Water interface adsorption at air

Anand, K., Damodaran, S. (1996). Dynamics of exchange between asi-casein and p-casein during adsorption at air-water interface. Journal of Agricultural and Food Chemistry, 44, 1022-1028. 

Adsorption at Air -Water Interface. The data for the adsorption of /3-casein at the clean air—water interface (Figures 2 and 3) can be combined to give surface pressure-molecular area (A) curves for the adsorbed protein films. For -casein the resultant tt-A curve is similar to that obtained by spreading the protein (12,16,18) therefore, this flexible protein has essentially the same conformation when spread or adsorbed. At low 7T, A = 2 m2/mg or 38 A2/residue, so there is sufficient space for the peptide backbone to lie in the plane of the interface with no loops or tails of residues protruding into either bulk phase. A conformational change occurs at ir = 7 dynes/cm where loop-tail formation commences (12). Monolayer coverage (A 0.4 m2/mg = 1610 A2/molecule) is complete when Cp 10"4 %. At this point the protein is in a close-packed,... 

In many cases the adsorption rate is diffusion controlled, at least in the initial stages, with the rate adequately described by Eqs. (6) and (7) at low surface pressures [30-33]. The F versus t 12 plots for /3-casein and lysozyme adsorption at air/water interface give straight... 

Defeijter, J. A. Benjamins, J. Veer, F. A., Ellipsometry as a tool to study adsorption behavior of synthetic and biopolymers at air water interface, Biopolymers 1978, 17, 1759 1772... 

In contrast with inorganic salts whose adsorption at water-air interface is negative, surfactants are strongly adsorbed at water-air interface, and this results in depression of the surface tension. In very dilute solutions of surfactants, adsorption at water air interface can lead to substantial depletion of the solution. Orientation of surfactant molecules at air-water interface is illustrated in Fig. 4.64. 

It was shown in the detailed investigation of Graham and Phillips [34,36,43] that the F-Cb isotherm for /3-casein at air/water interface revealed a well-defined plateau over the wide concentration range. However, at Cb> 10 2 wt % the film thickness and F increase further (without any significant changes in 0) due to the presence of reversibly adsorbed molecules. This reversibility can be connected with either formation of second and subsequent layers [36] or molecular reorientation of adsorbed /3-cascin molecules [26]. The adsorption isotherms for lysozyme and bovine serum albumin (BSA) do not... 

As an example of a membrane model, phospholipid monolayers with negative charge of different density were used. It had already been found ( ) and discussed O) that the physical and biological behavior of phospholipid monolayers at air-water interfaces and of suspensions of liposomes are comparable if the monolayer is in a condensed state. Two complementary methods of surface measurements (using radioactivity and electrochemical measurements), were used to investigate the adsorption and the dynamic properties of the adsorbed prothrombin on the phospholipid monolayers. Two different interfaces, air-water and mercury-water, were examined. In this review, the behavior of prothrombin at these interfaces, in the presence of phospholipid monolayers, is presented as compared with its behavior in the absence of phospholipids. An excess of lipid of different compositions of phos-phatidylserine (PS) and phosphatidylcholine (PC) was spread over an aqueous phase so as to form a condensed monolayer, then the proteins were inject underneath the monolayer in the presence or in the absence of Ca. The adsorption occurs in situ and under static conditions. The excess of lipid ensured a fully compressed monolayer in equilibrium with the collapsed excess lipid layers. The contribution of this excess of lipid to protein adsorption was negligible and there was no effect at all on the electrode measurements. 

Kawamura K, Suzuki I, Fujii Y, Watarrabe O (1994) Ice core record of polycyclic aromatic hydrocarbons over the past 400 years. Naturwissenschaften 81 502-505 Kelly CP, Cramer CJ, Truhlar DG (2004) Predicting adsorption coefficients at air-water interfaces using universal solvation and surface area models. J Phys Chem B 108 12882-12897... 

SEIRA and SERS are powerful techniques for stmctural characterization of ultra thin films and well-ordered monolayer on metal surfaces. Thin films at interfaces are prepared by different procedures and developed for various applications. The fabrication and characterization of ultra thin films is a permanent area of research where some of the most interesting subjects are (a) bilayers and monolayers at liquid-liquid interface, (b) adsorption monolayers and Langmuir (water-insoluble) monolayers at air-water interface, (c) adsorption films and self-assembled monolayers (SAMs) at liquid-solid interface and Langmuir-Blodgett Alms, cast (deposit) films and spin-coat films at air-solid interface. Studies about molecular organization of monolayers of porphyrins derivatives, of azamacrocy-cles and their metallic derivatives among the many SEIRA applications to films and interfaces, were published . 

Due to diphylic character of MR and its ability of self-organization in a solution it can behave similarly to nonionic surfactants. Adsorption of MR was shown to be mixed-diffusion barrier controlled (pH 7.4). MR was also shown to change thermodynamic affinity of lysozyme to the solvent with the resulting the protein being slightly less or more surface active depending on MR concentration. Under used conditions MR and lysozyme can compete in adsorption process at air/water interface [4]. 

FIGURE 1 Dynamic curves of adsorption of MR in mixture with lysozyme at air/water interface at 25°C MR concentrations 1.63-67.2 mM and constant protein concentration 5.1X10- M. 

Martirosova, E. L Plashchina, I. G. Adsorption behavior of methylresorcinol and its mixtures with lysozyme at air-water interface. In Biochemistry and Biotechnology. Nova Science Publishers. N.-Y. 2012, 95-104. 

The different surfactants can exist at air-water interface in a form of ions and neutral molecules. When the SASs are adsorbed in the ionized state with the charge of their surface-active ions h-1 or -1, then the adsorption F, is calculated vs. concentration C using Equation 8. A.27 from Appendix 8. A at n = 2, that is,... 

In either case, near a metal or at an air/water interface, the extent of hydration of an ion tends to be restricted (Conway, 1975) due to limited accessibility of the solvent to the ion. This may lead to an increase or a decrease in energy dependent on whether the image, or equivalent polarization interactions on each side of the interface, are repulsive or attractive, respectively. At electrodes, the latter situation usually arises, because of the almost infinite dielectric constant of a metal, while at air/water interfaces the former arises, giving negative adsorption. 

It is generally found for simple inorganic ions that their adsorption or surface excess is negative at air/water interfaces. For sufficiently hydrophobic ions, however, e.g., alkyl- and aryl-ammonlum-type ions, or fatty acid anions, the is positive. 

Although a multilayer film formation is the mle at air-water interfaces [73-77], a monolayer film formation is the rule at sohd-water interfaces [68,78-86]. In fact, it is anticipated that study of monolayer adsorption of protein will shed light on understanding multilayer formation at air-water interfaees. 

Fig. 3. KCl 0.1 M + KI 0.1 M mixture at air-water interface. Top PM interface-ions potentials. Bottom HNC ionic interface distributions. Dotted lines image force + dispersion potentials of Ref 7. Thick lines an extra attraction must be added for the anions in order to reproduce the experimental adsorption. (From Ref. 10.)...

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