Monte Carlo calculation was performed to evaluate the ring-closure probability of short polysarcosine chains. Calculations were made for unperturbed trans- non-self-intersecting trans-, and non-self-intersecting trans- and non-self-intersecting trans/cis-polysarcosine chains. In the latter case, the main chain amide bond was allowed to take cis as well as trans conformations. The ring-closure probability for unperturbed trans-polysarcosine chains was found to be substantially greater than for non-self-intersecting trans chains. Virtually no difference was observed between the ring-closure probability was used to estimate the cyclization constant, i.e., the ratio of rate constant for the intramolecular reaction of the two groups attached to the polymer ends to that of the intermolecular one. The results were compared with the experimental data for the intrachain reaction proceeding on polysarcosine chain reported in the first paper of this series. The Monte Carlo results roughly reproduced the experimental data and the calculated chain length dependence was consistent with the observed one for longer chains.

Binding Sites↗

PubMedDate not supplied

Monte Carlo calculation on trans/cis-polysarcosine.

Monte Carolo calculations were made on unperturbed trans-polysarcosine chain, non-self-intersecting trans-polysarcosine chain, and also non-self-intersecting trans/cis-polysarcosine chain by using a hard-sphere model. In the last case, an attempt was first made to introduce cis amide bond into the Monte Carlo calculation of polypeptide chain. Dipeptide energy maps for four different trans/cis dyad sequences were calculated. The allowed regions were consistent with the pairs of dihedral angles observed in cyclo-pentasarcosyl and cyclo-octasarcosyl. The mean-square end-to-end distance and higher even moments were obtained. The distribution function of the end-to-end distance was calculated from the even moments by using Nagai's equation and compared with the direct Monte Carlo data. The best agreement was obtained by cutting off the terms containing much higher order even moments than a critical order. The fractions of cis amide bond and of the four different trans/cis dyad sequences in polysarcosine were calculated. The results of calculation were compared with the 220-MHz NMR spectra of polysarcosine in three different solvents. Qualitative agreement was stained for longer chains.

Amides↗

PubMedDate not supplied

Intrachain reactions of a pair of reactive groups attached to polymer ends. 3. Intrachain charge-transfer complex on polysarcosine chains having terminal electron donor and terminal electron acceptor groups in chloroform solution.

Polysarcosine having a terminal p-dimethylaminoanilide group and a terminal 3,5-dinitrobenzoyl group was synthesized. The number-average degree of polymerization n was varied from 6 to 25. In chloroform solution this polymer showed a distinct absorption band around 455 nm, which was attributed mostly to intramolecular charge-transfer interactions. The extinction coefficient of the charge-transfer complex was determined for low molecular weight model compounds. Using the same extinction coefficient, the fraction of polymers forming intrachain charge-transfer complex was evaluated at infinite dilution. The fraction was about 0.15 for n = 6 and decreased asymptotically with increasing n finally to 0.03 for n = 25. These values are almost 20-100 times as large as those estimated from the Monte Carlo calculation and on the basis of the intramolecularly catalyzed hydrolysis of polysarcosine chain. This indicates that the cyclized conformations of polysarcosine chain are greatly stabilized by the formation of intrachain charge-transfer complex. The fraction of the cyclized polymer was decreased with increasing temperature for short chains. The thermodynamic parameters characterizing the conformational change required for cyclization in chloroform were obtained and compared with those for the same reaction in ethanol solution, as well as those for the intramolecularly catalyzed hydrolysis on polysarcosine chain in aqueous solution.

Chemical Phenomena↗