Conformational preferences of TEMPO type radicals in complexes with cyclodextrins revealed by a combination of EPR spectroscopy, induced circular dichroism and molecular modeling

Abstract

Inclusion complexation of spin probes in cyclodextrins leads to induced circular dichroism.

Non-covalent interactions evidenced by EPR spectroscopy in cyclodextrin complexes

“…1) with natural or derivatized cyclodextrins has been analysed using EPR spectroscopy, [22][23][24] as well as a combination of EPR and circular dichroism. 25 Host-guest complexes of a series of mono-and poly-TEMPO radicals with cucurbit [6]uril (Q [6]) have also been investigated by EPR spectroscopy. 26 In addition to commercially available cyclodextrins [α-, β-, 2hydroxypropyl-β-(HPB), methyl-β-(MCD) and γ-CD], 25 polymeric, water-soluble β-CD-based nanocapsules [(CDS) n ] obtained via a disulphide cross-linking process were used.…”

“…25 Host-guest complexes of a series of mono-and poly-TEMPO radicals with cucurbit [6]uril (Q [6]) have also been investigated by EPR spectroscopy. 26 In addition to commercially available cyclodextrins [α-, β-, 2hydroxypropyl-β-(HPB), methyl-β-(MCD) and γ-CD], 25 polymeric, water-soluble β-CD-based nanocapsules [(CDS) n ] obtained via a disulphide cross-linking process were used. 22,25 The latter materials (average diameter 30 nm) form spontaneously during air oxidation of aqueous suspensions of per-thiolated β-CD.…”

“…26 In addition to commercially available cyclodextrins [α-, β-, 2hydroxypropyl-β-(HPB), methyl-β-(MCD) and γ-CD], 25 polymeric, water-soluble β-CD-based nanocapsules [(CDS) n ] obtained via a disulphide cross-linking process were used. 22,25 The latter materials (average diameter 30 nm) form spontaneously during air oxidation of aqueous suspensions of per-thiolated β-CD. 27 The stability of host-guest complexes is determined, in the first instance, by the geometric features of the host, namely the cavity size that depends on the number of repeating units.…”

“…This aspect has been discussed in detail in a recent study that combines EPR spectroscopy, circular dichroism spectroscopy and molecular modeling. 25 Compared to water, the cyclodextrin cavity has a relatively non-polar character, therefore it will readily accommodate non-polar molecules/molecular fragments rather than ionic species. The complexation of the TEMPO radical is independent on pH (Fig.…”

“…By correlating the EPR and circular dichroism data to molecular modeling results, the geometries of the inclusion complexes can be predicted. 25 The analysis of the changes in EPR parameters, combined with data provided by other techniques, can therefore lead to information on the geometric orientation of paramagnetic groups in the complexes.…”