Hydrolysis of glutaric anhydride to glutaric acid in the presence of β-cyclodextrin. Crystallographic and NMR study
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Crystallization of glutaric anhydride in the presence of β-cyclodextrin (βCD) from aqueous solution resulted in crystals of the glutaric acid/βCD inclusion complex. The result was verified by NMR spectroscopic experiments, which moreover showed that βCD does not protect glutaric anhydride from hydrolysis. The structure determination by X-ray crystallography revealed a host:guest ratio of 1:1 and crystal packing identical to that of natural βCD, i.e., herring bone packing, as is common for guest molecules of small size. Glutaric acid has partial occupancy in the complex and it is disordered in three positions and conformations inside the cavity. All three conformations are stabilised by: (a) Interactions among its carboxyl groups and the host’s primary side hydroxyls pointing towards the cavity, thus justifying the conformations of the latter and (b) by two water molecules located on either side of the cavity, as well as hydroxyl groups of neighbouring hosts. In all conformations the guest is not extended, oxygen atoms between the two carboxyl groups being within H-bond distance.
KeywordsCyclomaltoheptaose Glutaric acid Glutaric anhydride Hydrolysis Dicarboxylic acid Crystal structure
This work was supported by NCSR “Demokritos” (post-doctoral scholarships to A.P.). The support of the NoE program Nano2Life (NMP-4-CT-2003-500057) is acknowledged.
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