On the potentiality of Field-cycling NMR relaxometry for the characterization of microscopic and mesoscopic properties in biomembranes

FRAENZA, CARLA CECILIA; ANOARDO, ESTEBAN

Praga

Congreso; Euromar-European Congress on Magnetic Resonance; 2015

Lipid dynamics in biomembranes are known to influence the viscoelastic and hydrodynamic properties. The microscopic and mesoscopic fluctuations occur over a broad time scale, covering almost 20 decades from fast molecular internal processes to slow trans-bilayer flipflop process. While many experimental techniques have been used for the characterization of membrane dynamics (including NMR spectroscopy), most of these are only capable of monitoring a single aspect of the dynamics and/or a very limited time scale. On the contrary, fast-field-cycling (FFC) NMR relaxometry allow scanning the molecular dynamics in a broad time-scale, although the obtained information is strongly model dependent. FFC relaxometry studies in 1,2-dimyristoyl-sn-glycero-3-posphocholine(DMPC) and 1,2-dioleoyl-sn-glycero-3-posphocholine (DOPC) liposomal samples revealed the high potentiality for the technique when a consistent model can be derived [1,2]. The success of the approach strongly suggests its general applicability for the study of lipid dynamics in more complex membrane compositions. As a first case of this sort, the effect of cholesterol on the local ordering and dynamics of the lipid molecules were evaluated. Theresults are found to be most consistent with the partitioning of the lipids into affected and unaffected populations, allowing to speculate about the quantity of lipid molecules that are ordered by the cholesterols, depending on relative concentrations [3]. This result is the first evidence providing experimental backup to the findings of many computational molecular dynamics studies. In this work we will outline the general problem and show how the technique can be used to determine the elastic properties of the biomembrane using a simplified model, and measurements in a restricted frequency range. We will also advance new results in a different liposomal formulation based on DMPC and sodium deoxycholate.[1]- C. J. Meledandri, J. Perlo, E. Farrher, D. F. Brougham, E. Anoardo, J. Phys. Chem. B2009, 113, 15532? 15540.[2]- J. Perlo, C. J. Meledandri, E. Anoardo, D. F. Brougham, J. Phys. Chem. B2011, 115, 3444 ?3451.[3]- C. Fraenza, C. Meledandri, E. Anoardo, D. Brougham, ChemPhysChem 2014, 15, 425? 435.