Metal oxide surfaces, immobilized

Our interest in polyethylene glycols centered on a simple scheme to immobilize these materials onto metal oxide surfaces. The surface of silica gel contains both silanol-OH groups and -0-strained siloxane groups(29). A simple synthetic pathway to produce covalently bonded glycols was proposed where reaction(30) would occur between the OH group of the glycol and the surface of a refractory oxide. 

Table I. Polyalkylene Glycols Immobilized onto Metal Oxide Surfaces...

Two schemes can be imagined wherein (1) the component forming the anion, e.g., AICI3 is reacted first then followed by the organic cation component (dialkylimidazolium chloride) or (2) the surface is reacted with a derivative of the cation component which shows a reactive tail for the metal oxide surface, such as trialkoxysilane, and then the anion component is reacted with this immobilized component. For example, using conventional chemistry for decorating metal oxide surfaces with reactive compounds, silica has been decorated first with a dialkylimidazolium chloride and then this surface compound was reacted with AICI3 to form an immobilized... 

Nevertheless, the possibility of demonstrating the very remarkable specificity of the catalytic power of proteins immobilized on electrodes—to collect or supply electrons from the encounter of enzyme electrodes with entities in solution—looks so attractive that it has spurred investigators (e.g., Bowden, 1993) to efforts that have proved rewarding. The most important advance was made by replacing a bare metal or metal oxide surface with monolayers of organics of a particular type (Fig 14.37) (Eddowes and Hill, 1979). 

Adsorption is the simplest method to immobilize nucleic acids on surfaces. The method does not require special reagents or nucleic acid modifications. Materials reported for this type of immobilization include nitrocellulose, nylon membranes, polystyrene, metal oxide surfaces (palladium or aluminum oxide), or carbon transducers. 

Silanes are often used to modify metal oxide surfaces, especially those rich in hydroxyl groups, to enable a broad range of functionalities such as hydrophilicity, immobilization of therapeutic agents, polymers, and cells, and the creation of model surfaces [67-72]. The easiest methods of deposition of silane compounds involve dipping or solution casting techniques. Other methods for depositing silanes include microwave and vapor deposition techniques [70, 71, 73]. 

The aim of the present study was to immobilize PEG on metal oxide surfaces such as silicon dioxide, titanium dioxide, and niobium pentoxide. The adsorption behavior of polyelectrolytes on such metal oxide surfaces has been characterized, " and polycations, in particular, were found to form stable adsorbed layers on negatively charged oxides such as silicon dioxide and titanium dioxide. 

Pluronics, diblock copolymers consisting of poly(propylene oxide) flanked by two poly(ethylene oxide) chains, are commonly used to immobilize PEG on hydrophobic surfaces. However, Pluronics F-108 and F-68 were found not to adsorb onto any of the metal oxide surfaces investigated here and, as a result, did not show any protein-adsorption-suppressing properties. 

Ebitani, K., Fujie, Y. and Kaneda, K. (1999). Immobilization of a Ligand-Preserved Giant Palladium Cluster on a Metal Oxide Surface and its Nobel Heterogeneous Catalysis for Oxidation of AUylic Alcohols in the Presence of Molecular Oxygen, Langmuir, 15, pp. 3557—3562. 

The utility of such reagents in the oxidation processes is compromised due to their inherent toxicity, cumbersome preparation, potential danger in handling of metal complexes, difficulties encountered in product isolation and waste disposal problems. Immobilization of metallic reagents on solid supports has circumvented some of these drawbacks and provided an attractive alternative in organic synthesis because of the selectivity and associated ease of manipulation. Further, the localization of metals on the mineral oxide surfaces reduces the possibility of their leaching into the environment. 

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