Cationic zwitterionic, surface

Fig. 9 Example of a contact-killing and microbe-repelling surface, (a) Antimicrobial cationic polyW.iV-dimethyl-iVTethoxycarbonylmethyll-iV-P -tniethacryloyloxylethyll-ammonium bromide) left structure) effectively kills bacteria, (b) The polymer is converted into the corresponding nonfouling zwitterionic derivative (right structure) upon hydrolysis, (c) Dead bacteria remaining on the surface are repelled from the nonfouling surface, (d) The zwitterionic surface itself is highly resistant to bacterial adhesion. Reproduced and adapted from [136]...

Structure Formation in Surfactant Solutions. Surfactants, also referred to as soaps, detergents, tensides, or surface active agents, are amphiphilic molecules possessing both hydrophilic and hydrophobic regions. They can be classified as anionic, cationic, zwitterionic, or nonionic (neutral) depending upon the nature of the polar... 

All dispersing agents are surface active and they can be simple surfactants (anionic, cationic, zwitterionic or nonionic), polymers or polyelectrolytes. The dispersing agent should be soluble (or at least dispersible) in the liquid medium and it should adsorb at the solid/liquid interface. 

Surfactants used as lubricants are added to polymer resins to improve the flow characteristics of the plastic during processing they also stabilise the cells of polyurethane foams during the foaming process. Surfactants are either nonionic (e.g. fatty amides and alcohols), cationic, anionic (dominating class e.g. alkylbenzene sulfonates), zwitterionic, hetero-element or polymeric (e.g. EO-PO block copolymers). Fluorinated anionic surfactants or super surfactants enable a variety of surfaces normally regarded as difficult to wet. These include PE and PP any product required to wet the surface of these polymers will benefit from inclusion of fluorosurfactants. Surfactants are frequently multicomponent formulations, based on petro- or oleochemicals. 

The effect of micelles on these spontaneous hydrolyses is difficult to explain in terms of kinetic solvent effects on these reactions. Mukerjee and his coworkers have refined earlier methods for estimating apparent dielectric constants or effective polarities at micellar surfaces. For cationic and zwitterionic betaine sulfonate micelles Def is lower by ca 15 from the value in anionic dodecyl sulfate micelles (Ramachandran et al., 1982). We do not know whether there is a direct connection between these differences in effective dielectric constant and the relation between reaction rates and micellar charge, but the possibility is intriguing. 

Several additional studies were carried out to obtain information about the precise behavior of the various components in the model system. The interplay between the manganese porphyrin and the rhodium cofactor was found to be crucial for an efficient catalytic performance of the whole assembly and, hence, their properties were studied in detail at different pH values in vesicle bilayers composed of various types of amphiphiles, viz. cationic (DODAC), anionic (DHP), and zwitterionic (DPPC) [30]. At pH values where the reduced rhodium species is expected to be present as Rh only, the rate of the reduction of 13 by formate increased in the series DPPC < DHP < DODAC, which is in line with an expected higher concentration of formate ions at the surface of the cationic vesicles. The reduction rates of 12 incorporated in the vesicle bilayers catalyzed by 13-formate increased in the same order, because formation of the Rh-formate complex is the rate-determining step in this reduction. When the rates of epoxidation of styrene were studied at pH 7, however, the relative rates were found to be reversed DODAC DPPC < DHP. Apparently, for epoxidation to occur, an efficient supply of protons to the vesicle surface is essential, probably for the step in which the Mn -02 complex breaks down into the active epoxidizing Mn =0 species and water. Using a-pinene as the substrate in the DHP-based system, a turnover number of 360 was observed, which is comparable to the turnover numbers observed for cytochrome P450 itself. 

Lewis RNAH, McElhaney RN (2000) Surface charge markedly attenuates the nonlamellar phase-forming propensities of lipid bilayer membranes calorimetric and P-31-nuclear magnetic resonance studies of mixtures of cationic, anionic, and zwitterionic lipids. Biophys J 79 1455-1464... 

Both we and others have established various radical cation structure types, which deviate in important features from the structures of their neutral diamagnetic precursors. The pursuit of these novel structure types has given new direction to radical cation chemistry. We have noted that some of these species resemble plausible transition structures for the thermal rearrangement of the parent molecules, i.e. saddle points on the corresponding potential surfaces. From a different point of view, they can be envisaged as one-electron oxidation products of biradicals or zwitterions. However, this relationship rarely serves as a practical approach to their generation, since the potential bifunctional precursors are often unstable and not readily accessible. These radical cations are usually generated from related hydrocarbons or cyclic azo compounds. 

More recently, Chen et al. described a surface modification whereby the polymer poly(Ar,Ar-dimethyl-Af-(ethoxycarbonylmethyl)-Ar-[2/-(methacryloyloxy)ethyl]-ammonium bromide) was grafted from a surface via ATRP [136], The cationic polymer effectively kills E. coli and is subsequently converted into a zwitterionic polymer by hydrolysis of the head group (Fig. 9). It then repels all attached cells dead or alive. This is the first example of a surface that can kill microbes on contact and repels them after that. The only downside of this elegant system is that it will eventually exhaust and turn into a more or less effective repelling surface. 

Studies of the interaction of monovalent cations with the dipalmytoyl phosphatidylcholine/water system have shown that monovalent cations have practically no effect on the lamellar phase repeat distance [293-295]. Direct measurements of the force versus distance relationship between zwitterionic phospholipid bilayers deposited on mica surfaces have also demonstrated that double layer forces arising from ion binding are... 

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