FIGURE 1.

Structure in the vicinity of Q_A in the RC of Rb. sphaeroides (Brookhaven data bank entry 1AIG (3)) with the H-bonds (a), or the D-bonds (b) to the two carbonyl oxygens, O₁ and O₄. The principal axes of the g-tensor are along the molecular axes x, y, z (a). The principal axes of the hfc tensors of the protons in H-bonds are along the axes x′, y′, z′ (for simplicity x′ and y′ are not shown, they lie in the plane perpendicular to z′), and are related to the g-tensor axes by the Euler angles φ and θ (31) (a). The proton in the hydrogen bond is characterized by the bond-length r and the angles θ and φ (a). The principal axes of the nqc tensor are along x″, y″, z″ (for simplicity x″ and y″ are not shown, they lie in the plane perpendicular to z″), and are related to the g-tensor axes by the Euler angles α, β and γ (31) (for simplicity γ is not shown) (b).