RESUMO
The properties of lipid bilayers in sucrose solutions have been intensely scrutinized over recent decades because of the importance of sugars in the field of biopreservation. However, a consensus has not yet been formed on the mechanisms of sugar-lipid interaction. Here, we present a study on the effect of sucrose on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine bilayers that combines calorimetry, spectral fluorimetry, and optical microscopy. Intriguingly, our results show a significant decrease in the transition enthalpy but only a minor shift in the transition temperature. Our observations can be quantitatively accounted for by a thermodynamic model that assumes partial delayed melting induced by sucrose adsorption at the membrane interface.
Assuntos
1,2-Dipalmitoilfosfatidilcolina/química , Bicamadas Lipídicas/química , Sacarose/química , Soluções , Termodinâmica , Temperatura de TransiçãoRESUMO
Electro-oxidation of tetra-methyl-tetra-thia-fulvalene (TMTTF) in the presence of the chiral anion (1S)-camphor-10-sulfonate (S-camphSO3 (-)) in tetra-hydro-furan/water medium afforded a 1/1 salt formulated as TMTTF·S-camphSO3·2H2O or 2-(4,5-dimethyl-1,3-di-thiol-2-yl-idene)-4,5-dimethyl-1,3-di-thiole radical ion (1+) [(1S)-7,7-dimethyl-2-oxobi-cyclo-[2.2.1]heptan-1-yl]methane-sulfonate dihydrate, C10H12S4 (+)·C10H15O4S(-)·2H2O. In this salt, two independent TMTTF units are present but, in both cases, the observed bond lengths and especially the central C=C distance [1.392â (6) and 1.378â (6)â Å] are in agreement with a complete oxidation of TMTTF which is thus present as TMTTF (.) (+) radical cations. These cations form one-dimensional stacks in which they are associated two by two, forming dimers with short [3.472â (1) to 3.554â (2)â Å] Sâ¯S contacts. The two S-camphSO3 anions present also form stacks and are connected with each other via the water mol-ecules with many O-Hâ¯O hydrogen bonds ranging from 1.86â (3) to 2.15â (4)â Å; the O-Hâ¯O hydrogen-bonding network can be described as being constituted of C 2 (2)(6) chains bearing R 3 (3)(11) lateral rings. On the other hand, the columns of cations and anions are connected through C-Hâ¯O hydrogen bonds, forming a system expanding in three directions; finally, the result is a three-dimensional network of O-Hâ¯O and C-Hâ¯O hydrogen bonds.