Surface anchoring mode-dependent hydrolysis reactions of hydrazone groups on gold examined by pH-dependent Raman spectroscopy

Abstract

We conducted a comparative study of the pH-dependent anchoring behaviors of 3-methyl-2-benzothiazolinone hydrazone (3M2BH) and benzophenone hydrazone (BPH) on gold nanoparticles (AuNPs) by means of interfacial Raman spectroscopy. We found that several bands of 3M2BH in the highly alkaline pH region disappeared as the colloidal conditions became more neutral and acidic. The vibrational band at 919, 1174, and 1222 cm(-1) at pH 10.0 disappeared below pH 9.2, which may be because of the hydrolysis reactions that cleave the labile =N-NH2 group of 3M2BH, indicating a rather perpendicular orientation via the sulfur atom at the surfaces. A fairly high transition pH value was assumed to be because of the interaction of the =N-NH2 group in the vicinity of the surfaces. Several characteristic bands, including 1584 and 1617 cm(-1), also exhibited different intensities, suggesting that the adsorbates on Au surfaces underwent structural transformations of the =N-NH2 group after the pH value became neutral or acidic. These changes were not observed for BPH, presumably because of the direct and robust binding of the hydrazone onto Au surfaces. Our results revealed that the pH-dependent cleavage reactions may vary depending on the surface anchoring modes of the adsorbates. Copyright (C) 2015 John Wiley & Sons, Ltd.