A rapid non-equilibrium critical precipitation assay to assess aluminium-ligand interactions

Abstract

In many natural situations (e.g. environmental and biological) aqueous metal-ligand interactions occur in complex, dynamic solutions and do not adhere to true equilibrium. Nonetheless, equilibrium-based assays in simple solutions are generally used to model metal-ligand interactions of natural systems. Moreover, these are time consuming and not easily applied or understood by many applied scientists. Here, a ‘critical precipitation assay’ was used to investigate the interaction of common ligands with aluminium at pH 7.0, under non-equilibrium conditions. Results obtained were correlated with literature-derived stability constants for the aluminium-ligand interactions, while high-resolution ¹H nuclear magnetic resonance spectroscopy (¹H NMR) was used to confirm the nature of observed interactions. Weak interaction with aluminium was confirmed for traditional weak ligands (e.g. bicarbonate) as these were unable to compete with the hydroxide ion for aluminium at pH 7.0. Two types of interaction were seen for the ‘stronger’ ligands that could compete with hydroxy-polymerisation. Firstly, distinct aluminium:ligand stoichiometric ratios were observed for ligands such as ethylenediaminetetra-acetic acid (1:1) or 1,3,5-trideoxy-1,3,5-tris( dimethylamino)-cis-inositol (1:2). Secondly, most ligands, including citrate and maltol, did not prevent hydroxy-polymerisation but did maintain more aluminium ‘in solution’ (approximately 2.5:1 aluminium:ligand) than permitted by acceptable aluminium:ligand stoichiometric ratios, suggesting the formation of dynamic metastable hydroxy-bridged aluminium-ligand complexes. ¹H NMR with aluminium and maltol or citrate, supported this idea as complex spectral patterns were observed prior to precipitation. Aluminium maintained in solution at pH 7.0 correlated, with literature-derived stability constants suggesting that non-equilibrium aluminium-ligand interactions approximate to equilibrium and that this assay could be used as a quick screening method for investigation of aluminium-ligand interactions.     

Bioclimatic analysis in a region of southern Italy (Calabria)

In this study, an analysis of precipitation and temperature data has been performed over 67 series observed in a region of southern Italy (Calabria). At first, to detect possible trends in the time series, an analysis was performed with the Mann–Kendall non-parametric test applied at monthly and seasonal scale. An additional investigation, useful for checking the climate change effects on vegetation, has also been included analysing bioclimatic indicators. In particular, Emberger, Rivas-Martinez and De Martonne indices were calculated by using monthly temperature and precipitation data in the period 1916–2010. The spatial pattern of the indices has been evaluated and, in order to link the vegetation and the indices, different indices maps have been intersected with the land cover data, given by the Corine Land Cover map. Moreover, the temporal evolution of the indices and of the vegetation has been analysed. Results suggest that climate change may be responsible for the forest cover change, but, given also the good relationship between the various types of bioclimate and forest formations, human activities must be considered.     

Direct and indirect effects of climate on decomposition in native ecosystems from central Argentina

Abstract Climate affects litter decomposition directly through temperature and moisture, determining the ecosystem potential decomposition, and indirectly through its effect on plant community composition and litter quality, determining litter potential decomposition. It would be expected that both the direct and indirect effects of climate on decomposition act in the same direction along gradients of actual evapotranspiration (AET). However, studies from semiarid ecosystems challenge this idea, suggesting that the climatic conditions that favour decomposition activity, and the consequent ecosystem potential decomposition, do not necessarily lead to litter being easier to decompose. We explored the decomposition patterns of four arid to subhumid native ecosystems with different AET in central‐western Argentina and we analysed if ecosystem potential decomposition (climatic direct effect), nutrient availability and leaf litter potential decomposition (climatic indirect effect) all increased with AET. In general, the direct effect of climate (AET) on decomposition (i.e. ecosystem potential decomposition), showed a similar pattern to nutrient availability in soils (higher for xerophytic and mountain woodlands and lower for the other ecosystems), but different from the pattern of leaf litter potential decomposition. However, the range of variation in the ecosystem potential decomposition was much higher than the range of variation in litter potential decomposition, indicating that the direct effect of climate on decomposition was far stronger than the indirect effect through litter quality. Our results provide additional experimental evidence supporting the direct control of climate over decomposition, and therefore nutrient cycling. For the ecosystems considered, those with the highest AET are the ecosystems with the highest potential decomposition. But what is more interesting is that our results suggest that the indirect control of climate over decomposition through vegetation characteristics and decomposability does not follow the same trend as the direct effect of climate. This finding has important implications in the prediction of the effects of climate change on semiarid ecosystems.     

三北工程区降水量长时间序列与多尺度变化趋势检验及预测

三北防护林体系建设工程区（以下简称"三北工程区"）早期的植被建设忽略了水资源承载力，对三北防护林的可持续维护产生了不利影响。为落实"以水定林草"的发展理念，在三个空间尺度上，基于1951-2018年降水量，采用Mann-Kendall非参数检验方法、自回归积分滑动平均模型（Autoregressive Integrated Moving Average Model，ARIMA）和地理信息系统空间分析等方法，开展全年、生长季和非生长季降水量多尺度变化趋势与未来30年预测研究，结果表明："三北工程区"全年和生长季降水量呈增长趋势的面积百分比分别为73.64%和70.10%，主要分布在西北荒漠区；非生长季降水量呈增长趋势的面积比例达92.06%，除黄土高原南部和风沙区的少部分地区而外，均呈增长趋势。全年、生长季和非生长季降水量呈增长趋势且置信度为90%以上的面积百分比分别为45.43%、37.31%和36.79%。18个重点建设区的雷达统计图显示：生长季与全年降水量的变化趋势一致，由东向西，松辽平原等7个区域以不显著减少趋势为主，松嫩平原等7个区域以不显著增长趋势为主，西部的柴达木盆地等4个区域以显著性达到90%或95%的增长趋势为主；非生长季除晋陕峡谷、泾河渭河流域以非显著减少趋势为主而外，其他地区均以增长趋势为主。5个"重点县"的降水统计量UF_k与其反序统计量UB_k两条曲线出现交点，表明年降水量有突变发生，库尔勒市、磴口县、科尔沁左翼后旗UF_k与UB_k曲线多处出现交点，表明年降水量突变发生频繁。采用ARIMA预测得出未来30年的年降水量，计算得到未来30年间的年降水量变化数据，并绘制其空间分布图。本研究可为三北工程区开展基于水资源承载能力的林草资源优化配置提供基础数据，为发展"雨养林草植被"提供科学支撑。     

Development and optimization of fractional precipitation for the pre-purification of (+)-dihydromyricetin

A novel fractional precipitation process, both simple and efficient, was developed for producing (+)-dihydromyricetin in high purity and high yield from crude extracts. The optimal acetone composition in water, initial (+)-dihydromyricetin concentration in crude extract, storage temperature, storage time, and pH were 1/5 (v/v), 0.1 g/mL, 4°C, 32 h, and 9.0, respectively. Crude extracts were efficiently pre-purified using fractional precipitation of (+)-dihydromyricetin by differences of solubility in an acetone solution, increasing purity from 55.0 to over 84.9% with an overall yield of 97.5%. The use of fractional precipitation for pre-purification allowed for rapid and efficient separation of (+)-dihydromyricetin from interfering compounds and dramatically increased the purity of crude (+)-dihydromyricetin for subsequent purification steps.     

Evapotranspiration,crop coefficient and water use efficiency of giant reed (Arundo donax L.) and miscanthus (Miscanthus × giganteus Greef et Deu.) in a Mediterranean environment.

Giant reed (Arundo donax L.) and miscanthus (Miscanthus × giganteus Greef et Deu.) are two perennial rhizomatous grasses (PRGs), considered as promising sources of lignocellulosic biomass for renewable energy production. Although the agronomic performance of these species has been addressed by several studies, the literature dedicated to the crop water use of giant reed and miscanthus is still limited. Our objective was thus to investigate giant reed and miscanthus water use by assessing crop evapotranspiration (ET_c), crop coefficients (K_c) and water use efficiency (WUE). The study was carried out in central Italy and specifically designed water-balance lysimeters were used to investigate the water use of these PRGs during the 2010 and 2011 growing seasons. Giant reed showed the highest cumulative evapotranspiration, with an average consumption of approximately 1100 mm, nearly 20% higher than miscanthus (900 mm). Crop evapotranspiration rates differed significantly between the species, particularly during the midseason (from June to September), when average daily ET_c was 7.4 and 6.2 mm in giant reed and miscanthus respectively. The K_c values determined in our study varied from 0.4 to 1.9 for giant reed and 0.3 to 1.6 for miscanthus. Finally, WUE was higher in miscanthus than in giant reed, with average values of 4.2 and 3.1 g L⁻¹ respectively. Further studies concerning water use under nonoptimal water conditions should be carried out and an assessment of the response to water stress of both crops is necessary to integrate the findings from this study.     

Factors Controlling Microbially Induced Desaturation and Precipitation (MIDP) via Denitrification during Continuous Flow

Three continuous-flow column experiments were conducted to investigate the effects of nitrate loading rate and input concentrations of acetate and calcium on the effectiveness of denitrification to promote microbially induced desaturation and precipitation (MIDP). MIDP differs from microbially induced carbonate precipitation (MICP) in that it relies upon desaturation by biogenic gas production, along with carbonate precipitation, to improve the behavior of saturated granular soil. Denitrification is a stepwise process that is susceptible to inhibition and accumulation of intermediates, like nitrite, due to unfavorable chemical conditions (e.g., low pH). Therefore, nitrate reduction, nitrite accumulation, calcite saturation, and formation of carbonate precipitates were monitored in the columns. Factors investigated in these experiments included the effects of nitrate loading rate and input concentrations of calcium and acetate. Low nitrate-loading rates (i.e., ≤0.7?mol/m²-day) generally led to favorable outcomes (i.e., less accumulation of intermediates and more efficient carbonate precipitation). However, faster precipitation rates associated with low nitrate-loading rates led to smaller carbonate crystals and a less uniform precipitation pattern (i.e., precipitation focused near the nutrient source). Input concentrations of calcium and acetate also affected MIDP, but to a lesser extent than nitrate loading rate. The most important stimulated denitrifying bacteria, identified via 16S rDNA sequencing of suspended and dissolved DNA in the soil columns, were Bacillus species, Pseudomonas species, Brevundimonas species, and members of the Rhizobiaceae family. The results support that lower nitrate loading rates can be beneficial for MIDP although higher nitrate loading rates might be useful for some soil improvement applications.