Studies of electrochemical quantized capacitance charging of surface ensembles of silver nanoparticles

CTAB-stabilized silver nanoparticles were synthesized by NaBH4 reduction. The as-prepared nanoparticles can be self-assembled on 3-mercaptopropionic acid (MPA) modified gold electrode, which was supported strongly by XPS measurements. Exceptional long-term stability of the as-prepared colloidal silver aqueous solution and the desorption of silver nanoparticle ensemble on MPA after alcohol rinsing proved that these CTAB molecules adsorbed on silver core formed interdigitated bilayer structure. DPV and differential capacitance measurements were performed to characterize the as-prepared silver nanoparticle ensemble. and the interesting quantized capacitance charging behaviors were observed.

Conformational transition of DNA induced by cationic lipid vesicle in acidic solution: spectroscopy investigation

The conformational transition of DNA induced by the interaction between DNA and a cationic lipid vesicle, didodecyidimethylammonium bromide (DDAB), had been investigated by circular dichroism (CD) and UV spectroscopy methods. We used singular value decomposition least squares method (SVDLS) to analyze the experimental CD spectra. Although pH value influenced the conformation of DNA in solution, the results showed that upon binding to double helical DNA, positively charged liposomes induced a conformational transition of DNA molecules from the native B-form to more compact conformations. At the same time, no obvious conformational changes occurred at single-strand DNA (ssDNA). While the cationic lipid vesicles and double-strand DNA (dsDNA) were mixed at a high molar ratio of DDAB vesicles to dsDNA, the conformation of dsDNA transformed from the B-form to the C-form resulting in an increase in duplex stability (DeltaT(m) = 8 +/- 0.4 degreesC). An increasing in T-m was also observed while the cationic lipid vesicles interacted with ssDNA.

Preparation, characterization and luminescence properties of ultrathin films containing polyoxometalates

Ultrathin multilayer films of poly(allylamine hydrochloride) (PAH) and a polyoxotungstoeuropate cluster K-13[Eu(SiW11O39)(2)] (Eu(SiW11)(2)) have been prepared by the layer-by-layer self-assembly method. The Eu(SiW11)(2)/PAH multilayer films have been characterized by X-ray photoelectron spectra and atomic force microscopy (AFM). UV-Vis measurements reveal regular film growth with each Eu(SiW11)(2) adsorption. The photoluminescent behavior of the film at room temperature was to show the characteristic Eu3+ emission pattern of D-5(o) --> F-7(J). The occurrence of photoluminescent activity confirms the potential for creating luminescent multilayers with polyoxometalates.

Preparation and luminescence properties of the mesoporous MCM-41s intercalated with rare earth complex

Rare earth complex Eu(DBM)(3)phen (DBM: dibenzoylmethane, phen: 1.10-phenanthroline) hits been incorporated into unmodified MCM-41 and modified MCM-41s by aminopropyltriethoxysilane (APTES) or N-[(3-triethoxysilyl)propyl]ethylenediamine(TEPED). Thus, the assemblies of unmodified or modified MCM-41s with rare earth (RE) complex have been obtained. XRD spectra. NMR spectra. diffuse reflectance spectra. and the luminescence spectra were used to characterize the pure RE complex and the corresponding assemblies. The assemblies have better luminescence properties under UV irradiation. and their fluorescence lifetimes on the excited state are longer than that of the corresponding pure complex. The possible mechanisms are also discussed in the context.

Photoluminescent multilayer films based on polyoxometalates

Ultrathin multilayer films consisting of the polyoxotungstoeuropate cluster K-12[EuP5W30O110] (EuP5W30) and poly( allylamine hydrochloride) (PAH) have been prepared by the layer-by-layer self-assembly method. The (EuP5W30 /PAH) multilayer films have been characterized by small-angle X-ray reflectivity measurements, X-ray photoelectron spectra, and atomic force microscopy (AFM). From the AFM images, the thickness of the {PEI/PSS/PAH(EuW30/PAH)} multilayer film was estimated to be 6.5 nm, corresponding to an average thickness of ca. 1.1 nm for a EuW30/PAH layer pair. The photoluminescent behavior of the film at room temperature was investigated to show the characteristic Eu3+ emission pattern of D-5(0)-->F-7(J). The fluorescence behavior of the multilayer film is essentially identical to that of H-n[EuP5W30O110]((12-n)-) in a concentrated aqueous solution, except for the relative intensities and peak bandwidths. The occurence of photoluminescent activity confirms the potential for creating luminescent multilayers with polyoxometalates (see ref. 23).

Preparation and characterization of PSt-b-PHEMA metal hybrids

The block copolymer polystyrene-b-poly[2-(trimethylsilyloxy)ethylene methacrylate] (PSt-b-PTMSEMA) was synthesized using atom-transfer radical polymerization (ATRP). The hydrolysis of PSt-b-PTMSEMA led to the formation of an amphiphilic block copolymer, polystyrene-b-poly(2-hydroxylethyl methacrylate) (PSt-b-PHEMA), which was characterized by GPC and H-1-NMR. TEM showed that the PSt-b-PHEMA formed a micelle, which is PSt as the core and PHEMA as the shell. Under appropriate conditions, the nickel or cobalt ion cause chemical reactions in these micelles and could be reduced easily. ESCA analysis showed that before reduction the metal existed as a hydroxide; after reduction, the metal existed as an oxide, and the metal content of these materials on the surface is more than that on the surface of the copolymer metal ion. XRD analysis showed that the metal existed as a hydroxide before reduction and existed as a metal after reduction.

Characterization of Y2O3 : Eu coated with polystyrene

The core-shell Y2O3:Eu3+/polystyrene particles was prepared by surface modification with citric acid and emulsion polymerization method of styrene. The DTA curve of coated particles exhibits a small and wide exothermic peak of organic compound around 387 degreesC. The carbonyl stretching vibration band was shifted to low wavenumber in FTIR spectrum and the binding energy of Y3d5/2 was shifted to high-energy band in XPS spectrum. The results of FTIR and XPS show that citric acid was coupled to the particles surface. The hydrophilic surface became amphiphilic by modification of citric acid. So styrene could adsorb on particles surface to form emulsion structure which inorganic core was inside. EDS spectra show that Y2O3:Eu3+ particles were coated uniformly with polystyrene.

Synthesis and electrochemical characteristics of lanthanide complexes with 2-nitro-5,10,15,20-tetraphenylporphyrin and acetylacetonate

Four lanthanide complexes with 2-nitro-5,10,15,20-tetraphenylporphyrin and acetylacetonate were prepared and characterized by elemental analyses, LR, UV-Visible,H-1 NMR, XPS and molar conductance. The redox properties of the lutetium complex with 2-nitro-5,10,15,20-tetraphenylporphyrin and acetylacetonate in dichloromethane were studied by cyclic voltammetry.

Preparation, characterization and photophysical properties of layered zirconium bis(monohydrogenphosphate) intercalated with rare earth complexes

Two kinds of rare earth (RE) complexes were intercalated into zirconium bis(monohydrogenphosphate) (alpha -ZrP) by exchanging the RE complexes into the p-methyoxyaniline (PMA) preintercalated compound Zr(O3POH)(2). 2PMA (alpha -ZrP . 2PMA). Powder X-ray diffraction patterns reveal that Eu(DBM)(3)phen (DBM: dibenzoylmethane, phen: 1,10-phenanthroline) and Tb(AA)(3)phen (AA: acetylacetone) intercalated into alpha -ZrP . 2PMA. This was confirmed by the UV-visible spectra of both the RE complexes and the assemblies. At the same time, the assemblies have better luminescent properties, and the fluorescent lifetimes of RE3+ in the excited state in the assemblies are much longer than those in the complexes. The stabilities of the assemblies under UV radiation are much better than those of the RE complexes.

Voltammetric and spectroscopic studies on methyl green and cationic lipid bound to calf thymus DNA

DNA interaction with cationic lipids promises to be a versatile and effective synthetic transfection agent. This paper presents the study on binding of a simple artifical cationic lipid, cetyltrimethylammonium bromide (CTAB), to calf thymus DNA (CT DNA) prior to the condensation process, taking methyl green (MG) as a probe. The results show that the CTAB binds to DNA through electrostatic interaction forming a hydrophobic complex, thus changing the micro-environment of duplex of DNA, so the binding state of MG and DNA is changed, and a complex CTAB-CT DNA-MG is formed. This fact suggests a new way to mediate the conformation of molecular assemblies of DNA and lipids. (C) 2000 Elsevier Science B.V. All rights reserved.

Comparative studies on electrochemical behavior and electrocatalytic properties of heteropolyanion-containing multilayer films prepared by two methods

Two modification methods for multilayer formation, i.e. immersion growth and electrochemical growth, were studied comparatively for their influence on the electrochemical behavior and the electrocatalytic properties of the thus-fabricated SiMo11V-containing multilayer films. Electrochemical growth was proven to be a more suitable method than immersion growth in preparing uniform ultrathin multilayer self-assemblies with good functions. We investigated the effects of scan rate and pH on the electrochemical behavior of the monolayer and multilayer films. We also compared the electrocatalytic effects on the reduction of BrO3- and HNO2 by the multilayer films prepared by the two methods. Moreover, the influence of multilayer thickness and the identity of the outermost layer on the electrocatalytic properties were studied. Much higher catalytic currents appeared on the thicker multilayer films than those on the thinner ones. On the other hand, the catalytic currents became smaller when the multilayer films with SiMo11V as the outermost layer were covered with an additional quarternized poly(4-vinylpyridine) layer partially complexed with osmium bis(2,2'-bypyridine) chloride (QPVP-Os layer). These influences were believed to be due to the different quantities of electrocatalyst loaded in the multilayer films and the blocking effect of the QPVP-Os outermost layer. (C) 2000 Elsevier Science S.A. All rights reserved.

A novel potentiodynamic method of electrochemical growth for layer-by-layer film formation based on electrostatic interaction

A novel method of electrochemical growth was developed for layer-by-layer film formation and proven more advantageous than the commonly used immersion growth in obtaining more uniform multilayer assemblies, as well as being able to proceed in salt-containing solutions without competitive adsorption from the salt ions. (C) 1999 Elsevier Science S.A. All rights reserved.

Synthesis, electrochemistry, fluorescence and ECL of Ru (phen)(2) (dcbpy) (PF6)(2)

A new ECL-active species, Ru (phen)(2) (dcbpy) (PF6)(2), has been designed and synthesized. Its structure was confirmed by means of IR, ESI-MS and 2D NMR. Also, its properties of electrochemistry, fluorescence and ECL are reported, which have suggested a good hope of being used in electrochemiluminescent immunoassay and nucleic acid hybridization.

FTIR-ATR study of self-assembled thiol monolayers on gold

Self-assembled monolayers of 1-teradecanethiol on gold were characterized by means of FTIR-ATR measurements, XPS and contact angle measurements. Linear dichroism measurements using FTIR-ATR are used to estimate the orientation of the alkyl chains. An equation for calculating the orientation angles of the alkyls chains was deduced. (C) 1998 Elsevier Science Limited. All rights reserved.

Synthesis and investigation of monoesters of polymaleic acids with azo-group

A series of amphiphilic polymers, monoesters of polymaleic acid containing ate-side groups (PMAN-A(n)Me) was synthesized by the reaction of alcohol(A,Me) with polymaleic anhydride (PMAN) for Langmuir-Blodgett assembly. The effects of the length of flexible spacer in the side chain on the pi-A isotherms and LB films were investigated. The UV-Vis and infrared linear dichroism spectra showed that the ate-side groups were highly oriented in PMAN-A(6)Me LB film deposited on silica or CaF2 substrate.