Schematic of the COSY Experiment

Transcription

1 Schematic of the COSY Experiment 9 o 9 o (d) t 2 (aq) homonuclear COSY But what happens for a heteronuclear experiment? The 9 o pulses will not cover both sets of nuclei, and there would be issues with observation of both nuclei simultaneously. a These issues could (perhaps) be addressed by something like: 9 o H 9 o H possible heteronuclear COSY 9 o C (d) 9 o C t 2 C (aq) Pg.

2 Cartoon of a Full Heteronuclear COSY If we attempted this hetero-cosy exp, it would look something like the cartoon on the right, except that the shaded regions are hugely exaggerated: the H region would cover ~ppm or.5 MHz, F (MHz) regions would cover ~2ppm or.25 MHz F2 (MHz) 6 Pg. 2

3 The Diagonals of a Heteronuclear COSY along diagonal 2 3 F (MHz) along diagonal F2 (MHz) 6 Pg. 3

4 The Diagonals of a Heteronuclear COSY 2 3 F (MHz) along diagonal 4 5 actually would see full H- H COSY here F2 (MHz) Pg. 3

5 The Diagonals of a Heteronuclear COSY along diagonal 3 3 C- C COSY at natural abundance would give just diagonal, as crosspeaks would be % of % =.% max intensity. An important variant 3 3 of C- C COSY is called INADEQUATE F (MHz) F2 (MHz) 6 Pg. 3

6 Heteronuclear COSY HETCOR Direct observation of, with indirect evolution of H (in /F), was the first widely used heteronuclear COSY experiment. It is compatible with older hardware (e.g., the ACs), but suffers from the relatively poor sensitivity of directly-observed 3 C. HETCOR F ( H observe in MHz) F2 ( C observe in MHz) 6 Pg. 4

7 Regions of Heteronuclear COSY Direct observation of H, with indirect 3 evolution of C (in /F), offers 8 the sensitivity of the HETCOR exp., but this inverse exp. ( is only one of many variants) must, to high precision, remove H bonded 2 to C (99%) during F2, requiring newer/ better hardware. This inverse exp. is now commonplace in NMR labs. 3 C in F ] F2 ( H observe in MHz) F ( C observe in MHz) Pg. 5

8 Regions of Heteronuclear COSY 3 C in F] COSY along diagonal COSY along diagonal HETCOR F (indirectly observed dimension) F2 (directly observed dimension) 6 Pg. 6

9 Schematic of the Experiment 9 o H 9 o H 9 o C (d) 9 o C t 2 C (aq) Impracticalities of performing the full experiment as shown on the previous pages, and it s superior sensitivity, makes the heteronuclear experiment to perform. : H directly observed/evolving in t 2/F2 3 C indirectly observed/evolving in t /F. Pg. 7

10 Schematic of the Experiment 3 C in F] (d) t 2 C (aq) 3 Don t need st proton pulse for C evolution in. Pg. 8

11 Schematic of the Experiment 3 C in F] (d) t 2 C (aq) 3 Don t need st proton pulse for C evolution in. Pg. 8

12 Schematic of the Experiment 3 C in F] (d) t 2 C (aq) Don t need 3 3 C detection during t 2 ( C observed indirectly). Pg. 9

13 Schematic of the Experiment 3 C in F] (d) Don t need 3 3 C detection during t 2 ( C observed indirectly). Pg. 9

14 Schematic of the Experiment 3 C in F] (d) Can improve sensitivity by allowing IS I x z y before detection, and include decoupling (removing heteronuclear coupling in t ). 2 Pg.

15 Schematic of the Experiment 3 C in F] /2J (d) Can improve sensitivity by allowing IS I x z y before detection, and include decoupling (removing heteronuclear coupling in t ). 2 Pg.

16 Schematic of the Experiment 3 C in F] IS X Z I Y S Y IS Z X Pg.

17 Schematic of the Experiment 3 C in F] /2J (d) 3/2 3 H C) H detection is ( / more sensitive than C detection. We can improve the experiment by another factor of by providing H excitation (now utilizing polarization transfer in the other direction: I I S I S S. y x z z x y ) H C Pg.

18 Schematic of the Experiment 3 C in F] /2J /2J (d) 3/2 3 H C) H detection is ( / more sensitive than C detection. We can improve the experiment by another factor of by providing H excitation (now utilizing polarization transfer in the other direction: I I S I S S ). y x z z x y H C Pg.

19 Schematic of the Experiment 3 C in F] I Y IS X Z IS X Z I Y IS Z X IS Z X +S Y Pg.

20 Schematic of the Experiment 3 C in F] /2J /2J (d) o 8 pulses remove chemical shift during the J-evolution (polarization transfer) sections of the experiment. Other components of a usable experiment, involving novel spin gymnastics (e.g., the BIRD sequence), and/or phase cycling, and/or pulsed-field gradients, are required to remove the 2 99% of protons bonded to C. Pg. 2

21 Schematic of the Experiment /2J /2J (d) Theoretically (fairly close to empirical observations), 5/2 3 is 4 ~ 32 better than C direct (but 3 for NOE, so ~ more sensitive, ~ better in time). 5/2 5 5 ~ 32 better than N direct ( in time). Pg. 3