Effect of structural changes on mesophase stability of some model compounds based on the aryl benzoate group

Compounds based on 4,4'-substituted phenylbenzoate \[ R O-C6H4COO-C6H4- X ] ( I ), where X is a cyano group and R is a terminal alkyl chain ranging from 12 to 30 carbon atoms, and alternatively where R is held at 16 carbons and X is CN, COOH, OH, COOCH2C6H4, OCH2C6H4 and OC16H33 , were prepared and their mesophase stabilities characterized. Similarly, compounds based on symmetric dimers of terminally alkoxy-substituted phenyl esters \[C16H33O-C6H5COO- A -OOCC6H5-OC16H33] ( II ), the central linkage A being 1,2-, 1,3- and 1,4-phenylene, and 4,4'-biphenyl, were synthesized and studied. A partial success was achieved in the synthesis of compounds similar to series II , but where the ester groups were reversed (series III ), in order to assess the influence of this structure variation on the liquid crystallinity.     

Langmuir monolayers of the zwitterionic surfactant hexadecyl 1-N-L-tryptophan glycerol ether

We report the formation of Langmuir monolayers of pure zwitterionic hexadecyl 1-N-L-tryptophan glycerol ether (C(16)-TGE) surfactant and mixed monolayers of cationic-zwitterionic surfactant obtained modifying the pH of the subphase. The pressure-area and surface potential-area isotherms and fluorescence microscopy measurements have been used to characterize the surface phase transitions in the monolayers. These transitions appeared at larger areas as the pH decreased from 6.0 to 2.0 and almost disappeared as the pH decreased further. The analysis of the surface potential and the infrared reflection-absorption spectroscopy data suggests that the phase transition is associated with a change of orientation of both the hydrocarbon chain and the aromatic group of the surfactant with respect to the air-water surface. The surface rheology of the monolayers was studied by quasielastic light scattering and by the oscillatory barrier technique. The results indicate that there is at least one relaxation process in the monolayer.     

Effect of alkyl chain length and hydroxyl group functionalization on the surface properties of imidazolium ionic liquids

Properties of the surface of ionic liquids, such as surface tension, ordering, and charge and density profiles, were studied using molecular simulation. Two types of modification in the molecular structure of imidazolium cations were studied: the length of the alkyl side chain and the presence of a polar hydroxyl group at the end of the side chain. Four ionic liquids were considered: 1-ethyl-3-methylimidazolium tetrafluoroborate, [C(2)C(1)im][BF(4)]; 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate, [C(2)OHC(1)im][BF(4)]; 1-octyl-3-methylimidazolium tetrafluoroborate, [C(8)C(1)im][BF(4)] and 1-(8-hydroxyoctyl)-3-methylimidazolium tetrafluoroborate, [C(8)OHC(1)im][BF(4)]. The surface tension was calculated using both mechanical and thermodynamic definitions, with consistent treatment of the long-range corrections. The simulations reproduce the available experimental values of surface tension with a maximum deviation of ±10%. This energetic characterization of the interface is completed by microscopic structural analysis of orientational ordering at the interface and density profiles along the direction normal to the interface. The presence of the hydroxyl group modifies the local structure at the interface, leading to a less organized liquid phase. The results allow us to relate the surface tension to the structural ordering at the liquid-vacuum interface.     

Structural effect of synthetic zwitterionic cosolutes on the stability of DNA duplexes

The molecular design of useful cosolutes for polymerase chain reaction (PCR), which is one of the most important techniques in molecular biology, plays a significant role in amplification of highly stable genome sequences because during PCR, strand dissociation sometimes fails due to high melting temperature. Here, we designed and synthesized eight new zwitterionic cosolutes derived from glycine betaine, a destabilizing reagent for GC-rich DNA duplexes, and systematically compared their ability to destabilize DNA duplexes and to amplify genome DNA by PCR. We found that introduction of n-butyl groups rather than methyl groups into the ammonium group reduced the melting temperature of DNA duplexes 11-fold more than what was observed for the scaffold cosolute, glycine betaine, and furthermore, the cosolute can amplify the stable genome sequence by PCR.     

Effect of stearate preheating on the thermal stability of plasticized PVC compounds

Effect of preheating of stearates on the processing and post-processing thermal stability of poly(vinyl chloride) compounds, plasticized with di(2-ethylhexyl) phthalate (DEHP) and epoxidized soybean oil (ESO), using several ratios of calcium/zinc stearates and DEHP/ESO is reported. The compounds were prepared as follows: (1) dry-blending the compound components, (2) pelletizing the dry-blend and (3) extruding the pellets to obtain a ribbon geometry. Processing stability was determined by: (a) mechanical characterization and (b) visual color comparison of extruded samples. Post-processing thermal stability was followed by: (a) measurement of HCl release from heated pellets and (b) color changes in heated ribbon samples. From a practical point of view, the preheating has a negligible effect on the initial color of formulations; except for the case of formulations without both ESO and CaSt₂. However, the effect of the preheating on the post-processing thermal stability is strongly determined by the composition formulation.     

Effect of excess electron and one water molecule on relative stability of the canonical and zwitterionic tautomers of glycine

The anionic and neutral complexes of glycine with water were studied at at the coupled cluster level of theory with single, double, and perturbative triple excitations. The most stable neutral complex has a relatively small dipole moment (1.74 D) and does not bind an electron. Other neutral complexes involve a polar conformer of canonical glycine and support dipole-bound anionic states. The most stable anion is characterized by an electron vertical detachment energy of 1576 cm(-1), in excellent agreement with the experimental result of 1573 cm(-1). The (Gly.H(2)O)(-) complex supports local minima, in which the zwitterionic glycine is stabilized by one water and one excess electron. They are, however, neither thermodynamically nor kinetically stable with respect to the dipole-bound states based on the canonical tautomers of glycine. The electron correlation contributions to excess electron binding energies are important, in particular, for nonzwitterionic complexes. Our results indicate that the condensation energies for Gly((0,-))+H(2)O-->(Gly.H(2)O)((0,-)) are larger than the adiabatic electron affinity of Gly.H(2)O. The above results imply that collisions of Gly(-) with H(2)O might effectively remove Gly(-) from the ion distribution. This might explain why formation of Gly(-) and (Gly.H(2)O)(-) is very sensitive to source conditions. We analyzed shifts in stretching mode frequencies that develop upon formation of intra- and intermolecular hydrogen bonds and an excess electron attachment. The position of the main peak and a vibrational structure in the photoelectron spectroscopy spectrum of (Gly.H(2)O)(-) are well reproduced by our theoretical results.     

Heteroditopic receptor based on crown ether and cyclen units for the recognition of zwitterionic amino acids

The molecular recognition of five targeted amino acids differing in the nature of the side (R)- group and in the size of the aliphatic chain, glycine (Hgly), phenylalanine (Hphe), glutamic acid (Hglu^?), 4-aminobutyric acid (Hgaba), and 6-aminohexanoic acid (Heahx), has been studied with a new heteroditopic receptor based in two distinct macrocycles, a cyclen and a crown ether moiety. The bismacrocycle L was synthesized via the bis-aminal route allowing to obtain the designed compound in gram scale and in good yield. Protonation constants of L and its binding constants with amino acids were determined by potentiometry in H₂O/MeOH (1:1 v/v) solutions at 298.2 K and I=0.10 mol dm^?3 in NMe₄NO₃. Stronger binding ability of the H_nLⁿ⁺ receptor for α-amino acids, Hgly and Hphen, than for the other studied substrates were found. Structural data derived from NMR studies showed that the binding of α-amino acids result from the cooperative participation of hydrogen bonds between the carboxylate group of amino acids and the polyammonium sites of cyclen, and the ion-dipole interactions between the ammonium group of the amino acids and the oxygen atoms of the crown ether.     

Convenient syntheses of bulky group containing imidazolium ionic liquids

We report syntheses of bulky group containing imidazolium based ionic liquids. The bulky groups were introduced at N‐1, C‐2, and N‐3 positions of the imidazole ring using convenient methodologies. J. Heterocyclic Chem., (2012).     

Effect of counter-ion on the thermotropic liquid crystal behaviour of bis(alkyl)-tris(imidazolium salt) compounds

Recently, new thermotropic ionic liquid crystals (LCs) with a hexyl-linked tris(imidazolium bromide) core and two terminal alkyl chains were synthesised and characterised. To explore the effect of different counter-ions on the LC behaviour of this system, derivatives with BF₄^? and Tf₂N^? counter-ions were prepared and analysed. Five of the BF₄^? derivatives were found to exhibit thermotropic LC behaviour. The 12-, 14- and 16-carbon tail BF₄^? compounds form SmA phases. The 18- and 20-carbon tail homologues form what appears to be a smectic phase but are weakly mesogenic and harder to characterise. Only two of the Tf₂N^? derivatives exhibited mesogenic behaviour. The 18-carbon tail Tf₂N^? compound forms an as-yet unidentified, highly periodic smectic phase with positional order while the 20-carbon tail homologue forms a periodic SmA phase. The Tf₂N^? mesogens have much lower clearing points even though their LC phases have more order than the Br^? and BF₄^? mesogens. X-ray diffraction showed that these mesogens have different amounts of tail interdigitation between the smectic layers depending on the counter-ion present. Atomistic molecular dynamics simulations indicated that counter-ion size plays an important role in defining the density of the ionic region, which in turn affects the amount of interdigitation in the smectic phases.     

Effect of active acidic compounds on storage stability of coker naphtha

Coker naphtha was separated into ten distillation fractions equal in volume via Engler distillation. It was found that the mercaptan sulphur compounds were mainly concentrated in the lighter fractions, whereas the basic nitrogen compounds were concentrated in the heavier fractions. The gum content increased gradually with increasing the boiling point of each fraction after storage for 21 days under ambient conditions (25°C, 101 kPa). The active organic acidic compounds in coker naphtha extracted with aqueous solution of 20 mass % NaOH represented 0.26 mass %. The GC-MS analysis of the active organic acidic compounds showed the amounts of small molecule thiols, thiophenols (including benzyl mercaptan) and phenolic compounds to be 2.6%, 4.4% and 90.0%, respectively. After removal of the active acidic compounds by caustic scrubbing, the increase in the rate of gum formation was much slower than that of the blank coker naphtha after 27 days of storage under ambient conditions, indicating that the effect of these acidic compounds on the gum formation is more significant than with basic nitrogen compounds. It is demonstrated that the storage stability of coker naphtha was decreased in the presence of large amounts of phenolic compounds, which may accelerate the acid-catalysed polymerisation of olefins.     

Progress on predicting the electrochemical stability window of electrolytes

The advancement of novel electrical energy storage systems with high energy density encourages the development of electrolytes with wide electrochemical stability windows (ESWs). For the design of electrolytes, atomistic simulations have been used to investigate their electrochemical stability, providing a fast and economical approach for electrolytes screening, in which the simulation models are the key to predicting the electrolyte ESWs. Herein, the completing progress of the simulation models on predicting electrolyte ESWs is overviewed, which ranges in complexity from an isolated molecule/ion model to a solvation model and finally to a complex model of the electrode–electrolyte interface. We highlight the limitation and applicability of these models in detail and advocate a perspective of possible future research on the prediction of the electrolyte ESWs.     

烷基咪唑离子液体对脂肪酶催化酯水解反应活性的影响

考察了1-烷基-3-甲基咪唑类离子液体对柱状假丝酵母脂肪酶(CRL)催化橄榄油水解反应活性的影响,利用电导法确定了磷酸盐缓冲液中Br^-,Cl^-,[BF₄]^-系列咪唑离子液体的临界胶束浓度(CMC)和[PF₆]^-系列咪唑离子液体的溶解度.结果显示,离子液体的阴、阳离子对酶活性的影响规律与离子液体的Kosmotropicity性质无明显关联,但与离子液体在体系中的含量密切相关,在最适离子液体含量时,酶活性达到最高;阳离子[C_nMIM]⁺中的n越大,可促进酶活性的离子液体适宜含量越低;Br^-,[BF₄]^-系列离子液体的浓度超过CMC时则抑制酶活;阴离子对酶活性的最大促进作用顺序为Br^->Cl^->[BF₄]^->[PF₆]^-.离子液体对酶活性的影响随体系pH和温度的不同而改变,在最适离子液体浓度时的最适pH均为7.000.在pH 7.000,30 ^oC以及[C₈MIM]Br离子液体浓度为47.6 mmol/L的最佳条件下,最高相对酶活力和比活力分别达到1734%和54.4 U/mg protein.     

糖类化合物在两性离子亲水作用色谱柱上的保留行为评价

糖类化合物因其极性强,在反相色谱模式下保留较弱,因此常用亲水作用色谱(HILIC)对其进行分离分析。本文以9种糖类化合物的混合物为研究对象,系统评价了其在Click TE-Cys亲水色谱柱上的保留行为,分别考察了流动相中有机相比例和盐浓度对其保留行为的影响。实验证明:9种糖类化合物按极性由小到大的顺序依次从Click TE-Cys色谱柱上被洗脱下来。随着有机相比例的增加,糖类化合物的保留增强;随着盐浓度的增加,除唾液酸外的糖类化合物的保留增强。用顶替-吸附液相相互作用模型模拟了糖类化合物在HILIC上的保留行为,采用保留方程ln k=a+blnC_B+cC_B描述HILIC的保留规律,对HILIC的保留值进行多元线性回归。结果表明糖类化合物在Click TE-Cys色谱柱上的保留行为符合HILIC的保留规律。     

含氮大环化合物的研究

总结十五年来在氮杂冠醚和大环多胺的合成和性质研究方面的主要成果：氮杂冠醚和大环多胺合成的方法学研究,氮杂冠醚和大环多胺的NMR研究,含氮杂冠醚结构单元的吲哚啉螺苯并吡喃类信息接受体的合成和性质研究,桥连环糊精二聚体的分子识别研究。     

Effect of Antioxidants on the Stability of Poly(ether ether ketone) and the Investigation on the Effect Mechanism of the Antioxidants to Poly(ether ether ketone)

Two types of antioxidants (a phenolic antioxidant and a phosphorous antioxidant) were used to improve the stability of poly (ether ether ketone) (PEEK). To evaluate the effect of the antioxidants on the properties of PEEK and the stabilization mechanism, some characterization methods were carried out, such as rheometer, TGA, and electron spin resonance (ESR). The results indicated that the efficiency of the phosphorous antioxidant (DS) in improving the stability of PEEK was better than that of the phenolic antioxidant (DN) and the thermal stability of PEEK sample containing 0.07 wt% DS was the best among all samples due to the decrease of the free radicals density, as proven by ESR measurement. The possible stabilization mechanism of the antioxidants to PEEK was proposed to reveal the reason that caused the different performances of the two types of antioxidants to PEEK.     

Vesicle stability in aqueous mixtures of zwitterionic/anionic surfactants

It was studied that the influences of the aging, temperature, addition of the polymer and cosolvent on the stability of the vesicles spontaneously formed in the mixtures of zwitterionic surfactant (dodecyl carboxyl betaine, C₁₂BE) and double-tailed anionic surfactant (sodium bis(2-ethylhexyl) sulfosuccinate, AOT) under the inducement of salt by means of freeze-fracture and negative-staining transmission electron microscopy (TEM), dynamic light scattering (DLS) and turbidity measurements. It is found that the vesicles can exist over a long period of aging (about 300 days) at room temperature, show good stability after a heating–cooling cycle of 90–25 °C and a freeze–thaw cycle of −10 to 25 °C, respectively, and may be transformed from spherical vesicles to tubelike structures induced by high temperature 90 °C. Under the effect of (PEO)₁₃(PPO)₃₀(PEO)₁₃ (L64), the transition from unilameller vesicles to large multivesicular vesicles. The presence of ethanol may decrease the stability of vesicles, resulting in the fusion among vesicles to form large vesicles. The excessive amount of ethanol may destroy the vesicles, and the order of ability of destroying vesicles was obtained to be C₅H₁₁OH > C₄H₉OH > C₃H₇OH > C₂H₅OH > CH₃OH.     

Structure and phase stability of binary zintl-phase compounds: lithium-group 13 intermetallics and metal-doped group 14 clathrate compounds

The structure/bonding relationship in a series of intermetallic phases of Li with Al, Ga, and In was investigated by density functional theory and complemented by a model based on tight-binding theory and the method of moments. The combination of these two approaches provides a simple scheme which allows for both a comprehensive understanding of structural trends and the ability to predict low-energy structures for a given composition. This analysis gives a straightforward picture of phase stability in terms of local geometric features such as triangular, square, and hexagonal arrangements of atoms. The approach was extended to examine the structural properties of metal-doped clathrate compounds of C, Si, Ge, and Sn. Clathrate-type phases based on the frameworks Si172, Ge172, Si40, and Ge40 are not only likely to be energetically favorable but may also exhibit high thermoelectric efficiency.     

Effect of shear on the crystallization of the poly(ether ether ketone)

The effect of shear on the crystallization behavior of the poly(ether ether ketone) (PEEK) has been investigated by means of ex situ wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering, and differential scanning calorimetry (DSC). The changes of the intensity of WAXD patterns along shear direction of the PEEK induced by short‐term shear were observed when the samples crystallized at 330 °C. The results showed that the dimensions of the crystallites perpendicular to the (110) and (111) planes reduced with the increase of shear rate, whereas the dimensions of the crystallites perpendicular to (200) plane increased with the increase of shear rate. Moreover, increasing shear rate can lead to the increase of the crystallinity as well as the average thickness of the crystalline layers. Correspondingly, a new melting peak at higher temperature was found during the subsequent DSC scanning when the shear rate was increased to 30 s^?1. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 220–225, 2010     

Thermal stability of 1,3-disubstituted imidazolium tetrachloroferrates,magnetic ionic liquids

Thermal stability of synthesized magnetic liquids, tetrachloroferrates of 1,3-disubstitued derivatives of imidazolium, was examined. An effect of the cation structure on thermal stability of ionic liquids was considered and a mechanism of thermal destruction was suggested.