221st ACS National Meeting
April 1 - April 5, 2001
San Diego, California



Barron Research Group Abstracts

Reversible binding of a Lewis base to a gallium aryloxide polymer: An example of a molecular sensor.
Laura G. van Poppel,a Simon G. Bott,b Andrew R. Barron.a*
aDepartment of Chemistry, Rice University, Houston, TX 77005 and bDepartment of Chemistry, University of Houston, Houston, TX 77204
The oligomeric species [{(tBu)2Ga}(µ-OC6H4O)]n has been formed from the reaction of tri-tert butyl gallium with hydroquinone in a noncoordinating solvent. Dissolution of [{(tBu)2Ga}(µ-OC6H4O)]n in pyridine gives the monomer [(tBu)2Ga(py)2]2(µ-OC6H4) which has been characterized by single crystal X-ray diffraction. In the solid state, [(tBu)2Ga(py)2]2(µ-OC6H4) loses 2 equivalents of pyridine at 125°C, reforming the oligomeric species. This process is reversible and is accompanied by a change in color from yellow to colorless. The characterization of this Lewis acid/base interaction will be presented

Kimberly A. DeFriend-Varela and Andrew R. Barron, Department of Chemistry, Rice University, Houston, TX 77005
We have investigated the use of carboxylate-substituted alumina nanoparticles (carboxylate-alumoxanes) as ceramic precursors to provide surface repair to machined ceramic surfaces. We have also developed a method to form an equivalent to a CMCFC'c, ceramic matrix ceramic fiber composites, at a low cost, by infiltrating a porous ceramic with the alumoxanes. The effects of solution concentration, number of coatings, and increased strength have been determined. ESEM, AFM, elemental mapping, micro-hardness testing, and 3 point bend test results will be presented.

Cement hydration inhibition: In situ creation of composite structures
Maximilienn Bishop1, and Simon G. Bott2, Andrew R. Barron1. (1) Department of Chemistry, Rice University, 6100 main Street, Houston, TX 77005, Fax: 713-348-5619, arb@rice.edu, (2) Department of Chemistry, University of Houston
The effects of organophosphonates retarders on the hydration of the main components of Portland Cement and the formation of ettringite have been investigated in order to gain insight into the different mechanisms of hydration inhibition. It was found that the organophosphonate initially accelerates the hydration of the aluminate phase and the formation of ettringite, then halts the reactions completely for several hours. In addition, nitrilotris(methylene)triphosphonic acid enhances the dissolution of calcium oxide and subsequently precipitates a layered calcium phosphonate polymer. The structure of this material and the dissolution-precipitation mechanism are discussed with regard to cement hydration inhibition. The formation of an in-situ composite structures is discussed.

Molecular coupling layers formed by reactions with self-assembled carboxylate monolayers grown on the native oxide of aluminum
Christopher L. Edwards, Cullen T. Vogelson, Andrea Keys, and Andrew R. Barron, Department of Chemistry, Rice University, Houston, TX 77005
In order to produce molecular coupling layers, epoxy resins cross-linked with self-assembled monolayers (SAMs) grown on the native oxide of aluminum have been investigated. Initially, SAMs have been formed by the attachment of carboxylic acids RCO2H [R=C17H35, CH3, C6H4-3-Br, C6H4-4-OH, C6H4-4-SH, and C(NH2)(CH2)4NH2] to the native oxides of aluminum thin films on silicon substrates. In order to investigate the cross-linking reaction between carboxylate monolayers and an epoxide, grown monolayers of p-hydroxybenzoate and lysine were reacted with a mono-epoxy resin, 1,2-epoxy-3-phenoxypropane. The SAM systems have been characterized by Grazing Angle Specular Reflectance FTIR, XPS, EDX analysis, and contact angle measurements. In addition to these surface materials, aluminum oxide surfaces supporting either lysine or p-hydroxybenzoate monolayers were reacted in pairs with a di-epoxide (DER 332) to form an adhesive layer between the two surfaces. This epoxy-SAM interaction is shown to form a "molecular glue" type interface which has been characterized by SEM and contact angle. Finally, aluminum oxide surfaces supporting p-thiobenzoate monolayers were reacted with gold surfaces.

The effect of organic admixtures on the hydration and surface chemistry of tricalcium aluminate and tricalcium silicate.
 M. Bishop, S.G. Bott, and A.R. Barron*, Rice University, Houston, Texas 77005.
The desire for precise control of the hydration and setting of Portland Cement has inspired research into the mechanisms of cement hydration inhibition. The effects of several organic additives on the hydration of tricalcium aluminate and tricalcium silicate, two of the main components of Portland Cement, were investigated. Use of an organophosphonate retarder lead to the development of a calcium phosphonate model compound which is thought to bind to the surface of tricalcium aluminate and [the mineral] ettringite. The interactions of the calcium phosphonate with the surface of ettringite and tricalcium aluminate and their relationship to cement hydration inhibition will be discussed.

Aluminum and gallium chloride stabilized arene-mercury complexes
Alexander S. Borovik1, and Simon G. Bott2, Andrew R. Barron1. (1) Department of Chemistry, Rice University, Houston, TX 77005, Fax: 713-348-5619, arb@rice.edu, (2) Department of Chemistry, University of Houston
Novel Lewis acid-base mercury (II) complexes featuring strong coordination of arenes toward mercury have been prepared by the reaction of mercury dichloride with two equivalents of the trichlorides of aluminum and gallium in a variety of aromatic solvents. These new compounds were found to be extremely efficient activators of C-H bonds. The catalytic proton-deuterium exchange and the olefin addition to the aromatic ring will be discussed. Toluene, ethylbenzene, o-xylene, trimethylbenzene complexes were characterized by X-ray crystallography.

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