed and the procedure of diagnosing Aleutian mink disease (AMD) has been described here. © 2003 Elsevier B.V. All rights reserved

Adsorption of Lead(II) and Cadmium(II) ions on the surface of a cellulose membrane modified with denaturated deoxyribonucleic acid

The sorption of Pb(II) and Cd(II) ions on a nitrocellulose membrane modified with denaturated deoxyribonucleic acid (d-DNA) was studied. A method for constructing isotherms of adsorption of heavy metals on the surface of an amperometric biosensor incorporating a d-DNA-modified nitrocellulose membrane and a stationary mercury-film electrode was proposed. An analysis of isotherms of joint sorption of Pb(II) and Cd(II) from a mixture of these ions showed that Pb(II) is bound to d-DNA more strongly than Cd(II), in agreement with the theoretical assumption that there are additional modes for binding Pb(II) with nitrogen-containing heterocycles of the d-DNA molecule. The constants of binding of Pb(II) and Cd(II) on d-DNA were determined by the Scatchard method

Structure, stability, and ligand exchange of copper(II) complexes with oxidized glutathione

Formation constants and structures of copper(II) complexes with oxidized glutathione (L) have been determined by computer modelling of spectrophotometric and NMR relaxation measurements data over a wide range of pH (1-13) and metal and ligand concentrations in aqueous KNO3 (1 M) at 298 K. Among 11 found complexes, four forms were characterized for the first time. Based on a comparison of thermodynamic, relaxation, and optical and EPR spectroscopy parameters the structural conclusions were made. In particular, the CuLH 2 and CuLH- complexes both contain two isomers which are similar to mono- and bis-aminoacid copper(II) complexes. In the Cu2L and Cu3L2 2- species one of the copper atoms is bound only with the carboxylate or carbonyl groups and the others are coordinated similarly to aminoacid chelates. Along with the last, in Cu 2LH-2 2- two bridging OH- groups in one isomer or two chelate rings including deprotonated peptide nitrogen and glycinyl carboxylate oxygen in another are also present. In Cu3L 2H-4 6- the mixed variant of coordination between CuL2- (CuN2O2) and Cu 2LH-4 4- (CuN3O) is realized. The structures of polynuclear complexes have been optimized in density functional theory computations. Rate constants of ligand exchange reactions of Cu(LH) 2 4- and CuL2 6- with participation of the LH3- and L4- forms were determined for the first time. Factors determining rates of these processes have been revealed and their proceeding by associative substitution mechanism shown. © 2005 Elsevier Inc. All rights reserved

Complexation and ligand exchange in aqueous of Cu(II) and Ni(II) with hydrazides of some aromatic acids

Solvation and complexation of Cu(II) and Ni(II) with benzoic (L′), p-methoxybenzoic (L″), and isonicotinic (L) acid hydrazides in aqueous-ethanol solutions (ethanol mole fraction 0.07-0.68) were studied by pH-metry, spectrophotometry, and nuclear magnetic relaxation. The formation constants of the species M(L′)2+, M(L′) 2 2+ , M(L″)2+, M(L″) 2 2+ , M(LH)3+, M(L)2+, M(L)(LH)3+, and M(L) 2 2+ , where M = Cu2+ and Ni2+, were determined. With isonicotinic acid hydrazide, a change in the coordination mode was observed in an isomer of Cu(L) 2 2+ , with one of the ligands coordinating in the bidentate fashion, and the other, in the monodentate fashion via the pyridine nitrogen atom. The suggested structures were confirmed by analysis of the parameters of the ESR and electronic absorption spectra of the complexes. The rate constants of ligand exchange and formation of the complexes Cu(L′)2+, Cu(L′) 2 2+ , Cu(L″)2+, and Cu(L″) 2 2+ in aqueous solutions were determined from nuclear magnetic relaxation measurements; the reactions occur by the associative mechanism. A cyclic process of reduction of Cu(II) to colloidal copper in the presence of L″ and atmospheric oxygen is described. © Pleiades Publishing, Inc., 2006

Spatial structures of tripeptides glycylglycyl-l-histidine and glycylglycyl-l-tyrosine based on residual dipolar couplings and quantum-chemical computations

A novel approach to the determination of the spatial structure of oligopeptides on the basis of an analysis of the residual dipolar couplings 1H-13C assisted by quantum-chemical computations with considering solvent effects is proposed to characterize the conformations of the tripeptides GlyGlyHis and GlyGlyTyr with significant folding of the latter to left-handed helix. © 2011 Mendeleev Communications. All rights reserved

Complex formation, chemical exchange, species structure, and stereoselective effects in the copper(II)- L/DL-histidine systems

The formation of copper(ii) complexes with l- and dl-histidine (HisH) has been studied by means of pH-potentiometry and spectrophotometry over a wide range of pH (2-14), ligand-to-metal ratio (1:1-15:1), and temperature (15-55°C) in aqueous solutions with 1.0 mol dm -3 KNO 3 as background. Formation constants and spectral characteristics of 13 complex types were found. Fine stereoselective effects have been detected with preferential coordination of two ligands with identical configuration in Cu(His)(HisH) + and opposite configuration in Cu(His) 2. The stereoselective effect for Cu(His)(HisH) + is explained by hydrogen bond formation between the carboxyl and imidazolyl groups of neighboring ligands at cis-arrangement of amino groups (3N eq-form). The opposite sign of stereoselective effect for Cu(His) 2 is derived from favourable axial coordination of the imidazole group in meso-form with cis-structure (3N eqN ax-form). A significant tetrahedral distortion was revealed for the first time in the prevalent cis-isomer of the Cu(l-His) 2 4N eq-form. These findings were confirmed by EPR data and DFT computations at the B3LYP/TZVP level. The prevalence of cis-isomers for these complexes has been assigned to the rather strong trans effect of the amino groups. The structures of other detected complexes are briefly discussed on the basis of spectroscopic data. Chemical exchange reactions in the copper(ii)- l/dl-hishidine systems have been investigated by the NMR relaxation of water protons. A unique proton exchange reaction with short-term proton dissociation from the coordinated imidazolyl group catalyzed by hydroxide ion was characterised for the first time. The discovered enantioselective effects in the ligand exchange reactions between Cu(His) 2 and HisH or His - species were attributed to the associative substitution mechanism. © 2012 The Royal Society of Chemistry

Research findings from Africa in relation to WIPO development agenda priorities

Research findings indicate that there are several factors that inhibit access to knowledge, including unaffordability, unavailability and in some cases the lack of a reading culture. The African Copyright and Access to Knowledge (ACA2K) research studies further the understanding of the relationship between national copyright environments and access to knowledge (learning materials in particular). The World Intellectual Property Organization (WIPO) Development Agenda recognises that renewed efforts are required ‘to further facilitate access to knowledge and technology for developing countries and least developed countries (LDCs) to foster creativity and innovation.

Electrochemical amination. Ti(IV)/Ti(III) mediator system in aqueous solutions of sulfuric acid

As a result of polarographic and spectrophotometric studies, and mathematical modeling, the dependence of electrochemical properties of the Ti(IV)/Ti(III) pair on the composition of the Ti(IV) complexes is established in sulfuric acid solutions. It is found that Ti(IV) in 1-17 M H2SO 4 at the metal ion concentrations used in the process of amination of aromatic compounds can exist in the form of twelve basic complex forms, of which seven, including the binuclear and two tetranuclear ones, are observed for the first time. Ten forms are electrochemically active. An increase in the overall amount of reversibly reducing cationic mononuclear hydrosulfate complexes of Ti(IV) among these at a growing H2SO4 concentration results in an increase in the redox potential of the Ti(IV)/Ti(III) mediator system and therefore in an increase in the yield of the electrochemical amination products. © Pleiades Publishing, Ltd., 2010

Amperometric DNA biosensor for the determination of auto-antibodies using DNA interaction with Pt(II) complex

A method of denatured DNA immobilisation on cellulose nitrate film has been developed. A modified film of uniform and stable surface has been used as a bio-sensitive part of amperometric DNA biosensor based on the stationary mercury-film covered silver electrode. The biosensor has been used to devise a new variant of solid-phase immunoassay of auto-antibodies (Ab) in blood serum without separation of components. The content of auto-Ab was monitored by measuring the currents of catalytic hydrogen evolution (with potentials of -1.2 and -1.4V) resulting from the complexing of Pt(II) with DNA or auto-Ab respectively. The determination has been performed within a wide concentration area of 5.0×10-10 to 7.0×10-8M. The limit of detection is 3.0×10-10M. The affinity constants for the immunoreaction of DNA-antibodies have been found to be 1.25×10 9 and 2.50×108M-1, which confirms the specificity of the interaction. The protocol of the immunoassay has been proposed and the procedure of diagnosing Aleutian mink disease (AMD) has been described here. © 2003 Elsevier B.V. All rights reserved