Polyampholyte, defined

Because of the relatively rigid structure of adsorbed globular protein molecules, the adsorption isotherms display well-defined plateau values. The adsorption pattern, the effects of pH (i.e., charge of the protein), and ionic strength are in agreement with those of a polyampholyte the adsorbed mass generally is at a maximum around the isoelectric point of the protein/surface complex, that is, at conditions where the charges on the protein and the surface just compensate each other. 

Polymers are defined as hydrophobic if they are repelled by water, lipophobic if they are repelled by oils and hydrocarbons, hydrophilic if they are attracted to water, and lipophilic if they are attracted to oils and nonpolar solvents. Some polymers are repelled by both polar and nonpolar solvents and are called oleaginous. Others are known to contain both hydrophilic and hydrophobic components on the same polymer and are often referred to as polyampholytes. Polymers can be ionic or nonionic and, as a rule of thumb, polymers that are nonionic will be more comfortable in nonionic surroundings and ionic polymers will be more comfortable in polar surroundings. 

Solution Properties. The aqueous solution behavior of polyampholytes is dictated by coulombic interactions between the basic and acidic residues. Polyampholytes have the ability to exhibit both polyelectrolyte and antipolylelectrolyte behavior in aqueous media. Which type of behavior is exhibited depends on factors such as solution pH, copolymer composition, the relative strengths of the acidic and basic residues, and the presence/absence of low molecular weight electrolyte (239). A feature of polyampholytes—in particular those comprised of weak acidic and basic residues—is the so-called isoelectric point, or lEP. This is simply defined as the solution pH at which the polyampholyte is electrically neutral. Statistical polyampholytes often remain soluble at and around the lEP whereas block polyampholytes tend to be soluble above and below but insoluble at this critical pH. The lEP may be determined either by titration or by measuring the reduced viscosity as a function of pH—the lEP also represents the point at which the polyampholyte chain is in its most compact conformation and thus corresponds to the minimum in reduced viscosity (239,266). With a knowledge of the respective piiLa s and copolymer composition it is also possible to predict the lEP (267). 

Ampholytic block copolymer contains both positive and negative charges on different segments of the diblock copolymer. Stimuli responsive, water-soluble polyampholyte-Qo polymer has also been synthesized by ATRP [86]. First, a well-defined, stable Cl-terminated P(tBMAio2-b-DMAEMA,57)-Cl block copolymer was prepared by ATRP in the presence of the CuCl/HMTETA catalyst system [87]. ATRA of P(tBMA-b-DMAEMA)-Cl macro-initiator to excess C > using the same catalyst system at 90 °C offered a well-defined block copolymer-C ) (Scheme 3.5). Subsequently, the specific hydrolysis of P(tBMA-b-DMAEMA)-f)-C ) to remove the tert-butyl group in the presence of concentrated HCl in 1,4-dioxane offered well-defined polyampholyte P(MAA-b-DMAEMA)-b-Ca) polymer, which is responsive to both pH and temperature. 

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