Neutral Solution (neutral + solution)

Distribution by Scientific Domains


Selected Abstracts


Electroactivity of Polyaniline Multilayer Films in Neutral Solution and Their Electrocatalyzed Oxidation of ,-Nicotinamide Adenine Dinucleotide

ADVANCED FUNCTIONAL MATERIALS, Issue 6 2003
S. Tian
Abstract In this paper, we report an alternative simple method to shift the electroactivity of polyaniline (PANI) films to neutral pH conditions by forming multilayer assemblies with poly(anions) using the layer-by-layer (LBL) deposition method. A series of self-assembled PANI multilayer films with poly(anions), such as sulfonated polyaniline (SPANI), poly(acrylic acid) (PAA), poly(vinyl sulfonate) (PVS), and poly(styrene sulfonate) (PSS), were prepared by the LBL method. Their electrochemical behavior and catalytic ability for the oxidation of ,-nicotinamide adenine dinucleotide (NADH) in neutral solution were investigated by electrochemistry (EC) combined with surface plasmon spectroscopy (SPS) and the quartz crystal microbalance (QCM) technique. Results indicated that all the films showed very good stability, reversibility, and electroactivity in neutral solution. All the multilayer films can electrocatalyze the oxidation of NADH, with the catalytic ability of PANI/SPANI being higher than that of the other assemblies under the same conditions. The catalytic abilities of the films with the same thickness prepared by the copolymerization method and the LBL method were also compared. [source]


Spectroelectrochemical and Voltammetric Studies of L -DOPA

ELECTROANALYSIS, Issue 2 2003
Xiaoqiang Liu
Abstract The electrooxidation of L -dopa at GC electrode was studied by in situ UV-vis spectroelectrochemistry (SEC) and cyclic voltammetry. The mechanism of electrooxidation and some reaction parameters were obtained. The results showed that the whole electrooxidation reaction of L -dopa at glassy carbon (GC) electrode was an irreversible electrochemical process followed by a chemical reaction in neutral solution (EC mechanism). The spectroelectrochemical data were treated by the double logarithm method together with nonlinear regression, from which the formal potential E0=228,mV, the apparent electron-transfer number of the electrooxidation reaction ,n=0.376 (R=0.99, SD=0.26), the standard electrochemical rate constant k0=(3.93±0.12)×10,4,cm s,1 (SD=1.02×10,2), and the formation equilibrium constant of the following chemical reaction kc=(5.38±0.34)×10,1,s,1 (SD=1.02×10,2) were also obtained. [source]


Signal-On Electrochemiluminescence Biosensors Based on CdS,Carbon Nanotube Nanocomposite for the Sensitive Detection of Choline and Acetylcholine

ADVANCED FUNCTIONAL MATERIALS, Issue 9 2009
Xiao-Fei Wang
Abstract This work describes for the first time signal-on electrochemiluminescence (ECL) enzyme biosensors based on cadmium sulfide nanocrystals (CdS NCs) formed in situ on the surface of multi-walled carbon nanotubes (MWCNTs). The MWCNT,CdS can react with H2O2 to generate strong and stable ECL emission in neutral solution. Compared with pure CdS NCs, the MWCNT,CdS can enhance the ECL intensity by 5.3-fold and move the onset ECL potential more positively for about 400,mV, which reduces H2O2 decomposition at the electrode surface and increases detection sensitivity of H2O2. Furthermore, the ECL intensity is less influenced by the presence of oxygen in solution. Benefiting from these properties, signal-on enzyme-based biosensors are fabricated by cross-linking choline oxidase and/or acetylcholine esterase with glutaraldehyde on MWCNT,CdS modified electrodes for detection of choline and acetylcholine. The resulting ECL biosensors show wide linear ranges from 1.7 to 332,µM and 3.3 to 216,µM with lower detection limit of 0.8 and 1.7,µM for choline and acetylcholine, respectively. The common interferents such as ascorbic acid and uric acid in electrochemical enzyme-based biosensors do not interfere with the ECL detection of choline and acetylcholine. Furthermore, both ECL biosensors possess satisfying reproducibility and acceptable stability. [source]


Fluorescence Regeneration as a Signaling Principle for Choline and Carnitine Binding: A Refined Supramolecular Sensor System Based on a Fluorescent Azoalkane,

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2006
H. Bakirci
Abstract The fluorescent azoalkane, 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), forms inclusion complexes with p -sulfonatocalix[4]arene (CX4). The binding constants are on the order of 103,M,1 in water. The addition of CX4 to DBO solutions results in an efficient fluorescence quenching (up to 90,%). This supramolecular system can be used as a truly water-soluble sensor system to signal the binding of organic ammonium ions over a large pH range. Addition of choline and carnitine derivatives and tetraalkylammonium ions results in regeneration of this fluorescence, from which the binding constants (KC,=,103,105,M,1) are calculated by means of a competitive complexation model. Electrostatic effects are observed, namely, a more-than-one order of magnitude weaker binding of the carnitines in neutral solution. [source]


Electroactivity of Polyaniline Multilayer Films in Neutral Solution and Their Electrocatalyzed Oxidation of ,-Nicotinamide Adenine Dinucleotide

ADVANCED FUNCTIONAL MATERIALS, Issue 6 2003
S. Tian
Abstract In this paper, we report an alternative simple method to shift the electroactivity of polyaniline (PANI) films to neutral pH conditions by forming multilayer assemblies with poly(anions) using the layer-by-layer (LBL) deposition method. A series of self-assembled PANI multilayer films with poly(anions), such as sulfonated polyaniline (SPANI), poly(acrylic acid) (PAA), poly(vinyl sulfonate) (PVS), and poly(styrene sulfonate) (PSS), were prepared by the LBL method. Their electrochemical behavior and catalytic ability for the oxidation of ,-nicotinamide adenine dinucleotide (NADH) in neutral solution were investigated by electrochemistry (EC) combined with surface plasmon spectroscopy (SPS) and the quartz crystal microbalance (QCM) technique. Results indicated that all the films showed very good stability, reversibility, and electroactivity in neutral solution. All the multilayer films can electrocatalyze the oxidation of NADH, with the catalytic ability of PANI/SPANI being higher than that of the other assemblies under the same conditions. The catalytic abilities of the films with the same thickness prepared by the copolymerization method and the LBL method were also compared. [source]


Impedance measurements on oxide films on aluminium obtained by pulsed tensions

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2003
K. Belmokre
Anodisation; Elektrochemische Impedanzspektroskopie (EIS); pulsierende Spannung; Alterung von Oxidfilmen Abstract We have performed this study on oxide films sealed or not in boiling water. The films are first obtained on type 1050 A aluminium substrat by pulsed tensions anodizing technique, in a sulfuric acid solution. Afterwards the, Electrochemical Impedance Spectroscopy (EIS) is employed to appreciate the films behaviour in a neutral solution of 3.5% K2SO4, in which the interface processes interest only the ageing phenomenon of the oxide films and not their corrosion. We have also attempted a correlation between pulse parameters of anodization and the electrical parameters characterizing these films. The sealing influence on ageing has been studied as well. For all films, ageing is appreciated using impedance diagrams evolution versus time. The results show: , the existence of two capacitive loops confirming the presence of two oxide layers characteristic of oxide films obtained in a sulfuric acid medium. The first loop, at high frequencies, is related to the external porous layer and the second one, at lower freqencies, is related to the internal barrier layer. , the thickness of the barrier layer varies between 25 and 40 nm in relation with the electrical pulse parameters. , the sealing acts favorably against anodic oxide films ageing. Impedanzmessungen an durch pulsierende Spannung erzeugten Oxidfilmen auf Aluminium Die vorliegenden Untersuchungen wurden an versiegelten und nicht versiegelten Oxidfilmen in kochendem Wasser durchgeführt. Die Filme wurden zuerst auf Aluminiumsubstrat des Typs 1050A durch anodische Technik mit pulsierender Spannung in einer Schwefelsäurelösung erzeugt. Anschließend wurde die elektrochemische Impedanzspektroskopie eingesetzt, um das Filmverhalten in einer neutralen 3,5% K2SO4 -Lösung zu beurteilen, wobei bezüglich der Grenzflächenprozesse nur das Alterungsphänomen der Oxidfilme und nicht ihr Korrosionsverhalten interessierte. Es wurde versucht, eine Korrelation zwischen den Pulsparametern der Anodisierung und den elektrischen Parametern, die diese Filme charakterisieren, zu finden. Ebenfalls wurde der Versiegelungseinfluss auf die Alterung untersucht. Für alle Filme wurde die Alterung mit Hilfe der Entwicklung von Impedanzdiagrammen über die Zeit beurteilt. Die Ergebnisse zeigen: , die Existenz von zwei kapazitiven Schleifen, die die Anwesenheit von zwei Oxidschichten bestätigen, was charakteristisch ist für Oxidfilme, die in einer Schwefelsäurelösung erzeugt wurden. Die erste Schleife, bei hohen Frequenzen, bezieht sich auf die äußere poröse Schicht und die zweite, bei niedrigeren Frequenzen, bezieht sich auf die innere Barriereschicht , die Dicke der Barriereschicht variiert zwischen 25 und 40 nm, abhängig von den elektrischen Pulsparametern , die Versiegelung wirkt günstig gegenüber der Alterung des anodischen Oxidfilms. [source]


Geological and Geochemical Characteristics of the Hydrothermal Clay Alteration in South Korea

RESOURCE GEOLOGY, Issue 4 2000
Sang-Mo KOH
Abstract: Hydrothermally altered areas forming pyrophyllite-kaolin-sericite-alunite deposits are distributed in Chonnam and Kyongsang areas, Cretaceous volcanic field of the Yuchon Group. The Chonnam alteration area is located within depression zone which is composed of volcanic and granitic rocks of late Cretaceous age. The clay deposits of this area show the genetic relationship with silicic lava domes. The Kyongsang alteration area is mainly distributed within Kyongsang Basin comprising volcanic, sedimentary and granitic rocks of Cretaceous and Tertiary age. Most of the clay deposits of this area are closely related to cauldrons. Paleozoic clay deposit occurs in the contact zone between Precambrian Hongjesa granite gneiss and Paleozoic Jangsan quartzite of Choson Supergroup. Cretaceous igneous rocks of the both alteration areas belong to high K calc-alkaline series formed in the volcanic arc of continental margin by subduction-related magmatism. Chonnam igneous rocks show more enrichment of crustal components such as K, La, Ce, Sm, Nd and Ba, higher (La/Yb)cn ratio, and higher initial 87Sr/86Sr ratio (0. 708 to 0. 712) than those of Kyongsang igneous rocks. This might be due to the difference of degree of crustal contamination during Cretaceous magmatism. The most characteristic alteration minerals of Chonnam clay deposits are alunite, kaolin, quartz, pyrophyllite and diaspore which were formed by acidic solution. Those of Kyongsang clay deposits are sericite, quartz and pyrophyllite which were formed by weak acid and neutral solution. The formation ages of the clay deposits of two alteration areas range from 70. 1 to 81. 4 Ma and 39. 7 to 79. 4 Ma, respectively. The Daehyun clay deposit in Ponghwa area of Kyongsang province shows the alteration age range from 290 to 336 Ma. This result shows the different alteration episode from the hydrothermal alteration of Cretaceous to early Tertiary in the Kyongsang and Chonnam alteration areas. These data indicate, at least, three hydrothermal activities of Tertiary (middle to late Eocene), late Cretaceous (Santonian to Maastrichtian) and Paleozoic Carboniferous Periods in South Korea. [source]


Influence of topical antifungal drugs on ciliary beat frequency of human nasal mucosa,

THE LARYNGOSCOPE, Issue 7 2010
An In Vitro Study
Abstract Objectives/Hypothesis: Topical antifungal treatment is a subject of discussion in the treatment of chronic rhinosinusitis. The aim of this research was to study the effects of antifungal drugs on ciliary beat frequency (CBF) of human nasal mucosa under in vitro conditions. Study Design: Case series of in vitro experiments and in vitro study of cultured ciliated cells of human nasal mucosa. Methods: Human nasal mucosa was acquired during routine endoscopic sinus surgery. Cells were cultivated on object slides and exposed to different antifungal drugs in a newly developed test system. This system allowed continuous and reproducible exposure to different drugs at constant temperature, pH value, and osmolarity. The drugs were amphotericin B in two different concentrations and itraconazole. Results: Rinsing with higher concentrations of amphotericin B led to an immediate decrease of CBF, with a total stop after 15 minutes. A different result was seen in the group with lower concentrations; CBF decreased again quickly after rinsing with the test drug, but all of them recovered after rinsing with neutral solution. When using itraconazole a decline in CBF was observed again; one half of the samples returned to activity. Conclusions: Our in vitro results demonstrate a dose-dependent effect of the antifungal drugs amphotericin B and itraconazole on ciliary beat frequency of human nose epithelium. Laryngoscope, 2010 [source]


Hydrogen-Bond-Guided Self-Assembly of Nucleotides on a Receptor-Array Surface

CHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2010
Dr. Dmitry
Abstract The hydrogen-bond-guided self-assembly of 5,-ribonucleotides bearing adenine(A), cytosine (C), uracil (U), or guanine (G) bases from aqueous solution on a lipid-like surface decorated with synthetic bis(ZnII,cyclen) (cyclen=1,4,7,10-tetraazacyclodododecane) metal,complex receptor sites is described. The process was studied by using surface plasmon resonance spectroscopy. The data show that the mechanism of nucleotide binding to the 2D template is influenced by the chemistry of the bases and the pH,value of the solution. In a neutral solution of pH,7.5, the process is cooperative and selective with respect to Watson,Crick pairs (A,U and C,G), which form stable double planes in accordance with the Chargaff rule. In a more acidic solution at pH,6.0, the interactions between complementary partners become non-cooperative and the surface also stabilizes mismatched and wobble pairs due to the pH-induced changes in the receptor coordination state. The results suggest that hydrogen bonding plays a key role in the self-assembly of complementary nucleotides at the lipid-like interface, and the cooperative character of the process stems from the ideal matching of the orientation and chemistry of all the interacting components with respect to each other in neutral solution. [source]


Inorganic reactions of iodine(+1) in acidic solutions

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2004
Guy Schmitz
We present a thorough analysis of the former works concerning the hydrolysis of iodine and its mechanism in acidic or neutral solutions and recommend values of equilibrium and kinetic constants. Since the literature value for the reaction H2OI+ , HOI + H+ appeared questionable, we have measured it by titration of acidic iodine solutions with AgNO3. Our new value, K(H2OI+ , HOI + H+) , 2 M at 25°C, is much larger than accepted before. It decreases slowly with the temperature. We have also measured the rate of the reaction 3HOI , IO3, + 2I, + 3H+ in perchloric acid solutions from 5 × 10,2 M to 0.5 M. It is a second order reaction with a rate constant nearly independent on the acidity. Its value is 25 M,1 s,1 at 25°C and decreases slightly when the temperature increases, indicating that the disproportionation mechanism is more complicated than believed before. An analysis of the studies of this disproportionation in acidic and slightly basic solutions strongly supports the importance of a dimeric intermediate 2HOI , I2O·H2O in the mechanism. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:480,493, 2004 [source]


In vitro biostability evaluation of polyurethane composites in acidic, basic, oxidative, and neutral solutions

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2008
SuPing Lyu
Abstract New and improved properties can often be achieved by compounding two or more different but compatible materials. But, can failure possibility also be increased by such a compounding strategy? In this article, we compared the in vitro biostability of composites with that of the pure polymer. We tested three model composites in oxidative, acidic, basic, and neutral solutions. We found that oxidation degradation was much more profound in the composites than in the corresponding pure polymer. This degradation seemed to be an intrinsic property of composite materials. We also observed the well documented interfacial debonding between filler and matrix and its effects on the mechanical reinforcement of the hydrated composites. The improvements in acid and base resistance were also observed. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source]


Synthesis of hydroxyl silylated rhenium and (99mTc)technetium ,3+1' mixed ligand complexes

JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 8 2002
Torsten Kniess
Abstract The synthesis of hydroxyl silylated thiols as monodentate ligands is described. These monodentates were used to build with Re and 99mTc trimethyl-, triethyl- and triphenyl-silylated ,3+1' mixed ligand complexes, using 3thiapentane-1,5-dithiol as co-ligand. The Re complexes were characterized by 1H NMR and elemental analysis, the 99mTc complexes were detected by radio HPLC. While the trimethyl silylated derivatives hydrolysed in aqueous media, the triethyl- and triphenyl silylated complexes have proved to be stable in neutral solutions. Copyright © 2002 John Wiley & Sons, Ltd. [source]


Study of the adsorption of benzimidazole and 2-mercaptobenzothiazole on an iron surface by confocal micro-Raman spectroscopy

JOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2004
G. Wang
Abstract Benzimidazole (BIMH) and 2-mercaptobenzothiazole (HMBT) dissolved in ethanol were chosen for the investigation of the interaction between organic molecules and surface atoms of iron or iron oxide by confocal micro-Raman spectroscopy. Both BIMH and HMBT show enhanced and highly structured spectra in the 200,1500 cm,1 region when the iron is at a potential of ca ,0.7 to ,0.9 V in a neutral medium. BIMH had a weak interaction with the iron surface in a basic medium but it was chemically adsorbed in a neutral medium. HMBT was chemically adsorbed on the iron via the exocyclic S and N atoms in acidic and neutral solutions, whereas in basic media it was bound electrostatically. Copyright © 2004 John Wiley & Sons, Ltd. [source]