Raman fingerprint of the interaction of K⁺ with the COO⁻ group of zwitterionic alanine

Abstract

The interaction of K + with the zwitterionic form of alanine (ZAla) is investigated using Raman spectroscopy and density functional theory calculations. The Raman spectra of an aqueous solution of Ala and its mixture with KOH at different molar concentrations [ZAla + xKOH, x = 1-5 M] have been recorded in the spectral region 400-1800 cm À1 . The wavenumber position of the band at~529 cm À1 shows a red shift of 14 cm À1 , while the Raman band at~634 cm À1 shows a blue shift of 10 cm À1 with the increasing x from 1 to 5 M. The intensity ratio I 634 /I 529 is increased with increasing x, and it could be because of the increase in concentration of the [ZAla + K + ] complex in the solution. The new Raman band appeared at~1079 cm À1 in the Raman spectra of [ZAla + xKOH, x = 1-5] complex. To determine the most probable site for the interaction of K + with ZAla, the structures of ZAla and the [ZAla + K + ] were optimized at B3LYP/6-311++G(d,p) level of theory. The electrostatic potential calculation carried out for ZAla reveals that the maximum density of electron is lying over COO À , and therefore, COO À would be the most probable site for the interaction of K + with ZAla. The theoretically calculated Raman spectra of ZAla, [ZAla + K + ] and the [ZAla À + K + ] are in good agreement with experimentally observed Raman spectra. Thus, the Raman bands at~529, 634, and 1079 cm À1 may be used as the Raman fingerprint for the interaction of K + with COO À of the ZAla and ZAla À .

Ionic and tautomeric conformers of adenine at different pH investigated by Raman spectroscopy combined with DFT calculations

“…Raman spectroscopy and resonance Raman spectroscopy are efficient and well‐suited techniques for accessing structural modifications and the tautomeric forms of Ade under different pH conditions. In our recent work, direct Raman analysis has successfully employed for obtaining information about the stable conformer and structural modification of alanine upon interaction with K + at different molar concentrations . The tautomerism‐based study of the nucleic acid bases has been carried out in only a few cases by direct Raman analysis .…”

“…In our recent work, direct Raman analysis has successfully employed for obtaining information about the stable conformer and structural modification of alanine upon interaction with K + at different molar concentrations. [25] The tautomerism-based study of the nucleic acid bases has been carried out in only a few cases by direct Raman analysis. [26,27] In a recent work, [28] experimental resonance Raman spectra, in combination with the theoretical study of the tautomers of Ade, Ade-N9, Ade-N7 and their cations have been performed, and the experimental results were found to be in good agreement with theoretical results.…”

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

“…[52] Workers from the same research group in a closely related study carried out vibrational and conformational characterizations of arginine at different pH values investigated using Raman spectroscopy combined with DFT calculations. [53] Cinta Pinzaru and co-workers combined near-IR Raman and DFT calculations of okadaic acid DSP marine biotoxin microprobe. They used a new μ-RIM® stainless steel hydrophobic substrate to record near-IR micro-Raman spectra of okadaic acid (OA), a DSP marine biotoxin from 75 μg recrystallized toxin after drop coating deposition.…”

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

“…have used Raman as a fingerprint of the interaction of K + with the COO ‐ group of zwitterionic alanine (ZAla). They find that the Raman bands at ∼ 529, 634, and 1079 cm −1 may be used as the Raman fingerprint for the interaction of K + with COO ‐ of the ZAla and ZAla ‐ . Hooijschuur and co‐workers have used Raman spectroscopy to study photodegradation, self‐absorption and quantification of carotenoids in microorganisms and mineral matrices for future planetary space exploration.…”