Mössbauer study of the magnetocaloric compound AlFe<Subscript>2</Subscript><Emphasis Type="Bold">B</Emphasis><Subscript>2</Subscript>

Mössbauer spectroscopy in the ferromagnetic AlFe₂ B ₂ reveals T_c=299 K and shows good agreement with magnetic measurements. The crystals are plate-shaped. The flakes are found from X-ray diffraction to be in the crystallographic ac-plane in the orthorhombic system. The axes of the principle electric field gradient tensor are, by symmetry, colinear with the crystal a-, b- and c-axes. By using information about the quadrupole splitting and line asymmetry in the paramagnetic regime together with the quadrupole shift of the resonance lines in the ferromagnetic regime the magnetic hyperfine field direction is found to be in the ab-plane having an angle =40^° to the b-axis.     

Structural changes in apolipoproteins bound to nanoparticles

Nanoparticles are widely used in the pharmaceutical and food industries, but the consequences of exposure to the human body have not been thoroughly investigated. Apolipoprotein A-I (apoAI), the major protein in high-density lipoprotein (HDL), and other lipoproteins are found in the corona around many nanoparticles, but data on protein structural and functional effects are lacking. Here we investigate the structural consequences of the adsorption of apoAI, apolipoprotein B100 (apoB100), and HDL on polystyrene nanoparticles with different surface charges. The results of circular dichroism, fluorescence spectroscopy, and limited proteolysis experiments indicate effects on both secondary and tertiary structures. Plain and negatively charged nanoparticles induce helical structure in apoAI (negative net charge) whereas positively charged nanoparticles reduce the amount of helical structure. Plain and negatively charged particles induce a small blue shift in the tryptophan fluorescence spectrum, which is not noticed with the positively charged particles. Similar results are observed with reconstituted HDL. In apoB100, both secondary and tertiary structures are perturbed by all particles. To investigate the generality of the role of surface charge, parallel experiments were performed using human serum albumin (HSA, negative net charge) and lysozyme (positive net charge). Again, the secondary structure is most affected by nanoparticles carrying an opposite surface charge relative to the protein. Nanoparticles carrying the same net charge as the protein induce only minor structural changes in lysozyme whereas a moderate change is observed for HSA. Thus, surface charge is a critical parameter for predicting structural changes in adsorbed proteins, yet the effect is specific for each protein.     

Structural analysis of a Ni-methyl species in methyl-coenzyme M reductase from Methanothermobacter marburgensis

We present the 1.2 ? resolution X-ray crystal structure of a Ni-methyl species that is a proposed catalytic intermediate in methyl-coenzyme M reductase (MCR), the enzyme that catalyzes the biological formation of methane. The methyl group is situated 2.1 ? proximal of the Ni atom of the MCR coenzyme F(430). A rearrangement of the substrate channel has been posited to bring together substrate species, but Ni(III)-methyl formation alone does not lead to any observable structural changes in the channel.     

HARVESTING ECONOMIC MODELS AND CATCH‐TO‐BIOMASS DEPENDENCE: THE CASE OF SMALL PELAGIC FISH

Abstract In the case of small pelagic fish, it seems reasonable to consider harvest functions depending nonlinearly on fishing effort and fish stock. Indeed, empirical evidence about these fish species suggests that marginal catch does not necessarily react in a linear way neither to changes in fishing effort nor in fish stock levels. This is in contradiction with traditional fishery economic models where catch‐to‐input marginal productivities are normally assumed to be constant. While allowing for nonlinearities in both catch‐to‐effort and catch‐to‐stock parameters, this paper extends the traditional single‐stock harvesting economic model by focusing on the dependence of the stationary solutions upon the nonlinear catch‐to‐stock parameter. Thus, we analyze equilibrium responses to changes in this parameter, which in turn may be triggered either by climatic or technological change. Given the focus in this study on the case of small pelagic fish, the analysis considers positive but small values for the catch‐to‐stock parameter.