Study on surface acid-base property of carboxylic acid-terminated self-assembled monolayers by cyclic voltammetry and electrochemical impedance spectroscopy

Cyclic voltammetry and electrochemical impedance spectroscopy were used to study the surface acid-base property of carboxylic acid-terminated self-assembled monolayers (SAMs). A carboxylic acid-terminated thiol, such as thioctic acid (1,2-dithiolane-3-pentanoic add), was self-assembled on gold electrodes. Electron transfer between the bulk solution and the SAM modified electrode was studied at different pH using Fe(CN)(6)(3-) as a probe. The surface pK(a) of thioctic acid was determined by cyclic voltammetry and electrochemical impedance spectroscopy to be 5.6 +/- 0.1 and 5.8 +/- 0.1, respectively. The method is compared with other methods of monolayer pK(a) measurement.

The role of redox property of La2-x(Sr,Th)(x)CuO4 +/-lambda playing in the reaction of NO decomposition and NO reduction by CO

Two systems of mixed oxides, La2-xSrxCuO4 +/- lambda (0.0 less than or equal to x less than or equal to 1.0) and La(2-x)Tn(x)CuO(4 +/-) (lambda) (0.0 less than or equal to x less than or equal to 0.4), with K2NiF4 structure were prepared. The average valence of Cu ions and oxygen nonstoichiometry (lambda) were determined by means of chemical analysis. Meanwhile, the adsorption and activation of nitrogen monoxide (NO) and the mixture of NO + CO over the mixed oxide catalysts were studied by means of mass spectrometry temperature-programmed desorption (MS-TPD). The catalytic behaviors in the reactions of direct decomposition of NO and its reduction by CO were investigated, and were discussed in relation with average valence of Cu ions, A and the activation and adsorption of reactant molecules. It has been proposed that both reactions proceed by the redox mechanism, in which the oxygen vacancies and the lower-valent Cu ions play important roles in the individual step of the redox cycle. Oxygen vacancy is more significant for NO decomposition than for NO + CO reaction. For the NO + CO reaction, the stronger implication of the lower-valent Cu ions or oxygen vacancy depends on reaction temperature and the catalytic systems (Sr- or Th-substituted). (C) 2000 Elsevier Science B.V. All rights reserved.

Effect on the property of the photoinduced carrier transport of CdS as sensitizer for TiO2 nanoparticulate thin films

The TiO2 nanoparticle thin films have been sensitized in situ with CdS nanoparticles. The SPS measurement showed that large surface state density was present on the TiO2 nanoparticles and the surface state can be efficiently decreased by sensitization as well as selecting suitable heat treatment, Both the photocurrent response and the charge recombination kinetics in TiO2 thin films were strongly influenced by trapping/detrapping of surface states. The slow photocurrent response of TiO2 nanoparticulate thin films upon the illumination was attributed to the trap saturation effects, The semiconductor sensitization made the slow photoresponse disappeared and the steady-state photocurrent value increased drastically, which suggested that the sensitization of TiO2 thin films with CdS could get a better charge separation and provide a simple alternative to minimize the effect of surface state on the photocurrent response.

Quantitative structure-property relationship research to the analysis of photoionization sensitivity of organic compounds in gas chromatography

The A(m) index and molecular connectivity index were used for studying the photoionization sensitivity of some organic compounds in gas chromatography. The analysis of structure-property relationship between the photoionization sensitivity of the compounds and the A(m) indices or molecular connectivity indices has been carried out. The genetic algorighm was used to build the correlation model in this field. The results demonstrate that the property of compounds can be described by both A(m) indices and molecular connectivity indices, and the mathematical model obtained by the genetic algorithm was better than that by multivariate regression analysis.

Selection for variables in quantitative structure-activity/property relationship studies - Comparison between methods of orthogonal descriptors and leaps-and-bounds regression analysis

In this paper, the comparison of orthogonal descriptors and Leaps-and-Bounds regression analysis is performed. The results obtained by using orthogonal descriptors are better than that obtained by using Leaps-and-Bounds regression for the data set of nitrobenzenes used in this study. Leaps-and-Bounds regression can be used effectively for selection of variables in quantitative structure-activity/property relationship(QSAR/QSPR) studies. Consequently, orthogonalisation of descriptors is also a good method for variable selection for studies on QSAR/QSPR.

The preparation and property studies of transparent resins containing rare earth terbium(III) complex

The binary and ternary rare-earth terbium(m) complexes were introduced into the styrene/alpha -methylacrylic acid copolymerization system, and some optical resins that possess a high transparency in visible light region were obtained. The study of the optical property showed that they have good luminescent properties such as a high luminous intensity and a long luminous lifetime, In addition, we investigated the relationship among the transparency, the luminescent property of the copolymer, and the content of the components in the polymeric system. The results indicated that the optical resins can provide a relatively stable environment for composite rare earth complexes, which is good to exhibit the luminescent properties of rare earth complexes. At the same time, the rare earth complexes can offer the transparent resin a novel function.

Morphology, structure, and rheological property of linear low-density polyethylene grafted with acrylic acid

The chain structure, spherulite morphology, and theological property of LL-DPE-g-AA were studied by using electronspray mass spectroscopy, C-13-NMR, and rheometer. Experimental evidence proved that AA monomers grafted onto the LLDPE backbone formed multiunit AA branch chains. It was found that AA branch chains could hinder movement of the LLDPE main chain during crystallization. Spherulites of LLDPE became more anomalous because of the presence of AA branch chains. Rheological behavior showed that AA branch chains could act as an inner plasticizer at the temperature range of 170-200 degreesC, which made LLDPE-g-AA easy to further process. (C) 2001 John Wiley & Sons, Inc.

Polyimide structure-property relationships - I. Polyimide properties vs dianhydride configuration

X-ray crystal structures of 2,2',3,3'-and 3,3',4,4'-biphenyltetracarboxylic dianhydride (2,2',3,3'- and 3,3',4,4'-BPDA) were determined. The dianhydride isomers have different symmetry caused by difference in two anhydride group positions and the dihedral angles between the two phenyl rings are 62.9 degrees for 2,2',3,3',-BPDA and 0 degrees for 3,3',4,4'-BPDA respectively. The polyimides from 2,2',3,3'-BPDA exhibit enhanced solubility, higher thermal stability, and higher glass transition temperature (T-g) compared with those from 3,3',4,4'-BPDA.

Transport property of polyaniline and its molecular weight dependence

The electrical conductivity of polyaniline doped with camphor sulfonic acid (PAn-CSA) was studied. The results indicate that there is a critical temperature (T-c) and the temperature dependence of PAn-CSA conductivity shows metallic and semiconductor characteristics above and below T-c, respectively. The higher the molecular weight of PAn, the lower the T-c. The conductivity was enhanced remarkably when PAn-CSA film was stretched, its room temperature conductivity is up to 750 S/cm when elogonation is 60%; however, T-c was independent of elongation.

Structure-property relationships in Li1-xHxIO3 type complex crystals

Chemical bond parameters and the linear and nonlinear optical (NLO) properties of all constituent chemical bonds in Li1-xHxIOx [x (the amount of hydrogen) = 0.0, 0.28, and 0.34] (LHIO) type complex crystals have been investigated from the chemical bond viewpoint, At the same time, the relationship between the crystal structure and its optical properties has been obtained, based on the calculated results of LiIO3, Li0.72H0.28IO3, and Li0.66H0.34IO3. The nonlinear optical properties of LHIO single crystals are found to be particularly sensitive to the H+ impurity concentration. (C) 1998 Academic Press.

Synthesis and solvent enhanced relaxation property of water-soluble endohedral metallofullerenols

Gadolinium fullerenols, as novel and potential contrast agents for magnetic resonance imaging, were synthesized, which showed excellent efficiency in enhancing water proton relaxation with a relaxivity of 47.0+/-1.0 mM(-1).s(-1).

Barrier property and structure of acrylonitrile/acrylic copolymers

A series of acrylonitrile (AN) copolymers with methyl acrylate (MA) or ethyl acrylate (EA) as comonomer (5-23 wt%) was prepared by free-radical copolymerisation. The permeability coefficients of the copolymers to oxygen and carbon dioxide were measured at 1.0 MPa and at 30 degrees C, and those to water vapor also measured at 100% relative humidity and at 30 degrees C. All the AN/acrylic copolymers are semicrystalline. As the acrylate content increase, the permeability coefficients of the copolymers to oxygen and carbon dioxide are increased progressively, but those to water vapor are decreased progressively. The gas permeability coefficients of the polymers were correlated with free-volume fractions or the ratio of free volume to cohesive energy.

Structure-property relationship of phenoxynaphthacenequinones and their relatives

Like 6-phenoxy-5,12-naphthacenequinone (1), 6-[4-(2-( 8-hydroxyphenyl) isopropyl)phenoxy]-5, 12-naphthacenequinone (2) and 6-naphthyloxynaphthacenequinone (6) showed normal photochromism, The relative initial rates of trans to ana photoconversion were in the order: 1, 100; 2, 37; 6, 21, 6-[4-(Phenylazo)phenoxyl-5,12-naphthacenequinone (3), 6-[4-(p-ethoxyphenylazo) phenoxy]-5,12-naphthacenequinone (4), 6-[4-(p-nitrophenylazo)phenoxy]-5,12-naph cenequinone (5) had only slight W-induced photochromism for the phenoxynaphthacenequinone photochrome. 6-(2-Nitrosonaphthyloxy)-5,12-naphthacenequinone (7) exhibited no photochromism and underwent irreversible photoreaction.

Study on the Property of Vitamin B-12-Modified Electrode and its Electrocatalysis for the Reduction of Oxygen

It was found that vitamin B-12 could be strongly adsorpted on the anodized glassy carbon electrode to form a vitamin Thy-modified glassy carbon electrode. The modified electrode is stable in a wide pH range. The electrochemical characteristics of the modified electrode were studied in details. In addition, it was found that the reduction of oxygen could be catalyzed by the modified electrode to form H2O2. An EC mechanism was suggested for the process, and the follow up chemical reaction might he the rate determined step.