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At least 973 records · Page 54Linked to original sources
PubMed1997

Gold Clustering at the Terminal Functions of Long-Chain Thiols and Amines.

Treatment of 1,6-hexanedithiol with (4)/(3) mol equiv of tris[(triphenylphosphino)aurio(I)]oxonium tetrafluoroborate and sodium tetrafluoroborate affords (n-hexane-1,6-dithiolato)tetrakis-[(triphenylphosphine)gold(I)] bis(tetrafluoroborate) (1). The analogous reactions with beta-mercaptoethylamine, HS(CH(2))(2)NH(2), 1,4-diaminobutane, H(2)N(CH(2))(4)NH(2), and n-butyl- and n-octylamine, CH(3)(CH(2))(n)()NH(2) (n = 3 or 7), give the corresponding penta- (2), hexa- (3), and trinuclear (4, 5) complexes, respectively. The crystal structures of compounds 3 and 5 have been determined by single-crystal X-ray diffraction studies. In the hexanuclear complex 3, three gold atoms are bonded to each nitrogen, putting each of these atoms at the apex of an NAu(3) pyramid. There are no intra- or intermolecular interactions between the gold centers of different nitrogen atoms. The trinuclear complex 5 features the unfolded aliphatic chain at the apex of such a pyramid. In both compounds the gold atoms show close contacts of 3.0 +/- 0.1 Å, indicating significant bonding, which is probably the main driving force for the clustering of seemingly closed-shell (d(10)) gold(I) metal atoms.

Journal Article↗
PubMed2003

Further studies on spot tests and microcrystal tests for identification of cocaine.

The presence of cocaine in illicit drug samples is still being determined in some laboratories using spot tests and microcrystal tests. Seventeen chemical species were tested using three different spot tests (Wagner, Marquis, and cobalt thiocyanate followed by stannous chloride reactions) and two microcrystal tests (gold chloride and platinic chloride) to determine whether the results could be differentiated from the results of these tests on cocaine. The data obtained indicated that nine of the 17 compounds gave results similar to those from cocaine using the three spot tests, but that the results from microcrystal testing allowed for differentiation of all nine compounds from cocaine.

Cobalt↗
PubMed2005

SERS studies of the adsorption of guanine derivatives on gold colloidal nanoparticles.

Surface enhanced Raman scattering spectra of guanine, guanosine and 2'-deoxyguanosine adsorbed on gold colloidal nanoparticles were obtained. From the striking similarity of the SERS spectra of these compounds, it can be evidenced that guanosine and 2'-deoxyguanosine adsorb on gold nanoparticles through the guanine moiety. The molecular sites involved in the interaction with the gold surface are the same for the 3 compounds: the oxygen of the carbonilic group and the N(7) atom. Guanine, guanosine and 2'-deoxyguanosine adsorb on the gold substrates with a tilted orientation with respect to the metal surface. SERS data were interpreted taking into account density functional theoretical (DFT) calculations of guanine.

Adsorption↗
PubMed2006

Gold(I) catalyzed isomerization of 5-en-2-yn-1-yl acetates: an efficient access to acetoxy bicyclo[3.1.0]hexenes and 2-cycloalken-1-ones.

The gold(I) catalyzed rearrangement of 5-en-2-yn-1-yl acetates into functionalized acetoxy bicyclo[3.1.0]hexenes is described. The mild reaction conditions employed allow the efficient and rapid synthesis of a variety of such bicyclic compounds via a sequence of two gold(I)-catalyzed isomerization steps. Acetoxy bicyclo[3.1.0]hexenes products can be further transformed to 2-cycloalkenones by simple methanolysis.

Journal Article↗
PubMed2006

Stereoselective synthesis of vinylsilanes by a gold(I)-catalyzed acetylenic sila-cope rearrangement.

Cationic tri-tert-butylphosphinegold(I) serves as a catalyst in the sila-Cope rearrangement of acetylenic allylsilanes. When phenol is employed as a nucleophile, the reaction allows for the stereoselective synthesis of vinylsilanes. Alternatively, use of methanol as a nucleophile leads to cyclic vinylsilanes, which can be viewed as latent vinylsilanes that are revealed on treatment with a mild Lewis acid. Thus, both of these reagents serve as useful reagents for stereoselective synthesis of trisubstituted olefins through transition-metal-catalyzed cross-coupling reactions.

Alkynes↗
PubMed1985

Retrograde tracing of neural pathways with a protein gold complex. II. Electron microscopic demonstration of projections and collaterals.

This paper describes a sensitive method for tracing neural connections at the electron microscopic (EM) level using a new compound produced through the coupling of colloidal gold particles to a wheat germ agglutinin horseradish peroxidase conjugate (the WGA*HRP-gold complex). Visualization of retrogradely labeled cells at the EM level was achieved either directly by gold particles scanning or after silver enhancement. By using different sizes of gold particles individually coupled to WGA*HRP and injected in different brain areas EM detection of multiple retrograde labeling was possible. Thus retrogradely labeled cells were first identified at the light microscopic level through HRP histochemistry with tetramethylbenzidine as a chromogen and then examined under the electron microscope after osmication and embedding. Gold particles were readily identified as electron dense, round dots in spherical grey vesicles. Identification of different sizes of gold particles often localized in the same vesicle established that the protein-gold complex can be used to study collateralisation of parental axons.

Animals↗
PubMed2005

Gold-polyaniline composite. Part I. Moving electrochemical interface.

The controlled growth of gold nanoclusters in polyaniline is predicated by the ability of PANI to switch from conducting to insulating form and by the fact that imine nitrogens form a strong complex with chloroaurate anions. The principal technique used in this study has been chronopotentiometric stripping. The chronopotentiograms indicate that the electrochemical interface for the Pt/Au/polyaniline/electrolyte shifts back and forth from the solution/PANI interface to Au/PANI interface. By adjusting experimental conditions the size and the size distribution of Au clusters can be controlled.

Aniline Compounds↗
PubMed2001

Protein adsorption to oligo(ethylene glycol) self-assembled monolayers: experiments with fibrinogen, heparinized plasma, and serum.

Low protein adsorption is believed advantageous for blood-contacting materials and ethylene glycols (EG)-based polymeric compounds are often attached to surfaces for this purpose. In the present study, the adsorption of fibrinogen, serum, and plasma were studied by ellipsometry on a series of well-defined oligo(EG) terminated alkane-thiols self-assembled on gold. The layers were prepared with compounds of the general structure HS-(CH2)15-CONH-EGn, where n = 2, 4, and 6. Methoxy-terminated tri(EG) undecanethiol and hydroxyl-terminated hexadecanethiol self-assembled monolayers (SAMs) were used as references. The results clearly demonstrate that the adsorption depends on the experimental conditions with small amounts of fibrinogen adsorbing from a single protein solution, but larger amounts of proteins from serum and plasma. The adsorption of fibrinogen and blood plasma decreased with an increasing number of EG repeats and was temperature-dependent. Significantly less serum adsorbed to methoxy tri(EG) than to hexa(EG) and more proteins remained on the latter surface after incubation in a sodium dodecyl sulfate (SDS) solution, indicating a looser protein binding to the methoxy-terminated surface. All surfaces adsorbed complement factor 3 (C3) from serum and plasma, although no surface-mediated complement activation was observed. The present study points to the importance of a careful choice of the protein model system before general statements regarding the protein repellant properties of potential surfaces can be made.

Adsorption↗
PubMed1996

Induction of Defense-Related Ultrastructural Modifications in Pea Root Tissues Inoculated with Endophytic Bacteria.

The stimulation exerted by the endophytic bacterium Bacillus pumilus strain SE34 in plant defense reactions was investigated at the ultrastructural level using an in vitro system in which root-inducing T-DNA pea (Pisum sativum L.) roots were infected with the pea root-rotting fungus Fusarium oxysporum f. sp. pisi. In nonbacterized roots, the pathogen multiplied abundantly through much of the tissue including the vascular stele, whereas in prebacterized roots, pathogen growth was restricted to the epidermis and the outer cortex In these prebacterized roots, typical host reactions included strengthening the epidermal and cortical cell walls and deposition of newly formed barriers beyond the infection sites. Wall appositions were found to contain large amounts of callose in addition to being infiltrated with phenolic compounds. The labeling pattern obtained with the gold-complexed laccase showed that phenolics were widely distributed in Fusarium-challenged, bacterized roots. Such compounds accumulated in the host cell walls and the intercellular spaces as well as at the surface or even inside of the invading hyphae of the pathogen. The wall-bound chitin component in Fusarium hyphae colonizing bacterized roots was preserved even when hyphae had undergone substantial degradation. These observations confirm that endophytic bacteria may function as potential inducers of plant disease resistance.

Journal Article↗
PubMed2000

A novel cleaning method of gold-coated atomic force microscope tips for their chemical modification

For chemical modification of gold-coated AFM tips with thiol or sulfide compounds, a new two-step precleaning procedure was studied. The two-step cleaning procedure involves (i) oxidation of organic contaminants on the AFM tips with ozone treatment and (ii) reduction of the oxidized gold surface by immersing the oxidized tip into pure hot ethanol at ca. 65 degrees C. The chemically modified tips prepared from gold-coated AFM tips precleaned by the two-step procedure gave almost the same tip characteristics as those chemically modified immediately after gold vapor deposition in a factory. The present two-step cleaning procedure can be used widely for chemical modification of commercially available gold-coated AFM tips with thiol or disulfide compounds for chemical force microscopy.

Journal Article↗
PubMed1992

Kinetic studies on the formation and decomposition of compounds II and III. Reactions of lignin peroxidase with H2O2.

The present study characterizes the serial reactions of H2O2 with compounds I and II of lignin peroxidase isozyme H1. These two reactions constitute part of the pathway leading to formation of the oxy complex (compound III) from the ferric enzyme. Compounds II and III are the only complexes observed; no compound III* is observed. Compound III* is proposed to be an adduct of compound III with H2O2, formed from the complexation of compound III with H2O2 (Wariishi, H., and Gold, M. H. (1990) J. Biol. Chem. 265, 2070-2077). We provide evidence that demonstrates that the spectral data, on which the formation of compound III* is based, are merely an artifact caused by enzyme instability and, therefore, rule out the existence of compound III*. The reactions of compounds II and III with H2O2 are pH-dependent, similar to that observed for reactions of compounds I and II with the reducing substrate veratryl alcohol. The spontaneous decay of the compound III of lignin peroxidase results in the reduction of ferric cytochrome c. The reduction is inhibited by superoxide dismutase, indicating that superoxide is released during the decay. Therefore, the lignin peroxidase compound III decays to the ferric enzyme through the dissociation of superoxide. This mechanism is identical with that observed with oxymyoglobin and oxyhemoglobin but different from that for horseradish peroxidase. Compound III is capable of reacting with small molecules, such as tetranitromethane (a superoxide scavenger) and fluoride (a ligand for the ferric enzyme), resulting in ferric enzyme and fluoride complex formation, respectively.

Anisoles↗
PubMed2006

Gold films deposited over regular arrays of polystyrene nanospheres as highly effective SERS substrates from visible to NIR.

Gold nanostructured films of various thicknesses (15, 30, and 60 nm) are deposited over regular arrays of polystyrene nanospheres in an attempt to evaluate their potential as SERS-active substrates. Atomic force microscopy is used to topographically characterize the substrates as well as to ensure the thickness of the deposited gold films. The optical response of the prepared substrates recommends their use in SERS experiments with multiple laser lines from visible and NIR spectral domains. The assessment of the substrates' SERS activity is performed by using the 532, 633, and 830 nm excitation lines and different average enhancement factor (EF) values are obtained depending on the film thickness and employed laser line. The 60 nm gold nanostructured film generates the greatest local electromagnetic field confinement under NIR excitation and consequently gives rise to maximum SERS enhancement. The large tunability of surface plasmon excitation combined with the advantage of relatively high exhibited average EF values obtained under NIR excitation recommends these substrates as outstanding candidates for upcoming investigations of biological relevant molecules.

Aniline Compounds↗
PubMed2003

A molecular approach to self-assembly of trimethylsilylacetylene derivatives on gold.

We recently discovered that a linear multifunctional trimethylsilylacetylene (TMSA) compound forms long-range and highly stable self-assembled monolayers (SAMs) on reconstructed Au(111). To better understand the interactions governing self-assembly in this new system, we synthesized a series of homologue organosilanes and performed scanning tunneling microscopy (STM) measurements at the Au(111)/n-tetradecane interface. The four TMSA-terminated linear silanes that we synthesized self-assemble in similar ways on gold, with the molecules standing upright on the surface. In contrast, compounds with a slightly modified terminal group but the same polyunsaturated linear chain above the TMSA head do not self-assemble. In particular, substituting a methyl group of TMSA with a more bulky one prevents self-assembly. Removing the C triple bond C triple bond of TMSA or substituting the Si atom by a C atom also hinders self-assembly. Finally, substituting one methyl group of TMSA by a hydrogen atom induces self-assembly but in a different geometry, with the molecules lying flat on the gold surface in a quasi-epitaxy mode. Our molecular approach demonstrates the key role played by the TMSA head in self-assembly, its origin being twofold: 1) the TMSA layers are commensurate to the Au(111) adlattice along the <112> direction, and 2) the C triple bond C triple bond of TMSA activates the Si atom and induces the creation of a surface Si-Au chemical bond. The highly stable TMSA-based SAMs appear then as promising materials for applications in surface modification.

Journal Article↗
PubMed2002

Effects of gold-chloroquine complexes on respiratory burst of polymorphonuclear leukocytes.

The effects of gold-chloroquine derivatives with the formula [Au(PR3)(CQ)]PF6 (where R = Ph (1), Et or Me) on the superoxide anion production by human neutrophils (PMNs, polymorphonuclear cells) were investigated. When these complexes (0.1-3 mumol/l) were added to PMNs prior to the activators formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol myristate acetate (PMA), they inhibited isoluminol-horseradish peroxidase-dependent chemiluminescence (CLisol). The inhibition was a direct result of effects on PMNs since chemiluminescence in the cell-free system (horseradish peroxidase-hydrogen peroxidase-isoluminol) was not affected. The above mentioned concentrations of the complexes did not show in vitro toxicity on the cells. On the other hand, when 1 mumol/l of complex 1 was added to cells after stimulation, the chemiluminescence of PMNs stimulated by PMA was inhibited, but not the chemiluminescence stimulated by fMLP. The gold-chloroquine binding was essential for the referred activity as chemiluminescence was not influenced by the precursors chloroquine (CAS 54-05-7) and AuCl(PPh3). Furthermore, the extent of inhibition of chemiluminescence in PMNs activated by PMA did not increase with the duration of preincubation in presence of 1 mumol/l of 1. Extensive washing of cells after preincubation with 1 mumol/l of 1 reversed the aforementioned inhibition. All these results show that the gold-chloroquine binding can lead to compounds with specific properties that could make them useful in the treatment of some inflammatory diseases.

Adenosine Triphosphate↗
PubMedDate not supplied

Receptor binding and internalization of a unique biologically active angiotensin II-colloidal gold conjugate: morphological analysis of angiotensin II processing in isolated vascular strips.

It is well recognized that following binding of ligand, many receptors undergo a process of agonist-induced receptor-mediated endocytosis (RME) or internalization. We recently characterized the intracellular pathway and kinetics of angiotensin II (AII)-RME in cultured explant-derived rat aortic vascular smooth muscle cells (VSMCs). To definitively study vascular internalization of AII, however, it is critical to examine AII binding and uptake in intact, differentiated VSM. For the present study, we used a unique, biologically active AII-colloidal gold conjugate to qualitatively examine, by transmission electron microscopy, the ultrastructural details of AII binding and internalization in intact VSM. Strips of isolated, cleaned, and denuded rat aortic smooth muscle were incubated with AII-gold probe for 2 h at 4 degrees C to allow binding of the complex without simultaneous internalization. After rinsing to remove unbound AII-gold, the strips were incubated at 37 degrees C (5-90 min) to initiate internalization. These studies show that AII initially binds over the entire surface of medial VSMCs. Following binding, the AII is internalized via small receptosomes which likely represent clathrin-coated vesicles. By 20 min after internalization, gold particles are evident within large lysosome-like vesicles deep within the VSM. There was no evidence of association of gold particles with the Golgi network at any of the time periods examined. Gold particles were occasionally observed in perinuclear regions after 90 min at 37 degrees C, although this did not appear to represent a typical pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗