Assessing Arctic Grayling Relative Abundance and Distribution Through Environmental DNA Analysis

Research Poste

Longer than 2 hours to antibiotics is associated with doubling of mortality in a multinational community-acquired bacterial meningitis cohort

To optimally define the association between time to effective antibiotic therapy and clinical outcomes in adult community-acquired bacterial meningitis. A systematic review of the literature describing the association between time to antibiotics and death or neurological impairment due to adult community-acquired bacterial meningitis was performed. A retrospective cohort, multivariable and propensity-score based analyses were performed using individual patient clinical data from Australian, Danish and United Kingdom studies. Heterogeneity of published observational study designs precluded meta-analysis of aggregate data (I(2) = 90.1%, 95% CI 71.9–98.3%). Individual patient data on 659 subjects were made available for analysis. Multivariable analysis was performed on 180–362 propensity-score matched data. The risk of death (adjusted odds ratio, aOR) associated with treatment after two hours was 2.29 (95% CI 1.28–4.09) and increased substantially thereafter. Similarly, time to antibiotics of greater than three hours was associated with an increase in the occurrence of neurological impairment (aOR 1.79, 95% CI 1.03–3.14). Among patients with community-acquired bacterial meningitis, odds of mortality increase markedly when antibiotics are given later than two hours after presentation to the hospital

The role of superheated water on the crystallization of N,N'-1,2-ethanediyl-bis(6-hydroxy-hexanamide): Implications on crystallography and phase transitions

A symmetrical, hydrogen bonded low molecular weight molecule N,N'-1,2-etrianediyl-bis(6-riydroxy-hexanamide), crystallized from melt or from the superheated state of water, is examined. Thermodynamic and structural changes during phase transitions are followed by DSC, time-resolved X-ray techniques and polarized optical microscopy. Considering the hydrogen bonding motifs present in this bisamide-diol, it is selected as a model compound for crystalline domains present in semicrystalline polyamides. By studying this model compound it was moreover aimed to elucidate the specific role of water molecules that are likely to reside in the crystals obtained from the superheated state of water. On heating the melt crystallized sample, the observed crystalline transitions are not the same as observed in polyamides. However, similar to polyamides the origin of the transition is due to the electron exchange between the hydrogen bonding moieties and conformational changes in the aliphatic sequences. At low temperatures (below 22 °C) non-trans conformations in the central diamine methylene moieties induce a different triclinic structure, having unit cell parameters close to monoclinic, with potential existence of intersheet hydrogen bonding. Crystallization from superheated water entails remarkable differences in the physical behavior. A metastable crystalline structure, obtained from the superheated state of water and having relatively large interchain and intersheet distances, transforms into another hydrogen bonded crystal via sequential temperature cycles. When compared with the melt crystallized sample the crystal obtained after sequential temperature cycles show considerable difference in the crystal-to-crystal phase transition while melting remains the same. In combination with the increased crystal-to-crystal transition temperature, an expansion along the c-axis suggests a stabilizing effect of rigid hydroxylic protons that contribute to the unit cell parameters. © 2008 American Chemical Society

Additive Manufacturing of alpha-Amino Acid Based Poly(ester amide)s for Biomedical Applications

[Image: see text] α-Amino acid based polyester amides (PEAs) are promising candidates for additive manufacturing (AM), as they unite the flexibility and degradability of polyesters and good thermomechanical properties of polyamides in one structure. Introducing α-amino acids in the PEA structure brings additional advantages such as (i) good cytocompatibility and biodegradability, (ii) providing strong amide bonds, enhancing the hydrogen-bonding network, (iii) the introduction of pendant reactive functional groups, and (iv) providing good cell–polymer interactions. However, the application of α-amino acid based PEAs for AM via fused deposition modeling (FDM), an important manufacturing technique with unique processing characteristics and requirements, is still lacking. With the aim to exploit the combination of these advantages in the creation, design, and function of additively manufactured scaffolds using FDM, we report the structure–function relationship of a series of α-amino acid based PEAs. The PEAs with three different molecular weights were synthesized via the active solution polycondensation, and their performance for AM applications was studied in comparison with a commercial biomedical grade copolymer of l-lactide and glycolide (PLGA). The PEAs, in addition to good thermal stability, showed semicrystalline behavior with proper mechanical properties, which were different depending on their molecular weight and crystallinity. They showed more ductility due to their lower glass transition temperature (T(g); 18–20 °C) compared with PLGA (57 °C). The rheology studies revealed that the end-capping of PEAs is of high importance for preventing cross-linking and further polymerization during the melt extrusion and for the steadiness and reproducibility of FDM. Furthermore, our data regarding the steady 3D printing performance, good polymer–cell interactions, and low cytotoxicity suggest that α-amino acid based PEAs can be introduced as favorable polymers for future AM applications in tissue engineering. In addition, their ability for formation of bonelike apatite in the simulated body fluid (SBF) indicates their potential for bone tissue engineering applications

Formation of cyclic structures in the cationic ring-opening polymerization of 1,3-dioxolane

The cationic ring-opening polymerization of acetals is prone to cyclization of the polymer chains. This is also the case for the polymerization of 1,3-dioxolane. Literature states that this cyclization can be reduced by applying the Active Monomer mechanism, at least if no competition with the Active Chain End mechanism occurs. In this work, a detailed characterization of the different distributions resulting from the cationic ring-opening polymerization of 1,3-dioxolane via the Active Monomer mechanism is made by a combination of gel permeation chromatography, H-1 NMR, and for the first time by matrix assisted laser desorption/ionization time of flight mass spectrometry. The influence of monomer addition speed, catalyst to initiator ratio and solvent were studied on both kinetics and composition of the product. Furthermore, it was found that increasing the conversion and monomer to initiator ratios leads to an increased amount of cyclic structures and to broader distributions, in correspondence with the Jacobson-Stockmayer theory. Furthermore, ion trapping experiments using P-31 NMR provide insights into the actual reaction mechanism. Finally, purification of the products after the reactions led to a reduction of the cyclic fraction

Formation of cyclic structures in the cationic ring-opening polymerization of 1,3-dioxolane

The cationic ring-opening polymerization of acetals is prone to cyclization of the polymer chains. This is also the case for the polymerization of 1,3-dioxolane. Literature states that this cyclization can be reduced by applying the Active Monomer mechanism, at least if no competition with the Active Chain End mechanism occurs. In this work, a detailed characterization of the different distributions resulting from the cationic ring-opening polymerization of 1,3-dioxolane via the Active Monomer mechanism is made by a combination of gel permeation chromatography, H-1 NMR, and for the first time by matrix assisted laser desorption/ionization time of flight mass spectrometry. The influence of monomer addition speed, catalyst to initiator ratio and solvent were studied on both kinetics and composition of the product. Furthermore, it was found that increasing the conversion and monomer to initiator ratios leads to an increased amount of cyclic structures and to broader distributions, in correspondence with the Jacobson-Stockmayer theory. Furthermore, ion trapping experiments using P-31 NMR provide insights into the actual reaction mechanism. Finally, purification of the products after the reactions led to a reduction of the cyclic fraction

Promotion of molecular diffusion and/or crystallization in fused deposition modeled poly(lactide) welds

Fused deposition modeled parts of polymeric origin exhibit inferior interlayer mechanical properties. To enhance interfacial weld stiffness, poly(lactide) blends containing low molecular weight polymers of chemically identical but enantiomerically different nature are explored. The enantiomeric composition of the low molecular weight fraction is either random or opposite, promoting molecular diffusion or nucleation respectively. The structure-relationship of the interfaces is studied using torsional stiffness, calorimetry, and rheology. Fully miscible, non-crystallizable low molecular weight additives of random L and D enantiomeric composition reduce melt viscosity and crystallization rate, promoting molecular diffusion. Nevertheless, incomplete entangling and crystallization upon interfacial mixing induce poor interfacial stiffening. Poly(lactide) stereocomplex enriched interfaces promote crystallization. Chains across weld interfaces may be mechanically anchored in crystals, but hindered diffusion limits molecular mixing and thus the extent of mechanical stiffening. Ultimately, combining melt plasticization and increased crystallization rates distinctly increases weld stiffness and thermodynamic/geometrical stability of fused deposition modeled poly(lactides).</p