孕甾烯酮的C-15羟基衍生物的生物合成

近年来,人们从海洋生物中分离出多羟基甾体化合物,而且发现海星中存在尤为最多[1,2],并具有较强的生理活性,这引起了人们在甾体骨架上立体选择引入羟基的极大兴趣.用化学合成方法在C-15引入羟基,反应条件要求较高,合成步骤也较复杂[3].     

Synthesis and Crystal Structure of a 3-Arylamino-3-Deoxy Sugar Derivative

1INTRODUCTION Amino sugars in which a hydroxyl group of a mo-nosaccharide is replaced by an amino group play a wide variety of important biological roles[1]and have broad applications in chemical,biochemical,medi-cinal,and pharmaceutical fields[2,3].Amino sugars are chiral synthon of azasugar and polyose,many of which are found to be potential chemotherapeutic agents for the treatment of diseases,such as diabetes and cancer,inflammation and viral infections,inclu-ding HIV[4].Particularly…     

Interpreting a period-adding bifurcation scenario in neural bursting patterns using border-collision bifurcation in a discontinuous map of a slow control variable

<正>To further identify the dynamics of the period-adding bifurcation scenarios observed in both biological experiment and simulations with the differential Chay model,this paper fits a discontinuous map of a slow control variable of the Chay model based on simulation results.The procedure of period adding bifurcation scenario from period k to period k + 1 bursting(k = 1,2,3,4) involved in the period-adding cascades and the stochastic effect of noise near each bifurcation point is also reproduced in the discontinuous map.Moreover,dynamics of the border-collision bifurcation are identified in the discontinuous map,which is employed to understand the experimentally observed period increment sequence.The simple discontinuous map is of practical importance in the modeling of collective behaviours of neural populations like synchronization in large neural circuits.     

新型烯醇醚高碳糖的自动氧化及晶体结构

自从1956年Harman在分子生物学的基础上提出自由基学说以来,经过多年研究,已经证明自由基对机体是有害的.维生素C是一个具有六碳原子的酸性多羟基化合物,其分子中的两个烯醇式羟基极易解离,释放出H+,而被氧化成脱氧抗坏血酸.这种氧化型与还原型之间的相互转变,使得它具有氧化还原性质,它的许多生理活性都与这种性质有关.维生素C作为自由基清除剂,可以直接或间接消除自由基,从而可保护生物膜完整性,改善机体功能.我们在合成高碳糖的过程中发现烯醇醚同样非常容易氧化为二醇,本文报道含有烯醇醚片断的新型高碳糖1在碱性溶液中的自动氧化反应及其所生成的笼状化合物2的晶体结构.     

Intermittent Chaotic Neural Firing Characterized by Non-Smooth Features

A chaotic firing pattern, characterized by non-smooth features and generated through the routine of intermittency from period 3, is observed in biological experiments on a neural firing pacemaker and reproduced in simulations by using a theoretical neuronal model with multiple time scales. This chaotic activity exhibits a scale law very similar to those of both the type-Ⅰ intermitteney generated in smooth systems and the type-Ⅴ intermittency in non-smooth systems.     

紫外分光光度法测定产氢颗粒污泥中聚-β-羟基丁酸酯的含量

产氢颗粒污泥中聚-β-羟基丁酸酯(PHB)的紫外检测主要包括两步:污泥的预处理和紫外分光光度测定。样品经次氯酸钠法处理后,用二氯甲烷萃取,加入5mL硫酸,水浴加热10min,在波长235nm处测量吸光度。残留的三氯甲烷蒸发60 min可除尽。PHB的质量浓度在4.0mg·L-1以内与其吸光度呈线性关系,检出限(3s/k)为0.023mg·L-1。方法用于产氢颗粒污泥的分析,加标回收率在90.5%~108%之间,测定值的相对标准偏差(n=6)小于2%。