Morales-Blanco, Alexis J.

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    Supramolecular host-guest interactions of cyclodextrins and calixarenes with niobocene and vanadocene
    (2010) Morales-Blanco, Alexis J.; Meléndez, Enrique; College of Arts and Sciences - Sciences; Hernández, Samuel P.; Cruz Pol, Astrid; Cádiz, Mayra E.; Department of Chemistry; Hernández, Arturo
    Cyclodextrins (CDs) and calixarenes act as a molecular host to a variety of guests: ions, metal complexes, polar and nonpolar organic molecules. These inclusion complexes have found pharmaceutical applications due to the increased aqueous solubility of the drugs, better oral absorption and their improved stability towards heat, light, oxidizing reagents and acidic conditions. Host-guest interactions between α-, β-, and γ-cyclodextrins with Cp2VCl2 and Cp2NbCl2 have been investigated by a combination of TGA, DSC, PXRD, solid state/solution EPR spectroscopy and solid state/solution NMR spectroscopy. The solid state results demonstrated that only β- and γ-cyclodextrins do form 1:1 inclusion complexes, while α-cyclodextrin does not form an inclusion complex with Cp2VCl2 or Cp2NbCl2. The β- and γ-CD-Cp2VCl2 inclusion complexes exhibited anisotropic electron-51V (I = 7/2) hyperfine coupling constants whereas the α-CD-Cp2VCl2 system showed only an asymmetric peak with no anisotropic hyperfine constant. PXRD, NMR, and thermal analysis showed that the organometallic molecules of Cp2NbCl2OH are included in the cavities of β - and γ- cyclodextrins, possibly adopting a symmetrical conformation in the complex, with each glucose unit in a similar environment. This suggests that vanadocene and niobocene penetrates deeper into the γ-CD cavity than in the β-CD cavity, as a result of the cavity size. In addition possible inclusion complexes of Cp2NbCl2 into calixarenes hosts have been investigated. The existence of a true inclusion complex in the solid state was confirmed by a combination of NMR, ab-initio calculation, thermogravimetric analysis, FTIR, Raman and PXRD. Ab-initio calculation, 1H NMR solution and solid state 13CP MAS NMR results demonstrated that sulfa-calix[6]arene does form inclusion complexes with the organometallic molecule. Ab-initio and Raman spectroscopy results showed metal coordination with the sulfa oxygen as part of the interaction with the organometallic molecule. Meanwhile, the solution 1H NMR results demonstrated that calix[6]arene does not form inclusion complexes with the organometallic molecule. Ab-initio and NMR spectroscopy showed that the organometallic molecule of Cp2NbCl2 is included in the sulfa-calix[6]arene cavity, with a shallow penetration, possibly adopting a symmetrical conformation in the complex, with each phenol unit in a similar environment. However, the organometallic molecule of Cp2NbCl2 is not included in the calix[6]arene cavity, possibly the lack of the hydrophilic sulfa heads precludes the adoption of a better symmetrical conformation with each phenol unit in a similar environment.