We report an observation of long-lived spin-singlet states in a 13C-1H spin pair in a zero magnetic field. In 13C-labeled formic acid, we observe spin-singlet lifetimes as long as 37 s, about a factor of 3 longer than the T1 lifetime of dipole polarization in the triplet state. In contrast to common high-field experiments, the observed coherence is a singlet-triplet coherence with a lifetime T2...

We describe several homo- and heteronuclear 2D NMR strategies dedicated to the analysis of anisotropic (2)H spectra of a mixture of dideuterated unlike/like stereoisomers with two remote stereogenic centers, using weakly orienting chiral liquid crystals. To this end, we propose various 2D correlation experiments, denoted "D(H)(n)D" or "D(H)(n)C" (with n=1, 2), that involve two heteronuclear pol...

0009-2614/$ see front matter 2008 Elsevier B.V. A doi:10.1016/j.cplett.2008.11.089 * Corresponding author. E-mail addresses: [email protected], [email protected] gmx.ch (B.H. Meier). We describe a low-power approach for heteronuclear cross-polarization (CP) at high magic-angle spinning (MAS) frequencies. It is based on second-order CP at the n = 0 Hartmann–Hahn condition. The mechanism for the polarizati...

The relative stereochemistry of tris-heteroleptic ruthenium complexes [Ru(pp)(pp')(pp'')](PF(6))(2), where pp = 1,10-phenanthroline-4-carboxamide, pp' = 5,6-dimethyl-1,10-phenanthroline, and pp'' = 7,8-dimethyl dipyrido[3,2-a:2',3'-c]phenazine, was studied using NMR spectroscopy. The (1)H and (13)C spectra were assigned by using double-quantum-filtered correlation spectroscopy (DQF-COSY), heter...

Three new cycloartane-type triterpene glycosides have been isolated from the aerial parts of Astragalus trojanus. The structures were established mainly by a combination of one- and two-dimensional NMR techniques [1H-1H-correlation spectroscopy (COSY), 1H-13C-heteronuclear multiple quantum correlation spectroscopy (HMQC), and 1H-13C-heteronuclear multiple-bond correlation spectroscopy (HMBC)] a...

A series of 3 H-pyrazolo[3,4-d][1,2,3]triazin-4-one derivatives were synthesized as candidate herbicides by diazotization of different 5(3)-amino- N-phenyl-1 H-pyrazole-4-carboxamide derivatives prepared by the reaction of substituted 5(3)-amino-pyrazole-4-carbonyl chloride with a substituted aniline. Their structures were identified by (1)H NMR and elemental analyses. The isomers D and E were ...

A novel two-dimensional NMR pulse sequence, H2BC, for long-range correlation of 1H and 13C nuclei is presented. The experiment has several attractive features compared to the widely used HMBC experiment, for example, (a) typically strong enhancement of correlations over two bonds while suppressing those over more bonds, that is, resolving ambiguities in standard HMBC spectra and showing two-bon...

Four new (1-4), along with six known (5-10) dihydro-β-agarofuran sesquiterpene polyesters were isolated from the whole plants of Parnassia wightiana. The new compounds were structurally elucidated through spectroscopic analysis including UV (Ultraviolet Spectrum), IR (Infrared Spectrum), ¹H-NMR (¹Hydrogen-Nuclear Magnetic Resonance), ¹³C-NMR (¹³Carbon-Nuclear Magnetic Resonance), DEPT (Distorti...

Using aggregation-volume-bias Monte Carlo simulations along with successive umbrella sampling and histogram re-weighting, we study the phase diagram of a system of dumbbells formed by two touching spheres having variable sizes, as well as different interaction properties. The first sphere (h) interacts with all other spheres belonging to different dumbbells with a hard-sphere potential. The sec...