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Surface Sites (surface + site)
Selected AbstractsChemInform Abstract: Orthogonal, Convergent Syntheses of Dendrimers Based on Melamine with One or Two Unique Surface Sites for Manipulation.CHEMINFORM, Issue 3 2002Wen Zhang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] New insight on ,-lactoglobulin binding sites by 1-anilinonaphthalene-8-sulfonate fluorescence decayPROTEIN SCIENCE, Issue 10 2000Maddalena Collini Abstract The fluorescence time decay parameters of the ,-lactoglobulin-1-anilinonaphthalene-8-sulfonate complex have been investigated under physical and chemical perturbations (2 < pH < 8 and added electrolyte 0 < NaCl < 0.5 M) to obtain new insight on the nature of the protein binding interactions. A double exponential decay of the bound probe lifetime has been confirmed by the presence of a longer component, 11 to 14.5 ns, and a shorter component, 2.5 to 3.5 ns. The two lifetimes are ascribed to different binding modes associated also with different exposure to the solvent; in particular, the longer component is attributed to binding inside the hydrophobic beta barrel, while a "surface" site is suggested for the shorter component. A detailed analysis of the lifetime fractional intensities correlates the binding constants with ionic strength and supports the presence of electrostatic effects at both sites. A Debye,Hückel approach, applied to extrapolate the electrostatic free energy contribution vs. pH at vanishing ionic strength, gives interesting clues on the effective charge felt by the ANS ligands in the proximity of each site. In particular, binding is found to parallel the aspartate and glutamate titrations between pH 3 and pH 4.5; the "surface" site mainly responds to the presence of these local titrating charges while the "internal" site more closely follows the overall protein net charge. [source] Estimating the top-of-atmosphere longwave radiative forcing due to Saharan dust from satellite observations over a west African surface siteATMOSPHERIC SCIENCE LETTERS, Issue 3 2007H. E. Brindley Abstract This paper presents a methodology for estimating the longwave top-of-atmosphere direct radiative forcing due to Saharan dust aerosol from satellite observations made by the Spinning Enhanced Visible and Infrared Imager (SEVIRI) and Geostationary Earth Radiation Budget (GERB) instruments. Narrow-band observations from SEVIRI are used to detect dust presence and quantify its loading, while GERB provides an estimate of the dust impact on the total outgoing longwave radiation. Applying the technique to observations made over the Banizoumbou surface station in Niger through March,June 2006 indicates a midday longwave forcing efficiency of 17 ± 5 W m,2 per unit aerosol optical depth. Copyright © 2007 Royal Meteorological Society [source] Mercury binding on activated carbonENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 4 2006Bihter Padak Abstract Density functional theory has been employed for the modeling of activated carbon (AC) using a fused-benzene ring cluster approach. Oxygen functional groups have been investigated for their promotion of effective elemental mercury binding on AC surface sites. Lactone and carbonyl functional groups yield the highest mercury binding energies. Further, the addition of halogen atoms has been considered to the modeled surface, and has been found to increase the AC's mercury adsorption capacity. The mercury binding energies increase with the addition of the following halogen atoms, F > Cl > Br > I, with the fluorine addition being the most promising halogen for increasing mercury adsorption. © 2006 American Institute of Chemical Engineers Environ Prog, 2006 [source] Poorly crystalline mineral phases protect organic matter in acid subsoil horizonsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2005M. Kleber Summary Soil minerals are known to influence the biological stability of soil organic matter (SOM). Our study aimed to relate properties of the mineral matrix to its ability to protect organic C against decomposition in acid soils. We used the amount of hydroxyl ions released after exposure to NaF solution to establish a reactivity gradient spanning 12 subsoil horizons collected from 10 different locations. The subsoil horizons represent six soil orders and diverse geological parent materials. Phyllosilicates were characterized by X-ray diffraction and pedogenic oxides by selective dissolution procedures. The organic carbon (C) remaining after chemical removal of an oxidizable fraction of SOM with NaOCl solution was taken to represent a stable organic carbon pool. Stable organic carbon was confirmed as older than bulk organic carbon by a smaller radiocarbon (14C) content after oxidation in all 12 soils. The amount of stable organic C did not depend on clay content or the content of dithionite,citrate-extractable Fe. The combination of oxalate-extractable Fe and Al explained the greatest amount of variation in stable organic C (R2 = 0.78). Our results suggest that in acid soils, organic matter is preferentially protected by interaction with poorly crystalline minerals represented by the oxalate-soluble Fe and Al fraction. This evidence suggests that ligand exchange between mineral surface hydroxyl groups and negatively charged organic functional groups is a quantitatively important mechanism in the stabilization of SOM in acid soils. The results imply a finite stabilization capacity of soil minerals for organic matter, limited by the area density of reactive surface sites. [source] Coastal paleogeography and human land use at Tecolote Canyon, southern California, U.S.A.GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 2 2004René L. Vellanoweth A buried archaeological site at Tecolote Canyon provides an ideal case study for relating past human land use patterns to changes in coastal paleogeography. Postglacial sea level transgression, erosion, and other marine and fluvial processes form the context for examining two deeply buried archaeological components excavated at CA-SBA-72. Archaeological shellfish assemblages provide proxy data for evaluating the evolution of local marine environments. Pismo clams dominate shellfish assemblages dated to 5800 cal yr B.P., suggesting the presence of a broad and sandy, high-energy beach environment. At 5500 cal yr B.P., the almost exclusive use of California mussels by humans signals the development of rocky intertidal habitats. During the late Holocene, estuarine species dominate the marine mollusk assemblages at CA-SBA-72, reflecting the development of local estuarine conditions or trade with nearby Goleta Slough villages. The buried components at Tecolote Canyon appear to have served as temporary camps for shellfish harvesting and processing. While general changes in coastal paleogeography and human subsistence have been reconstructed for the Santa Barbara Coast, high resolution ecological data from Tecolote Canyon suggest that Native peoples also adapted to localized and shorter-term shifts in intertidal habitats, changes not evident in most larger or more disturbed surface sites in the region. Linking these changes with shifts in human land use patterns highlights the interaction between humans and a dynamic coastal system. These data demonstrate the importance of small, buried sites in understanding the full spectrum of human subsistence and settlement choices and local environmental change. © 2004 Wiley Periodicals, Inc. [source] Sensing of toxic metals through pH changes using a hybrid sorbent material: Concept and experimental validationAICHE JOURNAL, Issue 11 2009Prasun K. Chatterjee Abstract This article reports a new hybrid sorbent material that is capable of detecting trace concentration of toxic metals, such as zinc, lead, copper, nickel, etc., through pH changes only. The material is essentially a composite granular material synthesized through rapid fusion of a mixture of amorphous hydrated ferric oxide (HFO) and akermanite or calcium magnesium silicate (Ca2MgSi2O7). When a water sample is rapidly passed through a mini-column containing this hybrid material, effluent pH at the exit always remains alkaline (,9.0) because of slow hydrolysis of akermanite and steady release of hydroxyl (OH,) ions. This exit solution turns pink through the addition of a phenolphthalein indicator. Commonly encountered electrolytes containing sodium, calcium, chloride, and sulfate have no impact on the exit pH from the mini-column. However, when trace concentration of a heavy metal (say lead) is present in the sample water, a considerable drop in pH (>2 units) is observed for the exiting solution. At this point, the solution turns colorless through the addition of a phenolphthalein indicator. Moreover, the change in the slope of pH, i.e., ,dpH/dBV, provides a sharp, noticeable peak for each toxic metal where BV is the bed volumes of solution fed. The technique allowed detection of zinc and lead through pH swings in synthesized samples, spiked Bethlehem City water, and also in Lehigh River water in the presence of phosphate and natural organic matter (NOM). Using a simple preconcentration technique, lower than 10 ,g/l of lead was detected with a significant peak. From a mechanistic viewpoint, high sorption affinity of HFO surface sites toward toxic metal cations, ability of akermanite to maintain near-constant alkaline pH for a prolonged period through slow hydrolysis and labile metal-hydroxy complex formation causing dissipation of OH, ions from the aqueous phase provide a synergy that allows detection of toxic metals at concentrations well below 100 ,g/l through pH changes. Nearly all previous investigations pertaining to toxic metals sensing use metal-selective enzymes or organic chromophores. This simple-to-operate technique using an inexpensive hybrid material may find widespread applications in the developing world for rapid detection of toxic metals through pH changes. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] A retrospective analysis of two independent prospective cartilage repair studies: autogenous perichondrial grafting versus subchondral drilling 10 years post-surgeryJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 2 2002Phianne S. J. M. Bouwmeester Background: Experimental data indicate that perichondrial grafting to restore articular cartilage defects will result in repair with hyaline-like cartilage. In contrast, debridement and drilling results in repair with fibro-cartilage. In this retrospective study the longterm clinical results of both procedures were compared to evaluate the theoretical benefit of repair with hyaline-like tissue. Methods: From two independent studies patients were selected with a cartilage defect in their knee. The selection was performed using strict inclusion criteria published elsewhere [Bouwmeester et al. Int. Orthop. 21 (1997) 313]. The patients were treated with either a perichondrium transplantation (PT group, n = 14) or with an ,open' debridement and drilling procedure (DD group, n = 11). The results of both procedures after 10,11 years were evaluated using the Hospital for Special Surgery Knee Score (HSSS), X-ray examination, clinical examination and visual analogue scales (VAS) for pain during walking and at rest. Results: Both procedures resulted in a general improvement compared to the situation before the operation. After an average of 10 years in the PT group there were three failures, in the DD group none, success rates were 78% and 100%, respectively. When comparing the successful PT patients with the DD patients, there were no differences in HSSS and VAS data. Both groups showed an equal number of irregular operation surface sites on X-ray (PT 9/11 versus DD 8/10). Conclusions: This study shows that clinically at 10 years follow-up no difference was observed between debridement and drilling and perichondrium transplantation for treatment of an isolated cartilage defect. This raises questions about ongoing research to develop methods in order to improve the results of debridement and drilling as therapy for an isolated cartilage defect in a young patient (, 40 years). © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] Accurate long-range distance measurements in a doubly spin-labeled protein by a four-pulse, double electron,electron resonance methodMAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2008Michela G. Finiguerra Abstract Distance determination in disordered systems by a four-pulse double electron,electron resonance method (DEER or PELDOR) is becoming increasingly popular because long distances (several nanometers) and their distributions can be measured. From the distance distributions eventual heterogeneities and dynamics can be deduced. To make full use of the method, typical distance distributions for structurally well-defined systems are needed. Here, the structurally well-characterized protein azurin is investigated by attaching two (1-oxyl-2,2,5,5-tetramethylpyrroline-3-methyl) methanethiosulfonate spin labels (MTSL) by site-directed mutagenesis. Mutations at the surface sites of the protein Q12, K27, and N42 are combined in the double mutants Q12C/K27C and K27C/N42C. A distance of 4.3 nm is found for Q12C/K27C and 4.6 nm for K27C/N42C. For Q12C/K27C the width of the distribution (0.24 nm) is smaller than for the K27C/N42C mutant (0.36 nm). The shapes of the distributions are close to Gaussian. These distance distributions agree well with those derived from a model to determine the maximally accessible conformational space of the spin-label linker. Additionally, the expected distribution for the shorter distance variant Q12C/N42C was modeled. The width is larger than the calculated one for Q12C/K27C by 21%, revealing the effect of the different orientation and shorter distance. The widths and the shapes of the distributions are suited as a reference for two unperturbed MTSL labels at structurally well-defined sites. Copyright © 2008 John Wiley & Sons, Ltd. [source] Surface and interface investigations using radioactive atomsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004K. Potzger Abstract The magnetic behavior of isolated nonmagnetic probe atoms (Cd) at ferromagnetic Ni surfaces and interfaces have been studied using perturbed angular correlation (PAC) spectroscopy. Atomic resolution is achieved making it possible to distinguish between probe atoms at various surface sites, i.e., in/at terraces, atomic steps, kinks. These different atomic surface sites have differing Ni coordination numbers, (i.e., the number of Ni nearest neighbours). With decreasing coordination number, a continuous nonlinear dependent correlation was found with increasing magnetic hyperfine fields (Bhf). Furthermore, experimental evidence is presented, that the induced s-moments on the Cd isolated impurity is independent of the details of the surface symmetry but essentially determined only by the coordination number. Finally, it has been observed that monolayers of Pd on Ni form large unit cells, which offer selected sites to the Cd impurity. We discuss this finding as basic research towards future applications with self-organizing patterned structures. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||