Synthesis and Supramolecular Studies of Chiral Boronated Platinum(II) Complexes: Insights into the Molecular Recognition of Carboranes by β‐Cyclodextrin |
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Authors: | Dr H Y Vincent Ching Dr Sarah Clifford Dr Mohan Bhadbhade Dr Ronald J Clarke Prof Louis M Rendina |
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Institution: | 1. School of Chemistry, The University of Sydney, Sydney, NSW 2006 (Australia), Fax: (+61)?2‐9351‐3329;2. Département de Chimie Minérale, Analytique et Appliqué, Université de Genève quai Ernest‐Ansermet 30, 1211 Genève 4 (Switzerland);3. Solid State & Elemental Analysis Unit, Mark Wainwright Analytical Centre, The University of New South Wales, Sydney, NSW 2052 (Australia) |
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Abstract: | The synthesis and characterisation of a novel isomeric family of closo‐carborane‐containing PtII complexes ((R/S)‐( 1 – 4 )?2 NO3) are reported. Related complexes ( 5 ?NO3 and 6 ?NO3) that contain the 7,8‐nido‐carborane cluster were obtained from the selective deboronation of the 1,2‐closo‐carborane analogues. The corresponding water‐soluble supramolecular 1:1 host–guest β‐cyclodextrin (β‐CD) adducts ((R/S)‐( 1 – 4 ) ? β‐CD?2 NO3) were also prepared and fully characterised. HR‐ESI‐MS experiments confirmed the presence of the host–guest adducts, and 2D‐1H{11B} ROESY NMR studies showed that the boron clusters enter the β‐CD from the side of the wider annulus. Isothermal titration calorimetry (ITC) experiments revealed enthalpically driven 1:1 and higher‐order supramolecular interactions between β‐CD and (R/S)‐( 1 – 4 )?2 NO3 in aqueous solution. A comparison of the predominate 1:1 binding mode established that the affinity of β‐CD for the guest molecule is mainly influenced by the pyridyl ring substitution pattern and chirality of the host, whilst the nature of the closo‐carborane isomer also plays some role, with the most favourable structural features for β‐CD binding being the presence of the 4‐pyridyl ring, 1,12‐closo‐carborane, and an S configuration. The results reported here represent the first comprehensive calorimetric study of the supramolecular interactions between closo‐carborane compounds and β‐CD, and it provides fascinating insights into the structural features influencing the thermodynamics of this phenomenon. |
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Keywords: | boron cluster calorimetry carborane cyclodextrin molecular recognition platinum |
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