1,721,258 research outputs found
On the possibility of the observation of intramolecular reaction dynamics in liquids by time-resolved X-ray scattering
Full text linkThe feasibility of time-resolved structural studies using pulsed X-ray radiation from a 3rd generation synchrotron is discussed and compared with scattering experiments which might be possible with a future free electron laser (X-FEL). As an example, it is shown that the structural changes during the isomerisation process of trans-stilbene into cis-stilbene can be observed using time-resolved X-ray diffraction in the gas- phase as well as in solution
Time-resolved and in-situ X-ray scattering methods beyond photoactivation: Utilizing high-flux X-ray sources for the study of ubiquitous non-photoactive proteins
No full textX-ray scattering technique, comprising of small-angle/wide-angle X-ray scattering (SAXS/WAXS) techniques is increasingly used to characterize the structure and interactions of biological macromolecules and their complexes in solution. It is a method of choice to characterize the flexible, partially folded and unfolded protein systems. X-ray scattering is the last resort for proteins that cannot be investigated by crystallography or NMR and acts as a complementary technique with different biophysical techniques to answer challenging scientific questions. The marriage of the X-ray scattering technique with the fourth dimension “time” yields structural dynamics and kinetics information for protein motions in hierarchical timescales from picoseconds to days. The arrival of the high-flux X-ray beam at third generation synchrotron sources, exceptional X-ray optics, state-of-the-art detectors, upgradation of X-ray scattering beamlines with microfluidics devices and advanced X-ray scattering data analysis procedures are the important reasons behind the shining years of X-ray scattering technique. The best days of the X-ray scattering technique are on the horizon with the advent of the nanofocus X-ray scattering beamlines and fourth generation X-ray lightsources, i.e., free electron lasers (XFELs). Complementary to the photon-triggered time-resolved X-ray scattering techniques, we will present an overview of the time-resolved and in-situ X-ray scattering techniques for structural dynamics of ubiquitous non-photoactive proteins
Structure determination of the intramolecular charge transfer state in crystalline 4-(diisopropylamino)benzonitrile from picosecond X-ray diffraction
No full textPhotophysical characteristics of directly linked pyrene-dimethylaniline derivatives
No full textExperimental and theoretical investigations of the spectroscopic properties have been carried out on three charge-transfer model systems, covalently linked donor-acceptor compounds of the type pyrene and derivatives of N,N-dimethylaniline (dimethyl(4-pyren-1-ylphenyl)amine (PyDMA), dimethyl(3-methyl-4-pyren-1-ylphenyl)amine (PyMDMA), and (3,5-dimethyl-4-pyren-1-ylphenyl)dimethylamine (PyDMDMA)). Comparing stationary absorption and emission spectra as well as fluorescence lifetimes in different solvents, one can show that small chemical changes such as substitution of ortho-hydrogens by methyl groups on the DMA moiety introduces dramatic effects in spectroscopic and kinetic behavior. On the basis of infrared measurements and quantum chemical calculations, the experiments are interpreted within a statistical framework, with particular emphasis on the discussion of preferred large amplitude motion (twist angle) and pyrene-specific vibronic coupling
Ultrafast Processes in Isomeric Pyrene-N-methylacetamides: Formation of Hydrogen Bond Induced Static Excimers with Varied Coupling Strength
No full textPyrene based molecules are inclined to form excimers through self-association upon photoexcitation. In this work, the pyrene core is functionalized with N-methylacetamide group at the position 1 or 2, to develop pyren-1-methylacetamide (PyMA1) and pyren-2-methylacetamide (PyMA2), respectively. Upon photoexcitation, PyMA1 and PyMA2, at 1.0mM,in toluene, have formed predominantly static excimers. The steady state spectroscopic studies have showed that the excitonic coupling of PyMA1 dimers are much stronger in solution than its isomeric counterpart, PyMA2. The transient absorption (TA) measurements over fs-ps regime (fs-TA) showed that the formation of static excimers with the strongly-coupled pre-associated dimers, in PyMA1, happens in approx. 560fs, whereas, the excimers for the weakly-coupled pre-associated dimers in PyMA2 have formed in much slower time scale (approx. 65ps). The introduction of methylacetamide group at the position 1 or 2 on pyrene ring, was believed to have allowed forming hydrogen bonded excimers with different degrees of excitonic coupling
Time-resolved fluorescence and solvatochromy of directly linked pyrene-DMA derivatives in alcoholic solution.
Full text linkPicosecond transient absorption spectroscopy and picosecond spectro-streak fluorescence measurements have been carried out in order to understand the complex photophysical dynamics of directly linked donor-acceptor systems and the solvation dynamics in longer-chain alcohols. With these techniques, the fast solvent response to optically generated charge transfer (CT) species can be followed. Studies were performed on covalently linked donor-acceptor systems of the type pyrene with derivatives of N,N-dimethylaniline: dimethyl-(4-pyren-1-yl-phenyl)-amine, dimethyl-(3-methyl-4-pyren-1-yl-phenyl)-amine and (3,5-dimethyl-4-pyren-1-yl-phenyl)-dimethylamine. The results are interpreted with particular emphasis on solvation dependent electronic restructuring of the CT species. We suggest a mechanism where the adiabatic electronic restructuring coincides with the coupling to the torsional degrees of freedom of the solvent
Crystal structure of trans -1-{2-[4-(dimethylamino)phenyl]ethyl}-4-[2-(pyren-1-yl)ethyl]cyclohexane
Full text linkThe title compound, CHN, is a pyrene derivative in which the pyrene ring system is linked to an ethylcyclohexane unit which, in turn, carries a [4-(dimethylamino)phenyl]ethyl substituent in the para position. The central cyclohexane ring has a chair conformation, with the exocyclic C—C bonds inequatorial orientations. The benzene ring is inclined to the mean plane of the pyrene ring system [maximum deviation =0.038 (4) Å] by 14.84 (15) ̊ . In the crystal, molecules are linked by C—H ... interactions, forming chains propagating along [010]. The crystal was refined as a non-merohedral twin [domain ratio = 0.9989 (4):0.0011 (4)]
Limitations of high-intensity soft X-ray laser fields for the characterisation of water chemistry: coulomb explosion of the octamer water cluster
Full text linkIn this work, the Coulomb explosion of the octamer water cluster has been studied employing a theoretical approach. Instead of the usual methodology that makes use of classical molecular dynamics, time-dependent density functional theory has been applied to tackle the problem. This method explicitly accounts for the laser field and thus does not impose any constraint on the interaction between the laser pulse and the cluster. We focus on the effects of energetic changes in the system under high-intensity soft X-ray laser pulses. The motions of the ions and their velocities during this process show significant differences for the three applied laser intensities (10(14), 10(15) and 10(16) W cm(-2)). Very strong soft X-ray free electron laser (FEL) pulses must be short to allow for investigations of ultra-fast wet chemistry, according to the principle of collect and destroy
Contribution of Coulomb Explosion to Form Factors and Mosaicity Spread in Single Particle X-Ray Scattering
Full text linkThe Coulomb explosion of the octamer water cluster has been studied employing time-dependent density functional theory explicitly accounting for the laser field and thus not imposing any constraint on the interaction between the laser pulse and the cluster. We focus on the effects of electron density changes in the system under high-intensity (10 and 10 W cm) soft X-ray laser pulses and their fingerprint in the reciprocal space, namely the ultrafast changes in X-ray diffuse scattering signals in k-space (in the investigated -space range from 10 up to 10 Å). The present simulations indicate that diffusional components in X-ray intensity changes propagate from low reciprocal resolution (resembling the small-angle X-ray scattering regime) to very high resolution (the wide-angle X-ray scattering regime) during the Coulomb explosion process
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