Supramolecular catalytic systems based on 1, 4-diazabicyclo[2.2.2]octane,its alkylated quaternary derivatives,and lanthanum nitrate

Spectrophotometry was used to study the catalytic effects of the systems composed of N-monoand N, N-dialkylated 1, 4-diazabicyclo[2.2.2]octanes and lanthanum nitrate on the hydrolysis rate of O-alkyl O-4-nitrophenyl chloromethylphosphonates (Alk = Et, Buⁿ, and n-hexyl). The mechanism of action and efficiency of the catalytic system depend on the structure of the heterocycle, its propensity to aggregation and complexation with the lanthanum cation, and the relative content of the components in solution. The maximum catalytic effect (a ～115-fold increase in the hydrolysis rate constant) was achieved in micellar solutions of the cationic monoalkylated derivative of 1, 4-diazabicyclo[2.2.2]octane and lanthanum nitrate.

     

Polysaccharides of algae 67. Carrageenan from Pacific red alga Turnerella mertensiana (Gigartinales,Rhodophyta)

A sulfated galactan composed of nearly equimolar amounts of d-galactose, 3,6-anhydro-d-galactose, and sulfate was isolated from the red alga Turnerella mertensiana collected in the Sea of Japan. The structures of native polysaccharide and its alkaline modification products were studied by NMR spectroscopy. The polysaccharide molecules were shown to contain a linear carbohydrate chain consisting of alternating 3-linked β-d-galactopyranose 4-sulfate and 4-linked 3,6-anhydro-α-d-galactopyranose residues (known as к-carrageenan), which is typical of carrageenans, but the regularity of polymer structure is masked by the presence of some 3,6-anhydro-α-d-galactose 2-sulfate (ι-carrageenan units) and α-D-galactose 6-sulfate (µ-carrageenan units) instead of 3,6-anhydro-α-d-galactose. Upon addition of potassium chloride (up to 4%) to a solution of the native polysaccharide, about half of the substance transforms into gel. The gel-forming fraction is к-ι-µ-hybrid carrageenan with the ～65 : 15 : 20 ratio of к-, ι-, and µ-units. The non-gelling fraction contains the к-, ι-, and µ-units at the ratio of ～46 : 12 : 42. The gel-forming carrageenan product free of µ-units can be otained in ～30% yield (based on the dry biomass) by alkaline treatment of the alga prior to extraction of the polysaccharide.

     

Design of phosphonate analogs of short peptides by “click” chemistry

Methods were developed for the first time for the modification of the natural neuropeptides Ile–Gly–Leu and Leu–Gly–Leu simultaneously with the phosphonate moiety and the triazole ring or solely with the triazole ring by means of click chemistry. All of the peptidomimetics synthesized were isolated as a mixture of diastereomers and were characterized by spectroscopic methods.

     

Enthalpies of the Diels–Alder reactions of a series of dienes with tetracyanoethylene and 4-phenyl-1,2,4-triazoline-3,5-dione

Russian Chemical Bulletin - The enthalpies of the Diels–Alder reactions of twenty dienes with two active dienophiles, tetracyanoethylene and 4-phenyl-1,2,4-triazoline-3,5-dione, are compared,...     

The characteristics of the hydrotropic Miscanthus pulp

Russian Chemical Bulletin - The characteristics of the Miscanthus pulp obtained by hydrotropic processing under different conditions were studied. The pulping conditions were optimized to achieve...     

Diphenyl[(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadienylidene)-methyl]phosphonate in reactions with o-phenylenediamine

Russian Journal of General Chemistry -     

Coordination properties of trimeric porphyrin in acetic acid

Trimeric porphyrin H₆TP as well as its binuclear Cu₂H₂TP and trinuclear Cu₃TP copper complexes have been prepared. Kinetic features of H₆TP and Cu₂H₂TP complexes formation with copper(II) acetate in acetic acid as well as dissociation kinetics of Cu₂H₂TP and Cu₃TP in acetic acid medium in the presence of sulfuric acid have been studied.