A study on the adsorption structure of an adhesive monomer for precious metals by surface-enhanced Raman scattering spectroscopy

In order to clarify the role of a primer on the adhesion between dental pre cious metals and resin, surface-enhanced Raman scattering (SERS) technique has been applied to the structural analysis of the adhesive monomer, 6-(N-( 4-vinylbenzyl)propylamino)1,3,5-triazine-2,4-dithione (VBATDT) adsorbed on colloidal Au surfaces. VBATDT is one of the major components of commercial primers. A mixture of a methanol solution of VBATDT and aqueous Au colloid was illuminated by the 647.1 nm line from a Kr ion laser to obtain the SERS . The most intense peak at 458 cm(-1) due to C=S stretching in the Raman sp ectrum of solid VBATDT disappears completely in the SERS, while all the oth er peaks due to vinylbenzyl group vibrations remain unchanged. It suggests that some structural change occurs in VBATDT upon adsorption on Au which in volves the C=S bonds and that the molecule undergoes thione-thiol-type taut omerization in the adsorption process. The SERS spectrum of a commercial pr imer containing VBATDT exhibits a similar spectral pattern. The present res ults lead us to conclude that some specific interactions exist between the sulfur atoms of VBATDT and Au surface to form chemical bond likes, which ar e effective to improve the bond strength between dental precious metals and resin. The ambivalent properties of the primer, chemical stability in stor age and chemical affinity to Au, are also explained by the thione-thiol-typ e tautomerization of VBATDT on the basis of the spectroscopic evidence. (C) 1999 Elsevier Science Ltd. All rights reserved.