Magnetic Resonance in Chemistry

(−)-Gallocatechin gallate (GCg) formed a 1:1 inclusion complex with γ-cyclodextrin (γ-CD), in which the A and C rings of GCg were inserted deep at the head of the A ring into the γ-CD cavity from the wide secondary hydroxyl group side, the B and B' rings were left outside the cavity.

Theoretical energy-based conformational analysis of bis(2-phenethyl)vinylphosphine and related phosphine oxide, sulfide and selenide synthesized from available secondary phosphine chalcogenides and vinyl sulfoxides is performed at the MP2/6-311G** level to study stereochemical behavior of their ³¹P–¹H spin–spin coupling constants measured experimentally and calculated at different levels of theory. All four title compounds are shown to exist in the equilibrium mixture of two conformers: major planar s-cis and minor orthogonal ones while ³¹P–¹H spin-spin coupling constants under study are found to demonstrate marked stereochemical dependences with respect to the geometry of the coupling pathways and to the internal rotation of the vinyl group around the P(X)-C bonds (X = LP, O, S and Se) opening a new guide in the conformational studies of unsaturated phosphines and phosphine chalcogenides.

The application of a 2D broadband homodecoupled proton NMR experiment is presented to the visualisation of enantiomers. We show that this approach, which relies on a spatial encoding of the NMR sample, is particularly well-suited to the analysis of enantiomeric mixtures, since it allows, within one single 2D experiment, to detect subtle chemical shift differences between enantiomers, even in the presence of several couplings.

The gelation mechanism of 1% (w/w) iota-carrageenan with increasing Na⁺ ion content is investigated. Rheological and ²³Na T₁ relaxation time measurements reveal that the gel formation is correlated with decreases in ion mobility. ²³Na single-quantum (SQ) and double-quantum-filtered (DQF) NMR experiments provide evidence for a ‘bound’ sodium ion fraction in a specifically ordered environment. From these results, a three-stage model for the carrageenan gelation mechanism in the presence of Na⁺ ions is proposed.

Complete assignment of the ¹H and ¹⁹F chemical shifts in 4-fluoro-AF4 (1) were based on the nOes seen in the ¹⁹F-¹H HOESY spectrum. This allowed for identification of features which were further applied to the assignment of the regiochemistry of di-substituted AF4s 2–4.

A new method for the automatic phase correction of multidimensional NMR spectra is described. It is based on the whitening concept formulated as the 'maximization of the number of white pixels into a bitmap that corresponds to the spectrum'. The algorithm can efficiently phase either homonuclear or heteronuclear experiments and, unlike other previous methods, it can also process automatically spectra containing positive or negative peaks so that it is not necessary to deal with individual or special cases.

The Glu-237 → Gln mutant of Leuconostoc mesenteroides sucrose phosphorylase catalyses glucosyltransfer from α-D-glucosyl-1-phosphate to formate and acetate resulting in α-D-glucosyl-1-formate and α-D-glucosyl-1-acetate, which serve as starting materials to study acyl group migration, mutarotation, and hydrolysis. 1D and 2D in situ¹H NMR is used to identify, characterize, and quantify temporary accumulated acyl D-glucoses from the reaction mixture. Time courses of transformations give insight into pH dependence of acyl group migration.

The reliable determination of stereocenters contained within chemical structures usually requires utilization of NMR data, chemical derivatization, molecular modeling, quantum-mechanical calculations and, if available, X-ray analysis. In this article we show that the number of stereoisomers which need to be thoroughly verified can be significantly reduced using NMR chemical shift calculations for the full stereoisomer set of possibilities using a fragmental approach based on HOSE codes. The applicability of this suggested method is illustrated using a series of complex chemical structures.

⁷⁹Br NMR spectroscopy has been used to monitor a series of reactions in which the bromide ion is produced. Both the utility of the process in following reactions which may be difficult to analyse using other techniques and the practical limitations associated with solvent choice are discussed.

2-Bromocyclohexanone exhibits a ⁴J_H2–H6 long-range coupling, which provides experimental evidence that orbital interactions involving the carbonyl group contribute for its conformation isomerism.

The ING2 PHD finger is recruited to the nucleosome through specific binding to histone H3 trimethylated at lysine 4 (H3K4me3). Here, we describe backbone and side chain assignments of the ING2 PHD finger, analyze its binding to the unmodified and modified histone and p53 peptides, and map the histone H3 and H3K4me3 binding sites based on chemical shift perturbation analysis.

Two new steroids isolated from EtOH extracts of the South China Sea soft coral Chromonephthea sp. were identified. One-dimensional (1D) and two-dimensional (2D) NMR experiments including COSY, HSQC, HMBC and NOESY were used for the determination of their structure.

Anthraquinone derivatives are secondary metabolites that have been isolated from plants, fungi, lichens, and corals. A number of studies reported that anthraquiones inhibited the growth and proliferation of various cancer cells. In a continued study of marine fungi, three new anthraquinone derivatives: Fusaquinon A (1), B (2), and C (3) were isolated from the fungus Fusarium sp. (No. ZH-210). HREIMS, FT-IR, NMR experiments including gCOSY, gHMQC, gHMBC, and NOE were used for the determination of the structures and NMR spectral assignments.

An unprecedented new natural product named nocarsin A, 5H-4a,6,7a-triazacyclopenta[cd]indene-5,7(6H)-dione, together with seven known nitrogen containing compounds, was isolated from the Nocardia alba sp. nov (YIM 30243^T). Structure elucidation of these compounds was achieved by the use of one- and two-dimensional NMR methods. We report the unambiguous assignments of the ¹H and ¹³C NMR spectra of the new compound nocarsin A.