Coenzyme models. IV. Effect of polymer micelles on rate and equilibrium of addition of cyanide ion to N‐substituted 3‐carboxamidopyridinium ions

The water‐soluble poly(1‐vinyl‐2‐ethylimidazole) quaternized with ethyl bromide and lauryl bromide was prepared; lauryl group content, 8.8 mol% (L‐9), 28.9 mol% (L‐29), and 40.9 mol% (L‐41). The λ_max value of methyl orange near 460 nm shifted to shorter wavelengths (417–433 nm) in the aqueous solution of L‐29 and L‐41, and the intrinsic viscosity of L‐29 was more than ten times smaller than that of L‐9. The rate and equilibrium constants (k_ƒ and K) for addition of cyanide ion to the N‐substituted 3‐carboxamidopyridinium ions were studied at 30°C, where N‐substituents employed were n‐propyl, n‐hexyl, benzyl, 2,6‐dichlorobenzyl, and n‐lauryl. The kinetic parameters for n‐lauryl‐3‐carboxamidopyridinium were markedly increased in the presence of L‐29 and L‐41 and with increasing polymer concentrations (84‐fold for k_ƒ and 7800‐fold for K), especially at low ionic strength, whereas L‐9 decelerated the addition reaction. These distinct behaviors mean that L‐29 and L‐41 are classified as micellelike polymers and L‐9 as a polyelectrolytelike polymer. However, L‐29 depressed the rate of the forward reaction for benzyl‐3‐carboxamidopyridinium, acting like a simple polyelectrolyte. Therefore, the polymer micelle can provide both the microenvironments characteristic of polyelectrolytes and micelles, depending on the hydrophobicity of substrates.