Infrared spectroscopy of phytochrome and model pigments

Fourier-transform infrared difference spectra between the red-absorbing and far-red-absorbing forms of oat phytochrome have been measured in H2O and 2H2O. The difference spectra are compared with infrared spectra of model compounds, i.e. the (5Z,10Z,15Z)- and (5Z,10Z,15E)-isomers of 2,3,7,8,12,13,17,18-octaethyl-bilindion (Et8-bilindion), 2,3-dihydro-2,3,7,8,12,13,17,18-octaethyl-bilindion (H2Et8-bilindion), and protonated H2Et8-bilindion in various solvents. The spectra of the model compounds show that only for the protonated forms can clear differences between the two isomers be detected. Since considerable differences are present between the spectra of Et8-bilindion and H2Et8-bilindion, it is concluded that only the latter compound can serve as a model system of phytochrome. The 2H2O effect on the difference spectrum of phytochrome supports the view that the chromophore in red-absorbing phytochrome is protonated and suggests, in addition, that it is also protonated in far-red-absorbing phytochrome. The spectra show that protonated carboxyl groups are influenced. The small amplitudes in the difference spectra exclude major changes of protein secondary structure

Theoretical evaluation of PAH dications properties

Aims. We present a systematic theoretical study on 40 polycyclic aromatic hydrocarbons dications (PAHs++) containing up to 66 carbon atoms. Methods. We performed our calculations using well established quantum-chemical techniques in the framework of the density functional theory (DFT) to obtain the electronic ground-state properties, and of the time-dependent DFT (TD-DFT) to evaluate the excited\textendash state properties. Results. For each PAH++ considered we computed the absolute visible-UV photo-absorption cross-section up to about 30 eV. We also evaluated their vibrational properties and compared them to those of the corresponding neutral and singly-ionised species. We estimated the adiabatic and vertical second ionisation energy DeltaI through total energy differences. Conclusions. The DeltaI values obtained fall in the energy range 8-13 eV, confirming that PAHs could reach the doubly-ionised state in HI regions. The total integrated IR absorption cross-sections show a marked increase upon ionization, being on the average about two and five times larger for PAHs++ than for PAHs+ and PAHs, respectively. The visible-UV photo-absorption cross-sections for the 0, +1 and +2 charge-states show comparable features but PAHs++ are found to absorb slightly less than their parent neutrals and singly ionized species between ~7 and ~12 eV. Combining these pieces of information we found that PAHs++ should actually be more stable against photodissociation than PAHs and PAHs+,_if_ dissociation tresholds are nearly unchanged by ionization.Comment: 13 pages, 7 figures, accepted for pubblication in A&A (25/09/06

Die Entwicklung des zellularen Mobilfunks in den USA

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