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Nuclear magnetic resonance spectroscopy has proven to be powerful for the study of dynamic processes. A new pulse sequence, SirX, is designed to provide boundary conditions that simplify the McConnell equations. Both an initial rate approximation and a whole curve fitting to the time course of magnetization can be used to calculate the exchange rate. These methods were used to study the exchange kinetics of N,N-dimethylacetamide. As compared with the well-established exchange spectroscopy suitable to studies of slow exchange, SirX has the advantage of being less time consuming and capable of providing more reliable kinetic data. Furthermore, by setting the observation on X-nuclei with larger chemical shift dispersion as compared with an observation on (1)H resonance, SirX extends the upper limit of a reliable determination of exchange rates.

A previous study showed that together with the festuclavine synthase FgaFS, the old yellow enzyme FgaOx3 from Aspergillus fumigatus catalyzed the conversion of chanoclavine-I aldehyde to festuclavine in the biosynthesis of ergot alkaloids. In the absence of FgaFS, a mixture containing two compounds with a ratio of 7:3 was detected in the enzyme assay of FgaOx3. NMR experiments including (DQF)-COSY, HSQC, HMBC and NOESY identified their structures as E/Z isomers of N-methyl-N-[(5R,10R)-10-(2-oxo-propyl)-2,4,5,10-tetrahydrobenzo[cd]indol-5-yl]formamide and proved the migration of the formyl group at C-8 in chanoclavine I-aldehyde to N-6 in the identified products. Copyright © 2011 John Wiley & Sons, Ltd.

The conformation of [bis-(N,N′-difluoroboryl)]-3,3′-diethyl-4,4′,8,8′,9,9′,10,10′-octamethyl-2,2′-bidipyrrin (1) in solution was studied by analyzing the 13C19F and 19F19F through-space spin–spin couplings. The 1H and 13C NMR spectra were assigned on the basis of nuclear Overhauser effect spectroscopy (NOESY), heteronuclear single-quantum correlation (HSQC), and heteronuclear multiple-bond correlation (HMBC) experiments. The 19F spectrum of 1 was compared with that of 2-ethyl-1,3,5,6,7-pentamethyl-4,4-difluoro-4-bor-3a,4a-diaza-s-indacen (2). The 19F19F through-space spinspin coupling in 1 was thus assigned and the coupling constant was obtained by simulating the coupling patterns. The obtained conformation of 1 was compared with those of the known complexes [bis-(N,N′-difluoroboryl)]-3,3′,8,8′,9,9′-hexaethyl-4,4′,10,10′-tetramethyl-6,6′-(4-methylphenyl)-2,2′-bidipyrrin (3)and [bis-(N,N′-difluoroboryl)]-9,9′-diethyl-4,4′,8,8′,10,10′-hexamethyl-3,3′-bis(methoxycarbonylethyl)-2,2′-bidipyrrin (4). The conformational dynamics of 1, 3, and 4 was surveyed by observing the temperature dependence of the through-space coupling constants between 253 and 333 K. The 13C19F and 19F19F through-space spin–spin couplings thus confirm similar conformations of different BisBODIPYs in solution in contrast to earlier findings in the solid state. Copyright © 2009 John Wiley & Sons, Ltd.

The stereochemistry of γ-butyrolactons tetrahydro-6a-phenylfuro[3,4-b]furan-2(3H)-one (1), 1,4,5,9b-tetrahydro-3a-methylnaphtho[2,1-b]furan-2(3aH)-one (2), 1,4,5,9 b-tetrahydro-3a-methylfuro[2,3-c]quinolin-2(3aH)-one (3) and hexahydro-furo[3,2-c]benzofuran-2-one (4) was studied using DPFGSE-NOE experiments. Compounds 1–3 contain two stereocenters, while 4 contains three. Both 1H and 13C spectra showed a single diastereomer of all the compounds. Routine 2D experiments (DQF)-COSY, HMQC/HSQC, and HMBC were used to assign 1H and 13C spectra completely. Diastereotopic methylene protons with resolved 1H NMR signals as well as protons of cyclohexane served as references for the construction of the spatial arrangement in the molecules. NOE contacts between protons attached to the stereocenter and the diastereotopic protons were thus used to determine the configuration of the molecules. Vicinal coupling constants 3J assisted the assignment of the conformational arrangement of the cyclohexane ring of 4. Copyright © 2007 John Wiley & Sons, Ltd.

Gradient-selected (gs) HSQC-NOESY type experiments are often applied in order to obtain NOE cross peaks in symmetrical molecules or in complex organic molecules, e.g. carbohydrates. Since the coherence-selecting gradients in these pulse sequences are separated by several delays, including the mixing time, the gs-HSQC-NOESY spectra exhibit severe signal attenuation due to diffusion effects. The respective NOE information unaffected by diffusion effects can be obtained by X-half-filtered gs-NOESY-HSQC spectra. In this paper, an X-half-filtered version of the gs-NOESY-HSQC experiment is presented and the NOE cross peak integrals of its spectra are compared with those of a standard gs-HSQC-NOESY experiment. With phenanthrene as an example of symmetrical molecules, it is shown that the relative signal attenuation of gs-HSQC-NOESY cross peaks versus gs-NOESY-HSQC cross peaks is caused by diffusion effects and follows the Stejskal-Tanner equation. In contrast, the X-half-filtered gs-NOESY-HSQC experiment provides NOE cross peaks with reasonable signal-to-noise ratios even for long-range interactions in the presence of quadrupolar relaxation. This is demonstrated by the spectra of lithium dimethylcuprate.

Paramagnetic vanadocene gives easily recordable 1H and 13C solid-state NMR signals which are shifted by more than 300 and 500 ppm (to high and low frequency, at room temperature), respectively. The strong temperature dependence of these shifts is the basis of new NMR signal shift thermometers for solutions and for the solid state. Since different signal shifts are found for the two states, primary referencing is established by using a resistance thermometer for solutions and absorbed glycol for the solid state. In the MAS experiment the sample temperature, Ts, depends linearly on the temperature set on the controller, as verified for five rotor spinning rates, νr, between 6 and 12 kHz. The slope and the intercept of the calibration curves depend on νr. In a Tsvs. νr2 plot, a non-linear correlation is found. In addition to 1H, 13C is a useful nucleus for measuring Ts. With simple spectrometer handling and favourable signal shift data, vanadocene meets the requirements of an internal temperature standard for MAS NMR studies. © 1997 John Wiley & Sons, Ltd.