Elzbieta Galezowska

G Quadruplex-Based FRET Probes with the Thrombin-Binding Aptamer (TBA) Sequence Designed for the Efficient Fluorometric Detection of the Potassium Ion

The dual‐labeled oligonucleotide derivative, FAT‐0, carrying 6‐ carboxyfluorescein (FAM) and 6‐carboxytetramethylrhodamine (TAMRA) labels at the 5′ and 3′ termini of the thrombin‐binding aptamer (TBA) sequence 5′‐GGT TGG TGT GGT TGG‐3′, and its derivatives, FAT‐n (n=3, 5, and 7) with a spacer at the 5′‐end of a TBA sequence of TmA (m=2, 4, and 6) have been designed and synthesized. These fluorescent probes were developed for monitoring K+ concentrations in living organisms. Circular dichroism, UV‐visible absorption, and fluorescence studies revealed that all FAT‐n probes could form intramolecular tetraplex structures after binding K+. Fluorescence resonance energy transfer and quenching results are discussed taking into account dye–dye contact interactions. The relationship between the fluorescence behavior of the probes and the spacer length in FAT‐n was studied in detail and is discussed.

Spectral properties and binding study of DNA complexes with a rigid bisintercalator 1,4-bis((N-methylquinolinium-4-yl)vinyl)benzene.

The DNA binding behavior of potentially bisintercalating ligand 1,4-bis((N-methyl quinolinium-4-yl)vinyl)benzene was studied by spectrophotometric titration, circular dichroism and matrix-assisted laser desorption-ionization-time-of-flight (MALDI-TOF) mass spectrometry. The formation of large DNA-ligand aggregates observed at low DNA concentration was ascribed to the interstrand cross-linking due to the bisintercalation and/or electrostatic interactions. On the other hand, a monointercalation was observed at higher DNA concentration and in the presence of higher content of NaCl. Intercalative DNA-ligand complex was featured by red shifted absorption band, modest hypochromicity and the presence of induced CD signal. MALDI-TOF mass spectra of short oligonucleotide-ligand systems revealed the formation of 1:1 complexes of the ligand with duplex and single-stranded oligonucleotides as well as a higher molecular weight species.

Bioactive papaverine derivatives bind G-quadruplexes selectively

G-quadruplexes are a family of DNA secondary structures resulting from the folding of a guanine-rich sequence. Targeting quadruplexes by small molecules is an approach that is currently being studied with the aim of exploring their biological roles and developing new anti-cancer agents. There is evidence that the formation of G4 structures by telomeric DNA can be used to inhibit the enzyme activity of telomerase, and thereby to activate the pathway to senescence in tumour cells. It was previously shown that the papaverine oxidation products 6a,12a-diazadibenzo-[a,g]fluorenylium derivative (ligand I) and 2,3,9,10-tetramethoxy-12-oxo-12H-indolo[2,1-a]isoquinolinium chloride (ligand II) bind to G-quadruplex representing the human telomeric sequence. These ligands possess the ability to inhibit telomerase and polymerase action at the micromolar level. Here we report a DNA binding study on these two ligands and a new derivative 2-(2-carboxy-4,5-dimethoxyphenyl0-6,7-dimethoxyisoquiloliniuminner salt (ligand III) in order to evaluate their binding selectivity to samples of nucleic acids (ssDNA, dsDNA, triplexes, and quadruplexes). Simultaneous investigations on several DNA-ligand complexes carried out using an equilibrium dialysis approach revealed pronounced binding selectivity of ligand I and ligand II to tetraplex DNA structures over the doublestranded DNA forms.

Fluorescence Energy Transfer Study of Interstrand DNA Cross-linking Caused by Rigid Bisintercalator

The intermolecular cross-linking of DNA with a rigid bisintercalator, 1,4-bis(( N -methylquinolinium-4-yl)vinyl)benzene (pMQVB) has been studied using fluorescence resonance energy transfer (FRET), fluorescence anisotropy measurements, and dynamic fluorescence microscopy. Short DNA duplexes, single-labeled with fluorescein (donor) and x-rhodamine (acceptor), were used as energy transfer partners. Due to the quenching effect of pMQVB on the emission of both fluorescein and x-rhodamine, the energy transfer was monitored using the corrected Stern-Volmer plots. The cross-linking ability of pMQVB depended on the ligand structure; the planar E , E isomer cross-linked DNA contrary to the non-planar E , Z isomer. Dynamic fluorescence microscopy observation also demonstrated the ability of pMQVB to cross-link large T4 DNA molecules.

Sensitive determination of nitrite by means of a Landolt-type reaction in fluorescent aggregates of a binaphthyl-based amphiphile

The iodine quenching effect on the fluorescence of a binaphthyl-based amphiphile, C8BNC6N, was used for monitoring the Landolt-type reaction between nitrite, iodide, and thiosulfate. Due to the possibility of iodine detection in the 10−8–10−7M range, and to the effective concentration of anionic reagents on the surface of cationic aggregates, the indicator reaction can be monitored using reagents at concentration levels as low as 10−7M. To optimize the analytical system, the effect of pH and reagent concentrations on the rate of indicator reaction were studied. The influence of the matrix of water samples and effect of side-reactions increasing the value of a blank test were examined. A procedure for nitrite determination in water was developed, using the diazo reaction for selective nitrite removal to provide a reference solution, which avoided possible effects of the matrix components. The usefulness of this method was tested by determining trace amounts of nitrite in water samples. The procedure allows determination of nitrite down to 5 ng/ml (detection limit about 2ng/ml) with r.s.d. of 10% in the 20–250 ng/ml range.