Ferricytochrome c encapsulated in silica hydrogels: correlation between active site dynamics and solvent structure.
Ferricytochrome c encapsulated in silica hydrogels has been prepared by the sol-gel technique following, with some modifications, the procedure originally developed by Zink et al. A suitable preparation of hydrogels enables to have 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 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 to probe 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. At difference, 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.
Santangelo
Maria Grazia
MG
National Institute for the Physics of Matter (INFM) and Department of Physical and Astronomical Sciences (DSFA), University of Palermo, via Archirafi 36, I-90123 Palermo, Italy.
Levantino
Matteo
M
Vitrano
Eugenio
E
Cupane
Antonio
A
D000818:Animals; D001665:Binding Sites; D002214:Capsules / Q000737:chemistry; D003574:Cytochrome c Group / Q000008:administration & dosage / Q000737:chemistry*; D005615:Freezing; D006736:Horses; D020100:Hydrogels / Q000737:chemistry* / Q000627:therapeutic use; D058428:Silica Gel; D012822:Silicon Dioxide / Q000737:chemistry / Q000627:therapeutic use; D013057:Spectrum Analysis; D013696:Temperature; D014867:Water / Q000737:chemistry
D002214:Capsules; D003574:Cytochrome c Group; D020100:Hydrogels; D014867:Water; D058428:Silica Gel; D012822:Silicon Dioxide