Electrochemical surface-enhanced Raman spectroscopy (E-SERS) of novel biodegradable ionic liquids

Abstract

Electrochemical SERS (E-SERS) was used for the first time to study the interfacial behavior of a class of pyridinium-based biodegradable ionic liquids at a silver nanoparticle (AgNP) electrode surface. An isomeric series of ionic liquids (IL) based on 3-butoxycarbonyl-1-methylpyridinium bis(trifluoromethanesulfonyl)imide were prepared, which have demonstrable biodegradability. It was found that all four of the isomeric ionic liquids studied exhibited excellent electrochemical stability as binary mixtures combined with methanol, with the absence of any specific redox processes occurring over nearly 3.0 V of applied potential. Normal Raman measurements of the neat isobutyl IL showed a signal rich in vibrational features, with strong contributions from both the anion and the bulky organic cation. E-SERS of the neat isobutyl IL was shown to exhibit excellent potential stability, with no potential-induced orientational change at the metal surface. When the ionic liquids were prepared as methanolic binary mixtures, dissociation of the IL ions was observed, and only the organic cation was shown to adsorb at the Ag/solution interface. The nature of the substituent on the ester group of the IL series was observed to have a significant effect on the orientation of the cation on the metal surface, based on the application of the metal surface selection rules combined with computational data. Notably, the isobutyl and sec-butyl isomers were observed to have an orientation wherein the pyridinium ring was oriented perpendicular to the surface, while the tert-butyl and n-butyl isomers were observed to have an orientation wherein the pyridinium ring was lying flat on the metal surface.

Advances in surface-enhanced vibrational spectroscopy at electrochemical interfaces

“…The nanoparticle ensemble approach to EC-SERS has been applied to various systems in recent years including ionic liquid adsorption [40,41], pyridine adsorption [42], uric acid detection [43] and DNA hybridisation [44]. The dye compound Nile Blue (NB) has found significant attention as a probe molecule in this arena due to its strong resonance Raman signal which is lost upon its two-electron reduction [45][46][47][48][49][50].…”

Applications of Ionic Liquids in Spectroscopy

“…[80][81][82][83][84][85][86][87] Umebayashi et al 80 The effect of the chain length in the structure of imidazolic ionic liquids and dimethylformamide solutions is probed by Rodrigues and Santos using Raman spectroscopy. [80][81][82][83][84][85][86][87] Umebayashi et al 80 The effect of the chain length in the structure of imidazolic ionic liquids and dimethylformamide solutions is probed by Rodrigues and Santos using Raman spectroscopy.…”

Spectroscopic study of ionic liquid adsorption from solution onto gold

“…8,26 An understanding of reactivity, binding mechanisms, orientation, and layer structure at solid interfaces is required if ILs are to be selected or designed for these applications (and others), and spectroscopic techniques are most often chosen for this task. In the area of IL solutions, fewer experiments have been performed, with a limited number of SERS studies, 30 ex situ spectroscopic measurements of wear films formed during friction studies, 3,4,6 and some NMR spectroscopic studies of IL lubricant additive interactions with metals. In the area of IL solutions, fewer experiments have been performed, with a limited number of SERS studies, 30 ex situ spectroscopic measurements of wear films formed during friction studies, 3,4,6 and some NMR spectroscopic studies of IL lubricant additive interactions with metals.…”