Antioxidant activity of compounds isolated from the pyroligneous acid, Rhizophora apiculata

The polyphenols (CPAE II) was isolated from the dichloromethane extract of the pyroligneous acid, Rhizophora apiculata by simultaneous acid base and solvent extraction method. Its qualitative and quantitative composition was studied by gas chromatography mass spectroscopy (GC/MS) and out of 57 peaks, 52 compounds were identified, representing 95.47% of the total polyphenols. The CPAE II was then fractionated to four fractions (F1–F4) by means of thin layer chromatography and silica gel column chromatography with dichloromethane, dichloromethane/chloroform/ethyl acetate mixture (8:1:1; 4:3:3, v/v/v), and ethyl acetate, respectively. The antioxidant properties of the CPAE II and the fractions were evaluated. Among the four fractions, fraction 1 (F1) was the most potent in DPPH radical scavenging activity and molybdenum (VI) reducing power. It was subjected to further purification by means of silica gel column chromatography with hexane, hexane/diethyl ether mixture (9:1, 6:1, 3:1, v/v), and diethyl ether, respectively. 2,6-Dimethoxyphenol (syringol) and dihydroxybenzenes (catechol and 3-methoxycatechol) were isolated and identified by GC/MS, ¹H NMR, ¹³C NMR spectral analyses, and confirmed by GC co-injection with authentic standards. Syringol, catechol and 3-methoxycatechol constitute 39.08, 4.21 and 1.10% of F1, respectively. Their antioxidant activities were evaluated by DPPH radical scavenging activity, ABTS radical cation scavenging activity, phosphomolybdenum and ferric reducing antioxidant power (FRAP). The trend in antioxidant capacity was similar in all the four assays, with dihydroxybenzenes > 2,6-dimethoxyphenols, although discrepancies in the ranking within the dihydroxybenzenes were present. These three compounds which showed significant antioxidant activities were isolated for the first time from the pyroligneous acid, R. apiculata.     

Effects of human activities on benthic macroinvertebrate community composition and water quality in the upper catchment of the Mara River Basin,Kenya

Land‐use changes in the upper reaches of the Mara River Basin have modified their biophysical and hydrological processes, resulting in water quality degradation in streams. This study was conducted to investigate the effects of human activities on water quality and macroinvertebrates along the Nyangores River, one of the main tributaries of the Mara River, Kenya. Seven sampling sites were chosen to correspond to the loss of riparian cover, livestock watering and human activities (e.g. laundry washing, bathing, cultivation, wastewater inputs, dumping of solid wastes from urban areas and settlements along the river). Physical–chemical variables and water samples for nutrient analyses were collected monthly from February to July 2012. Benthic macroinvertebrates also were collected at the same sites as for the water quality samples. Two‐way analysis of variance tested the significant differences for each variable among the sites. Similarity percentages (SIMPER) analysis was used to identify the key taxa contributing to differences between minimally disturbed and most disturbed conditions in the study area. The results indicated increased nutrient concentrations in agricultural and settlement areas. Significant (P < 0.05) spatial–temporal variations in water quality variables were observed. A total of 42 macroinvertebrate genera were encountered, with Ephemeroptera, Plecoptera and Trichoptera orders dominating the minimally disturbed areas, and Diptera dominating the disturbed areas receiving point and no‐point solid and liquid wastes, including nutrients, from urban areas and settlements. Canonical correspondence analysis (CCA) revealed significant relationships between macroinvertebrate communities and measured physicochemical variables. The results of this study indicate the need for protection of riparian zones and treatment of sewerage wastes before their release into waterways. The dumping of solid wastes near streams and rivers also is discouraged, to maintain the quality of surface waters and aquatic organisms.     

Characterising polysaccharides in cherimoya (Annona cherimola Mill.) purée and their enzymatic liquefaction

Polysaccharides isolated in the alcohol-insoluble residues (AIR) from cherimoya (Annona cherimola Mill.) were characterised for contents of soluble pectin, cellulose, hemicellulose and lignin, and the distribution of neutral sugars and uronides in water-soluble pectin (WSP) and water-insoluble AIR (WAIR) fractions. For WSP, the predominant neutral sugar was arabinose and, for WAIR, cellulosic glucose and xylose. Two enzyme preparations were tested for their capacity to release neutral sugars and uronides from WAIR. The optimal incubation temperature (45 °C) and the most effective preparation—rich in pectinase, cellulase and xylanase activities—were selected according to a central composite rotatable design (CCRD). Enzyme was also applied to native cherimoya purée according to another CCRD, varying the enzyme concentration and incubation time. Native purée exhibited strong shear-thinning behaviour with high, extrapolated, yield stress. During enzymatic treatment, behaviour was less shear thinning, and yield stress, consistency index and Bostwick consistency tended to decrease, giving rise to purées of different rheological properties.     

丝胶蛋白酶解产物抗氧化活性的研究

本实验采用六种蛋白酶对丝胶蛋白进行酶解,并分析其酶解产物清除二苯代苦味酰基 (DPPH) 自由基能力.通过脂质过氧化体系、还原力、金属螯合能力评价其酶解4h酶解产物的抗氧化活性.结果表明:各种酶解产物都呈现一定的清除DPPH自由基的能力,其中以碱性蛋白酶最强 (p＜0.05);各种酶解产物都存在抑制脂质过氧化活性,与其他蛋白酶相比碱性蛋白酶的抑制活性显著的高于其他酶 (p＜0.05);各种蛋白酶解产物具有一定的还原力和金属螯合能力.这些结果表明:六种酶解产物都具有显著的抗氧化活性.     

三峡库区龙河流域降雨和人类活动对水沙关系变化贡献率分析

以三峡库区中心区域的龙河流域为研究对象,利用1963—2010年流域水沙资料,采用Pettitt突变点检验、累积距平法及双累积曲线法分析了该流域输沙量和降雨量的变化趋势,判别出降雨量在1982年、输沙量在1982年和1990年发生了突变。并采用累积量斜率变化率比较法分析了1963—1981年,1982—1990年,1991—2010年3个时段降雨量和人类活动在龙河流域输沙量变化中的相对贡献率。研究表明:以1963—1981年为基准期,1982—1990年间降雨量和人类活动贡献率分别为29.49%和60.51%,1991—2010年间分别为3.38%和96.62%;以1982—1990年为基准期时,1991—2010年人类活动对输沙减小的贡献率为100%。该研究揭示了1963—2010年输沙量的变化趋势及降雨和人类活动对其贡献率,研究不仅对该区水土流失治理、水土保持效益评价具有重要意义,同时为研究三峡水库区间水沙锐减的原因提供一定的理论支持。     

Effects of climate change and anthropogenic activities on runoff change of the Weihe River basin,Northwest China

The Weihe River has experienced a significant runoff decline in the past few decades, but the detailed and systematic analysis of different sub-regions of the Weihe River basin (WRB) for a long time is insufficient. Based on the data of five hydrological stations from 1957 to 2018, this study investigated the variation of annual runoff both in the whole Weihe River basin (WWRB) and its sub-regions: the upper, middle, and lower reaches of the Weihe River (URWR, MRWR, LRWR, respectively), the Jing River basin (JRB), and the Beiluo River basin (BLRB). Moreover, the contribution of climate change and anthropogenic activities on runoff change was quantified by double mass curve (DMC) and hydrological sensitivity analysis (HSA) methods. The results showed that runoff of the URWR, MRWR, JRB, BLRB, and WWRB showed significant downward trends, and with the change-point years of 1993, 1990, 1996, 1994, and 1993, respectively. Both results of DMC and HSA showed that anthropogenic activities were the main factors for runoff reduction. The contribution of human activities was largest in the JRB and BLRB, whereas lowest in the MRWR. Over the study period, land use has changed significantly in the basin, mainly manifested in the reduction of farmland, and the increase of construction land and grassland, indicating that intense anthropogenic activities have taken place. Moreover, the total water consumption of the WWRB increased evidently, which exacerbated the contradiction between supply and demand of water resources. The results of HSA showed that runoff was more sensitive to precipitation than to E_p. Precipitation reduced the runoff, while E_p increased runoff in the basin. The results of this study are helpful for understanding the regional hydrological situation in more detail, and can act as a reference for formulating reasonable water resources allocation schemes.     

南水北调工程项目代建制模式下代建方寻租行为博弈分析

在综合分析项目代建制制度下南水北调项目业主和代建方相互作用关系的基础上,根据公共寻租理论,分析了代建方发生寻租行为的动机;并运用博弈论的方法建立了南水北调项目业主和代建方之间的博弈模型,并对代建方的寻租行为进行了博弈分析。基于博弈分析的结果,对防止南水北调项目代建制下代建方发生寻租行为提出了政策建议。     

基于二元水循环模式的水资源评价理论方法

国内外流域水资源评价方法是随着水资源稀缺性的逐渐增强而不断发展的。时至今日,传统的水资源评价方法在描述人类活动干扰和满足不同层次水资源规划要求方面面临严峻挑战。本文提出了水资源全口径层次化动态评价方法,即以降水为资源评价的全口径通量,遵照有效性、可控性和可再生性原则对降水的资源结构进行解析,实现广义水资源、狭义水资源、径流性水资源和国民经济可利用量的层次化评价。在手段上,构建了由分布式水循环模拟模型与集总式水资源调配模型耦合而成的二元水资源评价模型,并将下垫面变化和人工取用水作为模型变量以实现动态评价。     

洪积扇的分布与地质条件及人类工程活动的关系

洪积扇对人类的生产和工程活动具有重要意义,从地质条件入手,对洪积扇与地质条件和人类工程活动的关系进行了分析,指出在水电工程建设时,洪积扇可作为良好的天然建筑材料且可以削减地震能量,同时还是山区人们重要的生产资源,所以应合理开发,做到开发与保护并举。