Showing papers in "Langmuir in 1993"

A new hydrosol of gold clusters. 1. Formation and particle size variation

Abstract: Aqueous reduction of hydrogen tetrachloroaurate(III) with alkaline tetrakis(hydroxymethyl)phosphonium chloride yields gold in an ultrafinely divided form as a stable colloidal hydrosol, with mean metal-cluster diameter between 1 and 2 nm, without the need for large organic stabilizing molecules. The ultraviolet-visible extinction spectrum is very similar to those of other gold colloids of similar dimensions and includes a weak plasmon feature. Dispersions with characteristics of yet finer clusters are prepared using lower initial concentrations of Au3+ ions. Boiling the sols in the presence of appropriate colloidal stabilizers (ionic and/or polymeric) is a route to coarser (3-10 nm particle diameter) gold hydrosols. © 1993 American Chemical Society.

Preparation of ordered colloid monolayers by electrophoretic deposition

Abstract: published in Advance ACS Abstracts, November 1, 1993. (1) (a) Pieranski, P.; Strzelecki, L.; Pansu, B. Phys. Rev. Lett. 1983, 50,900. (b) Pansu, B.; Pieranski, P. J. Phys. (Paris) 1984,45,331. (c) Pieranski, P. Phys. Rev. Lett. 1980,45,569. (2) Van Winkle, D. H.; Murray, C. A. Phys. Rev. A 1986, 34, 562. (3) Onoda, G. Y. Phys. Rev. Lett. 1985,55, 226. (4) Giersig, M.; Kunath, W. Eur. J. Biol. Suppl. 1989, 27, 28. (5) Denkov, N. D.; Velev, 0. D.; Kralchevsky, P. A.; Ivanov, I. B.; Yoshimura, H.; Nagayama, K. Langmuir 1992,8, 3183. (6) Dusemund, B.; Hoffmann, A,; Salzmann, T.; Kreibig, U.; Schmid, G. 2. Phys. D 1991,20, 305. (7) Brom, H. B.;van Staveren, M. P. J.; de Jongh, L. J.Z. Phys. D 1991, 20, 281. (Munich) 1990,169, 11. (8) Kreibig,U.;Fauth, K.; Granqvist, C.-G.; Schmid, G. Z.Phys. Chem. (9) Deriarmin. B. V.: Muller. V. M.: Rabinovich. Ya. I. Kolloid Zh. 1969, 31, 302. . (10) Parsegian,V. A.; Weiss, G. H.; Schrader,M. E. J. Colloidlnterjace Sci. 1977, 61, 356. (11) Parsegian, V.

Thioaromatic monolayers on gold: a new family of self-assembling monolayers

Abstract: Self-assembling (SA) monolayers of the aromatic compounds thiophenol (TP), p-biphenyl mercaptan (BPM), and p-terphenyl mercaptan (TPM) were prepared on gold electrodes. Contact angle (CA) measurements and ellipsometry indicate that TP forms poorly defined layers, while BPM and TPM form monolayers with reproducible CAs and ellipsometric thicknesses. BPM and TPM films are substantially more stable than TP layers toward various electrochemical conditions and replacement by alkanethiols as shown by the combined CAs, ellipsometric thicknesses, and the electrochemical measurements of the corresponding monolayer-covered electrodes. The surface coverages of the three monolayer systems, determined from the electrochemical responses of the respective electrodes, show that the blocking efficiency increases with the number of phenyl rings in the molecule. Three electrochemical techniques, namely gold oxide formation/removal, cyclic voltammetry (CV), and ac impedance were used to determine the monolayer surface coverage. The ac impedance technique proves to be superior for surface coverage determination, mainly due to the milder conditions applied. Molecular mechanics calculations show that BPM and TPM might form (√3 x √3)R30° overlayers on Au(llI) with the molecules nearly perpendicular to the gold surface. Such overlayers would have favorable intermolecular interactions and retain the usual structure for sulfur on Au(llI).

Pore size heterogeneity and the carbon slit pore: a density functional theory model

Abstract: We present model isotherms predicted by nonlocal density functional theory for adsorption of simple fluids in carbon slit pores. The effects of pore size, temperature, and solid-fluid potential interaction strength are examined. Our results are summarized into a classification scheme based upon regimes of continuous pore filling, capillary condensation, and 0 1 layering transitions. The descriptions we have devised depart from the IUPAC convention in that the filling behavior, rather than the physical width of the pore, is used as a guide to classification. Our results suggest that while the magnitude of the solid-fluid interactions dictates the pressure at which pore filling occurs, the type of filling depends primarily upon the ratio of pore width to adsorbate molecular diameter. The critical pore widths that denote the boundaries between various regimes of filling behavior are strongly dependent upon the temperature. To confirm the accuracy of the theoretical results, we compare adsorption isotherms and density profiles calculated from nonlocal theory and Gibbs ensemble simulation. The results from theory and simulation are found to be in good agreement. We conclude with a discussion of the problems associated with estimating solid-fluid potential parameters from experiment for use in theoretical computations. A comparison of nonlocal theory model isotherms and experimental nitrogen uptake measurements on nonporous carbon is presented.

Formation of self-assembled monolayers of n-alkanethiols on gold: a scanning tunneling microscopy study on the modification of substrate morphology

Abstract: Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Formation of self-assembled monolayers of n-alkanethiols on gold: a scanning tunneling microscopy study on the modification of substrate morphology K. Edinger, A. Goelzhaeuser, K. Demota, C. Woell, and M. Grunze Langmuir, 1993, 9 (1), 4-8• DOI: 10.1021/la00025a002 • Publication Date (Web): 01 May 2002 Downloaded from http://pubs.acs.org on February 24, 2009

Membrane-induced interactions between inclusions

Abstract: The properties of membranes containing inclusions, such as proteins or colloidal particles, are calculated as a function of the bilayer interfacial energy and bending coefficients. We find that the inclusion-imposed perturbation leads to damped oscillations in the membrane profile and, hence, to nonmonotonic shortranged, membrane-induced interactions between inclusions. The preferred spacing between inclusions is predicted to depend on the spontaneous curvature of the amphiphile and the magnitude of the perturbation at the inclusion boundary.

Protein binding to supported lipid membranes: investigation of the cholera toxin-ganglioside interaction by simultaneous impedance spectroscopy and surface plasmon resonance

Abstract: The specific recognition reaction between cholera toxin (ChTo) and the ganglioside GM1 was investigated in situ on planar supported lipid layers using simultaneous surface plasmon resonance (SPR) and electrochem. impedance measurements. The lipid monolayers contg. different amts. of GM1 were formed on alkanethiol-coated gold surfaces by a new lipid/detergent diln. technique. The formation of the layers was investigated using both SPR and impedance measurements. While the optical properties of the different lipid layers remained unchanged, the layer capacitance was seen to depend on the GM1 to POPC molar ratio. The selective binding of ChTo to these layers was detected with high sensitivity by SPR. The comparatively small impedance changes assocd. with the protein adsorption suggest a high water content of the ChTo layers. The B5 subunit interacts similarly with these supported lipid layers. [on SciFinder (R)]

Surface reactions on thin layers of silane coupling agents

Abstract: The reactivity of immobilized functional groups in thin layers of (3-aminopropyl)triethoxysilane (APS), (3-mercaptopropyl)trimethoxysilane, (3-bromopropyl)trimethoxysilane, and (8-bromooctyl)trimethoxysilane on oxidized aluminum substrates was studied with reflection-adsorption infrared spectroscopy (RAIR), optical ellipsometry and contact-angle measurements. Mass changes on the surface associated with the surface-confined reactions were measured with the quartz crystal microbalance (QCM). Single layers of (3-aminopropyl)triethoxysilane on oxidized aluminum react with chlorodimethylsilane to give [(-O)[sub 3]Si(CH[sub 2])[sub 3]NH[sub 2][sup +]SiMe[sub 2]H]Cl[sup [minus]] and single layers of (3-mercaptopropyl)trimethoxysilane on oxidized aluminum react with phenylmercury hydroxide to give [(-O)[sub 3]Si(CH[sub 2])[sub 3]SHgPh], while no substitution reaction of (3-bromopropyl)trimethoxysilane and (8-bromooctyl)trimethoxysilane monolayers occurred with cyanide. Films of APS were further utilized to immobilize pepsin. It is discussed to which extent known reactions from solution can be transferred to interface reactions. 50 refs., 8 figs., 5 tabs.

Entangled versus multiconnected network of wormlike micelles

Abstract: Laboratoire d'Ultrasona et de Dynamique des Fluides Complexes, URA du CNRS No. 851, Universit6 Louis Pasteur, 4 rue Blaise Pascal, 67070 Strasbourg cedex, France, Groupe de Dynamique des Phases Condensi?es, URA du CNRS No. 233, Universite des Sciences et Techniques du Languedoc, 34095 Montpellier cedex 05, France, and Laboratoire de Physique Statistique, associ6 au CNRS, 24 rue Lhomond, 75231 Paris cedex 05, France

Determination of surface pKa values of surface-confined molecules derivatized with pH-sensitive pendant groups

Abstract: : Two methods for in-situ electrochemical measurements of surface pKa values air, reported. The methods are applied to surface-confined monolayers consisting of organomercaptan molecules derivitized with pH-sensitive pendant groups. The first technique relies upon pH-dependent electrostatic binding of redox probe molecules to the charged monolayer surface: the surface concentration of the probe molecules reflects the degree of surface protonation. The second method relates the differential capacitance of the monolayer-modified electrode surface to the surface pKa. The two methods yield essentially identical results and are consistent with a recently developed theoretical model. The surface pKa values of 4-mercaptopyridine and 4-aminothiophenol are 3. 7 and 5.7, respectively.