EPR investigation and spectral simulations of iron-catecholate complexes and iron-peptide models of marine adhesive cross-links

Electron paramagnetic resonance (EPR) spectra are presented for iron complexes of catecholate, tironate, and a 3,4-dihydroxyphenylalanine (DOPA)-containing peptide of sequence Ac-Ala-DOPA-Thr-Pro-CONH2 ("AdopaTP"). This peptide was prepared to model potential metal-protein cross-links in the adhesive used by marine mussels, Mytilus edulis, for affixing themselves to surfaces. Spectra are shown for iron bound to each ligand in mono, bis, and tris coordination environments. For example, the catecholate complexes {Fe(cat)}, {Fe(cat)2}, and [Fe(cat)3]3- are provided. Detailed simulations are presented to describe the origin of spectra for the iron-catecholate and iron-peptide species, which show that the spectral features can be accounted for only with the inclusion of D- and E-strain. The spectroscopy of each compound is shown under both anaerobic and aerobic conditions. When exposed to air, the high-spin Fe3+ signal of [Fe(AdopaTP)3]3- decreases and an organic radical is formed. No other sample exhibited an appreciable radical signal. These data are discussed in light of the biomaterial synthesis carried out by marine mussels.     

Structural effects of crosslinking a biopolymer hydrogel derived from marine mussel adhesive protein

In an effort to explore new biocompatible substrates for biomedical technologies, we present a structural study on a crosslinked gelatinous protein extracted from marine mussels. Prior studies have shown the importance of iron in protein crosslinking and mussel adhesive formation. Here, the structure and properties of an extracted material were examined both before and after crosslinking with iron. The structures of these protein hydrogels were studied by SEM, SANS, and SAXS. Viscoelasticity was tested by rheological means. The starting gel was found to have a heterogeneous porous structure on a micrometer scale and, surprisingly, a regular structure on the micron to nanometer scale. However disorder, or "no periodic structure", was deduced from scattering on nanometer length scales at very high q. Crosslinking with iron condensed the structure on a micrometer level. On nanometer length scales at high q, small angle neutron scattering showed no significant differences between the samples, possibly due to strong heterogeneity. X-ray scattering also confirmed the absence of any defined periodic structure. Partial crosslinking transformed the viscoelastic starting gel into one with more rigid and elastic properties.     

A new strategy of endosymbiont midgut bacteria in ant (Ponerinae)

The location and ultrastructure of bacteria associated with microvilli in the midgut of Odontomachus bauri were examined by transmission electron microscopy. These filamentous type bacteria are the second morphotype described in the midgut of this ant. They colonizes only the ectoperitrophic space, more specifically attaching along microvilli. A thick capsule attaches bacteria to microvilli and protect them from acidic pH and digestive enzymes. Details of the location and association with microvilli are discussed.     

Spectroscopic measurements and electrical diagnostics of microhollow cathode discharges in argon flow at atmospheric pressure

This paper is dedicated to the study of the electrical and optical characteristics of direct current microhollow cathode discharges (MHCD) in argon flow. Experiments have been carried out in order to determine the so-called Paschen’s curves in a static open MHCD. Current-voltage characteristics were obtained as a function of the pressure and hole diameter. MHCD enable stable direct current discharge operation, which could be ignited for pressures ranging from 12 to 800 Torr, in a very wide range of current densities and electrodes materials. Optical emission spectroscopy and analysis of the spectral line broadening of plasma line emissions were performed in order to measure parameters such as electron number density (2–4 × 10¹⁴ cm^-3)^{-3}), gas temperature (460–640 K), excitation temperature (~ 7000 K) and electron temperature (~ 8500 K), for current ranging from 7 to 15 mA. Lower gas temperature was measured compared to the static MHCD ones.     

A phylogenomic reconstruction of the protein world based on a genomic census of protein fold architecture

The protein world has a hierarchical and redundant organization that can be specified in terms of evolutionary units of molecular structure, the protein domains. The Structural Classification of Proteins (SCOP) has unified domains into a comparatively small set of folding architectures, the protein fold families and superfamilies, and these have been further grouped into protein folds. In this study, we reconstruct the evolution of the protein world using information embedded in a structural genomic census of fold architectures defined by a phylogenomic analysis of 185 completely sequenced genomes using advanced hidden Markov models and 776 folds described in SCOP release 1.67. Our study confirms the existence of defined evolutionary patterns of architectural diversification and explores how phylogenomic trees generated from folds relate to those reconstructed from fold superfamilies. Evolutionary patterns help us propose a general conceptual model that describes the growth of architectures in the protein world. © 2006 Wiley Periodicals, Inc. Complexity 12: 27–40, 2006     

Robust and Adhesive Hydrogels from Cross‐Linked Poly(ethylene glycol) and Silicate for Biomedical Use

A systematic approach to develop robust and adhesive hydrogels by photopolymerizing poly(ethylene glycol) (PEG)‐diacrylate and methoxy‐PEG‐acrylate in the presence of charged silicate nanoparticles (Laponite) is presented. PEG‐diacrylate and silicate are used for covalent and physical cross‐linking, thus providing the hydrogel with mechanical and adhesive strengths. Methoxy‐PEG‐acrylate is used as a softening agent. The resulting hydrogels can be extensively elongated and the hydrogels readily adhere to tissue even in the elongated state. These hydrogels may aid the development of adhesive tissue engineering matrixes, wound dressings, sealants, and the adhesive components of biomedical devices.

     

Anhydrous crystals of DNA bases are wide gap semiconductors

We present the structural, electronic, and optical properties of anhydrous crystals of DNA nucleobases (guanine, adenine, cytosine, and thymine) found after DFT (Density Functional Theory) calculations within the local density approximation, as well as experimental measurements of optical absorption for powders of these crystals. Guanine and cytosine (adenine and thymine) anhydrous crystals are predicted from the DFT simulations to be direct (indirect) band gap semiconductors, with values 2.68 eV and 3.30 eV (2.83 eV and 3.22 eV), respectively, while the experimentally estimated band gaps we have measured are 3.83 eV and 3.84 eV (3.89 eV and 4.07 eV), in the same order. The electronic effective masses we have obtained at band extremes show that, at low temperatures, these crystals behave like wide gap semiconductors for electrons moving along the nucleobases stacking direction, while the hole transport are somewhat limited. Lastly, the calculated electronic dielectric functions of DNA nucleobases crystals in the parallel and perpendicular directions to the stacking planes exhibit a high degree of anisotropy (except cytosine), in agreement with published experimental results.