Antioxidant activity of rosemary extracts in solution and embedded in polymeric systems

The rosemary extract was encapsulated in polyethylene or in covalently-based network gels. The covalent gels were obtained by the reaction of isocyanate end-capped polyethylene glycol (PEG) with β-cyclodextrin or glycerol. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was used to evaluate the antioxidant activity (AA) of rosemary extract entrapped in polymeric structures and in ethanol or water solutions. The AA of the rosemary extract was determined using a DPPH radical for samples prepared in ethanol, and a water-soluble derivative, the sulphonated DPPH radical (DPPH-SO3Na), for the rosemary extract in water. Formulation of the rosemary extract in polymeric gels ensures a rapid release which determines the AA values similar to those in solution.

Properties of polyethylene glycol/cyclodextrin hydrogels revealed by spin probes and spin labelling methods

The properties of a gel consisting of a covalent network formed by the reaction of isocyanate end-capped polyethylene glycol (PEG) with β-cyclodextrin, were investigated by EPR spectroscopy. Spin-labelled cyclodextrin was incorporated into the cross-link points of the gel and at the chain ends. The dynamics of the gel fibres as reported by the spin label, was found to be sensitive to the H-bonding ability of the solvent, density of cross-links and temperature. Addition of spin probes (e.g., TEMPO and adamantane-TEMPO) to the unlabelled gel made it possible to characterise the solvent pools in the gel. While TEMPO was uniformly distributed throughout the solvent pools, the adamantane derivative was located at the gel fibre-solvent pool interface; these two probes thus reported on the different locations in the solvent pools. At low temperature, the gels were shown to prevent ice crystallisation in the solvent pools resulting in the formation of supercooled water. Both probes showed that the water froze at ca. 250 K, thus suggesting that the properties of the supercooled water are uniform across the solvent pools.

Sorption of metal ions by poly(ethylene glycol)/β-CD hydrogels leads to gel-embedded metal nanoparticles

Inorganic nanoparticles can be embedded within gels by selectively preloading them with suitable molecular precursors followed by reduction or another suitable reaction. Here, we exploit the selective sorption properties of cross-linked β-cyclodextrin/poly(ethylene glycol) hydrogels, in analogy with polyurethane foams, to preconcentrate metal salts (HAuCl4 and K2[Co(SCN)4]) and subsequently generate gel-embedded metal nanoparticles (10-50 nm). The nanoparticles are shown to be immobilized within the gel network as a consequence of their large dimensions in comparison to the gel network pore size. We suggest this is a useful approach for the generalized synthesis of hybrid soft-hard nanomaterials.

EPR and circular dichroism solution studies on the interactions of bovine serum albumin with ionic surfactants and β-cyclodextrin

The interactions of bovine serum albumin (BSA) with ionic surfactants (sodium dodecyl sulfate, SDS, and cetyltrimethylammonium bromide, CTAB) and β-cyclodextrin (β-CD) have been investigated by electron paramagnetic resonance (EPR) and circular dichroism measurements. The spin probe selected to report on the interaction of albumin with surfactants and/or β-CD was 4-N,N-dimethyl hexadecyl ammonium-2,2,6,6-tetramethylpiperidine-1-oxyl iodide (CAT16), on account of (a) its balance between electrostatic and hydrophobic character and (b) the ability of BSA to form complexes with various organic molecules. The distribution of the spin probe among different environments in solutions containing only BSA was confirmed by the existence of two components in the EPR spectra: one revealing a restricted mobility of the spin probe, attributed to the protein-spin probe complex, and another one showing free movement, attributed to the spin probe in solution. The presence of surfactants and/or β-CD alters the distribution of CAT16 between various compartments in each system. Formation of protein aggregates as a result of thermal denaturation was evidenced by the appearance of an immobilized component in the EPR spectrum. This component is not present in the EPR spectra of CAT16 in protein/surfactant or protein/cyclodextrin solutions. Circular dichroism spectra of BSA provided information about changes in the secondary structure of the protein induced by the presence of surfactants and/or cyclodextrin in solution. The results demonstrate that β-CD hinders the interaction between the employed surfactants and the protein. The cationic surfactant (CTAB) induces changes in protein conformation at a lower concentration compared to the anionic surfactant (SDS).

Chemical and biological evaluation of some new antipyrine derivatives with particular properties

Starting from 4-amino-antipyrine, six new compounds were synthesized and characterized. The new compounds contain moieties with particular properties, such are ionophore (benzo-15-crown-5), fluorescent (nitrobenzofurazan), stable free radical (nitroxide), or other types of biological active residues, like nitroderivatives, antipyrine or isoniazid residues. They were fully characterized by appropriate means ((1)H and (13)C NMR, IR, UV-Vis, fluorescence, EPR, elemental analysis) and some of their biological properties were evaluated. Hydrophobicity (R(M0), log P), total antioxidant capacity (TAC), and antimicrobial properties are also presented and discussed.

Inclusion complexes of cyclodextrins with nitroxide-based spin probes in aqueous solutions

Formation of inclusion complexes between several cyclodextrin derivatives and TEMPO and DOXYL-based spin probes was studied by EPR spectroscopy. Competition between alkyl chains and nitroxide functionalities for cyclodextrin cavities leads to different types of complexation. Long alkyl chains in amphiphilic spin probes interact preferentially with cyclodextrins, and TEMPO units in such molecules are unaffected by complexation. DOXYL-type spin probes however form stronger complexes with cyclodextrins; this complexation changes hyperfine splitting and tumbling rate of the nitroxide group. Comparison of EPR spectra of free cyclodextrin and cyclodextrin-based polymeric nanocapsules made it possible to assess the tumbling of the spin probe inside the cyclodextrin units without the contribution of the tumbling of the whole complex.

Inclusion complexes of cyclodextrins with biradicals linked by a polyether chain—an EPR study

Complexation of beta-cyclodextrin with flexible nitroxide biradicals linked by a polyethylene glycol chain was monitored by EPR spectroscopy. The EPR spectra of the uncomplexed biradicals show an exchange interaction due to the flexibility of the polyethylene glycol chain. Complexation with cyclodextrin leads to the disappearance of the exchange interaction in the EPR spectra. The complexation can be reversed by the addition of competing guests (e.g., adamantane derivatives). At high concentration, the inclusion complexes precipitate, and differential scanning calorimetry (DSC) of the precipitates proved the formation of complexes. Elemental analysis data revealed that the complexes contain several cyclodextrin units per biradical but that the composition was not stoichiometric.