Brownian Translational Dynamics on a Flexible Surface: Nuclear Spin Relaxation of Fluid Membrane Phases

Abstract

A general model for nuclear magnetic resonance (NMR) relaxation studies of fluid bilayer systems is introduced, combining a mesoscopic Brownian dynamics description of the bilayer with atomistic molecular dynamics (MD) simulations. An example is given for dipalmitoylphosphatidylcholine in 2H2O solvent and compared with the experiment. Experimental agreement is within a factor of 2 in the water relaxation rates, based on a postulated model with fixed parameters, which are largely available from the MD simulation. Relaxation rates are particularly sensitive to the translational diffusion of water perturbed by the interface dynamics and structure. Simulation results suggest that a notable deviation in the relaxation rates may follow from the commonly used small-angle approximation of bilayer undulation. The method has the potential to overcome the temporal and spatial limitations in computing NMR relaxation with atomistic MD, as well as the shortcomings of continuum models enabling a consistent description of experiments performed on a solvent lipid and added spin probes. This work opens for possibilities to understand relaxation processes involving systems such as micelles, multilamellar vesicles, red blood cells, and so forth at biologically relevant timescales in great detail.

Relaxometry models compared with Bayesian techniques: ganglioside micelle example

“…These models can can incorporate more experimental data at higher field and an other direction is to incorporate information from MD simulations and for-instance resolve the order parameter and population. 8 It is found that approximate tools to compare models can deviate from the complete integral (AIC), or qualitatively follow (BIC), however, the later at large discrepancy at logarithmic scale. The finds suggest that MCMC simulation of Bayesian evidence will play important role in development of NMRD theory, however, method is completely general and can find ample use in other areas of physical chemistry as well.…”

“…3 To obtain more meaningful information from relaxation experiments, relaxation models are utilized to provide details of the mechanisms underlying spin relaxation. 4 Starting from the spinsystem under study relevant mechanism to include may involve dipole-dipole, chemical exchange, paramagnetic and quadrupole contributions, [5][6][7][8][9][10][11][12] as well as chemical shift anisotropy. 13 The challenges in building models involves incorporation of consistent molecular dynamics processes to explain experimental observations and account for spin-dynamics at sufficient accuracy.…”

“…27,28 A deeper understanding of approximations in analytical models as well as a partial or complete reduction of adjustable parameters has been obtained with molecular dynamics simulations. In relaxometry studies this is achieved for paramagnetic relaxation enhancement, 29 rotation and translation of small molecules, 30 water at bilayer interface, 8 water in cement, 31 and ionic liquid, 13 lyotropic phases, 14,32 porous organic cages 7 and proteins. 33 The simulation studies opens for exploration of the validity of analytical models and for some systems serves as the method of choice.…”

A consistent model for the key complex in chronic beryllium disease

“…Hence, in the case of testing the structure models 3-5 in a protein framework and in aqueous solution we require a model how the EFG undergoes dynamics due to local bonds and the structure around the Be atoms as well as how the whole protein reorient in solution to allow a computation model of the relaxation rates [39]. Fortunately, modelling of relaxation in complex materials has progressed [37,40], involving cost effective methods for the required quantum chemistry EFGdynamics combined with methods for important slower dynamics. Modelling along this line, combined with collection of experimental data is ongoing to provide both a test of best candidate structural model as well as providing information on the local Be dynamics and the dynamics of the protein as a whole.…”

Relaxometry Models Compared with Bayesian Technique: Ganglioside Micelle Example

“…4 Starting from the spinsystem under study relevant mechanism to include may involve dipole-dipole, chemical exchange, paramagnetic and quadrupole contributions. [5][6][7][8][9][10][11][12] The challenges in building models involves incorporation of consistent molecular dynamics processes to explain experimental observations and account for spin-dynamics at sufficient ac- curacy. [13][14][15] Hence, these challenges may come in the form of (i) multiple physical interpretations, (ii) more than one parametrization within a specific physical picture.…”