Triazolium-containing metal-organic frameworks: Control of catenation in 2-D Copper(II) paddlewheel structures

Paper accepted for publication 6th November 2012One approach to exploit MOFs as heterogeneous catalyst platforms requires the development of materials containing groups that can be utilised to anchor a catalytic moiety into the links within the structure. Here we report the synthesis of the first integrated triazolium-containing MOF linker and the first MOFs containing linkers of this type. 1,4-Bis(4-benzoic acid)-1-methyl-1H-1,2,3-triazolium chloride, H₂L1ᴹᵉ, was synthesised in three steps by a 'Click' reaction of methyl 4-ethynylbenzoate with methyl 4-azidobenzoate, methylation using methyl triflate, followed by ester hydrolysis in overall 74% yield. The equivalent neutral triazole precursor, 1,4-bis(4-benzoic acid)-1H-1,2,3-triazole hydrochloride, H₂L1(HCl), was also prepared and a comparison of the chemistry with Zn(NO₃)2·6H₂O and Cu(NO₃)₂·3H₂O is presented. [Zn(L1)₂(H₂O)₂] is a 2-D MOF with infinite chains of zinc carboxylates bridged by L1, while an equivalent structure is not observed for L1ᴹᵉ. In turn, two catenation isomers of [Cu₂(DMF)2(L1ᴹᵉ)2](NO3)₂ were isolated from a single reaction of L1ᴹᵉ and Cu(NO₃)₂·3H₂O. The α-form, a close-packed 3-fold interpenetrated structure, was obtained from reactions undertaken in the presence of nitric acid or at lower temperatures, while undertaking the reaction at higher temperatures leads to a predominance of the 2-fold interpenetrated and potentially porous β-form of the structure. The work presented provides further support for the use of reaction conditions to control interpenetration and additional evidence that charge on structurally similar ligands can drastically alter the types of structures that are accessible due to the requirements for charge balance in the final product.Alexandre M. Burgun, Christian J. Doonan, and Christopher J. Sumb

Preprint and ChemRxiv : New Trends in Chemical Scientific Publishing

特集：日本薬学会第140年会シンポジウ

Protein Modification at Tyrosine with Iminoxyl Radicals

Post-translational modifications (PTMs) of proteins are a biological mechanism for reversibly controlling protein function. Synthetic protein modifications (SPMs) at specific canonical amino acids can mimic PTMs. However, reversible SPMs at hydrophobic amino acid residues in proteins are especially limited. Here we report a tyrosine (Tyr)-selective SPM utilizing persistent iminoxyl radicals, which are readily generated from sterically hindered oximes via single electron oxidation. The reactivity of iminoxyl radicals with Tyr was dependent on the steric and electronic demands of oximes; isopropyl methyl piperidinium oxime 1f formed stable adducts, whereas the reaction of tert-butyl methyl piperidinium oxime 1o was reversible. The difference in reversibility between 1f and 1o, differentiated only by one methyl group, is due to the stability of iminoxyl radicals, which is partly dictated by the bond dissociation energy of oxime O‒H groups. The Tyr-selective modifications with 1f and 1o proceeded under physiologically-relevant, mild conditions. Specifically, the stable Tyr-modification with 1f introduced functional small molecules, including an azobenzene photoswitch, to proteins, whereas the reversible modification of Tyr with 1o switched protein function on and off in an enzyme and in a monoclonal antibody by modification and deconjugation processes