Two difluoroboron dipyrromethene (BODIPY) based fluorescent dyes - 4,4-difluoro-3-{2-[4-(dimethylamino)phenyl]ethenyl}-8-[4-(methoxycarbonyl)phenyl]-1,5,7-trimethyl-3a,4a-diaza-4-bora-s-indacene (1) and 4,4-difluoro-3-[2-(4-fluoro-3-hydroxyphenyl)ethenyl]-8-[4-(methoxycarbonyl)phenyl]-1,5,7-trimethyl-3a,4a-diaza-4-bora-s-indacene (3) - have been synthesized via condensation of p-N,N-dimethylaminobenzaldehyde and 4-fluoro-3-hydroxybenzaldehyde, respectively, with 4,4-difluoro-8-[4-(methoxycarbonyl)phenyl]-1,3,5,7-tetramethyl-3a,4a-diaza-4-bora-s-indacene (2). UV-vis spectrophotometry and steady-state and time-resolved fluorometry have been used to study the spectroscopic and photophysical characteristics of in various solvents. The multi-parameter Kamlet-Taft {pi*, alpha, beta} solvent scales and a new, generalized treatment of the solvent effect, proposed by Catalán (J. Phys. Chem. B, 2009, 113, 5951-5960), have been used in the analysis of the solvatochromic shifts of the UV-vis absorption and fluorescence emission maxima of 1-3, and the rate constants of excited-state deactivation via fluorescence (k(f)) and radiationless decay (k(nr)). The four Catalán solvent scales (dipolarity, polarizability, acidity and basicity of the medium) are the most appropriate for describing the solvatochromic effects. Solvent dipolarity and polarizability are the important causes for the solvatochromism of 1. Conversely, the absorption and emission maxima of 2 and 3 are hardly dependent on the solvent: the small changes reflect primarily the polarizability of the solvent surrounding the dye. Fluorescence decay profiles of 1 can be described by a single-exponential function in aprotic solvents, whereas two decay times are found in alcohols. The fluorescence decays of 2 (lifetimes tau in 1.9-2.9 ns range) and 3 (tau between 3.5 and 4.0 ns) are mono-exponential in all solvents studied. The fluorescence properties of dye are very sensitive to the solvent: upon increasing solvent dipolarity, the fluorescence quantum yields and k(f) values decrease and the emission maxima become more red-shifted. The k(f) values of 2 [(1.6 +/- 0.3) x 10(8) s(-1)] and 3 [(1.5 +/- 0.2) x 10(8) s(-1)] are practically independent of the solvent properties. The crystal structure of reveals that the BODIPY core is nearly planar with the boron atom moved out of the plane. The angle between the phenyl group at the meso-position and the BODIPY plane equals 80 degrees.

The potential energy surface and the reaction pathway for the intramolecular hydrogen transfer in o-hydroxyaryl ketimines are characterized using DFT methods. Structural changes in the proton-transfer process in quasi-aromatic hydrogen bonding are described. A transition state and a state with a low proton-transfer barrier were studied in sterically compressed o-hydroxyaryl ketimines (2(N-methyl-alpha-iminoethyl)phenols) possessing two potential minimums. The potentials for proton vibration in the OH and HN tautomers of o-hydroxyaryl ketimines were investigated and anharmonic frequencies were determined. Solvent and substituent effects were analyzed. The energies of the various conformers of the OH and HN tautomers were compared with the related forms of o-hydroxyaryl aldimine.

The synthesis and X-ray measurements of four Schiff bases were carried out at 100 K. The HOMA and HOSE aromaticity indices were estimated on the basis of the experimental data. The aromaticity of the phenyl ring and the chelate chain was analysed. A comparison of the aromaticity of naphthalene and phenyl derivatives of hydroxy aryl Schiff bases is presented. The balance between the aromaticity of adjacent rings of the naphthalene fragment and its effect on proton transfer is defined. Research on the interrelations between aromaticity and the intramolecular proton transfer in hydroxy aryl Schiff bases is shown.The synthesis of the hydroxy aryl Schiff bases from stoichiometric mixtures of ketones and anilines in methanol was performed according to Reference [30] .The intensity data were collected at 100 K using a Kuma KM4CCD diffractometer and graphite-monochromated MoKa (0.71073 Å ) radiation generated by an X-ray tube operating at 50 kV and 35 mA. The images were indexed, integrated and (www.interscience.wiley.com)

Dimerization of the epidermal growth factor receptor (EGFR) is crucial for initiating signal transduction. We employed raster image correlation spectroscopy to continuously monitor the EGFR monomer-dimer equilibrium in living cells. EGFR dimer formation upon addition of EGF showed oscillatory behavior with a periodicity of about 2.5 min, suggesting the presence of a negative feedback loop to monomerize the receptor. We demonstrated that monomerization of EGFR relies on phospholipase Cγ, protein kinase C, and protein kinase D (PKD), while being independent of Ca2+ signaling and endocytosis. Phosphorylation of the juxtamembrane threonine residues of EGFR (T654/T669) by PKD was identified as the factor that shifts the monomer-dimer equilibrium of ligand bound EGFR towards the monomeric state. The dimerization state of the receptor correlated with the activity of an extracellular signal-regulated kinase, downstream of the EGFR. Based on these observations, we propose a novel, negative feedback mechanism that regulates EGFR signaling via receptor monomerization.