Zwitterion adsorption

Fig. 3 a-c. Summary of data from different laboratories, obtained by surface force measurement, on the average layer thickness L as a function of tethered chain length for flat, tethered layers constructed by adsorption of amphiphilic polymers on mica. Adapted from Ref. 21. (a) Data of reference 20 on poly-tert-butylstyrene chains anchored by adsorbing blocks of poly-2-vinylpyridine. (b) Data of references 11 and 12 on polystyrene chains anchored by adsorbing blocks of poly-2-vinylpyridine. (c) Data of references 13 and 14 on polystyrene chains anchored by adsorbing zwitterionic groups [13] or by small adsorbing blocks of polyethyleneoxide [14]... 

Holmlin RE, Chen X, Chapman RG, Takayama S, Whitesides GM (2001) Zwitterionic SAMs that resist nonspecific adsorption of protein from aqueous buffer. Langmuir 17 2841-50... 

In the present work, we have synthesized two betaines and three sulfobetaines in very pure form and have determined their surface and thermodynamic properties of micellization and adsorption. From these data on the two classes of zwitterionics, energetics of micellization and adsorption of the hydrophilic head groups have been estimated and compared to those of nonionic surfactants. 

There has been a recent revival of interest in zwitterionic surfactants (L 4) because of certain useful properties shown by these molecules, including 1) mild behavior on the skin, 2) compatability with both anionics and cationics, 3) adsorption onto skin and hair, and 4) lime soap dispersing ability. Although this type of surfactant has been produced and used industrially for the last few decades, there have been few studies of the properties of well purified surfactants of this type (5-11) and almost all of these have been concerned with the micellar properties of these compounds rather than with their behavior at interfaces. 

The adsorption of amino acids on rutile and hydroxyapatite exhibits some characteristics of specific adsorption. The results can be interpreted in terms of electrostatic models of adsorption, however, if reorientation of adsorbed molecules is taken into consideration. The electrokinetic behavior of hydroxyapatite in glutamic acid is complicated because of a chemical reaction, possibly involving calcium ions. The study shows that it is necessary to take into consideration the orientation of adsorbed molecules, particularly for zwitterionic surfactants. 

MEKC is also performed using cationic, nonionic, and zwitterionic surfactants. Widely employed are cationic surfactant consisting of a long chain tetralkylammonium salt, such as cetyltrimeth-ylammonium bromide, which causes the reversal of the direction of the EOE, due to the adsorption of the organic cation on the capillary wall. Other interesting options include the use of mixed micelles resulting from the simultaneous incorporation into the BGE of ionic and nonionic or ionic and zwitterionic surfactants. Chiral surfactants, either natural as bile salts [207] or synthetic [208] are employed for enantiomer separations. 

Li et al. [278] have studied adsorption of L-phenylalanine at Au(lll) electrodes using electrochemical and subtractively normalized interfacial FTIR methods. It has been found that the adsorbed molecules change their orientation with the electrode potential. At a negatively charged surface, the compound was predominantly adsorbed in the neutral form of the amino acid. At potentials positive with respect to pzc, L-phenylalanine was adsorbed predominantly as zwitterion with —GOO ... 

Lipkowski and coworkers [332] have applied several electrochemical techniques to study adsorption of A -dodecyl-A, N-dimethyl-3-ammonio-l-propanesulfonate, a model zwitterionic surfactant, on Au(lll) electrode. Adsorption of this compound proceeded via a few states. The first two states were observed at potentials close to the zero charge potential. At low bulk concentrations, a nearly flat film of the adsorbed molecules was formed, which was converted into a hemimicellar state at higher concentrations. The second state at negative potentials corresponded to... 

One of the common charging mechanisms is the preferential adsorption of an ion from a solution on an initially uncharged surface. An example of this mechanism is the binding of a Ca2+ ion on a zwitterionic (which implies that the surface group consists of surface dipoles but no net charge) head group of a lipid layer. 

We previously have used electrophoretic mobility and 31P-NMR measurements to study the adsorption of alkaline earth cations to bilayer membranes formed from the zwitterionic lipid phosphatidyl choline (PC) (1). The lipids used in this previous study had unsaturated or... 

Capillary isoelectric focusing (cIEF) is used to separate zwitterionic compounds, such as peptides and proteins, on the basis of isoelectric point. The separation occurs as a result of a pH gradient that is established inside the capillary. It is important in cIEF to use coated capillaries to reduce or eliminate the EOF and to minimize solute adsorption if the EOF is too swift, it could sweep the analytes past the detector before the separation is complete. 

Tables 1 and 2 contain the formation heat values for adsorption complexes of sulfur-containing amino acids on a silica surface from gas phase and for their zwitterions with a hydrated environment...

The adsorption of sulfur-containing aminoacids from the gaseous phase occurs in the molecular form, while sorption from solution is more favorable in zwitterion forms saving the hydration shell. 

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