Thermal degradation kinetics and pyrolysis GC-MS study of curcumin.

The objective of this work was to study kinetics of thermal degradation of curcumin in ambient-1023 K range and identify degradation products by GC-MS. No weight loss was observed up to ∼470 K and two major weight losses occurred beyond this. Sixteen degradation products were identified by GC-MS. Pharmacological properties, including LD50, LC50, gastrointestinal absorption, blood-brain barrier permeation and effect on cytochromes, of the products were calculated using standard software. The LD50 values indicated that the degradation products are more toxic than curcumin. All the decomposition products, except 2-methyl-6-(4-methylphenyl)-hept-2-en-4-one, have the potential to cross the blood-brain barrier that can affect brain functions. Twelve of the compounds showed the potential to inhibit the metabolism of xenobiotics and all the compounds appeared to be non-inhibitors of CYP2C9 and CYP3A4 in contrast to curcumin. Thus, this study suggests that the food materials containing curcumin when heated beyond 470 K will produce toxic substances.

Isolation and identification of bioactive compounds from chloroform fraction of methanolic extract of Carissa opaca roots.

Carissa opaca is a shrub known for its variety of medicinal applications. This study reports isolation and identification of four chemical compounds from its roots for the first time. The methanolic extract of the roots was fractionated into various solvents with increasing polarity. Chloroform fraction was subjected to column and thin layer chromatography to ultimately yield 2H-cyclopropanaphthalene-2-one, 7-hydroxy-6-methoxy-2H-1-benzopyran-2-one, 3-(4-methoxyphenyl)-2,6-dimethylbenzofuran and 5(1H)-azulenone, 2,4,6,7,8,8a-hexahydro-3,8-dimethyl-4-(1-methylethylidene)-,(8S-cis). They were identified by GC-MS analysis. The compounds exhibited considerable antimicrobial activities against Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Candida albicans and Aspergillus niger with zones of inhibition ranging from 10 to 13 mm as compared to the standard drug amoxicillin with zones of inhibition 13-17 mm under the similar conditions. In conclusion, the roots of C. opaca can provide new leads for future antimicrobial drugs.

Thermal analysis of some natural polysaccharide materials by isoconversional method.

Isoconversional thermal analysis of some important polysaccharides from functional foods is reported. Various thermal parameters including apparent activation energy (Ea), pre-exponential factor (A) were worked out, and the fitness of data to different models describing the degradation kinetics of polysaccharides was studied. The polysaccharides from Mimosa pudica (MP), Plantago ovata (PO), Argyreia speciosa (AS), Acacia nilotica (AN), P. ovata husk (HK) and Acacia modesta (AM) exhibited multistep degradation while those from Astragalus gummifer (AG), Salvia aegyptiaca (SA) and Ocimum basicilicum (OB) degraded mainly in single step. Generally, the degradation was exothermal. The average Ea values as determined by Flynn-Wall-Ozawa method were found to be in the range 132-187 kJ mol(-1). The mean comprehensive index of thermal stability (ITS) fell in the range 0.33-0.43. All the materials under investigation except those from SA and AS appear to be as stable as some of the important commercial materials used as pharmaceutical ingredients. Model-fitting analysis revealed that the major degradation step follows first-order kinetics.

Kinetics and mechanism of thermal degradation of pentose- and hexose-based carbohydrate polymers.

This work aims at study of thermal degradation kinetics and mechanism of pentose- and hexose-based carbohydrate polymers isolated from Plantago ovata (PO), Salvia aegyptiaca (SA) and Ocimum basilicum (OB). The analysis was performed by isoconversional method. The materials exhibited mainly two-stage degradation. The weight loss at ambient-115°C characterized by low activation energy corresponds to loss of moisture. The kinetic triplets consisting of E, A and g(α) model of the materials were determined. The major degradation stage represents a loss of high boiling volatile components. This stage is exothermic in nature. Above 340°C complete degradation takes place leaving a residue of 10-15%. The master plots of g(α) function clearly differentiated the degradation mechanism of hexose-based OB and SA polymers and pentose-based PO polymer. The pentose-based carbohydrate polymer showed D(4) type and the hexose-based polymers showed A(4) type degradation mechanism.