Theoretical Study of the C2H5 + HO2 Reaction: Mechanism and Kinetics.

The mechanism and kinetics for the reaction of the HO2 radical with the ethyl (C2H5) radical have been investigated theoretically. The electronic structure information of the potential energy surface (PES) is obtained at the MP2/6-311++G(d,p) level of theory, and the single-point energies are refined by the CCSD(T)/6-311+G(3df,2p) level of theory. The kinetics of the reaction with multiple channels have been studied by applying variational transition-state theory (VTST) and Rice⁻Ramsperger⁻Kassel⁻Marcus (RRKM) theory over wide temperature and pressure ranges (T = 220⁻3000 K; P = 1 × 10-4⁻100 bar). The calculated results show that the HO2 radical can attack C2H5 via a barrierless addition mechanism to form the energy-rich intermediate IM1 C2H5OOH (68.7 kcal/mol) on the singlet PES. The collisional stabilization intermediate IM1 is the predominant product of the reaction at high pressures and low temperatures, while the bimolecular product P1 C2H5O + OH becomes the primary product at lower pressures or higher temperatures. At the experimentally measured temperature 293 K and in the whole pressure range, the reaction yields P1 as major product, which is in good agreement with experiment results, and the branching ratios are predicted to change from 0.96 at 1 × 10-4 bar to 0.66 at 100 bar. Moreover, the direct H-abstraction product P16 C2H6 + ³O2 on the triplet PES is the secondary feasible product with a yield of 0.04 at the collisional limit of 293 K. The present results will be useful to gain deeper insight into the understanding of the kinetics of the C2H5 + HO2 reaction under atmospheric and practical combustion conditions.

Theoretical Study of ClOO + NO Reaction: Mechanism and Kinetics.

Theoretical investigations are performed on mechanism and kinetics of the reaction of halogen peroxy radical ClOO with NO radical. The electronic structure information for both of the singlet and triplet potential energy surfaces (PESs) is obtained at the MP2/6-311 + G(2df) level of theory, and the single-point energies are refined by the CCSD(T)/6-311 + G(2df) level. The rate constants for various product channels of the reaction in the pressure range of 1-7600 Torr are predicted. The main results are as follows: On the singlet surface, the addition-elimination mechanism is the most important. First, the N atom of the NO radical can attack the O atom of the ClOO radical to form an energy-riched intermediate IM1 ClOONOtp (21.3 kcal/mol) barrierlessly, then IM1 could isomerizes to IM2 ClOONOcp (22.1 kcal/mol) via a low energy barrier. Both IM1 and IM2 can dissociate to the primary product P1 ClNO + ¹O2 and the secondary product P2 ClO + NO2. On the triplet surface, the direct Cl-abstraction reaction is the most feasible pathway. The Cl-abstraction can take place via a van der Waals complex, ³IM1 ONClOO (4.1 kcal/mol), then it fragments readily to give P1' ClNO + ³O2 with a small barrier. The kinetic calculations show that at low temperatures, the singlet bimolecular product P1 is the primary product, while at high temperatures, the triplet product P1' becomes the primary one; only at high pressures and low temperatures, the unimolecular products IM1 and IM2 can be found with quite small yields. At experimentally measured temperature 213 K, ClNO is the primary product in the whole pressure range, which is consistent with the previous experiment. The present study may be useful for further experimental studies for the title reaction.

Foot-and-mouth disease virus-like particles produced by a SUMO fusion protein system in Escherichia coli induce potent protective immune responses in guinea pigs, swine and cattle.

Foot-and-mouth disease virus (FMDV) causes a highly contagious infection in cloven-hoofed animals. The format of FMD virus-like particles (VLP) as a non-replicating particulate vaccine candidate is a promising alternative to conventional inactivated FMDV vaccines. In this study, we explored a prokaryotic system to express and assemble the FMD VLP and validated the potential of VLP as an FMDV vaccine candidate. VLP composed entirely of FMDV (Asia1/Jiangsu/China/2005) capsid proteins (VP0, VP1 and VP3) were simultaneously produced as SUMO fusion proteins by an improved SUMO fusion protein system in E. coli. Proteolytic removal of the SUMO moiety from the fusion proteins resulted in the assembly of VLP with size and shape resembling the authentic FMDV. Immunization of guinea pigs, swine and cattle with FMD VLP by intramuscular inoculation stimulated the FMDV-specific antibody response, neutralizing antibody response, T-cell proliferation response and secretion of cytokine IFN-γ. In addition, immunization with one dose of the VLP resulted in complete protection of these animals from homologous FMDV challenge. The 50% protection dose (PD50) of FMD VLP in cattle is up to 6.34. These results suggest that FMD VLP expressed in E. coli are an effective vaccine in guinea pigs, swine and cattle and support further development of these VLP as a vaccine candidate for protection against FMDV.

An ELISA based on a truncated soluble ORF2 protein for the detection of PCV2 antibodies in domestic pigs.

Postweaning multisystemic wasting syndrome (PMWS) is an important swine disease that is closely associated with porcine circovirus type 2 (PCV2). The capsid protein (Cap protein) is a major structural protein that has at least three immunoreactive regions, and it can be a suitable candidate antigen for detecting the specific antibodies of a PCV2 infection. In the present study, an indirect enzyme-linked immunosorbent assay (TcELISA) based on a truncated soluble Cap protein produced in Escherichia coli (E.coli) was established and validated for the diagnostic PCV2 antibodies in swine. The TcELISA was validated by comparison with an indirect immunofluorescence assay (IIFA). The diagnostic sensitivity (DSN), specificity (DSP), and accuracy of the TcELISA were 88.6%, 90.7% and 89.4%, respectively. The agreement rate was 89.38% between results obtained with TcELISA and IIFA on 113 field sera. A cross-reactivity assay showed that the method was PCV2-specific by comparison with other sera of viral disease. Therefore,the TcELISA will be helpful for the development of a reliable serology diagnostic test for large scale detection of PCV2 antibodies and for the evaluation of vaccine against PCV2 in swine.

Steroidal saponins and cytoxicity of the wild edible vegetable-Smilacina atropurpurea.

Four new steroidal saponins, smilacinoside A (1), B (2), C (3), and D (4), together with three known saponins, funkioside D (5), aspidistrin (6) and 26-O-beta-d-glucopyranosyl-22-methoxyl-(25R)-furost-5-en-3beta,26-diol 3-O-beta-d-glucopyranosyl-(1-->2)-beta-d-glucopyranosyl-(1-->4)-beta-d-galactopyranoside (7) were isolated from the dried tender aerial parts of Smilacina atropurpurea (Franch.) Wang et Tang. The structures of new compounds were elucidated as diosgenin 3-O-alpha-l-rhamnopyranosyl-(1-->2)-O-beta-d-galactopyranoside (1), diosgenin 3-O-alpha-l-rhamnopyranosyl-(1-->3)-[6-O-palmitoxyl]-O-beta-d-galactopyranoside (2), 26-O-beta-d-glucopyranosyl-(25R)-furost-5-en-3beta,22xi,26-triol 3-O-alpha-l-rhamnopyranosyl-(1-->2)}-beta-d-galactopyranoside (3) and 26-O-beta-d-glucopyranosyl-22-methoxyl-(25R)-furost-5-en-3beta,26-diol 3-O-alpha-l-rhamnopyranosyl-(1-->2)-beta-d-galactopyranoside (4) on the basis of chemical methods and detailed spectroscopic analysis, including 1D and 2D NMR techniques and single-crystal X-ray diffraction, respectively. Six of these compounds and MeOH extract were tested for their in vitro cytotoxicity toward K562 human tumor cells by an improved MTT method. Smilacinoside A, funkioside D and aspidistrin exhibited significant in vitro cytotoxicity against K562 with IC(50) values of 1.09, 2.93 and 0.47microg/mL, respectively.

[Steroidal constituents from Dioscorea parviflora].

AIM: To study the chemical constituents of Dioscorea parviflora. METHODS: The chemical constituents were isolated by silica gel and RP-18 column chromatography, and their chemical structures were elucidated by IR, NMR and MS. RESULTS: Eleven steroides have been isolated from EtOH extract of Dioscorea parviflora and identified as isonarthogenin 3-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-glucopyranoside (I), diosgenin-diglucoside (II), prosapogenin A of dioscin (III), dioscin (IV), deltonin (V), deltoside (VI), methyl deltoside (VII), diosgenin 3-O-beta-D-glucopyranosyl (1-->3)-beta-D-glucopyranosyl-(1-->4)-[alpha-L-rhamnopyranosyl-(1-->2)]-beta-D-glucopyranoside (VIII), parvifloside (IX), methyl parvifloside (X), diosgenin (XI), and a mixture of beta-sitosterol and stigmasterol. CONCLUSION: Compound X is a new compound. Compounds VII and X were methyl ethers of VI and IX, respectively, and may be produced during isolation. Compound I is isolated from Dioscorea L., and II, IV from Dioscorea parviflora for the first time.