Vollhardt D, Fainerman V B
Max-Planck-Institut für Kolloid und Grenzflächenforschung, Potsdam/Golm, Germany.
Adv Colloid Interface Sci. 2000 May 24;86(1-2):103-51. doi: 10.1016/s0001-8686(00)00034-8.
The review demonstrates the recent theoretical and experimental progress in the understanding of penetration systems at the air-water interface in which a dissolved amphiphile (surfactant, protein) penetrates into a Langmuir monolayer. The critical review of the existing theoretical models which describe the thermodynamics of the penetration are critically reviewed. Although a rigorous thermodynamic analysis of penetration systems is unavailable due to their complexity, some model assumptions, e.g. the invariability of the activity coefficient of the insoluble component of the monolayer during the penetration of the soluble component results in reasonable solutions. New theoretical models describing the equilibrium behaviour of the insoluble monolayers which undergo the 2D aggregation in the monolayer, and the equations of state and adsorption isotherms which assume the existence of multiple states (conformations) of a protein molecule within the monolayer and the non-ideality of the adsorbed monolayers are now available. The theories which describe the penetration of a soluble surfactant into the main phases of Langmuir monolayers were presented first for the case of the mixture of the molecules possessing equal partial molar surfaces (the mixture of homologues), with further extension of the models to include the interesting process of the protein penetration into the monolayer of 2D aggregating phospholipid. This extension was based on a concept which subdivides the protein molecules into independent fragments with areas equal to those of the phospholipid molecule. Various mechanisms for the effect of the soluble surfactant on the aggregation of the insoluble component were considered in the theoretical models: (i) no effect on the aggregate formation process; (ii) formation of mixed aggregates; and (iii) the influence on the aggregating process via the change of aggregation constant, but without any formation of mixed aggregates. Accordingly depending on the mechanism, different forms of the equations of state of the monolayer and of the adsorption isotherms of soluble surfactant are predicted. Based on the shape of the experimental pi-A isotherms, interesting conclusions can be drawn on the real mechanism. First experimental evidence has been provided that the penetration of different proteins and surfactants into a DPPC monolayer in a fluid-like state induces a first order main phase transition of pure DPPC. The phase transition is indicated by a break point in the pi(t) penetration kinetics curves and the domain formation by BAM. Mixed aggregates of protein with phospholipid are not formed. These results agree satisfactorily with the predictions of the theoretical models. New information on phase transition and phase properties of Langmuir monolayers penetrated by soluble amphiphiles are obtained by coupling of the pi(t) penetration kinetics curves with BAM and GIXD measurements. The GIXD results on the penetration of beta-lactoglobulin into DPPC monolayers have shown that protein penetration occurs without any specific interactions with the DPPC molecules and the condensed phase consists only of DPPC.
该综述展示了在理解溶解的两亲分子（表面活性剂、蛋白质）渗透到朗缪尔单分子层的气-水界面渗透体系方面的近期理论和实验进展。对描述渗透热力学的现有理论模型进行了批判性审视。尽管由于渗透体系的复杂性，无法进行严格的热力学分析，但一些模型假设，例如在可溶性组分渗透过程中，单分子层不溶性组分的活度系数不变，能得出合理的解决方案。现在已有描述在单分子层中经历二维聚集的不溶性单分子层平衡行为的新理论模型，以及假设单分子层内蛋白质分子存在多种状态（构象）且吸附单分子层具有非理想性的状态方程和吸附等温线。描述可溶性表面活性剂渗透到朗缪尔单分子层主相的理论，首先是针对具有相等偏摩尔表面积的分子混合物（同系物混合物）的情况提出的，随后模型进一步扩展，将蛋白质渗透到二维聚集磷脂单分子层这一有趣过程纳入其中。这种扩展基于一个概念，即将蛋白质分子细分为面积与磷脂分子相等的独立片段。理论模型中考虑了可溶性表面活性剂对不溶性组分聚集的各种作用机制：（i）对聚集体形成过程无影响；（ii）形成混合聚集体；（iii）通过改变聚集常数对聚集过程产生影响，但不形成任何混合聚集体。相应地，根据作用机制，预测了单分子层状态方程和可溶性表面活性剂吸附等温线的不同形式。基于实验π-A等温线的形状，可以就实际作用机制得出有趣的结论。已提供首个实验证据，即不同蛋白质和表面活性剂渗透到处于类流体状态的二棕榈酰磷脂酰胆碱（DPPC）单分子层中会引发纯DPPC的一级主相变。相变由π(t)渗透动力学曲线中的断点和BAM观察到的畴形成表明。未形成蛋白质与磷脂的混合聚集体。这些结果与理论模型的预测令人满意地相符。通过将π(t)渗透动力学曲线与BAM和掠入射X射线衍射（GIXD）测量相结合，获得了关于被可溶性两亲分子渗透的朗缪尔单分子层相变和相性质的新信息。β-乳球蛋白渗透到DPPC单分子层的GIXD结果表明，蛋白质渗透过程中与DPPC分子没有任何特异性相互作用，凝聚相仅由DPPC组成。
