Scaled quantum chemical studies of the structure and vibrational spectra of 2,4-diaminoquinazoline and 4-amino-2-methylquinoline

Solid state forms of 4-aminoquinaldine - From void structures with and without solvent inclusion to close packing

Polymorphs of 4-aminoquinaldine (4-AQ) have been predicted in silico and experimentally identified and characterised. The two metastable forms, AH (anhydrate) II and AH III, crystallise in the trigonal space group [Formula: see text] and are less densely packed than the thermodynamically most stable phase AH I° (P21/c ). AH II can crystallise and exist both, as a solvent inclusion compound and as an unsolvated phase. The third polymorph, AH III, is exclusively obtained by desolvation of a carbon tetrachloride solvate. Theoretical calculations correctly estimated the experimental 0K stability order, confirmed that AH II can exist without solvents, gave access to the AH III structure, and identified that there exists a subtle balance between close packing and number of hydrogen bonding interactions in the solid state of anhydrous 4-AQ. Furthermore, the prevalence of void space and solvent inclusion in [Formula: see text] structures is discussed.

The spectroscopic (FT-IR, FT-Raman and NMR), first order hyperpolarizability and HOMO-LUMO analysis of 2-mercapto-4(3H)-quinazolinone

The FTIR and FT-Raman spectra of 2-mercapto-4(3H) quinazolinone have been recorded in the region 4000-450 and 4000-100 cm(-1), respectively. The optimized geometry, frequency and intensity of the vibrational bands of 2-mercapto-4(3H) quinazolinone (2MQ) were obtained by the density functional theory (DFT) using 6-311++G(d,p) basis set. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. The (1)H and (13)C nuclear magnetic resonance chemical shifts of the molecule were also calculated using the gauge independent atomic orbital (GIAO) method. The theoretical UV-VIS spectrum of the compound and the electronic properties, such as HOMO (highest occupied molecular orbital) and LUMO (lowest occupied molecular orbital) energies were performed by time-dependent DFT (TD-DFT) approach. The change in electron density (ED) in the σ(*) antibonding orbitals and stabilization energies E((2)) have been calculated by natural bond (NBO) analysis, to give clear evidence of stabilization originating in the hyper conjugation of hydrogen-bonded interactions. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with molecular electrostatic potential (MESP).

Analysis of vibrational spectra of 1-chloro-2,4-dinitrobenzene based on density functional theory calculations

This work deals with the vibrational spectroscopy of 1-chloro-2,4-dinitrobenzene (CDNB) by means of quantum chemical calculations. The FTIR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6-311+G** basis set combinations, and was scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled quantum mechanical force field. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound, which showed excellent agreement with the observed spectra.

Perspectives in the use of spectroscopy to characterise pharmaceutical solids

Knowledge of the solid-state properties is one of the key issues in understanding the performance of drugs. Recent developments in spectroscopic techniques have made them popular tools for solid phase analysis; they are fast, accurate and suitable for real-time measurements during processing, and further, they can be used to obtain structural understanding of solid forms, for example, by the use of multivariate analysis and computational chemistry. In this article emerging topics related to spectroscopic analysis of pharmaceutical solids are reviewed. The following areas are highlighted: (1) the importance of multivariate methods in the analysis of solid forms when using spectroscopic techniques, (2) spectroscopic analysis of processing-induced solid phase transformations in the manufacturing setting, (3) novel spectroscopic techniques and pharmaceutical examples of their use, and (4) the advantages and the use of computational simulation of vibrational spectra. The topics listed are thought to be of the foremost importance in improving the understanding of pharmaceutical materials, processes and formulations.

Analysis of vibrational spectra of 4-amino-2,6-dichloropyridine and 2-chloro-3,5-dinitropyridine based on density functional theory calculations

This work deals with the vibrational spectroscopy of 4-amino-2,6-dichloropyridine (ADCP) and 2-chloro-3,5-dinitropyridine (CDNP) by means of quantum chemical calculations. The mid and far FTIR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6-31G(*) and B3LYP/6-311+G(**) methods and basis set combinations, and was scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results of the calculations were applied to simulated infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra.