Search

A pair of novel polymorphic ionic cocrystals of 3,4‐dicyanotelluradiazole and tetraphenylphosphonium bromide are synthesized and are characterized by single‐crystal XRD. Strong and directional non‐covalent chalcogen bonds (ChB) between Te and Br are analyzed via solid‐state NMR to reveal large and anisotropic J(125Te,79/81Br) coupling tensors, providing unequivocal evidence for non‐Fermi contact contributions across ChBs. Along with large 79/81Br quadrupolar couplings for the Br− anions, these data provide new tools to characterize chalcogen bonds and to differentiate between ChB polymorphs. [ABSTRACT FROM AUTHOR]

127I nuclear quadrupole resonance (NQR) spectroscopy is established as a rapid and robust method to indicate the formation of iodine–nitrogen halogen bonds in co‐crystalline powders. Once the relevant spectral frequency range has been established, diagnostic 127I NQR spectra can be acquired in seconds. The method is demonstrated for a series of co‐crystals of 1,4‐diiodobenzene. Changes in the 127I quadrupolar coupling constant (CQ) by up to 74.4 MHz correlate with the length of the C−I donor covalent bond and inversely with the I⋅⋅⋅N halogen‐bond length. The predictive power of this technique is validated on two previously unknown co‐crystalline powders prepared mechanochemically. Single‐crystal growth via co‐sublimation and structure determination by single‐crystal X‐ray diffraction cross‐validates the findings. Natural localized molecular‐orbital analyses provide insight into the origins of the quadrupolar coupling constants. [ABSTRACT FROM AUTHOR]

Protein structure and function is dependent on myriad noncovalent interactions. Direct detection and characterization of these weak interactions in large biomolecules, such as proteins, is experimentally challenging. Herein, we report the first observation and measurement of long-range 'through-space' scalar couplings between methyl and backbone carbonyl groups in proteins. These J couplings are indicative of the presence of noncovalent C−H⋅⋅⋅π hydrogen-bond-like interactions involving the amide π network. Experimentally detected scalar couplings were corroborated by a natural bond orbital analysis, which revealed the orbital nature of the interaction and the origins of the through-space J couplings. The experimental observation of this type of CH⋅⋅⋅π interaction adds a new dimension to the study of protein structure, function, and dynamics by NMR spectroscopy. [ABSTRACT FROM AUTHOR]