ŻYWNOŚĆ. Nauka. Technologia. Jakość, 2004, 3 (40) Supl., 37  - 44

KRZYSZTOF DWIECKI, ALEKSANDER SIEGER, PAWEŁ GÓRNAŚ, MAŁGORZATA NOGALA-KAŁUCKA, KRZYSZTOF POLEWSKI

INTERACTIONS BETWEEN THE LIPID MEMBRANE AND D-α-TOCOPHEROL DEPENDING ON ITS CONCENTRATION

S u m m a r y

The objective of the investigations performed was to determine the mechanism of interactions between particles of D-α-tocopherol in relation to its concentration in organic solvents and in a lipid membrane. The latter one is the simple model of a cellular membrane. One of the aspects investigated was to assess the impact of increased concentration of this homologue on the membrane structure.

The investigations in question comprised measurements of spectroscopic properties (absorbance and emission of fluorescence) of D-α-tocopherol showing different concentration levels in the lipid membrane, methanol, and n-hexane.

Results of the measured values of absorbance and emission of fluorescence showed that dimers were formed while the concentration value of D-α-tocopherol increased. The formation of dimers resulted from the fact that particles of D-α-tocopherol began to non-covalently interact among each other as soon as the concentration level was over 460 mM in n-hexane, and 180 mM in methanol. The mechanism of D-α-tocopherol interacting in membranes and with membranes differs from the mechanism of such an interaction in homogeneous solvents. It was stated that when D-α-tocopherol was present in the lipid membrane, then, it impacted the structure of this membrane. The monomers of D-α-tocopherol were built into the membrane, and when the concentration of D-α-tocopherol exceeded the limiting concentration levels in the lipid membrane (140 mM at a concentration level of the membrane of 0.2 mg/cm³, and 420 mM – at 2 mg/cm³), the lamellar structure of bilayer was disordered, and conglomerates appeared, which bonded the D-α-tocopherol and removed it from the aqueous dispersion. It was also evidenced that owing to quenching the fluorescence with acrylamide, the D-α-tocopherol including the chromanol ring were entirely located in the lipid phase.

Key words: lipid membrane, D-α-tocopherol, fluorescence, absorbance