Three dimensional models of Cu(2+)-Aβ(1-16) complexes from computational approaches

Elucidation of the coordination of metal ions to Aβ is essential to understand their role in its aggregation and to rationally design new chelators with potential therapeutic applications in Alzheimer disease. Because of that, in the last 10 years several studies have focused their attention in determining the coordination properties of Cu(2+) interacting with Aβ. However, more important than characterizing the first coordination sphere of the metal is the determination of the whole Cu(2+)-Aβ structure. In this study, we combine homology modeling (HM) techniques with quantum mechanics based approaches (QM) to determine plausible three-dimensional models for Cu(2+)-Aβ(1-16) with three histidines in their coordination sphere. We considered both ε and δ coordination of histidines 6, 13, and 14 as well as the coordination of different possible candidates containing oxygen as fourth ligand (Asp1, Glu3, Asp7, Glu11, and CO(Ala2)). Among the 32 models that enclose COO(-), the lowest energy structures correspond to [O(E3),N(δ)(H6),N(ε)(H13),N(ε)(H14)] (1), [O(E3),N(δ)(H6),N(δ)(H13),N(δ)(H14)] (2), and [O(D7),N(ε)(H6),N(δ)(H13),N(δ)(H14)] (3). The most stable model containing CO(Ala2) as fourth ligand in the Cu(2+) coordination sphere is [O(c)(A2),N(ε)(H6),N(δ)(H13),N(ε)(H14)] (4). An estimation of the relative stability between Glu3 (1) and CO(Ala2) (4) coordinated complexes seems to indicate that the preference for the latter coordination may be due to solvent effects. The present results also show the relationship between the peptidic and metallic moieties in defining the overall geometry of the complex and illustrate that the final stability of the complexes results from a balance between the metal coordination site and amyloid folding upon complexation.     

Chemical modification and structural analysis of protein isolates to produce hydrogel using Whitemouth croaker (Micropogonias furnieri) wastes

Recovery and alteration of fish protein from wastes and its use has been regarded as a promising alternative to develop useful products once polymer gels have a high capacity of water uptake. This study aims to produce hydrogel, a super absorbent biopolymer from modified fish protein, in order to evaluate the protein structure. In the modified proteins, analyses of the extent of modification of the lysine residues, electrophoresis, and electrometric titration were performed. In the hydrogels were realized assays of swelling water. The proteins with more modifications were shown as 63.5% and 75.9% of lysine residues, from fish protein isolate obtained with alkaline and acid solubilization, respectively. The modified protein in that same rate presented 332.0 and 311.4 carboxyl groups. Accordingly, the hydrogel produced from alkaline and acid isolates reached a maximum water uptake in 24 h of 79.42 and 103.25 g_water/g_{dry gel}, respectively.     

Sliding a body on snow

Snow is considered as an ideal nonlinear elastoplastic medium. A body performs planeparallel motion on snow. The area of its contact with snow is a part of a rectangular plate. The contact zone changes during the motion of the body. Steady motions are found from the derived equations of motion in the case when the constant external forces and the moment exerted on the body are given. The inverse problem of determining the forces and moments is solved for a given steady motion of a vehicle.     

Interaction of glycine with isolated hydroxyl groups at the silica surface: first principles B3LYP periodic simulation

The adsorption of a glycine molecule on a model silica surface terminated by an isolated hydroxyl group has been studied ab initio using a double-zeta polarized Gaussian basis set, the hybrid B3LYP functional, and a full periodic treatment of the silica surface/glycine system. The hydroxylated silica surface has been simulated using either a 2D slab or a single polymer strand cut out from the (001) surface of an all-silica edingtonite. A number of B3LYP-optimized structures have been found by docking glycine on the silica surface exploiting all possible hydrogen bond patterns. Whereas glycine is generally adsorbed in its neutral form, two structures show glycine adsorbed as a zwitterion, the surface playing the role of a "solid solvent" whereas intrastrand hydrogen bond cooperativity stabilizes the zwitterions. The adsorbed zwitterionic structures are no longer formed at a lower glycine coverage as simulated by enlarging the unit cell so as to break intrastrand hydrogen bonds, showing the importance of H-bond cooperativity in stabilizing the zwitterionic forms. Each structure has been characterized by computing its harmonic vibrational spectrum at the Gamma point, which also allowed us to calculate the free energy of adsorption. The experimental infrared features of chemical-vapor-deposited glycine on a silica surface are in agreement with those computed for glycine adsorbed in its neutral form and engaging three hydrogen bonds with the surface silanols, two of them involving the C=O bond and one originating from the glycine OH group. The NH(2) group plays only a minor role as a weak hydrogen bond donor.     

In vitro evaluation of osteoblast‐like cells on hydroxyapatite‐coated porous stainless steel implants by synchrotron radiation x‐ray fluorescence

The successful application of artificial implants requires osseointegration in the implanted structures. To stimulate bone growth, synthetic hydroxyapatite obtained by the coprecipitation process was coated onto porous stainless steel substrates in order to enhance the biocompatibility and, consequently, mineralization. The substrate of choice was porous 316L stainless steel for its high resistance, mechanical strength and low density due to its foam structure. The aim of the present study was to investigate the biological response of the fabricated implants cultured with MC3T3‐E1 mouse osteoblast‐like cells by analyzing the variation in the elemental concentration, mainly calcium, along with the cellular differentiation and mineralization. By employing synchrotron radiation x‐ray fluorescence spectroscopy (SRXRF), intracellular elemental distribution and concentration could be determined, revealing a clear increase in the total calcium content. This preliminary data suggests that synthetic hydroxyapatite on porous stainless steel substrates might be successfully used for biocompatible medical implants. Copyright © 2009 John Wiley & Sons, Ltd.     

Microparticles based on chitosan–hyaluronic acid interpolyelectrolyte complex,which provide stability of aqueous dispersions

Turbidimetric titration and laser scattering methods were used to assess the phase behavior of mixtures of chitosan and hyaluronic acid in aqueous solutions in relation to interaction conditions. Conditions were found in which stable water dispersions with particle size of up to 573 nm can be obtained. It was found that the molar ratios and the overall concentration mode of the starting-polyelectrolyte solutions affect the particle size.     

New microbial-friendly polyaniline nanoparticles on the base of nitrilotriacetic acid: comparison with PANI prepared by standard techniques

This paper describes the influence of polyaniline (PANI) nanoparticles prepared in the presence of the nitrilotriacetic acid (NTA) in comparison with PANI prepared by standard techniques, on mixed microbial cultures in the form of a biological extract from soil and activated sludge and partially digested sludge, both sourced from a municipal wastewater treatment plant. The presence of PANI prepared by standard techniques in aqueous environment has a negative effect on the activity of mixed microbial cultures in the form of activated sludge, digested sludge (anaerobic conditions), and natural soil. According to biological oxygen demand (BOD) values—respirometric test, the slight inhibiting effect of nanoparticles is attributed to impurities and oligomers from aniline polymerization. The use of NTA in the production of PANI, resulted in nanotubes with channels through which NTA is incorporated into the structure. A sample thus obtained shows higher values of BOD, which is associated with the fact that NTA is released from PANI nanotube channels followed by its biodegradation.     

Trapping the δ Isomer of the Polyoxometalate‐Based Keggin Cluster with a Tripodal Ligand

We report the synthesis, structural, and electronic characterization of the theoretically predicted, but experimentally elusive δ‐isomer of the Keggin polyoxometalate polyanion. A family of δ‐Keggin polyoxoanions of the general formula, (TEA)H_pNa_q [H₂M₁₂(XO₄)O₃₃(TEA)]?r H₂O where p, q, r=[2,3,8] for 1 and [4,1,4] for 2 were isolated by the reaction of tungstate(VI) and vanadium(V) with triethanolammonium ions (TEAH), acting as a tripodal ligand grafted to the surface of the cluster thereby stabilizing the polyanionic δ‐Keggin archetype. The δ‐Keggin species were characterized by single‐crystal X‐ray diffraction, FT‐IR, UV/Vis, NMR, and ESI‐MS spectrometry. Electronic structure and structure–stability correlations were evaluated by means of DFT calculations. The compounds exhibited multi‐electron transfer and reversible photochromic properties by undergoing single‐crystal‐to‐single‐crystal (SC–SC) transformations accompanied with color changes under light.