Aleksey Vasilev

Novel Green Procedure for the Synthesis of 2-Arylbenzothiazoles Under Microwave Irradiation in Peg 200 Or Peg 400

An improved green procedure for the synthesis of 2-aryl- and 2-hetarylbenzothiazoles by condensation of equivalent amounts of 2,2′-diaminodiphenyldisulfides or 2-aminothiophenols and various aromatic aldehydes in PEG 200/400 under microwave irradiation has been developed. This method allows the synthesis of 2-arylbenzothiazoles in high yields and with high purity regardless of the state of the starting compounds (liquid or solid) or the nature of the substituents in the aromatic ring.

Probing the Structural Properties of DNA/RNA Grooves with Sterically Restricted Phosphonium Dyes: Screening of Dye Cytotoxicity and Uptake

To explore in greater detail the recently reported rare kinetic differentiation between homo‐polymeric and alternating AT‐DNA sequences by using sterically restricted phosphonium dyes that form dimers within the DNA minor groove, new analogues were prepared in which the quinolone phosphonium moiety was kept constant, while the size and hydrogen bonding properties of the rest of the molecule were varied. Structure–activity relationship studies revealed that a slight increase in length by an additional methylene unit results in loss of kinetic AT selectivity, but yielded an AT‐selective fluorescence response. These DNA/RNA‐groove‐bound dyes combine very low cytotoxicity with efficient cellular uptake and intriguingly specific fluorescent marking of mitochondria. In contrast to longer analogues, a decrease in length (by methylene unit removal) and rearrangement of positive charge resulted in dyes that had switched to the intercalative binding mode to GC DNA/dsRNA but that still form dimers in the minor groove of AT sequences, consequently yielding a significantly different chiro‐optical response. The latter dyes also revealed strongly selective antiproliferative activity toward HeLa cancer cells.

Kinetic differentiation between homo- and alternating AT-DNA by sterically restricted phosphonium dyes

By sterically controlled monomer-dimer equilibrium novel dyes kinetically differentiate between homo-AT and alternating AT-AT polynucleotides and finely probe width and sterical occupation of DNA minor groove by induced CD signals.

New fluorogenic dyes for analysis of cellular processes by flow cytometry and confocal microscopy.

Fluorescent microscopy and fluorescent imaging by flow cytometry are two of the fastest growing areas in the medical and biological research. Innovations in fluorescent chemistry and synthesis of new dye probes are closely related to the development of service equipment such as light sources, and detection techniques. Among compounds known as fluorescent labels, the cyanine-based dyes have become widely used since they have high excitation coefficients, narrow emission bands and high fluorescence upon binding to nucleic acids. The key methods for evaluation of apoptosis and cell cycle allow measuring DNA content by several flow cytometric techniques. We have synthesized new monomethine cyanine dyes and have characterized their applicability for staining of live and/or apoptotic cells. Imaging experiments by flow cytometry and confocal laser scanning microscopy (CLSM) have been also performed. Two of the dyes have shown high-affinity binding to the nuclei at high dilutions, up to 10(-9)M. Flow cytometry and CLSM have confirmed that these dyes labeled selectively non-living, e.g. ethanol-fixed cells that makes them appropriate for estimations of cell viability and apoptosis. The novel structures proved to be appropriate also for analysis of the cell cycle.

Fluorescence Study of Lipid Bilayer Interactions of Eu(III) Coordination Complexes

The interaction between Eu(III) tris-β-diketonato coordination complexes (EC), displaying antitumor activity, and lipid vesicles composed of zwitterionic lipid phosphatidylcholine has been studied using fluorescence spectroscopy techniques. To characterize EC-membrane binding, several fluorescent probes, including pyrene, Prodan and 1,6-diphenyl-1,3,5-hexatriene, have been employed. It has been found that EC display effective partitioning into lipid phase, giving rise to structural modifications of both polar and nonpolar lipid bilayer regions, viz. enhancement of membrane hydration and increase in tightness of lipid chain packing. The fact that EC accumulating in lipid bilayer are incapable of inducing significant disruption of membrane structural integrity creates strong prerequisites for development of liposomal nanocarriers of these potential antitumor drugs. Such a possibility is also corroborated by the observation that EC membrane incorporation does not prevent lipid bilayer partitioning of long-wavelength squaraine dyes which represent promising candidates for visualization of liposome biodistribution.

A Novel Squarylium Dye for Monitoring Oxidative Processes in Lipid Membranes

A novel squaraine probe SQ-1 has been found to be appropriate for monitoring the peroxidation processes in membrane systems. Formation of free radicals was triggered by methemoglobin (metHb) or cytochrome c (cyt c) binding to the model lipid membranes composed of zwitterionic lipid phosphatidylcholine (PC) and anionic lipid cardiolipin (CL). Protein association with the lipid vesicles was followed by drastic quenching of SQ-1 fluorescence. The observed spectral changes were suppressed in the presence of free radical scavengers, butylated hydroxytoluene (BHT) and thiourea (TM) suggesting that SQ-1 decolorization can be attributed to its reactions with lipid radicals.

Assembly of New Merocyanine Chromophores with a 1,8-Naphthalimide Core by a New Method for the Synthesis of the Methine Function

A new method for the synthesis of the monomethine group using nitro as a leaving group in an SN-Ar reaction is described. A series of novel merocyanine dyes has been synthesised and their photophysical properties have been elucidated. The longest wavelength absorption occurs in the range 519–619 nm and the molar absorptivities vary with the substituents and are in the range 1000–47700 L mol–1 cm–1. The dyes show high chemical and photostability. One example from the series has the ability to distinguish methanol from ethanol. The introduction of a quinoid fragment into the structure leads to a pronounced intramolecular charge transfer and hence a noticeable positive solvatochromism. The structures and electronic properties of the compounds have been studied by density functional theory (DFT) and time-dependent DFT.

Fluorescence study of the membrane effects of aggregated lysozyme.

The last decade has seen unprecedented upsurge of interest in the structural and toxic properties of particular type of protein aggregates, amyloid fibrils, associated with a number of pathological states. In the present study fluorescence spectroscopy technique has been employed to gain further insight into the membrane-related mechanisms of amyloid toxicity. To this end, erythrocyte model system composed of liposomes and hemoglobin was subjected to the action of oligomeric and fibrillar lysozyme. Acrylamide quenching of lysozyme fluorescence showed that solvent accessibility of Trp62 and Trp108 increases upon the protein fibrillization. Resonance energy transfer measurements suggested the possibility of direct complexation between hemoglobin and aggregated lysozyme. Using the novel squaraine dye SQ-1 it was demonstrated that aggregated lysozyme is capable of inhibiting lipid peroxidation processes. Fluorescent probes pyrene, Prodan and diphenylhexatriene were employed to characterize the membrane-modifying properties of hemoglobin and lysozyme. Both oligomeric and fibrillar forms of lysozyme were found to exert condensing influence on lipid bilayer structure, with the membrane effects of fibrils being less amenable to modulation by hemoglobin.

Cyanine dyes as fluorescent non-covalent labels for nucleic acid research

Publisher Summary The applications of cyanine dyes as nucleic acid probes in the field of biotechnology are numerous and continuously expanding. Among the most numerous applications of cyanine dyes is the visuazation of DNA by following different biological processes and quantification of DNA in solution. YOYO-1-labeled complexes may be employed as qualitative DNA markers in intracellular delivery studies. With the combination of a green-fluorescent SYTO 9 dye and red-fluorescent hexidium iodide, it is possible to perform a fluorescent assay for gram reaction. When mixed populations of live gram-negative and gram-positive bacteria are simultaneously stained with the membrane permeable SYTO 9 dye in combination with hexidium iodide, the gram-negative bacteria fluoresce green and the gram-positive bacteria fluoresce red-orange. Dead bacteria do not exhibit predictable staining patterns. Generally, all intercalating cyanine dyes are suitable for polymerase chain reaction (PCR) if they are added after the completion of the reaction, thus giving a fluorescence signal. The best methods for quantitative PCR are commonly known as realtime PCR because one can monitor the product accumulation during the reaction, rather than merely assaying it at the end. The most used dye for real-time PCR is SYBR Green I (SG).

Halogen-containing thiazole orange analogues – new fluorogenic DNA stains

Novel asymmetric monomeric monomethine cyanine dyes 5a–d, which are analogues of the commercial dsDNA fluorescence binder thiazole orange (TO), have been synthesized. The synthesis was achieved by using a simple, efficient and environmetally benign synthetic procedure to obtain these cationic dyes in good to excellent yields. Interactions of the new derivatives of TO with dsDNA have been investigated by absorption and fluorescence spectroscopy. The longest wavelength absorption bands in the UV–vis spectra of the target compounds are in the range of 509–519 nm and these are characterized by high molar absorptivities (63000–91480 L·mol−1·cm−1). All investigated dyes from the series are either not fluorescent or their fluorescence is quite low, but they become strongly fluorescent after binding to dsDNA. The influence of the substituents attached to the chromophores was investigated by combination of spectroscopic (UV–vis and fluorescence spectroscopy) and theoretical (DFT and TDDFT calculations) methods.