Nucleation in complex multi-component and multi-phase systems : General discussion

Price, Sarah and Rimez, Bart and Sun, Wenhao and Peters, Baron and Christenson, Hugo and Hughes, Colan and Sun, Changquan Calvin and Veesler, Stéphane and Pan, Haihua and Brandel, Clement and Biscans, Beatrice and Meekes, Hugo and Rosbottom, Ian and Roth, Wieslaw J. and Seton, Linda and Taulelle, Francis and Black, Simon and Threlfall, Terence and Vekilov, Peter and Poornachary, Sendhil and Diemand, Jürg and Toroz, Dimitrios and Salvalaglio, Matteo and Tipduangta, Pratchaya and Sefcik, Jan and Booth, Samuel and Rasmuson, Ake and Janbon, Sophie and Ter Horst, Joop and Simone, Elena and Hammond, Robert and Bertran, Celso Aparecido and Vetter, Thomas and Sear, Richard and De Yoreo, Jim and Harris, Kenneth and Ristic, Radoljub and Kavanagh, Anne and Roberts, Kevin and Breynaert, Eric and Myerson, Allan and Coquerel, Gerard and Wu, David and Cölfen, Helmut and Cuppen, Herma and Smets, Mireille and Wu, David T. (2015) Nucleation in complex multi-component and multi-phase systems : General discussion. Faraday Discussions, 179. pp. 503-542. ISSN 1359-6640

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Abstract

Kenneth Harris opened a general discussion of the paper by Herma Cuppen: It is well established from solid-state NMR and other techniques that the NH3+ group in crystalline amino acids undergoes rapid rotation about the C–NH3+ bond. Is the phase transition between the β and α phases of DL-norleucine associated with any significant discontinuity in the rate of this motion, and/or the temperature dependence of the rate of this motion? Furthermore, is there any evidence for disorder (dynamic or static) of the alkyl chain of the norleucine molecules in the α and β phases, and if so, does the nature of this disorder change significantly at the phase transition? Herma Cuppen answered: Rotation barriers about the C–NH3+ bond depend on the motive of the hydrogen bonding network in the crystalline phases. For DL-norleucine this motive stays intact during the transition, and I therefore do not expect a large difference for the two phases. The changes occur where the aliphatic chains interact. In a previous study,1 we determined the rotation barrier of the methyl group by means of molecular dynamics simulations for both phases. We found them to be identical, and to be in agreement with experimental values for DL-norvaline2 and DL-norleucine.3 We did not find any correlation between internal movement of the molecules and the onset of the transition.