Reaction kinetics in dilute solutions of chain molecules carrying randomly spaced reactive and catalytic chain substituents. I. Estimation of ring closure probabilities from kinetic data and computer simulation

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Abstract
Acrylamide was copolymerized with small proportions of monomers containing a p‐nitrophenyl ester group and a small amount of a monomer containing a pyridine residue. The hydrolysis of the ester groups was studied under conditions where the rate of the process was controlled by interaction with pyridine residues attached to the same chain. Variables studied included the mode of attachment of the ester groups to the chain backbone, the concentration of the catalytic pyridine residues in the chain and the fraction of the pyridine present in the unprotonated, catalytically active form. Kinetic data obtained at different pH values gave the same results if the extent of reaction was expressed as a function of the product of the experimental time and the fraction of pyridine residues in the basic form. This proves that the intramolecular process is not controlled by the rate at which cyclic conformations are formed but by their probability. The reaction deviated from first‐order kinetics because the reactive groups had varying spacings from the catalytic groups. Experimental data were in good agreement with the kinetics derived by computer simulation if the probability of group interaction was made inversely proportional to the square of their separation along the chain molecule. Initial apparent first‐order rate constants were about 40% of the value predicted on the basis of a simple theory based on the average extension of the polymer coils.
Funding Information
  • National Institutes of Health (MG-05811)