The gradient selection generally provides superior quality data in considerably less time than the traditional NOE difference method. Thus, so-called transient NOEs are sampled with this method and percentage NOE enhancements are not recorded directly (nor do thay have the same significance) as in the 1D NOE difference experiment. The NOEs observed originate only from the selected proton(s) and are generated during a mixing period in a similar manner to the 2D NOESY experiment. The selected target may then represent the starting point for magnetisation transfer through scalar coupling ( TOCSY) or the NOE ( NOESY), thus providing specific information on the NMR interactions of the target spins.Ī 1D NOE technique based on the use of the DPFGSE for selective excitation of a target proton. The method is quick and clean, typically providing complete suppression of all other signals. The method can, for example, be employed to investigate molecular size, complexation phenomena, binding and aggregation.ĭPFGSE excitation: Double Pulsed Field Gradient Spin-Echo excitationĪn excitation method based on pulsed field gradients ( PFGs) to selectively excite a resonance or group of resonances in a spectrum. The diffusion coefficients are determined from the NMR signal intensity decays in a sequence of 1D spectra recorded with increasing amplitudes of pulsed field gradients (PFGs) which are used to map the translational behaviour of the solutes. See also: TOCSY HSQC-TOCSY HMQC-TOCSY DPFGSE-TOCSYĪ pseudo-2D NMR experiment which presents chemical shifts on one axis versus the self-diffusion coefficients of the solutes on the other. The multi-pulse element is applied as a repeated sequence to define a total "mixing time" during which magnetisation is allowed to flow between coupled spins. It is most often used in the TOCSY experiment as a so-called "isotropic mixing" sequence, for which the DIPSI-2 element is most commonly employed. The DIPSI element (decoupling in the presence of scalar interactions) is sequence of pulses clustered together that serve to transfer magnetisation between protons that share scalar couplings.
Note that because quaternary carbons do not possess a directly bonded proton, they do not produce responses in standard DEPT experiments, although these can be seen (often more weakly) in the DEPTQ variant.ĭEPTQ: DEPT with retention of QuaternariesĪ variant of the above DEPT experiment in which the signals of non-protonated carbons (such as quaternary centres, hence the "Q") are also retained (albeit with reduced intensities) and are displayed with signs similar to that of CH 2 groups. The experiment is typically run using different final proton pulse angles (the numbers below), resulting in differing signs (+ve or -ve) for the various carbon resonances: The editing feature alters the amplitude and sign of the carbon resonances according to the number of directly attached protons, allowing the identification of carbon multiplicities. This gain stems from the larger population differences associated with protons, which are four times those of carbon. The sensitivity gain comes from starting the experiment with proton excitation and subsequently transferring the magnetisation onto carbon (the process known as polarisation transfer). Most often used to analyse coupling relationships between protons, but may be used to correlate any high-abundance homonuclear spins eg 31P, 19F and 11B.ĭEPT: Distortionless Enhancement by Polarisation TransferĪ 1D experiment used for enhancing the sensitivity of carbon observation and for editing of 13C spectra. The presence of off-diagonal peaks (cross-peaks) in the spectrum directly correlates the coupled partners.
Used to identify nuclei that share a scalar (J) coupling. This carbon-detected experiments has largely been superseded by the more sensitive proton-detected HMBC experiment. The modification in APT aims to improve the intensity of the slowly relaxing non-protonated centres by using a smaller initial excitation pulse to reduce saturation.ĬOLOC: Correlation through Long-Range CouplingĪ 2D experiment for determining long-range (2 or 3-bond) correlations between proton and carbon nuclei and thus piecing together organic structures. An experiment derived from the JMOD experiment and also used for the multiplicity editing of carbon-13 spectra.