Comparative study of Factor Xa fluorogenic substrates and their influence on the quantification of LMWHs

Low molecular weight heparins (LMWHs) are recognised as the preferred anticoagulants in the prevention and treatment of venous thromboembolism. Anti-Factor Xa (anti-FXa) levels are used to monitor the anticoagulant effect of LMWHs and such assays are routinely employed in hospital diagnostic laboratories. In this study, a fluorogenic anti-FXa assay was developed using a commercially available fluorogenic substrate with an attached 6-amino-1-naphthalene-sulfonamide (ANSN) fluorophore and was used for the determination of two LMWHs, enoxaparin and tinzaparin and the heparinoid, danaparoid. The assay was based on the complexation of heparinised plasma with 100 nM exogenous FXa and 25 μM of the fluorogenic substrate Mes-D-LGR-ANSN (C₂H₅)₂ (SN-7). The assay was tested with pooled plasma samples spiked with anticoagulant concentrations in the range 0–1.6 U mL⁻¹. The statistically sensitive assay range was 0–0.4 U mL⁻¹ for enoxaparin and tinzaparin and 0–0.2 U mL⁻¹ for danaparoid, with assay variation typically below 10.5%. This assay was then compared with a previously published fluorogenic anti-FXa assay developed with the peptide substrate, methylsulfonyl-d-cyclohexylalanyl-glycyl-arginine-7-amino-4-methylcoumarin acetate (Pefafluor FXa). Both assays were compared in terms of fluorescence intensity, lag times and sensitivity to anticoagulants.     

Vibrational coordinates in the electron jump model

The role of quantization of vibrational coordinates in the electron jump model of alkali atom, dimer plus halogen molecule collisions is examined. Despite the bound states of the molecule ions involved, a classical approximation may offer good approximation over a wide collision energy range for the energy distributions of the ions in a single electron jump. Some results are calculated for K + Br₂ and K₂ + Br₂. The theory assumes that the electron jump probability is governed by the electronic matrix element H₁₂ alone. Elementary arguments are offered to suggest that this may be a reasonable approximation.     

Reactive scattering of alkali dimers: chemi-ionization

Measurements of total cross sections Q_i for chemi-ionization in scattering of a K₂ dimer beam by a range of halogen containing molecules, at translational energies E ～ 7–11 kcal mol^-1, are reported. Substantial cross sections, Q_i ～ 2–10 Ų are exhibited by the halogen molecules Br₂, ICl, IBr, I₂. Distinctly lower values Q_i ～ 0·1–0.2 Ų are exhibited by BrCN and the mercuric and stannic halides, HgX₂, SnX₄. The results show a close correlation with the chemi-ionization exoergicities, particularly for formation of a K⁺,X^- ion pair. These chemi-ionization data and results from previous reactive scattering studies are compared, in order to estimate relative reaction yields for different reaction paths. The reaction dynamics for K₂ with halogen molecules and cyanohalides are rationalized in terms of the electronic structure of the potential surface, where the orientation of the K₂ dimer plays a crucial role.     

Teaching Science as Science Is Practiced: Opportunities and Limits for Enhancing Preservice Elementary Teachers' Self‐Efficacy for Science and Science Teaching

Science teaching in elementary schools, or the lack thereof, continues to be an area of concern and criticism. Preservice elementary teachers' lack of confidence in teaching science is a major part of this problem. In this mixed‐methods study, we report the impacts of an inquiry‐based science course on preservice elementary teachers' self‐efficacy for science and science teaching, understanding of science, and willingness to teach it in their future careers. Our findings suggest that for some students, the inquiry‐based science course positively influenced their self‐efficacy for science and science teaching. Gains were made in a majority of students' conceptual understanding of science, understanding of the science process and scientific research, and confidence with science and science teaching. The subjects did not experience the course uniformly, however. Rather, there appeared to be two distinct groups, one on a trajectory of improving their outlook on science teaching and one worsening. The results presented here therefore provoke some interesting questions regarding preservice elementary teachers' preparation for science teaching.     

The Flow Lab: A Simple Activity for Generating NOS Principles

While there is near universal agreement within the science education community that a strong understanding of nature of science (NOS) ‐ both as a student goal and a teacher attribute ‐ is critical, we still struggle with how to achieve these aims. Barriers range from pragmatic logistics to fundamental curricular tensions. In this paper, we share a classroom activity designed to aid in the learning of key NOS principles that we have found constructive. We discuss the basic activity, connections to science studies literature, and opportunities for explicit reflection on nature of science.     

Oxygen‐Promoted C?H Bond Activation at Palladium

[Pd(P(Ar)(tBu)₂)₂] ( 1 , Ar=naphthyl) reacts with molecular oxygen to form Pd^II hydroxide dimers in which the naphthyl ring is cyclometalated and one equivalent of phosphine per palladium atom is released. This reaction involves the cleavage of both C H and O O bonds, two transformations central to catalytic aerobic oxidizations of hydrocarbons. Observations at low temperature suggest the initial formation of a superoxo complex, which then generates a peroxo complex prior to the C H activation step. A transition state for energetically viable C H activation across a Pd peroxo bond was located computationally.     

Assessment of cross-flow filtration for the size fractionation of freshwater colloids and particles

This research has evaluated the ability of cross-flow filtration (CFF) to perform correct size fractionation of natural aquatic colloids (materials from 1 nm to 1 μm in size) and particles (>1 μm) using scanning electron microscopy (SEM) combined with atomic force microscopy (AFM). SEM provided very clear images at high lateral resolution (ca. 2-5 nm), whereas AFM offered extremely low resolution limits (sub-nanometer) and was consequently most useful for studying very small material. Both SEM and AFM were consistent in demonstrating the presence of colloids smaller than 50 nm in all fractions including the retentates (i.e. the fractions retained by the CFF membrane), showing that CFF fractionation is not fully quantitative and not based on size alone. This finding suggests that previous studies that investigated trace element partitioning between dissolved, colloidal and particulate fractions using CFF may need to be re-visited as the importance of particles and large colloids may have been over-estimated. The observation that ultra-fine colloidal material strongly interacted with and completely coated a mica substrate to form a thin film has important potential implications for our understanding of the behaviour of trace elements in aquatic systems. The results suggest that clean, ‘pure’ surfaces are unlikely to exist in the natural environment. As surface binding of trace elements is of great importance, the nature of this sorbed layer may dominate trace element partitioning, rather than the nature of the bulk particle.     

Calculated structures and heats of formation of some predicted C,N, O,F molecules

Twelve molecules containing only C, N, O, and F, which are of interest in the context of energetic materials, were found to have true local energy minima at the HF/6-31G^* computational level. Both HF/6-31G^* and MP2/6-31G^* geometries are presented. A density functional procedure was used to find gas phase heats of formation. These are strongly positive for most of the molecules. The nitroso group significantly increases H _o ^f.25C compared to the nitro analogue.