鞘氨醇与DPPC, DPPE单层膜的热力学特性及形态观察

鞘氨醇(sphingosine)是生物体内合成鞘脂的母体化合物, 是生物膜中的重要组分之一. 通过分析表面压力和平均分子面积(π-A)等温线数据分别研究了鞘氨醇与二棕榈酰基磷脂酰胆碱(DPPC)和二棕榈酰基磷脂酰乙醇胺(DPPE)二元组分单层膜的热力学特性, 并在恒定膜压下制备不同摩尔比例的混合脂膜用原子力显微镜进行观测. 实验结果表明: (1)鞘氨醇与DPPC组成的系统中, XD-Sph＝0.2, 0.4, 0.6时, 过量分子面积与过量吉布斯自由能在所研究的表面压力下表现为负值, 而当XD-Sph＝0.8时, 表现为正值; (2)鞘氨醇与DPPE组成的系统中, 当表面压力 π＜25 mN•m－1时, 过量分子面积与过量吉布斯自由能在所研究的组分比例下表现为负值, 当π≥25 mN•m－1时为正值. 混合单层膜的分子面积与表面吉布斯自由能决定了分子间的相互作用, 当为负值时分子间相互作用表现为吸引力, 出现凝聚现象; 为正值时分子间相互作用表现为排斥力, 促使单层膜出现相分离现象. 过量吉布斯自由能值越小, 单层膜的热稳定性越高. 弹性系数曲线分析和AFM图片观测进一步验证了理论分析的结果.     

聚吡咯薄膜的电特性

含有不同的链长的w-吡咯烷基二甲基氯硅烷作为粘合剂通过自组装（SAMs）吸附于二氧化硅表面,然后聚吡咯膜化学沉积于该粘合剂修饰的表面。化学沉积的聚吡咯膜的表面形貌用扫描电镜（SEM）及原子力显微镜（AFM）表征。除短链外不同链长的粘合剂对聚吡咯膜的厚度影响不大。聚吡咯膜的电特性用电流-电压表征。结果显示电流与粘合剂的链长无关。电特性表明载流子迁移率为1.4 ´ 10-4 cm2×V-1.s –1。     

基于顺丁烯二酸和N,N螯合配体构筑的两个新型三维氢键型超分子体系: 结构、磁性质与理论化学研究

通过调变辅助配体,设计合成了两个新的Cu(II)化合物Cu(mal)(tap)(H2O)]n(1) 和 [Cu2(mal)2(bpym)2(H2O)2]·2H2O(2) (其中H2mal =顺丁烯二酸, tap=1,4,5,8-四氮杂菲,bpym=2,2′-联嘧啶),并用X-射线单晶衍射技术对其进行了结构表征。化合物1是一维弓背状配位聚合链通过氢键和π–π 堆积作用拓展形成的三维超分子体系;化合物2 展现一个具有六连接α-Po(46)拓扑的3D→3D二重穿插结构。此外根据晶体结构,利用Gaussian 03W中的DFT方法对化合物1和2进行几何构型优化,同时,用DFT-BS方法研究了两个化合物的磁性,结果表明计算结果与实验结果吻合,它们均具有弱的反铁磁相互作用。     

4-[(E)-2-(3,4,5-三甲氧基苯基)乙烯基]苯氧基羧酸酯的合成及抗肿瘤活性研究

二苯乙烯的多种衍生物表现出一系列的生理活性,如3,4,5.三羟基二苯乙烯(白藜芦醇)具有预防心脏病,抑制血小板凝聚,调控脂质和脂蛋白代谢,抗氧化及对癌症的治疗等作用[1-3].     

稀碱金属铷、铯盐-混合溶剂多元体系相平衡研究进展

稀碱金属铷、铯资源的成功开发,需以相应的相平衡与相图研究成果为指导,开展稀碱金属盐-混合溶剂体系相平衡的研究,对这些金属盐的提纯开发利用具有重要的意义.本文主要从不同的铷、铯盐-混合溶剂三元及四元体系两个方面,归纳总结了此类体系的相平衡研究进展,探讨了研究中存在的一些问题,为深入研究稀碱金属-混合溶剂体系的相平衡奠定了基础.     

5-氟胞嘧啶气相及水助质子转移异构化的理论研究

采用密度泛函B3LYP/6-311G**方法,对6种5-氟胞嘧啶异构体孤立分子的稳定性及质子转移引起的酮式-烯醇式、氨基式-亚胺式互变异构反应机理进行了计算研究,获得了零点能、吉布斯自由能及质子转移过程的反应焓、活化能、活化吉布斯自由能和速率常数等参数.计算结果表明,气相中烯醇-氨基式FC4是最稳定的异构体.分子内质子转移设计了FC1→FC2和FC1→FC6两条通道,分别标记为P(1)和P(2),各通道速控步骤的活化能和速率常数分别为155.9 kJ·mol-1,4.70×10-15 s-1和173.1 kJ·mol-1,1.41×10-18 s-1.水助催化时,相应通道P(3) 和P(4) 速控步骤的活化能和速率常数分别为51.0 kJ·mol-1,1.41×103 s-1和88.2 kJ·mol-1,4.53×10-3 s-1.可见,水分子的加入极大地降低了质子转移的活化能垒.另外发现,水分子参与形成协同的双质子转移机理比水助单质子转移机理更利于降低活化能垒.     

Probing the microenvironment of surface-attached pyrene formed by a thermo-responsive oligomer

We have constructed a novel molecular assembly attached to quartz, oxidized silicon and indium-doped tin oxide coated substrates, where a tethered pyrene derivative is co-immobilized with oligo-N-isopropyl acrylamide (oligo-NIPAM). The addition of tethered oligo-NIPAM to the adlayer creates two different, temperature-dependent microenvironments for the surface-bound pyrene. X-ray photoelectron spectroscopy (XPS) and ellipsometry measurements demonstrate the covalent attachment of both oligo-NIPAM and pyrene in our adlayers. Contact angle results confirm the thermo-responsive nature of the oligo-NIPAM on the substrate surface. Steady-state fluorescence data show that the presence of oligo-NIPAM moieties reduces the extent of pyrene excimer formation and provides different environments for the chromophore at temperatures above and below the phase transition. Fluorescence lifetime decay data on surface-bound pyrene are biexponential, consistent with multiple local environments, regardless of whether tethered oligo-NIPAM is present or not. Quenching studies reveal that we can manipulate the sensing properties of this new film simply by adjusting the conformations of oligo-NIPAM.     

On some testable conditions for excitability and transparency of a class of time-delay systems with point delays

This article is concerned with the excitability of positive linear time-invariant systems subject to internal point delays. It is proved that the excitability independent of delay is guaranteed if an auxiliary delay-free system is excitable. Necessary and sufficient conditions for excitability and transparency are formulated in terms of the parameterization of the dynamics and control matrices and, equivalently, in terms of strict positivity of a matrix of an associate system obtained from the influence graph of the original system. Such conditions are testable through simple algebraic tests involving moderate computational effort.     

On the index of Fredholm pairs of idempotents

Using the technique of block-operators, in this note, we prove that if P and Q are idempotents and （P - Q）^2n＋1 is in the trace class, then （P - Q）^2m＋1 is also in the trace class and tr（P - Q）^2m＋1 = dim（k（P） ∩ k（Q）^⊥） -dim（k（P）^⊥ N k（Q））, for all m ≥ n. Moreover, we prove that dim（k（P）∩ k（Q）^⊥） = dim（k（P）^⊥ ∩k（Q）） if and only if there exists a unitary U such that UP = QU and PU = UQ, where k（T） denotes the range of T. Keywords Fredholm, orthogonal projection, positive operator     

Effects of population dispersal and impulsive control tactics on pest management

In this paper, we firstly consider a Lotka–Volterra predator–prey model with impulsive constant releasing for natural enemies and a proportion of killing or catching pests at fixed moments, and we have proved that there exists a pest-eradication periodic solution which is globally asymptotically stable. Further, we extend the model for the population to move in a two-patch environment. The effects of population dispersal and impulsive control tactics are investigated, i.e. we chiefly address the question of whether population dispersal is beneficial or detrimental for pest persistence. To do this, some special cases are theoretically investigated and numerical investigations are done for general case. The results indicate that for some ranges of dispersal rates, population dispersal is beneficial to pest control, but for other ranges, it is harmful. These clarify that we can get some new effective pest control strategies by controlling the dispersal rates of pests and natural enemies.