Groot Carien C M, Velikov Krassimir P, Bakker Huib J
FOM Institute AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands.
Unilever R&D, Olivier van Noortlaan 120, 3133 AC Vlaardingen, The Netherlands and Soft Condensed Matter & Biophysics, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
Phys Chem Chem Phys. 2016 Oct 26;18(42):29361-29368. doi: 10.1039/c6cp05883c.
Though it is commonly known that a small amount of water can be present in triglyceride oil, a molecular picture of how water molecules organize in the oil phase is lacking. We investigate the hydrogen-bond configuration and dynamics of water in triacetin, tributyrin and trioctanoin using linear infrared and time-resolved two-dimensional infrared (2DIR) spectroscopy of the water hydroxyl stretch vibration. We identify water molecules with a single strong hydrogen bond to the triglyceride, water molecules with two weaker hydrogen bonds to the triglycerides, and water clusters. These species do not interconvert on the 20 ps timescale of the experiment, as evidenced by the absence of cross-peaks in the 2DIR spectrum. The vibrational response of water molecules with a single strong hydrogen bond to the triglyceride depends strongly on the excitation frequency, revealing the presence of different subspecies of singly-bound water molecules that correspond to different hydrogen-bond locations. In contrast, the water molecules with two weaker hydrogen bonds to the triglyceride correspond to a single, specific hydrogen-bond configuration; these molecules likely bridge the carbonyl groups of adjacent triglyceride molecules, which can have considerable influence on liquid triglyceride properties.
尽管人们普遍知道甘油三酯油中可能存在少量水，但目前仍缺乏关于水分子在油相中如何排列的分子层面的描述。我们使用水羟基伸缩振动的线性红外光谱和时间分辨二维红外（2DIR）光谱，研究了三醋精、三丁酸甘油酯和三辛酸甘油酯中水的氢键构型和动力学。我们识别出与甘油三酯形成单一强氢键的水分子、与甘油三酯形成两个较弱氢键的水分子以及水簇。在实验的20皮秒时间尺度上，这些物种不会相互转化，这在2DIR光谱中没有交叉峰得到了证明。与甘油三酯形成单一强氢键的水分子的振动响应强烈依赖于激发频率，这揭示了对应于不同氢键位置的单键合水分子存在不同的亚类。相比之下，与甘油三酯形成两个较弱氢键的水分子对应于单一的特定氢键构型；这些分子可能桥接相邻甘油三酯分子的羰基，这可能对液态甘油三酯的性质产生相当大的影响。
