Restoring symmetry in two-dimensional solid-state NMR correlation spectra

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Multi-nuclear NMR of axially chiral biaryls in polypeptide orienting solvents: spectral discriminations and enantiorecognition mechanisms

International audienceDue to the importance of axially chiral biaryl derivatives as chiral auxiliaries and/or ligands for asymmetric synthesis as well as their structural role in bioactive natural products, continuous efforts have been undertaken to propose efficient methods for their atropo-selective synthesis. As a consequence, proposing robust and reliable analytical tools able to discriminate the signal of atropisomeric enantiomers becomes crucial to evaluate the enantiomeric excesses of mixtures. In this work, we show how several multi-nuclear 1D/2D-NMR techniques using homopolypeptide chiral liquid crystals as aligning solvents can provide a panel of analytical possibilities (through differences of chemical shift anisotropies, dipolar and quadrupolar residual couplings) to spectrally discriminate enantiomers of a large collection of trisubstituted axially chiral biphenyls. Approaches involving 31P, 13C and 2H 1D- or 2D-NMR experiments at natural abundance level are explored. Among noteworthy results, the first examples of spectral enantioseparations using 31P nuclei as nuclear probe are reported. Finally, the role of electronic factors and shape anisotropy that affects the efficiency of chiral discrimination mechanisms are examined and discussed. Molecular modeling calculations were carried out to establish the electronic profile of these analytes in order to understand and rationalize the 13C-{1H} NMR results

Understand, elucidate and rationalize the coordination mode of pyrimidylmethylamines: an intertwined study combining NMR and DFT methods †

International audiencea Conception of new pyrimidylmethylamine (pyrma) ligands and their corresponding Pd(II) complexes has been described. Both symmetrical and non-symmetrical ligands were prepared and subjected to complexation. Two different coordination modes, Pd(N,N)– or Pd(C,N,N)–pyrma, have been evidenced depending on the substitution of the pyrimidine ring and the nature or the shape of the additional pendant arm. In a non-symmetrical pyrimidine series, the substituent-induced discrimination of each heterocyclic nitrogen atom provoked regio-controlled coordination to the metal center. The molecular structure of pyrma–Pd(II) complexes in the solution state has been elucidated thanks to combined NMR experiments and DFT calculations. This study highlights the potency of 15 N and 13 C NMR spectroscopy for the elucidation of the regio-selective coordination to the Pd(II) in the pyrma-based complex series. DFT calculations were highly relevant to the identification of crucial factors that govern the regio-selectivity and the complexation modes. Close predicted and experimental chemical shift values put into relief the reliability of coordination modes for the most stable complexes in solution, depicted by DFT approaches

Large-Scale Production of Microcrystals and Precipitates of Proteins and Their Complexes

International audienceThe optimum conditions for the formation of plate-like and urchin-like microcrystals of biomolecules and their transfer to rotors for solid-state NMR spectroscopy depend on a variety of factors, of which minimizing the manipulation of the microcrystals and storing the sample for several months at 277 K (4 degrees C) play an important role. Three biological systems were investigated: Hen Egg-White (HEW) lysozyme (129 residues), the lengthened C-terminal domain (LCter) of Human centrin 2 (89 residues), and the complex between the C-terminal domain (Cter) of Human centrin 2 (79 residues) and the P17-XPC peptide (17 residues)