Estudo DFT e caracterização estrutural e vibracional de cristais de 5-metiluridina a altas temperaturas e adenosina hidroclorídrica a altas pressões

Abstract

The objective of this work is to study the stability of 5-methyluridine hemihydrate (5mU) at high temperatures and of adenosine hydrochloride (AC) at high pressures by Raman spectroscopy, in addition to calculating the theoretical spectra and global reactivity indices and analyzing the Hirshfeld surface. 5mU was investigated in the temperature range from 300 to 460 K by TGA, DSC, X-ray powder diffraction and Raman spectroscopy. Additionally, vibrational spectra, frontier molecular orbital energies and global reactivity indices were calculated using the DFT method. The calculated vibrational spectra showed a good similarity with the experimental data. Reactivity indices showed that 5mU appears to be a stable molecule. Furthermore, the results showed that this crystalline material undergoes two consecutive dehydration processes: around 380 K and at 410 420 K, with a change in structure from orthorhombic (P21212) to triclinic (P1) and then transitioning for monoclinic (P21). For AC crystals, the Raman spectrum was calculated under ambient conditions, in addition to the analysis of the Hirshfeld surface; then studied the stability of the crystal at high pressures by Raman spectroscopy from 0.1 to 8.4 GPa. Calculated spectra show considerable similarities with the experimental data. The behavior of AC at high pressures is unique, as the Raman spectra showed changes from 0.4 GPa, changing up to 5.6 GPa. From the analysis of the spectral changes, three phase transitions were identified: the first in the range of 0.4 to 0.7 GPa, the second between 1.5 and 2.4 GPa and the third in the pressure range of 3, 5 to 5.2 GPa, the first two of the conformational type and the third structural. The crystalline structure of AC appears to be flexible with each increase in pressure, as vibrational modes assigned to all portions of the molecule undergo changes during the increase of the pressure. This flexibility may be related to the diversity of biological functions of adenosine and chlorine ion. Thus, nucleosides are important biomolecules in the human body and understanding their behavior to external factors such as pressure and temperature helps us to have more information about these materials to correlate with their biological functions.