title: Quantum tunneling in the quadruple proton rearrangement on a hydroxyl hydrogen bond ring in calix[4]arene.
abstract: Proton rearrangement rates in hydrogen bond networks are dominated by classical activation and quantum tunneling at higher and lower temperatures, respectively. Calix[4]arene (C4A) has a square-ring network composed of four hydroxyl groups with the O···O length of ~0.265 nm. Calorimetry and dielectric relaxation measurements were applied to determination of the rates in the crystals of C4A and its deuteron analogue (C4A-d). The rearrangement rates in C4A-d exhibited Arrhenius dependence in the measured temperature range. On the other hand, the rates in C4A showed the same dependence as those in C4A-d above 200 K, deviated from this dependence at around 180 K, and became independent of temperature at around 10(-4) s(-1) below 100 K. This evidenced that the tunneling in the quadruple proton rearrangement proceeds at a very slow rate of 10(-4) s(-1). This is the first determination by calorimetry of the proton tunneling rate.
authors.affiliation: Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Tokyo 152-8551, Japan. ueda.kohei@riken.jp
authors.forename: Kouhei
authors.initials: K
authors.lastname: Ueda
authors.forename: Masaharu
authors.initials: M
authors.lastname: Oguni
mesh_terms: D047250:Calixarenes / Q000737:chemistry*; D006860:Hydrogen Bonding; D017665:Hydroxyl Radical / Q000737:chemistry*; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory; D013696:Temperature
chemical_list: D010636:Phenols; D011522:Protons; C121325:calix(4)arene; D047250:Calixarenes; D017665:Hydroxyl Radical