This paper presents a computational study on the low-temperature mechanism and kinetics of the reaction between molecular oxygen and alkyl radicals of methyl propanoate (MP), which plays an important role in low-temperature oxidation and/or autoignition processes of the title fuel. Their multiple reaction pathways either accelerate the oxidation process via chain branching or inhibit it by forming relatively stable products. The potential energy surfaces of the reactions between three primary MP radicals and molecular oxygen, namely, C(•)H2CH2COOCH3 + O2, CH3C(•)HCOOCH3 + O2, and CH3CH2COOC(•)H2 + O2, were constructed using the accurate composite CBS-QB3 method. Thermodynamic properties of all species as well as high-pressure rate constants of all reaction channels were derived with explicit corrections for tunneling and hindered internal rotations. Our calculation results are in good agreement with a limited number of scattered data in the literature. Furthermore, pressure- and temperature-dependent rate constants for all reaction channels on the multiwell-multichannel potential energy surfaces were computed with the quantum Rice-Ramsperger-Kassel (QRRK) and the modified strong collision (MSC) theories. This procedure resulted in a thermodynamically consistent detailed kinetic submechanism for low-temperature oxidation governed by the title process. A simplified mechanism, which consists of important reactions, is also suggested for low-temperature combustion at engine-like conditions.

Accurate description of reactions between methyl acetate (MA) radicals and molecular oxygen is an essential prerequisite for understanding as well as modeling low-temperature oxidation and/or ignition of MA, a small biodiesel surrogate, because their multiple reaction pathways either accelerate the oxidation process via chain branching or inhibit it by forming relatively stable products. The accurate composite CBS-QB3 level of theory was used to explore potential energy surfaces for MA radicals ? O 2 system. Using the electronic structure calculation results under the framework of canonical statistical mechanics and transition state theory, thermodynamic properties of all species as well as high-pressure rate constants of all reaction channels were derived with explicit corrections for tunneling and hindered internal rotations. Our calculated results are in good agreement with a limited number of scattered data in the literature. Furthermore, pressure-and temperature-dependent rate constants were then computed using the Quantum RiceRamsperger-Kassel and the modified strong collision theories. This procedure resulted in a thermodynamically consistent detailed kinetic mechanism for low-temperature oxidation of the title fuel. We also demonstrated that even the detailed mechanism consists of several reactions of different reaction types, only the addition of the reactants and the re-dissociation of the initially formed adducts are important for low-temperature combustion at engine-liked conditions.

In this study, the extraction of anthocyanin colorant from karanda fruit (Carissa carandas L.) was carried out and optimized with multiple single factor assays. Selected conditions for yield maximization consisted of ripen fruits with black-purple color, material size of thin slices (1.0–1.5 mm), solvent of EtOH 50%, material/ solvent ratio of 1:3, temperature of 50 °C, extraction time of 45 min, and two extraction cycles. The anthocyanin content in the extract was 277.2 mg/L, which is equivalent to 9.33 mg anthocyanin per gram of dry material. Aqueous solutions of the extract and dried extracts from Carissa carandas fruit were evaluated for stability at two temperature conditions, namely room temperature (30 ± 2 °C) and 45 °C. The temperature exerted great impact on color change, anthocyanin content and the degree of polymerization of anthocyanin. Aqueous solutions of extract with citric acid (3.0–5.0 g/L) were generally more color stable and less anthocyanin degradable than those without citric acid. In the DPPH (1,1-diphenyl-2-picrylhydrazyl) scavenging assay, The half maximal inhibitory concentration (IC50) of the dried extract was 87.56 μg/mL, which was approximately 29 times higher than that of vitamin C. After 3-month storage at −18 °C, IC50 of the dried extract was 173.67 μg/mL.

Thermal rate constants of the CH 4 ? O 2 = CH 3 ? HO 2 reaction were calculated from first principles using both the conventional transition state theory (TST) and canonical variational TST methods with correction from the explicit hindered rotation treatment. The CCSD(T)/ aug-cc-pVTZ//BH&HLYP/aug-cc-pVDZ method was used to characterize the necessary potential energy surface along the minimum energy path. We found that the correction for hindered rotation treatment, as well as the re-crossing effects noticeably affect the rate constants of the title process. The calculated rate constants for both forward and reverse directions are expressed in the modified Arrhenius form as k CVT=HR forward ¼ 2:157  10 À18  T 2:412  exp ðÀ 25812 T Þ and k CVT=HR reverse ¼ 1:375  10 À19  T 2:183  exp ð 2032 T Þ (cm 3 molecule-1 s-1) for the temperature range of 300-2,500 K. Being in good agreement with literature data, the results provide solid basis information for the investigation of the entire alkane ? O 2 = alkyl radical ? HO 2 reaction class.