Search

Experimental realizations of two-dimensional (2D) electronic spectroscopy in the ultraviolet (UV) must so far contend with a limited bandwidth in both the excitation and particularly the probe frequency. The pump bandwidth is at best 1500 cm-1 (full width at half maximum) at a fixed wavelength of 267 nm or 400 cm-1 for tunable pulses. The use of a replica of the pump pulse as a probe limits the observation of photochemical processes to the excitation region and makes the disentanglement of overlapping signal contributions difficult. We show that 2D Fourier transform spectroscopy can be conducted in a shaper-assisted collinear setup comprising fully tunable UV pulse pairs and supercontinuum probe spanning 250-720 nm. The pump pulses are broadened up to a useable spectral coverage of 2000 cm-1 (25 nm at 316 nm) by self-phase modulation in bulk CaF2 and compressed to 18 fs. By referencing the white light probe and eliminating pump stray light contributions, high signal-to-noise ratios even for weak probe intensities are achieved. Data acquisition times as short as 4 min for a selected population time allow the rapid recording of 2D spectra for photolabile biological samples even with the employed 1 kHz laser system. The potential of the setup is demonstrated on two representative molecules: pyrene and 2,2-diphenyl-5,6-benzo(2H)chromene. Well-resolved cross-peaks are observed and the excitation energy dependence of the relaxation processes is revealed. [ABSTRACT FROM AUTHOR]

We show that Förster resonance energy transfer (FRET) in an orthogonally arranged donor-acceptor pair can be induced by environmental noise, although direct transfer is prohibited. Environmental fluctuations break the strict orthogonal dipole arrangement and cause effective fluctuating excitonic interactions. Using a scaling argument, we show that interaction fluctuations are coupled to those of the energy levels and are strong enough to induce large FRET rates. This mechanism also explains the temperature dependence observed in a recent experiment on a perylene bisimide dyad and predicts a modified distance dependence as compared to standard Förster theory. [ABSTRACT FROM AUTHOR]

We give a full description of a state-of-the-art femtosecond transient spectrometer. The setup has been put together under full consideration of all technical and conceptual developments that became available in the last few years. Particular care was taken to avoid any unneeded components and modules. The spectrometer is operated at 1 kHz and based on a commercial Ti:sapphire amplifier. A noncollinear parametric amplifier and frequency doubling are used to provide pump tuning from the UV to the NIR. A CaF2 based single filament white light allows for 290 to 720 nm probing. The multichannel detection is operated at the full 1 kHz rate and chopping of the pump light avoids the use of a reference channel. The resulting high detection sensitivity of better than ΔOD=10−4 allows for the simultaneous recording of the spectral features of electronic states and species with differing transition strengths. A prism-based polychromator is employed to avoid the order sorting problem with the more than octave wide probe spectrum and to enhance the throughput. Flow cells with 200 μm windows and down to 120 μm sample thickness reduce the coherent artifact and the group velocity mismatch. This results in an overall sub-50 fs temporal resolution. [ABSTRACT FROM AUTHOR]

We show that the combination of a free-running 24 kHz supercontinuum fiber laser with a kHz femtosecond laser renders a sensitive and easy to implement transient spectrometer. It can directly extend the observation range of a standard broadband femtosecond spectrometer from the usual limit of a few nanoseconds to 1 millisecond and with the additional use of a chopper to seconds. The transmission signal from all supercontinuum pulses is recorded and assigned to the proper delay time by data post-processing. To demonstrate the performance of the device, the relaxation dynamics of Nd:YAG is measured. [ABSTRACT FROM AUTHOR]

Background and Purpose: Recently, a small molecule (Q94) was reported to selectively block PAR(1) /Gα(q) interaction and signalling. Here, we describe the pharmacological properties of Q94 and two analogues that share its benzimidazole scaffold (Q109, Q89). Q109 presents a modest variation from Q94 in the substituent group at the 2-position, while Q89 has quite different groups at the 1- and 2-positions.Experimental Approach: Using human microvascular endothelial cells, we examined intracellular Ca(2+) mobilization and inositol 1,4,5-trisphosphate accumulation as well as isoprenaline- or forskolin-stimulated cAMP production in response to thrombin.Key Results: Q89 (10 µM) produced a leftward shift in the thrombin-mediated intracellular Ca(2+) mobilization concentration-response curve while having no effect on the E(max) . Both Q94 (10 µM) and Q109 (10 µM) reduced intracellular Ca(2+) mobilization, leading to a decrease in E(max) and an increase in EC(50) values. Experiments utilizing receptor-specific activating peptides confirmed that Q94 and Q109 were selective for PAR(1) as they did not alter the Ca(2+) response mediated by a PAR(2) activating peptide. Consistent with our Ca(2+) results, micromolar concentrations of either Q94 or Q109 significantly reduced thrombin-induced inositol 1,4,5-trisphosphate production. Neither Q94 nor Q109 diminished the inhibitory effects of thrombin on cAMP production, indicating they inhibit signalling selectively through the G(q) pathway. Our results also suggest the 1,2-disubstituted benzimidazole derivatives act as 'allosteric agonists' of PAR(1) .Conclusions and Implications: The Q94 and Q109 benzimidazole derivatives represent a novel scaffold for the development of new PAR(1) inhibitors and provide a starting point to develop dual signalling pathway-selective positive/negative modulators of PAR(1) . [ABSTRACT FROM AUTHOR]

BACKGROUND AND PURPOSE Recently, a small molecule (Q94) was reported to selectively block PAR1/Gαq interaction and signalling. Here, we describe the pharmacological properties of Q94 and two analogues that share its benzimidazole scaffold (Q109, Q89). Q109 presents a modest variation from Q94 in the substituent group at the 2-position, while Q89 has quite different groups at the 1- and 2-positions. EXPERIMENTAL APPROACH Using human microvascular endothelial cells, we examined intracellular Ca2+ mobilization and inositol 1,4,5-trisphosphate accumulation as well as isoprenaline- or forskolin-stimulated cAMP production in response to thrombin. KEY RESULTS Q89 (10 µM) produced a leftward shift in the thrombin-mediated intracellular Ca2+ mobilization concentration-response curve while having no effect on the Emax. Both Q94 (10 µM) and Q109 (10 µM) reduced intracellular Ca2+ mobilization, leading to a decrease in Emax and an increase in EC50 values. Experiments utilizing receptor-specific activating peptides confirmed that Q94 and Q109 were selective for PAR1 as they did not alter the Ca2+ response mediated by a PAR2 activating peptide. Consistent with our Ca2+ results, micromolar concentrations of either Q94 or Q109 significantly reduced thrombin-induced inositol 1,4,5-trisphosphate production. Neither Q94 nor Q109 diminished the inhibitory effects of thrombin on cAMP production, indicating they inhibit signalling selectively through the Gq pathway. Our results also suggest the 1,2-disubstituted benzimidazole derivatives act as 'allosteric agonists' of PAR1. CONCLUSIONS AND IMPLICATIONS The Q94 and Q109 benzimidazole derivatives represent a novel scaffold for the development of new PAR1 inhibitors and provide a starting point to develop dual signalling pathway-selective positive/negative modulators of PAR1. [ABSTRACT FROM AUTHOR]