基于光波导分光光谱技术研究蛋白质与亚甲基蓝的竞争吸附行为

通过利用时间分辨光波导分光光谱技术原位测量从蛋白质-亚甲基蓝(MB)混合水溶液吸附到亲水玻璃光波导表面的MB可见光吸收谱,观测到在溶液pH值低于蛋白质等电点时MB与牛血清蛋白(BSA)以及MB与血红蛋白(Hb)存在竞争吸附行为,进一步测得这种竞争吸附行为对蛋白质浓度十分敏感,可以用于简单测定溶液中的蛋白质含量.基于Langmuir等温吸附理论推导出了两种分子竞争吸附的动力学方程,并利用该动力学方程对实验测得的吸光度随时间变化曲线进行了最佳拟合,揭示了玻璃表面吸附的MB分子个数在达到最大值后随时间呈指数衰减,同时得出拟合参数与蛋白质浓度呈准线性关系.     

光波导分光光谱技术研究染料分子在玻璃表面的吸附特性

光波导分光光谱技术利用光波导表面的消逝场敏感地测定有色物质亚单分子吸附层的偏振吸收光谱, 非常适合于研究染料、颜料、荧光分子、量子点、金属纳米粒子、带色基的蛋白质等在固/液界面的吸附行为. 本文使用宽频带卤钨灯、棱镜耦合的薄膜玻璃光波导和基于电荷耦合器件(CCD)的光谱分析仪设计制作了具有时间分辨本领的光波导分光光谱装置, 并利用该装置实时监测了罗丹明6G(R6G)和亚甲基蓝(MB)在玻璃表面的吸附特性. 通过比较在横电(TE)和横磁(TM)偏振模式下的吸收光谱, 发现R6G主要以二聚体和单体的形式吸附在玻璃表面, 而MB主要以多聚体的形式吸附在玻璃表面, 并分别估算了它们的平均取向角.     

基于偏振光波导分光光谱技术原位研究纳米金-细胞色素c 自组装过程

时间分辨偏振光波导分光光谱技术是一种用于研究表面分子吸附动力学的强大工具. 利用该技术实时、原位监测纳米金与细胞色素c的静电自组装过程, 发现随着吸附层数的增加, 纳米金粒子吸附层产生的局域等离子体共振(LSPR)吸收峰发生了红移, 而且在横磁(TM)模式下的红移比横电(TE)模式下的红移更快; 细胞色素c在纳米金表面的吸附导致LSPR吸收峰的峰位和强度在TM模式下显著红移和升高, 相比之下, TE模式下的LSPR吸收峰无明显变化. 对实验数据的分析验证了纳米金在细胞色素c单分子层表面的吸附动力学行为遵循扩散控制模型, 细胞色素c在纳米金单粒子层表面的吸附动力学行为遵循Langmuir等温吸附模型, 进一步估算了细胞色素c在纳米金表面的吸附速率常数、脱附速率常数和吸附自由能.     

分子氧在锐钛矿型TiO2表面的光助吸附和光助脱附

本文采用真空-质谱技术研究了紫外线照射下分子氧在锐钛矿型TiO₂表面的吸附和脱附机理。氧光助吸附后,锐钛矿表面成为活化表面。活化表面的O₂^-(分子氧在锐钛矿表面的吸附态)在1.33×10^-3Pa的真空中,在能量大于锐钛矿禁带宽度2.9eV的紫外线照射下成为分子氧脱附,氧脱附后的表面在无紫外线照射的氧气氛中对分子氧有吸附作用,该O₂^-饱和吸附量大于相同氧压下紫外线照射下O₂的饱和吸附量。在氧压和光强度相同的条件下,O₂^-吸附量与表面羟基化程度呈线性关系。     

银表面罗丹明6G的电化学表面增强拉曼光谱研究

罗丹明6G（Rhodamine 6G,R6G）是单分子表面增强拉曼光谱（SM-SERS）研究中最常用的探针分子之一,对R6G分子在表面吸附行为的研究有助于了解R6G分子和表面的相互作用. 本文应用电化学和电化学表面增强拉曼光谱技术,研究不同电位下R6G的银电极表面的吸附行为. 结果表明,随着电位负移罗丹明6G在银表面上从垂直吸附转为倾斜吸附,该变化和碱性条件下吸附于金纳米粒子上R6G的吸附构象一致. 这说明,在部分单分子实验中所发现的R6G反常光谱其来源是单个R6G分子在表面吸附取向变化. 本研究对后续详细分析SM-SERS研究中单分子SERS谱峰变化的机制有一定的参考价值.     

硅烷化活性炭的吸附性质

本工作测定了25℃和35℃时硅烷化活性炭自水溶液中吸附苯甲酸和苯甲醛的等温线;计算了吸附过程的ΔGⅲ,ΔHⅲ和ΔSⅲ;用Hill-deBoer方程处理了实验结果。所得结果表明:(1)随硅烷化时间延长,苯甲酸和苯甲醛的吸附量(mol.m^-^2)明显增加;-ΔGⅲ和-ΔHⅲ略有升高,ΔSⅲ为正值;(2)吸附分子之间的相互作用很弱,吸附分子与活性炭表面间的作用随硅烷化程度增加而加大;(3)芳香化合物可能是以苯环吸附在炭表面上的。     

奥美拉唑对映体在自制手性柱上吸附等温线的测定

采用吸附-脱附法研究了奥美拉唑对映体在自制的纤维素三苯基氨基甲酸酯涂敷型手性柱上的吸附性能,并用Langmuir方程拟合出吸附平衡方程.当样品浓度降低时,Langmuir方程退化为直线关系,直线斜率即为吸附平衡常数.这一吸附平衡常数与从脉冲色谱流出曲线求得的吸附平衡常数相等,表明吸附-脱附法测得的吸附平衡关系准确,Langmuir方程能描述这一吸附平衡关系.     

酚类化合物在BSA和Aldrich-HA上吸附常数的QSAR研究

应用密度泛函方法(DFT)在B3LYP/6-311G**水平上全优化计算酚类化合物的量子化学参数,结合疏水性参数与酚类化合物在小牛血清蛋白BSA和腐殖质Aldrich-HA上的吸附常数进行定量构效关系研究(QSAR).经逐步回归筛选变量后,所建2个多元线性回归方程的相关系数R及去一法(LOO)交互检验复相关系数R2cv分别为0.955,0.882和0.943,0.819,用预测集样本进行了外部预测,所得外部预测集交互检验系数Q2ext分别为0.891和0.925.模型结果表明,ELUMO愈低,分子体积V愈大,化合物在BSA上吸附常数lgKDOC愈大;酚类化合物在腐殖质Aldrich-HA上不仅存在疏水作用吸附,还存在分子间作用力吸附,并以疏水作用吸附为主.     

罗丹明标记的磷脂分子在亲水表面的单个分子行为

单个分子实验有很重要的意义,一方面，对于非均相体系，单个分子实验可得到分子性质分布信息；另一方面，对于均相和非均相体系，单个分子轨迹直接记录了分子性质的涨落，包含了丰富的动力学信息.在诸多单个分子检测技术中，单分子光学检测技术具有快速、无损、可探测到凝聚相内部单个分子的能力.进行单分子检测的关键是消除拉曼和瑞利散射以及杂质荧光等背景的干扰，利用共焦、近场和隐失场激发减少激发体积和检测体积，可以降低背底，提高信噪比.本实验利用共焦荧光显微镜观测单个罗丹明标记的磷脂分子在亲水玻璃表面的扩散、脱附，及其荧光闪烁的行为.实验表明，除由表面的平均力场阻碍分子运动外，还有一些特殊位点会造成长时间的特异性吸附，并得到特异性吸附的分子的脱附速率，（5.9±0.2）s－1.用穿越时间分布函数测得分子在表面的扩散速率为(3.3±0.1)×10－8 cm2•s－1，与分子在磷脂膜中的扩散速率相当.观测到了一些吸附的分子出现了荧光闪烁的现象，并对其产生原因进行了一些分析.     

树状高分子溶液在粘度计毛细管表面的吸附现象

本文测定了树状高分子DAB(PA) n 水溶液和脂肪族超支化聚酯及其硅烷化衍生物溶液性质 .通过粘度测量 ,得到了吸附常数k ,半数吸附浓度ca,分子间缔合常数Km ,特性粘度 [η]等参数 ,解释了特性粘度的反常行为 ,重点研究了吸附现象 .发现树状高分子和超支化高分子溶液在粘度计毛细管表面形成了多层吸附 ,高分子之间的相互作用及高分子与溶剂分子间的氢键作用是形成多层吸附的重要原因     

Spreading of proteins and its effect on adsorption and desorption kinetics

The kinetics of adsorption of lysozyme and alpha-lactalbumin from aqueous solution on silica and hydrophobized silica has been studied. The initial rate of adsorption of lysozyme at the hydrophilic surface is comparable with the limiting flux. For lysozyme at the hydrophobic surface and alpha-lactalbumin on both surfaces, the rate of adsorption is lower than the limiting flux, but the adsorption proceeds cooperatively, as manifested by an increase in the adsorption rate after the first protein molecules are adsorbed. At the hydrophilic surface, adsorption saturation (reflected in a steady-state value of the adsorbed amount) of both proteins strongly depends on the rate of adsorption, but for the hydrophobic surface no such dependency is observed. It points to structural relaxation ("spreading") of the adsorbed protein molecules, which occurs at the hydrophobic surface faster than at the hydrophilic one. For lysozyme, desorption has been studied as well. It is found that the desorbable fraction decreases after longer residence time of the protein at the interface.     

The charging properties of monodisperse colloidal silica in symmetrical quaternary ammonium ion solutions

The zeta potentials of monodisperse colloidal silica were measured as a function of pH and as a function of the concentration of tetramethyl-, tetrapropyl-, and tetrapentylammonium bromide in aqueous solution. The variation of the potential with pH was explained by a simple, point ion adsorption model from which a dissociation constant and Gibbs free energy of dissociation were obtained. By contrast, the results obtained with tetraalkyl ammonium ions could not be explained using this simple model. However, incorporation of a hydrophobic adsorption term and finite ion size in a more sophisticated model gave good agreement with experimental measurements. The validity of the model is supported by the reasonable dissociation constants which were obtained on fitting the experimental data. Dissociation constants and the corresponding Gibbs free energies were calculated for both hydrophobic and site binding adsorption for each tetraalkyl ammonium ion. The stability of colloidal silica in solutions of these ions can now be satisfactorily explained in terms of the electrostatic repulsion between particles rather than by a hydrophobic/hydrophilic solvation effect previously proposed.     

The surface energy of hydrophilic and hydrophobic adsorbents

Water vapor adsorption and heats of water wetting are studied for hydrophilic quartz, hydrophobic-hydrophilic talc, and hydrophobized Silochrom samples. Water contact angles on the materials under examination are found. The surface thermodynamic parameters of the sorbents are calculated from the data obtained. It is shown that boundary water layers on hydrophilic quartz surface are ordered to a higher extent, while those on hydrophobic basal surfaces of talc particles and hydrophobic surfaces of modified Silochrom samples are ordered to a lower extent relative to liquid water. An empirical equation relating the surface pressure of water films adsorbed on hydrophilic high-energy surfaces with the surface free energy of the latter is proposed. The values of surface free energy are estimated from this equation for a number of important hydrophilic adsorbents.     

On the wettability of lipid DPPC films

By employing temperature-programmed desorption and time-of-flight secondary ion mass spectroscopy, the adsorption of water on the hydrophilic and hydrophobic surfaces of a lipid (DPPC) film has been investigated. It could be shown that it is possible to prepare lipid films ex situ with a preferential orientation of the lipid molecules on a solid support and to retain their specific properties under ultrahigh vacuum conditions. The water adsorption and desorption kinetics on the hydrophilic and hydrophobic surfaces provided by a lipid film are discussed in terms of their structural and chemical properties.     

Mass transfer model of triethylamine across the n-decane/water interface derived from dynamic interfacial tension experiments

This publication presents a detailed experimental and theoretical study of mass transfer of triethylamine (TEA) across the n-decane/water interface. In preliminary investigations, the partition of TEA between n-decane and water is determined. Based on the experimental finding that the dissociation of TEA takes place in the aqueous and in the organic phase, we assume that the interfacial mass transfer is mainly affected by adsorption and desorption of ionized TEA molecules at the liquid/liquid interface. Due to the amphiphilic structure of the dissociated TEA molecules, a dynamic interfacial tension measurement technique can be used to experimentally determine the interfacial mass transport. A model-based approach, which accounts for diffusive mass transport in the finite liquid bulk phases and for adsorption and desorption of ionized TEA molecules at the interface, is employed to analyze the experimental data. In the equilibrium state, the interfacial tension of dissociated TEA at the n-decane/water interface can be adequately described by the Langmuir isotherm. The comparison between the theoretical and the experimental dynamic interfacial tension data reveals that an additional activation energy barrier for adsorption and desorption at the interface has to be regarded to accurately describe the mass transport of TEA from the n-decane phase into the aqueous phase. Corresponding adsorption rate constants can be obtained by fitting the theoretical predictions to the experimental data. Interfacial tension measurements of mass transfer from the aqueous into the organic phase are characterized by interfacial instabilities caused by Marangoni convection, which result in an enhancement of the transfer rate across the interface.     

Conformational reorientation of immunoglobulin G during nonspecific interaction with surfaces.

To achieve a better understanding of the nonspecific adsorption process of proteins on solid surfaces, the mechanism of this interaction was investigated by a model system comprising the structurally flexible ("soft") protein goat anti-rabbit immunoglobulin G and a set of chemically defined surfaces. The thermodynamic properties of both protein and surfaces were derived from contact angle measurements by applying the Lifshitz-van der Waals acid-base approach, and the Gibbs free enthalpy of interaction was calculated. The protein shows two conformational states, one hydrophobic and the other hydrophilic. The interaction energy indicates that the hydrophobic conformation favorably adsorbs onto the surfaces. With real-time binding kinetics, measured by a supercritical angle fluorescence biosensor, we show that during the nonspecific adsorption the protein performs a reorientation in its three-dimensional amino acid structure from a hydrophilic to a hydrophobic molecular structure. Unlike the rates of adsorption and desorption, the transition rate is independent of the type of surface and only influenced by the structural reorganization of the protein.     

Ion-specific weak adsorption of salts and water/octanol transfer free energy of a model amphiphilic hexapeptide

An amphiphilic hexapeptide has been used as a model to quantify how specific ion effects induced by addition of four salts tune the hydrophilic/hydrophobic balance and induce temperature-dependant coacervate formation from aqueous solution. The hexapeptide chosen is present as a dimer with low transfer energy from water to octanol. Taking sodium chloride as the reference state in the Hofmeister scale, we identify water activity effects and therefore measure the free energy of transfer from water to octanol and separately the free energy associated to the adsorption of chaotropic ions or the desorption of kosmotropic ions for the same amphiphilic peptide. These effects have the same order of magnitude: therefore, both energies of solvation as well as transfer into octanol strongly depend on the nature of the electrolytes used to formulate any buffer. Model peptides could be used on separation processes based on criteria linked to "Hofmeister" but different from volume and valency.     

Hydrophobic and electrostatic interactions in adsorption of surface-active substances. Tetraalkylammonium salts

A relationship between the standard free energies of adsorption from aqueous solution at the oil/water interface and the radii of organic cations as exemplified by symmetric tetraakylammonium salts has been studied. Hydrophobic effects are shown to be major contributors to the interaction of surfactants with the interface. An adsorption coefficient to quantitate the hydrophobic effects and to specify the changes of standard adsorption energy depending upon the cavity surface area of the detergent hydrocarbon radical in aqueous solution has been proposed. A new formulation of the Traube rule, taking into account the hydrophobic effects concomitant with a transfer of surfactants from the water bulk onto the interface, has also been given.Standard free energies for the adsorption of organic and inorganic ions from aqueous solution at the interface of immiscible liquids have been found. The proposed method is based on an extrapolation of the relationship between the standard adsorption energy of tetraalkylammonium salts and the square of cationic radius to zero ionic radius. The standard free energy of adsorption for an inorganic counter-ion is derived from an intercept on the y-axis cut off by a straight line. The experimental adsorption data on inorganic salts have been used to calculate the standard free energies of adsorption for a variety of ions.A method of estimating the difference in potential at the oil/water interface between the adsorption plane and the aqueous solution has been proposed. The sign of potential provides a clue to the orientation of water molecules at the interface between immiscible liquids.