Chaim N. Sukenik

Synthesis and characterization of TiO2 thin films on organic self-assembled monolayers: part I. Film formation from aqueous solutions

Self-assembled monolayers (SAMs) bearing sulfonate (-SO 3 H) surface functional groups, on single-crystal Si wafers, were used as substrates for the deposition of TiO 2 thin films from aqueous solutions. Polycrystalline TiO 2 thin films over 50 nm thick formed in 2 h by hydrolysis of TiCl 4 in aqueous HCI solutions at 80 °C. The films were pore-free, showed excellent adherence and uniformity, and consisted of anatase crystallites 2–4 nm in diameter. Annealing at temperatures up to 600 °C caused coarsening of the anatase grains, but no loss of adherence or structural integrity.

Functionalized siloxy-anchored monolayers with exposed amino, azido, bromo, or cyano groups

Abstract The creation of new, uniformly functionalized, surfaces has been achieved with mono layers bearing NH 2 , N 3 , Br, or CN functional groups.

Synthesis and characterization of TiO 2 thin films on organic self-assembled monolayers: Part II. Film formation via an organometallic route

Crystalline, uniform, adherent, ultrathin films of TiO 2 were deposited onto OH-functionalized organic self-assembled monolayers (SAMs) on single-crystalline Si at low-temperature ( 2 by x-ray photoelectron spectroscopy, electron diffraction, and energy-dispersive x-ray microanalysis. Transmission electron microscopy showed the films to be uniform in thickness (2 ± 0.5 nm) and continuous. On bare Si, in contrast, there was no evidence of TiO 2 deposition under identical conditions. Unlike the anatase films deposited on SAMs from aqueous solutions (described in the preceding paper), the electron diffraction patterns of the films deposited from alkoxide solutions suggest that they were the rutile phase. It is suggested that the functionalized SAMs enable the anchoring of the Ti alkoxide and initiate the formation of an adherent oxide film, and that they are sufficiently uniform that the resulting film is continuous and uniform in thickness.

CELL TYPE-SPECIFIC MODULATION OF FIBRONECTIN ADHESION FUNCTIONS ON CHEMICALLY-DERIVATIZED SELF-ASSEMBLED MONOLAYERS

Cell type-specific responses (microfilament stress fibers for fibroblasts or neurites for neuroblastoma cells) were evaluated in culture on inert and chemically-derivatized silane substrata adsorbed with fibronectin (Fn). Substrata of self-assembled monolayers contain a 14-17 carbon aliphatic chain terminating with different chemical endgroups -- [CH3], [C=C], [Br], [CN], [Diol], [COOH], [NH2], [SH], [SCOCH3], or [SO3H]. Fn adsorbed effectively to all derivatized surfaces. 3T3 fibroblasts or neuroblastoma cells attached equivalently to all surfaces preadsorbed with Fn, indicating availability of receptor binding sites on Fns. However, transmembrane signaling from Fn(adsorbed): receptor(cell) surface complexes yielded a range of abilities for generating F-actin stress fibers in fibroblasts or neurites in neuroblastoma cells. Efficiency for stress fiber formation was very different from that of neurite extension. The same chemical endgroups on glass, titanium, or germanium yielded the same patterns of cellular physiological responses, indicating that inert substrata do not act at a distance and that only chemical endgroups regulate Fn signaling functions. When adhesion-inert albumin is co-adsorbed with Fn, efficiency of neurite extension is improved on some surfaces or diminished on others. These results indicate that the conformation of Fn(adsorbed) changes in specific ways on derivatized substrata. Change in Fn conformation was confirmed by FTIR/ATR spectroscopy experiments of Fn(adsorbed). Overall, these studies indicate changes in Fn conformations on chemically-derivatized self-assembled monolayers leading to up- or down-regulation of cell type-specific physiological responses from receptors via their signaling pathways. They also offer predictability for regulating responses of specific cell types when these cells interact with biomaterial implants in vivo.

Problems and approaches in covalent attachment of peptides and proteins to inorganic surfaces for biosensor applications.

SummarySome of the fundamental problems in covalent attachment of peptides and proteins to putative biosensor surfaces are reviewed and specific approaches to these problems discussed. In addition, selected aspects of our recent work utilizing self-assembled monolayer (SAM) systems designed to react selectively with the thiol side chain of Cys in proteins are presented. Uniform attachment of a 21-amino acid peptide antigen through a single Cys residue with retention of biological function (antibody binding) has been attained. Further work with this system may lead to solutions for some of the problems which currently prevent the development of reliable biosensors for industrial and medical use.

Micellar perturbation of enone reduction

Abstract The reduction of several enones using BH 4 − in the presence of cationic surfactants has been investigated. These reductions are all shifted by the micelle towards the formation of conjugate reduction products.

The reaction of LiAlH4/HMPA with oximes: Mechanism and synthetic applications

Abstract Three aspects of the reaction of LiAlH4 in HMPA with oximes have been studied: the mechanism of the conversion of ketoximes into ketones, application of this reaction to the selective reduction of enones to ketones via the ene-oxime, and the conversion of aldoximes to either nitriles or aldehydes as a function of substrate structure.

Deposition of oxide thin films on silicon using organic self-assembled monolayers

Crystalline oxide thin films have been synthesized at low temperatures from aqueous liquid solutions. A key element of the approach is the use of organic self-assembled monolayers (SAMs) on the substrate to promote the growth of adherent inorganic films. A SAM is a close- packed, highly ordered array of long-chain hydrocarbon molecules, anchored to the substrate by covalent bonds. The terminating functional group on the SAM surface is chosen so as to initiate and help sustain the formation of the oxide film when the substrate is immersed in the oxide precursor solution. Synthesis, microstructural characterization, and properties of TiO2, ZrO2, SiO2, and Y2O3 films are surveyed. Crystalline films were formed either directly from solution, or through subsequent heat treatments at temperatures that in most cases were lower than typical sol-gel or vapor phase deposition processes. All depositions were from aqueous solutions onto single-crystal (100) silicon. The ability to produce patterned films on a micron scale has been demonstrated, taking advantage of the selective deposition characteristics towards different surface functional groups of the SAM. The role of the SAM in oxide film formation is discussed.

Glass and metal surfaces derivatized with self-assembled monolayers: cell type-specific modulation of fibronectin adhesion functions

Methods were developed to chemically derivatize glass, titanium, and germanium surfaces with a covalently-linked, siloxane-anchored, and ordered thin film of functionalized organic molecules (self-assembled monolayer). Monolayers are comprised of a 14–17 carbon aliphatic chain terminating with one of many different chemical endgroups. The following endgroups were analyzed — [CH3], [C=C], [Br], [CN], [Diol], [COOH], [NH2], [SH], [SCOCH3], and [SO3H]. Plasma fibronectin (FN) adsorbed as effectively to all derivatized surfaces as to underivatized surfaces. Mouse 3T3 fibroblasts and Platt human neuroblastoma cells attached equivalently to all surfaces preadsorbed with FN, indicating the availability of receptor binding sites on adsorbed FN molecules. In contrast, transmembrane signaling from FNadsorbed:Receptorcell surface complexes yielded a range of abilities for generating F-actin stress fibers within fibroblasts, as well as neurite extensions from the neuroblastoma cells. Efficiency patterns on these various substrata for stress fiber formation were very different from the patterns of neurite extension. In addition, the same chemical endgroup on glass, titanium, or germanium yielded the same cellular physiological responses, indicating that the inert substratum cannot act at a distance and that the chemical endgroup regulates FN functions in adhesion. When adhesion-inert albumin is co-adsorbed with FN, efficiency of neurite extension can be greatly improved on some surfaces or diminished on other surfaces. These and other results indicate that these two cell types use different receptors interacting with different binding sites on FNadsorbed to mediate their transmembrane signals and that the conformation of FNadsorbed changes in specific ways on derivatized substrata. This latter hypothesis was confirmed by FTIR/ATR spectroscopy experiments of FNadsorbed. These studies indicate cell type-specific changes in FN conformations on chemically-derivatized self-assembled monolayers leading to up- or down-regulation of specific cellular physiological responses from receptors. They also offer optimism for regulating responses of specific cell types when various cell types interact with biomaterial implants in situ.

Selective Mercuration of Dienes in Micellar Medium: Mechanism and Potential Synthetic Application

The potential for application of micellar catalysis to synthetically useful transformations is large and unexplored. We present herein a brief summary of previous work in this area and preliminary results of our work aimed at using the environment of an anionic aqueous micelle to direct the course of the hydroxymercuration of organic substrates. We have found this medium to be both a useful way to selectively mono-functionalize non-conjugated dienes and to be able to control the competition between diol and cyclic ether formation in these same substrates.