Effects of Co-60 gamma-irradiation and refrigerated storage on the quality of Shatang mandarin

The effectiveness of Co-60 gamma irradiation in controlling citrus red mite(Panonychus citri McGregor)had been proved in our earlier work.However,whether it could be used as an alternative method to replace the current way of quarantine treatment against citrus red mites depends on the performances of effective doses on citrus fruits.This study was conducted to explore the effects of Co-60 gamma irradiation on the nutrient composition of citrus(Shatang mandarin);selected fruits were divided into different groups and each group was irradiated at 0.0,0.2,0.3,0.4,0.5,and 0.6,respectively.And then the treated fruits were stored at 4◦C and the nutrient composition was studied in the following days.The results showed that the shelf-life could be extended when fruits were irradiated in the dose range of 0.2–0.4 kGy,while most unirradiated citrus decayed by 15 d.It also turned out that the citrus irradiated at 0.5 and 0.6 kGy were fully decayed within 45 d of refrigerated storage.The content of total soluble solids(TSS),total sugar,ascorbic acid(AA),and titratable acidity had no significant differences compare to those of the control during the 15 d storage period.Nevertheless,the activities of peroxidase(POD)and superoxide dismutase(SOD)decreased after 15 d;the improvement of storage quality and shelf life may be explained by the change of the protective enzyme activity.In conclusion,the results of citrus fruit treated with irradiation at a certain dose indicated the potential use of Co-60 gamma irradiation as a safe quarantine treatment.©2014 Beijing Academy of Food Sciences.Production and hosting by Elsevier B.V.All rights reserved.

重要性采样方法与自由能计算

分子动力学模拟与自由能计算已经在化学、生物学与材料学等领域得到广泛的应用。然而,由于在传统分子动力学模拟的时间尺度内,体系很难跨越较高的自由能能垒,在相空间内的采样大大受限,采样困难使自由能计算难以收敛。增强采样是解决这一问题的有效途径,重要性采样方法就是其中一类。本文综述了四种广泛应用的重要性采样方法——伞状采样方法、metadynamics方法、自适应偏置力方法和温度加速分子动力学方法的原理和进展,其中重点概述了自适应偏置力方法的最新发展——扩展自适应偏置力方法和扩展广义自适应偏置力方法,并对这四种重要性采样方法的优缺点进行了比较。最后,讨论和展望了重要性采样与自由能计算方法面临的挑战和前景,并提出了对自适应偏置力方法可能的改进,如与加速分子动力学(aMD)或弦方法结合以提高在高维度空间中的采样效率。

基于几何约束的蛋白质-配体准确结合自由能计算

蛋白质-配体的结合过程伴随着复杂的结构变化,在分子模拟可及的时间尺度内难以完全捕获,这使得准确估计蛋白质-配体的结合自由能十分困难.一种有效的解决途径是采用几何约束减小需要采样的构象空间,再通过后处理方式扣除约束的影响.本文综述了三种几何约束策略——漏斗状约束、球形约束和七自由度约束与自由能计算算法结合准确计算结合自由能的原理和进展,重点概述理论严谨的七自由度约束的最新进展以及与Alchemistry或重要性采样方法的联用策略,最后,讨论了如何针对不同体系选择合适的计算策略以及蛋白质-配体准确结合自由能计算在药物设计等领域中的挑战和前景,并提出了将上述方法进一步运用于研究更复杂的蛋白质-蛋白质问题的可能性.