Charles L. McCormick

Water-soluble polymers. 72. Synthesis and solution behavior of responsive copolymers of acrylamide and the zwitterionic monomer 6-(2-acrylamido-2-methylpropyldimethylammonio) hexanoate

A novel carboxybetaine monomer, 6-(2-Acrylamido-2-methylpropyldimethylammonio) hexanoate (AMPDAH), has been synthesized and copolymerized with acrylamide in an aqueous NaBr solution. The feed ratio of AM (M1): AMPDAB(M2), was varied from 98.5 : 2.5 to 0 : 100 mol %. The polymerizations were carried out to 20–30% conversion. Copolymer compositions were determined with 13C NMR by integration of the amido carbonyl resonances. Reactivity ratios determined from the nonlinear least-squares method gave values of r1 = 0.98 and r2 = 0.85, indicating random incorporation of the comonomers into the final copolymer. Molecular weights ranged from 7.3 to 4.7 × 106 g/mol. The solubility behavior of the copolymers is dependent on the mol % AMPDAH incorporated into the copolymers. When 25 mol % or more is incorporated, the copolymers are only swellable in aqueous media and attempts to solubilize these systems were unsuccessful. AMPDAH incorporation of 10 mol % or less resulted in copolymers soluble in aqueous media under a variety of conditions. The viscometric properties of copolymers with 10 mol % or less is reported as a function of pH and added electrolytes. At high pH in deionized water, the polyzwitterions show both inter- and intramolecular associations, which are disrupted by the addition of sodium chloride. In deionized water, as the pH of the aqueous medium is lowered, the copolymers exhibit dramatic increases in viscosity as the carboxylate groups are protonated and charge–charge repulsions of the quaternary ammonium groups induce polyelectrolyte behavior.

Water‐soluble polymers. 71. pH responsive behavior of terpolymers of sodium acrylate, acrylamide, and the zwitterionic monomer 4‐(2‐acrylamido‐2‐methylpropanedimethylammonio)butanoate

Terpolymers of sodium acrylate (NaA), acrylamide (AM), and the zwitterionic monomer 4-(2-acrylamido-2-methylpropanedimethylammonio) butanoate (AMPDAB) were prepared by the free radical polymerization in 0.5M NaBr aqueous solution using potassium persulfate as the initiator. The feed ratio of AMPDAB : NaA : AM was varied from 5 : 5 : 90 to 40 : 40 : 20 mol %, with the total monomer concentration held constant at 0.45M. Terpolymer compositions were determined by 13C NMR. Molecular weights varied from 3.0 × 105 to 9.7 × 106 g/mol. All terpolymers were soluble in deionized water and salt solutions at all pH values. The dilute and semidilute solution behavior of the terpolymers was studied as a function of composition, pH, and added electrolytes. Polyelectrolyte behavior was observed for all terpolymers at pH 8.5, as evidenced by high viscosity values at low polymer concentrations and viscosity decrease in the presence of added electrolytes. The reduced viscosity as a function of decreasing pH exhibits a minimum as the terpolymer undergoes a polyanion/polyzwitterion/polycation transition. Comparison of the solution behavior of the terpolymers to terpolymers of 3-(2-acrylamido-2-methylpropane dimethylammonio)-1-propane sulfonate (AMPDAPS), AM, and NaA (AADAPS series) as well as copolymers of AMPDAB and AM (AMPDAB series) have been made.

Water soluble polymers : 70. Effects of methylene versus propylene spacers in the pH and electrolyte responsiveness of zwitterionic copolymers incorporating carboxybetaine monomers

Abstract Water soluble polyzwitterions have been synthesized by free radical copolymerization of acrylamide with the novel carboxybetaine monomer, 2-(2-acrylamido-2-methylpropyldimethylammonio) ethanoate (AMPDAE). Feed ratios of 10 to 100 mol% AMPDAE were employed to give the polyzwitterion series, DAEAM. Copolymer compositions of low conversion samples were determined from 13 C n.m.r. by integration of the carbonyl resonances. Reactivity ratios were determined yielding an r 1 r 2 value of 0.6. Molecular weights range from 6.3 to 10.4 × 10 6 g mol −1 as determined by low angle laser light scattering. Dilute solution properties of the copolymers have been studied as a function of added electrolytes and pH. Intrinsic viscosity behaviour in NaCl solutions is dependent on the mol% of AMPDAE incorporated into the copolymers. Reduced viscosities were also examined as a function of the nature of added electrolytes, displaying higher viscosity values in accord with the Hoffmiester lyotropic series. The copolymers exhibit an enhancement in viscosity as pH is lowered due to protonation of the carboxylate groups which renders the polymer coil cationic due to the presence of quaternary ammonium groups. The solution behaviour of the copolymer containing 25 mol% AMPDAE, which possesses one methylene unit between the quaternary ammonium group and the carboxylate group, is compared to that of a copolymer containing 25 mol% 4-(2-acrylamido-2-methylpropyldimethylammonio) butanoate, which possesses three methylene units between the charged centres.

pH responsive microdomain formation in a De Novo polypeptide

Recombinant DNA technology has been employed to produce a polypeptide capable of forming pH responsive hydrophobic microdomains. The design of this peptide is based upon an idealized conceptual model in which electrostatic, hydrophobic, and hydration forces are responsible for the association of amphipathic alpha-helical elements. Reduction in solution pH is responsible for reducing electrostatic repulsions between similarly charged residues, promoting the hydrophobic collapse of helical elements. A polymerizable synthetic element (dn31) has been synthesized and inserted into an appropriate expression vector. A clone containing a single copy of the dn31 gene (designated dn3lx1) was isolated and the corresponding gene product DN3Lx1 isolated. The physical properties of DN3Lx1 were examined in solution by gel filtration chromatography. CD, and fluorescence probe analysis. It was determined that DN3Lx1 self-associates in solution with the degree of aggregation dependent on pH and ionic strength. An initial objective of this work was to examine domain organization in higher molecular weight species containing ten or more repetitive sequences. However, attempts to express multiple repeats of DN3Lxn from concatemers were unsuccessful.