Bestechend einfach: Eine neue Methode wird vorgestellt, mit der der Diffusionskoeffizient eines kleinen Moleküls nur anhand des Molekulargewichts und der Viskosität des Lösungsmittels abgeschätzt werden kann. Die Methode ermöglicht die quantitative Interpretation der Diffusionsdomäne diffusionsgeordneter NMR‐Spektren (siehe Bild).

Durch Unterdrücken der Multiplettstruktur von Protonen‐NMR‐Spektren (siehe Bild) lässt sich eine spektrale Auflösung erreichen, die der Verwendung eines GHz‐Spektrometers gleichkommt. Solche „Pure‐Shift“‐Techniken lassen sich auch leicht auf mehrdimensionale Techniken wie DOSY übertragen.

Resolution in proton NMR spectra can be greatly enhanced by collapsing all homonuclear coupling structure to give a "pure shift" spectrum. Where protons are strongly coupled, greatly improved results can be obtained by 13 C isotope filtration using a modified bilinear rotation decoupling [1] (BIRD) method. Here it is shown for the first time that a pure shift spectrum can be obtained even in the notoriously difficult case of the methylene envelope of a long alkyl chain.Proton NMR spectroscopy is the single most important structural tool in chemistry; it is so familiar that its limitations are often taken for granted. Chief among these is the problem of resolution: the limited range of chemical shifts means that multiplets overlap in all but the simplest spectra, complicating analysis and obscuring information. There has been a recent revival of interest in pure shift NMR spectroscopy, in which broadband homonuclear decoupling is used to collapse multiplets to singlets, greatly improving spectral resolution. [1][2][3][4][5][6][7][8][9][10] The largest family of techniques derives from the experiment of Zangger and Sterk [2] (ZS), in which a 1808 pulse that is selective both for chemical shift and for spatial position causes a subset of protons to evolve as though they lack homonuclear couplings. Such methods are effective and versatile, but suffer one severe disadvantage. The narrow range of proton chemical shifts, as well as placing a premium on resolution, increases the likelihood of strong coupling, which is responsible for many of the most intractable problems in spectral assignment. Unfortunately such effects can severely complicate or indeed vitiate ZS pure shift methods.There is, however, a close analogy between ZS methods and the BIRD [1] method, which uses the dilute 13 C isotope to allow the subset of protons directly bonded to 13 C to be manipulated. Where a signal in the normal proton spectrum is strongly coupled, the 13 C satellites will generally be weakly coupled, so a pure shift experiment based on BIRD should circumvent the problem. Paradoxically, although BIRD was originally proposed as a pure shift method, it seems never to have been used as such, instead becoming a standard building block in heteronuclear multidimensional NMR spectroscopy; only very recently has it formed the basis of a fully decoupled pure shift HSQC experiment. [8] Both ZS and BIRD pure shift methods rely on applying a selective perturbation to a subset of spins, to refocus the effects of homonuclear J modulation while retaining that of the chemical shift. In the ZS case the perturbation uses a selective pulse in the presence of a magnetic field gradient, so that the active spins are restricted to those in a thin slice close to resonance. In BIRD, the net effect of the four pulses is to apply a 1808 rotation only to those protons bound directly to 13 C. In each case the price of simplification is a loss in sensitivity, in ZS because only a thin slice of sample is used for any given chemical shift, and in BIRD because of the ...

Psychisch stark: Ein flexibles und allgemeines „Pure shift“‐Experiment (PSYCHE) übertrifft herkömmliche Methoden zur Homokern‐Breitbandentkopplung bezüglich Empfindlichkeit, Übersichtlichkeit der Spektren und Toleranz starker Kopplungen. Dies zeigt ein Vergleich von Teilspektren von Östradiol in [D6]DMSO, die mit gewöhnlicher 1H‐NMR‐Spektroskopie und mit PSYCHE erhalten wurden.