Fig. 1 Chemical structure of chloroquine (CLQ) and hydroxychloroquine (CLQ-OH). (a) CLQ. (b) CLQ-OH. (c) CLQ-OH extended conformer. (d) CLQ-OH in water. (e) Typical condensed conformer of CLQ. (f) CLQ in water. The molecules in (c–f) are shown in either tube or sphere rendering (carbon, green; nitrogen, blue; oxygen, red; hydrogen, white). In (c) and (e), the chlorine atom of CLQ and CLQ-OH is indicated by an arrow.