Interactions of Safranin T with nucleic acids

The interactions of Safranin T (ST) with several nucleic acids have been investigated by electrochemical, UV-visible and CD spectroscopic techniques. The form of the nucleic acid-ST complexes is sensitive to the ratio of the two species. Two electrochemically inactive complexes such as, nucleic acid-ST and nucleic acid-2ST, were formed while ST interacts with nucleic acids. Two processes were obtained from spectral experiments: (1) at the high value of R (R is defined as the ratio of the total concentration of ST to that of nucleic acid), ST is groove-binding with stacking, (2) st the low value of R, ST is groove-binding without stacking. Intrinsic binding constants were obtained by spectral methods. The experiments also show that electrostatic binding plays an important role in the interaction of ST with nucleic acids.

Hydrogen peroxide biosensor based on sol-gel-derived glasses doped with Eastman AQ polymer

A hydrogen peroxide biosensor based on sol-gel-derived glasses doped with poly(ester sulfonic acid) Eastman AQ 55D was constructed. Thionine (TH), as a mediator, was incorporated in this matrix by electrostatic force between TH+ and the negatively charged sulfonic acid group in Eastman AQ polymer. Performance and characteristics of the sensor were evaluated with respect to response time, sensitivity and storage stability. The enzyme electrode has a sensitivity of 11.36 muA mM(-1) with a detection limit of 5.0 x 10(-7) M H2O2, and the sensor achieved 95% of the steady state current within 20 s. (C) 2001 Elsevier Science B.V. All rights reserved.

Selective crystallization of BaF2 under a compressed Langmuir monolayer of behenic acid

Selective crystallization of BaF2 crystals under a compressed Langmuir monolayer of behenic acid [CH3(CH2)(20)COOH] has been studied by using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive X-ray analysis. It was found that, in the absence of a monolayer, three kinds of crystals (Ba2ClF3, BaClF, and BaF2) can be obtained by mixing BaCl2 with a NH4F solution. However, in the presence of the monolayer of behenic acid, only BaF2 crystals appear at the monolayer-subphase interface and crystals have a special crystal face (100). During this process of crystallization, the monolayer plays a very important role and acts as a template that can preferentially select a special crystal and a special crystal face. The above results can be explained in terms of a specific molecular interaction between ions and the headgroups of the monolayer and specific electrostatic, geometric, and stereochemical interactions at the organic-inorganic interface.

Characterization of multilayer film using electrochemical impedance spectroscopy

A new multilayer film fabricated based on electrostatic attraction in this laboratory was firstly characterized by the electrochemical impedance spectroscopy. The relationship between the charge-transfer resistance and double-layer capacitance with the number of layers was obtained through analyzing the impedance data. It demonstrated that the multilayer film showed a unique structure with the film growth. Compared to other electrochemical methods, the electrochemical impedance spectroscopy was proved to be a very sensitive and useful technique for characterizing the multilayer films.

Electrochemical behavior of heteropoly acid anions adsorbed in electrodes modified with mesoporous molecular sieve silica

Heteropoly acid H4SiW12O48 (denoted as SiW12) was assembled with the mesoporous materials MCM-41 modified with 3-aminopropyltriethoxysilane (APTES) (denote MCM-41((m))). The electrochemical behavior of SiW12/MCM-41((m)) complexes-based electrode indicated SiW12 anion was adsorbed by MCM-41((m)). In MCM-41((m)) electrode, large voltammetric waves, showing that the electrostatic bound ions adsorbed in MCM-41((m)) were electrochemically active. The potential application as amperometric sensors for nitrite is anticipated.

The effect of KSCN on the partition of proteins in polyethylene glycol/(NH4)(2)SO4 aqueous two-phase system

The effect of potassium thiocyanate on the partitioning of lysozyme and BSA in polyethylene glycol 2000/ammonium sulfate aqueous two-phase system has been investigated. As a result of the addition of potassium thiocyanate to the PEG/ammonium sulfate system, the PEG/mixed salts aqueous two-phase system was formed. It was found that the potassium thiocyanate could alter the pH difference between the two phases, and, thus, influence the partition coefficients of the differently charged proteins. The relationship between partition coefficient of the proteins and pH difference between two phases has been discussed. It was proposed that the pH difference between two phases could be employed as the measurement of electrostatic driving force for the partitioning of charged proteins in polyethylene glycol 2000/ammonium sulfate aqueous two-phase system.

Cobalt(II)hexacyanoferrate film modified glassy carbon electrode for construction of a glucose biosensor

An amperometric glucose biosensor was constructed based on a glassy carbon electrode modified with a Cobalt(II)hexacyanoferrate film which catalyzes electroreduction of hydrogen peroxide. Gelatin was used as immobilization matrix. Interference could be effectively eliminated by the combination of low detection potential with a Nafion coating. A low applied potential can avoid oxidation of interferences such as ascorbic acid, uric acid, p-acetyl-aminophenol, etc.. Nafion coating prevents interferences from access to the electrode surface by electrostatic repulsion. A wide linear range of detection was obtained. Analytical performance parameters are given and kinetic analysis discussed.

Hydrothermal synthesis and crystal structure of Co(En)(3)MoO4

Co(En)(3)MoO4 was synthesized by using the method of hydrothermal synthesis and characterized by elemental analysis, IR, ESR and single-crystal X-ray methods. It crystallizes in hexagonal space group P (3) over bar C1 with a=1.596 4(2) nm, b=1.596 4(2) nm, c = 0.993 5(2) nm, alpha=beta=90 degrees gamma=120 degrees, M-c=399.18, V=2.192 6(6) nm(3), D-c=1.814 g/nm(3), Z=6, F(000)=1 2181 R-1=0.070 3, R-w=0.220 7. According to separation of anion which acted on electrostatic potential, the anion and cation ions formed a type of organic and inorganic material.

Electrochemical growth and characterization of polyoxometalate-containing monolayers and multilayers on alkanethiol monolayers self-assembled on gold electrodes

A general strategy has been developed for fabrication of ultrathin monolayer and multilayer composite films composed of nearly all kinds of polyoxometalates (POMs), including isopolyanions (IPAs), and heteropolyanions (HPAs). It involves stepwise adsorption between the anionic POMs and a cationic polymer on alkanethiol (cysteamine and 3-mercaptopropionic acid) self-assembled monolayers (SAMs) based on electrostatic interaction. Here a Keggin-type HPA SiMo11VO405- was chosen as a main representative to elucidate, in detail, the fabrication and characterization of the as-prepared composite films. A novel electrochemical growth method we developed for film formation involves cyclic potential sweeps over a suitable potential range in modifier solutions. It was comparatively studied with a commonly used method of immersion growth, i.e., alternately dipping a substrate into modifier solutions. Growth processes and structural characteristics of the composite films are characterized in detail by cyclic voltammetry, UV-vis spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), micro-Fourier transform infrared reflection-absorption spectroscopy (FTIR-RA), and electrochemical quartz crystal microbalance (EQCM). The electrochemical growth is proven to be more advantageous than the immersion growth. The composite films exhibit well-defined surface waves characteristic of the HPAs' redox reactions. In addition, the composite films by the electrochemical growth show a uniform structure and an excellent stability. Ion motions accompanying the redox processes of SiMo11VO405- in multilayer films are examined by in situ time-resolved EQCM and some results are first reported. The strategy used here has been successfully popularized to IPAs as well as other HPAs no matter what structure and composition they have.

A QSAR study of the antiallergic activities of substituted benzamides and their structures

Multiple regression analysis (MRA) and comparative molecular field analysis (CoMFA) have been used in studies of the correlation between the antiallergic activities of substituted benzamides and their structures. The results achieved using Coh IFA based on 3D factors are much better than those obtained using MRA based on mainly 2D structural information. The CoMFA results reveal that the steric effects are more important than the electrostatic effects for the activities of substituted benzamides. (C) 1999 Elsevier Science B.V. All rights reserved.

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.

Electrospray ionization mass spectrometry of cyclodextrin complexes with amino acids in incubated solutions and in eluates of gel permeation chromatography

1:1 complexes of beta-cyclodextrin (CD) with three amino acids (Gly, Phe and Trp) have been detected as ions in the gas phase using infusion positive and negative ion electrospray ionization mass spectrometry (ESI-MS). In contrast with the positive ion ESI mass spectra of simple aqueous solutions, the aggregates and adducts usually formed in the ESI process did not appear in the positive ion ESI spectra of solutions buffered with ammonium acetate (NH4Ac), even at higher analyte concentrations, These studies suggest that addition of buffer and/or use of a low analyte concentration should be used to overcome formation of aggregates and metal ion adducts in such mass spectrometry studies. Also, the deprotonated complexes are dissociated by collision induced dissociation (CID) to form an abundant product ion, the deprotonated CD, requiring transfer of a proton to the amino acid carboxyl group, To understand formation of complexes in the gas phase, gel permeation chromatography (GPC) was used to separate free amino acids (AAs) from complexes in an incubated solution. The ESI mass spectra of the GPC fractions show the presence of 1:1 complexes of both CD-aromatic amino acids and CD-aliphatic amino acids. Compared with CD-aliphatic amino acid complexes, CD-aromatic amino acid complexes appear to be destabilized in the gas phase, possibly because the hydrophobic interaction which binds the aromatic group of amino acids in the CD cavity in solution may become repulsive when solvent evaporates from the droplets during the electrospray process, whereas those complex ions formed as proton bound dimers are stabilized by electrostatic forces, the major binding force for such complexes in the gas phase. In addition, the GPC technique coupled with off-line ESI-MS can rapidly separate CD complexes by size, and provides some information on the character of the complexes in solution. (C) 1998 John Wiley & Sons, Ltd.

Electrochemistry of heteropolyanions in coulombically linked self-assembled monolayers

A composite film containing heteropolyanion was fabricated on gold by attaching the Keggin-type heteropolyanion, PMo12O403- on a 4-aminothiophenol SAM via Au-S bonding. Reflection FTIR, cyclic voltammetry and XPS were used for the characterization of the composite film. Reflection FTIR studies indicate that there is some Coulombic interaction between PMo12O403- and the surface amino group in the composite film, which greatly improves the film stability and prevents effectively the destructive intermolecular aggregation. The composite him shows three reversible redox couples within the pH range pH less than or equal to 7.0, attributed to three two-electron and two-proton electrochemical reduction-oxidation processes of PMo12O403-. Compared with PMo12O403- in the solution, the PMo12O403- of the composite film electrode can exist in a larger pH range, and shows smaller peak-to-peak separation, and more reversible reaction kinetics. Moreover, the composite him obtained shows a good catalytic activity for the reduction of BrO3-. (C) 1998 Elsevier Science S.A. All rights reserved.

Studies on quantitative structure-activity relationship between the structures of derivatives of benzamide and their antiallergic activities

Molecular connectivity index and comparative molecular field analysis (CoMFA) have been applied to the studies of the correlation of the derivatives of benzamide and their antiallergic activities. The results achieved by using CoMFA based on 3D factors are much better than that obtained by using multiple regression analysis based on majorly 2D structural information. The CoMFA results show that the dominant factor which affects activity is steric, whereas electrostatic effect only plays an unimportant role.

Studies on beta-cyclodextrin amino acids inclusion complexes by electrospray ionization mass spectrometry

The positive- and negative-ion electrospray ionization mass spectra of beta-cyclodextrin-amino acids complexes in NH4Ac buffer have been reported in this paper. Compared with positive-ion ESI mass spectra of beta-cyclodextrin-amino acids complexes under the same condition, negative-ion mass spectra obtained for inclusion complexes of beta-cyclodextrin (CD) with tyrosine, phenylalanine and tryptophan, respectively, were completely dominated by deprotonated complex ions and [CD-H](-) ion which is the only daughter ion in collision-induced dissociation (CID) experiment of deprotonated complexes, The results indicated that the charged position for protonated and deprotonated complexes is different from each other. In addition, two complex ions for the same complex have similarly relative dissociation energies, which are higher than that of [CD+NH4](+), indicating that complexes observed in gasphase are not electrostatic adducts at all but complexes formed by hydrogen bonds.