Monitoring structural fluctuations of discotic liquid crystal during phase transitions.

The discotic liquid crystal 4-((2, 3, 4-tris (octyloxy) phenyl) diazenyl) benzoic acid, hereafter referred as DLC A8, exhibited in dimeric form has been studied using a combination of quantum chemical approaches and vibrational spectroscopy. This study investigates the structural alteration of DLC A8 associated with phase transition. The phase transitions of DLC A8 are Iso â†’ Discotic nematic â†’ Columnar â†’ Crystalline, which have been investigated using differential scanning calorimetry (DSC) accompanied with polarized optical microscopy (POM). Monotropic columnar mesophase was observed during the cooling cycle while discotic nematic mesophase was observed in both the heating and cooling cycles. Density functional theory (DFT) along with IR and Raman spectroscopic techniques were utilized to study the dynamics of molecules during phase transition. To predict the most stable conformation of the molecule, one-dimensional PES scans have been performed along 31 flexible bonds using DFT/B3LYP/6-311G++(d,p) method. Vibrational normal modes were analyzed in detail, taking potential energy contribution into account. The spectral analysis of FT-IR and FT-Raman was done by deconvoluting the structural sensitive bands. The agreement between the calculated IR and Raman spectra and the observed FT-IR and Raman spectra at room temperature confirms our theoretically predicted molecular model of investigated discotic liquid crystal. Moreover, our studies have unraveled the existence of intact intermolecular H-bonding of dimers throughout the phase transitions.

Stability of Ceftazidime Pentahydrate Investigated by Thermal Analysis Techniques.

Cephalosporins are among the most frequently used broad-spectrum antimicrobial agents. Ceftazidime is a semisynthetic ß-lactam antibiotic for parenteral administration widely used in the clinical practice, which has been categorized as a third-generation cephalosporin antibiotic. This drug crystallizes as a pentahydrate and, as all cephalosporins, it is unstable and subject to hydrolytic degradation. Taking this into account, this study investigates the stability under 2 different conditions (high temperature and exposition to vacuum) by using various techniques, as thermal analysis, Raman spectroscopy, and X-ray powder diffraction supported by multivariate curve resolution. It was proved that ceftazidime pentahydrate is unstable under the studied variables, exhibiting several transformation processes, which were discussed in terms of the crystalline structure.