S-苄基-L-半胱氨酸的合成

由溴化苄和L-半胱氨酸直接合成S-苄基-L-半胱氨酸,通过正交试验及统计分析,检验了各影响因子的显著性,确定了最佳工艺条件为：反应时间2.5h,反应温度45℃,原料配比n（溴化苄）：n（L-半胱氨酸）=1：1.在此条件下反应,摩尔产率可达到95%.     

酶法制备S-苄基-γ-L-谷氨酰-L-半胱氨酸的动力学模型

以Bacillus subtilis NX-2产γ-谷氨酰转肽酶(GGT)为催化荆,以L-谷氨酰胺(L-Gln)为γ-谷氨酰基供体,S-苄基-L-半胱氨酸(S-Bal-Cys)为受体,催化合成了S-苄基-γ-L-谷氨酰-L-半胱氨酸(S-Bzl-GGC).在反应机理分析的基础上,建立了定量描述该过程的动力学模型,模型计算值和实测值能较好吻合,平均相对误差为5.57%.通过模型分析得知,供体浓度的增加有利于转肽反应,但更多的是自转肽反应;受体浓度增加对提高转肽产物S-Bzl-GGC有一定的作用,对自转肽反应几乎没有影响;酶含量增加提高了反应速率,但不提高转肽产物的最大浓度.     

离子交换法分离S-苄基-g-L-谷氨酰-L-半胱氨酸

采用离子交换法对酶法合成的S-苄基-g-L-谷氨酰-L-半胱氨酸(S-Bzl-GGC)进行了分离纯化. 研究了Q Sephrose FF阴离子交换树脂对S-Bzl-GGC的吸附等温线,很好地符合Sips吸附等温线模型. 考察了pH值、洗脱梯度、流速和进样量等条件对纯化效果的影响,建立了一套基于Q Sephrose FF阴离子交换树脂的纯化方案. 结果表明,在pH 8.2、洗脱梯度0~30% B(Tris-HCl缓冲液+1 mol/L NaCl) 12 mL、流速2 mL/min、进样量500 mL的优化条件下,经一步分离,产物纯度可达98.5%,经1H-NMR鉴定产物结构正确.     

DL-苯丙氨酸的酶法拆分研究

利用氨基酰化酶能立体专一地水解氨基酰化物的特点,选择性地水解N-乙酰-L-苯丙氨酸得到L-苯丙氨酸,经分离后再水解N-乙酰-D-苯丙氨酸得到D-苯丙氨酸。研究中分别考察了pH值、温度、酶用量、底物浓度和钴离子对反应的影响。在优选条件下(底物浓度为0.1mol·L-1,pH7.0,温度37℃,酶用量为w(酶)/w(底物)=1∶41.4,加入浓度为1×10-3mol/L的Co2+,将N-乙酰-D-苯丙氨酸用有机溶剂结晶和盐酸水解10h)得到光学纯度OP=98.8%的L-苯丙氨酸,收率70.3%;OP=96%的D-苯丙氨酸,收率63%。     

S-甲基-L-半胱氨酸的合成

以 L-半胱氨酸为原料 ,磷酸三甲酯为甲基化试剂合成了 S-甲基 - L-半胱氨酸。研究了 p H值、温度等反应条件对产品品质和收率的影响。发现在严格控制 p H为 7.0 ,反应温度不高于 37°C的条件下 ,并不出现消旋作用。这一合成路线可用于工业上大规模生产     

D-(-)-扁桃酸拆分DL-半胱氨酸盐酸盐的研究

改进了D-(-)-扁桃酸拆分DL-半胱氨酸盐酸盐制备D-半胱氨酸盐酸盐的方法。DL-半胱氨酸盐酸盐与D-(-)-扁桃酸在水中成盐后,得到的非对映体盐,纯化后经盐酸分解、10%的乙醇-丙酮溶液重结晶后得到目标产物,拆分收率25·6%。     

化学酶法合成γ-L-谷氨酰-L-半胱氨酸

以Bacillus subtilis NX-2产γ-谷氨酰转肽酶为催化剂,以L-谷氨酰胺和S-苄基-L-半胱氨酸为底物,利用转肽反应合成了S-苄基-γ-L-谷氨酰-L-半胱氨酸,考察了反应时间、初始酶浓度、供体/受体比以及投料方式等条件对反应过程的影响.结果表明,在L-谷氨酰胺浓度为20 mmol/L,S-苄基-L-半胱氨酸浓度为20 mmol/L,酶浓度为0.0208 U/mL以及pH9条件下,于40℃水浴中反应3 h,S-苄基-γ-L-谷氨酰-L-半胱氦酸得率为5.14 mmol/L,对谷胺酰胺的转化率为25.7%.采用分批投料方式可有效提高谷氨酰供体转化率.S-苄基-γ-L-谷氨酰-L-半胱氨酸以三氟甲磺酸脱除苄基保护基,经RPC纯化后可得产物GGC,产物纯度为91.2%,收率为75.7%.     

色氨酸合成酶酶法合成S-苯基-L-半胱氨酸的研究

利用重组色氨酸合成酶催化合成S-苯基-L-半胱氨酸,考察了反应温度、pH、底物摩尔比和底物浓度对色氨酸合成酶酶活影响。最佳转化条件为：反应温度为37 篊,pH为8,L-丝氨酸与苯硫酚的适宜底物摩尔比为1:1.2,底物最适合浓度为400 mmol/L,反应达到平衡时间为16 h,底物L-丝氨酸摩尔转化率达到91%,苯硫酚与色氨酸合成酶活性位点Ser 235和Gly 233形成稳定的氢键。     

色氨酸合成酶酶法合成S-苯基-L-半胱氨酸

利用重组色氨酸合成酶催化合成S-苯基-L-半胱氨酸,考察了反应温度、pH、底物摩尔比和底物浓度对色氨酸合成酶酶活的影响。最佳转化条件为:反应温度为37℃,pH=8,苯硫酚与L-丝氨酸的适宜底物摩尔比为1.2∶1,底物最适合浓度为400 mmol/L,反应达到平衡时间为16 h,底物L-丝氨酸摩尔转化率达到91%,苯硫酚与色氨酸合成酶活性位点Ser 235和Gly 233形成稳定的氢键。     

氨基酰化酶拆分制备手性蛋氨酸工艺条件研究

以N-乙酰DL-蛋氨酸(N-Ac-DL-Met)为拆分底物,对氨基酰化酶法拆分工艺参数如反应温度、pH、激活剂Co2 浓度以及底物浓度等因素进行了初步考察。结果表明,在反应温度37℃,缓冲体系pH7.5,Co2 浓度为0.5 mmol/L,初始底物N-Ac-DL-Met的浓度为0.06 mol/L,氨基酰化酶加入量为5μg/mL的较佳条件下,L-蛋氨酸(L-Met)的产率可达45%;产物L-Met结晶的光学纯度(用对映体过量值%e.e表示)为95.4%。实验中首次采用多组分标准曲线法,提高了茚三酮显色法在氨基酰化酶法拆分制备手性氨基酸的检测精确度     

15N标记L-天冬酰胺的合成

以L-天冬氨酸作为手性源,采用先选择性酯化后再氨解的方法,制备得到15N标记L-天冬酰胺。对影响反应收率的多种因素如酯化催化剂种类、氨解温度、反应时间和氨用量等进行了考察。结果表明,在POCl3作为酯化催化剂,n(NH3)/n(L-天冬氨酸-β-甲酯)=7,反应时间60 h和反应温度为50°C条件下可获得良好的L-天冬酰胺收率。产物经旋光仪、HPLC、红外、质谱和元素分析等证实,合成过程未发生消旋化和同位素丰度稀释现象。     

手性扁桃酸光学拆分研究进展

介绍了手性扁桃酸的各种拆分方法,讨论了各种方法的优缺点。以手性苯甘氨酸丁酯为拆分剂的方法操作简单、收率较高,适于工业化生产。     

Kinetics and modeling of L-cysteine effect on the Cu(II)-induced oxidation of quercetin

Abstract

This study aimed at investigating the effect of L-cysteine on the Cu²⁺-induced oxidation of quercetin, within a pH range varying from 6.7 to 8.3 and temperatures varying from 53 to 87?°C. Initial examinations showed that quercetin degradation obeyed apparent first-order kinetics and it was significantly temperature-dependent. Modelling of the effect of L-cysteine by implementing response surface methodology suggested that L-cysteine did not inhibit quercetin oxidation, but it acted as an oxidation stimulant. Liquid chromatography-diode array-mass spectrometry analyses revealed the presence of typical quercetin degradation and oxidation products, including protocatechuic acid, 2-(hydroxybenzoyl)-2-hydroxybenzofuran-3(2H)-one and a quinone methide. However, the presence of two tentative quercetin/L-cysteine adducts evidenced the implication of L-cysteinyl radicals in the relevant reactions. It was concluded that the formation of L-cysteinyl radicals may promote quercetin oxidation, giving rise to substances with unknown biological significance. This fact merits further attention to illuminate possible beneficial or adverse nutritional consequences of such reactions in foods.     

On the mechanical stability of mesoporous silica SBA-15

Mesoporous silica SBA-15 was synthesised at 80 °C. The calcined solids were exposed to a unilateral external pressure in the range 16–191 MPa in order to monitor the impact of the mechanical pressure on the properties of SBA-15. N₂ adsorption–desorption measurements, XRD and UV-Raman spectroscopy was used in order to evaluate the changes occurring in the SBA-15. For the XRD measurement, an internal Si standard was used to correct the position of the SBA-15 patterns. It appeared that the elevated pressure has no influence on the hexagonal cell parameter a. Through the N₂ sorption measurements the fraction of the preserved mesoporous structure was estimated to be 60% when the highest pressure has been used. As the remaining part of the material is irreversibly disintegrated into small particles, the pressed sample is considered to be heterogeneous. However, the preserved fraction is slightly modified, showing a smaller pore width and plugs located within the mesopores. The plugs most likely originate from a disintegrated fraction of the SBA-15. UV-Raman spectroscopy shows that the relative intensity of the band associated with the siliceous network (ω₁) has decreased on the pressed samples resulting in a less ordered material possessing an enhanced population of silanols as compared to parent SBA-15. We propose that the disorder introduced by pressing is responsible for the observed expansion of the SBA-15 walls, which is detected for the samples treated at higher pressures (112, 191 MPa).     

Growth response to fertilisation and recovery of 15N-labelled fertiliser by young hoop pine plantations of subtropical Australia

The stand growth responses to fertilisation were investigated in 1-year-old and 5-year- old second rotation (2R) hoop pine (Araucaria cunninghamii) plantations in subtropical Australia. At the 1-year-old plantation, 4 rates of nitrogen (N) fertiliser (0, 20, 60 and 120 kg N ha-1) were banded either with or without basal fertilisers (BF) containing 60 kg P ha-1 and 50 kg K ha-1. In the 5-year-old plantation, 4 rates of N fertiliser (0, 100, 300, 600 kg N ha-1) were banded with or without the BF. At both sites N fertiliser was applied as ammonium sulphate in 4 equal split dressings over 2 growing seasons. 15N-labelled ammonium sulphate was also used at the 5-year-old plantation in conjunction with the 100 kg N ha-1 treatment. The 15N-labelled fertiliser was applied to 3 trees during the first split application in spring, and to 3 more trees during the second split application in midsummer. The 15N-labelled trees were harvested and the surrounding soil excavated 6 months after the second 15N application. In the 1-year-old plantation, no stand growth response to fertilisation was noted, indicating that fertilisation at plantation establishment was unlikely to increase plantation productivity. In contrast, a significant stand response to N fertilisation was demonstrated at the 5-year-old site. There were no significant differences between the plus N treatments and the increase in basal area and volume due to N fertilisation 2.3 years after commencement of the trial was 45.1 and 43.5%, respectively. No response to basal fertiliser was observed. The mean 15N recovery from the soil–plant system was 79%, with no significant difference noted between the two split applications. The mean 15N recovery in the tree biomass was 56%, with the majority being partitioned into the foliage. On average 21% of the applied 15N could not be accounted for, and was assumed to be lost from the soil–plant ecosystem.     

介孔材料Al-SBA-15的合成研究进展

Al掺杂的介孔SBA-15材料不仅保持了介孔SBA-15材料原有的结构特征,还赋予了材料新的催化活性位,成为近年来介孔材料领域最为活跃的研究对象之一。本文详细阐述了近十几年来Al-SBA-15介孔材料的研究进展,比较了各合成方法之间的区别,并讨论了Si/Al摩尔比、合成方法和反应条件等因素对Al原子嵌入SBA-15介孔骨架的效率以及介孔材料的有序性、稳定性和酸性的影响。同时总结出加深对合成机理的研究,优化合成过程,使用较简单且高效的方法制备具有完全晶化骨架和较高Al含量的介孔Al-SBA-15是未来介孔Al-SBA-15合成研究的新方向。     

Nitrogen use efficiency,floodwater properties,and nitrogen-15 balance in transplanted lowland rice as affected by liquid urea band placement

Alternative N fertilizer management practices are needed to increase productivity and N use efficiency in lowland rice (Oryza sativa L.). In 1986 dry season, a field study using¹⁵N-labeled urea evaluated the effect of time and method of fertilizer N application on grain yield and N use efficiency. Conventional fertilizer application was compared with band placement of liquid urea and point placement of urea supergranules (USG). Grain yields were significantly higher with either band or point placement than with broadcast and incorporation or surface application. Partial pressure of NH₃ (NH₃) was significantly reduced when N was deep-placed.¹⁵N balance data show that fertilizer N applied basally and incorporated gave a total¹⁵N recovery of 52% and crop (grain + straw) recovery of 30%. Band placement of liquid urea N resulted in 82–90% total and 57–65% crop¹⁵N recovery. USG point placement gave 94% total and 70% crop¹⁵N recovery. Deep placement of second N application gave only slightly higher (98%)¹⁵N recovery compared with broadcast application (89%).     

Recovery of 15N-labelled fertilizer applied to winter wheat and perennial ryegrass crops and residual 15N recovery by succeeding wheat crops under different crop residue management practices

The recovery of ¹⁵N-labelled fertilizer applied to a winter wheat (120 kg N ha^–1) and also a perennial ryegrass (60 kg N ha^–1) crop grown for seed for 1 year in the Canterbury region of New Zealand in the 1993/94 season was studied in the field. After harvests, ryegrass and wheat residues were subjected to four different residue management practices (i.e. ploughed, rotary hoed, mulched and burned) and three subsequent wheat crops were grown, the first succeeding wheat crop sown in 1994/95 to examine the effects of different crop residue management practices on the residual ¹⁵N recovery by succeeding wheat crops. Total ¹⁵N recoveries by the winter wheat and ryegrass (seed, roots and tops) were 52% and 41%, respectively. Corresponding losses of ¹⁵N from the crop-soil systems represented by un-recovered ¹⁵N in crop and soil were 12% and 35%, respectively. These losses were attributed to leaching and denitrification. The proportions of ¹⁵N retained in the soil (0-400 mm depth) at the time of harvest of winter wheat and ryegrass were 36% and 24%, respectively. Although the soil functioned as a substantial sink for fertilizer N, the recovery of this residual fertilizer by subsequent three winter wheat crops was low (1-5%) and this was not affected by different crop residue management practices.