Furan derivatives of group I elements (review)

Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsikiicheskikh Soedinenii, No. 4, pp. 435–473, April, 1995. Original article submitted February 22, 1995.     

Peculiarities of the chemical properties of vicinally disubstituted veratrole and synthesis of 1-methyl-4,5-dimethoxybenzimidazole derivatives

Various paths for the synthesis of 4-methylamino-3-aminoveratrole (I) from 4-amino-3-nitroveratrole (II) were investigated, and it was found that I can be obtained in a high overall yield of 65% through the tosyl derivative of II. 1-Methyl-4,5-dimethoxybenzimidazolone, 1-methyl-4,5-dimethoxybenzimidazole and its 2-phenyl-, 2-chloro-, and 2-dimethylamino derivatives were synthesized on the basis of I in order to investigate their biological activity. It was established that the chemical properties of vicinally disubstituted veratrole, particularly the increased basicity of II, are determined to a significant degree by steric strains caused by bulky substituents. It is shown that 85% formic acid can be successfully used in place of 98–100% formic acid for the N-formylation of aromatic amines with a mixture of formic acid and acetic anhydride.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1387–1392, October, 1970.     

Ammonolysis of aziridinecarboxylic acid esters

The ammonolysis of 1-(2-methoxycarbonylvinyl)- and 1-(1,2-dimethoxycarbonylvinyl)-2-methoxycarbonylaziridines at normal pressure leads to 1-(2-methoxycarbonylvinyl)-and 1-(1,2-dicarbamoylvinyl)-2-carbamoylaziridines, respectively, whereas 1,3-diazabicyclo[3.1.0]hexan-4-one derivatives are formed under pressure.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 350–352, March, 1983.     

1, 2-Dithiolium salts

4-(p-Tolyl)-1,2-dithiolium hydrogen sulfate (I) is not a specific analytical reagent for the majority of anions, and it is not very selective, only in a few cases attaining pD=5 (MoO₄ ^2–, [Hg(CNS)₄]^2–, and [PtCl₆]^2–). All strongly colored anions give colored salts with I. Among the weakly colored anions, the [Fe(CN)₆]^4– anion is worthy of special note, since it forms a deeply colored salt with I. This anion can be detected with I in the presence of Cl^–, Br^–, I^–, CNS^–, ClO₄ ^–, IO₄ ^–, and ReO₄ ^–, which form fairly readily soluble salts with I. Compound I is also a fairly selective reagent for Pd²⁺ in acid solution (pD=5).For part II, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 5, pp. 595–597, May, 1970.     

Spectroscopic studies of ionic solvation. XVIII. Solvation of the lithium ion in acetone and acetone-nitromethane mixtures

Solvation of the lithium ion by acetone was studied in acetone-nitromethane solutions by Raman, infrared, and⁷Li and³⁵Cl NMR spectroscopic techniques. It was confirmed that the 390-cm^?1 IR acetone band is split by the lithium ion and that a 369-cm^?1 IR band, attributed by other authors to Li⁺-nitromethane vibration, is due to the vibration of acetone in the lithium inner solvation shell. The frequency of the Li⁺-nitromethane vibrational band is strongly anion dependent due to contact-ion-pair formation. Several different techniques indicate that Li⁺ is solvated by four acetone molecules, and approximate equilibrium-constant values for the stepwise solvation reaction were calculated. The influence of weak complexing agents on Li⁺ ClO ₄ ^? ion-pair formation was investigated.     

Peculiarities of dislocation generation by block boundaries in alkali halide crystals during ultrasonic vibrations

The generation of dislocations by block boundaries in alkali-halide crystals under the action of ultrasound was investigated making use of a computer defet modeling method. Ultrasonic vibrations were excited in a double piezoelectric oscillator at the frequencies 60 and 73 kHz. Specimens of KCl and KBr with =0° and =30°, where is the angle between the fourfold axis and the propagation direction of the ultrasound, were investigated. The change in the dislocation structure was determined from the volt-ampere characteristics. It was established that the dislocation sources located near the block boundaries started to operate at stress values one third of those at which other sources operated. Modeling showed that the existence of boundaries had a significant effect on the operation of small-size sources. The experimental estimate of the reduction of the critical stress exceeds the theoretical one.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 52–55, March, 1984.     

Griffith energy criterion of fracture for an edge crack

The paper considers a problem in the mechanics of brittle fracture, viz., determination of the elastic energy of a surface crack in a specimen under tension with a constant stress _G. An expression for the threshold crack-initiating stress _G is obtained on the basis of the Griffith energy criterion of fracture. The equality of the Griffith stress _G and the safe stress ₀, which emerges from the balance of the elastic energy of the chemical bonds at the crack tip and the surface energy of the fracture surface, serves as the starting point for a proposed relation for determining the size of a surface submicrocrack in the specimen. It is shown that the results obtained can be applied to quasibrittle fracture.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 55–61, December, 1978.     

Single-molecule nanopore sensing of actin dynamics and drug binding

Actin is a key protein in the dynamic processes within the eukaryotic cell. To date, methods exploring the molecular state of actin are limited to insights gained from structural approaches, providing a snapshot of protein folding, or methods that require chemical modifications compromising actin monomer thermostability. Nanopore sensing permits label-free investigation of native proteins and is ideally suited to study proteins such as actin that require specialised buffers and cofactors. Using nanopores, we determined the state of actin at the macromolecular level (filamentous or globular) and in its monomeric form bound to inhibitors. We revealed urea-dependent and voltage-dependent transitional states and observed the unfolding process within which sub-populations of transient actin oligomers are visible. We detected, in real-time, filament-growth, and drug-binding at the single-molecule level demonstrating the promise of nanopore sensing for in-depth understanding of protein folding landscapes and for drug discovery.

Nanopipettes were used for real-time investigation into actin dynamics and drug binding at single-molecule resolution, showing promise for a better understanding of the mechanism of protein–protein interactions and drug discovery.     

A self-assembled multivalent pseudopolyrotaxane for binding galectin-1

A self-assembled pseudopolyrotaxane consisting of lactoside-displaying cyclodextrin (CD) "beads" threaded onto a linear polyviologen "string" was investigated for its ability to inhibit galectin-1-mediated T-cell agglutination. The CDs of the pseudopolyrotaxane are able to spin around the axis of the polymer chain as well as to move back and forth along its backbone to alter the presentation of its ligand. This supramolecular superstructure incorporates all the advantages of polymeric structures, such as the ability to span large distances, along with a distinctively dynamic presentation of its lactoside ligands to afford a neoglycoconjugate that can adjust to the relative stereochemistries of the lectin's binding sites. The pseudopolyrotaxane exhibited a valency-corrected 10-fold enhancement over native lactose in the agglutination assay, which was greater than the enhancements observed for lactoside-bearing trivalent glycoclusters and a lactoside-bearing chitosan polymer tested using the same assay. The experimental results indicate that supramolecular architectures, such as the pseudopolyrotaxane, provide tools for investigating protein-carbohydrate interactions.