Articles

Optical limiting properties of carbon nanotubes
- Vivien L.
- Riehl D.
- Hache François
- Anglaret E.
Physica B: Condensed Matter, Elsevier , 2002, 323 (1-4), pp.233-234 . We review a series of investigations on nonlinear optical properties of carbon nanotube suspensions for optical limiting application. Z-scan, pump-probe, and shadowgraphics experiments allowed us to study the mechanism responsible for optical limiting. The main effect is nonlinear scattering, which is due to heat transfer from particles to solvent, leading to solvent bubble formation and to sublimation of carbon nanotubes. (10.1016/S0921-4526(02)00974-2)
DOI : 10.1016/S0921-4526(02)00974-2
Eau liquide : le film" à l'échelle femtoseconde
- Gallot Guilhem
- Bratos S.
- Gale Geoffrey
- Lascoux Noëlle
- Leicknam J.-Cl.
- Pommeret S.
- Amir Wafa
Bulletin de la Societe Francaise de Physique , 2002, 134 (1), pp.8 . L'eau est de loin le liquide le plus important sur terre. Il est présent à tous les échelons de l'écosystème terrestre, des océans qui couvrent les 3/5 de la surface, au corps humain dont il représente 70% du volume. Sans l'eau, les systèmes biologiques ne fonctionneraient pas et la vie telle que nous la connaissons n'existerait pas. Si l'eau joue un rôle aussi fondamental dans la nature [1], c'est grâce à ses propriétés exceptionnelles qui proviennent essentiellement de la liaison hydrogène [2, 3]. Dans ces conditions, il n'est pas surprenant que D'immenses efforts aient été portés par le passé, efforts qui continuent de nos jours, pour mieux comprendre ce liquide si particulier. Ses propriétés mécaniques, physicochimiques et moléculaires ont ainsi été étudiées en détails et ont été soigneusement décrites dans un grand nombre d'ouvrages [4, 5]. L'arrivée au début des années 90 de lasers délivrant des impulsions pico- puis femtoseconde va cependant bouleverser la situation en ouvrant la voie à la femtochimie de l'eau liquide. Grâce à ces impulsions incroyablement brèves, la dynamique moléculaire de l'eau peut maintenant être étudiée. Il est même possible de " filmer " les mouvements des molécules d'eau et de la liaison hydrogène en temps réel. C'est ce thème qUE NOUS ALLONS MAINTENANT TRAITER.
Influence of the hole population on the transient reflectivity signal of annealed low-temperature-grown GaAs
- Ortiz Valentin
- Nagle J.
- Alexandrou Antigoni
Applied Physics Letters, American Institute of Physics , 2002, 80 (14), pp.2505 . We study the influence of the carrier dynamics on the transient reflectivity of low-temperature-grown GaAs samples. We report a precise modeling of the recorded reflectivity data, which exhibit multiexponential decays and changes in sign, using a standard point defect model and taking into account the effects of the band filling, band gap renormalization, and trap absorption. We show that the valence-band hole population plays an important role in the behavior of the signals, and that it must be taken into account in order to optimize low-temperature-grown GaAs-based devices. Cop. 2002 American Institute of Physics. (10.1063/1.1463209)
DOI : 10.1063/1.1463209
Spectroscopie non-linéaire femtoseconde cohérente à deux dimensions spectrales [Coherent femtosecond nonlinear spectroscopy with two spectral dimensions]
- Belabas Nadia
- Joffre Manuel
Journal de Physique IV Proceedings, EDP Sciences , 2002, 12 (5), pp.393-395 . La spectroscopie non-linéaire femtoseconde cohérente multidimensionnelle est une technique optique analogue à la résonance magnétique nucléaire multidimensionnelle. Elle repose sur l'utilisation d'impulsions femtosecondes et est démontrée ici dans le cas d'un processus de génération d'infrarouge par différence de fréquence dans une cristal non-linéaire avec accord de phase. Dans le domaine de l'infrarouge moyen, elle permet notamment la spectroscopie vibrationnelle de molécules et l'étude de nanostructures semiconductrices. (10.1051/jp4:20020205)
DOI : 10.1051/jp4:20020205
Coupling between molecular rotations and OH***O motions in liquid water: Theory and experiment
- Gallot Guilhem
- Bratos S.
- Pommeret S.
- Lascoux Noëlle
- Leicknam J.-Cl.
- Kozinski M.
- Amir W.
- Gale Geoffrey
The Journal of Chemical Physics, American Institute of Physics , 2002, 117 (24), pp.11301 . A new theory is proposed to describe spectral effects of the coupling between molecular rotations and OH⋯O motions in liquid water. The correlation function approach is employed together with a special type of development in which the coupling energy of these two motions is the expansion parameter. The isotropy of the liquid medium plays an essential role in this study. Based on this theory, a new infrared pump-probe experiment is described permitting a visualization of molecular rotations at subpicosecond time scales. Full curves relating the mean squared rotational angle and time, and not only the rotational relaxation time, are measured by this experiment. However, very short times where the incident pulses overlap must be avoided in this analysis. The lifetime of OH⋯O bonds in water is rotation-limited. © 2002 American Institute of Physics. (10.1063/1.1522378)
DOI : 10.1063/1.1522378
Muscarinic effects of the Caribbean ciguatoxin C-CTX-1 on frog atrial heart muscle
- Sauviat Martin-Pierre
- Marquais Michel
- Vernoux Jean-Paul
Toxicon, Elsevier , 2002, 40 (8), pp.1155 . The effects of Caribbean ciguatoxin (C-CTX-1) isolated from horse-eye jack (Caranx latus) on the electrical and mechanical activities of frog auricle were studied. C-CTX-1 (1pM-50nM) dose-dependently shortened the duration of the plateau and the repolarizing phase of the action potential (AP). The AP shortening induced by C-CTX-1 (50nM) was suppressed or prevented either by tetrodotoxin (TTX; 0.6nM) or by atropine (0.1mM). C-CTX-1 (50nM) prolonged the TTX (0.6nM)-sensitive electrical response of the vagus nerve branches, which innervate the auricle. The C-CTX-1 (50nM)-induced shortening of the plateau and of the repolarization phase were prevented or reversed by gallamine (20µM) and pirenzepine (0.5µM), respectively. C-CTX-1 (50nM) decreased the amplitude of the peak contraction and shortened its duration. In the presence of gallamine (20µM), C-CTX-1 decreased the amplitude of the peak contraction and shortened its duration in the presence of pirenzepine (0.5µM). C-CTX-1 (50nM) decreased the time constant of the relaxation phase of the peak contraction suggesting that it increased the Na+/Ca2+ exchange activity. Acetylcholine (ACh; 1pM) shortened APD, decreased the peak contraction and mimics the effects of C-CTX-1. In conclusion, the presented data show that C-CTX-1 released ACh from atrial cholinergic nerve terminals which activated M1 and M2 muscarinic receptors subtype (mAChR). Our findings suggest that M1 and M2 mAChR are present in frog atrial tissue and play a previously unrecognized role in the modulation of the AP duration and of the mechanical activity of cardiac tissue. Cop. 2002 Elsevier Science Ltd. All rights reserved. (10.1016/S0041-0101(02)00117-4)
DOI : 10.1016/S0041-0101(02)00117-4
Wavelength dependence of nonlinear circular dichroism in a chiral ruthenium-tris(bipyridyl) solution
- Mesnil H.
- Schanne-Klein Marie-Claire
- Hache François
- Alexandre M.
- Lemercier G.
- Andraud Chantal
Physical Review A : Atomic, molecular, and optical physics [1990-2015], American Physical Society , 2002, 66 (1), pp.138021 . Nonlinear circular dichroism is studied in a solution of ruthenium-tris(bipyridyl) salt in one-beam and pump-probe experiments by tuning the laser wavelength across the circular dichroism structure. The dispersion of the nonlinear circular dichroism is measured. This wavelength dependence is well accounted for by a model calculation where nonlocality is included in the optical response of a two-coupled-oscillator system. This calculation also allows us to address the question of the contribution of electric quadrupolarization to the nonlinear optical activity of an isotropic liquid of chiral molecules. © 2002 The American Physical Society (10.1103/PhysRevA.66.013802)
DOI : 10.1103/PhysRevA.66.013802
Coherent infrared emission from myoglobin crystals: An electric field measurement
- Groot Marie-Louise
- Vos Marten H.
- Schlichting I.
- van Mourik F.
- Joffre Manuel
- Lambry Jean-Christophe
- Martin Jean-Louis
Proceedings of the National Academy of Sciences of the United States of America, National Academy of Sciences , 2002, 99 (3), pp.1323 . We introduce coherent infrared emission interferometry as a X(2) vibrational spectroscopy technique and apply it to studying the initial dynamics upon photoactivation of myoglobin (Mb). By impulsive excitation (using 11-fs pulses) of a Mb crystal, vibrations that couple to the optical excitation are set in motion coherently. Because of the order in the crystal lattice the coherent oscillations of the different proteins in the crystal that are associated with charge motions give rise to a macroscopic burst of directional multi-teraHertz radiation. This radiation can be detected in a phase-sensitive way by heterodyning with a broad-band reference field. In this way both amplitude and phase of the different vibrations can be obtained. We detected radiation in the 1,000-1,500 cm-1 frequency region, which contains modes sensitive to the structure of the heme macrocycle, as well as peripheral protein modes. Both in carbonmonoxy-Mb and aquomet-Mb we observed emission from six modes, which were assigned to heme vibrations. The phase factors of the modes contributing to the protein electric field show a remarkable consistency, taking on values that indicate that the dipoles are created "emitting" at t = 0, as one would expect for impulsively activated modes. The few deviations from this behavior in Mb-CO we propose are the result of these modes being sensitive to the photodissociation process and severely disrupted by it. (10.1073/pnas.251662698)
DOI : 10.1073/pnas.251662698
Carbon nanotubes for optical limiting
- Vivien L.
- Lançon P.
- Riehl D.
- Hache François
- Anglaret E.
Carbon, Elsevier , 2002, 40 (10), pp.1789-1797 . This paper reviews the optical limiting properties of carbon nanotubes. The nonlinear optical properties of nanotubes were investigated in water and in chloroform suspensions. Nonlinear transmittance measurements were reported for various pulse durations and wavelengths and show that carbon nanotubes are good candidates for effective optical limiting over broad temporal and laser energy ranges. Z-Scans and pump-probe time-resolved experiments were achieved to identify the origin of optical limiting in nanotubes. The main phenomenon is a strong nonlinear scattering, originating from solvent vapour bubble growth and sublimation of nanotubes at high fluences. Heat transfer from particles to solvent is particularly effective as compared to carbon black suspensions because of the large surface area of the carbon nanotubes. (10.1016/S0008-6223(02)00046-5)
DOI : 10.1016/S0008-6223(02)00046-5
Visible-infrared two-dimensional Fourier-transform spectroscopy
- Belabas Nadia
- Joffre Manuel
Optics Letters, Optical Society of America - OSA Publishing , 2002, 27 (22), pp.2043 . We report on a new class of optical multidimensional Fourier-transform spectroscopy associated with a visible excitation-infrared emission configuration, in which the emitted field results from second-order optical nonlinearities. This configuration is demonstrated on a phase-matched sample of known nonlinear response by coherent measurement of the mid-infrared field emitted after a femtosecond visible double-pulse excitation. (C) 2002 Optical Society of America. (10.1364/OL.27.002043)
DOI : 10.1364/OL.27.002043
Shadowgraphic imaging of carbon nanotube suspensions in water and in chloroform
- Vivien L.
- Moreau J.
- Riehl D.
- Alloncle P.A.
- Autric M.
- Hache François
- Anglaret E.
Journal of the Optical Society of America B, Optical Society of America , 2002, 19 (11), pp.2665 . Carbon nanotube suspensions are known to display interesting optical limiting properties as a result of the formation of solvent or carbon-vapor bubbles that scatter the laser beam. In this study we present an original experiment that permits direct observation of the changes that occur in the focal zone in carbon nanotube suspensions by using a shadowgraphic experiment coupled with a monochromatic pump-probe experiment. We have observed a clear correlation between the radius of the scattering centers and the evolution in transmittance of the sample. We compared bubble growth in chloroform and water and found good agreement with previously obtained results. We also observed the presence of compression waves, which propagate parallel to the laser beam and can produce secondary cavitation phenomena after reflection on the cell walls. Cop. 2002 Optical Society of America. (10.1364/JOSAB.19.002665)
DOI : 10.1364/JOSAB.19.002665
Nonlinear optical activity in chiral molecules: Surface second harmonic generation and nonlinear circular dichroism
- Hache François
- Schanne-Klein Marie-Claire
- Mesnil Hugues
- Alexandre M.
- Lemercier G.
- Andraud Chantal
Comptes Rendus. Physique, Académie des sciences (Paris) , 2002, 3 (4), pp.429 . Nonlinear optical activity in chiral molecules is investigated. We first examine the importance of the nonlocality of the light-matter interaction in optical activity and extend this concept to second-order (surface second harmonic generation) and third-order (nonlinear circular dichroism) nonlinear optical phenomena. Microscopic models are also discussed. Various phenomena derived from these considerations are demonstrated experimentally with specially-synthesized chiral molecules. Cop. 2002 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS. (10.1016/S1631-0705(02)01327-0)
DOI : 10.1016/S1631-0705(02)01327-0
Nitric oxide (NO) traffic in endothelial NO synthase. Evidence for a new NO binding site dependent on tetrahydrobiopterin?
- Slama-Schwok Anny
- Négrerie Michel
- Berka V.
- Lambry Jean-Christophe
- Tsai Ah-Lim
- Vos Marten H.
- Martin Jean-Louis
Journal of Biological Chemistry, American Society for Biochemistry and Molecular Biology , 2002, 277 (9), pp.7581 . Nitric oxide (NO) traffic within the reduced ferrous-nitrosyl complex of endothelial nitric-oxide synthase (eNOS) has been studied by ultrafast time-resolved absorption spectroscopy. In the presence of tetrahydrobiopterin, the rate of NO rebinding to the heme upon photodissociation depends on the NO concentration. The time scale of this process, picoseconds to nanoseconds, precludes a diffusion from the solution toward the protein medium, and altogether the data point at a new NO binding site within the protein. Comparison of the kinetics of pterin-bound and -depleted eNOS points out that the existence of this new site depends on the presence of tetrahydrobiopterin. The new non-heme site may act as a "doorstep" to the heme pocket and control NO escape from eNOS. (10.1074/jbc.M108657200)
DOI : 10.1074/jbc.M108657200
Strong chiroptical effects in surface second harmonic generation obtained for molecules exhibiting excitonic coupling chirality
- Schanne-Klein Marie-Claire
- Boulesteix T.
- Hache François
- Alexandre M.
- Lemercier G.
- Andraud Chantal
Chemical Physics Letters, Elsevier , 2002, 362 (1-2), pp.103 . We measured nonlinear optical activity in second harmonic generation (SHG) by reflection on a thin film of chiral molecules. We selected the structure of our molecules in order to obtain very large chiroptical effects. We indeed measured an angle of rotation of the second harmonic polarization as large as 66° for an acridine substituted Tröger base. This is in good agreement with our theoretical expectations for such an excitonic coupling chirality. Cop. 2002 Elsevier Science B.V. All rights reserved. (10.1016/S0009-2614(02)01030-8)
DOI : 10.1016/S0009-2614(02)01030-8
Toxicité du lindane sur la reproduction [Different aspects of lindane toxicity: effect on reproduction]
- Pages Nicole
- Sauviat Martin-Pierre
- Bouvet Suzanne
- Goudey-Perrière F.
Journal de la Société de Biologie , 2002, 196 (4), pp.325 . Dans cette revue sont présentés les principaux effets du lindane (isomère y de l'hexachlorocyclohexane) sur les fonctions endocriniennes et reproductrices des Mammifères. Le lindane est utilisé chez l'Homme, comme produit phytosanitaire contre les parasites (poux et gale). Il a aussi été largement utilisé comme insecticide et désinfectant en agriculture, sylviculture et en élevage. Dans ces domaines, son usage a été, dès 1975, progressivement réduit aux USA et en Europe (où il est interdit depuis 2000) mais se poursuit dans le reste du monde. Absorbé par voie respiratoire, digestive ou transcutanée, le lindane s'accumule dans les tissus riches en lipides. Il provoque chez l'Homme des atteintes hépatiques, rénales, neurologiques, immunologiques et des cancers. L'absorption chronique de lindane perturbe sévèrement la reproduction des Oiseaux mais aussi celle des Mammifères. Pour des doses comprises entre 1 et 40 mg/kg, il perturbe la morphologie testiculaire, diminue la spermatogenèse, inhibe la stéroïdogenèse testiculaire et réduit les concentrations plasmatiques d'androgènes, menaçant ainsi les capacités reproductrices des mâles. Chez la femelle, il retarde la puberté, perturbe le cycle oestral, réduit les taux sériques d'oestrogènes et de progestérone et diminue la réceptivité sexuelle; chez les femelles gravides, il réduit la fertilité et la taille des portées. Ces effets se retrouvent chez un petit nombre d'animaux exposés à des doses résiduelles présentes dans l'environnement. Ces différentes atteintes sont d'autant plus marquées que l'exposition de l'individu se fait à des stades précoces de la vie, durant les phases critiques de différenciation et de développement sexuels. Les mécanismes impliqués font intervenir (i) des altérations des membranes cellulaires des gonades et des gamètes, (ii) des altérations du métabolisme cellulaire (atteinte des échanges calciques et potassiques, altération directe ou par l'intermédiaire de radicaux libres de la stéroïdogenèse, (iii) enfin des atteintes de l'axe hypothalamo-hypophyso-endocrinien qui retentissent sur les performances sexuelles des parents et, plus encore, sur celle de leurs petits exposés in utero ou pendant l'allaitement.
Rotation moléculaire en temps réel dans l'eau liquide [Real-time molecular rotation in water]
- Amir W.
- Lascoux Noëlle
- Gallot Guilhem
- Gale Geoffrey
- Pommeret S.
- Leicknam J.-Ci.
- Bratos S.
Journal de Physique IV Proceedings, EDP Sciences , 2002, 12 (5), pp.381 . La connaissance déjà acquise sur la dynamique de la liaison hydrogène dans l'eau liquide grâce au développement de laser délivrant des impulsions ultra-courtes dans l'infrarouge moyen nous permet de filmer la rotation de molécules HDO dans une solution D2O. L'expérience réalisée au laboratoire est basée sur la technique de spectroscopie pompe sonde résolue en polarisation. L'anisotropie mesurée permet de détecter en temps réel l'angle de déflexion du moment dipolaire de transition dont le point de départ est la direction du faisceau laser de pompe. (10.1051/jp420020200)
DOI : 10.1051/jp420020200
Ultrafast ligand rebinding in the heme domain of the oxygen sensors FixL and Dos: General regulatory implications for heme-based sensors
- Liebl Ursula
- Bouzhir-Sima Latifa
- Négrerie Michel
- Martin Jean-Louis
- Vos Marten H.
Proceedings of the National Academy of Sciences of the United States of America, National Academy of Sciences , 2002, 99 (20), pp.12771 . Heme-based oxygen sensors are part of ligand-specific two-component regulatory systems, which have both a relatively low oxygen affinity and a low oxygen-binding rate. To get insight into the dynamical aspects underlying these features and the ligand specificity of the signal transduction from the heme sensor domain, we used femtosecond spectroscopy to study ligand dynamics in the heme domains of the oxygen sensors FixL from Bradyrhizobium japonicum (FixLH) and Dos from Escherichia coli (DosH). The heme coordination with different ligands and the corresponding ground-state heme spectra of FixLH are similar to myoglobin (Mb). After photodissociation, the excited-state properties and ligand-rebinding kinetics are qualitatively similar for FixLH and Mb for CO and NO as ligands. in contrast to Mb, the transient spectra of FixLH after photodissociation of ligands are distorted compared with the ground-state difference spectra, indicating differences in the heme environment with respect to the unliganded state. This distortion is particularly marked for O-2. Strikingly, heme-O-2 recombination occurs with efficiency unprecedented for heme proteins, in approximate to5 ps for approximate to90% of the dissociated O-2. For DosH-O-2, which shows 60% sequence similarity to FixLH, but where signal detection and transmission presumably are quite different, a similarly fast recombination was found with an even higher yield. Altogether these results indicate that in these sensors the heme pocket acts as a ligand-specific trap. The general implications for the functioning of heme-based ligand sensors are discussed in the light of recent studies on heme-based NO and CO sensors. (10.1073/pnas.192311699)
DOI : 10.1073/pnas.192311699
An alternative flavin-dependent mechanism for thymidylate synthesis
- Myllykallio Hannu
- Lipowski Gérard
- Leduc D
- Filee Jonathan
- Forterre Patrick
- Liebl Ursula
Science, American Association for the Advancement of Science (AAAS) , 2002, 297 (5578), pp.105 . Although deoxythymidylate cannot be provided directly by ribonucleotide reductase, the gene encoding thymidylate synthase ThyA is absent from the genomes of a large number of nonsymbiotic microbes. We show that ThyX (Thy1) proteins of previously unknown function form a large and distinct class of thymidylate synthases. ThyX has a wide but sporadic phylogenetic distribution, almost exclusively limited to microbial genomes lacking thyA. ThyX and ThyA use different reductive mechanisms, because ThyX activity is dependent on reduced flavin nucleotides. Our findings reveal complexity in the evolution of thymidine in present-day DNA. Because ThyX proteins are found in many pathogenic microbes, they present a previously uncharacterized target for antimicrobial compounds. (10.1126/science.1072113)
DOI : 10.1126/science.1072113
Picosecond and nanosecond polychromatic pump-probe studies of bubble growth in carbon-nanotube suspensions
- Vivien L.
- Riehl D.
- Delouis J.-F.
- Delaire J.
- Hache François
- Anglaret E.
Journal of the Optical Society of America B, Optical Society of America , 2002, 19 (2), pp.208-214 . Optical limiting in carbon-nanotube suspensions, whose origin lies in a strong nonlinear scattering due to solvent vapor bubbles and sublimation of the nanotubes, is investigated in the picosecond and nanosecond regimes by polychromatic pump-probe experiments. Samples were pumped either with 532-nm or 1064-nm pulses, and probed from 400 nm to 650 nm. Using a model based on Mie theory, we determine the time evolution of the radius and the concentration of the scattering centers for both temporal regimes. We compare the transmission signals for single-wall carbon nanotubes suspended in water and in chloroform and for multiwall carbon nanotubes in water. Several conclusions can be drawn. First, coalescence of gaseous cavities is more effective in water than in chloroform, leading to nonlinear scattering by a smaller number of larger bubbles. Second, in spite of the smaller size of the scattering centers, the limiting efficiency of chloroform suspensions is better than that of water suspensions, due to a larger volume fraction of the gaseous phase. However, the characteristic times for the growth of laser-induced bubbles are too long to allow efficient limiting of subnanosecond laser pulses. Cop. 2002 Optical Society of America. (10.1364/JOSAB.19.000208)
DOI : 10.1364/JOSAB.19.000208
Optique non-linéaire et chiralité [Nonlinear optics and chirality]
- Schanne-Klein Marie-Claire
- Weisman H.
- Gotzendorfer A.
- Hache François
Journal de Physique IV Proceedings, EDP Sciences , 2002, 12 (5), pp.77 . Nous étudions les propriétés physiques des molécules chirales en étendant les techniques d'optique non-linéaire aux effets chiroptiques pour ainsi mesurer une "activité optique non-linéaire". La génération de second harmonique en surface est particulièrement sensible à la chiralité moléculaire, avec des rotations de polarisation du second harmonique et des différences circulaires et linéaires très importantes. Pour comprendre l'origine physique de ces effets chiroptiques, nous généralisons les principaux modèles microscopiques de chiralité aux effets non-linéaires d'ordre deux et montrons qu'une chiralité à un électron n'a pas la même signature à l'ordre deux qu'une chiralité par couplage excitonique. Des expériences avec des molécules test pour ces deux types de chiralité montrent un bon accord avec ces modélisations théoriques. (10.1051/jp420020099)
DOI : 10.1051/jp420020099
Interactions between heme d and heme b(595) in quinol oxidase bd from Escherichia coli: A photoselection study using femtosecond spectroscopy
- Borisov Vitaly
- Liebl Ursula
- Rappaport F.
- Martin Jean-Louis
- Zhang Jie
- Gennis Robert
- Konstantinov Alexander
- Vos Marten H.
Biochemistry, American Chemical Society , 2002, 41 (5), pp.1654 . Femtosecond spectroscopy was performed on CO-liganded (fully reduced and mixed-valence states) and O-2-liganded quinol oxidase bd from Escherichia coli. Substantial polarization effects, unprecedented for optical studies of heme proteins, were observed in the CO photodissociation spectra, implying interactions between heme d (the chlorin ligand binding site) and the close-lying heme b(595) on the picosecond time scale; this general result is fully consistent with previous work [Vos, M. H., Borisov, V. B., Liebl, U., Martin, J.-L., and Konstantinov, A. A. (2000) Proc. Natl. Acad. Sci. U.S.A. 97, 15541559]. Analysis of the data obtained under isotropic and anisotropic polarization conditions and additional flash photolysis nanosecond experiments on a mutant of cytochrome bd mostly lacking heme b595 allow to attribute the features in the well-known but unusual CO dissociation spectrum of cytochrome bd to individual heme d and heme b595 transitions. This renders it possible to compare the spectra of CO dissociation from reduced and mixed-valence cytochrome bd under static conditions and on a picosecond time scale in much more detail than previously possible. CO binding/dissociation from heme d is shown to perturb ferrous heme b595, causing induction/loss of an absorption band centered at similar to435 nm. In addition, the CO photodissociation-induced absorption changes at 50 ps reveal a bathochromic shift of ferrous heme b595 relative to the static spectrum. No evidence for transient binding of CO to heme b595 after dissociation from heme d is found in the picosecond time range. The yield of CO photodissociation from heme d on a time scale of INFERIEUR 15 ps is found to be diminished more than 3-fold when heme b(595) is oxidized rather than reduced. In contrast to other known heme proteins, molecular oxygen cannot be photodissociated from the mixed-valence cytochrome bd at all, indicating a unique structural and electronic configuration of the diheme active site in the enzyme. (10.1021/bi0158019)
DOI : 10.1021/bi0158019
Picosecond dynamics and mechanisms of photoexcited Cu(II)-5,10,15,20-meso-tetrakis(4-N-methylpyridyl)porphyrin quenching by oxygen-containing Lewis-base solvents
- Chirvony V.
- Martin Jean-Louis
- Négrerie Michel
- Turpin P.-Y.
Journal of Physical Chemistry A, American Chemical Society , 2002, 106 (24), pp.5760 . Deactivation of the lowest excited triplet (pi,pi*) state, (3)(pi,pi*), of the cationic water-soluble Cu(II)-5,10,15,20-meso-tetrakis(4-N-methylpyridyl)porphyrin (CuTMpyP4) was studied by femtosecond transient absorption spectroscopy in three oxygen-containing solvents (Lewis bases) of various polarity, water, methanol, and dimethyl sulfoxide (DMSO). In all of these solvents, the (3)(pi,pi*) state depopulation follows biexponential kinetics. A majority of the (3)(pi,pi*) state population (similar to80%) deactivates very quickly with a time constant of about 1-2 ps to give rise to formation of an exciplex (CuTMpyP4)*-L between the porphyrin in its excited (d,d) state and a solvent molecule, L, the latter playing the role of porphyrin axial ligand. The exciplex lifetime is found to depend on the solvent dielectric constant E and increases from 7 ps in water (epsilon = 78.3) to 27 ps in methanol (epsilon = 32.7), through 23 ps in DMSO (epsilon = 46.5). A minor part of the initial (3)(pi,pi*) state population (similar to20%) deactivates to the ground state, without any detectable intermediate, with time constants of 25, 8, and 11 ps in water, DMSO, and methanol, respectively. These rather fast pathways (picosecond time scale) of excitation deactivation to the ground state are interpreted in terms of quenching influence of some low-lying intramolecular charge-transfer states that belong to four- and five-coordinate CuTMpyP4. A partitioning mechanism of (3)(pi,pi*) state CuTMpyP4 molecules into two populations decaying by different paths, that is, through exciplex formation and "directly" to the ground state, is proposed. (10.1021/jp0134998)
DOI : 10.1021/jp0134998
Application of classical models of chirality to surface second harmonic generation
- Hache François
- Mesnil H.
- Schanne-Klein Marie-Claire
The Journal of Chemical Physics, American Institute of Physics , 2001, 115 (14), pp.6707 . Two classical models (Kuhn and Kauzmann) are extended to calculate the second-order nonlinear response of an isotropic layer of chiral molecules. Calculation of the various nonlinear susceptibilities (electric dipolar, magnetic dipolar, and electric quadrupolar) is performed and applied to the derivation of the second harmonic field radiated by the molecules. It is shown that the two models give strikingly different results about the origin of the chiral response in such experiments. Previously published results are analyzed in view of this calculation which allows to understand the different interpretations proposed. This calculation emphasizes the interest of surface second harmonic generation to access information about the microscopic origin of optical activity in chiral molecules. © 2001 American Institute of Physics. (10.1063/1.1404983)
DOI : 10.1063/1.1404983
Dynamics of nitric oxide in the active site of reduced cytochrome c oxidase aa3
- Vos Marten H.
- Lipowski Gérard
- Lambry Jean-Christophe
- Martin Jean-Louis
- Liebl Ursula
Biochemistry, American Chemical Society , 2001, 40 (26), pp.7806 . Nitric oxide (NO) is involved in the regulation of respiration by acting as a competitive ligand for molecular oxygen at the binuclear active site of cytochrome c oxidase. The dynamics of NO in and near this site are not well understood. We performed flash photolysis studies of NO from heme a3 in cytochrome c oxidase from Paracoccus denitrificans, using femtosecond transient absorption spectroscopy. The formation of the product state--the unliganded heme a3 ground state--occurs in a similar stepwise manner (period approximately 700 fs) as previously observed for carbon monoxide photolysis from this enzyme and interpreted in terms of ballistic ligand motions in the active site on the subpicosecond time scale [Liebl, U., Lipowski, G., Négrerie, M., Lambry, J.-C., Martin, J.-L., and Vos, M. H. (1999) Nature 401, 181-184]. A fraction (approximately 35% at very low NO concentrations) of the dissociated NO recombines with heme a3 in 200-300 ps. The presence of this recombination phase indicates that a transient bond to the second ligand-binding site, a copper atom (CuB), has a short lifetime or may not be formed. Increasing the NO concentration increases the recombination yield on the hundreds of picoseconds time scale. This effect, unprecedented for heme proteins, implies that, apart from the one NO molecule bound to heme a3, a second NO molecule can be accommodated in the active site, even at relatively low (submicromolar) concentrations. Models for NO accommodation in the active site, based on molecular dynamics energy minimizations are presented. Pathways for NO motion and their relevance for the regulation of respiration are discussed. (10.1021/bi010060x)
DOI : 10.1021/bi010060x
Experimental observation of nonlinear circular dichroism in a pump-probe experiment
- Mesnil H.
- Schanne-Klein Marie-Claire
- Hache François
- Alexandre M.
- Lemercier G.
- Andraud Chantal
Chemical Physics Letters, Elsevier , 2001, 338 (4-6), pp.269-276 . We present experimental evidence of nonlinear optical activity in a time-resolved pump-probe experiment carried out in a liquid of chiral molecules. By modulating the polarization of the probe or of the pump, we measure a variation of the circular dichroism (CD) induced by the pump. Application of these techniques to time-resolved spectroscopy of excited molecules is discussed. Cop. 2001 Elsevier Science B.V. (10.1016/S0009-2614(01)00239-1)
DOI : 10.1016/S0009-2614(01)00239-1