Anomalous Temperature Dependence of the Lowest-Frequency Lattice Vibration in Crystalline γ-Aminobutyric Acid

Abstract

Crystalline γ-aminobutyric acid (GABA) exhibits unusual thermal behavior in a low-frequency lattice vibration that occurs at 37.2 cm −1 at 290 K but decreases dramatically by 34.0% when the sample is cooled to 78 K. Lattice vibrations in molecular crystals are indicators of intermolecular force characteristics, and the extraordinary temperature sensitivity of this vibration offers new insight into the local environment within the solid. Solid-state density functional theory simulations of the GABA crystal have found this anomalous frequency shift is based in unexpected differences in the strengths of the intermolecular hydrogen bonds that are cursorily the same. This was accomplished through mapping of the potential energy surfaces governing the terahertz-frequency motions of the GABA solid and use of the quasiharmonic approximation to model the response of all the lattice vibrations to temperature-induced unit cell volume changes brought about through the anharmonic character of the intermolecular interactions. The analysis reveals that the vibration in question is rotational in nature and involves the significant distortion of a specific weak intermolecular N−H•••O hydrogen bond in the crystal that results in its unique thermal response.

Broadband terahertz recognizing conformational characteristics of a significant neurotransmitter γ-aminobutyric acid

“…All the absorption peaks become more distinct upon cooling. The results of variable temperature experiment agrees well with that of Dampf et al 20 They attributed the unusual thermal behaviour to the distortion of a specic weak intermolecular hydrogen bond in solid GABA, and they explained the spectral features generally narrow and shi to higher frequencies in response to cooling as the crystallographic unit cell changes with temperature. Besides, the degree of shi in different peaks is not the same, this is probably due to different vibrational modes having different degrees of response to the temperature change.…”

“…16 The broadband THz response does not interfere with THz sensitivity to biomolecular binding and the universal THz binding sensitivity has application potential for biosensing. 19 Recently, Dampf et al 20 studied temperature-dependent THz-TDS spectra from 10 to 135 cm À1 (1 THz $33.33 cm À1 ) of GABA, they found an anomalous frequency shi upon cooling and further explained it by the quasiharmonic approximation in solid-state density functional theory (DFT) simulations. da Silva et al 2 investigated GABA in the range of 30 to 1700 cm À1 with Raman spectroscopy between 1 atm and 7.1 GPa, and they interpreted the modications in the Raman spectra mainly on the basis of the conformational changes of the molecules in the unit cell.…”

Temperature-Dependent Low-Frequency Vibrations of Thiamine Crystal Containing Hydrated Ions

“…High-frequency peak shift with increasing temperature is anomalous for a crystalline system. Very recently, high-frequency peak shift with increasing temperature was reported in the THz energy region . Peaks 6 and 13–15 are assigned to intramolecular modes that contain large eigenvector atomic displacements around chloride ions (Figure b).…”

A Quantitative Interpretation for the Difference of Terahertz Spectra of dl- and l-Alanine: Origins of Infrared Intensities in Terahertz Spectroscopy

“…The intensities of THz bands constitute another valid source of information about the crystal symmetry, intermolecular interactions, and the nature of the vibrational modes. The potentials of intensity data have been well-recognized in the past by many groups. − …”