Chemistry Department, Ecole Normale Supérieure, UMR ENS-CNRS-UPMC 8640, rue Lhomond, 75005 Paris, France.
J Phys Chem B. 2010 Mar 4;114(8):3052-9. doi: 10.1021/jp9116886.
The hydrogen bond dynamics of water in a series of amphiphilic solute solutions are investigated through simulations and analytic modeling with an emphasis on the interpretation of experimentally accessible two-dimensional infrared (2D IR) photon echo spectra. We evidence that for most solutes the major effect in the hydration dynamics comes from the hydrophilic groups. These groups can retard the water dynamics much more significantly than can hydrophobic groups by forming strong hydrogen bonds with water. By contrast, hydrophobic groups are shown to have a very moderate effect on water hydrogen bond breaking kinetics. We also present the first calculation of the 2D IR spectra for these solutions. While 2D IR spectroscopy is a powerful technique to probe water hydrogen bond network fluctuations, interpretations of aqueous solution spectra remain ambiguous. We show that a complementary approach through simulations and calculation of the spectra lifts the ambiguity and provides a clear connection between the simulated molecular picture and the experimental spectroscopy data. For amphiphilic solute solutions, we show that, in contrast with techniques such as NMR or ultrafast anisotropy, 2D IR spectroscopy can discriminate between waters next to the solutes hydrophobic and hydrophilic groups. We also evidence that the water dynamics slowdown due to the hydrophilic groups is dramatically enhanced in the 2D IR spectral relaxation, because these groups can induce a slow chemical exchange with the bulk, even when recognized exchange signatures are absent. Implications for the understanding of water around chemically heterogeneous systems such as protein surfaces and for the interpretation of 2D IR spectra in these cases are discussed.
通过模拟和分析建模研究了一系列两亲性溶质溶液中水分子的氢键动力学，重点是解释可实验获取的二维红外（2D IR）光子回波光谱。我们证明，对于大多数溶质，水动力学中的主要影响来自亲水基团。这些基团通过与水形成强氢键，可以比疏水基团更显著地延迟水动力学。相比之下，疏水基团对水氢键断裂动力学的影响非常温和。我们还首次计算了这些溶液的 2D IR 光谱。虽然 2D IR 光谱是探测水氢键网络波动的强大技术，但对水溶液光谱的解释仍然存在歧义。我们表明，通过模拟和光谱计算的补充方法可以消除歧义，并在模拟分子图像和实验光谱数据之间建立清晰的联系。对于两亲性溶质溶液，我们表明，与 NMR 或超快各向异性等技术相比，2D IR 光谱可以区分溶质疏水和亲水基团附近的水。我们还证明，由于亲水基团，水动力学的减缓在 2D IR 光谱弛豫中显著增强，因为这些基团即使不存在可识别的交换特征，也可以与体相发生缓慢的化学交换。讨论了这对理解化学不均匀体系（如蛋白质表面）周围的水以及在这些情况下解释 2D IR 光谱的意义。
