title: Ferricytochrome c encapsulated in silica hydrogels: correlation between active site dynamics and solvent structure.
abstract: Ferricytochrome c encapsulated in silica hydrogels has been prepared by the sol-gel technique following, with some modifications, the procedure originally developed by Ellerby et al. (Science 255 1113 (1992)). A suitable preparation of hydrogels enables having both 'wet' and 'dry' samples. Wet samples have a high water content: as the temperature is lowered below approximately 260 K, water freezes and the samples crack. On the contrary, dry samples have a low water content (hydration h approximately equal 0.35): in these conditions water does not freeze even at cryogenic temperatures and the samples remain transparent and non-cracking. The dynamics of ferricytochrome c and its dependence on the surrounding medium have been studied by optical absorption spectroscopy in the temperature range 10-300 K. At each temperature, spectra were collected both in the Soret region and in the near infrared at approximately 1.45 microm (the water overtone band); this enables probing the local dynamics of the protein active site as well as the 'structure' of water molecules present in the sample. The data show that sol-gel encapsulation 'per se' does not alter the protein active site dynamics, but rather introduces an increased local heterogeneity. We find a correlation between active site dynamics and water structure: in the wet hydrogel, freezing of water quenches the ensemble of soft modes linearly coupled to the Soret transition; while, in the dry hydrogel, water does not freeze and an active site dynamic behavior--similar to the non-freezing water/glycerol solution--is observed.
authors.affiliation: National Institute for the Physics of Matter and Department of Physical and Astronomical Sciences, University of Palermo, via Archirafi 36, I-90123, Palermo, Italy.
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Santangelo
authors.forename: Matteo
authors.initials: M
authors.lastname: Levantino
authors.forename: Eugenio
authors.initials: E
authors.lastname: Vitrano
authors.forename: Antonio
authors.initials: A
authors.lastname: Cupane
mesh_terms: D000818:Animals; D003574:Cytochrome c Group / Q000737:chemistry*; D004339:Drug Compounding / Q000379:methods; D004355:Drug Stability; D006736:Horses; D020100:Hydrogels / Q000737:chemistry*; D007700:Kinetics; D012822:Silicon Dioxide / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D003574:Cytochrome c Group; D020100:Hydrogels; D012997:Solvents; D014867:Water; D012822:Silicon Dioxide