RESUMEN
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.
Asunto(s)
Ciclodextrinas/química , Óxidos de Nitrógeno/química , Marcadores de Spin , Agua/química , Aire , Reactivos de Enlaces Cruzados/química , Óxidos N-Cíclicos/química , Disulfuros/química , Espectroscopía de Resonancia por Spin del Electrón , Interacciones Hidrofóbicas e Hidrofílicas , Nanocápsulas/química , Oxidación-Reducción , Solubilidad , SolucionesRESUMEN
The effect of solvent used during the synthesis and postsynthesis treatment on textural properties of organized mesoporous aluminas was investigated and related to the behavior of spin probes studied by electron spin resonance (ESR) spectroscopy. It was found that the structure of surfactant aggregates serving in the as-synthesized precipitates as templates could be easily modified by treatment with different solvents. This treatment induces corresponding variations in surface areas, mesopore volumes, and mesopore diameters of the final products. The ESR spectrum of 5-doxyl stearic acid spin probe properly reflects the changes in template structure based on changes of the solvent used and represents an early indicator of the corresponding textural modifications of the mesoporous alumina.
RESUMEN
A series of Au nanoparticles functionalised with nitroxide spin labels has been prepared and studied by EPR spectroscopy. Samples with low coverage of the spin label were used to investigate the dynamics of the surface-attached labels at different distances from the Au surface. The rotational correlation times of spin labels vary from 10(-10) s to more than 3 x 10(-9) s, depending on the chain length of the label and the surrounding ligand. The samples with higher coverage of the spin label show an increasing contribution of the exchange interaction between nitroxides adsorbed in a close proximity to each other on the same nanoparticle. Quantitative analysis of the EPR spectra of these samples suggests the presence of non-equivalent binding sites on the surface of Au nanoparticles. Additionally, EPR signals of isolated radical pairs were observed at intermediate coverage.