A method for probing the strength of B-N dative bonds is reported. The activation parameters for nitrogen inversion in a series of azetidines tethered to boronate esters have been quantified by VT-NMR and the measured barriers correlated with data obtained by (11)B NMR, X-ray crystallography and MP2 calculations.

Human dipeptidyl-peptidase III (h.DPP III) is a zinc-exopeptidase that hydrolyses dipeptides from the N-terminus of its substrates. Its mechanism of action was assumed to be similar to that of thermolysin, but was never thoroughly investigated. This study presents the first insight into the reaction mechanism of h.DPP III, determined on the model and real (hydrated enzyme with Leu-enkephalin bo...

Rates of pyramidal motion in an aziridine are controlled by reversible trans to cis photoisomerisation of an azobenzene unit attached to the ring nitrogen atom. The dynamics of the inversion process and activation parameters are derived by variable temperature NMR, and are supported by ab initio calculations.

Dipolar addition of cyclic azomethine imines with cyclic vinyl sulfones gave rise to functionalized tricycles that exhibited fluxional behavior in solution at room temperature. The scope of the synthetic methodology was explored, and the origin of the fluxional behavior was probed by NMR methods together with DFT calculations. This behavior was ultimately attributed to stereochemical inversion ...

The intrinsic conformational and structural properties of the tropinone azabicycle have been investigated in a supersonic jet expansion using rotational spectroscopy. The spectrum revealed the presence of equatorial and axial conformers originated by the inversion of the N-methyl group, with the tropane motif adopting a distorted chair configuration. The determination of substitution and effect...

Three-dimensional HNCO and HNCA subspectra from a small protein (agitoxin, 4 kDa, enriched in carbon-13 and nitrogen-15), have been obtained by direct frequency-domain excitation of selected carbon and nitrogen sites. This new technique applies an array of several simultaneous soft radiofrequency spin-inversion pulses, encoded (on or off) according to nested Hadamard matrices, and the resulting...

N-Allyl-N-methyl-2-aminopropane (AMAP) is a relatively simple tertiary amine that has a chiral center at the pyramidal nitrogen. Racemization occurs by inversion-rotation at nitrogen. For each AMAP enantiomer, conformational exchanges occur via isolated rotation about carbon-nitrogen and carbon-carbon bonds. The 1H and 13C{1H} dynamic NMR (DNMR) spectra of AMAP show a higher temperature decoale...

Although amine nitrogen atoms are potential stereogenic centers, their configurational lability arising from lone-pair inversion has typically prevented their utility in synthesis.NHalogenation can dramatically slow lone-pair inversion and therefore raise the temperature at which the configurational lability ceases. We therefore considered that if a suitable system could be found, N-chloramines...