DFT study of vibrational circular dichroismspectra ofd-lactic acid–water complexes

Abstract

This paper presents a discussion of the interaction energies, conformations, vibrational absorption (VA, harmonic and anharmonic) and vibrational circular dichroism (VCD) spectra for conformers of monomeric chiral d(-)-lactic acid and their complexes with water at the DFT(B3LYP)/aug-cc-pVDZ and DFT(B3LYP)/aug-cc-pVTZ levels. A detailed analysis has been performed principally for the two most stable complexes with water, differing by lactic acid conformation. The VCD spectra were found to be sensitive to conformational changes of both free and complexed molecules, and to be especially useful for discriminating between different chiral forms of intermolecular hydrogen bonding complexes. In particular, we show that the VCD modes of an achiral water molecule after complex formation acquire significant rotational strengths whose signs change in line with the geometry of the complex. Using the theoretical prediction, we demonstrate that the VCD technique can be used as a powerful tool for structural investigation of intermolecular interactions of chiral molecules and can yield information complementary to data obtained through other molecular spectroscopy methods.

Experimental and theoretical studies of vacuum‐ultraviolet electronic circular dichroism of hydroxy acids in aqueous solution

“…4) had lengths of 1.73–2.13 Å, which is very consistent with results previously observed for L ‐alanine (1.75–1.95 Å) 11. Previous optimization studies of the structures of LA and D ‐lactic acid with a few water molecules in vacuo and PCM suggested that both compounds take the most stable conformation when intramolecular hydrogen bonds are formed between the OH and COO − groups 22, 23, 33. However, no such intramolecular hydrogen bond was formed in any of the optimized structures with seven water molecules, and the COO – and OH groups formed hydrogen bonds with the water molecules only.…”

“…The hydrated structure of L ‐alanine could be optimized with six water molecules around the COO − group and three water molecules around the NH 3 + group 11. On the other hand, Sadlej et al successfully optimized the hydrated structure of D ‐lactic acid with one water molecule around the OH group using the DFT method 22. Therefore, we constructed eight initial structures of LA with one and six water molecules around the OH and COO − groups, respectively, for dihedral‐angle pairs (ϕ, φ) of (0°, −90°), (0°, 0°), (0°, 90°), (0°, 180°), (90°, −90°), (90°, 0°), (90°, 90°), and (90°, 180°).…”

“…In a previous study, we successfully optimized the hydrated structure of L ‐alanine with nine water molecules using the DFT method at the B3LYP/6‐31G* level 11. The DFT method has also been used for optimizing the LA structure in aqueous solution 22, 23. Therefore, we adopted the DFT method to optimize the LA structure at the B3LYP/6‐31G* level.…”

Theoretical Prediction and the First IR Matrix Observation of Several L‐Cysteine Molecule Conformers

“…[43][44][45] Recently, it has been shown that the VCD method can also be a powerful tool in studying the intermolecular interactions of chiral molecules. [46,47] Continuing our previous study, [35] we undertook a detailed investigation on the conformation behavior of gas-phase cysteine isolated in low-temperature Ar and N 2 matrices. The experimental findings are interpreted by means of the anhar- Conformer no.…”

NMR analysis and chemical shift calculations of poly(lactic acid) dimer model compounds with different tacticities

“…The quantum chemical method used was HF or B3LYP, 41 and the basis sets used were 6311 þ G*, [42][43][44] TZVP [45][46][47] and cc-pVTZ. [48][49][50][51][52] The conformational energy calculation was also performed for isotactic and syndiotactic dimer model compounds for the preferred conformations selected from the Ramachandran map of the monomer model compound.…”