P.E.COSY

The E.COSY group of experiments E.COSY [5.33, 5.127, 5.128], P.E.COSY [5.34] and P.COSY [5.35] have been developed to achieve the same quality of cross peak as a DQF spectra, but with the restriction that the cross peaks relate only to those transitions involving the nucleus directly. Whilst in a DQF COSY experiment the structure of the cross peaks is related to the active and passive coupling, in a E.COSY experiments the passive couplings are suppressed. 

The E.COSY experiment uses extensive phase cycling and in an effort to reduce the long acquisition times the P.E.COSY and P.COSY techniques have been developed. However these techniques require excessive post-processing of the data and consequently only the E.COSY experiment will be illustrated in Check it 5.4.1.6. For a comprehensive review of the other techniques the reader is referred to the literature [5.34,5.35]. 

Over the following years many experiments were developed whereby the signal structure contains a lot of information on the coupling constants, cf. E-COSand P.E.COSY. Others stem from heteronuclear experiments, such as the method of Bermel et which is a good illustration of the way problems were approached at the time, and, more recently, the heteronuclear XLOC experiments which show structures similar to E.COSY spectra. 

P.E.COSY COSY with simplified multiplet structure. P.E.COSY allows for the accurate measurements of homonuclear coupling constants... 

Figure 12 H, region of the 500 MHz P.E.COSY spectrum of cyclo(-Tic-Pro-Phe-Gly-Pro-Pro-Thr-Leu-) in DMSO at 300 K. The enlarged view is of the Phe H , cross peaks. The displacement of the multiplet patterns can be used to determine the passive couplings with high accuracy. H means the low field p proton and the high field proton.

Willker and Leibfritz (1992a) introduced an extension of the E.COSY principle that yields additional flexibility. In addition to coherence transfer between the active spins i and j, polarization of spin p, which is passive during is transferred to a spin q, which plays the role of the passive spin during t - Hence, in general, the E.COSY triad is opened up. The two- and three-dimensional JHH-TOCSY experiments for the determination of coupling constants of Willker and Leibfritz (1992a) use a combination of homonuclear TOCSY transfer and two BIRD (bilinear rotation decou-... 

In addition to the J-resolved experiments several other enhanced chemical shift correlated experiments are available for determining coupling constants. A short overview and classification is given in Table 5.8. Some experiments like the P.COSY or E.COSY experiment are explained in more detail in section 5.4.1.1. 

D HNCA-E.COSY-TROSY 3D HNCA(a/p-J-CAHAN)-TROSY... 

Isoflavones Leaves of Trifolium pratense Stop-flow h cosy, noesy 400 MHz, 120 p.E cell D2O, ACN 86 n 0... 

The /aH,pH vicinal coupling constants can be determined from Exclusive COSY (E-COSY) type experiments and, together with intraresidue NOEs, can be used to obtain stereospecific assignments of P-methylene protons and side-chain x angle restraints (Table 2). 

Figure 6.11 A 3D heteronuclear HMQC-COSY spectrum of a tripepiide. The o),-axis represents N chemical shifts, whereas the (Or and 88, copyright (1988), with permission from Academic Pre.ss, Inc.)...

The full 300 MHz H NMR spectrum of A in CDC13 solution is shown in trace a opposite expanded multiplets from that spectrum are shown in trace c. The COSY spectrum, d, and the one-dimensional spectrum, e, on p. 100, were obtained in a CDCI3-C6D6 mixture. Trace c, p. 99, shows expanded multiplets from the CDCb-CgD spectrum. Scale markers below the expanded multiplets are 10 Hz each. 

Maes M, Scharpe S, Meltzer HY, Bosnians E, Suy E, Calabrese J, Cosy ns P (1993) Relationships between interleukin-6 activity, acute phase proteins, and function of the hypothalamic-pituitary-adrenal axis in severe depression. Psychiatry Res 49 11-27. 

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