Inverse freezing in molecular binary mixtures of α-cyclodextrin and 4-methylpyridine

Year: 2010

Authors: Plazanet M., Bartolini P., Sangregorio C., Taschin A., Torre R., Trommsdorff H.P.

Autors Affiliation: Univ Florence, European Lab Nonlinear Spect LENS, I-50019 Florence, Italy; Inst Max Von Laue Paul Langevin, F-38042 Grenoble, France; Univ Grenoble 1, CNRS, UMR 5588, Spectrometrie Phys Lab, F-38402 St Martin Dheres Cx, France; Univ Florence, Dipartimento Chim, I-50019 Florence, Italy; Univ Florence, INSTM, I-50019 Florence, Italy; Univ Florence, Dipartimento Fis, I-50019 Florence, Italy.

Abstract: Ternary solutions of alpha-cyclodextrin (alpha CD) in 4-methylpyridine (4MP)/water mixtures solidify when heated and melt when cooled, and the crystalline solid phase exhibits a rich phase behavior as a function of temperature. In this work, we extend these earlier investigations to pure binary mixtures of alpha CD in water free 4MP, characterized via temperature and time dependent measurements of viscosity, X-ray diffraction, and infrared spectroscopy, complemented by observations of acoustic properties and small angle neutron diffraction. At high concentrations (>500 g l(-1)), these solutions enter an amorphous solid phase not only with decreasing but also with increasing temperature, before crystallizing at higher temperatures. This inverse solidi. cation is attributed to the growth of hydrogen bonded clusters, leading to a steep increase of the viscosity with temperature.

Journal/Review: PHYSICAL CHEMISTRY CHEMICAL PHYSICS

Volume: 12 (26)      Pages from: 7026  to: 7031

More Information: We are grateful to E. m Kats, Mark Johnson, Roberto Righini and Paolo Foggi for many interesting discussions and valuable suggestions. We thank the Interdisciplinary Center for Structural Crystallography (Crist) of the University of Florence for the use of the X-ray diffraction facility. This work was supported by the EC grant N.RII3-CT-2003-506350, by CRS-INFM-Soft Matter (CNR) and MIUR-COFIN-2005 grant N. 2005023141-003.
KeyWords: System; Water
DOI: 10.1039/b923682a

Citations: 2
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