Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering , Shaanxi Normal University , Xi'an 710119 , China.
J Phys Chem B. 2018 Dec 20;122(50):12131-12138. doi: 10.1021/acs.jpcb.8b10058. Epub 2018 Dec 4.
The microscopic structure of dimethyl sulfoxide (DMSO) aqueous solutions was investigated by Fourier transform infrared (FTIR) spectroscopy and ultrafast IR spectroscopy. The structural dynamics of the binary mixtures were reflected by using thiocyanate anion (SCN) as a local vibrational probe. FTIR spectra of SCN anion showed that the hydrogen bond networks of water are affected by the presence of DMSO molecules, and the peak position and bandwidth of SCN anions are red shifted and narrowed accordingly because of the weak hydration in the binary mixture. The vibrational lifetime of the SCN anion showed almost linear enhancement with the increase of DMSO, which can be explained by the weak interaction between SCN and the hydrophobic groups in the DMSO molecule. However, the rotational dynamics of SCN are slowing down significantly and showed a maximum response at X (mole fraction) of 0.35, which is mainly caused by the confinement of SCN anions positioned in the vicinity of the complex structure formed between DMSO and water molecules. The concentration-dependent rotational dynamics of water molecules and SCN anions are having similar behavior, indicating that the complex structure can be formed between water and DMSO molecules because of the strong interaction. The result also demonstrates that the structural inhomogeneity in aqueous solution can be unraveled by monitoring the vibrational relaxation dynamics of SCN anion serving as the local vibrational probe.
采用傅里叶变换红外（FTIR）光谱和超快红外光谱研究了二甲基亚砜（DMSO）水溶液的微观结构。通过使用硫氰酸根阴离子（SCN）作为局部振动探针来反映二元混合物的结构动力学。SCN 阴离子的 FTIR 光谱表明，水的氢键网络受到 DMSO 分子的影响，由于二元混合物中弱的水合作用，SCN 阴离子的峰位置和带宽相应地红移变窄。SCN 阴离子的振动寿命几乎呈线性增强，随着 DMSO 的增加而增强，这可以用 SCN 与 DMSO 分子中的疏水分子基团之间的弱相互作用来解释。然而，SCN 的旋转动力学明显减慢，并在 X（摩尔分数）为 0.35 时达到最大值，这主要是由于 SCN 阴离子位于 DMSO 和水分子形成的复杂结构附近而受到限制。水分子和 SCN 阴离子的浓度依赖性旋转动力学具有相似的行为，表明由于强相互作用，水和 DMSO 分子之间可以形成复合物结构。该结果还表明，可以通过监测作为局部振动探针的 SCN 阴离子的振动弛豫动力学来揭示水溶液中的结构不均匀性。
