Butterfly Effect in Cytarabine: Combined NMR-NQR Experiment, Solid-State Computational Modeling, Quantitative Structure-Property Relationships and Molecular Docking Study.

Cytarabine (Ara-C) is a synthetic isomer of cytidine that differs from cytidine and deoxycytidine only in the sugar. The use of arabinose instead of deoxyribose hinders the formation of phosphodiester linkages between pentoses, preventing the DNA chain from elongation and interrupting the DNA synthesis. The minor structural alteration (the inversion of hydroxyl at the 2' positions of the sugar) leads to change of the biological activity from anti-depressant and DNA/RNA block builder to powerful anti-cancer.

Elucidating the Role of Noncovalent Interactions in Favipiravir, a Drug Active against Various Human RNA Viruses; a H-N NQDR/Periodic DFT/QTAIM/RDS/3D Hirshfeld Surfaces Combined Study.

Favipiravir (6-fluoro-3-hydroxypyrazine-2-carboxamide, FPV), an active pharmaceutical component of the drug discovered and registered in March 2014 in Japan under the name Avigan, with an indication for pandemic influenza, has been studied. The study of this compound was prompted by the idea that effective processes of recognition and binding of FPV to the nucleic acid are affected predominantly by the propensity to form intra- and intermolecular interactions. Three nuclear quadrupole resonance experimental techniques, namely H-N cross-relaxation, multiple frequency sweeps, and two-frequency irradiation, followed by solid-state computational modelling (density functional theory supplemented by the quantum theory of atoms in molecules, 3D Hirshfeld Surfaces, and reduced density gradient) approaches were applied.

NMR and NQR study of polymorphism in carbamazepine.

Four polymorphic forms of carbamazepine have been simultaneously investigated by H NMR and N NQR. The results show that the proton spin-lattice relaxation time and the N NQR spectra can be used to differentiate between various polymorphic forms. Spontaneous transformations from Form II to Form III and from Form IV to Form III have been investigated through their influence on the N NQR spectrum and the proton NMR signal and spin-lattice relaxation.

A rapid determination of nuclear quadrupole resonance frequencies using field-cycling magnetic resonance and frequency modulated RF excitations.

A modification of Slusher-Hahn's double resonance technique is described and experimentally tested. It is based on application of multiple frequency sweeps and can be used for a rapid location of nuclear quadrupole resonance (NQR) frequencies. The resolution of the present technique is relatively low but, when the NQR frequencies are located, it is easy to use either the Slusher-Hahn's technique or pulse NQR to determine the NQR frequencies with a higher precision.

N NQR spectroscopy reveals the proton position in N-HN bonds: a case study with proton sponges.

The position of protons in hydrogen bonds is often uncertain to some degree, as the technique most often used for structure determination, X-ray diffraction, is sensitive to electron density, which is not particularly abundant around protons. In hydrogen bonds, protons introduce an additional problem: the potential for proton motion is inherently anharmonic and thus requires the consideration of nuclear quantum effects (NQEs). Here, we demonstrate that 14N NQR spectroscopy is able to rather accurately determine proton positions in N-HN bonds, in certain cases with an accuracy comparable to that of X-ray and neutron diffraction at room temperature.