Crystal structure analysis of the imidazole associates with 1,1′-binaphthyl-8,8′-dicarboxylicacid (1), [1a, triclinic, P1, a = 7.569(4), b = 8393(2), c = 8.634(1) Å, α = 93.21(2), β = 106.88(3), γ = 105.17(3)°, Dc = 1.36 g/cm3, Z = 1, R = 0.045 for 1031 data] and with 2,2′-dihydroxy-1,1′-binaphthyl (2), [2a, tetragonal P41212, a = 8.519(1), c = 29.821(2), Dc = 1.30 g/cm3, Z = 4, R = 0.051 for 1236 reflections] revealed 1:1 and 1:2 stoichiometry, respectively. Spontaneous resolution occur during crystallization in both compound crystals. 1a is a salt-like associate with hydrogen bonds between the carboxylate and imidazolium ion pairs while the neutral 2a has also well defined hydrogen bonds between host and guest molecules. In a modeling experiment corresponding Brookhaven Protein Data Bank atomic coordinates from the active site of the bacterial serine protease enzyme Subtilisin BPN were fitted to the crystal packing of the small molecule associate la crystal. The relative displacement of the ion pair components and a symmetry related carboxyl function in la has fair steric resemblance to similar moieties in the active site of Subtilisin (Δave = 0.24 A for 9 fitted atoms). The agreement in the results of two fully independent and totally different (i.e. a native protein active site and an artificial small molecule associate) crystal structure determinations underlines the assumed conceptual similarity of crystals (“giant supramolecules”) to protein sequences optimized through evolution.
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