view article
Figure 8
Noncovalent interactions around the chromophore. (a) Distribution of the noncovalent interaction surface around the chromophore derived from the MAM. The bond paths for hydrogen bonds are represented as gray curves. The reduced density gradient [s(ρ) = 0.4] isosurface is colored according to a blue–green–red scale over the range −0.01 < sign(λ2)ρ < +0.01 e a0−3. λ2 and a0 are the second eigenvalue of the Hessian and the Bohr radius, respectively. Blue indicates attraction, green indicates very weak attraction and red indicates repulsion. (b) A side view of the interaction surfaces. The abbreviation `lp' is short for `lone pair'. (c) The distribution of interacting electrons in the corresponding region to (b). The cyan surface represents the deformation electron density at contour levels of +0.2 and +0.5 e Å−3. The pink surface represents the Fo − Fc OMIT map for H atoms of Thr62 contoured at 3.5σ. (d) A schematic representation of the resonance structure of the anionic chromophore. Interactions stabilizing each resonance state are indicated. The preceding theoretical calculations predicted that the quinone form is favored (Fig. 4[link]) or that both states are almost equivalent (Martin et al., 2004BB54; Petrone et al., 2013BB62), while the phenolate form was predominant in our experiments.

IUCrJ
Volume 6| Part 3| May 2019| Pages 387-400
ISSN: 2052-2525
https://doi.org/10.1107/S205225251900246X