High negative ion production yield in 30 keV F2+ + adenine (C5H5N5) collisions

In collisions between slow F2+ ions (30 keV) and molecular targets, adenine, scattered particle production yields have been measured directly by simultaneous detection of neutrals, positive and negative ions. The relative cross-section for a negative ion formation channel was measured to be 1%. Despite a slight decrease compared to a larger target, the fullerene C-60, the measured negative ion formation cross section is still at least one order of magnitude larger than the yield in ion-atom interactions.

Simultaneous genotyping of multiplex single nucleotide polymorphisms of the K-ras gene with a home-made kit

Accurate and fast genotyping of single nucleotide polymorphisms (SNPs) is important in the human genome project. Here an automated fluorescent method that can rapidly and accurately genotype multiplex known SNPs was developed by using a homemade kit, which has lower cost but higher resolution than commercial kit. With this method, oncogene K-ras was investigated, four known SNPs of K-ras gene exon 1 in 31 coloerctal cancer patients were detected. Results indicate that mutations were present in 8(26%) of 31 patients, and most mutations were localized in codon 12. The presence of these mutations is thought to be a critical step and plays an important role in human colorectal carcinogenesisas. (C) 2003 Elsevier B.V. All rights reserved.

accurate and self-consistent ocean color algorithm:simultaneous retrieval of aerosol optical properties and chlorphyll concentrations

A new algorithm has been developed for simultaneous retrieval of aerosol optical properties and chlorophyll concentrations in case I waters. This algorithm is based on an improved complete model for the inherent optical properties and accurate simulations of the radiative transfer process in the coupled atmosphere-ocean system. It has been tested against synthetic radiances generated for the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) channels and has been shown to be robust and accurate. A unique feature of this algorithm is that it uses the measured radiances in both near-IR and visible channels to find that combination of chlorophyll concentration and aerosol optical properties that minimizes the error across the spectrum. Thus the error in the retrieved quantities can be quantified.

Genomic organization, nucleotide sequence analysis of the core histone genes cluster in Chlamys farreri and molecular evolution assessment of the H2A and H2B

This work represents the nucleotide sequence of the core histone gene cluster from scallop Chlamys farreri. The tandemly repeated unit of 5671 bp containing a copy of the four core histone genes H4, H2B, H2A and H3 was amplified and identified by the techniques of homology cloning and genomic DNA walking. All the histone genes in the cluster had the structures in their 3' flanking region which related to the evolution of histone gene expression patterns throughout the cell cycle, including two different termination signals, the hairpin structure and at least one AATAAA polyadenylation signal. In their 5' region, the transcription initiation sites with a conserved sequence of 5'-PyATTCPu-3' known as the CAP site were present in all genes except to H2B, generally 37-45 bp upstream of the start code. Canonical TATA and CAAT boxes were identified only in certain histone genes. In the case of the promoters of H2B and H2A genes, there was a 5'-GATCC-3' element, which had been found to be essential to start transcription at the appropriate site. After this element, in the promoter of H2B, there was another sequence, 5'-GGATCGAAACGTTC-3', which was similar to the consensus sequence of 5'-GGAATAAACGTATTC-3' corresponding to the H2B-specific promoter element. The presence of enhancer sequences (5'-TGATATATG-3') was identified from the H4 and H3 genes, matching perfectly with the consensus sequence defined for histone genes. There were several slightly more complex repetitive DNA in the intergene regions. The presence of the series of conserved sequences and reiterated sequences was consistent with the view that mollusc histone gene cluster arose by duplicating of an ancestral precursor histone gene, the birth-and-death evolution model with strong purifying selection enabled the histone cluster less variation and more conserved function. Meanwhile, the H2A and the H2B were demonstrated to be potential good marks for phylogenetic analysis. All the results will be contributed to the characterization of repeating histone gene families in molluscs.

Concentrations of alkyphenol polyethoxylates entering UK estuaries

Concentrations of the weakly oestrogenic degradation products of alkylphenol polyethoxylate (APE) surfactants (nonylphenol, octylphenol, nonylphenol monoethoxylate and nonylphenol diethoxylate) were measured in water and sediments from British rivers and estuaries collected during 1994 and 1995. In addition, a series of samples of tissues of wild fish from the River Aire, and from a laboratory dosing experiment were analysed for alkylphenols, to assess the degree of bioaccumulation of these compounds. Measurable concentrations of APE residues were recorded in the River Aire (15–76 μg/l total extractable alkylphenols), the River Mersey (6–11 μg/l) and the Tees estuary (up to 76 μg/l). These levels exceed, or are close to, the no observed effect concentration for the induction of vitellogenesis in caged trout (5–20 μg/l total extractable alkylphenols), and may be sufficient to exert an oestrogenic effect on fish populations in these areas. A sediment sample from Bingley on the River Aire contained 15 μg/g (dry weight) nonylphenol, and concentrations in sediments from the Tees and Mersey estuaries exceeded 1 μg/g. These rivers receive a variety of trade waters via sewage treatment works (STW) effluents containing significant concentrations of APE. Elsewhere, concentrations in water and sediments were near or below limits of detection and biological effects are unlikely, suggesting that any oestrogenic effects observed in sewage outfalls and rivers not directly impacted by APE-containing trade-waters may be caused by other chemicals. Analysis of samples of trout muscle taken from a tank dosed at 65 μg/l nonylphenol indicated a bioaccumulation factor of between 90 and 125 after 3 weeks exposure. Samples of wild fish from the River Aire contained up to 0.8 μg/g nonylphenol in the muscle, a tissue bioaccumulation factor of approximately 50 relative to measured concentrations in water samples. A series of fish samples taken from offshore for food quality assurance purposes contained no detectable levels of APE residues (0.05–0.1 μg/g nonylphenol).

Small-molecule-directed assembly: A gold nanoparticle-based strategy for screening of homo-adenine DNA duplex binders

By using AuNP-modified homo-adenine DNA conjugate as a model system, simple colorimetric and resonance Rayleigh scattering assays have been developed for screening small molecules that trigger the formation of the non-Watson-Crick homo-adenine duplexes. The assay presented here is more simplified in format as it involves only one type of ssDNA modified Au-NP, and can be easily adapted to high-throughput screening.

Effect of hydroxyl and amino groups on electrochemiluminescence activity of tertiary amines at low tris(2,2 '-bipyridyl)ruthenium(II) concentrations

ECL of several amines containing different numbers of hydroxyl and amino groups was investigated. N-butyldiethanolamine is found to be more effective than 2-(dibutylamino)ethanol at gold and platinum electrodes, and is the most effective coreactant reported until now. Surprisingly, ECL intensities of monoamines, such as 2-(dibutylamino)ethanol and N-butyldiethanolamine, are much stronger than that of diamines including N,N,N',N'-tetrakis-(2-hydroxyethyl)-ethylenediamine and N,N,N',N'-tetrakis-(2-hydroxypropyl)ethlenediamine. The striking contrast between ECL signals of the investigated monoamines and diamines may result from more significant side reactions of diamines, such as the intramolecular side reactions between oxidative amine cation radicals and reductive amine free radicals.

Nucleobase-metal hybrid materials: Preparation of submicrometer-scale, spherical colloidal particles of adenine-gold(III) via a supramolecular hierarchical self-assembly approach

We report a simple and effective supramolecular route for facile synthesis of submicrometer-scale, hierarchically self-assembled spherical colloidal particles of adenine - gold(III) hybrid materials at room temperature. Simple mixture of the precursor aqueous solutions of adenine and HAuCl4 at room temperature could result in spontaneous formation of the hybrid colloidal particles. Optimization of the experimental conditions could yield uniform-sized, self-assembled products at 1:4 molar ration of adenine to HAuCl4. Transmission electron microscopy results reveal the formation of hierarchical self-assembled structure of the as-prepared colloidal particles. Concentration dependence, ratio dependence, time dependence, and kinetic measurements have been investigated. Moreover, spectroscopic evidence [i.e., Fourier transform infrared (FTIR) and UV-vis spectra and wide-angle X-ray scattering data] of the interaction motives causing the formation of the colloidal particles is also presented.

Silver nanoparticles coated with adenine: preparation, self-assembly and application in surface-enhanced Raman scattering

We describe herein the preparation of silver nanoparticles (AgNPs) using nucleobase adenine as protecting agent through the in situ chemical reduction of AgNO3 with NaBH4 in an aqueous medium at room temperature. As-prepared AgNPs were characterized by UV-visible spectra, transmission electron microscopy and x-ray photoelectron spectroscopy. All these data confirmed the formation of AgNPs. On the basis of electrostatic interactions between as-prepared AgNPs and anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS), we successfully fabricated (PSS/AgNP)n (n = 0-9) multilayers on a 3-mercaptopropyltrimethoxysilane/AgNP functionalized indium tin oxide (ITO) substrate via the layer-by-layer self-assembly technique and characterized as-formed multilayers with UV-visible spectra. Furthermore, these ITO substrates coated with multilayers of different thickness were investigated as surface-enhanced Raman scattering (SERS)-active substrates using p-aminothiophenol as a probe molecule, implying that these multilayers substrates may be promising for a new type of SERS-active substrate.

Determination of ultra-trace concentrations of elements in high purity tellurium by inductively coupled plasma mass spectrometry after Fe(OH)(3) coprecipitation

In this work, a method was established for the determination of impurities in high purity tellurium by inductively coupled plasma mass spectrometry (ICP-MS) after Fe(OH)(3) coprecipitation. After comparison of coprecipitation ability and separation efficiency between Fe(OH), and Al(OH)(3), Fe(OH)(3) was chosen as the precipitate. A separation factor of 160 for 200 mg tellurium was obtained under conditions of pH 9 and 2 mg of Fe3(+). The 13 elements, such as Bi, Sn, Pb, In, Tl, Cd, Cu, Co, Ni, Zn, Ti, Be and Zr, could be almost completely coprecipitated under these conditions. In addition, Te memory effect imposed on the ICP-MS instrument was assessed, as well as Te matrix effect that caused the low recovery of Ga, As, Sb and V in real sample was discussed. Finally, the method was evaluated through recovery test and was applied to practical sample analysis, with detection limits of most of the elements being below 0.15 mug g(-1) and R.S.D. below or at approximately 10%, which indicated that this method could fully satisfy the requirements for analysis of 99.999% similar to 99.9999% high purity Te.

Electrochemical behavior of FAD at a gold electrode studied by electrochemical quartz crystal microbalance

The electrochemical behavior of flavine adenine dinucleotide (FAD) at a gold electrode involving adsorption of the reduced form FADH(2) and desorption of the oxidized form FAD has been studied by using electrochemical quartz crystal microbalance (EQCM). EQCM can present information not only about the electrochemical behavior but also about the mass changes on the electrode surface. The electrochemical properties and frequency shifts were investigated in FAD solutions at different pH values, concentrations and scan rates. Reversible voltammograms were observed when pH<4.5 and irreversible voltammograms were found when pH greater than or equal to 4.5. It is found to be a diffusion controlled process when the concentration of FAD is lower than 2x10(-4) moll(-1) (pH 1.5). On the contrary, at concentrations higher than 2x10(-4) moll(-1) (pH 1.5), it is found to be an adsorption controlled process.

A COMPARATIVE-STUDY ON STM IMAGING AND ELECTROCATALYTIC ACTIVITY OF DIFFERENT SURFACES MODIFIED WITH FLAVIN ADENINE-DINUCLEOTIDE

Flavin adenine dinucleotide (FAD) was modified onto the highly oriented pyrolytic graphite (hopg) and glassy carbon electrode (gee) surfaces with three methods, respectively. Corresponding image analysis for FAD-modified hopg surfaces has been performed by scanning tunnelling microscope (STM) for the first time. The molecular resolution STM image of FAD adsorbed on the freshly-cleaved hopg was obtained, the quantitative size determination suggests that the FAD molecules adsorb side lying on the substrate surface. The anodization treatment of hopg surface yields many pits, which were clearly observed under STM. These pits provide active sites on the hopg surface for modification and the treated hopg can strongly adsorb FAD molecules, the latter exhibiting an irregular cluster structure on such a surface. When FAD was electrochemically deposited on the substrate surface, a chain structure was successfully observed. The adsorbed FAD on anodized glassy carbon electrode (gee) surface can effectively catalyze the reduction of glucose oxidase, hemoglobin and myoglobin, with a large decrease in the overvoltage, whereas the deposited FAD film exhibits excellent electrocatalysis towards dioxygen reduction.

ELECTROCATALYTIC REDUCTION OF DIOXYGEN BY AN ELECTROCHEMICALLY POLYMERIZED FLAVIN ADENINE-DINUCLEOTIDE FILM

An electrochemically polymerized flavin adenine dinucleotide (FAD) film electrode is reported for the first time. The polymerized film was prepared by a two-step method. The electrocatalytic reduction of dioxygen at a glassy carbon electrode (GCE) modifie