Kimura M, Maeda H, Ikeda S
Department of Chemistry, Faculty of Science, Nagoya University, Japan.
Biophys Chem. 1988 Jun;30(2):185-92. doi: 10.1016/0301-4622(88)85015-4.
The standard free energy change of the unimolecular conversion between the folded-chain beta-structure and random coil of uncharged poly(S-carboxymethyl-L-cysteine) was evaluated from the potentiometric titration curves extrapolated to zero time to reduce the effect of aggregation which occurred at slower rates than chain folding for most degrees of ionization. To reduce the remaining contribution from the aggregation, the results obtained at finite concentrations were further extrapolated to zero polymer concentration. A value of -(400 +/- 100) cal/mol was obtained for a sample of chain length 630. From the titration curves at the aggregation equilibrium, the total free energy change of the whole solution associated with the same conversion was determined. The contribution made by aggregation to the stability was determined from the difference between these two quantities, which turned out to be comparable with that from the unimolecular conversion.
通过将电位滴定曲线外推至零时间，评估了不带电荷的聚（S-羧甲基-L-半胱氨酸）折叠链β结构与无规卷曲之间单分子转化的标准自由能变化，以减少聚集的影响，在大多数电离度下，聚集发生的速率比链折叠慢。为了减少聚集的剩余贡献，将有限浓度下获得的结果进一步外推至零聚合物浓度。对于链长为630的样品，得到的值为-(400±100) cal/mol。根据聚集平衡时的滴定曲线，确定了与相同转化相关的整个溶液的总自由能变化。由聚集对稳定性的贡献通过这两个量之间的差值确定，结果表明其与单分子转化的贡献相当。
