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Extracellular enzymatic activities in soils are essential for the cycling of organic matter. These activities take place in multiphase environments where solid phases profoundly affect biocatalytic activities. Aspergillus niger is ubiquitous in soils; its β-glucosidase plays an important role in the degradation of cellulose, and therefore in the global carbon cycle and in the turnover of soil organic matter. However, the information on the interactions of this protein with soil minerals is very limited, and even less is known about their consequences for the hydrolysis of the natural substrate cellobiose. We therefore characterised the sorptive interactions of this enzyme with the soil minerals montmorillonite, kaolinite and goethite and quantified the resulting changes in the hydrolysis rate of cellobiose. Fractions of adsorbed protein, and the resulting catalytic activity loss, were lower for montmorillonite than for kaolinite and goethite at given experimental conditions; adsorption was 9.7 ± 7.3% for montmorillonite, 70.3 ± 3.1% for kaolinite and 71.4 ± 1.8% for goethite, respectively. Adsorption of the protein to the minerals caused a total decrease in the catalytic activity of 18.8 ± 3.4% for kaolinite and 17.9 ± 4.7% for goethite whereas it was not significant for montmorillonite. The average catalytic activity lost by the pool of adsorbed molecules was 26.8% for kaolinite and 25.0% for goethite. Both the amount of adsorbed protein and the resulting loss of catalytic activity were found to be independent of the specific surface areas yet were influenced by the electrical properties of the mineral surfaces. Under the experimental conditions, montmorillonite and kaolinite are negatively charged whereas goethite is positively charged. However, because of the adsorption of phosphate anions from the buffer, a charge reversal took place at the surface of goethite. This was confirmed by zeta (ζ)-potential measurements in phosphate buffer, revealing negative values for all the tested minerals. Indeed goethite interacted with the enzyme as a negatively charged surface: the amount of adsorbed protein and the resulting catalytic activity loss were very similar to those of kaolinite. Our results show that, even if an important fraction of β-glucosidase is adsorbed to the minerals, the catalytic activity is largely retained. We suggest that this strong activity retention in presence of soil minerals results from a selective pressure on A. niger, which benefits from the activity of the adsorbed, and thus stabilized, enzyme pool. 相似文献
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高岭石-甲醇夹层复合体的合成及其特性 总被引：1，自引：0，他引：1
以水合联胺,10 mol尿素水溶液及甲醇先后与高岭石反应,合成了晶面间距为1.0 nm的高岭石甲醇夹层复合物。复合物不太稳定,在常温下 (约放置72 h) 或1050C加热下 (2 min)晶面间距收缩为0.85 nm。于2000C加热时,晶面间距进一步收缩为0.79 nm。0.79 nm复合物在3000C条件下长时间加热也未再发生变化。由层间膨胀值的大小及甲醇分子的最小厚度推测,0.85 nm及0.79 nm夹层复合体中甲醇分子明显地嵌入了高岭石的结构内部。其甲基可能嵌入了硅氧四面体的六角环空洞中,而羟基嵌入了铝氧八面体内。IR图谱表明0.79 nm复合物中甲醇分子与高岭石的相互作用较之0.85 nm复合物更强。 相似文献
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柠檬酸对酸沉降下高岭石的溶解作用 总被引：2，自引：0，他引：2
采用间歇法(batch method)模拟研究酸沉降下的高岭石在柠檬酸溶液中的长期溶解效应。研究表明:柠檬酸能显著促进高岭石Al和Si的释放,且Al、Si的释放能力随柠檬酸浓度的增加而增强;高岭石溶解同步性与柠檬酸浓度有关,随着柠檬酸浓度的提高,其溶解的同步性增强,且反应前期高岭石都表现为Al的优先释放,而在反应后期Al、Si趋于同步释放。柠檬酸对高岭石的溶解速率一般较无机酸高1个数量级左右,且其溶解速率表现出对柠檬酸浓度的饱和性。 相似文献
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针铁矿-高岭石二元体的微观结构与形成机制 总被引：3，自引：0，他引：3
制备了针铁矿-高岭石复合物,以其混合物为对照,分析了它们的微观结构与形成机制。结果表明,复合物中的针铁矿较好地包被在高岭石表面,而混合物中两固相之间的包被作用微弱。相对针铁矿和高岭石两单体而言,二元体中针铁矿和高岭石的主要晶面间距没有明显变化;复合物的孔体积增多、平均孔径减小,混合物的孔体积和平均孔径都接近两单体的平均值;两种二元体的表面分形度(D)增大,且D混合物>D复合物。红外光谱显示,二元体中≡Fe-OH的振动频率升高,而≡Al-OH、Al-O、Si-O和Fe-O的振动频率降低;高岭石与针铁矿胶结后,核磁共振波谱中29Si和27Al的化学位移均向正方向移动。根据波谱分析的结果推断,针铁矿与高岭石的胶结主要通过针铁矿表面≡FenOH2(n/2)+(n=1,2,3)与高岭石表面≡Si-OH、≡Al-OH02.5+等Lewis酸之间的阳离子交换、高岭石表面≡Si-O-和≡Al-OH0.5-与针铁矿表面铁羟基(≡Fe-OH)间的阴离子交换以及高岭石表面O与针铁矿表面Fe间的配位等作用而实现,其胶结力主要为氢键和静电引力。复合物中≡Fe-OH、≡Al-OH等主要基团的振动频率以及29Si、27Al的化学位移的漂移均大于混合物中的变化量,说明复合物中针铁矿与高岭石间的胶结强度大于混合物中两固相间的胶结作用。 相似文献
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室温下(25℃±1℃)采用间歇法(batchmethod)模拟研究高岭石在pH5.5、pH4.5和pH3.5的HAC/NH4AC缓冲液中的溶解。实验结果表明:质子能够促进高岭石Al和Si的释放,且Al、Si的释放能力随反应液酸度的增加而增强,Al、Si溶解的一致性与酸度有关。pH5.5时,可能因Al的沉积而导致整个实验期间Al、Si释放表观不一致;pH4.5和pH3.5时,反应前期Al优先释放,而在反应后期Al、Si趋于一致。pH5.5、pH4.5和pH3.5的HAC/NH4AC缓冲液中高岭石溶解速率分别为:3.09×10-14mol/(m2·s)、6.31×10-14mol/(m2·s)和1.13×10-13mol/(m2·s)。HAC/NH4AC缓冲液中质子作用下高岭石溶解反应级数和速率常数分别为0.28和1.12×10-12。 相似文献
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连续解吸中离子强度对可变电荷土壤和高岭石体系pH的影响 总被引：4，自引：0，他引：4
研究了两种可变电荷土壤中在去离子水中和0.1 mol L-1 Na NO3溶液中吸附铜离子和钙离子后依次被浓度从低到高的Na NO3溶液连续解吸时,离子强度变化对每次解吸前后体系p H变化(Δp H)的影响,为了进一步了解其相关机理,作为对照,也研究了各种条件下,离子强度变化对高岭石Δp H的影响。结果表明,无论是否有吸附性二价阳离子的存在,或者吸附性阳离子属性(专性吸附型离子或电性吸附型离子)如何,当样品依次被去离子水、0.01 mol L-1 Na NO3、0.1 mol L-1 Na NO3以及1 mol L-1 Na NO3解吸时,在去离子水中和Na NO3溶液中的解吸过程对Δp H的影响截然不同。总体而言,如果解吸时体系离子强度趋于降低,Δp H将为正值,反之则为负值,且Δp H变幅开始增大时的起始点所对应的p H吸附基本相同,该起始点应该与高岭石ZPC(电荷零点)紧密相关。对上述结果的分析表明,解吸过程中,引起上述Δp H变化规律的根本原因之一是连续解吸过程中的离子强度变化导致的可变电荷表面的表面电位变化。 相似文献
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腐殖酸?高岭土?铜在多孔介质中的迁移及相互作用 总被引：1，自引：0，他引：1
[目的]控制重金属在地下水深处污染。[方法]采用静态吸附试验和动态模拟试验比较了腐殖酸和高岭土对铜的吸附及其在多孔介质中的迁移。[结果]铜的存在抑制了高岭土在多孔介质中的迁移,高岭土胶体在多孔介质中沉积量增大,导致高岭土对铜的迁移促进作用不明显,腐殖酸降低了胶体沉积的同时促进了铜的迁移,在动态迁移过程中腐殖酸和高岭土对铜产生了竞争吸附,同时高岭土占据了腐殖酸在石英砂上的吸附点位,促进了腐殖酸的迁移。[结论]减少地下水中腐殖酸含量可以降低重金属在地下水深处的富集。 相似文献