Pérez-Mas Luis, Martín-Molina Alberto, Quesada-Pérez Manuel, Moncho-Jordá Arturo
Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Granada, Avenida Fuentenueva S/N, 18001 Granada, Spain.
Phys Chem Chem Phys. 2018 Jan 24;20(4):2814-2825. doi: 10.1039/c7cp07679g.
In this work the equilibrium absorption of nanometric cosolutes (which could represent drugs, reactants, small globular proteins and other kind of biomacromolecules) inside neutral hydrogels is studied. We specially focus on exploring, for different swelling states, the competition between the steric exclusion induced by the cross-linked polymer network constituting the hydrogel, and the solvent-induced short-range hydrophobic attraction between the polymer chains and the cosolute particle. For this purpose, the cosolute partition coefficient is calculated by means of coarse-grained grand canonical Monte Carlo simulations, and the results are compared to theoretical predictions based on the calculation of the excluded and binding volume around the polymer chains. For small hydrophobic attractions or large cosolute sizes, the steric repulsion dominates, and the partition coefficient decreases monotonically with the polymer volume fraction, ϕ. However, for large enough hydrophobic attraction strength, the interplay between hydrophobic adhesion and the steric exclusion leads to a maximum in the partition coefficient at certain intermediate polymer density. Good qualitative and quantitative agreement is achieved between simulation results and theoretical predictions in the limit of small ϕ, pointing out the importance of geometrical aspects of the cross-linked polymer network, even for hydrogels in the swollen state. In addition, the theory is able to predict analytically the onset of the maximum formation in terms of the details of the cosolute-monomer pair interaction, in good agreement with simulations too. Finally, the effect of the many-body attractions between the cosolute and multiple polymer chains is quantified. The results clearly show that these many-body attractions play a very relevant role determining the cosolute binding, enhancing its absorption in more than one order of magnitude.
在这项工作中，研究了纳米级共溶质（可代表药物、反应物、小球形蛋白质和其他种类的生物大分子）在中性水凝胶中的平衡吸收情况。我们特别关注探索在不同溶胀状态下，构成水凝胶的交联聚合物网络所引起的空间排斥与聚合物链和共溶质颗粒之间溶剂诱导的短程疏水吸引力之间的竞争。为此，通过粗粒化巨正则蒙特卡罗模拟计算共溶质分配系数，并将结果与基于聚合物链周围排除体积和结合体积计算的理论预测进行比较。对于小的疏水吸引力或大的共溶质尺寸，空间排斥起主导作用，分配系数随聚合物体积分数ϕ单调下降。然而，对于足够大的疏水吸引力强度，疏水粘附和空间排斥之间的相互作用导致在一定中间聚合物密度下分配系数出现最大值。在小ϕ极限下，模拟结果与理论预测之间实现了良好的定性和定量一致性，这表明即使对于处于溶胀状态的水凝胶，交联聚合物网络的几何方面也很重要。此外，该理论能够根据共溶质 - 单体对相互作用的细节解析预测最大值形成的起始点，这也与模拟结果高度吻合。最后，量化了共溶质与多条聚合物链之间多体吸引力的影响。结果清楚地表明，这些多体吸引力在决定共溶质结合方面起着非常重要的作用，使其吸收增强了一个多数量级。
