Water lubricates hydrogen-bonded molecular machines

• Published in: Nature chemistry Vol. 5; no. 11; pp. 929 - 934
• Main Authors: Panman, Matthijs R., Bakker, Bert H., den Uyl, David, Kay, Euan R., Leigh, David A., Buma, Wybren Jan, Brouwer, Albert M., Geenevasen, Jan A. J., Woutersen, Sander
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-11-2013; Nature Publishing Group
• Subjects: 639/925/927/339; Acetonitriles - chemistry; Analytical Chemistry; Benzene Derivatives - chemistry; Biochemistry; Chemistry; Chemistry/Food Science; Friction; Hydrogen; Hydrogen Bonding; Inorganic Chemistry; Lubricants & lubrication; Magnetic Resonance Spectroscopy - methods; Models, Molecular; Organic Chemistry; Physical Chemistry; Pyridines - chemistry; Rotaxanes - chemistry; Solvents; Spectroscopy; Spectroscopy, Fourier Transform Infrared; Water - chemistry; United Kingdom > UK
• ISSN: 1755-4330; 1755-4349
• DOI: 10.1038/nchem.1744

The mechanical behaviour of molecular machines differs greatly from that of their macroscopic counterparts. This applies particularly when considering concepts such as friction and lubrication, which are key to optimizing the operation of macroscopic machinery. Here, using time-resolved vibrational spectroscopy and NMR-lineshape analysis, we show that for molecular machinery consisting of hydrogen-bonded components the relative motion of the components is accelerated strongly by adding small amounts of water. The translation of a macrocycle along a thread and the rotation of a molecular wheel around an axle both accelerate significantly on the addition of water, whereas other protic liquids have much weaker or opposite effects. We tentatively assign the superior accelerating effect of water to its ability to form a three-dimensional hydrogen-bond network between the moving parts of the molecular machine. These results may indicate a more general phenomenon that helps explain the function of water as the ‘lubricant of life’.
Although much is understood about the mechanical behaviour of macroscopic machinery, less is known about their molecular equivalents. It is now shown that for molecular machinery consisting of hydrogen-bonded components their relative motion is strongly accelerated by adding small amounts of ‘lubricating’ water, whereas other protic liquids have much weaker or opposite effects.