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PubMed2006

Nanoscale patterning of two metals on silicon surfaces using an ABC triblock copolymer template.

Patterning technologically important semiconductor interfaces with nanoscale metal films is important for applications such as metallic interconnects and sensing applications. Self-assembling block copolymer templates are utilized to pattern an aqueous metal reduction reaction, galvanic displacement, on silicon surfaces. Utilization of a triblock copolymer monolayer film, polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) (PS-b-P2VP-b-PEO), with two blocks capable of selective transport of different metal complexes to the surface (PEO and P2VP), allows for chemical discrimination and nanoscale patterning. Different regions of the self-assembled structure discriminate between metal complexes at the silicon surface, at which time they undergo the spontaneous reaction at the interface. Gold deposition from gold(III) compounds such as HAuCl4(aq) in the presence of hydrofluoric acid mirrors the parent block copolymer core structure, whereas silver deposition from Ag(I) salts such as AgNO3(aq) does the opposite, localizing exclusively under the corona. By carrying out gold deposition first and silver second, sub-100-nm gold features surrounded by silver films can be produced. The chemical selectivity was extended to other metals, including copper, palladium, and platinum. The interfaces were characterized by a variety of methods, including scanning electron microscopy, scanning Auger microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy.

Journal Article↗
PubMed1987

Variation in physical and biological properties of solid gold sodium thiomalate on dissolution: an electron microscopic and energy dispersive spectroscopic study.

The dissolution of solid gold sodium thiomalate (GSTM) in water results in loss of yellow color. We studied the initial reaction on dissolution. It was associated with the disappearance of 2 absorption peaks on ultraviolet spectrum, one a well defined peak at 335 nm and the other a shoulder at 370 nm. This solution caused platelet aggregation and on transmission electron microscopy, dense gold containing particles measuring 125 nm are seen. Within 10 min of onset of dissolution, no gold containing particulate matter was detectable on electron microscopy. By 20 min, fibrillar particles measuring 40-150 nm appear. These resembled in general morphology and element composition the particles seen within aurosomes in platelets treated with Myochrysine (GSTM) and in synovium and other tissues by other workers. Our data elaborate on previous physical and chemical studies and correlate with morphological variations of gold containing particles at different phases. These variations in GSTM may be due to polymer size and/or structural change within the polymer. The biochemical significance of our data should provide better understanding of the biological effects of these gold thiol compounds in vivo.

Blood Platelets↗
PubMed2005

Three-layer composite magnetic nanoparticle probes for DNA.

A method for synthesizing composite nanoparticles with a gold shell, an Fe3O4 inner shell, and a silica core has been developed. The approach utilizes positively charged amino-modified SiO2 particles as templates for the assembly of negatively charged 15 nm superparamagnetic water-soluble Fe3O4 nanoparticles. The SiO2-Fe3O4 particles electrostatically attract 1-3 nm Au nanoparticle seeds that act in a subsequent step as nucleation sites for the formation of a continuous gold shell around the SiO2-Fe3O4 particles upon HAuCl4 reduction. The three-layer magnetic nanoparticles, when functionalized with oligonucleotides, exhibit the surface chemistry, optical properties, and cooperative DNA binding properties of gold nanoparticle probes, but the magnetic properties of the Fe3O4 inner shell.

DNA↗
PubMed2006

Lewis acid-catalyzed [4 + 2] benzannulation between enynal units and enols or enol ethers: novel synthetic tools for polysubstituted aromatic compounds including indole and benzofuran derivatives.

The reaction of enynals 1, including o-(alkynyl)benzaldehydes, and carbonyl compounds 2, such as aldehydes and ketones, in the presence of a catalytic amount of AuBr3 in 1,4-dioxane at 100 degrees C gave the functionalized aromatic compounds 3 in high yields. Similarly, the AuBr3-catalyzed reactions of 1 with acetal compounds 5 afforded the corresponding aromatic compounds 3 in good yields. On the other hand, when the reaction was carried out in the presence of a catalytic amount of Cu(NTf2)2 and 1 equiv of H2O in (CH2Cl)2 at 100 degrees C, the decarbonylated naphthalene products 4 were obtained selectively over 3. Benzofused heteroaromatic compounds, such as indole derivatives 13 and benzofuran derivatives 15, were also synthesized by using the present benzannulation methodology.

Aldehydes↗
PubMed2001

Synthesis of ferrocenethiols containing oligo(phenylenevinylene) bridges and their characterization on gold electrodes.

Ferrocene-terminated oligo(phenylenevinylene) (OPV) methyl thiols have been prepared by orthogonal coupling of phenylene monomers. Ethoxy substituents on the phenyl rings improve the solubility of OPV, enabling the synthesis of longer oligomers. Self-assembled monolayers containing a mixture of a ferrocene OPV methyl thiol and a diluent alkanethiol were deposited on gold. A cyclic voltammetric study of monolayers containing oligomers of the same length with and without ethoxy solubilizing groups reveals that both solubilized and unsolubilized oligomers form well-packed self-assembled monolayers. Changing the position of the solubilizing groups on an oligomer chain does not preclude packing of the oligomer in the monolayer. Conventional chronoamperometry, which can be used to measure rate constants up to approximately 10(4) s(-1), is too slow to measure the electron-transfer rate through these oligomers over distances up to 35 A. OPV bridges are expected to be highly conjugated unlike oligo(phenyleneethynylene) bridges, which may be only partially conjugated because of rotation of the phenyl rings about the ethynylene bonds. Because of its high conjugation, OPV may prove useful as a molecular wire.

Catalysis↗
PubMed1988

Induction of the 32-kD human stress protein by auranofin and related triethylphosphine gold analogs.

Challenge of human cells with auranofin, 2,3,4,6-tetra-O-acetyl-1-thio-beta-D-glucopyranosato-S-triethylpho sphine gold(I) (Ridaura), a gold-containing compound approved by the FDA for the treatment of rheumatoid arthritis, induces the specific synthesis of a 32-kD stress protein (p32) [Caltabiano et al., Biochem. biophys. Res. Commun. 138, 1074 (1986)]. To establish a structure-activity relationship for this effect, a series of auranofin ligands, gold analogs, and other anti-arthritic agents were examined for their abilities to stimulate p32 synthesis. The results indicate that the gold atom is necessary for enhanced expression of p32. However, the structure of co-ordinated ligands also affected potency, and gold complexes bearing several phosphine or thiosugar groups exhibited the greatest activity. These data indicate that the distinct potencies of auranofin analogs probably reflect their membrane permeability and subsequent delivery of pharmacologically active concentrations of gold to the cytoplasmic compartment.

Arthritis↗
PubMed2004

Governing the oxidative addition of iodine to gold(I) complexes by ligand tuning.

While several gold(I) complexes of the type (L)AuX (X = Cl, Br) are known to undergo oxidative addition of elemental chlorine and bromine (X2), respectively, to give the corresponding gold(III) complexes (L)AuX3, the addition of iodine to (iodo)gold(I) compounds is strongly ligand-dependent, suggesting a crucial threshold in the oxidation potentials. A systematic investigation of this particular oxidative addition of iodine using a large series of tertiary phosphines as ligands L has shown that both electronic and steric effects influence the course of the reaction. The reactions were followed by 31P NMR spectroscopy and the products crystallized from dichloromethane-pentane solutions. Complexes with small triakylphosphines (PMe3, PEt3) are readily oxidized, while those with more bulky ligands (PiPr3, PtBu3) are not. With L taken from the triarylphosphine series [PPh3, P(2-Tol)3, P(3-Tol3), P(4-Tol)3] no oxidation takes place at all, but mixed alkyl/aryl-phosphines [PMenPh(3-n)] induce oxidation for n = 3 and 2, but not for n = 1 and 0. However, in cases where no oxidation of the gold atoms is observed, the synthons may crystallize as adducts with molecular iodine of the polyiodide type instead, which have an iodine rich stoichiometry. This fact explains inconsistent reports in the literature. The metal atoms in (L)AuI coordination compounds with L representing a tri(heteroaryl)phosphine [P(2-C4H3E)3, E = O, S], a phosphite [P(OR)3] or a trialkenylphosphine [PVi3] are all not subject to oxidative addition of iodine. The dinuclear complex of the ditertiary phosphine Ph2PCH2PPh2, (dppm)(AuI)2, gives an iodine adduct (without oxidation of the metal atoms), but with 1,2-Ph2P(C6H4)PPh2(dppbe) an ionic complex [(dppbe)AuI2]+I3- with a chelated gold(III) centre is obtained. The gold(I) bromide complexes with tertiary phosphines are readily oxidized by bromine to give the corresponding gold(III) tribromide complexes, as demonstrated for (BzMePhP)AuBr and (Ph3P)AuBr. With (dppm)(AuBr)2 the primary product with mixed oxidation states was also isolated: (dppm)AuBr(AuBr3). The crystal structures of the following representative examples and reference compounds have been determined: (Me3P)AuI3, (Me2PhP)AuI3, (iPr3P)AuI.1.5I2, (Ph3P)AuI.I2, [[(2-Tol)3P]AuI]2.I2, [(2-Tol)3P]AuI, (dppm)(AuX)2 (with X = Br, I), (dppm)AuBr(AuBr3) and [(dppbe)AuI2]+I3-. The structures are discussed focusing on the steric effects. It appears that e.g. the reluctance of (Ph3P)AuI to add I2 is an electronic effect, while that of (iPr3P)AuI has its origin in the steric influence of the ligand.

Journal Article↗
PubMed1997

A covalent fluorescent-gold immunoprobe: simultaneous detection of a pre-mRNA splicing factor by light and electron microscopy.

Immunoprobes that combine a fluorescent label with a 1.4-nm gold cluster compound have been prepared by covalent conjugation with polyclonal antibody Fab' fragments. These new immunoconjugates allow the collection of two complementary sets of data, from fluorescence and electron microscopy, from a single labeling experiment. We find that incorporation of one or more fluorescein moieties into the coordinated ligands of the 1.4-nm Nanogold gold cluster label yields a stable, dual-function immunolabel in which fluorescence quenching is negligible. In a second synthetic strategy, Nanogold and fluorescein were separately covalently conjugated to Fab' fragments to yield a probe with very similar properties. With the use of Fab' fragments, the entire probe is smaller than a whole IgG molecule, and it exhibited excellent penetration properties. It was used to localize the pre-mRNA splicing factor SC35 in the HeLa cell nucleus by both fluorescence and electron microscopy.

Fluorescein↗
PubMed1999

Electron transfer between ferrocene-modified Au/octadecanethiol/lipid BLM electrode and redox couples in solution.

Bilayers incorporated with ferrocene consisting of self-assembled octadecanethiol and lipid monolayer on gold substrates were fabricated. Its electrochemical behaviors in solutions containing different redox couples were investigated by cyclic voltammetry and ac impedance. The transmembrane electron transfer reaction across octadecanethiol self-assembled film and an adsorbed phospholipid layer mediated by ferrocene have been observed in the solution of Fe(CN)6(3-/4-). The formal potential difference between mediator in bilayer lipid membrane (BLM) and redox couple in solution has a great impact on the transmembrane electron transfer behavior. The ferrocene-modified BLM electrodes might be useful for constructing a bilayer-based electrochemical current rectifying device.

Algorithms↗
PubMed1986

Inter-strand cross-links and single-strand breaks produced by gold(I) and gold(III) coordination complexes.

The ability of gold coordination complexes to bind to DNA and produce inter-strand cross-links in DNA was assessed in an assay system based on the fluorescence properties of the DNA intercalative dye, ethidium bromide. Results from these studies using a variety of gold(I) and gold(III) complexes suggest that the ability of gold complexes to bind to and produce inter-strand cross-links in DNA is not dependent on the oxidation state of gold in the complex but is influenced by the nature of the coordinating ligands. Those complexes in which the gold was ligated through one or more weakly coordinating ligands showed evidence for DNA binding. However, only those complexes with two or more of these relatively weak coordinating ligands produced inter-strand cross-links. Both the amount of binding to and cross-linking of DNA by these compounds were decreased by treatment of the gold-DNA complex with 2-mercaptoethanol and other thiol containing agents. As shown by agarose gel electrophoresis, 2-mercaptoethanol caused a dissociation of the gold-DNA complexes and a regeneration of closed circular superhelical pBR322 DNA. DNA strand breakage also resulted from treatment of a number of gold-DNA complexes with 2-mercaptoethanol; this was observed with the gold compounds which were shown to produce inter-strand cross-links in DNA. The amount of DNA strand breakage produced by treatment of gold-DNA complexes with 2-mercaptoethanol was influenced by the initial conformation of the DNA; gold-DNA complexes which resulted from the binding of gold compounds to covalently closed superhelical DNA were more sensitive to the breakage induced by 2-mercaptoethanol treatment than those complexes in which closed circular, relaxed DNA was used as substrate. The DNA breakage was not reduced in partially anaerobic conditions or by free-radical scavengers, suggesting that it is not mediated by oxygen. The results are discussed with respect to the potential for the interaction of gold complexes with intracellular DNA and chromatin and their biological implications.

Anaerobiosis↗
PubMed2004

Dendrimers and gold nanoparticles as exo-receptors sensing biologically important anions.

Dendrimers, alkylthiol-gold nanoparticles and gold-nanoparticle-cored dendrimers containing tethers terminated by a redox group (typically an iron sandwich) attached to a hydrogen-bonding group (amido, amino, silyl) are selective and efficient exo-receptors for the recognition, sensing and titration of oxo-anions, including ATP(2-), or halogens, mostly using cyclic voltammetry. Various positive dendritic effects were disclosed (in contrast to catalysis), and large gold-nanoparticle-cored redox dendrimers of this type that contain several hundred equivalent ferrocenyl groups readily adsorb on Pt electrodes, providing useful regenerable electrochemical sensors.

Anions↗
PubMed2003

Nanoscopic assemblies between supramolecular redox active metallodendrons and gold nanoparticles: synthesis, characterization, and selective recognition of H2PO4-, HSO4-, and adenosine-5'-triphosphate (ATP2-) anions.

Tri- and nonaferrocenyl thiol dendrons have been synthesized and used to assemble dendronized gold nanoparticles either by the ligand-substitution method from dodecanethiolate-gold nanoparticles (AB(3) units) or Brust-type direct synthesis from a 1:1 mixture of dodecanethiol and dendronized thiol (AB(9) units). The dendronized colloids are a new type of dendrimers with a gold colloidal core. Two colloids containing a nonasilylferrocenyl dendron have been made; they bear respectively 180 and 360 ferrocenyl units at the periphery. These colloids selectively recognize the anions H(2)PO(4)(-) and adenosine-5'-triphosphate (ATP(2)(-)) with a positive dendritic effect and can be used to titrate these anions because of the shift of the CV wave even in the presence of other anions such as Cl(-) and HSO(4)(-). Recognition is monitored by the appearance of a new wave at a less positive potential in cyclic voltammetry (CV). The anion HSO(4)(-) is also recognized and titrated by the dendronized colloid containing the tris-amidoferrocenyl units, because of the progressive shift of the CV wave until the equivalence point. These dendronized colloids can form robust modified electrodes by dipping the naked Pt electrode into a CH(2)Cl(2) solution containing the colloids. The robustness is all the better as the dendron is larger. These modified electrodes can recognize H(2)PO(4)(-), ATP(2)(-) and HSO(4)(-), be washed with minimal loss of adsorbed colloid, and be reused.

Adenosine Triphosphate↗
PubMed2000

Cytotoxicity, DNA damage, and cell cycle perturbations induced by two representative gold(III) complexes in human leukemic cells with different cisplatin sensitivity.

The gold(III) complexes [Au(phen)Cl2]Cl and [Au(dien)Cl]Cl2 were recently shown to exert important cytotoxic effects in vitro on human tumor cell lines. To elucidate the biochemical mechanisms leading to cell death, the effects produced by these gold(III) complexes on the leukemic CCRF-CEM cell line--either sensitive (CCRF-CEM) or resistant to cisplatin (CCRF-CEM/CDDP)--were analyzed in detail by various techniques. For comparison purposes the effects produced by equitoxic concentrations of cisplatin were also analyzed. First, the dependence of the IC50 values of either complex on the incubation time was investigated. Cytotoxicity experiments confirmed that both gold(III) compounds retain their efficacy against the cisplatin-resistant line: only minimal cross-resistance with cisplatin was detected. Notably, [Au(phen)Cl2]Cl is more cytotoxic than [Au(dien)Cl]Cl2, with IC50 values of 7.4 and 6.0 M at 24 and 72 h, respectively, on the resistant line. Results of the COMET assay point out that both gold(III) complexes directly damage nuclear DNA. Remarkably, DNA damage inferred by either gold(III) complex in the two cell lines is larger than that produced by equitoxic cisplatin concentrations. Finally, the effects that either gold(III) complex produces on the cell cycle were investigated by flow cytometry. It was found that both complexes cause only moderate and transient cell cycle perturbations. Larger cell cycle perturbations are induced by equitoxic concentrations of cisplatin. The implications of the present results for the mechanism of action of cytotoxic gold(III) complexes are discussed.

Antineoplastic Agents↗
PubMed2004

Immobilization of the nanoparticle monolayer onto self-assembled monolayers by combined sterically enhanced hydrophobic and electrophoretic forces.

The immobilization of surface-derivatized gold nanoparticles onto methyl-terminated self-assembled monolayers (SAMs) on gold surface was achieved by the cooperation of hydrophobic and electrophoretic forces. Electrochemical and scanning probe microscopy techniques were utilized to explore the influence of the SAM's structure and properties of the nanoparticle/SAM/gold system. SAMs prepared from 1-decanethiol (DT) and 2-mercapto-3-n-octylthiophene (MOT) were used as hydrophobic substrates. The DT SAM is a closely packed and organized monolayer, which can effectively block the underlying gold and inhibit a variety of solution species including organic and inorganic molecules from penetrating, whereas the MOT monolayer is poorly packed or disorganized (because of a large difference in dimension between the thiophene head and the alkylchain tail) and permeable to many organic probes in aqueous solution but not to inorganic probes. Thus, the MOT monolayer provides a more energetically favorable hydrophobic surface for the penetration and adsorption of organic species than the DT monolayer. This hypothesis is supported by experiments in which the density of hydrophobically immobilized nanoparticles on the MOT SAM is much larger than that on the DT SAM. The results also suggest new approaches for modification of macroscopic surfaces with nanoscopic particles.

Electrochemistry↗
PubMed2006

Reagentless, reusable, ultrasensitive electrochemical molecular beacon aptasensor.

A bifunctional derivative of the thrombin-binding aptamer with a redox-active Fc moiety and a thiol group at the termini of the aptamer strand was synthesized. The ferrocene-labeled aptamer thiol was self-assembled through S-Au bonding on a polycrystalline gold electrode surface and the surface was blocked with 2-mercaptoethanol to form a mixed monolayer. By use of a fluorescent molecular beacon, the effect of counterions on quadruplex formation was established. The aptamer-modified electrode was characterized electrochemically by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The modified electrode showed a voltammetric signal due to a one-step redox reaction of the surface-confined ferrocenyl moiety of the aptamer immobilized on the electrode surface in 10 mM N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid (HEPES) buffer of pH 8.0. An increase in the DPV current signal was evident after blocking with 2-mercaptoethanol, effectively removing aptamer nonspecifically absorbed rather than bound to electrode surface or due to the formation of the aptamer-thrombin affinity interaction. The impedance measurement, in agreement with the differential pulse voltammetry (DPV), showed decreased Faradaic resistances in the same sequence. The "signal-on" upon thrombin association could be attributed to a change in conformation from random coil-like configuration on the probe-modified film to the quadruplex structure. The DPV of the modified electrode showed a linear response of the Fc oxidation signal to the increase in the thrombin concentration in the range between 5.0 and 35.0 nM with a linear correlation of r = 0.9988 and a detection limit of 0.5 nM. The molecular beacon aptasensor was amenable to full regeneration by simply unfolding the aptamer in 1.0 M HCl, and could be regenerated 25 times with no loss in electrochemical signal upon subsequent thrombin binding.

Aptamers, Nucleotide↗
PubMed2003

Beta-cyclodextrin-based ferrocene-imprinted gold electrodes.

A new stepwise self-assembly procedure is described for the preparation of functional cyclodextrin-modified electrodes. The approach is based on the formation of alkanethiol/lipoylamide-beta-cyclodextrin monolayers with the thiol component responsible for blocking of the electrode surface and lipoylamide-beta-cyclodextrin molecules-for controlled opening of the access of the electroactive probe to the electrode. Functionalization of the electrode is achieved by means of a new cyclodextrin derivative-mono(6-deoxy-6-lipoylamide)-per-2,3,6-O-acetyl-beta-cyclodextrin-prepared in the peracetyl form and deacetylated directly on the electrode surface following the cyclodextrin self-assembly. The progress of deacetylation was monitored by the MALDI MS technique. Deacetylation caused opening of the active sites toward solution probes. The response toward ferrocene was found to be highly improved when ferrocene was added to the solution following self-assembly of cyclodextrin but prior to the thiol self-assembly step (imprinting method). The proposed synthesis and sequential monolayer formation scheme lead to well-organized and stable modified electrode surfaces with improved sensitivity toward solution species compared to other procedures of electrode modification with the cyclodextrin derivatives.

Algorithms↗