圆柱形纳米孔道内受限溶液I2/Ar的分子动力学模拟研究

利用分子动力学模拟方法, 考察了受限于圆柱形纳米孔道内I2/Ar溶液的振动传能及扩散动力学. 计算得到了溶质振动弛豫时间T1、溶剂轴向扩散系数Dz随孔道半径变化的规律. 结果表明: T1随着孔道半径的增大而减小; 而Dz随着孔道半径的增大而增大; 与预期的一致, 随着孔道半径的增大, 孔道的限制作用逐渐减小, T1与Dz趋近于相应的非受限溶液体相值. 此外, 通过考察溶质、溶剂与孔道的相互作用, 在原子、分子层次上揭示了限制作用对传能与传质影响的机制.     

Synthesis of a bicyclic analogue of AZT restricted in an unusual O4'-endo conformation.

The [3.2.0]bicyclic beta-nucleoside analogue 5 has been designed as a conformationally restricted analogue of the anti-HIV drug AZT. The synthesis of 5 as well as its alpha-anomer 29 is hereby described. The synthesis was accomplished from D-arabinose via a modified Corey-Link procedure stereoselectively incorporating the azide moiety as well as a methyl ester function. When the tert-butyldiphenylsilyl group was used as a permanent protecting group, a selective formation of an oxetane ring failed. When using the p-methoxyphenyl group as a permanent protecting group, 5 and 29 were efficiently obtained via a selective reduction of the ester, a nucleobase coupling followed by separation of the anomers and ring-closing procedures. The nucleoside 5 is conformationally restricted in an unusual O4'-endo (East) conformation, which is an intermediate between the North- and South-type conformations. Nevertheless, neither 5 nor 29 displayed any anti-HIV activity.     

Acid generation and deprotecting reaction by diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate in a novolak positive photoresist based on chemical amplification

In a positive photoresist composed of diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate as a novel photoacid generator, bisphenol A protected with tertbutoxycarbonyl group as a dissolution inhibitor, and a novolak resist matrix, the efficiency of photo-acid generation and deprotective reaction were investigated by means of UV-visible and IR spectroscopies. The quantitative measurement of photogenerated acid by using the acid-sensitive dye exhibited 0.18 as the quantum yield of acid generation in novolak resin film. The lithographic evaluation of this system as a chemically amplified resist was studied. The catalytic chain length for the acid-catalyzed deprotection step was determined as about 100 when 10 min post-exposure bake (PEB) at 80°C was given. The sensitivity and the resolution as a positive resist are 180 mJ/cm² and higher than 1 μm, respectively under the PEB conditions mentioned above.     

Separation of glycosylated caseinomacropeptide at pilot scale using membrane adsorption in direct-capture mode

A direct-capture anion-exchange membrane adsorption process for the separation of a pure glycosylated (gCMP) fraction of caseinomacropeptide (CMP) was successfully developed at pilot plant scale. The method was evolved using a commercial CMP isolate as feedstock as well as fresh sweet whey from skim milk. The former resulted in a binding capacity (BC) of 0.28 mg gCMP/cm² membrane surface with a purity of 97% while the latter afforded a gCMP fraction with a purity of 91% and a BC of 0.21 mg gCMP/cm² membrane surface. The main difference was a significant fouling of the membrane adsorber module when the whey was applied, which resulted in a loss of 46% BC after at least five loading/elution cycles. This effect was not observed using the pure CMP isolates and indicates a blocking of the ion-exchange ligands. Triglycerides, as detected by lipid analysis, as well as protein aggregates and casein-flocculates, are mainly responsible for the fouling process. The fouling was decreased using microfiltered whey or by increasing the temperature of the adsorption process. Additionally, a method of repeated elution was shown to decrease the volume of the eluate as well as the NaCl consumption of the elution buffer. The process development further included a desalting and concentration step, which was performed by a 10 kDa ultrafiltration/diafiltration (UF/DF). The efficiency of the UF was strongly influenced by the pH of the solutions and showed best performance at pH 4.1 for the eluate. The residual solution had to be adjusted at pH 6.5 as there was a strong decrease of flux at lower pH levels.     

Hydrotalcite catalysis for the synthesis of new chiral building blocks

The use of hydrotalcites for the synthesis of two chiral building blocks in a simple way is described as a new and green methodology. The synthesis of these compounds implies a regioselective Baeyer–Villiger reaction in a very selective way with ulterior opening and lactonisation. This methodology should be considered green for the use of hydrogen peroxide as the only oxidant and hydrotalcites as the catalyst, and because no residues are produced apart from water. The procedure is very adequate for using in gram scale, in order to increase the value of the obtained compounds. The conditions are excellent and can be applied for nonstable compounds, as they are very mild. The synthesised compounds are magnific starting materials for the synthesis of biologically active or natural compounds. The use of a cheap, commercial and chiral compound as carvone disposable in both enantiomeric forms adds an extra value to this methodology.     

Autonomously Propelled Motors for Value‐Added Product Synthesis and Purification

A proof‐of‐concept design for autonomous, self‐propelling motors towards value‐added product synthesis and separation is presented. The hybrid motor design consists of two distinct functional blocks. The first, a sodium borohydride (NaBH₄) granule, serves both as a reaction prerequisite for the reduction of vanillin and also as a localized solid‐state fuel in the reaction mixture. The second capping functional block consisting of a graphene–polymer composite serves as a hydrophobic matrix to attract the reaction product vanillyl alcohol (VA), resulting in facile separation of this edible value‐added product. These autonomously propelled motors were fabricated at a length scale down to 400 μm, and once introduced in the reaction environment showed rapid bubble‐propulsion followed by high‐purity separation of the reaction product (VA) by the virtue of the graphene–polymer cap acting as a mesoporous sponge. The concept has excellent potential towards the synthesis/isolation of industrially important compounds, affinity‐based product separation, pollutant remediation (such as heavy metal chelation/adsorption), as well as localized fuel‐gradients as an alternative to external fuel dependency.     

The Thermodynamic Driving Force for Kinetics in General and Enzyme Kinetics in Particular

The thermodynamic driving force of a reaction is usually taken as the chemical potential difference between products and reactants. The forward and backward reaction rates are then related to this force. This procedure is of very limited validity, as the resulting expression contains no kinetic factor and gives little information on reaction kinetics. The transformation of the reaction rate as a function of concentration (and temperature) into a function of chemical potential should be more properly performed, as illustrated by a simple example of an enzymatic reaction. The proper thermodynamic driving force is the difference between the exponentials of the totaled chemical potentials of reactants and products.     

Fast procedure for reconstruction of full-atom protein models from reduced representations

We introduce PULCHRA, a fast and robust method for the reconstruction of full-atom protein models starting from a reduced protein representation. The algorithm is particularly suitable as an intermediate step between coarse-grained model-based structure prediction and applications requiring an all-atom structure, such as molecular dynamics, protein-ligand docking, structure-based function prediction, or assessment of quality of the predicted structure. The accuracy of the method was tested on a set of high-resolution crystallographic structures as well as on a set of low-resolution protein decoys generated by a protein structure prediction algorithm TASSER. The method is implemented as a standalone program that is available for download from http://cssb.biology.gatech.edu/skolnick/files/PULCHRA.     

三明治式双极膜的制备及其光催化性能

以Cr3+交联羧甲基纤维素钠(CMC)作为阳膜层,戊二醛改性壳聚糖(CS)作为阴膜层,纳米TiO2光催化剂作为双极膜的中间层,在TiO2上涂布光敏剂八羟基喹啉（Oxine）以增强其光催化解离水的性能,制备了三明治式的双极膜（mCMC/TiO2-Oxine/mCS BPM)。 该双极膜在紫外光照射下,具有高的水解离效率,优良的亲水性能,双极膜阻抗小,工作电压低,当工作电流密度达0.12 A/cm2时,电槽工作电压小于5.0 V。     

Life—a complex polymer system

After a discussion of the different levels of macromolecules, the phenomenon of life is regarded as a complex polymer system. The thermodynamic basis of general system theory is explained as well as the character of system laws. The important notion of emergent system properties is stressed, and life is explained as a system property of a sufficiently complex system. The general applicability of the systemic approach is pointed out, and some examples are provided. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 471–478, 2004     

On the use of alumina in HPLC with aqueous mobile phases at extreme pH

Summary The applicability of alumina as a stationary phase in liquid chromatography is considered. Despite the presence of hydroxyl groups on wetted alumina, chemical modification with silanes by analogy to silica is not successful. Although depolarisation can be achieved with hexamethyldisilazane, the product is not stable to hydrolysis in aqueous media. The use of alumina as an ion-exchanger is more promising, especially because alumina appears to be stable over a very broad pH range. As a result of its amphoteric character alumina can be used either as an anion-exchanger or as a cation-exchanger. The latter possibility is more profitable in alkaline solvents and allows the separation of strongly basic compounds at pH values as high as 12. Retention can be controlled by judicious choice of ionic strength, counter ion and pH.     

Enzyme-based biocatalysis for the treatment of organic pollutants and bioenergy production

Enzyme-based biocatalysis is emerging as an advanced technique to develop green processes that help to maintain the sustainability of the environment. The bioremediation of toxic organic pollutants and waste to bioenergy production using enzymes as biocatalysts is rapidly growing due to its eco-friendly and sustainable nature. Additionally, a range of microbial species that typically grow on organic wastes can be used to produce these enzymes in an efficient manner. This is seen as a potential strategy for the development of cost-effective manufacturing for a number of biotechnological applications. The present study discusses biocatalysis as a promising and sustainable method toward the bioremediation of hazardous organic pollutants as well as for bioenergy production, based on the immense potential of enzymes as biocatalysts. Emphasis has been placed on evaluating the critical elements that can enhance the production of enzymes used as biocatalysts, as well as their functional effectiveness and stability.     

Sequential injection with lab-at-valve (LAV) approach for potentiometric determination of chloride

Sequential injection with “Lab-at-Valve (LAV)” approach is demonstrated for potentiometric determination of chloride. The LAV flow-through electrode system consists of two Ag/AgCl electrodes: one as a reference electrode, silver chloride activated surface-silver wire soaked in a constant-concentration chloride ion solution in a small tube covered with a polymer-membrane, another as a working electrode (a similar silver chloride activated surface-silver wire) placed in a flow channel. The electrode system is attached at one port of a 10 port multiposition valve. A modified autoburette was used as a propelling device. Using SI operation via a program written in-house, based on LabVIEW^®, a standard/sample is inserted, via the selection valve, in potassium nitrate as an electrolyte and water is used as a carrier. The zones are transported from the holding coil to the flow cell to monitor the difference in potential due to concentration cell behavior. The potential difference is then recorded as a peak. Peak height is proportional to logarithm of chloride concentration. The SI-LAV for chloride determination is very simple, fast, precise, accurate, automatic and economical. Applications to mineral drinking water and surface water have been made. The results agree with those of IC and titrimetric methods.     

Copper(I) complexes with bipyridyl and phosphine ligands: a systematic study

Phosphorescent copper(I) complexes carrying 2,2'-bipyridyl derivatives and phosphine ligands have been prepared and fully characterised. The role of the bipyridyl as well as the phosphine ligands in defining the optical, as well as the chemical properties of the complexes, are discussed. The light emission of these complexes is investigated as a function of the molecular geometry: rigid complexes with restricted freedom to rearrange in the excited state are found to show a quantum yield of phosphorescence one order of magnitude higher than those complexes with no steric constraint. The complexes have been extruded in a polymer matrix as a proof of principle of their processability.     

Novel porous polyurethane films

Polyurethane films treated in a two-stage process with aqueous bromine and ammonia solutions underwent significant modifications in crystalline and surface structure as well as in mechanical and physical properties. Bromine was sorbed on the film, and formed several charge transfer complexes with the soft and hard segments of the polyurethane as well as bridges between adjacent chains. In the second stage, ammonia reacted with the sorbed bromine producing gaseous nitrogen and ammonium bromide. The expansion of the gas resulted in a repacking of the polymeric chains and the formation of a porous structure. The bromine concentrations used and the times of contact between the films and the bromine were 0.02–0.06 normal and 1–10 min, respectively. The contact angle of the films decreased, depending on treatment conditions, from 73 to 20. The water vapor permeability increased three-fold. The treatment appeared to bring about a crystallization in the hard as well as in the soft segments of the PU as shown by differential scanning calorimetry measurements. Possible applications of the treated films for wound dressing are discussed. © 1998 John Wiley & Sons, Ltd.     

Interaction of soybean agglutinin with leukemic T-cells and its use for their in vitro separation from normal lymphocytes by lectin-affinity chromatography

A procedure for separation of leukemic T-cells from normal lymphocytes, using lectin-affinity column chromatography, is described. CNBr-activated Sepharose 6MB was used as a non-mobile phase. The gel was covalently coupled with soybean agglutinin (SBA), then served as an affinity probe for fractionation of mixture of normal lymphocytes and leukemic cells. Leukemic cell lines, derived from acute lymphoblastic leukemia (Jurkat, MOLT-4, RPMI-8402), were tested. The elution of normal lymphocytes was carried out by PBS(-). The leukemic T-cells, interacting with SBA, were removed by N-acetyl-D-galactosamine or low-concentration acetic acid. The type and viability of the separated cell fractions were analyzed by flow cytometry and fluorescent microscopy, using adequate fluorescent antibodies. The interaction of leukemic T-cells with free SBA, as well as with SBA-conjugated Sepharose beads, was examined fluorimetrically and visualized by fluorescent microscopy, using FITC-SBA as a marker. The rate of cell elution on SBA-affinity column decreased in order: normal > leukemic T-cells. Both normal lymphocytes and leukemic T-cells were removed in a mixture from SBA-free Sepharose 6MB by PBS(-) and were not fractionated discretely. The leukemic T-cells specifically interacted with SBA as well as with SBA-affinity adsorbent. In contrast, the normal lymphocytes did not interact with free SBA as well as with SBA-conjugated Sepharose beads in the concentrations applied. The method potentially combines a discrete cell fractionation with manifestation of a specific target cytotoxicity of SBA against leukemic T-cells, without any influence on normal lymphocytes.     

The photodegradation of cis-1,4-polybutadiene, polystyrenebutadiene and polyisoprene

The photodegradation of the synthetic rubbers cis-1,4-polybutadiene, polystyrenebutadiene and polyisoprene was studied. The chemical structure of the polymers as well as the effect of changing the solvent and the additive were particularly taken into consideration. The polychloroprene rubber in this study was irradiated either as a film or in solution. The presence of methylene blue affects the endothermic peaks observed in its differential scanning calorimetry diagrams. Methylene blue acts as a photostabilizer dye in solutions and films of polychloroprene. Mixtures of methylene blue, β-carotene as a singlet oxygen quencher and Fmbanox as a known anti-oxidant showed synergystic behaviour.     

Ordered macroporous quercetin molecularly imprinted polymers: Preparation,characterization, and separation performance

Ordered macroporous molecularly imprinted polymers were prepared by a combination of the colloidal crystal templating method and the molecular imprinting technique by using SiO₂ colloidal crystal as the macroporogen, quercetin as the imprinting template, acrylamide as the functional monomer, ethylene glycol dimethacrylate as the cross‐linker and tetrahydrofuran as the solvent. Scanning electron microscopy and Brunauer–Emmett–Teller measurements show that the ordered macroporous molecularly imprinted polymers have a more regular macroporous structure, a narrower pore distribution and a greater porosity compared with the traditional bulk molecularly imprinted polymers. The kinetic and isothermal adsorption behaviors of the polymers were investigated. The results indicate that the ordered macroporous molecularly imprinted polymers have a faster intraparticle mass transfer process and a higher adsorption capacity than the traditional bulk molecularly imprinted polymers. The ordered macroporous molecularly imprinted polymers were further employed as a sorbent for a solid‐phase extraction. The results show that the ordered macroporous molecularly imprinted polymers can effectively separate quercetin from the Gingko hydrolysate.     

Influence of temperature on ultrasonic velocity measurements of ethanol+water+1-propanol mixtures

The ultrasonic velocity of the ternary mixtures ethanol+water+1-propanol at the range 288.15–323.15 K and atmospheric pressure, has been measured over the whole concentration range. The corresponding change of isentropic compressibility was computed from the experimental data. The results were fitted by means of a temperature dependent equation, such parameters being gathered. The obtained experimental values indicate varying extent of interstitial accommodation among unlike molecules as a function of steric hindrance attending to 1-propanol composition as key component and as a function of hydrogen bond and temperature attending to ethanol composition as key component.     

Aniline Carbamates: A Versatile and Removable Motif for Palladium‐Catalyzed Directed CH Activation

The aniline carbamate is introduced as a new removable directing group for C?H activation. Its versatility and ability as a directing group are demonstrated by its use in the ortho‐arylation of a wide variety of aniline derivatives under palladium(II) catalysis, with symmetric diaryliodonium salts as aryl donors. The reaction differs from previously reported arylations in its selectivity and its mechanism, as elucidated by kinetic and isotopic experiments. The directing group can also be easily removed under a variety of conditions.