Articles

Quantum yield measurements of short-lived photoactivation intermediates in DNA photolyase: Toward a detailed understanding of the triple tryptophan electron transfer chain
- Byrdin Martin
- Lukacs Andras
- Thiagarajan Viruthachalam
- Eker André P.M.
- Brettel Klaus
- Vos Marten H.
Journal of Physical Chemistry A, American Chemical Society , 2010, 114 (9), pp.3207-3214 . The light-dependent DNA repair enzyme photolyase contains a unique evolutionary conserved triple tryptophan electron transfer chain (W382−W359−W306 in photolyase from E. coli) that bridges the 15 Å distance between the buried flavin adenine dinucleotide (FAD) cofactor and the surface of the protein. Upon excitation of the semireduced flavin (FADH°), electron transfer through the chain leads to formation of fully reduced flavin (FADH−; required for DNA repair) and oxidation of the most remote tryptophan residue W306, followed by its deprotonation. The thus-formed tryptophanyl radical W306°+ is reduced either by an extrinsic reductant or by reverse electron transfer from FADH−. Altogether the kinetics of these charge transfer reactions span 10 orders of magnitude, from a few picoseconds to tens of milliseconds. We investigated electron transfer processes in the picosecond−nanosecond time window bridging the time domains covered by ultrafast pump−probe and "classical" continuous probe techniques. Using a recent dedicated setup, we directly show that virtually no absorption change between 300 ps and 10 ns occurs in wild-type photolyase, implying that no charge recombination takes place in this time window. In contrast, W306F mutant photolyase showed a partial absorption recovery with a time constant of 0.85 ns. In wild-type photolyase, the quantum yield of FADH− W306°+ was found at 19 ± 4%, in reference to the established quantum yield of the long-lived excited state of [Ru(bpy)3]2+. With this yield, the optical spectrum of the excited state of FADH° can be constructed from ultrafast spectroscopic data; this spectrum is dominated by excited state absorption extending from below 450 to 850 nm. The new experimental results, taken together with previous data, allow us to propose a detailed kinetic and energetic scheme of the electron transfer chain. (10.1021/jp9093589)
DOI : 10.1021/jp9093589
Nonlinear beam shaper for femtosecond laser pulses, from Gaussian to flat-top profile
- Mercier Brigitte
- Rousseau Jean-Philippe
- Jullien A.
- Antonucci Laura
Optics Communications, Elsevier , 2010, 283 (14), pp.2900 . We present a straightforward method to transform a spatially Gaussian femtosecond laser beam into a flattop shaped beam. The proposed technique takes advantage of a nonlinear phase induced in positive Kerr medium followed by a simple optical system. The variation of the refractive index with the laser intensity creates a phase plate which induces changes in the beam profile after propagation; flat-top and doughnut profiles are observed. The shaping conditions are computed numerically and confirmed experimentally. The method does not introduce energy losses. The device is very simple, self-regulated, flexible and does not need a manufactured phase plate or precise alignment. This method can be useful for light-matter interaction and laser machining. Cop 2010 Elsevier B.V. All rights reserved. (10.1016/j.optcom.2010.04.004)
DOI : 10.1016/j.optcom.2010.04.004
Polarization-resolved Second Harmonic microscopy in anisotropic thick tissues
- Gusachenko Ivan
- Latour Gaël
- Schanne-Klein Marie-Claire
Optics Express, Optical Society of America - OSA Publishing , 2010, 18 (18), pp.19339-19352 . We thoroughly analyze the linear propagation effects that affect polarization-resolved Second Harmonic Generation imaging of thick anisotropic tissues such as collagenous tissues. We develop a theoretical model that fully accounts for birefringence and diattenuation along the excitation propagation, and polarization scrambling upon scattering of the harmonic signal. We obtain an excellent agreement with polarization-resolved SHG images at increasing depth within a rat-tail tendon for both polarizations of the forward SHG signal. Most notably, we observe interference fringes due to birefringence in the SHG depth profile when excited at π/4 angle from the tendon axis. We also measure artifactual decrease of ρ = χxxx/χxyy with depth due to diattenuation of the excitation. We therefore derive a method that proves reliable to determine both ρ and the tendon birefringence and diattenuation. © 2010 Optical Society of America (10.1364/OE.18.019339)
DOI : 10.1364/OE.18.019339
Nitric oxide binds to the proximal heme coordination site of the ferrocytochrome c/cardiolipin complex: Formation mechanism and dynamics
- Silkstone G.
- Kapetanaki Sofia M.
- Husu I.
- Vos Marten H.
- Wilson M.T.
Journal of Biological Chemistry, American Society for Biochemistry and Molecular Biology , 2010, 285 (26), pp.19785 . Mammalian mitochondrial cytochrome c interacts with cardiolipin to form a complex (cyt. c/CL) important in apoptosis. Here we show that this interaction leads to structural changes in ferrocytochrome c that leads to an open coordinate site on the central iron, resulting from the dissociation of the intrinsic methionine residue, where NO can rapidly bind (k = 1.2 x 10(7) m(-1) s(-1)). Accompanying NO binding, the proximal histidine dissociates leaving the heme pentacoordinate, in contrast to the hexacoordinate nitrosyl adducts of native ferrocytochrome c or of the protein in which the coordinating methionine is removed by chemical modification or mutation. We present the results of stopped-flow and photolysis experiments that show that following initial NO binding to the heme, there ensues an unusually complex set of kinetic steps. The spectral changes associated with these kinetic transitions, together with their dependence on NO concentration, have been determined and lead us to conclude that NO binding to cyt. c/CL takes place via an overall scheme comparable to that described for cytochrome c' and guanylate cyclase, the final product being one in which NO resides on the proximal side of the heme. In addition, novel features not observed before in other heme proteins forming pentacoordinate nitrosyl species, include a high yield of NO escape after dissociation, rapid (<1 ms) dissociation of proximal histidine upon NO binding and its very fast binding (60 ps) after NO dissociation, and the formation of a hexacoordinate intermediate. These features all point at a remarkable mobility of the proximal heme environment induced by cardiolipin. (10.1074/jbc.M109.067736)
DOI : 10.1074/jbc.M109.067736
High Up-Conversion Efficiency of YVO4:Yb,Er Nanoparticles in Water down to the Single-Particle Level
- Mialon Genevieve
- Tuerkcan Silvan
- Dantelle Geraldine
- Collins Daniel P.
- Hadjipanayi Maria
- Taylor Robert A.
- Gacoin Thierry
- Alexandrou Antigoni
- Boilot Jean-Pierre
Journal of Physical Chemistry C, American Chemical Society , 2010, 114 (51), pp.22449 . We report up-conversion emission from an aqueous solution of YVO4:Yb3+,Er3+ nanocrystals synthesized by an original method that produces nanoparticles with excellent crystallinity and no porosity. We show that these YVO4:Yb3+,Er3+ nanocrystals are not very sensitive to nonradiative relaxations, leading to a high green-to-red emission ratio of 6.3. Using a comparison with YVO4:Eu3+ particles, we determined the quantum yield of the up-conversion emission of the aqueous YVO4:Yb3+,Er3+ dispersion to be 0.09 +/- 0.04% for an excitation intensity of only 0.55 kW.cm(-2) at 970 nm. Furthermore, single YVO4:Yb,Er particles with an estimated size down to 10 nm can be detected using a wide-field microscope under a 970 nm, 8 kW.cm(-2) excitation. Because of their unexpectedly high up-conversion emission without intermittency, their water dispersibility, and their photostability, YVO4:Yb3+,Er3+ nanoparticles are highly appropriate both for single-biomolecule and for in vivo imaging. (10.1021/jp107900z)
DOI : 10.1021/jp107900z
Imaging by second harmonic generation: the example of pulmonary and renal fibrosis. [Imagerie par génération de seconde harmonique: l'exemple des fibroses pulmonaires et rénales.]
- Schanne-Klein Marie-Claire
Annales de Pathologie, Elsevier Masson , 2010, 30 (5 Suppl 1), pp.56 .
Density of states and vibrational modes of PDMS studied by terahertz time-domain spectroscopy
- Podzorov Alexander
- Gallot Guilhem
Chemical Physics Letters, Elsevier , 2010, 495 (40969), pp.46 . Using time-domain spectroscopy (TDS), we performed high-precision spectroscopic measurements of polydimethylsiloxane (PDMS) in the terahertz domain. We investigated the influence of crosslinking on the terahertz absorption and refractive index, and modeled the data with vibrational density of states and coupling between photons and vibrational modes of the polymer molecules. We also investigated the influence of the temperature on PDMS, and observed the glass transition temperature, as well as the cold crystallization peak and the melting zone. Cop. 2010 Elsevier B.V. All rights reserved. (10.1016/j.cplett.2010.06.050)
DOI : 10.1016/j.cplett.2010.06.050
Dynamic aberration correction for multiharmonic microscopy.
- Olivier Nicolas
- Débarre Delphine
- Beaurepaire Emmanuel
Optics Letters, Optical Society of America - OSA Publishing , 2009, 34 (20), pp.3145-7 . We demonstrate image-based aberration correction in a third-harmonic generation (THG) microscope. We describe a robust, mostly sample-independent correction scheme relying on prior measurement of the influence of aberration modes produced by a deformable mirror on the quality of THG images. We find that using image sharpness as an image quality metric, correction of N aberration modes is achieved using 2(2N+1) measurements in a variety of samples. We also report aberration correction in combined multiharmonic and two-photon excited fluorescence experiments. Finally, we demonstrate time-dependent adaptive THG imaging in developing embryonic tissue.
The crystal structure of ORF14 from Sulfolobus islandicus filamentous virus
- Goulet Adeline
- Spinelli Silvia
- Blangy Stéphanie
- van Tilbeurgh Herman
- Leulliot Nicolas
- Basta Tamara
- Prangishvili David
- Cambillau Christian
- Campanacci Valérie
Proteins - Structure, Function and Bioinformatics, Wiley , 2009, 76 (4), pp.1020-1022 . (10.1002/prot.22448)
DOI : 10.1002/prot.22448
Multiplexed two-photon microscopy of dynamic biological samples with shaped broadband pulses.
- Pillai Rajesh S.
- Boudoux Caroline
- Labroille Guillaume
- Olivier Nicolas
- Veilleux Israel
- Farge Emmanuel
- Joffre Manuel
- Beaurepaire Emmanuel
Optics Express, Optical Society of America - OSA Publishing , 2009, 17 (15), pp.12741-52 . Coherent control can be used to selectively enhance or cancel concurrent multiphoton processes, and has been suggested as a means to achieve nonlinear microscopy of multiple signals. Here we report multiplexed two-photon imaging in vivo with fast pixel rates and micrometer resolution. We control broadband laser pulses with a shaping scheme combining diffraction on an optically-addressed spatial light modulator and a scanning mirror allowing to switch between programmable shapes at kiloHertz rates. Using coherent control of the two-photon excited fluorescence, it was possible to perform selective microscopy of GFP and endogenous fluorescence in developing Drosophila embryos. This study establishes that broadband pulse shaping is a viable means for achieving multiplexed nonlinear imaging of biological tissues. (10.1364/OE.17.012741)
DOI : 10.1364/OE.17.012741
Structure and function of a novel endonuclease acting on branched DNA substrates.
- Ren Bin
- Kühn Joelle
- Meslet-Cladiere Laurence
- Briffotaux Julien
- Norais Cedric
- Lavigne Regis
- Flament Didier
- Ladenstein Rudolf
- Myllykallio Hannu
EMBO Journal, EMBO Press , 2009, 28 (16), pp.2479-89 . We show that Pyrococcus abyssi PAB2263 (dubbed NucS (nuclease for ss DNA) is a novel archaeal endonuclease that interacts with the replication clamp PCNA. Structural determination of P. abyssi NucS revealed a two-domain dumbbell-like structure that in overall does not resemble any known protein structure. Biochemical and structural studies indicate that NucS orthologues use a non-catalytic ssDNA-binding domain to regulate the cleavage activity at another site, thus resulting into the specific cleavage at double-stranded DNA (dsDNA)/ssDNA junctions on branched DNA substrates. Both 3' and 5' extremities of the ssDNA can be cleaved at the nuclease channel that is too narrow to accommodate duplex DNA. Altogether, our data suggest that NucS proteins constitute a new family of structure-specific DNA endonucleases that are widely distributed in archaea and in bacteria, including Mycobacterium tuberculosis. (10.1038/emboj.2009.192)
DOI : 10.1038/emboj.2009.192
The thermo- and acido-stable ORF-99 from the archaeal virus AFV1
- Goulet Adeline
- Spinelli Silvia
- Blangy Stéphanie
- van Tilbeurgh Herman
- Leulliot Nicolas
- Basta Tamara
- Prangishvili David
- Cambillau Christian
- Campanacci Valérie
Protein Science, Wiley , 2009, 18 (6), pp.1316-1320 . (10.1002/pro.122)
DOI : 10.1002/pro.122
Two-photon microscopy with simultaneous standard and extended depth of field using a tunable acoustic gradient-index lens.
- Olivier Nicolas
- Mermillod-Blondin Alexandre
- Arnold Craig B.
- Beaurepaire Emmanuel
Optics Letters, Optical Society of America - OSA Publishing , 2009, 34 (11), pp.1684-1686 . We describe a simple setup that allows depth of field switching at kilohertz rates in a nonlinear microscope. Beam profile and/or divergence are modulated using a tunable, acoustically driven gradient-index fluid lens. We demonstrate two modulation strategies, one based on fast varifocus scanning during each pixel and the other based on pseudo-Bessel beam excitation. Average beam shape is switched every line during scanning, resulting in the interlaced acquisition of two different images. We apply this approach to the simultaneous standard and 4.5x-extended depth-of-field imaging of developing embryos. © 2009 Optical Society of America (10.1364/OL.34.001684)
DOI : 10.1364/OL.34.001684
HIV-1 IN alternative molecular recognition of DNA induced by raltegravir resistance mutations
- Mouscadet J.-F.
- Arora Rakesh
- André J.
- Lambry Jean-Christophe
- Delelis O.
- Malet I.
- Marcelin A.-G.
- Calvez V.
- Tchertanov L.
Journal of Molecular Recognition, Wiley , 2009, 22 (6), pp.480-494 . Virologic failure during treatment with raltegravir, the first effective drug targeting HIV integrase, is associated with two exclusive pathways involving either Q148H/R/K, G140S/A or N155H mutations. We carried out a detailed analysis of the molecular and structural effects of these mutations. We observed no topological change in the integrase core domain, with conservation of a newly identified V-shaped hairpin containing the Q148 residue, in particular. In contrast, the mutations greatly altered the specificity of DNA recognition by integrase. The native residues displayed a clear preference for adenine, whereas the mutant residues strongly favored pyrimidines. Raltegravir may bind to N155 and/or Q148 residues as an adenine bioisoster. This may account for the selected mutations impairing raltegravir binding while allowing alternative DNA recognition by integrase. This study opens up new opportunities for the design of integrase inhibitors active against raltegravir-resistant viruses. Copyright Cop. 2009 John Wiley and Sons, Ltd. Supporting information may be found in the online version of this article. (10.1002/jmr.970)
DOI : 10.1002/jmr.970
Unobtrusive interferometer tracking by path length oscillation for multidimensional spectroscopy
- Lee Kevin F.
- Bonvalet Adeline
- Nuernberger Patrick
- Joffre Manuel
Optics Express, Optical Society of America - OSA Publishing , 2009, 17 (15), pp.12379-12384 . We track the path difference between interferometer arms with few-nanometer accuracy without adding optics to the beam path. We measure the interference of a helium-neon beam that copropagates through the interferometer with midinfrared pulses used for multidimensional spectroscopy. This can indicate motion, but not direction. By oscillating the path length of one arm with a mirror on a piezoelectric stack and monitoring the oscillations of the recombined helium-neon beam, the direction can be calculated, and the path delay can be continuously tracked. © 2009 Optical Society of America. (10.1364/OE.17.012379)
DOI : 10.1364/OE.17.012379
Apports récents des techniques de quantification de la fibrose pour l'examen anatomopathologique en transplantation rénale
- Servais A.
- Meas-Yedid V.
- Morelon E.
- Strupler Mathias
- Schanne-Klein Marie-Claire
- Legendre C.
- Olivo-Marin J.-C.
- Thervet É.
Médecine/Sciences, EDP Sciences , 2009, 25 (11), pp.945-950 . La néphropathie chronique d'allogreffe constitue la cause principale de perte des greffons rénaux à long terme. Elle peut être détectée précocement par des biopsies de dépistage effectuées de manière systématique. La classification usuelle, semi-quantitative, souffre d'une mauvaise reproductibilité. Diverses méthodes morphométriques ont donc été développées pour quantifier la fibrose interstitielle qui caractérise cette néphropathie. Certaines utilisent la coloration spécifique par le rouge Sirius. L'analyse d'image couleur par segmentation permet une quantification automatique, rapide et robuste de la fibrose interstitielle. Elle utilise une segmentation couleur associée à une analyse de couleur, de localisation spatiale et de forme sur des biopsies colorées au trichrome de Masson. À l'avenir, l'étude des collagènes fibrillaires par la génération de second harmonique pourrait permettre une approche spécifique des composants de la fibrose. (10.1051/medsci/20092511945)
DOI : 10.1051/medsci/20092511945
Picosecond Transient Circular Dichroism of the Photoreceptor Protein of the Light-Adapted Form of Blepharisma Japonicum
- Hache François
- Khuc Mai-Thu
- Brazard Johanna
- Plaza Pascal
- Martin Monique M.
- Checcucci Giovanni
- Lenci Francesco
Chemical Physics Letters, Elsevier , 2009, 483, pp.133 . We present a picosecond transient circular dichroism study of OBIP, the putative photoreceptor protein involved in the photophobic response of Blepharisma Japonicum. The probe wavelength was chosen at 230 nm. The results are compared to those of the isolated chromophore, OxyBP, in solution. The CD changes in OBIP and OxyBP do not show the same dynamics: OBIP's signal relaxes in a few ps whereas no such decay is obtained for OxyBP. This observation brings support to the formerly evoked existence of a fast photoinduced reaction in the chromoprotein, and demonstrates the implication of local geometrical changes that accompany this process. (10.1016/j.cplett.2009.10.059)
DOI : 10.1016/j.cplett.2009.10.059
Erratum to : Application of time-resolved circular dichroism to the study of conformational changes in photochemical and photobiological processes
- Hache François
Journal of Photochemistry and Photobiology A: Chemistry, Elsevier , 2009, 205 (1), pp.77 . (10.1016/j.jphotochem.2009.05.017)
DOI : 10.1016/j.jphotochem.2009.05.017
Interaction of carbon monoxide with the apoptosis-inducing cytochrome c-cardiolipin complex
- Kapetanaki Sofia M.
- Silkstone G.
- Husu I.
- Liebl Ursula
- Wilson M.T.
- Vos Marten H.
Biochemistry, American Chemical Society , 2009, 48 (7), pp.1613 . The interaction of mitochondrial cytochrome (cyt) c with cardiolipin (CL) is involved in the initial stages of apoptosis. This interaction can lead to destabilization of the heme−Met80 bond and peroxidase activity [Basova, L. V., et al. (2007) Biochemistry 46, 3423−3434]. We show that under these conditions carbon monoxide (CO) binds to cyt c, with very high affinity (5 × 107 M−1), in contrast to the native cyt c protein involved in respiratory electron shuttling that does not bind CO. Binding of CO to the cyt c−CL complex inhibits its peroxidase activity. Photodissociated CO from the cyt c−CL complex shows <20% picosecond geminate rebinding and predominantly bimolecular rebinding, with a second-order rate constant of 107 M−1 s−1, an order of magnitude higher than in myoglobin. These findings contrast with those of Met80X mutant cyt c, where picosecond geminate recombination dominates due to the rigidity of the protein. Our data imply that CL leads to substantial changes in protein conformation and flexibility, allowing access of ligands to the heme. Together with the findings that (a) 30 CL per cyt c are required for full CO binding and (b) salt-induced dissociation indicates that the two negative headgroup charges interact with 5 positive surface charges of the protein, these results are consistent with a CL anchorage model with an acyl chain impaled in the protein [Kalanxhi, E., and Wallace, C. J. A. (2007) Biochem. J. 407, 179−187]. The affinity of CO for the complex is high enough to envisage an antiapoptotic effect of nanomolar CO concentrations via inhibition of the cyt c peroxidase activity. (10.1021/bi801817v)
DOI : 10.1021/bi801817v
New insights into size effects in luminescent oxide nanocrystals
- Mialon G.
- Türkcan Silvan
- Alexandrou Antigoni
- Gacoin Thierry
- Boilot Jean-Pierre
Journal of Physical Chemistry C, American Chemical Society , 2009, 113 (43), pp.18699 . We here investigate the emission properties of rare-earth-doped oxide nanoparticles with the aim to understand the commonly observed altered properties of nanoparticles as compared to the bulk counterparts. This is usually attributed to the detrimental effect of surface states that quench the excited states involved in the emission process. We study the influence of crystalline defects that are present due to the low temperature of the synthesis of 30 nm sized YVO4/Eu nanoparticles. Annealing treatments up to 1000 °C in a porous silica matrix allow the recovery of perfectly crystalline particles as colloidal suspensions and compare their properties to those of the pristine particles obtained by conventional colloid chemistry. Emission properties of pristine and annealed particles are compared with those of the bulk material. A simple model of the emission process allows an accurate fit of the luminescence decay and of the dependence of the quantum yield on europium content. Our results show that pristine particles exhibit altered emission properties mainly due to quenching from defects, among which are surface OH groups, and altered energy transfers within the particle. Annealed particles exhibit properties that are almost the same as those of the bulk material, except that the emission yield for the optimum Eu content is limited to 40 instead of 70% for the bulk material. We show that the difference may be simply explained by the difference of the radiative lifetime that results from the lower effective refractive index in the case of the particles. This effect then seems to be the ultimate limitation for the emission properties of perfectly well-crystallized nanoparticles as compared to those of the bulk material. This work provides an example of a general strategy toward the investigation of the physical properties of nanocrystals which may be altered by crystalline defects. Cop. 2009 American Chemical Society. (10.1021/jp907176x)
DOI : 10.1021/jp907176x
NO formation by neuronal NO-synthase can be controlled by ultrafast electron injection from a nanotrigger
- Beaumont Edward
- Lambry Jean-Christophe
- Blanchard-Desce M.
- Martasek P.
- Panda S.P.
- van Faassen E.E.H.
- Brochon J.-C.
- Deprez E.
- Slama-Schwok Anny
ChemBioChem, Wiley-VCH Verlag , 2009, 10 (4), pp.690 . Nitric oxide synthases (NOSs) are unique flavohemoproteins with various roles in mammalian physiology. Constitutive NOS catalysis is initiated by fast hydride transfer from NADPH, followed by slower structural rearrangements. We used a photoactive nanotrigger (NT) to study the initial electron transfer to FAD in native neuronal NOS (nNOS) catalysis. Molecular modeling and fluorescence spectroscopy showed that selective NT binding to NADPH sites close to FAD is able to override Phe1395 regulation. Ultrafast injection of electrons into the protein electron pathway by NT photoactivation through the use of a femtosecond laser pulse is thus possible. We show that calmodulin, required for NO synthesis by constitutive NOS, strongly promotes intramolecular electron flow (6.2-fold stimulation) by a mechanism involving proton transfer to the reduced FADb site. Site-directed mutagenesis using the S1176A and S1176T mutants of nNOS supports this hypothesis. The NT synchronized the initiation of flavoenzyme catalysis, leading to the formation of NO, as detected by EPR. This NT is thus promising for time-resolved X-ray and other cellular applications. Cop. 2009 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim. (10.1002/cbic.200800721)
DOI : 10.1002/cbic.200800721
Measurement of the Second-Order Hyperpolarizability of the Collagen Triple Helix and Determination of Its Physical Origin
- Deniset-Besseau Ariane
- Duboisset Julien
- Benichou Emmanuel
- Hache François
- Brevet Pierre-Francois
- Schanne-Klein Marie-Claire
Journal of Physical Chemistry B, American Chemical Society , 2009, 113 (40), pp.13437-13445 . We performed Hyper-Rayleigh Scattering (HRS) experiments to measure the second-order nonlinear optical response of the collagen triple helix and determine the physical origin of second harmonic signals observed in collagenous tissues. HRS experiments yielded a second-order hyperpolarizability of 1.25 x 10(-27) esu for rat-tail type I collagen, a Surprisingly large value considering that collagen presents no strong harmonophore in its amino acid sequence. Polarization-resolved experiments showed intramolecular coherent contributions to the HRS signal along with incoherent contributions that are the only contributions for molecules with dimensions much smaller than the excitation wavelength. We therefore modeled the effective second-order hyperpolarizability of the 290 nm long collagen triple helix by summing coherently the nonlinear response of well-aligned moieties along the triple helix axis. This model was confirmed by HRS measurements after denaturation of the collagen triple helix and for a collagen-like short model peptide [(Pro-Pro-Gly)(10)](3). We concluded that the large collagen nonlinear response originates in the tight alignment of a large number of small and weakly efficient harmonophores, presumably the peptide bonds, resulting in a coherent amplification of the nonlinear signal. (10.1021/jp9046837)
DOI : 10.1021/jp9046837
Single europium-doped nanoparticles measure temporal pattern of reactive oxygen species production inside cells
- Casanova Didier
- Bouzigues Cédric
- Nguyên Thanh-Liêm
- Ramodiharilafy Rivo O.
- Bouzhir-Sima Latifa
- Gacoin Thierry
- Boilot Jean-Pierre
- Tharaux Pierre-Louis
- Alexandrou Antigoni
Nature Nanotechnology, Nature Publishing Group , 2009, 4 (9), pp.581 . Low concentrations of reactive oxygen species, notably hydrogen peroxide (H 2 O 2), mediate various signalling processes in the cell. Production of these signals is highly regulated and a suitable probe is needed to measure these events. Here, we show that a probe based on a single nanoparticle can quantitatively measure transient H 2 O 2 generation in living cells. The Y 0.6 Eu 0.4 VO 4 nanoparticles undergo photoreduction under laser irradiation but re-oxidize in the presence of oxidants, leading to a recovery in luminescence. Our probe can be regenerated and reliably detects intracellular H 2 O 2 with a 30-s temporal resolution and a dynamic range of 1-45?M. The differences in the timing of intracellular H 2 O 2 production triggered by different signals were also measured using these nanoparticles. Although the probe is not selective towards H 2 O 2, in many signalling processes H 2 O 2 is, however, the dominant oxidant. In conjunction with appropriate controls, this probe is a powerful tool for unravelling pathways that involve reactive oxygen species. Cop. 2009 Macmillan Publishers Limited. All rights reserved. (10.1038/nnano.2009.200)
DOI : 10.1038/nnano.2009.200
Inferring maps of forces inside cell membrane microdomains
- Masson J.-B.
- Casanova Didier
- Türkcan Silvan
- Voisinne G.
- Popoff Michel
- Vergassola M.
- Alexandrou Antigoni
Physical Review Letters, American Physical Society , 2009, 102 (4), pp.48103 . Mapping of the forces on biomolecules in cell membranes has spurred the development of effective labels, e.g., organic fluorophores and nanoparticles, to track trajectories of single biomolecules. Standard methods use particular statistics, namely the mean square displacement, to analyze the underlying dynamics. Here, we introduce general inference methods to fully exploit information in the experimental trajectories, providing sharp estimates of the forces and the diffusion coefficients in membrane microdomains. Rapid and reliable convergence of the inference scheme is demonstrated on trajectories generated numerically. The method is then applied to infer forces and potentials acting on the receptor of the toxin labeled by lanthanide-ion nanoparticles. Our scheme is applicable to any labeled biomolecule and results show its general relevance for membrane compartmentation. Cop. 2009 The American Physical Society. (10.1103/PhysRevLett.102.048103)
DOI : 10.1103/PhysRevLett.102.048103
Femtosecond spectroscopy from the perspective of a global multidimensional response function
- Nuernberger Patrick
- Lee Kevin F.
- Joffre Manuel
Accounts of Chemical Research, American Chemical Society , 2009, 42 (9), pp.1433-1441 . At the microscopic level, multidimensional response functions, such as the nonlinear optical susceptibility or the time-ordered response function, are commonly used tools in nonlinear optical spectroscopy for determining the nonlinear polarization resulting from an arbitrary excitation. In this Account, we point out that the approach successfully developed for the nonlinear polarization can also be used in the case of a directly observable macroscopic quantity. This observable can be, for example, the electric field radiated in a nonlinear mixing experiment, the rate of fluorescence resulting from one- or two-photon absorption, or the rate of a photochemical reaction. For each of these physical processes, perturbation theory can be used to expand the measured quantity in a power series of the exciting field, and an appropriate global response function can be introduced for each order of perturbation. At order n, the multidimensional response function will depend on n variables (either time or frequency) and have the same general properties as the nonlinear susceptibility resulting, for example, from time invariance or causality. The global response function is introduced in this Account in close analogy with the nonlinear susceptibility or the time-ordered microscopic response. We discuss various applications of the global response function formalism. For example, it can be shown that in the weak field limit, a stationary signal induced in a time-invariant system is independent of the spectral phase of the exciting field. Although this result had been demonstrated previously, the global response function enables its derivation in a more general way because no specific microscopic model is needed. Multidimensional spectroscopy is obviously ideally suited to measure the global multidimensional response function. It is shown that the second (or third)-order response can be exactly measured with 2D (or 3D) spectroscopy by taking into account the exact shape of the exciting pulses. In the case of a 2D measurement of the third-order response, a particular projection of the complete 3D response function is actually measured. This projection can be related to a mixed time and frequency representation of the response function when the pulses are assumed to be infinitely short. We thus show that the global response function is a useful tool for deriving general results and that it should help in designing future experimental schemes for femtosecond spectroscopy. Cop. 2009 American Chemical Society. (10.1021/ar900001w)
DOI : 10.1021/ar900001w