MACROMOLECULES
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2011
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IF 4.838
Yanwu Zhou,Junpo He,Changxi Li,Linxiang Hong,Yuliang Yang
The thermal decomposition of different classes of RAFT/MADIX agents, namely dithioesters, trithiocarbonates, xanthates, and dithiocarbamates, were investigated through heating in solution. It was found that the decomposition behavior is complicated interplay of the effects of stabilizing Z-group and leaving R-group. The mechanism of the decomposition is mainly through three pathways, i.e., β-elimination, α-elimination, and homolysis of dithiocarbamate (particularly for universal RAFT agent). The most important pathway is the β-elimination of thiocarbonylthio compounds possessing β-hydrogen, leading to the formation unsaturated species. For the leaving group containing solely α-hydrogen, such as benzyl, α-elimination takes place, resulting in the formation of (E)-stilbene through a carbene intermediate. Homolysis occurs specifically in the case of a universal RAFT agent, in which a thiocarbonyl radical and an alkylthio radical are generated, finally forming thiolactone through a radical process. The stabilities of the RAFT/MADIX agents are investigated by measuring the apparent kinetics and activation energy of the thermal decomposition reactions. Both Z-group and R-group influence the stability of the agents through electronic and steric effects. Lone pair electron donating heteroatoms of Z-group show a remarkable stabilizing effect while electron withdrawing substituents, either in Z- or R-group, tends to destabilize the agent. In addition, bulkier or more β-hydrogens result in faster decomposition rate or lower decomposition temperature. Thus, the stability of the RAFT/MAIDX agents decreases in the order where R is (with identical Z = phenyl) −CH2Ph (5) > −PS (PS-RAFT 15) > −C(Me)HPh (2) > −C(Me)2C(═O)OC2H5 (7) > −C(Me)2Ph(1) > −PMMA (PMMA-RAFT 16) > −C(Me)2CN (6). For those possessing identical leaving group such as 1-phenylethyl, the stability decreases in the order of O-ethyl (11) > –N(CH2CH3)2 (13) > –SCH(CH3)Ph (8) > −Ph (2) > −CH2Ph (4) > −PhNO2 (3). These results consort with the chain transfer acitivities measured by the CSIRO group and agree well with the ab initio theoretical results by Coote. In addition, the difference between thermal stabilities of the universal RAFT agents at neutral and protonated states has also been demonstrated.
研究领域:
化学
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材料科学
✓ 已验证
产品关联
DOI
高影响因子
SCIENCE OF THE TOTAL ENVIRONMENT
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2017
·
IF 4.9
Jirui Yang,Feng Shen,Mo Qiu,Xinhua Qi
This paper reports a nonreductive dechlorination pathway (dehydrochlorination) of lindane in the presence of N -MWCNTs (CNT-N1 and CNT N2) under environmentally relevant conditions. The enhanced catalytic dehydrochlorination at mild pH values (7.0–9.0) was mainly attributed to the Lewis base nature of nitrogen functional groups on the surface of N -MWCNTs, based on FT-IR spectra, X-ray photoelectron spectroscopy and CO 2 -TPD profile. Amine and pyridinic nitrogen species were inferred as the main basic sites that were responsible for the dehydrochlorination of lindane. The concentration of lindane was unchanged in homogenous alkaline aqueous solutions at pH 7.0 and 8.0 within 6 d, and up to 89.5% of lindane remained at pH 9.0. In sharp contrast, the reaction rate constant ( k obs ) increased from 0.024 to 0.876 d − 1 with the increasing pH from 7.0 to 9.0 when CNT-N2 catalyst was used. All lindane was transformed in the presence of CNT-N2 at pH 9.0, leading to a much greater k obs as compared to that obtained in homogenous solution (0.876 vs 0.019 d − 1 ). Even at neutral pH condition, the k obs obtained in the presence of CNT-N2 was higher than that observed in weakly alkaline solution (0.024 d − 1 at pH 7.0 vs 0.019 d − 1 at pH 9.0). γ-1,3,4,5,6-pentachlorocyclohexene and trichlorobenzene isomers were detected as the intermediate and final products, respectively. It might be inferred that amine and pyridinic nitrogen species could attack the hydrogen atom attached to the β‑carbon, and the dehydrochlorination of lindane followed a β-elimination mechanism. This study provides an alternative dechlorination way for making lindane less toxic and better biodegradable under mild conditions, which is beneficial for complete mineralization of lindane when coupled with microbial degradation.
研究领域:
环境科学
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化学
✓ 已验证
产品关联
DOI
PubMed
高影响因子
Algal Research-Biomass Biofuels and Bioproducts
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2022
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IF 5.276
Tiancheng Tang,Benwei Zhu,Zhong Yao
Ulvan , extracted from the marine green algae belonging to the genus Ulva , is a complex water-soluble sulfated polysaccharide which mainly composed of four monosaccharides consisting of rhamnose , xylose , glucuronic acid and iduronic acid . Its complex monosaccharide composition gives ulvan great potential for application in the fields of food, pharmaceuticals, and chemistry. And it can be degraded by ulvan lyases mainly from Polysaccharide Lyases (PL) family of PL24, PL25 and PL28 through β -elimination mechanism, which cleaves the β -glycosidic bond between sulfated rhamnose and glucuronic acid or iduronic acid, thereby producing an Ulva oligosaccharide with unsaturated bond. In this study, we have identified a putative ulvan lyase from Alteromonas sp. TK-45 (2). We heterologously expressed, purified, and biochemically characterized the ulvan lyase, which has removed signal peptide . The results show that ULA-1 had best activity at 45 °C and pH 8.0. The K m and V max values were 13.25 μg·mL −1 and 1.719 μmol·min −1 ·mL −1 , respectively. The thermostability of ULA-1 was excellent, and its activity hardly decreased after incubation at 45 °C for 1 h. ESI-MS analysis showed that the primary end-product were disaccharides to tetrasaccharides . In conclusion, our research has expanded the database of ulvan lyase, and provided the possibility to make full use of ulvan, a huge marine biomass resource .
研究领域:
海洋生物学
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酶学
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生物技术
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生物化学
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF APPLIED PHYCOLOGY
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2023
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IF 3.3
Tang Tiancheng,Li Chen,Zhu Benwei,Yao Zhong
Ulvan lyase is a useful tool which can degrade ulvan into oligosaccharides with a range of biological activities. In this study, the ulvan lyase ULA-3 from Alteromonas sp. 76–1, which was a 1467-bp encoded 489-amino acid residue protein, has been cloned, heterologously expressed and biochemically characterized. ULA-3 showed the maximum activity at 45 ˚C and pH 9.0. The K m is 1.879 mg mL −1 and V max is 2.597 µmol min −1 mL −1 . Its enzyme activity was outstanding at 11.754 U mg −1 . Moreover, its metal ion stability is exceptionally good and most metal ions at a concentration of 1 mM have no inhibitory effect on its activity. It can endolytically degrade ulvan into oligosaccharides with a degree of polymerization (Dp) of 2–4 and with unsaturated double bond through the β -elimination reaction, which mainly cleaves the glycosidic bond between rhamnose and uronic acids. All in all, our study has increased the ulvan lyase database and offers the opportunity to fully utilize ulvan, a green biomass resource from marine algae.
研究领域:
生物化学
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生物技术
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海洋生物学
✓ 已验证
产品关联
DOI
高影响因子
APPLIED BIOCHEMISTRY AND BIOTECHNOLOGY
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2020
·Vol. 192
·期 1
·71-84
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IF 2.277
Zhu Hang-Qin,Tang Xiao-Ling,Zheng Ren-Chao,Zheng Yu-Guo
Tyrosine phenol-lyase (TPL) is a valuable and cost-effective biocatalyst for the biosynthesis of L-tyrosine and its derivatives, which are valuable intermediates in the pharmaceutical industry. A TPL from Morganella morganii ( Mm -TPL) was overexpressed in Escherichia coli and characterized. Mm -TPL was determined as a homotetramer with molecular weight of 52 kDa per subunit. Its optimal temperature and pH for β-elimination of L-tyrosine were 45 °C and pH 8.5, respectively. Mm -TPL manifested strict substrate specificity for the reverse reaction of β-elimination and ortho - and meta -substituted phenols with small steric size were preferred substrates. The enzyme showed excellent catalytic performance for synthesis of L-tyrosine, 3-fluoro-L-tyrosine, and L-DOPA with a yield of 98.1%, 95.1%, and 87.2%, respectively. Furthermore, the fed-batch bioprocess displayed space-time yields of 9.6 g L −1 h −1 for L-tyrosine and 4.2 g L −1 h −1 for 3-fluoro-L-tyrosine with a yield of 67.4 g L −1 and 29.5 g L −1 , respectively. These results demonstrated the great potential of Mm -TPL for industrial application.
研究领域:
生物化学
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生物技术
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药学
✓ 已验证
产品关联
DOI
PubMed
高影响因子
CARBOHYDRATE POLYMERS
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2023
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IF 11.2
Jirong Wang,Chengying Zhao,Shaojie Zhao,Xingmiao Lu,Mengyu Ma,Jinkai Zheng
The amidation of pectin by amino acids has been widely applied due to its safety and excellent gelling properties. This study systematically examined the effects of pH on the gelling properties of lysine-amidated pectin during amidation and gelation . Pectin was amidated over the range of pH 4–10, and the amidated pectin obtained at pH 10 showed the highest degree of amidation (DA, 27.0 %) due to the de-esterification, electrostatic attraction, and the stretching state of pectin. Moreover, it also exhibited the best gelling properties due to its greater numbers of calcium-binding regions (carboxyl groups) and hydrogen bond donors (amide groups). During gelation, the gel strength of CP (Lys 10) at pH 3–10 first increased and then decreased, with the highest gel strength at pH 8, which was due to the deprotonation of carboxyl groups, protonation of amino groups, and β-elimination. These results show that pH plays a key role in both amidation and gelation, with distinct mechanisms, and would provide a basis for the preparation of amidated pectins with excellent gelling properties. This will facilitate their application in the food industry.
研究领域:
食品科学
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化学
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材料科学
✓ 已验证
产品关联
DOI
PubMed
高影响因子
危险品化学品经营许可证（带存储）