Investigating excited state dynamics of salinixanthin and xanthorhodopsin in the near-infrared.

Excited state dynamics of native Xanthorhodopsin (XR), of an XR sample with a reduced prosthetic group, and of the associated Carotenoid (CAR) salinixanthin (SX) in ethanol were investigated by hyperspectral Near Infrared (NIR) probing. Global kinetic analysis shows that: (1) unlike the transient spectra recorded in the visible, fitting of the NIR data requires only two phases of exponential spectral evolution, assigned to internal conversion from S(2) → S(1) and from S(1) → S(0) of the carotene. (2) The rate of the internal conversion from S(2) → S(1) in the reduced sample is well fit with a decay time of 130 fs, significantly longer than in XR and in SX, both of which are well fit with τ ≈ 100 fs.

Photoselective ultrafast investigation of xanthorhodopsin and its carotenoid antenna salinixanthin.

Excited-state dynamics of xanthorhodopsin (XR) and of salinixanthin (SX) in ethanol were investigated by ultrafast pump-hyperspectral probe spectroscopy. Following excitation to the strongly allowed S(2) state of the SX chromophore, transient spectra were recorded photoselectively in the range 430-850 nm. Global kinetic analysis of these data shows the following.

Retinal-salinixanthin interactions in xanthorhodopsin: [corrected] a circular dichroism (CD) spectroscopy study with artificial pigments.

Xanthorhodopsin (xR) is a recently discovered retinal protein that contains, in addition to the retinal chromophore, a carotenoid (salinixanthin) absorbing at 456, 486, and 520 nm, which functions as a light-harvesting antenna. We have studied the interactions between the two chromophores by monitoring the absorbance and circular dichroism (CD) spectroscopies of artificial pigments derived from synthetic retinal analogues characterized by shifted absorption maxima. In addition, we have followed the binding process of the synthetic chromophores to the apomembrane of xR.

Design of an optical switch for studying conformational dynamics in individual molecules of GroEL.

We describe the design of an optical switch in the chaperonin GroEL that is opened and closed by its ATP- and cochaperonin GroES-driven conformational changes. The switch, based on a fluorophore and a quencher, is engineered into the single-ring variant of the chaperone, and shows dramatic modulation of its fluorescent intensity in response to the transition of the protein between its allosteric states. It, therefore, forms a sensitive probe for the dynamics of the allosteric transitions of this machine, both in the bulk and in single molecules.

Chromophore interaction in xanthorhodopsin--retinal dependence of salinixanthin binding.

Xanthorhodopsin is a light-driven proton pump in the extremely halophilic bacterium Salinibacter ruber. Its unique feature is that besides retinal it has a carotenoid, salinixanthin, with a light harvesting function. Tight and specific binding of the carotenoid antenna is controlled by binding of the retinal.

Design of organometallic group IV heteroallylic complexes and their catalytic properties for polymerizations and olefin centered transformations.

The use of metallocenes in many stoichiometric and catalytic processes has been the impetus for the development of new organometallic complexes, especially those containing early transition metals. The formation of coordinative unsaturated complexes using allylic, benzamidinate and aminopyridine families is presented. The synthesis and structural parameters of the new complexes, their activation and use in the polymerization of alpha-olefins and dienes, in the dehydrogenative coupling of silanes and in the hydroamination reactions comprise the objectives of this review.