Mode of insertion of chlorophyll a in a lipid layer. A conformational approach

A new procedure for conformational analysis is described to define the orientation of chlorophyll a in model membranes. The method allows to predict the configuration of assembled amphiphilic molecules. The minimal conformational energy is calculated as the sum of the contributions, resulting from the Van der Waals interactions, the torsional potentials, the electrostatic interactions and the transfer energy. In the calculated conformation, the porphyrin ring is orientated at an angle of 45° ± 5° to the membrane interface, with the phytol chain inserted into the lipid layer. This orientation of the porphyrin ring is in excellent agreement with the experimental value obtained with model membranes. The method could allow to define the orientation of other components in the thylakoid membrane.