Title: NMR Manual for Cross Polarization Magic Angle Spinning (CPMAS) Experiment Purpose This CPMAS manual will help NMR users to understand the advantages of Cross Polarization Magic Angle Spinning and to follow the procedures to conduct this experiment with little or no NMR staff assistance Introduction Solid state NMR is very different from solution NMR. The significant difference is the NMR peaks are much broader. The broad peaks are caused by three anisotropic nuclear spin interactions: chemical shielding anisotropy dipole-dipole coupling quadruple coupling To overcome these broadening factors, CPMAS with high power proton decoupling is applied as the most common technique in solid state NMR. Even with this technique, the peaks are still hundred times broader in solid NMR than that in solution NMR. Why do we need to do solid state NMR, since there seem no advantages? There are two occasions: if a sample is not soluble in any solvent if there could be a structural change to the sample in the solution In such a case, solid state NMR is the only choice. Although not many users are doing solid state NMR (only about 5%), the technique is still a powerful tool to help NMR users get structural information. CPMAS is commonly applied to C13 NMR, but can be applied to the other hetero-nuclei also, such as Al27, Si29, P31, Sn119, etc. There are two advantages from CP: to assist in observing dilute spin, such as C13 (natural abundance 1.1%), and increasing peak intensity to shorten the delay time, and therefore, to shorten the data acquiring time The advantage of MAS is that to reduce the dipole and quadruple interactions, and therefore, to make NMR peaks sharper. Preparation Spectrometer: NMR-S400 only Probe: 5mm HXY probe or 3.2mm HXY probe Prerequisite: users have done the basic and solid NMR training; also users should understand the differences between solution and solid NMR, such as hardware, T1 and T2, etc. Sample: must be in powder form; and 160 mg or more are required Reading: http://www-f9.ijs.si/~krizan/sola/sempod/0607/rangus-seminar.pdf http://en.wikipedia.org/wiki/Solid-state_nuclear_magnetic_resonance http://mutuslab.cs.uwindsor.ca/schurko/ssnmr/ssnmr_schurko.pdf Experiment Setup 1) 2) 3) 4) Login on FOM system and login as walkon on Solid400 computer Load solid sample into a rotor, put rotor into the probe, insert probe into magnet Open a standard file, e.g. C13_tancpx, into the current buffer, e.g. exp1 Check all the parameter values are the newly updated, e.g. pwX90 (Figure 1) Check probeConnect on screen is ’H1 C13 Si29’, for instance (Figure 1) Check hardware cable connections correct, e.g. cable channel 2 connected to X on probe 5) Start spinning the sample to appropriate rpm by pressing 'Start', as shown in Figure 2 Figure 1. Parameters in Channels Panel. Figure 3. Manual tuning Interface. Figure 2. Parameters in Spin Panel. Figure 4. Parameters in Acquisition Panel. 6) Tune the nuclei, e.g. C13 and H1, by a command mtune. Usually, tune C13 first in Channel 2, then H1 in Channel 1 (Figure 3). Hit button Start Probe Tune, then tune it manually using the rods on the probe (2 red rods always for H1, and X and Y depend on probe mode) and watch the dip position moving; if it’s good, stop and quit 7) Acquire data with appropriate nt and bs (Figure 4), then hit Acquire button 8) Preview the spectrum by wft when bs1 is completed; decide to stop or keep running 9) Save data into a correct folder, i.e. /walkon/PI_name/user_netid/ Ending Work 1) Stop acquiring and stop spinning 2) Take rotor out of probe 3) Take sample out of rotor and clean up the rotor 4) Write a note in Log Book 5) Keep desk top clean 6) Logout from S400 computer and FOM Manual Created by: IMSERC Lab, Department of Chemistry, Northwestern University Manual Revised Date: March 2014