Laboratoire d'optique et biosciences
Laboratoire d'optique et biosciences
Laboratoire d'optique et biosciences

Articles

  • 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
  • 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
  • Cardiotoxicité du lindane, un isomère gamma de l'hexachlorocyclohexane [Cardiotoxicity of lindane, a gamma isomer of hexachlorocyclohexane ]
    • Sauviat Martin-Pierre
    • Pages Nicole
    Journal de la Société de Biologie , 2002, 196 (4), pp.339 . The goal of the present review is to collect information concerning membrane effects induced by lindane intoxication, a y isomer of hexachiorocyclohexane (gamma-HCH) that has been largely used as an insecticide and disinfectant in agriculture and entered also in the composition of some lotions, creams and shampoos used against parasites (lice and scabies). Absorbed through respiratory, digestive or transcutaneous pathways, lindane accumulates within lipid rich tissues. Lindane accumulation depends on the duration of the exposure and affects tissues in the following order: adipose tissues > brain > kidney > muscle > lungs > heart > liver > blood. Whatever the mode of lindane absorption, it accumulates in blood and is distributed throughout the body. It may affect human health by exerting systemic, immunologic, teratogenic, and/or cancerogenic effects. The symptoms of lindane intoxication are different according to the mode of intoxication, acute or chronic. The absorption of high doses of gamma-HCH is particularly toxic for the central nervous system and for the female and male reproduction apparatus in mammals where lindane is considered as an endocrine disruptor. Lindane is highly lipophilic and incorporates into biological membranes according to the following sequence: mitochondria > sarcoplasmic reticulum > myelin > brain microsomes > erythrocytes. Lindane exerts a stimulating action on synaptic transmission and inhibits the chloride current activated by gamma-amino butyric acid (GABA) of many muscular and nervous preparations by interacting with the receptors GABA-chloride channel complex. It seems to affect calcium homeostasis of many tissues. The similarity between lindane and inositol (1, 4, 5) phosphate (IP3) suggested that lindane releases Ca2+ from IP3-sensitive intracellular stores in macrophages and myometrial cells. Ca2+ release from reticulum endoplasmic, mitochondria and other Ca2+ stores has been reported in cat kidney cells. Lindane altered energetic metabolism of hepatic mitochondria and the inositol-phosphate synthesis in neuronal cells. However, lindane does not compete with the IP3 receptor. Lindane produces a Ca2+ influx in mice peritoneal macrophage cells responsible for the Ca2+ induced Ca2+ release produced by phospholipase C via IP3 pathway and resulting in a maintained increase of the free cytosolic Ca2+ concentration. Lindane decreased the membrane erythrocyte and cerebral cell concentration of phosphatidyl inositol PI, PIP and PIP2 in rats repetitively exposed to lindane for 3 or 6 months. Lindane induces oxidative stress; it modifies the activity of the scavenger enzymes. This effect is involved in the inhibition of intercellular gap junctions. Modifications of the electrocardiogram (ECG), sinusal rhythm alteration and negative and dysphasic variations of T wave, similar to those produced by hyperkaliemia, have been reported after lindane absorption. During acute lindane poisoning, the activities of serum transaminases (SGOT, SGTP), and lactate deshydrogenase (LDH) increase. Lindane produces histological alterations of cardiac tissues and a cardio-vascular dystrophy (contracture, degenerescence and necrosis) mainly in the left ventricular wall and a hypertrophy of the left ventricle. Chronic application of residual doses of lindane shortened the action potential duration in rat papillary muscle. These effects were similar to those induced by hyperthyroidism. Lindane increases the triiodothyronine (T3) serum level in hyperthyroid rats. T3 plays an important role in the postnatal development of the rat ventricle by increasing the density of potassium channels which contribute to action potential shortening during the development. Thyroid hormones influence the regulation and the expression of messengers ARN which encode different potassium channels involved in action potential repolarization (Kvl.2; Kvl.4; Kvl.5; Kv2.1; Kv4; HCN2). The thyrotropine-releasing hormone (TRH) modulates the HERG-type rapid delayed potassium channel (IKr) encoded by the human gene ether-a-go-go in rat anterior pituitary cells GH3/B6. This channel is involved in the cardiac long QT syndrome. TRH modifies the current kinetics of human HERG potassium channel co-expressed in Xenopus oocytes with the TRH receptor, whose activity is modulated via the protein kinase C pathway linked to a G protein-coupled receptor and is regulated by changes in the PIP2 concentration in the membrane. IKr channels regulation is also dependent on sexual hormones. In conclusion, lindane affects the excitable membranes and the cardio circulatory system. These alterations (may) represent a potential risk for human health.
  • 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
  • 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
  • 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
  • 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.
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • Coherent broadband pulse shaping in the mid infrared
    • Belabas Nadia
    • Likforman Jean-Pierre
    • Canioni Lionel
    • Bousquet Bruno
    • Joffre Manuel
    Optics Letters, Optical Society of America - OSA Publishing , 2001, 26 (10), pp.743 . We demonstrate broadband infrared pulse shaping by difference-frequency mixing of two visible phase-locked linearly chirped pulses in GaAs. Control of the temporal profile of the emitted field is achieved through this direct tailoring of the exciting visible intensity. The results are in agreement with a simulation with no adjustable parameter. (C) 2001 Optical Society of America. (10.1364/OL.26.000743)
    DOI : 10.1364/OL.26.000743
  • Magnetic chiroptical effects in surface second harmonic reflection
    • Schanne-Klein Marie-Claire
    • Hache François
    • Brotin Thierry
    • Andraud Chantal
    • Collet A.
    Chemical Physics Letters, Elsevier , 2001, 338 (2-3), pp.159-166 . We perform surface second harmonic reflection (SHR) to study a chiral stilbene. It exhibits a strong circular intensity difference in the second harmonic signal, but no linear intensity difference and no rotation of polarization. This SHR optical activity is characteristic of strong magnetic effects and proves that the molecule under study exhibits a one-electron chirality. (C) 2001 Elsevier Science B.V. All rights reserved. (10.1016/S0009-2614(01)00275-5)
    DOI : 10.1016/S0009-2614(01)00275-5
  • Alterations of transmembrane currents in frog atrial heart muscle induced by photoexcited gymnochrome a purified from the crinoid, Gymnochrinus richeri
    • Sauviat Martin-Pierre
    • Benoit Anne-Gaëlle
    • Debitus Cécile
    • Pouny I.
    • Laurent Dominique
    Photochemistry and Photobiology, Blackwell Wiley [1962-....] , 2001, 74 (2), pp.115-119 . The effects of gymnochrome A were tested on the electrical activity of the frog atrial heart muscle. Gymnochrome A (1-5 µM) did not alter the resting potential. Gymnochrome A (5 µM) slowed the initial depolarizing phase of the spontaneously beating action potential. Under voltage-clamp conditions gymnochrome A (5 µM) did not affect the electrical constant of the membrane and the kinetic parameters of the peak Na+ current (INa) recorded in the Ringer solution containing tetraethylammonium (2 mM) and Cd2+ (1 mM) but shifted the membrane potential at which the current both activated and reached its maximal value toward more negative membrane potentials. It did not alter the reversal potential for INa, indicating that the selectivity of the Na+ channels had not changed. These observations suggest that gymnochrome A binds to the membrane and shifts the activation of INa on the voltage axis by modifying the free negative fixed charges present at the membrane surface rather than by occupying a specific site on the Na+ channel. Photoexcited gymnochrome A transiently triggered an early outward current which lengthened the time-to-peak of INa and decreased its amplitude. In addition, photoexcited gymnochrome A blocked the background K+ current. This is, to our knowledge, the first time that such effects are reported on the cardiac muscle. These observations suggest that the photoexcitation of gymnochrome produces physico-chemical effects which lead to intracellular changes. Further experiments are required to determine their nature. (10.1562/0031-8655(2001)0740115AOTCIF2.0.CO2)
    DOI : 10.1562/0031-8655(2001)0740115AOTCIF2.0.CO2
  • 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
  • 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
  • Control of Nitric Oxide Dynamics by Guanylate Cyclase in Its Activated State
    • Négrerie Michel
    • Bouzhir Latifa
    • Martin Jean-Louis
    • Liebl Ursula
    Journal of Biological Chemistry, American Society for Biochemistry and Molecular Biology , 2001, 276 (50), pp.46815 . Soluble guanylate cyclase (sGC) is the target of nitric oxide (NO) released by nitric-oxide synthase in endothelial cells, inducing an increase of cGMP synthesis in response. This heterodimeric protein possesses a regulatory subunit carrying a heme where NO binding occurs, while the second subunit harbors the catalytic site. The binding of NO and the subsequent breaking of the bond between the proximal histidine and the heme-Fe2+ are assumed to induce conformational changes, which are the origin of the catalytic activation. At the molecular level, the activation and deactivation mechanisms are unknown, as is the dynamics of NO once in the heme pocket. Using ultrafast time-resolved absorption spectroscopy, we measured the kinetics of NO rebinding to sGC after photodissociation. The main spectral transient in the Soret band does not match the equilibrium difference spectrum of NO-liganded minus unliganded sGC, and the geminate rebinding was found to be monoexponential and ultrafast (t = 7.5 ps), with a relative amplitude close to unity (0.97). These characteristics, so far not observed in other hemoproteins, indicate that NO encounters a high energy barrier for escaping from the heme pocket once the His-Fe2+ bond has been cleaved; this bond does not reform before NO recombination. The deactivation of isolated sGC cannot occur by only simple diffusion of NO from the heme; therefore, several allosteric states may be inferred, including a desensitized one, to induce NO release. Thus, besides the structural change leading to activation, a consequence of the decoupling of the proximal histidine may also be to induce a change of the heme pocket distal geometry, which raises the energy barrier for NO escape, optimizing the efficiency of NO trapping. The nonsingle exponential character of the NO picosecond rebinding coexists only with the presence of the protein structure surrounding the heme, and the single exponential rate observed in sGC is very likely to be due to a closed conformation of the heme pocket. Our results emphasize the physiological importance of NO geminate recombination in hemoproteins like nitric-oxide synthase and sGC and show that the protein structure controls NO dynamics in a manner adapted to their function. This control of ligand dynamics provides a regulation at molecular level in the function of these enzymes. (10.1074/jbc.M102224200)
    DOI : 10.1074/jbc.M102224200
  • Stimulated scattering and its dynamics in semiconductor microcavities at 80 K under nonresonant excitation conditions
    • Alexandrou Antigoni
    • Bianchi G.
    • Peronne Emmanuel
    • Hallé B.
    • Boeuf F.
    • André R.
    • Romestain R.
    • Dang Le Si
    Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society , 2001, 64 (23), pp.2333181 . We have observed stimulated scattering in a II-VI microcavity at 80 K under nonresonant excitation conditions. This stimulated scattering manifests itself through probe amplification in a pump-probe reflectivity experiment and through a highly nonlinear emission at an energy corresponding to a k? ? 0 state on the lower polariton branch. We were able to follow the onset and decline of stimulated scattering by measuring the temporal evolution of the probe amplification. (10.1103/PhysRevB.64.233318)
    DOI : 10.1103/PhysRevB.64.233318