We performed FTIR measurements on carboxy-myoglobin (MbCO) embedded in a sucrose-water matrix to study the degrees of freedom coupling between protein and external matrix in such a system. The work was undertaken on the light of recent results by Giuffrida et al. (J. Phys. Chem. B 2003, 107, 13211-13217), who evidenced, in trehalose-coated MbCO, a structured water-sugar environment of the protein, tightly coupled to the heme pocket structure. Such information was obtained through a suitable analysis of the temperature dependence of the CO stretching and of the water association bands in samples of different content of residual water. We applied here the same analysis to sucrose-coated MbCO. Comparison between the results obtained in the two saccharide systems points out the different free-energy landscape experienced by the protein and matrix atoms. This is put forward by the differences in heme pocket structure (shape of the CO stretching band) and in protein environment (shape of the water association band). Furthermore, our data evidence a tighter protein-matrix coupling in trehalose than in sucrose. We suggest this difference to be at the basis for the better efficiency, as biopreservant, of trehalose with respect to sucrose, since the appearance of damages on biological structures will more involve structural variations of the surrounding matrix in the former sugar.