tailieunhanh - Lecture Coherence order and coherence selection

Lecture Coherence order and coherence selection. After studying this section will help you understand: why we need coherence selection, concept of coherence order, coherence transfer pathways (CTPs), selecting a CTP with phase cycling, . | EUROMAR 2011 Outline Further information Why we need coherence selection PDF of these slides available at Coherence order and http Concept of coherence order coherence selection See also Coherence transfer pathways CTPs Understanding NMR Spectroscopy Selecting a CTP with phase cycling James Keeler Wiley Chapt. 11 James Keeler Selecting a CTP with gradients Suppression of zero-quantum Spin Dynamics. Basics of Nuclear coherence Magnetic Resonance Malcolm Levitt Wiley Department of Chemistry Why we need coherence selection Coherence order p Properties of coherence order Defined by phase acquired during takes values 0 1 2 DQF COSY rotation by about z 0 is z-magnetization 1 is single quantum ρˆ p rotate by φ about z ρˆ p exp ipφ DQ spectrum 2 is double quantum etc. phase acquired is pφ only p 1 is observable NOESY maximum minimum value is N where The spins don t know what we want different p separated by using this property N is number of spins We want one out of many possibilities 1 Effect of pulses Coherence transfer pathway CTP Heteronuclear experiments Indicates the desired coherence order RF pulse all possible p at each point HMQC values of p - which is why we need selection special case DQ spect. NOESY DQF COSY 180 pulse separate p for each nucleus pI pS p p note always starts at p 0 ends with p 1 on observed nucleus always ends at p 1 pulse to S only affects pS Frequency discrimination - or alternatively and lineshapes in 2D for absorption mode spectra must retain p 1 during t1 symmetrical pathways N-type Phase cycling P-type 1. record two separate spectra echo or N-type p 1 during t1 combine this with frequency discrimination anti-echo or P-type p 1 during t1 using TPPI or States 2. combine to give absorption spectrum 2 Pulse phase Receiver rx. phase Receiver phase rx. phase fixed rx. phase If the signal generated by the pulse sequence shifts in phase then this can always be compensated for by shifting rx. phase the receiver by the same