Formation of glasses from liquids and biopolymers

Glasses can be formed by many routes. In some cases, distinct polyamorphic forms are found. The normal mode of glass formation is cooling of a viscous liquid. Liquid behavior during cooling is classified between "strong" and "fragile," and the three canonical characteristics of relaxing liquids are correlated through the fragility. Strong liquids become fragile liquids on compression. In some cases, such conversions occur during cooling by a weak first-order transition. This behavior can be related to the polymorphism in a glass state through a recent simple modification of the van der Waals model for tetrahedrally bonded liquids. The sudden loss of some liquid degrees of freedom through such first-order transitions is suggestive of the polyamorphic transition between native and denatured hydrated proteins, which can be interpreted as single-chain glass-forming polymers plasticized by water and cross-linked by hydrogen bonds. The onset of a sharp change in ddT( is the Debye-Waller factor and T is temperature) in proteins, which is controversially indentified with the glass transition in liquids, is shown to be general for glass formers and observable in computer simulations of strong and fragile ionic liquids, where it proves to be close to the experimental glass transition temperature. The latter may originate in strong anharmonicity in modes ("bosons"), which permits the system to access multiple minima of its configuration space. These modes, the Kauzmann temperature T(K), and the fragility of the liquid, may thus be connected.     

Ordering in a fluid inert gas confined by flat surfaces

High-resolution transmission electron microscopy images of room-temperature fluid xenon in small faceted cavities in aluminum reveal the presence of three well-defined layers within the fluid at each facet. Such interfacial layering of simple liquids has been theoretically predicted, but observational evidence has been ambiguous. Molecular dynamics simulations indicate that the density variation induced by the layering will cause xenon, confined to an approximately cubic cavity of volume approximately 8 cubic nanometers, to condense into the body-centered cubic phase, differing from the face-centered cubic phase of both bulk solid xenon and solid xenon confined in somewhat larger (>/=20 cubic nanometer) tetradecahedral cavities in face-centered cubic metals. Layering at the liquid-solid interface plays an important role in determining physical properties as diverse as the rheological behavior of two-dimensionally confined liquids and the dynamics of crystal growth.     

黄酒中生物胺的测定

[目的]为测定黄酒中生物胺的含量寻求一种快速、简单、灵敏的检测方法。[方法]以丹磺酰氯为衍生剂,室温离子液体作为萃取、富集、衍生介质来测定黄酒中生物胺的含量。[结果]用室温离子液体[HMIM]PF6为介质来衍生、萃取和富集黄酒中的生物胺。通过试验得出比较理想的衍生条件:衍生剂量1.5 ml,硼砂缓冲液的pH 9.10,硼砂缓冲液量为2.0 ml,1.0 ml[HMIM]PF6离子液,超声时间为30 min。所得出的6种生物胺回收率为87.5%～109.8%,相对标准偏差为0.75%～3.21%,检出限量为0.005～0.025μg/ml。该方法将衍生、萃取和富集3个步骤集于一体,大大简化了试验,离子液体可有效促进分离,稳定性良好,所建立的方法线性范围良好。[结论]以丹磺酰氯为衍生剂,室温离子液体作为萃取、富集、衍生介质来测定生物胺的含量,是测定黄酒及其他饮料中痕量生物胺含量的一种快速、简单、灵敏的检测方法。     

六种离子液体的合成研究

离子液体被认为是环境友好的“绿色”反应溶剂,引起了研究者将离子液体应用于食品工业和农业等领域的浓厚兴趣.根据离子液体种类不同,建立不同的合成方法,合成一系列离子液体,用核磁共振氢谱表征,并对合成方法进行研究,以满足离子液体大规模生产和应用的需要.     

离子液体在香料制备中的应用

离子液体作为环境友好的＂绿色＂溶剂和＂可设计＂溶剂在合成化学中得到了广泛应用。离子液体的应用为各种香料和香豆素提供了高效、环保的制备途径,特别是功能化离子液体的应用避免了使用额外的催化剂,建立了更加经济、环境友好的反应工艺。综述了离子液体在香料制备中的应用进展。     

Trace element partition coefficient in ionic crystals

Partition coefficient monovalent trace ions between liquids and either solid NaNO(2) or KCl were determined. The isotropic elastic model of ionic crystals was used for calculating the energy change caused by the ionic substitutions. The observed values of partition coefficients in KCl good agreement with calculate values.     

土壤性质对1-丁基-3-甲基咪唑类离子液体吸附/脱附行为的影响

研究了2 种咪唑类离子液体（ILs）—氯化1-丁基-3-甲基咪唑（[Bmim][Cl]）和1-丁基-3-甲基咪唑双三氟甲磺酰亚胺盐（[Bmim][（CF₃SO₂）₂N]）在16种土壤上的吸附/脱附规律,探讨了土壤理化性质对于吸附/脱附行为的影响。研究发现,[Bmim][Cl]和[Bmim][（CF₃SO₂）₂N]的土壤吸附系数与土壤阳离子交换量（CEC）呈正相关性,相关系数（R²）分别为0.842 9和0.835 3（P<0.05）,表明土壤主要通过静电作用来吸附ILs,而与土壤总有机碳含量（TOC%）的R² 值仅分别为0.003 5和0.073 0（P< 0.01）,说明ILs 与土壤有机质的疏水结合作用为相对次要。ILs 阴离子基团对吸附行为有一定的影响,但并不明显。ILs 吸附/脱附的迟滞系数（HI）均小于1,可能与（ILs）在土壤粘土/有机质上的不可逆结合有关。其中,CEC 和[Bmim][Cl]和[Bmim][（CF₃SO₂）₂N]的HI之间存在较大的相关性（R²分别为0.772 9,0.781 5,P<0.01）,说明CEC 对迟滞行为有着不可忽视的影响。     

Use of ionic liquids for pi-conjugated polymer electrochemical devices

pi-Conjugated polymers that are electrochemically cycled in ionic liquids have enhanced lifetimes without failure (up to 1 million cycles) and fast cycle switching speeds (100 ms). We report results for electrochemical mechanical actuators, electrochromic windows, and numeric displays made from three types of pi-conjugated polymers: polyaniline, polypyrrole, and polythiophene. Experiments were performed under ambient conditions, yet the polymers showed negligible loss in electroactivity. These performance advantages were obtained by using environmentally stable, room-temperature ionic liquids composed of 1-butyl-3-methyl imidazolium cations together with anions such as tetrafluoroborate or hexafluorophosphate.     

木质素和纤维素在离子液体中的溶解性能及催化裂解研究进展

离子液体作为一种环境友好型绿色溶剂,因其独特的物理化学性质,在木质素和纤维素的溶解和催化裂解中得到了广泛的应用。在介绍木质素、纤维素和相关离子液体的组成和结构的基础上,综述了离子液体在溶解、分离木质素和纤维素及作为催化介质或催化剂方面的研究进展,分析讨论了离子液体的结构与其溶解性能的关系及可能的溶解机理。最后,对离子液体的应用前景进行了展望。     

碱性功能化离子液体在Knoevenagel缩合反应中的应用进展

Knoevenagel缩合反应被广泛应用于合成香豆素、化妆品及药物中间体功能化离子液体的设计、合成为Knoevenagel缩合反应提供了高效、环保的制备途径。以功能化离子液体为催化剂或者溶剂,一系列的醛和酮类化合物与活泼亚甲基化合物的缩合反应可以顺利进行,避免了使用额外的催化剂。文章综述了碱性功能化离子液体在Knoev...     

不同烃链长度咪唑类离子液体对玉米幼苗生长的影响

为探讨离子液体(ILs)对农业生物的毒性,以典型农作物玉米为材料,采用水培法研究三种不同烃链长度离子液体1-丁基-3-甲基咪唑氯盐([C4mim]Cl)、1-己基-3-甲基咪唑氯盐([C6mim]Cl)和1-辛基-3-甲基咪唑氯盐([C8mim]Cl)在不同浓度下对幼苗的根、茎生长以及部分生理生化指标的影响。结果表明:三种离子液体对玉米幼苗根、茎干重均有显著抑制作用。由EC50值得出,抑制程度表现为[C4mim]Cl[C6mim]Cl[C8mim]Cl,且对根重的抑制大于茎重。随三种离子液体处理浓度增加,玉米幼苗根、茎抗氧化酶系(SOD、POD、CAT、APX)总体呈下降趋势,而丙二醛(MDA)含量显著升高,表明氧化胁迫可能是离子液体产生毒性的重要原因。     

咪唑型离子液体溶液中纤维素酶荧光活性测定

为考查纤维素酶在离子液体溶液中的酶活,采用荧光光谱分析法对离子液体中纤维素酶的荧光活性测定,研究离子液体的浓度、类型对纤维素酶的活性影响。结果表明:纤维素酶在咪唑类离子液体溶液中荧光活性随离子液体浓度的升高而降低。离子液体为[C4 mim]Cl、[C4 mim]Br,且浓度为0.1 mol/L使纤维素酶的荧光强度减低最小,即对酶活性影响最小。     

Molecular ordering of organic molten salts triggered by single-walled carbon nanotubes

When mixed with imidazolium ion-based room-temperature ionic liquid, pristine single-walled carbon nanotubes formed gels after being ground. The heavily entangled nanotube bundles were found to untangle within the gel to form much finer bundles. Phase transition and rheological properties suggest that the gels are formed by physical cross-linking of the nanotube bundles, mediated by local molecular ordering of the ionic liquids rather than by entanglement of the nanotubes. The gels were thermally stable and did not shrivel, even under reduced pressure resulting from the nonvolatility of the ionic liquids, but they would readily undergo a gel-to-solid transition on absorbent materials. The use of a polymerizable ionic liquid as the gelling medium allows for the fabrication of a highly electroconductive polymer/nanotube composite material, which showed a substantial enhancement in dynamic hardness.     

Disintegration of charged liquid jets: results with isopropyl alcohol

Disintegration processes occurring with charged jets of isopropyl alcohol differ in several respects from results obtained with water. Although bimodal distributions of drop size shift to smaller diameters with increasing electrification for both liquids, the lower surface tension of the alcohol promotes the formation of secondary jets and a fan configuration not observed for water.     

Seismological constraints on core composition from Fe-O-S liquid immiscibility

Earth's core is composed primarily of iron (Fe) with about 10% by weight of lighter elements. The lighter elements are progressively enriched in the liquid outer core as the core cools and the inner core crystallizes. Thermodynamic modeling of Fe-O-S liquids shows that immiscible liquids can exist at outer-core pressures (136 to 330 gigapascals) at temperatures below 5200 kelvin and lead to layering in the outer core if the concentrations of the lighter elements are high enough. We found no evidence for layering in the outer core in the travel times and wave forms of P4KP seismic waves that reflect internally in the core. The absence of layers therefore constrains outer-core compositions in the Fe-O-S system to be no richer than 6 +/- 1 weight % (wt %) O and 2 to 15 wt % S. A single core liquid composition of 10.5 +/- 3.5 wt % S and 1.5 +/- 1.5 wt % O is compatible with wave speeds and densities throughout the outer core.     

室温离子液体催化对羟基苯甲酸乙酯的合成研究

[目的]研究室温离子液体催化对羟基苯甲酸乙酯的合成。[方法]选择4种1,3二烷基咪唑离子液体催化合成对羟基苯甲酸乙酯反应,考察反应温度、反应时间、催化剂用量、酸醇摩尔比对反应产率的影响及离子重复使用性能。[结果]以[BMIm]BF4为催化剂,其用量为3 ml,酸醇摩尔比为1.0∶2.5,反应时间为2.5 h,反应温度为80℃,产率最高,为79.7%;且产物与离子液体催化体系不容而分层,便于分离,离子液体可以稳定重复使用5次。[结论]离子液体可以作为一种新型绿色溶剂,有效催化合成对羟基苯甲酸乙酯反应,并可减少环境污染。     

离子液体预处理纤维素及木质纤维素的研究进展

稳定性好、溶解能力强的离子液体,能够快速瓦解木质纤维素网络结构,提高纤维素酶的可及度和酶解效率,可大幅度降低预处理成本。本文综述了常见离子液体的组成、离子液体对木质纤维素的溶解分离等预处理方法及其原理。     

Insights into phases of liquid water from study of its unusual glass-forming properties

The vitrification of pure water is compared with that of molecular solutions rich in water, and gross differences are noted. Thermodynamic reasoning and direct observations on noncrystallizing nanoconfined water indicate that the glass transition in ambient-pressure water is qualitatively distinct from that found in the usual molecular liquids. It belongs instead to the order-disorder class of transition seen in molecular and ionic crystalline materials. The distinctive "folding funnel" energy landscape for this type of system explains the extreme weakness of the glass transition of water as well as the consequent confusion that has characterized its scientific history; it also explains the very small excess entropy at the glass transition temperature. The relation of confined water behavior to that of bulk is discussed, and the "fragile-to-strong" transition for supercooled water is interpreted by adding a "critical point-free" scenario to the two competing scenarios for understanding supercooled bulk water.     

Structure of MsbA from E. coli: a homolog of the multidrug resistance ATP binding cassette (ABC) transporters

Multidrug resistance (MDR) is a serious medical problem and presents a major challenge to the treatment of disease and the development of novel therapeutics. ABC transporters that are associated with multidrug resistance (MDR-ABC transporters) translocate hydrophobic drugs and lipids from the inner to the outer leaflet of the cell membrane. To better elucidate the structural basis for the "flip-flop" mechanism of substrate movement across the lipid bilayer, we have determined the structure of the lipid flippase MsbA from Escherichia coli by x-ray crystallography to a resolution of 4.5 angstroms. MsbA is organized as a homodimer with each subunit containing six transmembrane alpha-helices and a nucleotide-binding domain. The asymmetric distribution of charged residues lining a central chamber suggests a general mechanism for the translocation of substrate by MsbA and other MDR-ABC transporters. The structure of MsbA can serve as a model for the MDR-ABC transporters that confer multidrug resistance to cancer cells and infectious microorganisms.     

Supramolecular Archimedean cages assembled with 72 hydrogen bonds

Self-assembly of multiple components into well-defined and predictable structures remains one of the foremost challenges in chemistry. Here, we report on the rational design of a supramolecular cage assembled from 20 ions of three distinct species through 72 hydrogen bonds. The cage is constructed from two kinds of hexagonal molecular tiles, a tris(guanidinium)nitrate cluster and a hexa(4-sulfonatophenyl)benzene, joined at their edges through complementary and metrically matched N-H···O-S hydrogen bonds to form a truncated octahedron, one of the Archimedean polyhedra. The truncated octahedron, with an interior volume of 2200 cubic angstroms, serves as the composite building unit of a body-centered cubic zeolite-like framework, which exhibits an ability to encapsulate a wide range of differently charged species, including organic molecules, transition metal complexes, and "ship-in-a-bottle" nanoclusters not observed otherwise.