Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Lipid Dynamics:Motions, time scalesand experimental methodsRelationship between frequency and correlation timeModels of Motion for lipids and proteins in bilayersIsotropic rotationConical rotationIsotropic rotationRotation along long axisDiffusion in the planeProbes to measure membrane “fluidity/dynamics”TEMPOElectron Paramagnetic Resonance (EPR) for monitoring membrane motionsEnergy01-10-11MIms=1/2ms= -1/2NO-EPR spectrumenergyEPR spectra and hyperfine interactionsTEMPOSpin labeled lipidIsotropic tumblingRestricted motionS = order parameterBoth the g-tensor and A-tensors are anisotropicHyperfine Tensor Directions/DefinitionsDirector Axis and Definitions of Aperp and AparDirector axisExamples of EPR line shapes for spin labeled lipidsMobility gradient into the bilayerEPR lineshapes can be used to investigate phase transitions2H NMR : Quadrupole PatternsQuadrupole Lineshape for 2H, I=1 nucleusOther faster motions average the splitting:222Need to think about 0o and 90o orientationsEzeemanQuadrupole 90o0oisoAxial symmetry C-D (aliphatic bond)MLVsOriented parallel to fieldOriented perpendicularto fieldOrder parameters determined from both 2H and EPR methodsEPRNMRKeep in mind comparison between EPR and NMR:typically the 2H is less perturbing than the EPR spin probe or a fluorescent probe. But, NMR sensitivity is less. There is always a compromise.From NMR relaxation studies:Membrane “Fluidity” Measured by TEMPO partitioningf = fraction in the bilayerHyperfine splitting is sensitive to polarityH is “bilayer”P is aqueous bufferShows Gel to liquid
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