Laszlo Jicsinszky | Search PubMed

PubMed2006

Nitroxide bound beta-cyclodextrin: is there an inclusion complex?

236CDTIPNO, a derivative of the persistent free radical TIPNO (1,1-dimethylethyl 2-methyl-1-phenylpropyl nitroxide) covalently bound to a permethylated-beta-cyclodextrin, was prepared. Self-association of 236CDTIPNO in water was proved by solvent- and competition-dependent EPR spectroscopy experiments with 2,6-di-O-Me-beta-cyclodextrin (DIMEB) and permethylated-beta-cyclodextrin (TRIMEB) as external hosts competing for accommodation of the TIPNO moiety. Temperature-dependent EPR spectra were simulated with a novel two-dimensional (field-temperature) EPR simulation program that afforded a full determination of the thermodynamic parameters characterizing the rate constants of the self-inclusion reaction derived from Arrhenius and Eyring models. This method allows separating the line broadening effects due to relaxation from a chemical exchange, even if only the fast exchange regime is accessible experimentally. The activation parameters for the forward and backward steps were consistent with an equilibrium between a nonassociated form and a weakly associated form, with activation free enthalpies for each reaction of around 34 kJ.mol(-)(1).

Journal Article↗

PubMed2004

Synthesis of 6I-amino-6I-deoxy-2I-VII,3I-VII-tetradeca-O-methyl-cyclomaltoheptaose.

The preparation of 6(I)-amino-6(I)-deoxy-2(I-VII),3(I-VII)-tetradeca-O-methyl-cyclomaltoheptaose is reported. Two different routes (A and B), both starting from beta-cyclodextrin (betaCD), have been examined. Route A involved: (i) synthesis of heptakis(6-O-tert-butyldimethylsilyl)-betaCD from betaCD; (ii) permethylation of the secondary hydroxyl groups with methyl iodide and sodium hydride; (iii) desilylation of the primary hydroxyls with ammonium fluoride; (iv) monotosylation at O-6 position of per-(2,3-O-methyl)-betaCD; (5) nucleophilic replacement of the tosyl group with azide anion; (v) reduction of the azido group by catalytic transfer hydrogenation using hydrazine hydrate in the presence of Pd/C in methanol/water. Route B started from the known 6(I)-monoazido-6(I)-monodeoxy-beta-CD (two steps from beta-CD) and entailed: (i) protection of the remaining primary hydroxyls using tert-butyldimethylsilylchloride (TBDMSCl); (ii) exhaustive methylation of the secondary hydroxyls with methyl iodide and sodium hydride; (iii) removal of the TBDMS protecting groups with ammonium fluoride; (iv) reduction of the azido group as above. Route A was found to be less convenient than Route B due to the inherent difficulty of controlling the monotosylation of per-(2,3-O-methyl)-betaCD.

Molecular Structure↗