Alexander S. Fisyuk

Efficient sensitization of lanthanide luminescence by tetrazole-based polydentate ligands

Tetrazolate groups have been included by a convenient synthetic route in diverse ligand topologies, which have allowed the incorporation of lanthanide ions into highly luminescent double- and triple-helical complexes, demonstrating their potential for the expansion of lanthanide chemistry and the development of lanthanide-based applications.

Mixed alkylthiophene-based heterocyclic polymers containing oxadiazole units via electrochemical polymerisation: spectroscopic, electrochemical and spectroelectrochemical properties

Symmetric alkylthiophene-based mixed heterocyclic trimer and pentamer, containing central oxadiazole units, have been prepared. Because of the electron-withdrawing properties of oxadiazole, the trimer cannot be electropolymerised and undergoes an oxidative-type destruction at high potentials. In contrast, the pentamer readily polymerises, giving a short chain polymer. Both trimer and pentamer exhibit strong photoluminescence with a maximum at 399 nm (13% quantum yield) and 467 nm (46% quantum yield), respectively. The polymer resulting from the electropolymerisation of the pentamer is also luminescent with the maximum of the excitation band at 528 nm (33% quantum yield). The polymer can be oxidatively doped as demonstrated by cyclic voltammetry, showing a clear anodic peak at 0.62 V versus Ag/Ag+ and its cathodic counterpart at 0.56 V, associated with the undoping process. The significantly higher potential of the oxidative doping of the prepared mixed heterocyclic polymer, as compared to the poly(alkylthiophene) homopolymer of similar molecular weight, is caused by the presence of the oxadiazole unit, which lowers the electron density in the π-electron system of the oligothiophene subunit and makes its oxidation more difficult. The spectroelectrochemical investigation of the polymer is consistent with its voltammetric behaviour, exhibiting doping-induced bleaching of the band originating from the π-π* transition and simultaneous growth of the bipolaron bands. The observed clear and reversible spectroelectrochemical behaviour makes the developed polymer a promising candidate for applications in electrochromic devices or electrochemical sensors.

Synthesis of 5,6-Dihydropyridin-2(1H)-ones, 1,5,6,8,8a-Hexahydroisoquinolin-3(2H)-ones and 4a,5,6,7,8,8a-Hexahydroquinolin-2(1H)-ones by Intramolecular Wittig Reaction

A new, universal and diastereospecific method has been developed for the synthesis of 5,6-dihydropyridin-2(1H)-ones, 1,5,6,8,8a-hexahydroisoquinolin-3(2H)-ones and 4a,5,6,7,8,8a-hexahydroquinolin-2(1H)-ones (4) based on the intramolecular Wittig cyclization of the triphenyphosphonium salts 2 derived from the N-(3-oxoalkyl)–chloroacetamides 1.

Synthesis of new, highly luminescent bis(2,2’-bithiophen-5-yl) substituted 1,3,4-oxadiazole, 1,3,4-thiadiazole and 1,2,4-triazole

Summary A new synthetic approach towards the preparation of functionalised, soluble, donor–acceptor (DA) alkylbithiophene derivatives of oxadiazole, thiadiazole and triazole is reported. Taking advantage of the Fiesselmann reaction, reactive bithiophene synthons having alkyl or alkoxy substituents at designated positions are prepared. Following a synthetic strategy, featuring the bottom-up approach, sequential structural elements are built, starting from a simple thiophene compound, until the target molecule is obtained, all in good yield. Supplementing the well established methods of oxadiazole and thiadiazole synthesis, efficient ring closure reaction affording a 4H-1,2,4-triazole unit is presented. All target ambipolar compounds display strong photoluminescence with measured quantum yields up to 0.59. Modification of the demonstrated synthetic routes may be exploited for the preparation of longer, specifically functionalised oligothiophenes, coupled to other heteroaromatic cores.

Star-shaped conjugated molecules with oxa- or thiadiazole bithiophene side arms.

Star-shaped conjugated molecules, consisting of a benzene central unit symmetrically trisubstituted with either oxa- or thiadiazole bithiophene groups, were synthesized as promising molecules and building blocks for application in (opto)electronics and electrochromic devices. Their optical (Eg (opt)) as well as electrochemical (Eg (electro)) band gaps depended on the type of the side arm and the number of solubilizing alkyl substituents. Oxadiazole derivatives showed Eg (opt) slightly below 3 eV and by 0.2 eV larger than those determined for thiadiazole-based compounds. The presence of alkyl substituents in the arms additionally lowered the band gap. The obtained compounds were efficient electroluminophores in guest/host-type light-emitting diodes. They also showed a strong tendency to self-organize in monolayers deposited on graphite, as evidenced by scanning tunneling microscopy. The structural studies by X-ray scattering revealed the formation of supramolecular columnar stacks in which the molecules were organized. Differences in macroscopic alignment in the specimen indicated variations in the self-assembly mechanism between the molecules. The compounds as trifunctional monomers were electrochemically polymerized to yield the corresponding polymer network. As shown by UV/Vis-NIR spectroelectrochemical studies, these networks exhibited reversible electrochromic behavior both in the oxidation and in the reduction modes.

Sulfur-containing compounds quench 3,7-dihydro-2-methyl-6-(4-methoxyphenyl)imidazol[1,2-a]pyrazine-3-one chemiluminescence: Discrimination between true antioxidants and quenchers using xanthine oxidase.

The probe 3,7-dihydro-2-methyl-6-(4-methoxyphenyl)imidazol[1,2-a]pyrazine-3-one (MCLA) is widely used for studying the superoxide anion production and the efficiency of antioxidants in biological systems. Here we report that a number of sulfur-containing compounds applied in biochemical and cytological studies are able to suppress MCLA-derived chemiluminescence (MDCL) independent of their capability to scavenge superoxide anion. The most effective MDCL quenchers appeared to be the substances with thiocarbamoyl and thiocarbonyl groups coupled to cyclic molecules and several thiol- and disulfide-containing compounds. The analysis of MDCL kinetics in a xanthine oxidase system allows one to rapidly discriminate between true antioxidants and the quenchers of chemiluminescence.

Unusually high stability of a poly(alkylquaterthiophene-alt-oxadiazole) conjugated copolymer in its n and p-doped states

Incorporation of electron accepting units (oxadiazole) into the 2,5-thienylene conjugated chain leads to a significant improvement in the n-doping-undoping redox stability of the resulting polymer.

Synthesis and antiradical activity of 4-aryl(hetaryl)-substituted 3-aminopyridin-2(1Н)-ones

The reaction of aryl(hetaryl)-substituted 1,3-diketones with chloroacetamide gave the respective N-(3-oxoalkenyl)chloroacetamides, which were converted to 3-pyridinium-substituted pyridin-2(1Н)-ones upon heating with excess of pyridine in n-butanol. The decomposition of pyridinium salts with hydrazine hydrate resulted in new 4-aryl(hetaryl)-substituted 3-aminopyridin-2(1Н)-ones, which showed strong antiradical activity with respect to ABTS and DPPH radicals.

Cyclization of N-(3-Oxoalkyl)chloroacetamides Under Basic Conditions. Synthesis of cis-3,4-Epoxypiperidin-2-ones

It has been shown that N-(3-oxoalkyl)chloroacetamides (1) can be converted into cis-3,4-epoxypiridin-2-ones (2) upon treatment with t-BuOK in a t-BuOH-C6H6 solution due to a resulting intramolecular Darzens reaction. It has been found that under kinetically controlled reaction conditions (NaOH/C6H6), besides the intramolecular Darzens reaction an intramolecular alkylation takes place.

Ice Recrystallization in a Solution of a Cryoprotector and Its Inhibition by a Protein: Synchrotron X-Ray Diffraction Study.

Ice formation and recrystallization is a key phenomenon in freezing and freeze-drying of pharmaceuticals and biopharmaceuticals. In this investigation, high-resolution synchrotron X-ray diffraction is used to quantify the extent of disorder of ice crystals in binary aqueous solutions of a cryoprotectant (sorbitol) and a protein, bovine serum albumin. Ice crystals in more dilute (10 wt%) solutions have lower level of microstrain and larger crystal domain size than these in more concentrated (40 wt%) solutions. Warming the sorbitol-water mixtures from 100 to 228 K resulted in partial ice melting, with simultaneous reduction in the microstrain and increase in crystallite size, that is, recrystallization. In contrast to sorbitol solutions, ice crystals in the BSA solutions preserved both the microstrain and smaller crystallite size on partial melting, demonstrating that BSA inhibits ice recrystallization. The results are consistent with BSA partitioning into quasi-liquid layer on ice crystals but not with a direct protein-ice interaction and protein sorption on ice surface. The study shows for the first time that a common (i.e., not-antifreeze) protein can have a major impact on ice recrystallization and also presents synchrotron X-ray diffraction as a unique tool for quantification of crystallinity and disorder in frozen aqueous systems.