Theoretical Analysis of the Effect Provoked by Bromine-Addition on the Thermolysis and Chemiexcitation of a Model Dioxetanone

Chemi-/bioluminescence are phenomena in which chemical energy is converted into electronically excited singlet states, which decay with light emission. Given this feature, along with high quantum yields and other beneficial characteristics, these systems have gained numerous applications in bioanalysis, in biomedicine, and in the pharmaceutical field. Singlet chemiexcitation is made possible by the formation of cyclic peroxides (as dioxetanones) as thermolysis provides a route for a ground state reaction to produce singlet excited states. However, such thermolysis can also lead to the formation of triplet states. While triplet states are not desired in the typical applications of chemi-/bioluminescence, the efficient production of such states can open the door for the use of these systems as sensitizers in photocatalysis and triplet-triplet annihilation, among other fields. Thus, the goal of this study is to assess the effect of heavy atom addition on the thermolysis and triplet chemiexcitation of a model dioxetanone. Monobromination does not affect the thermolysis reaction but can improve the efficiency of intersystem crossing, depending on the position of monobromination. Addition of bromine atoms to the triplet state reaction product has little effect on its properties, except on its electron affinity, in which monobromination can increase between 3.1 and 8.8 kcal mol−1.

Characterization of powder from the permeate of yacon extract by ultrafiltration and dehydrated by spray drying

ABSTRACT Yacon root is a functional food which contains antioxidants and prebiotics compounds. This study aimed to evaluate the physical, chemical and prebiotic characteristics of a yacon extract powder obtained by ultrafiltration (UF) with membranes of 10 and 30 kDa and encapsulation of the resulting permeate by spray drying. Drying air temperatures of 140 and 160 ºC and concentrations of gum arabic of 10 and 15% were tested. The samples had solubility values greater than 90% while the hygroscopicity decreased with increasing gum concentration and drying temperature. Electron microscopy showed a strong tendency to agglomeration of smaller particles around the larger ones, mainly at a temperature of 140 ºC. Regarding color, the parameter L* showed that drying at 160 ºC produced darker samples and the parameters a* and b* indicated that all samples were greenish yellow. The concentration of inulin decreased during drying, whereas the levels of glucose and fructose increased due to the thermolysis reaction, which led to degradation of inulin chains at drying temperature. The permeates and retentates from the UF membranes had prebiotic activity, while only the encapsulated product from UF-30 membrane, metabolized by Lactobacillus acidophilus LA-5(r), presented activity scores without significant difference to that of glucose.

Pyrolysis of azetidinones. Part 2. Kinetics and mechanism of thermolysis of β-lactams and β-thiolactams

The kinetics of the gas-phase thermolysis reaction of seven β-lactams and their thione analogues were investigated over the temperature range 533–603 K for the β-lactams and 463–542 K for the β-thiolactams. The average values of the energy of activation (Ea) (kJ mol−1) and Arrhenius log A (s–1) were, respectively, 170.8 ± 18.6 and 12.4 ± 1.6 for the lactams and 131.7 ± 18.2 and 11.0 ± 2.0 for the thione analogues. The entropy of activation (ΔS#) was negative for of the substrates and slightly positive for three. The rate constants (k) (s−1) were calculated for 510 K and compared for the two series of azetidinones. The effects of substituents on rates and the novel role played by the C=O and C=S moieties on the relative reactivities of the cyclic amides are rationalized on the basis of a formal retro[2+2]cycloaddition mechanism used earlier to explain the products of the gas-phase thermolysis reaction of the present azetidinones.

Crystal structure and thermal decomposition of the Silanimine tBu2Si=N-SitBu3·thf

The thf-complexed silanimine tBu2Si=N–Sit- Bu3·thf (1(thf); monoclinic, space group C2/c) was prepared by the reaction of 1 equivalent of tBu2SiClN3 with 1 equivalent of Na[SitBu3] in Bu2O and subsequent addition of thf. By heating a benzene solution over a period of 11 d –140 °C, 1(thf) slowly released the thf donor to form the uncomplexed silanimine 1. However, under these conditions the silanimine 1 is unstable and is thermolized to give the ene reaction product of 1 with isobutene, H2C=C(CH2SitBu2–NH–SitBu3)2. By contrast, the thermolysis reaction of Me2Si=N–SitBu3·thf yielded the silanimine dimer (Me2SiNSitBu3)2 in 51 % and the vinyl ether Me2Si(OCH=CH2)NHSitBu3 in 49 % yield.

α-Bromodiazoacetamides – a new class of diazo compounds for catalyst-free, ambient temperature intramolecular C–H insertion reactions

In this work, we introduce a new class of halodiazocarbonyl compounds, α-halodiazoacetamides, which through a metal-free, ambient-temperature thermolysis perform intramolecular C–H insertions to produce α-halo-β-lactams. When carried out with α-bromodiazoacetamides bearing cyclic side chains, the thermolysis reaction affords bicyclic α-halo-β-lactams, in some cases in excellent yields, depending on the ring size and substitution pattern of the cyclic amide side chains.

Peroxyl Radical Scavenging Ability of Fifty Kinds of Chinese Medicines Determined by an ESR Spin-Trapping Technique

The peroxyl radical scavenging abilities of fifty Chinese herbal medicines were determined accurately by an electron spin resonance (ESR) spin-trapping technique using 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) as a spin-trapping reagent. The peroxyl radical was generated by the thermolysis reaction of 2,2’-Azobis(isobutyronitrile) (AIBN) in the presence of the spin-tap DMPO and with or without sample. As a result of these studies, a strong scavenging ability of peroxyl radical was found in Chinese medicines for diseases of anti-aging and blood circulation.