Molecular modelling of chloroquine (CLQ) interaction with sialic acids. (a,b) Surface representation of the CLQ–sialic acid (Neu5Ac) complex. Two opposite views of the complex are shown. Note the geometric complementarity between the L-shape conformer of CLQ dissolved in water (in blue) and Neu5Ac (in red). (c) Neu5Ac bound to CLQ via a combination of CH-π and electrostatic interactions with one of the cationic groups of CLQ (+). (d) Molecular modelling of CLQ bound to N-acetyl-9-O-acetylneuraminic acid (9-O-SIA). From right to left, the dashed lines indicate a series of van der Waals, OH-π and electrostatic contacts with both cationic groups of CLQ (+). (e,f) Surface representations of the CLQ–9-O-SIA complex.