Self-assembly of a modified amyloid peptide fragment: pH-responsiveness and nematic phase formation

The self-assembly of peptide YYKLVFFC based on a fragment of the amyloid beta (A) peptide, A beta 16-20, KLVFF has been studied in aqueous solution. The peptide is designed with multiple functional residues to examine the interplay between aromatic interactions and charge on the self-assembly, as well as specific transformations such as the pH-induced phenol-phenolate transition of the tyrosine residue. Circular dichroism (CD) and Fourier-transform infrared (FTIR) spectroscopies are used to investigate the conditions for beta-sheet self-assembly and the role of aromatic interactions in the CD spectrum as a function of pH and concentration. The formation of well-defined fibrils at pH 4.7 is confirmed by cryo-TEM (transmission electron microscope) and negative stain TEM. The morphology changes at higher pH, and aggregates of short twisted fibrils are observed at pH 11. Polarized optical microscopy shows birefringence at a low concentration (1 wt.-%) of YYKLVFFC in aqueous solution, and small-angle X-ray scattering was used to probe nematic phase formation in more detail. A pH-induced transition from nematic to isotropic phases is observed on increasing pH that appears to be correlated to a reduction in aggregate anisotropy upon increasing pH.

Influence of the Photorhabdus luminescens phosphomannose isomerase gene, manA, on mannose utilization, exopolysaccharide structure, and biofilm formation

Extracellular polysaccharide (EPS) is produced by diverse bacterial pathogens and fulfills assorted roles, including providing a structural matrix for biofilm formation and more specific functions in virulence, such as protection against immune defenses. We report here the first investigation of some of the genes important for biofilm formation in Photorhabdus luminescens and demonstrate the key role of the phosphomannose isomerase gene, manA, in the structure of functional EPS. Phenotypic analyses of a manA-deficient mutant showed the importance of EPS in motility, insect virulence, and biofilm formation on abiotic surfaces as well as the requirement of this gene for the use of mannose as the sole carbon source. Conversely, this defect had no apparent impact on symbiosis with the heterorhabditid nematode vector. A more detailed analysis of biofilm formation revealed that the manA mutant was able to attach to surfaces with the same efficiency as that of the wild-type strain but could not develop the more extended biofilm matrix structures. A compositional analysis of P. luminescens EPS reveals how the manA mutation has a major effect on the formation of a complete, branched EPS.

Oppositely charged polyelectrolytes: complex formation and effects of chain asymmetry

The formation of complexes in solutions of oppositely charged polyions has been studied by Monte Carlo simulations. The amount as well as the length, and thus, the absolute charge of one of the polyions have been varied. There is an increasing tendency to form large clusters as the excess of one kind of polyion decreases. When all polyions have the same length, this tendency reaches a maximum near, but off, equivalent amounts of the two types of polyions. When one kind of polyion is made shorter, the propensity to form large clusters decreases and the fluctuations in cluster charge increases. Simple free-energy expressions have been formulated on the basis of a set of simple rules that help rationalize the observations. By calculating cluster distributions in both grand canonical and canonical ensembles, it has been possible to show the extent of finite-size effects in the simulations.

Complex formation in solutions of oppositely charged polyelectrolytes at different polyion compositions and salt content

The formation of complexes in solutions containing positively charged polyions (polycations) and a variable amount of negatively charged polyions (polyanions) has been investigated by Monte Carlo simulations. The polyions were described as flexible chains of charged hard spheres interacting through a screened Coulomb potential. The systems were analyzed in terms of cluster compositions, structure factors, and radial distribution functions. At 50% charge equivalence or less, complexes involving two polycations and one polyanion were frequent, while closer to charge equivalence, larger clusters were formed. Small and neutral complexes dominated the solution at charge equivalence in a monodisperse system, while larger clusters again dominated the solution when the polyions were made polydisperse. The cluster composition and solution structure were also examined as functions of added salt by varying the electrostatic screening length. The observed formation of clusters could be rationalized by a few simple rules.

Trinuclear and tetranuclear adduct formation between sodium perchlorate and copper(II) complexes of salicylaldimine type ligands: structural characterization and theoretical investigation

The synthesis of two new sodium perchlorate adducts (1:2 and 1:3) with copper(II) "ligand-complexes'' is reported. One adduct is trinuclear [(CuL(1))(2)NaClO(4)] (1) and the other is tetranuclear [(CuL(2))(3)Na]ClO(4)center dot EtOH (2). The ligands are the tetradentate di-Schiff base of 1,3-propanediamines and salicylaldehyde (H(2)L(1)) or 2-hydroxyacetophenone (H(2)L(2)). Both complexes have been characterized by X-ray single crystal structure analyses. In both structures, the sodium cation has a six-coordinate distorted octahedral environment being bonded to four oxygen atoms from two Schiff-base complexes in addition to a chelated perchlorate anion in 1 and to six oxygen atoms from three Schiff-base complexes in 2. We have carried out a DFT theoretical study (RI-B97-D/def2-SVP level of theory) to compute and compare the formation energies of 1:2 and 1:3 adducts. The DFT study reveals that the latter is more stabilized than the former. The X-ray crystal structure of 1 shows that the packing of the trinuclear unit is controlled by unconventional C-H center dot center dot center dot O H-bonds and Cu(2+)-pi non-covalent interactions. These interactions explain the formation of 1 which is a priori disfavored with respect to 2.

Applications of micromorphology to understanding activity areas and site formation processes in experimental hut floors

Experimental buildings at Butser Ancient Farm and St. Fagans (UK) and Lejre (Denmark) were sampled to investigate micromorphology of known activity areas, to contribute to our understanding of the internal use of space in excavated buildings and formation processes of house floor deposits. The experimental buildings provided important information relating to activity residues and sediments over the 16 years that the buildings were in use. Specifically, these results contribute to our understanding of the routes and cycles for transportation of materials in occupation contexts, which can be used to inform archaeological studies. It has been possible to identify internal ‘hot spots’ within the buildings for the deposition of activity residues and for the formation of specific deposit types. Analysis also highlighted postdepositional alterations occurring in internal occupation deposits, which has provided a means of identifying roofed and unroofed spaces in the archaeological record.

Dimer formation by symbiotic donor–acceptor interaction between two molecules of a specially designed dioxomolybdenum(VI) complex containing both donor and acceptor centers – A structural, spectroscopic and DFT study

This work presents a model study for the formation of a dimeric dioxomolybdenum(VI) complex [MoO2L]2, generated by simultaneous satisfaction of acceptor and donor character existing in the corresponding monomeric Mo(VI) complex MoO2L. This mononuclear complex is specially designed to contain a coordinatively unsaturated Mo(VI) acceptor centre and a free donor group, (e.g. –NH2 group) strategically placed in the ligand skeleton [H2L = 2-hydroxyacetophenonehydrazone of 2-aminobenzoylhydrazine]. Apart from the dimer [MoO2L]2, complexes of the type MoO2L·B (where B = CH3OH, γ-picoline and imidazole) are also reported. All the complexes are characterized by elemental analysis, spectroscopic (UV–Vis, IR, 1H NMR) techniques and cyclic voltammetry. Single crystal X-ray structures of [MoO2L]2 (1), MoO2L·CH3OH (2), and MoO2L.(γ-pic) (3) have been determined and discussed. DFT calculation on these complexes corroborates experimental data and provides clue for the facile formation of this type of dimer not reported previously. The process of dimer formation may also be viewed as an interaction between two molecules of a specially designed complex acting as a monodentate ligand. This work is expected to open up a new field of design and synthesis of dimeric complexes through the process of symbiotic donor–acceptor (acid–base) interaction between two molecules of a specially designed monomer.

The response of the sea ice edge to atmospheric and oceanic jet formation

The sea ice edge presents a region of many feedback processes between the atmosphere, ocean, and sea ice (Maslowski et al.). Here the authors focus on the impact of on-ice atmospheric and oceanic flows at the sea ice edge. Mesoscale jet formation due to the Coriolis effect is well understood over sharp changes in surface roughness such as coastlines (Hunt et al.). This sharp change in surface roughness is experienced by the atmosphere and ocean encountering a compacted sea ice edge. This paper presents a study of a dynamic sea ice edge responding to prescribed atmospheric and oceanic jet formation. An idealized analytical model of sea ice drift is developed and compared to a sea ice climate model [the Los Alamos Sea Ice Model (CICE)] run on an idealized domain. The response of the CICE model to jet formation is tested at various resolutions. It is found that the formation of atmospheric jets at the sea ice edge increases the wind speed parallel to the sea ice edge and results in the formation of a sea ice drift jet in agreement with an observed sea ice drift jet (Johannessen et al.). The increase in ice drift speed is dependent upon the angle between the ice edge and wind and results in up to a 40% increase in ice transport along the sea ice edge. The possibility of oceanic jet formation and the resultant effect upon the sea ice edge is less conclusive. Observations and climate model data of the polar oceans have been analyzed to show areas of likely atmospheric jet formation, with the Fram Strait being of particular interest.

Effect of asparaginase on flavour formation in roasted coffee

The use of asparaginase, an enzyme that hydrolyses the acrylamide precursor asparagine into aspartic acid and ammonia, is seen as a promising procedure to mitigate the formation of the potential human carcinogen acrylamide in food products, without compromising desirable sensory qualities. This study examines the effect of asparaginase treatment on the asparagine and aspartic acid content of green coffee beans prior to roasting as well as the impact on the formation of acrylamide and thermally generated aroma compounds in roasted coffee

The Bone Formation Capabilities of the Anorganic Bone Matrix-Synthetic Cell-Binding Peptide 15 Grafts in an Animal Periodontal Model: A Histologic and Histomorphometric Study in Dogs

Background: The aim of this study is to verify the regenerative potential of particulate anorganic bone matrix synthetic peptide-15 (ABM-P-15) in class III furcation defects associated or not with expanded polytetrafluoroethylene membranes. Methods: Class III furcation defects were produced in the mandibular premolars (P2, P3, and P4) of six dogs and filled with impression material. The membranes and the bone grafts were inserted into P3 and P4, which were randomized to form the test and control groups, respectively; P2 was the negative control group. The animals were sacrificed 3 months post-treatment. Results: Histologically, the complete closure of class III furcation defects was not observed in any of the groups. Partial periodontal regeneration with similar morphologic characteristics among the groups was observed, however, through the formation of new cementum, periodontal ligament, and bone above the notch. Histologic analysis showed granules from the bone graft surrounded by immature bone matrix and encircled by newly formed tissue in the test group. The new bone formation area found in the negative control group was 2.28 +/- 2.49 mm(2) and in the test group it was 6.52 +/- 5.69 mm(2), which showed statistically significant differences for these groups considering this parameter (Friedman test P <0.05). There was no statistically significant difference among the negative control, control, and test groups for the other parameters. Conclusions: The regenerative potential of ABM-P-15 was demonstrated through new bone formation circumscribing and above the graft particles. The new bone also was accompanied by the formation of new cementum and periodontal ligament fibers. J Periodontol 2010;81:594-603.

Arrest of root formation in a permanent maxillary central incisor subsequent to trauma and pulp necrosis to the primary predecessor

This paper reports a case in which a previous traumatic injury at the age of 2 and pulp necrosis to a primary incisor resulted in a rare injury to the permanent successor tooth. The radiographic examination at the age of 9 showed the arrest of root formation of the permanent maxillary right central incisor, which did not erupt. Tooth 11 was extracted and a functional removable space maintainer was prepared. At the age of 17, the patient received an anterior fixed prosthesis for re-establishment of the esthetics, phonetics and deglutition.

Cell death and lumen formation in spheroids of MCF-7 cells

3D (three-dimensional) cell culture permits a more integrated analysis of the relationship between cells, inserting them into a structure more closely resembling the cellular microenvironment in vivo. The development of in vitro parameters to approximate in vivo 3D cellular environments makes a less reductionist interpretation of cell biology possible. For breast cells, in vitro 3D culture has proven to be an important tool for the analysis of luminal morphogenesis. A greater understanding of this process is necessary because alterations in the lumen arrangement are associated with carcinogenesis. Following lumen formation in 3D cell culture using laser scanning confocal microscopy, we observed alterations in the arrangement of cytoskeletal components (F-actin and microtubules) and increasing levels of cell death associated with lumen formation. The formation of a polarized monolayer facing the lumen was characterized through 3D reconstructions and the use of TEM (transmission electron microscopy), and this process was found to occur through the gradual clearing of cells from the medullary region of the spheroids. This process was associated with different types of cell death, such as apoptosis, autophagy and entosis. The present study showed that changes in the extracellular matrix associated with long periods of time in 3D cell culture lead to the formation of a lumen in MCF-7 cell spheroids and that features of differentiation such as lumen and budding formation occur after long periods in 3D culture, even in the absence of exogenous extracellular compounds.

Synthesis, mechanism of formation, and molecular orbital calculations of arylamidoximes

A simple and easy synthesis of ten arylamidoximes from arylnitriles and hydroxylamine is described. The formation of the arylamides has been observed to a much lesser extent in the present work. A new mechanism for the formation of arylamidoximes, as well as arylamides, from arylnitriles and hydroxylamine is suggested. Quantum mechanical calculations have been carried out to support this mechanism. The enthalpy of formation in conjunction with atomic charges of the reactants and intermediates helped to understand more about the generation of the products.

Conformational behavior of different possible ways of oligoglycine formation in a solvent-free environment

The possible ways for glycine oligopeptide formation in gas phase, both in the extended P-strand like conformation and folded 2(7)-ribbon like conformations are analyzed using quantum chemical calculations. We focus on the sequential formation of peptide bond through upgradation of the immediate lower order molecule and observe the consequences in other related processes like oligoglycine formation through simultaneous peptide linkage of n glycine monomers and interchange of molecular conformation through peptide linkage. A comparison is made between the structures and binding energies obtained for both conformers. All binding energies are increased by the zero-point energy contribution. The role of electron correlation effects is briefly analyzed. The folded 2(7)-ribbon-like conformations in vacuo are found to be more stable in comparison to the extended structure. (c) 2007 Elsevier B.V. All rights reserved.

Lead(II)-induced formation and coordination of 3,4-dihydro-3-thioxo-1,2,4-triazin-5(2H)-one

Cyclization of (n)butyl glyoxylate thiosemicarbazone (HBuTSC) under reflux in the presence of Pb(OAc)(2) led to tile formation of the complex [Pb(HTz)(2)] (H(2)Tz = 3,4-dihydro-3-thioxo-1,2,4-triazin-5(2H)-one), which after recrystallization from DMSO afforded the polymer [Pb(Tz)](n), the first example of a Tz(2-) metal complex. (C) 2008 Elsevier B.V. All rights reserved.