Complex Substitution Patterns Research Articles

Carrageenans with complex substitution patterns from red algae of the genus Erythroclonium

Extracellular polysaccharides from three Erythroclonium spp. were shown, by a combination of compositional, linkage analyses, and Fourier transform infrared and 13C-nuclear magnetic resonance spectroscopy, to be highly substituted carrageenans with at least five types of repeating disaccharide units. These are the carrabiose 2,4′-disulfate of ι-carrageenan, carrabiose 2-sulfate of α-carrageenan, the 6′- O-methylated counterparts of each of these repeating units, and 4′,6′- O-(1-carboxyethylidene)carrabiose 2-sulfate. The polysaccharides also contain significant amounts of unsubstituted, 4-linked galactopyranose and small amounts of 4-linked 3- O-methylgalactopyranose and terminal glycosyl residues. The carrageenan preparations of the three species are similar, differing only in the proportions of some components.

Two‐dimensional nuclear magnetic resonance of resins

AbstractA group of resins was synthesised from a series of phenols and aldehydes, and their structures comprehensively deduced from two‐dimensional nuclear magnetic resonance spectroscopy (2‐D NMR). Correlation spectroscopy, in particular carbon‐proton heteronuclear chemical shift correlation spectroscopy, was shown to be especially incisive in assigning structural features to the NMR signals.The method has permitted fuller structural characterisation of these materials than was heretofore possible, and has identified, inter alia, methylene and methyleneoxy bridges unequivocally: complex substitution patterns in the phenol‐derived aromatic rings have also been elucidated.It is demonstrably possible to apply the same techniques to similar complex resin structures, and to utilise these structural insights to determine the mechanistic processes involved in their syntheses.

Interactions between drugs and nucleic acids. Part 1. Dichroic studies of doxorubicin, daunorubicin, and their basic chromophore, quinizarin

The interpretation of the electronic spectra of complexes between DNA and antitumour drugs must rely on the knowledge of the directions of the transition moments of the drug chromophore. This paper reports the linear and circular dichroism studies (including magnetic c.d.) and semiempirical INDO/S calculations carried out in order to provide evidence for the directions of the transition dipole moments within the quinizarin chromophore present in the antitumour drugs daunorubicin and doxorubicin. The c.d. technique also demonstrated that these two drugs, in spite of the complex substitution pattern of the anthraquinone moiety, have the same sequence of u.v.–visible electronic transitions as the unsubstituted quinizarin. The partial orientation of the investigated molecules required to run their linear dichroism spectra was achieved by using liquid crystalline solvents (both thermotropic and aqueous lyotropic) according the modulated liquid-crystal–linear dichroism technique.

The structure of hydroxyethyl starch.

1. It is suggested that the structure currently used to describe hydroxyethyl starch (a blood plasma volume expander) is a gross oversimplification.2. A model having a much more complex substitution-pattern is proposed, and an accurate, rapid test has been devised for distinguishing between the two models.3. This test shows that the simple model has no basis in reality, and that the more complex substitution pattern is correct.4. Studies involving the enzymic hydrolysis of hydroxyethyl starch are shown to provide qualitative support for the new model, and the significance of the findings is discussed.