Weak Intermolecular CH···N Hydrogen Bonding: Determination of 13CH-15N Hydrogen-Bond Mediated J Couplings by Solid-State NMR Spectroscopy and First-Principles Calculations.

Weak hydrogen bonds are increasingly hypothesized to play key roles in a wide range of chemistry from catalysis to gelation to polymer structure. Here, 15N/13C spin-echo magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) experiments are applied to "view" intermolecular CH···N hydrogen bonding in two selectively labeled organic compounds, 4-[15N] cyano-4'-[13C2] ethynylbiphenyl (1) and [15N3,13C6]-2,4,6-triethynyl-1,3,5-triazine (2). The synthesis of 2-15N3,13C6 is reported here for the first time via a multistep procedure, where the key element is the reaction of [15N3]-2,4,6-trichloro-1,3,5-triazine (5) with [13C2]-[(trimethylsilyl)ethynyl]zinc chloride (8) to afford its immediate precursor [15N3,13C6]-2,4,6-tris[(trimethylsilyl)ethynyl]-1,3,5-triazine (9). Experimentally determined hydrogen-bond-mediated 2hJCN couplings (4.7 ± 0.4 Hz (1) and 4.1 ± 0.3 Hz (2)) are compared with density functional theory (DFT) gauge-including projector augmented wave (GIPAW) calculations, whereby species-independent coupling values 2hKCN (29.0 × 1019 kg m-2 s-2 A-2 (1) and 27.9 × 1019 kg m-2 s-2 A-2 (2)) quantitatively demonstrate the J couplings for these "weak" CH···N hydrogen bonds to be of a similar magnitude to those for conventionally observed NH···O hydrogen-bonding interactions in uracil (2hKNO: 28.1 and 36.8 × 1019 kg m-2 s-2 A-2). Moreover, the GIPAW calculations show a clear correlation between increasing 2hJCN (and 3hJCN) coupling and reducing C(H)···N and H···N hydrogen-bonding distances, with the Fermi contact term accounting for at least 98% of the isotropic 2hJCN coupling.

Structure of 1,5-benzodiazepinones in the solid state and in solution: Effect of the fluorination in the six-membered ring.

Two novel tetrafluorinated 1,5-benzodiazepinones were synthesized and their X-ray structures determined. 6,7,8,9-Tetrafluoro-4-methyl-1,3-dihydro-2H-1,5-benzodiazepin-2-one crystallizes in the monoclinic P21/c space group and 6,7,8,9-tetrafluoro-1,4-dimethyl-1,3-dihydro-2H-1,5-benzodiazepin-2-one in the triclinic P-1 space group. Density functional theory studies at the B3LYP/6-311++G(d,p) level were carried out on these compounds and on four non-fluorinated derivatives, allowing to calculate geometries, tautomeric energies and ring-inversion barriers, that were compared with the experimental results obtained by static and dynamic NMR in solution and in solid state.

13C and 15N NMR spectra of aminobenzimidazoles in solution and in the solid state.

The (13)C [hexadeutero-dimethylsulfoxide (DMSO-d(6)), hexamethyl-phosphoramide (HMPA)-d(18)and solid-state] and (15)N (solid-state) NMR spectra of six C-aminobenzimidazoles have been recorded. The tautomerism of 4(7)-aminobenzimidazoles and 5(6)-aminobenzimidazoles has been determined and compared with B3LYP/6-311 + + G(d,p) calculations confirming the clear predominance of the 4-amino tautomer and the slight preference for the 6-amino tautomer. GIAO-calculated absolute shieldings compare well with experimental chemical shifts.

13C and 15N NMR chemical shifts of 1-(2',4'-dinitrophenyl) and 1-(2',4',6'-trinitrophenyl) pyrazoles in the solid state and in solution.

The (13)C and (15)N CPMAS NMR spectra of 18 pyrazoles substituted at position 1 by dinitrophenyl and trinitrophenyl (picryl) groups have been recorded. To help in the assignments, some of these compounds were studied in DMSO-d(6) solution. Phenomena such as the conformation of the N-aryl groups and broadening of splittings due to quadrupolar nuclei are discussed.

Ethodin: pharmacological evidence of the interaction between smooth muscle and mast cells in the myometrium.

Ethodin has been used to induce labor through a mechanism that does not involve the estrogen-preparatory process being postulated as necessary for ensuring the events in a normal labor. The cellular mechanisms involved in that process are unknown. We used an isolated organ bath preparation for mouse uterine horns and a primary culture of mouse myometrial smooth muscle cells to analyze the cellular mechanisms involved in the contractile action of this drug in the myometrium. Ethodin at a concentration of 10 microM and Compound 48/80 (1 microg/ml) evoked contractions of uterine horns in an isolated organ bath preparation. Uterine contractile responses showed a transient increase in contractile tension that lasted 2 to 3 min. Tachyphylaxis was observed after four or five successive stimuli, which consisted in additions and washings of the drug at an interval of 10 min. The primary smooth muscle mouse myometrium cells contained a high proportion of relaxed cells that varied widely in length (5-160 microm). Cell lengths decreased in response to the application of serotonin (10 microM) and oxytocin (0.1 microM) but were not affected after the addition of ethodin (10 microM). However, the cells contracted after a purified fraction of mast cells that had been degranulated by the action of the drug ethodin, which was added to the culture medium. These results provide some evidence related to the mechanism of myometrial contractile action of ethodin and support the hypothesis that mast cells may be involved in the regulation of myometrium contractility.