To determine whether selenolates are viable alternatives to thiolates for self-assembled monolayers
(SAMs), the formation and oxidative stability of monolayers made from diphenyl diselenide (DPDSe)
solution were assessed by surface-enhanced Raman spectroscopy. Upon adsorption, the diselenide bond
is cleaved to form benzeneselenolate, analogous to formation of benzenethiolate monolayers from diphenyl
disulfide (DPDS). DPDSe displaces benzenethiolate from gold, but DPDS does not displace benzeneselenolate. Competitive adsorption experiments show that adsorption of DPDSe is more favorable by ∼0.7
kcal/mol. Unlike benzenethiolate, the benzeneselenolate monolayer is unstable both in air and to UV
light. Long-term exposure to air results in oxidation to protonated and deprotonated benzeneseleninic
acid. Exposure to UV results in C−Se bond cleavage (analogous to C−S bond cleavage in benzenethiolate)
and formation of SeO2 and SeO3
2-. The higher adsorptivity of benzeneselenolate and its similar oxidative
behavior to benzenethiolate suggests that selenolates are an attractive alternative to thiolates for building
SAMs.
Summaryμ-Raman spectroscopy has been used to characterize two types of biomedical materials: a multilayer, silicone elastomer used in implants, and a thin, polyethylene layer used in a medical device. Raman spectroscopy is the collection of light inelastically scattered by a material or compound. The technique is based on the Raman effect, which involves the interaction of light and matter. When light strikes a material, the light is inelastically scattered and is frequency shifted according to the vibrations of the chemical-functional groups and/or macrostructure of the material. The result is a Raman spectrum of the material that can be interpreted to determine the characteristics of the material, including identity, macrostructure, and quantity of a specific material within a matrix.The application of Raman spectroscopy in the characterization of polymers has been well established. The technique has been used to determine the chemical composition and morphology of polymers. Raman spectroscopy could therefore be a powerful tool for characterizing polymeric biomaterials.The silicone elastomer characterized in this work consisted of three layers: polydimethylsiloxane, polydimethyl/polydiphenyl siloxane, and polydimethylsiloxane.
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