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Issue 2, 2011
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Synthesis, carbohydrate- and DNA-binding studies of cationic 2,2′:6′,2′′-terpyridineplatinum(ii) complexes containing N- and S-donor boronic acid ligands

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Abstract

A series of platinum(II) complexes of the type [Pt(trpy)L](NO3)n (L = 3- or 4-pyridineboronic acid (3- or 4-pyB, respectively), n = 2; HL = 4-mercaptophenylboronic acid (HmpB), n = 1; trpy = 2,2′:6′,2′′-terpyridine) and [{Pt(trpy)}2(μ-pzB)](NO3)3 (HpzB = 4-pyrazoleboronic acid) were synthesized and fully characterized by means of multinuclear (1H, 13C, 11B, and 195Pt) 1D- and 2D-NMR spectroscopy and elemental analysis. The triflate derivatives [Pt(trpy)(4-pyB)](OTf)2 and [{Pt(trpy)}2(μ-pzB)](OTf)3 were also prepared, and their molecular structures were confirmed by X-ray crystallography. Variable pH 1H NMR spectroscopy showed that hydroxylation of the boronic acid group occurs in aqueous solution at pH > 5 and the pKa values for the complexes were determined. In buffered aqueous solution (pH 7.4), the complexes bind strongly to simple diols such as catechol and monosaccharides including D-fructose, D-ribose, D-sorbitol and D-mannitol, as determined by isothermal titration calorimetry (ITC). The equilibrium binding constants for these reactions were determined and were found to exceed those of organic boronic acids such as phenylboronic acid by an order of magnitude or greater, an effect that can be directly attributed to the cationic charge of the complexes. 2D-NMR methods (HSQC and HMBC) were used to elucidate the structures of the carbohydrate adducts [Pt(trpy)(3-pyB)]·D-fructose·NO3 and [Pt(trpy)(4-pyB)]·D-fructose·NO3 in aqueous solution. DNA-binding experiments with calf-thymus DNA (CT-DNA) indicate an avid DNA-binding interaction by the mononuclear complexes, as determined using thermal melting methods and ITC, but the behaviour of the dinuclear species [{Pt(trpy)}2(μ-pzB)](NO3)3 is complicated and could not be modeled adequately; higher ionic strength solutions and lower temperatures resulted in a similar DNA binding interaction to the mononuclear complexes. The presence of excess D-fructose did not significantly affect the binding of the platinum(II)-trpy complexes to CT-DNA.

Graphical abstract: Synthesis, carbohydrate- and DNA-binding studies of cationic 2,2′:6′,2′′-terpyridineplatinum(ii) complexes containing N- and S-donor boronic acid ligands

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Supplementary files

Article information


Submitted
22 Jul 2010
Accepted
21 Oct 2010
First published
19 Nov 2010

Dalton Trans., 2011,40, 506-513
Article type
Paper

Synthesis, carbohydrate- and DNA-binding studies of cationic 2,2′:6′,2′′-terpyridineplatinum(II) complexes containing N- and S-donor boronic acid ligands

S. S. Hosseini, M. Bhadbhade, R. J. Clarke, P. J. Rutledge and L. M. Rendina, Dalton Trans., 2011, 40, 506
DOI: 10.1039/C0DT00892C

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