I. Timtcheva

Homodimeric monomethine cyanine dyes as fluorescent probes of biopolymers

The fluorescence properties of newly synthesized homodimeric monomethine cyanine dyes in the presence of biopolymers are investigated. They do not fluoresce in TE buffer and bidistilled water but become strongly fluorescent (Q(F)=0.3-0.9) in the region 530-650 nm when bound to dsDNA and ssDNA. The detection limit of dsDNA is about 1.7 ng/ml. Some of dyes studied are able to distinguish between dsDNA and ssDNA, RNA, BSA in solution and gel electrophoresis. The influence of different factors (temperature, pH and viscosity of the medium, presence of histone) on the formation of the dye-biopolymer complexes is investigated. The results of steady-state and dynamic fluorescence measurements concerning the different types of binding between dyes and biopolymers show that the new dyes are applicable in molecular biology as highly sensitive fluorescence labels.

New asymmetric monomethine cyanine dyes for nucleic-acid labelling: absorption and fluorescence spectral characteristics

Abstract Absorption spectra and fluorescence properties of a series of newly synthesized asymmetric monomethine cyanine dyes are studied. The dyes carry one or two positive charges. They are devoid of their own fluorescence in solution and become fluorescent upon binding to nucleic acids only. The fluorescence maxima of the new dyes are localized between 530 and 650xa0nm. The wavelength and intensity of fluorescence are dependent on molecular structure of the dye, type of nucleic acid and the concentration of both nucleic acid and salts. Some of the dyes are capable of distinguishing between single-stranded and double-stranded (ds) polynucleotides giving fluorescence maxima localized at different wavelengths. Detection threshold for dsDNA for most of the dyes is comparable to that of ethidium bromide. The sensitivity of the dye-dsDNA complexes to NaCl concentrations show that the new dyes interact with dsDNA by both intercalation and electrostatically.

Synthesis of homodimeric monomethine cyanine dyes as noncovalent nucleic acid labels and their absorption and fluorescence spectral characteristics

Abstract Several novel homodimeric asymmetric monomethine cyanine dyes based on the thiazole orange (TO) chromophore were synthesised via an improved synthetic procedure. The two TO chromophores [1-(ω-bromoalkyl)-4-[(3-methyl-2-(3H)-benzothiazolilyden)methyl] quinolinium iodide], with different chain lengths of the methylene linker between the quinolinium ring and the quaternary ammonium nitrogen, were connected by bisquaternization with N,N,N′,N′-tetramethyl-1,3-propanediamine, N,N,N′,N′-tetramethyl-1,6-hexanediamine, 1,4-diazabicyclo- [2,2,2]octane and 1,4′-bipyridine. The homodimeric dyes have large molar absorptivity (e 130xa0000–180xa0000 l mol−1 cm−1) at 505–506 nm. In the presence of ds DNA, their fluorescence maxima were located at 530–534 nm and the fluorescence quantum yields were in the range 0.48–0.96. Fluorescence maxima between 560–650 nm and fluorescence quantum yields of 0.3–0.8 were observed in the presence of ss DNA.

Fluorescence Characteristics of Variously Charged Asymmetric Monomethine Cyanine Dyes in the Presence of Nucleic Acids

Three asymmetric monomethine cyanine dyes bearing one, two, and three positive charges have been synthesized, and their absorption and fluorescence characteristics in the presence of nucleic acids were studied. The maxima of their longest wavelength absorption band lie between 500 and 520 nm. The dyes do not show fluorescence of their own in TE buffer (pH = 7.5), but become strongly fluorescent (QF = 0.2–0.6) on binding to double-stranded DNA. The fluorescence maxima of the investigated dye-dsDNA complexes are in the region of 530–550 nm. The influence of the dye/DNA ratio on both the position and intensity of the fluorescence maxima of the complexes is investigated.

Photophysical properties of some derivatives of 3-arylmethylene-1(3H)-isobenzofuranone : Indication of intermolecular hydrogen-bond formation in the singlet excited state

Abstract The fluorescence behavior of some derivatives of 3-phenylmethylene-1(3H)-isobenzofuranone and 5-amino-3-phenylmethylene-1(3H)-isobenzofuranone in different media at room temperature and in frozen matrix at 77xa0K are reported. It is found, that in the cases of the amino substituted compounds at 293xa0K the dependencies of the fluorescence Franck–Condon transition energy and the fluorescence quantum yield on the ET(30) constant of the solvent, as well as the fluorescence decay curves, are strongly influenced by the proton donating ability of the solvent. These experimental results indicate formation of intermolecular hydrogen bonded solute–solvent complexes in the fluorescent excited state at room temperature in protic solvents. The effect of the substituents in the p-position of the phenyl ring in the investigated isobenzofuranones on the deactivation processes of their singlet excited state is discussed.

Unsymmetrical azines of 4-acetyl-3-methyl-1-phenyl-5-pyrazolone. Spectral characteristics and structure

Abstract The spectral characteristics of some unsymmetrical azines derived from 4-acetyl-3-methyl-1-phenyl-5-pyrazolone have been studied. The compounds exhibit a weak fluorescence (QF

Radiationless deactivation of 5-amino-2-arylindan-1,3-diones via intermolecular hydrogen bonds

Abstract Steady-state and dynamic photophysical characteristics of a number of 4- and 5-amino-2-phenylindan-1,3-dione derivatives have been studied at 293 and 77 K in solvents of widely different polatiry and hydrogen-bonding ability. The observed changes of the fluorescence Franck-Condon transition energy, and of the fluorescence quantum yields and the singlet lifetimes, as well as the solvent deuterium-isotope effect, indicate the formation of intermolecular hydrogen bonds in the excited state with protic solvents for the 5-amino compounds at room temperature.

Deactivation processes of the excited states of 3-hetarylmethylene-1(3H)-isobenzofuranones in solution: possibility of the formation of intermolecular hydrogen bonds

Abstract The absorption and fluorescence characteristics of some heterocyclic analogues of benzylidene phthalides in solvents of different polarity and hydrogen bonding ability are reported. It is shown that the replacement of the phenyl ring of benzylidene phthalides by heteroaromatic five-membered cycle does not have a remarkable influence on the photophysical properties. The observed dependence of the fluorescence Franck—Condon transition energies and the fluorescence quantum yields of the compounds with the amino substituted in the phthaloyl fragment on the ET(30) constants of the solvents indicates that the nature of the emitting state in protic and non-protic solvents is different, probably owing to the formation of intermolecular hydrogen bonds in the excited state between the substance and the protic solvent.

Effect of the medium acidity on the photophysical characteristics of some 2-aryl- and 2-hetaryl-benzothiazoles

Abstract The absorption and fluorescence spectral characteristics of 2-aryl- and 2-hetaryl-benzothiazoles and their protonated forms in solution were studied. The influence of structural modifications on the position of their absorption and fluorescence maxima, as well as interesting features with respect to competition in protonation between the benzothiazole and aniline or hetaryl nitrogen atom in the ground ( S 0 ) state has been studied. The influence of pH on the absorption and the emission spectra of all the compounds has been investigated in order to identify the ground state species present as a function of acidity.

Absorption and fluorescence characteristics of some 2-aryl- and 2-hetaryl-benzothiazoles

Abstract The absorption and fluorescence characteristics of some 2-aryl- and 2-hetarylbenzothiazoles were studied with respect to the nature of the substituents and the polarity of the solvents. The longest wavelength absorption maximum of these compounds is in the region 27000–34000 cm −1 . The PPP-SCF-CI quantum chemical calculations show that they result from a singlet π-π * transition. The fluorescence Franck-Condon transition is between 19000 and 28000cm −1 . The fluorescence quantum yield of most of the investigated benzothiazoles exceeds 0.5. The compounds do not phosphoresce in frozen ethanol solutions at 77 K.