title: Water lubricates hydrogen-bonded molecular machines.
abstract: 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'.
authors.affiliation: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands.
authors.forename: Matthijs R
authors.initials: MR
authors.lastname: Panman
authors.forename: Bert H
authors.initials: BH
authors.lastname: Bakker
authors.forename: David
authors.initials: D
authors.lastname: den Uyl
authors.forename: Euan R
authors.initials: ER
authors.lastname: Kay
authors.forename: David A
authors.initials: DA
authors.lastname: Leigh
authors.forename: Wybren Jan
authors.initials: WJ
authors.lastname: Buma
authors.forename: Albert M
authors.initials: AM
authors.lastname: Brouwer
authors.forename: Jan A J
authors.initials: JA
authors.lastname: Geenevasen
authors.forename: Sander
authors.initials: S
authors.lastname: Woutersen
mesh_terms: D000097:Acetonitriles / Q000737:chemistry*; D001555:Benzene Derivatives / Q000737:chemistry; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D011725:Pyridines / Q000737:chemistry; D043862:Rotaxanes / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water / Q000737:chemistry*
chemical_list: D000097:Acetonitriles; D001555:Benzene Derivatives; D011725:Pyridines; D043862:Rotaxanes; D014867:Water; C032159:acetonitrile