月桂胺盐酸晶体相变的红外光谱研究

在290-365K的温度区间内考察了月桂胺盐酸盐晶体红外光谱随温度的变化规律。结果表明:月桂胺盐酸盐在339K发生了固-固结构相变, 该相变的预相变起始点为327K。在327K以下的低温相中, 晶体中分子的碳氢链以高度有序的全反式构象存在, 极性头部的三个N-H-Cl氢键是不等价的。在327-339K的中间过渡相, 碳氢链中出现了旁式构象, 分子链间相互作用减弱。不等价的N-H-Cl氢键的差异减小。在339K以上的高温相中, 分子旁式链构象的增多导致了分子链横向堆积无序性的明显增加, 三个N-H-Cl氢键已变得等价。     

月桂胺盐酸晶体相变的红外光谱研究

在290-365K的温度区间内考察了月桂胺盐酸盐晶体红外光谱随温度的变化规律。结果表明:月桂胺盐酸盐在339K发生了固-固结构相变, 该相变的预相变起始点为327K。在327K以下的低温相中, 晶体中分子的碳氢链以高度有序的全反式构象存在, 极性头部的三个N-H-Cl氢键是不等价的。在327-339K的中间过渡相, 碳氢链中出现了旁式构象, 分子链间相互作用减弱。不等价的N-H-Cl氢键的差异减小。在339K以上的高温相中, 分子旁式链构象的增多导致了分子链横向堆积无序性的明显增加, 三个N-H-Cl氢键已变得等价。     

氯化癸铵的低频拉曼光谱研究

在290—340 K的温度范围内考察了氯化癸铵的低频拉曼光谱, 指认了210 cm~(-1)附近的谱带为分子烷基链的纵向声子振动带, 低于100 cm~(-1)的谱带为晶格振动带, 结果表明DeAC晶体存在313 K和321 K两个结构相变。在313 K以下的低温相, DeAC分子以完全有序的全反式链构象存在, 在313—321 K的中间相, 分子烷基链出现了旁式构象, 高温相与中间相相比主要是分子链横向堆积有序度明显降低, 而分子链构象特征无明显差异。     

十六烷基三甲基溴化铵水溶液热致相变的红外光谱研究

在280～320K的温度范围内考察了30％十六烷基三甲基溴化铵水溶液的红外光谱随温度的变化。结果表明该体系的凝聚胶-液晶相转变温度为300K。在300K以下的凝聚胶相,分子的极性头部基团处于高度“固定”的状态,分子的碳氢链以有序的相互平行方式排列,极性头与碳氢链之间有一定的倾斜角。在300K以上的液晶相,极性头内部CH_3-(N~+)基团以及整个极性头与碳氢链之间发生了旋转,碳氢链变为以六方亚晶胞填充形式存在,旦扭曲式构象异构体数量显著增多,极性头与碳氢链之间已不存在倾斜角,分子的亲水极性头和疏水碳氢链部分都处于“融化”状态。     

菌类多糖链构象及其表征方法研究进展

概述了菌类多糖在溶液中链构象及其表征方法的研究进展.主要报道从各种真菌(香菇、茯苓、灵芝、木耳、黄单胞菌、裂褶菌等)中提取的多糖在溶液中的分子量、分子形态和尺寸,即链构象.同时介绍多糖链构象对生物活性的影响,并且指出多糖刚性链带电基团及适量分子量有利于促进它与免疫细胞上受体结合,从而抑制肿瘤细胞增殖.由此表明,多糖链构象的研究对弄清其生物功能和推动生命科学发展十分重要.多糖在溶液中主要以无规线团、双螺旋、三螺旋、蠕虫状、棒状链以及聚集体构象存在,它取决于单糖组成、糖苷键、支链结构以及分子内和分子间作用力.测定链构象的方法主要包括光散射、黏度、显微技术(透射电镜,扫描电镜以及原子力显微镜)、微量热法和小角X-射线散射等.此外,介绍了多糖溶液理论以及计算链构象参数的表达式.     

链缠结对聚合物结晶行为的影响

链缠结是聚合物分子链相互作用的一种形式 ,它主要影响分子链的长程运动 .自链缠结的概念被提出以来 ,人们对聚合物粘弹性、流变行为和网络平衡力学等进行了理论研究和实验验证 .然而 ,在聚合物结晶领域 ,链缠结对结晶过程的影响一直存在着很大的争论 .Flory等 [1] 认为 ,聚合物结晶时分子链根本没有足够的时间进行构象调整 ,分子链进入晶格后 ,使大量的缠结链段被挤入非晶区 ,并由此建立了聚合物结晶“插线板”模型 .Hoffman等 [2 ]根据单根分子链从过冷熔体“卷饶”到晶体前沿所需的时间进行估算 ,结果比 Flory预言的快约 3～ 5个数量级…     

聚肽分子链构象转变研究

聚肽分子链在一定的条件下可发生右旋分子链构象与左旋分子链构象间的构象转变 .文中提出了一个有关这一现象的统计理论解释 ,理论包含了两个重要的参数γ、ρ .γ与右旋和左旋分子链构象间能量差别有关 ;ρ与在左旋分子链段中启始一个右旋构象的结构单元所需能量有关 .进一步考虑了体系中酸分子存在对构象转变的影响 ,以解释新近发现的聚肽左、右旋多重分子链构象转变现象 .此外 ,运用核磁共振 (NMR)手段还对这一现象做了进一步的研究 .通过与实验结果和文献中报告的数据比较 ,证明这一理论可以很好地解释聚肽分子链中发生的左、右旋分子链构象转变     

变温傅里叶红外光谱技术研究硬脂酸C-H伸缩振动

采用傅里叶红外光谱技术研究了温度对于硬脂酸C-H伸缩振动、分子脂肪链构象改变和分子间作用力的影响。运用变温红外技术在293~393K范围内,分别测定了硬脂酸C-H的一维红外光谱、二阶导数红外光谱、四阶导数红外光谱和去卷积红外光谱。结果表明:1在293~333K范围内,一维红外光谱中2 965,2 870cm-1附近的弱吸收谱带分别归属于甲基的不对称伸缩振动模式νas(-CH3)和对称伸缩振动模式νs(-CH3),相应的导数光谱及去卷积红外光谱能提高一维红外谱的分辨率;2在293~333K范围内,硬脂酸脂肪链处于全反式构象,在348~353K范围内,硬脂酸分子脂肪链构象由全反式构象向无序构象转变;3随着测量温度的升高,硬脂酸分子间的作用力不断降低。     

菌类多糖链构象及其表征方法研究进展 （专题报道）

 概述了菌类多糖在溶液中链构象及其表征方法的研究进展.主要报道从各种真菌（香菇、茯苓、灵芝、木耳、黄单胞菌、裂褶菌等）中提取的多糖在溶液中的分子量、分子形态和尺寸,即链构象.同时介绍多糖链构象对生物活性的影响,并且指出多糖刚性链带电基团及适量分子量有利于促进它与免疫细胞上受体结合,从而抑制肿瘤细胞增殖.由此表明,多糖链构象的研究对弄清其生物功能和推动生命科学发展十分重要.多糖在溶液中主要以无规线团、双螺旋、三螺旋、蠕虫状、棒状链以及聚集体构象存在,它取决于单糖组成、糖苷键、支链结构以及分子内和分子间作用力.测定链构象的方法主要包括光散射、黏度、显微技术（透射电镜,扫描电镜以及原子力显微镜）、微量热法和小角X-射线散射等.此外,介绍了多糖溶液理论以及计算链构象参数的表达式.     

癸胺盐酸盐分子构象的拉曼光谱

用拉曼光谱考察了物态变化、水溶液浓度、温度和稀土离子等对癸胺盐酸盐分子构象的影响。结果表明固态标题化合物分子以有序的全反式链构象存在,在大于临界胶束浓度的水溶液中分子以无序的旁式链构象存在;增加浓度、升高温度和添加稀土离子都使得链的扭曲和无序程度增加。     

四氯合锌酸二(正十一烷基铵)晶体相变的Raman光谱

用Raman光谱研究了[n-C~11H~23NH~3]~2ZnCl~4(简记为C~nZn)配合物的固-固相变。结果表明, 配合物产生的固-固相变主要与烷烃链的堆积结构和分子构象变化有关, 在T~cl=25℃的相变是由于烷烃链的侧向堆积和分子构象的有序到部分无序变化。在中间相, 分子链局部产生旁式构象。在T~c2=87℃的相变主要来源于烷烃链从部分构象有序到完全无序的变化, 高温相形成了构象完全无序相, 相应于烷烃链的"熔化"。     

Relation between packing density and thermal transitions of alkyl chains on layered silicate and metal surfaces

Self-assembled layers of alkyl chains grafted onto the surfaces of layered silicates, metal, and oxidic nanoparticles are utilized to control interactions with external media by tuning the packing density of the chains on the surface, head group functionality, and chain length. Characterization through experiment and simulation shows that the orientation of the alkyl layers and reversible phase transitions on heating are a function of the cross-sectional area of the alkyl chains in relation to the available surface area per alkyl chain. On even surfaces, a packing density less than 0.2 leads to nearly parallel orientation of the alkyl chains on the surface, a high degree of conformational disorder, and no reversible melting transitions. A packing density between 0.2 and 0.75 leads to intermediate inclination angles, semicrystalline order, and reversible melting transitions on heating. A packing density above 0.75 results in nearly vertical alignment of the surfactants on the surface, a high degree of crystalline character, and absence of reversible melting transitions. Curved surfaces can be understood by the same principle, taking into account a local radius of curvature and a distance-dependent packing density on the surface. In good approximation, this simple model is independent from the length of the alkyl chains (a minimum length of C10 is required to form sufficiently distinctive patterns), the chemical nature of the surface, and of the surfactant head group. These structural details primarily determine the functionality of alkyl modified surfaces and the temperature of thermal transitions.     

RAMAN STUDIES OF STRUCTURAL PHASE TRANSITION IN[n-C_(11)H_(28)NH_8]_2ZnCl_4

The perovskite type of compound [n-C_(11)H_(23)N_3]_2ZnCl_4(abr.C_(11)Zn)exhibits two solid-solid phasetransitions at T_(c1)=298.7 K and T_(c2)=360.1 K.A temperature dependence study of Raman spectra of C_(11)Znprovides the evidence of occurence of the structural phase transition related to the dynamics of thealkylammonium ions.The room temperature phase is ordered and contains the all-trans alkyl chains.Theintermediate temperature phase presents a partial conformational disorder and liquidlike state of allconformational disorder occurs at high-temperature phase.     

Disproportionation of pyrazine in NH+...N hydrogen-bonded complexes: new materials of exceptional dielectric response

Centrosymmetric pyrazinium NH+...N bonded complexes allow their dielectric properties to be analyzed separately from the bulk ferroelectric polarization observed in the noncentrosymmetric DABCO monosalts. The method of dielectric permittivity measurements has been employed for monitoring polarization fluctuations generated by proton transfers in the NH+...N bonded linear polycations. The revealed dielectric response of [C4H5N2]+BF4- and [C4H5N2]+ClO4- cannot be reconciled with the centrosymmetric symmetry of their structures, but suggests formation of polar defects or nanoregions. Unique transformations of the pyrazine [C4H5N2]+BF4- complex between linear NH+...N hydrogen-bonded polycationic aggregates antiparallel in phase gamma, perpendicular chains in phase beta, and with NH+...N bonds broken in phase alpha have been observed. The [C4H5N2]+ClO4- and [C4H5N2]+BF4- complexes as grown at 290 K are isostructural in orthorhombic phase , space group Pbcm, with linear polycationic chains arranged antiparallel. On heating, the tetrafluoroborate and perchlorate salts each undergoes two first-order phase transitions at similar temperatures about 340-360 K, while on cooling only one phase transition has been observed. An extremely unique sequence of two phase transitions subsequently lowering the symmetry of the [C4H5N2]+BF4- crystal when temperature is increased has been evidenced: the orthorhombic phase heated above 343 K transforms into the monoclinic C2/c-symmetric phase beta, in which the NH+...N bonded linear chains assume perpendicular arrangement; and at about 353-357 K the anions and cations adopt a typical ionic-crystal packing without homonuclear NH+...N hydrogen bonds in a still lower-symmetry monoclinic P21/n-symmetric structure. The exceptional perpendicular arrangement of the linear NH+...N bonded chains in phase beta constitutes a unique system where polarization of small regions can assume various orientations within a plane, depending on the H+ sites. No phase transitions or anomalous dielectric response were observed in the NH+...O bonded [C4H5N2]+NO3- complex. The unprecedented structure-property relations of the pyrazinium complexes fully confirm the role of the NH+...N bond transformations for the dielectric response of analogous DABCO ferroelectrics.     

四氯合铜酸二烷基铵相变的热分析和红外光谱

用DSC和TG研究了(n-C_nH_(2n+1)NH_3)_2CuCl_4(n=7-12)(记为C_nM)配合物的热稳定性和固-固相变。由红外光谱讨论了C_9Cu三个相的性质。发现C_nM的热稳定性呈奇偶效应; 主相变峰温随链长增长而升高; 相变总ΔH和ΔS也随链增长而加大; 当n≤9时, 高温相为部分无序相; 而n≤10时, 高温相为构象无序相。C_9Cu的主相变主要源自链间堆积结构变化。而在307.7 K的相变主要与烃链有序-无序变化有关。     

Adsorption mechanism in reversed-phase liquid chromatography. Effect of the surface coverage of a monomeric C18-silica stationary phase

The effect of the bonding density of the octadecyl chains onto the same silica on the adsorption and retention properties of low molecular weight compounds (phenol, caffeine, and sodium 2-naphthalene sulfonate) was investigated. The same mobile phase (methanol:water, 20:80, v/v) and temperature (T = 298 K) were applied and two duplicate columns (A and B) from each batch of packing material (neat silica, simply endcapped or C1 phase, 0.42, 1.01, 2.03, and 3.15 micromol/m2 of C18 alkyl chains) were tested. Adsorption data of the three compounds were acquired by frontal analysis (FA) and the adsorption energy distributions (AEDs) were calculated using the expectation-maximization method. Results confirmed earlier findings in linear chromatography of a retention maximum at an intermediate bonding density. From a general point of view, the saturation capacity of the adsorbent tends to decrease with increasing bonding density, due to the vanishing space intercalated between the C18 bonded chains and to the decrease of the specific surface area of the stationary phase. The equilibrium constants are maximum for an intermediary bonding density (approximately 2 micromol/m2). An enthalpy-entropy compensation was found for the thermodynamic parameters of the isotherm data. Weak equilibrium constants (small deltaH) and high saturation capacities (large deltaS) were observed at low bonding densities, higher equilibrium constants and lower saturation capacities at high bonding densities, the combinations leading to similar apparent retention in RPLC. The use of a low surface coverage column is recommended for preparative purposes.     

Structure and phase transitions in poly[bis-(2,2,3,3-tetrafluoropropoxy) phosphazene]

The structure and phase transitions in poly[bis-(2,2,3,3-tetrafluoropropoxy)phosphazene] have been studied by differential scanning calorimetry (DSC) and x-ray diffraction. Two crystalline phases and one mesomorphic phase are found, denoted I, II, and III, respectively. These phases convert reversibly one into the other on heating and cooling. The Phase I–Phase II transition occurs in a temperature range from 5 to 30°C whereas the Phase II mesophase (Phase III) transition proceeds above 80°C. Heats of transitions are measured to be about 29.0 J/g and 3.6 J/g, respectively. Crystalline Phase I is characterized by a monoclinic unit cell with the parameters: α = 24.4 Å, b = 9.96 Å, c = 4.96 Å, γ = 123°. The axes of both chains, traversing the unit cell, are directed along the “c” axis, the main chains having cis-trans conformation. Phase I is the common crystalline structure for the main chain and side chains. The structure of Phase II is controlled mainly by packing of the side chains. Transition of Phase II into mesomorphic Phase III is accompanied with distortion of packing of the side chains. Only regular packing of the main chains of macromolecules in the plane perpendicular to their axes exists in Phase III. Mesomorphic phase III is stable up to the degradation temperature of the polymer. A significant effect of stress on the Phase II–III transition in oriented samples was found.     

Positron annihilation and phase transitions in argon intercalated n-nonadecane

Positron annihilation method was applied to study phase transitions in argon intercalated n-nonadecane. Particular phases are easily recognizable due to large differences in ortho-positronium lifetimes. It was found that melting temperature is a non-monotonous function of pressure. In the range of temperatures 301.5–303 K with the rise of pressure the phase sequence rotator – liquid–rigid crystal was observed. After the pressure induced transition to the rigid phase the sample structure became porous due to escape of dissolved argon. The triple point in intercalated samples is located at much lower pressure and temperature than in pure ones. An admixture of alkane with other length of carbon chain increases the ortho-positronium lifetime in rigid phase, indicating Ps location in the interlamellar gaps.