Interfacial conformation

The plots of Ef in Figure 6.13 for the longer SGs look similar to the plots for the shortest SGs—CF3SO3H and CH3SO3H—presented in Roudgar et al. This corroborates that basic interfacial conformations and correlations are independent of the chemical architecture of polymeric side chains. It implies that the main structural effects at hydrated interfacial arrays in PEMs are due to the structure of the acid head group and the packing density of SGs. 

Complementary information about the interfacial conformation of the carbosilane dendrimers was obtained from u-A isotherms measured during compression of molecular films at the air/water interface [74]. The full reversibility of the isotherm in Fig. 13 a indicated that the experiment was done under equilibrium conditions, and that the data give direct evidence on the phase behavior. Two transitions, marked by I and II in Fig. 13 a, were observed for the OH terminated carbosilane dendrimer (dendrimer 2 in Fig. 8). The first transition (I) was... 

These calculations suggest that /3-casein and egg yolk lecithin do not mix ideally, but the interaction between them promotes a condensation or non-additivity of molecular areas. Also, tt in the egg lecithin—/3-casein system can be as high as 29 dynes/cm (Figure 4) whereas the maximum pressure exerted by the protein alone is about 22 dynes/cm (Figure 2). Of course, the assumption that the interfacial conformation of the protein is unchanged by the presence of lipid is valid only when is less than the collapse pressure of the pure protein film. Between this point and 29 dynes/cm the protein has probably only partially penetrated. Further information about the nature of the lipid-protein interaction can be gained from the data in Figure 4. 

Interfacial conformational transitions. Once adsorption equilibrium is achieved, replacement of the equilibrium bulk solution with pure solvent (or buffer solution) does not general 1> lead to much desorption, especial Ilf with high molecular weight macromolecules. The interfacial laifer then remains in a metastable state where it is possible to test its structural response to external pertubations such as variations of pH, temperature, ionic strength or ionic composition. However, if the solvent power is significantly increased with respect to adsorption conditions, significant desorption may occur, and the thickness veiriations then reflect variations of both molecular interfacial dimensions and concentration. 

As discussed before in the case of nucleic acids the authors have also considered the incidence of the interfacial conformation of the hemoproteins on the appearance of the SERRS signals from the chromophores. Although under their Raman conditions no protein vibration can be observed, the possibility of heme loss or protein denatura-tion are envisaged to explain a direct interaction of the heme chromophores with the electrode surface in the case of the adsorl Mb. extensive denaturation of Cytc at the electrode appears unlikely to the authors on the basis of the close correspondence of the surface and solution spectra. Furthermore, the sluggish electron transfer kinetics measured by cyclic voltammetry in the case of Cytc is also an argument in favour of some structural hindrance for the accessibility to the heme chromophore in the adsorbed state of Cytc. This electrochemical aspect of the behaviour of Cytc has very recently incited Cotton et al. and Tanigushi et al. to modify the silver and gold electrode surface in order to accelerate the electron transfer. The authors show that in the presence of 4,4-bipyridine bis (4-pyridyl)disulfide and purine an enhancement of the quasi-reversible redox process is possible. The SERRS spectroscopy has also permitted the characterization of the surface of the modified silver electrode. It has teen thus shown, that in presence of both pyridine derivates the direct adsorption of the heme chromophore is not detected while in presence of purine a coadsorption of Cytc and purine occurs In the case of the Ag-bipyridyl modified electrode the cyclicvoltammetric and SERRS data indicate that the bipyridyl forms an Ag(I) complex on Ag electrodes with the appropriate redox potential to mediate electron transfer between the electrode and cytochrome c. 

Here we attempt to briefly introduce the principle of the AFM based SMFS and then focus on using SMFS to address three main questions force induced conformation transition, interaction between small molecules and polymers, and the interfacial conformation and adhesive energy of polymers. 

Figure 10.1. Binding of an interfacial enzyme to a substrate interface. Upon binding, the enzyme adopts an interfacial conformation. The kinetics of binding is described by the rate constants of binding (kon) and dissociation (koff).

Such observations raise the importance of interfacial conformation and the role this conformation plays in fat crystal microstructure, particularly in emul-... 

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