Long-lived charge-separated states in bacterial reaction centers isolated from Rhodobacter sphaeroides

AbstractWe studied the accumulation of long-lived charge-separated states in reaction centers isolated from Rhodobacter sphaeroides, using continuous illumination, or trains of single-turnover flashes. We found that under both conditions a long-lived state was produced with a quantum yield of about 1%. This long-lived species resembles the normal P+Q− state in all respects, but has a lifetime of several minutes. Under continuous illumination the long-lived state can be accumulated, leading to close to full conversion of the reaction centers into this state. The lifetime of this accumulated state varies from a few minutes up to more than 20 min, and depends on the illumination history. Surprisingly, the lifetime and quantum yield do not depend on the presence of the secondary quinone, QB. Under oxygen-free conditions the accumulation was reversible, no changes in the normal recombination times were observed due to the intense illumination. The long-lived state is responsible for most of the dark adaptation and hysteresis effects observed in room temperature experiments. A simple method for quinone extraction and reconstitution was developed

Social system of transition society theoretical scheme: economy, culture and ecology interrelations

Changes in transcription factor levels, epigenetic status, splicing kinetics and mRNA degradation can each contribute to changes in the mRNA dynamics of a gene. We present a novel method to identify which of these processes is changed in cells in response to external signals or as a result of a diseased state. The method employs a mathematical model, for which the kinetics of gene regulation, splicing, elongation and mRNA degradation were estimated from experimental data of transcriptional dynamics. The time-dependent dynamics of several species of adipose differentiation-related protein (ADRP) mRNA were measured in response to ligand activation of the transcription factor peroxisome proliferator-activated receptor δ (PPARδ). We validated the method by monitoring the mRNA dynamics upon gene activation in the presence of a splicing inhibitor. Our mathematical model correctly identifies splicing as the inhibitor target, despite the noise in the data

Coherent generation of symmetry-forbidden phonons by light-induced electron-phonon interactions in magnetite

Symmetry breaking across phase transitions often causes changes in selection rules and emergence of optical modes which can be detected via spectroscopic techniques or generated coherently in pump-probe experiments. In second-order or weakly first-order transitions, fluctuations of the order parameter are present above the ordering temperature, giving rise to intriguing precursor phenomena, such as critical opalescence. Here, we demonstrate that in magnetite (Fe$_3$O$_4$) light excitation couples to the critical fluctuations of the charge order and coherently generates structural modes of the ordered phase above the critical temperature of the Verwey transition. Our findings are obtained by detecting coherent oscillations of the optical constants through ultrafast broadband spectroscopy and analyzing their dependence on temperature. To unveil the coupling between the structural modes and the electronic excitations, at the origin of the Verwey transition, we combine our results from pump-probe experiments with spontaneous Raman scattering data and theoretical calculations of both the phonon dispersion curves and the optical constants. Our methodology represents an effective tool to study the real-time dynamics of critical fluctuations across phase transitions

Vibrational Relaxation and Intersystem Crossing of Binuclear Metal Complexes in Solution

The ultrafast vibrational-electronic relaxation upon excitation into the singlet (1)A(2u) (d sigma*-> p sigma) excited state of the d(8)-d(8) binuclear complex [Pt-2(P2O5H2)(4)](4-) has been investigated in different solvents by femtosecond polychromatic fluorescence up-conversion and femtosecond broadband transient absorption (TA) spectroscopy. Both sets of data exhibit clear signatures of vibrational relaxation and wave packet oscillations of the Pt-Pt stretch vibration in the (1)A(2u) state with a period of 224 fs, that decay on a 1-2 ps time scale, and of intersystem crossing (ISC) into the (3)A(2u), state. The vibrational relaxation and ISC times exhibit a pronounced solvent dependence. We also extract from the TA measurements the spectral distribution of the wave packet at a given delay time, which reflects the distribution of Pt-Pt bond distances as a function of time, i.e., the structural dynamics of the system. We clearly establish the vibrational relaxation and coherence decay processes, and we demonstrate that PtPOP represents a clear example of a harmonic oscillator that does not comply with the optical Bloch description due to very efficient coherence transfer between vibronic levels. We conclude that a direct Pt-solvent energy dissipation channel accounts for the vibrational cooling in the singlet state. ISC from the (1)A(2u) to the (3)A(2u) state is induced by spin-vibronic coupling with a higher-lying triplet state and/or (transient) symmetry breaking in the (1)A(2u) excited state. The particular structure, energetics, and symmetry of the molecule play a decisive role in determining the relatively slow rate of ISC, despite the large spin-orbit coupling strength of the Pt atoms

Aqueous Solvation Dynamics at Metal Oxide Surfaces

Broadband transient absorption (TA) spectroscopy, three-pulse photon echo peak shift (3PEPS), and anisotropy decay measurements were used to study the solvation dynamics in bulk water and interfacial water at ZrO2 surfaces, using Eosin Y as a probe. The 3PEPS results show a multiexponential behavior with two subpicosecond components that are similar in bulk and interfacial water, while a third component of several picoseconds is significantly lengthened at the interface. The bandwidth correlation function from TA spectra exhibits the same behavior, and the TA spectra are well reproduced using the doorway-window picture with the time constants from PEPS. Our results suggest that interfacial water is restricted to a thickness of less than 5 angstrom. Also the high-frequency collective dynamics of water does not seem to be affected by the interface. On the other hand, the increase of the third component may point to a slowing down of diffusional motion at the interface, although other effects, may play a role, which are discussed

Clocking the onset of bilayer coherence in a high-Tc{T}_{c} cuprate

In cuprates, a precursor state of superconductivity is speculated to exist above the critical temperature TC. Here we show via a combination of far-infrared ellipsometry and ultrafast broadband optical spectroscopy that signatures of such a state can be obtained via three independent observables in an underdoped sample of NdBa2Cu3O6+δ. The pseudogap correlations were disentangled from the response of laser-broken pairs by clocking their characteristic time scales. The onset of a superconducting precursor state was found at a temperature TONS>TC, consistent with the temperature scale identified via static optical spectroscopy. Furthermore, the temperature evolution of the coherent vibration of the Ba ion, strongly renormalized by the onset of superconductivity, revealed a pronounced anomaly at the same temperature TONS. The microscopic nature of such a precursor state is discussed in terms of preformed pairs and enhanced bilayer coherence

Time-Resolved Visible and Infrared Study of the Cyano Complexes of Myoglobin and of Hemoglobin I from Lucina pectinata

AbstractThe dynamics of the ferric CN complexes of the heme proteins Myoglobin and Hemoglobin I from the clam Lucina pectinata upon Soret band excitation is monitored using infrared and broad band visible pump-probe spectroscopy. The transient response in the UV-vis spectral region does not depend on the heme pocket environment and is very similar to that known for ferrous proteins. The main feature is an instantaneous, broad, short-lived absorption signal that develops into a narrower red-shifted Soret band. Significant transient absorption is also observed in the 360–390nm range. At all probe wavelengths the signal decays to zero with a longest time constant of 3.6ps. The infrared data on MbCN reveal a bleaching of the C≡N stretch vibration of the heme-bound ligand, and the formation of a five-times weaker transient absorption band, 28cm−1 lower in energy, within the time resolution of the experiment. The MbC≡N stretch vibration provides a direct measure for the return of population to the ligated electronic (and vibrational) ground state with a 3–4ps time constant. In addition, the CN-stretch frequency is sensitive to the excitation of low frequency heme modes, and yields independent information about vibrational cooling, which occurs on the same timescale

Biomechanics of cells and tissues: What can we learn when we combine mechanical stimuli with microscopy?

Understanding the mechanical properties of biological tissues can shed light on how those tissues work and why, at times, they lose their functionality. Furthermore, a full characterization of a tissue’s viscoelastic behavior may provide relevant hints for tissue reparation and tissue engineering. To measure these properties in in-vitro or ex-vivo experiments, researchers often make use of indentation instruments, which looks at how a material deforms under the effect of a calibrated mechanical load. In the first part of my talk, I will show how this technique can be used to determine the mechanical properties of brain slices, and I will comment on which kind of information those measurements can provide. I will show, for instance, that different regions of the brain have remarkably different viscoelastic properties, which seem to be correlated with the cell density measured, in a parallel experiment, via fluorescent microscopy. As this example highlights, indentation measurements alone are often not sufficient to understand why certain tissues have certain mechanical properties. Under a (not transparent) surface, biological materials are often inhomogeneous and anisotropic. Because the indentation stress propagates several microns deep into the sample, without a proper imaging tool coupled to the indentation instrument, it is impossible to extract useful information on the mechanics of the material the sample is made of. As a point in case, I will show our latest measurements of the mechanical properties of chick embryos, where, combining indentation with optical coherence tomography (OCT), we could precisely map the stiffness of the spine from head to tail – a measurement that may provide interesting cues in the analysis of somites formation and growth. I will also show how the combination of indentation and OCT might find its way in scar and burn classification, introducing a new instrument for skin characterization that our group has just recently completed. Finally, I will show some preliminary results on the use of multiphoton imaging for tissue mechanics characterization. In this last part of the talk, I will show that it is indeed possible to look at the displacement and deformation of cells in a thin slice of tissue while the tissue is compressed by a calibrated mechanical stroke. This approach may pave the way for a much more thorough analysis of the origin of certain mechanical properties of tissues, where the contribution of the individual cells to the viscoelastic features of the materials can be finally disentangle from that of the extracellular matrix. This project was supported by LASERLABEUROPE under the EC’s Seventh Framework Program (Grant agreement No. 284464), by the European Union’s Seventh Framework Programme (FP/20072013)/ERC grant agreement no. 615170, by the Dutch Technology Foundation (STW) under the OMNE program (13183 and under the iMIT program (P11–13). Declaration of interest: Davide Iannuzzi is founder, shareholder, and advisor of Optics11