Surface enhanced Raman spectroscopic (SERS) behavior of substituted propenoic acids used in heterogeneous catalytic asymmetric hydrogenation

Abstract

The strength and geometry of adsorption of substituted propenoic acids on silver surface were studied by means of surface enhanced Raman spectroscopy (SERS) using silver sol. Based on their SERS behavior, two classes of phenylpropenoic acids studied were distinguished. The first class of propenoic acids (atropic acid, (E)‐2,3‐diphenylpropenoic acid, (E)‐2‐(2‐methoxyphenyl)‐3‐phenylpropenoic acid, (E)‐2,3‐di‐(4‐methoxyphenyl)phenylpropenoic acid and (E)‐2‐(2‐methoxyphenyl)‐3‐(4‐fluorophenyl)propenoic acid) has shown strong charge transfer (CT) effect. We suggest bidentate carboxyl bonded species based on the SERS enhanced bands of νCOO− around 1394 cm−1 and νC―C of the ―C―COO− moiety at 951 cm−1. In these series the plane of the α‐phenyl group (γCH out‐of‐plane vibrations at 850–700 cm−1) is almost parallel to the silver surface, while the β‐phenyl group is in tilted position depending on the type and the position of substituent(s) showing strong SERS enhanced bands of νCC + βCH (in‐plane mode) at 1075 cm−1, νCC (ring breathing mode, in‐plane) at 1000 cm−1 and γCCC (out‐of‐plane mode) around 401 cm−1. The other class of propenoic acids (cinnamic acid, (E)‐2‐phenyl‐3‐(4‐methoxyphenyl)propenoic acid) has shown weak electromagnetic (EM) enhancement (CC bands is enhanced in cinnamic acid). In this case no significant carboxyl enhancement was observed, so we suggest that adsorbed species lie parallel to the surface. The two types of adsorption can be related to the dissociation ability of the carboxylic group. In the first case the carboxylic H dissociates, while in the second case it does not, as indicated also by the characteristic νCO band at 1686 cm−1 in the FT‐Raman spectra of methanolic solutions. Copyright © 2015 John Wiley & Sons, Ltd.

Surface enhanced Raman spectroscopic (SERS) behavior of phenylpyruvates used in heterogeneous catalytic asymmetric cascade reaction

“…[29,30]). Since the out-of-plane deformations, especially the ring skeleton CCC are well enhanced, we can conclude that there is strong coordination between the benzene ring and Ag surface with a parallel orientation [10]. Additionally, the weak band at 529 cm -1 can be assigned to S-S indicating the formation of disulfide bond [31].…”

“…Detailed characterization by UV-Vis spectroscopy and transmission electron microscopy (TEM) of the as-prepared silver sol is described in our previous paper [10]. In short, polydisperse silver particles with cca.…”

“…The Surface Enhanced Raman Spectroscopy (SERS) is a useful tool to get the fingerprint of the studied compounds [4,5], to obtain information about the orientation of adsorbed molecules [6][7][8][9][10], the changes in their chemical bonds [11,12], and the formation of new chemical bonds between the adsorbed molecules and the metal surface [13,14]. Our aim was to get information about the adsorption geometry (tilted or flat) of a series of phenylpyruvates by means of SERS method using silver sol.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part X

“…Firkala and co‐workers have used SERS to study the behavior of substituted propenoic acids used in heterogeneous catalytic asymmetric hydrogenation. Based on their SERS behavior, two classes of phenylpropenoic acids were studied and distinguished . Furini et al .…”

“…Based on their SERS behavior, two classes of phenylpropenoic acids were studied and distinguished. [29] Furini et al described detection and quantitative analysis of carbendazim (MBC) herbicide on Ag nanoparticles via SERS. They studied the adsorption of the MBC onto the nanoparticle surface by SERS under different experimental conditions, such as different synthesis methods of nanoparticle, variable excitation wavelength, and fungicide concentration with the aim to detect MBC at low concentrations.…”