49 research outputs found
Aplanktonic zones in the Red Sea
No full textWe use micropalaeontological and stable isotope results for a series of cores from north to south through the Red Sea, to assess temporal and spatial patterns of change in planktonic foraminiferal faunas leading up to the remarkable full-glacial Red Sea aplanktonic zones. Aplanktonic zones reflect salinities in the Red Sea in excess of the lethal 49 p.s.u. limit, caused by reduced exchange transport through the Strait of Bab el Mandab due to glacial sea-level lowering. Concerning the last glacial cycle, aplanktonic conditions began at 39 ka BP in the north, where salinities eventually reached 55–57 p.s.u. Paradoxically, planktonic faunas are reported to have survived the last glacial maximum in the northern Gulf of Aqaba, suggesting a poorly understood freshwater dilution at that time. Aplanktonic conditions (S?49 p.s.u.) reached the south-central Red Sea by 22 ka BP, while planktonic foraminiferal faunas continued, albeit in very low abundances and limited diversity (S?45 p.s.u.), in the southernmost Red Sea. During marine isotope stage (MIS) 6, the 49 p.s.u. isohaline appears to have resided in the central Red Sea, between cores KL11 and MD921017. We observe a systematic sequence of species disappearances before all glacial maxima of the last 500 kyr. Absence of a logical relationship with sea levels suggests that the disappearance sequences are not related to a general salinity increase. Instead, we argue that the sequences were driven by complex reorganisations in hydrography (stratification), productivity (food availability) and subsurface oxygenation (reproduction-habitats). The onset is marked by dramatic basin-wide expansion of conditions that today are restricted to only the southern Red Sea, suggesting an expansion of the dominance of NE monsoonal circulation over the entire Red Sea. This expansion occurred 15 or more kyr before the aplanktonic zones of MIS-12, 6 and 2, and also before MIS-10 and 8, which never reach the aplanktonic stage. Regarding the last glacial cycle, this event occurred as early as 75 ka BP (MIS-4/5 boundary). After this major climatic reorganisation, we reconstruct progressive intensification of the new conditions, especially marked by northward expansion and intensification of the subsurface oxygen minimum zone (OMZ). During the last glacial cycle, a shallow and very distinct OMZ affected the central Red Sea as early as 68 ka BP, and the north as late as 55 ka BP. The OMZ expansion/intensification appears to have been interrupted by episodes of increased ventilation
BILIPROTEINS FROM THE BUTTERFLY Pieris brassicae STUDIED BY TIME-RESOLVED FLUORESCENCE AND COHERENT ANTI-STOKES RAMAN SPECTROSCOPY
No full textThe fluorescence decay time of the biliverdin IX7 chromophore present in biliproteins isolated from Pieris brassicae is determined to be 44 ± 3 ps. This value suggests a cyclic helical chromophore structure. The vibrational frequencies determined by CARS-spectroscopy are compared with those of model compounds. The data confirm that the chromophore in the protein-bound state adopts a cyclic-helical, flexible conformation
Picosecond time-resolved fluorescence of phycobiliproteins
No full textThe α- and β-subunits of C-phycocyanin from Mastigocladus laminosus were prepared according to revised procedures. Both subunits are isolated as dimers, which can be dissociated into monomers with detergent mixtures. The fluorescence decay kinetics are similar for the respective monomers and dimers. In no case could they be fitted by only one (α-subunit) or two exponentials (β-subunit) which are predicted by theory for samples with a unique chromophore—protein arrangement containing one and two chromophores, respectively. It is suggested that there exists a heterogeneity among the chromophores of the subunits, which may persist in the highly aggregated complexes present in cyanobacterial antennas
Characterization of solid dispersions of carbamazepine and PEG6000/vinylcaprolactam/vinylacetate copolymer
No full textPurpose.
to investigate the solid-state properties and dissolution performances of solid dispersions of carbamazepine and a new
marketed copolymer proposed for hot melt extrusion.
Methods.
Physical mixtures [PM] were prepared by mixing in mortar and pestle for 10 min carbamazepine [CBZ, polymorphic form
III] and PEG6000/vinylcaprolactam/vinylacetate copolymer (Soluplus® BASF) in various drug/polymer ratios (1:9, 3:7, 1:1,
7:3 w/w). Co-melted formulations [CM] were prepared by heating the PM at 170°C on a hot plate for 15 min, allowing to cool at room temperature and grinding the resulting glasses in a mortar. PXRD study, DSC analysis and dissolution test
(paddle apparatus, 500mL of 0.0125% SLS solution, 37±0.5°C, 100 rpm, UV detection at 287 nm) were performed on all samples.
Results.
drug-polymer solid-state interaction, resulting in complete loss of CBZ crystallinity was found to occur in CM with
drug/polymer ratios 1:9 and 3:7 w/w. Accordingly, the glass transition recorded for these dispersions was lowered with
respect to that of the pure polymer. Non-interacted crystalline CBZ was detected in all PM as well as in 1:1 and 7:3 CM
formulations. Furthermore, non-interacted amorphous CBZ was thought to be present in the 7:3 CM formulation, resulting in
drug crystallization up on heating in the DSC experiment. As far as dissolution properties are concerned, PM presented
similar or only slightly higher dissolution rate with respect to the pure drug, whilst 1:9 and 3:7 CMF demonstrated a remarkable improvement of dissolution rate (the amount dissolved at t=10min doubled that of the pure CBZ). The 7:3 CM formulation was affected by a decreased dissolution rate probably caused by the formation of CBZ hydrate during the test.
Conclusion.
solid dispersion of CBZ with a new PEG6000/vinylcaprolactam/vinylacetate copolymer can be successfully prepared by comelting method, resulting in a high degree of drug-polymer interaction and consequently a remarkable improvement of drug
dissolution rate
FÖRSTER TRANSFER CALCULATIONS BASED ON CRYSTAL STRUCTURE DATA FROM Agmenellum quadruplicatum C-PHYCOCYANIN
No full textExcitation energy transfer in C-phycocyanin is modeled using the Forster inductive resonance mechanism. Detailed calculations are carried out using coordinates and orientations of the chromophores derived from X-ray crystallographic studies of C-phycocyanin from two different species (Schirmer et al, J. Mol. Biol. 184, 257–277 (1985) and ibid., 188, 651-677 (1986)). Spectral overlap integrals are estimated from absorption and fluorescence spectra of C-phycocyanin of Mastigocladus laminosus and its separated subunits. Calculations are carried out for the β-subunit, αβ-monomer, (αβ)3-trimer and (αβ)0-hexamer species with the following chromophore assignments: β155 = 's’(sensitizer), β84 =‘f (fluorescer) and α84 =‘m’(intermediate):]:. The calculations show that excitation transfer relaxation occurs to 3=98% within 200 ps in nearly every case; however, the rates increase as much as 10-fold for the higher aggregates. Comparison with experimental data on fluorescence decay and depolarization kinetics from the literature shows qualitative agreement with these calculations. We conclude that Forster transfer is sufficient to account for all of the observed fluorescence properties of C-phycocyanin in aggregation states up to the hexamer and in the absence of linker polypeptides
Dissociating effect of chromophore modifications on C-phycocyanin heterohexamers
No full textThe bilin chromophores of the α or β subunit of C-phycocyanin (PC) from Mastigocladus laminosus were modified, and subsequently recombined with the respective complementary unmodified chromophores. The modifications consisted of photobleaching (350 nm) or reversible reduction of the verdin- to rubin-type chromophore(s). Recombination led to heterodimers (αβ)1, but the heterohexameric aggregation state (αβ)3 could not be obtained with the modified chromophores. Autoxidation of the reduced α-84 chromophore in such a hybrid, which occurred on standing under aerobic conditions, induced reaggregation to heterohexamers. Chemical re-oxidation of the reduced chromophores did not produce reaggregation, and it was not promoted by a 22 kDa linker peptide fragment (Gottschalk et al., Photochem. Photobiol., 54 (1991) 283), which in unmodified samples stabilized heterohexameric aggregates. Binding of the mercurial p-chloromercury-benzenesulphonate to the single free cysteine of PC near (approximately 0.4 nm) the β-84 chromophore had only a moderately destabilizing effect on the heterohexamer (αβ)3. It was concluded that the intact chromophore structure is an important factor determining the quaternary structure of biliproteins. The tendency of heterohexamer destabilization is related to the situation in phycoerythrocyanin, where photoisomerization of the violobilin chromophore of the α subunit near the heterodimer—heterodimer contact region is also responsible for aggregate destabilization (Siebzehnrübl et al., Photochem. Photobiol., 46 (1989) 753)
ENERGY TRANSFER IN TRIMERIC C-PHYCOCYANIN STUDIED BY PICOSECOND FLUORESCENCE KINETICS
No full textThe excited state kinetics of trimeric C-phycocyanin from Mastigocladus laminosus has been measured as a function of the emission and excitation wavelength by the single-photon timing technique with picosecond resolution and simultaneous data analysis. A fast decay component of 22 ps (C-phycocyanin with linker peptides) and 36 ps (C-phycocyanin lacking linker peptides) is attributed to efficient energy transfer from sensitizing to fluorescing chromophores. At long detection wavelengths the fast decay components are found to turn into a rise term. This finding further corroborates the concept of intramolecular energy transfer. Previous reports on the conformational heterogeneity of the chromophores and/or proteins in C-phycocyanin are confirmed. Our data also provide indications for the importance of the uncoloured linker peptides for this heterogeneity
Global Governance as a Complex Adaptive System
No full textThe recent advent of Internet technologies has greatly intensified existing globalization processes. The development of full multimedia international communications has the potential to democratize information flows. Citizens can communicate with each other and with governments to create and document public and private accountabilities beyond jurisdictional borders. Ironically, it is also now possible to achieve intensive and intrusive surveillance of individuals and organisations, virtually untraceable criminal exchanges of data, and even forms of cyberwarfare. These possibilities are all part of the global information commons. Like physical common spaces, beneficial and nefarious elements coexist. A working definition of the global information commons is the set of all information systems critical to managing global resources and governance, and the set of protocols for their exchange. While both cumbersome and broad, this definition of the global information commons helps to ground it as a concept that can be modelled and managed. It responds to Dahl’s query about the possibility of a third transformation of democracy beyond the nation-state. This article considers key issues for the emerging global information commons. These relate to the role of new technologies in possible forms of global governance. Global governance is here considered to be the emerging mechanisms for managing trans-national issues and resources. These can be particular to a specific issue or resource, such as the fisheries, or may be more formal, such as the European Union. Governance can be seen as a management function, much as the “governors” on early steam trains. First, the author presents an overview of technology as socially determined, followed by a sketch of how global governance may be seen as a complex adaptive system. This includes an analysis of how models might embed democratic structures. Finally, examples of sub-systems of the global information commons demonstrate the range of actors and rules such a system would need to consider. This theoretical perspective builds on empirical work in the physical, biological, and social sciences and emphasizes the value of modelling governance at all scales. This approach is seen as fruitful for identifying and monitoring dynamic patterns. It provides useful insights for managing the global information commons. In human systems, the rules of interaction and information exchange are determined by the values of the actors (Theys, 1998). Modelling can help to articulate these values. In complex human systems, the direction of change can be as important as absolute measures.</jats:p
Effect of protein environment and the excitonic coupling on the excited-state properties of the bilinchromophores in C-Phycocyanin
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