Vlastimil Fidler

Femtosecond to nanosecond solvation dynamics in pure water and inside the γ-cyclodextrin cavity

The dynamics of solvation of an excited chromophore in pure water and in a restricted space with a limited number of water molecules have been studied. The time-dependent Stokes shift of Coumarin 480 (C480) and Coumarin 460 (C460) were measured using femtosecond fluorescence upconversion and time-correlated single-photon-counting techniques. The system with a limited number of water molecules was an inclusion complex of Coumarin dyes with γ-cyclodextrin (γCD). The results of molecular dynamics simulations are compared with the observed solvent response in pure water and in the γCD cavity. The observed relaxation times range from <100 fs to 1.2 ns. Solvation of C480 in pure water is observed to occur with time constants of <50 and 310 fs. In sharp contrast with the solvation response in pure water, in the case of the C480/γCD inclusion complex, additional long solvation time constants of 13, 109 and 1200 ps are observed. The stoichiometry, structure and dynamics of the Coumarin/γCD complexes are also discussed.

Structure and properties of fluorescent reactive dyes : Electronic structure and spectra of some benzanthrone derivatives

Absorption and fluorescence spectra of N-(disubstituted-1,3,5-triazinyl)-3-aminobenzanthrones, 3-acetylaminobenzanthrone and 3-methoxybenzanthrone have been investigated. Excitation energies and the character of the first absorption band have been calculated by the PPP-MO method. Some data on substituent and solvent effects on fluorescence spectral position and quantum yields are reported. The connection between electron density distribution in the electronic ground and excited state, and spectroscopic properties of those compounds, is explained.

Dynamics of isotachophoretic separation : I. Computer simulation

Abstract A simulation model formulated on an EAI 690 hybrid computer system is described. This model makes it possible to simulate with very good precision the dynamics not only of isotachophoretic, but also of any electrophoretic separation of the maximum number of four strong, uni—univalent electrolytes with a common counter ion.

Dynamics of isotachophoretic separation : II. Impurities in the electrolytes and sample injection

Abstract The behaviour and effects of impurities in the electrophoretic separation of the cations of strong electrolytes for the case when four components are involved in the separation was studied. The separation dynamics were studied for two characteristic cases, namely, the behaviour and effects of impurities present in the terminating electrolyte and those present in the leading electrolyte. The effect of sample injection on the course of the isotachophoretic separation was studied. Cases corresponding to real experimental conditions were considered, when the sample was mixed in various ways with the leading and terminating electrolytes during the injection.

Time‐resolved fluorescence study of a calcium‐induced conformational change in prothrombin fragment 1

The wavelength dependent fluorescence decay properties of bovine prothrombin fragment 1 have been investigated employing a picosecond time‐correlated single photon counting technique. All observations are discussed with using the crystal structure (Soriano‐Garcia et al., Biochemistry 31:2554–2566, 1992). Fluorescence lifetimes distribution and conventional multiexponential analysis, as well as acrylamide quenching studies lead to the identification of six distinguishable tryptophan excited‐states. Accessibility to the quencher and the known structure are used to associate a fluorescence decay of the tryptophan present in the Gla domain (Trp42) with two red shifted components (2.3 and 4.9 ns). The two kringle domain tryptophans (Trp90 and Trp126) exhibit four decay times (0.06, 0.24, 0.68, and 2.3 ns), which are blue shifted. The calcium‐induced fluorescence quenching is a result of static quenching: the five decay times remain unchanged, whereas the fluorescence intensity of Trp42 is decreased. The static quenching process is a consequence of a ground state interaction between the Cys18‐Cys23 disulfide bridge and Trp42. The monomolecular equilibrium constant for this disulfide‐π‐electron interaction is found as 4.8.

Luminescence as a tool for crosslinking determination in plasma polysilylenes prepared from organosilanes

Abstract The photoluminescence (PL) in polysilanes during the change from linear one-dimensional (1D) Si chain to amorphous three-dimensional (3D) Si network was studied. The excitonic absorption observed in 1D Si at 320 nm undergoes a blue-shift and broadening of main-chain σ–σ* transitions on introducing branching and networking defects. With the gradual transition to the 3D structure the extensive redistribution of oscillator intensity along the absorption edge with the loss of the resolved σ–σ* band edge. Further, the gradual disappearance of main-chain exciton σ–σ* and appearance of the defect luminescence centred approximately at 450 nm and exhibiting red-shift with increasing 3D networking are observed.

Time-resolved fluorescence study of micellizing block copolymers

Abstract We have studied the dynamics of polystyrene-block-hydrogenated polyisoprene samples, fluorescently labelled on the polystyrene block, by steady-state and time-resolved fluorometry. In selective precipitants for the labelled block, fluorescent probes are trapped and immobilized in compact micellar cores. The rotation of pendant fluorophors is frozen. However, the fast torsional vibrations depolarize partially the fluorescence. As the rotation of micelles is slow as compared with the fluorescence life-time, a significant residual anisotropy is observed. In good solvents for both blocks, fluorescent probes in expanded copolymer coils are exposed to solvent molecules and free to rotate.

Nanosecond fluorometry of the single tryptophan in cytochrome P-450e (P450IIB2)

Properties of the single tryptophan residue in rat liver microsomal phenobarbital-inducible cytochrome P-450e (P450IIB2) were studied by the nanosecond time-resolved fluorometry. The tryptophan fluorescence decay time was found to be 3.6 ns and it was not affected by the addition of substrate (perhydrophenanthrene). This result strongly indicates that the tryptophan residue is not a part of the substrate-binding site.

Editorial: 8th Conference on Methods and Applications of Fluorescence: Spectroscopy, Imaging and Probes

The contributions in this issue are contributed by the participants of the 8th Conference on Methods and Applications of Fluorescence: Spectroscopy, Imaging and Probes (8th MAF), held in Prague, The Czech Republic, August 24–27, 2003. We believe that this meeting, as part of the highly recognized series of conferences devoted to fluorescence, helped us to better understand the basic features of molecular fluorescence and, that it promotes and stimulates new crossdisciplinary ideas and collaboration among physics, chemistry, biology, medicine, and pharmacology where there are many important applications of fluorescence spectroscopy, probes, imaging, and other fluorescence-based techniques. We are very grateful to all 305 participants from 35 countries and 5 continents for directly contributing to the successes of the Conference. In particular, we would like to thank the 23 plenary lecturers for accepting our invitation, to the 180 poster presenters for sharing their most recent scientific results and advances in technology and instrumentation, and to the contributors to this special issue of Journal of Fluorescence. Special thanks go to the sponsoring firms and to the exhibitors at the Conference who helped us finance the 8th MAF meeting, and especially to those who enabled us to support young scientists and participants from less endowed countries. The organizing teams are grateful for the support and understanding provided by their home institutions: The Research Center for the Structure and Dynamics of Complex Molecular Systems and Biomolecules (grant MSMT CR LN 00A032), J. Heyrovsk ́ y Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, and the Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, CR (grant MSMT CR J04/98:210000022). We, and we are sure, most of the participants of the 8th MAF are already looking forward to the 9th Conference on Methods and Applications of Fluorescence: Spectroscopy, Imaging and Probes, which will take place in Lisbon on September 4th–7th, 2005. Details can be found on the following website: http://maf9.ist.utl.pt

Luminescence in plasma polysilylenes prepared from organosilanes

Abstract The photoluminescence in polysilanes (exemplified on poly(methylphenylsilylene) – PMPSi) during the change from linear 1D Si chain to amorphous 3D Si networks was studied. The excitonic absorption observed in 1D Si at 320 nm undergoes a blue shift on introducing branching and networking defects. With the transition to the 3D structure the redistribution of oscillator intensity along the absorption edge with the loss of the resolved σ–σ * band edge occurs. Further, the disappearance of main-chain exciton σ–σ * and appearance of the defect luminescence at 450 nm exhibiting red shift with increasing 3D networking are observed.