FREE-ENERGY OF COFACTORS AT THE QUINONE Q(A) SITE OF THE PHOTOSYNTHETIC REACTION-CENTER OF RHODOBACTER-SPHAEROIDES CALCULATED BY MINIMIZINGTHE STATISTICAL ERROR

The free energy difference of the binding of benzoquinones and naphtho quinones at the Q(A) site of the photosynthetic reaction center from R hodobacter sphaeroides immersed in water and hexane is calculated and compared with experimental values. The water-to-hexane solvent-transfe r free energies are also calculated. An improved thermodynamic perturb ation technique with double-wide sampling is employed which takes the asymmetry of the distribution of data into account and minimizes the s tatistical error by using optimal midpoints. Dependencies on different atomic partial charges and different degrees of solvation are discuss ed.