Current Organic Chemistry - Volume 5, Issue 3, 2001

The structural elucidation of complex organic molecules relies heavily on the application of proton detected heteronuclear NMR. Among these techniques, the HMBC NMR experiment is probably the most useful 2D NMR method The HMBC (C-H) experiment allows the assignment of structural fragments through correlations between protons and carbons separated by more than one bond, usually two or three bonds ( Read More

The siderophores produced by the so-called fluorescent members of the bacterial genus Pseudomonas called pyoverdins are chromopeptides with complex structures. Their peptidic part - linear or partially cyclic - comprises unusual and partially modified amino acids. So far about fifty different pyoverdines have been encountered. A fast establishing at least of their gross structure is of importance for the identification of strains i Read More

Proton transfer processes play a key role in many reactions of organic compounds and in many biochemical mechanisms. In particular, proton transfer in hydrogen bond complexes in solutions has attracted considerable attention. NMR spectroscopy is known to be a powerful tool in studying hydrogen bond and the proton transfer equilibrium. This review focuses on one specific application of this method, based isotope effect Read More

Saponins and triterpenoid glycosides are polar constituents of plants many of which exhibit a broad spectrum of biological activities. They often occur as intricate mixtures difficult to separate by conventional procedures. Improvements in liquid chromatographic techniques and availability of new matrices have improved the possibility of purifying even the isomeric saponins. The application of newer isolation and purification p Read More

In the last two decades sensitive physico-chemical methods enabling analyses of natural products mixtures (secondary metabolites and biopolymers) have been developed. Hyphenation of chromatograhic techniques with different types of mass spectrometers is one of the most effective analytical methods for identification and structural studies of compounds demonstrating different physico-chemical properties Read More

In complex organic molecules, macromolecules and biological samples, 1 H NMR spectra can be very complex and assignments of resonances can be difficult. Thus NMR pulse sequence methods to edit and simplify spectra have been introduced. During the last few years, there have been a number of reports on the use of heteronuclear multiple-quantum filtration to simplify 1 H NMR spectra. The method is known as inverse- Read More

The regularities of the solvent effect manifested in the absorption spectra of certain types of Schiff bases were investigated. In solvents capable of hydrogen-bonding, this solvent effect is observed for those Schiff bases in which there is an OH group in an ortho or para position on the aldehyde ring, and the electron density of the azomethine nitrogen is appropriately high. Studies in solvent mixtures demonstrated that the pheno Read More