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Melting of Low Molecular Weight Compounds in Confinement Observed by H-2-Solid State NMR: Biphenyl, a Case Study

Amadeu, N. D. and Grünberg, B. and Frydel, J. and Werner, M. and Limbach, H. H. and Breitzke, H. and Buntkowsky, G. (2012):
Melting of Low Molecular Weight Compounds in Confinement Observed by H-2-Solid State NMR: Biphenyl, a Case Study.
In: Zeitschrift Fur Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics, pp. 1169-1185, 226, (11-12), [Article]

Abstract

The H-2-NMR solid echo spectra of biphenyl molecules as guests in the mesopores of neat and silylated SBA-15 have been measured as a function of temperature. At low temperatures typical H-2-Pake patterns with parameters of (Q(zz) = 132 kHz, corresponding to Q(cc) = 176 kHz) and (eta = 0.04) are observed. All samples exhibit a strong reduction of the melting point from the bulk value of 342.4 K to values between 222 K and 229 K, depending on both the pore diameter and the surface state and a glass like behavior of the biphenyl molecules in the melting regime. Employing the Roessler two-phase model of the modeling of glass-transitions by H-2-solid state NMR the distribution of activation energies for the rotational motions has been determined. At temperatures closely below the glass-transition temperature deviations from a static Pake pattern of an aromatic deuteron are observed, which indicate a pre-melting motion of biphenyl, which could be caused by C-2-ring flips of the phenyl rings.

Item Type: Article
Erschienen: 2012
Creators: Amadeu, N. D. and Grünberg, B. and Frydel, J. and Werner, M. and Limbach, H. H. and Breitzke, H. and Buntkowsky, G.
Title: Melting of Low Molecular Weight Compounds in Confinement Observed by H-2-Solid State NMR: Biphenyl, a Case Study
Language: English
Abstract:

The H-2-NMR solid echo spectra of biphenyl molecules as guests in the mesopores of neat and silylated SBA-15 have been measured as a function of temperature. At low temperatures typical H-2-Pake patterns with parameters of (Q(zz) = 132 kHz, corresponding to Q(cc) = 176 kHz) and (eta = 0.04) are observed. All samples exhibit a strong reduction of the melting point from the bulk value of 342.4 K to values between 222 K and 229 K, depending on both the pore diameter and the surface state and a glass like behavior of the biphenyl molecules in the melting regime. Employing the Roessler two-phase model of the modeling of glass-transitions by H-2-solid state NMR the distribution of activation energies for the rotational motions has been determined. At temperatures closely below the glass-transition temperature deviations from a static Pake pattern of an aromatic deuteron are observed, which indicate a pre-melting motion of biphenyl, which could be caused by C-2-ring flips of the phenyl rings.

Journal or Publication Title: Zeitschrift Fur Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics
Volume: 226
Number: 11-12
Uncontrolled Keywords: solid state nmr confinement melting premelting biphenyl mesoporous silica materials nuclear-magnetic-resonance potential applications phase-transitions internal-rotation phenylene motion spin-diffusion drug-delivery glass formers exchange nmr
Divisions: 07 Department of Chemistry > Physical Chemistry
07 Department of Chemistry
Date Deposited: 27 Oct 2014 20:34
Additional Information:

Sp. Iss. SI 067TE Times Cited:1 Cited References Count:88

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