31P and13C chemical shielding tensors in the phosphoenolpyruvate moiety from rotary resonance recoupling13C and31P MAS and single crystal31P NMR

Electronic Properties of Furyl Substituents at Phosphorus and Their Influence on 31P NMR Chemical Shifts

The electronic properties of 2-furyl and 3-furyl substituents attached to phosphanes and phosphonium salts were studied by means of IR spectroscopy and experimental and computational (31)P NMR spectroscopy. The heteroaromatic systems proved to be electron withdrawing with respect to phenyl substituents. However, phosphorus atoms with attached furyl substituents are strongly shielded in NMR. The reason for this phenomenon was studied by solid state (31)P MAS NMR experiments. The chemical shift tensor was extracted, and the orientation within the molecules was determined. The tensor component sigma(33), which is effected the most by furyl systems, is oriented perpendicular to the P-C bonds of the substituents. P-furyl bonds are shorter than P-phenyl bonds. We assume therefore a lower ground-state energy of the molecules, because of the electron withdrawing properties of the 2-furyl systems. The sigma(para) component of the (31)P NMR magnetic shielding is therefore smaller, which results in an overall increase of the magnetic shielding.

Magnitudes and Orientations of 31P Chemical Shielding Tensors in Pt(II)−Phosphine Complexes and Other Four-Fold Coordinated Phosphorus Sites

31P MAS and double-quantum filtered 31P MAS NMR experiments at and near the n = 0 rotational resonance condition, as well as off-magic angle spinning 31P NMR experiments on two polycrystalline samples of Pt(II)-phosphine thiolate complexes are reported. Numerical simulations yield complete descriptions of the two 31P spin pairs. 195Pt MAS NMR spectra are straightforward to obtain but sensitively reflect only some parameters of the 195Pt(31P)2 three-spin system. Based on the 31P NMR results obtained and in conjunction with a large body of literature data and irrespective of the chemical nature of the specimen, a unified picture of the dominating motif of 31P chemical shielding tensor orientations of phosphorus sites with 4-fold coordination is identified as a local (pseudo)plane rather than the directions of P element bond directions.

Correlations between 31P Chemical Shift Anisotropy and Molecular Structure in Polycrystalline O,O‘-Dialkyldithiophosphate Zinc(II) and Nickel(II) Complexes: 31P CP/MAS NMR and Ab Initio Quantum Mechanical Calculation Studies

Different potassium salts and zinc(II) and nickel(II) O,O'-dialkyldithiophosphate complexes were studied by solid-state 31P CP/MAS and static NMR and ab initio quantum mechanical calculations. Spectra were obtained at different spinning frequencies, and the intensities of the spinning sidebands were used to estimate the chemical shift anisotropy parameters. Useful correlations between the shapes of the 31P chemical shift tensor and the type of ligand were found: terminal ligands have negative values of the skew kappa, while bridging and ionic ligands have positive values for this parameter. The experimental results were compared with known X-ray diffraction structures for some of these complexes as well as with ab initio quantum mechanical calculations, and a useful correlation between the delta22 component of the 31P chemical shift tensor and the S-P-S bond angle in the O,O'-dialkyldithiophoshate zinc(II) and nickel(II) complexes was found: delta22 increases more than 50 ppm with the increase of S-P-S bond angle from ca. 100 degrees to 120 degrees , while the other two principal values of the tensor, delta11 and delta33, are almost conserved. This eventually leads to the change in sign for kappa in the bridging type of ligand, which generally has a larger S-P-S bond angle than the terminally bound O,O'-dialkyldithiophosphate group forming chelating four-membered P(ss)Me heterocycles.

Binding of the natural substrates and products to KDO8P synthase: 31P and 13C solution NMR characterization

Proton decoupled 31P and 13C solution NMR experiments were applied to mixtures of 3-deoxy-D-manno-2-octulosonate-8-phosphate (KDO8P) synthase, with each of its natural substrates, phosphoenolpyruvate and arabinose-5-phosphate (ASP), and product KDO8P to identify the formation of the enzyme-substrate and enzyme-product complexes. Effects arising from ligand interactions with the enzyme are reported via chemical shifts and line broadening with respect to those of the free ligands in solution, depending on the strength and dynamics of binding under thermodynamic equilibrium conditions. The characterization was done both at low and high field spectrometers, 200 and 500 MHz (1H frequencies), and in cases of 31P NMR measurements, it was demonstrated that only the low field spectrometer is capable of providing direct experimental evidence on the enzyme-ligand interactions. Since both the substrate A5P and the product KDO8P exhibit multiple anomeric forms in solution, evidence for the preference of recognition and binding of particular forms is sought.