醋酸纤维素—纤维素增强膜的结构特征和分离性能

本文描述了醋酸纤维素－纤维素大孔增强超滤膜的结构特征一分离性能之间的关系。详细论述了膜材料含量和粘连剂含量及其分子量对膜结构和性能的影响。论述了不同配方铸膜液的膜，其孔径，水通量和截留率随操作压力的变化规律。实验证明这种高强度的ＣＡＣ膜经多次重复使用后，其结构性能保持完好。     

Methacrylic acid–acrylamide-g-poly(ethyleneterephthalate) fibres for urea hydrolysis

This paper presents the results of urease immobilization onto methacrylic acid–acrylamide grafted poly(ethyleneterephthalate) fibres. The graft yield strongly affected the maximum activity of the immobilized enzyme up to a value of 70·2%. Higher grafting caused a decline in urease activity and led to the degradation of the fibres. The minor changes observed in K_m and V_max demonstrated that the conformational changes existed during immobilization were not extensive. However, 70·2% methacrylic acid–acrylamide-g-fibres containing urease were more stable towards acidic and alkaline pH, high temperature and storage conditions compared with free enzyme. Apart from the increase in stability to heat inactivation, the initial enzymatic activity of the urease–fibre system remained almost unchanged even after 40 repeated assays corresponding to 10 h of operation in 4 months, indicating the excellent durability of the system.     

The influence of soil properties on the effectiveness of phenylphosphorodiamidate (PPD) in reducing ammonia volatilization from surface applied urea

Urea can be an inefficient N source due to rapid hydrolysis by soil urease leading to NH₃ volatilization. The current study investigated the effect of the urease inhibitor phenylphosphorodiamidate (PPD) incorporated at two concentrations (0.5% and 1% w/w) within the fertilizer granule on NH₃ volatilization from surface applied urea. The daily rates of NH₃ loss from 20 soils of widely differing properties from Northern Ireland were measured over 14 days using ventilated enclosures under simulated spring conditions. Cumulative loss rates were calculated and fitted to a logistic model from which total NH₃ loss (Amax) and the time to maximum rate of loss (Tmax) were determined. Stepwise multiple linear regression analysis related the effectiveness of PPD in reducing NH₃ volatilization from urea to soil properties.The total cumulative loss of ammonia from unamended urea varied from 0.37 to 29.2% depending on soil type. Ammonia volatilization appeared to be greatest on a soil with a high pH (R² = 0.65), a low titratable acidity (TA) (R² = 0.63) and a soil that was drying out (R² = 0.50). Soil pH was negatively correlated with TA (r = –0.826, P < 0.001) suggesting that soils with a low TA may have received recent lime. Including cation exchange capacity (CEC) and % N as well as pH-KCl in the multiple linear regression equation explained 86% of the variance.The effectiveness of PPD in reducing Amax varied between 0% to 91% depending on soil type, the average over all 20 soils being 30 and 36% for 0.5% and 1% PPD respectively. The most important soil properties influencing the effectiveness of the urease inhibitor were soil pH-H₂O and TA accounting for 33% and 29% of the variance respectively. PPD was less effective on a soil with a high pH and low TA. These were the soil conditions that led to high NH₃ volatilization from unamended urea and may explain why PPD had limited success in reducing ammonia loss on these soils. Multiple linear regression analysis indicated that 75% of the variation in the % inhibition of NH₃ loss by PPD could be significantly accounted for by pH-H₂O, initial soil NO ₃ ^- -N concentration, % moisture content and % moisture loss.The delay in Tmax by PPD ranged from 0.19 to 7.93 days, the average over all 20 soils being 2.5 and 2.8 days for 0.5% and 1% PPD respectively. TA, % moisture content, urease activity and CEC were soil properties that significantly explained 83% of the variation in the % delay in Tmax by PPD in multiple linear regression analysis. However, none of these soil properties were significant on their own. As urea hydrolysis occurs rapidly in soil, delaying Tmax under field conditions would increase the chance of rain falling to move the urea below the soil surface and reduce NH₃ volatilization. A urease inhibitor should be more effective than PPD on soils with a high pH and low TA to be successful in reducing high NH₃ losses.     

In vitro effects of urease inhibitors on rate of urea hydrolysis in soils

We studied the effect of urease inhibitors on the urea hydrolysis in some Sundanese soils belonging to the orders of Vertisol and Entisol. The hydrolysis showed a lag period of about 3 days and its rate (Y) per unit time (t) could be described by a two constants exponential equation of the general form Y = K₁t^K ₂. Statistical analysis showed that the intercept K₁ (rate of urea hydrolysis) was significantly affected by soil type rather than treatment. It seems that K₁ is associated with the soils' initial urease activity as it closely correlates with the Michaelis constant (km).The gradient, K₂, being significantly affected by soil type as well as treatment is probably associated with the induced urease activity with time and it, therefore, varied with variations in soils and treatments. Of the so-called urease inhibitors used in this study Ca(OH)₂, p-benzoquinone (PBQ) and orthophosphoric acid (OP) only PBQ reduced urea hydrolysis while the other chemicals have effects possibly related to modifying the soil pH. Inhibitor treated soils had substantial amounts of unacounted for N which was believed to be present, presumably, in the form of carbamate.Contribution from the Department of Biochemistry and Soil Science, Faculty of Agriculture, Shambat, Sudan.     

壳聚糖固定化脲酶生物传感器选择性测定铜离子

基于重金属对脲酶的抑制作用,研制了用于测定铜离子的生物传感器。该生物传感器的制备以壳聚糖为载体,将脲酶固定于pH电极表面。由于壳聚糖对Cu2+的富集,该生物传感器展现出高灵敏度。在样品溶液中加入5 mmol/L NaI,可以消除Hg2+和Ag+的干扰,从而实现Cu2+的选择性检测。在0.005～0.5μg/mL的浓度范围内,脲酶活性的抑制率与Cu2+浓度的对数呈良好的线性响应关系,其检出限为0.002μg/mL。将使用后的生物传感器浸泡于0.5 mmol/L的EDTA溶液再生5 min,被Cu2+抑制的脲酶的活性可以得到恢复。     

低浓度重金属离子的富集及其对脲酶活性影响

利用树脂对水中重金属离子进行有效吸附富集,再利用富集的重金属离子对脲酶活性的抑制影响来确定金属离子的浓度。研究了在不同条件下树脂对不同重金属离子的吸附性能,采用分光光度法得到了金属离子浓度及铵离子浓度的标准曲线,同时还研究了温度、树脂质量、缓冲液、尿素、离子种类、离子浓度等对脲酶活性的抑制关系。结果表明,0.5 g树脂完全可以吸附体积为50 mL,质量浓度不大于0.7 mg/mL的重金属离子,而在一定的浓度范围内,铜离子和铅离子对脲酶有明显的抑制作用,且具有线性关系。     

Encapsulation of urease in double‐layered hydrogels of macroporous poly(2‐hydroxyethyl methacrylate) core and poly(ethylene oxide) outer layer: fabrication and biosensing properties

Double‐layered hydrogels of super‐macroporous poly(2‐hydroxyethyl methacrylate) (PHEMA) cryogel core and poly(ethylene oxide) (PEO) hydrogel outer layer for encapsulation of the enzyme urease were constructed. The enzyme was entrapped into the pores of PHEMA cryogel by soaking and then the core was covered with a PEO layer. The leaking of urease from the core was prevented when the density of the PEO network was increased by incorporation of the crosslinking agent, poly(ethylene glycol) diacrylate. The hybrid system exhibited a nearly constant enzyme activity with time and maintained its structural integrity after several reactions of hydrolysis of urea. The potential of double‐layered hydrogels containing urease for establishment of water pollution with copper was investigated as well. Copyright © 2011 Society of Chemical Industry     

新型方法制备固定化脲酶基质材料及固定化脲酶的性能研究

以微晶纤维素(Microcrystalline cellulose,MCC)为原料,采用新型水热氧化方法,制备纤维素基质固定化脲酶载体材料-双醛纤维素(Dialdehyde cellulose,DAC)。采用红外光谱(IR)、固体核磁共振(CP/MAS 13C NMR)、X-射线衍射(XRD)和扫描电镜(SEM)表征产物结构。测试制备的纤维素基质固载脲酶的酶学性能,并与交联壳聚糖、双醛淀粉固载脲酶的酶学性能进行比较分析,构建酶学性能理论方程。结果表明:采用新型水热氧化反应可成功制备高醛基含量的氧化纤维素,与交联壳聚糖和双醛淀粉固定化脲酶相比,所得氧化纤维素载体材料固定化脲酶的米氏常数小(0.0108mol·L-1),对底物亲和能力强,重复使用率高,在pH=5.0~9.0能保持酶活性,建立的理论方程较好地表征了固载酶酶学性能。     

脲解型微生物诱导矿化沉积的研究进展

微生物矿化技术作为一种新兴绿色环保技术得到关注,其中脲解型微生物研究最常见。本文针对脲解型微生物在生物矿化方面的研究进行综述,阐述其生物矿化机理,对其生物矿化影响因素分环境因素、岩土材料特性及改良工艺三个方面展开分析。     

Sporosarcina pasteurii诱导碳酸盐-铀共沉淀修复低浓度铀废水的试验研究

对有钙源条件下Sporosarcina pasteurii诱导碳酸盐-铀共沉淀修复低浓度铀废水的性能开展了试验研究。试验结果表明,该细菌能分泌脲酶水解尿素诱导产生方解石并促使其与铀发生共沉淀,使废水中铀的去除率达到95.38%;该细菌能够耐受的铀浓度高达500 mg/L;铀的去除率随Ca²⁺浓度的升高而增加;温度在30℃左右和碱性环境有利于方解石与铀的共沉淀。对沉淀产物进行XRD、SEM-EDS表征分析表明,其主要成分为方解石,且包含铀元素;消解分析表明,在方解石形成过程中铀以共沉淀的方式被固定到了沉淀产物中。本研究表明,Sporosarcina pasteurii诱导碳酸盐-铀共沉淀对修复低浓度铀废水有潜在应用前景。