J. K. Kang

Phase transitions and molecular motions in a model biomembrane (C12H25NH3)2SnCl6

Abstract Two successive phase transitions in bis-n-dodecylammonim hexachlorostannate, (n-C12H25NH3)2SnCl6, were studied by means of 1H NMR. From the temperature dependent dipolar splitting, the low and the high temperature transition were attributed to an order–disorder transition and a conformational transition of the rigid hydrocarbon chain, respectively. The spin-lattice relaxation rate in the low and the intermediate temperature phase was well fitted with four types of molecular motions, and the ammonium group was revealed to dictate the order–disorder transition temperature.

Critical chain dynamics near the interdigitated–noninterdigitated chain configurational phase transition in decylammonium chloride

We have carried out a 1H nuclear magnetic resonance line shape analysis near the irreversible interdigitated-to-noninterdigitated chain configurational phase transition in decylammonium chloride (C10H21NH3Cl), a model biomembrane. The splitting parameter corresponding to the nematic order of the hydrocarbon chain shows a two-dimensional Ising behavior and indicates a chain defect motion in addition to the chain reorientational motion. The origin of the low-frequency critical fluctuation is attributed to a critical slowing down of the collective gear-like reorientation of the rigid hydrocarbon chain.

Phase transitions in layer structured (C10H21NH3)2SnCl6

Phase transitions in the quasi-two-dimensional layer structured (C10H21NH3)2SnCl6, an order–disorder transition and a conformational transition of the hydrocarbon chains, were studied by means of 1H NMR (nuclear magnetic resonance). A newly defined order parameter in the low-temperature phase, the dipolar splitting of the rigid hydrocarbon lineshape component, was shown to represent the order–disorder motion of the hydrocarbon chains, explicitly revealing its three-dimensionality. The conformational transition was marked by a discontinuity in the spin-lattice relaxation rate (1/T1). On the other hand, no obvious anomaly was observed in the spin-lattice relaxation rate at the order–disorder transition at 200 MHz, whereas a weak anomaly was observed at 45 MHz, indicating that the critical dynamics associated with the order–disorder transition is manifest in the low-frequency region of the spectral density.

Phase transitions and critical dynamics in (C18H37NH3)2SnCl6

Phase transitions in the layer structured (C18H37NH3)2SnCl6 were studied using 1H NMR. The spin‐lattice relaxation rate reflects the critical slowing down around the order–disorder phase transition temperature, and is compatible with the three‐dimensional Ising model. A critical slowing down is also observed at the conformational transition in the second moment measurement, presumably for the first time.

35Cl nuclear quadrupole resonance study of lattice dynamics in SnCl4⋅5H2O comprising uncoordinated water molecules

Lattice dynamics and bond characteristics in SnCl4⋅5H2O have been investigated using 35Cl nuclear quadrupole resonance (NQR). Two chemically inequivalent chlorine sites in SnCl4⋅5H2O were distinguished from the temperature dependences of the NQR frequency and from the spin–lattice (T1Q) and spin–spin relaxation times (T2Q). The anomalous temperature dependence of the NQR frequency of one of the two sites was attributed to a thermal weakening of the crystal field from uncoordinated water molecules. In addition, high temperature activated molecular motion was observed.