Spectroscopic Characterisation of Metallo-Cyclodextrins for Potential Chiral Separation of Amino Acids and L/D-DOPA
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The derivatives 6-Deoxy-6-[1-(2-amino)ethylamino]-β-Cyclodextrin (CDEn), 6-Deoxy-6-[1-(3-amino)propylamino]-β-Cyclodextrin (CDPn) and 6-Deoxy-6-[1-(4-amino)butylamino]-β-Cyclodextrin (CDBn) were assessed with a view to demonstrating that increasing the chain length of the diaminoalkane moiety can affect the chiral selectivity of the metallo-complexes of these materials. It was shown that IR and Raman spectroscopies can be used to characterise these compounds. The results obtained from the electronic absorption spectra suggested the formation of CuCDAm binary complexes and that the derivatives CDEn and CDPn act as bidentate ligands while CDBn acts as a monodentate ligand due to its longer alkane chain. This study also showed that in the ternary complexes with DOPA there is further coordination of the metal ion to the amino nitrogen atom and the hydroxyl oxygen atom of the drug. On the basis of the results of the circular dichroic spectroscopic studies it was suggested that CuCDEn is the better enantioselective material for DOPA and it acts in a multi-site recognition manner, utilising the inclusion properties of the CD cavity in cooperation with the coordination properties of the metal ion.
KeywordsDOPA electronic and circular dichroic spectroscopies IR and Raman spectroscopies metallo-cyclodextrins
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This work has been carried out (in part) within the structures of the Focas Institute at the Dublin Institute of Technology (DIT), which is funded under the National Development Plan 2000–2006 with assistance from the European Regional Development Fund.
The authors would also like to acknowledge funding from the IT Sector I Postgraduate R & D Skills Programme and DIT.
Elemental analysis and NMR spectra were obtained at the National University of Ireland Dublin.
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