Fig. (4) Structure of the azithromycin-Zn⁺⁺ complex. (A) 3-D total charge density contour envelope. Green volumes represent positively charged zones while pink volumes show negatively charged zones. Zinc (center) is completely surrounded by a large negatively charged continuum. (B) Chemical structure of the azithromycin-Zn⁺⁺ complex. (C) 3-D structure of the azithromycin-Zn⁺⁺ complex with the zinc cation in dark grey.