Intracellular water is highly confined with approximately 40% of the cell volume occupied by biomolecules. Crowding alters water dynamics and interactions with biomolecules. In biochemical experiments, artificial crowders are commonly used to mimic intracellular environments, but their effects on biomolecules remain elusive. Here, we investigate the crowding effects by directly accessing the picosecond hydrogen-bond dynamics in crowded solutions using ultrafast two-dimensional infrared spectroscopy and all-atom molecular dynamics simulations. We quantify the effects of different crowding agents: small sugars; polysaccharides; and polyethylene glycol (PEG). Our results show that crowders introduce disorder within the first two solvation shells but stabilize ice-like order in water >1 nm from the crowder. The results show that accounting for crowder chemical structure, conformation, and crowder-solvent interactions is a key step toward a complete description of crowded solutions for in vitro for biomolecular studies.

细胞内水高度受限于生物分子占据的细胞体积的约40％。拥挤改变了水动力学以及与生物分子的相互作用。在生物化学实验中，通常使用人工拥挤物来模拟细胞内环境，但是它们对生物分子的影响仍然难以捉摸。在这里，我们通过使用超快速二维红外光谱和全原子分子动力学模拟直接访问拥挤溶液中的皮秒氢键动力学来研究拥挤效应。我们量化了不同拥挤剂的影响：小糖；多糖; 和聚乙二醇（PEG）。我们的结果表明，拥挤剂在前两个溶剂化壳中引入了混乱，但在离拥挤剂大于1 nm的水中稳定了类似冰的顺序。体外进行生物分子研究。