Specificity of Cyanine Dye L-21 Aggregation in Solutions with Nucleic Acids

Optical spectroscopy experiments were used to study the features of cyanine dye 3,3′-dimethyl-9-(2-thienyl)-thiacarbocyanine iodide (L-21) aggregation in binary solutions DMF:Tris–HCl buffer (pH = 8) containing nucleic acids (DNA or RNA). The appearance of absorption and luminescence bands associated with J-aggregates and dimers that are formed within the minor groove of DNA has been observed. The model of L-21 J-aggregate structure is proposed. It has been found that dimers are the building blocks of L-21 J-aggregates. Disorientation in dimers caused by the minor groove curvature is reason of observation of Davydov splitting in absorption spectrum of L-21 J-aggregates. In the solution containing DNA the absorption and luminescence bands of L-21 J-aggregates exhibit the specific properties that allows the dye L-21 to be used as a fluorescent probe for DNA detection.     

Pseudoisocyanine J-aggregate to optical waveguiding crystallite transition: microscopic and microspectroscopic exploration

Using fluorescent microscopy and microspectroscopy, optical properties and morphology transformations in individual pseudoisocyanine (PIC) J-aggregates in aqueous electrolyte solutions have been explored. A stringlike structure of J-aggregates with a string diameter much less than 1 microm has been observed. Photodestruction of the strings under short-wavelength excitation has been revealed. Rodlike PIC crystallites, about 1 microm in diameter, have been observed with time. The fluorescence spectrum of rodlike crystallites has been found to differ from that of stringlike J-aggregate and from PIC crystal powder spectra. The crystallites are very stable, and their photodestruction has not been observed under any excitation conditions. It has been found that rodlike crystallites in contrast to stringlike J-aggregates possess optical waveguide properties. The luminescence of crystallites can be observed only at the excitation spot and at butt ends located up to hundreds of micrometers from the excitation spot.     

Temperature-dependent segregation of Pr3+ impurity ions in Y2SiO5:Pr3+ and YPO4:Pr3+ nanocrystals

Stationary and time-resolved spectroscopic methods are used to show that the impurity ions in Y₂SiO₅:Pr³⁺ and YPO₄:Pr³⁺ nanocrystals are distributed nonuniformly. This nonuniform distribution is found to be caused by the temperature-dependent segregation of Pr³⁺ ions near the surface of a nanocrystal. The motion of the activator ions from the bulk of a nanocrystal to the near-surface layer is traced when the activator concentration and the heat-treatment parameters are varied over wide ranges, and the main parameters of this effect (impurity redistribution intensity and time, diffusion coefficient) are estimated.     

Hydrophobicity effect on interactions between organic molecules in nanocages of surfactant micelle

Interactions between the cationic polymethine dyes 3,3′-diethyloxacarbocyanaine iodide (DiOC₂), 3,3′-dioctadecyloxacarbocyanine iodide (DiOC₁₈), and 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI) in the nano-scale volume of anionic sodium dodecylsulfate (SDS) micelles have been studied using optical spectroscopy techniques. The solubilization of pairs of dye molecules (DiOC₁₈/DiI or DiOC₂/DiI) within SDS micelles was monitored by Forster resonance energy transfer (FRET) between the dyes in each pair. The influence of the hydrophobicity of the dyes DiOC₂ and DiOC₁₈ on the efficiency of their binding to SDS micelles and, consequently, on the efficiency of FRET between DiOC₁₈ and DiI or DiOC₂ and DiI fluorophors has been analyzed. It has been shown that hydrophobic interactions in addition to electrostatic interactions are of key importance for the binding between the positively charged dyes and negatively charged surfactant micelles. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 646–652, September–October, 2008.     

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.     

Echo spectroscopy of two-level systems in a Y2SiO5: Pr3+ crystal

The results of an experimental investigation of low-temperature optical spectra and phase relaxation of electronic excitations of Pr³⁺ impurity ions in a Y₂SiO₅ crystal are reported. It is established that at low temperatures spectral lines are broadened by a mechanism that is uncharacteristic for crystals and is due to the interaction of impurity ions with two-level systems. The constants characterizing the interaction of Pr³⁺ impurity ions with phonons and two-level systems are found. Zh. éksp. Teor. Fiz. 115, 704–715 (February 1999)     

Microspectroscopic Study of Liposome-to-cell Interaction Revealed by Förster Resonance Energy Transfer

We report the Förster resonance energy transfer (FRET)-labeling of liposomal vesicles as an effective approach to study in dynamics the interaction of liposomes with living cells of different types (rat hepatocytes, rat bone marrow, mouse fibroblast-like cells and human breast cancer cells) and cell organelles (hepatocyte nuclei). The in vitro experiments were performed using fluorescent microspectroscopic technique. Two fluorescent dyes (DiO as the energy donor and DiI as an acceptor) were preloaded in lipid bilayers of phosphatidylcholine liposomes that ensures the necessary distance between the dyes for effective FRET. The change in time of the donor and acceptor relative fluorescence intensities was used to visualize and trace the liposome-to-cell interaction. We show that FRET-labeling of liposome vesicles allows one to reveal the differences in efficiency and dynamics of these interactions, which are associated with composition, fluidity, and metabolic activity of cell plasma membranes.     

Strong segregation of doped ions in Y2SiO5:Pr3+ nanocrystals

Strong temperature controlled segregation of doped ions in Y₂SiO₅:Pr³⁺ nanocrystals detected by spectroscopic techniques is reported. The elastic interactions stimulate Pr³⁺ segregation thus leading to non-uniform distribution of doped ions, pair formation and, as a consequence, to abnormal low threshold of luminescence concentration quenching for Y₂SiO₅:Pr³⁺ nanocrystals.     

Study of exciton transport in luminescent molecular nanoclusters using energy traps

We used a squarylium dye SQ as a specific exciton trap for J aggregates of the amphiphilic cyanine dye amphi-PIC. The exciton transport parameters in amphi-PIC J aggregates were estimated using a modified Stern–Volmer equation. We found that SQ quenches 50% of the luminescence of amphi-PIC J aggregates for a ratio of 1 SQ molecule per 80 amphi-PIC molecules. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 1, pp. 50–53, January–February, 2009.