Lake levels in the southern Bolivian Altiplano (19°-21°S) during the Late Glacial based on diatom studies

This study is focused on the endorheic Uyuni-Coipasa Basin located in the southern Bolivian Altiplano. Stratigraphical and fossil diatom studies based on a detailed radiocarbon chronology revealed six phases in water-level changes and paleosalinity variations. At 15,430 +- 80 yr B.P., lacustrine conditions settled in the southern Bolivian Altiplano. A saline lake, characterized by benthic meso-metasaline species, reached +4 m altitude above the present bottom of the basin. After 15,430 +- 80 yr B.P. the level rapidly rose to + 27 m, as suggested by a tychoplanktonic mesoline flora. Between 14,500 years and 13,000 years, finely lamited sediments at + 32 m contained successively a dominance of epiphytic mesosaline to hypersaline species and tychoplanktonic oligosaline diatoms, indicating weak fluctuations in water-level and salinity. At 13,000 years, strong changes in the diatom flora occurred: epiphytic oligo-hypersaline diatoms were replaced by planktonic meso-polysaline species. They indicate a deep salt lake (the lake level reached + 100 m). After 12,j000 yars, the lake level abruptly dropped, as suggested by fluviatile sediments with a benthic mesopolysaline diatom flora. The main lake was replaced by shallow saline ponds. A wet pulse occurred at 11,400 years, characterizad by low water level ( + 7 m) and high salinity. This lacustrine phase remained until 10,400 yr B.P. These data indicate changes in Precipitation minus Evaporation (P-E). Our regional interpretations are based on a comparison with the available data on the northern (Lake Titicaca) and southern (Lipez area) Bolivian Altiplano and on the northern Chilean Altiplano (Atacama Desert). (Résumé d'auteur)

La dernière transition glaciaire/interglaciaire des Andes tropicales sud (Bolivie) d'après l'étude des variations des niveaux lacustres et des fluctuations glaciaires

Une comparaison entre les variations des niveaux lacustres dans le bassin de Uyuni-Coipasa et les fluctuations glaciaires dans la Cordillère Orientale montre que les lacs et les glaciers ont simultanément enregistré les changements des précipitations. Un intense maximum lacustre (environ 13-12 14C ka BP) a eu lieu aux latitudes tropicales sud de la Bolivie, 4 000 à 6 000 ans avant le maximum lacustre de l'Afrique nord-équatoriale. (Résumé d'auteur

Métabolisme du 4-hydroxy-4’-chlorobiphényle par les enzymes de la voie catabolique du biphényle

Dans ce travail, nous avons déterminé le profil des métabolites produits à partir du 4-hydroxy-4’-chlorobiphényle par la bactérie Pandoraea pnomenusa B356 induite au biphényle et par sa biphényle dioxygenase. Lorsque l’analogue du biphényle doublement substitué en position para servait de substrat pour la réaction catalysée par la dioxygénase du biphényle de la souche B356, aucun des métabolites dihydro-dihydroxy attendus n'a pas été détecté. Ce substrat était plutôt converti en 3,4-dihydroxybiphényle, qui était rapidement ré-oxydé par la dioxygénase du biphényle pour générer du 3,4,5-trihydroxy-4'-chlorobiphényle, ce dernier représentant le métabolite majeur de cette réaction. On y retrouvait aussi plusieurs autres métabolites mineurs, dont entre autres, du 4-(4-chlorophényle)-cis-5,6- dihydroxycyclohex-3-en-1-one et du 2’,3’,4-trihydroxy-4’-chlorobiphényle. Les mécanismes impliqués dans la production de ces métabolites inattendus restent inconnus, mais l’ensemble de nos données montre que les dérivés dihydro-dihydroxy du 4-hydroxy-4’-chlorobiphényle sont soit sujet à un réarrangement ou ils sont transformés à l'intérieur de la poche catalytique de la biphényle dioxygénase pour générer des métabolites dont plusieurs ne peuvent pas être métabolisés par les enzymes subséquents de la voie cataboliques et ils s'accumulent dans le milieu de culture.</p

Nanonization of megestrol acetate by laser fragmentation in aqueous milieu

Faculté de PharmacieNanonization is a simple and effective method to improve dissolution rate and oral bioavailability of drugs with poor water solubility. There is growing interest to downscale the nanocrystal production to enable early preclinical evaluation of new drug candidates when compound availability is scarce. The purpose of the present study was to investigate laser fragmentation to form nanosuspensions in aqueous solution of the insoluble model drug megestrol acetate (MA) using very little quantities of the drug. Laser fragmentation was obtained by focusing a femtosecond (fs) or nanosecond (ns) laser radiation on a magnetically stirred MA suspension in water or aqueous solution of a stabilizing agent. The size distribution and physicochemical properties of the drug nanoparticles were characterized, and the in vitro dissolution and in vivo oral pharmacokinetics of a laser fragmented formulation were evaluated. A MA nanosuspension was also prepared by media milling for comparison purpose. For both laser radiations, smaller particles were obtained as the laser power was increased, but at a cost of higher degradation. Significant nanonization was achieved after a 30-min fs laser treatment at 250 mW and a 1-h ns laser treatment at 2500 mW. The degradation induced by the laser process of the drug was primarily oxidative in nature. The crystal phase of the drug was maintained, although partial loss of crystallinity was observed. The in vitro dissolution rate and in vivo bioavailability of the laser fragmented formulation were similar to those obtained with the nanosuspension prepared by media milling, and significantly improved compared to the coarse drug powder. It follows that this laser nanonization method has potential to be used for the preclinical evaluation of new drug candidates.IRSC - CRNS

Detection of a close supernova gravitational wave burst in a network of interferometers, neutrino and optical detectors

Trying to detect the gravitational wave (GW) signal emitted by a type II supernova is a main challenge for the GW community. Indeed, the corresponding waveform is not accurately modeled as the supernova physics is very complex; in addition, all the existing numerical simulations agree on the weakness of the GW emission, thus restraining the number of sources potentially detectable. Consequently, triggering the GW signal with a confidence level high enough to conclude directly to a detection is very difficult, even with the use of a network of interferometric detectors. On the other hand, one can hope to take benefit from the neutrino and optical emissions associated to the supernova explosion, in order to discover and study GW radiation in an event already detected independently. This article aims at presenting some realistic scenarios for the search of the supernova GW bursts, based on the present knowledge of the emitted signals and on the results of network data analysis simulations. Both the direct search and the confirmation of the supernova event are considered. In addition, some physical studies following the discovery of a supernova GW emission are also mentioned: from the absolute neutrino mass to the supernova physics or the black hole signature, the potential spectrum of discoveries is wide.Comment: Revised version, accepted for publication in Astroparticle Physic

Influence of incentive networks on landscape changes: A simple agent-based simulation approach

International audienceThe aim of this paper is to implement a simple model for exploring the influence of different multi-scale incentive networks affecting farmer decision on landscape changes. Three scales of networks are considered: a global ‘policy’ network promoting specific land uses, an intermediate ‘social’ network where land use practices are shared and promoted collectively and a local ‘neighborhood’ network where land use practices are influenced by those of their neighbors. We assess the respective and combined influence of these networks on landscape pattern (fragmentation and heterogeneity) and dynamics, taking into account agronomic constraints (assimilated to crop successions). Simulations show that combination of incentive networks does not have linear and/or cumulative influence on landscape changes. Comparison of simulated scenarios highlights that a combination of two networks tends to improve landscape heterogeneity and fragmentation; scenarios combining all networks could lead to two opposite landscape configuration illustrating emergence of landscape dynamics. Finally, this study emphasizes that landscape complexity has also to be understood through the multiplicity of pathways of landscape changes rather than the assessment of the resulting landscape patterns

Investigation of gain ripple in two-pump fiber optical parametric amplifiers

International audienceBy using the four-sideband theory, we analyze the gain spectrum in wideband two-pump fiber optical parametric amplifiers and predict gain ripples over the flat gain region. We derive an approximation of their pseudo-periods and discuss methods for reducing their amplitude

Revisiting the regiospecificity of burkholderia xenovorans LB400 biphenyl dioxygenase toward 2,2′-dichlorobiphenyl and 2,3,2′,3′-tetrachlorobiphenyl

ABSTRACT: 2,2'-Dichlorobiphenyl (CB) is transformed by the biphenyl dioxygenase of Burkholderia xenovorans LB400 (LB400 BPDO) into two metabolites (1 and 2). The most abundant metabolite, 1, was previously identified as 2,3-dihydroxy-2'-chlorobiphenyl and was presumed to originate from the initial attack by the oxygenase on the chlorine-bearing ortho carbon and on its adjacent meta carbon of one phenyl ring. 2,3,2',3'-Tetrachlorobiphenyl is transformed by LB400 BPDO into two metabolites that had never been fully characterized structurally. We determined the precise identity of the metabolites produced by LB400 BPDO from 2,2'-CB and 2,3,2',3'-CB, thus providing new insights on the mechanism by which 2,2'-CB is dehalogenated to generate 2,3-dihydroxy-2'-chlorobiphenyl. We reacted 2,2'-CB with the BPDO variant p4, which produces a larger proportion of metabolite 2. The structure of this compound was determined as cis-3,4-dihydro-3,4-dihydroxy-2,2'-dichlorobiphenyl by NMR. Metabolite 1 obtained from 2,2'-CB-d(8) was determined to be a dihydroxychlorobiphenyl-d(7) by gas chromatographic-mass spectrometric analysis, and the observed loss of only one deuterium clearly shows that the oxygenase attack occurs on carbons 2 and 3. An alternative attack at the 5 and 6 carbons followed by a rearrangement leading to the loss of the ortho chlorine would have caused the loss of more than one deuterium. The major metabolite produced from catalytic oxygenation of 2,3,2',3'-CB by LB400 BPDO was identified by NMR as cis-4,5-dihydro-4,5-dihydroxy-2,3,2',3'-tetrachlorobiphenyl. These findings show that LB400 BPDO oxygenates 2,2'-CB principally on carbons 2 and 3 and that BPDO regiospecificity toward 2,2'-CB and 2,3,2,',3'-CB disfavors the dioxygenation of the chlorine-free ortho-meta carbons 5 and 6 for both congeners

Biochemical Studies and Ligand-bound Structures of Biphenyl Dehydrogenase from Pandoraea pnomenusa Strain B-356 Reveal a Basis for Broad Specificity of the Enzyme

ABSTRACT: Biphenyl dehydrogenase, a member of short-chain dehydrogenase/reductase enzymes, catalyzes the second step of the biphenyl/polychlorinated biphenyls catabolic pathway in bacteria. To understand the molecular basis for the broad substrate specificity of Pandoraea pnomenusa strain B-356 biphenyl dehydrogenase (BphB(B-356)), the crystal structures of the apo-enzyme, the binary complex with NAD(+), and the ternary complexes with NAD(+)-2,3-dihydroxybiphenyl and NAD(+)-4,4'-dihydroxybiphenyl were determined at 2.2-, 2.5-, 2.4-, and 2.1-A resolutions, respectively. A crystal structure representing an intermediate state of the enzyme was also obtained in which the substrate binding loop was ordered as compared with the apo and binary forms but it was displaced significantly with respect to the ternary structures. These five structures reveal that the substrate binding loop is highly mobile and that its conformation changes during ligand binding, starting from a disorganized loop in the apo state to a well organized loop structure in the ligand-bound form. Conformational changes are induced during ligand binding; forming a well defined cavity to accommodate a wide variety of substrates. This explains the biochemical data that shows BphB(B-356) converts the dihydrodiol metabolites of 3,3'-dichlorobiphenyl, 2,4,4'-trichlorobiphenyl, and 2,6-dichlorobiphenyl to their respective dihydroxy metabolites. For the first time, a combination of structural, biochemical, and molecular docking studies of BphB(B-356) elucidate the unique ability of the enzyme to transform the cis-dihydrodiols of double meta-, para-, and ortho-substituted chlorobiphenyls