Layer-by-layer assembly of multilayer films consisting of silicotungstate and a cationic redox polymer on 4-aminobenzoic acid modified glassy carbon electrode and their electrocatalytic effects

A novel 4-aminobenzoic acid (4-ABA) monolayer film is formed on glassy carbon electrode (GCE) by amino cation radical method. Silicotungstic heteropolyanion (SiW12O404-, denoted as SiW12)-containing multilayer films have been fabricated on the 4-ABA modified GCE surface by alternate deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)(2)Cl](2+/+) (denoted as QPVP-Os). Cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and X-ray reflectivity (XR) have been used to characterise the as-prepared multilayer films. It is proved that the multilayer films are uniform and stable. The average thickness for a bilayer of QPVP-Os/SiW12 in the multilayer film is 30.2 Angstrom. The electrocatalytic activities of the multilayer films have been investigated on the reduction of three substrates of important analytical interests, HNO2, BrO3- and H2O2. Especially, the influence of layer number of the multilayer films on the electrocatalytic reduction of HNO2 has been investigated in detail. (C) 2000 Elsevier Science B.V. All rights reserved.

Investigation of the model compounds at 4-aminobenzoic acid modified glassy carbon electrode by scanning electrochemical microscopy

In this paper, we studied the reactions of both potassium ferricyanide and hexaammineruthenium(III) chloride at a 4-aminobenzoic acid (4-ABA) modified glassy carbon electrode (GCE) by scanning electrochemical microscopy (SECM) in different pH solutions. The surface of the modified electrode has carboxyl groups, the dissociation of which are strongly dependent upon the solution pH values. The rate constant kb of the oxidation of ferrocyanide on the modified electrode can be obtained by fitting the experimental tip current-distance (I-T-d) curves with the theoretical values. The surface pK(a) of the 4-ABA modified GCE was estimated from the plot of standard rate constant k(o) versus the solution pH and is equal to 3.2, which is in good agreement with the reported result. The SECM approach curves for Ru(NH3)(6)(3+) both on the bare and the modified electrodes show similar diffusion control processes. These results can be explained by the electrostatic interactions between the modified electrode surface and the model compounds with different charges. (C) 2001 Elsevier Science BN. All rights reserved.

Two dimensional nuclear magnetic resonance analysis of ruthenium-(4,4'-dimethyl-2,2'-bipyridine)(2) (2,2'-bipyridine-4,4'-dicarboxylic acid) (PF6)(2)

The (1) H and C-13 NMR spectra are reported for Ru(4, 4'-dimethyl-2,2'-bipyridene)(2) (2,2'-bipyridine-4,4'-dicarboxylic acid) (PF6)(2) that can be used as a new electrochemiluminescent probe in immunoasssay and nucleic acid hybridization assay. Because of the effect ol:Ru atom ligands and complex steric configuration, it is difficult to attribute spectra of the title molecular, By using 2D (1) H-(1) H COSY and (1) H-C-13 HETCOR method, the proton and C-13 NMR spectra are assigned completely, which provides a satisfactory method to quantitative and qualitative, analysis of the title moleculer in the further study.

Two dimensional nuclear magnetic resonance analysis of bis(2,2 '-bipyridine)(2,2 '-bipyridine-4,4 '-dicarboxylic acid)ruthenium(II) hexafluorophosphate

The H-1 and C-13 nuclear magnetic resonance(NMR) spectra are reported for bis(2, 2'-bipyridine)(2, 2'-bipyridine-,4,4'-dicarboxylic acid) ruthenium(II) hexafluoruphosphate that has been used as a tagged molecule of electrochemiluminescent immunoassay. Because of the effect of Ru atom on ligands, it is difficult to assign its NMR spectra. BS' means of two dimensional H-1-H-1 COSY and H-1-C-13 COSY techniques, the H-1 and C-13 NMR spectra of bis (2, 2'-bipylidine) (2, 2'-bipyridine-4, 4-dicarboxylic acid) ruthenium(II) hexafluorophosphate are assigned completely. This provides a basis for NMR characterization of the nerv similar tagged molecules.

Photophysical properties of rare earth complexes with 3,4-furandicarboxylic acid and 1,10-phenanthroline

Synthesis, IR spectra, UV-vis spectra and photophysical properties of Gd3+, Eu3+, Tb3+ complexes with 3,4-furandicarboxylic acid and 1,10-phenanthroline are reported. Intramolecular energy transfer process for these complexes is discussed in detail. It is found that the intramolecular energy transfer efficiency depends on the relative positions between the resonance energy levels of the central rare earth ions and the lowest triplet state energies of ligands.

Electrochemical behavior of 3,4-dihydroxybenzoic acid in self-assembled monolayer electrode system

The self-assembled monolayer of cystamine was prepared on gold electrode and 3,4-dihydroxybenzoic acid (DHBA) was electrochemically deposited on cystamine surface as a functional group by electrostatic adsorption, namely, molecular deposition. It shows that the MD/SAM structure has a higher stability, and E-1/2 of the DBAH in MD/SAM shifts more negative than that of on naked gold electrode, The n-decanethiol was also used to fill defects in MD/SAM, it results in much better cyclic voltermmetric behavior.

SYNTHESIS AND VIBRATIONAL SPECTRUM STUDIES OF RARE EARTH COMPLEXES WITH CYCLOHEXANE CARBOXYLIC ACID

The solid state complexes of trivalent lanthanid, yttrium and scandium with cyclohexane carboxylic acid have been isolated and characterized by IR and Raman spectroscopy. It was found that there are only chelated carboxylate groups in the scandium complex and that there are the chelated, bridged and chelate-bridged carboxylate groups in other rare earth complexes. The former is a mononuclear complex and the latter is a polynuclear polymer. The RE—O coordinate bonds possess the characters of convalent ionic ...

Polymorphism in Sulfadimidine/4-Aminosalicylic Acid Cocrystals: Solid-State Characterization and Physicochemical Properties

Polymorphism of crystalline drugs is a common phenomenon. However, the number of reported polymorphic cocrystals is very limited. In this work, the synthesis and solid-state characterization of a polymorphic cocrystal composed of sulfadimidine (SD) and 4-aminosalicylic acid (4-ASA) is reported for the first time. By liquid-assisted milling, the SD:4-ASA 1:1 form I cocrystal, the structure of which has been previously reported, was formed. By spray drying, a new polymorphic form (form II) of the SD:4-ASA 1:1 cocrystal was discovered which could also be obtained by solvent evaporation from ethanol and acetone. Structure determination of the form II cocrystal was calculated using high-resolution X-ray powder diffraction. The solubility of the SD:4-ASA 1:1 cocrystal was dependent on the pH and predicted by a model established for a two amphoteric component cocrystal. The form I cocrystal was found to be thermodynamically more stable in aqueous solution than form II, which showed transformation to form I. Dissolution studies revealed that the dissolution rate of SD from both cocrystals was enhanced when compared with a physical equimolar mixture and pure SD.

The N-terminal domain modulates α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor desensitization

AMPA receptors are tetrameric glutamate-gated ion channels that mediate fast synaptic neurotransmission in mammalian brain. Their subunits contain a two-lobed N-terminal domain (NTD) that comprises over 40% of the mature polypeptide. The NTD is not obligatory for the assembly of tetrameric receptors, and its functional role is still unclear. By analyzing full-length and NTD-deleted GluA1-4 AMPA receptors expressed in HEK 293 cells, we found that the removal of the NTD leads to a significant reduction in receptor transport to the plasma membrane, a higher steady state-to-peak current ratio of glutamate responses, and strongly increased sensitivity to glutamate toxicity in cell culture. Further analyses showed that NTD-deleted receptors display both a slower onset of desensitization and a faster recovery from desensitization of agonist responses. Our results indicate that the NTD promotes the biosynthetic maturation of AMPA receptors and, for membrane-expressed channels, enhances the stability of the desensitized state. Moreover, these findings suggest that interactions of the NTD with extracellular/synaptic ligands may be able to fine-tune AMPA receptor-mediated responses, in analogy with the allosteric regulatory role demonstrated for the NTD of NMDA receptors.

The 21-dehydroxglation of corticosteroids of Eubacterium lentum and the dehalogenation of 4-chlorobenzoic acid by 4-chlorobenzoate dehalogenase

Two enzyme mechanisms were investigated: the 21-dehydroxylation of corticosteroids by Eubacterium lentum and the dehalogenation of 4-chlorobenzoic acid by Pseudomonas sp. CBS 3. , Chemical and enzymic methods of reduction of 21-oxo steroids were used to generate C-21-d1 compounds of tetrahydrodeoxycorticosterone, with both predominant stereochemistries. It was found that during the dehydroxylation the pro-S hydrogen at the C-21 position was lost preferentially. This suggests that the enzyme removes the pro-S hydrogen during binding to the active site as the ene-diol. To study the hydrolytic replacement of chlorine by hydroxyl , p-chlorobenzoic acid-d4 was prepared and sent to Germany for an ~ncubation with an enzyme preparation of 4-Chlorobenzo~te Dehalogenase. Results suggests the possible loss of deuterium during the conversion of p-chlorobenzoate to p-hydroxybenzoate, from all four ring positions. Many methods of preparing the control compound p-hydroxybenzoic acid-d4 were investigated.

Solubility of 4-Nitrobenzoic Acid in Water & Salt Solutions

Solubilities of 4-nitrobenzoic acid at 25°, 35° and 42°C have been determined in water and in the presence of several concentrations of electrolytes. The free energies, enthalpies and entropies of transfer are also reported. The data have been rationalized by considering the structure-breaking effects of the ions of the salts and the requirement of the localized hydrolysis model. The theory of Symons is not satisfactory to rationalise the experimental data.