We present a thermodynamic study of the interaction of synthetic, linear polyelectrolytes with bovine serum albumin (BSA). All polyelectrolytes are based on poly(allyl glycidyl ether) which has been modified by polymer-analogous reaction with anionic (-SO₃Na), cationic (-NH₃Cl or -NHMe₂Cl) or zwitterionic groups (-NMe₂(CH₂)₃SO₃). While the anionic polymer shows a very weak interaction, the zwitterionic polymer exhibits no interaction with BSA (pI = 4.7) under the applied pH = 7.4, ionic strength (I = 23–80 mM) and temperature conditions (T = 20–37 °C). A strong binding, however, was observed for the polycations bearing primary amino or tertiary dimethyl amino groups, which could be analysed in detail by isothermal titration calorimetry (ITC). The analysis was done using an expression which describes the free energy of binding, DG_b, as the function of the two decisive variables, temperature, T, and salt concentration, c_s. The underlying model splits DG_b into a term related to counterion release and a term related to water release. While the number of released counter ions is similar for both systems, the release of bound water is more important for the primary amine compared to the tertiary N,N-dimethyl amine presenting polymer. This finding is further traced back to a closer contact of the polymers’ protonated primary amino groups in the complex with oppositely charged moieties of BSA as compared to the bulkier protonated tertiary amine groups. We thus present an investigation that quantifies both driving forces for electrostatic binding, namely counterion release and change of hydration, which contribute to a deeper understanding with direct impact on future advancements in the biomedical field.

中文翻译：

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线性聚电解质与蛋白质的相互作用：特定电荷-电荷相互作用和离子强度的作用

我们提出了合成线性聚电解质与牛血清白蛋白 (BSA) 相互作用的热力学研究。所有聚电解质均基于聚（烯丙基缩水甘油醚），该聚（烯丙基缩水甘油醚）已通过与阴离子（-SO ₃ Na）、阳离子（-NH ₃ Cl 或 -NHMe ₂ Cl）或两性离子基团（-NMe ₂ (CH ₂ ) ₃ SO ₃）。虽然阴离子聚合物表现出非常弱的相互作用，但在施加的 pH = 7.4、离子强度 (I = 23–80 mM) 和温度条件 (T = 20–37 °) 下，两性离子聚合物与 BSA (pI = 4.7) 没有相互作用C）。然而，对于带有伯氨基或叔二甲基氨基的聚阳离子，观察到了强结合，这可以通过等温滴定量热法 (ITC) 进行详细分析。使用描述结合自由能 D G _b的表达式进行分析，作为两个决定性变量温度T和盐浓度c _s的函数。底层模型拆分 D G _b分为与抗衡离子释放相关的术语和与水释放相关的术语。虽然两种系统释放的抗衡离子的数量相似，但结合水的释放对于伯胺而言比提供N，N-二甲基胺的叔胺聚合物更重要。与体积更大的质子化叔胺基团相比，该发现进一步追溯到复合物中聚合物的质子化伯氨基与 BSA 的带相反电荷部分的更紧密接触。因此，我们提出了一项研究，量化静电结合的驱动力，即反离子释放和水合作用的变化，这有助于更深入的了解，直接影响生物医学领域的未来发展。