Kh. A. Abduazimov

Complexation of Caffeic and Ferulic Acids by Transition-Metal Ions

Potentiometric titration and IR and UV spectroscopies are used to study complexation of caffeic and ferulic acids by metal ions. Caffeic and ferulic acids, which occur in lignin, are shown to react with metal ions mainly through an ionic mechanism. However, coordination bonding is also possible depending on the nature of the ligand and metal ion and the ratio of starting components. The strongest complex forms between caffeic acid and CuCl2(2:1 ratio)

Lignins of herbaceous plants

Literature information on the formation, chemical composition, and structural features of lignins of herbaceous plants for 1980–1992 is generalized and analyzed.

Sulfomethylation of lignins

Water-soluble derivatives have been obtained by the sulfomethylation of technical lignins. Their semiempirical formulas have been calculated and the introduction of a sulfomethyl group into the lignin macromolecule is discussed on the basis of these formulas.

Interaction of lignosulfonate with certain metal ions

The reaction of lignosulfonate with the Co2+, Ni2+, and Cu2+ ions has been studied by the methods of gel chromatography, potentiometric titration, and UV spectroscopy. Lignosulfonate forms polymer-metal complexes with the metal ions over a wide pH range. In this process the size of the macromolecule scarcely changes, thanks to the reticular structure of the lignosulfonate. The capacity of lignin with respect to Cu2+ ions has been determined.

Nitration of Lignin and Sorptive Properties of the Resulting Products

The possible use of lignin as an inexpensive and nontoxic sorbent make it necessary to study its sorptive properties. The medicinal preparation Polyphepanum is well known and has a high sorptive capacity for bacterial cells and the toxins released by them [1]. Modification is recognized as the main direction for resolving problems with the use of lignin. Lignin preparations obtained under different conditions are not identical. Thus, nitration, oxidation, demethoxylation, and destruction of lignin molecules are noted upon treatment with nitric acid [2]. Naturally, they occur differently under different conditions. We studied the effect of nitration conditions on the sorptivity of nitrolignins. The nitrating agent was a 50% blend (45% HNO 3, 3.8% H2SO4). Table 1 shows results obtained using hydrolyzed lignin (HL) from cotton-seed husks and various lignin(g):blend(l) ratios. It was found that the solubility of lignin samples o f a single size (0.25 mm) vary from 10 to 66%. Furthermore, the solubility of samples of different sizes (0.5, 0.25, 0.08 mm) th at were treated with the blend under identical conditions are similar to those of samples in Expt. No. 4. Similar results were obtained for the N content. Elemental analyses for N content of the insoluble part showed varying degree of nitration (from 0.83 to 2.08%) of lignin samples of a single size depending on the nitration conditions. For samples of different sizes treated under identical conditi ons, the degree of nitration was practically the same. Therefore, the degree of nitration and the solubility of lignin samples seem s to depend on the nitration conditions and not the particle size. Molecular weights (determined by ultracentrifugation) of the soluble part of the lignin samples prepared under different nitration conditions were similar in magnitude. It can be assumed that destruction processes occurring during nitration were approximately the same.

lignins of Allochruza paniculata and Glycyrrhiza glabra

The natural lignin of Allochruza paniculata and Glycyrrhiza glabra is studied by catalytic hydrogenolysis. Three types of lignin structural units are present: guaiacyl, syringyl, and p-coumaryl, which are characteristic of annual and perennial herbaceous plants. The structure of DLA from these plants is confirmed by UV, IR and PMR spectra.

Complexation in the Nitrolignin-Pectin-Copper Ion System

Potentiometric titration, spectrophotometry, and viscosimetry were used to study complexation of nitrolignin macromolecules, pectin, and their mixture with copper ions. The salt mechanism of formation of intramolecular polymer-metal complexes was established. Stability constants and extinction coefficients of the complexes were measured.

A study of the polysaccharides, hydrolysates, and sulfuric-acid lignin of cottonplant stems

A comparative investigation of the acid hydrolysis of the guza-paya [stems and bolls] and seed husks of the cotton plant has shown that the hydrolysates differ in their quantitative levels of monosaccharides, but in the pentose hydrolysates xylose predominates in both cases. The extracts after the preliminary enrichment of the raw material contain a large amount of xylose. The sulfuric-acid lignin obtained from the guza-paya contains a far smaller amount of unhydrolyzed polysaccharide and a larger amount of functional groups than the lignin from the husks.

Nitrobenzene oxidation of fractions of cotton-plant dioxane lignin

SummaryAnalysis of the products of alkaline nitrobenzene oxidation of lignin fractions has confirmed their chemical inhomogeneity and has shown that in the various fractions the amounts of condensed syringly and guaiacyl structures differed markedly.

Interaction of nitrolignin with metal ions

Lignin is a high-tonnage waste of the hydrolysis industry. All investigations of lignin and its derivatives are therefore connected with the necessity of solving the ecological problem of the practical use of these wastes. The most effective use of lignin requires an all-sided study of its reactivity with various reagents. We have studied the interaction of nitrolignin (NL) with metal ions (Me 2+) Co 2+ , Zn 2+, Mn 2+. The interaction between nitrolignin macromolecules and metal ions is accompanied by a shift in the ac id -base equilibrium in the system. This can well be seen from potentiometric titration curves (Fig. 1A) at various NL:Me 2+ ratios. The NL--Me 2+ titration curves are located below the nitrolignin titration curve. This indicates that the reaction between the NL macromolecule and metal ions proceeds by an electrostatic mechanism with the liberation of protons. As is known, nitrolignin is obtained from hydrolysis lignin with the aid of a mixture of concentrated H2SO 4 and concentrated HNO 3 [1], and, therefore, not only nitration but also oxidation processes may occur. In actual fact the carboxy group content increases from 0.12 in hydrolysis lignin to 0.4 per phenylpropane unit in nltrolignin. In view of this, the interaction of NL with metal ions can be represented in the form: