Irek R. Nizameev

Novel bolaamphiphilic pyrimidinophane as building block for design of nanosized supramolecular systems with concentration-dependent structural behavior.

A new macrocyclic bolaamphiphile with thiocytosine fragments in the molecule (B1) has been synthesized and advanced as perspective platform for the design of soft supramolecular systems. Strong concentration-dependent structural behavior is observed in the water-DMF (20% vol) solution of B1 as revealed by methods of tensiometry, conductometry, dynamic light scattering, and atomic force microscopy. Two breakpoints are observed in the surface tension isotherms. The first one, around 0.002 M, is identified as a critical micelle concentration (cmc), whereas the second critical concentration of 0.01 M is a turning point between the two models of the association involved. Large aggregates of ca. 200 nm are mostly formed beyond the cmc, whereas small micelle-like aggregates exist above 0.01 M. The growth of aggregates between these critical points occurs, resulting in a gel-like behavior. An unusual decrease in the solution pH with concentration takes place, which is assumed to originate from the steric hindrance around the B1 head groups. Because of controllable structural behavior, B1 is assumed to be a candidate for the development of biomimetic catalysts, nanocontainers, drug and gene carriers, etc.

A facile synthetic route to convert Tb(III) complexes of novel tetra-1,3-diketone calix[4]resorcinarene into hydrophilic luminescent colloids

The work presents the synthesis of a novel calix[4]resorcinarene cavitand bearing four 1,3-diketone groups at the upper rim and its complex formation with Tb(III) ions in DMF and DMSO solutions. Electrospray ionization mass spectra, 1H NMR, UV-Vis and luminescence spectra indicate a long (three hours at least) equilibration time for the complex formation between the cavitand and Tb(III) in alkaline DMF and DMSO solutions. These results are explained by the restricted keto–enol conversion, resulting from the steric hindrance effect of the methylenedioxy-groups linking the benzene rings within the cavitand framework. A facile synthetic route to convert luminescent Tb(III) complexes of various stoichiometries into luminescent hydrophilic colloids is disclosed in this work. The route is based on the reprecipitation of the Tb(III) complexes from DMF to aqueous solutions with further polyelectrolyte deposition without prior separation of the luminescent complexes. The luminescent colloids exhibit high stability over time and in buffer systems, which is a prerequisite for their applicability in analysis and biolabeling.

Mediated electrochemical synthesis of Pd0 nanoparticles in solution

Efficient electrosynthesis of palladium(0) nanoparticles is carried out in solution by mediated electrochemical reduction of a complex dianion [PdCl4]2– in the DMSO/0.1 M Bu4NCl medium. The mediator function was performed by methylviologen and tetraviologen calix[4]resorcines MVCA-Cn8+ with methyl (n = 1), n-pentyl (n = 5), and n-decyl (n = 10) substituents in resorcinol rings at the potentials of redox pairs MV2+/MV•+, MVCA-Cn8+/MVCA-Cn4•+. The resulting metal nanoparticles gradually aggregate to yield coarser particles. The smallest size (255 nm) have metal particles obtained in the presence of MVCA-C58+ for the rest mediators, metal particles of the micron size are formed. Sonication results in disintegration of aggregates to nanoparticles.

Structural, biocomplexation and gene delivery properties of hydroxyethylated gemini surfactants with varied spacer length.

Gemini surfactants with hexadecyl tails and hydroxyethylated head groups bridged with tetramethylene (G4), hexamethylene (G6) and dodecamethylene (G12) spacers were shown to self-assemble at the lower critical micelle concentration compared to their conventional m-s-m analogs. The lipoplex formation and the plasmid DNA transfer into different kinds of host cells were studied. In the case of eukaryotic cells, high transfection efficacy has been demonstrated for DNA-gemini complexes, which increased as follows: G6<G4<G12. Different activity series, i.e., G6>G4>G12 has been obtained in the case of transformation of bacterial cells with plasmid DNA-gemini complexes, mediated by electroporation technique. Solely G6 shows transformation efficacy exceeding the control result (uncomplexed DNA), while the inhibitory effect occurs for G4 and G12. Analysis of physico-chemical features of single surfactants and lipoplexes shows that compaction and condensation effects change as follows: G6<G4 ≤ G12, i.e., agree with the order of transfection efficacy, which is supported by membrane tropic properties of G12. On the other hand, gel retardation assay and docking study testify low electrostatic affinity in G12/DNA pair, thereby indicating that hydrophobic effect probably plays important role in the lipoplex formation. Two factors are assumed to be responsible for the inhibition effect of gemini in the case of transformation of bacterial cells. They are (i) an unfavorable influence of cationic surfactants on the electroporation procedure due to depressing the electrophoretic effect; and (ii) antibacterial activity of cationic surfactants that may cause the disruption of integrity of cell membranes.

Electrochemical mediated synthesis of silver nanoparticles in solution

Methyl viologen MV2+ and tetraviologen calix[4]resorcinol MVCA-C58+ with n-pentyl substituents in the resorcinol rings at potentials of MV2+/MV•+ and MVCA-C58+ /MVCA-C54•+ redox couples proved to be effective mediators of the electrochemical reduction of Ag+ ions in DMF/0.1 M Bu4NPF6. The potentiostatic nondiaphragm electrolysis at controlled mediator reduction potentials at room temperature using an Ag anode as an in situ supplier of Ag+ led to the formation of metallic silver nanoparticles in solution. The only resulting effect of electrolysis was the quantitative transfer of the metal anode into the metal nanoparticles in solution. In the case of MV2+, the nanoparticles aggregated into larger particles. MVCA-CC58+ serves not only as a mediator, but also, to some extent, as a stabilizer of silver nanoparticles and can be recorded by a set of experimental methods.

High performance magneto-fluorescent nanoparticles assembled from terbium and gadolinium 1,3-diketones

Polyelectrolyte-coated nanoparticles consisting of terbium and gadolinium complexes with calix[4]arene tetra-diketone ligand were first synthesized. The antenna effect of the ligand on Tb(III) green luminescence and the presence of water molecules in the coordination sphere of Gd(III) bring strong luminescent and magnetic performance to the core-shell nanoparticles. The size and the core-shell morphology of the colloids were studied using transmission electron microscopy and dynamic light scattering. The correlation between photophysical and magnetic properties of the nanoparticles and their core composition was highlighted. The core composition was optimized for the longitudinal relaxivity to be greater than that of the commercial magnetic resonance imaging (MRI) contrast agents together with high level of Tb(III)-centered luminescence. The tuning of both magnetic and luminescent output of nanoparticles is obtained via the simple variation of lanthanide chelates concentrations in the initial synthetic solution. The exposure of the pheochromocytoma 12 (PC 12) tumor cells and periphery human blood lymphocytes to nanoparticles results in negligible effect on cell viability, decreased platelet aggregation and bright coloring, indicating the nanoparticles as promising candidates for dual magneto-fluorescent bioimaging.

Luminescent silica nanoparticles for sensing acetylcholinesterase-catalyzed hydrolysis of acetylcholine

This work highlights the H-function of Tb(III)-doped silica nanoparticles in aqueous solutions of acetic acid as a route to sense acetylcholinesterase-catalyzed hydrolysis of acetylcholine (ACh). The H-function results from H(+)-induced quenching of Tb(III)-centered luminescence due to protonation of Tb(III) complexes located close to silica/water interface. The H-function can be turned on/switched off by the concentration of complexes within core or nanoparticle shell zones, by the silica surface decoration and adsorption of both organic and inorganic cations on silica surface. Results indicate the optimal synthetic procedure for making nanoparticles capable of sensing acetic acid produced by enzymatic hydrolysis of acetylcholine. The H-function of nanoparticles was determined at various concentrations of ACh and AChE. The measurements show experimental conditions for fitting the H-function to Michaelis-Menten kinetics. Results confirm that reliable fluorescent monitoring AChE-catalyzed hydrolysis of ACh is possible through the H-function properties of Tb(III)-doped silica nanoparticles.

Electrochemical synthesis of nanocomposite of palladium nanoparticles with polymer viologen-containing nanocapsule

An efficient mediated electrosynthesis of the spherical (85 nm) nanocomposite material Pd@p(MVCA8+-co-St) was carried out in an aqueous medium. Ultrasmall palladium nanoparticles (3—8 nm) are stabilized in nanocapsules of water-soluble nanoparticles of the copolymer p(MVCA8+-co-St) consisting of tetraviologen calix[4]resorcinol (MVCA8+) with styrene (St). The role of the mediator is played by viologen units of a polymer nanoparticle at potentials of the MV2+/MV∙+ redox couple. The high catalytic activity of the nanocomposite material in the reduction of nitrophenol with sodium borohydride is shown.

Oxygen reduction reaction catalyzed by nickel complexes based on thiophosphorylated calix[4]resorcinols and immobilized in the membrane electrode assembly of fuel cells

The catalytic activity of the nickel complexes of thiophosphorylated calix[4]resorcinols for oxygen reduction in a polymer electrolyte membrane fuel cell (PEMFC) has been studied. The conformation of the macrocyclic ligand determines the morphology and catalytic properties of the resulting organometallic species.

Nickel Complexes Based on Thiophosphorylated Calix[4]Resorcinols as Effective Catalysts for Hydrogen Evolution

Nickel complexes of thiophosphorylated calix[4]resorcinols showed high catalytic activity for hydrogen evolution from acidic solutions and stability in the electro-assisted catalysis at the surface of both glassy carbon and Hg-pool electrodes. The conformation of the macrocyclic ligand determines the dimensionality and shape of the catalytically active species generated on the electrode.