苄泽类非离子型表面活性剂与明胶的相互作用

采用表面张力和稳态荧光光谱法考察了具有不同疏水结构的2种苄泽类非离子型表面活性剂Brij58和Brij78与明胶之间的相互作用。结果表明,苄泽类非离子型表面活性剂与明胶之间相互作用的驱动力为疏水作用力,且两者之间的相互作用受到其疏水基团的影响,Brij78在明胶溶液中的临界聚集浓度低于Brij58体系,表明疏水链更长的Brij78与明胶之间的相互作用更强。明胶分子的内源荧光光谱强度受苄泽类非离子型表面活性剂的影响,但最大吸收峰位置未发生蓝移,Brij78/明胶体系的内源荧光强度高于Brij58/明胶体系;此外,表面活性剂浓度较低时,明胶的加入使溶液中疏水微区极性明显降低,且明胶浓度越大降低程度越大。     

A method for calculating the Gibbs energies of hydrophobic effects and specific interactions of nonelectrolytes in aqueous solutions

The thermodynamic characteristics of hydrophobic hydration, the Gibbs energies of hydrophobic effect, were calculated. The method for calculations was based on the division of the Gibbs energy of hydration into contributions of nonspecific interactions, specific interactions between solutes and solvents (if they exist), and hydrophobic effect. In the absence of specific interactions between solutes and water, the Gibbs energy of hydrophobic effect depended linearly on the characteristic molecular volume of the solute for substances with different structures and properties. The universality of this dependence allows the suggestion to be made that it remains valid also in the presence of specific interactions. This allows the Gibbs energy of specific interactions in water to be determined for a wide range of compounds, in particular, for aliphatic alcohols.     

The synergistic effect between hydrophobic and electrostatic interactions in the uptake of amino acids by strongly acidic cation-exchange resins

The goal of this work was to investigate the synergistic effect between the electrostatic and hydrophobic interactions upon the uptake of organic ions with hydrophobic moieties by ion-exchange resins with hydrophobic matrixes. The uptake of neutral amino acids by a macroporous polystyrene-based strongly acidic cation-exchange resin (D001) and two strongly acidic cation-exchange resins (poly(2-acrylamido-2-methyl propanesulfonic acid) and poly(vinylsulfonic acid)) with much less hydrophobic matrixes essentially follow an ion exchange stoichiometry. However, the thermodynamic parameters of the uptakes indicate that besides electrostatic interaction, hydrophobic interaction also contributes to the affinity of the amino acids with hydrophobic side chains for D001. No detectable uptake capacities for the amino acids by D001AM, which was obtained by amidation of the sulfonic acid groups of D001, can be determined. Thus, it is deduced that the hydrophobic interaction alone contributes little to the uptake of these amino acids by D001, of which hydrophobicity is the same with or lower than that of D001AM. These results indicate that synergistic effect exists between the electrostatic and hydrophobic interactions when the two interactions exist in a chelate manner and the hydrophobic interaction contributes to the uptake even if the hydrophobic interaction is so weak that it contributes little to the uptake when it acts alone.     

Intramolecular rearrangement for regioselective complexation by intramolecular CH/pi interaction in a hydrophobic cavity of a ruthenium coordination sphere

A Ru(II) complex with a hydrophobic cavity formed from two 1-naphthoylamide groups was prepared. Its reactions with beta-diketones gave beta-diketonato complexes in which hydrophobic pi-pi or CH/pi interactions were confirmed by NMR spectroscopy and X-ray crystallography. In the case of the asymmetric beta-diketone benzoylacetone, an isomer with a CH/pi interaction was afforded as the sole product owing to thermodynamic control. The reaction was found to involve a novel intramolecular rearrangement from the phenyl-included isomer to the methyl-included one without rupture of Ru-beta-diketonato coordination bonds (activation energy 52 kJ mol(-1)). This indicates that CH/pi interactions can be more favored thermodynamically than pi-pi interactions in a suitable hydrophobic environment.     

Hydrophobic Effects. Opinions and Facts

The term hydrophobic interactions denotes the tendency of relatively apolar molecules to stick together in aqueous solution. These interactions are of importance in many chemical disciplines, including the chemistry of in vivo processes. Enzyme-substrate interactions, the assembly of lipids in biomembranes, surfactant aggregation, and kinetic solvent effects in water-rich solutions are all predominantly governed by hydrophobic interactions. Despite extensive research efforts, the hydration of apolar molecules and the noncovalent interactions between these molecules in water are still poorly understood. In fact, the question as to what the driving force for hydrophobic intractions is shifts the study into a quest for a detailed understanding of the remarkable properties of liquid water. This review highlights some of the novel insights that have been obtained in the past decade. The emphasis is on both hydrophobic hydration and hydrophobic interactions since both phenomena are intimately connected. Several traditional views have been found to be deeply unsatisfactory, and courageous attempts have been made to conceptualize the driving force behind pairwise and bulk hydrophobic interactions. The review presents an admittedly personal selection of the recent experimental and theoretical developments, and when necessary, reference is made to relevant studies of earlier date.     

Host-guest interactions with hydrophobic cyclophanes in aqueous media

Hydrophobic cyclophanes containing amide nitrogens in a rigid macrocyclic skeleton and flexible hydrocarbon chains, branched out at such nitrogen atoms, were prepared and their substrate-binding behavior was studied in aqueous media. the fluorescence spectroscopy was primarily adopted for the investigation of host-guest interactions by the aid of various hydrophobic probes. These host molecules provide cavities that are deep and hydrophobic enough to incorporate hydrophobic substrates of various bulkiness through an induced-fit mechanism originated from the flexible character of the alkyl branches. In addition to the hydrophobic interaction, the roles of electrostatic and charge-transfer interactions in molecular recognitions were clarified. Much hydrophobic, less polar, and highly viscous binding sites for hydrophobic guest molecules were provided by the octopus azaparacyclophane bearing eight hydrocarbon chains and the tetraazacyclotetradecane-capped azaparacyclophane having four flexible hydrocarbon chains connecting both macrocycles.     

Hydrophobic interactions and clustering in a porous capsule: option to remove hydrophobic materials from water

The investigation of hydrophobic interactions under confined conditions is of tremendous interdisciplinary interest. It is shown that based on porous capsules of the type {(pentagon)}(12){(linker)}(30) ≡ {(Mo)Mo(5)(12){Mo(2)(ligand)}(30), which exhibit different hydrophobic interiors-achieved by coordinating related ligands to the internal sites of the 30 {Mo(2)} type linkers-there is the option to study systematically interactions with different uptaken/encapsulated hydrophobic molecules like long-chain alcohols as well as to prove the important correlation between the sizes of the related hydrophobic cavities and the option of water encapsulations. The measurements of 1D- and 2D-NMR spectra (e.g. ROESY, NOESY and HSQC) allowed the study of the interactions especially between encapsulated n-hexanol molecules and the hydrophobic interior formed by propionate ligands present in a new synthesized capsule. Future detailed studies will focus on interactions of a variety of hydrophobic species with different deliberately constructed hydrophobic capsule interiors.     

THE ROLE OF INTERFACIAL INTERACTIONS IN THE PARTICLE/BUBBLE ATTACHMENT

The Van Oss surface thermodynamic theory of polar and apolar interfacial interactions was extended to the interaction between mineral surfaces and bubbles across liquid media. The acid base (polar) interfacial interactions are supposed to be responsible for the hydration repulsion between a hydrophilic mineral and a bubble as well as for the hydrophobic attraction between a hydrophobic mineral and the bubble.     

Hydrophobic interactions

Recent advances in theoretical and experimental studies of hydrophobic interactions are reviewed. The theory of water structure as applied to hydrophobic bonding, theoretical estimates for the free energy of unfolding of proteins, and the statistical mechanical theory of hydrophobic bonding in polyamino acids are summarized. Experimental estimates of the thermodynamic parameters of the hydrophobic bond can be obtained from solubility and dimerization data of low molecular weight compounds. Recent studies of the interaction of proteins with nonpolar solutes are discussed. Hydrophobic bonds can also be important in various other kinds of interactions involving proteins. The observed effect of urea is mentioned, although no theoretical interpretation of this effect is available yet. In conclusion the methods available for the detection of hydrophobic interactions are reviewed.     

Role of hydrophobic and electrostatic interactions for initial enteric virus retention by MF membranes

Membranes are of increasing interest for the removal of human enteric viruses from wastewater, especially when the goal of treatment is reuse. Limited work has been undertaken on fundamental issues such as aggregation and the role of electrostatic and hydrophobic interactions, as opposed to the sieving of viruses by membranes. One apparently critical factor would be the iso-electric point (pI) of a virus. As an example of a worst-case model virus, the retention of bacteriophage MS-2 was investigated using hydrophobic (GVHP) and hydrophilic (GVWP) 0.22 μm MF membranes at different pH levels and with different salts. High retention levels were measured at the iso-electric point of MS-2, pH 3.9 (5 log retention) and pH 7 (4.3 log retention) in the presence of salts and with a hydrophobic membrane. When retention was compared on a hydrophilic membrane, it was clear that hydrophobic interactions dominated virus retention, and this was improved by salt, presumably causing reduction of the Gouy double-layer when MS-2 was charged (pH 7). This paper shows that knowledge of the adsorption characteristics of viruses and the suspending conditions are important to predict removal of viruses by hydrophobic MF membranes, and discusses some of the practical implications of these important hydrophobic interactions.     

Analysis of pH-dependent protein interactions with gel filtration medium.

A prepacked Superose 12 HR 10/30 column was used to study the effects of elution ionic strength and pH on the chromatographic behaviour of a strong hydrophobic Clostridium thermocellum endoglucanase (1) and two weak hydrophobic proteins, Clostridium thermocellum endoglucanase C and egg white lysozyme. Ion-exclusion or ion-exchange interactions between weakly hydrophobic proteins and the gel matrix were observed at low ionic strength, depending on whether the pH of the elution buffer was higher or lower than the pI values of the proteins. These interactions were due to the presence of negatively charged groups on the surface of Superose and could be eliminated at any pH by adding electrolyte at a concentration determined by its chemical identity. The optimum results were observed with sodium sulphate at a concentration of 100 mM. The chromatographic behaviour of strong hydrophobic endoglucanase (1) on a Superose column as a function of pH was much more complex because of two interplaying effects, electrostatic and hydrophobic. Ideal size-exclusion chromatography could be achieved only in a narrow range of the conditions: first, the mobile phase must contain a weak salting-out electrolyte such as NaCl, and second, the mobile phase pH must be high enough that hydrophobic interactions between the solute and support are balanced by their electrostatic repulsion. At pH greater than pI, the retardation of endoglucanase (1) gradually increased with decreasing pH as a result of lowering of repulsive electrostatic interactions whether or not the buffer ionic strength was high. At pH less than pI a drastic increase in the capacity factor k' was observed owing to the additivity of hydrophobic and ion-exchange effects.(ABSTRACT TRUNCATED AT 250 WORDS)     

The hydration of hydrophobic substances

A model of the hydration of hydrophobic substances in water is suggested. The models of fluctuation formation of empty cavities in water as a stage of hydration extensively used in the literature were shown to be at variance with experiment. The fundamental role played by the interphase boundary surface was emphasized. On this surface, the successive addition of water molecules with the formation of capsules around hydrophobic molecules occurred. The physical meaning of the Ostwald equation was revealed. This equation characterized the distribution of hydrophobic volatile substances between the gas and aqueous phases. The method of optical probes (hydrophobic aromatic molecules) was used to reveal the synergistic character of autocorrelation of dispersion interactions between water and hydrophobic substance molecules. This synergism was at variance with the Lennard-Jones potential. The synergism (superadditivity) of dispersion attraction forces, which strengthened their directional character, caused the self-organization and enhanced stability of hydration capsules with encapsulated hydrophobic molecules. Computer models were used to show that the spatially directional character of dispersion interactions necessary for the self-organization of hydrated aggregates could be simulated by the molecular mechanics method on the basis of orientational correlation of water molecules and hydrophobic substances in the starting system.     

SURFACE ENTHALPY AND ENTROPY AND THE PHYSICO-CHEMICAL NATURE OF HYDROPHOBIC AND HYDROPHILIC INTERACTIONS

The attractive Interactions between typically hydrophobic molecules such as hexane or CCl₄, and the repulsive Interactions between extremely hydrophilic molecules such as poly(ethylene oxide) (PEO), when immersed in water, as well as the interactions between these molecules and water, have been examined from a surface thermodynamic viewpoint, taking the changes in surface free energy into account, as a function of temperature. It was found that attractive hydrophobic Interactions are not, as vas generally believed up to now, invariably entropic. Hydrophobic Interactions can be mainly enthalpic or mainly entropic, or more or less equal mixtures of both, depending on each individual case; however, all hydrophobic interactions are polar (in the sense of Lewis acid-base) in nature. Repulsive hydrophilic interactions are enthalpic, and also polar in nature. The interaction between hydrophobic solutes and water is mainly enthalpic, and is apolar in nature.     

Modified langmuir-like model for modeling the adsorption from aqueous solutions by activated carbons

A new equation, a modified Langmuir-like equation (M-LLE), for describing adsorption from solution by activated carbons is proposed for the first time in this work. The M-LLE assumes that there are two types of interactions: (a) specific interactions which are typical, enthalpy-driven interactions and (b) nonspecific interactions driven by the loss of water structuring, upon adsorption (hydrophobic bonding), around the nonpolar parts of the drug. The proposed model was evaluated by studying the adsorption of three drugs: procaine, fluoxetine, and phenobarbital by four different activated carbons under different experimental conditions. As the hydrophobicity of the drug increased, the capacity constant representing the interactions driven by hydrophobic bonding (K(HB), M-LLE equation) increased. Experimental conditions that decrease hydrophobic bonding, such as increased temperature and higher cosolvent concentration, resulted in a decrease in K(HB). Salts that tend to increase water structuring and hydrophobic bonding caused an increase in K(HB). All of these studies support the M-LLE, because they support the notion of hydrophobic-bonding-driven interactions.     

Gelation of spontaneously formed catanionic vesicles by water soluble polymers

The gelation of two spontaneously formed charged catanionic vesicles by four water soluble polymers was systematically studied by tube inversion method and rheology. Eight phase maps were successfully documented for the catanionic vesicle–polymer mixtures. The experimental results, as represented by the relaxation time and the storage modulus at 1 Hz, revealed that the catanionic vesicle–polymer interactions at play were of electrostatic and hydrophobic origin. Firstly, no association between charged catanionic vesicles and the polymer without charge/hydrophobic modification was observed due to lack of both electrostatic and hydrophobic effects. Secondly, hydrophobic interactions accounted for the association between the hydrophobically modified polymer without charge and charged catanionic vesicles with hydrophobic grafts of the polymer inserting in the catanionic vesicle bilayer. Thirdly, the positively charged polymer without hydrophobic modification could interact with negatively charged catanionic vesicles through electrostatic force on one hand but could not interact with positively charged catanionic vesicles on the other hand. Finally, the positively charged polymer with hydrophobic modification could interact both electrostatically and hydrophobically with negatively charged catanionic vesicles, resulting in the formation of strong gels. The hydrophobic interaction might even overcome the unfavorable electrostatic interaction between the positively charged vesicles and the polymer with positive charge/hydrophobic modification.     

Dynamic control of protein conformation transition in chromatographic separation based on hydrophobic interactions: Molecular dynamics simulation

Conformational transitions of a protein in hydrophobic interaction based chromatography, including hydrophobic interaction chromatography (HIC) and reversed-phase liquid chromatography (RPLC), and their impact on the separation process and performance were probed by molecular dynamics simulation of a 46-bead β-barrel coarse-grained model protein in a confined pore, which represents the porous adsorbent. The transition of the adsorbed protein from the native conformation to an unfolded one occurred as a result of strong hydrophobic interactions with the pore surface, which reduced the formation of protein aggregates. The conformational transition was also displayed in the simulation once an elution buffer characterized by weaker hydrophobicity was introduced to strip protein from pore surface. The discharged proteins that underwent conformational transition were prone to aggregation; thus, an unsatisfactory yield of the native protein was obtained. An orthogonal experiment revealed that in addition to the strengths of the protein–protein and protein–adsorbent hydrophobic interactions, the elution time required to reduce the above-mentioned interactions also determined the yield of native protein by HIC and RPLC. Stepwise elution, characterized by sequential reduction of the hydrophobic interactions between the protein and adsorbent, was presented as a dynamic strategy for tuning conformational transitions to favor the native conformation and reduce the formation of protein aggregates during the elution process. The yield of the native protein obtained by this dynamic operation strategy was higher than that obtained by steady-state elution. The simulation study qualitatively reproduced the experimental observations and provided molecular insight that would be helpful for designing and optimizing HIC and RPLC separation of proteins.     

表皮生长因子受体和抑制剂之间分子对接的研究

研究了表皮生长因子受体(EGFR)和4-苯胺喹唑啉类抑制剂之间的相互作用模式，表皮生长因子受体的三维结构通过同源蛋白模建的方法得到，而抑制剂和靶酶结合复合物结构则通过分子力学和分子动力学结合的方法计算得到。从模拟结果得到的抑制剂和靶酶之间的相互作用模式表明范德华相互作用、疏水相互作用以及氢键相互作用对抑制剂的活性都有重要的影响，抑制剂的苯胺部分位于活性口袋的底部，能够与受体残基的非极性侧链产生很强的范德华和疏水相互作用，抑制剂双环上的取代基团也能和活性口袋外部的部分残基形成一定的范德华和疏水性相互作用，而抑制剂喹唑啉环上的氮原子能和周围的残基形成较强的氢键相互作用，对抑制剂的活性有较大的影响，计算得到抑制剂和靶酶之间的非键相互作用能以及抑制剂和靶酶之间的相互作用信息能够很好地解释抑制剂活性和结构的关系，为全新抑制剂的设计提供了重要的结构信息。     

Resolution enhancement in hydrophobic interaction chromatography via electrostatic interactions

In this work, a new type of hydrophobic stationary phase that provide electrostatic interactions with analytes was developed by bonding β-phenylethylamine as a functional ligand to silica. This stationary phase can separate proteins with similar hydrophobicity that traditional hydrophobic resins cannot. Hen egg white was separated to examine the selectivity. The results show that the introduced electrostatic interactions are an important factor for the resolution enhancement and the new resin could have important applications in separation and purification of biological macromolecules.     

静电和疏水效应对SARS冠状病毒3CL蛋白酶二聚体稳定性的影响

从TGEV3CL蛋白酶二聚体结构出发,研究了TGEV3CL蛋白酶二聚体单体之间的静电和疏水相互作用.蛋白质的静电相互作用通过有限差分方法求解Poisson-Boltzmann方程得到,疏水相互作用通过分析溶剂可及性表面模型得到.考察了不同pH值对SARS3CL蛋白酶二聚体静电和疏水相互作用的影响,在pH=5.5～8.5时,二聚体静电相互作用能、静电去溶剂化能和疏水自由能都具有较小的数值,表明在该条件下静电和疏水相互作用有利于二聚体的稳定存在.由于SARS3CL蛋白酶活性模式为二聚体,因此,在该pH值范围内,有利于蛋白酶保持活性.在pH=7.0条件下,蛋白酶单体之间具有最强的静电和疏水相互作用,从而使蛋白酶具有最强的活性,这与实验结果相一致.pH值对静电去溶剂化能的影响大于疏水自由能,表明静电作用是造成强酸或强碱条件下二聚体不能稳定存在的主要原因.