Nouvelles technologies de l’information et de la communication et anciens instruments de régulation : l’exemple d’Internet en France

L’étude de la jurisprudence française relative à Internet entre 1996 et 1997 montre que, loin d’être un « espace de non-droit », le réseau des réseaux est assujetti au respect de règles juridiques. Ainsi, l’exemple de l’exercice de la liberté d’expression met en exergue que le droit français peut s’appliquer à Internet comme à tout autre vecteur de communication, même si l’édifice jurisprudentiel paraît encore fragile. Quant aux droits intellectuels, le juge français, s’il doit respecter les textes applicables, doit également tenir compte de l’esprit libéral du réseau.A study of the case law regarding French language use on the Internet during 1996 and 1997 demonstrates that, far from being a non-legal issue, the network requires juridical boundaries. For example, the exercise of freedom of expression highlights the fact that French law can be applied to the Internet as it does to other vehicles of communication, regardless of the continuing ambiguity surrounding legal provision in this area. As to intellectual rights, in the French context, a judge is obliged to respect existing legal texts as well as the liberal spirit of the network

Ultrafast excited state deactivation and energy transfer in guanine-cytosine DNA double helices

International audienceThe stability of DNA components with respect to UV radiation is considered to be a prerequisite for the development of the genetic code. But it is also known that UV light absorbed by DNA bases may damage the double helix and lead to carcinogenic mutations.1 The interplay between stability and photodamage depends on the way that the energy of a UV photon is distributed among the electronic excited states of the double helix before it is eliminated as heat. Ultrafast dissipation of the excitation energy is indeed a common property of all the monomeric DNA building blocks: the major part of the excited state population of nucleosides and nucleotides in aqueous solution lives for less than one picosecond.2,3 When applied to double helices, composed exclusively of adenine-thymine base pairs (A-T duplexes, both homopolymeric and alternating), femtosecond spectroscopy reveals a different picture: organization of the bases within duplexes causes an overall lengthening of the excited state lifetimes.4-9 This is due to the emergence of new excited states, shared between at least two bases. The existence of delocalized excited states allows ultrafast energy transfer to occur5,8-10 by-passing the prerequisites of Förster transfer which are not fulfilled in the case of DNA bases

Excited-state dynamics of dGMP measured by steady-state and femtosecond fluorescence spectroscopy.

International audienceThe room-temperature fluorescence of 2'-deoxyguanosine 5'-monophosphate (dGMP) in aqueous solution is studied by steady-state and time-resolved fluorescence spectroscopy. The steady-state fluorescence spectrum of dGMP shows one band centered at 334 nm but has an extraordinary long red tail, extending beyond 700 nm. Both the fluorescence quantum yield and the relative weight of the 334 nm peak increase with the excitation wavelength. The initial fluorescence anisotropy after excitation at 267 nm is lower than 0.2 for all emission wavelengths, indicating an ultrafast S(2) --> S(1) internal conversion. The fluorescence decays depend strongly on the emission wavelength, getting longer with the wavelength. A rise time of 100-150 fs was observed for wavelengths longer than 450 nm, in accordance with a gradual red shift of the time-resolved spectra. The results are discussed in terms of a relaxation occurring mainly on the lowest excited (1)pi pi*-state surface toward a conical intersection with the ground state, in line with recent theoretical predictions. Our results show that the excited-state population undergoes a substantial "spreading out" before reaching the CI, explaining the complex dynamics observed

Excited States and Energy Transfer in G-Quadruplexes

International audienceDNA nanostructures formed by association of four oligonucleotides d(TGGGGT) (TG4T quadruplexes) are studied by steady-state and time-resolved optical spectroscopy with femtosecond resolution using fluorescence upconversion. A comparison between single-stranded and four-stranded structures and the corresponding stoichiometric mixture of noninteracting nucleotides shows how horizontal and vertical organization affects the properties of the excited states. Emission from guanine excimers is observed only for single strands, where conformational motions favor their formation. Quadruplex fluorescence arises from a multitude of excited states generated via electronic coupling between guanines; the average fluorescence lifetime is longer and the fluorescence quantum yield higher compared to those of noninteracting nucleotides. The fluorescence anisotropy recorded on the subpicosecond time scale, where molecular motions are hindered, reveals that energy transfer takes place among the bases composing the nanostructure. These results are in line with the conclusions drawn from similar studies on model DNA duplexes

High-Energy Long-Lived Excited States in DNA Double Strands

International audienceDark DNA light: Dark excited states of alternating GC double strands emit fluorescence at 4000 cm-1 higher energy (see spectrum) and with four orders of magnitude longer lifetime compared to the bright * states. Such high-energy long-lived excited states are expected to play a key role in the DNA photoreactivity associated with the appearance of carcinogenic mutations

Fluorescence of Natural DNA: From the Femtosecond to the Nanosecond Time Scales

International audienceThe fluorescence of calf thymus DNA is studied by steady-state and time-resolved spectroscopy combining fluorescence upconversion and time-correlated single photon counting. The fluorescence spectrum is very similar to that of a stoichiometric mixture of monomeric chromophores, arising from bright ππ* states, and contrasts with the existing picture of exciplex emission in natural DNA. Yet, the DNA fluorescence decays span over five decades of time, with 98% of the photons being emitted at times longer than 10 ps. These findings, in association with recent studies on model duplexes, are explained by the involvement of dark states, possibly related to charge separation, serving as a reservoir for the repopulation of the bright ππ* states

Local structure of dilute aqueous DMSO solutions, as seen from molecular dynamics simulations

The information about the structure of dimethyl sulfoxide (DMSO)-water mixtures at relatively low DMSO mole fractions is an important step in order to understand their cryoprotective properties as well as the solvation process of proteins and amino acids. Classical MD simulations, using the potential model combination that best reproduces the free energy of mixing of these compounds, are used to analyze the local structure of DMSO-water mixtures at DMSO mole fractions below 0.2. Significant changes in the local structure of DMSO are observed around the DMSO mole fraction of 0.1. The array of evidence, based on the cluster and the metric and topological parameters of the Voronoi polyhedra distributions, indicates that these changes are associated with the simultaneous increase of the number of DMSO-water and decrease of water-water hydrogen bonds with increasing DMSO concentration. The inversion between the dominance of these two types of H-bonds occurs around X-DMSO = 0.1, above which the DMSO-DMSO interactions also start playing an important role. In other words, below the DMSO mole fraction of 0.1, DMSO molecules are mainly solvated by water molecules, while above it, their solvation shell consists of a mixture of water and DMSO. The trigonal, tetrahedral, and trigonal bipyramidal distributions of water shift to lower corresponding order parameter values indicating the loosening of these orientations. Adding DMSO does not affect the hydrogen bonding between a reference water molecule and its first neighbor hydrogen bonded water molecules, while it increases the bent hydrogen bond geometry involving the second ones. The close-packed local structure of the third, fourth, and fifth water neighbors also is reinforced. In accordance with previous theoretical and experimental data, the hydrogen bonding between water and the first, the second, and the third DMSO neighbors is stronger than that with its corresponding water neighbors. At a given DMSO mole fraction, the behavior of the intensity of the high orientational order parameter values indicates that water molecules are more ordered in the vicinity of the hydrophilic group while their structure is close-packed near the hydrophobic group of DMSO. Published by AIP Publishing

A crowdsourced analysis to identify ab initio molecular signatures predictive of susceptibility to viral infection

The response to respiratory viruses varies substantially between individuals, and there are currently no known molecular predictors from the early stages of infection. Here we conduct a community-based analysis to determine whether pre- or early post-exposure molecular factors could predict physiologic responses to viral exposure. Using peripheral blood gene expression profiles collected from healthy subjects prior to exposure to one of four respiratory viruses (H1N1, H3N2, Rhinovirus, and RSV), as well as up to 24 h following exposure, we find that it is possible to construct models predictive of symptomatic response using profiles even prior to viral exposure. Analysis of predictive gene features reveal little overlap among models; however, in aggregate, these genes are enriched for common pathways. Heme metabolism, the most significantly enriched pathway, is associated with a higher risk of developing symptoms following viral exposure. This study demonstrates that pre-exposure molecular predictors can be identified and improves our understanding of the mechanisms of response to respiratory viruses