Measurement of the bending elastic modulus in unilamellar vesicles membranes by fast field cycling NMR relaxometry

PERLO, JOSEFINA; DOMINGUEZ, G.; ANOARDO, E.

Torino

Conferencia; 8th Conference on Fast Field Cycling NMR Conference; 2013

Lipid vesicles can be used as idealized model systems of real biomembranes. They have attracted much interest in biophysical research, particularly for the study of different processes related to the viscoelastic and mechanical properties of the membrane. Different experimental techniques are implemented for the analysis of membrane elasticity. However, easy available benchtop instruments (generally based on optical microscopy) are only useful for giant unilamellar vesicles. On the other hand, successful techniques used in large/small (LUV/SUV) unilamellar vesicles turned to be based on large scale instrumentation like conventional NMR [1] or neutron spin-echo [2]. It is worth to mention the atomic force microscopy (AFM) as an exception, allowing the study of mechanical properties in LUV with small scale instrumentation, although more invasive than the previous [3].  Low cost reliable benchtop instruments allowing precise determination of the bending elastic modulus and/or other viscoelastic parameters in LUVs and SUVs are thus very much attractive within this picture. Previous studies of unilamellar liposomes using proton NMR field-cycling relaxometry suggested that the collective nature of the lipid dynamics should be considered for a consistent interpretation of the measured relaxation disperssions [4,5]. Later, it turned to be clear that relevant information about the elastic properties of the membrane can be extracted from the collective dynamics contribution within a restricted Larmor frequency-range [6]. In the ideal situation, this should be done in a small benchtop dedicated instrument. To test this concept, the proton spin-lattice relaxation rate (R1) was scanned within a restricted Larmor frequency range (typically 200kHz to 2MHz), but using a standard instrument with degraded magnet homogeneity (lower than 350ppm/cm3), thus simulating extreme conditions for the relaxometry experiment. The potentiality of NMR relaxometry at inhomogeneous field conditions is analyzed within this picture and for this particular case, i.e., low magnetic field homogeneity, proton diluted sample & low signal to noise ratio.   [1]- G. Althoff, O. Stauch, M. Vilfan, D. Frezzato, G. Moro, P. Hauser, R. Schubert and G. Kothe, J. Phys. Chem. B 106, 5517 (2002). [2]- Z. Yi, M. Nagao and D. P. Bossev, J. Phys.: Condens. Matter DOI: 10.1088/0953-8984/21/15/155104 (2009). [3]- N. Delmore and A. Fery, Phys. Rev. E DOI: 10.1103/PhysRevE.74.030901 (2006). [4]- C. Meledandri, J. Perlo, E. Farrher, D. Brougham and E. Anoardo, J. Chem. Phys. B 113, 15532 (2009). [5]- J. Perlo, C. Meledandri, E. Anoardo and D. Brougham, J. Chem. Phys. B 115, 3444 (2011). [6]- Josefina Perlo, PhD. Thesis. Universidad Nacional de Córdoba (2011).