Magnetization transfer by NOE between spins can be quantified.It is typically set to around 600 msec for small molecules. By convention, this delay is D8 in Bruker pulse sequences. The NOE builds up during a delay in the experiment called the “mixing time”. NOESY experiments always include a kinetic aspect.It is worthwhile to take as many scans as possible to reveal weak NOE peaks. NOE peaks are weak – typically less than 2% of the intensity of the excited peak, often as little as 0.01%.1D NOESY spectra of small molecules are displayed with the large excited peak phased negative and the NOE peaks phased positive.2D NOESY experiments generally run ~2.5 – 12 hours on typical organic samples, but 1D NOESY experiments can yield significant results in about ten minutes.Oftentimes one runs sets of 1D NOESY spectra, selectively exciting several peaks in separate experiments. 2D NOESY can be run without significant user intervention, but 1D NOESY requires manual selection of one peak for excitation.It can even be used to determine forward/backward rates for systems in equilibrium on the 0.1 – 5 second timescale (NOESY is called EXSY when used for this purpose). It’s good for answering qualitative structural questions like “is this H axial or equatorial?” and “which of these geminal vinyl Hs corresponds to which NMR multiplet?” It can also be used for structure determination, including quantitative 1H- 1H distance measurement (if done carefully). Please recall that the 1H- 1H NOESY shows which hydrogen atoms are close together in space (under 4 or 5 Å), regardless of the chemical bonds between them. Where to find QR codes at the spectrometer computer Why NOESY?
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |