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At least 757 records · Page 42Linked to original sources
PubMed2006

Selective photoelectrochemical detection of DNA with high-affinity metallointercalator and tin oxide nanoparticle electrode.

Selective detection of double-stranded DNA (ds-DNA) in solution was achieved by photoelectrochemistry using a high-affinity DNA intercalator, Ru(bpy)2dppz (bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine) as the signal indicator and tin oxide nanoparticle as electrode material. When Ru(bpy)2dppz alone was irradiated with 470-nm light, anodic photocurrent was detected on the semiconductor electrode due to electron injection from its excited state into the conduction band of the electrode. The current was sustained in the presence of oxalate in solution, which acted as a sacrificial electron donor to regenerate the ground-state metal complex. After addition of double-stranded calf thymus DNA into the solution, photocurrent dropped substantially. The drop was attributed to the intercalation of Ru(bpy)2dppz into DNA and, consequently, the reduced mass diffusion of the indicator to the electrode, as well as electrostatic repulsion between oxalate anion and negative charges on DNA. The degree of signal reduction was a function of the DNA concentration, thus forming the basis for real-time DNA detection. The signal reduction was selective for ds-DNA, as no such effect was observed for single-stranded polynucleotides such as poly-G, poly-C, poly-A, and poly-U. The detection limit of calf thymus ds-DNA reached 1.8 x 10(-10) M in solution.

DNA↗
PubMed2006

On-chip amperometric measurement of quantal catecholamine release using transparent indium tin oxide electrodes.

Carbon-fiber amperometry has been extensively used to monitor the time course of catecholamine release from cells as individual secretory granules discharge their contents during the process of quantal exocytosis, but microfabricated devices offer the promise of higher throughput. Here we report development of a microchip device that uses transparent indium tin oxide (ITO) electrodes to measure quantal exocytosis from cells in microfluidic channels. ITO films on a glass substrate were patterned as 20-mum-wide stripes using photolithography and wet etching and then coated with polylysine to facilitate cell adherence. Microfluidic channels (100 mum wide by 100 mum deep) were formed by molding poly(dimethylsiloxane) (PDMS) on photoresist and then reversibly sealing the PDMS slab to the ITO-glass substrate. Bovine adrenal chromaffin cells were loaded into the microfluidic channel and adhered to the ITO electrodes. Cells were stimulated to secrete by perfusing a depolarizing "high-K" solution while monitoring oxidation of catecholamines on the ITO electrode beneath the cell using amperometry. Amperometric spikes with charges ranging from 0.1 to 1.5 pC were recorded with a signal-to-noise ratio comparable to that of carbon-fiber electrodes. Further development of this approach will enable high-throughput measurement of quantal catecholamine release simultaneously with optical cell measurements such as fluorescence.

Adrenal Glands↗
PubMed2006

Electropolymerization on microelectrodes: functionalization technique for selective protein and DNA conjugation.

A critical shortcoming of current surface functionalization schemes is their inability to selectively coat patterned substrates at micrometer and nanometer scales. This limitation prevents localized deposition of macromolecules at high densities, thereby restricting the versatility of the surface. A new approach for functionalizing lithographically patterned substrates that eliminates the need for alignment and, thus, is scalable to any dimension is reported. We show, for the first time, that electropolymerization of derivatized phenols can functionalize patterned surfaces with amine, aldehyde, and carboxylic acid groups and demonstrate that these derivatized groups can covalently bind molecular targets, including proteins and DNA. With this approach, electrically conducting and semiconducting materials in any lithographically realizable geometry can be selectively functionalized, allowing for the sequential deposition of a myriad of chemical or biochemical species of interest at high density to a surface with minimal cross-contamination.

Benzaldehydes↗
PubMed2005

Evolution of functional cyclohexadiene-based synthetic reagents: the importance of becoming aromatic.

Suites of new precursors designed around a cyclohexadiene core and intended to mediate "clean" radical chain syntheses have been prepared and tested. 1-Functionalized cyclohexa-2,5-dienes were found to readily donate H-atoms, and the resulting cyclohexadienyl radicals rapidly extruded their functional group as a free radical, because this beta-scission restored aromaticity to the ring. This concept was employed to generate designer radicals from esters of the corresponding alcohols with 1-methyl- or 1-phenylcyclohexa-2,5-diene-1-carboxylic acids. In a similar way, pre-adapted carbamoyl radicals were obtained from cyclohexadienyl-amides and proved advantageous for syntheses of alpha- and beta-lactams. Oxime ether substituted carbamoyl radicals cyclized successfully in convenient syntheses of dihydroindolin-2-ones with N-functionality at the 3-position. Similarly, silicon-centered radicals were obtained from 1-silylated cyclohexadienes, and these reagents proved to be very efficient, environmentally benign organotin hydride substitutes. Radical reactions including reductions, cyclizations, intermolecular additions, and hydrosilylations were carried out in high yields with this reagent. Other heteroatom-centered radicals, especially N-centered radicals, were obtained from appropriate cyclohexadienes enabling chain hydroaminations to be conducted. Several of the cyclohexadiene precursors proved to be useful for electron paramagnetic resonance (EPR) spectroscopic purposes, and this enabled rate constants for fragmentations of the cyclohexadienyl radicals to be obtained. Kinetic data for H-atom abstraction from cyclohexadienes, the second propagation step of the chain processes, was derived from customized radical clocks and from EPR measurements. In this way, conceptual tools were developed for improving future synthetic methodology based around these reagents.

Acids↗
PubMedDate not supplied

Synthesis and nca-radioiodination of arylstannyl-cobalamin conjugates. Evaluation of aryliodo-cobalamin conjugate binding to transcobalamin II and biodistribution in mice.

A new method of preparing radiolabeled cobalamin derivatives has been developed. The method involves the use of cobalamin-tri-n-butylstannyl hippurate conjugates as intermediates to obtain radioiodinated cobalamin-iodohippurate conjugates. The arylstannyl functionality was used as an exchangeable group to obtain high specific activity radioiodinations and to circumvent some deleterious side reactions common to cobalamins under electrophilic iodination conditions. The first step in the synthesis of tri-n--butylstannyl hippurate conjugates was to obtain free carboxylate groups on the cobalamin moiety. This was accomplished by mild acid hydrolysis of the b-, d-, or e-propionamide side chains on the corrin ring, followed by careful separation of the isomeric products. The second step was to couple a linking molecule (diaminododecane) to the carboxylate. The final step was to conjugate p-tri-n-butylstannyl hippurate to the cobalamin-diaminododecane adduct. All three isomeric cobalamin-p-tri-n-butylstannyl hippurate conjugates were prepared, as were the corresponding cobalamin-p-iodohippurate conjugates (HPLC standards). Radioiodination reactions were conducted with N-chlorosuccinimide and Na[*I]I in Me OH using conditions previously developed for arylstannylations. However, unlike the previous reactions, a key factor in obtaining the desired radioiodinated cobalamins was that the reaction be conducted under neutral conditions. Isolated yields of 40-65% were obtained for all three cobalamin isomers. Specific activities of 10-33% theoretical were obtained for the radioiodinated cobalamins. Evaluation of competitive binding of (nonradioactive) cobalamin-iodohippurate conjugates with recombinant human transcobalamin II showed that the e-isomer bound nearly as well as [57Co]cyanocobalamin (50%), whereas the b-isomer had decreased binding (6%) and the d-isomer was significantly decreased in its binding (0.7%). Two biodistributions of the radioiodinated e-isomer were conducted in athymic mice. One biodistribution investigated tissue localization in mice bearing a renal cell carcinoma xenograft, and the other biodistribution investigated tissue localization when the radioiodinated cyanocobalamin was mixed with 1% BSA prior to injection. A comparison of the results of the two biodistributions and a discussion of how they relate to previous [57/60Co]cyanocobalamin biodistributions are provided.

Animals↗
PubMed1998

Molecular, enzymatic, and regulatory characterization of rat kidney cytochromes P450 4A2 and 4A3.

The cDNAs encoding cytochromes CYP 4A2 and 4A3 were cloned by RT-PCR amplification of male rat kidney and liver RNAs, respectively. Sequence analysis demonstrated that these cDNAs were nearly identical to the published sequences for CYPs 4A2 and 4A3. CYP 4A2 and 4A3 share extensive sequence homology that extends into their 3'- and 5'-untranslated segments ( approximately 97% overall nucleotide identity). Analysis of cDNA and genomic DNA sequences shows that a sequence of 123 bp, recognized as an intron during the processing of CYP 4A2 transcripts, is conserved in the 4A3 mRNAs and that these otherwise highly homologous genes show different exon-intron distributions. The CYP 4A2 and 4A3 cDNAs were expressed in a baculovirus-insect cell expression system. Purified recombinant CYP 4A2 oxidized arachidonic acid to a mixture of 19- and 20-hydroxyeicosatetraenoic acids (20 and 80% of the total products, respectively). Reaction rates were maximal when CYP 4A2 was reconstituted in the presence of an equimolar concentration of cytochrome b5 and a 10-fold molar excess of NADPH-cytochrome P450 reductase. Studies using microsomal fractions isolated from noninfected insect cells and from cells infected with CYP 4A3 recombinant baculoviruses showed (a) the presence of an endogenous lauric acid omega-hydroxylase and arachidonic acid epoxygenase in the noninfected cells, (b) the CYP 4A3-dependent oxidation of lauric acid to 11- and 12-hydroxylaurate (24 and 76% of the total products, respectively), and (c) the lack of arachidonic acid metabolism by microsomal recombinant CYP 4A3. Nucleic acid hybridization and immunoelectrophoresis studies demonstrated that (a) CYP 4A2 transcripts are abundantly expressed in the female kidney and that CYP 4A3 is expressed in female but not in male liver, (b) anti-CYP 4A2 immunoreactive material was detected only in the male kidney, (c) male and female livers or kidneys support only low levels of CYP 4A3 translation, and (d) excess dietary salt does not alter the kidney levels of mRNA transcripts encoding CYP 4A1, 4A2, or 4A3 or change the levels of microsomal anti-4A1 or -4A2 immunoreactive proteins. Finally, no significant differences were observed between Dahl salt resistant or Dahl salt sensitive rats in the levels and/or salt regulation of mRNA transcripts enecoding CYP 4A1, 4A2, or 4A3 or the in levels of the corresponding proteins.

Amino Acid Sequence↗
PubMed2006

Complete combustion of methane over indium tin oxides catalysts.

Indium tin oxide (ITO) catalysts with different In/Sn ratios have been prepared by the co-precipitation method. The catalysts were evaluated for methane combustion at different temperatures (673-873 K) with a space velocity of 30 000 h(-1). The results showed that methane could be completely oxidized at 873 K with ITO catalysts. Doping an appropriate amount of tin into In2O3 could greatly improve its activity, while the performances of Indium-doped tin oxides were worse than that of SnO2. A significant improvement of the activity was obtained on the catalyst In8Sn2, which contains 80 wt. % of indium oxide and 20 wt. % of tin oxide. Crystal defection and the amount of oxygen vacancy caused by doping were the main factors that would affect catalytic activity of ITO catalysts. The catalytic activity is strongly inhibited by the presence of a large amount of water vapor at the entire temperature range, while only the activity at low temperature (under 823 K) decreased in the presence of sulfur dioxide. By doping Sn into In2O3, its tolerance to SO2 could be enhanced due to the higher resistance of SnO2.

Air Pollution↗
PubMed2005

Synthesis and molecular and extended structures for a diaminonaphthalene-derived bis(amido)stannylene.

The cyclic bis(amido)tin(II) compound Sn[1,8-((iPrN)2C10H6] (2) was isolated from the reaction of Li2[1,8-((iPrN)2C10H6] (1) and SnCl2. Solid-state structural analysis of 2 showed it to be a mononuclear species with a pyramidal Sn center as part of a nonplanar metallaheterocycle. The packing diagram of 2 revealed an extended one-dimensional head-to-tail chain structure with short intermolecular Sn/arene-C interactions. Computational examination of 2 (DFT/PW91 and MP2 with 6-31G* and 6-311G** basis functions) indicated that the optimum gas-phase structure of 2,which displays a Sn center in the plane of the naphthyl backbone with a slightly twisted metallaheterocycle, is approximately 24 kcal/mol lower in energy than the X-ray structure. The solid-state geometry of 2 is attributed to the intermolecular donation of the naphthalene pi-electrons to a Lewis acidic Sn center, which leads to the observed supramolecular structure. The crystal structure of 1 is also reported.

Journal Article↗
PubMed1997

Synthesis and Structure of the Zintl Phase SrSn(3)Sb(4).

The new Zintl compound strontium tin antimonide, SrSn(3)Sb(4), has been synthesized, and its structure has been determined by single-crystal X-ray diffraction methods. It crystallizes in the orthorhombic space group -Pnma with a = 10.060(2) Å, b = 4.361(1) Å, c = 22.934(4) Å, and Z = 4 at 22 degrees C. The structure of SrSn(3)Sb(4) may be described as consisting of large, narrow channels running along [010] defined by 30-membered rings constructed from an anionic framework of linked SnSb(4) tetrahedra, SnSb(3) trigonal pyramids, and zigzag Sb-Sb chains. Sr(2+) cations are situated within these channels. The channel structures of SrSn(3)Sb(4) and Ba(2)Sn(3)Sb(6) are closely related.

Journal Article↗
PubMed2002

Moving beyond molecules: patterning solid-state features via dip-pen nanolithography with sol-based inks.

Herein, we described a new dip-pen nanolithography (DPN)-based method for the direct patterning of organic/inorganic composite nanostructures on silicon and oxidized silicon substrates. The approach works by the hydrolysis of metal precursors in the meniscus between an AFM tip and a surface according to the reaction 2MCln + nH2O --> M2On + 2nHCl; M = Al, Si, and Sn. The inks are hybrid composites of inorganic salts with amphiphilic block copolymer surfactants. Three proof-of-concept systems involving Al2O3, SiO2, and SnO2 nanostructures on silicon and silicon oxide surfaces have been studied. Arrays of dots and lines can be written easily with control over feature size and shape on the sub-200 nm level. The structures have been characterized by atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray analysis. This work is important because it opens up the opportunity for using DPN to deposit solid-state materials rather than simple organic molecules onto surfaces with the resolution of an AFM without the need for a driving force other than chemisorption (e.g., applied fields).

Aluminum Oxide↗
PubMed2004

Proton-coupled electron transfer of flavodoxin immobilized on nanostructured tin dioxide electrodes: thermodynamics versus kinetics control of protein redox function.

In this paper, we report a spectroelectrochemical investigation of proton-coupled electron transfer in flavodoxin D. vulgaris Hildenborough (Fld). Poly-L-lysine is used to promote the binding of Fld to the nanocrystalline, mesoporous SnO(2) electrodes. Two reversible redox couples of the immobilized Fld are observed electrochemically and are assigned by spectroelectrochemistry to the quinone/semiquinone and semiquinone/hydroquinone couples of the protein's flavin mononucleotide (FMN) redox cofactor. Comparison with control data for free FMN indicates no contamination of the Fld data by dissociated FMN. The quinone/semiquinone and semiquinone/hydroquinone midpoint potentials (E(q/sq) and E(sq/hq)) at pH 7 were determined to be -340 and -585 mV vs Ag/AgCl, in good agreement with the literature. E(q/sq) exhibited a pH dependence of 51 mV/pH. The kinetics of these redox couples were studied using cyclic voltammetry, cyclic voltabsorptometry, and chronoabsorptometry. The semiquinone/quinone reoxidation is found to exhibit slow, potential-independent but pH-sensitive kinetics with a reoxidation rate constant varying from 1.56 s(-)(1) at pH 10 to 0.0074 s(-)(1) at pH 5. The slow kinetics are discussed in terms of a simple kinetics model and are assigned to the reoxidation process being rate limited by semiquinone deprotonation. It is proposed that this slow deprotonation step has the physiological benefit of preventing the undesirable loss of reducing equivalents which results from semiquinone oxidation to quinone.

Crystallization↗
PubMed2005

Tailoring the optical property by a three-dimensional epitaxial heterostructure: a case of ZnO/SnO2.

Epitaxial growth, as a best strategy to attain a heterostructure with a well-defined and clean interface, usually takes place on a planar substrate. In this paper, using a ZnO/SnO2 core-shell heterostructure as an example, we demonstrate the possibility of establishing a three-dimensional epitaxial interface between two materials with different crystal systems for the first time and show possible tailoring optical properties by building the heteroepitaxial crystal interface. The characterization results of element mapping, high-resolution transmission electron microscopy, and selected area electric diffraction reveal that the as-prepared ZnO/SnO2 heterostructure has a tetrapod-like ZnO core and a SnO2 shell with 15-30 nm, and their special epitaxial relation is (010)SnO2//(010)ZnO and [100]SnO2//[0001]ZnO. Such three-dimensional epitaxy between the ZnO core and SnO2 shell is quite different from the usual planar epitaxy or three-dimensional epitaxy between materials having the same crystal structure. A rational model of such complicated epitaxy has been proposed through investigating the certain structural comparability between the wurtzite ZnO and rutile SnO2 crystals. The as-prepared T-ZnO/SnO2 epitaxial heterostructure exhibits unique luminescence properties in contrast with individual tetrapod ZnO and SnO2 nanostructures, in which the epitaxial interface induces new luminescence properties. This result may inspire great interest in exploring other complicated epitaxy systems and their potential applications in laser, gas sensor, solar energy conversion, photo catalysis, and nanodevices in the future.

Crystallization↗
PubMed2005

Low-temperature activation and deactivation of high-Curie-temperature ferromagnetism in a new diluted magnetic semiconductor: Ni2+-Doped SnO2.

We report the synthesis of colloidal Ni(2+)-doped SnO(2) (Ni(2+):SnO(2)) nanocrystals and their characterization by electronic absorption, magnetic circular dichroism, X-ray absorption, magnetic susceptibility, scanning electron microscopy, and X-ray diffraction measurements. The Ni(2+) dopants are found to occupy pseudooctahedral Sn(4+) cation sites of rutile SnO(2) without local charge compensation. The paramagnetic nanocrystals exhibit robust high-Curie-temperature (T(C)) ferromagnetism (M(s)(300 K) = 0.8 mu(B)/Ni(2+), T(C) >> 300 K) when spin-coated into films, attributed to the formation of interfacial fusion defects. Facile reversibility of the paramagnetic-ferromagnetic phase transition is also observed. This magnetic phase transition is studied as a function of temperature, time, and atmospheric composition, from which the barrier to ferromagnetic activation (E(a)) is estimated to be 1200 cm(-1). This energy is associated with ligand mobility on the surfaces of the Ni(2+):SnO(2) nanocrystals. The phase transition is reversed under air but not under N(2), from which the microscopic identity of the activating defect is proposed to be interfacial oxygen vacancies.

Colloids↗
PubMed2006

Interplay of structure and reactivity in a most unusual furan Diels-Alder reaction.

Difluorinated alkenoate ethyl 3,3-difluoro-2-(N,N-diethylcarbamoyloxy)-2-propenoate reacts rapidly and in high yield with furan and a range of substituted furans in the presence of a tin(IV) catalyst. Non-fluorinated congener 2-(N,N-diethylcarbamoyloxy)-2-propenoate fails to react at all under the same conditions. These reactions have been explored using density functional theory (DFT) calculations. They reveal a highly polar transition state, which is stabilized by the Lewis acid catalyst SnCl(4) and by polar solvents. In the presence of both catalyst and solvent, a two-step reaction is predicted, corresponding to the stepwise formation of the two new carbon-carbon bonds via transition states which have similar energies in all cases. Our experimental observations of the lack of reaction of the non-fluorinated dienophile, the stereochemical outcomes, and the rate acceleration accompanying furan methylation are all well predicted by our calculations. The calculated free energy barriers generally correlate well with measured reaction rates, supporting a reaction mechanism in which zwitterionic character is developed strongly. An in situ ring opening reaction of exo-cycloadduct ethyl exo-2-(N,N-diethylcarbamoyloxy)-3,3-difluoro-7-oxabicyclo[2.2.1]hept-5-enyl-2-endo-carboxylate, which results in the formation of cyclic carbonate ethyl 4,4-difluoro-5-hydroxy-2-oxo-5,7a-dihydro-4H-benzo[1,3]dioxole-3a-carboxylate by a Curtin-Hammett mechanism, has also been examined. Substantial steric opposition to Lewis acid binding prevents carbonate formation from 2-substituted furans.

Alkenes↗
PubMed2006

Water-dissolvable sodium sulfate nanowires as a versatile template for the fabrication of polyelectrolyte- and metal-based nanotubes.

This study presents the synthesis of water-dissolvable sodium sulfate nanowires, where Na(2)SO(4) nanowires were produced by an easy reflux process in an organic solvent, N,N-dimethylformamide (DMF) and formed from the coexistence of AgNO(3), SnCl(2), dodecylsodium sulfate (SDS), and cetyltrimethylammonium bromide (CTAB). Na(2)SO(4) nanowires were derived from SDS, and the morphology control of the Na(2)SO(4) nanowires was established by the cooperative effects of Sn and NO(3)(-), while CTAB served as the template and led to homogeneous nanowires with a smooth surface. Since the as-synthesized sodium sulfate nanowires are readily dissolved in water, these nanowires can be treated as soft templates for the fabrication of nanotubes by removing the Na(2)SO(4) core. This process is therefore significantly better than other reported methodologies to remove the templates under harsh condition. We have demonstrated the preparation of biocompatible polyelectrolyte (PE) nanotubes using a layer-by-layer (LbL) method on the Na(2)SO(4) nanowires and the formation of Au nanotubes by the self-assembly of Au nanoparticles. In both nanotube synthesis processes, PEI (polyethylenimine), PAA (poly(acrylic acid)), and Au nanoparticles served as the building blocks on the Na(2)SO(4) templates, which were then rinsed with water to remove the core templates. This unique water-dissolvable template is anticipated to bring about versatile and flexible downstream applications.

Coated Materials, Biocompatible↗