Magnetic resonance studies of magnetically aligned polyelectrolytes

The Nuclear Magnetic Resonance (NMR) signals from I > 1/2 nuclei display the quadrupolar interaction with an external electric field gradient in the form of increased linewidths and extra peaks in the NMR spectrum. The NMR signals obtained from I = 3/2 23Na ions dissolved in salt solutions of magnetically aligned filamentous bacteriophage Pfl particles display 2I+1 resonances. The peak-to-peak separation of these resonances is proportional to the ambient electric field gradient, which originates from the surface of the negatively charged polyelectrolyte units. The combination of the charged units and the dissolved ions necessitates the use of the Poisson Boltzmann equation (PBE), which describes charge densities in the solution as a function of the distance from the polyelectrolyte unit. The cell model is used to describe the potential arising from two adjacent Pfl units. Numerical solutions to the PBE indicate that the positive ions display higher quadrupolar couplings as they inhabit higher field gradient regions near the positively charged polyelectrolyte. The negative ions report lower coupling values as they get occluded in the central spaces between two Pfl particles. The ions provide a similar probe of magnetically aligned phospholipid bicelles that are composed of dimyristoyl phosphatidylcholine and dihexanoyl phosphatidylcholine. Variable temperature NMR studies allow the probe of a previously uncharacterized high temperature crystalline phase that has a higher degree of order compared to the bicellar phase.; Relaxation studies of 23Na in solutions of NaCl dissolved in filamentous bacteriophage Pfl reveal two contributions to the phenomenon, the isotropic tumbling and distortion of the arrangement of water molecules around the ion, which causes a stochastic fluctuation in the direction and magnitude of the electric field gradient, and the radial movement of the ion from the surface of Pfl that results in a fluctuation in the electric field gradient magnitude. The Redfield formalism allows a description of this phenomenon in terms of the Fokker-Planck equation (FPE) which describes the random nature of the fluctuations in both isotropic and aligned cases. The additional mathematical term in the FPE for the aligned phase, originating from the charged polyelectrolyte results in an alignment dependent modification of the spectral density functions and ultimately in a deviation of 23Na relaxation rates from the normally observed trends. This is experimentally verified.; The idea of employing alignment to study anisotropic interactions in otherwise isotropic solutions is routinely applied to study dipolar couplings in target biomolecules. In a novel extension of this methodology, surrogate alignment can be used to study dissolved quadrupolar nuclei in biomolecules where natural alignment is not a possibility. The target molecule is a 12-base oligonucleotide (G4T4G4)2 with Na+ as counterions. Pfl is employed to introduce alignment. Studying chemical exchange between the two independently relaxing sites of unique quadrupolar couplings elucidates the dynamics in the solution.