The Time-Resolved Fluorescence Stokes Shift of Cucurbit[6]Uril Complexes with a Pyridinium Styryl Dye.

The time-resolved Stokes shift of fluorescence of styryl dye, trans-4-[4-(dimethylamino)-styryl]-1-methylpyridinium iodide (DASPI), and its host-guest complexes with cucurbit[6]uril (CB[6]) was studied by up-conversion technique on a 5 ps time scale. In all cases, the solvation time correlation function - that describes relaxation of the fluorescent state - contains two components. The time constant of the first component, which is related to the vibrational relaxation of the dye cation, increases from 118 fs without CB[6] to 224 fs in the presence CB[6]. It suggests the production of CB[6] complexes to disturb the hydrogen-bond net in the vicinity of DASPI cation. The time constant of the second component, which is associated with solvation, changes from 0.81 ps without CB[6] to 1.15 ps in the presence of the cavitand. The observed increase can be related to the displacement of the dye cation deeper into CB[6] that allows considering DASPI-CB[6] complexes as a light-controlled molecular machine with a response time on the picosecond scale.

Analysis of binding centers in nicotinic receptors with the aid of synthetic peptides.

We studies the receptor-binding specificity of the synthetic peptide HAP (High Affinity Peptide) and its analogues, which are regarded as a model of the orthosteric site nicotinic acetylcholine receptors (nAChR). Using radioligand analysis, electrophysiology tests, and calcium imaging, we assessed the ability of HAP to interact with nAChR antagonists: long α-neurotoxins and α-conotoxins. A high affinity of HAP for α-bungarotoxin and the absence of its interaction with α-cobratoxin and α-conotoxins was found. The synthesized analogues of HAP in general retained the properties of the original peptide. Thus, HAP cannot be a model of a ligand-binding site.

[Comparative analysis of natural and synthetic antimutagens as regulators of gene expression in human cells under exposure to ionizing radiation].

This paper studies the effect of plant peptides of thionine Ns-W2 extracted from seeds of fennel flower (Nigella sativa) and ß-purothionine from wheat germs (Triticum kiharae), as well as a synthetic antimutagen (crown-compound), on the expression of several genes involved in the.control of cellular homeostasis, processes of carcinogenesis, and radiation response in human rhabdomyosarcoma cells (RD cells), T-lymphoblastoid cell line Jurkat, and blood cells. All of these agents acted as antimutagens-anticarcinogens, reducing the expression of genes involved in carcinogenesis (genes of families MMP, TIMP, and IAP and G-protein genes) in a tumor cell. A pronounced reduction in the mRNA level of these genes was caused by thionine Ns-W2, and the least effect was demonstrated by ß-purothionine. Antimutagens had very little effect on the mRNA levels of the several studied genes in normal blood cells.

[Synthesis of spyropyran derivatives of retinal and study of their interaction with bacterioopsin from Halobacterium salinarum].

The synthesis of retinal analogue series that contain a spyropyran moiety instead of a trimethylcyclohexene ring was proposed. The process of the retinal analogue interaction with bacterioopsin from apomembranes of Halobacterium salinarum and the spectral properties of the newly formed pigments were studied. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2008, vol. 34, no. 2; see also http://www.maik.ru.

Multimode anharmonic third-order harmonic generation in a photonic-crystal fiber.

While the third harmonic of a monochromatic pump field with a frequency omega0 is generated exactly at the frequency 3omega0, frequency tripling of broadband ultrashort pump pulses in extended nonlinear media tends to generate isolated spectral peaks substantially shifted from 3omega0. We demonstrate this phenomenon by studying nonlinear spectral transformations of femtosecond Cr:forsterite laser pulses in multimode photonic-crystal fibers. Third-harmonic generation is shown to map adjacent guided modes of the third harmonic onto a manifold of spectral peaks within a 150-THz range around 3omega0. The spectral shifts and the widths of these peaks are controlled by the phase and group-velocity mismatch between the pump field and third-harmonic modes, as well as the length of nonlinear-optical interaction and broadening of the pump spectrum, allowing the spectral content of the third-harmonic signal to be engineered by tailoring the fiber dispersion.

Cross-phase-modulation-induced instability in photonic-crystal fibers.

Cross-phase-modulation-induced instability is identified as a significant mechanism for efficient parametric four-wave-mixing frequency conversion in photonic-crystal fibers. Fundamental-wavelength femtosecond pulses of a Cr, forsterite laser are used in our experiments to transform the spectrum of copropagating second-harmonic pulses of the same laser in a photonic-crystal fiber. Efficient generation of sidebands shifted by more than 80 THz with respect to the central frequency of the second harmonic is observed in the output spectrum of the probe field.

Cross-correlation frequency-resolved optical gating coherent anti-Stokes Raman scattering with frequency-converting photonic-crystal fibers.

Photonic-crystal fibers provide a high efficiency of frequency upconversion of regeneratively amplified femtosecond pulses of a Cr: forsterite laser, permitting the generation of subpicosecond anti-Stokes pulses with a smooth temporal envelope and a linear positive chirp, ideally suited for femtosecond coherent nonlinear spectroscopy. These pulses from a photonic-crystal fiber were cross correlated in our experiments with the femtosecond second-harmonic output of the Cr: forsterite laser in toluene solution, used as a test object, in boxcars geometry to measure the spectra of coherent anti-Stokes Raman scattering (CARS) of toluene molecules (XFROG CARS).

Phase-matched four-wave mixing of sub-100-TW/ cm2 femtosecond laser pulses in isolated air-guided modes of a hollow photonic-crystal fiber.

Hollow-core photonic-crystal fibers are shown to allow propagation and nonlinear-optical frequency conversion of high-intensity ultrashort laser pulses in the regime of isolated guided modes confined in the hollow gas-filled fiber core. With a specially designed dispersion of such modes, the 3omega=2omega+2omega-omega four-wave mixing of fundamental (omega) and second-harmonic (2omega) sub-100- TW/ cm(2) femtosecond pulses of a Cr:forsterite laser can be phase matched in a hollow photonic-crystal fiber within a spectral band of more than 10 nm, resulting in the efficient generation of femtosecond pulses in a well-resolved higher-order air-guided mode of 417-nm radiation.

Monolayers of a novel ionoselective butadienyl dye.

The novel amphiphilic benzodithia-18-crown-6 butadienyl dye (1) forms relatively stable insoluble monolayers on distilled water (collapse pressure of 41 mN/m) and on aqueous subphases containing alkali metal or heavy metal salts (collapse pressures in the range of 27-38 mN/m, respectively). The dye 1 monolayer organization depends on chromophore association and interactions (especially complex formation) with heavy and alkali metal ions as deduced from surface pressure-area and surface potential-area isotherms as well as reflection spectra and Brewster angle microscopy observations. Dye 1 undergoes specific interactions with Hg(2+) and Ag(+), respectively (formation of different complexes). Nonspecific interactions have been observed with other salts, such as KClO(4) or Pb(ClO(4))(2). Further, dye 1 monolayers on 1 mM Hg(ClO(4))(2) solution undergo reversible photoisomerization, in contrast to monolayers on water and other aqueous salt subphases.

[Synthesis of amphiphilic photochromic benzo-15(18)-crown-5(6)-ethers and their properties in monolayers]. / Sintez amfifil'nykh fotokhromnykh benzo-15(18)-kraun-5(6)-éfirov i ikh issledovaniie v monosloiakh.

New amphiphilic photochromic benzo-15(18)-crown-5(6) ethers (APC) differing in the position of the octadecyl substituent and the size of the crown cavity were synthesized. The compounds form stable monolayers in the air/water and air/alkaline metal salt solution interfaces. The results of the pressure isotherm measurements, atomic force microscopy (AFM), and electronic spectroscopy show that the structure of the monolayers formed depends on the structure of the parent APC and the nature of the cation in salt solutions. The area per molecule of APC in the monolayer (specific area) is the smallest on the water surface and increases by 20-40% on the aqueous subphase surface with an increasing concentration of salts therein to indicate the formation of APC complexes with the metal cations. When the hydrophobic aliphatic substituent is displaced from position 3 to position 5 of the benzothiazole ring, the specific area on the surface of water and subphases decreases twofold, which indicates the compactization of the monolayer on this modification. A reversible E-Z-photoisomerization of APC was found in the monolayers formed in the salt solution/air interface. The features of the reaction are defined by the specific organization of the amphiphilic molecules in the monolayer and by the nature of the cation.

Coherent anti-Stokes Raman scattering microspectroscopy of silicon components with a photonic-crystal fiber frequency shifter.

Coherent anti-Stokes Raman scattering (CARS) microspectroscopy of silicon components is demonstrated with pump and probe fields delivered by a mode-locked Cr:forsterite laser and the frequency-shifted soliton output of a photonic-crystal fiber as a Stokes field. CARS microspectroscopy is shown to allow a visualization of microscale features and defects on the surface of silicon wafers, offering much promise for online diagnostics of electronic and photonic silicon chip components.

Antimutagenic characteristics of new diazacrown compounds with N-carboxyalkyl substitutes.

Two new benzodiaza-15-crown-5 compounds containing two N-hydroxycarbonylmethyl or N-hydroxycarbonylpropyl substitutes were synthesized. The first of these compounds exhibited more pronounced protective effects towards human cells according to criteria of primary DNA injury and cell survival after exposure to gamma-radiation and CdCl2; by antimutagenic activity this compound was comparable to garlic extract. The antimutagenic effect of these compounds was realized not through the antioxidant mechanism.

Supramolecular assemblies of crown-containing 2-styrylbenzothiazole with amino acids.

Assemblies of 2-styrylbenzothiazole containing an 18-crown-6 ether fragment with perchlorates of amino acids ClO4-NH3+(CH2)nCOOH (n = 2, 10) were studied by UV, NMR spectroscopy, time-resolved fluorescence spectroscopy and quantum-chemical calculations. The obtained data showed that complex formation of the crown-containing 2-styrylbenzothiazole with amino acids occurs through mono- or ditopic coordination. The formation of a ditopic complex influences the E-Z photoisomerization reaction of 2-styrylbenzothiazole.

Tuning the frequency of ultrashort laser pulses by a cross-phase-modulation-induced shift in a photonic crystal fiber.

Femtosecond pulses of fundamental Cr:forsterite laser radiation are used as a pump field to tune the frequency of copropagating second-harmonic pulses of the same laser through cross-phase modulation in a photonic crystal fiber. Sub-100-kW femtosecond pump pulses coupled into a photonic crystal fiber with an appropriate dispersion profile can shift the central frequency of the probe field by more than 100 nm, suggesting a convenient way to control propagation and spectral transformations of ultrashort laser pulses.

Time-resolved fluorescence of crown ether styrul dyes.

Photophsical processes are studied in a new class of dyes contining a chromophoric part and a crown ether part. Fluorescence decays were oebserved to be strongly dependent on temperature in the range from 294 to 4 K. Photoinduced isomerization and electron transfer are considered as possible mechanisms to explain the results.

Nonradiative relaxation of thiacarbocyanine dyes in binary mixtures.

It was found that preferential solvation of cyanine dyes in binary mixtures can strongly affect both their isomerization and aggregation; the comparison of absorption and fluorescence excitation spectra might be a useful tool for studying these nonradiative processes.