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PubMed1993

Synthetic peptides as receptors in affinity sensors: a feasibility study.

A relatively simple method for immobilizing synthetic peptides as a receptor onto a gold surface using the self-assembling monolayer (SAM) technique has been investigated. A synthetic peptide with an amino acid sequence similar to the 9-21 gD sequence of herpes simplex virus type 1 was modified with an alkylthiol chain and adsorbed in combination with an alkylthiol chain without peptide according to the SAM procedures. The resulting self-assembled receptor layers (SARs) were able to specifically interact with a monoclonal antibody directed against the 9-21 gD peptide. Binding studies monitored with a surface plasmon resonance setup showed that the response to the antibody depended on the composition of the SAR; a maximum response was reached at approximately 3 mol% peptide coverage. The response itself exceeded the value obtained from passive adsorption of the antibodies under similar conditions, indicating that the formed antibody layer is highly oriented. The equilibrium binding properties of the immobilized receptor molecules were found to be identical to those found when the immobilized antibodies interacted with the receptor molecule. The presence of a hydrophobic moiety in the alkylthiol derivates contributes to the ordering of the monolayer: a less specific interaction occurred when SARs without hydrophobic moiety were used.

Antibodies, Monoclonal↗
PubMed2002

Interactions between acid- and base-functionalized surfaces.

In this paper we present an AFM force study on interactions between chemically modified surfaces. Surfaces with terminal groups of either NH(2) or COOH were obtained by chemisorption of a silane-based compound (3-amino-propyltriethoxysilane) on silica or a thiol compound (11-mercapto undecanoic acid) on gold. The surfaces were characterized by streaming potential and contact angle measurements. For the NH(2) surfaces the density of functional groups strongly depends on the pretreatment of the silica. Both the NH(2) and COOH surfaces show a steady and ongoing loss of functional groups, but on the time scale of our force measurements they can be considered to be stable. Interaction curves for the various combinations of surfaces in aqueous solutions show a strong correlation with the ionization state of the surface groups. The approach curves can be explained on the basis of electrostatic interactions. On retraction a pH-dependent adhesion is found, the strongest being between NH(2) and COOH surfaces as a result of acid-base interactions. Between NH(2) layers and between COOH layers there is also adhesion, due to the formation of H bonds. The corresponding work of adhesion W was calculated using the DMT (Derjaguin, Muller, Toporov) equation. The values of W obtained are small compared to literature data and suggest that only a fraction of the functional groups in the contact area is involved in acid-base or H-bond interactions. This is attributed mainly to the roughness of the surfaces, which substantially reduces adhesion. A rough estimate is made for the rupture force of the NH(2)-COOH acid-base bond in water.

Journal Article↗
PubMed1985

Degradative intracellular transport of antisecretory component in cultured hepatocytes. An alternate pathway for the immunoglobulin A receptor.

The liver efficiently transports dimeric immunoglobulin A (dIgA) from blood to bile in a direct, nonlysosomal pathway involving smooth-surfaced vesicles. Secretory component (SC), the plasma membrane receptor for dIgA, is released into bile still bound to its ligand by disulfide bridges. Rabbit IgG antirat SC binds specifically to plasma membrane SC, yet the biliary secretion of anti-SC is markedly lower than that of dIgA, suggesting that the IgG antibodies utilize an alternate transhepatocellular pathway. Uptake of commercially available antihuman SC conjugated to horseradish peroxidase was examined by quantitative electron microscopic immunocytochemistry using primary rat hepatocyte monolayer cultures. Coincubation with human polymeric IgA, rabbit antiserum to rat SC, free human SC, human secretory IgA, and rat bile, all significantly suppressed uptake of anti-SC-horseradish peroxidase, thus demonstrating the specificity of the labeled antibody. Coated vesicles accounted for greater than 70% of the total uptake of either the anti-SC-horseradish peroxidase preparation or colloidal gold-labeled IgG antirat SC. Both compounds could also be observed in other structures associated with the degradative pathway, i.e., multivesicular bodies and lysosomes. Moreover, the extent to which 125I-anti-SC was degraded was significantly greater than that of 125I-dIgA. These data demonstrate that dIgA and anti-SC utilize different intracellular pathways, with anti-SC undergoing lysosomal degradation.

Animals↗
PubMed1991

The effect of alloxan-induced diabetes on triamine lesions in the ventromedial hypothalamus.

It has been demonstrated that the ventromedial hypothalamus (VMH) of alloxan-induced diabetic mice is protected from subsequent gold thioglucose (GTG)-induced lesions. Another compound, 3,3'-methyliminobis-(N-methylpropylamine) (MIMPA), a triamine structurally unrelated to GTG, has been shown to cause similar VMH lesions in mice. We chose to investigate the effect of alloxan-induced diabetes on VMH lesion formation in MIMPA-treated mice. In this study CF-1 female mice were made diabetic by a simple intravenous (IV) injection of alloxan and subsequently treated with MIMPA by subcutaneous injection (SC). Contrary to studies which showed that GTG-induced VMH lesions are insulin dependent, an insulin deficiency did not inhibit MIMPA-induced lesions in the VMH of mice. Our data suggests, albeit GTG is suspected to induce VMH necrosis by attaching to glucoreceptors and insulin-sensitive neurons, MIMPA works by a different and as yet unknown mechanism. We conclude that MIMPA-induced lesions in the VMH of mice are not insulin dependent.

Animals↗
PubMed1984

Absorption and circular dichroism studies of a gold (I)-DNA complex.

The DNA binding properties of the Au(I)-containing antiarthritic drug Ridaura and related Au(I) complexes have been investigated. Absorption and circular dichroism spectroscopy show that if the gold ion possesses an easily displaced ligand, e.g., Cl- or Br-, Au(I) is capable of interacting, in a nondenaturing fashion, with calf thymus DNA. Absorption studies with the four DNA nucleosides suggest that guanine and cytosine bases are important in the Au(I)DNA interaction.

Animals↗
PubMed2006

Environmental assessment of mercury dispersion, transformation and bioavailability in the Lake Victoria Goldfields, Tanzania.

Environmental dispersion and transformation of mercury discharged from gold mining operations has been investigated in field and laboratory studies in order to provide better understanding of the degree of mercury (Hg) pollution and bioavailability in the Lake Victoria goldfields (LVGF) ecosystems. This paper reviews results already published elsewhere and presents additional data on Hg dynamics in the LVGF. Studies conducted at the Mugusu and Rwamagaza artisanal mines indicated different degrees of Hg contamination and dispersion in environmental matrices. Mercury concentration in contaminated river sediments near the Mugusu mine varied from 6.0 to 0.5 mg/kg on a dry weight basis. The highest Hg contamination levels (165-232 mg/kg) were associated with mine tailings at the Rwamagaza mine. Mercury concentrations in fish representing different dietary habits on the southwestern shore of Lake Victoria at the Nungwe Bay were very low (2-35 microg/kg) and thought to represent background levels. These and other results suggested that the use of Hg in gold extraction in the LVGF has not caused high Hg levels in lake fish. The study of Hg in lichens showed Parmelia lichen to be an effective bioindicator for atmospheric Hg contamination due to Hg emissions from gold-amalgam firing and purification operations. The Hg levels in the lichens around the Mugusu mine ranged from 3.1 to 0.1 microg/g; the highest levels were recorded in the lichens sampled close to gold-amalgam processing sites. The regional background level in the Parmelia lichen was 0.05-0.10 microg/g, with a mean level of 0.07 microg/g. Studies of Hg transformation in the mine tailings revealed unexpectedly high methylmercury (MeHg) levels in the tailings (629-710 ng/g), which indicated that oxidation and methylation of metallic Hg in the tailings occurred at significant levels under tropical conditions. Re-equilibration of the tailings with freshwater (FW) indicated the MeHg was firmly bound in the tailings and therefore very little MeHg was released to the water column (0.2-1.5 ng/L). The methylation of Hg in tropical loamy clay soil contaminated with HgCl(2) (5 mg Hg/kg) yielded MeHg concentrations of 11 and 14 ng/g when inundated with seawater and FW, respectively, for 4 weeks. Little MeHg was transferred from the soil to the equilibrated water (< or = 0.4 ng/L). Atmospheric exposure of the soil pre-inundated with FW resulted in net degradation of MeHg during the 1st week of exposure, followed by net production and accumulation of MeHg in the soil (up to 15.5 ng/g) during atmospheric desiccation. Mercury uptake by fish from the Hg(0)-contaminated aquatic sediment-tailings system in the aquarium experiment was found to be low, suggesting the low availability of MeHg for bioaccumulation in the system. These and other results provide useful insights into Hg transformation, mobility and bioavailability in tropical aquatic systems affected by Hg pollution from gold mining operations.

Animals↗
PubMed2001

Integrated pulsed amperometric detection of glufosinate, bialaphos and glyphosate at gold electrodes in anion-exchange chromatography.

A rapid and practical method for direct detection of the herbicides (glufosinate, bialaphos and glyphosate) in anion-exchange chromatography has been developed with integrated pulsed amperometric detection (IPAD). The electrochemical behavior of these herbicides showed catalytic currents based on the oxidation of amines in their structures. Waveform in IPAD was similar to that for amino acids, which exhibited adsorption/desorption catalytic features at gold electrode surface in alkaline solution. Under optimized conditions, detection limits (signal-to-noise ratio of 3) for glufosinate, bialaphos and glyphosate were 20, 65 and 50 ng ml(-1), respectively, with correlation coefficients of 0.995, 0.997 and 0.996 over concentration ranges of 0.1-45, 0.3-32 and 0.1-50 microg ml(-1), respectively. The relative standard deviations (n=5) were 1.7-3.0%. The present method was successfully applied to the determination of glyphosate in urine and serum.

Aminobutyrates↗
PubMed1997

High-performance liquid chromatographic assay using electrochemical detection for the combined measurement of amifostine, WR 1065 and the disulfides in plasma.

A high-performance liquid chromatographic (HPLC) method was developed for the combined analysis of the chemoprotective agent, amifostine, its active metabolite, WR 1065, and the (symmetrical and mixed) disulfides of WR 1065 in plasma. These three compounds were quantified by measuring WR 1065 after three different sample pretreatment procedures. During these procedures, amifostine and the disulfides were quantitatively converted into WR 1065, by incubating the sample either at a low pH or in the presence of dithiothreitol, respectively. The resulting amounts of WR 1065 were determined by HPLC with electrochemical detection (Au electrode, + 1.00 V). The lower limit of quantitation of WR 1065 was 0.15 microM. The within-day and between-day precision were < or =4.4 and < or =8.2% for WR 1065, < or =4.9 and < or =13.1% for amifostine and < or =8.5 and < or =5.5% for the disulfides, respectively. The within-day and between-day accuracy ranged from 97.2 to 109.8% and from 97.6 to 101.5% for WR 1065, from 88.3 to 110.7% and from 99.4 to 101.5% for amifostine and from 99.2 to 110.2% and from 103.3 to 104.9% for the disulfides, respectively. This method is superior to other described methods due to its simple and relatively rapid analysis of all three compounds in one system. Furthermore, it is at least as sensitive as earlier reported methods for one of the compounds and the application of the gold electrode requires only minor maintenance. Therefore, this method is very suitable for pharmacokinetic studies of amifostine and its metabolites. As an example, the plasma concentrations of amifostine, WR 1065 and the disulfides are shown in a patient after receiving an i.v. dose of 740 mg/m2 amifostine.

Amifostine↗
PubMed2004

Voltammetric detection of metal nanoparticles separated by liquid chromatography.

Fast-scan cyclic voltammetric (FSCV) detection of the separation of small (< 2-nm core diameter) organothiolate monolayer-protected gold clusters (MPCs) by high-performance liquid chromatography (HPLC) is demonstrated in this paper. Cyclic voltammograms taken at 1-s intervals (scan rate 150 V/s) display distinctive current-potential patterns for different MPCs, aiding in their identification. Previous amperometric detection of MPC separations required multiple HPLC runs at different electrode potentials to construct hydrodynamic current-potential voltammograms. Theory for ratiometric response of photodiode array absorbance and constant potential amperometry detectors was further tested on the fast-scan voltammetric detector and gave reasonable relative core size results for a mixture of Au140 and Au38 MPCs. In the first analysis of mixed MPC monolayer composition that is not simply an overall average result, preliminary HPLC experiments on MPCs with mixed hexanethiolate and ferrocenyl-octanethiolate monolayers resolved peaks that are shown to correspond to different average numbers of ferrocene-labeled ligands per MPC.

Chromatography, High Pressure Liquid↗
PubMed1999

An Au nanoparticle/bisbipyridinium cyclophane-functionalized ion-sensitive field-effect transistor for the sensing of adrenaline.

A film consisting of polyethyleneimine (PEI), Au nanoparticles (12 +/- 1 nm) and coadsorbed cyclobis(paraquat-p-phenylene) (1) was assembled as a sensing interface on the Al2O3 insulating layer of an ion-sensitive field-effect transistor (ISFET). Adrenaline (2) was sensed by the functionalized ISFET with a detection limit of 1 x 10(-6) M. The sensing ability of the nanostructured device for the analysis of adrenaline originates from the preconcentration of the analyte in the cyclophane by pi-pi donor-acceptor interactions. Analysis of adrenaline is accomplished by the measurement of the source-drain current, Isd, or by the gate-source voltage, Vgs. The sensing device is reusable (at least 100 cycles) and exhibits high stability.

Epinephrine↗
PubMedDate not supplied

Modeling and analysis of biooxidation of gold bearing pyrite-arsenopyrite concentrates by Thiobacillus ferrooxidans.

The results of modeling the biooxidation of a mixed sulfidic concentrate by Thiobacillus ferrooxidans is reported here. A kinetic model, which accounts for the dissolution of sulfide matrix due to both bacterial attachment onto the mineral surface and indirect leaching, has been proposed. A comprehensive system approach is employed for modeling the complex biooxidation process by (a) the decomposition of the complete system into several subsystems, (b) modeling individual systems, and (c) integrating the subsystems model in a final system model. The model for subsystems was developed by writing mass balance equations for the different species involved. The bacterial balance accounts for its growth, both on solid substrate and in solution, and for the attachment to and detachment from the surface. The kinetic parameters of the model were determined by designing the experiments in such a manner that only one subsystem was operational. This model was tested in both laboratory scale batch and continuous biooxidation processes. The model predictions agreed with the experimental data reasonably well. A further analysis of the model was carried out to predict the conditions for efficient biooxidation. Studies on the effect of residence time and pulp density on steady-state behavior showed that there is a critical residence time and pulp density below which washout conditions occur. Operation at pulp densities lower than 5% and residence times lower than 72 h was found unfavorable for efficient leaching.

Arsenicals↗
PubMed2002

Novel spherical assembly of gold nanoparticles mediated by a tetradentate thioether.

The ability to construct three- and two-dimensional architectures via nanoscale engineering is important for emerging applications of nanotechnology in sensors, catalysis, controlled drug delivery, microelectronics, and medical diagnostics. In this paper, we report novel 3D assembly using multidentate molecular building blocks. It is demonstrated that the interparticle linking of gold nanoparticles (3.7 nm core size) by a tetradentate thioether, tetra[(methylthio)methyl]silane, leads to the formation of a spherical assembly. The spherical size (30-80 nm diameter) is dependent on reaction time and relative ratio of the building blocks. The novelty of this approach is the viability of multidentate thioethers to link nanoparticles and produce spherical assemblies that can be readily assembled and disassembled. The spherical assembly can also be partially "melted" depending on the nature of interfacial interactions between the assembly and the substrate. These unusual morphological properties in shape and surface interaction and the intriguing assembling-disassembling capabilities may form the basis of designing and fabricating novel functional nanostructures.

Gold↗
PubMed2002

Density functional theory study of enantiospecific adsorption at chiral surfaces.

Density functional theory calculations are carried out for the adsorption of a chiral molecule, (S)- and (R)-HSCH(2)CHNH(2)CH(2)P(CH(3))(2), on a chiral surface, Au(17 11 9)(S)(). The S-enantiomer is found to bind more strongly than the R-enantiomer by 8.8 kJ/mol, evidencing that the chiral nature of the kink sites at the Au(17 11 9) surface leads to enantiospecific binding. The adsorption of two related chiral molecules, HSCH(2)CHNH(2)COOH ("cysteine") and HSCH(2)CHNH(2)CH(2)NH(2), does not, however, lead to enantiospecific binding. The results of the density functional calculations are broken down into a local binding model in which each of the chiral molecule's three contact points with the surface provides a contribution to the overall adsorption bond strength. The enantiospecific binding is demonstrated to originate from the simultaneous optimization of these three local bonds. In the model, the deformation energy costs of both the molecule and the surface are further included. The model reveals that the molecule may undergo large deformations in the attempt to optimize the three bonds, while the surface deforms to a lesser extent. The most favorable binding configurations of each enantiomer are, however, characterized by small deformation energies only, justifying a local binding picture.

Adsorption↗
PubMed2005

Thiolate ligands for synthesis of water-soluble gold clusters.

Water-soluble monolayer-protected gold clusters (MPCs) have been an object of investigation by many research groups since their first syntheses were reported in 1998 and 1999. The basic requirements for a ligand to form a monolayer protecting a gold cluster were established some time ago for alkanethiolate MPCs, but there has been no such information published for water-soluble MPCs. We identify 6 new ligands capable of forming water-soluble MPCs, as well as 22 water-soluble ligands that fail to form MPCs. Our findings contribute not only to the definition of the requirements for MPC formation but also to the variety of MPCs available for applications in chemistry and biology.

Gold↗
PubMed2006

Rotational polymorphism in 2-naphthalenethiol SAMs on Au(111).

We evidence by STM that 2-naphthalenethiol self-assembled monolayers formed at the n-tetradecane/Au(111) interface coexist as two structural phases which both possess molecules into two different orientations (standing and lying). Such a rotational polymorphism is observed and understood at the molecular level for the first time.

Crystallization↗
PubMed2002

An exceptional red shift of emission maxima upon fluorine substitution.

The effect of perfluorination on photophysical properties was investigated through synthesis and photophysical characterization of two isostructural donor-acceptor-donor dye molecules. The synthesis of two versatile fluorinated benzene compounds, 1,4-difluoro-2,5-diperfluorooctylbenzene (1) and 1,4-dibromo-2,5-difluoro-3,6-diperfluorooctylbenzene (2), is presented. The X-ray structure of 2 has been determined and shows that the perfluorinated octyl chains segregate from the benzene rings in the solid state, giving rise to a layered structure. The further synthesis through Suzuki coupling reactions using 4-formylbenzeneboronic acid with (2) and 1,4-dibromo-2,5-dioctylbenzene (3) gave, respectively, 1,4' '-diformyl-2',5'-difluoro-3',6'-diperfluorooctyl-p-terphenylene (4) and 1,4' '-diformyl-2',5'-dioctyl-p-terphenylene (5). The condensation of the dialdehydes 4 and 5 with 9,10-phenanthrenequinone and ammoniumbicarbonate in glacial acetic acid gave the dye molecules 1,4' '-bis(1H-phenanthro[9,10-d]imidazol-2-yl)-2',5'-difluoro-3',6'-diperfluorooctyl-p-terphenylene (6) and 1,4' '-bis(1H-phenanthro[9,10-d]imidazol-2-yl)-2',5'-dioctyl-p-terphenylene (7), respectively. The UV-vis spectra of the two molecules are nearly identical, whereas the fluorescence spectra are very different. Compound 7 shows blue fluorescence with little solvent dependence (lambda(emission) = 410 nm in THF, CH2Cl2, and hexane), whereas compound 6 shows a highly solvent-dependent emission wavelength (lambda(emission) = 583 nm in THF, lambda(emission) = 560 nm in CH2Cl2, and lambda(emission) = 450 nm in hexane). The fluorescence red shift of compound 6 in a series of solvents with different polarity is discussed using the Lippert-Mataga equation. Fluorescence lifetime and quantum yields were also determined. Ultraviolet photoelectron spectroscopy (UPS) was performed on thin films of compound 6 and 7 on a gold substrate. The observed ionization potential was 6.15 eV for 6 and 5.85 eV for 7" [correction].

Journal Article↗
PubMed2005

Adsorption of 1,10-phenanthroline within a dodecanethiol monolayer: an approach to a switchable electrode surface.

A simple method was used to prepare a "switchable" electrode surface by using self-assembled monolayers of dodecanethiol on a gold electrode. The dodecane-modified electrode was electrochemically inactive until the monolayer was soaked in solutions of 1,10-phenanthroline or 2,2'-bipyridine. The electroactive form of the electrode could be reverted back to the nonelectroactive form by rinsing the electrode. Surface IR results showed that both dodecanethiol and 1,10-phenanthroline exist in the mixed monolayer.

2,2'-Dipyridyl↗