Gabriela Ionita

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.

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).

Influence of Cyclodextrins on the Kinetics of Oxidation of Amino Acids and BSA by Hydrazyl Radicals

The kinetics of oxidation of amino acids (Arg, His, Lys, Phe, Thr and Tyr), a dipeptide (Gly-His), and BSA (bovine serum albumin) by two persistent water soluble free radicals of the hydrazyl type has been studied.The rate decreases in the order Arg>Lys>Tyr>Thr>His∼BSA∼Phe∼Gly-His with bothfree radicals. Addition to the reaction mixture of α- and β-cyclodextrin decreases the oxidation rate, probably due to amino acidencapsulation in the cyclodextrin cavity. β-Cyclodextrin protects more efficiently against oxidation than α-cyclodextrin.

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.

A New Crown Compound with Multifunctional Capabilities

A new crown ether, derived from the 2,2-diphenyl-1-picrylhydrazyl free radical (DPPH) and diaza-18-crown-6 (kryptofix 22) was synthesized.The physico-chemical properties of this new compound were studied using 1H- and 13C-NMR, EPR, UV-Vis, and IR spectroscopy. The compound has acid-base and redox properties, each of these involving a colour change (i.e., fromyellow to red-brown for acid-base processes, and from yellow to violet for redox processes).The transport properties of the compound were studied by means of biphasic (l/l or s/l) systems. Thus, by an acid-base process alkaline cations were transported into an organic phase, as well as arginine; by a redox process, short-lived freeradicals such as .C6H5 and .H were generated and observed by the EPR spin-trapping technique, using t-butyl-phenyl-nitrone (PBN) as spin-trap.

Exploring porous nanosilica-TEMPO as heterogeneous aerobic oxidation catalyst: the influence of supported gold clusters

Abstract TEMPO stable free radical has been supported on porous silica nanoparticles in different ways and the resulted materials have been tested as heterogeneous oxidation catalyst of three benzylic alcohols using air as final oxidant and nitrosonium tetrafluoroborate as cocatalyst. Good to excellent yields were obtained. The catalytic system consists in fact in two coupled cycles, NO/NO2 and TEMPO+/TEMPO, able to convert under mild conditions (room temperature, air, metal and halogen free condition) alcohols into aldehydes or ketones. Under these conditions, supported TEMPO on silica nanoparticles containing gold clusters lowers the efficiency of the catalyst.

Hydrazyl, Nitronyl-, and imino-nitroxides: Synthesis, properties and reaction with nitric oxide and nitrogen dioxide

Ten novel and stable free radicals of nitronyl-, imino-nitroxide and hydrazyl type compounds were synthesized and their physico-chemical properties investigated. UV-Vis and ESR spectroscopic data, as well as the lipophilicities and specific hydrophobic areas of the compounds are compiled. The reaction of these radical compounds with nitric oxide and nitrogen dioxide was also investigated. The radicals synthesized, show selectivity in their reaction with these nitric oxides, depending on their structure (nitronyl-nitroxide radicals react with NO, while hydrazyl radicals react with NO2). The processes are easily monitored by UV-Vis or ESR spectroscopy.

Planar Chromatographic and Electrophoretic Study of Thermally Induced Conformational Modifications of Protein Structure

It is well known that the structure of BSA explains its capacity to interact both hydrophobically and hydrophilically with other biochemical species. In the native state the BSA molecule takes such a conformation that the polar residues of amino-acids are oriented towards the outside the molecule and the non-polar residues are directed prevalently towards the inside of the molecule. The main effect of heat on the conformation of the albumin is supposed to consist in the redirection of the amino acid moieties which involves a change in the hydrophobic–hydrophilic balance. A sequence of conformational modifications is assumed to result from different refolding processes of thermally denatured BSA. This leads, because of the large number of degrees of freedom of the macromolecule, from the largely featureless ensemble of denatured conformations to structures modified do different extents compared with the one structure of the native albumin molecule [1]. In this way the capacity of the protein to interact or bind with other species is modified, as is well observed in its chromatographic and electrophoretic behavior. Our paper deals with use of these techniques to study the effect of the refolding process on thermally denatured BSA.

Inclusion complexes of steroidal heterocyclic compounds with cyclodextrins in aqueous solution and in the solid state

The complex formation of five steroidal heterocyclic compounds (1-5) with β-cyclodextrin and hydroxypropyl-β-cyclodextrin was investigated in aqueous solution and in solid state in order to find the strenght of interaction. The complex formation of these steroidic compounds with CDs in aqueous solution was studied by solubility analysis and ultraviolet absorption methods. For the study of solid state interaction, solid complexes were prepared by the solvent evaporation method and complexes obtained were analysed by thermal analysis. Also, synthesis, NMR and IR data of the new steroidic compounds 1,2, and 3are presented.