N‐methylmyristohydroxamic acid (1) bound to polymer micelles of laurylated poly(2‐ and 4‐vinylpyridines) (lauryl group contet: 2VP‐L, 30 mol%; 4VP‐L, 33 mol%) quantitatively reacted with p‐nitrophenyl acetate (NpAc) within a few seconds at 30°C, pH 8.95. Second order rate constants ka were 34,000 M−1 sec−1 for 1–2VP‐L and 11,400 M−1 sec−1 for 1–4VP‐L at μ = 0.5, and they were pronouncedly improved by a decrease in ionic strength (ka = 27,500–80,200 M−1 sec−1 at μ = 0.08). In contrast, poly(N‐ethyl‐4‐vinylpyridinium bromide) hardly affected the nucleophilicity of the hydroxamate ion. Therefore, the enhancement was considered to be associated with some micellar characteristics. Typical saturation phenomena of the reaction rate were observed for p‐nitrophenyl hexanoate (NpOCOPe) and 3‐nitro‐4‐acetoxybenzoic acid (NpAcCOOH). It was suggested that binding of NpOCOPe is caused by the hydrophobic interaction, while that of NpAcCOOH is probably induced by the electrostatic interaction. It is demonstrated that the cationic polymer micelle enormously activates the bound hydroxamate anion, and these complexes would be of much interest as a biomimetic system for enzyme catalysis.
All Science Journal Classification (ASJC) codes
- Organic Chemistry