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沉淀-陈化-返溶作用和压力对热液中氟钛络合物高温水解的影响及地质意义 总被引：3，自引：3，他引：0
钛是自然界中最不活泼的金属元素之一,然而越来越多的证据显示钛可以在特定条件下能进入热液流体中发生迁移,其中氟可能在其中扮演着重要的角色。本文研究了300℃和50~400MPa压力条件下氟钛络合物(K2Ti F6)的稳定性以及沉淀-陈化-返溶作用和压力对氟钛络合物水解行为的影响。研究结果显示,氟钛络合物水解的过程中,由于Ti O2沉淀物的陈化作用,在稳定的温度和压力条件下,沉淀物的返溶很难发生;但在缓慢降温和机械性振荡过程中,沉淀物的返溶会明显发生。而且,在温度不变的情况下,压力的改变对K2Ti F6水解并没有显著的影响,显示氟钛络合物不管在高压还是低压环境下均遵循近似的水解规律。本文认为主要的原因在于压力的增高会促进水解反应沉淀物的陈化,进而抑制沉淀物的返溶,但并不破坏水解反应的平衡。最后,本文提出金属络合物的形成-水解-沉淀/返溶-陈化过程是水-岩作用或热液成矿过程中高场强元素活化、迁移和成矿的主要机制。 相似文献
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温度、浓度对流体中氟钛络合物水解的影响:对深部地质过程中钛元素活动的制约 总被引：6，自引：3，他引：3
Ti是自然界中丰度最高的高场强元素(HFSE),其主要赋存矿物——金红石的溶解度决定了俯冲带HFSE的活动与循环。而富氟流体被认为是影响Ti等HFSE能否活化、迁移的重要因素。本文对不同浓度的氟钛络合物(K2Ti F6)在100MPa压力和200~500℃温度下的稳定性进行了研究,结果显示其在热液条件下发生显著水解,水解程度与温度和初始浓度密切相关,即温度越高、初始浓度越低,则水解程度越剧烈。对实验数据进行拟合,首次获得了K2Ti F6的表观水解常数与温度的关系式:-ln K=(8972±788)/T-(4.16428±1.40362),其中获得的热力学参数为:ΔrHΘ=74.59±6.55k J/mol,ΔrSΘ=34.62±11.67J/(mol·K)。同时,运用上述获得的关系式将温度推广到俯冲带条件,计算了金红石溶解度和流体中Ti的最大迁移量之间的关系。结果显示,当金红石的溶解度大于1000μg/m L时,富F流体能有效迁移的Ti大于1μg/m L;随着金红石溶解度的增加,Ti的有效迁移百分比也逐渐增大,但俯冲流体中Ti的最大迁移量可能不超过6700μg/m L,比之前的预计要低得多。本文的研究证实了富F流体能最大程度活化并迁移Ti等HFSE。其中,对于岩浆-热液体系而言,F主要通过在岩浆中预富集,然后再大量分配进入晚期流体中而形成富F流体;对于俯冲带而言,多硅白云母的脱水或热解是形成富F流体/超临界流体的有效途径。 相似文献
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R. Danovaro N. Della Croce A. Dell&#x;Anno A. Pusceddu 《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(12):1411-1420
The Atacama trench, the deepest ecosystem of the southern Pacific Ocean (ca. 8000 m depth) was investigated during the Atacama Trench International Expedition. Sediments, collected at three bathyal stations (1040–1355 m depth) and at a hadal site (7800 m) were analyzed for organic matter quantity and biochemical composition (in terms of phytopigments, proteins, carbohydrates and lipids), bacterial abundance, biomass and carbon production and extracellular enzymatic activities. Functional chlorophyll-a (18.0±0.10 mg m−2), phytodetritus (322.2 mg m−2) and labile organic carbon (16.9±4.3 g C m−2) deposited on surface sediments at hadal depth (7800 m) reached concentrations similar to those encountered in highly productive shallow coastal areas. High values of bacterial C production and aminopeptidase activity were also measured (at in situ temperature and 1 atm). The chemical analyses of the Atacama hadal sediments indicate that this trench behaves as a deep oceanic trap for organic material. We hypothesize that, despite the extreme physical conditions, benthic microbial processes might be accelerated as a result of the organic enrichment. 相似文献
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The observation that a fraction of organic matter produced in marine systems evades the concerted efforts of microbial communities and is buried in sediments suggests that there are ‘speed bumps’ in carbon degradation pathways that impede microbially driven remineralization processes. The initial step in degradation of macromolecules, extracellular enzymatic hydrolysis, is often stated to be ‘the’ rate-limiting step in carbon remineralization. Experimental investigations described here, however, demonstrate that at least in certain cases, microbes produce extracellular enzymes on time scales of hours to tens of hours in response to substrate addition, and hydrolysis is extremely rapid. If enzymatic hydrolysis can be rapid, what factors slow or stop organic matter degradation? A lack of the correct inducer to initiate enzyme production, and/or a lack of the correct organism to produce the required enzyme, may result in a complete lack of hydrolysis in certain environments—a barricade, rather than a speed bump. Preliminary evidence supporting this hypothesis includes a comparison of polysaccharide hydrolysis in seawater and sediments, which demonstrates that the spectrum of enzymes active in seawater and sediments are fundamentally different. Furthermore, a survey of enzyme activities in surface waters from a range of locations suggests that pelagic microbial communities also differ widely in their abilities to express specific extracellular enzymes. Trans-membrane transport through porins is yet another potential location of structure-related selectivity.Our efforts to identify speed bumps and barricades are hampered by our inability to structurally characterize in sufficient detail the macromolecular structures present in marine systems. Furthermore, assessments of organic matter ‘quality’ from a chemical perspective do not necessarily accurately reflect the availability of organic carbon to microbial communities. For these communities, in fact, ‘quality’ may be a variable, which depends on the enzymatic and uptake capabilities of community members. To begin to assess substrate structure and quality from a microbial perspective, we will have to combine specific knowledge of macromolecular structures with detailed investigations of the enzymatic and transport capabilities of heterotrophic marine microbes. 相似文献
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为了能够有效利用糙刺参内脏蛋白,以水解度为主要指标,对酶解蛋白酶进行了筛选,并系统研究了酶解温度、p H、加酶量和水解时间等单因素对水解度的影响。在此基础上,利用响应面中心组合设计实验,对酶解工艺进行了优化,得到以温度、p H、加酶量及水解时间为因子的二次方程,通过方差分析和验证性实验得出,此二次方程能较好反应海参内脏团蛋白水解度的变化规律,得到最佳水解条件为:温度52.66℃,p H 6.71,加酶量2.5%(质量分数),酶解时间10 h,预测最高水解度为49.58%。最佳酶解条件下所得多肽74%以上分子质量小于500 Da。利用DPPH法测定最佳条件酶解所得多肽的抗氧化活性,3 g/L的抗氧化率达到了24.8%,利用ABTS法测定最佳条件酶解所得多肽的抗氧化活性,3 g/L的抗氧化率达到了0.255μmol/g。为海参内脏蛋白的利用提供了参考。 相似文献
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Competition between enzymatic and abiotic reduction of uranium(VI) under iron reducing conditions 总被引：1，自引：0，他引：1
Reduction of U(VI) under iron reducing conditions was studied in a model system containing the dissimilatory metal-reducing bacterium Shewanella putrefaciens and colloidal hematite. We focused on the competition between direct enzymatic uranium reduction and abiotic reduction of U(VI) by Fe(II), catalyzed by the hematite surface, at relatively low U(VI) concentrations (< 0.5 μM) compared to the concentrations of ferric iron (> 10 mM). Under these conditions surface catalyzed reduction by Fe(II), which was produced by dissimilatory iron reduction, was the dominant pathway for uranium reduction. Reduction kinetics of U(VI) were identical to those in abiotic controls to which soluble Fe(II) was added. Strong adsorption of U(VI) at the hematite surface apparently favored the abiotic pathway by reducing the availability of U(VI) to the bacteria. In control experiments, lacking either hematite or bacteria, the addition of 45 mM dissolved bicarbonate markedly slowed down U(VI) reduction. The inhibition of enzymatic U(VI) reduction and abiotic, surface catalyzed U(VI) reduction by the bicarbonate amendments is consistent with the formation of aqueous uranyl-carbonate complexes. Surprisingly, however, more U(VI) was reduced when dissolved bicarbonate was added to experimental systems containing both bacteria and hematite. The enhanced U(VI) reduction was attributed to the formation of magnetite, which was observed in experiments. Biogenic magnetite produced as a result of dissimilatory iron reduction may be an important agent of uranium immobilization in natural environments. 相似文献
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Humic substances isolated from water, sediment, and soil were characterized by applying elemental analysis, spectroscopic analysis, and gelchromatographic molecular size distribution. In addition, the amounts and pattern of enzymatically released amino acids were determined. Depending on the origin of the humic substances, the percentage of released amino acid nitrogen related to the total nitrogen was in the range of 0.4 to 26.7%. The samples particularly differed in the content of leucine und tyrosine. The total amount of released amino acids was compared with the results obtained from the other characterization methods. This approach indicated that humic substances with a high content of hydrolysable amino acids had high N/C and O/C ratios and low molecular sizes. Beside this, the absorption of these substances in the UV and visible wavelength range was quite low, while the measured ratios of SAK(254)/SAK(436) showed high values. This work leads to the conclusion that the extent of enzymatically releasable amino acids is not only dependant on the nitrogen content of humic substances. Other physical and chemical properties have to be considered for the understanding of the results obtained by the described biochemical characterization method. 相似文献
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