Isotropic cubic phase of 4-n-pentadecyloxy-3-nitrobiphenyl4-carboxylic acid (ANBC-15): DSC, microscopic and dynamic viscoelastic studies

The phase behaviour of 4-n-pentadecyloxy-3-nitrobiphenyl-4-carboxylic acid (ANBC-15) was investigated by differential scanning calorimetry, polarizing optical microscopy, and dynamic viscoelastic measurements. The phase sequence for the virgin sample of ANBC-15 is crystalsmectic C (SmC)-cubic (D)-smectic A (SmA)-'structured liquid' (I1)-isotropic liquid (I2) on first heating. It was found that the appearance of the D phase on the second heating depends on the top temperature of the first heating. It was also shown that the D phase is formed on heating when the preceding SmC phase is 'solid-like' from the viscoelastic point of view, i.e. storage modulus (G) loss modulus (G) at 62.8 rad sec -1, while the 'liquid-like' SmC phase is transformed directly into the SmA phase without showing the D phase on heating. The isothermal frequency scans at a temperature in the D phase showed the existence of a cross-over point, G G , with G G in the lower frequency side, suggesting a structural fluctuation of the D phase. These results are ascribed to the molecular structure of ANBC-15, which has a critical alkoxy chain length in ANBC series.     

吲哚环衍生物在直链淀粉柱上的拆分

选用不同的醇改性剂,在自制的直链淀粉-三(3,5-二甲基苯基氨基甲酸酯)(ADMPC)手性固定相上,对2种吲哚环衍生物对映体进行了手性拆分研究,并考察了样品的保留时间和立体选择性.     

Polymorphism of even-numbered carbon atom n-alkanes revisited through topological P-T diagrams

The phase relationships involving the metastable orthorhombic (R(I)) phase and the stable triclinic (T) phase were established for even-numbered carbon atom n-alkanes in the range of 8-20 carbon atoms. It is shown that the R(I) phase behaves monotropically whatever the pressure and temperature (i.e., the R(I) phase exhibits no stable pressure-temperature (P-T) region). Then, the incidence of the overall monotropic behavior of the R(I) phase on the construction of the temperature-composition (T-x) phase diagrams involving at least one even member was examined through four temperature-molar fraction (T-x) phase diagrams. Discussion on the location of the R(I)-T-vapor (upsilon) triple points in the P-T diagrams of this series of n-alkanes was determined and extended to higher even members.     

X-ray diffraction and Raman studies of the CuGeO3(III)-(IV) transformation under high pressures

Both X-ray diffraction and Raman spectroscopy measurement were carried out on the same powder sample of CuGeO(3)(III) in a diamond anvil cell to high pressures at room temperature. The phase transformation of (III)-(IV) phase was observed at about 7GPa with both methods and the results were also in accord with previous powder diffraction and Raman measurements, respectively. However, the powder diffraction data were strikingly different from those reported in a recent single-crystal study on the phase (III). It is, therefore, evident that the phase transformations in CuGeO(3)(III) would be as complicated as those in CuGeO(3)(I) and that the monoclinic phase obtained from single-crystal phase (III) at approximately 7GPa is not the phase (IV) previously observed but rather a new phase (IVa) in CuGeO(3).     

聚4-甲基-5-乙烯基噻唑键合硅胶柱的选择性研究

 较为系统地研究了聚4甲基5乙烯基噻唑键合硅胶固定相(PMVCAphase)与C18,C8及苯基柱在反相色谱中甲醇水体系下的选择性差别。结果表明,该固定相与常用反相色谱固定相有相似性,显示了一般反相色谱固定相填料的特性;另一方面,又由于其特殊结构,更多地显示了其在反相色谱上的特殊选择性。     

Comparison of common mobile‐phase volume markers with polar‐group‐containing reversed‐phase stationary phases

A systematic study of the behavior of several common mobile‐phase volume markers using traditional and polar‐group‐containing reversed‐phase stationary phases is presented. Examined mobile‐phase volume markers include two neutral molecules, uracil and thiourea, concentrated (0.10 M) and dilute (0.0001 M) KNO₃, and D₂O. Mobile‐phase volumes are examined over the entire reversed‐phase mobile‐phase range of 100% water to 100% methanol or acetonitrile. The behavior of these mobile‐phase volume markers is compared with a maximum theoretical value (i.e. the void volume), as determined by pycnometry. The data suggest that: (i) uracil begins to fail as a mobile‐phase volume marker in mobile phases below about 40% strong solvent for polar group containing phases; (ii) in nearly all cases, the mobile‐phase volume measured dynamically is smaller than the pycnometric void volume; (iii) a significant dependence of measured mobile‐phase volume on salt concentration is seen on the polar endcapped phase, which is not observed on the traditional and embedded polar group phase; and (iv) D₂O does not work well as a mobile‐phase volume marker with polar‐group‐containing phases, possibly due to interaction with the stationary phase polar group.     

Comparison of liquid chromatographic behaviors on N-methylimidazolium functionalized ZrO(2)/SiO(2)-4 and N-methylimidazolium functionalized SiO(2) stationary phases

A new stationary phase N-methylimidazolium functionalized ZrO(2)/SiO(2)-4 (Zr/SilprMim) has been prepared. The chromatographic property of this stationary phase is investigated by ion chromatography (IC) with inorganic and organic anions, and normal phase HPLC with basic compounds and hydroxybenzenes. The effects of pH and the strength of Lewis base of eluent on separation of anions are studied. This new stationary phase is also compared with a N-methylimidazolium functionalized SiO(2) stationary phase (SilprMim). The results show that this new stationary phase can be used in analysis of inorganic anions with great prospects. At the same time, successful separations of some organic anions can be obtained by using phosphate buffer solution as mobile phase. This new stationary phase also has a distinct advantage in the separation of basic compounds in normal phase. But due to the presence of Lewis acid sites on the surface of ZrO(2)/SiO(2)-4, Lewis bases such as hydroxybenzenes adsorb very strongly on this new stationary phase, and Lewis acid sites can be masked or modified by the eluent that contain Lewis base groups.     

Vesicle Phases with Semipolar Additives

We examined the influence of semipolar additives on the phase behavior of mixed zwitterionic surfactant/consurfactant systems. It is shown that in these systems with increasing concentration esters like hexylacetate (HA) and ketones like hexylmethylketone (HMK) can behave both like consurfactants and like hydrocarbons. In solutions of 200 mM tetradecyldimethylamineoxide (TDMAO)/cosurfactant the additives cause first a phase transformation from the micellar L(1) phase to a lamellar L(alpha) phase. Upon further increasing concentration, the L(alpha) phase is transformed into a microemulsion. The L(alpha) phase consists of densely packed multilamellar vesicles. The vesicles are shown by electron microscopy. The multilamellar character of the vesicles is also reflected in the conductivity of the phase. It is up to 10 times lower than the conductivity of the L(1) phase. In some systems the vesicles are transformed on rest into a multidomain stacked L(alpha) phase. It is furthermore demonstrated that the two-phase L(1)/L(alpha) region in these systems is very narrow. In situations where enough HA is added to be close to the boundary of the L(1) phase, it is shown that very small amounts of cosurfactant can transform the L(1) phase into the L(alpha) phase. In extreme situations 1 mM cosurfactant is sufficient for transforming the L(1) phase with 200 mM TDMAO into the L(alpha) phase. In the investigated systems the L(alpha) phase is a highly viscoelastic fluid in which the storage modulus is 1 order of magnitude larger than the loss modulus. Besides the conventional way to prepare samples by adding all ingredients and stirring the solution intensively, all investigated systems were additionally prepared without applying any shear forces. In a surfactant/cosurfactant solution the additive was brought into the sample by diffusion. The phase behavior of both types of samples showed fundamental differences in some cases, which give insight into the influence of shear forces on these systems. Copyright 2001 Academic Press.     

Microemulsion formed by alkyl polyglucoside and an alkyl glycerol ether with weakly charged films

We have studied the effects on phase equilibria of a nonionic surfactant mixture-water-oil system when replacing small amount of surfactant molecules by ionic surfactant, sodium dodecyl sulfate (SDS). The nonionic surfactant system contains dodecyl-beta-D-maltoside (C(12)AG2) and iso-octyl glyceryl ether (i-C(8)GE) as cosurfactant, water and cyclohexane at constant water to oil ratio of 60/40 (w/w). Adding a small amount of SDS has large impact on the phase behavior. Clear liquid crystalline phase and upper microemulsion phase are added to the phase sequence at high i-C(8)GE/(C(12)AG2+i-C(8)GE) ratio. We also compare the phase equilibria of pure dodecyl maltoside system with polyglucosides mixture system.     

Selectivity of stationary phases in reversed-phase liquid chromatography based on the dispersion interactions

Selectivity of 15 stationary phases was examined, either commercially available or synthesized in-house. The highest selectivity factors were observed for solute molecules having different polarizability on the 3-(pentabromobenzyloxy)propyl phase (PBB), followed by the 2-(1-pyrenyl)ethyl phase (PYE). Selectivity of fluoroalkane 4,4-di(trifluoromethyl)-5,5,6,6,7,7,7-heptafluoroheptyl (F13C9) phase is lowest among all phases for all compounds except for fluorinated ones. Aliphatic octyl (C8) and octadecyl (C18) phases demonstrated considerable selectivity, especially for alkyl compounds. While PBB showed much greater preference for compounds with high polarizability containing heavy atoms than C18 phase, F13C9 phase showed the exactly opposite tendency. These three stationary phases can offer widely different selectivity that can be utilized when one stationary phase fails to provide separation for certain mixtures. The retention and selectivity of solutes in reversed-phase liquid chromatography is related to the mobile phase and the stationary phase effects. The mobile phase effect, related to the hydrophobic cavity formation around non-polar solutes, is assumed to have a dominant effect on retention upon aliphatic stationary phases such as C8, C18. In a common mobile phase significant stationary phase effect can be attributed to dispersion interaction. Highly dispersive stationary phases such as PBB and PYE retain solutes to a significant extent by (attractive) dispersion interaction with the stationary phase ligands, especially for highly dispersive solutes containing aromatic functionality and/or heavy atoms. The contribution of dispersion interaction is shown to be much less on C18 or C8 phases and was even disadvantageous on F13C9 phase. Structural properties of stationary phases are analyzed and confirmed by means of quantitative structure-chromatographic retention (QSRR) study.     

μ3-S盖帽的外消旋金属簇合物的直接手性拆分

在自制的涂敷型纤维素 三(3,5 二甲基苯基氨基甲酸酯)手性固定相上直接拆分了μ3 S盖帽的外消旋四面体金属簇合物.同时考察了温度、流动相中的极性改性剂的种类及结构对手性拆分的影响.结果发现,在相同的色谱条件下,被拆分簇合物在异丙醇作改性剂的流动相中的拆分效果较好.     

Low-pH-induced transformation of bilayer membrane into bicontinuous cubic phase in dioleoylphosphatidylserine/monoolein membranes

Cubic biomembranes, nonbilayer membranes with connections in three-dimensional space that have a cubic symmetry, have been observed in various cells. Interconversion between the bilayer liquid-crystalline (L(alpha)) phase and cubic phases attracted much attention in terms of both biological and physicochemical aspects. Herein we report the pH effect on the phase and structure of dioleoylphosphatidylserine (DOPS)/monoolein (MO) membranes under a physiological ion concentration condition, which was revealed by small-angle X-ray scattering (SAXS) measurement. At neutral pH, DOPS/MO membranes containing high concentrations of DOPS were in the L(alpha) phase. First, the pH effect on the phase and structure of the multilamellar vesicles (MLVs) of the DOPS/MO membranes preformed at neutral pH was investigated by adding various low-pH buffers into the MLV suspension. For 20%-DOPS/80%-MO MLVs, at and below pH 2.9, a transition from the L(alpha) to cubic (Q(224)) phase occurred within 1 h. This phase transition was reversible; a subsequent increase in pH to a neutral one in the membrane suspension transformed the cubic phase into the original L(alpha) phase. Second, we found that a decrease in pH transformed large unilamellar vesicles of DOPS/MO membranes into the cubic phase under similar conditions. We have proposed the mechanism of the low-pH-induced phase transition and also made a quantitative analysis on the critical pH of the phase transition. This finding is the first demonstration that a change in pH can induce a reversible phase transition between the L(alpha) and cubic phases of lipid membranes within 1 h.     

键合纤维素(4-甲基苯甲酸酯)手性固定相的制备及其手性拆分

采用包夹聚合法,将硅小球同硅烷化试剂反应制得乙烯基硅胶,然后将该乙烯基硅胶同经十一烯酰氯、4-甲基苯甲酰氯衍生的纤维素共聚,制备出含不同官能团的聚合物包夹硅基的键合型纤维素(4-甲基苯甲酸酯)类手性固定相。分别以正己烷异丙醇、正己烷四氢呋喃为流动相,对此键合型手性固定相的手性识别能力进行了评价。为了与同类型的涂敷型纤维素(4-甲基苯甲酸酯)手性固定相作比较,合成了涂敷型纤维素(4-甲基苯甲酸酯)手性固定相。结果表明,键合型纤维素(4-甲基苯甲酸酯)手性固定相具有一定的手性识别能力,可以拆分所研究的6种手性化合物中的4种。     

Struture stability and compressibility of iron-based superconductor Nd(O0.88F0.12)FeAs under high pressure

The high-pressure angle-dispersive X-ray diffraction experiments on the iron-based superconductor Nd(O0.88F0.12)FeAs were performed up to 32.7 GPa at room temperature. An isostructural phase transition starts at approximately 10 GPa. When pressure is higher than 13.5 GPa, Nd(O0.88F0.12)FeAs completely transforms to a high-pressure phase, which remains the same tetragonal structure with a larger a-axis and smaller c-axis than those of the low-pressure phase. The ambient conditions isothermal bulk moduli B0 are derived as 102(2) and 245(9) GPa for the low-pressure phase and high-pressure phase, respectively. The structure analysis based on the Rietveld refinement methods shows the difference of pressure dependence of the Fe-As and Nd-(O, F) bonding distances, as well as As-Fe-As and Nd-(O, F)-Nd angles between the low-pressure phase and high-pressure phase.     

环氧化聚丁二烯-聚苯乙烯嵌段共聚物对聚苯醚/环氧体系反应诱导 相分离行为的影响

采用扫描电镜、光学显微镜和光散射仪研究了环氧化聚丁二烯-聚苯乙烯嵌段共聚物(EBS)对聚苯醚(PPO)/双酚A型环氧树脂(DGEBA)/4,4’-二(2,6-二甲基苯胺基)甲烷(DIM-DDM)体系反应诱导相分离行为的影响. 实验结果表明, EBS的加入对PPO/DGEBA/DIM-DDM体系反应诱导相分离的演化过程有阻滞作用. 随着EBS加入量的增加, 体系形成双连续相结构所需的PPO含量范围变宽, 而对于相同PPO含量、形成双连续相的体系则相结构尺寸减小.     

Far-infrared and x-ray studies on poled semicrystalline poly(vinylidene fluoride)

Far-infrared (FIR) Fourier-transform transmission spectra and x-ray diagrams of poly(vinylidene fluoride) films are examined in terms of poling-field action on the crystalline phase (α and β forms) and on the amorphous phase. We show that the poling field induces an increase of crystallinity in the α phase as well as in the β phase, and for the latter an orientation of dipoles in the field direction. For samples containing a mixture of phases α and β we note an α to β phase transition, a rotation of the dipoles in the β phase, and an increase of the crystallinity of the sample. Part of the β phase is generated from the amorphous phase.     

Phase behavior of model lipid bilayers

We investigated the phase behavior of double-tail lipids, as a function of temperature, headgroup interaction and tail length. At low values of the head-head repulsion parameter a(hh), the bilayer undergoes with increasing temperature the transitions from the subgel phase L(c) via the flat gel phase L(beta) to the fluid phase L(alpha). For higher values of a(hh), the transition from the L(c) to the L(alpha) phase occurs via the tilted gel phase L(beta)(') and the rippled phase P(beta)('). The occurrence of the L(beta)(') phase depends on tail length. We find that the rippled structure (P(beta)(')) occurs if the headgroups are sufficiently surrounded by water and that the ripple is a coexistence between the L(c) or L(beta)(') phase and the L(alpha) phase. The anomalous swelling, observed at the P(beta)(') --> L(alpha) transition, is not directly related to the rippled phase, but a consequence of conformational changes of the tails.     

反相液相色谱法分离2-(4-羟基苯氧基)丙酸酯对映体

合成了三-(4-甲基苯甲酸)纤维素酯(MCTB)手性固定相，用反相高效液相色谱法在该手性固定相上对2-(4-羟基苯氧基)丙酸酯对映体进行拆分．实验结果表明，在三-(4-甲基苯甲酸)纤维素酯手性固定相上，以甲醇与水的体积分数为75：25做流动相能较好的拆分2-(4-羟基苯氧基)丙酸甲酯、乙酯和丁酯对映体，其分离因子分别为1．38、1．49、0．98；同时还发现2-(4-羟基苯氧基)丙酸酯中酯基团的大小对其对映体的分离也有明显的影响，其中以乙酯的拆分效果最佳。     

Reaction-induced phase separation in polyethersulfone-modified epoxy-amine systems studied by temperature modulated differential scanning calorimetry

In epoxy-amine systems with a thermoplastic additive, the initially homogeneous reaction mixture can change into a multi-phase morphology as a result of the increase in molecular weight or network formation of the curing matrix. Temperature modulated DSC (TMDSC) allows the real-time monitoring of this reaction-induced phase separation. A linear polymerizing epoxy-amine (DGEBA–aniline) and a network-forming epoxy-amine (DGEBA–methylene dianiline), both with an amorphous engineering thermoplastic additive (polyethersulfone, PES), are used to illustrate the effects of phase separation on the signals of the TMDSC experiment. The non-reversing heat flow gives information about the reaction kinetics. The heat capacity signal also contains information about the reaction mechanism in combination with effects induced by the changing morphology and rheology such as phase separation and vitrification. In quasi-isothermal (partial cure) TMDSC experiments, the compositional changes resulting from the proceeding phase separation are shown by distinct stepwise heat capacity decreases. The heat flow phase signal is a sensitive indication of relaxation phenomena accompanying the effects of phase separation and vitrification. Non-isothermal (post-cure) TMDSC experiments provide additional real-time information on further reaction and phase separation, and on the effect of temperature on phase separation, giving support to an LCST phase diagram. They also allow measurement of the thermal properties of the in situ formed multi-phase materials.     

氟环唑外消旋体在纤维素-三(3,5-二甲基苯基氨基甲酸酯)手性固定相上的高效液相色谱法拆分

在纤维素-三(3,5-二甲基苯基氨基甲酸酯)（CDMPC）手性固定相上,分别采用正相、反相及极性有机相色谱模式对氟环唑外消旋体进行了拆分,并考察了流动相组成在手性识别中对手性分离的影响。氟环唑在Chiralcel OD-H手性色谱柱（填充CDMPC手性固定相）上采用反相色谱模式,以甲醇-水(体积比为80∶20)为流动相,获得了最佳的拆分,其两对对映异构体的分离度Rs分别为1.64和6.50。