X-ray scattering study of the effect of hydration on the cross-beta structure of amyloid fibrils

We have investigated the effect of sample hydration on the wide-angle X-ray scattering patterns of amyloid fibrils from two different sources, hen egg white lysozyme (HEWL) and an 11-residue peptide taken from the sequence of transthyretin (TTR105-115). Both samples show an inter-strand reflection at 4.7 Å and an inter-sheet reflection which occurs at 8.8 and 10 Å for TTR105-115 and HEWL fibrils, respectively. The positions, widths, and relative intensities of these reflections are conserved in patterns obtained from dried stalks and hydrated samples over a range of fibril concentrations. In 2D scattering patterns obtained from flow-aligned hydrated samples, the inter-strand and inter-sheet reflections showed, respectively, axial and equatorial alignment relative to the fibril axis, characteristic of the cross-β structure. Our results show that the cross-β structure of the fibrils is not a product of the dehydrating conditions typically employed to produce aligned samples, but is conserved in individual fibrils in hydrated samples under dilute conditions comparable to those associated with other biophysical and spectroscopic techniques. This suggests a structure consisting of a stack of two or more sheets whose interfaces are inaccessible to bulk water.

Quantum mechanics studies of the tautomers of diacetylformoin, an important maillard product and odorant

Diacetylformoin (3,4-dihydroxy-3-hexene-2,5-dione) has 16 tautomers, many with several possible conformations and all have been geometry optimised using quantum mechanics at the HF/6-31+G* level. Eleven structures have been identified with energies within 10 kcal mol(-1) of the minimum energy structure. Of these eight are acyclic and three cyclic. Calculations of NMR spectra have clarified the identity of the acyclic and cyclic structures found experimentally. The mechanism for cyclisation has been investigated and transition states obtained. The lowest energy reaction path requires the loss and gain of a proton during cyclisation. (c) 2006 Elsevier B.V. All rights reserved.

Synthesis and X-ray crystal structure of the triethylammonium magnesium β-octamolybdate(VI)salt[Et3NH]2[Mg(H2O)6Mo8O26]·2H2O

[Et3NH]4[Mo8O26] reacted with MgCl2 giving the triethylammonum magnesium β-octamolybdate(VI) salt [Et3NH]2[Mg(H2O)6Mo8O26]·2H2O (3) and the triethylammonium hydronium β-octaamolybdate(VI) salt [Et3NH]3[(H3O)Mo8O26·2H2O (4), respectively. A small amount of [Et3NH]2[Mo6O269] was formed as a by-product. The salts 3 and 4 were characterized by X-ray crystallography. The [Mg(H2O)6Mo8O26]2− moiety in 3 is polymeric, with each octahedral [Mg(H2O)6]2+ ion sandwiched between two β[Mo8O26]4− ions, being hydrogen bonded to three terminal MOO oxygen atoms on one face of each β[Mo8O26]4− ion. The X-ray crystal structure of 4 corresponds to the reported previously. IR and conductivity data are given for 3 and 4.

Synthesis and reactions of [Et3NH]4[Mo8O6]: X-ray crystal structure of [Et3NH]3[NaMo8O26]

[Et3NH]4[Mo8O26] (1) was prepared by reacting triethylamine with either molybdenum trioxide dihydrate or with a solution of ammonium molybdate in aqueous HCl. An aqueous solution of complex 1 reacted with an excess of sodium chloride to give a mixture of [Et3NH]3[NaMo8O26] (2) and [Et3NH]2[Mo6O19] (3). Complex 2 was also formed on reacting sodium molybdate with triethylamine in aqueous HCl. In the reaction of 1 with potassium chloride the nature of the product obtained was critically dependent upon reaction time. After a 5.5 h reflux period a mixture of [Et3NH]3[KMo8O26] (4) and 3 was obtained, whereas upon prolonged reflux (24 h) only K4Mo8O26 · H2O (5) was precipitated. The X-ray crystal structure of 2 shows it to be polymeric, with each Na+ ion sandwiched between two β[Mo8O26]4− ions. Four oxygen atoms on one face of each β[Mo8O26]4− ion are coordinated to a Na+ ion, and four oxygens from the opposite face are bonded to the next Na+ ion in the polymer chain. This produces a zig-zag arrangement of Na+ ions throughout the molecular structure. Spectral, conductivity and voltammetry data are given.

Alkenyl derivatives of the metals. Oxidative addition to intermediate tin(II) alkenyls; isolation, and crystal and molecular structure of n-butyltris(triphenylethenyl)tin(IV)

Reaction of tin(II) chloride with Li(CPhCPh2) at –78 °C in diethyl ether–hexane–tetrahydrofuran affords a deep red solution whose colour fades on warming, and which we believe contains the (unstable) first dialkenyltin(II) species. The latter survives long enough at low temperatures to undergo intermolecular oxidative addition, and one such adduct leads ultimately to the formation of Sn(CPhCPh2)3Bun, which has been fully characterised including a crystal and molecular structure study. The mechanism of formation of the final product has been examined and results are reported.

The impact of price promotions on producer strategies in markets with large product heterogeneity

Although current research indicates that increasing the number of options has negative effects on the cognitive ability of consumers, little understanding has been given to the consequences on producers and their strategic behavior. This article tests whether a large portfolio of products is beneficial to producers by observing UK consumer response to price promotions. The article shows that discounts induce mainly segment switching (74% of the total impact), with a limited effect on stockpiling (26%) and no impact on purchase incidence. Consequently, consumers prefer to “follow the discount” rather than purchase multiple units of the same wine. This result seems to explain the current structure of the market, and suggests that discounts may conflict with segment loyalty, a situation that disfavors producers, particularly in very populated segments. Results also casts doubts on the economic sustainability of competition based on an intense product differentiation in the wine sector.

Synthesis, crystal structure, and magnetic properties of a very rare double μ-1,1-azido- and a μ-1,1-(OMe)-bridged FeIII dimer containing a N,N,O-donor tridentate Schiff base ligand

Two new Fe-III complexes, [Fe2L2(mu-OMe)(2)(NCS)(2)] (1) and [Fe2L2(mu-N-3)(2)(N-3)(2)] (2), have been synthesized using a N,N,O-donor tridentate Schiff base ligand HL {2-[(2-dimethylaminoethylimino)methyl]phenol}, the condensation product of salicylaldehyde and N,N-dimethyl-1,2-diaminoethane. The complexes were characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Both crystal structures are centrosymmetric dimers containing two Fe-III atoms, which are bridged in compound 1 by two methoxy anions and in compound 2 by two mu-1,1-azides. The chelating tridentate Schiff base and a terminal thiocyanato (for 1) or azido (for 2) group complete the hexacoordination of the distorted octahedral environment of each iron center. The magnetic properties of compound 1 show the presence of antiferromagnetic exchange interactions mediated by double methoxy bridges (J = -29.45 cm(-1)). Compound 2 shows the presence of very weak ferromagnetic exchange interactions mediated by double mu-1,1-N-3 bridges (J = 1.08 cm(-1)).

Structure and magnetic properties of a tetranuclear Cu(II) complex containing the 2-(pyridine-2-yliminomethyl)-phenol ligand

A tetranuclear Cu(II) complex [Cu4L4(H2O)4](ClO4)4 has been synthesized using the terdentate Schiff base 2-(pyridine-2-yliminomethyl)-phenol (HL) (the condensation product of salicylaldehyde and 2-aminopyridine) and copper perchlorate. Chemical characterizations such as IR and UV/Vis of the complex have been carried out. A single-crystal diffraction study shows that the complex contains a nearly planar tetranuclear core containing four copper atoms, which occupy four equivalent five-coordinate sites with a square pyramidal environment. Magnetic measurements have been carried out over the temperature range 2–300K and with 100Oe field strengths. Analysis of magnetic susceptibility data indicates a strong antiferromagnetic (J1=−638cm−1) exchange interaction between diphenoxo-bridged Cu(II) centers and a moderate antiferromagnetic (J2=−34cm−1) interaction between N–C–N bridged Cu(II) centers. Magnetic exchange interactions (J’s) are also discussed on the basis of a computational study using DFT methodology. The spin density distribution (singlet ground state) is calculated to visualize the effect of delocalization of spin density through bridging groups.

Optimization of a sponge cake formulation with inulin as fat replacer: structure, physicochemical, and sensory properties

The effects of several fat replacement levels (0%, 35%, 50%, 70%, and 100%) by inulin in sponge cake microstructure and physicochemical properties were studied. Oil substitution for inulin decreased significantly (P < 0.05) batter viscosity, giving heterogeneous bubbles size distributions as it was observed by light microscopy. Using confocal laser scanning microscopy the fat was observed to be located at the bubbles’ interface, enabling an optimum crumb cake structure development during baking. Cryo-SEM micrographs of cake crumbs showed a continuous matrix with embedded starch granules and coated with oil; when fat replacement levels increased, starch granules appeared as detached structures. Cakes with fat replacement up to 70% had a high crumb air cell values; they were softer and rated as acceptable by an untrained sensory panel (n = 51). So, the reformulation of a standard sponge cake recipe to obtain a new product with additional health benefits and accepted by consumers is achieved.

Spatial expansion and population structure of the neotropical malaria vector, Anopheles darlingi (Diptera: Culicidae)

Extensive population structuring is known to occur in Anopheles darlingi, the primary malaria vector of the Neotropics. We analysed the phylogeographic structure of the species using the mitochondrial cytochrome oxidase I marker. Diversity is divided into six main population groups in South America: Colombia, central Amazonia, southern Brazil, south-eastern Brazil, and two groups in north-east Brazil. The ancestral distribution of the taxon is hypothesized to be central Amazonia, and there is evidence of expansion from this region during the late Pleistocene. The expansion was not a homogeneous front, however, with at least four subgroups being formed due to geographic barriers. As the species spread, populations became isolated from each other by the Amazon River and the coastal mountain ranges of south-eastern Brazil and the Andes. Analyses incorporating distances around these barriers suggest that the entire South American range of An. darlingi is at mutation-dispersal-drift equilibrium. Because the species is distributed throughout such a broad area, the limited dispersal across some landscape types promotes differentiation between otherwise proximate populations. Moreover, samples from the An. darlingi holotype location in Rio de Janeiro State are substantially derived from all other populations, implying that there may be additional genetic differences of epidemiological relevance. The results obtained contribute to our understanding of gene flow in this species and allow the formulation of human mosquito health protocols in light of the potential population differences in vector capacity or tolerance to control strategies. (C) 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 854-866.

THE ENDOPARASITE PILOSTYLES ULEI (APODANTHACEAE - CUCURBITALES) INFLUENCES WOOD STRUCTURE IN THREE HOST SPECIES OF MIMOSA

Pilostyles species (Apodanthaceae) are endoparasites in stems of the plant family Fabaceae. The body comprises masses of parenchyma in the host bark and cortex, with sinkers, comprising groups of twisted tracheal elements surrounded by parenchyma that enter the secondary xylem of the host plant. Here we report for the first time the effects of Pilostyles parasitism on host secondary xylem. We obtained healthy and parasitized stems from Mimosa foliolosa, M. maguirei and M. setosa and compared vessel element length, fiber length, vessel diameter and vessel frequency, measured through digital imaging. Also, tree height and girth were compared between healthy and parasitized M. setosa. When parasitized, plant size, vessel diameter, vessel element length and fiber length are all less than in healthy plants. Also, vessel frequency is greater and vessels are narrower in parasitized stems. These responses to parasitism are similar to those observed in stressed plants. Thus, hosts respond to the parasite by changing its wood micromorphology in favour of increased hydraulic safety.

STRUCTURE OF THE SHRUB-ARBOREAL COMPONENT OF AN ATLANTIC FOREST FRAGMENT ON A HILLOCK IN THE CENTRAL LOWLAND OF RIO DE JANEIRO, BRAZIL

The present study describes and evaluates the horizontal and vertical structures of a lowland forest fragment on a hillock in the municipality of Silva Jardim, Rio de Janeiro State, Brazil (22 degrees 31`56 `` S and 42 degrees 20`46 `` W). Twenty plots (10x2m) totaling 0.5ha were laid out following the slope grade using DBH >= 5cm as the inclusion criterion. A total of 734 individuals were encountered, yielding a total density of 1468 ind./ha and a total basal area of 10783m(2). The richness values (129 species/41 families), Shannon-Wiener diversity (4.22) and equitability (0.87) indices indicated an accentuated floristic heterogeneity and low ecological dominance. Lauraceae, Myrtaceae, Fabaceae and Euphorbiaceae showed the greatest species richness, corroborating other studies that indicated these species as the most representative of Atlantic Forest areas in southeastern Brazil. The species with the greatest importance values (VI) were Aparisthmium cordatum, Guapira opposita, Lacistema pubescens, Xylopia sericea, Tapirira guianensis and Piptocarpha macropoda. The high diversity observed was influenced by earlier anthropogenic actions and by the current successional stage. The forest fragment studied demonstrated closer floristic similarity to areas inventoried in a close-by biological reserve than to fragments dispersed throughout the coastal plain. Similarities in soil type, degree of soil saturation and use-history of forest resources all support these relationships. The fragmented physiognomy of the central lowland in this region and the use-history of the landscape make these small remnant forest areas important in terms of establishing strategies for landscape restoration and species conservation.

Dependence of the product on the P-P ligand in reactions of [RuCl(3)(NO)(P-P)] complexes (P-P = aromatic diphosphines) with 2-mercaptopyridine

This study presents the syntheses and characterization of 2-mercaptopyridine (pyS(-)) complexes containing ruthenium(II) with the following general formula [Ru(pyS)(2)(P-P)], P-P = (c-dppen) = cis-1,2-bis(diphenylphosphino)ethylene) (1); (dppe)=1,2-bis(diphenylphosphino)ethane (2); (dppp)=1,3-bis(diphenylphosphino)propane (3) and (dppb) = 1,4-bis(diphenylphosphino)butane (4). The complexes were synthesized from the mer- or fac-[RuCl(3)(NO)(P-P)] precursors in the presence of triethylamine in methanol solution with dependence of the product on the P-P ligand. The reaction of pyS- with a ruthenium complex containing a bulky aromatic diphosphine dppb disclosed a major product with a dangling coordinated dppbO-P, the [Ru(pyS)(2)(NO)(eta(1)-dppbO-P)]PF(6) (5). In addition, this work also presents and discusses the spectroscopic and electrochemical behavior of 1-5. and report the X-ray structures for I and S. (C) 2009 Elsevier Ltd. All rights reserved.

Quantitative structure-activity studies on a series of migrastatin analogs as inhibitors of cancer cell metastasis

Migrastatin, a macrolide natural product, and its structurally related analogs are potent inhibitors of cancer cell metastasis, invasion and migration. In the present work, a specialized fragment-based method was employed to develop QSAR models for a series of migrastatin and isomigrastatin analogs. Significant correlation coefficients were obtained (best model, q(2) = 0.76 and r(2) = 0.91) indicating that the QSAR models possess high internal consistency. The best model was then used to predict the potency of an external test set, and the predicted values were in good agreement with the experimental results (R(2) (pred) = 0.85). The final model and the corresponding contribution maps, combined with molecular modeling studies, provided important insights into the key structural features for the anticancer activity of this family of synthetic compounds based on natural products.

Synthesis and characterization of a new copper(II) complex with nadolol, an aminoalcoholic beta-blocker. Crystal structure of Na[Cu(nadololate)(CO(3))] center dot H(2)O

This work reports the synthesis and characterization of a new copper complex with nadolol, a beta-blocker aminoalcohol. The stoichiometry found was Na[Cu(nadololate)(CO(3))] center dot H(2)O. Electronic and vibrational spectroscopy analysis was performed, and the crystal structure of Na[Cu(nadololate)-(CO(3))] center dot H(2)O was determined by X-ray diffraction.