Electric dichroism studies of the bonding of Co(III) chelate with synthetic polyelectrolytes

Abstract

The interactions of bis-2-(2-pyridylazo)-1-naphthol Co(III), [Co(III) (αPAN) 2 +], with five kinds of synthetic polyelectrolytes have been studied by spectrophotometric and transient electric dichroism measurements. The polyelectrolytes were: poly(styrene sulphonic acid) (PSS); poly(acrylic acid) (PAA); poly( l-glutamic acid) (PLG); poly(N e ,N e - dicarboxylmethyl- l-lysine (PDCML); and poly( l-lysine) (PLL). The equilibrium constant of the reaction: ▪ with P = polyelectrolyte residue was determined spectrophotometrically: K 1 is > 10 7 M −1 (PSS); (1.4 ± 0.2) × 10 4 M −1 (PAA); (4.0 ± 0.4) × 10 3 M −1 (PLG); (1.4 ± 0.2) × 10 6 M −1 (PDCML); and < 10 2 M −1 (PLL) at pH 6–8. From transient electric dichroism, the angle (ψ) between the αPAN plane and the polymer axis was determined to be 65° (PSS); 52° (PAA); 55° (PLG); and 52° (PDCML). The large K 1 and ψ values for PSS are ascribed to the hydrophobic interaction between the aromatic αPAN ring and the styrene sulphonate residues of PSS. Using stopped-flow electric dichroism measurements, rapid transfer of a bound Co(III) chelate from the PDCML to PSS chains was shown to occur.