自溶液中的吸附——XIV.硅胶自Triton X—100和几种烷基硫酸钠的混合水溶液中的吸附

本文测定了硅胶自水中对Triton X-100的吸附,其吸附等温线呈不平常的S型,极限吸附量相当于1.00nm~2/分子,约比气液界面上的大一倍。加入0.1M的NaCl和改变pH对吸附无可察觉的影响。硅胶基本不吸附烷基硫酸钠。当Triton X-100的浓度低于其在混合溶液中的CMC时,烷基硫酸钠的存在对Triton X-100的吸附无影响;但其极限吸附量则随烷基硫酸钠浓度的增大而降低;烷基硫酸钠的碳氢链越长,这种效应就越显著。根据相分离模型,以及只有分子状态的Triton X-100被吸附而胶团不被吸附的假设,可以解释所得结果。     

辛酸钠-醇-水溶液体系的表面化学性质研究

辛酸钠水溶液中加入不同种类醇后,使溶液最低表面张力及临界胶束浓度降低,在所研究醇中,最有效提高表面活性的是正己醇,即较长碳链醇更易参加胶团形成和在表面吸附,另外实验还发现加入醇引起胶束解离度增加,这是由于醇碳氢链可插入形成胶束的表面活性剂分子碳氢链中使胶团表面电荷密度降低,使反离子易于解离。     

对称正、负离子表面活性剂的胶团化和表面吸附自由能

根据所建议的表面活性剂疏水碳氢基在水溶液中自卷曲的分子构型和碳氢链/水界面自由能降低模型导出了对称正-负离子表面活性剂胶团化和表面吸附自由能及疏水自由能公式, 计算结果支持上述理论模型。     

对称正-负离手表面活性剂的胶团化和表面吸附自由能

根据所建议的表面活性剂疏水碳氢基在水溶液中自卷曲的分子构型和碳氢链/水界面自由能降低模型导出了对称正-负离子表面活性剂胶团化和表面吸附自由能及疏水自由能公式,计算结果支持上述理论模型。     

用2D NOESY和1H NMR弛豫研究月桂醇聚氧乙烯(23)醚(Brij-35)胶团的结构状态

浓度为100倍临界胶团浓度(cmc)的月桂醇聚氧乙烯(23)醚的¹H NMR自旋-晶格弛豫时间、自旋-自旋弛豫时间和核-核Overhauser效应谱表明,处于胶团核外面的亲水聚氧乙烯链呈卷曲收缩状均匀地堆积在胶团核的表面,在结构上形成了一个包含一定量水分子的厚而疏松的亲水网络层.亲水网络层是和溶剂(即水)相溶合的,这样可以作为一个过渡层保持胶团溶液的稳定.¹H NMR弛豫时间表明亲水聚氧乙烯链的运动和疏水烷基链的运动一样,都是受阻的.2D NOESY实验所观察到的胶团核外亲水链和它内部的疏水链质子间的相互作用,直接证明了Brij-35胶团亲水部分和疏水部分质子间距很短.     

四乙铵离子对阴离子表面活性剂及其混合体系的表面活性和胶团形成的影响

研究了溴化四乙铵介质中十二烷基硫酸四乙铵、全氟辛基磺酸四乙铵及其混合体系的表面化学性质。四乙铵离子在浓度较小时主要起电解质反离子作用,在浓度较大时则明显参与表面吸附和胶团的形成,其作用相当于在表面活性离子的疏水链上“引入”碳氢链,从而导致表面活性提高和碳氢/碳氟表面活性剂混合体系中碳氢/碳氟链间的互疏作用减弱等。     

参数Z对疏水色谱中胍变蛋白质分子构象变化的表征

用计量置换参数Ｚ对疏水色谱流动相中存在盐酸胍时蛋白质分子构象变化进行了表征。除溶菌酶外，其余４种蛋白质的Ｚ值随盐酸胍浓度的增大先增大，而后减小。将盐酸胍和脲对蛋白质Ｚ值的影响进行了比较后发现，在疏水色谱中Ｚ值作为蛋白质分子构象变化表征的一个重要的结论是随变性剂浓度的增大，埋藏在蛋白质分子内部的疏水性氨基酸残基暴露到分子表面的程度逐渐增大，造成了Ｚ值随蛋白质分子构象变化程度的增大而减小。蛋白质的Ｚ值随盐酸胍及脲浓度变化的不同特点，反映了两者对蛋白质变性机理的不同。     

表面活性剂胶团形成的自由能改变——碳氢链卷曲构象证据之一

用两种方法对各种类型表面活性剂水溶液胶团形成的碳氢链部分的标准自由能改变进行了计算: 一种是根据表面活性剂同系物的临界胶团浓度实验数据; 另一种是按照分子结构与碳氢链构象的模型。两种计算结果相符, 说明假设的分子结构与构象模型合理, 首次提供了表面活性剂长碳氢链在水中自卷曲的一种证据。     

碳氟表面活性剂与碳氢表面活性剂混合水溶液的表面吸附和胶团形成——Ⅱ.全氟辛酸钠-十烷基硫酸钠体系

测定了不同摩尔比的全氟辛酸钠(7CFNa)-十烷基硫酸钠(C_(10)SNa)混合水溶液(加NaCl,恒定离子强度μ=0.1m)的表面张力和界面张力(正庚烷-水溶液界面张力)。由表(界)面张力-浓度关系求出混合体系的表(界)面吸附和临界胶团浓度(cmc)。结果表明:(1)7CFNa和C_(10)SNa在μ=0.1m的溶液中,cmc相近,两者表面活性相近;但7CFNa降低水表面张力的能力较强,在cmc时的表面张力可低达～23mNm~(-1)。因此,在混合溶液的表面上,7CFNa的表面活性较高,优先吸附于表面。对于各种摩尔比的混合溶液,7CF~-在表面层中的比例皆大于在溶液内部的比例。(2)正庚烷-水溶液界面上的吸附与表面吸附截然不同。7CF~-在界面吸附层中的比例低于溶液内部,表明其吸附能力比C_(10)S~-为弱。这是由于界面一边的正庚烷与C_(10)SNa碳氢链之间的作用大于与7CFNa碳氟链之间的作用。亦即碳氟链与碳氢链“互憎”作用在界面上的表现。(3)在不同摩尔比的混合溶液中,各组分的cmc接近一恒值,进一步说明混合溶液中存在碳氟链与碳氢链间的互憎作用,以致两种表面活性剂在混合溶液中(有过量无机盐时)基本上各自形成胶团。     

脲和盐酸胍诱导的牛碳酸酐酶B的去折叠

采用非变性聚丙烯酰胺凝胶电泳、十二烷基硫酸钠-聚丙烯酰胺凝胶电泳、高效凝胶排阻色谱和激光光散射光谱研究了脲和盐酸胍诱导的牛碳酸酐酶B的去折叠.实验结果表明,在脲和盐酸胍诱导的牛碳酸酐酶B的去折叠过程中,溶液中只含有单分子牛碳酸酐酶B和二分子牛碳酸酐酶B集聚体;二分子牛碳酸酐酶B集聚体是通过单分子牛碳酸酐酶B之间的疏水和...     

Conformational flexibility and structure of creatine kinase.

The structural flexibility of creatine kinase has been investigated with the covalent hydrophobic probe 2-[4'-(2"-iodoacetamido) phenyl] aminonaphthalene-6-sulfonic acid (IAANS) which reacts at vastly different rates with the two subunits to give a protein conjugate with fluorescence characteristic of reaction with a site in a hydrophobic cleft. Binding of purine nucleotides greatly enhances the probe fluorescence while pyrimidine nucleotides quench the fluorescence. Small anions bind to nucleotide-free creatine kinase near the location of the transferable phosphoryl group and quench both the IAANS fluorescence of modified creatine kinase and the tryptophan fluorescence of native creatine kinase. Chloride and nitrate non-competitively inhibit MgADP binding both with and without creatine. Fluorescence energy transfer demonstrates that the active sites of creatine kinase are well separated and become further apart after the nucleotide-induced conformational change.     

Thermodynamics of glycine solution in aqueous urea. Rule \sqrt m

The solution heats of glycine in aqueous urea have been determined by calorimetry at 298 K (molality 0–13) and 313 K (molality 0–22). The solution heat of the amino acid is described by the linear dependence of this quantity on the square root of the urea molality. The enthalpy, entropy, and Gibbs energy of the transfer of glycine from water to aqueous urea, as well as the heat capacity, entropy variation, and Gibbs energy of glycine solution have been calculated for the temperature range 273–323 K. It is found that urea additions to water reverse the sign of the heat capacity of solution.     

Effect of urea on the behaviour of poly(2-hydroxyethyl methacrylate)-water mixtures

The effect of urea solutions on the equilibrium swelling of lightly crosslinked poly(2-hydroxyethyl methacrylate) (PHEMA) gels and on the viscometric behaviour of PHEMA, for various concentrations of urea and temperatures, has been studied. Urea raises the degree of swelling of gels and the intrinsic viscosity of PHEMA; the temperature coefficient of both quantities is negative. A thermodynamic analysis of the swelling data shows that a change in entropy is the driving force for the increase in swelling at low temperatures, while at higher temperatures (50–80°) a negative change in enthalpy prevails, both corresponding to the transport of PHEMA from the aqueous medium into urea solutions. The entropy and enthalpy of dilution parameters derived from viscometric measurements have negative values, and their absolute values decrease with increasing urea concentration. It has also been found that the PHEMA molecules in urea solutions under the θ-conditions are much more coiled than in an organic θ-solvent. The results are interpreted in terms of the existence of inter- and intramolecular hydrophobic bonds and by the destruction of hydrophobic clusters caused by urea.     

Force Measurements between Semifluorinated Thiolate Self-Assembled Monolayers: Long-Range Hydrophobic Interactions and Surface Charge

Long-range interactions between self-assembled monolayers (SAMs) of semifluorinated alkanethiols have been studied by direct force measurements in water and aqueous NaCl solutions. SAMs prepared from three different thiols, with identical fluorinated head groups but varying hydrocarbon spacer lengths, were investigated: CF(3)(CF(2))(9)(CH(2))(x)SH, where x=2, 11, or 17. Force measurements show that the interactions in water and electrolyte solutions are composed of both double-layer interactions emerging from what appears to be charges adsorbed onto the surfaces and long-range "hydrophobic" attractions, in excess of the expected van der Waals forces. The three investigated thiols produce similar results in force measurements, though the contact angles with water are slightly different. The "hydrophobic" attraction has the form of step-like attractive discontinuities in the force profiles at separations ranging from 20 to 40 nm, caused by bridging of microscopic bubbles residing at the surfaces. The shape or range of these discontinuities are not significantly affected by replacement of the water with either 1 mM or 1 M NaCl solutions. The origin of the charges causing the electrostatic double-layer interaction is unclear, but some possible causes are discussed. Copyright 2001 Academic Press.     

Temperature dependence on the binding of butyl orange by bovine serum albumin: The effect of urea

The effect of urea on the extent of the binding of butyl orange by bovine serum albumin has been examined by an equilibrium dialysis method. The first binding constants and the thermodynamic parameters for the formation of the first dye anion–protein complex have been calculated. Addition of urea to the binding system causes a marked decrease in the absolute magnitude of the free energy change. The enthalpy change during binding becomes more exothermic, and the entropy change tends to decrease with increasing concentration of urea. These results can be interpreted in terms of the concept that urea reduces the structure of the aqueous environment and hence lowers the tendency of apolar groups of the dye and the albumin to participate in the formation of hydrophobic interactions.     

2-Chloromercuri-4-nitrophenol-modified Sites of Creatine Kinase Confirmed by FPLC

MNP-modified tryptic peptides of creatine kinase have been separated with two-dimensional electrophoresis, but the location of the SH groups of creatine kinase modified by MNP still seemed to be vague until recently (Laue, M. C. & Quiocho, F. A. , 1977). Two peptides have now been found to be the MNP-modified peptides with reversed-phase FPLC methods, and the amino acid compositions of these two peptides are in agreement with those of the two peptides around Cys-145 and Cys-253, respectively. These findings indicate that the two buried SH groups of creatine kinase have been modified by MNP.     

The oxidation of aqueous thiols on a graphite intercalation compound adsorbent

Aqueous phase adsorption of thiols onto a graphite intercalation compound (GIC) adsorbent was shown to be accompanied by surface assisted oxidation of the thiols to their disulfide dimer. This effect was studied for three thiols; ethanethiol, propanethiol and sec-butanethiol. Unlike the case of thiol oxidation on activated carbons in aqueous conditions, the generation of dimer did not affect the adsorbent’s ability to oxidise the thiols in solution in the concentration range studied (0–100 ppm). This was attributed to the non-porous, crystalline nature of the adsorbent. This meant that once formed the dimers migrated from the active sites for thiol oxidation, believed to be mainly at the edges of the graphite planes, onto the hydrophobic basal plane where they could be adsorbed. Oxidation of the GIC adsorbent in the anodic compartment of an electrochemical cell was shown to attenuate the adsorbent’s ability to oxidise thiols. It was inferred that this was a result of a decrease in the amount of CO groups at the plane edges caused by this oxidation process.     

Interaction of urea with poly(2-hydroxyethyl methacrylate) hydrogels

The interaction of poly(2-hydroxyethyl methacrylate) [poly(HEMA)] and other similar hydrogels with dilute urea solution has been studied by a variety of techniques, including swelling experiments, fluorescence quenching, near infrared spectroscopy and fundamental band infrared spectroscopy. The results obtained indicate that the anomalous swelling behavior of poly(HEMA) gels in the presence of such dilute urea solutions is probably not due to the disruption of a secondary hydrophobic bond structure as has been generally believed. Although poly(HEMA) gels do contain sites that can participate in hydrophobic bonding, the evidence gathered indicates that dilute urea solutions have no effect on such bonds. A plausible model that does fit all the data involves the interaction of urea with a secondary structure composed of hydrogen-bonded hydroxyl groups, stabilized by the exclusion of water molecules from the regions containing the bonds.     

Molecularly imprinted solid-phase extraction combined with molecularly imprinted polymer-sensor: a diagnostic tool applicable to creatine deficiency syndrome

Primary creatine deficiency syndromes (CDS) are a new group of disorders caused by guanidinoacetate methyltransferase (GAMT) deficiency, which affects endogenous creatine biosynthesis with depletion of body creatine. A deficiency in creatine can be corrected by treatment with oral creatine supplementation and this necessitates a simple and sensitive screening method for early detection of creatine in dilute physiologic fluids. In this work an artificial receptor, molecularly imprinted polymer (MIP), for creatine was used both as a material for solid-phase extraction (SPE) and as a sensing element in a voltammetric sensor. Using the combination of molecularly imprinted solid-phase extraction (MISPE) with a complementary MIP sensor, the minimum detectable amount was found to be 0.0015 ng mL(-1) (RSD = 1.3%, S/N = 3). The MISPE-MIP sensor combination provided up to 60-fold preconcentration, which was more than sufficient for achieving the required quantification limit 50 ng mL(-1) (or 0.0025 ng mL(-1) after 2 x 10(4)-fold dilution) for creatine in human blood serum.     

Synthesis of Amphiphilic Oligomers of Acrylic Acid

Synthesis of amphiphilic oligomers of acrylic acid via radical polymerization in the presence of thiols as molecular mass regulators is described. The effect of the length of the introduced hydrophobic terminal group on the critical micellization concentration of the acrylic acid oligomers has been elucidated. It has been shown that the incorporation of an antituberculous drug (prothionamide) in the micelles of acrylic acid oligomers is enhanced with the increase in the length of the hydrophobic moiety. The preparation of hydroxyapatite-filled calcium-polycarboxylate bone cements containing prothionamide (promising for the sealing of postoperative cavities) is described.