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Chemical Environment (chemical + environment)
Selected AbstractsNon-Tethered Organometallic Phosphonate Inhibitors for Lipase Inhibition: Positioning of the Metal Center in the Active Site of Cutinase,,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 28 2008Cornelis A. Kruithof Abstract Organometallic NCN-pincer complexes, bearing either a p -nitrophenyl phosphonate ester or a phosphonic acid group directly attached to the aromatic ring of the pincer complex, were synthesized. These compounds were tested as covalent inhibitors for the lipase cutinase. In a stoichiometric reaction of the NCN-pincer platinum phosphonate p -nitrophenyl ester 2 with cutinase, a 94,% conversion to the protein,pincer metal complex hybrid was obtained in 48 h. The NCN-pincer metal phosphonic acid derivatives (3, 4) appeared to be inactive as cutinase inhibitors. In contrast to our previous work which entails propyl tethered phosphonate esters connected to pincer metal complexes, the presented strategy allows positioning of metal complexes inside the active site of lipases. This opens up the possibility for fine-tuning the chemical environment (second coordination sphere) around a synthetic metal center inside the pocket of an enzyme for diagnostic and catalytic purposes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Taxon-specific variation in the stable isotopic signatures (,13C and ,15N) of lake phytoplanktonFRESHWATER BIOLOGY, Issue 5 2006KRISTIINA VUORIO Summary 1. The variability in the stable isotope signatures of carbon and nitrogen (,13C and ,15N) in different phytoplankton taxa was studied in one mesotrophic and three eutrophic lakes in south-west Finland. The lakes were sampled on nine to 16 occasions over 2,4 years and most of the time were dominated by cyanobacteria and diatoms. A total of 151 taxon-specific subsamples covering 18 different phytoplankton taxa could be isolated by filtration through a series of sieves and by flotation/sedimentation, followed by microscopical identification and screening for purity. 2. Substantial and systematic differences between phytoplankton taxa, seasons and lakes were observed for both ,13C and ,15N. The values of ,13C ranged from ,34.4, to ,5.9, and were lowest in chrysophytes (,34.4, to ,31.3,) and diatoms (,30.6, to ,26.6,). Cyanobacteria were most variable (,32.4, to ,5.9,), including particularly high values in the nostocalean cyanobacterium Gloeotrichia echinulata (,14.4, to ,5.9,). For ,13C, the taxon-specific amplitude of temporal changes within a lake was usually <1,8, (<1,4, for microalgae alone and <1,8, for cyanobacteria alone), whereas the amplitude among taxa within a water sample was up to 31,. 3. The values of ,15N ranged from ,2.1, to 12.8, and were high in chrysophytes, dinophytes and diatoms, but low in the nitrogen-fixing cyanobacteria Anabaena spp., Aphanizomenon spp. and G. echinulata (,2.1, to 1.6,). Chroococcalean cyanobacteria ranged from ,1.4, to 8.9,. For ,15N, the taxon-specific amplitude of temporal changes within a lake was 2,6,, (2,6, for microalgae alone and 2,4, for cyanobacteria alone) and the amplitude among taxa within a water sample was up to 11,. 4. The isotopic signatures of phytoplankton changed systematically with their physical and chemical environment, most notably with the concentrations of nutrients, but correlations were non-systematic and site-specific. 5. The substantial variability in the isotopic signatures of phytoplankton among taxa, seasons and lakes complicates the interpretation of isotopic signatures in lacustrine food webs. However, taxon-specific values and seasonal patterns showed some consistency among years and may eventually be predictable. [source] Living under an atomic force microscopeGEOBIOLOGY, Issue 3 2005An optimized approach for in vivo investigations on surface alterations towards biomineral nucleation on cyanobacterial cells ABSTRACT An approach for long-term in vivo investigations on cyanobacterial cell surface changes at high spatial resolution by Atomic Force Microscopy (AFM) was developed in this study. Until recently, changes of bacterial cell surfaces due to changes of the chemical environment could neither be investigated in situ nor in vivo. However, in vivo investigations give insights into kinetics of cell response to environmental changes and mineral nucleation at the cell's surface. Continuously cultured cyanobacteria of the representative freshwater strain Synechococcus leopoliensis (PCC 7942) were washed and artificially immobilized on poly-l-lysine-coated glass slides. Both immobilization and environmental conditions were optimized in order to facilitate long-term experiments (> 100 h) with living cells. AFM samples were investigated in situ in two different solutions: Culture medium was used for cultivation experiments and nutrient-free NaHCO3/CaCl2 solutions (supersaturated with respect to calcite) for long-term characterizations of the changes in cell surface topography. Cell viability under these conditions was investigated by AFM, TEM and epifluorescence microscopy, independently. No indications for extended starvation were found within the relevant timescales. Analysing the influence of Ca2+ on the surface of S. leopoliensis, we found significant changes compared to a Ca-free solution. Few hours after CaCl2 was added to the circumfluent solution, small protuberances were observed on the cell surface. These are promising results to environmental scientists for a wide range of applications, as cell response to environmental changes can now be monitored online and in vivo at timescales, which are relevant for natural processes. Most especially studies of biomineralization and mineral nucleation on bacterial cell surfaces will profit from this new approach. [source] Tunable Full-Color Pixels: Bioinspired Electrochemically Tunable Block Copolymer Full Color Pixels (Adv. Mater.ADVANCED MATERIALS, Issue 30 200930/2009) The cover represents 1D periodic lamellar block-copolymer photonic gels swollen with methanol and acetic acid and laser-etched to form the outline of a squid. Edwin Thomas and co-workers show on p. 3078 that the gel displays different colors in different areas due to the variation of the relative amounts of the two solvents. In nature, real cephalopods (squid, octopus, and cuttlefish) have the ability to change the chemical environment around their one-dimensional reflectors thus creating naturally tunable photonic elements. [source] An accurate total energy density functionalINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2007Baojing Zhou Abstract We propose a new density functional for the evaluation of the total electronic energy by subtracting the Roothaan energy, i.e. the Hartree energy of the density residual, from the Hohenberg,Kohn,Sham (HKS) functional, which is normally used in self-consistent Kohn,Sham (KS) density functional theory (DFT) calculations. Because of the positive semi-definite nature of the Roothaan energy, the resulting Wang,Zhou (WZ) functional always produces a total energy lower than that from the HKS functional and usually converges to the exact total energy from below. Following the same spirit of the Zhou,Wang-, (ZW,) functional in the recently proposed orbital-corrected orbital-free (OO) DFT method (Zhou and Wang, J Chem Phys 2006, 124, 081107), we linearly mix the WZ functional with the HKS functional to allow further systematic error cancellations. The resulting Wang,Zhou-, (WZ,) functional is compared with the ZW, functional in OO-DFT calculations for systems within different chemical environment. We find that the optimal value of , for the WZ, functional is more stable than that of , for the ZW, functional. This is because the WZ functional remedies the oscillatory convergence behavior of the Harris functional and renders the direct evaluation of , for the WZ, functional more plausible in the application of the linear-scaling OO-DFT method for large systems. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Accurate prediction of proton chemical shifts.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2001Abstract Forty-five proton chemical shifts in 14 aromatic molecules have been calculated at several levels of theory: Hartree,Fock and density functional theory with several different basis sets, and also second-order Møller,Plesset (MP2) theory. To obtain consistent experimental data, the NMR spectra were remeasured on a 500 MHz spectrometer in CDCl3 solution. A set of 10 molecules without strong electron correlation effects was selected as the parametrization set. The calculated chemical shifts (relative to benzene) of 29 different protons in this set correlate very well with the experiment, and even better after linear regression. For this set, all methods perform roughly equally. The best agreement without linear regression is given by the B3LYP/TZVP method (rms deviation 0.060 ppm), although the best linear fit of the calculated shifts to experimental values is obtained for B3LYP/6-311++G**, with an rms deviation of only 0.037 ppm. Somewhat larger deviations were obtained for the second test set of 4 more difficult molecules: nitrobenzene, azulene, salicylaldehyde, and o -nitroaniline, characterized by strong electron correlation or resonance-assisted intramolecular hydrogen bonding. The results show that it is possible, at a reasonable cost, to calculate relative proton shieldings in a similar chemical environment to high accuracy. Our ultimate goal is to use calculated proton shifts to obtain constraints for local conformations in proteins; this requires a predictive accuracy of 0.1,0.2 ppm. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1887,1895, 2001 [source] Community development along a proglacial chronosequence: are above-ground and below-ground community structure controlled more by biotic than abiotic factors?JOURNAL OF ECOLOGY, Issue 5 2010Matthew L. Carlson Summary 1.,We studied vascular plant and soil-dwelling testate amoeba communities in deglaciated sites across a range of substrate ages in Kenai Fjords, Alaska, USA to test four hypotheses. (i) Patterns of community assembly are similar for vascular plants and testate amoebae. (ii) Vascular plant and testate amoeba communities are more strongly correlated to abiotic variables than to each other, since these communities are not directly linked trophically. (iii) Plant community structure becomes less associated with abiotic condition in succession relative to testate amoebae, as species replacement is believed to be more common for plants than testate amoebae. (iv) Above- and below-ground communities become more strongly linked over the succession, due a shift from predominantly allogenic to autogenic forces. 2.,We assessed relationships among biotic communities and abiotic site variables across the chronosequence using multiple factor analysis, redundancy analysis (RDA) and a moving-window analysis. 3.,The diversity patterns and the communities' response to site and soil variables differed between groups. The composition of both communities was significantly explained by bedrock type and moisture regime. The vascular plant community, however, was more influenced by distance from the glacier. 4.,Testate amoeba and vascular plant community patterns were significantly linked to each other and to location and physical conditions. The moving-window RDA indicates the variation explained by the physical and chemical environment tended to slightly decrease through the chronosequence for testate amoebae, while a bell-shape response was evidenced for vascular plants. The variation of the microbial community explained by the plant community was very low in the early stages of the succession and became higher than the variation explained by the environmental variables later in the chronosequence. 5.,Synthesis. These results suggest that vascular plants and testate amoebae are as linked or more in ecosystem development than either community is to changes in site condition. Furthermore, the strength of interactions varies along the succession. Thus, ecological links may be more important than macro-scale abiotic site condition is to community development, even between communities without direct trophic interactions. [source] Olfactory receptors: G protein-coupled receptors and beyondJOURNAL OF NEUROCHEMISTRY, Issue 6 2009Marc Spehr Abstract Sensing the chemical environment is critical for all organisms. Diverse animals from insects to mammals utilize highly organized olfactory system to detect, encode, and process chemostimuli that may carry important information critical for health, survival, social interactions and reproduction. Therefore, for animals to properly interpret and react to their environment it is imperative that the olfactory system recognizes chemical stimuli with appropriate selectivity and sensitivity. Because olfactory receptor proteins play such an essential role in the specific recognition of diverse stimuli, understanding how they interact with and transduce their cognate ligands is a high priority. In the nearly two decades since the discovery that the mammalian odorant receptor gene family constitutes the largest group of G protein-coupled receptor (GPCR) genes, much attention has been focused on the roles of GPCRs in vertebrate and invertebrate olfaction. However, is has become clear that the ,family' of olfactory receptors is highly diverse, with roles for enzymes and ligand-gated ion channels as well as GPCRs in the primary detection of olfactory stimuli. [source] Environmental damage and occlusal contact area wear of composite restorativesJOURNAL OF ORAL REHABILITATION, Issue 1 2002A. U. J. Yap The chemical environment is one aspect of the oral environment, which could have an appreciable influence on the in-vivo degradation of composite resins. The resin matrix can be softened and fillers constituents can be leached out when composites are exposed to certain chemicals/food-simulating liquids (FSLs). A reciprocal compression sliding wear device was used to study the effects of the chemical environment on occlusal contact area (OCA) wear of four composite restoratives (Silux Plus, Z100, Ariston pHc and Surefil). The effects of FSL on hardness was also investigated and correlated to wear. Thirty-six hardness/wear specimens of each material were made and stored in artificial saliva at 37 °C for 24 h. The specimens were then divided into six groups of six specimens and stored in the following FSL for 1 week at 37 °C: distilled water (W), 0·02 N citric acid (C), 0·02 N lactic acid (L), heptane (H) and 75,25% ethanol,water solution (E). Conditioning in artificial saliva (S) was used as control. After conditioning, the specimens were wear tested at 20 MPa contact stress against SS304 counter-bodies in the respective FSL/artificial saliva up to 20 000 cycles. Wear depth (lm, n=6) was measured using profilometry. Change in hardness (,KHN, Knoop hardness number) was determined by microhardness testing pre- and post-conditioning. Results of statistical analyses (ANOVA/Scheffe's at significance level 0·05) of wear data were as follows: Silux , S, W > L, H, E and C, L > H; Z100 , S, W > all other mediums and E > H; Ariston , all other mediums > H; Surefil , W, C > S, L, H, E (> indicates significantly more wear). With the exception of Surefil, the greatest wear was observed with conditioning and wear testing in water. This ranged from 93·18 ± 21·96 lm for Z100 to 31·43 ± 2·80 lm for Surefil. For all materials, conditioning in heptane resulted in the least wear. This ranged from 8·9 ± 2·2 ,m for Ariston to 16·5 ± 5·9 lm for Silux. The effects of the different FSL on OCA wear were material dependent. No correlation was observed between ,KHN and wear. [source] Probing residue-specific interactions in the stabilization of proteins using high-resolution NMR: A study of disulfide bond compensationJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2010Andria L. Skinner Abstract It is well established that the oxidation state of cysteine residues in proteins is critical to overall physical stability. Disulfide bonds most often impart thermodynamic stability, but in some cases, diminish it. Predicting the circumstances that lead to each outcome is difficult because mechanistic information is lacking. Because the techniques typically used to study protein stability do not provide sufficient detail, high-resolution NMR was used in combination with low-resolution analysis to obtain mechanistic information regarding disulfide bond formation in a model protein. Tm (CD) and Tonset (SLS) for the reduced and oxidized wild type and C104S and C49S mutants were measured. The mutant proteins have altered Tms and Tonsets compared to the reduced wild type, indicating that differences in local interactions of the Cys side chains are important for stability. The NMR spectra clearly show distinct differences in the chemical environment surrounding these Cys residues and the overall tertiary structure. The C49S protein, which is less stable and more aggregation prone than reduced wild type, lacks a hydrogen bond between Y53 and H103. Increased flexibility of the Y53-containing loop is correlated with increased dynamics and unraveling of ,2, which likely leads to edge strand initiated aggregation of the central ,-sheet. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 2643,2654, 2010 [source] Mass spectrometry in bioinorganic analytical chemistryMASS SPECTROMETRY REVIEWS, Issue 2 2006Ryszard Abstract A considerable momentum has recently been gained by in vitro and in vivo studies of interactions of trace elements in biomolecules due to advances in inductively coupled plasma mass spectrometry (ICP MS) used as a detector in chromatography and capillary and planar electrophoresis. The multi-isotopic (including non-metals such as S, P, or Se) detection capability, high sensitivity, tolerance to matrix, and large linearity range regardless of the chemical environment of an analyte make ICP MS a valuable complementary technique to electrospray MS and MALDI MS. This review covers different facets of the recent progress in metal speciation in biochemistry, including probing in vitro interactions between metals and biomolecules, detection, determination, and structural characterization of heteroatom-containing molecules in biological tissues, and protein monitoring and quantification via a heteroelement (S, Se, or P) signal. The application areas include environmental chemistry, plant and animal biochemistry, nutrition, and medicine. © 2005 Wiley Periodicals, Inc. Mass Spec Rev 25:255,289, 2006 [source] Changes in afferent activity after spinal cord injury,NEUROUROLOGY AND URODYNAMICS, Issue 1 2010William C. de Groat Abstract Aims To summarize the changes that occur in the properties of bladder afferent neurons following spinal cord injury. Methods Literature review of anatomical, immunohistochemical, and pharmacologic studies of normal and dysfunctional bladder afferent pathways. Results Studies in animals indicate that the micturition reflex is mediated by a spinobulbospinal pathway passing through coordination centers (periaqueductal gray and pontine micturition center) located in the rostral brain stem. This reflex pathway, which is activated by small myelinated (A,) bladder afferent nerves, is in turn modulated by higher centers in the cerebral cortex involved in the voluntary control of micturition. Spinal cord injury at cervical or thoracic levels disrupts voluntary voiding, as well as the normal reflex pathways that coordinate bladder and sphincter function. Following spinal cord injury, the bladder is initially areflexic but then becomes hyperreflexic due to the emergence of a spinal micturition reflex pathway. The recovery of bladder function after spinal cord injury is dependent in part on the plasticity of bladder afferent pathways and the unmasking of reflexes triggered by unmyelinated, capsaicin-sensitive, C-fiber bladder afferent neurons. Plasticity is associated with morphologic, chemical, and electrical changes in bladder afferent neurons and appears to be mediated in part by neurotrophic factors released in the spinal cord and the peripheral target organs. Conclusions Spinal cord injury at sites remote from the lumbosacral spinal cord can indirectly influence properties of bladder afferent neurons by altering the function and chemical environment in the bladder or the spinal cord. Neurourol. Urodynam. 29: 63,76, 2010. © 2009 Wiley-Liss, Inc. [source] Environmental Effects on the Photochemistry of A2-E, a Component of Human Retinal Lipofuscin,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2001Laura Ragauskaite ABSTRACT Several retinal dystrophies are associated with the accumulation of lipofuscin, a pigment mixture, in the retinal pigment epithelium (RPE). One of the major fluorophores of this mixture has been identified as the bis-retinoid pyridinium compound, A2-E. Because this compound absorbs incident radiation that is transmitted by the anterior segment of the human eye, photophysical and photochemical studies were performed to determine if A2-E could photosensitize potentially damaging reactions. Steady-state fluorescence measurements indicate that the fluorescence emission maximum and quantum yield are very sensitive to the chemical environment and a correlation between these two parameters and the solvent dielectric constant is observed. Time-resolved absorption experiments of A2-E in pure organic solvents showed no formation of transient species on the timescale of our experiments. However, when these measurements were repeated for A2-E in Triton X-100 micelles, a short-lived (,, 14 ,s), weak absorption was observed. This species is quenched by oxygen (k= 2 × 109M,1 s,1) and by the addition of the antioxidants, cysteine and N,N,N,,N, -tetramethylphenylenediamine. Quenching of this species by 2,3,5-trimethylhydroquinone results in the formation of the 2,3,5-trimethylsemiquinone free radical and an increase in yield of the A2-E,derived species. Sensitization of the A2-E triplet excited state indicates that the species observed in micelles upon direct excitation is not consistent with the triplet excited state. Based on these data we tentatively assign this absorption to a free radical. In the RPE these initial processes can ultimately lead to damage to the tissue through the formation of peroxides and other oxidized species. [source] Core-level shifts in complex metallic systems from first principlePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2006Weine Olovsson Abstract We show that core-level binding energy shifts (CLS) can be reliably calculated within density functional theory. The scheme includes both the initial (electron energy eigenvalue) as well as final state (relaxation due to core-hole screening) effects in the same framework. The results include CLS as a function of composition in substitutional random bulk and surface alloys. Sensitivity of the CLS to the local chemical environment in the bulk and at the surface is demonstrated. A possibility to use the CLS for structural determination is discussed. Finally, an extension of the model is made for Auger kinetic energy shift calculations. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ab initio investigation of the LiNbO3 (0001) surfacePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010Simone Sanna Abstract The polar surfaces of ferroelectric LiNbO3 have been investigated by an ab initio thermodynamical approach. Basing on density functional theory total energy calculations, we discuss the relative stability of a series of candidate surface structures with varying stoichiometry and surface reconstruction in dependence on the chemical environment. We determine the equilibrium geometry for the positively and negatively polarised surfaces and then discuss the influence of different stabilising mechanisms on the preferred terminations. Positive and negative surfaces are found to have different structure, stoichiometry and ionisation energy. The positive surface is found to contain more oxygen than the negative surface at similar conditions. Different stabilisation mechanisms like stoichiometry modification and reconstruction contribute to stabilise the polar surfaces (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Denaturing and refolding of protein molecules on surfacesPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 11 2007Bryan Holtz Abstract Keeping protein molecules in the active state on a solid surface is essential to protein microarrays and other protein-based biosensors. Here, we show that the 2-D chemical environment controls the refolding of the denatured green fluorescent proteins tethered to solid surfaces. Refolding occurs readily on the repulsive PEG functionalized surface but is inhibited on the attractive ,NH2 functionalized surface. This result shows the critical importance of the 2-D chemical environment in the maintenance and revival of protein activity on surfaces and opens the door to designing 2-D molecular chaperones for protein folding. [source] Microwave-assisted specific chemical digestion for rapid protein identificationPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 2 2006Lin Hua Abstract We have developed a rapid microwave-assisted protein digestion technique based on classic acid hydrolysis reaction with 2% formic acid solution. In this mild chemical environment, proteins are hydrolyzed to peptides, which can be directly analyzed by MALDI-MS or ESI-MS without prior sample purification. Dilute formic acid cleaves proteins specifically at the C-terminal of aspartyl (Asp) residues within 10,min of exposure to microwave irradiation. By adjusting the irradiation time, we found that the extent of protein fragmentation can be controlled, as shown by the single fragmentation of myoglobin at the C-terminal of any of the Asp residues. The efficacy and simplicity of this technique for protein identification are demonstrated by the peptide mass maps of in-gel digested myoglobin and BSA, as well as proteins isolated from Escherichia coli,K12 cells. [source] Extraction of functional motion in trypsin crystal structuresACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2005Andrea Schmidt The analysis of anisotropic atomic displacement parameters for the direct extraction of functionally relevant motion from X-ray crystal structures of Fusarium oxysporum trypsin is presented. Several atomic resolution structures complexed with inhibitors or substrates and determined at different pH values and temperatures were investigated. The analysis revealed a breathing-like molecular motion conserved across trypsin structures from two organisms and three different crystal forms. Directional motion was observed suggesting a change of the width of the substrate-binding cleft and a change in the length of the specificity pocket. The differences in direction of motion across the structures are dependent on the mode of substrate or inhibitor binding and the chemical environment around the active-site residues. Together with the occurrence of multiple-residue conformers, they reflect spatial rearrangement throughout the deacylation pathway. [source] Hip holes: kangaroo (Macropus spp.) resting sites modify the physical and chemical environment of woodland soilsAUSTRAL ECOLOGY, Issue 5 2002D. J. Eldridge Abstract Hip holes are shallow, reniform-shaped depressions found next to the trunks of many trees and shrubs in arid and semi-arid Australia. They are constructed by kangaroos (Macropus spp.), who use them as diurnal resting sites, particularly during hot weather. Physical and chemical properties of soils in hip holes were compared with non-hole microsites adjacent to the trunk (,trunk'), microsites below the canopy (,canopy') and microsites out in the open (,open') under two trees (Eucalyptus intertexta, Alectryon oleifolius) and one shrub (Dodonaea viscosa) in a semi-arid woodland in eastern Australia. Overall, there were few effects under D. viscosa apart from a greater (10-fold) mass of litter in the hip holes compared with the trunk microsite. Hip holes under E. intertexta and A. oleifolius, however, contained six times more dung compared with the trunk microsite. For the two tree species, soils in the hip holes were significantly more erodible, as measured by aggregation levels, compared with the other microsites, but there were no significant differences in bulk density nor pH. Steady-state infiltration rates at the hip hole and trunk microsites were significantly greater than those in the open, but there was no significant hip hole effect. Soils in the hip holes contained greater levels of exchangeable calcium and magnesium (E. intertexta) and greater exchangeable sodium (A. oleifolius) compared with trunk microsites. Hip holes under E. intertexta contained approximately 68% more organic carbon, total carbon and nitrogen, and 86% more sulfur compared with trunk microsites. Similarly, hip holes under A. oleifolius contained on average 38% more organic and total carbon, and 47% more nitrogen than trunk microsites. Given the density of hip holes and their impact on soil chemistry, kangaroos are considered to be important elements in the maintenance of heterogeneity in these woodlands. [source] Plagioclase replacement textures in partially eclogitised gabbros from the Sanddal mafic-ultramafic complex, Greenland CaledonidesJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2001H. M. Lang Abstract The Sanddal mafic-ultramafic complex (SMUK) is a cluster of variably eclogitised mafic and ultramafic bodies that comprise the westernmost known eclogite facies locality in the North-East Greenland eclogite province (NEGEP). Although there are no true eclogites in the SMUK, we interpret three distinct textural types of plagioclase replacement to record sequential stages in adjustment of SMUK olivine gabbro-norites to eclogite facies conditions. The earliest stage, in which plagioclase was replaced by omphacite/spinel symplectite before nucleation of garnet (Type 1A & 1B) has not previously been described. Documentation of this texture provides clear evidence that, at least in some cases, garnet nucleation is delayed relative to nucleation of omphacite and is a rate-limiting step for eclogitisation. Type 1C domains were produced by scattered nucleation of garnet in the same sample. In Type 2 domains, plagioclase was replaced by a layered corona with an outer layer of garnet, an inner layer of omphacite and an interior of inclusion-rich plagioclase. In Type 3 domains, the omphacite layer was overgrown by the garnet rim, and omphacite is preserved only as inclusions in garnet. In more coarse grained leucogabbros, recrystallization was more complete, plagioclase replacement textures were less localised, and could not be divided into distinct stages. Plagioclase replacement in SMUK samples was not isochemical, and required diffusion of at least Mg and Fe from replacement of mafic phases in the surroundings. Strong compositional gradients in garnet reflect disequilibrium and were controlled by the different diffusion rates of Mg/Fe and Ca, different local chemical environments, and progress of the plagioclase breakdown reaction. The presence of small amounts of hydrous minerals (amphibole, phlogopite and clinozoisite) in local equilibrium in plagioclase domains of most SMUK samples indicates that a small amount of H2O was present during high pressure metamorphism. [source] DFT-GIAO 1H and 13C NMR prediction of chemical shifts for the configurational assignment of 6,-hydroxyhyoscyamine diastereoisomersMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2009Marcelo A. Muñoz Abstract 1H and 13C NMR chemical shift calculations using the density functional theory,gauge including/invariant atomic orbitals (DFT,GIAO) approximation at the B3LYP/6-311G++(d,p) level of theory have been used to assign both natural diastereoisomers of 6,-hydroxyhyoscyamine. The theoretical chemical shifts of the 1H and 13C atoms in both isomers were calculated using a previously determined conformational distribution, and the theoretical and experimental values were cross-compared. For protons, the obtained average absolute differences and root mean square (rms) errors for each comparison showed that the experimental chemical shifts of dextrorotatory and levorotatory 6,-hydroxyhyoscyamines correlated well with the theoretical values calculated for the (3R,6R,2,S) and (3S,6S,2,S) configurations, respectively, whereas for 13C atoms the calculations were unable to differentiate between isomers. The nature of the relatively large chemical shift differences observed in nuclei that share similar chemical environments between isomers was asserted from the same calculations. It is shown that the anisotropic effect of the phenyl group in the tropic ester moiety, positioned under the tropane ring, has a larger shielding effect over one ring side than over the other one. Copyright © 2009 John Wiley & Sons, Ltd. [source] Molecular approach to aquatic environmental bioreporting: differential response to environmental inducers of cytochrome P450 monooxygenase genes in the detritivorous subalpine planktonic Crustacea, Daphnia pulexMOLECULAR ECOLOGY, Issue 9 2003P. David Abstract In order to examine the usefulness of detoxifying genes as molecular markers in different chemical environments, isolation of cytochrome P450 genes (CYPs) belonging to the CYP4 family was performed in different samples from two subalpine populations of Daphnia pulex. The use of degenerate primers allowed us to isolate seven cDNAs. Four of them were assigned to the CYP4C subfamily, and were closely related to previously isolated crustacean CYP4s while the others were assigned to new CYP4AN and CYP4AP subfamilies. Expression studies, using semiquantitative polymerase chain reaction (PCR) followed by Southern blot hybridization with specific probes revealed differences in CYP4C32 and CYP4AP1 expressions between the two populations, which differ in the polyphenol richness of the vegetation surrounding their aquatic habitat. Further exposure to toxic dietary polyphenols showed different CYP induction patterns. Taken together, these preliminary results suggest a possible involvement of CYP4s in the ecological differentiation of subalpine D. pulex populations related to the polyphenol richness of the environmental vegetation. CYP4s may thus be considered as possible molecular markers in aquatic environmental bioreporting. [source] Synthesis and structure of BN-doped multi-walled and single-walled carbon nanotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006S. Enouz Abstract We report on the direct synthesis of different kinds of BN,C multi-walled and single-walled nanotubes exhibiting a segregation between BN and C domains. Multi-walled BN,C nanotubes (MW-BN/C-NTs) were synthesized using the aerosol method whereas single-walled BN,C nanotubes (SW-BN/C-NTs) have been for the first time produced using a continuous CO2 -laser vaporization process [S. Enouz et al., to be published]. Degrees of purity, homogeneity and yield have been estimated from a systematic inspection of the samples by scanning electron microscopy. Structure of these tubes and spatial distribution of C, B and N as well as their chemical environments have been inspected at the nanometer scale by combining high resolution transmission microscopy and nano-electron energy loss spectroscopy. These analyses provide clear evidence of new kinds of arrangements of C, B and N within the graphene layer, which are due to the segregation properties of h-BN and graphite. Thus, combining BN and C elements into nanotubular systems can open the way to a broad range of new nanodevices. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ionic polymer-metal composites as multifunctional materialsPOLYMER COMPOSITES, Issue 1 2003Mohsen Shahinpoor This paper presents a description and a set of experimental results on Ionic Polymer-Metal Composites (IPMC's) as dynamic sensors, transducers, and actuators. Strips of IPMC can exhibit large dynamic deformation if placed in a time-varying electric field of the order of 10's of volts/mm. Conversely, dynamic deformation and flexing of such ionic polymers produces dynamic electric fields that closely follow the form of the electric signal. The underlying principle of such a mechanoelectric effect in IPMC's can be explained by the linear irreversible thermodynamics in which ion and solvent transport are the fluxes and electric field and solvent pressure gradient are the forces. Important parameters include the material conductance and the solvent permeability. The dynamic sensing, transduction, and actuation responses of a strip of IPMC under an impact-type loading is also discussed. When a cantilever strip of IPMC is flipped, a damped oscillatory electric response is produced across a pair of electrodes placed at the cantilever of the strip, which is highly repeatable with a broad frequency range above 104 Hz. Such direct mechanoelectric responses of IMPC's are related to the endo-ionic mobility due to stresses imposed. Imposition of a finite solvent flux without allowing a current flux causes the material to create a certain conjugate electric field that can be dynamically monitored and measured. IPMC's are shown to be highly capacitive at low frequencies while they are highly resistive under high frequency excitations. IN a sending mode, IPMC strips can also sense chemical environments and humidity. These types of sensors/transducers/actuators conceivably can replace piezoresistive and piezoelectric sensors with just one sensor for broad ranges of frequencies. [source] Bond lengths in organic and metal-organic compounds revisited: X,H bond lengths from neutron diffraction dataACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010Frank H. Allen The number of structures in the Cambridge Structural Database (CSD) has increased by an order of magnitude since the preparation of two major compilations of standard bond lengths in mid-1985. It is now of interest to examine whether this huge increase in data availability has implications for the mean bond-length values published in the late 1980s. Those compilations reported mean X,H bond lengths derived from rather sparse information and for rather few chemical environments. During the intervening years, the number of neutron studies has also increased, although only by a factor of around 2.25, permitting a new analysis of X,H bond-length distributions for (a) organic X = C, N, O, B, and (b) a variety of terminal and homometallic bridging transition metal hydrides. New mean values are reported here and are compared with earlier results. These new overall means are also complemented by an analysis of X,H distances at lower temperatures (T, 140,K), which indicates the general level of librational effects in X,H systems. The study also extends the range of chemical environments for which statistically acceptable mean X,H bond lengths can be obtained, although values from individual structures are also collated to further extend the chemical range of this compilation. Updated default `neutron-normalization' distances for use in hydrogen-bond and deformation-density studies are also proposed for C,H, N,H and O,H, and the low-temperature analysis provides specific values for certain chemical environments and hybridization states of X. [source] A neutron diffraction study of xylitol: derivation of mean square internal vibrations for H atoms from a rigid-body descriptionACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2003Anders Østergaard Madsen A neutron diffraction study of xylitol (C5O5H12) is presented. The nuclear anisotropic displacement parameters have been analysed showing that the carbon,oxygen skeleton conforms to a rigid-body (TLS) description. Applying this TLS model to the xylitol H atoms allows characterization of the internal molecular displacements of the H nuclei, assuming that the observed H nuclear mean-square displacements are a sum of the internal displacements and rigid-body displacements. These internal molecular displacements are very similar for chemically equivalent H atoms and in good agreement with the values obtained by other methods. In all cases the smallest eigenvector of the residual mean-square displacement tensor is almost parallel to the X,H bond. The use of ab initio calculations to obtain the internal vibrations in xylitol is discouraging. Another 12 structures extracted from the literature which have been investigated by neutron diffraction were subjected to a similar analysis. The results for the nine compounds investigated at low temperature conform to the results from xylitol and provide estimates of the internal vibrations of H atoms in a range of chemical environments. [source] Windows to cell function and dysfunction: Signatures written in the boundary layersBIOESSAYS, Issue 6 2010Peter J. S. Smith Abstract The medium surrounding cells either in culture or in tissues contains a chemical mix varying with cell state. As solutes move in and out of the cytoplasmic compartment they set up characteristic signatures in the cellular boundary layers. These layers are complex physical and chemical environments the profiles of which reflect cell physiology and provide conduits for intercellular messaging. Here we review some of the most relevant characteristics of the extracellular/intercellular space. Our initial focus is primarily on cultured cells but we extend our consideration to the far more complex environment of tissues, and discuss how chemical signatures in the boundary layer can or may affect cell function. Critical to the entire essay are the methods used, or being developed, to monitor chemical profiles in the boundary layers. We review recent developments in ultramicro electrochemical sensors and tailored optical reporters suitable for the task in hand. [source] | |||||||||||||||||||||||||||||||||||||