Magnetic Resonance in Chemistry

NMR metabolic profiling associated with ANOVA and LDA statistical methods was used to probe the origin of durum wheat. A linear statistical model was build to discriminate among three different locations achieving a success prediction level up to 80%.

The temperature dependent correlation times of ¹¹B were derived from the ¹¹B T₁ minimum of the Arrhenius plots for an anion BF₄ in room-temperature ionic liquids composed of a quaternary ammonium cation (DEME) and a lithium salt doped system.

The use of a small volume 1-mm probe along with the adapted titration protocol allows economizing up to 90% the consumption of the ligand amounts required for intermolecular interaction studies. This enables interaction studies and K_D determination that would otherwise be prohibitively expensive or require more material than available from complex synthesis routes or natural sources.

The ACCORDEPT experiment afforded significant enhancements for the resonances with the larger ¹J_CH couplings, similar SNR for aliphatic resonances, and slightly reduced SNR for aliphatic resonances as compared with the standard DEPT experiment. The ACCORDEPT is straightforward to implement, does not require any supplementary calibration procedures and can be used under automated conditions.

Analysis of the ¹HNMR spectra of some monosubstituted cyclobutanes combined with the prediction of the conformer ⁴J_HH couplings allows the determination of the conformer energies.

Azalomycin F_4a 2-ethylpentyl ester (1) and Azalomycin F_5a 2-ethylpentyl ester (2), together with Azalomycins F_3a, F_4a and F_5a, were identified from metabolites of Streptomyces sp. 211726 isolated from mangrove rhizosphere soil. The complete ¹H and ¹³C assignments of these compounds were achieved by using ¹H, ¹³C, DEPT, HSQC, ¹H¹H COSY and HMBC spectra, and some errors in the ¹H and ¹³C assignments published of Azalomycins F_3a, F_4a and F_5a were revised.

A theoretical treatment of the 2D exchange NQR pulse sequence is presented and successfully tested for the exchange spectra of hindered trichloromethyl groups of p-chlorobenzotrichloride, where the conventional approach without taking into account the off-resonance phenomena has failed. The mixing dynamics by exchange and the expected diagonal- and cross-peak intensities as a function of the mixing time have been derived. It is shown that the off-resonance effects are of crucial importance for the quantitative description of the NQR exchange spectra.

Chalcones, intermediates in flavonoid biosyntheses, can exhibit antibacterial, antiproliferative, and anti-inflammatory properties. Assignments of NMR peaks in the spectra of hydroxylated and/or methoxylated chalcones can help in identifying novel chalcone derivatives isolated from natural sources by referencing these data against NMR spectra obtained from known chalcones. We report here the syntheses of 20 chalcones and complete assignments of ¹H and ¹³C NMR spectra.

Two new steroids, named 4α,22-dimethyl-Cholest-22-en-3β-ol (1) and 4α-methyl-Cholest-7,22 -dien-3β-ol (2) were isolated from the soft coral Sinularia brassica. Their structures were determined on the basis of extensive NMR and mass data analysis.