Department of Chemistry, Nara Medical University, 840 Shijo-cho, Kashihara 634-8521, Japan.
Biomacromolecules. 2021 May 10;22(5):1944-1954. doi: 10.1021/acs.biomac.1c00061. Epub 2021 Apr 15.
Our earlier report described that a cyclic hemoglobin (Hb) monomer with two β subunits of a Hb molecule (αβ) bound through a flexible polyethylene glycol (PEG) chain undergoes reversible supramolecular ring-opening polymerization (S-ROP) to produce a supramolecular Hb polymer with a Hb-PEG alternating structure. In this work, we polymerized cyclic Hb monomers with different ring sizes (2, 5, 10, or 20 kDa PEG) to evaluate the thermodynamics of S-ROP equilibrium. Quantification of the produced supramolecular Hb polymers and the remaining cyclic Hb monomers in the equilibrium state revealed a negligibly small enthalpy change in S-ROP (Δ ≤ 1 kJ·mol) and a markedly positive entropy change increasing with the ring size (Δ = 26.8-33.2 J·mol·K). The results suggest an entropy-driven mechanism in S-ROP: a cyclic Hb monomer with the larger ring size prefers to form a supramolecular Hb polymer. The S-ROP used for this study has the potential to construct submicrometer-sized Hb-PEG alternating polymers having structural regularity.
我们之前的报告描述了一种通过柔性聚乙二醇 (PEG) 链连接两个血红蛋白 (Hb) 分子的β亚基的环状 Hb 单体发生可逆的超分子开环聚合 (S-ROP)，生成具有 Hb-PEG 交替结构的超分子 Hb 聚合物。在这项工作中，我们聚合了具有不同环大小（2、5、10 或 20 kDa PEG）的环状 Hb 单体，以评估 S-ROP 平衡的热力学。对平衡状态下产生的超分子 Hb 聚合物和剩余的环状 Hb 单体进行定量分析表明，S-ROP 的焓变可忽略不计（Δ ≤ 1 kJ·mol），并且随着环大小的增加，熵变明显为正（Δ = 26.8-33.2 J·mol·K）。结果表明 S-ROP 是一种熵驱动的机制：具有较大环大小的环状 Hb 单体更倾向于形成超分子 Hb 聚合物。用于本研究的 S-ROP 有可能构建具有结构规则的亚微米 Hb-PEG 交替聚合物。
