Anu M. Kantola

Ultrafast multidimensional Laplace NMR for a rapid and sensitive chemical analysis

Traditional nuclear magnetic resonance (NMR) spectroscopy relies on the versatile chemical information conveyed by spectra. To complement conventional NMR, Laplace NMR explores diffusion and relaxation phenomena to reveal details on molecular motions. Under a broad concept of ultrafast multidimensional Laplace NMR, here we introduce an ultrafast diffusion-relaxation correlation experiment enhancing the resolution and information content of corresponding 1D experiments as well as reducing the experiment time by one to two orders of magnitude or more as compared with its conventional 2D counterpart. We demonstrate that the method allows one to distinguish identical molecules in different physical environments and provides chemical resolution missing in NMR spectra. Although the sensitivity of the new method is reduced due to spatial encoding, the single-scan approach enables one to use hyperpolarized substances to boost the sensitivity by several orders of magnitude, significantly enhancing the overall sensitivity of multidimensional Laplace NMR.

Cholesterol under oxidative stress-How lipid membranes sense oxidation as cholesterol is being replaced by oxysterols.

The behavior of oxysterols in phospholipid membranes and their effects on membrane properties were investigated by means of dynamic light scattering, fluorescence spectroscopy, NMR, and extensive atomistic simulations. Two families of oxysterols were scrutinized-tail-oxidized sterols, which are mostly produced by enzymatic processes, and ring-oxidized sterols, formed mostly via reactions with free radicals. The former family of sterols was found to behave similar to cholesterol in terms of molecular orientation, roughly parallel to the bilayer normal, leading to increasing membrane stiffness and suppression of its membrane permeability. In contrast, ring-oxidized sterols behave quantitatively differently from cholesterol. They acquire tilted orientations and therefore disrupt the bilayer structure with potential implications for signaling and other biochemical processes in the membranes.

DEUTERIUM NMR SPECTROSCOPY AND FIELD-INDUCED DIRECTOR DYNAMICS IN LIQUID CRYSTALS

Deuterium NMR spectroscopy together with spectral simulations have been used to investigate the field-induced director dynamics in a nematic liquid crystal, 4-pentyl-4′-cyanobiphenyl (5CB), confined in a slab between two electrodes. The NMR spectra have been measured when turning the electric field on and turning it off. Measurements were also made at different temperatures to explore how the temperature effects the director relaxation. At higher temperatures, some complications arise as peculiar oscillations are observed in the spectra. With spectral simulation this phenomena is shown to result from the relaxation of the director on a timescale comparable to that of the experiment which is the effective spin-spin relaxation time. The simulated spectra are compared with the experimental spectra for the specifically deuteriated 5CB-d2.

Magnetic field-induced nuclear quadrupole coupling in atomic 131Xe

Magnetic-field dependence of the interaction tensors of the nuclear magnetic resonance spin Hamiltonian has been experimentally observed in one case so far, in the 131Xe quadrupole coupling of atomic xenon in isotropic gas and liquid phases. We revisit the problem both computationally and experimentally. First-principles electronic structure calculations are carried out at the four-component relativistic Dirac–Hartree–Fock and Dirac-density-functional levels of theory, as well as at various non-relativistic levels using novel, completeness-optimised basis sets. The results are compared to earlier theory, where relativistic effects were considered perturbationally, as well as to experimental data. New measurements of the 131Xe spectrum in the gas phase at natural abundance are reported. The new calculations and experiments provide improved numerical precision as compared to the earlier data, and are in good agreement with each other.

Field-induced alignment of the nematic director: Studies of nuclear magnetic resonance spectral oscillations in the limit of fast director rotation

Time-resolved NMR spectroscopy is a powerful method to investigate field-induced rotation of the director in a nematic liquid crystal. The method requires that the director does not rotate significantly during the acquisition of the free induction decay and hence the NMR spectrum. We have extended the method to systems where this is not the case and the observed NMR spectra are now found to contain novel oscillatory features. To understand these oscillations, we have developed a model combining both director and spin dynamics. In addition to increasing the information content of the time-resolved NMR spectra, it also proves possible to determine the field-induced relaxation time from a single spectrum.