Effects of Anisotropic Nanoconfinement on Rotational Dynamics of Biomolecules: An Electron Spin Resonance Study

Abstract

The development of nanostructured materials for next-generation nanodevice technologies requires a better understanding of dynamics of the objects as confined in nanospace. Here, we characterize the rotational dynamics of a long (14-residue) proline-based peptide (approximately 4 nm in length) under anisotropic nanoconfinement using spin-labeling CW/pulsed ESR techniques as well as spectral simulations. We show by pulsed ESR experiments that the conformations of the peptide in several different nanochannels and a bulk solvent are retained. Parameters characterizing the dynamics of the peptide regarding temperature (200–300 K) and nanoconfinement are determined from nonlinear least-squares fits of theoretical calculations to the multifrequency experimental spectra. Remarkably, we find that this long helical peptide undergoes a large degree of rotational anisotropy and orientational ordering inside the nanochannels, but not in the bulk solvent. The rotational anisotropy of the helical peptide barely changes with the nanoconfinement effects and remains substantial, as the nanochannel diameter is varied from 6.1 to 7.1 and 7.6 nm. This finding is advantageous for addressing purposes of anisotropic nanoconfinement and for advancing our understanding of the rotational dynamics of nano-objects as confined deeply inside the nanostructures of materials