(−)‐R‐Mevalonolactone Studied by ROA and SERS Spectroscopy

Abstract

Here we present for the first time the experimental and theoretical (DFT/B3LYP/6-311++G**) Raman optical activity (ROA) spectra of (-)-R-mevalonic acid as the δ-lactone form in neat liquid and in the aqueous solution. Quantum chemical calculations show the conformational diversity of (-)-R-mevalonolactone originated from small energy differences between the various conformation of the six-membered ring and the arrangement of the hydroxyl group. According to calculations, the investigated compound takes predominantly the chair conformation with the hydroxyl group in axial position, but the contribution of the other chair and boat conformers in the equilibrium at room temperature is not negligible. Additionally, we present normal Raman and the surface enhanced Raman (SERS) spectra of (-)-R-mevalonolactone adsorbed on the colloidal silver.

On the structural intricacies of a metabolic precursor: Direct spectroscopic detection of water-induced conformational reshaping of mevalonolactone

“…Our observations thus provide a new perspective on the structure of MV in hydrated media: previous studies with MV using Raman optical activity in neat liquid and aqueous solutions indicate no apparent structural change due to the presence of water. 16 Under micro-solvated conditions, however, we show that water aggregation clearly mediates the conformational reshaping of MV. This observation could shed light onto the balance achieved between the acid and lactone forms of MV in physiological environments.…”

“…15 From a previous study on the potential energy surface of MV, we identify the lowest energy conformers having the methyl group in the equatorial position. 16 Ring puckering generates another series of stable conformers but at higher energies. These species will not be considered in this study.…”

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“…This technique has advantages such as it is non-invasive, solvents are not required, ease of handling, analysis can be performed without any preparations, and availability of portable equipment can produce results in seconds [41][42][43] . Along with the conventional Raman dispersion phenomenon, various variants are available with diverse applications Table 1 [44][45][46][47][48][49][50][51][52][53][54] .…”

Raman Spectroscopy for Quantitative Analysis in the Pharmaceutical Industry

“…The diversity of the types of device configurations allows amplifying the sensitivity of the technique and allows a variety of applications, ranging from the quantification of drug substances in tablets and mixtures of powders to multiplex samples (3,(10)(11)(12)(13)(14)(15)(16)(17), samples in low concentrations (18,19), molecular traces (20)(21)(22), samples inside packs (23) and materials in nanometric scale (Table 1) (24,25). Conventional Raman spectroscopy requires high sample concentration and it is affected by fluorescence.…”

“…In the Surface-enhanced Raman spectroscopy (SERS), the sample is adsorbed on a colloidal metal surface or by nanostructures such as nanotubes typically made of gold (Au), silver (Ag) or copper (Cu) (20)(21)(22). This approach improves the intensity of signals and also extinguishes fluorescence.…”