Oleg M. Demchuk

Novel supramolecular organogels based on a hydrazide derivative: non-polar solvent-assisted self-assembly, selective gelation properties, nanostructure, solvent dynamics

In this work, we report the complementary studies of supramolecular organogels composed of a newly synthesized low molecular mass gelator 4-(4-morpholinyl)-3-nitro-benzoylhydrazide (1) with benzene, toluene, and p-xylene. Intermolecular hydrogen bonding and π–π stacking interactions are the main driving forces promoting gelation of the system and the self-assembly of the new gelator molecules. The former interactions were revealed by the FT-IR and Raman studies, whereas the latter ones were postulated on the basis of the molecular structure of the gelator, UV-Vis spectra and comparison with the previously published data for other hydrazide derivatives. The strengths of the hydrogen bonding interactions are comparable as indicated by the FT-IR spectra analysis. Therefore, we correlated the differences in the calculated enthalpies of the gelator aggregates of 1 in the gels studied with the differences in the strengths of the π–π stacking interactions. The gel of 1 with benzene is characterized by the highest value of enthalpy. The images taken by the SEM and POM methods reveal differences in the architecture of gelator 1 aggregates, which are lamellar-like in toluene and fibrillar in benzene and p-xylene. The dispersion of spin–lattice relaxation times of solvents in the gel phase, observed by the NMR relaxometry method at low frequencies, is an indicator of the solvent–gelator interactions. As a result of this interaction, a significant slowing down of the motion (5 orders of magnitude as compared to bulk solvents) of the fraction of solvent molecules at the pore surface in the gel phase takes place. The diffusion of solvents in gels is restricted as shown by PGSE NMR. The apparent diffusion coefficient measured as a function of diffusion time can be used to estimate the pore size of the gel matrix, which for the gel of 1 with toluene is about 22 μm.

Rational design of novel ligands for environmentally benign cross-coupling reactions*

Transition-metal (TM) complexes of new phosphines, readily prepared by a straight-forward three-step modular synthesis, were successfully employed in difficult cross-coupling reactions conducted under mild conditions (water, “open-flask”, low temperature) that aspire to meet green chemistry criteria. High yielding catalyzed by bismuth or rhodium complexes oxidative arylation of naphthoquinone gave the key 2-arylnaphthoquinone intermediates for facile bismuth triflate-catalyzed Michael addition of secondary phosphine oxides. Subsequent O-methylation and reductions of the resulting products gave access to the target air-stable phosphine ligands in good overall yields (up to 60 %).

The utilization of chiral phosphorus ligands in atroposelective cross-coupling reactions

GRAPHICAL ABSTRACT Abstract Atroposelective synthesis of axially chiral biaryls mediated by palladium complexes of chiral phosphorus ligands is discussed. Analysis of the literature data allowed us to compare the activity and selectivity of used phosphorus ligands and, in some cases, connected them with the ligand structure. We also propose some practical remarks concerning a comparison of efficiency of structurally different ligands.

Molecular interactions in high conductive gel electrolytes based on low molecular weight gelator.

Organic ionic gel (OIG) electrolytes, also known as gel electrolytes or ionogels are one example of modern functional materials with the potential to use in wide range of electrochemical applications. The functionality of OIGs arises from the thermally reversible solidification of electrolytes or ionic liquids and their superior ionic conductivity. To understand and to predict the properties of these systems it is important to get the knowledge about the interactions on molecular level between the solid gelator matrix and the electrolyte solution. This paper reports the spectroscopic studies (FT-IR, UV-Vis and Raman) of the gel electrolyte based on low molecular weight gelator methyl-4,6-O-(p-nitrobenzylidene)-α-d-glucopyranoside and solution of quaternary ammonium salt, tetramethylammonium bromide. The solidification process was based on sol-gel technique. Below characteristic temperature, defined as gel to sol phase transition temperature, Tgs, the samples were solid-like and showed high conductivity values of the same order as observed for pure liquid electrolytes. The investigations were performed for a OIGs in a wide range of molar concentrations of the electrolyte solution.

Organophosphorus ligands: Recent developments in design, synthesis, and application in environmentally benign catalysis

GRAPHICAL ABSTRACT ABSTRACT The application of important organophosphorus ligand-based complex catalysts in potentially environmentally benign processes was overviewed. In particular, the focus was put on the phosphoorganic systems of special properties (water-soluble, immobilized in/on fluorous phase as well as solid phase supported transition metal phosphine complexes) used in different types of modern catalytic reactions.

General approach to the synthesis of prochiral atropisomeric biaryls.

General approach to the synthesis of prochiral precursors of chiral atropisomeric biaryls based on several complementary methods has been developed. Biaryls were obtained in good to excellent yields depending on their structure and selected method of synthesis. Furthermore, we demonstrate a possibility of utilisation of the obtained compounds possessing 2 or 3 ortho substituents around the aryl-aryl bond in direct and directed arylation reaction leading through transition metal-mediated C–H bond activation to atropisomeric compounds.

Green in water sonochemical synthesis of tetrazolopyrimidine derivatives by a novel core-shell magnetic nanostructure catalyst

A green approach for the one-pot four-component sonochemical synthesis of 5-methyl-7-aryl-4,7-dihydrotetrazolo[1,5-a]pyrimidine-6-carboxylic esters from the reaction of 2-cyano-guanidine, sodium azide, various aromatic aldehydes and methyl or ethyl acetoacetate in the presence of a catalytic amount of Fe2O3@SiO2-(CH2)3NHC(O)(CH2)2PPh2 as a new hybrid organic-inorganic core-shell nanomagnetic catalyst is described. This is the first design, preparation, characterization and application of the present nanomaterial and also the first ultrasound irradiated synthesis of the biologically and pharmaceutically important heterocyclic compounds in water as a green solvent. This novel sonocatalysis/nanocatalysis protocol offers several advantages such as high yields, short reaction times, environmentally-friendly reaction media, easily isolation of the products, simple preparation, full characterization and recoverability of the nanocatalyst by an external magnet and reusing several times without significant loss of activity.

A clean and simple method for deprotection of phosphines from borane complexes

Abstract Simple, efficient, clean, and stereospecific protocols of protection of phosphorus atom with borane and deprotection from the borane complexes of the tertiary phosphines in mild conditions are reported. The proposed protection/deprotection reactions tolerate a range of functional groups and lead to pure products with excellent yield with no need for application of chromatographic or crystallisation purification procedures. For the first time mechanisms of the reactions of phosphine protection and deprotection have been studied based on experimental kinetic data as well as quantumchemical calculations, which allows designing reaction conditions suitable for a given substrate.

1,4-Naphthoquinone derivatives potently suppress Candida albicans growth, inhibit formation of hyphae and show no toxicity toward zebrafish embryos

Purpose. In this study, we applied various assays to find new activities of 1,4‐naphthoquinone derivatives for potential anti‐Candida albicans applications. Methodology. These assays determined (a) the antimicrobial effect on growth/cell multiplication in fungal cultures, (b) the effect on formation of hyphae and biofilm, (c) the influence on cell membrane integrity, (d) the effect on cell morphology using atomic force microscopy, and (e) toxicity against zebrafish embryos. We have demonstrated the activity of these compounds against different Candida species and clinical isolates of C. albicans. Key findings. 1,4‐Naphthoquinones significantly affected fungal strains at 8‐250 mg l−1 of MIC. Interestingly, at concentrations below MICs, the chemicals showed effectiveness in inhibition of hyphal formation and cell aggregation in Candida. Of note, atomic force microscopy (AFM) analysis revealed an influence of the compounds on cell morphological properties. However, at low concentrations (0.8‐31.2 mg l−1), it did not exert any evident toxic effects on zebrafish embryos. Conclusions. Our research has evidenced the effectiveness of 1,4‐naphthoquinones as potential anti‐Candida agents.

A Quantum-Chemical DFT Approach to Elucidation of the Chirality Transfer Mechanism of the Enantioselective Suzuki–Miyaura Cross-Coupling Reaction

The DFT calculations of the simplified model of the asymmetric Suzuki–Miyaura coupling reaction were performed at the M062x/LANL2DZ theory level at first. It was found that enantioselective reactions mediated by the palladium complexes of chiral C,P-ligands follow a four-stage mechanism similar to that proposed previously as one of the most credible mechanisms. It should be underlined that the presence of substituents in the substrates and the chiral ligand at ortho positions determines the energies of possible diastereoisomeric transition states and intermediates in initial reaction steps. This suggests that, in practice, a sharp selection of theoretically possible paths of chirality transfer from the catalyst to the product should have a place and, therefore, the absolute configuration of the formed atropisomeric product is defined and can be predicted.