Conformational Analysis,RIS Models and Single‐Chain Properties of Structurally Modified Polycarbonates, 1. Effect of Cyclohexyl and Phenyl Ring Substitutions

Conformational properties of segments and chains of structurally different polycarbonates are investigated in detail. Conformational analysis and rotational isomeric state (RIS) models for some of the polycarbonates and single‐chain properties of all the polycarbonates are reported here for the first time. Substitution of the methyl group on the bisphenol phenyl rings results in increased energy barriers to rotations as well as changes in positions of local minima, compared to the case without substitutions. Conformational structure about the isopropylidene linkage C_α atom is not altered by ortho methyl substitutions on the rings. Substitution by a cyclohexyl ring rigidly attached to the C_α atom restricts conformational mobility within the bisphenol unit. Rotational flexibility of the phenyl–oxygen bond is hindered by additional substitutions on the cyclohexyl ring. The carbonate group prefers the trans–trans conformation in all the polycarbonates. The energy difference between the cis–trans and trans–trans states of the carbonate group is lowered by the ortho methyl substituent on the phenyl rings. There is a reduction in 〈R²〉, 〈S²〉, and C_n accompanying the substitutions. The introduction of other substituents on a cyclohexyl polycarbonate results in an increase in all chain dimensions including the persistence length. Also, the cyclohexyl or trimethylcyclohexyl substituents do not significantly alter the overall average shape of the chains. Substitutions both on the phenyl rings and at the isopropylidene linkage lead to a compaction of the polymer chain, but the effect is more pronounced when due to substituents on phenyl rings.     

具有新型梯形双金属链的铕羧酸-膦酸配合物的晶体结构及其发光性质研究

采用溶剂热反应,成功合成一例基于羧酸-膦酸配体的铕配位聚合物,[Eu(5-pnc)(H₂O)_0.5]·H₂O(1)。晶体结构分析表明,聚合物1具有三维超分子网络结构,其中二聚体[Eu₂(μ3-O)₂]通过两个O-P-O和两个O-C-O单元构成梯形双金属链,沿着a轴无限延伸,这些梯形双金属链通过有机膦酸配体交联。研究了配位聚合物1的热稳定性、紫外可见光谱和发光性能。     

Unfolding pathway and its identifiability in heterogeneous chains of bistable units

We investigate the behavior of a chain of bistable units with an heterogeneous distribution of energy jumps between the folded and unfolded states. For homogeneous chains, loaded by soft or hard devices, all units at each switching occurrence have the same probability to unfold and it is therefore impossible to identify an unfolding pathway. Conversely, the heterogeneity represents a quenched disorder from the statistical mechanics point of view, and is able to break the symmetry eventually generating an unfolding pathway. We prove that the most probable pathway is realized by arranging the energy jumps in ascending order. Hence, the mechanics of this system is able to implement a statistical sorting procedure. We quantitatively evaluate the identifiability of the obtained unfolding pathway in terms of the variance of the heterogeneous energy jumps and the temperature. This concept is applied to both deterministic and random distributions of energy jumps within the chain.     

镓原子链的结构稳定性和电子结构

The structural stabilities and electronic structures of Ga atomic chains are studied by the first-principles plane wave pseudopotential method based on the density functional theory. The present calculations show that gallium can form planar chains in linear-, zigzag- and ladder-form one-dimensional structures. The most stable one among the studied structures is the zigzag chain with a unit cell rather close to equilateral triangles with four nearest neighbors, and all the other structures are metastable. The relative structural stability, the energy bands and the charge densities are discussed based on the ab initio calculations and the Jahn-Teller effect.     

Targeted Synthesis of 3,3′-, 3,4′- and 3,6′-Phenylpropanoid Sucrose Esters

In this study, we report on an orthogonal strategy for the precise synthesis of 3,3′-, 3,4′-, and 3,6′-phenylpropanoid sucrose esters (PSEs). The strategy relies on carefully selected protecting groups and deprotecting agents, taking into consideration the reactivity of the four free hydroxyl groups of the key starting material: di-isopropylidene sucrose 2. The synthetic strategy is general, and potentially applies to the preparation of many natural and unnatural PSEs, especially those substituted at 3-, 3′-, 4′- and 6′-positions of PSEs.     

用遗传算法快速提取近红外光谱特征区域和特征波长

提出了一种遗传区间偏最小二乘法(GA-iPLS),并用该方法快速提取苹果糖度近红外光谱的特征区域,在此基础上采用遗传偏最小二乘法(GA-PLS)提取苹果糖度近红外光谱的特征波长,进行苹果糖度预测。结果表明,整个光谱等分为40个子区间,遗传区间偏最小二乘法能快速寻找出5个特征子区间(第4,6,8,11,18号);在5个特征子区间的基础上用遗传偏最小二乘法继续优化,从中提取44个特征波长。建立在5个特征子区间和44个特征波长上的偏最小二乘法模型精度均优于全光谱偏最小二乘法模型,对预测集的预测相关系数提高了近10%;且模型得到了很大的简化,用于建模的主因子数减少了7个。这些结果表明,用这两种方法不但可以建立简洁、数据运算量少的模型,还可以快速地提取近红外光谱的特征区域和特征波长。     

Combined Molecular Dynamics Simulation and Rouse Model Analysis of Static and Dynamic Properties of Unentangled Polymer Melts with Different Chain Architectures

Chain architecture effect on static and dynamic properties of unentangled polymers is explored by molecular dynamics simulation and Rouse mode analysis based on graph theory. For open chains, although they generally obey ideal scaling in chain dimensions, local structure exhibits nonideal behavior due to the incomplete excluded volume(EV) screening, the reduced mean square internal distance(MSID) can be well described by Wittmer' theory for linear chains and the resulting chain swelling is architecture dependent, i.e., the more branches a bit stronger swelling. For rings, unlike open chains they are compact in term of global sizes. Due to EV effect and nonconcatenated constraints their local structure exhibits a quite different non-Gaussian behavior from open chains, i.e., reduced MSID curves do not collapse to a single master curve and fail to converge to a chain-length-independent constant, which makes the direct application of Wittmer's theory to rings quite questionable.Deviation from ideality is further evidenced by limited applicability of Rouse prediction to mode amplitude and relaxation time at high modes as well as the non-constant and mode-dependent scaled Rouse mode amplitudes, while the latter is architecture-dependent and even molecular weight dependent for rings. The chain relaxation time is architecture-dependent, but the same scaling dependence on chain dimensions does hold for all studied architectures. Despite mode orthogonality at static state, the role of cross-correlation in orientation relaxation increases with time and the time-dependent coupling parameter rises faster for rings than open chains even at short time scales it is lower for rings.     

烟草中糖类物质的高效毛细管电泳-安培检测研究

将高效毛细管电泳－安培检测技术（ＨＰＣＥ－ＡＤ）用于不同烟草样品中糖类物质的测定。在 １×１０－６ｍｏｌ／Ｌ～１×１０－３ ｍｏｌ／Ｌ范围内,存在良好的线性关系,葡萄糖、果糖、蔗糖和麦牙糖的检测限均小于 ５．０ ×１０－７ｍｏｌ／Ｌ,结果令人满意。     

Cn单超球上全纯映射的单叶性准则II

本文利用从属链方法给出一个一般性判别全纯映射为单叶的准则．其中,含有一个全纯映射与一个实函数,通过其全纯映射以及实函数的不同选取可获得一批具体的单叶性准则,其中的一些是已有著名结果的推广、另一些是新的结果,     

反射光谱装置及定量分析设计

设计了一种反射光谱测量装置。该装置由光纤传导并用于定量分析。通过测定还原糖与斐林试剂反应生成的Cu₂O,建立测定还原糖的反射光谱分析方法。还原反应在微型反应池中进行,生成鲜红色Cu₂O,光纤探头直接测定降于池底的沉淀。探讨了该方法的基本原理、影响因素及测定条件。该方法具有操作方便,灵敏度高,试剂用量少等优点。还原糖在20～120 μg范围内呈良好的线性关系,用于实际样品测定,结果满意。