ESR study of molecular orientation and dynamics of TEMPO derivatives in CLPOT 1D nanochannels

Abstract

The molecular orientations and dynamics of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) radical derivatives with large substituent groups at the 4-position (4-X-TEMPO) in the organic one-dimensional nanochannels within the nanosized molecular template 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) were examined using ESR. The concentrations of guest radicals, including 4-methoxy-TEMPO (MeO-TEMPO) or 4-oxo-TEMPO (TEMPONE), in the CLPOT nanochannels in each inclusion compound (IC) were reduced by co-including 4-substituted-2,2,6,6-tetramethylpiperidine (4-R-TEMP) compounds at a ratio of 1 : 30-1 : 600. At higher temperatures, the guest radicals in each IC underwent anisotropic rotational diffusion in the CLPOT nanochannels. The rotational diffusion activation energy, Ea , associated with MeO-TEMPO or TEMPONE in the CLPOT nanochannels (6-7 kJ mol(-1) ), was independent of the size and type of substituent group and was similar to the Ea values obtained for TEMPO and 4- hydroxy-TEMPO (TEMPOL) in our previous study. However, in the case in which TEMP was used as a guest compound for dilution (spacer), the tilt of the rotational axis to the principal axis system of the g-tensor, and the rotational diffusion correlation time, τR , of each guest radical in the CLPOT nanochannels were different from the case with other 4-R-TEMP. These results indicate the possibility of controlling molecular orientation and dynamics of guest radicals in CLPOT ICs through the appropriate choice of spacer. Copyright © 2016 John Wiley & Sons, Ltd.

Alamethicin self-assembling in lipid membranes: concentration dependence from pulsed EPR of spin labels

“…Finally, we believe that the EPR techniques exploited in this work to study peptide aggregates (channels) in membranes can be productively extended to related research topics, such as the channel-forming inclusion compounds. 52,53…”

Electron Spin Resonance Study of Molecular Orientation and Dynamics of Phenyl Imino and Nitronyl Nitroxide Radicals in Organic 1D Nanochannels of Tris(o-phenylenedioxy)cyclotriphosphazene

“…30−32 In addition, the molecular orientation and dynamics of organic radicals in confined nanospace such as not only in 1D nanochannels but also in 0D cavities in cyclodextrins 33 or in micelles has been reported. 34 1D nanochannels of 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) 35 crystals have also been used for the confinement of several 4-substituted-TEMPO derivatives (4-X-TEMPO) 36,37 and 4-substituted-phenylnitronylnitroxide (4-XPNN) radicals. 38 Especially when 4-XPNNs were used as guest radicals, the possibility of developing a new ESR spin probe technique using NN groups was suggested by using the molecular orientation and dynamics of NN radicals in confined spaces determined by ESR measurements and spectral simulation.…”