Thermal decomposition of allantoin as probed by matrix isolation FTIR spectroscopy

Abstract

Low temperature matrix isolation and room temperature crystalline state IR spectra Thermal decomposition a b s t r a c tThe optimized geometries, energies of the possible conformers of allantoin (2,5-dioxo-4-imidazolidinyl urea, the diureide of glyoxylic acid) as well as the barriers for conformational interconversion have been calculated using the density functional theory [DFT(B3LYP)/6-311þþG(d,p)] method. The calculations predicted the existence of four conformers (gC, tT, g 0 C, and g 0 T; where the first and second symbols in the name of the conformers designate the conformation around the exocyclic NHC-NHCO and CNH-CO axes, respectively), with the gC form contributing to more than 98% of the population in gas phase at room temperature. This conformer is different from that corresponding to the monomeric unit found in crystalline RS-allantoin (g 0 C; Mootz, D. Acta Crystallogr. 1965, 19, 726), stressing the importance of intermolecular H-bonding in determining the structure of the crystal. Upon sublimation under vacuum (10 À6 mbar), the compound was found to undergo extensive decomposition to urea, isocyanic acid, NH 3 , and carbon. The identification of the decomposition products was made by using matrix isolation infrared spectroscopy. In consonance with the theoretical predictions, the allantoin molecules surviving thermal decomposition were found to undergo conformational isomerization and be present in the cryogenic argon matrix in both the gC and g 0 C conformations. The solid state room temperature infrared spectrum of allantoin was also investigated and assigned.

Formulation, optimization and characterization of allantoin-loaded chitosan nanoparticles to alleviate ethanol-induced gastric ulcer: in-vitro and in-vivo studies

“…Besides, the peaks at 1663 and 761 cm −1 are correlated to C=O (amide) stretching and C=O (ring) bending vibrations, respectively. The obvious bands appeared in the region of 1060–1605 cm −1 are due to the N–H in plane bending and rocking vibrations of NH 2 group, while bands at 1326 and 870 cm −1 are attributed to C−N, of ring and ureidyl moiety, stretching vibrations 50 , 51 .

Figure 6 Solid characterization.

…”

“…Figure 6B illustrates the DSC thermograms of ALL, CS, STPP, and their physical mixture as well as plain and medicated CS/STPP (F-9). Two characteristic endothermic peaks of ALL (i) were detected at 237 °C and 256 °C corresponding to its melting point besides its phase transformation from the solid crystalline phase to the gaseous phase, respectively 50 . CS thermogram (ii) disclosed an exothermic peak at 303 °C which indicates its degradation due to depolymerization and dehydration.…”

Conformers of β-aminoisobutyric acid probed by jet-cooled microwave and matrix isolation infrared spectroscopic techniques

“…Hence, subtle spectroscopic differences due to conformational changes can be clearly noticed, and the identity of the various conformers present in the matrix established with certainty. [28][29][30][31][32][33][34] On the other hand, when the energy barriers separating different conformers are only of a few kJ mol −1 , conformational cooling can take place during matrix deposition leading to conversion of higher energy conformers into lower energy forms. In this case, the relative populations of the conformers trapped in the cryogenic matrix may differ substantially from those existing in the gas phase prior to deposition.…”

Ring‐Closure on the Rocks in a Prebiotic Environment

“…Band attribution was based on previous IR studies. [86,87] The C=O and NH 2 characteristic bands corresponding to the ureido groups decrease in intensity during activation until they completely disappear at 240 °C. The cycle C=O band and the HÀ CÀ N vibrations of the cycle appear as early as 130 °C and continue to increase in intensity.…”