POLY(N-ETHYL METHACRYLAMIDE): A MODEL POLYMER FOR THERMAL DENATURATION OF A PROTEIN

Lower Critical Solution Temperature of aqueous poly(N-ethyl methacrylamide), (PNEMA), {dollar}({lcub}rm Tsb{lcub}p{rcub} = 63spcirc C{rcub}),{dollar} was found to be sensitive to the type of anion, cation and concentration of the electrolyte. The precipitation phenomenon of aqueous PNEMA was investigated over the range of 25-65{dollar}spcirc{lcub}rm C{rcub}{dollar} using intrinsic viscosity, partial specific volume, light scattering and carbon-13 NMR spin-lattice relaxation measurements.; A modified viscosity relationship, {dollar}{lcub}rm nsb{lcub}rel{rcub}{rcub}{dollar} = 1 + (n) c, was found to fit the dilute aqueous solution viscosity behavior. The intrinsic viscosity measurements revealed that with increasing temperatures a "shrinkage" in the hydrodynamic volume occurred. The effect of 1-propanol and urea on the intrinsic viscosity showed a minimum as the addend concentration increased indicating that the effect of hydrogen bond breakers is similar to that of increasing the temperature. Partial specific volume of aqueous PNEMA (0.538 {dollar}{lcub}rm cm{rcub}sp3{dollar}/g at {dollar}25spcirc{lcub}rm C{rcub}){dollar} increased with the temperature. The concomitant increase with the shrinkage suggests that the association/aggregation is taking place. The apparent molecular weight increased with temperature as revealed by analysis of light scattering data. Such an increase in particle weight has been attributed to aggregation of polymer chains with increasing temperature. The second virial coefficient was found to be negative at all temperatures and the value increased approaching the vanishing point as the temperature of precipitation is approached.; The carbon-13 NMR longitudinal relaxation time carbonyl carbon in concentrated aqueous solutions of PNEMA showed an inverse temperature transition over the range 43-50{dollar}spcirc{lcub}rm C{rcub}.{dollar}; The mechanism of precipitation is viewed as a two-state denaturation process. The coil shrinks upon increasing the temperature favoring polymer-polymer contracts, such small spheres than coalesce to form aggregates leading to the precipitation of the polymer. The aggregation and the precipitation observed were reversible and non-cooperative. The aggregates was stabilized by the classical hydrophobic bonding.; The system is proposed to be a simple yet potential "model" for the thermal denaturation of water soluble proteins.; The solubility rule, that the precipitation temperature decreased as the relative hydrophobicity in a system increased was demonstrated by preparing two series of copolymers, using both a lower and a higher homologue of N-ethyl methacrylamide as the comonomers.