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1

Pulsed hydrogen/deuterium exchange mass spectrometry for time-resolved membrane protein folding studies.  

PubMed

Kinetic folding experiments by pulsed hydrogen/deuterium exchange (HDX) mass spectrometry (MS) are a well-established tool for water-soluble proteins. To the best of our knowledge, the current study is the first that applies this approach to an integral membrane protein. The native state of bacteriorhodopsin (BR) comprises seven transmembrane helices and a covalently bound retinal cofactor. BR exposure to sodium dodecyl sulfate (SDS) induces partial unfolding and retinal loss. We employ a custom-built three-stage mixing device for pulsed-HDX/MS investigations of BR refolding. The reaction is triggered by mixing SDS-denatured protein with bicelles. After a variable folding time (10?ms to 24?h), the protein is exposed to excess D(2) O buffer under rapid exchange conditions. The HDX pulse is terminated by acid quenching after 24?ms. Subsequent off-line analysis is performed by size exclusion chromatography and electrospray MS. These measurements yield the number of protected backbone N-H sites as a function of folding time, reflecting the recovery of secondary structure. Our results indicate that much of the BR secondary structure is formed quite late during the reaction, on a time scale of 10?s and beyond. It is hoped that in the future it will be possible to extend the pulsed-HDX/MS approach employed here to membrane proteins other than BR. PMID:23280751

Khanal, Anil; Pan, Yan; Brown, Leonid S; Konermann, Lars

2012-12-01

2

Infrared spectroscopic study of photoreceptor membrane and purple membrane. Protein secondary structure and hydrogen deuterium exchange  

SciTech Connect

Infrared spectroscopy in the interval from 1800 to 1300 cm-1 has been used to investigate the secondary structure and the hydrogen/deuterium exchange behavior of bacteriorhodopsin and bovine rhodopsin in their respective native membranes. The amide I' and amide II' regions from spectra of membrane suspensions in D2O were decomposed into constituent bands by use of a curve-fitting procedure. The amide I' bands could be fit with a minimum of three theoretical components having peak positions at 1664, 1638, and 1625 cm-1 for bacteriorhodopsin and 1657, 1639, and 1625 cm-1 for rhodopsin. For both of these membrane proteins, the amide I' spectrum suggests that alpha-helix is the predominant form of peptide chain secondary structure, but that a substantial amount of beta-sheet conformation is present as well. The shape of the amide I' band was pH-sensitive for photoreceptor membranes, but not for purple membrane, indicating that membrane-bound rhodopsin undergoes a conformation change at acidic pH. Peptide hydrogen exchange of bacteriorhodopsin and rhodopsin was monitored by observing the change in the ratio of integrated absorbance (Aamide II'/Aamide I') during the interval from 1.5 to 25 h after membranes were introduced into buffered D2O. The fraction of peptide groups in a very slowly exchanging secondary structure was estimated to be 0.71 for bacteriorhodopsin at pD 7. The corresponding fraction in vertebrate rhodopsin was estimated to be less than or equal to 0.60. These findings are discussed in relationship to previous studies of hydrogen exchange behavior and to structural models for both proteins.

Downer, N.W.; Bruchman, T.J.; Hazzard, J.H.

1986-03-15

3

Hydrogen-deuterium exchange studies of the rat thyroid transcription factor 1 homeodomain.  

PubMed

The 1H NMR solution structure of the rat thyroid transcription factor 1 homeodomain (TTF-1 HD) showed that the molecule folds like classical homeodomains. The C-terminal extension of helix III (fragment 51-59) appeared to adopt a helical geometry, albeit not as rigid as the preceding portion, but the hydrogen-deuterium exchange of backbone amides and the NOE data provided evidence of a discontinuity between the two moieties of helix III at the highly conserved fragment Asn51-His52-Arg53. Analysis of quantitative measurements of isotope exchange rates allows one to recognize the general occurrence, in that region of HD motifs, of opposite effects to helix III stability. Asparagine, histidine and arginine residues occur most frequently at the beginning and end of protein helices. In TTF-1 HD a local fluctuation is observed in the fragment 51-53 which either kinks or tightens the alpha-helix. A search through the protein structure database reveals that the three most common variants of HD fragments 51-53 are often involved in helices and, frequently, in helix initiation or termination. For homeodomains in general, the nature of the fragment 51-53 may be related to the conformational dynamics of their DNA-recognition helix (helix III). Besides the specific results on fragment 51-53, the complete isotope exchange analysis of TTF-1 HD data shows that the partially solvent-exposed recognition helix is stabilized by hydrophobic interactions, like most of the structured regions of the molecule. Hydrophobic stabilization of the contacting regions meets the requirements of a DNA-interaction mechanism which, as shown with other DNA-protein complexes, should entail negative heat capacity variations due to changes in solvent exposure of the nonpolar protein surface. PMID:9255944

Esposito, G; Fogolari, F; Damante, G; Formisano, S; Tell, G; Leonardi, A; Di Lauro, R; Viglino, P

1997-06-01

4

Probing backbone dynamics with hydrogen/deuterium exchange mass spectrometry.  

PubMed

Protein dynamics can be probed by the solution technique amide hydrogen/deuterium exchange. The exchange rate of hydrogen for deuterium along a peptide backbone is dependent on the extent of hydrogen bonding from secondary structure, accessibility by D2O, and protein motions. Both global and local conformational changes that alter bonding or structure will lead to changes in the amount of deuterium incorporated. The deuterium can be localized via pepsin digestion of the protein and quantified by electrospray ionization mass spectrometry through the mass shifts of the resulting peptides. The technique is emerging as an essential tool to study protein structure in solution due to the exceptional capability of examining both dynamic and structural changes related to protein function. PMID:24061917

Singh, Harsimran; Busenlehner, Laura S

2014-01-01

5

Probing protein ensemble rigidity and hydrogen-deuterium exchange  

NASA Astrophysics Data System (ADS)

Protein rigidity and flexibility can be analyzed accurately and efficiently using the program floppy inclusion and rigid substructure topography (FIRST). Previous studies using FIRST were designed to analyze the rigidity and flexibility of proteins using a single static (snapshot) structure. It is however well known that proteins can undergo spontaneous sub-molecular unfolding and refolding, or conformational dynamics, even under conditions that strongly favor a well-defined native structure. These (local) unfolding events result in a large number of conformers that differ from each other very slightly. In this context, proteins are better represented as a thermodynamic ensemble of ‘native-like’ structures, and not just as a single static low-energy structure. Working with this notion, we introduce a novel FIRST-based approach for predicting rigidity/flexibility of the protein ensemble by (i) averaging the hydrogen bonding strengths from the entire ensemble and (ii) by refining the mathematical model of hydrogen bonds. Furthermore, we combine our FIRST-ensemble rigidity predictions with the ensemble solvent accessibility data of the backbone amides and propose a novel computational method which uses both rigidity and solvent accessibility for predicting hydrogen-deuterium exchange (HDX). To validate our predictions, we report a novel site specific HDX experiment which characterizes the native structural ensemble of Acylphosphatase from hyperthermophile Sulfolobus solfataricus (Sso AcP). The sub-structural conformational dynamics that is observed by HDX data, is closely matched with the FIRST-ensemble rigidity predictions, which could not be attained using the traditional single ‘snapshot’ rigidity analysis. Moreover, the computational predictions of regions that are protected from HDX and those that undergo exchange are in very good agreement with the experimental HDX profile of Sso AcP.

Sljoka, Adnan; Wilson, Derek

2013-10-01

6

Probing protein ensemble rigidity and hydrogen-deuterium exchange.  

PubMed

Protein rigidity and flexibility can be analyzed accurately and efficiently using the program floppy inclusion and rigid substructure topography (FIRST). Previous studies using FIRST were designed to analyze the rigidity and flexibility of proteins using a single static (snapshot) structure. It is however well known that proteins can undergo spontaneous sub-molecular unfolding and refolding, or conformational dynamics, even under conditions that strongly favor a well-defined native structure. These (local) unfolding events result in a large number of conformers that differ from each other very slightly. In this context, proteins are better represented as a thermodynamic ensemble of 'native-like' structures, and not just as a single static low-energy structure. Working with this notion, we introduce a novel FIRST-based approach for predicting rigidity/flexibility of the protein ensemble by (i) averaging the hydrogen bonding strengths from the entire ensemble and (ii) by refining the mathematical model of hydrogen bonds. Furthermore, we combine our FIRST-ensemble rigidity predictions with the ensemble solvent accessibility data of the backbone amides and propose a novel computational method which uses both rigidity and solvent accessibility for predicting hydrogen-deuterium exchange (HDX). To validate our predictions, we report a novel site specific HDX experiment which characterizes the native structural ensemble of Acylphosphatase from hyperthermophile Sulfolobus solfataricus (Sso AcP). The sub-structural conformational dynamics that is observed by HDX data, is closely matched with the FIRST-ensemble rigidity predictions, which could not be attained using the traditional single 'snapshot' rigidity analysis. Moreover, the computational predictions of regions that are protected from HDX and those that undergo exchange are in very good agreement with the experimental HDX profile of Sso AcP. PMID:24104456

Sljoka, Adnan; Wilson, Derek

2013-10-01

7

Online hydrogen/deuterium exchange performed in the ion mobility cell of a hybrid mass spectrometer.  

PubMed

The present paper describes the performance of online, gas-phase hydrogen/deuterium exchange implemented in the ion mobility cell of a quadrupole time-of-flight mass spectrometer. Deuterium oxide and deuterated methanol were utilized to create deuterated vapor that is introduced into the ion mobility region of the mass spectrometer. Hydrogen/deuterium exchange occurs spontaneously in the milliseconds time frame without the need of switching the instrument into ion mobility mode. The exchange was studied in case of low molecular weight molecules and proteins. The observed number of exchanged hydrogens was equal to the number of theoretically exchangeable hydrogens for all low molecular weight compounds. This method needs only minimal instrumental modifications, is simple, cheap, environment friendly, compatible with ultraperformance liquid chromatography, and can be implemented on commercially available instruments. It does not compromise choice of liquid chromatographic solvents and accurate mass or parallel-fragmentation (MS(E)) methods. The performance of this method was compared to that of conventional alternatives where the deuterated solvent is introduced into the cone gas of the instrument. Although the degree of exchange was similar between the two methods, the "cone gas method" requires 10 times higher deuterated solvent volumes (50 muL/min) and offers reduced sensitivity in the tandem mass spectrometry (MS/MS) mode. The presented method is suggested as a standard future element of mass spectrometers to aid online structural characterization of unknowns and to study conformational changes of proteins with hydrogen/deuterium exchange. PMID:19848411

Nagy, Kornél; Redeuil, Karine; Rezzi, Serge

2009-11-15

8

Hydrogen\\/deuterium exchange of hydrophobic peptides in model membranes by electrospray ionization mass spectrometry  

Microsoft Academic Search

We demonstrate here that the hydrogen\\/deuterium solvent exchange (HDX) properties of the transmembrane fragment of the M2\\u000a protein of Influenza A (M2-TM) incorporated into lipid vesicles or detergent micelles can be studied with straightforward electrospray (ESI) and\\u000a nanospray mass spectrometry (MS) configurations provided that key factors, including sample preparation techniques, are optimized.\\u000a Small unilamellar vesicle preparations were obtained by solubilizing

Raino K. Hansen; R. William Broadhurst; Paul C. Skelton; Isaiah T. Arkin

2002-01-01

9

Hydrogen/deuterium exchange in interstellar ice analogs  

NASA Astrophysics Data System (ADS)

Context: For several reasons, methanol is believed to be formed on grain surfaces and, in warm environments, released in the gas phase. In the past, multiply deuterated isotopologues of methanol have been detected in gas phase around several low-mass protostars. In all these sources, there is significantly more CH2DOH than CH3OD. Various hypotheses have been suggested to explain this anomaly, but none is fully convincing. Aims: In this work, we test a new hypothesis experimentally: the spontaneous exchange between hydrogen and deuterium atoms in water ice as responsible for the deficiency of CH3OD with respect to CH2DOH. Methods: We follow the temperature dependence of the composition of interstellar ice analogs initially composed of CD3OD and H2O. To this aim, thin films of intimate H2O:CD3OD ice mixtures, condensed at low temperature (<110 K), are monitored by Fourier transform infrared (FTIR) spectroscopy up to the complete evaporation of CD3OD (~170 K). Results: Rapid hydrogen/deuterium (H/D) exchange is observed, at 120 K and above, through the growth of the ?_OD stretching mode of HDO at ~2425 cm-1. It is also shown that H/D exchange occurs i) on the hydroxyl functional group of methanol, i.e through hydrogen bonds, and ii) before the completion of crystallization. Conclusions: The present results suggest that the much lower abundance of CH3OD compared to CH2DOH in low-mass protostars could reflect H/D exchanges in water ice either prior to or definitely during the grain mantle sublimation. This solid-state depletion mechanism, so far neglected in the astronomical literature, might affect other deuterated molecules with hydrogen bonds.

Ratajczak, A.; Quirico, E.; Faure, A.; Schmitt, B.; Ceccarelli, C.

2009-03-01

10

Photoactivation of Rhodopsin Causes an Increased Hydrogen-Deuterium Exchange of Buried Peptide Groups  

Microsoft Academic Search

A key step in visual transduction is the light-induced conformational changes of rhodopsin that lead to binding and activation of the G-protein transducin. In order to explore the nature of these conformational changes, time-resolved Fourier transform infrared spectroscopy was used to measure the kinetics of hydrogen\\/deuterium exchange in rhodopsin upon photoexcitation. The extent of hydrogen\\/deuterium exchange of backbone peptide groups

Parshuram Rath; Willem J. DeGrip; Kenneth J. Rothschild

1998-01-01

11

A Hydrogen-Deuterium Exchange Study on Nickel-based Binary-Ternary Amorphous and Crystalline Membranes  

NASA Astrophysics Data System (ADS)

Hydrogen is a major role player in current global sustainable energy scenario. Research around the world is carried out to harness hydrogen from all possible sources. One of these sources is water gas shift reaction after the coal gasification process. Sustainable infrastructure can be viable in countries like USA and Australia, making this process viable. Various methods are used to harness this hydrogen from the water gas. One of these methods is the use of inorganic membranes based on Pd, Ag, Ni, Zr and other transition metals. Pd addition to the membranes makes the membranes more expensive for commercial use. Various bulk properties like hydrogen permeation and absorption are studied on Pd and Pd-based alloys. Alternate alloys based on Ni, V, Ta etc are being studied to substitute the use of Pd making this technology more cost efficient. A current balance in research in this area is fund to exist by coating the non-precious metal membranes with Pd to improve the surface interaction with hydrogen. The nature of membranes used for hydrogen separation is important aspect for the overall performance. Crystalline materials provide better bulk properties, however, are not durable under high temperature and hydrogen pressure. In this research, non-Pd coated Ni-based amorphous membranes were made by melt spin technique, which have been studied for their surface properties. Gas phase H2-D2 exchange reaction has been carried out on the membrane surface. This provides a measure of catalytic activity of the above mentioned membranes. More studies included the crystallographic phase change determination, bulk hydrogen solubility measurements, surface conduction measurements and surface morphological studies. During this research, it has been observed that crystalline materials provide more surface activity for hydrogen than their amorphous counterparts. Ni64Zr36 alloy has been shown to exhibit similar kinetic rates as metallic Ni. Also, microkinetic analysis was performed to determine the heat of hydrogen absorption and desorption on the alloy surface. Electrochemical Impedance Spectroscopy was conducted on the membranes to determine the surface resistance and it was found that Ni64Zr36 as-spun ribbon displayed highest resistance while Ni60Ta20Zr20 showed lowest resistance. Absorption studies on Ni60V 40 binary alloy and Ni60V20Zr20 ternary alloy indicated that the addition of Zr to these non-coated alloys increased the hydrogen solubility in the bulk. SEM and TEM analyses showed the presence of possible nano crystalline phases in Ni64Zr36 membrane. XRD and SEM studies conducted on post treated samples showed the possible phase segregation of Ni and ZrO2. Ni60Nb40 did not show any phase transformations after hydrogen heat treated unlike its ternary composition, Ni60Nb20Zr20. It is noteworthy to mention that bubbles were observed during SEM on Ni 64Zr36 post-treated sample on the surface due to possible hydrogen trapping and subsequent release of hydrogen gas.

Adibhatla, Anasuya

12

Subzero temperature chromatography for reduced back-exchange and improved dynamic range in amide hydrogen/deuterium exchange mass spectrometry.  

PubMed

Amide hydrogen/deuterium exchange is a commonly used technique for studying the dynamics of proteins and their interactions with other proteins or ligands. When coupled with liquid chromatography and mass spectrometry, hydrogen/deuterium exchange provides several unique advantages over other structural characterization techniques including very high sensitivity, the ability to analyze proteins in complex environments, and a large mass range. A fundamental limitation of the technique arises from the loss of the deuterium label (back-exchange) during the course of the analysis. A method to limit loss of the label during the separation stage of the analysis using subzero temperature reversed-phase chromatography is presented. The approach is facilitated by the use of buffer modifiers that prevent freezing. We evaluated ethylene glycol, dimethyl formamide, formamide, and methanol for their freezing point suppression capabilities, effects on peptide retention, and their compatibilities with electrospray ionization. Ethylene glycol was used extensively because of its good electrospray ionization compatibility; however, formamide has potential to be a superior modifier if detrimental effects on ionization can be overcome. It is demonstrated using suitable buffer modifiers that separations can be performed at temperatures as low as -30 °C with negligible loss of the deuterium label, even during long chromatographic separations. The reduction in back-exchange is shown to increase the dynamic range of hydrogen/deuterium exchange mass spectrometry in terms of mixture complexity and the magnitude with which changes in deuteration level can be quantified. PMID:23025328

Venable, John D; Okach, Linda; Agarwalla, Sanjay; Brock, Ansgar

2012-11-01

13

Conformational dynamics of human FXR-LBD ligand interactions studied by hydrogen/deuterium exchange mass spectrometry: Insights into the antagonism of the hypolipidemic agent Z-guggulsterone.  

PubMed

Farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily of transcription factors that plays a key role in the regulation of bile acids, lipid and glucose metabolisms. The regulative function of FXR is governed by conformational changes of the ligand binding domain (LBD) upon ligand binding. Although FXR is a highly researched potential therapeutic target, only a limited number of FXR-agonist complexes have been successfully crystallized and subsequently yielded high resolution structures. There is currently no structural information of any FXR-antagonist complexes publically available. We therefore explored the use of amide hydrogen/deuterium exchange (HDX) coupled with mass spectrometry for characterizing conformational changes in the FXR-LBD upon ligand binding. Ligand-specific deuterium incorporation profiles were obtained for three FXR ligand chemotypes: GW4064, a synthetic non-steroidal high affinity agonist; the bile acid chenodeoxycholic acid (CDCA), the endogenous low affinity agonist of FXR; and Z-guggulsterone (GG), an in vitro antagonist of the steroid chemotype. A comparison of the HDX profiles of their ligand-bound FXR-LBD complexes revealed a unique mode of interaction for GG. The conformational features of the FXR-LBD-antagonist interaction are discussed. PMID:24953769

Yang, Liping; Broderick, David; Jiang, Yuan; Hsu, Victor; Maier, Claudia S

2014-09-01

14

Gas phase hydrogen\\/deuterium exchange of proteins in an ion trap mass spectrometer  

Microsoft Academic Search

Electrospray ionization ion trap mass spectrometry (ESI-ITMS) coupled with gas phase hydrogen\\/deuterium (H\\/D) exchange is demonstrated to be a useful tool to investigate the gas phase conformations of proteins when coupled with a mechanistic understanding of exchange. We have investigated the H\\/D exchange of multiple charge states of lysozyme, cytochrome c, ubiquitin, insulin, thioredoxin and melittin with deuterated methanol in

Sarah E. Evans; Nathan Lueck; Elaine M. Marzluff

2003-01-01

15

Influence of Murchison or Allende minerals on hydrogen-deuterium exchange of amino acids.  

PubMed

Deuterium-enriched amino acids occur in the Murchison carbonaceous chrondrite. This meteorite underwent a period of aqueous alteration with isotopically light water. With the objective of setting limits on the conditions of aqueous alteration, the exchange of the carbon-bonded hydrogen atoms of amino acids with D2O has been studied from 295 to 380 K as a function of time and meteorite/heavy water ratio. The amount of Murchison or Allende dust present has a significant effect on the rate and amount of hydrogen-deuterium exchange observed. At elevated temperatures, the alpha-hydrogens of all the amino acids studied were found to exchange with deuterium. In glycine and aspartic acid, this process resulted in total exchange of the carbon-bonded hydrogen. A completely deuterated isotopomer of alanine was produced in significant quantities only when the rock/water ratio was greater than 0.5. No exchange of carbon-bonded hydrogens was observed in the case of amino acids which do not possess an alpha-hydrogen atom. The rates of H/D exchange for amino acids observed here did not correspond to deuterium enrichment of the amino acids in the Murchison meteorite. These results suggest that H/D exchange with water had a negligible effect on the observed deuterium enrichment of amino acids found in Murchison and that the temperature at which the amino acids were exposed to liquid water was close to 273 K. PMID:11540046

Lerner, N R

1995-04-01

16

Localized Hydration in Lyophilized Myoglobin by Hydrogen-Deuterium Exchange Mass Spectrometry. 1. Exchange Mapping  

PubMed Central

The local effects of hydration on myoglobin (Mb) in solid matrices containing mannitol or sucrose (1:1 w/w, protein:additive) were mapped using hydrogen-deuterium exchange with mass spectrometric analysis (HDX-MS) at 5°C and compared to solution controls. Solid powders were exposed to D2O(g) at controlled activity (aw) followed by reconstitution and analysis of the intact protein and peptides produced by pepsin digestion. HDX varied with matrix type, aw, and position along the protein backbone. HDX was less in sucrose matrices than in mannitol matrices at all aw while the difference in solution was negligible. Differences in HDX in the two matrices were detectable despite similarities in their bulk water content. The extent of exchange in solids is proposed as a measure of the hydration of exchangeable amide groups, as well as protein conformation and dynamics; pepsin digestion allows these effects to be mapped with peptide-level resolution.

Sophocleous, Andreas M.; Zhang, Jun; Topp, Elizabeth M.

2012-01-01

17

Hydrogen-deuterium exchange of weak carbon acids under phase-transfer catalysis conditions  

SciTech Connect

A practical method for hydrogen-deuterium exchange is obtained via extractive hydroxide ion initiated phase-transfer catalysis. The reaction of NaOD/D/sub 2/O system allows the easy production of compounds that otherwise would require very strong bases and aprotic solvents. The strong basicity of OD/sup -/ anion is attributable to its relative freedom from water molecules when OD/sup -/ is extracted into the depth of the organic layer. 22 references, 1 table.

Feldman, D.; Halpern, M.; Rabinovitz, M.

1985-05-17

18

Advantages of isotopic depletion of proteins for hydrogen/deuterium exchange experiments monitored by mass spectrometry.  

PubMed

Solution-phase hydrogen/deuterium exchange (HDX) monitored by mass spectrometry is an excellent tool to study protein-protein interactions and conformational changes in biological systems, especially when traditional methods such as X-ray crystallography or nuclear magnetic resonance are not feasible. Peak overlap among the dozens of proteolytic fragments (including those from autolysis of the protease) can be severe, due to high protein molecular weight(s) and the broad isotopic distributions due to multiple deuterations of many peptides. In addition, different subunits of a protein complex can yield isomeric proteolytic fragments. Here, we show that depletion of (13)C and/or (15)N for one or more protein subunits of a complex can greatly simplify the mass spectra, increase the signal-to-noise ratio of the depleted fragment ions, and remove ambiguity in assignment of the m/z values to the correct isomeric peptides. Specifically, it becomes possible to monitor the exchange progress for two isobaric fragments originating from two or more different subunits within the complex, without having to resort to tandem mass spectrometry techniques that can lead to deuterium scrambling in the gas phase. Finally, because the isotopic distribution for a small to medium-size peptide is essentially just the monoisotopic species ((12)C(c)(1)H(h)(14)N(n)(16)O(o)(32)S(s)), it is not necessary to deconvolve the natural abundance distribution for each partially deuterated peptide during HDX data reduction. PMID:20337424

Bou-Assaf, George M; Chamoun, Jean E; Emmett, Mark R; Fajer, Piotr G; Marshall, Alan G

2010-04-15

19

Affinity capture of biotinylated proteins at acidic conditions to facilitate hydrogen/deuterium exchange mass spectrometry analysis of multimeric protein complexes.  

PubMed

Characterization of conformational and dynamic changes associated with protein interactions can be done by hydrogen/deuterium exchange mass spectrometry (HDX-MS) by comparing the deuterium uptake in the bound and unbound state of the proteins. Investigation of local hydrogen/deuterium exchange in heteromultimeric protein complexes poses a challenge for the method due to the increased complexity of the mixture of peptides originating from all interaction partners in the complex. Previously, interference of peptides from one interaction partner has been removed by immobilizing the intact protein on beads prior to the HDX-MS experiment. However, when studying protein complexes of more than two proteins, immobilization can possibly introduce steric limitations to the interactions. Here, we present a method based on the high affinity biotin-streptavidin interaction that allows selective capture of biotinylated proteins even under the extreme conditions for hydrogen/deuterium exchange quenching i.e. pH 2.5 and 0 °C. This biotin-streptavidin capture strategy allows hydrogen/deuterium exchange to occur in proteins in solution and enables characterization of specific proteins in heteromultimeric protein complexes without interference of peptides originating from other interaction partners in the complex. The biotin-streptavidin strategy has been successfully implemented in a model system with two recombinant monoclonal antibodies that target nonoverlapping epitopes on the human epidermal growth factor receptor (EGFR). We present a workflow for biotinylation and characterization of recombinant antibodies and demonstrate affinity capture of biotinylated antibodies under hydrogen/deuterium exchange quench conditions by the biotin-streptavidin strategy. PMID:23534402

Jensen, Pernille Foged; Jørgensen, Thomas J D; Koefoed, Klaus; Nygaard, Frank; Sen, Jette Wagtberg

2013-08-01

20

Gas chromatography mass spectrometry study of hydrogen deuterium exchange reactions of volatile hydrides of As, Sb, Bi, Ge and Sn in aqueous media  

NASA Astrophysics Data System (ADS)

The H-D exchange processes in MH n or MD n hydrides (M = As, Sb, Bi, n = 3; M = Ge, Sn, n = 4) taking place when they are in contact with H 2O or D 2O solution at different pH or pD values (interval of pH = [0,13]) have been investigated using gas chromatography-mass spectrometry (GC-MS). MH n or MD n compounds were injected into the headspace of reaction vials (4-12 ml) containing 1-2 ml of buffered solution maintained under stirring or shaking conditions. The isotopic composition of the gaseous phase hydrides/deuterides was determined at regular intervals in the range of time 0-15 min. The MH n or MD n compounds were synthesized in separate vials and their purity was checked separately before injection into the reaction vials. The mass spectra were deconvoluted in order to estimate the relative abundance of each species formed following the H-D exchange process (AsH nD 3- n , SbH nD 3- n, BiH nD 3- n, n = 0-3; GeH nD 4- n, SnH nD 4- n, n = 0-4) and the relative abundance of H and D. In the investigated pH (or pD) interval arsanes and stibanes undergo H-D exchange in alkaline media for pH > 7. No H-D exchange was detected for the other hydrides, where the prevailing process is their decomposition in the aqueous phase. A reaction model, based on the formation of protonated or deprotonated intermediates is proposed for H-D exchange of MH n or MD n compounds placed in contact with H 2O or D 2O at different pH or pD values. The H-D exchange in the already formed hydrides can be source of the interference in mechanistic studies on hydride formation performed using labeled reagents; no H-D exchange was detected within the following pH intervals that can be considered free from interference: arsanes pH = [0,7), stibanes pH = [0,7), bismuthanes, germanes and stannanes pH = [0,13].

D'Ulivo, Alessandro; Mester, Zoltan; Meija, Juris; Sturgeon, Ralph E.

2006-07-01

21

Pulsed hydrogen-deuterium exchange mass spectrometry probes conformational changes in amyloid beta (A?) peptide aggregation.  

PubMed

Probing the conformational changes of amyloid beta (A?) peptide aggregation is challenging owing to the vast heterogeneity of the resulting soluble aggregates. To investigate the formation of these aggregates in solution, we designed an MS-based biophysical approach and applied it to the formation of soluble aggregates of the A?42 peptide, the proposed causative agent in Alzheimer's disease. The approach incorporates pulsed hydrogen-deuterium exchange coupled with MS analysis. The combined approach provides evidence for a self-catalyzed aggregation with a lag phase, as observed previously by fluorescence methods. Unlike those approaches, pulsed hydrogen-deuterium exchange does not require modified A?42 (e.g., labeling with a fluorophore). Furthermore, the approach reveals that the center region of A?42 is first to aggregate, followed by the C and N termini. We also found that the lag phase in the aggregation of soluble species is affected by temperature and Cu(2+) ions. This MS approach has sufficient structural resolution to allow interrogation of A? aggregation in physiologically relevant environments. This platform should be generally useful for investigating the aggregation of other amyloid-forming proteins and neurotoxic soluble peptide aggregates. PMID:23959898

Zhang, Ying; Rempel, Don L; Zhang, Jun; Sharma, Anuj K; Mirica, Liviu M; Gross, Michael L

2013-09-01

22

Evidence for a bound water molecule next to the retinal Schiff base in bacteriorhodopsin and rhodopsin: a resonance Raman study of the Schiff base hydrogen/deuterium exchange.  

PubMed Central

The retinal chromophores of both rhodopsin and bacteriorhodopsin are bound to their apoproteins via a protonated Schiff base. We have employed continuous-flow resonance Raman experiments on both pigments to determine that the exchange of a deuteron on the Schiff base with a proton is very fast, with half-times of 6.9 +/- 0.9 and 1.3 +/- 0.3 ms for rhodopsin and bacteriorhodopsin, respectively. When these results are analyzed using standard hydrogen-deuteron exchange mechanisms, i.e., acid-, base-, or water-catalyzed schemes, it is found that none of these can explain the experimental results. Because the exchange rates are found to be independent of pH, the deuterium-hydrogen exchange can not be hydroxyl (or acid-)-catalyzed. Moreover, the deuterium-hydrogen exchange of the retinal Schiff base cannot be catalyzed by water acting as a base because in that case the estimated exchange rate is predicted to be orders of magnitude slower than that observed. The relatively slow calculated exchange rates are essentially due to the high pKa values of the Schiff base in both rhodopsin (pKa > 17) and bacteriorhodopsin (pKa approximately 13.5). We have also measured the deuterium-hydrogen exchange of a protonated Schiff base model compound in aqueous solution. Its exchange characteristics, in contrast to the Schiff bases of the pigments, is pH-dependent and consistent with the standard base-catalyzed schemes. Remarkably, the water-catalyzed exchange, which has a half-time of 16 +/- 2 ms and which dominates at pH 3.0 and below, is slower than the exchange rate of the Schiff base in rhodopsin and bacteriorhodopsin. Thus, there are two anomalous results, the inconsistency of the observed hydrogen exchange rates of retinal Schiff base in the two pigments with those predicted from the standard exchange schemes and the enhancement of the rate of hydrogen exchange in the two proteins over the model Schiff base in aqueous solution. We suggest that these results are explained by the presence of a structural water molecule (or molecules) at the retinal binding sites of the two pigments, quite close, probably-hydrogen bonded, to the Schiff base proton. In this case, the rate of exchange can be faster than that found for the model compound due to an "effective water concentration" near the Schiff base that is increased from that found in aqueous solution.

Deng, H.; Huang, L.; Callender, R.; Ebrey, T.

1994-01-01

23

Identifying Zn-bound histidine residues in metalloproteins using hydrogen-deuterium exchange mass spectrometry.  

PubMed

In this work, we have developed a method that uses hydrogen-deuterium exchange (HDX) of C2-hydrogens of histidines coupled with mass spectrometry (MS) to identify Zn-bound histidines in metalloproteins. This method relies on differences in HDX reaction rates of Zn-bound and Zn-free His residues. Using several model peptides and proteins, we find that all Zn-bound His residues have substantially lower HDX reaction rates in the presence of the metal. The vast majority of non-Zn-binding His residues undergo no significant changes in HDX reaction rates when their reactivity is compared in the presence and absence of Zn. Using this new approach, we then determined the Zn binding site of ?-2-microglobulin, a protein associated with metal-induced amyloidosis. Together, these results suggest that HDX-MS of His C2-hydrogens is a promising new method for identifying Zn-bound histidines in metalloproteins. PMID:24313328

Dong, Jia; Callahan, Katie L; Borotto, Nicholas B; Vachet, Richard W

2014-01-01

24

Activation of AMP-activated protein kinase revealed by hydrogen/deuterium exchange mass spectrometry.  

PubMed

AMP-activated protein kinase (AMPK) monitors cellular energy, regulates genes involved in ATP synthesis and consumption, and is allosterically activated by nucleotides and synthetic ligands. Analysis of the intact enzyme with hydrogen/deuterium exchange mass spectrometry reveals conformational perturbations of AMPK in response to binding of nucleotides, cyclodextrin, and a synthetic small molecule activator, A769662. Results from this analysis clearly show that binding of AMP leads to conformational changes primarily in the ? subunit of AMPK and subtle changes in the ? and ? subunits. In contrast, A769662 causes profound conformational changes in the glycogen binding module of the ? subunit and in the kinase domain of the ? subunit, suggesting that the molecular binding site of the latter resides between the ? and ? subunits. The distinct short- and long-range perturbations induced upon binding of AMP and A769662 suggest fundamentally different molecular mechanisms for activation of AMPK by these two ligands. PMID:24076403

Landgraf, Rachelle R; Goswami, Devrishi; Rajamohan, Francis; Harris, Melissa S; Calabrese, Matthew F; Hoth, Lise R; Magyar, Rachelle; Pascal, Bruce D; Chalmers, Michael J; Busby, Scott A; Kurumbail, Ravi G; Griffin, Patrick R

2013-11-01

25

In-ESI source hydrogen/deuterium exchange of carbohydrate ions.  

PubMed

We present the investigation of hydrogen/deuterium (H/D) exchange of carbohydrates ions occurring in the electrospray ion source. The shape of the deuterium distribution was observed to be considerably dependent on the temperature of the ion transfer tube and the solvent used. If deuterated alcohol (EtOD or MeOD) or D2O/deuterated alcohol is used as an electrospray solvent, then for high temperatures (>350 °C), intensive back exchange is observed, resulting in ?30% depth of the deuterium exchange. At low temperatures (<150 °C), the back exchange is weaker and the depth of the deuterium exchange is ?70%. In the intermediate temperature region (?250 °C), the deuterium distribution is unusually wide for methanol and bimodal for ethanol. The addition of 1% formic acid results in low (?30%) depth of the deuterium exchange for any temperature in the operating region. The bimodal distribution for the ethanol can be possibly explained by the presence of differently folded gas-phase ions of carbohydrates. PMID:24499243

Kostyukevich, Yury; Kononikhin, Alexey; Popov, Igor; Nikolaev, Eugene

2014-03-01

26

Computational investigation and hydrogen\\/deuterium exchange of the fixed charge derivative tris(2,4,6-Trimethoxyphenyl) phosphonium: Implications for the aspartic acid cleavage mechanism  

Microsoft Academic Search

Aspartic acid (Asp)-containing peptides with the fixed charge derivative tris(2,4,6trimethoxyphenyl) phosphonium (tTMP-P+) were explored computationally and experimentally by hydrogen\\/deuterium (H\\/D) exchange and by fragmentation studies to probe\\u000a the phenomenon of selective cleavage C-terminal to Asp in the absence of a “mobile” proton. Ab initio modeling of the tTMP-P+ electrostatic potential shows that the positive charge is distributed on the phosphonium

Kristin A. Herrmann; Vicki H. Wysocki; Erich R. Vorpagel

2005-01-01

27

Peptide-Column Interactions and Their Influence on Back Exchange Rates in Hydrogen/Deuterium Exchange-MS  

NASA Astrophysics Data System (ADS)

Hydrogen/deuterium exchange (HDX) methods generate useful information on protein structure and dynamics, ideally at the individual residue level. Most MS-based HDX methods involve a rapid proteolytic digestion followed by LC/MS analysis, with exchange kinetics monitored at the peptide level. Localizing specific sites of HDX is usually restricted to a resolution the size of the host peptide because gas-phase processes can scramble deuterium throughout the peptide. Subtractive methods may improve resolution, where deuterium levels of overlapping and nested peptides are used in a subtractive manner to localize exchange to smaller segments. In this study, we explore the underlying assumption of the subtractive method, namely, that the measured back exchange kinetics of a given residue is independent of its host peptide. Using a series of deuterated peptides, we show that secondary structure can be partially retained under quenched conditions, and that interactions between peptides and reversed-phase LC columns may both accelerate and decelerate residue HDX, depending upon peptide sequence and length. Secondary structure is induced through column interactions in peptides with a solution-phase propensity for structure, which has the effect of slowing HDX rates relative to predicted random coil values. Conversely, column interactions can orient random-coil peptide conformers to accelerate HDX, the degree to which correlates with peptide charge in solution, and which can be reversed by using stronger ion pairing reagents. The dependency of these effects on sequence and length suggest that subtractive methods for improving structural resolution in HDX-MS will not offer a straightforward solution for increasing exchange site resolution.

Sheff, Joey G.; Rey, Martial; Schriemer, David C.

2013-07-01

28

Protein Conformation in Amorphous Solids by FTIR and by Hydrogen/Deuterium Exchange with Mass Spectrometry  

PubMed Central

Solid-state hydrogen/deuterium exchange (ssHDX) with electrospray ionization mass spectrometry (ESI-MS) and Fourier transform infrared (FTIR) spectroscopy were used to assess protein conformation in amorphous solids. Myoglobin, lysozyme, ?-lactoglobulin, ribonuclease A, E-cadherin 5, and concanavalin A were co-lyophilized with carbohydrates (trehalose, raffinose, and dextran 5000), linear polymers (polyvinyl alcohol and polyvinyl pyrrolidone) or guanidine hydrochloride (negative control). For ssHDX, samples were exposed to D2O vapor at 33% relative humidity and room temperature, and then reconstituted at low temperature (4°C) and pH 2.5 and analyzed by ESI-MS. Peptic digestion of selected proteins was used to provide region-specific information on exchange. FTIR spectra were acquired using attenuated total reflectance. FTIR and ssHDX of intact proteins showed preservation of structure by raffinose and trehalose, as indicated by FTIR band intensity and protection from exchange. ssHDX of peptic digests further indicated that these protective effects were not exerted uniformly along the protein sequence but were observed primarily in ?-helical regions, a level of structural resolution not afforded by FTIR. The results thus demonstrate the utility of HDX with ESI-MS for analyzing protein conformation in amorphous solid samples.

Sinha, Sandipan; Li, Yunsong; Williams, Todd D.; Topp, Elizabeth M.

2008-01-01

29

Conformational analysis of recombinant monoclonal antibodies with hydrogen/deuterium exchange mass spectrometry.  

PubMed

Understanding the conformation of antibodies, especially those of therapeutic value, is of great interest. Many of the current analytical methods used to probe protein conformation face issues in the analysis of antibodies, either due to the nature of the antibody itself or due to the limitations of the method. One method that has recently been utilized for conformational analysis of antibodies is hydrogen/deuterium exchange mass spectrometry (H/DX MS). H/DX MS can be used to probe the conformation and dynamics of proteins in solution, requires small sample quantities, is compatible with many buffer systems, and provides peptide-level resolution. The application of H/DX MS to immunoglobulin gamma 1 (IgG1) recombinant monoclonal antibodies can provide information about IgG1 conformation, dynamics, and changes to conformation as a result of protein modification(s), changes in storage conditions, purification procedures, formulation, and many other parameters. In this article we provide a comprehensive H/DX MS protocol for the analysis of an antibody. PMID:23475726

Houde, Damian; Engen, John R

2013-01-01

30

Polarized Fourier transform infrared spectroscopy of bacteriorhodopsin. Transmembrane alpha helices are resistant to hydrogen\\/deuterium exchange  

Microsoft Academic Search

The secondary structure of bacteriorhodopsin has been investigated by polarized Fourier transform infrared spectroscopy combined with hydrogen\\/deuterium exchange, isotope labeling and resolution enhancement methods. Oriented films of purple membrane were measured at low temperature after exposure to H2O or D2O. Resolution enhancement techniques and isotopic labeling of the Schiff base were used to assign peaks in the amide I region

T. N. Earnest; J. Herzfeld; K. J. Rothschild

1990-01-01

31

Hydrogen\\/Deuterium Exchange and Aggregation of a Polyvaline and a Polyleucine Helix Investigated by Matrix-assisted Laser Desorption Ionization Mass Spectrometry  

Microsoft Academic Search

The membrane-associated pulmonary surfactant protein C (SP-C), containing a polyvaline -helix, and a synthetic SP-C analogue with a polyleucine helix (SP-C(Leu)) were studied by hydrogen\\/deuterium exchange matrix-assisted laser desorption ionization (MALDI) mass spectrometry. SP-C, but not SP-C(Leu), formed abundant amyloid fibrils under experimental conditions. In CD3OD\\/D2O, 91:9 (v\\/v), containing 2 mM ammonium acetate, SP-C(Leu) and SP-C exchanged 40% of their

Waltteri Hosia; Jan Johansson; William J. Griffiths

32

Interrupted Hydrogen/Deuterium Exchange Reveals the Stable Core of the Remarkably Helical Molten Globule of ?-? Parallel Protein Flavodoxin  

PubMed Central

Kinetic intermediates that appear early during protein folding often resemble the relatively stable molten globule intermediates formed by several proteins under mildly denaturing conditions. Molten globules have a substantial amount of secondary structure but lack virtually all tertiary side-chain packing characteristics of natively folded proteins. Due to exposed hydrophobic groups, molten globules are prone to aggregation, which can have detrimental effects on organisms. The molten globule that is observed during folding of ?-? parallel flavodoxin from Azotobacter vinelandii is a remarkably non-native species. This folding intermediate is helical and contains no ?-sheet and is kinetically off-pathway to the native state. It can be trapped under native-like conditions by substituting residue Phe44 for Tyr44. To characterize this species at the residue level, in this study, use is made of interrupted hydrogen/deuterium exchange detected by NMR spectroscopy. In the molten globule of flavodoxin, the helical region comprising residues Leu110-Val125 is shown to be better protected against exchange than the other ordered parts of the folding intermediate. This helical region is better buried than the other helices, causing its context-dependent stabilization against unfolding. Residues Leu110–Val125 thus form the stable core of the helical molten globule of ?-? parallel flavodoxin, which is almost entirely structured. Non-native docking of helices in the molten globule of flavodoxin prevents formation of the parallel ?-sheet of native flavodoxin. Hence, to produce native ?-? parallel protein molecules, the off-pathway species needs to unfold.

Nabuurs, Sanne M.; van Mierlo, Carlo P. M.

2010-01-01

33

Gas-phase hydrogen/deuterium exchange in a travelling wave ion guide for the examination of protein conformations  

PubMed Central

Accumulating evidence suggests that solution-phase conformations of small globular proteins and large molecular protein assemblies can be preserved for milliseconds after electrospray ionization. Thus, the study of proteins in the gas-phase on this time-scale is highly desirable. Here we demonstrate that a travelling wave ion guide (TWIG) of a Synapt mass spectrometer offers a highly suitable environment for rapid and efficient gas-phase hydrogen/deuterium exchange (HDX). Gaseous ND3 was introduced into either the source TWIG or the TWIG located just after the ion mobility cell, such that ions underwent HDX as they passed through the ND3 on the way to the time-of-flight analyzer. The extent of deuterium labeling could be controlled by varying the quantity of ND3 or the speed of the travelling wave. The gas-phase HDX of model peptides corresponded to labeling of primarily fast exchanging sites due to the short labeling times (ranging from 0.1 to 10 ms). In addition to peptides, gas-phase HDX of ubiquitin, cytochrome c, lysozyme and apomyoglobin were examined. We conclude that HDX of protein ions in a TWIG is highly sensitive to protein conformation, enables the detection of conformers present on sub-milliseconds timescales and can readily be combined with ion mobility spectrometry.

Rand, Kasper D.; Pringle, Steven D.; Murphy, James P.; Fadgen, Keith E.; Brown, Jeff; Engen, John R.

2009-01-01

34

Platform dependencies in bottom-up hydrogen/deuterium exchange mass spectrometry.  

PubMed

Hydrogen-deuterium exchange mass spectrometry is an important method for protein structure-function analysis. The bottom-up approach uses protein digestion to localize deuteration to higher resolution, and the essential measurement involves centroid mass determinations on a very large set of peptides. In the course of evaluating systems for various projects, we established two (HDX-MS) platforms that consisted of a FT-MS and a high-resolution QTOF mass spectrometer, each with matched front-end fluidic systems. Digests of proteins spanning a 20-110 kDa range were deuterated to equilibrium, and figures-of-merit for a typical bottom-up (HDX-MS) experiment were compared for each platform. The Orbitrap Velos identified 64% more peptides than the 5600 QTOF, with a 42% overlap between the two systems, independent of protein size. Precision in deuterium measurements using the Orbitrap marginally exceeded that of the QTOF, depending on the Orbitrap resolution setting. However, the unique nature of FT-MS data generates situations where deuteration measurements can be inaccurate, because of destructive interference arising from mismatches in elemental mass defects. This is shown through the analysis of the peptides common to both platforms, where deuteration values can be as low as 35% of the expected values, depending on FT-MS resolution, peptide length and charge state. These findings are supported by simulations of Orbitrap transients, and highlight that caution should be exercised in deriving centroid mass values from FT transients that do not support baseline separation of the full isotopic composition. PMID:23197788

Burns, Kyle M; Rey, Martial; Baker, Charles A H; Schriemer, David C

2013-02-01

35

Dynamic Structural Changes During Complement C3 Activation Analyzed by Hydrogen/Deuterium Exchange Mass Spectrometry  

PubMed Central

Proteolytic cleavage of component C3 to C3b is a central step in the activation of complement. Whereas C3 is largely biologically inactive, C3b is directly involved in various complement activities. While the recently described crystal structures of C3 and C3b provide a molecular basis of complement activation, they do not reflect the dynamic changes that occur in solution. In addition, the available C3b structures diverge in some important aspects. Here we have utilized hydrogen/deuterium exchange coupled with mass spectrometry (HDX-MS) to investigate relative changes in the solution-phase structures of C3 and C3b. By combining two forms of mass spectrometry we could maximize the primary sequence coverage of C3b and demonstrate the feasibility of this method for large plasma proteins. While the majority of the 82 peptides that could be followed over time showed only minor alterations in HDX, we observed clear changes in solvent accessibility for 16 peptides, primarily in the ?-chain (?’NT, MG6-8, CUB, TED, C345C domains). Most of these peptides could be directly linked to the structural transitions visible in the crystal structures and revealed additional information about the probability of the structural variants of C3b. In addition, a discontinuous cluster of seven peptides in the MG3, MG6, LNK and ?’NT domains showed a decreased accessibility after activation to C3b. Although no gross conformational changes are detected in the crystal structure, this area may reflect a structurally flexible region in solution that contributes to C3 activation and function.

Schuster, Michael C.; Ricklin, Daniel; Papp, Krisztian; Molnar, Kathleen S.; Coales, Stephen J.; Hamuro, Yoshitomo; Sfyroera, Georgia; Chen, Hui; Winters, Michael S.; Lambris, John D.

2008-01-01

36

Resolving isotopic fine structure to detect and quantify natural abundance- and hydrogen/deuterium exchange-derived isotopomers.  

PubMed

Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) is used for analyzing protein dynamics, protein folding/unfolding, and molecular interactions. Until this study, HDX MS experiments employed mass spectral resolving powers that afforded only one peak per nominal mass in a given peptide's isotope distribution, and HDX MS data analysis methods were developed accordingly. A level of complexity that is inherent to HDX MS remained unaddressed, namely, various combinations of natural abundance heavy isotopes and exchanged deuterium shared the same nominal mass and overlapped at previous resolving powers. For example, an A + 2 peak is comprised of (among other isotopomers) a two-(2)H-exchanged/zero-(13)C isotopomer, a one-(2)H-exchanged/one-(13)C isotopomer, and a zero-(2)H-exchanged/two-(13)C isotopomer. Notably, such isotopomers differ slightly in mass as a result of the ?3 mDa mass defect between (2)H and (13)C atoms. Previous HDX MS methods did not resolve these isotopomers, requiring a natural-abundance-only (before HDX or "time zero") spectrum and data processing to remove its contribution. It is demonstrated here that high-resolution mass spectrometry can be used to detect isotopic fine structure, such as in the A + 2 profile example above, deconvolving the isotopomer species resulting from deuterium incorporation. Resolving isotopic fine structure during HDX MS therefore permits direct monitoring of HDX, which can be calculated as the sum of the fractional peak magnitudes of the deuterium-exchanged isotopomers. This obviates both the need for a time zero spectrum as well as data processing to account for natural abundance heavy isotopes, saving instrument and analysis time. PMID:24328359

Liu, Qian; Easterling, Michael L; Agar, Jeffrey N

2014-01-01

37

Atmospheric Pressure Photo Ionization Hydrogen/Deuterium Exchange Mass Spectrometry—a Method to Differentiate Isomers by Mass Spectrometry  

NASA Astrophysics Data System (ADS)

In this report, a method for in-source hydrogen/deuterium (H/D) exchange at atmospheric pressure is reported. The method was named atmospheric pressure photo ionization hydrogen/deuterium exchange mass spectrometry (APPI HDX MS). H/D exchange was performed by mixing samples dissolved in toluene with CH3OD solvent and analyzing the mixture using atmospheric pressure photo ionization mass spectrometry (APPI-MS). The APPI HDX spectra obtained with contact times between the analyte solution and methanol-OD (CH3OD) of < 0.5 s or 1 h showed the same pattern of H/D exchange. Therefore, it was concluded that APPI HDX occurred in the source but not in the solution. The proposed method does not require a specific type of mass spectrometer and can be performed at atmospheric pressure. H/D exchange can be performed in any laboratory with a mass spectrometer and a commercial APPI source. Using this method, multiple H/D exchanges of aromatic hydrogen and/or H/D exchange of active hydrogen were observed. These results demonstrated that H/D exchange can be used to distinguish between isomers containing primary, secondary, and tertiary amines, as well as pyridine and pyrrole functional groups.

Ahmed, Arif; Kim, Sunghwan

2013-12-01

38

Characterization of the Hydrogen-Deuterium Exchange Activities of the Energy-Transducing HupSL Hydrogenase and H2Signaling HupUV Hydrogenase in Rhodobacter capsulatus  

Microsoft Academic Search

Rhodobacter capsulatus synthesizes two homologous protein complexes capable of activating molecular H2 ,a membrane-bound (NiFe) hydrogenase (HupSL) linked to the respiratory chain, and an H2 sensor encoded by the hupUV genes. The activities of hydrogen-deuterium (H-D) exchange catalyzed by the hupSL-encoded and the hupUV-encoded enzymes in the presence of D2 and H2O were studied comparatively. Whereas HupSL is in the

PAULETTE M. VIGNAIS; BERNARD DIMON; NIKOLAY A. ZORIN; MASAMITSU TOMIYAMA; ANNETTE COLBEAU

2000-01-01

39

Polar Aprotic Modifiers for Chromatographic Separation and Back-Exchange Reduction for Protein Hydrogen/Deuterium Exchange Monitored by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry  

PubMed Central

Hydrogen/deuterium exchange monitored by mass spectrometry is an important non-perturbing tool to study protein structure and protein–protein interactions. However, water in the reversed-phase liquid chromatography mobile phase leads to back-exchange of D for H during chromatographic separation of proteolytic peptides following H/D exchange, resulting in incorrect identification of fast-exchanging hydrogens as unexchanged hydrogens. Previously, fast high-performance liquid chromatography (HPLC) and supercritical fluid chromatography have been shown to decrease back-exchange. Here, we show that replacement of up to 40% of the water in the LC mobile phase by the modifiers, dimethylformamide (DMF) and N-methylpyrrolidone (NMP) (i.e., polar organic modifiers that lack rapid exchanging hydrogens), significantly reduces back-exchange. On-line LC micro-ESI FT-ICR MS resolves overlapped proteolytic peptide isotopic distributions, allowing for quantitative determination of the extent of back-exchange. The DMF modified solvent composition also improves chromatographic separation while reducing back-exchange relative to conventional solvent.

Valeja, Santosh G.; Emmett, Mark R.; Marshall, Alan G.

2013-01-01

40

Effects of protein-ligand interactions on hydrogen/deuterium exchange kinetics: canonical and noncanonical scenarios.  

PubMed

Hydrogen/deuterium exchange (HDX) methods are widely used for monitoring protein-ligand interactions. This approach relies on the fact that ligand binding can modulate the extent of protein structural fluctuations that transiently disrupt hydrogen bonds and expose backbone amides to the solvent. It is commonly observed that ligand binding causes a reduction of HDX rates. This reduction can be restricted to elements adjacent to the binding site, but other regions can be affected as well. Qualitatively, ligand-induced HDX protection can be rationalized on the basis of two-state models that equate structural dynamics with global unfolding/refolding. Unfortunately, such models tend to be unrealistic because the dynamics of native proteins are dominated by subglobal transitions and local fluctuations. Ligand binding lowers the ground-state free energy. It is not obvious why this should necessarily be accompanied by a depletion of excited-state occupancies, which would be required for a reduction of HDX rates. Here, we propose a framework that implies that ligand binding can either slow or accelerate amide deuteration throughout the protein. These scenarios are referred to as "type 1" and "type 2", respectively. Evidence for type 1 binding is abundant in the literature, whereas the viability of type 2 interactions is less clear. Using HDX mass spectrometry (MS), we demonstrate that the oxygenation of hemoglobin (Hb) provides a dramatic example of a type 2 scenario. The observed behavior is consistent with cooperative T ? R switching, where part of the intrinsic O2 binding energy is reinvested for destabilization of the ground state. This destabilization increases the Boltzmann occupancy of unfolded conformers, thereby enhancing HDX rates. Surprisingly, O2 binding to myoglobin (Mb) also induces elevated HDX rates. These Mb data reveal that type 2 behavior is not limited to cooperative multisubunit systems. Although enhanced protection from deuteration is widely considered to be a hallmark of protein-ligand interactions, this work establishes that an overall deuteration increase also represents a viable outcome. HDX-based ligand screening assays, therefore, have to allow for canonical as well as noncanonical effects. PMID:24904985

Sowole, Modupeola A; Konermann, Lars

2014-07-01

41

Structural Dynamics of Soluble Chloride Intracellular Channel Protein CLIC1 Examined by Amide Hydrogen-Deuterium Exchange Mass Spectrometry (DXMS)†  

PubMed Central

Chloride intracellular channel protein 1 (CLIC1) functions as an anion channel in plasma and nuclear membranes when its soluble monomeric form converts to an integral-membrane form. The transmembrane region of CLIC1 is located in its thioredoxin-like domain 1 but the mechanism whereby the protein converts to its membrane conformation has yet to be determined. Since channel formation in membranes is enhanced at low pH (5 to 5.5), a condition that is found at the surface of membranes, the structural dynamics of soluble CLIC1 was studied at pH 7 and at pH 5.5 in the absence of membranes by amide hydrogen-deuterium exchange mass spectrometry (DXMS). Rapid hydrogen exchange data indicate that CLIC1 displays a similar core structure at these pH values. Domain 1 is less stable than the all-helical domain 2 and, while the structure of domain 1 remains intact, its conformational flexibility is further increased in an acidic environment (pH 5.5). In the absence of membrane, an acidic environment appears to prime the solution structure of CLIC1 by destabilising domain 1 in order to lower the activation energy barrier for its conversion to the membrane-insertion conformation. The significantly enhanced H/D-exchange rates at pH 5.5 displayed by two segments (peptides 11-31 and 68-82) could be due to the protonation of acidic residues in salt bridges. One of these segments (peptide 11-31) includes part of the transmembrane region which, in the solution structure, consists of helix ?1. This helix is intrinsically stable and is most likely retained in the membrane conformation. Strand ?2, another element of the transmembrane region, displays a propensity to form a helical structure and has putative N- and C-capping motifs, suggesting that it too most likely forms a helix in a lipid bilayer.

Stoychev, Stoyan H.; Nathaniel, Christos; Fanucchi, Sylvia; Brock, Melissa; Li, Sheng; Asmus, Kyle; Woods, Virgil L.; Dirr, Heini W.

2009-01-01

42

Structural basis of specific interactions of Lp-PLA2 with HDL revealed by hydrogen deuterium exchange mass spectrometry.  

PubMed

Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)), specifically Group VIIA PLA(2), is a member of the phospholipase A(2) superfamily and is found mainly associated with LDL and HDL in human plasma. Lp-PLA(2) is considered as a risk factor, a potential biomarker, a target for therapy in the treatment of cardiovascular disease, and evidence suggests that the level of Lp-PLA(2) in plasma is associated with the risk of future cardiovascular and stroke events. The differential location of the enzyme in LDL/HDL lipoproteins has been suggested to affect Lp-PLA(2) function and/or its physiological role and an abnormal distribution of the enzyme may correlate with diseases. Although a mutagenesis study suggested that a surface helix (residues 362-369) mediates the association between Lp-PLA(2) and HDL, the molecular details and mechanism of association has remained unknown. We have now employed hydrogen deuterium exchange mass spectrometry to characterize the interaction between recombinant human Lp-PLA(2) and human HDL. We have found that specific residues 113-120, 192-204, and 360-368 likely mediate HDL binding. In a previous study, we showed that residues 113-120 are important for Lp-PLA(2)-liposome interactions. We now find that residues 192-204 show a decreased deuteration level when Lp-PLA(2) is exposed to apoA-I, but not apoA-II, the most abundant apoproteins in HDL, and additionally, residues 360-368 are only affected by HDL.The results suggest that apoA-I and phospholipid membranes play crucial roles in Lp-PLA(2) localization to HDL. PMID:23089916

Cao, Jian; Hsu, Yuan-Hao; Li, Sheng; Woods, Virgil L; Dennis, Edward A

2013-01-01

43

Direct evidence for a two-state protein unfolding transition from hydrogen-deuterium exchange, mass spectrometry, and NMR.  

PubMed

We use mass spectrometry in conjunction with hydrogen-deuterium exchange and NMR to characterize the conformational dynamics of the 62-residue IgG binding domain of protein L under conditions in which the native state is marginally stable. Mass spectra of protein L after short incubations in D2O reveal the presence of two distinct populations containing different numbers of protected protons. NMR experiments indicate that protons in the hydrophobic core are protected in one population, whereas all protons are exchanged for deuterons in the other. As the exchange period is increased, molecules are transferred from the former population to the latter. The absence of molecules with a subset of the core protons protected suggests that exchange occurs in part via a highly concerted transition to an excited state in which all protons exchange rapidly with deuterons. A steady increase in the molecular weight of the population with protected protons, and variation in the exchange rates of the individual protected protons indicates the presence of an additional exchange mechanism. A simple model in which exchange results from rapid (> 10(5)/s) local fluctuations around the native state superimposed upon transitions to an unfolded excited state at approximately 0.06/s is supported by qualitative agreement between the observed mass spectra and the mass spectra simulated according to the model using NMR-derived estimates of the proton exchange rates. PMID:8762137

Yi, Q; Baker, D

1996-06-01

44

Enhanced gas-phase hydrogen-deuterium exchange of oligonucleotide and protein ions stored in an external multipole ion reservoir.  

PubMed

Rapid gas-phase hydrogen-deuterium (H-D) exchange from D(2)O and ND(3) into oligonucleotide and protein ions was achieved during storage in a hexapole ion reservoir. Deuterated gas is introduced through a capillary line that discharges directly into the low-pressure region of the reservoir. Following exchange, the degree of H-D exchange is determined using Fourier transform ion cyclotron resonance mass spectrometry. Gas-phase H-D exchange experiments can be conducted more than 100 times faster than observed using conventional in-cell exchange protocols that require lower gas pressures and additional pump-down periods. The short experimental times facilitate the quantitation of the number of labile hydrogens for less reactive proteins and structured oligonucleotides. For ubiquitin, we observe approximately 65 H-D exchanges after 20 s. Exchange rates of > 250 hydrogens s(-1) are observed for oligonucleotide ions when D(2)O or ND(3) is admitted directly into the external ion reservoir owing to the high local pressure in the hexapole. Partially deuterated oligonucleotide ions have been fragmented in the reservoir using infrared multiphoton dissociation (IRMPD). The resulting fragment ions show that exchange predominates at charged sites on the 5'- and 3'-ends of the oligonucleotide, whereas exchange is slower in the core. This hardware configuration is independent of the mass detector and should be compatible with other mass spectrometric platforms including quadrupole ion trap and time-of-flight mass spectrometers. PMID:10633235

Hofstadler, S A; Sannes-Lowery, K A; Griffey, R H

2000-01-01

45

Structural dynamics of soluble chloride intracellular channel protein CLIC1 examined by amide hydrogen-deuterium exchange mass spectrometry.  

PubMed

Chloride intracellular channel protein 1 (CLIC1) functions as an anion channel in plasma and nuclear membranes when its soluble monomeric form converts to an integral-membrane form. The transmembrane region of CLIC1 is located in its thioredoxin-like domain 1, but the mechanism whereby the protein converts to its membrane conformation has yet to be determined. Since channel formation in membranes is enhanced at low pH (5 to 5.5), a condition that is found at the surface of membranes, the structural dynamics of soluble CLIC1 was studied at pH 7 and at pH 5.5 in the absence of membranes by amide hydrogen-deuterium exchange mass spectrometry (DXMS). Rapid hydrogen exchange data indicate that CLIC1 displays a similar core structure at these pH values. Domain 1 is less stable than the all-helical domain 2, and, while the structure of domain 1 remains intact, its conformational flexibility is further increased in an acidic environment (pH 5.5). In the absence of membrane, an acidic environment appears to prime the solution structure of CLIC1 by destabilizing domain 1 in order to lower the activation energy barrier for its conversion to the membrane-insertion conformation. The significantly enhanced H/D-exchange rates at pH 5.5 displayed by two segments (peptides 11-31 and 68-82) could be due to the protonation of acidic residues in salt bridges. One of these segments (peptide 11-31) includes part of the transmembrane region which, in the solution structure, consists of helix alpha1. This helix is intrinsically stable and is most likely retained in the membrane conformation. Strand beta2, another element of the transmembrane region, displays a propensity to form a helical structure and has putative N- and C-capping motifs, suggesting that it too most likely forms a helix in a lipid bilayer. PMID:19650640

Stoychev, Stoyan H; Nathaniel, Christos; Fanucchi, Sylvia; Brock, Melissa; Li, Sheng; Asmus, Kyle; Woods, Virgil L; Dirr, Heini W

2009-09-01

46

Top-down mass spectrometry and hydrogen/deuterium exchange for comprehensive structural characterization of interferons: implications for biosimilars.  

PubMed

Rapid development in biopharmaceuticals has put high demands on analytical tools that can provide accurate and comprehensive characterization of protein drugs, including biosimilars. Although the enzyme digestion based "bottom-up" approach is usually the method of choice for this purpose, it only gives peptide-level information and sequence coverage is often incomplete. In this work, we used top-down MS with electron capture dissociation (ECD) to characterize both the primary and higher order structures of a therapeutic protein interferon and its variants. Accurate mass measurement at the intact protein level combined with top-down ECD fragmentation enabled unambiguous protein sequence confirmation and identification of all PTMs. Combining hydrogen/deuterium exchange and rapid disulfide reduction with top-down ECD on the LC time scale, we have investigated the differences in higher order structure between the protein variants, as well as the impact of PTMs on protein conformation. PMID:24574185

Pan, Jingxi; Borchers, Christoph H

2014-05-01

47

Mass spectral characterization of ergot alkaloids by electrospray ionization, hydrogen/deuterium exchange, and multiple stage mass spectrometry: Usefulness of precursor ion scan experiments.  

PubMed

Six ergot alkaloids belonging to the lysergic acid derivatives (ergonovine (EGN) and methysergide hydrogen maleinate (MHM)) and peptide-type derivatives (ergocristine (EGR), ergotamine (EGT), ergocornine (EGC) and alpha-ergokryptine (EGK)) were studied by positive electrospray tandem mass spectrometry. The fragmentation mechanisms of these compounds were studied by collision-induced dissociation (CID) using triple quadrupole and ion trap mass spectrometers, and the nature of the major product ions further confirmed by hydrogen/deuterium (H/D) exchange experiments. A common abundant product ion at m/z 223 was characteristic of the two classes of ergot alkaloids. Therefore, a precursor ion scan of m/z 223 that triggers information data acquisition (IDA) in combination with CID experiments was used to identify other potential ergot alkaloids. Using this approach, it was possible to confirm the presence of ergosine, another peptide-type ergot alkaloid, in a rye flour extract at trace levels. PMID:16941545

Mohamed, Rayane; Gremaud, Eric; Tabet, Jean-Claude; Guy, Philippe A

2006-01-01

48

Identification of the degradation product of ezlopitant, a non-peptidic substance p antagonist receptor, by hydrogen deuterium exchange, electrospray ionization tandem mass spectrometry (ESI\\/MS\\/MS) and nuclear magnetic resonance (NMR) spectroscopy  

Microsoft Academic Search

The degradation product of ezlopitant was isolated from low specific activity material and identified by solution phase hydrogen\\/deuterium (H\\/D) exchange and electrospray ionization tandem mass spectrometry (ESI\\/MS\\/MS) to be an isopropyl peroxide analog of ezlopitant. The structure of the degradant was further confirmed by nuclear magnetic resonance (NMR) spectroscopy utilizing complete 1H and 13C assignments. Studies were also performed to

Amin M Kamel; Kathleen S Zandi; Walter W Massefski

2003-01-01

49

NMR-Based Amide Hydrogen-Deuterium Exchange Measurements for Complex Membrane Proteins: Development and Critical Evaluation  

NASA Astrophysics Data System (ADS)

A method for measuring site-specific amide hydrogen-deuterium exchange rates for membrane proteins in bilayers is reported and evaluated. This method represents an adaptation and extension of the approach of Dempsey and co-workers ( Biophys. J. 70, 1777-1788 (1996)) and is based on reconstituting 15N-labeled membrane proteins into phospholipid bilayers, followed by lyophilization and rehydration with D 2O or H 2O (control). Following incubation for a time t under hydrated conditions, samples are again lyophilized and then solubilized in an organic solvent system, where 1H- 15N HSQC spectra are recorded. Comparison of spectra from D 2O-exposed samples to spectra from control samples yields the extent of the H-D exchange which occurred in the bilayers during time t. Measurements are site specific if specific 15N labeling is used. The first part of this paper deals with the search for a suitable solvent system in which to solubilize complex membrane proteins in an amide "exchange-trapped" form for NMR quantitation of amide peak intensities. The second portion of the paper documents application of the overall procedure to measuring site-specific amide exchange rates in diacylglycerol kinase, a representative integral membrane protein. Both the potential usefulness and the significant limitations of the new method are documented.

Czerski, Lech; Vinogradova, Olga; Sanders, Charles R.

2000-01-01

50

Application of atmospheric pressure photo ionization hydrogen/deuterium exchange high-resolution mass spectrometry for the molecular level speciation of nitrogen compounds in heavy crude oils.  

PubMed

We report here for the first time the application of atmospheric pressure photo ionization hydrogen/deuterium exchange (APPI HDX) coupled to high-resolution mass spectrometry for molecular level speciation of nitrogen containing compounds in crude oils. The speciation was done based on different combinations of ions produced from nitrogen containing compounds with various functional groups. To prove the concept, 20 nitrogen containing standard compounds were analyzed. As a result, it was shown that the nitrogen containing compound (M) with a primary amine functional group mainly produced a combination of [M - 2H + 2D](•+) and ([M - 2H + 2D] + D)(+) ions, one with a secondary amine including alkylated or phenylated pyrrole a combination of [M - H + D](•+) and ([M - H + D] + D)(+), one with a tertiary amine including N-alkylated or phenylated pyrrole a combination of [M](•+) and [M + D](+), and one with a pyridine functional group mostly [M + D](+) ions. The concept was successfully applied to do nitrogen speciation of resins fractions of two oil samples. Combined with the subsequent investigation of double bond equivalence distribution, it was shown that resins of Qinhuangdao crude oil sample contained mostly alkylated pyrrole and N-alkylated pyrrole type compounds but resins of shale oil extract contained mostly pyridine type nitrogen compounds. It was also shown that the speciation of individual elemental composition was also possible by use of this method. Overall, this study clearly shows that atmospheric pressure photo ionization hydrogen/deuterium exchange (APPI HDX) coupled to high-resolution mass spectrometry is a powerful analytical method to do nitrogen speciation of crude oil compounds at the molecular level. PMID:24033284

Cho, Yunju; Ahmed, Arif; Kim, Sunghwan

2013-10-15

51

Polarized Fourier transform infrared spectroscopy of bacteriorhodopsin. Transmembrane alpha helices are resistant to hydrogen/deuterium exchange  

SciTech Connect

The secondary structure of bacteriorhodopsin has been investigated by polarized Fourier transform infrared spectroscopy combined with hydrogen/deuterium exchange, isotope labeling and resolution enhancement methods. Oriented films of purple membrane were measured at low temperature after exposure to H2O or D2O. Resolution enhancement techniques and isotopic labeling of the Schiff base were used to assign peaks in the amide I region of the spectrum. alpha-helical structure, which exhibits strong infrared dichroism, undergoes little H/D exchange, even after 48 h of D2O exposure. In contrast, non-alpha-helical structure, which exhibits little dichroism, undergoes rapid H/D exchange. A band at 1,640 cm-1, which has previously been assigned to beta-sheet structure, is found to be due in part to the C = N stretching vibration of protonated Schiff base of the retinylidene chromophore. We conclude that the membrane spanning regions of bR consist predominantly of alpha-helical structure whereas most beta-type structure is located in surface regions directly accessible to water.

Earnest, T.N.; Herzfeld, J.; Rothschild, K.J. (Boston Univ., MA (USA))

1990-12-01

52

Changes in the Factor VIII C2 domain upon membrane binding determined by hydrogen-deuterium exchange MS.  

PubMed

Factor VIII enhances the catalytic activity of Factor IXa in a membrane-bound enzyme complex and both proteins are necessary to prevent haemophilia. Tandem lectin-like C domains mediate the membrane binding of Factor VIII and membrane-interactive residues have been identified. However, the available data provide little insight into the dynamic changes that occur upon membrane binding. We used time-based hydrogen-deuterium exchange MS to evaluate the dynamics of FVIII-C2 (Factor VIII C2 domain) alone and when membrane bound. The results confirm the participation of previously identified membrane-interactive loops in the binding mechanism. In addition, they indicate that a long peptide segment, encompassing a membrane-interactive loop and strands of the ?-barrel core, is remarkably dynamic prior to membrane binding. The flexibility is reduced following membrane binding. In addition, regions that interact with the A1 and C1 domains have reduced solvent exchange. Thus the isolated C2 domain has extensive flexibility that is subject to stabilization and could be related to interactions between domains as well as between Factor VIII and Factor IXa or Factor X. These results confirm that the proposed membrane-binding loops of the FVIII-C2 interact with the membrane in a manner that leads to protection from solvent exposure. PMID:24814520

Pantazatos, Dionysios; Gessner, Christopher R; Woods, Virgil L; Gilbert, Gary E

2014-08-01

53

Characterization of IgG1 Conformation and Conformational Dynamics by Hydrogen/Deuterium Exchange Mass Spectrometry  

SciTech Connect

Protein function is dictated by protein conformation. For the protein biopharmaceutical industry, therefore, it is important to have analytical tools that can detect changes in protein conformation rapidly, accurately, and with high sensitivity. In this paper we show that hydrogen/deuterium exchange mass spectrometry (H/DX-MS) can play an important role in fulfilling this need within the industry. H/DX-MS was used to assess both global and local conformational behavior of a recombinant monoclonal IgG1 antibody, a major class of biopharmaceuticals. Analysis of exchange into the intact, glycosylated IgG1 (and the Fab and Fc regions thereof) showed that the molecule was folded, highly stable, and highly amenable to analysis by this method using less than a nanomole of material. With improved chromatographic methods, peptide identification algorithms and data-processing steps, the analysis of deuterium levels in peptic peptides produced after labeling was accomplished in 1--2 days. On the basis of peptic peptide data, exchange was localized to specific regions of the antibody. Changes to IgG1 conformation as a result of deglycosylation were determined by comparing exchange into the glycosylated and deglycosylated forms of the antibody. Two regions of the IgG1 (residues 236-253 and 292-308) were found to have altered exchange properties upon deglycosylation. These results are consistent with previous findings concerning the role of glycosylation in the interaction of IgG1 with Fc receptors. Moreover, the data clearly illustrate how H/DX-MS can provide important characterization information on the higher order structure of antibodies and conformational changes that these molecules may experience upon modification.

Houde, Damian; Arndt, Joseph; Domeier, Wayne; Berkowitz, Steven; Engen, John R.; (NEU); (Biogen)

2009-04-22

54

Hydrogen/deuterium exchange in parallel with acid/base induced protein conformational change in electrospray droplets.  

PubMed

The exposure of electrospray droplets to vapors of deuterating reagents during droplet desolvation in the interface of a mass spectrometer results in hydrogen/deuterium exchange (HDX) on the sub-millisecond time scale. Deuterated water is used to label ubiquitin and cytochrome c with minimal effect on the observed charge state distribution (CSD), suggesting that the protein conformation is not being altered. However, the introduction of deuterated versions of various acids (e.g., CD3 COOD and DCl) and bases (ND3 ) induces unfolding or refolding of the protein while also labeling these newly formed conformations. The extent of HDX within a protein CSD associated with a particular conformation is essentially constant, whereas the extent of HDX can differ significantly for CSDs associated with different conformations from the same protein. In some cases, multiple HDX distributions can be observed within a given charge state (as is demonstrated with cytochrome c) suggesting that the extent of HDX and CSDs share a degree of complementarity in their sensitivities for protein conformation. The CSD is established late in the evolution of ions in electrospray whereas the HDX process presumably takes place in the bulk of the droplet throughout the electrospray process. Back exchange is also performed in which proteins are prepared in deuterated solvents prior to ionization and exposed to undeuterated vapors to exchange deuteriums for hydrogens. The degree of deuterium uptake is easily controlled by varying the identity and partial pressure of the reagent introduced into the interface. Since the exchange occurs on the sub-millisecond time scale, the use of deuterated acids or bases allows for transient species to be generated and labeled for subsequent mass analysis. Copyright © 2014 John Wiley & Sons, Ltd. PMID:24913396

Kharlamova, Anastasia; Fisher, Christine M; McLuckey, Scott A

2014-06-01

55

Hexicon 2: Automated Processing of Hydrogen-Deuterium Exchange Mass Spectrometry Data with Improved Deuteration Distribution Estimation  

NASA Astrophysics Data System (ADS)

Hydrogen-deuterium exchange (HDX) experiments analyzed by mass spectrometry (MS) provide information about the dynamics and the solvent accessibility of protein backbone amide hydrogen atoms. Continuous improvement of MS instrumentation has contributed to the increasing popularity of this method; however, comprehensive automated data analysis is only beginning to mature. We present Hexicon 2, an automated pipeline for data analysis and visualization based on the previously published program Hexicon (Lou et al. 2010). Hexicon 2 employs the sensitive NITPICK peak detection algorithm of its predecessor in a divide-and-conquer strategy and adds new features, such as chromatogram alignment and improved peptide sequence assignment. The unique feature of deuteration distribution estimation was retained in Hexicon 2 and improved using an iterative deconvolution algorithm that is robust even to noisy data. In addition, Hexicon 2 provides a data browser that facilitates quality control and provides convenient access to common data visualization tasks. Analysis of a benchmark dataset demonstrates superior performance of Hexicon 2 compared with its predecessor in terms of deuteration centroid recovery and deuteration distribution estimation. Hexicon 2 greatly reduces data analysis time compared with manual analysis, whereas the increased number of peptides provides redundant coverage of the entire protein sequence. Hexicon 2 is a standalone application available free of charge under http://hx2.mpimf-heidelberg.mpg.de.

Lindner, Robert; Lou, Xinghua; Reinstein, Jochen; Shoeman, Robert L.; Hamprecht, Fred A.; Winkler, Andreas

2014-06-01

56

Hexicon 2: Automated Processing of Hydrogen-Deuterium Exchange Mass Spectrometry Data with Improved Deuteration Distribution Estimation  

NASA Astrophysics Data System (ADS)

Hydrogen-deuterium exchange (HDX) experiments analyzed by mass spectrometry (MS) provide information about the dynamics and the solvent accessibility of protein backbone amide hydrogen atoms. Continuous improvement of MS instrumentation has contributed to the increasing popularity of this method; however, comprehensive automated data analysis is only beginning to mature. We present Hexicon 2, an automated pipeline for data analysis and visualization based on the previously published program Hexicon (Lou et al. 2010). Hexicon 2 employs the sensitive NITPICK peak detection algorithm of its predecessor in a divide-and-conquer strategy and adds new features, such as chromatogram alignment and improved peptide sequence assignment. The unique feature of deuteration distribution estimation was retained in Hexicon 2 and improved using an iterative deconvolution algorithm that is robust even to noisy data. In addition, Hexicon 2 provides a data browser that facilitates quality control and provides convenient access to common data visualization tasks. Analysis of a benchmark dataset demonstrates superior performance of Hexicon 2 compared with its predecessor in terms of deuteration centroid recovery and deuteration distribution estimation. Hexicon 2 greatly reduces data analysis time compared with manual analysis, whereas the increased number of peptides provides redundant coverage of the entire protein sequence. Hexicon 2 is a standalone application available free of charge under http://hx2.mpimf-heidelberg.mpg.de.

Lindner, Robert; Lou, Xinghua; Reinstein, Jochen; Shoeman, Robert L.; Hamprecht, Fred A.; Winkler, Andreas

2014-03-01

57

Automated Hydrogen/Deuterium Exchange Electron Transfer Dissociation High Resolution Mass Spectrometry Measured at Single-Amide Resolution  

NASA Astrophysics Data System (ADS)

Hydrogen deuterium exchange mass spectrometry (HDX-MS) is a well established method for the measurement of solution-phase deuterium incorporation into proteins, which can provide insight into protein conformational mobility. However, most HDX measurements are constrained to regions of the protein where pepsin proteolysis allows detection at peptide resolution. Recently, single-amide resolution deuterium incorporation has been achieved by limiting gas-phase scrambling in the mass spectrometer. This was accomplished by employing a combination of soft ionization and desolvation conditions coupled with the radical-driven fragmentation technique electron transfer dissociation (ETD). Here, a hybrid LTQ-Orbitrap XL is systematically evaluated for its utility in providing single-amide deuterium incorporation for differential HDX analysis of a nuclear receptor upon binding small molecule ligands. We are able to show that instrumental parameters can be optimized to minimize scrambling and can be incorporated into an established and fully automated HDX platform making differential single-amide HDX possible for bottom-up analysis of complex systems. We have applied this system to determine differential single amide resolution HDX data for the peroxizome proliferator activated receptor bound with two ligands of interest.

Landgraf, Rachelle R.; Chalmers, Michael J.; Griffin, Patrick R.

2012-02-01

58

Hexicon 2: automated processing of hydrogen-deuterium exchange mass spectrometry data with improved deuteration distribution estimation.  

PubMed

Hydrogen-deuterium exchange (HDX) experiments analyzed by mass spectrometry (MS) provide information about the dynamics and the solvent accessibility of protein backbone amide hydrogen atoms. Continuous improvement of MS instrumentation has contributed to the increasing popularity of this method; however, comprehensive automated data analysis is only beginning to mature. We present Hexicon 2, an automated pipeline for data analysis and visualization based on the previously published program Hexicon (Lou et al. 2010). Hexicon 2 employs the sensitive NITPICK peak detection algorithm of its predecessor in a divide-and-conquer strategy and adds new features, such as chromatogram alignment and improved peptide sequence assignment. The unique feature of deuteration distribution estimation was retained in Hexicon 2 and improved using an iterative deconvolution algorithm that is robust even to noisy data. In addition, Hexicon 2 provides a data browser that facilitates quality control and provides convenient access to common data visualization tasks. Analysis of a benchmark dataset demonstrates superior performance of Hexicon 2 compared with its predecessor in terms of deuteration centroid recovery and deuteration distribution estimation. Hexicon 2 greatly reduces data analysis time compared with manual analysis, whereas the increased number of peptides provides redundant coverage of the entire protein sequence. Hexicon 2 is a standalone application available free of charge under http://hx2.mpimf-heidelberg.mpg.de . PMID:24676893

Lindner, Robert; Lou, Xinghua; Reinstein, Jochen; Shoeman, Robert L; Hamprecht, Fred A; Winkler, Andreas

2014-06-01

59

Mass Spectrometric Approaches Using Electrospray Ionization Charge States and Hydrogen-Deuterium Exchange for Determining Protein Structures and Their Conformational Changes  

Microsoft Academic Search

Electrospray ionization (ESI) mass spectrometry (MS) is a powerful analytical tool for elucidating structural details of proteins in solution especially when coupled with am- ide hydrogen\\/deuterium (H\\/D) exchange analysis. ESI charge-state distributions and the envelopes of charges they form from proteins can provide an abundance of information on solution conformations that is not readily available through other biophysical techniques such

Xuguang Yan; Jeffrey Watson; P. Shing Ho; Max L. Deinzer

2003-01-01

60

Thermodynamic and kinetic characterization of hydrogen-deuterium exchange in beta-phase palladium.  

PubMed

A Sieverts' apparatus coupled with a residual gas analyzer (RGA) is an effective method to detect composition variations during isotopic exchange. This experimental setup provides a tool for the thermodynamic and kinetic characterization of H-D isotope exchange on Pd. The H or D concentrations in the gas and solid phases during the exchanges starting from (H(2) + Pd(x)D) and (D(2) + Pd(x)H) in beta-phase Pd were monitored over a temperature range from 173 to 298 K. The equilibrium properties, i.e., the H-D separation factors alpha and equilibrium constants K(HD), were obtained and found to be very close to those in the literature. The values of equilibrium constant reported here are the only experimental K(HD) data for H-D-Pd system. The H-D exchange rates on beta-Pd were measured for both exchange directions. A comprehensive kinetic model is proposed that correlates the exchange rate and the driving force composed of the reactant concentrations and the extent of deviation from equilibrium. The rate constants were obtained using this model for two exchange directions. The rates for the two exchange directions were found to be close to each other at 173 K, but they differ with temperature increase in such a way that the (D(2) + Pd(x)H) has a higher rate than (H(2) + Pd(x)D). The exchange activation energies obtained are 2.0 and 3.5 kJ/mol for the (H(2) + Pd(x)D) and (D(2) + Pd(x)H) directions, respectively. The difference in activation energies results from the difference in the energy states of (H(2) + Pd(x)D) and (D(2) + Pd(x)D). The calculated exchange profiles using this model agree with the experimental values reasonably well. PMID:19735117

Luo, Weifang; Cowgill, Donald F; Causey, Rion A

2009-10-01

61

Dissecting the effect of RNA aptamer binding on the dynamics of plasminogen activator inhibitor 1 using hydrogen/deuterium exchange mass spectrometry.  

PubMed

RNA aptamers, selected from large synthetic libraries, are attracting increasing interest as protein ligands, with potential uses as prototype pharmaceuticals, conformational probes, and reagents for specific quantification of protein levels in biological samples. Very little is known, however, about their effects on protein conformation and dynamics. We have employed hydrogen/deuterium exchange (HDX) mass spectrometry to study the effect of RNA aptamers on the structural flexibility of the serpin plasminogen activator inhibitor-1 (PAI-1). The aptamers have characteristic effects on the biochemical properties of PAI-1. In particular, they are potent inhibitors of the structural transition of PAI-1 from the active state to the inactive, so-called latent state. This transition is one of the largest conformational changes of a folded protein domain without covalent modification. Binding of the aptamers to PAI-1 is associated with substantial and widespread protection against deuterium uptake in PAI-1. The aptamers induce protection against exchange with the solvent both in the protein-aptamer interface as well as in other specific areas. Interestingly, the aptamers induce substantial protection against exchange in ?-helices B, C and I. This observation substantiates the relevance of structural instability in this region for transition to the latent state and argues for involvement of flexibility in regions not commonly associated with regulation of latency transition in serpins. PMID:24138169

Trelle, Morten B; Dupont, Daniel M; Madsen, Jeppe B; Andreasen, Peter A; Jørgensen, Thomas J D

2014-01-17

62

Enhanced Digestion Efficiency, Peptide Ionization Efficiency, and Sequence Resolution for Protein Hydrogen/Deuterium Exchange Monitored by FT-ICR Mass Spectrometry  

PubMed Central

Solution-phase hydrogen/deuterium exchange (HDX) monitored by high-resolution FT-ICR mass spectrometry offers a rapid method to study protein conformations and protein-protein interactions. Pepsin is usually used to digest proteins in HDX and is known as lack of cleavage specificity. To improve digestion efficiency and specificity, we have optimized digestion conditions and cleavage preferences for pepsin and protease type XIII from Aspergillus saitoi. A dilution series of the proteases was used to determine the digestion efficiency for several test proteins. Protease type XIII prefers to cleave on the C-terminal end of basic amino acids and produced the highest number of fragments and the best sequence coverage compared to pepsin or protease type XVIII from Rhizhopus. Furthermore, protease type XIII exhibited much less self-digestion than pepsin, and thus is superior for HDX experiments. Many highly overlapped segments from protease type XIII and pepsin digestion, combined with high-resolution FT-ICR mass spectrometry, provide high sequence resolution (to as few as one or two amino acids) for the assignment of amide hydrogen exchange rate. Our H/D exchange results correlate well with the secondary and tertiary structure of myoglobin. Such assignments of highly overlapped fragments promise to greatly enhance the accuracy and sequence resolution for determining conformational differences resulting from ligand binding or protein-protein interactions.

Zhang, Hui-Min; Kazazic, Sasa; Schaub, Tanner M.; Tipton, Jeremiah D.; Emmett, Mark R.; Marshall, Alan G.

2009-01-01

63

Synthesis, spectroscopy, and hydrogen/deuterium exchange in high-spin iron(II) hydride complexes.  

PubMed

Very few hydride complexes are known in which the metals have a high-spin electronic configuration. We describe the characterization of several high-spin iron(II) hydride/deuteride isotopologues and their exchange reactions with one another and with H2/D2. Though the hydride/deuteride signal is not observable in NMR spectra, the choice of isotope has an influence on the chemical shifts of distant protons in the dimers through the paramagnetic isotope effect on chemical shift. This provides the first way to monitor the exchange of H and D in the bridging positions of these hydride complexes. The rate of exchange depends on the size of the supporting ligand, and this is consistent with the idea that H2/D2 exchange into the hydrides occurs through the dimeric complexes rather than through a transient monomer. The understanding of H/D exchange mechanisms in these high-spin iron hydride complexes may be relevant to postulated nitrogenase mechanisms. PMID:24555749

Dugan, Thomas R; Bill, Eckhard; MacLeod, K Cory; Brennessel, William W; Holland, Patrick L

2014-03-01

64

Analysis of Protein Conformation and Dynamics by Hydrogen/Deuterium Exchange MS  

PubMed Central

synopsis Recent technological advances hydrogen exchange MS have led to improvements in the technique’s ability to analyze the shape and movements of proteins. John Engen of Northeastern University gives a much needed update on the field. The cover, created by Engen, shows proteins “swimming” in an H2O/D2O solution with a sample mass spectrum in the background.

Engen, John R.

2009-01-01

65

The pH dependence of hydrogen-deuterium exchange in trp repressor: the exchange rate of amide protons in proteins reflects tertiary interactions, not only secondary structure.  

PubMed Central

The pH dependence of amide proton exchange rates have been measured for trp-repressor. One class of protons exchanges too fast to be measured in these experiments. Among the protons that have measurable hydrogen-deuterium exchange rates, two additional classes may be distinguished. The second class of protons are in elements of secondary structure that are mostly on the surface of the protein, and exchange linearly with increasing base concentration (log kex versus pH). The third class of amide protons is characterized by much higher protection against exchange at higher pH. These protons are located in the core of the protein, in helices B and C. The exchange rate in the core region does not increase linearly with pH, but rather goes through a minimum around pH 6. The mechanism of exchange for the slowly exchanging core protons is interpreted in terms of the two-process model of Hilton and Woodward (1979, Biochemistry 18:5834-5841), i.e., exchange through both a local mechanism that does not require unfolding of the protein, and a mechanism involving global unfolding of the protein. The increase in exchange rates at low pH is attributed to a partial unfolding of the repressor. It is concluded that the formation of secondary structure alone is insufficient to account for the high protection factors seen in the core of native proteins at higher pH, and that tertiary interactions are essential to stabilize the structure.

Finucane, M. D.; Jardetzky, O.

1996-01-01

66

Local Conformational Stability of HIV-1 gp120 in Unliganded and CD4-Bound States as Defined by Amide Hydrogen/Deuterium Exchange? †  

PubMed Central

The binding reaction of the HIV-1 gp120 envelope glycoprotein to the CD4 receptor involves exceptional changes in enthalpy and entropy. Crystal structures of gp120 in unliganded and various ligand-bound states, meanwhile, reveal an inner domain able to fold into diverse conformations, a structurally invariant outer domain, and, in the CD4-bound state, a bridging sheet minidomain. These studies, however, provide only hints as to the flexibility of each state. Here we use amide hydrogen/deuterium exchange coupled to mass spectrometry to provide quantifications of local conformational stability for HIV-1 gp120 in unliganded and CD4-bound states. On average, unliganded core gp120 displayed >10,000-fold slower exchange of backbone-amide hydrogens than a theoretically unstructured protein of the same composition, with binding by CD4 reducing the rate of gp120 amide exchange a further 10-fold. For the structurally constant CD4, alterations in exchange correlated well with alterations in binding surface (P value = 0.0004). For the structurally variable gp120, however, reductions in flexibility extended outside the binding surface, and regions of expected high structural diversity (inner domain/bridging sheet) displayed roughly 20-fold more rapid exchange in the unliganded state than regions of low diversity (outer domain). Thus, despite an extraordinary reduction in entropy, neither unliganded gp120 nor free CD4 was substantially unstructured, suggesting that most of the diverse conformations that make up the gp120 unliganded state are reasonably ordered. The results provide a framework for understanding how local conformational stability influences entropic change, conformational diversity, and structural rearrangements in the gp120-CD4 binding reaction.

Kong, Leopold; Huang, Chih-chin; Coales, Stephen J.; Molnar, Kathleen S.; Skinner, Jeff; Hamuro, Yoshitomo; Kwong, Peter D.

2010-01-01

67

Hydrogen/Deuterium Exchange Mass Spectrometry and Site-Directed Disulfide Cross-Linking Suggest an Important Dynamic Interface between the Two Lysostaphin Domains  

PubMed Central

Lysostaphin is a peptidoglycan hydrolase secreted by Staphylococcus simulans. It can specifically lyse Staphylococcus aureus and is being tested as a novel antibacterial agent. The protein contains an N-terminal catalytic domain and a C-terminal cell wall targeting domain. Although the two domains from homologous enzymes were structurally determined, the structural organization of lysostaphin domains remains unknown. We used hydrogen/deuterium exchange mass spectrometry (H/DX-MS) and site-directed disulfide cross-linking to probe the interface between the lysostaphin catalytic and targeting domains. H/DX-MS-mediated comparison of peptides from full-length lysostaphin and the separated domains identified four peptides of lower solvent accessibility in the full-length protein. Cross-linking analysis using cysteine pair substitutions within those peptides showed that two pairs of cysteines can form disulfide bonds, supporting the domain association role of the targeted peptides. The cross-linked mutant exhibited a binding capacity to S. aureus that was similar to that of the wild-type protein but reduced bacteriolytic activity probably because of restraint in conformation. The diminished activity was further reduced with increasing NaCl concentrations that can cause contractions of bacterial peptidoglycan. The lytic activity, however, could be fully recovered by reducing the disulfide bonds. These results suggest that lysostaphin may require dynamic association of the two domains for coordinating substrate binding and target cleavage on the elastic peptidoglycan. Our study will help develop site-specific PEGylated lysostaphin to treat systemic S. aureus infections.

Lu, Hai-Rong; Gu, Mei-Gang; Huang, Qiang; Huang, Jin-Jiang; Lu, Wan-Ying; Lu, Hong

2013-01-01

68

Assessment of differences in the conformational flexibility of hepatitis B virus core-antigen and e-antigen by hydrogen deuterium exchange-mass spectrometry.  

PubMed

Hepatitis B virus core-antigen (capsid protein) and e-antigen (an immune regulator) have almost complete sequence identity, yet the dimeric proteins (termed Cp149d and Cp(-10)149d , respectively) adopt quite distinct quaternary structures. Here we use hydrogen deuterium exchange-mass spectrometry (HDX-MS) to study their structural properties. We detect many regions that differ substantially in their HDX dynamics. Significantly, whilst all regions in Cp(-10)149d exchange by EX2-type kinetics, a number of regions in Cp149d were shown to exhibit a mixture of EX2- and EX1-type kinetics, hinting at conformational heterogeneity in these regions. Comparison of the HDX of the free Cp149d with that in assembled capsids (Cp149c ) indicated increased resistance to exchange at the C-terminus where the inter-dimer contacts occur. Furthermore, evidence of mixed exchange kinetics were not observed in Cp149c , implying a reduction in flexibility upon capsid formation. Cp(-10)149d undergoes a drastic structural change when the intermolecular disulphide bridge is reduced, adopting a Cp149d -like structure, as evidenced by the detected HDX dynamics being more consistent with Cp149d in many, albeit not all, regions. These results demonstrate the highly dynamic nature of these similar proteins. To probe the effect of these structural differences on the resulting antigenicity, we investigated binding of the antibody fragment (Fab E1) that is known to bind a conformational epitope on the four-helix bundle. Whilst Fab E1 binds to Cp149c and Cp149d , it does not bind non-reduced and reduced Cp(-10)149d , despite unhindered access to the epitope. These results imply a remarkable sensitivity of this epitope to its structural context. PMID:24715628

Bereszczak, Jessica Z; Watts, Norman R; Wingfield, Paul T; Steven, Alasdair C; Heck, Albert J R

2014-07-01

69

Oxazolone versus macrocycle structures for leu-enkephalin b 2 –b 4 : Insights from infrared multiple-photon dissociation spectroscopy and gas-phase hydrogen\\/deuterium exchange  

Microsoft Academic Search

The collision-induced dissociation (CID) products b2-b4 from Leu-enkephalin are examined with infrared multiple-photon dissociation (IR-MPD) spectroscopy and gas-phase hydrogen\\/deuterium\\u000a exchange (HDX). Infrared spectroscopy reveals that b2 exclusively adopts oxazolone structures, protonated at the N-terminus and at the oxazolone ring N, based on the presence\\u000a and absence of diagnostic infrared vibrations. This is correlated with the presence of a single HDX

Xian Chen; Jeffrey D. Steill; Jos Oomens; Nick C. Polfer

2010-01-01

70

High-field fourier transform ion cyclotron resonance mass spectrometry for simultaneous trapping and gas-phase hydrogen\\/deuterium exchange of peptide ions  

Microsoft Academic Search

Gas-phase hydrogen\\/deuterium exchange of D2O with [M+H]+ ions of angiotensin II, angiotensin I, [Sar1]-angiotensin II, bradykinin, des-Arg1-bradykinin, des-Arg9-bradykinin, luteinizing hormone releasing hormone (LH-RH), and substance P has been examined by Fourier transform ion cyclotron\\u000a resonance mass spectrometry at 9.4 tesla. Because the FTICR dynamic range increases quadratically with magnetic field, parent\\u000a ions from a mixture of several peptides may be

Michael A. Freitas; Christopher L. Hendrickson; Mark R. Emmett; Alan G. Marshall

1998-01-01

71

Using Hydrogen/Deuterium Exchange Mass Spectrometry to Define the Specific Interactions of the Phospholipase A2 Superfamily with Lipid Substrates, Inhibitors, and Membranes*  

PubMed Central

The phospholipase A2 (PLA2) superfamily consists of 16 groups and many subgroups and constitutes a diverse set of enzymes that have a common catalytic activity due to convergent evolution. However, different PLA2 types have unique three-dimensional structures and catalytic residues as well as specific tissue localization and distinct biological functions. Understanding how the different PLA2 enzymes associate with phospholipid membranes, specific phospholipid substrate molecules, and inhibitors on a molecular basis has advanced in recent years due to the introduction of hydrogen/deuterium exchange mass spectrometry. Its theory, practical considerations, and application to understanding PLA2/membrane interactions are addressed.

Cao, Jian; Burke, John E.; Dennis, Edward A.

2013-01-01

72

Conformational studies of the robust 2-Cys peroxiredoxin Salmonella typhimurium AhpC by solution phase hydrogen/deuterium (H/D) exchange monitored by electrospray ionization mass spectrometry.  

PubMed

This is the first comprehensive HX-MS study of a "robust" 2-Cys peroxiredoxin (Prx), namely Salmonella typhimurium AhpC (StAhpC). Prx proteins control intracellular peroxide levels and are abundant antioxidant proteins in eukaryotes, archaea and bacteria. Crystal structural analyses and structure/activity studies of several bacterial and mammalian 2-Cys Prxs have revealed that the activity of 2-Cys Prxs is regulated by redox-dependent oligmerization and a sensitivity of the active site cysteine residue to overoxidation. The propensity to overoxidation is linked to the conformational flexibility of the peroxidatic active site loop. The HX-MS results emphasize the modulation of the conformational motility of the active site loop by disulfide formation. To obtain information on the conformational impact of decamer formation on the active site loop motility, mutants with Thr77 substituted by Ile, a decamer-disrupting mutation or by Val, a decamer-stabilizing mutation, were studied. For the isoleucine mutant, enhanced mobility was observed for regions encompassing the ?4 helix located in the dimer-dimer interface and regions surrounding the peroxidatic loop. In contrast, the T77V mutation resulted in an increase in conformational stability in most regions of the protein except for the active site loop and the region encompassing the resolving cysteine. PMID:21516234

Nirudodhi, Sasidhar; Parsonage, Derek; Karplus, P Andrew; Poole, Leslie B; Maier, Claudia S

2011-04-30

73

First-principles study of temperature-dependent diffusion coefficients: Hydrogen, deuterium, and tritium in ?-Ti  

NASA Astrophysics Data System (ADS)

We report the prediction of temperature-dependent diffusion coefficients of interstitial hydrogen, deuterium, and tritium atoms in ?-Ti using transition state theory. The microscopic parameters in the pre-factor and activation energy of the impurity diffusion coefficients are obtained from first-principles total energy and phonon calculations including the full coupling between the vibrational modes of the diffusing atom with the host lattice. The dual occupancy case of impurity atom in the hcp matrix is considered, and four diffusion paths are combined to obtain the final diffusion coefficients. The calculated diffusion parameters show good agreement with experiments. Our numerical results indicate that the diffusions of deuterium and tritium atoms are slower than that of the hydrogen atom at temperatures above 425 K and 390 K, respectively.

Lu, Yong; Zhang, Ping

2013-05-01

74

Characterization of the hydrogen-deuterium exchange activities of the energy-transducing HupSL hydrogenase and H(2)-signaling HupUV hydrogenase in Rhodobacter capsulatus.  

PubMed

Rhodobacter capsulatus synthesizes two homologous protein complexes capable of activating molecular H(2), a membrane-bound [NiFe] hydrogenase (HupSL) linked to the respiratory chain, and an H(2) sensor encoded by the hupUV genes. The activities of hydrogen-deuterium (H-D) exchange catalyzed by the hupSL-encoded and the hupUV-encoded enzymes in the presence of D(2) and H(2)O were studied comparatively. Whereas HupSL is in the membranes, HupUV activity was localized in the soluble cytoplasmic fraction. Since the hydrogenase gene cluster of R. capsulatus contains a gene homologous to hoxH, which encodes the large subunit of NAD-linked tetrameric soluble hydrogenases, the chromosomal hoxH gene was inactivated and hoxH mutants were used to demonstrate the H-D exchange activity of the cytoplasmic HupUV protein complex. The H-D exchange reaction catalyzed by HupSL hydrogenase was maximal at pH 4. 5 and inhibited by acetylene and oxygen, whereas the H-D exchange catalyzed by the HupUV protein complex was insensitive to acetylene and oxygen and did not vary significantly between pH 4 and pH 11. Based on these properties, the product of the accessory hypD gene was shown to be necessary for the synthesis of active HupUV enzyme. The kinetics of HD and H(2) formed in exchange with D(2) by HupUV point to a restricted access of protons and gasses to the active site. Measurement of concentration changes in D(2), HD, and H(2) by mass spectrometry showed that, besides the H-D exchange reaction, HupUV oxidized H(2) with benzyl viologen, produced H(2) with reduced methyl viologen, and demonstrated true hydrogenase activity. Therefore, not only with respect to its H(2) signaling function in the cell, but also to its catalytic properties, the HupUV enzyme represents a distinct class of hydrogenases. PMID:11029418

Vignais, P M; Dimon, B; Zorin, N A; Tomiyama, M; Colbeau, A

2000-11-01

75

Structural basis of specific interactions of Lp-PLA2 with HDL revealed by hydrogen deuterium exchange mass spectrometry[S  

PubMed Central

Lipoprotein-associated phospholipase A2 (Lp-PLA2), specifically Group VIIA PLA2, is a member of the phospholipase A2 superfamily and is found mainly associated with LDL and HDL in human plasma. Lp-PLA2 is considered as a risk factor, a potential biomarker, a target for therapy in the treatment of cardiovascular disease, and evidence suggests that the level of Lp-PLA2 in plasma is associated with the risk of future cardiovascular and stroke events. The differential location of the enzyme in LDL/HDL lipoproteins has been suggested to affect Lp-PLA2 function and/or its physiological role and an abnormal distribution of the enzyme may correlate with diseases. Although a mutagenesis study suggested that a surface helix (residues 362–369) mediates the association between Lp-PLA2 and HDL, the molecular details and mechanism of association has remained unknown. We have now employed hydrogen deuterium exchange mass spectrometry to characterize the interaction between recombinant human Lp-PLA2 and human HDL. We have found that specific residues 113–120, 192–204, and 360–368 likely mediate HDL binding. In a previous study, we showed that residues 113–120 are important for Lp-PLA2-liposome interactions. We now find that residues 192–204 show a decreased deuteration level when Lp-PLA2 is exposed to apoA-I, but not apoA-II, the most abundant apoproteins in HDL, and additionally, residues 360–368 are only affected by HDL.The results suggest that apoA-I and phospholipid membranes play crucial roles in Lp-PLA2 localization to HDL.

Cao, Jian; Hsu, Yuan-Hao; Li, Sheng; Woods, Virgil L.; Dennis, Edward A.

2013-01-01

76

PAS Domain Allostery and Light-Induced Conformational Changes in Photoactive Yellow Protein upon I2 Intermediate Formation, Probed with Enhanced Hydrogen/Deuterium Exchange Mass Spectrometry  

PubMed Central

Photoactive yellow protein (PYP) is a small bacterial photoreceptor that undergoes a light-activated reaction cycle. PYP is also the prototypical PAS (Per-Arnt-Sim) domain. PAS domains, found in diverse multi-domain proteins from bacteria to humans, mediate protein-protein interactions and function as sensors and signal transducers. Here, we investigate conformational and dynamic changes in solution in wild-type PYP upon formation of the long-lived putative signaling intermediate I2 with enhanced hydrogen/deuterium exchange mass spectrometry (DXMS). The DXMS results showed that the central ?-sheet remains stable but specific external protein segments become strongly deprotected. Light-induced disruption of the dark-state hydrogen-bonding network in I2 produces increased flexibility and opening of PAS core helices ?3 and ?4, releases the ?4-?5 hairpin, and propagates conformational changes to the central ?-sheet. Surprisingly, the first ~10 N-terminal residues, which are essential for fast dark state recovery from I2, become more protected. By combining the DXMS results with our crystallographic structures, which reveal detailed changes near the chromophore, but limited protein conformational change, we propose a mechanism for I2 state formation. This mechanism integrates the results from diverse biophysical studies of PYP, and links an allosteric T- to R-state conformational transition to three pathways for signal propagation within the PYP fold. Based upon the observed changes in PYP plus commonalities shared among PAS domain proteins, we further propose that PAS domains share this conformational mechanism, which explains the versatile signal transduction properties of the structurally conserved PYP/PAS module by framework-encoded allostery.

Brudler, Ronald; Gessner, Chris R.; Li, Sheng; Tyndall, Sammy; Getzoff, Elizabeth D.; Woods, Virgil L.

2008-01-01

77

Enumeration of labile hydrogens in natural organic matter by use of hydrogen/deuterium exchange Fourier transform ion cyclotron resonance mass spectrometry.  

PubMed

A method to enumerate labile hydrogens in all constituents of molecular ensemble of natural organic matter (NOM) based on our previously developed simple hydrogen/deuterium (H/D) exchange (electrospray ionization (ESI) ion source (Kostyukevich et al. Anal. Chem. 2013, 85, 5330) and ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry is presented. The method was applied for analysis of Suwannee River fulvic acid (SRFA), which is an International Humic Substances Society standard, as well as Siberian crude oil; and lignosulfonate. We found that SRFA and lignosulfonate molecules contain 2-5 labile hydrogens, and their number increases with the number of oxygens in the molecule. Also, we observed that compounds of Siberian crude oil ionizing in positive-ESI mode do not have labile hydrogens, while compounds ionizing in negative-ESI mode have one labile hydrogen that detaches during ESI ionization. PMID:24098913

Kostyukevich, Yury; Kononikhin, Alexey; Popov, Igor; Kharybin, Oleg; Perminova, Irina; Konstantinov, Andrey; Nikolaev, Eugene

2013-11-19

78

Hydrogen-deuterium exchange in vivo to measure turnover of an ALS-associated mutant SOD1 protein in spinal cord of mice.  

PubMed

Mutations of cytosolic Cu/Zn superoxide dismutase 1 (SOD1) in humans and overexpression of mutant human SOD1 genes in transgenic mice are associated with the motor neuron degenerative condition known as amyotrophic lateral sclerosis (ALS; Lou Gehrig's disease). Gain-of-function toxicity from the mutant protein expressed in motor neurons, associated with its misfolding and aggregation, leads to dysfunction and cell death, associated with paralyzing disease. Here, using hydrogen-deuterium exchange in intact mice in vivo, we have addressed whether an ALS-associated mutant protein, G85R SOD1-YFP, is subject to the same rate of turnover in spinal cord both early in the course of the disease and later. We find that the mutant protein turns over about 10-fold faster than a similarly expressed wild-type fusion and that there is no significant change in the rate of turnover as animals age and disease progresses. PMID:21780215

Farr, George W; Ying, Zheng; Fenton, Wayne A; Horwich, Arthur L

2011-10-01

79

Unfolding and aggregation of a glycosylated monoclonal antibody on a cation exchange column. Part II. Protein structure effects by hydrogen deuterium exchange mass spectrometry.  

PubMed

Hydrogen-deuterium exchange mass spectrometry (HX-MS) with proteolytic fragmentation is used to determine patterns of unfolding, as measured by increased solvent exposure, with peptide-level resolution for a glycosylated monoclonal antibody both when eluted from a tentacle-type cation exchange column (Fractogel EMD SO3-) and while bound to the resin. Two peaks are obtained when the bound protein is eluted with either a NaCl gradient or with two NaCl steps at increasing concentration. The first, early eluting peak contains only monomeric species whose structure is consistent with the native monomer. The second, late eluting peak contains a mixture of monomeric and aggregated species. The monomeric species in this mixture is also found to have a structure consistent with that of the native mAb, showing no evidence of increased solvent exposure. The aggregated species show instead significant unfolding in areas of the protein structure contained within the Fc region. The same peptides that exhibit the greatest level of solvent exposure in the aggregated species are also found in the fraction of protein that elutes from the resin only at high salt concentration, indicating that the aggregates are formed when the strongly-bound unfolded intermediate is desorbed at high salt. There is no evidence that the unfolded intermediate, formed while the protein is bound on the resin, is present in any of the eluted fractions indicating that, upon desorption from the resin, the intermediate either quickly refolds or forms aggregates which end-up co-eluting with the refolded protein at high salt concentrations. PMID:25011681

Guo, Jing; Carta, Giorgio

2014-08-22

80

External reflection FTIR of peptide monolayer films in situ at the air/water interface: experimental design, spectra-structure correlations, and effects of hydrogen-deuterium exchange.  

PubMed Central

A Fourier transform infrared spectrometer has been interfaced with a surface balance and a new external reflection infrared sampling accessory, which permits the acquisition of spectra from protein monolayers in situ at the air/water interface. The accessory, a sample shuttle that permits the collection of spectra in alternating fashion from sample and background troughs, reduces interference from water vapor rotation-vibration bands in the amide I and amide II regions of protein spectra (1520-1690 cm-1) by nearly an order of magnitude. Residual interference from water vapor absorbance ranges from 50 to 200 microabsorbance units. The performance of the device is demonstrated through spectra of synthetic peptides designed to adopt alpha-helical, antiparallel beta-sheet, mixed beta-sheet/beta-turn, and unordered conformations at the air/water interface. The extent of exchange on the surface can be monitored from the relative intensities of the amide II and amide I modes. Hydrogen-deuterium exchange may lower the amide I frequency by as much as 11-12 cm-1 for helical secondary structures. This shifts the vibrational mode into a region normally associated with unordered structures and leads to uncertainties in the application of algorithms commonly used for determination of secondary structure from amide I contours of proteins in D2O solution.

Flach, C R; Brauner, J W; Taylor, J W; Baldwin, R C; Mendelsohn, R

1994-01-01

81

Predicting Protein Aggregation during Storage in Lyophilized Solids Using Solid State Amide Hydrogen/Deuterium Exchange with Mass Spectrometric Analysis (ssHDX-MS).  

PubMed

Solid state amide hydrogen/deuterium exchange with mass spectrometric analysis (ssHDX-MS) was used to assess the conformation of myoglobin (Mb) in lyophilized formulations, and the results correlated with the extent of aggregation during storage. Mb was colyophilized with sucrose (1:1 or 1:8 w/w), mannitol (1:1 w/w), or NaCl (1:1 w/w) or in the absence of excipients. Immediately after lyophilization, samples of each formulation were analyzed by ssHDX-MS and Fourier transform infrared spectroscopy (FTIR) to assess Mb conformation, and by dynamic light scattering (DLS) and size exclusion chromatography (SEC) to determine the extent of aggregation. The remaining samples were then placed on stability at 25 °C and 60% RH or 40 °C and 75% RH for up to 1 year, withdrawn at intervals, and analyzed for aggregate content by SEC and DLS. In ssHDX-MS of samples immediately after lyophilization (t = 0), Mb was less deuterated in solids containing sucrose (1:1 and 1:8 w/w) than in those containing mannitol (1:1 w/w), NaCl (1:1 w/w), or Mb alone. Deuterium uptake kinetics and peptide mass envelopes also indicated greater Mb structural perturbation in mannitol, NaCl, or Mb-alone samples at t = 0. The extent of deuterium incorporation and kinetic parameters related to rapidly and slowly exchanging amide pools (Nfast, Nslow), measured at t = 0, were highly correlated with the extent of aggregation on storage as measured by SEC. In contrast, the extent of aggregation was weakly correlated with FTIR band intensity and peak position measured at t = 0. The results support the use of ssHDX-MS as a formulation screening tool in developing lyophilized protein drug products. PMID:24816133

Moorthy, Balakrishnan S; Schultz, Steven G; Kim, Sherry G; Topp, Elizabeth M

2014-06-01

82

Hydrogen/deuterium exchange mass spectrometry reveals specific changes in the local flexibility of plasminogen activator inhibitor 1 upon binding to the somatomedin B domain of vitronectin.  

PubMed

The native fold of plasminogen activator inhibitor 1 (PAI-1) represents an active metastable conformation that spontaneously converts to an inactive latent form. Binding of the somatomedin B domain (SMB) of the endogenous cofactor vitronectin to PAI-1 delays the transition to the latent state and increases the thermal stability of the protein dramatically. We have used hydrogen/deuterium exchange mass spectrometry to assess the inherent structural flexibility of PAI-1 and to monitor the changes induced by SMB binding. Our data show that the PAI-1 core consisting of ?-sheet B is rather protected against exchange with the solvent, while the remainder of the molecule is more dynamic. SMB binding causes a pronounced and widespread stabilization of PAI-1 that is not confined to the binding interface with SMB. We further explored the local structural flexibility in a mutationally stabilized PAI-1 variant (14-1B) as well as the effect of stabilizing antibody Mab-1 on wild-type PAI-1. The three modes of stabilizing PAI-1 (SMB, Mab-1, and the mutations in 14-1B) all cause a delayed latency transition, and this effect was accompanied by unique signatures on the flexibility of PAI-1. Reduced flexibility in the region around helices B, C, and I was seen in all three cases, which suggests an involvement of this region in mediating structural flexibility necessary for the latency transition. These data therefore add considerable depth to our current understanding of the local structural flexibility in PAI-1 and provide novel indications of regions that may affect the functional stability of PAI-1. PMID:22957734

Trelle, Morten Beck; Hirschberg, Daniel; Jansson, Anna; Ploug, Michael; Roepstorff, Peter; Andreasen, Peter A; Jørgensen, Thomas J D

2012-10-16

83

Is the pre-Tg DSC endotherm observed with solid state proteins associated with the protein internal dynamics? Investigation of bovine serum albumin by solid state hydrogen/deuterium exchange.  

PubMed

DSC thermograms of solid state pure proteins often show a distinct endotherm at a temperature far below the glass transition temperature of the system (Tg). We hypothesized this endotherm represents enthalpy recovery associated with an internal mobility transition of the protein molecule. Although the existence of an internal transition has been postulated, whether this endotherm is associated with such a transition has not previously been discussed. The purpose of this study was to investigate the origin of the pre-Tg endotherm in lyophilized bovine serum albumin (BSA). Due to strong glass behavior, the system Tg was determined by extrapolating Tg data of disaccharide/BSA formulations to zero saccharide. A small pre-Tg endotherm around 40-60 °C was observed in amorphous BSA equilibrated at 11%RH. The apparent activation energy suggested the endotherm was "?-mobility"-related. A solid state hydrogen/deuterium exchange study using FTIR was conducted over a temperature range spanning the endotherm. We found a fast phase, followed by essentially a plateau level which is highly temperature dependent in the 40-60 °C range, suggesting enhanced internal protein motion as the system passes through the temperature range of the endotherm. These results suggest the pre-Tg endotherm is associated with a protein internal mobility transition. PMID:23669417

Mizuno, Masayasu; Pikal, Michael J

2013-10-01

84

The effect of glucosyl-?-cyclodextrin on the hydrogen-deuterium exchange rate constant of the peptide bonds of chicken egg white lysozyme in a D 2O solution  

NASA Astrophysics Data System (ADS)

FT-IR spectroscopy revealed that the hydrogen-deuterium (H-D) exchange reaction rate of the peptide hydrogen atoms of chicken egg white lysozyme in a deuterated aqueous solution was significantly accelerated in the presence of glucosyl-?-cyclodextrin at 55 °C. The addition of methyl ?- D-glucopyranoside, which has no inclusion ability, rather decelerated the H-D exchange reaction rate at the same temperature. The H-D exchange rate constant of lysozyme was evaluated by the time dependence of the absorbance ratio of the amide II infrared band against the amide I'. The H-D exchange rate constant was not influenced by the addition of glucosyl-?-cyclodextrin at 45 °C, however, it became twice larger than that in the absence of the cyclodextrin at 55 °C. These results strongly suggest that peptide bonds of lysozyme become exposed to the aqueous medium due to the inclusion by glucosyl-?-cyclodextrin to accelerate the H-D exchange rate.

Yoshikiyo, Keisuke; Sugimoto, Masatoshi; Aso, Yuji; Takahashi, Tetsuya; Matsui, Yoshihisa; Yamamoto, Tatsuyuki

2008-10-01

85

Investigating the Refolding Pathway of Human Acidic Fibroblast Growth Factor (hFGF-1) from the Residual Structure(s) Obtained by Denatured-State Hydrogen/Deuterium Exchange  

PubMed Central

Human fibroblast growth factor 1 (hFGF-1) consists of 12 anti-parallel ?-strands arranged into a ?-trefoil architecture. We directly measured hydrogen/deuterium exchange rates on the urea-denatured hFGF-1 to obtain the information with regard to the persistent residual interaction(s) in the unfolded hFGF-1. Thirty-eight residues whose heteronuclear single quantum coherence cross-peaks can be observed after exchange show higher protections than those predicted for the same residues in a random coil conformation, suggesting the existence of residual structure(s). The urea-denaturation of hFGF-1 tested by both circular dichroism and fluorescence spectroscopy indicated that the unfolding process is a cooperative two-state process and that the residual structures observed did not originate from the existence of a partially structured intermediate. The coincident disappearance of the native heteronuclear single quantum coherence cross-peaks during the urea-denaturation process suggests that the residual structures observed contain no nativelike interactions. The protected residues (fold ons) in the urea-denatured state are mostly those that exchange slowly in the native state H/D exchange. The distribution of these fold ons in the native structure of hFGF-1 suggests that the refolding starts by collisions between the residual structures (microdomains) between the ?-strands VI and VII, and between the ?-strands II and III, which appear to be two independent refolding coordinates during the refolding process.

Wang, Han-Min; Yu, Chin

2011-01-01

86

Changes in MM-CK conformational mobility upon formation of the ADP-Mg(2+)-NO(3)(-)-creatine transition state analogue complex as detected by hydrogen/deuterium exchange.  

PubMed

In the presence of ADP, Mg(2+), creatine, and the planar nitrate ion, creatine kinase isoenzymes undergo significant structural changes accompanying the formation of a very stable transition state analogue complex (TSAC). We have compared, by using hydrogen/deuterium exchange followed by proteolysis of the labeled enzyme and mass spectrometric analysis of the peptic peptides, the backbone dynamics fluctuations of the free enzyme and those of the TSAC. In most peptides, exchange is not affected by ligand binding, except that observed in seven areas located in or at the entrance to the active site, where some protection is detected. On the basis of a comparison with the three-dimensional structures of free or liganded guanidino kinases, four of these peptides (residues 54-72, 226-234, 287-311, and 315-333) can be considered part of the substrate binding site. The other three (residues 162-186, 193-201, and 202-224) are not directly involved in the binding of substrates and are located in a dynamic domain, which allows the enzyme to properly align the substrates for optimal catalysis. PMID:14622006

Mazon, Hortense; Marcillat, Olivier; Forest, Eric; Vial, Christian

2003-11-25

87

Fluoroketone Inhibition of Ca2+-Independent Phospholipase A2 through Binding Pocket Association Defined by Hydrogen/Deuterium Exchange and Molecular Dynamics  

PubMed Central

The mechanism of inhibition of group VIA Ca2+-independent phospholipase A2 (iPLA2) by fluoroketone (FK) ligands is examined by a combination of deuterium exchange mass spectrometry (DXMS) and molecular dynamics (MD). Models for iPLA2 were built by homology with the known structure of patatin and equilibrated by extensive MD simulations. Empty pockets were identified during the simulations and studied for their ability to accommodate FK inhibitors. Ligand docking techniques showed that the potent inhibitor 1,1,1,3-tetrafluoro-7-phenylheptan-2-one (PHFK) forms favorable interactions inside an active-site pocket, where it blocks the entrance of phospholipid substrates. The polar fluoroketone headgroup is stabilized by hydrogen bonds with residues Gly486, Gly487, and Ser519. The nonpolar aliphatic chain and aromatic group are stabilized by hydrophobic contacts with Met544, Val548, Phe549, Leu560, and Ala640. The binding mode is supported by DXMS experiments showing an important decrease of deuteration in the contact regions in the presence of the inhibitor. The discovery of the precise binding mode of FK ligands to the iPLA2 should greatly improve our ability to design new inhibitors with higher potency and selectivity.

2012-01-01

88

Mechanism and kinetics of dehydrogenation of higher n-paraffins on promoted platinum catalysts. I. Hydrogen/deuterium isotope exchange in n-decane  

SciTech Connect

To clarify the mechanism of the dehydrogenation reaction of n-decane on promoted platinum-alumina catalysts, we have examined the kinetics of deuterium isotope exchange with n-decane and its reaction products and measured the kinetic isotope effects. The reaction of n-decane proceeds via slow stages of desorption of olefins and dienes and of decatriene formation, while the aromatic products are rapidly desorbed. The reaction is mainly stepwise.

Krylova, T.L.; Nekrasov, N.V.; Gudkov, B.S.; Gurevich, V.R.; Kiperman, S.L.

1981-06-01

89

Probing Lactate Dehydrogenase Activity in Tumors by Measuring Hydrogen/Deuterium Exchange in Hyperpolarized l-[1-13C,U-2H]Lactate  

PubMed Central

13C magnetic resonance spectroscopy and spectroscopic imaging measurements of hyperpolarized 13C label exchange between exogenously administered [1-13C]pyruvate and endogenous lactate, catalyzed by lactate dehydrogenase (LDH), has proved to be a powerful approach for probing tissue metabolism in vivo. This experiment has clinical potential, particularly in oncology, where it could be used to assess tumor grade and response to treatment. A limitation of the method is that pyruvate must be administered in vivo at supra-physiological concentrations. This problem can be avoided by using hyperpolarized [1-13C]lactate, which can be used at physiological concentrations. However, sensitivity is limited in this case by the relatively small pyruvate pool size, which would result in only low levels of labeled pyruvate being observed even if there was complete label equilibration between the lactate and pyruvate pools. We demonstrate here a more sensitive method in which a doubly labeled lactate species can be used to measure LDH-catalyzed exchange in vivo. In this experiment exchange of the C2 deuterium label between injected hyperpolarized l-[1-13C,U-2H]lactate and endogenous unlabeled lactate is observed indirectly by monitoring phase modulation of the spin-coupled hyperpolarized 13C signal in a heteronuclear 1H/13C spin–echo experiment.

2012-01-01

90

ETD in a Traveling Wave Ion Guide at Tuned Z-Spray Ion Source Conditions Allows for Site-Specific Hydrogen/Deuterium Exchange Measurements  

PubMed Central

The recent application of electron transfer dissociation (ETD) to measure the hydrogen exchange of proteins in solution at single-residue resolution (HX-ETD) paves the way for mass spectrometry-based analyses of biomolecular structure at an unprecedented level of detail. The approach requires that activation of polypeptide ions prior to ETD is minimal so as to prevent undesirable gas-phase randomization of the deuterium label from solution (i.e., hydrogen scrambling). Here we explore the use of ETD in a traveling wave ion guide of a quadrupole-time-of-flight (Q-TOF) mass spectrometer with a “Z-spray” type ion source, to measure the deuterium content of individual residues in peptides. We systematically identify key parameters of the Z-spray ion source that contribute to collisional activation and define conditions that allow ETD experiments to be performed in the traveling wave ion guide without gas-phase hydrogen scrambling. We show that ETD and supplemental collisional activation in a subsequent traveling wave ion guide allows for improved extraction of residue-specific deuterium contents in peptides with low charge. Our results demonstrate the feasibility, and illustrate the advantages of performing HX-ETD experiments on a high-resolution Q-TOF instrument equipped with traveling wave ion guides. Determination of parameters of the Z-spray ion source that contribute to ion heating are similarly pertinent to a growing number of MS applications that also rely on an energetically gentle transfer of ions into the gas-phase, such as the analysis of biomolecular structure by native mass spectrometry in combination with gas-phase ion-ion/ion-neutral reactions or ion mobility spectrometry.

Rand, Kasper D.; Pringle, Steven D.; Morris, Michael; Engen, John R.; Brown, Jeffery M.

2012-01-01

91

"TOF2H": A precision toolbox for rapid, high density/high coverage hydrogen-deuterium exchange mass spectrometry via an LC-MALDI approach, covering the data pipeline from spectral acquisition to HDX rate analysis  

PubMed Central

Background Protein-amide proton hydrogen-deuterium exchange (HDX) is used to investigate protein conformation, conformational changes and surface binding sites for other molecules. To our knowledge, software tools to automate data processing and analysis from sample fractionating (LC-MALDI) mass-spectrometry-based HDX workflows are not publicly available. Results An integrated data pipeline (Solvent Explorer/TOF2H) has been developed for the processing of LC-MALDI-derived HDX data. Based on an experiment-wide template, and taking an ab initio approach to chromatographic and spectral peak finding, initial data processing is based on accurate mass-matching to fully deisotoped peaklists accommodating, in MS/MS-confirmed peptide library searches, ambiguous mass-hits to non-target proteins. Isotope-shift re-interrogation of library search results allows quick assessment of the extent of deuteration from peaklist data alone. During raw spectrum editing, each spectral segment is validated in real time, consistent with the manageable spectral numbers resulting from LC-MALDI experiments. A semi-automated spectral-segment editor includes a semi-automated or automated assessment of the quality of all spectral segments as they are pooled across an XIC peak for summing, centroid mass determination, building of rates plots on-the-fly, and automated back exchange correction. The resulting deuterium uptake rates plots from various experiments can be averaged, subtracted, re-scaled, error-barred, and/or scatter-plotted from individual spectral segment centroids, compared to solvent exposure and hydrogen bonding predictions and receive a color suggestion for 3D visualization. This software lends itself to a "divorced" HDX approach in which MS/MS-confirmed peptide libraries are built via nano or standard ESI without source modification, and HDX is performed via LC-MALDI using a standard MALDI-TOF. The complete TOF2H package includes additional (eg LC analysis) modules. Conclusion "TOF2H" provides a comprehensive HDX data analysis package that has accelerated the processing of LC-MALDI-based HDX data in the authors' lab from weeks to hours. It runs in a standard MS Windows (XP or Vista) environment, and can be downloaded or obtained from the authors at no cost.

Nikamanon, Pornpat; Pun, Elroy; Chou, Wayne; Koter, Marek D; Gershon, Paul D

2008-01-01

92

Omegatron mass spectrometer in a hydrogen/deuterium detached plasma  

NASA Astrophysics Data System (ADS)

Diagnostics of the relative concentrations of the atomic and molecular ions were carried out in hydrogen/deuterium plasma with hydrogen/deuterium gas puff in the linear plasma device, TPD-SheetIV. An omegatron ion mass spectrometer is used for analyzing ion species.

Tonegawa, A.; Nishijima, T.; Ishioka, H.; Nakanowatari, A.; Kawamura, K.

2008-03-01

93

Hydrogen/deuterium isotope effects in water and aqueous solutions of organic molecules and proteins  

NASA Astrophysics Data System (ADS)

It is pointed out that hydrogen/deuterium substitution, frequently used in neutron scattering studies of the structure and dynamics of hydrogenous samples, can have significant effects on structure, phase behavior and protein stability. The effects must be kept in mind in the interpretation of such experiments. In suitable cases, these effects can be mitigated by an appropriate choice of experimental conditions.

Price, David L.; Fu, Ling; Bermejo, F. Javier; Fernandez-Alonso, Felix; Saboungi, Marie-Louise

2013-10-01

94

Hydrogen\\/Deuterium Exchange Mass Spectrometry Analysis of Protein Aggregates  

Microsoft Academic Search

The elucidation of the structure of amyloid fibrils and related aggregates is an important step toward understanding the pathogenesis of diseases like Alzheimer's disease, which feature protein misfolding and\\/or aggregation. However, the large size, heterogeneous morphology, and poor solubility of amyloid?like fibrils make them resistant to high?resolution structure determination. Using amyloid fibrils and protofibrils of the Alzheimer's plaque peptide amyloid

Indu Kheterpal; Kelsey D. Cook; Ronald Wetzel

2006-01-01

95

Hydrogen (deuterium) vibron frequency as a pressure comparison gauge at multi-Mbar pressures  

NASA Astrophysics Data System (ADS)

The Raman spectra of compressed hydrogen (deuterium) have been measured in the multi-Mbar pressure range in the diamond anvil cell using the position of the stressed first-order Raman diamond edge (DE) to estimate pressure. We find that the Raman spectra are very consistent in repeated experiments for the critical frequencies of the hydrogen (deuterium) bands at the phase transition pressure-temperature (P-T) points. However, measurements of pressure determined from the DE in different experiments vary substantially with virtually identical Raman spectra of H2 (D2), giving in some cases a pressure variation as high as 20 GPa. These variations do not only depend on sample and sample chamber geometry but also on the P-T path taken, thus making the DE pressure determination uncertain. Therefore, we propose in experiments on hydrogen (deuterium) to use the Raman frequency of the intramolecular vibration (vibron) of H2(D2) as a pressure sensor. By comparing the vibron frequencies and considering the geometrical changes of the sample chamber caused by very high pressures, we propose an alternative explanation to the recent claims of a transformation to a metallic liquid state of hydrogen (deuterium).

Howie, Ross T.; Gregoryanz, Eugene; Goncharov, Alexander F.

2013-08-01

96

Precision Measurement of the Hydrogen-Deuterium 1S-2S Isotope Shift  

SciTech Connect

Measuring the hydrogen-deuterium isotope shift via two-photon spectroscopy of the 1S-2S transition, we obtain 670 994 334 606(15) Hz. This is a 10-times improvement over the previous best measurement [A. Huber et al., Phys. Rev. Lett. 80, 468 (1998)] confirming its frequency value. A calculation of the difference of the mean square charge radii of deuterium and hydrogen results in {sub d}-{sub p}=3.820 07(65) fm{sup 2}, a more than twofold improvement compared to the former value.

Parthey, Christian G.; Matveev, Arthur; Alnis, Janis; Pohl, Randolf; Udem, Thomas; Kolachevsky, Nikolai; Haensch, Theodor W. [Max-Planck-Institut fuer Quantenoptik, 85748 Garching (Germany); Jentschura, Ulrich D. [Department of Physics, Missouri University of Science and Technology, Rolla, Missouri 65409 (United States)

2010-06-11

97

The ground state properties of spin-aligned atomic hydrogen, deuterium, and tritium  

NASA Technical Reports Server (NTRS)

The internal energy, pressure, and compressibility of ground-state, spin-aligned atomic hydrogen, deuterium, and tritium are calculated assuming that all pair interactions occur via the atomic triplet (spin-aligned) potential. The conditions required to obtain atomic hydrogen and its isotopes in bulk are discussed; such a development would be of value in propulsion systems because of the light mass and energetic recombination of atomic hydrogen. Results show that atomic triplet hydrogen and deuterium remain gaseous at 0 K, and that tritium forms a liquid with a binding energy of approximately -0.75 K per atom at a molar volume of 130 cu cm per mole. The pair distribution function for these systems is calculated, and the predicted superfluid behavior of atomic triplet hydrogen and tritium is briefly discussed.

Etters, R. D.; Dugan, J. V., Jr.; Palmer, R. W.

1975-01-01

98

Nano-scaled TiO(OD)2: a time resolved 1H/2D isotope exchange study observed in situ with neutron scattering at 20 °C and 40 °C.  

PubMed

In situ neutron diffraction measurements of the nanocrystalline deuterated oxyhydroxide TiO(OD)(2) compound were performed as a function of time and temperature under NH(3) gas flow in order to study the hydrogen-deuterium exchange mechanism. Data were collected on the instrument D20 at the ILL (France) and the analysis of the kinetics was directly based on the contrast variation of the incoherent neutron cross section of hydrogen and deuterium. The time evolution of the hydrogenated phase fraction was described using the well-known Kolmogorov-Johnson-Mehl-Avrami (KJMA) expression. The H/D exchange reaction is complete within 140 s at 20 °C and within 120 s at 40 °C. The activation energy for the H/D exchange reaction is estimated to be 37 kJ mol(-1). PMID:23328794

Legrand, Vincent; Merdrignac-Conanec, Odile; Paulus, Werner

2013-03-21

99

Investigation of hydrogen/deuterium isotope effects in coal-conversion processes  

SciTech Connect

This paper reports on the investigation of hydrogen/deuterium isotope effects in catalytic coal char gasification experiments been conducted to obtain information about the mechanisms of hydrogasification and steam gasification reactions. Hydrogasification and steam gasification experiments were conducted with or without K/sub 2/CO/sub 3/ catalyst (K/C atomic ratio 0.04) using H/sub 2/ or D/sub 2/ for hydrogasification and H/sub 2/O or D/sub 2/O for steam gasification. Three pairs of hydrogasification experiments have been made to investigate the deuterium isotope effect: one pair with noncatalyzed char and two pairs with K/sub 2/CO/sub 3/-catalyzed char. The K/C atomic ratio in both catalyzed chars was 0.04. In the case of the noncatalyzed char, little, if any, isotope effect was observed. In contrast, a strong reverse isotope effect was found for the K/sub 2/CO/sub 3/-catalyzed char, at both 750 and 850/sup 0/C. The value of the rate (D/sub 2/)/rate (H/sub 2/) ratio was 2.5 at 750/sup 0/C and 2.2 at 850/sup 0/C, read at around the midpoint of the rate versus weight loss curve (at 33% weight loss). Noncatalyzed hydrogasification of char in hydrogen to form methane can be described by a two-step mechanism according to Blackwood and coworkers. Chemisorption of hydrogen takes place at active centers on the char surface in the first step; the surface complex formed by chemisorption reacts with hydrogen to form methane in the second step. A refinement of this mechanism was also proposed, postulating a stepwise formation of the surface complex G(H)/sub 2/.

Heredy, L.A.; McCoy, L.R.; Goldberg, I.B.

1983-01-01

100

Irreversible thermal denaturation of cytochrome c studied by electrospray mass spectrometry  

Microsoft Academic Search

This work uses electrospray ionization mass spectrometry (ESI-MS) in conjunction with hydrogen\\/deuterium exchange (HDX) and\\u000a optical spectroscopy for characterizing the solution-phase properties of cytochrome c (cyt c) after heat exposure. Previous work demonstrated that heating results in irreversible denaturation for a subpopulation of\\u000a proteins in the sample. However, that study did not investigate the physical reasons underlying this interesting effect.

Jiangjiang Liu; Lars Konermann

2009-01-01

101

Infrared, Raman, and coherent anti-Stokes Raman spectroscopy of the hydrogen/deuterium isotopomers of nitromethane  

SciTech Connect

The vibrational spectroscopy of the four hydrogen/deuterium isotopomers of nitromethane was investigated. Infrared, Raman, and coherent anti-Stokes Raman spectroscopy (CARS) of the isotopomers were used to determine vibrational frequencies for each isotopomer. Results for the d{sub 0}, d{sub 2}, and d{sub 3} isotopomers agree well with literature values. Gas- and liquid-phase spectra for the d{sub 1} isotopomer are presented, and the measured vibrational frequencies compare well with a theoretical prediction. In addition, high-resolution Raman spectra of the CN stretch mode were used to analyze the elements of the anharmonic coupling matrix involving this mode. Finally, the relative differential Raman scattering cross section of the Cn stretch mode of each isotopomer was determined.

Hill, J.R.; Moore, D.S.; Schmidt, S.C.; Storm, C.B. (Los Alamos National Lab., NM (United States))

1991-04-18

102

Analysis of proton exchange kinetics with time-dependent exchange rate.  

PubMed

Mass spectrometry is used to probe the kinetics of hydrogen-deuterium exchange in lysozyme in pH 5, 6 and 7.4. An analysis based on a Verhulst growth model is proposed and effectively applied to the kinetics of the hydrogen exchange. The data are described by a power-like function which is based on a time-dependence of the exchange rate. Experimental data ranging over many time scales is considered and accurate fits of a power-like function are obtained. Results of fittings show correlation between faster hydrogen-deuterium exchange and increase of pH. Furthermore a model is presented that discriminates between easily exchangeable hydrogens (located in close proximity to the protein surface) and those protected from the exchange (located in the protein interior). A possible interpretation of the model and its biological significance are discussed. PMID:20056171

Rutkowska-Wlodarczyk, Izabela; Kierdaszuk, Borys; Wlodarczyk, Jakub

2010-04-01

103

Epitope mapping by epitope excision, hydrogen/deuterium exchange, and peptide-panning techniques combined with in silico analysis.  

PubMed

The fine characterization of protective B cell epitopes plays a pivotal role in the development of novel vaccines. The development of epitope-based vaccines, in fact, cannot be possible without a clear definition of the antigenic regions involved in the binding between the protective antibody (Ab) and its molecular target. To achieve this result, different epitope-mapping approaches have been widely described (Clementi et al. Drug Discov Today 18(9-10):464-471, 2013). Nowadays, the best way to characterize an Ab bound region is still the resolution of Ab-antigen (Ag) co-crystal structure. Unfortunately, the crystallization approaches are not always feasible. However, different experimental strategies aimed to predict Ab-Ag interaction and followed by in silico analysis of the results may be good surrogate approaches to achieve this result. Here, we review few experimental techniques followed by the use of "basic" informatics tools for the analysis of the results. PMID:24515481

Clementi, Nicola; Mancini, Nicasio; Criscuolo, Elena; Cappelletti, Francesca; Clementi, Massimo; Burioni, Roberto

2014-01-01

104

Branching in the Gaseous Reaction Monatomic Hydrogen + Deuterium Chloride as a Function of Collision Energy  

NASA Astrophysics Data System (ADS)

Branching in the gas-phase reaction H + DCl to HD + Cl (1) (termed abstraction) and to HCl + D (2) (exchange) has been measured by monitoring the atomic products, Cl and D, by resonantly -enhanced multiphoton ionization. The collision energy has been varied in the range 1.0-2.4 eV by alteration in the photolytic source of H. Within the error limits, the cross-section for abstraction was found to remain constant at 0.16 +/- 0.06 A^2 over this energy range. The cross-section for exchange exhibited a moderate decrease from 0.6 +/- 0.3 to 0.2 +/- 0.1 A^2 with increasing collision energy. The findings for the abstraction reaction stand in good agreement with the results of a quasi-classical trajectory computation, reported here, on the GQQ potential-energy surface, the most-reliable PES available (D. W. Schwenke et al., J. Chem. Phys., 90, 3110 (1989)), whereas those concerning the exchange reaction stand in marked contrast. The experimental findings indicate that the GQQ PES may be deficient in the region of high collision energies where the reacting system, en route to exchange, accesses bent intermediate configurations for which ab initio data is lacking. Results obtained in the calibration procedures have shown that the photodissociation of DCl at 193 nm produces 81 +/- 3% of the chlorine in the ground state (^2P _{3/2}) and 19 +/- 3% in the excited state (^2P _{1/2}). This compares with the result of 67 and 33% Cl(^2P _{3/2}) and Cl( ^2P_{1/2}) for the photodissociation of HCl at 193 nm (E. Hirota et al., J. Chem. Phys., 88, 2457 (1988)). The two photon transition probability for the Cl(^2P _{3/2} to ^2 D_{3/2}) transition relative to the Cl(^2P_ {1/2} to ^2D _{3/2}) transition was found to be 2.7 +/- 0.3. The photodissociation cross-section for HCl at 248 nm was measured and a value of 3 +/- 2 times 10^{ -21} cm^2 was found when compared to the absorption cross-section of H _2S at 248 nm.

Collings, Bruce Andrew

1991-01-01

105

The folding energy landscape of apoflavodoxin is rugged: Hydrogen exchange reveals nonproductive misfolded intermediates  

Microsoft Academic Search

Many native proteins occasionally form partially unfolded forms (PUFs), which can be detected by hydrogen\\/deuterium exchange and NMR spectroscopy. Knowledge about these metastable states is required to better understand the onset of folding-related diseases. So far, not much is known about where PUFs reside within the energy landscape for protein folding. Here, four PUFs of the relatively large apoflavodoxin (179

Yves J. M. Bollen; Monique B. Kamphuis; Carlo P. M. van Mierlo

2006-01-01

106

The folding energy landscape of apoflavodoxin is rugged. hydrogen exchange reveals non-productive misfolded intermediates  

Microsoft Academic Search

Many native proteins occasionally form partially unfolded forms (PUFs), which can be detected by hydrogen\\/deuterium exchange and NMR spectroscopy. Knowledge about these metastable states is required to better understand the onset of folding-related diseases. So far, not much is known about where PUFs reside within the energy landscape for protein folding. Here, four PUFs of the relatively large apoflavodoxin (179

Y. J. M. Bollen; M. B. Kamphuis; Mierlo van C. P. M

2006-01-01

107

The hydrogen exchange core and protein folding.  

PubMed Central

A database of hydrogen-deuterium exchange results has been compiled for proteins for which there are published rates of out-exchange in the native state, protection against exchange during folding, and out-exchange in partially folded forms. The question of whether the slow exchange core is the folding core (Woodward C, 1993, Trends Biochem Sci 18:359-360) is reexamined in a detailed comparison of the specific amide protons (NHs) and the elements of secondary structure on which they are located. For each pulsed exchange or competition experiment, probe NHs are shown explicitly; the large number and broad distribution of probe NHs support the validity of comparing out-exchange with pulsed-exchange/competition experiments. There is a strong tendency for the same elements of secondary structure to carry NHs most protected in the native state, NHs first protected during folding, and NHs most protected in partially folded species. There is not a one-to-one correspondence of individual NHs. Proteins for which there are published data for native state out-exchange and theta values are also reviewed. The elements of secondary structure containing the slowest exchanging NHs in native proteins tend to contain side chains with high theta values or be connected to a turn/loop with high theta values. A definition for a protein core is proposed, and the implications for protein folding are discussed. Apparently, during folding and in the native state, nonlocal interactions between core sequences are favored more than other possible nonlocal interactions. Other studies of partially folded bovine pancreatic trypsin inhibitor (Barbar E, Barany G, Woodward C, 1995, Biochemistry 34:11423-11434; Barber E, Hare M, Daragan V, Barany G, Woodward C, 1998, Biochemistry 37:7822-7833), suggest that developing cores have site-specific energy barriers between microstates, one disordered, and the other(s) more ordered.

Li, R.; Woodward, C.

1999-01-01

108

Protein Dynamics in Phosphorylation-Mediated Allostery Probed by Amide Exchange Mass Spectrometry  

NASA Astrophysics Data System (ADS)

A major goal of molecular biology is to correlate molecular structure with function. Since most enzymes and biological catalysts are proteins, the focus for correlating 'form' with 'function' has been entirely on protein macromolecular structure. It is obvious that any understanding of protein function must come through an understanding protein dynamics. Furthermore, all of the regulatory reactions are through changes in dynamics brought about by post-translational modifications, the most important of which is phosphorylation. This review highlights the important role of covalent phosphorylation and noncovalent phosphates in regulating allosteric effects and function through a study of protein dynamics. Mass spectrometry is a relatively new and increasingly important tool for describing protein dynamics. All examples described in this review have been studied by amide hydrogen/deuterium exchange mass spectrometry.

Ghosh, Madhubrata; Anand, Ganesh S.

2013-11-01

109

Conformational changes in oxidatively stressed monoclonal antibodies studied by hydrogen exchange mass spectrometry.  

PubMed

Oxidation of methionine residues in biopharmaceuticals is a common and often unwanted modification that frequently occurs during their manufacture and storage. It often results in a lack of stability and biological function of the product, necessitating continuous testing for the modification throughout the product shelf life. A major class of biopharmaceutical products are monoclonal antibodies (mAbs), however, techniques for their detailed structural analysis have until recently been limited. Hydrogen/deuterium exchange mass spectrometry (HXMS) has recently been successfully applied to the analysis of mAbs. Here we used HXMS to identify and localise the structural changes that occurred in a mAb (IgG1) after accelerated oxidative stress. Structural alterations in a number of segments of the Fc region were observed and these related to oxidation of methionine residues. These included a large change in the hydrogen exchange profile of residues 247-253 of the heavy chain, while smaller changes in hydrogen exchange profile were identified for peptides that contained residues in the interface of the C(H)2 and C(H)3 domains. PMID:20162626

Burkitt, William; Domann, Paula; O'Connor, Gavin

2010-04-01

110

Hydrogen-deuterium isotope shift: From the 1S-2S-transition frequency to the proton-deuteron charge-radius difference  

SciTech Connect

We analyze and review the theory of the hydrogen-deuterium isotope shift for the 1S-2S transition, which is one of the most accurately measured isotope shifts in any atomic system, in view of a recently improved experiment. A tabulation of all physical effects that contribute to the isotope shift is given. These include the Dirac binding energy, quantum electrodynamic effects, including recoil corrections, and the nuclear-size effect, including the pertaining relativistic and radiative corrections. From a comparison of the theoretical result {Delta}f{sub th}=670 999 566.90(66)(60) kHz (exclusive of the nonrelativistic nuclear-finite-size correction) and the experimental result {Delta}f{sub expt}=670 994 334 605(15) Hz, we infer the deuteron-proton charge-radius difference {sub d}-{sub p}=3.820 07(65) fm{sup 2} and the deuteron structure radius r{sub str}=1.975 07(78) fm.

Jentschura, U.D. [Department of Physics, Missouri University of Science and Technology, Rolla, Missouri 65409-0640 (United States); Matveev, A.; Parthey, C.G.; Alnis, J.; Pohl, R.; Udem, Th.; Kolachevsky, N.; Haensch, T.W. [Max-Planck-Institut fuer Quantenoptik, DE-85748 Garching (Germany)

2011-04-15

111

Exchange Studies as Actor-Networks: Following Korean Exchange Students in Swedish Higher Education  

ERIC Educational Resources Information Center

This article explores how Korean exchange students organized their studies during exchange programs in Swedish higher education. For most students, the programs became a disordered period in relation to their education. The value of exchange studies seems mainly to be extra-curricular. Drawing upon actor network theory, the article argues that the…

Ahn, Song-ee

2011-01-01

112

The Deuterator: software for the determination of backbone amide deuterium levels from H\\/D exchange MS data  

Microsoft Academic Search

Background: The combination of mass spectrometry and solution phase amide hydrogen\\/deuterium exchange (H\\/D exchange) experiments is an effective method for characterizing protein dynamics, and protein-protein or protein-ligand interactions. Despite methodological advancements and improvements in instrumentation and automation, data analysis and display remains a tedious process. The factors that contribute to this bottleneck are the large number of data points produced

B. D. Pascal; M. J. Chalmers; S. A. Busby; C. C. Mader; N. F. Tsinoremas; P. R. Griffin

2007-01-01

113

NMR and protein folding: equilibrium and stopped-flow studies.  

PubMed Central

NMR studies are now unraveling the structure of intermediates of protein folding using hydrogen-deuterium exchange methodologies. These studies provide information about the time dependence of formation of secondary structure. They require the ability to assign specific resonances in the NMR spectra to specific amide protons of a protein followed by experiments involving competition between folding and exchange reactions. Another approach is to use 19F-substituted amino acids to follow changes in side-chain environment upon folding. Current techniques of molecular biology allow assignments of 19F resonances to specific amino acids by site-directed mutagenesis. It is possible to follow changes and to analyze results from 19F spectra in real time using a stopped-flow device incorporated into the NMR spectrometer.

Frieden, C.; Hoeltzli, S. D.; Ropson, I. J.

1993-01-01

114

Hydrogen bond stabilities in membrane-reconstituted alamethicin from amide-resolved hydrogen-exchange measurements.  

PubMed Central

Amide-resolved hydrogen-deuterium exchange-rate constants were measured for backbone amides of alamethicin reconstituted in dioleoylphosphatidylcholine vesicles by an exchange-trapping method combined with high-resolution nuclear magnetic resonance spectroscopy. In vesicles containing alamethicin at molar ratios between 1:20 and 1:100 relative to lipid, the exchange-rate constants increased with increasing volume of the D20 buffer in which the vesicles were suspended, indicating that exchange under these conditions is dominated by partitioning of the peptide into the aqueous phase. This was supported by observation of a linear relationship between the exchange-rate constants for amides in membrane-reconstituted alamethicin and those for amides in alamethicin dissolved directly into D2O buffer. Significant protection of amides from exchange with D2O buffer in membrane-reconstituted alamethicin is interpreted in terms of stabilization by helical hydrogen bonding. Under conditions in which amide exchange occurred by partitioning of the peptide into solution, only lower limits for hydrogen-bond stabilities in the membrane were determined; all the potentially hydrogen-bonded amides of alamethicin are at least 1000-fold exchange protected in the membrane-bound state. When partitioning of alamethicin into the aqueous phase was suppressed by hydration of reconstituted vesicles in a limiting volume of water [D2O:dioleoylphosphatidylcholine:alamethicin; 220:1:0.05; (M:M:M)], the exchange-protection factors exhibited helical periodicity with highly exchange-protected, and less well-protected, amides on the nonpolar and polar helix faces, respectively. The exchange data indicate that, under the conditions studied, alamethicin adopts a stable helical structure in DOPC bilayers in which all the potentially hydrogen-bonded amides are stabilized by helical hydrogen bonds. The protection factors define the orientation of the peptide helix with respect to an aqueous phase, which is either the bulk solution or water within parallel or antiparallel transmembrane arrays of reconstituted alamethicin.

Dempsey, C E; Handcock, L J

1996-01-01

115

HD desktop: An integrated platform for the analysis and visualization of H\\/D exchange data  

Microsoft Academic Search

Here we describe an integrated software platform titled HD Desktop designed specifically to enhance the analysis of hydrogen\\/deuterium\\u000a exchange (HDX) mass spectrometry data. HD Desktop integrates tools for data extraction with visualization components within\\u000a a single web-based application. The interface design enables users to navigate from the peptide view to the sample and experiment\\u000a levels, tracking all manipulations while updating

Bruce D. Pascal; Michael J. Chalmers; Scott A. Busby; Patrick R. Griffin

2009-01-01

116

Use of H/D isotope effects to gather information about hydrogen bonding and hydrogen exchange rates  

NASA Astrophysics Data System (ADS)

Polar side-chains in proteins play important roles in forming and maintaining three-dimensional structures, and thus participate in various biological functions. Until recently, most protein NMR studies have focused on the non-exchangeable protons of amino acid residues. The exchangeable protons attached to polar groups, such as hydroxyl (OH), sulfhydryl (SH), and amino (NH2) groups, have mostly been ignored, because in many cases these hydrogen atoms exchange too quickly with water protons, making NMR observations impractical. However, in certain environments, such as deep within the hydrophobic interior of a protein, or in a strong hydrogen bond to other polar groups or interacting ligands, the protons attached to polar groups may exhibit slow hydrogen exchange rates and thus become NMR accessible. To explore the structural and biological implications of the interactions involving polar side-chains, we have developed versatile NMR methods to detect such cases by observing the line shapes of 13C NMR signals near the polar groups, which are affected by deuterium-proton isotope shifts in a mixture of H2O and D2O. These methods allow the detection of polar side-chains with slow hydrogen–deuterium exchange rates, and therefore provide opportunities to retrieve information about the polar side-chains, which might otherwise be overlooked by conventional NMR experiments. Future prospects of applications using deuterium-proton isotope shifts to retrieve missing structural and dynamic information of proteins are discussed.

Takeda, Mitsuhiro; Miyanoiri, Yohei; Terauchi, Tsutomu; Yang, Chun-Jiun; Kainosho, Masatsune

2014-04-01

117

Parameter dependence of the radial electric field in the edge pedestal of hydrogen, deuterium and helium plasmas  

NASA Astrophysics Data System (ADS)

The characteristics of the edge radial electric field (Er) are studied in deuterium, hydrogen and helium plasmas at ASDEX Upgrade. The minimum of the Er well is analyzed as a function of pedestal parameters and the best correlation is found between the depth of the Er well and the ion pressure at the pedestal top. This result is consistent with Er being balanced by the main ion pressure gradient term. Studying the radial position of the Er minimum reveals that the Er well moves closer to the last closed flux surface the deeper the Er well is. This suggests that for deeper Er wells the distance between the steepest gradients in the ion temperature and ion density profile is reduced. The width of the Er well shows no significant variations despite changing the ion temperature, magnetic field and plasma particle species. At AUG, the Er well is on average 1.2 cm wide. A multi-machine comparison supports a machine size scaling of Er and indicates that the Er shear layer covers the outer 2% of the plasma minor radius independent of the size of the machine. Based on this scaling, the width of the Er well in ITER is estimated to ?4 cm.

Viezzer, E.; Pütterich, T.; McDermott, R. M.; Conway, G. D.; Cavedon, M.; Dunne, M. G.; Dux, R.; Wolfrum, E.; the ASDEX Upgrade Team

2014-07-01

118

Chiral sum frequency generation for in situ probing proton exchange in antiparallel ?-sheets at interfaces.  

PubMed

Studying hydrogen/deuterium (H/D) exchange in proteins can provide valuable insight on protein structure and dynamics. Several techniques are available for probing H/D exchange in the bulk solution, including NMR, mass spectroscopy, and Fourier transform infrared spectroscopy. However, probing H/D exchange at interfaces is challenging because it requires surface-selective methods. Here, we introduce the combination of in situ chiral sum frequency generation (cSFG) spectroscopy and ab initio simulations of cSFG spectra as a powerful methodology to probe the dynamics of H/D exchange at interfaces. This method is applied to characterize H/D exchange in the antiparallel ?-sheet peptide LK7?. We report here for the first time that the rate of D-to-H exchange is about 1 order of magnitude faster than H-to-D exchange in the antiparallel structure at the air/water interface, which is consistent with the existing knowledge that O-H/D dissociation in water is the rate-limiting step, and breaking the O-D bond is slower than breaking the O-H bond. The reported analysis also provides fundamental understanding of several vibrational modes and their couplings in peptide backbones that have been difficult to characterize by conventional methods, including Fermi resonances of various combinations of peptide vibrational modes such as amide I and amide II, C-N stretch, and N-H/N-D bending. These results demonstrate cSFG as a sensitive technique for probing the kinetics of H/D exchange in proteins at interfaces, with high signal-to-noise N-H/N-D stretch bands that are free of background from the water O-H/O-D stretch. PMID:23394622

Fu, Li; Xiao, Dequan; Wang, Zhuguang; Batista, Victor S; Yan, Elsa C Y

2013-03-01

119

Design study of plastic film heat exchanger  

NASA Astrophysics Data System (ADS)

This report presents the results of an effort to develop and design a unique thermoplastic film heat exchanger for use in an industrial heat pump evaporator system and other energy recovery applications. The concept for the exchanger is that of individual heat exchange elements formed by two adjoining and freely hanging plastic films. Liquid flows downward in a regulated fashion between the films due to the balance of hydrostatic and frictional forces. The fluid stream on the outside of film may be a free-falling liquid film, a condensing gas, or a noncondensing gas. The flow and structural principles are similar to those embodied in an earlier heat exchange system developed for use in waste water treatment systems (Sanderson). The design allows for high heat transfer rates while working within the thermal and structural limitations of thermoplastic materials. The potential of this new heat exchanger design lies in the relatively low cost of plastic film and the high inherent corrosion and fouling resistance. This report addresses the selection of materials, the potential heat transf er performance, the mechanical design and operation of a unit applied in a low pressure steam recovery system, and the expected selling price in comparison to conventional metallic shell and tube heat exchangers.

Guyer, E. C.; Brownell, D. L.

1986-02-01

120

On the role of atomic metastability in the production of Balmer line radiation from ‘cold’ atomic hydrogen, deuterium and hydrogenic ion impurities in fusion edge plasmas  

NASA Astrophysics Data System (ADS)

Published arguments, which assign an important role to atomic metastability in the production of ‘narrow’ Zeeman component radiation from the boundary region of fusion plasmas, are examined critically in relation to l-redistribution by proton and electron collisions, and mixing of unperturbed atomic states by the ion microfield and microfield gradient. It is concluded that these important processes indeed severely constrain the contribution from ‘metastable’ states to the generation of the hydrogen Balmer spectra, for electron concentrations above 1012 cm-3, as pointed out before by the present author (Hey et al 1999 J. Phys. B: At. Mol. Opt. Phys. 32 3555). The analysis of collision-induced l-redistribution represents an extension of that used previously (Hey et al 1996 Contrib. Plasma Phys. 36 583), applicable up to higher electron densities. For comparison purposes, we also consider the question of metastability of ionized helium in a low-temperature plasma, and that of some common hydrogenic impurities (C5+ and Ne9+) in a hydrogen (deuterium) fusion plasma. While for low nuclear charge Z the metastability of 2s1/2 levels is quenched by the plasma environment, it is much reduced in high-Z ions owing to the rapid increase with Z of the two-photon electric dipole (2E1) and magnetic dipole (M1) spontaneous transition rates to the ground state, whereas the role of the plasma in these cases is less important. The main new principle elaborated in this work is the sensitivity of atomic line strengths, and hence collision strengths, to perturbation by the plasma environment for transitions between fine-structure sublevels of the same principal quantum number. As the plasma microfield strength grows, ‘allowed’ transitions diminish in strength, while ‘forbidden’ transitions grow. However, owing to violation of the parity selection rule, there is an overall loss of collision strength available to transitions, resulting from the appearance of significant ‘self-strength’ contributions, in accord with the sum rules for the line strengths, which remain valid over the range of fields considered. Thus, the relative effectiveness per perturber of both electron and ion collisions, for inducing population transfer between fine-structure sublevels, diminishes as the sublevels evolve from a fine-structure dominated to a Stark-effect-dominated regime. In the concluding discussion, we mention that this finding may have a bearing on discrepancies claimed between Stark broadening theory developed by Griem (1967 Astrophys. J. 148 547) and by Watson (2006 J. Phys.B: At. Mol. Opt. Phys. 39 1889), and the measurements of Bell and co-workers (2000 Publ. Astron. Soc. Pac. 112 1236; 2011 Astrophys. Space Sci. 335 451) for high-n radio recombination lines from galactic H II regions. In the absence of detailed modelling to test this suggestion, however, it would be premature to attempt to draw any firm conclusions along these lines. This manuscript is dedicated to the memory of my esteemed colleague Dr. rer. nat. Manfred Korten (1940-2010).

Hey, J. D.

2012-03-01

121

High temperature heat exchanger studies for applications to gas turbines  

NASA Astrophysics Data System (ADS)

Growing demand for environmentally friendly aero gas-turbine engines with lower emissions and improved specific fuel consumption can be met by incorporating heat exchangers into gas turbines. Relevant researches in such areas as the design of a heat exchanger matrix, materials selection, manufacturing technology, and optimization by a variety of researchers have been reviewed in this paper. Based on results reported in previous studies, potential heat exchanger designs for an aero gas turbine recuperator, intercooler, and cooling-air cooler are suggested.

Min, June Kee; Jeong, Ji Hwan; Ha, Man Yeong; Kim, Kui Soon

2009-12-01

122

International Exchange as a Transformative Learning Experience: A Case Study  

ERIC Educational Resources Information Center

This study examines the role of international exchange programs on the transformative learning of English-speaking students. A student exchange program at a South Korean university is used for this case study. It explores how learning experiences are translated by participants onto their perceptions about the host country. An analysis of a pre-…

Choi, Sheena; Slaubaugh, Michael; Kim, Ae-Sook

2012-01-01

123

Determining the energy landscape of proteins by a fast isotope exchange NMR approach.  

PubMed

We present a new and efficient NMR method, BLUU-Tramp (Biophysics Laboratory University of Udine temperature ramp), for the collection of hydrogen-deuterium exchange experiments as a function of time and temperature for small and medium-sized proteins. Exchange rates can be determined to extract the underlying thermodynamic equilibrium or kinetic parameters by sampling hundreds of points over a virtually continuous temperature ramp. Data are acquired in a single experimental session that lasts some 20-60 h, depending on the thermal stability of the protein. Subsequent analysis provides a complete thermodynamic description of the protein energy landscape. The global thermal unfolding process and the partial or local structure opening events can be fully determined at the single-residue resolution level. The proposed approach is shown to work successfully with the amyloidogenic protein ?(2)-microglobulin. With (15)N-labeling, the unfolding landscape of a protein can also be studied in the presence of other unlabeled proteins and, in general, with ligands or cosolutes or in physiological environments. PMID:22380530

Rennella, Enrico; Corazza, Alessandra; Codutti, Luca; Bellotti, Vittorio; Stoppini, Monica; Viglino, Paolo; Fogolari, Federico; Esposito, Gennaro

2012-03-14

124

Spectroscopic and ion exchange studies on modified cotton linters  

Microsoft Academic Search

Cation exchange resin was prepared by phosphorylation of cotton linters. The effect of different treatments (alkali or acid) of cotton linters on phosphorylation process was studied. This treatment increases the efficiency of the produced resin toward metal ions uptake (Cu, Fe, Mn, Ni, Pb, Zn). The effect of pH value of metal ion solution on the efficiency of ion exchanger

A M A Nada; S S Hamed; S I Soliman; S Abd El Mongy

125

Study on dry decontamination using ion exchange polymer.  

National Technical Information Service (NTIS)

Through the project of (sup A) study on dry decontamination using ion exchange polymer(sup ,) the followings were investigated. 1. Highly probable decontamination technologies for the decontamination were investigated. 2. Development of gel type decontami...

K. J. Jung B. G. Ahn

1997-01-01

126

Ion exchange studies on natural and modified zeolites and the concept of exchange site accessibility  

Microsoft Academic Search

In the present study natural and Na-rich form of clinoptilolite are examined, in respect to ion exchange of Pb2+, Cu2+, Cr3+, and Fe3+. Equilibrium and kinetic studies performed, under the same normality (0.01 N). Equilibrium studies demonstrate that Na+ enrichment of clinoptilolite is beneficial in respect to metal uptake for all metals, except Cr3+, which is shown to have the same

Vassilis J. Inglezakis; Maria M. Loizidou; Helen P. Grigoropoulou

2004-01-01

127

An ESCA study of rhodium(III)-exchanged zeolite catalysts  

SciTech Connect

An ESCA study of rhodium(III)-exchanged zeolite catalysts which are active in hydrogenation and other reactions, showed that activation at 300/sup 0/C and 0.002 mm Hg reduced rhodium(III) in Y zeolite to metallic rhodium but did not affect rhodium(III) in A zeolite. This reduction occurred under milder conditions than known for other metal ions in zeolites, and the reduced species is probably the active catalyst in rhodium-exchanged zeolite.

Kuznicki, S.M.; Eyring, E.M.

1980-09-01

128

Hydrogen Isotope Separation by Combined Electrolysis Catalytic Exchange Under Reduced Pressure  

SciTech Connect

At the National Institute for Fusion Science experimental studies on hydrogen isotope separation by a Combined Electrolysis Catalytic Exchange (CECE) process have been carried out in order to apply it to the system of water detritiation for D-D burning experiments of the Large Helical Device. As an improvement of the CECE process, we have developed a reduced-pressure method as a means of enhancing the separation factor. The feasibility of this method is examined through application to a CECE process using a prototype separation column. Hydrogen-deuterium isotope separation experiments are performed in the two cases where column pressures are 12 and 101 kPa, and the separation factors for hydrogen and deuterium are obtained as 6.8 and 5.6, respectively. It is confirmed that the present method is applicable and useful to the CECE process. The values of Height Equivalent to a Theoretical Plate (HETP) are estimated by analyses with the equilibrium stage model. The HETP values are 15 cm at 12 kPa and 13 cm at 101 kPa. The increase of superficial velocity with decreasing pressure may spoil the efficiency of the mass transfer.

Sugiyama, T. [National Institute for Fusion Science (Japan); Asakura, Y. [National Institute for Fusion Science (Japan); Uda, T. [National Institute for Fusion Science (Japan); Abe, Y. [Nagoya University (Japan); Shiozaki, T. [Nagoya University (Japan); Enokida, Y. [Nagoya University (Japan); Yamamoto, I. [Nagoya University (Japan)

2005-07-15

129

Study of Children Who Received Exchange Transfusions.  

National Technical Information Service (NTIS)

Because murine leukemia can be transferred by injections of blood from one mouse to another, plus certain evidence suggesting leukemia in human beings to be infectious, this study attempted to determine whether there is a higher incidence of leukemia, (or...

A. G. Bridge

1969-01-01

130

A ROLE FOR ALTIMETER RADARS IN GAS EXCHANGE STUDIES  

Microsoft Academic Search

Accurate estimates of air-sea transfer rates of radiatively active gases are needed for studies of regional and global gas cycling and for climate change studies. However, estimates using traditional wind speed - gas transfer velocity parameterizations vary by a factor of 2- 3, contributing significantly to error budgets in global modeling of gas exchange and the carbon cycle. A decade

Nelson M. Frew; David M. Glover; Scott J. McCue

131

A New Method for Studying Kinetics of Ion Exchange with an Ion Exchanger  

Microsoft Academic Search

ESR technique can be used for rate measurement in an ion exchange process, since the signal responds to the presence of paramagnetic ions in the ion exchanger. Employment of this method, which gives continuously the rate curve in situ, is illustrated by an example of measurements on rates of Cu++-Zn++ exchange with polystyrene-sulfonic acid cation exchange resin. The measurements were

Nobufusa Fujita

1966-01-01

132

Simultaneous Monitoring of Peptide Aggregate Distributions, Structure, and Kinetics Using Amide Hydrogen Exchange: Application to A?(1-40) Fibrillogenesis  

PubMed Central

Increasing evidence indicates that soluble aggregates of amyloid beta protein (A?) are neurotoxic. However, difficulty in isolating these unstable, dynamic species impedes studies of A? and other aggregating peptides and proteins. In this study, hydrogen–deuterium exchange (HX) detected by mass spectrometry (MS) was used to measure A?(1–40) aggregate distributions without purification or modification that might alter the aggregate structure or distribution. Different peaks in the mass spectra were assigned to monomer, low molecular weight oligomer, intermediate, and fibril based on HX labeling behavior and complementary assays. After 1 h labeling, the intermediates incorporated approximately ten more deuterons relative to fibrils, indicating a more solvent exposed structure of such intermediates. HX-MS also showed that the intermediate species dissociated much more slowly to monomer than did the very low molecular weight oligomers that were formed at very early times in A? aggregation. Atomic force microscopy (AFM) measurements revealed the intermediates were roughly spherical with relatively homogenous diameters of 30–50 nm. Quantitative analysis of the HX mass spectra showed that the amount of intermediate species was correlated with A? toxicity patterns reported in a previous study under the same conditions. This study also demonstrates the potential of the HX-MS approach to characterizing complex, multi-component oligomer distributions of aggregating peptides and proteins.

Qi, Wei; Zhang, Aming; Patel, Dhara; Lee, Sungmun; Harrington, Jamie L.; Zhao, Liming; Schaefer, David; Good, Theresa A.; Fernandez, Erik J.

2009-01-01

133

Use of SAR in Regional Methane Exchange Studies  

NASA Technical Reports Server (NTRS)

Significant sources of uncertainty in global trace gas budgets are due to lack of knowledge concerning the areal and temporal extent of source and sink areas. Synthetic aperture radar (SAR) is particularly suited to studies of northern ecosystems because of its all-weather operating capability which enables the acquisition of seasonal data. As key controls on methane exchange, the ability to differentiate major vegetation communities, inundation, and leaf area index (LAI) with satellite and airborne SAR data would increase the accuracy and precision of regional and seasonal estimates of methane exchange. The utility of SAR data for monitoring key controls on methane emissions from Arctic and boreal ecosystems is examined.

Morrissey, L. A.; Livingston, G. P.; Durden, S. L.

1994-01-01

134

HEAT EXCHANGER DESIGN STUDIES FOR AN LHC INNER TRIPLET UPGRADE  

SciTech Connect

A luminosity upgrade of the CERN Large Hadron Collider (LHC) is planned to coincide with the expected end of life of the existing inner triplet quadrupole magnets. The upgraded inner triplet will have much larger heat loads to be removed from the magnets by the cryogenics system. A number of cryogenics design studies have been completed under the LHC Accelerator Research Program (LARP), including investigations of required heat exchanger characteristics to transfer this heat from the pressurized He II bath to the saturated He II system. This paper discusses heat exchangers both external to the magnet cold mass and internal to the magnet cold mass. A possible design for a heat exchanger external to the magnet cold mass is also presented.

Rabehl, R. J.; Huang, Y. [Fermi National Accelerator Laboratory Batavia, Illinois, 60510 (United States)

2008-03-16

135

TRACER STUDY OF VERTICAL EXCHANGE BY CUMULUS CLOUDS  

EPA Science Inventory

The exchange of material by convective cloud processes between the mixed layer and the overlying free troposphere is examined. The paper describes results of a field experiment that was conducted in Lexington, Kentucky during the period from July 20 to August 24, 1983 to study th...

136

HDX Workbench: Software for the Analysis of H/D Exchange MS Data  

NASA Astrophysics Data System (ADS)

Hydrogen/deuterium exchange mass spectrometry (HDX-MS) is an established method for the interrogation of protein conformation and dynamics. While the data analysis challenge of HDX-MS has been addressed by a number of software packages, new computational tools are needed to keep pace with the improved methods and throughput of this technique. To address these needs, we report an integrated desktop program titled HDX Workbench, which facilitates automation, management, visualization, and statistical cross-comparison of large HDX data sets. Using the software, validated data analysis can be achieved at the rate of generation. The application is available at the project home page http://hdx.florida.scripps.edu.

Pascal, Bruce D.; Willis, Scooter; Lauer, Janelle L.; Landgraf, Rachelle R.; West, Graham M.; Marciano, David; Novick, Scott; Goswami, Devrishi; Chalmers, Michael J.; Griffin, Patrick R.

2012-09-01

137

HDX Workbench: Software for the Analysis of H/D Exchange MS Data  

PubMed Central

Hydrogen/deuterium exchange mass spectrometry (HDX-MS) is an established method for the interrogation of protein conformation and dynamics. While the data analysis challenge of HDX-MS has been addressed by a number of software packages, new computational tools are needed to keep pace with the improved methods and throughput of this technique. To address these needs, we report an integrated desktop program titled HDX Workbench, which facilitates automation, management, visualization, and statistical cross-comparison of large HDX data sets. Using the software, validated data analysis can be achieved at the rate of generation. The application is available at the project home page http://hdx.florida.scripps.edu.

Pascal, Bruce D.; Willis, Scooter; Lauer, Janelle L.; Landgraf, Rachelle R.; West, Graham M.; Marciano, David; Novick, Scott; Goswami, Devrishi; Chalmers, Michael J.; Griffin, Patrick R.

2013-01-01

138

Forefront of Na+/Ca2+ exchanger studies: regulation kinetics of Na+/Ca2+ exchangers.  

PubMed

Five isoforms of Na+/Ca2+ exchanger have been identified: NCX1, NCX2, NCX3, NCX-SQ1, and CALX. In all of the exchangers, the Na+/Ca2+ exchange current, which was recorded in inside-out membrane patches, was regulated by cytoplasmic Ca2+. However, the mode of regulation is different among the exchangers. NCX1, NCX2, and NCX-SQ1 are positively regulated by cytoplasmic Ca2+, but CALX is negatively regulated. NCX3 apparently has both positive and negative regulation mechanisms. In this review, I briefly summarize the Ca2+ -dependent regulation mechanisms of the exchangers. PMID:15351790

Matsuoka, Satoshi

2004-09-01

139

Separation of organic ion exchange resins from sludge -- engineering study  

SciTech Connect

This engineering study evaluates the use of physical separation technologies to separate organic ion exchange resin from KE Basin sludge prior to nitric acid dissolution. This separation is necessitate to prevent nitration of the organics in the acid dissolver. The technologies under consideration are: screening, sedimentation, elutriation. The recommended approach is to first screen the Sludge and resin 300 microns then subject the 300 microns plus material to elutriation.

Duncan, J.B.

1998-08-25

140

Practical and economical implementation of online H/D exchange in LC-MS.  

PubMed

Structural elucidation is an integral part of drug discovery and development. In recent years, due to acceleration of the drug discovery and development process, there is a significant need for highly efficient methodologies for structural elucidation. In this work, we devised and standardized a simple and economical online hydrogen-deuterium exchange methodology, which can be used for structure elucidation purposes. Deuterium oxide (D2O) was infused as a postcolumn addition using the syringe pump at the time of elution of the analyte. The obtained hydrogen/deuterium (H/D) exchange spectrum of the unknown analyte was compared with the nonexchanged spectrum, and the extent of deuterium incorporation was delineated by using an algorithm to deconvolute partial H/D exchange, which confirmed the number of labile hydrogen(s) in the analyte. The procedure was standardized by optimizing flow rates of LC output, D2O infusion, sheath gas, and auxiliary gas using the model compound sulfasalazine. The robustness of the methodology was demonstrated by performing sensitivity analysis of various parameters such as concentrations of analyte, effect of matrices, concentrations of aqueous mobile phase, and types of LC modifiers. The optimized technique was also applied to chemically diverse analytes and tested on various mass spectrometers. Moreover, utility of the technique was demonstrated in the areas of impurity profiling and metabolite identification, taking pravastatin-lactone and N-oxide desloratidine, as examples. PMID:24117319

Shah, Ravi P; Garg, Amit; Putlur, Siva Prasad; Wagh, Santosh; Kumar, Vineet; Rao, Venugopala; Singh, Saranjit; Mandlekar, Sandhya; Desikan, Sridhar

2013-11-19

141

Correlation between solution and gas-phase protein conformation: H/D exchange, IRMPD, and ESI FT-ICR MS  

NASA Astrophysics Data System (ADS)

Infrared multiphoton dissociation (IRMPD) of the hydrogen/deuterium (H/D) exchanged 12+ charge state of gas-phase bovine ubiquitin was performed on a Fourier transform ion cyclotron resonance mass spectrometer. The H/D exchange of the 12+ charge state revealed two distinct isotopic distributions indicating the presence of at least two distinct conformations of the 12+ charge state. Following H/D exchange, IRMPD was used to dissociate the conformations. The fragments clearly showed little or no deuterium scrambling as evidenced by a nonstatistical distribution of deuterium incorporation. Analysis of the deuterium incorporation for the five most abundant fragment ions indicated a slow exchanging region of the fast exchanging conformation that corresponds to a stable (beta) - sheet observed by NMR in alcoholic solutions. The data suggest that protection of the amide hydrogens in the (beta) -sheet may result in the observed slow exchange rate and provides further evidence for the retention of secondary structure in gas phase.

Freitas, Michael A.; Hendrickson, Christopher L.; Marshall, Alan G.

2000-03-01

142

H/D Exchange Centroid Monitoring is Insufficient to Show Differences in the Behavior of Protein States  

NASA Astrophysics Data System (ADS)

Differential hydrogen/deuterium exchange (H/DX) coupled with mass spectrometry (H/DX-MS) offers a rapid and sensitive characterization of changes in proteins following perturbations induced by changes in folding, ligand binding, oligomerization, and modification. The characterization of H/DX rates by software tools and automated data processing often relies on the centroid mass calculation and, thereby, the deuterium distribution in the mass spectra is neglected. Here we present an example demonstrating the clear limitation of using only a centroid approach to characterize the H/DX rate, in which the change in protein is not reflected as the difference in deuterium uptake based on centroid calculation.

Zhang, Jun; Ramachandran, Pradeep; Kumar, Rajiv; Gross, Michael L.

2013-03-01

143

A structural core within apolipoprotein C-II amyloid fibrils identified using hydrogen exchange and proteolysis.  

PubMed

Plasma apolipoproteins show alpha-helical structure in the lipid-bound state and limited conformational stability in the absence of lipid. This structural instability of lipid-free apolipoproteins may account for the high propensity of apolipoproteins to aggregate and accumulate in disease-related amyloid deposits. Here, we explore the properties of amyloid fibrils formed by apolipoproteins using human apolipoprotein (apo) C-II as a model system. Hydrogen-deuterium exchange and NMR spectroscopy of apoC-II fibrils revealed core regions between residues 19-37 and 57-74 with reduced amide proton exchange rates compared to monomeric apoC-II. The C-terminal core region was also identified by partial proteolysis of apoC-II amyloid fibrils using endoproteinase GluC and proteinase K. Complete tryptic hydrolysis of apoC-II fibrils followed by centrifugation yielded a single peptide in the pellet fraction identified using mass spectrometry as apoC-II(56-76). Synthetic apoC-II(56-76) readily formed fibrils, albeit with a different morphology and thioflavinT fluorescence yield compared to full-length apoC-II. Studies with smaller peptides narrowed this fibril-forming core to a region within residues 60-70. We postulate that the ability of apoC-II(60-70) to independently form amyloid fibrils drives fibril formation by apoC-II. These specific amyloid-forming regions within apolipoproteins may underlie the propensity of apolipoproteins and their peptide derivatives to accumulate in amyloid deposits in vivo. PMID:17217959

Wilson, Leanne M; Mok, Yee-Foong; Binger, Katrina J; Griffin, Michael D W; Mertens, Haydyn D T; Lin, Feng; Wade, John D; Gooley, Paul R; Howlett, Geoffrey J

2007-03-01

144

Combining H/D exchange mass spectroscopy and computational docking reveals extended DNA-binding surface on uracil-DNA glycosylase  

PubMed Central

X-ray crystallography provides excellent structural data on protein–DNA interfaces, but crystallographic complexes typically contain only small fragments of large DNA molecules. We present a new approach that can use longer DNA substrates and reveal new protein–DNA interactions even in extensively studied systems. Our approach combines rigid-body computational docking with hydrogen/deuterium exchange mass spectrometry (DXMS). DXMS identifies solvent-exposed protein surfaces; docking is used to create a 3-dimensional model of the protein–DNA interaction. We investigated the enzyme uracil-DNA glycosylase (UNG), which detects and cleaves uracil from DNA. UNG was incubated with a 30 bp DNA fragment containing a single uracil, giving the complex with the abasic DNA product. Compared with free UNG, the UNG–DNA complex showed increased solvent protection at the UNG active site and at two regions outside the active site: residues 210–220 and 251–264. Computational docking also identified these two DNA-binding surfaces, but neither shows DNA contact in UNG–DNA crystallographic structures. Our results can be explained by separation of the two DNA strands on one side of the active site. These non-sequence-specific DNA-binding surfaces may aid local uracil search, contribute to binding the abasic DNA product and help present the DNA product to APE-1, the next enzyme on the DNA-repair pathway.

Roberts, Victoria A.; Pique, Michael E.; Hsu, Simon; Li, Sheng; Slupphaug, Geir; Rambo, Robert P.; Jamison, Jonathan W.; Liu, Tong; Lee, Jun H.; Tainer, John A.; Ten Eyck, Lynn F.; Woods, Virgil L.

2012-01-01

145

Thermal Performance Study of a Prototype Multiport Heat Exchanger  

NASA Astrophysics Data System (ADS)

Great efforts have been made to investigate the thermal performance and fluid flow behaviour in Minichannel Heat Exchangers (MICHX), however, the examination of air side in a multiport serpentine slab heat exchanger is rare. In the current investigation, experiments were conducted on air heating via a prototype multiport MICHX. Hot DI-water at different mass flow rates and a constant inlet temperature of 70°C was passed through the channels. The water side Reynolds numbers were varied from 255 to 411. The airside Reynolds numbers were calculated based on the free mean stream velocity and varied from 1750 to 5250, while, the air inlet temperatures were in the range of 22.5°C to 34.5°C. The effects of dimensional parameters, such as Reynolds number, Nusselt number, Prandtl number, Brinkman number, and Dean number on the heat transfer performance were investigated. The effect of the serpentine on the enhancement of DI water thermal performance behaviour was studied. Heat transfer correlations were established and compared to the results in the open literature.

Fotowat, Shahram

146

A Numerical Study on Flow and Heat Transfer Analysis of Various Heat Exchangers  

Microsoft Academic Search

This paper describes numerical methodologies of the flow and heat transfer analysis in heat exchangers of various types. Heat\\u000a exchangers considered in the present study include a louver fin radiator for a vehicle, a shell and tube heat exchanger for\\u000a HVAC and plate heat exchangers with patterns of herringbone and of dimple used in waste heat recovery. For the analysis

Myungsung Lee; Chan-Shik Won; Nahmkeon Hur

147

Diffusion exchange NMR spectroscopic study of dextran exchange through polyelectrolyte multilayer capsules  

NASA Astrophysics Data System (ADS)

Diffusion exchange of dextran with molecular weights 4.4 and 77 kDa through polyelectrolyte multilayer (PEM) hollow capsules consisting of four bilayers of polystyrene sulfonate/polydiallyldimethylammonium chloride has been investigated using two-dimensional nuclear-magnetic-resonance methods: diffusion-diffusion exchange spectroscopy (DEXSY) and diffusion-relaxation correlation spectroscopy (DRCOSY). Results obtained in DRCOSY experiments show that the diffusion process of dextran 77 kDa exhibits an observation time dependence suggesting a diffusion behavior restricted by confinement. We find evidence for both single capsule and capsule aggregate states, with a partitioning of the 77-kDa dextran between the free and capsule states much larger than that suggested by volume fraction alone. Results from DEXSY experiments show that dextran 77 kDa is in diffusive exchange through the capsules with an exchange time of around 1 s. In contrast, the capsules have no detectable influence on the diffusion process of the dextran 4.4 kDa. This quantitative information may be used in designing PEM capsules as drug carriers.

Qiao, Y.; Galvosas, P.; Adalsteinsson, T.; Schönhoff, M.; Callaghan, P. T.

2005-06-01

148

Diffusion exchange NMR spectroscopic study of dextran exchange through polyelectrolyte multilayer capsules.  

PubMed

Diffusion exchange of dextran with molecular weights 4.4 and 77 kDa through polyelectrolyte multilayer (PEM) hollow capsules consisting of four bilayers of polystyrene sulfonate/polydiallyldimethylammonium chloride has been investigated using two-dimensional nuclear-magnetic-resonance methods: diffusion-diffusion exchange spectroscopy (DEXSY) and diffusion-relaxation correlation spectroscopy (DRCOSY). Results obtained in DRCOSY experiments show that the diffusion process of dextran 77 kDa exhibits an observation time dependence suggesting a diffusion behavior restricted by confinement. We find evidence for both single capsule and capsule aggregate states, with a partitioning of the 77-kDa dextran between the free and capsule states much larger than that suggested by volume fraction alone. Results from DEXSY experiments show that dextran 77 kDa is in diffusive exchange through the capsules with an exchange time of around 1 s. In contrast, the capsules have no detectable influence on the diffusion process of the dextran 4.4 kDa. This quantitative information may be used in designing PEM capsules as drug carriers. PMID:15974795

Qiao, Y; Galvosas, P; Adalsteinsson, T; Schönhoff, M; Callaghan, P T

2005-06-01

149

Ion temperatures in HIP-1 and SUMMA from charge-exchange neutral optical emission spectra  

NASA Technical Reports Server (NTRS)

Ion temperatures were obtained from observations of the H sub alpha, D sub alpha, and He 587.6 nm lines emitted from hydrogen, deuterium, and helium plasmas in the SUMMA and HIP-1 mirror devices at Lewis Research Center. Steady state discharges were formed by applying a radially inward dc electric field between cylindrical or annular anodes and hollow cathodes located at the peaks of the mirrors. The ion temperatures were found from the Doppler broadening of the charge-exchange components of spectral lines. A statistical method was developed for obtaining scaling relations of ion temperature as a function of current, voltage, and magnetic flux density. Derivations are given that take into account triangular monochromator slit functions, loss cones, and superimposed charge-exchange processes. In addition, the Doppler broadening was found to be sensitive to the influence of drift on charge-exchange cross section. The effects of finite ion-cyclotron radius, cascading, and delayed emission are reviewed.

Patch, R. W.; Lauver, M. R.

1976-01-01

150

Tracer Study of Vertical Exchange by Cumulus Clouds.  

NASA Astrophysics Data System (ADS)

This paper examines the exchange of material by convective cloud processes between the mixed layer and the overlying free troposphere. It describes results of a field experiment that was conducted in Lexington, Kentucky, during the period from 20 July to 24 August 1983 to study the processes associated with the vertical transport of acidic pollutants by nonprecipitating cumulus convection. An aircraft released SF6 tracer either within or above the mixed layer, and it was sampled by another aircraft at various levels within or above the mixed layer in the active cumulus convective cloud zone, as well as on the ground. The results show that mixed layer pollutants are vented above the entrainment zone of its boundary layer into the overlying cloud layer by fields of active cumulus and that such active clouds may force cloud layer air downward into the mixed layer.

Ching, J. K. S.; Alkezweeny, A. J.

1986-11-01

151

Steady-state methods for the study of placental exchange.  

PubMed

Published and new data on steady-state exchange of tracers and oxygen are characterized by marked species differences. When the placenta is treated as an ideal diffusion cell of unknown vessel geometry and permeability, the exchange characteristics of oxygen can be used to prove that the exchange of tracers such as acetylene, nitrous oxide, tritiated water and antipyrine is entirely flow limited. The recorded patterns of transfer of flow-limited tracers reveal that some placentas are as effective as counter-current exchangers whereas others mimic the behavior of the less effective types of exchangers. These species differences in apparent geometry are unrelated to the histologic nature of the barrier. The patterns of flow-limited transfer are so similar to those of oxygen transfer that the diffusion resistance to oxygen must be small. The exchange of diffusion-limited (hydrophilic) tracers mimics exchange across capillary membranes in some species and exchange across cell membranes in others. These species differences in diffusion-limited transfer are clearly related to the histologic nature of the barrier and are independent of vessel geometry. PMID:410666

Faber, J J

1977-11-01

152

Study on heat transfer of heat exchangers in the Stirling engine - Performance of heat exchangers in the test Stirling engine  

NASA Astrophysics Data System (ADS)

The heat transfer performance of the actual heat exchangers obtained from the experimental results of the test Stirling engine is presented. The heater for the test engine has 120 heat transfer tubes that consist of a bare-tube part and a fin-tube part. These tubes are located around the combustion chamber and heated by the combustion gas. The cooler is the shell-and-tube-type heat exchanger and is chilled by water. It is shown that the experimental results of heat transfer performance of the heater and cooler of the test Stirling engine are in good agreement with the results calculated by the correlation proposed in our previous heat transfer study under the periodically reversing flow condition. Our correlation is thus confirmed to be applicable to the evaluation of the heat transfer coefficient and the thermal design of the heat exchangers in the Stirling engine.

Kanzaka, Mitsuo; Iwabuchi, Makio

1992-11-01

153

Is sterilised foreign exchange intervention effective after all? an event study approach  

Microsoft Academic Search

This study provides evidence supporting the effectiveness of sterilised foreign exchange market intervention by central banks using an event study approach. An event study framework is better suited to the study of sporadic and intense periods of official intervention, juxtaposed with continuously changing exchange rates, than standard time-series studies. Focusing on daily Bundesbank and US official intervention operations, we identify

Rasmus Fatum; Michael M. Hutchison

2003-01-01

154

Study of transient behavior of finned coil heat exchangers  

NASA Technical Reports Server (NTRS)

The status of research on the transient behavior of finned coil cross-flow heat exchangers using single phase fluids is reviewed. Applications with available analytical or numerical solutions are discussed. Investigation of water-to-air type cross-flow finned tube heat exchangers is examined through the use of simplified governing equations and an up-wind finite difference scheme. The degenerate case of zero air-side capacitance rate is compared with available exact solution. Generalization of the numerical model is discussed for application to multi-row multi-circuit heat exchangers.

Rooke, S. P.; Elissa, M. G.

1993-01-01

155

Study of transient behavior of finned coil heat exchangers  

NASA Astrophysics Data System (ADS)

The status of research on the transient behavior of finned coil cross-flow heat exchangers using single phase fluids is reviewed. Applications with available analytical or numerical solutions are discussed. Investigation of water-to-air type cross-flow finned tube heat exchangers is examined through the use of simplified governing equations and an up-wind finite difference scheme. The degenerate case of zero air-side capacitance rate is compared with available exact solution. Generalization of the numerical model is discussed for application to multi-row multi-circuit heat exchangers.

Rooke, S. P.; Elissa, M. G.

1993-11-01

156

High temperature heat exchanger studies for applications to gas turbines  

Microsoft Academic Search

Growing demand for environmentally friendly aero gas-turbine engines with lower emissions and improved specific fuel consumption\\u000a can be met by incorporating heat exchangers into gas turbines. Relevant researches in such areas as the design of a heat exchanger\\u000a matrix, materials selection, manufacturing technology, and optimization by a variety of researchers have been reviewed in\\u000a this paper. Based on results reported

June Kee Min; Ji Hwan Jeong; Man Yeong Ha; Kui Soon Kim

2009-01-01

157

An efficient and inexpensive refrigerated LC system for H/D exchange mass spectrometry.  

PubMed

Loss of deuterium label during the LC step in amide hydrogen/deuterium exchange mass spectrometry (H/D-MS) is minimized by maintaining an acidic mobile phase pH and low temperature (pH 2.5, 0 °C). Here we detail the construction and performance of a low-cost, thermoelectrically refrigerated enclosure to house high-performance liquid chromatography (HPLC) components and cool mobile phases. Small volume heat exchangers rapidly decrease mobile phase temperature and keep the temperature stable to ±0.2 °C. Using a superficially porous reversed-phase column, we obtained excellent chromatographic performance in the separation of peptides with a median peak width of 4.4 s. Average deuterium recovery was 80.2% with an average relative precision of 0.91%. PMID:21953202

Keppel, Theodore R; Jacques, Martin E; Young, Robert W; Ratzlaff, Kenneth L; Weis, David D

2011-08-01

158

Experimental Studies on Coherent Synchrotron Radiation at an Emittance Exchange Beamline  

SciTech Connect

One of the goals of the Fermilab A0 photoinjector is to experimentally investigate the transverse to longitudinal emittance exchange (EEX) principle. Coherent synchrotron radiation in the emittance exchange line could limit the performance of the emittance exchanger at short bunch lengths. In this paper, we present experimental and simulation studies of the coherent synchrotron radiation (CSR) in the emittance exchange line at the A0 photoinjector. We report on time-resolved CSR studies using a skew-quadrupole technique. We also demonstrate the advantages of running the EEX with an energy chirped beam.

Thangaraj, J.C.T.; Thurman-Keup, R.; Ruan, J.; Johnson, A.S.; Lumpkin, A.H.; Santucci, J.; /Fermilab

2012-04-01

159

Experimental studies on coherent synchrotron radiation at an emittance exchange beam line  

NASA Astrophysics Data System (ADS)

One of the goals of the Fermilab A0 photoinjector is to investigate experimentally the transverse to longitudinal emittance exchange (EEX) principle. Coherent synchrotron radiation in the emittance exchange line could limit the performance of the emittance exchanger at short bunch lengths. In this paper, we present experimental and simulation studies of the coherent synchrotron radiation (CSR) in the emittance exchange line at the A0 photoinjector. We report on time-resolved CSR studies using a skew-quadrupole technique. We also demonstrate the advantages of running the EEX with an energy-chirped beam.

Thangaraj, J. C. T.; Thurman-Keup, R.; Ruan, J.; Johnson, A. S.; Lumpkin, A. H.; Santucci, J.

2012-11-01

160

Ion exchange and adsorption equilibrium studies on clinoptilolite, bentonite and vermiculite  

Microsoft Academic Search

In the present paper three natural minerals used in many industrial and environmental applications namely zeolite clinoptilolite and the clays bentonite and vermiculite are studied by utilising ion exchange and adsorption. In particular, the Dubinin–Astakhov adsorption isotherm is used modified by introducing a solubility-normalized adsorption potential for studying the ion exchange process. The equation, is applied in experimental isotherms in

V. J. Inglezakis; M. Stylianou; M. Loizidou

2010-01-01

161

NMR studies of proton exchange kinetics in aqueous formaldehyde solutions.  

PubMed

Aqueous solutions of formaldehyde, formalin, are commonly used for tissue fixation and preservation. Treatment with formalin is known to shorten the tissue transverse relaxation time T2. Part of this shortening is due to the effect of formalin on the water T2. In the present work we show that the shortening of water T2 is a result of proton exchange between water and the major constituent of aqueous solutions of formaldehyde, methylene glycol. We report the observation of the signal of the hydroxyl protons of methylene glycol at 2ppm to high frequency of the water signal that can be seen at low temperatures and at pH range of 6.0±1.5 and, at conditions where it cannot be observed by the single pulse experiment, it can be detected indirectly through the water signal by the chemical exchange saturation transfer (CEST) experiment. The above finding made it possible to obtain the exchange rate between the hydroxyl protons of the methylene glycol and water in aqueous formaldehyde solutions, either using the dispersion of the spin-lattice relaxation rate in the rotating frame (1/T1?) or, at the slow exchange regime, from the line width hydroxyl protons of methylene glycol. The exchange rate was ?10(4)s(-1) at pH 7.4 and 37°C, the activation energy, 50.2kJ/mol and its pH dependence at 1.1°C was fitted to: k (s(-1))=520+6.5×10(7)[H(+)]+3.0×10(9)[OH(-)]. PMID:24632100

Rivlin, Michal; Eliav, Uzi; Navon, Gil

2014-05-01

162

NMR studies of proton exchange kinetics in aqueous formaldehyde solutions  

NASA Astrophysics Data System (ADS)

Aqueous solutions of formaldehyde, formalin, are commonly used for tissue fixation and preservation. Treatment with formalin is known to shorten the tissue transverse relaxation time T2. Part of this shortening is due to the effect of formalin on the water T2. In the present work we show that the shortening of water T2 is a result of proton exchange between water and the major constituent of aqueous solutions of formaldehyde, methylene glycol. We report the observation of the signal of the hydroxyl protons of methylene glycol at 2 ppm to high frequency of the water signal that can be seen at low temperatures and at pH range of 6.0 ± 1.5 and, at conditions where it cannot be observed by the single pulse experiment, it can be detected indirectly through the water signal by the chemical exchange saturation transfer (CEST) experiment. The above finding made it possible to obtain the exchange rate between the hydroxyl protons of the methylene glycol and water in aqueous formaldehyde solutions, either using the dispersion of the spin-lattice relaxation rate in the rotating frame (1/T1?) or, at the slow exchange regime, from the line width hydroxyl protons of methylene glycol. The exchange rate was ?104 s-1 at pH 7.4 and 37 °C, the activation energy, 50.2 kJ/mol and its pH dependence at 1.1 °C was fitted to: k (s-1) = 520 + 6.5 × 107[H+] + 3.0 × 109[OH-].

Rivlin, Michal; Eliav, Uzi; Navon, Gil

2014-05-01

163

Experimental Study of Coherent Synchrotron Radiation in the Emittance Exchange Line at the A0-Photoinjector  

NASA Astrophysics Data System (ADS)

Next generation accelerators will require a high current, low emittance beam with a low energy spread. Such accelerators will employ advanced beam conditioning systems such as emittance exchangers to manipulate high brightness beams. One of the goals of the Fermilab A0 photoinjector is to investigate the transverse to longitudinal emittance exchange principle. Coherent synchrotron radiation could limit high current operation of the emittance exchanger. In this paper, we report on the preliminary experimental and simulation study of the coherent synchroton radiation (CSR) in the emittance exchange line at the A0 photoinjector.

Thangaraj, Jayakar C. T.; Thurman-Keup, R.; Johnson, A.; Lumpkin, A. H.; Edwards, H.; Ruan, J.; Santucci, J.; Sun, Y. E.; Church, M.; Piot, P.

2010-11-01

164

Study of a compact spiral-coil cooling and dehumidifying heat exchanger  

Microsoft Academic Search

A spiral-coil heat exchanger consisting of a number of horizontal layers of spirally wound, finned tubes connected to vertical manifolds at the inner and outermost turns of each coil has been studied. A theoretical model predicting the thermal performance of the spiral-coil heat exchanger as a cooling and dehumidifying unit has been developed. Experiments on a laboratory model of the

J. C. Ho; N. E. Wijeysundera

1996-01-01

165

An experimental and computational study of approach air distribution for a finned-tube heat exchanger  

Microsoft Academic Search

The distribution of air flow approaching a finned-tube heat exchanger is one of the predominant factors influencing the heat exchanger's performance. This article describes a method for measuring and predicting the inlet air flow distribution using particle image velocimetry (PIV) and a computational fluid dynamics (CFD) model, highlighting the source and magnitude of air side maldistribution. The studied case was

David A. Yashar; Piotr A. Domanski; Hong Hyun Cho

2011-01-01

166

CFD Simulation Studies on the Performance of Rectangular Coil Heat Exchanger  

Microsoft Academic Search

The simulation studies are made to understand the concept of heat transfer by convection in a rectangular coiled type heat exchanger. The rectangular coil heat exchanger consists of inner and outer coil arrangements with several straight portions and bends so that the exterior flow is very similar to flow within tube-bundles. The present work focuses mainly on exploring the various

N. Samsudeen; N. Anantharaman; Pol. Raviraj

2010-01-01

167

Experimental study of thermo-hydraulic and fouling performance of enhanced heat exchangers  

Microsoft Academic Search

The present study investigated the effect of two tube inserts (wire coil and wire mesh) on the heat transfer enhancement, pressure drop and mineral salts fouling mitigation in tube of a heat exchanger. A 3\\/4-in. tube that is heated by band heaters, is used which simulated a tube of heat exchanger. Working fluid is water with certain quality. The heat

H. Pahlavanzadeh; M. R. Jafari Nasr; S. H. Mozaffari

2007-01-01

168

Quantitative Study for Exchange of Gases from Open Sewer Channel to Atmosphere  

Microsoft Academic Search

In this communication a quantitative modeling approach is applied to construct model for the exchange of gases from open sewer channel to the atmosphere. The data for the exchange of gases of the open sewer channel for the year January 1979 to December 2006 is utilized for the construction of the model. The study reveals that stream flow of the

Asif Mansoor; Nasiruddin Khan; Noreen Jamil

2008-01-01

169

Experimental Study on Impact/Fretting Wear in Heat Exchanger Tubes.  

National Technical Information Service (NTIS)

A data bank of field experiences with heat exchanger tube vibration reveals numerous cases of tube failures at, or near, the baffle. The objective of this study is to provide qualitative impact/fretting wear information for heat exchanger tubes through th...

J. H. Cha M. W. Wambsganss J. A. Jendrzejczyk

1985-01-01

170

High Performance Liquid Chromatographic Studies of the Ion Exchange Selectivity of Nafion.  

National Technical Information Service (NTIS)

Nafion films were coated on 5 micron octadecyl-derivatized silica. HPLC columns were packed with this film-modified ODS and the ion exchange selectivity of Nafion was studied. A homologous series of organic cations was used to probe the ion exchange prope...

R. B. Moore J. E. Wilkerson C. R. Martin

1984-01-01

171

Experimental study on impact\\/fretting wear in heat exchanger tubes  

Microsoft Academic Search

A data bank of field experiences with heat exchanger tube vibration reveals numerous cases of tube failures at, or near, the baffle. The objective of this study is to provide qualitative impact\\/fretting wear information for heat exchanger tubes through the performance of a series of tests involving the pertinent parameters: impact force level, between the tube and its support; tube

J. H. Cha; M. W. Wambsganss; J. A. Jendrzejczyk

1985-01-01

172

Spin-exchange polarization study at the TRIUMF OPPIS  

SciTech Connect

The TRIUMF optically pumped polarized ion source (OPPIS) now produces 56 {mu}A H{sup {minus}} ion current and 85% polarization for routine operation and 120 {mu}A and 78% polarization in high current mode. This is a result of the latest ECR primary proton source improvements and optimization of optical pumping efficiency. It has been shown that in a pulsed mode suitable for high energy accelerator applications, it is possible to produce 1--2 mA of polarized H{sup {minus}} current in a charge-exchange OPPIS based on the INR-scheme(1). A possible INR-scheme upgrade to the 10 mA range is discussed. The experimental results on spin-exchange polarization presented in this paper hold promise of polarized H{sup {minus}} current increasing to the 10 mA range.

Zelenski, A.N.; Levy, C.D.P.; van Oers, W.T.H.; Schmor, P.W.; Welz, J.; Wight, G.W. [TRIUMF, 4004 Wesbrook Mall, Vancouver, B.C. V6T 2A3 (Canada)

1995-07-15

173

Spin-exchange polarization study at the TRIUMF OPPIS  

NASA Astrophysics Data System (ADS)

The TRIUMF optically pumped polarized ion source (OPPIS) now produces 56 ?A H- ion current and 85% polarization for routine operation and 120 ?A and 78% polarization in high current mode. This is a result of the latest ECR primary proton source improvements and optimization of optical pumping efficiency. It has been shown that in a pulsed mode suitable for high energy accelerator applications, it is possible to produce 1-2 mA of polarized H- current in a charge-exchange OPPIS based on the INR-scheme(1). A possible INR-scheme upgrade to the 10 mA range is discussed. The experimental results on spin-exchange polarization presented in this paper hold promise of polarized H- current increasing to the 10 mA range.

Zelenski, A. N.; Levy, C. D. P.; van Oers, W. T. H.; Schmor, P. W.; Welz, J.; Wight, G. W.

1995-07-01

174

An automatically compensating heat-exchange calorimeter for metabolic studies  

Microsoft Academic Search

This paper describes an easily constructed calorimeter functioning on a heat-exchange principle in which a continuously flowing\\u000a coolant removes heat at a preset rate. Variations in heat loss from an experimental animal are compensated by a resistance\\u000a hot wire in a simple feed-back circuit so that calorimeter temperature is held constant. Accommodation for simultaneous measurement\\u000a of oxygen consumption (heat production)

George V. Pickwell

1968-01-01

175

NMR study of chemical exchange in mesoporous material MCM-41  

NASA Astrophysics Data System (ADS)

In this work we will explore behaviour of water molecules inside pores of mesoporous material MCM-41 and their interactions to the surface hydration sites, using proton NMR techniques. In NMR MAS experiments involving hydrated porous media, it is generally observed that the water and surface OH proton resonances tend to coalesce with increasing moisture content. It has been suggested that chemical exchange between surface OH groups and water may not be the only mechanism producing the coalescence in the mesoporous material MCM-41. [Chem. Eur. J. 10 (2004) 5689] Here the importance of such exchange was investigated in MCM-41, hydrated to one water molecule per OH group, using both NMR time domain and MAS techniques. The results suggest that the surface - water chemical exchange rate is too small to produce substantive proton spectral coalescence in the MCM-41 material at low hydration level. In the next step a hopping model for water molecules on surface of porous material has been introduced and resulting average resonance position for different proton species in mesoporous material MCM-41 based on this model, has been compared to experimental data.

Niknam, Mohamad; Liang, Jianzhen; Peemoeller, Hartwig

2012-02-01

176

Individual Basepair Stability of DNA and RNA Studied by NMR-Detected Solvent Exchange  

PubMed Central

In this study, we have optimized NMR methodology to determine the thermodynamic parameters of basepair opening in DNA and RNA duplexes by characterizing the temperature dependence of imino proton exchange rates of individual basepairs. Contributions of the nuclear Overhauser effect to exchange rates measured with inversion recovery experiments are quantified, and the influence of intrinsic and external catalysis exchange mechanisms on the imino proton exchange rates is analyzed. Basepairs in DNA and RNA have an approximately equal stability, and the enthalpy and entropy values of their basepair dissociation are correlated linearly. Furthermore, the compensation temperature, Tc, which is derived from the slope of the correlation, coincides with the melting temperature, and duplex unfolding occurs at that temperature where all basepairs are equally thermodynamically stable. The impact of protium-deuterium exchange of the imino hydrogen on the free energy of RNA basepair opening is investigated, and it is found that two A·U basepairs show distinct fractionation factors.

Steinert, Hannah S.; Rinnenthal, Jorg; Schwalbe, Harald

2012-01-01

177

Regulation of Phenylalanine Hydroxylase: Conformational Changes Upon Phenylalanine Binding Detected by H/D Exchange and Mass Spectrometry†  

PubMed Central

Phenylalanine acts as an allosteric activator of the tetrahydropterin-dependent enzyme phenylalanine hydroxylase. Hydrogen/deuterium exchange monitored by mass spectrometry has been used to gain insight into local conformational changes accompanying activation of rat phenylalanine hydroxylase by phenylalanine. Peptides in the regulatory and catalytic domains that lie in the interface between these two domains show large increases in the extent of deuterium incorporation from solvent in the presence of phenylalanine. In contrast, the effects of phenylalanine on the exchange kinetics of a mutant enzyme lacking the regulatory domain are limited to peptides surrounding the binding site for the amino acid substrate. These results support a model in which the N-terminus of the protein acts as an inhibitory peptide, with phenylalanine binding causing a conformational change in the regulatory domain that alters the interaction between the catalytic and regulatory domains.

Li, Jun; Dangott, Lawrence J.; Fitzpatrick, Paul F.

2010-01-01

178

Functional Tests in the Study of Water-Salt Exchange and Renal Function in Cosmonauts.  

National Technical Information Service (NTIS)

The alteration in the water-salt exchange and renal activities of cosmonauts in polonged space flight was studied. The factors influencing these functions are considered. Tabulated results are presented and include the following: (1) electrolyte content, ...

Y. V. Natochin G. I. Kozyrevskaya A. I. Grigoryev

1973-01-01

179

Study of Mechanical and Physicochemical Properties of Cementated Spent Ion-Exchange-Resins.  

National Technical Information Service (NTIS)

As first part of a study on the possibilities, to immobilize spent ion exchange resins, for final disposal, the dependence of compressive strength from the composition of cement - resin mixtures was detected. Powdered resins, bead resins and ashes from th...

P. Patek

1981-01-01

180

Continuation of Studies on Development of ODS Heat Exchanger Tubing  

SciTech Connect

The Department of Energy (DOE), National Energy Technology Center (NETL), has initiated a strategic plan for the development of advanced technologies needed to design and build fossil fuel plants with very high efficiency and environmental performance. These plants, referred to as 'Vision 21' and FutureGen programs by DOE, will produce electricity, chemicals, fuels, or a combination of these products, and possibly secondary products such as steam/heat for industrial use. MA956 is a prime candidate material being considered for a high temperature heat exchanger in the 'Vision 21' and FutureGen programs. This material is an oxide dispersion strengthened (ODS) alloy; however, there are some gaps in the data required to commit to the use of these alloys in a full-size plant. To fill the technology gaps for commercial production and use of the material for 'Advanced Power Generation Systems' this project has performed development activity to significant increase in circumferential strength of MA956 as compared to currently available material, investigated bonding technologies for bonding tube-to-tube joints through joining development, and performed tensile, creep and fire-side corrosion tests to validate the use and fabrication processes of MA956 to heat exchanger tubing applications. Development activities within this projected has demonstrated increased circumferential strength of MA956 tubes through flow form processing. Of the six fabrication technologies for bonding tube-to-tube joints, inertia friction welding (IFW) and flash butt welding (FBW) were identified as processes for joining MA956 tubes. Tensile, creep, and fire-side corrosion test data were generated for both base metal and weld joints. The data can be used for design of future systems employing MA956. Based upon the positive development activities, two test probes were designed and fabricated for field exposure testing at 1204 C ({approx}2200 F) flue gas. The probes contained tube portions with FBW and IFW welded MA956. Field testing of the probes and remaining heat exchanger design activity will be performed by Oak Ridge National Laboratory under DOE Contract DE-AC05-00OR22725.

Lawrence Brown; David Workman; Bimal Kad; Gaylord Smith; Archie Robertson; Ian Wright

2008-04-15

181

Study of thermal energy storage using fluidized bed heat exchangers  

NASA Technical Reports Server (NTRS)

The technical and economic feasibility of fluid bed heat exchangers (FBHX) for thermal energy storage (TES) in waste heat recovery applications is assessed by analysis of two selected conceptual systems, the rotary cement kiln and the electric arc furnace. It is shown that the inclusion of TES in the energy recovery system requires that the difference in off-peak and on-peak energy rates be large enough so that the value of the recovered energy exceeds the value of the stored energy by a wide enough margin to offset parasitic power and thermal losses. Escalation of on-peak energy rates due to fuel shortages could make the FBHX/TES applications economically attractive in the future.

Weast, T. E.; Shannon, L. J.; Ananth, K. P.

1980-01-01

182

Two-photon exchange effect studied with neural networks  

SciTech Connect

An approach to the extraction of the two-photon exchange (TPE) correction from elastic ep scattering data is presented. The cross-section, polarization transfer (PT), and charge asymmetry data are considered. It is assumed that the TPE correction to the PT data is negligible. The form factors and TPE correcting term are given by one multidimensional function approximated by the feedforward neural network (NN). To find a model-independent approximation, the Bayesian framework for the NNs is adapted. A large number of different parametrizations is considered. The most optimal model is indicated by the Bayesian algorithm. The obtained fit of the TPE correction behaves linearly in {epsilon} but it has a nontrivial Q{sup 2} dependence. A strong dependence of the TPE fit on the choice of parametrization is observed.

Graczyk, Krzysztof M. [Institute of Theoretical Physics, University of Wroclaw, pl. M. Borna 9, PL-50-204 Wroclaw (Poland)

2011-09-15

183

Patients' Attitudes Toward Electronic Health Information Exchange: Qualitative Study  

PubMed Central

Background In many countries, there has been substantial progress in establishing the electronic transmission of patients’ health information between health care providers, but little is known about how best to engage patients in the process. Objective We explored patients’ views about sharing of electronic health information and their preferences for learning about and participating in this process. Methods Patients in one Massachusetts community in the northeastern United States were recruited to participate in focus-group discussions. Prior to discussion, participants completed a written questionnaire that captured their reactions to draft educational materials and a consent form. The discussion moderator and two physicians analyzed the moderator’s detailed notes from each session and participants’ written comments, using an immersion-crystallization approach. Results Three dominant themes emerged: (1) concerns about privacy and security, (2) the potential benefit to a person’s health, and (3) the desire for more information about the consent process. On the pre-discussion questionnaire, 55 out of 62 participants (88%) indicated that they would provide consent for their information to be shared electronically among their health care providers, given the materials they had reviewed. Conclusions Patients are enthusiastic about electronic health information exchange, recognizing its capacity to improve the quality and safety of health care; however, they are also concerned about its potential to result in breached privacy and misuse of health data. As the exchange of electronic health information becomes more widespread, policy makers will need to ensure that patients have access to concise educational materials and opportunities to engage in conversations about the risks and benefits of participation.

Evans, J Stewart; Benjamin, Alison; Delano, David; Bates, David W

2009-01-01

184

HDX workbench: software for the analysis of H/D exchange MS data.  

PubMed

Hydrogen/deuterium exchange mass spectrometry (HDX-MS) is an established method for the interrogation of protein conformation and dynamics. While the data analysis challenge of HDX-MS has been addressed by a number of software packages, new computational tools are needed to keep pace with the improved methods and throughput of this technique. To address these needs, we report an integrated desktop program titled HDX Workbench, which facilitates automation, management, visualization, and statistical cross-comparison of large HDX data sets. Using the software, validated data analysis can be achieved at the rate of generation. The application is available at the project home page http://hdx.florida.scripps.edu . PMID:22692830

Pascal, Bruce D; Willis, Scooter; Lauer, Janelle L; Landgraf, Rachelle R; West, Graham M; Marciano, David; Novick, Scott; Goswami, Devrishi; Chalmers, Michael J; Griffin, Patrick R

2012-09-01

185

Study on the use of macroporous cation exchange resins for the separation and purification of uranium from thorium.  

National Technical Information Service (NTIS)

The possibility of using macroporous cation exchange resins for the purification of uranium from thorium relevant to the final purification of uranium after reprocessing thorium breeder fuel was explored. Two macroporous cation exchange resins were studie...

R. K. Rastogi M. A. Mahajan N. K. Chaudhuri

1992-01-01

186

Separation and identification of degradation products in eprinomectin formulation using LC, LTQ FT-MS, H/D exchange, and NMR.  

PubMed

The aim of this study was to evaluate the suitability of the compendial active pharmaceutical ingredient (API) method for the analysis of finished products and characterization of degradation products in eprinomectin (EPM) samples. Heat stressed sample tests revealed a limitation of the API method in distinguishing an impurity merging with the principal analyte peak. A new selective, specific and sensitive method was therefore developed for the determination of EPM in formulations that separates its degradation products currently undetectable with the official method. The determination was carried out by reversed-phase HPLC using an isocratic solvent elution. The method was validated and found to be precise, accurate and specific; the detector response was linear over 50-150 ?g/ml (EPM) and 0.1-3 ?g/ml (degradation product) range of concentrations. Two major degradation products detected with the new method were isolated from sample matrices and characterized using LC-PDA, high resolution FT-ICR MS, NMR and hydrogen/deuterium exchange (HX-MS) studies. FTMS analysis showed accurate mass of molecular ion peaks for EPM and its two degradation products at m/z 914.52505 (mass error ? 1 ppm) with almost identical fragmentation patterns. Given the isomeric nature of the compounds, all three were further evaluated by ¹H, ¹³C, 1D NOESY and 2D (COSY) NMR experiments. The interpretation of experimental data positively identified Unknown 1 as the 2-epimer of EPM and Unknown 2 as the structural isomer ?2,3-EPM containing a conjugated enoate. The new HPLC method and identification exercise is useful for analysis of EPM and its degradation products. PMID:22341479

Awasthi, Atul; Razzak, Majid; Al-Kassas, Raida; Greenwood, David R; Harvey, Joanne; Garg, Sanjay

2012-04-01

187

A theoretical study of thiophenic compounds adsorption on cation-exchanged Y zeolites  

Microsoft Academic Search

A density functional theory (DFT) method has been applied to study the adsorption of thiophenic compounds such as thiophene (TP), benzothiophene (BT), dibenzothiophene (DBT) on cation-exchanged Cu(I)Y, Ni(II)Y, Ce(III)Y zeolites. All of calculations were carried out by the generalized gradient approximation (GGA) with the BLYP exchange-correlation functional and DNP basis set. The calculated results indicate that the stable adsorption configuration

Lingtao Wang; Zhaolin Sun; Yong Ding; Yongchang Chen; Qiang Li; Ming Xu; Huailei Li; Lijuan Song

2011-01-01

188

Coming to Canada to Study: Factors that Influence Student's Decisions to Participate in International Exchange  

ERIC Educational Resources Information Center

Increasing numbers of students are participating in study abroad programs. Outcomes associated with these programs have been studied extensively, but relatively little is known about what motivates and influences students to participate. This study investigated factors that motivate and influence students to study on exchange and explored how…

Massey, Jennifer; Burrow, Jeff

2012-01-01

189

The Experimental Study on Heat Transfer Characteristics of The External Heat Exchanger  

NASA Astrophysics Data System (ADS)

Using the external heat exchanger in large-scale CFB boilers can control combustion and heat transfer separately, make the adjustments of bed temperature and steam temperature convenient. The state of gas-solid two phase flow in the external heat exchanger is bubbling fluidized bed, but differs from the regular one as there is a directional flow in it. Consequently, the temperature distribution changes along the flow direction. In order to study the heat transfer characteristics of the water cooled tubes in the bubbling fluidized bed and ensure the uniformity of heat transfer in the external heat exchanger, a physical model was set up according to the similarity principle and at the geometric ratio of 1?28 to an external heat exchanger of a 300MW CFB boiler. The model was connected with an electrically heated CFB test-bed which provides the circulating particles. The influencing factors and the distribution rule of the particles' heat transfer coefficient in the external heat exchanger were assessed by measuring the temperature changes of the water in the tubes and different parts of particles flow along the flow direction. At the end, an empirical correlation of particles' heat transfer coefficient in external heat exchanger was given by modifying the Veedendery empirical correlation.

Ji, X. Y.; Lu, X. F.; Yang, L.; Liu, H. Z.

190

Teacher Exchanges: Teaching "Billy Budd" as Secondary School Social Studies.  

ERIC Educational Resources Information Center

The question of why only English teachers and their students study Herman Melville's novel, "Billy Budd," is raised in this paper. The book offers insights and fundamental social questions for students in secondary school social studies. Suggestions are offered as to how social studies teachers (with their perspectives, concerns, and curriculum…

Allen, Rodney F.

191

Russian studies of the safety of anion exchange in nitric acid  

SciTech Connect

Synthetic ion exchange resins came into use in the Soviet Union in the 1950`s, and domestic anion exchange resins based on quaternary amine groups have long been used in the Russian nuclear industry. These resins are similar to resins used in the West, and include pyridine-based resins, as well as the more conventional aryl polymers with substituted methyl amines. (Slide 1) The sensitivity of these amines to reaction with nitric acid and other oxidants has been a concern in Russia as in the West, and numerous laboratory studies have been conducted on the reactions involved. Several incidents involving pressure or temperature excursions have provided incentives for such studies. (Slide 2) This report briefly summarizes this work. A report by the Russian authors of this paper providing greater detail is to be issued as a U.S. Dept. of Energy document. Additionally, a second report by these authors, describing new studies on anion exchange resin safety, will also be issued as a DOE report. The separation of plutonium, neptunium, etc. from other materials by ion exchange requires rather strong nitric acid (6-8 M). In some systems, such as the processing of {sup 238}Pu, intense ionizing radiation may also be present during ion exchange separation. As a result, it is necessary to consider not only thermal hydrolysis and oxidation and their effects on the resin, but also radiolysis. All of these were investigated in the Russian studies.

Hyder, M.L.; Bartenev, S.A.; Lazarev, L.N. [and others

1997-07-01

192

Experimental study of a novel manifold structure of micro-channel heat exchanger  

NASA Astrophysics Data System (ADS)

Refrigerant flow distribution with phase change heat transfer was experimentally studied for a micro-channel heat exchanger having horizontal headers. In order to solve the problem of maldistribution, a novel manifold structure with orifice and bypass tube was proposed and experimentally studied compared to the conventional structure. Tests were conducted with downward flow for mass flux from 70 to 110 kg m-2s-1 (air side flow velocity from 1 to 2ms-1). The surface temperature distribution of the heat exchanger recorded by thermal imager and the square deviation of it were used to judge the uniformity of flow distribution. It is shown that as mass flux increased, better flow distribution is obtained (small square deviation of temperature distribution means better flow distribution: conventional structure from 32 to 27, novel structure from 19 to 14), and flow distribution of the novel structure was much better than that of the conventional one. The heat transfer performances of the two heat exchangers were also studied. The cooling capacity of the novel heat exchanger was 14.8% higher than that of the conventional because of the better flow distribution. And the refrigerant pressure drop was 120% higher because of bigger mass flow and the resistance of the orifice. It's worth noting that the air pressure drop of novel heat exchanger was also higher (about 28.3%)than that of the conventional one, even when they have same fin and flat tube structure. From the pictures of the heat exchanger surfaces, it was found that some surface area of the conventional heat exchanger was not wet because of the low mass flow and high superheat, which leaded to a poor performance and relatively small air pressure drop.

Xu, Bo; Xu, Kunhao; Wei, Wei; Han, Qing; Chen, Jiangping

2013-07-01

193

Multivalency in the gas phase: H/D exchange reactions unravel the dynamic "rock 'n' roll" motion in dendrimer-dendrimer complexes.  

PubMed

Noncovalent dendrimer-dendrimer complexes were successfully ionized by electrospray ionization of partly protonated amino-terminated polypropylene amine (POPAM) and POPAM dendrimers fully functionalized with benzo[21]crown-7 on all branches. Hydrogen/deuterium exchange (HDX) experiments conducted on dendrimer-dendrimer complexes in the high vacuum of a mass spectrometer give rise to a complete exchange of all labile NH hydrogen atoms. As crown ethers represent noncovalent protective groups against HDX reactions on the ammonium group to which they are coordinated, this result provides evidence for a very dynamic binding situation: each crown is mobile enough to move from one ammonium binding site to another. Schematically, one might compare this motion with two rock 'n' roll dancers that swirl around each other without completely losing all contact at any time. Although the multivalent attachment certainly increases the overall affinity, the "microdynamics" of individual site binding and dissociation remains fast. PMID:24105808

Qi, Zhenhui; Schlaich, Christoph; Schalley, Christoph A

2013-10-25

194

Hydrogen-exchange stability analysis of Bergerac-Src homology 3 variants allows the characterization of a folding intermediate in equilibrium  

PubMed Central

Amide hydrogen/deuterium exchange rates have been determined for two mutants of ?-spectrin Src homology 3 domain (WT), containing an elongated stable (SHH) and unstable (SHA) distal loop. SHA, similarly to WT, follows a two-state transition, whereas SHH apparently folds via a three-state mechanism. Native-state amide hydrogen exchange is effective in ascribing energetic readjustments observed in kinetic experiments to species stabilized within the denatured base and distinguishing those from high-energy barrier crossings. Comparison of ?Gex and mex parameters for amide protons of these mutants demonstrates the existence of an intermediate and allows the identification of protons protected in this state. The consolidation of a form containing a prefolded long ?-hairpin induces the switch to a three-state mechanism in an otherwise two-state folder. It can be inferred that the unbalanced high stability of individual elements of secondary structure in a polypeptide could ultimately complicate its folding mechanism.

Viguera, Ana-Rosa; Serrano, Luis

2003-01-01

195

Heat Exchanger Design Options and Tritium Transport Study for the VHTR System  

SciTech Connect

This report presents the results of a study conducted to consider heat exchanger options and tritium transport in a very high temperature reactor (VHTR) system for the Next Generation Nuclear Plant Project. The heat exchanger options include types, arrangements, channel patterns in printed circuit heat exchangers (PCHE), coolant flow direction, and pipe configuration in shell-and-tube designs. Study considerations include: three types of heat exchanger designs (PCHE, shell-and-tube, and helical coil); single- and two-stage unit arrangements; counter-current and cross flow configurations; and straight pipes and U-tube designs in shell-and-tube type heat exchangers. Thermal designs and simple stress analyses were performed to estimate the heat exchanger options, and the Finite Element Method was applied for more detailed calculations, especially for PCHE designs. Results of the options study show that the PCHE design has the smallest volume and heat transfer area, resulting in the least tritium permeation and greatest cost savings. It is theoretically the most reliable mechanically, leading to a longer lifetime. The two-stage heat exchanger arrangement appears to be safer and more cost effective. The recommended separation temperature between first and second stages in a serial configuration is 800oC, at which the high temperature unit is about one-half the size of the total heat exchanger core volume. Based on simplified stress analyses, the high temperature unit will need to be replaced two or three times during the plant’s lifetime. Stress analysis results recommend the off-set channel pattern configuration for the PCHE because stress reduction was estimated at up to 50% in this configuration, resulting in a longer lifetime. The tritium transport study resulted in the development of a tritium behavior analysis code using the MATLAB Simulink code. In parallel, the THYTAN code, previously performed by Ohashi and Sherman (2007) on the Peach Bottom data, was revived and verified. The 600 MWt VHTR core input file developed in preparation for the transient tritium analysis of VHTR systems was replaced with the original steady-state inputs for future calculations. A Finite Element Method analysis was performed using COMSOL Multiphysics software to accurately predict tritium permeation through the PCHE type heat exchanger walls. This effort was able to estimate the effective thickness for tritium permeations and develop a correlation for general channel configurations, which found the effective thickness to be much shorter than the average channel distance because of dead spots on the channel side.

Chang H. Oh; Eung S. Kim

2008-09-01

196

Advances and challenges in analytical characterization of biotechnology products: mass spectrometry-based approaches to study properties and behavior of protein therapeutics  

PubMed Central

Biopharmaceuticals are a unique class of medicines due to their extreme structural complexity. The structure of these therapeutic proteins is critically important for their efficacy and safety, and the ability to characterize it at various levels (from sequence to conformation) is critical not only at the quality control stage, but also throughout the discovery and design stages. Biological mass spectrometry (MS) offers a variety of approaches to study structure and behavior of complex protein drugs and has already become a default tool for characterizing the covalent structure of protein therapeutics, including sequence and post-translational modifications. Recently, MS-based methods have also begun enjoying a dramatic growth in popularity as a means to provide information on higher order structure and dynamics of biotechnology products. In particular, hydrogen/deuterium exchange MS and charge state distribution analysis of protein ions in electrospray ionization (ESI)MS offer a convenient way to assess the integrity of protein conformation. Native ESI MS also allows the interactions of protein drugs with their therapeutic targets and other physiological partners to be monitored using simple model systems. MS-based methods are also applied to study pharmacokinetics of biopharmaceutical products, where they begin to rival traditional immunoassays. MS already provides valuable support to all stages of development of biopharmaceuticals, from discovery to post-approval monitoring, and its impact on the field of biopharmaceutical analysis will undoubtedly continue to grow.

Kaltashov, Igor A.; Bobst, Cedric E.; Abzalimov, Rinat R.; Wang, Guanbo; Baykal, Burcu; Wang, Shunhai

2011-01-01

197

Preliminary time-of-flight neutron diffraction studies of Escherichia coli ABC transport receptor phosphate-binding protein at the Protein Crystallography Station.  

PubMed

Inorganic phosphate is an essential molecule for all known life. Organisms have developed many mechanisms to ensure an adequate supply, even in low-phosphate conditions. In prokaryotes phosphate transport is instigated by the phosphate-binding protein (PBP), the initial receptor for the ATP-binding cassette (ABC) phosphate transporter. In the crystal structure of the PBP-phosphate complex, the phosphate is completely desolvated and sequestered in a deep cleft and is bound by 13 hydrogen bonds: 12 to protein NH and OH donor groups and one to a carboxylate acceptor group. The carboxylate plays a key recognition role by accepting a phosphate hydrogen. PBP phosphate affinity is relatively consistent across a broad pH range, indicating the capacity to bind monobasic (H2PO4(-)) and dibasic (HPO4(2-)) phosphate; however, the mechanism by which it might accommodate the second hydrogen of monobasic phosphate is unclear. To answer this question, neutron diffraction studies were initiated. Large single crystals with a volume of 8?mm(3) were grown and subjected to hydrogen/deuterium exchange. A 2.5?Å resolution data set was collected on the Protein Crystallography Station at the Los Alamos Neutron Science Center. Initial refinement of the neutron data shows significant nuclear density, and refinement is ongoing. This is the first report of a neutron study from this superfamily. PMID:24915101

Sippel, K H; Bacik, J; Quiocho, F A; Fisher, S Z

2014-06-01

198

Advances and challenges in analytical characterization of biotechnology products: mass spectrometry-based approaches to study properties and behavior of protein therapeutics.  

PubMed

Biopharmaceuticals are a unique class of medicines due to their extreme structural complexity. The structure of these therapeutic proteins is critically important for their efficacy and safety, and the ability to characterize it at various levels (from sequence to conformation) is critical not only at the quality control stage, but also throughout the discovery and design stages. Biological mass spectrometry (MS) offers a variety of approaches to study structure and behavior of complex protein drugs and has already become a default tool for characterizing the covalent structure of protein therapeutics, including sequence and post-translational modifications. Recently, MS-based methods have also begun enjoying a dramatic growth in popularity as a means to provide information on higher order structure and dynamics of biotechnology products. In particular, hydrogen/deuterium exchange MS and charge state distribution analysis of protein ions in electrospray ionization (ESI) MS offer a convenient way to assess the integrity of protein conformation. Native ESI MS also allows the interactions of protein drugs with their therapeutic targets and other physiological partners to be monitored using simple model systems. MS-based methods are also applied to study pharmacokinetics of biopharmaceutical products, where they begin to rival traditional immunoassays. MS already provides valuable support to all stages of development of biopharmaceuticals, from discovery to post-approval monitoring, and its impact on the field of biopharmaceutical analysis will undoubtedly continue to grow. PMID:21619926

Kaltashov, Igor A; Bobst, Cedric E; Abzalimov, Rinat R; Wang, Guanbo; Baykal, Burcu; Wang, Shunhai

2012-01-01

199

A comparative study of personality, sexual arousal, and behavior exchange in biological and nonbiological incestuous fathers  

Microsoft Academic Search

The primary purpose of this study was to examine whether biological and nonbiological incestuous fathers differ on personality characteristics, sexual arousal patterns, and behavior exchange in intimate relationships. Secondarily, this study examined internal consistency and test-retest reliability for responses by child molesters to a set of commercially available 35mm stimulus slides used for the phallometric assessment of sexual arousal related

Terrence Vaccaro

1992-01-01

200

Parametric sensitivity study of operating and design variables in wellbore heat exchangers  

Microsoft Academic Search

A numerical study was conducted to evaluate the potential for using Wellbore Heat Exchangers (WBHX) to extract heat for use in electricity generation. Variables studied included operational parameters such as wellbore geometries, working fluid properties, circulation rates, and regional properties including basal heat flux and formation rock type. Energy extraction is strongly affected by fluid residence time, heat transfer contact

Gopi Nalla; G. Michael Shook; Gregory L. Mines; K. Kit Bloomfield

2005-01-01

201

Benefits and problems of electronic information exchange as perceived by health care professionals: an interview study  

PubMed Central

Background Various countries are currently implementing a national electronic patient record (n-EPR). Despite the assumed positive effects of n-EPRs, their overall adoption remains low and meets resistance from health care providers. This study aims to increase our understanding of health care providers' attitude towards the n-EPR, by investigating their perceptions of the benefits and problems of electronic information exchange in health care and the n-EPR in particular. Methods The study was conducted in three Dutch health care settings: acute care, diabetes care, and ambulatory mental health care. Two health care organisations were included per setting. Between January and June 2010, interviews were conducted with 17 stakeholders working in these organisations. Relevant themes were deduced by means of thematic qualitative analysis. Results Health care providers perceived electronic information exchange to promote the efficiency and quality of care. The problems they perceived in electronic information exchange mainly concerned the confidentiality and safety of information exchange and the reliability and quality of patient data. Many problems perceived by health care providers did not specifically apply to the n-EPR, but to electronic information exchange in general. Conclusions The implementation of the Dutch n-EPR has mainly followed a top-down approach, thereby neglecting the fact that the perceptions and preferences of its users (health care providers) need to be addressed in order to achieve successful implementation. The results of this study provide valuable suggestions about how to promote health care providers' willingness to adopt electronic information exchange, which can be useful for other countries currently implementing an n-EPR. Apart from providing information about the benefits and usefulness of electronic information exchange, efforts should be focused on minimising the problems as perceived by health care providers. The safety and confidentiality of electronic information exchange can be improved by developing tools to evaluate the legitimacy of access to electronic records, by increasing health care providers' awareness of the need to be careful when using patient data, and by measures to limit access to sensitive patient data. Improving health care providers' recording behaviour is important to improve the reliability and quality of electronically exchanged patient data.

2011-01-01

202

SuperLig Ion Exchange Resin Swelling and Buoyancy Study  

SciTech Connect

The objective of this study was to achieve a fundamental understanding of SuperLig resin swelling and shrinking characteristics, which lead to channeling and early breakthrough during loading cycles. The density of salt solution that causes resin floating was also determined to establish a limit for operation. Specific tests performed include (a) pH dependence, (b) ionic strength dependence and (c) buoyancy effect vs. simulant composition.

Hassan, N.M.

2000-07-27

203

Comprehensive study of heat transfer enhancement in tubular heat exchangers  

NASA Astrophysics Data System (ADS)

A study was conducted of heat transfer enhancement in a heated tube in which a supercritical-pressure kerosene and oil flowed under the conditions of carbon deposit. This technique proved to be very effective when applied to boiling of heat carriers. At disperse and slug film boiling inside tubes, heat transfer increases three to eight times, and at surface boiling of water and water-glycerine mixtures, by 30-40 percent.

Kalinin, E. K.; Dreitser, G. A.; Paramonov, N. V.; Miakochin, A. S.; Tikhonov, A. I.; Zakirov, S. G.; Levin, E. S.; Ianovskii, L. S.

1991-11-01

204

Relaxivity and water exchange studies of a cationic macrocyclic gadolinium(III) complex.  

PubMed

We conducted relaxometric and water exchange studies of the cationic [Gd((S,S,S,S)-THP)(H2O)]3+ complex (THP 1,4,7,10-tetrakis(2-hydroxy-propyl)-1,4,7,10-tetraazacyclododecane). While the NMRD profiles obtained are typical for DOTA-like complexes (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate), variable-temperature 7O NMR investigations revealed a relatively high water exchange rate (k(298)(ex) = 1.89 x 10(7) s(-1)). These results differ from those reported for other cationic tetraamide macrocyclic Gd(III) complexes, which exhibit characteristically low exchange rates. Since the low exchange rates are attributed partially to the geometry of the M isomer (square antiprismatic) in the tetraamide derivatives, the atypical water exchange rate observed in [Gd((S,S,S,S)-THP-(H2O)]3+ may result from a twisted square antiprismatic structure in this complex and from the relatively high steric strain at the water coordination site as a result of the presence of methyl groups at the alpha-position with respect to the Gd(III)-bound O atoms of THP. PMID:11330890

Corsi, D M; Vander Elst, L; Muller, R N; van Bekkum, H; Peters, J A

2001-04-01

205

Hydrogen isotope exchange experiments with Mt Mazama ash  

NASA Astrophysics Data System (ADS)

The 2H/H ratio in hydrous minerals and volcanic glass are routinely used as paleo proxies to infer ?2H value of meteoric waters and thus paleo-climate conditions. There is a widely held assumption that once environmental water is taken up by the ash to ~3-4 wt%, hydrogen isotopes preserve original hydrologic environmental conditions through time. We report a series of 2H -H aqueous exposure experiments of 7600BP Mt Mazama ash from the Crater Lake eruption. Native Mt. Mazama ash, ~69% SiO2 contains ~3.75% H2O with ?2H -145 %. Water exposure experiments for this ash were done at 70, 40 and 25°C, time from 0 to >7000 h, to evaluate rates of hydrogen uptake from deuterated waters (650 % to pure D2O). Measurements were performed on 1-2 mg of ash using TCEA-MAT253 GSMS. We also employ a KBr pellet technique with infrared spectroscopy to measure total water and molecular water peaks. In this fashion an estimation of the distribution of water vs. SiOH is possible. Time series experiments aided by infrared measurements demonstrate the following new results: 1) Depending on exposure time and temperature we observe 5 to >100 % 2H uptake in dried samples positively correlated with temperature. In as little as 48 hours approximately 5% ?2H increases are seen in samples incubated at 70 °C with 650 % water. At this rate the ash at 70 °C would take ~2.9 years to fully react with 2H. Other separate samples reacted with pure D2O develop a clear infrared signal at ~ 2600 cm-1 due to OD bond stretching. 2) Step heating experiments on native ash indicate the ?2H of the remaining water does not change until the ash is heated to past 200-220 °C. 3) A sample immersed in 650 % ?2H water for >300 days at 70 °C degassed and sampled at increasing temperature intervals as above shows an enrichment ranging from 250 % at no water lost to 20 % at .10 % water when compared to native ash. 4) Ash dried under vacuum at ~130 °C shows mostly (~80%) loss of molecular water accompanied by minor (~20%) hydroxyl loss. 5) Native ash dried to <3% water and ~-145% ?2H), and reacted with the 650 % prepared water evinces a much higher rate of 2H incorporation compared to rates with the native ash under all the same conditions. Given linearity of ?2H exchange through time and modeling the reaction as (pseudo) first order in concentration of deuterium yields the following isotopic half life values: for 70° C 1.43 years, for 40° C 4.1 years, and for 25 °C 12.1 years. An Arrhenius treatment yields an activation energy of 32-38 kjoules. 6) A second order kinetic treatment can be used to follow the reaction. A calculation using the reaction constant k at 25 °C assuming native ash exposed to -60 % ?2H water indicates it would take 2 years to rise from a starting value of -150 to approximately -100 % ?2H. Results of these experiments put quantitative limits on reliability of ?2H in ash in paleo-climate studies that are primarily controlled by the isotopic environments and temperatures. We hypothesize that hydrogen-deuterium exchange occurs in native ash exposed to isotopically labeled water. The effect is mediated through surface correlated water in addition to diffusion with both having a rate determining effect. There is nothing to suggest that deuterium-hydrogen exchange is selective for molecular or SiOH hydrogen in the ash.

Nolan, G. S.; Bindeman, I. N.; Palandri, J. L.

2011-12-01

206

Structural Studies of NH4-exchanged Natrolites at Ambient Conditions and High Temperature  

SciTech Connect

We report here for the first time that fully and partially NH{sub 4}-exchanged natrolites can be prepared in hydrated states using the solution exchange method with potassium-natrolite. The structural models of the as-prepared hydrated phases and their dehydrated forms at elevated temperature were refined in space group Fdd2 using in situ synchrotron X-ray powder diffraction data and Rietveld methods. The unit-cell volumes of the hydrated NH{sub 4}-exchanged natrolites at ambient conditions, (NH{sub 4}){sub 16(2)}Al{sub 16}Si{sub 24}O{sub 80}{center_dot}14.1(9)H{sub 2}O and (NH{sub 4}){sub 5.1(1)}K{sub 10.9(1)}Al{sub 16}Si{sub 24}O{sub 80}{center_dot}15.7(3)H{sub 2}O, are found to be larger than that the original sodium-natrolite by ca. 15.6% and 12.8%, respectively. Upon temperature increase, the fully NH{sub 4}-exchanged natrolite undergoes dehydration at ca. 150 C with ca. 16.4% contraction in the unit-cell volume. The dehydrated phase of the fully NH{sub 4}-exchanged natrolite exhibits marginal volume expansion up to 425 C and then becomes amorphized during temperature decrease and exposure to atmospheric condition. In the case of the partially NH{sub 4}-exchanged natrolite, the dehydration starts from ca. 175 C with {approx}15.1% volume contraction and leads to a partial phase separation to show a phase related to the dehydrated K-natrolite. The degree of the phase separation decreases with temperature increase up to 475 C, concomitant to the gradual volume contraction occurring in the partially NH{sub 4}-exchanged natrolite in the dehydrared state. Upon temperature decrease and exposure to atmospheric condition, only the dehydrated K-natrolite is recovered as a crystalline phase from the partially NH{sub 4}-exchanged natrolite. In the hydrated model of the fully NH{sub 4}-exchanged natrolite, the ammonium cations and water molecules are statistically distributed along the elliptical channels, similar to the disordered pattern observed in natrolites exchanged with larger alkali metal cations such as the K-, Rb-, and Cs-forms. The dehydrated model of the fully NH{sub 4}-exchanged natrolite at 400 C is essentially same as the one reported previously from the sample prepared by direct melt exchange method using sodium-natrolite. Both the hydrated and dehydrated structures of the partially NH{sub 4}-exchanged natrolite at RT and at 400 C, respectively, are characterized by having two separate sites for the ammonium and potassium cations. Comparing the structural models of the monovalent cation forms studied so far, we find that the rotation angle of the natrolite chain is inversely proportional to the cation radius both in the hydrated and dehydrated phases. The distribution pattern of the non-framework species along the natrolite channel also seems to be related to the non-framework cation radius and hence to the chain rotation angle.

Y Lee; D Seoung; Y Jang; J Bai; Y Lee

2011-12-31

207

Interpersonal Exchanges in Discussion Forums: A Study of Learning Communities in Distance Learning Settings  

ERIC Educational Resources Information Center

Cooperative relationships are the foundation of a model of online learning based on communities. The development of a community depends on the interaction between community members. This study is based on the belief that the dynamics of exchange of thought, from a Piagetian perspective, are one possibility for understanding the process of…

Scherer Bassani, Patricia B.

2011-01-01

208

State Roundtable Case Studies: Idaho and South Dakota. Western Policy Exchange Project.  

ERIC Educational Resources Information Center

These two case studies were commissioned by the Western Interstate Commission for Higher Education (WICHE) as part of its Western Policy Exchange (WPE) Project, in an effort to understand the dynamics and perceived consequences of a "state roundtable" approach to fostering partnerships in education in order to advance systemic change and reforms…

Bender, Louis W.

209

STUDY OF PROTON EXCHANGE MEMBRANE FUEL CELLS (PZT-PEMFCS) WITH NOZZLE AND DIFFUSER  

Microsoft Academic Search

Previous theoretical studies have shown that piezoelectric proton exchange membrane fuel cells (PZT-PEMFCs) might solve water flooding problems and increase cell performance. The innovative design of PZT-PEMFCs results in more oxygen being compressed into the catalyst layer. This enhances the electrochemical reaction and the current density, especially at a high PZT vibration frequency (64 Hz). In this investigation, a single,

Hsiao-Kang Ma; Shih-Han Huang; Ya-Ting Cheng; Chrung Guang Hou

2009-01-01

210

Ligand exchange reactions in Cu(III) complexes: mechanistic insights by combined NMR and DFT studies.  

PubMed

NMR studies of (13)C/(12)C isotopic patterns in Cu(iii) intermediates and reaction products together with DFT calculations of possible reaction pathways indicate an intermolecular S(N)2 like substitution mechanism for ligand exchange reactions in square planar Cu(iii) complexes, which is proposed to be slow compared to reductive elimination at synthetic conditions. PMID:20461240

Gärtner, Tobias; Yoshikai, Naohiko; Neumeier, Maria; Nakamura, Eiichi; Gschwind, Ruth M

2010-07-01

211

Further studies on vinamidinium salt amine exchange reactions, borohydride reductions and subsequent transformations  

PubMed Central

Studies directed at the amine exchange reaction of vinamidinium salts followed by sodium borohydride reduction to secondary and tertiary allylic amines are described. The tertiary allylic amines were alkylated and subjected to base mediated rearrangement to yield a variety of highly functionalized tertiary homoallylic amines.

Gupton, John T.; Telang, Nakul; Jia, Xin; Giglio, Benjamin C.; Eaton, James E.; Barelli, Peter J.; Hovaizi, Mona; Hall, Kayleigh E.; Welden, R. Scott; Keough, Matthew J.; Worrall, Eric F.; Finzel, Kara L.; Kluball, Emily J.; Kanters, Rene P.F.; Smith, Timothy M.; Smith, Stanton Q.; Nunes, Shane R.; Wright, Mathew T.; Birnstihl, Jennifer M.

2010-01-01

212

The Role of Dissonance in Knowledge Exchange: A Case Study of a Knowledge Management System Implementation  

Microsoft Academic Search

This study examines the non-adoption of a knowledge management system for knowledge exchange among a distributed group of non-life insurance experts. The users participated with enthusiasm in the design process where they provided functional and data specifications for the system. However, a few months after introduction, the system was hardly being used at all. The analysis of the case suggests

Dulce T. Pumareja; Klaas Sikkel

2005-01-01

213

Multibody system model of a cargo airship to study the load exchange process  

Microsoft Academic Search

Projected cargo airships for the transport of large loads exceed the dimensions of existing aircrafts and gave rise to various technical problems. One important task in an airship mission is the loading and unloading of the heavy and spacious load from the payload bay of the airship. In order to study the dynamics of the load exchange process, mathematical models

Andreas Bockstedte; Edwin Kreuzer

2005-01-01

214

MEGHA-TROPIQUES, a satellite for studying the water cycle and energy exchanges in the tropiques  

Microsoft Academic Search

Supported by the French and Indian scientific communities, the MEGHA-TROPIQUES Mission aims at studying the water cycle and the energy exchanges in the tropical belt. It will be jointly developed by the Indian Space Research Organisation (ISRO) and the French Space Agency (CNES). The small satellite (<600 kg) could be launched as early as 2005 by Indian PSLV launcher in

J. P. Aguttes; J. Schrive; C. Goldstein; M. Rouze; G. Raju

2000-01-01

215

Experimental study on impact\\/fretting wear in heat exchanger tubes  

Microsoft Academic Search

The objective of this study is to provide qualitative impact\\/fretting wear information for heat exchanger tubes through the performance of a series of tests involving the pertinent parameters: force between the tube and its support; tube to support plate hole clearance; tube support plate thickness; preload; and tube vibration frequency. The characteristics of impact\\/fretting wear relative to material combinations and

J. H. Cha; M. W. Wambsganss; J. A. Jendrzejczyk

1986-01-01

216

Experimental study on impact\\/fretting wear in heat exchanger tubes  

Microsoft Academic Search

The objective of this study is to provide qualitative impact\\/fretting wear information for heat exchanger tubes through the performance of a series of tests involving the pertinent parameters: force between the tube and its support; tube to support plate hole clearance; tube support plate thickness; preload; and tube vibration frequency. The characteristics of impact\\/fretting wear relative to material combinations and

J. H. Cha; M. W. Wambsganss; J. A. Jendrzejczyk

1987-01-01

217

Conceptual study of in-tank cesium removal using an inorganic ion exchange material  

SciTech Connect

Presently, the Hanford Site contains approximately 230,000 m{sup 3} of mixed waste stored in 177 underground tanks. Approximately 55,000 m{sup 3} of this waste is sludge, 90,000 m{sup 3} is salt cake, and 80,000 m{sup 3} is supernate. Although the pretreatment and final disposal requirements for the waste have not been entirely defined, it is likely that some supernatant pretreatment will be required to remove {sup 137}Cs and possibly {sup 90}Sr and the transuranic components. The objective of this study was to estimate the number of HLW glass canisters resulting from the use of inorganic ion exchanger materials as in-tank pretreatment technology. The variables in the study were: number of contacts between waste and ion exchange material; ion exchange material; and decontamination requirement. This conceptual study investigates a generic in-tank Cs removal flowsheet using crystalline silico-titanates and IE-96 zeolites, and the impact of each ion exchanger on the number of glass canisters produced. In determining glass formulation, data based on current reference technology was used. Sample calculations from the worksheets and summaries of final calculated results are included at the end of this report.

Goheen, R.S.; Kurath, D.E.

1996-04-01

218

Student exchange for nursing students: Does it raise cultural awareness'? A descriptive, qualitative study.  

PubMed

With free movement for citizens within the European Union and with distant parts of our globe becoming more accessible, cultural awareness and cultural competence are becoming important skills for nurses. Internationalisation and raising awareness of other cultural contexts are essential elements in Swedish higher education, thus explaining the variety of student exchange programmes that are available. The aim of this study was to explore Swedish nursing students' perceptions of student exchange and their experiences. Data were collected through group interviews and then analysed following the principles of content analysis. Our analysis resulted in three categories: Preparing to go abroad, Reasons for going abroad and From expectation to experience. Cultural aspects and cultural awareness were emphasised as strong motivational factors, both personal and professional, behind participation in student exchange programmes. Information was also highlighted as a crucial means of reaching potential students as well as the power of knowledge through personal experience. This study highlights the importance of student exchange in expanding the individual student's personal and professional horizons. It also stresses the importance of including a transcultural nursing element in nursing curricula. PMID:24406034

Bohman, Doris M; Borglin, Gunilla

2014-05-01

219

Metallurgical study of a failed heat exchanger in a H-coal/sup (R)/ pilot plant  

SciTech Connect

On September 20, 1980, operation of the pilot plant was interrupted when a heat exchanger (a reactor effluent vapor/steam thermo syphon reboiler) failed. Three alloy 800 (Fe-32Ni-21Cr) tubes in the bottom return section (cold end) of the heat exchanger blew out of the tubesheet. The system was shut down and a team of investigators began an intense study to determine the cause of the failure. Purpose of the investigation was to determine if the failure was an isolated incident, so that the affected tubes could be plugged and the system continue to operate, or if the failures were more generic so as to require corrective action. After careful examination of the fractured tubes by optical and scanning electron microscopy, a conclusion was made that stress corrosion cracking originating at the exterior surface was the cause of the failure. Other tubes were found that were approaching a state of failure. Photographs of the heat exchanger and photomicrographs of microstructures that supported this study are presented. As the result of the investigation, remedial steps were taken by the plant operator to return the heat exchanger to line operation.

Gray, R.J. (Oak Ridge National Lab., TN); Keiser, J.R.; DeVan, J.H.; Searles, R.

1982-01-01

220

Theoretical study of exchange coupling in 3d-Gd complexes: large magnetocaloric effect systems.  

PubMed

Polynuclear 3d transition metal-Gd complexes are good candidates to present large magnetocaloric effect. This effect is favored by the presence of weak ferromagnetic exchange interactions that have been investigated using methods based on Density Functional Theory. The first part of the study is devoted to dinuclear complexes, focusing on the nature and mechanism of such exchange interactions. The presence of two bridging ligands is found more favorable for ferromagnetic coupling than a triple-bridged assembly, especially for complexes with small M-O···O-Gd hinge angles. Our results show the crucial role of the Gd 5d orbitals in the exchange interaction while the 6s orbital seems to have a negligible participation. The analysis of the atomic and orbital spin populations reveals that the presence of spin density in the Gd 5d orbital is mainly due to a spin polarization effect, while a delocalization mechanism from the 3d orbitals of the transition metal can be ruled out. We propose a numerical DFT approach using pseudopotentials to calculate the exchange coupling constants in four polynuclear first-row transition metal-Gd complexes. Despite the complexity of the studied systems, the numerical approach gives coupling constants in excellent agreement with the available experimental data and, in conjunction with exact diagonalization methods (or Monte Carlo simulations), it makes it possible to obtain theoretical estimates of the entropy change due to the magnetization/demagnetization process of the molecule. PMID:22640027

Cremades, Eduard; Gómez-Coca, Silvia; Aravena, Daniel; Alvarez, Santiago; Ruiz, Eliseo

2012-06-27

221

Results from the US/USSR exchange for heat load material studies of simulated tokamak disruptions.  

National Technical Information Service (NTIS)

This paper presents recent results from exchange I.2 of the US/USSR Exchange Program of Cooperation for Magnetic Confinement Fusion. Previous results from this exchange demonstrated much lower than expected ablation of graphites when the graphites were ex...

J. M. Gahl, J. F. Crawford, J. M. McDonald, R. T. McGrath, A. Zakharov

1992-01-01

222

Structural basis of sodium-potassium exchange of a human telomeric DNA quadruplex without topological conversion  

PubMed Central

Understanding the mechanism of Na+/K+-dependent spectral conversion of human telomeric G-quadruplex (G4) sequences has been limited not only because of the structural polymorphism but also the lack of sufficient structural information at different stages along the conversion process for one given oligonucleotide. In this work, we have determined the topology of the Na+ form of Tel23 G4, which is the same hybrid form as the K+ form of Tel23 G4 despite the distinct spectral patterns in their respective nuclear magnetic resonance (NMR) and circular dichroism spectra. The spectral difference, particularly the well-resolved imino proton NMR signals, allows us to monitor the structural conversion from Na+ form to K+ form during Na+/K+ exchange. Time-resolved NMR experiments of hydrogen–deuterium exchange and hybridization clearly exclude involvement of the global unfolding for the fast Na+/K+ spectral conversion. In addition, the K+ titration monitored by NMR reveals that the Na+/K+ exchange in Tel23 G4 is a two-step process. The addition of K+ significantly stabilizes the unfolding kinetics of Tel23 G4. These results offer a possible explanation of rapid spectral conversion of Na+/K+ exchange and insight into the mechanism of Na+/K+ structural conversion in human telomeric G4s.

Wang, Zi-Fu; Li, Ming-Hao; Hsu, Shang-Te Danny; Chang, Ta-Chau

2014-01-01

223

Cation exchange surface-mediated denaturation of an aglycosylated immunoglobulin (IgG1).  

PubMed

Cation exchange chromatography of an aglycosylated IgG1 resulted in two distinct peaks during gradient elution. The early eluting peak contained <1% high molecular weight (HMW) species, while the later peak contained 23% HMW species. Analysis by hydrogen-deuterium exchange and Fourier transform infrared spectroscopy (FTIR) indicated that aggregate formation and generation of the second peak were caused by antibody denaturation on the resin surface. Denaturation and HMW generation was increased by the use of strong cation exchange media, by increasing antibody residence time on the exchanger, or increasing temperature. Denaturation and HMW generation was reduced by increasing pH or ionic strength, by the use of preferentially excluded solutes such as citrate or glycine and controlled entirely by addition of 125 mM arginine to the process buffers. This leads to the hypothesis that denaturation and HMW generation of this antibody can be managed by reducing the strength of binding, by increasing its conformational stability, or by suppressing non-native protein-protein interactions. The glycosylated version of this antibody exhibited less than 2% denatured form, suggesting that glycosylation contributes significantly to the stability of this antibody. These findings may be helpful in managing aggregation in other antibodies, and particularly useful in developing purification processes for aglycosylated antibodies. PMID:22771262

Gillespie, Ron; Nguyen, Thao; Macneil, Sean; Jones, Laurie; Crampton, Shon; Vunnum, Suresh

2012-08-17

224

Parametric Sensitivity Study of Operating and Design Variables in Wellbore Heat Exchangers  

SciTech Connect

This report documents the results of an extensive sensitivity study conducted by the Idaho National Engineering and Environmental Laboratory. This study investigated the effects of various operating and design parameters on wellbore heat exchanger performance to determine conditions for optimal thermal energy extraction and evaluate the potential for using a wellbore heat exchanger model for power generation. Variables studied included operational parameters such as circulation rates, wellbore geometries and working fluid properties, and regional properties including basal heat flux and formation rock type. Energy extraction is strongly affected by fluid residence time, heat transfer contact area, and formation thermal properties. Water appears to be the most appropriate working fluid. Aside from minimal tubing insulation, tubing properties are second order effects. On the basis of the sensitivity study, a best case model was simulated and the results compared against existing low-temperature power generation plants. Even assuming ideal work conversion to electric power, a wellbore heat exchange model cannot generate 200 kW (682.4e+3 BTU/h) at the onset of pseudosteady state. Using realistic conversion efficiency, the method is unlikely to generate 50 kW (170.6e+3 BTU/h).

Nalla, G.; Shook, G.M.; Mines, G.L.; Bloomfield, K.K.

2004-05-01

225

Parametric Sensivity Study of Operating and Design Variables in Wellbore Heat Exchangers  

SciTech Connect

This report documents the results of an extensive sensitivity study conducted by the Idaho National Engineering and Environmental Laboratory. This study investigated the effects of various operating and design parameters on wellbore heat exchanger performance to determine conditions for optimal thermal energy extraction and evaluate the potential for using a wellbore heat exchanger model for power generation. Variables studied included operational parameters such as circulation rates, wellbore geometries and working fluid properties, and regional properties including basal heat flux and formation rock type. Energy extraction is strongly affected by fluid residence time, heat transfer contact area, and formation thermal properties. Water appears to be the most appropriate working fluid. Aside from minimal tubing insulation, tubing properties are second order effects. On the basis of the sensitivity study, a best case model was simulated and the results compared against existing low-temperature power generation plants. Even assuming ideal work conversion to electric power, a wellbore heat exchange model cannot generate 200 kW (682.4e+3 BTU/h) at the onset of pseudosteady state. Using realistic conversion efficiency, the method is unlikely to generate 50 kW (170.6e+3 BTU/h).

G. Michael Shook; Gopi Nalla; Gregory L. Mines; K. Kit Bloomfield

2004-05-01

226

Retrospective Study of Rapid-Exchange Monorail Versus Over-the-Wire Technique for Femoropopliteal Angioplasty  

Microsoft Academic Search

PurposeThe purpose of this study was to compare procedural outcome of rapid-exchange (RX) monorail versus conventional over-the-wire (OTW) technique for femoropopliteal angioplasty.Materials and MethodsDemographic data, procedure details, angioplasty success, and complications of 328 consecutive percutaneous transluminal angioplasties (PTAs) were collected from a prospective database and retrospectively analyzed. Procedure details included duration of fluoroscopy, area-dose product, amount of contrast agent, sheath

Thomas Jahnke; Jost Philipp Schaefer; Hendrik Bolte; Fritz Schaefer; Jens Michalek; Nicholas Charalambous; Marc Sapoval; Stefan Mueller-Huelsbeck

2008-01-01

227

Equilibrium exchange kinetics in PEP–PEO block copolymer micelles. A time resolved SANS study  

Microsoft Academic Search

The chain exchange kinetics in polymeric micelles has been studied by a novel time resolved small angle neutron scattering (TR-SANS) technique. The system investigated was the amphiphilic block copolymer poly(ethylene-alt-propylene)–poly(ethylene oxide) (PEP–PEO) in water\\/N,N-dimethylformamide (DMF) mixtures as selective solvent for PEO. The TR-SANS technique exploits the large difference in scattering length density of deuterated and protonated species allowing for a

R. Lund; L. Willner; J. Stellbrink; D. Richter

2006-01-01

228

A numerical study on heat transfer characteristics in a spray column direct contact heat exchanger  

Microsoft Academic Search

A reliable computational heat transfer model has been investigated to define the heat transfer characteristics of a spray\\u000a column direct contact heat exchanger, which is often utilized in the process involving counterflows for heat and mass transfer\\u000a operations. Most of the previous studies investigated are one-dimensional unsteady solutions based on rather fragmentary experimental\\u000a data. Development of a multidimensional numerical model

Yong Heack Kang; Nam Jin Kim; Byung Ki Hur; Chong Bo Kim

2002-01-01

229

Snow measurement techniques for land-surface-atmosphere exchange studies in boreal landscapes  

Microsoft Academic Search

Summary  ?Snow has been studied widely in hydrology for many decades whereas recent meteorological interest in snow is caused by increased\\u000a emphasis on high latitudes and wintertime in climate-change research as well as by the need to improve weather-forecast models\\u000a during these conditions. Ground-based measurements of snow properties are needed both to improve understanding of surface-atmosphere\\u000a exchange processes and to provide

A. Lundberg; S. Halldin

2001-01-01

230

Solar Wind Charge Exchange Studies Of Highly Charged Ions On Atomic Hydrogen  

Microsoft Academic Search

Accurate studies of low-energy charge exchange (CX) are critical to understanding underlying soft X-ray radiation processes in the interaction of highly charged ions from the solar wind with the neutral atoms and molecules in the heliosphere, cometary comas, planetary atmospheres, interstellar winds, etc.. Particularly important are the CX cross sections for bare, H-like, and He-like ions of C, N, O

I. N. Draganic´; D. G. Seely; D. McCammon; C. C. Havener

2011-01-01

231

A Study of Jordanian University Students' Perceptions of Using Email Exchanges with Native English Keypals for Improving Their Writing Competency  

ERIC Educational Resources Information Center

English foreign language learners generally tend to consider email exchanges with native speakers (NSs) as an effective tool for improving their foreign language proficiency. This study investigated Jordanian university students' perceptions of using email exchanges with native English keypals (NEKs) for improving their writing competency. A…

Mahfouz, Safi Mahmoud

2010-01-01

232

A Motivation Case Study of English/Japanese Language Exchange Partners Using Computer Mediated Communication and Telecommunication.  

ERIC Educational Resources Information Center

This case study examines the motivation of two intermediate foreign language learners engaged in a remote language exchange partnership. A learner of English in Japan and a learner of Japanese in Australia completed language exchange activities using the telephone, Internet text chat, and e-mail over 10 weeks. Quantitative and qualitative methods…

Long, Robert Harrison

233

Study and testing of direct contact heat exchangers for geothermal brines. Phase II, August 1976June 1977  

Microsoft Academic Search

The analytical and experimental studies completed under this project have explored several aspects of geothermal binary power cycles and column type direct contact heat exchangers between geothermal brine and isobutane. A major improvement of the heat exchanger was developed by the combination of the preheater and boiler into a single continuous column. At East Mesa, this new direct contact heat

W. B. Suratt; C. O. Lee

1978-01-01

234

Fe magnetic moment formation and exchange interaction in Fe2P: A first-principles study  

NASA Astrophysics Data System (ADS)

Electronic structure and magnetic properties of Fe2P have been studied by a first-principles density functional theory calculation. The ground state is ferromagnetic and the calculated magnetic moments for Fe1 (3f) and Fe2 (3g) are 0.83 and 2.30 ?B, respectively. The nearest neighbor inter-site magnetic exchange coupling parameter at the Fe1 layer (0.02 mRy) is much smaller than that at the Fe2 layer (1.29 mRy). The Fe moment at the 3f site is metastable and sensitive to the inter-site exchange interaction with its magnetic neighbors, which is responsible for the first order magnetic transition and large magneto-caloric effect around TC.

Liu, X. B.; Ping Liu, J.; Zhang, Qiming; Altounian, Z.

2013-03-01

235

Boron removal from aqueous solutions by ion-exchange resin: column sorption-elution studies.  

PubMed

A column sorption-elution study was carried out by using a strong base anion-exchange resin (Dowex 2 x 8) for the removal of boron from aqueous solutions. The breakthrough curve was obtained as a function of feed flow rate and the total and breakthrough capacity values of the resin were calculated. The boron on the resin was quantitatively eluted with 0.5M HCl solution at different flow rates. Three consecutive sorption-elution-washing-regeneration-washing cycles were applied to the resin in order to investigate the reusability of the ion-exchange resin. Total capacity values remained almost the same after three sorption-elution-regeneration cycles. The Thomas and the Yoon-Nelson models were applied to experimental data to predict the breakthrough curves and to determine the characteristic column parameters required for process design. The results proved that the models would describe the breakthrough curves well. PMID:17716813

Köse, T Ennil; Oztürk, Ne?e

2008-04-01

236

Study by XPS of different conditioning processes to improve the cation exchange in clinoptilolite  

NASA Astrophysics Data System (ADS)

We report the X-ray photoelectron spectroscopy (XPS) analysis of natural clinoptilolite from a mine in Sonora, México. From these measurements we determined the chemical state and binding energy of the elements in the zeolite framework and of those in the extra framework sites. The analysis was done on natural clinoptilolite and on cation-exchanged clinoptilolites with Na + and NH4+ ions. Complementary analysis by several experimental techniques was performed to determine the structural, chemical composition and chemical state modifications experimented by clinoptilolite samples processed by the two types of cation exchange. The clinoptilolite samples were studied by X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) to determine their structural composition, Energy Dispersive Spectroscopy (EDS) to measure the chemical composition and electronic paramagnetic resonance (EPR) spectroscopy to determine the chemical state of iron inside the natural zeolites.

Ruiz-Serrano, D.; Flores-Acosta, M.; Conde-Barajas, E.; Ramírez-Rosales, D.; Yáñez-Limón, J. M.; Ramírez-Bon, R.

2010-09-01

237

Metallurgical study of a failed heat exchanger in a h-coal pilot plant  

SciTech Connect

The H-Coal Pilot Plant at Catlettsburg, Kentucky, is designed to process 600 tons of coal per day and produce synthetic fuels. On September 20, 1980, operation of the pilot plant was interrupted when a heat exchanger (a reactor effluent vapor/steam thermo syphon reboiler) failed. Three alloy 800 (Fe-32Ni-21Cr) tubes in the bottom return section (cold end) of the heat exchanger blew out of the tubesheet. The system was shut down and a team of investigators began an intense study. After examination of the fractured tubes by optical and scanning electron microscopy, a conclusion was made that stress corrosion cracking originating at the exterior surface was the cause of the failure. Other tubes were found that were approaching a state of failure. 11 figures.

Gray, R.J.; Keiser, J.R.; DeVan, J.H.; Searles, R.

1981-01-01

238

Charge-exchange erosion studies of accelerator grids in ion thrusters  

NASA Technical Reports Server (NTRS)

A particle simulation model is developed to study the charge-exchange grid erosion in ion thrusters for both ground-based and space-based operations. Because the neutral gas downstream from the accelerator grid is different for space and ground operation conditions, the charge-exchange erosion processes are also different. Based on an assumption of now electric potential hill downstream from the ion thruster, the calculations show that the accelerator grid erosion rate for space-based operating conditions should be significantly less than experimentally observed erosion rates from the ground-based tests conducted at NASA Lewis Research Center (LeRC) and NASA Jet Propulsion Laboratory (JPL). To resolve this erosion issue completely, we believe that it is necessary to accurately measure the entire electric potential field downstream from the thruster.

Peng, Xiaohang; Ruyten, Wilhelmus M.; Keefer, Dennis

1993-01-01

239

Engineering study for the treatment of spent ion exchange resin resulting from nuclear process applications  

SciTech Connect

This document is an engineering study of spent ion exchange resin treatment processes with the purpose of identifying one or more suitable treatment technologies. Classifications of waste considered include all classes of low-level waste (LLW), mixed LLW, transuranic (TRU) waste, and mixed TRU waste. A total of 29 process alternatives have been evaluated. Evaluation parameters have included economic parameters (both total life-cycle costs and capital costs), demonstrated operability, environmental permitting, operational availability, waste volume reduction, programmatic consistency, and multiple utilization. The results of this study suggest that there are a number of alternative process configurations that are suitable for the treatment of spent ion exchange resin. The determinative evaluation parameters were economic variables (total life-cycle cost or capital cost) and waste volume reduction. Immobilization processes are generally poor in volume reduction. Thermal volume reduction processes tend to have high capital costs. There are immobilization processes and thermal volume reduction processes that can treat all classifications of spent ion exchange resin likely to be encountered. 40 refs., 19 figs., 17 tabs.

Place, B.G.

1990-09-01

240

Experimental study of the airside performance of tube row spacing in finned tube heat exchangers  

NASA Astrophysics Data System (ADS)

Almost all of the studies in dehumidifying coils are experimental studies. In this study, effect of tube regulation space on heat and mass transfer and friction factor for heat exchangers made from aluminum fins and cooper tubes are identified experimentally. External surface heat transfer coefficient, Colburn factor and friction factor was calculated by the help of the computer program by using experimental values done. After the diagrams investigated, with the decreasing of tube row spacing the external surface heat transfer in the dry surface and friction factor increased. If wet and dry surfaces are compared, Colburn and friction factor in wet surfaces is larger than Colburn and friction factor in dry surfaces.

Halici, Fethi; Taymaz, Imdat

2006-07-01

241

Experimental study on impact fretting in heat exchanger tubes with brush plated coatings  

SciTech Connect

The impact fretting wear of heat exchanger tubes with brush-plated copper, nickel and nickel-tungsten alloy coatings was experimentally studied. The test results showed that the wear rate of steel 10 specimens was highest, followed by copper coated, and those coated with a nickel and nickel-tungsten alloy, which performed best. The study suggested that tubes with a harder coating showed superior resistance to impact fretting wear. Scanning electron micrographs and metallographs clearly showed that the predominent wear process in this study was surface fatigue. 17 refs., 7 figs., 1 tab.

Zhendong Dai [Nanjing Univ. of Aeronautics and Astronautics (Canada)

1994-11-01

242

Residential air exchange rates for use in indoor air and exposure modeling studies.  

PubMed

Data on air exchange rates are important inputs to indoor air quality models. Indoor air models, in turn, are incorporated into the structure of total human exposure models. Fragmentary data on residential ventilation rates are available in various governmental reports, journal articles, and contractor reports. Most of the published papers present data on only a few homes to answer very specialized questions, and none of these publications summarize the ventilation rates of a large population of homes across the United States. Brookhaven National Laboratory (BNL) has conducted more than 4000 residential perfluorocarbon tracer (PFT) measurements and brought them together into a large data base from about 100 studies in the United States and elsewhere. This paper analyzes the BNL PFT data base to generate frequency distributions and summary statistics for different regions of the United States, different seasons, and different levels within the homes. The data analyses suggest that residential ventilation rates are similar in the northeastern and northwestern states but higher in the southwestern states. Winter and fall ventilation rates are similar, but the rates are slightly higher in spring, and much higher in summer. Multi-level residences have higher air exchange rates than single-level residences. Although the BNL data are not a representative sample of homes in the United States, these analyses give insight into the range of air exchange rates found in the United States under a great variety of conditions and are intended for use by developers of models of indoor air quality and total human exposure. PMID:8173341

Pandian, M D; Ott, W R; Behar, J V

1993-01-01

243

Exchange integrals in magnetoelectric hexagonal ferrite (SrCo2Ti2Fe8O19): A density functional study  

NASA Astrophysics Data System (ADS)

The exchange integrals in magnetoelectric hexagonal ferrite SrCo2Ti2Fe8O19 have been calculated by using density functional theory. To get 10 inter-sublattice and 3 intra-sublattice exchange integrals, the electronic structures and total energies of 20 spin arrangements have been calculated with General Gradient Approximation (GGA) + U method. The dependence of exchange integrals on U has been studied. The comparison between the exchange integrals in SrFe12O19 and those in SrCo2Ti2Fe8O19 shows that substitution of Co and Ti decreases the most interactions involving the 12 k sites. The investigation based on our exchange integrals indicates that magnetic interaction between R and S blocks reduces significantly in SrCo2Ti2Fe8O19.

Feng, Min; Shao, Bin; Lu, Yuan; Zuo, Xu

2014-05-01

244

Immucillin-H binding to purine nucleoside phosphorylase reduces dynamic solvent exchange.  

PubMed Central

The rate and extent of hydrogen/deuterium (H/D) exchange into purine nucleoside phosphorylase (PNP) was monitored by electrospray ionization mass spectrometry (ESI-MS) to probe protein conformational and dynamic changes induced by a substrate analogue, products, and a transition state analogue. The genetic deficiency of PNP in humans is associated with severe T-cell immunodeficiency, while B-cell immunity remains functional. Inhibitors of PNP have been proposed for treatment of T-cell leukemia, to suppress the graft-vs.-host response, or to counter type IV autoimmune diseases without destroying humoral immunity. Calf spleen PNP is a homotrimer of polypeptide chains with 284 amino residues, molecular weight 31,541. Immucillin-H inhibits PNP with a Kd of 23 pM when only one of the three catalytic sites is occupied. Deuterium exchange occurs at 167 slow-exchange sites in 2 h when no catalytic site ligands are present. The substrate analogue and product prevented H/D exchange at 10 of the sites. Immucillin-H protected 32 protons from exchange at full saturation. When one of the three subunits of the homotrimer is filled with immucillin-H, and 27 protons are protected from exchange in all three subunits. Deuterium incorporation in peptides from residues 132-152 decreased in all complexes of PNP. The rate and/or extent of deuterium incorporation in peptides from residues 29-49, 50-70, 81-98, and 112-124 decreased only in the complex with the transition state analogue. The peptide-specific H/D exchange demonstrates that (1) the enzyme is most compact in the complex with immucillin-H, and (2) filling a single catalytic site of the trimer reduces H/D exchange in the same peptides in adjacent subunits. The peptides most highly influenced by the inhibitor surround the catalytic site, providing evidence for reduced protein dynamic motion caused by the transition state analogue.

Wang, F.; Miles, R. W.; Kicska, G.; Nieves, E.; Schramm, V. L.; Angeletti, R. H.

2000-01-01

245

Lanthanide paramagnetic probes for NMR spectroscopic studies of fast molecular conformational dynamics and temperature control. Effective six-site proton exchange in 18-crown-6 by exchange spectroscopy.  

PubMed

(1)H and (13)C NMR measurements are reported for the CDCl(3) and CD(2)Cl(2) solutions of [La(18-crown-6)(NO(3))(3)] (I), [Pr(18-crown-6) (NO(3))(3)] (II), [Ce(18-crown-6)(NO(3))(3)] (III), and [Nd(18-crown-6)(NO(3))(3)] (IV) complexes. Temperature dependencies of the (1)H NMR spectra of paramagnetic II-IV have been analyzed using the dynamic NMR (DNMR) methods for six-site exchange. Two types of conformational dynamic processes were identified (the first one is conditioned by interconversion of complex enantiomeric forms and pseudorotation of a macrocycle molecule upon the C(2) symmetry axis; the second one is conditioned by macrocycle molecule inversion). Application of exchange spectroscopy (2D-EXSY) of DNMR for investigation of this dynamic system (II-IV) simplifies the assignment of the NMR signals and represents the first experimental study of multisite exchange. In the present work, the methodology of paramagnetic 4f (Ce, Pr, and Nd) probe applications for the study of free-energy, enthalpy, and entropy changes in chemical exchange processes, as well as the advantages of this method in a comparison with DNMR studies of diamagnetic substances, is discussed. In particular, as a result of paramagnetic chemical shifts in 4f complexes, the range of measurable rate constants expands considerably compared to the analogous range in diamagnetic compounds. Coordination compounds investigated in the paper represent new types of thermometric NMR sensors and lanthanide paramagnetic probes for in situ temperature control in solution. PMID:22250883

Babailov, Sergey P

2012-02-01

246

EFFECT OF LEAF ANATOMY ON HYPOSTOMATOUS LEAF GAS EXCHANGE: A THEORETICAL STUDY WITH THE 2DLEAF MODEL  

Microsoft Academic Search

PACHEPSKY L. B. and ACOCK B. Effect of leaf anatomy on hypostomatous leaf gas exchange: A theoretical study with the 2DLEAF model. BIOTRONICS 27, 1-14, 1998. The two-dimensional model of leaf gas exchange, 2DLEAF, which accounts for leaf intercellular structure, was used to study the effect of leaf anatomy on the photosynthesis and transpiration rates of hypostomatous Cg plants. The

L. B. P ACHEPSKYI; B. ACOCK

247

Retrospective Study of Rapid-Exchange Monorail Versus Over-the-Wire Technique for Femoropopliteal Angioplasty  

Microsoft Academic Search

Purpose  The purpose of this study was to compare procedural outcome of rapid-exchange (RX) monorail versus conventional over-the-wire\\u000a (OTW) technique for femoropopliteal angioplasty.\\u000a \\u000a \\u000a \\u000a Materials and Methods  Demographic data, procedure details, angioplasty success, and complications of 328 consecutive percutaneous transluminal angioplasties\\u000a (PTAs) were collected from a prospective database and retrospectively analyzed. Procedure details included duration of fluoroscopy,\\u000a area-dose product, amount of contrast agent,

Thomas Jahnke; Jost Philipp Schäfer; Hendrik Bolte; Fritz Schäfer; Jens Michalek; Nicholas Charalambous; Marc Sapoval; Stefan Müller-Hülsbeck

2008-01-01

248

Study of field ionization in the charge exchange injection for the IPNS upgrade  

SciTech Connect

The proposed I-MW neutron spallation source is a rapid-cycling synchrotron (RCS) with a design intensity of 1.04 {times} 10{sup 14} protons. A H- beam from the linac is injected into the synchrotron via the charge exchange process. Due to the high intensity of the beam, the minimization of beam loss is one of the primary concerns. In this paper, we study a possible beam loss associated with field ionization, which includes estimates of the charge fraction and level distribution of the excited hydrogen atoms after stripping, and an estimate of lifetime of the excited hydrogen atoms in the transverse magnetic field.

Chase, Yong-Chul, Cho, Yanglai

1995-07-01

249

Mathematical Model for the Study of Hemorrhagic Shock and Fluid Resuscitation: Transcapillary Exchange.  

National Technical Information Service (NTIS)

Mathematical models used to predict plasma volume responses to hemorrhage and fluid resuscitation must consider both fluid and solute exchange across the capillary wall. In this paper, we review four models of transcapillary exchange that might be incorpo...

T. J. Doherty

1993-01-01

250

Experimental studies on coherent synchrotron radiaiton in the emittance exchange line at the Fermilab A0 Photoinjector  

SciTech Connect

Future accelerators will employ advanced beam conditioning systems such as emittance exchangers to manipulate high brightness beams. Coherent synchrotron radiation (CSR) in the dipoles could limit the performance of the emittance exchanger. In this paper, we report the experimental studies on measuring CSR and its effects on the beam at the A0 photoinjector in the emittance exchange line. After reporting the CSR power measurements, we report on the diagnostic scheme based on a weak skew quad in the emittance exchange line to study the CSR effects on the beam and other beam dynamics. In this work, we have reported on CSR measurements and the effect of skew quad on the dogleg line with the 5-cell turned on and off. We plan to study CSR effects on the bunch with the 5-cell on at larger chirp. This is will not only increase the CSR self-effect but also reduce the beamsize at the screen for convenient beamsize measurements.

Thangaraj, J.C.T.; Keup, R.; Johnson, A.; ruan, J.; Piot, P.; Church, M.; Edwards, H.; Lumpkin, A.; Sun, Y.-E.; Santucci, J.; /Fermilab

2011-03-01

251

Tantalum Acetabular Augments in One-stage Exchange of Infected Total Hip Arthroplasty: A Case-control Study.  

PubMed

During the one-stage exchange procedure for periprosthetic joint infection (PJI) after total hip arthroplasty (THA), acetabular defects challenge reconstructive options. Porous tantalum augments are an established tool for addressing acetabular destruction in aseptic cases, but their utility in septic exchange is unknown. This retrospective case-control study presents the initial results of tantalum augmentation during one-stage exchange for PJI. Primary endpoints were rates of re-infection and short-term complications associated with this technique. Study patients had no higher risk of re-infection with equivalent durability at early follow-up with a re-infection rate in both groups of 4%. In conclusion, tantalum augments are a viable option for addressing acetabular defects in one-stage exchange for septic THA. Further study is necessary to assess long-term durability when compared to traditional techniques for acetabular reconstruction. PMID:24559522

Klatte, Till Orla; Kendoff, Daniel; Sabihi, Reza; Kamath, Atul F; Rueger, Johannes M; Gehrke, Thorsten

2014-07-01

252

Condensing heat exchanger microbial growth and control study-phase 2  

Microsoft Academic Search

The Space Station Temperature and Humidity Control Condensing Heat Exchangers will be utilized to collect and remove atmospheric water vapor generated by the metabolic and hygienic activity of crew members. The porous hydrophillic coating within the heat exchangers will always be wet. Cabin air will continuously flow through the heat exchangers during system operation which makes them a potential site

R. W. Marsh; M. E. Caron; C. Metselaar; J. Steele

1993-01-01

253

Structure, Identity, and Solidarity: A Comparative Field Study of Generalized and Direct Exchange  

Microsoft Academic Search

Here we propose an account of the link between exchange structure and the emergence of solidarity capable of accounting for the conflicting evidence social scientists have found regarding the relationship between social exchange structures and the emergence of intangible, affectively laden group sentiments. We argue that benefits received through exchange foster group identification and solidarity but that this effect is

Robb Willer; Francis J. Flynn; Sonya Zak

2012-01-01

254

Kinetic Method for Hydrogen-Deuterium-Tritium Mixture Distillation Simulation  

SciTech Connect

Simulation of hydrogen distillation plants requires mathematical procedures suitable for multicomponent systems. In most of the present-day simulation methods a distillation column is assumed to be composed of theoretical stages, or plates. However, in the case of a multicomponent mixture theoretical plate does not exist.An alternative kinetic method of simulation is depicted in the work. According to this method a system of mass-transfer differential equations is solved numerically. Mass-transfer coefficients are estimated with using experimental results and empirical equations.Developed method allows calculating the steady state of a distillation column as well as its any non-steady state when initial conditions are given. The results for steady states are compared with ones obtained via Thiele-Geddes theoretical stage technique and the necessity of using kinetic method is demonstrated. Examples of a column startup period and periodic distillation simulations are shown as well.

Sazonov, A.B.; Kagramanov, Z.G.; Magomedbekov, E.P. [Mendeleyev University of Chemical Technology of Russia (Russian Federation)

2005-07-15

255

NO and CO adsorption studies on transition metal-exchanged silico-aluminophosphate of type 34 catalysts  

Microsoft Academic Search

Adsorption of nitric oxide (NO) and carbon monoxide (CO) and the co-adsorption of (NO+CO) and (CO+NO) over the transition metal-exchanged SAPO-34 have been studied by infrared spectroscopy. Novel manganese-, cobalt-, and copper-exchanged silico-aluminophosphate of chabazite type catalysts were prepared and characterized using techniques such as elemental analysis, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and nitrogen sorption capacity (BET).Detailed

Deepak B. Akolekar; Suresh K. Bhargava

2001-01-01

256

A model study of circulation and cross-shelf exchange on the west Antarctic Peninsula continental shelf  

Microsoft Academic Search

Exchange of warm, nutrient-rich Circumpolar Deep Water (CDW) onto Antarctic continental shelves and coastal seas has important effects on physical and biological processes in these regions. The present study investigates the locations of this exchange and their dynamics in the west Antarctic Peninsula with a high-resolution three-dimensional numerical model. The model circulation is forced by daily wind stress along with

Michael S. Dinniman; John M. Klinck

2004-01-01

257

Theoretical study of annealed proton-exchanged Nd:LiNbO3 channel waveguide lasers with variational method  

Microsoft Academic Search

The controllable fabrication parameters, including anneal time, initial exchange time, channel width, dependences of TM00 mode size, corresponding effective refractive index, effective pump area, and coupling efficiency between pump and laser modes in z-cut annealed proton-exchanged (APE) Nd:LiNbO3 channel waveguide lasers were studied by using variational method. The effect of channel width on the surface index increment and the waveguide

Delong Zhang; Bo Wu; Yuanguo Xie; Guilan Ding; Yuming Cui; Caihe Chen

2001-01-01

258

In-situ Dehydration Studies of Fully K- Rb- and Cs-exchanged Natrolites  

SciTech Connect

In-situ synchrotron X-ray powder diffraction studies of K-, Rb-, and Cs-exchanged natrolites between room temperature and 425 C revealed that the dehydrated phases with collapsed frameworks start to form at 175, 150, and 100 C, respectively. The degree of the framework collapse indicated by the unit-cell volume contraction depends on the size of the non-framework cation: K-exchanged natrolite undergoes an 18.8% unit-cell volume contraction when dehydrated at 175 C, whereas Rb- and Cs-exchanged natrolites show unit-cell volume contractions of 18.5 and 15.2% at 150 and 100 C, respectively. In the hydrated phases, the dehydration-induced unit-cell volume reduction diminishes as the cation size increases and reveals increasingly a negative slope as smaller cations are substituted into the pores of the natrolite structure. The thermal expansion of the unit-cell volumes of the dehydrated K-, Rb-, and Cs-phases have positive thermal expansion coefficients of 8.80 x 10{sup -5} K{sup -1}, 1.03 x 10{sup -4} K{sup 01}, and 5.06 x 10{sup -5} K{sup -1}, respectively. Rietveld structure refinements of the dehydrated phases at 400 C reveal that the framework collapses are due to an increase of the chain rotation angles, {Psi}, which narrow the channels to a more elliptical shape. Compared to their respective hydrated structures at ambient conditions, the dehydrated K-exchanged natrolite at 400 C shows a 2.2-fold increase in {Psi}, whereas the dehydrated Rb- and Cs-natrolites at 400 C reveal increases of {Psi} by ca. 3.7 and 7.3 times, respectively. The elliptical channel openings of the dehydrated K-, Rb-, to Cs-phases become larger as the cation size increases. The disordered non-framework cations in the hydrated K-, Rb-, and Cs-natrolite order during dehydration and the subsequent framework collapse. The dehydrated phases of Rb- and Cs-natrolite can be stabilized at ambient conditions.

Y Lee; D Seoung; D Liu; M Park; S Hong; H Chen; J Bai; C Kao; T Vogt; Y Lee

2011-12-31

259

Sorption studies of chromium(VI) onto new ion exchanger with tertiary amine, quaternary ammonium and ketone groups.  

PubMed

A new acrylic anion exchanger with both tertiary and quaternary ammonium as well as ketone groups in the structural unit has been prepared by the nucleophilic substitution reaction of aminolyzed vinylacetate:acrylonitrile:divinylbenzene copolymer of porosity structure in the swelling state with 2-chloroacetone as a halogenated compound. The new compound exhibits better qualities of strong base exchange capacity than the weak base anion exchangers. The obtained acrylic anion exchanger was used to remove Cr(VI) from the aqueous solution. Batch adsorption studies have been carried out to determine the effect of contact time, concentration of hexavalent chromium in the solution and pH on the sorption capacity. The kinetic parameters were determined on the basis of the static results. The thermodynamic parameters of Cr(VI) sorption process on the anion exchanger were calculated based on the Langmuir and Freundlich isotherms. Sorption was studied in the pH range of 1.5-7 and it was found that it depends on the solution acidity. At the pH values of 3.5 and 7 the anion exchanger exhibited large values of chromium sorption capacity. The speciation of chromium was investigated in the studied pH range by the Diffuse Reflectance Spectroscopy (DRS) method. Reduction of chromium(VI) to chromium(III) under acidic conditions was observed. The performed acrylic strong base anion exchanger is superior compared to the conventional one based on the styrene:divinylbenzene matrix due to its ability for reposition of the long spacer arm for providing exchange sites, hydrophilic character of matrix, and possible hydrogen bonds provided by carbonyl functional groups. PMID:21497994

Wójcik, Grzegorz; Neagu, Violeta; Bunia, Ion

2011-06-15

260

Exchange interaction in hexagonal MnRhP from first-principles studies  

NASA Astrophysics Data System (ADS)

Electronic structure and magnetic properties for MnRhP have been studied from a first-principles density functional calculation. The calculated lattice constants, a = 6.228 Å and c = 3.571 Å, are in good agreement with the experimental values of a = 6.223 Å and c = 3.585 Å. The calculated moment of Mn is 3.1 ?B/atom, resulting in a total moment of 3.0 ?B/atom due to small moments induced at Rh and P sites. The magnetic moment of Mn decreases with unit cell size. The exchange interactions are dominated by positive Mn-Mn exchange coupling (J), implying a stable ferromagnetic ordering in Mn sublattice. In particular, J shows a maximum value (1.5 mRy) at the the optimized unit cell size. The structural distortion or unit cell size change will affect J, which is intimately related to the magneto-elastic and magneto-caloric effect.

Liu, X. B.; Zhang, Qiming; Yue, M.; Altounian, Z.; Ping Liu, J.

2014-05-01

261

Bromide ion exchange with a Keggin polyoxometalate on functionalized polymeric membranes: a theoretical and experimental study.  

PubMed

Noncovalent interactions between the polyoxometalate [PMo12O40](3-) and acryloyloxyundecyltrimethyl ammonium bromide surfactant, used during membrane preparation, were evaluated in the frame of density functional theory. The electronic solvation energy of [PMo12O40](3) and bromide anions was also evaluated, at the same level of theory, in order to predict a probable exchange on the polymeric surface between these anions at the water/polymer interface. Energy balances were theoretically assessed, showing that the bromide cannot be exchanged with this nanosized polyanion in large extent. In order to validate this theoretical conclusion, ad hoc and accurate measurements were carried out by using homemade polymeric membranes and by dipping them in an ca. 0.4 mM solution of Na3[PMo12O40] for 4 days. The Br(-) concentration, released in a polyoxometalate solution, was followed at different times during the test period by gravimetrical analysis. The agreement between the theoretical prediction and experimental data was remarkable, as the quantum calculations correctly accounted for the short-range intermolecular interactions involved in this phenomenon. Bearing in mind that the achieved conclusion is based on an ab initio quantum approach, the findings of this study can be considered rather general and then exploitable for other similar systems. PMID:24547925

De Luca, G; Bisignano, F; Figoli, A; Galiano, F; Furia, E; Mancuso, R; Saoncella, O; Carraro, M; Bonchio, M; Gabriele, B

2014-03-01

262

A study of entropy rise across supersonic pressure exchange enhancing rotors  

NASA Astrophysics Data System (ADS)

Pressure exchange can be envisioned as a process where work is done by a fluid with high kinetic energy on another fluid with relatively low kinetic energy by utilizing the non-steady pressure forces at the fluid-fluid interface in the laboratory frame of reference. A novel supersonic ejector based on this process was conceptualized and offers non-dissipative flow induction, improved efficiency and environmental benefits. Entropy production in such devices holds the key to any efficiency improvements and therefore, entropy generation from flow structures such as oblique shocks under supersonic flow conditions was studied using schlieren photography. Oblique shocks emanating from the apexes of three cone-vane type of rotors (Truncated Ramp Vane, Ramp Vane and Double cone type) of different semi-cone vertex angles (20 deg., 10 deg., 25 deg. respectively), designed to produce pressure exchange were captured for upstream mach numbers (M=1.5, 1.75, 2) in air. Entropy rise across the oblique shocks was estimated from shock angle measurements and compared to a theoretical entropy rise. Analysis revealed that Double Cone Rotor produced three orders of magnitude higher entropy rise than the Ramp Vane Rotor. Furthermore, an increase in entropy rise (approximately 0.5 orders of magnitude) due a small angle of attack (2.5 deg.) was observed in the Ramp Vane Rotor.

Bulusu, Kartik; Garris, Charles

2010-11-01

263

Histoenzymic studies in the myelinopathy provoked by the cerebrospinal fluid exchange.  

PubMed

A histochemical study was performed on the activity of several phosphatases, esterases and oxidoreductases in the spinal cord of cat in the course of the myelinopathy provoked by the cerebrospinal fluid (CSF) exchange. The following results were obtained: 1. Neuroglial cells of the spinal cord react with a slight, focal increase of TPP-ase activity already during the early stage of myelinopathy evoked by repeated withdrawal and reinjecting of CSF into the Cisterna magna of experimental cats. 2. During the late stage of this experimental disease-- the oligo-and astroglia of the spinal cord dtsplay considerably increased activities of ATP-ase, acP, and of various oxidoreductases. 3. The observed morphological and functional (increased enzymic activity) changes of the oligodendroglia as well as the demonstrable damage of myelin sheath, seem to be the results of vasogenous edema. 4. The results of investigations performed did not yield any arguments, which would speak in favour of the assumption, that the changes of the oligodendroglia cells function as the primary cause in the myelinopathy provoked by the CSF exchange, affecting secondary the myelin sheaths. 5. The decissively increased lysosomal acP activity in oligodendroglial cells of the spinal cord investigated during the early stage of this myelinopathy, accompanied by an evidently damaged Golgi apparatus, may be explained when the Golgi zone is not necessarily the only cellular site where acid phosphatase may be performed. PMID:404827

Wender, M; Kozik, M; Goncerzewicz, A

1977-01-01

264

A theoretical study of thiophenic compounds adsorption on cation-exchanged Y zeolites  

NASA Astrophysics Data System (ADS)

A density functional theory (DFT) method has been applied to study the adsorption of thiophenic compounds such as thiophene (TP), benzothiophene (BT), dibenzothiophene (DBT) on cation-exchanged Cu(I)Y, Ni(II)Y, Ce(III)Y zeolites. All of calculations were carried out by the generalized gradient approximation (GGA) with the BLYP exchange-correlation functional and DNP basis set. The calculated results indicate that the stable adsorption configuration of TP molecule adsorbed on the Cu(I)Y is the ?5 adsorption mode, whereas for BT and DBT, the ?1S adsorption mode was found for the both molecules. Only the ?1S adsorption mode can be obtained for the three thiophenic compounds adsorbed on the Ni(II)Y. The ?5 adsorption mode can be ascribed to the adsorption of thiophene molecules on the Ce(III)Y, but the competition of different adsorption modes could possibly occur during the adsorption process of BT and DBT on the Ce(III)Y. Moreover, the selectivity of TP adsorbed on the adsorbents is in the order of Cu(I)Y > Ce(III)Y > Ni(II)Y, while for BT and DBT, the order is Cu(I)Y > Ni(II)Y > Ce(III)Y.

Wang, Lingtao; Sun, Zhaolin; Ding, Yong; Chen, Yongchang; Li, Qiang; Xu, Ming; Li, Huailei; Song, Lijuan

2011-06-01

265

Experimental study of an integral catalytic combustor: Heat exchanger for Stirling engines  

NASA Technical Reports Server (NTRS)

The feasibility of using catalytic combustion with heat removal for the Stirling engine to reduce exhaust emissions and also improve heat transfer to the working fluid was studied using spaced parallel plates. An internally air-cooled heat exchanger was placed between two noble metal catalytic plates. A preheated fuel-air mixture passed between the plates and reacted on the surface of the catalyzed plates. Heat was removed from the catalytic surface by radiation and convection to the aircooled heat exchangers to control temperature and minimize thermal nitrogen oxide emissions. Test conditions were inlet combustion air temperatures from 850 to 900 K, inlet velocities of about 10 m/s, equivalence ratios from 0.5 to 0.9, and pressures from 1.3x10 to the 5th power to 2.0x10 to the 5th power Pa. Propane fuel was used for all testing. Combustion efficiencies greater than 99.5 percent were measured. Nitrogen oxide emissions ranged from 1.7 to 3.3 g NO2/kg fuel. The results demonstrate the feasibility of the concept and indicate that further investigation of the concept is warranted.

Bulzan, D. L.

1982-01-01

266

Mechanistic studies of isopentane activation over solid acid catalysts. HD exchange with USY zeolite, amorphous silica-alumina and Amberlyst-15  

Microsoft Academic Search

The mechanism of activation of isopentane on USY zeolite, amorphous silica-alumina and Amberlyst-15 catalysts was studied by H-D exchange. Only the zeolite showed exchange with the isopentane at 373 K. The addition of 10% of 2-methyl-1-butene to the isopentane accelerates the exchange with USY zeolite and promotes a small exchange with amorphous silica-alumina and Amberlyst-15. Nevertheless, the selectivity was different.

Claudio J. A. Mota; Sonia C. Menezes; Leonardo Nogueira; W. Bruce Kover

1996-01-01

267

Comparative studies on electrochemical characterization of homogeneous and heterogeneous type of ion-exchange membranes  

Microsoft Academic Search

Interpolymer films of poly-ethylene and styrene-divinyl benzene copolymer were subjected to chlorosulfonation or chloromethylation then amination for the preparation of homogeneous type of cation- or anion-exchange membranes, respectively. Heterogeneous types of ion-exchange membranes were prepared from polyvinyl chloride (PVC) as binder and ion-exchange resin powder in tetrahydrofuran solvent. Membrane potential and conductance measurements have been carried out in NaCl(aq), CuCl2(aq)

G. S. Gohil; Vinod K. Shahi; R. Rangarajan

2004-01-01

268

Use of energy-dispersive x-ray fluorescence analysis in clay mineral ion exchange studies  

Microsoft Academic Search

A rapid, reliable, semiquantitative method for following ion exchange processes in clay minerals is described. An energy-dispersive x-ray fluorescence technique is used. The completeness of the exchange process for the clay mineral montmorillonite was investigated for the ions Rb\\/sup +1\\/, Sr\\/sup +2\\/, and Y\\/sup +3\\/. Samples of clay, suspended on asbestos, were packed in an ion exchange column and solutions

J. F. Mucci; R. L. Stearns

1977-01-01

269

Ion exchange and dehydration experimental studies of clinoptilolite: Implications to zeolite dating  

Microsoft Academic Search

Variable effects were noted on the argon (Ar) and potassium (K) contents of clinoptilolite fractions used in ion-exchange and dehydration experiments. The K contents of clinoptilolite fractions were differently affected during cation exchange with Ca-, Cs-, K-, and Na-chloride solutions. Ar was generally less affected during these experiments, except for a Na-clinoptitolite fraction exchanged for five days. Loss of Ar

WoldeGabriel

1995-01-01

270

Theoretical and experimental studies of rectangular duct heat exchangers to be used in a high-altitude subsonic aircraft  

NASA Astrophysics Data System (ADS)

A unique need exists for heat exchangers that operate efficiently at an altitude of 85,000 feet. The application involves transferring heat to the low pressure ambient air at a low velocity that is in the laminar flow regime. Because it is desired that low pressure ambient air experience a small decrease in pressure, heat exchangers were examined with relatively short flowlengths and the boundary layers of the ambient air may be developing for a significant portion of the flowlength. These unique requirements of heat exchangers prompted an experimental study of compact heat exchangers made with relatively short rectangular fins that formed rectangular ducts. Compact heat exchangers made with rectangular fins were experimentally tested to determine the pressure drop of the air across the heat exchanger and the heat transfer to the air; the experiments were performed with air at Reynolds numbers between 100 and 1000. By placing the experimental apparatus in a chamber that was partially evacuated, experiments were also performed with air at a Reynolds number of approximately 250 at simulated elevated altitudes up to 83,000 feet. The results of the experiments performed at sea level and elevated altitudes compared very well. The results of the experiments that measured the pressure drop of the air determined the additional pressure drop caused by the developing boundary layers. An equation obtained from the data of the pressure drop measurements predicted the entrance length of the developing boundary layers. The Nusselt number of the air was calculated from the data of the heat transfer experiments. The Nusselt number significantly increased of the experiments performed with the boundary layers of the air developing for a significant portion of the rectangular duct. An equation was obtained that predicted the Nusselt number for compact heat exchangers with short flowlengths and with air at low Reynolds numbers. The equation that predicted the Nusselt number and the pressure drop data were used to design heat exchangers to operate at high altitudes.

Mathias, James Allen

271

An electrochemical quartz crystal microbalance study of a prospective alkaline anion exchange membrane material for fuel cells: anion exchange dynamics and membrane swelling.  

PubMed

A strategy has been devised to study the incorporation and exchange of anions in a candidate alkaline anion exchange membrane (AAEM) material for alkaline fuel cells using the electrochemical quartz crystal microbalance (EQCM) technique. It involves the electro-oxidation of methanol (CH3OH) under alkaline conditions to generate carbonate (CO3(2-)) and formate (HCOO(-)) ions at the electrode of a quartz crystal resonator coated with an AAEM film, while simultaneously monitoring changes in the frequency (?f) and the motional resistance (?R(m)) of the resonator. A decrease in ?f, indicating an apparent mass increase in the film, and a decrease in ?R(m), signifying a deswelling of the film, were observed during methanol oxidation. A series of additional QCM experiments, in which the effects of CH3OH, CO3(2-), and HCOO(-) were individually examined by changing the solution concentration of these species, confirmed the changes to be due to the incorporation of electrogenerated CO3(2-)/HCOO(-) into the film. Furthermore, the AAEM films were found to have finite anion uptake, validating the expected tolerance of the material to salt precipitation in the AAEM. The EQCM results obtained indicated that HCOO(-) and CO3(2-), in particular, interact strongly with the AAEM film and readily displace OH(-) from the film. Notwithstanding, the anion exchange between CO3(2-)/HCOO(-) and OH(-) was found to be reversible. It is also inferred that the film exhibits increased swelling in the OH(-) form versus the CO3(2-)/HCOO(-) form. Acoustic impedance analysis of the AAEM-film coated quartz resonators immersed in water showed that the hydrated AAEM material exhibits significant viscoelastic effects due to solvent plasticization. PMID:24588487

John, Jimmy; Hugar, Kristina M; Rivera-Meléndez, Johary; Kostalik, Henry A; Rus, Eric D; Wang, Hongsen; Coates, Geoffrey W; Abruña, Héctor D

2014-04-01

272

A study on the transport process in gas diffusion layer of proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

Gas diffusion layer (GDL) plays a great important role in proton exchange membrane fuel cell (PEMFC). Water transport mechanism in GDL is still not clear. In the present study, an ex-situ transparent setup is built to visualize the transport phenomena and to measure the threshold pressure of water in GDL at different temperatures. It is found that the relationship between the breakthrough pressure and the temperature is nearly linear (i.e. the pressure decreases linearly with the increase of temperature). To avoid the problems faced by the continuum models, the pore network model is developed to simulate the liquid water transport through the carbon paper. A uniform pressure boundary condition is used in simulation and the results are similar to the ones obtained in the experiment. The reason is that the contact angle and surface tension coefficient of water in GDLs change accordingly with the change of temperature.

Tan, Zetao; Jia, Li; Zhang, Zhuqian

2011-10-01

273

Optical studies of gap, exchange, and hopping energies in the insulating cuprates  

NASA Astrophysics Data System (ADS)

We have measured the insulating energy gap ? and the exchange interaction J in a series of cuprate crystals, including T'-phase M2CuO4 (M=Pr, Nd, Sm, Eu, and Gd), T*-phase La,Tb,Sr2CuO4, and T-phase La2CuO4. We find that the energy gap scales predominantly with the in-plane Cu-O distance, scaling as ? log?/ ? logd~-6. Furthermore, contrary to simple expectations, the energy gap increases with decreasing Cu-O distance, suggesting that Coulomb and other repulsive energies dominate the effects of band hybridization. Using a three-band Hubbard-model expression, our studies of ? and J in the cuprates allow us to estimate that the hopping energy t scales with Cu-O distance as ? logt/? logd~-4.

Cooper, S. L.; Thomas, G. A.; Millis, A. J.; Sulewski, P. E.; Orenstein, J.; Rapkine, D. H.; Cheong, S.-W.; Trevor, P. L.

1990-12-01

274

Study of X(3872) from effective field theory with pion-exchange interaction.  

PubMed

We study DD[over ¯]* (D*D[over ¯]) scattering in the framework of unitarized heavy meson chiral perturbation theory with pion exchange and a contact interaction. 3S1-3D1 mixing effects are taken into account. A loosely bound state X(3872), with the pole position being Mpole}=(3871.70-i0.39)??MeV, is found. The result is not sensitive to the strength of the contact interaction. Our calculation provides a theoretical confirmation of the existence of the 1++ state X(3872). The light quark mass dependence of the pole position indicates it has a predominately DD[over ¯]* (D*D[over ¯]) molecular nature. When the ? mass is larger than 142 MeV, the pole disappears, which makes impossible the lattice simulation of this state at large quark mass. PMID:23931357

Wang, P; Wang, X G

2013-07-26

275

Kafirin adsorption on ion-exchange resins: Isotherm and kinetic studies.  

PubMed

Kafirin is a natural, hydrophobic and celiac safe prolamin protein obtained from sorghum seeds. Today kafirin is found to be useful in designing delayed delivery systems and coatings of pharmaceuticals and nutraceuticals where its purity is important and this can be obtained by adsorptive chromatography. This study is the first scientific insight into the isotherm and kinetic studies of kafirin adsorption on anion- and cation-exchange resins for practical applications in preparative scale chromatography. Adsorption isotherms of kafirin were determined for five anion- and two cation-exchange resins in batch systems. Isotherm parameters such as maximum binding capacity and dissociation constant were determined from Langmuir isotherm, and adsorptive capacity and affinity constant from Freundlich isotherm. Langmuir isotherm was found to fit the adsorption equilibrium data well. Batch uptake kinetics for kafirin adsorption on these resins was also carried out and critical parameters including the diffusion coefficient, film mass transfer coefficient, and Biot number for film-pore diffusion model were calculated. Both the isotherm and the kinetic parameters were considered for selection of appropriate resin for kafirin purification. UNOsphere Q (78.26mg/ml) and Toyopearl SP-650M (57.4mg/ml) were found to offer better kafirin binding capacities and interaction strength with excellent uptake kinetics under moderate operating conditions. With these adsorbents, film diffusion resistance was found to be major governing factor for adsorption (Bi<10 and ?<1). Based on designer objective function, UNOsphere Q was found be best adsorbent for binding of kafirin. The data presented is valuable for designing large scale preparative adsorptive chromatographic kafirin purification systems. PMID:25022481

Kumar, Prashant; Lau, Pei Wen; Kale, Sandeep; Johnson, Stuart; Pareek, Vishnu; Utikar, Ranjeet; Lali, Arvind

2014-08-22

276

Educators Exchange Program Report, 1998-99. Program Report and Evaluation Study.  

ERIC Educational Resources Information Center

In 1998, the San Diego Community College District (SDCCD) completed a successful third cycle of Educators Exchange Program (EEP) activities. The goal of EEP is to promote binational cooperation, cultural understanding and economic development through faculty exchange and technical assistance programs. During the last six years of program…

Fawson, Kenneth D.; Abina, Armando; Alvarez, Rafael; Armstrong, William B.; Buyukkaya, Sonia; Kardos, Althea; Schubert, Cynthia

277

Kinetic and Mechanistic Studies of the Deuterium Exchange in Classical Keto-Enol Tautomeric Equilibrium Reactions  

ERIC Educational Resources Information Center

An extension of the classic keto-enol tautomerization of beta-dicarbonyl compounds into a kinetic analysis of deuterium exchange is presented. It is shown that acetylacetone and ethyl acetoacetate undergo nearly complete deuterium exchange of the alpha-methylene carbon when dissolved in methanol-d[subscript 4]. The extent of deuteration may be…

Nichols, Michael A.; Waner, Mark J.

2010-01-01

278

A comparative study of ion exchange kinetics in zinc\\/lead—modified zeolite-clinoptilolite systems  

Microsoft Academic Search

The kinetics of zinc and lead ions removal by modified zeolite-clinoptilolite has been investigated. The rate of the ion exchange process for lead ions is faster than for zinc ions, as well as the time needed to reach the equilibrium. The ion exchange capacity of zeolite of lead ions is doubly higher than that of zinc ions. Diffusion models according

M. Trgo; J. Peri?; N. Vukojevi? Medvidovi?

2006-01-01

279

Global changes and the air-sea exchange of chemicals. Reports and studies. No. 48.  

National Technical Information Service (NTIS)

Present and future changes to global environment have implications for marine pollution and for air-sea exchange of both anthropogenic and natural substances. This report addresses 3 issues related to potential impact of global change on air-sea exchange ...

1991-01-01

280

Muon spin relaxation study of exchange coupling in dilute AgMn alloys  

SciTech Connect

We have observed for the first time conduction-electron mediated muon-impurity coupling, and deduced the strength of the conduction electron-Mn exchange coupling. Our results are marginally consistent with a wave-vector dependent exchange model. 16 refs.

Heffner, R.H.; Cooke, D.W.; Hutson, R.L.; Schillaci, M.E.; Dodds, S.A.; Gist, G.A.; MacLaughlin, D.E.

1985-01-01

281

Russian studies of the safety of anion exchange in nitric acid  

Microsoft Academic Search

Synthetic ion exchange resins came into use in the Soviet Union in the 1950`s, and domestic anion exchange resins based on quaternary amine groups have long been used in the Russian nuclear industry. These resins are similar to resins used in the West, and include pyridine-based resins, as well as the more conventional aryl polymers with substituted methyl amines. (Slide

M. L. Hyder; S. A. Bartenev; L. N. Lazarev

1997-01-01

282

A STUDY OF THORIUM COMPLEXING BY MEANS OF ION EXCHANGE, INFRARED SPECTROSCOPY AND NUCLEAR MAGNETIC RESONANCE  

Microsoft Academic Search

Thorium complexing by malic acid, trihydroxyglutaric acid, tartaric ; acid, alpha -hydroxyisobutyric acid and mandelic acid was followed by means of ; ion exchange at various concentrations of complexing agent and pH. The ; instability constants, and composition of the complexes are listed. The average ; effective charge on the complex was determined by ion exchange. Polynuclear ; thorium complexes

I. Geletseanu; A. V. Lapitskii

1962-01-01

283

Density functional studies on Lewis acidity of alkaline earth metal exchanged faujasite zeolite  

Microsoft Academic Search

Lewis acidity of alkaline earth metal exchanged faujasite zeolite is investigated using density functional based reactivity descriptors with a 6T ring cluster which represents active site of the zeolite. We calculated global reactivity descriptors such as chemical hardness, chemical softness, electrophilicity index of the optimised cluster and local reactivity descriptors namely fukui function and relative electrophilicity of the exchanged cations

P. Mondal; K. K. Hazarika; A. Deka; R. C. Deka

2008-01-01

284

Numerical study of acoustic energy exchange mechanisms in a solid rocket motor  

Microsoft Academic Search

The numerical investigation described is part of an ongoing effort to understand the physical mechanisms by which energy is exchanged between the mean and the acoustic flow fields in solid propellant rocket motors. Energy exchange mechanisms between the mean flow and a standing acoustic wave in a cold flow solid rocket simulator were investigated previously. The combustor internal flow field

Frederik J. de Jong; Joseph D. Baum

1991-01-01

285

Reduction of Organic Matter in Macroporous Weak Anion Exchanger and Scavenger Filter. Field Studies.  

National Technical Information Service (NTIS)

In project K18 reduction of organic water has been tested in four plants with macroporous weak anion exchanger. In project K19 the reduction of organic matter has been tested in five plants. The plants have macroporous weak anion exchanger and scavenger f...

F. Persson

1982-01-01

286

A computational study of an HCCI engine with direct injection during gas exchange  

SciTech Connect

We present a new probability density function (PDF)-based computational model to simulate a homogeneous charge compression ignition (HCCI) engine with direct injection (DI) during gas exchange. This stochastic reactor model (SRM) accounts for the engine breathing process in addition to the closed-volume HCCI engine operation. A weighted-particle Monte Carlo method is used to solve the resulting PDF transport equation. While simulating the gas exchange, it is necessary to add a large number of stochastic particles to the ensemble due to the intake air and EGR streams as well as fuel injection, resulting in increased computational expense. Therefore, in this work we apply a down-sampling technique to reduce the number of stochastic particles, while conserving the statistical properties of the ensemble. In this method some of the most important statistical moments (e.g., concentration of the main chemical species and enthalpy) are conserved exactly, while other moments are conserved in a statistical sense. Detailed analysis demonstrates that the statistical error associated with the down-sampling algorithm is more sensitive to the number of particles than to the number of conserved species for the given operating conditions. For a full-cycle simulation this down-sampling procedure was observed to reduce the computational time by a factor of 8 as compared to the simulation without this strategy, while still maintaining the error within an acceptable limit. Following the detailed numerical investigation, the model, intended for volatile fuels only, is applied to simulate a two-stroke, naturally aspirated HCCI engine fueled with isooctane. The in-cylinder pressure and CO emissions predicted by the model agree reasonably well with the measured profiles. In addition, the new model is applied to estimate the influence of engine operating parameters such as the relative air-fuel ratio and early direct injection timing on HCCI combustion and emissions. The qualitative trends observed in the parametric variation study match well with experimental data in literature. (author)

Su, Haiyun; Vikhansky, Alexander; Mosbach, Sebastian; Kraft, Markus [Department of Chemical Engineering, University of Cambridge, Cambridge CB2 3RA (United Kingdom); Bhave, Amit [Reaction Engineering Solutions Ltd., 61 Canterbury Street, Cambridge CB4 3QG (United Kingdom); Kim, Kyoung-Oh; Kobayashi, Tatsuo [Higashifuji Technical Center, Toyota Motor Corporation, Mishuku 1200, Susono, Shizuoka 480-1193 (Japan); Mauss, Fabian [Division of Combustion Physics, Lund Institute of Technology, Box 118, S-22100 Lund (Sweden)

2006-10-15

287

Employee responses to relational fulfilment and work-life benefits : A social exchange study in the German public administration  

Microsoft Academic Search

Purpose – Investigating employee responses to relational fulfilment of the psychological contract and work-life benefits of a telecommuting program, this study aims to contribute to the literature on social exchange in employment. Design\\/methodology\\/approach – The setting of the study was the German public administration. Survey data from 947 Civil Servants were analyzed in structural equation models. Analysis of mean structure

Severin Hornung; Jürgen Glaser

2010-01-01

288

Megha-Tropiques: a Joint French and Indian Mission to Study Water Cycle and Energy Exchanges in the Tropiques  

Microsoft Academic Search

ISRO and CNES organisations have signed an agreement in May 2001 to carry out Phase B studies of the MEGHA-TROPIQUES mission. MEGHA-TROPIQUES is a satellite mission designed to study convective systems, focusing on the analysis of water cycle with water vapour distribution and transport, convective systems life cycle and energy exchanges in the tropical belt. The science goal is to

N. Karouche

2002-01-01

289

Advantages of the gas-exchange approach to microbiological studies. Memorandum report 1983-1985  

SciTech Connect

Studies of the effects of various chemical or physical stimuli on the growth rates of microorganisms generally involve some measure of biomass. In the case of algae, one might measure the cell number, the chlorophyll concentration, the fluorescence, or the wet weight of the culture as a function of time. Each such measurement requires a sampling of the culture which could be a disturbing factor in the system being measured. Another disadvantage of these traditional measurements is that the times required for significant change to take place in the culture might be hours or days; furthermore, growth rate measurements calculated from the data must be based on the assumption that during the time between measurements the growth rate was constant. This report describes another approach to the problem. It consists simply of monitoring the O/sub 2/ or CO/sub 2/ concentration of an air stream passing through the system (the gas exchange method), and it has several distinct advantages: 1) there is no need to take samples of the culture, 2) each measurement is a rate measurement and indicates the performance of the culture at that very moment, and 3) transitory changes in growth rates are readily detected. Examples are given of studies made previously with this method at NRL. Also the possible value of these methods in a study of the corrosion susceptibility of alloys is described.

Hannan, P.J.; Jones, D.S.

1986-04-03

290

Material Studies Related to the Use of NaK Heat Exchangers Coupled to Stirling Heater Heads  

NASA Technical Reports Server (NTRS)

NASA has been supporting design studies and technology development that could provide power to an outpost on the Moon, Mars, or an asteroid. Technology development efforts have included fabrication and evaluation of components used in a Stirling engine power conversion system. Destructive material evaluation was performed on a NaK shell heat exchanger that was developed by the NASA Glenn Research Center (GRC) and integrated with a commercial 1 kWe Stirling convertor from Sunpower Incorporated. The NaK Stirling test demonstrated Stirling convertor electrical power generation using a pumped liquid metal heat source under thermal conditions that represent the heat exchanger liquid metal loop in a Fission Power Systems (FPS) reactor. The convertors were operated for a total test time of 66 hr at a maximum temperature of 823 K. After the test was completed and NaK removed, the heat exchanger assembly was sectioned to evaluate any material interactions with the flowing liquid metal. Several dissimilar-metal braze joint options, crucial for the heat exchanger transfer path, were also investigated. A comprehensive investigation was completed and lessons learned for future heat exchanger development efforts are discussed.

Locci, Ivan E.; Bowman, Cheryl L.; Geng, Steven M.; Robbie, Malcolm G.

2011-01-01

291

Noncatalytic kinetic study on site-selective H/D exchange reaction of phenol in sub- and supercritical water  

NASA Astrophysics Data System (ADS)

The site-selective H/D exchange reaction of phenol in sub- and supercritical water is studied without added catalysts. In subcritical water in equilibrium with steam at 210-240 °C, the H/D exchange proceeds both at the ortho and para sites in the phenyl ring, with no exchange observed at the meta site. The pseudo-first-order rate constants are of the order of 10-4 s-1 50% larger for the ortho than for the para site. In supercritical water, the exchange is observed also at the meta site with the rate constant in the range of 10-6-10-4 s-1. As the bulk density decreases, the exchange slows down and the site selectivity toward the ortho is enhanced. The enhancement is due to the phenol-water interaction preference at the atomic resolution. The site selectivity toward the ortho is further enhanced when the reaction is carried out in benzene/water solution. Using such selectivity control and the reversible nature of the hydrothermal deuteration/protonation process, it is feasible to synthesize phenyl compounds that are deuterated at any topological combination of ortho, meta, and para sites.

Kubo, Masahito; Takizawa, Takeyuki; Wakai, Chihiro; Matubayasi, Nobuyuki; Nakahara, Masaru

2004-07-01

292

Speciation study of aluminium in beverages by Competitive Ligand Exchange-Adsorptive Stripping Voltammetry.  

PubMed

Competitive Ligand Exchange-Adsorptive Stripping Voltammetry (CLE-AdSV) was used for determining the speciation of aluminium in commonly consumed beverages (water, tea, infusion, coffee, orange juice, tomato juice, beer and red wine). Aluminium determination involves the adsorption of Al-complexes with the ligand cupferron onto a hanging mercury drop electrode. All samples were studied at pH 6.5 with an accumulation step at -0.60V (all potential values in the paper are given versus the Ag/AgCl, [KCl]=3M reference electrode) during 60s, and a final cupferron concentration of 4×10(-4)M. These conditions were used to establish (i) the concentration of electro-labile aluminium, (ii) the range of ligand concentrations and (iii) the conditional stability constants of beverage samples using titration procedures. The results based on Ruzic plots were compared to computer simulation with Visual MINTEQ. This comparison suggests that labile monomeric Al-forms and soluble organic complexes of low molecular weight can be quantified by the CLE-AdSV procedure. Overall the relative uncertainties on the determination of the electro-active Al fraction and the complexing parameters, i.e., concentration and conditional stability constant of natural ligands in the samples, are less than 15%. Thanks to these results, information on Al bioavailability in beverages was collected and discussed. This study also illustrates the value of computer simulations when complex, time-consuming voltammetric techniques are applied. PMID:24720958

Magnier, A; Fekete, V; Van Loco, J; Bolle, F; Elskens, M

2014-05-01

293

Metal ion coordination studies on a silica-based ion exchange resin before and after heating.  

SciTech Connect

Work designed to assess the potential of using a single material to sorb highly charged metal ions from aqueous solution and then microencapsulate and chemical fix those sorbed metal ions in vitreous silica is described. The basis for these studies is a chemically functionalized porous silica that is termed Diphosil. Diphosil was created by Chiarizia and coworkers (Solv. Extr. Ion Exch. 1996, 14(6), 1977-1100) as an ion exchange resin that strongly sorbs actinide and other highly charged metal ions from acid solutions. We have determined the maximum metal ion loading for Diphosil and shown that it sorbs trivalent ions from concentrated phosphoric acid. Using FT-IR analysis, we have shown that heating metal ion-loaded Diphosil in air converts its organic content primarily into carbon dioxide and water vapor. We have carried out studies on luminescence dynamics and spectroscopy, powder x-ray diffraction, and optical microscopy of metal ion-loaded Diphosil prior to and following heating in air. All of the results of our investigations are consistent with microencapsulation and chemical fixation of metal ions sorbed into Diphosil when that material is heated to 1273 K. In consequence, Diphosil is a promising basis for a single material approach to reducing nuclear waste volume by removing longlived alpha emitters from high level liquid radioactive waste and generating a vitreous silica nuclear waste form for the removed radionuclides that is suitable for geologic disposal.

Beitz, J. V.; Williams, C. W.; Chemistry

2001-07-31

294

Knowledge flow and exchange in interdisciplinary primary health care teams (PHCTs): an exploratory study  

PubMed Central

Objective: Improving the process of evidence-based practice in primary health care requires an understanding of information exchange among colleagues. This study explored how clinically oriented research knowledge flows through multidisciplinary primary health care teams (PHCTs) and influences clinical decisions. Methods: This was an exploratory mixed-methods study with members of six PHCTs in Ontario, Canada. Quantitative data were collected using a questionnaire and analyzed with social network analysis (SNA) using UCINet. Qualitative data were collected using semi-structured interviews and analyzed with content analysis procedures using NVivo8. Results: It was found that obtaining research knowledge was perceived to be a shared responsibility among team members, whereas its application in patient care was seen as the responsibility of the team leader, usually the senior physician. PHCT members acknowledged the need for resources for information access, synthesis, interpretation, or management. Conclusion: Information sharing in interdisciplinary teams is a complex and multifaceted process. Specific interventions need to be improved such as formalizing modes of communication, better organizing knowledge-sharing activities, and improving the active use of allied health professionals. Despite movement toward team-based models, senior physicians are often gatekeepers of uptake of new evidence and changes in practice.

Sibbald, Shannon L.; Wathen, C. Nadine; Kothari, Anita; Day, Adam M. B.

2013-01-01

295

Factors Affecting Exchange Relationships Among Subordinates and Supervisors: A Study of Military Officers.  

National Technical Information Service (NTIS)

This research examined the effect of organizational structure on the relationships between subordinates and their supervisors using measures of leader-member exchange (LMX), mentoring effectiveness, perceived organizational support (POS), perceived opport...

L. K. Richter

2001-01-01

296

Empirical Study of Relations between Stock Returns and Exchange Rate Fluctuations in China  

NASA Astrophysics Data System (ADS)

The existing theories tell us that there exist interaction relations between stock prices and exchange rates. However, empirical research results don’t always support these theories. This paper uses quantile regression techniques to check whether the above theories hold in Chinese markets. We first eliminate the impact of the calendar effect and the time trends on stock market returns and exchange rate fluctuations using Gallant, Rossi, and Tachen’s method (1992) by combination with stepwise regression method, and then do quantile regression analysis according to the adjusted data. The empirical results are summarized as follows: the influences of exchange rate fluctuations to stock returns are negative at most quantiles of stock returns; the opposite influences are not significant at most quantiles of exchange rate fluctuations. Some explanations according to these results are given.

Chen, Jian-Bao; Wang, Deng-Ling; Cheng, Ting-Ting

297

Study and elaboration of an efficient device measuring the contact resistance in certain exchanger technologies.  

National Technical Information Service (NTIS)

An experimental and analytical analysis of local contact resistance measuring methods is presented for three configurations of heat exchanger component: double thin tubes (thickness of about 1 mm), circular tubes with inserted fins (thickness of about 1/1...

J. P. Bardon B. Bourouga P. Lhote G. Leroy

1986-01-01

298

Pharmacodynamic Study of Polymerized Porcine Hemoglobin (pPolyHb) in a Rat Model of Exchange Transfusion  

PubMed Central

The objective of the present study is to evaluate the pharmacodynamic properties of polymerized porcine hemoglobin (pPolyHb) in an exchange transfusion model. Each of two groups of rats received a volume of pPolyHb or hetastarch that equalled 120–140% of estimated total blood volume (70 ml/kg) exchange transfusion. The results showed pPolyHb retained hemodynamic stability and exhibited superior volume expansion capability. Furthermore, pPolyHb effectively reverse anaerobic metabolism caused by a large amount of volume exchange. In comparison with hetastarch, pPolyHb increased blood oxygen content and tissue oxygenation. All these properties contribute to a higher effectiveness in sustaining the lives of rats in pPolyHb group.

Zhu, Hongli; Dang, Xiaodong; Yan, Kunping; Dai, Penggao; Luo, Chao; Ma, Jun; Li, Yan; Chang, Thomas Ming Swi; Chen, Chao

2012-01-01

299

NMR study of the exchange coupling in the trinuclear cluster of the multicopper oxidase Fet3p  

PubMed Central

Fet3p from Saccharomyces cerevisiae is a multicopper oxidase (MCO) which oxidizes Fe2+ to Fe3+. The electronic structure of the different copper centers in this family of enzymes has been extensively studied and discussed for years with a particular focus on the exchange coupling regime in the trinuclear cluster (TNC). Using NMR spectroscopy we have quantified the exchange coupling constant in the type 3 center in a fully metallated oxidase; this value in Fet3p is significantly higher than that reported for proteins containing isolated type 3 centers as in tyrosinase. We also provide evidence of exchange coupling between the type 2 and the type 3 Cu2+ ions, which supports the crystallographic evidence of dioxygen binding to the TNC. This work provides the foundation for the application of NMR to these complex systems.

Zaballa, Maria-Eugenia; Ziegler, Lynn; Kosman, Daniel J.; Vila, Alejandro J.

2010-01-01

300

Two-dimensional Pulsed EPR Studies of Vanadium-Exchanged ZSM-5  

Microsoft Academic Search

The pulsed electron paramagnetic resonance (EPR) technique of hyperfine sublevel correlation spectroscopy (HYSCORE) was used to obtain structural information about vanadium(VO2+) exchanged ZSM-5. HYSCORE spectra were obtained for vanadium exchanged ZSM-5 before and after dehydration and after adsorption of ammonia. For the hydrated samples, proton hyperfine coupling constants were measured and assigned to equatorial water ligands with orientations perpendicular and

James F. Woodworth; Michael K. Bowman; Sarah C. Larsen

2004-01-01

301

STUDY OF BEHAVIOR IN THE HEAT EXCHANGER OF A MIXED GAS JOULE-THOMSON COOLER  

Microsoft Academic Search

The object of the investigation is a mixed gas Joule-Thomson (J-T) cooler. A computa- tional model was developed, which makes it possible to investigate the steady state behavior of the refrigerant in the heat exchanger of a mixed gas J-T system. The calculations show that the temperature distribution as well as the pressure distribution in the heat exchanger channels depends

A. Alexeev; A. Thiel; Ch. Haberstroh; H. Quack

302

An experimental study on the thermal performance of ground heat exchanger  

SciTech Connect

A knowledge of ground thermal properties is most important for the proper design of large GHE (ground heat exchanger) systems. Thermal response tests have so far been used primarily not only for in situ determination of design data for GHE systems, but also for the evaluation of grout material, heat exchanger types and groundwater effects. The main purpose has been to determine in situ values of effective ground thermal conductivity, including the effect of groundwater flow and natural convection in boreholes. (author)

Lim, Kyoungbin; Lee, Sanghoon [Department of Mechanical Engineering, Hanbat University, Daejon (Korea); Lee, Changhee [Department of Mechanical Engineering, Hanyang University, 1271 Sa1 Ansan, Kyungki-do 425791 (Korea)

2007-08-15

303

Application of AVHRR vegetation index to study atmosphere-biosphere exchange of CO2  

NASA Technical Reports Server (NTRS)

The Advanced Very High Resolution Radiometer (AVHRR) satellite-borne sensor is presently used, together with field data, to determine the geographic distributions of the seasonal exchange of CO2 between the earth's atmosphere and the terrestrial biota. The exchange functions thus obtained are validated in virtue of the ability to reproduce the observed annual cycle of atmospheric CO2 in a three-dimensional tracer transport model. The AVHRR is carried by the TIROS-N series of polar-orbiting satellites.

Fung, I. Y.; Tucker, C. J.; Prentice, K. C.

1985-01-01

304

Study of toponium production including the effects of Higgs-boson exchange  

SciTech Connect

The production rates for toponium in {ital e}{sup +}{ital e{minus}} collisions are calculated for a top-quark mass in the range of 100--200 GeV including the effects of standard-model Higgs-boson exchange. The effects due to this exchange fall off rapidly with the Higgs-boson mass, but lead to changes comparable to those due to uncertainties in {Lambda} for a light Higgs boson.

Feigenbaum, J. (Physics Department, Case Western Reserve University, Cleveland, Ohio 44106 (US) )

1991-01-01

305

ANION EXCHANGE METHOD FOR THE DETERMINATION OF PLUTONIUM IN WATER: SINGLE-LABORATORY EVALUATION AND INTERLABORATORY COLLABORATIVE STUDY  

EPA Science Inventory

This report gives the results of a single-laboratory evaluation and an interlaboratory collaborative study of a method for determining plutonium in water. The method was written for the analysis of 1-liter samples and involved coprecipitation, acid dissolution, anion exchange, el...

306

Study of operating conditions and cell design on the performance of alkaline anion exchange membrane based direct methanol fuel cells  

Microsoft Academic Search

Direct methanol fuel cells using an alkaline anion exchange membrane (AAEM) were prepared, studied, and optimized. The effects of fuel composition and electrode materials were investigated. Membrane electrode assemblies fabricated with Tokuyama® AAEM and commercial noble metal catalysts achieved peak power densities between 25 and 168mWcm?2 depending on the operating temperature, fuel composition, and electrode materials used. Good electrode wettability

G. K. Surya Prakash; Frederick C. Krause; Federico A. Viva; S. R. Narayanan; George A. Olah

2011-01-01

307

Thermal time distributions in a tube heat exchanger. A study with application to sterilization of liquid foods.  

National Technical Information Service (NTIS)

The study deals with the distribution of heat treatment within the flow of heat exchangers. The distribution is induced by the combined effect of velocity and temperature gradients and is referred to as the thermal time distribution (TTD). The TTD is rega...

A. Ellborg

1989-01-01

308

Experimental study on heat transfer enhancement of a helically baffled heat exchanger combined with three-dimensional finned tubes  

Microsoft Academic Search

Heat transfer and pressure drop of helically baffled heat exchanger combined with petal-shaped finned tubes for oil (ISO VG-32) cooling with water as coolant was experimentally studied. The tube side heat transfer coefficient was obtained by a modified Wilson plot technique. Results were presented as plots of the shell side heat transfer coefficient based on the actual outside surface area

Zhang Zhnegguo; Xu Tao; Fang Xiaoming

2004-01-01

309

In Situ X-ray Diffraction Study of Cesium Exchange in Synthetic Umbite  

SciTech Connect

The exchange of Cs{sup +} into H{sub 1.22}K{sub 0.84}ZrSi{sub 3}O{sub 9} {center_dot} 2.16H{sub 2}O (umbite-(HK)) was followed in situ using time-resolved X-ray diffraction at the National Synchrotron Light Source. The umbite framework (space group P2{sub 1}/c with cell dimensions of a = 7.2814(3) {angstrom}, b = 10.4201(4) {angstrom}, c = 13.4529(7) {angstrom}, and {beta} = 90.53(1){sup o}) consists of wollastonite-like silicate chains linked by isolated zirconia octahedra. Within umbite-(HK) there are two unique ion exchange sites in the tunnels running parallel to the a-axis. Exchange Site 1 is marked by 8 member-ring (MR) windows in the bc-plane and contains K{sup +} cations. Exchange Site 2 is marked by a larger 8-MR channel parallel to [100], and contains H{sub 2}O molecules. The occupancy of the Cs{sup +} cations through these channels was modeled by Rietveld structure refinements of the diffraction data and demonstrated that there is a two-step exchange process. The incoming Cs{sup +} ions populated the larger 8-MR channel (Exchange Site 2) first and then migrated into the smaller 8-MR channel. During the exchange process a structural change occurs, transforming the exchanger from monoclinic P2{sub 1}/c to orthorhombic P2{sub 1}2{sub 1}2{sub 1}. This structural change occurs when Cs{sup +} occupancy in the small cavity becomes greater than 0.50. The final in situ ion exchange diffraction pattern was refined to yield umbite-(CsK) with the molecular formula H{sub 0.18}K{sub 0.45}Cs{sub 1.37}ZrSi{sub 3}O{sub 9} {center_dot} 0.98H{sub 2}O and possessing an orthorhombic unit cell with dimensions a = 10.6668(8) {angstrom}, b = 13.5821(11) {angstrom}, c = 7.3946(6) {angstrom}. Solid state {sup 133}Cs MAS NMR showed there is only a slight difference between the two cavities electronically. Valence bond sums for the completely occupied Exchange Site 1 demonstrate that Cs-O bonds of up to 3.8 {angstrom} contribute to the coordination of the Cs{sup +} cation.

C Fewox; A Clearfield; A Celestian

2011-12-31

310

Carbonylation of formaldehyde over ion exchange resin catalysts. 1. Batch reactor studies  

SciTech Connect

Methyl glycolate was synthesized as a precursor to ethylene glycol from the catalytic carbonylation of formaldehyde followed by esterification with methanol. Various cation exchange polystyrene-sulfonic acid resins showed excellent activity and methyl glycolate selectivity. The perfluorinated sulfonic acid resin Nafion-H showed higher activity per proton site, yet was less effective per weight of the catalyst. The effects of process variables such as pressure, temperature, catalyst loading, and solvent were studied. High CO pressures were required to promote formaldehyde carbonylation relative to side reactions between formaldehyde. The presence of water reduced the reaction rate, yet improved the selectivity to methyl glycolate. 1,4-Dioxane was found to be the best solvent in the presence of water. At 135 C, 3,500 psig, and reactant mole ratio of HCHO:H[sub 2]O:H[sup +] = 10:10:1, complete conversion of formaldehyde was achieved in 2-4 h with selectivities of methyl glycolate better than 80%. Catalysts did not show any significant deterioration in performance in repeated use up to 10 batches.

Sang Young Lee; Jae Chang Kim; Jae Sung Lee; Young Gul Kim (Pohang Inst. of Science and Technology (Korea, Republic of))

1993-02-01

311

A pulse NMR study of water exchange across the erythrocyte membrane  

NASA Astrophysics Data System (ADS)

A pulse nuclear magnetic resonance (NMR) technique is employed to study the temperature dependence (5-40°C) of the diffusional water exchange time ?exch for normal and p-hydroxymercuribenzoate ( p-HMB) treated bovine erythrocytes. The Arrhenius plot of ?exch for normal erythrocytes implies the activation energy Ea of 20.4 kJ/mol, similar to that for self-diffusion of water ( Ea = 19.3 - 20.1 kJ/mol), and the value ?exch of 12.5 ms at 20°C corresponds to the cell membrane diffusional water permeability coefficient P d of 3.6 × 10 -3 cm/s. The data for p-HMB treated cells display lengthening of ?exch (i.e., ?exch = 17.3 ms at 20°C) and increased E a of 29.0 kJ/mol. This E a value and a permeability coefficient P d of 2.6 × 10 -3 cm/s at 20°C, if compared to corresponding data for artificial lipid bilayer membranes, indicate either incomplete closure of the specialized water-selective protein channels on binding of p-HMB to their SH-groups, or complete channel closure plus new leaks.

Lahajnar, G.

1993-03-01

312

Scalable properties of metal clusters: A comparative study of modern exchange-correlation functionals  

NASA Astrophysics Data System (ADS)

The performance of eight generalized gradient approximation exchange-correlation (xc) functionals is assessed by a series of scalar relativistic all-electron calculations on octahedral palladium model clusters Pdn with n = 13, 19, 38, 55, 79, 147 and the analogous clusters Aun (for n up through 79). For these model systems, we determined the cohesive energies and average bond lengths of the optimized octahedral structures. We extrapolate these values to the bulk limits and compare with the corresponding experimental values. While the well-established functionals BP, PBE, and PW91 are the most accurate at predicting energies, the more recent forms PBEsol, VMTsol, and VT{84}sol significantly improve the accuracy of geometries. The observed trends are largely similar for both Pd and Au. In the same spirit, we also studied the scalability of the ionization potentials and electron affinities of the Pd clusters, and extrapolated those quantities to estimates of the work function. Overall, the xc functionals can be classified into four distinct groups according to the accuracy of the computed parameters. These results allow a judicious selection of xc approximations for treating transition metal clusters.

Koitz, Ralph; Soini, Thomas M.; Genest, Alexander; Trickey, S. B.; Rösch, Notker

2012-07-01

313

Solar Wind Charge Exchange Studies Of Highly Charged Ions On Atomic Hydrogen  

SciTech Connect

Accurate studies of low-energy charge exchange (CX) are critical to understanding underlying soft X-ray radiation processes in the interaction of highly charged ions from the solar wind with the neutral atoms and molecules in the heliosphere, cometary comas, planetary atmospheres, interstellar winds, etc.. Particularly important are the CX cross sections for bare, H-like, and He-like ions of C, N, O and Ne, which are the dominant charge states for these heavier elements in the solar wind. Absolute total cross sections for single electron capture by H-like ions of C, N, O and fully-stripped O ions from atomic hydrogen have been measured in an expanded range of relative collision energies (5 eV/u-20 keV/u) and compared to previous H-oven measurements. The present measurements are performed using a merged-beams technique with intense highly charged ion beams extracted from a 14.5 GHz ECR ion source installed on a high voltage platform at the Oak Ridge National Laboratory. For the collision energy range of 0.3 keV/u-3.3 keV/u, which corresponds to typical ion velocities in the solar wind, the new measurements are in good agreement with previous H-oven measurements. The experimental results are discussed in detail and compared with theoretical calculations where available.

Draganic, I. N.; Havener, C. C. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Seely, D. G. [Department of Physics, Albion College, Albion, MI 49224 (United States); McCammon, D. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States)

2011-06-01

314

Solar Wind Charge Exchange Studies of Highly Charged Ions on Atomic Hydrogen  

SciTech Connect

Accurate studies of low energy charge exchange (CX) are critical to understanding underlying soft X ray radiation processes in the interaction of highly charged ions from the solar wind with the neutral atoms and molecules in the heliosphere, cometary comas, planetary atmospheres, interstellar winds, etc.. Particularly important are the CX cross sections for bare, H like, and He like ions of C, N, O and Ne, which are the dominant charge states for these heavier elements in the solar wind. Absolute total cross sections for single electron capture by H like ions of C, N, O and fully stripped O ions from atomic hydrogen have been measured in an expanded range of relative collision energies (5 eV u 20 keV u) and compared to previous H oven measurements. The present measurements are performed using a merged beams technique with intense highly charged ion beams extracted from a 14.5 GHz ECR ion source installed on a high voltage platform at the Oak Ridge National Laboratory. For the collision energy range of 0.3 keV u 3.3 keV u, which corresponds to typical ion velocities in the solar wind, the new measurements are in good agreement with previous H oven measurements. The experimental results are discussed in detail and compared with theoretical calculations where available.

Draganic, Ilija N [ORNL; Seely, D. G. [Albion College; McCammon, D [University of Wisconsin, Madison; Havener, Charles C [ORNL

2011-01-01

315

Low Mass MS/MS Fragments of Protonated Amino Acids Used for Distinction of Their 13C- Isotopomers in Metabolic Studies  

NASA Astrophysics Data System (ADS)

Glu, Gln, Pro, and Ala are the main amino acids involved in ammonia detoxification in mosquitoes. In order to develop a tandem mass spectrometry method (MS2) to monitor each carbon of the above isotopically-labeled 13C-amino acids for metabolic studies, the compositions and origins of atoms in fragments of the protonated amino acid should be first elucidated. Thus, various electrospray (ESI)-based MS2 tools were employed to study the fragmentation of these unlabeled and isotopically-labeled amino acids and better understand their dissociation pathways. A broad range of fragments, including previously-undescribed low m/z fragments was revealed. The formulae of the fragments (from m/z 130 down to m/z 27) were confirmed by their accurate masses. The structures and conformations of the larger fragments of Glu were also explored by ion mobility mass spectrometry (IM-MS) and gas-phase hydrogen/deuterium exchange (HDX) experiments. It was found that some low m/z fragments ( m/z 27-30) are common to Glu, Gln, Pro, and Ala. The origins of carbons in these small fragments are discussed and additional collision induced dissociation (CID) MS2 fragmentation pathways are proposed for them. It was also found that small fragments (? m/z 84) of protonated, methylated Glu, and methylated Gln are the same as those of the underivatized Glu and Gln. Taken together, the new approach of utilizing low m/z fragments can be applied to distinguish, identify, and quantify 13C-amino acids labeled at various positions, either in the backbone or side chain.

Ma, Xin; Dagan, Shai; Somogyi, Árpád; Wysocki, Vicki H.; Scaraffia, Patricia Y.

2013-04-01

316

Low Mass MS/MS Fragments of Protonated Amino Acids used for Distinction of their 13C- Isotopomers in Metabolic Studies  

PubMed Central

Glu, Gln, Pro and Ala are the main amino acids involved in ammonia detoxification in mosquitoes. In order to develop a tandem mass spectrometry method (MS2) to monitor each carbon of the above isotopically-labeled 13C-amino acids for metabolic studies, the compositions and origins of atoms in fragments of the protonated amino acid should be first elucidated. Thus, various electrospray (ESI)-based MS2 tools were employed to study the fragmentation of these unlabeled and isotopically-labeled amino acids and better understand their dissociation pathways. A broad range of fragments, including previously-undescribed low m/z fragments was revealed. The formulae of the fragments (from m/z 130 down to m/z 27) were confirmed by their accurate masses. The structures and conformations of the larger fragments of Glu were also explored by ion mobility mass spectrometry (IM-MS) and gas-phase hydrogen/deuterium exchange (HDX) experiments. It was found that some low m/z fragments (m/z 27-30) are common to Glu, Gln, Pro and Ala. The origins of carbons in these small fragments are discussed and additional collision induced dissociation (CID) MS2 fragmentation pathways are proposed for them. It was also found that small fragments (? m/z 84) of protonated, methylated Glu and methylated Gln are the same as those of the underivatized Glu and Gln. Taken together, the new approach of utilizing low m/z fragments can be applied to distinguish, identify and quantify 13C-amino acids labeled at various positions, either in the backbone or side chain.

Ma, Xin; Dagan, Shai; Somogyi, Arpad; Wysocki, Vicki H.; Scaraffia, Patricia Y.

2013-01-01

317

Pulsed field gradient NMR study of phenol binding and exchange in dispersions of hollow polyelectrolyte capsules  

NASA Astrophysics Data System (ADS)

The distribution and exchange dynamics of phenol molecules in colloidal dispersions of submicron hollow polymeric capsules is investigated by pulsed field gradient NMR (PFG-NMR). The capsules are prepared by layer-by-layer assembly of polyelectrolyte multilayers on silica particles, followed by dissolution of the silica core. In capsule dispersion, 1H PFG echo decays of phenol are single exponentials, implying fast exchange of phenol between a free site and a capsule-bound site. However, apparent diffusion coefficients extracted from the echo decays depend on the diffusion time, which is typically not the case for the fast exchange limit. We attribute this to a particular regime, where apparent diffusion coefficients are observed, which arise from the signal of free phenol only but are influenced by exchange with molecules bound to the capsule, which exhibit a very fast spin relaxation. Indeed, relaxation rates of phenol are strongly enhanced in the presence of capsules, indicating binding to the capsule wall rather than encapsulation in the interior. We present a quantitative analysis in terms of a combined diffusion-relaxation model, where exchange times can be determined from diffusion and spin relaxation experiments even in this particular regime, where the bound site acts as a relaxation sink. The result of the analysis yields exchange times between free phenol and phenol bound to the capsule wall, which are on the order of 30 ms and thus slower than the diffusion controlled limit. From bound and free fractions an adsorption isotherm of phenol to the capsule wall is extracted. The binding mechanism and the exchange mechanism are discussed. The introduction of the global analysis of diffusion as well as relaxation echo decays presented here is of large relevance for adsorption dynamics in colloidal systems or other systems, where the standard diffusion echo decay analysis is complicated by rapidly relaxing boundary conditions.

Choudhury, Rudra Prosad; Schönhoff, Monika

2007-12-01

318

Structure and properties of metal-exchanged zeolites studied using gradient-corrected and hybrid functionals. I. Structure and energetics  

NASA Astrophysics Data System (ADS)

The structural and energetic properties of purely siliceous, proton-, and Cu- and Co-exchanged chabazite have been studied using periodic density-functional (DFT) calculations with both conventional gradient-corrected exchange-correlation functionals and hybrid functionals mixing exact (i.e., Hartree-Fock) and DFT exchange. Spin-polarized and fixed-moment calculations have been performed to determine the equilibrium and excited spin-configurations of the metal-exchanged chabazites. For the purely siliceous chabazite, hybrid functionals predict a slightly more accurate cell volume and lattice geometry. For isolated Al/Si substitution sites, gradient-corrected functionals predict that the lattice distortion induced by the substitution preserves the local tetrahedral symmetry, whereas hybrid functionals lead to a distorted Al coordination with two short and two long Al-O bonds. Hybrid functionals yield a stronger cation-framework binding that conventional functionals in metal-exchanged zeolites, they favor shorter cation-oxygen bonds and eventually also a higher coordination of the cation. Both types of functionals predict the same spin in the ground-state. The structural optimization of the excited spin-states shows that the formation of a high-spin configuration leads to a strong lattice relaxation and a weaker cation-framework bonding. For both Cu- and Co-exchanged chabazite, the prediction of a preferred location of the cation in a six-membered ring of the zeolite agrees with experiment, but the energy differences between possible cation locations and the lattice distortion induced by the Al/Si substitution and the bonding of the cation depends quite significantly on the choice of the functional. All functionals predict similar energy differences for excited spin states. Spin-excitations are shown to be accompanied by significant changes in the cation coordination, which are more pronounced with hybrid functionals. The consequences of electronic spectra and chemical reactivity are analyzed in the following papers.

Göltl, Florian; Hafner, Jürgen

2012-02-01

319

The folding energy landscape of apoflavodoxin is rugged: Hydrogen exchange reveals nonproductive misfolded intermediates  

PubMed Central

Many native proteins occasionally form partially unfolded forms (PUFs), which can be detected by hydrogen/deuterium exchange and NMR spectroscopy. Knowledge about these metastable states is required to better understand the onset of folding-related diseases. So far, not much is known about where PUFs reside within the energy landscape for protein folding. Here, four PUFs of the relatively large apoflavodoxin (179 aa) are identified. Remarkably, at least three of them are partially misfolded conformations. The misfolding involves side-chain contacts as well as the protein backbone. The rates at which the PUFs interconvert with native protein have been determined. Comparison of these rates with stopped-flow data positions the PUFs in apoflavodoxin’s complex folding energy landscape. PUF1 and PUF2 are unfolding excursions that start from native apoflavodoxin but do not continue to the unfolded state. PUF3 and PUF4 could be similar excursions, but their rates of formation suggest that they are on a dead-end folding route that starts from unfolded apoflavodoxin and does not continue all of the way to native protein. All PUFs detected thus are off the protein’s productive folding route.

Bollen, Yves J. M.; Kamphuis, Monique B.; van Mierlo, Carlo P. M.

2006-01-01

320

The folding energy landscape of apoflavodoxin is rugged: hydrogen exchange reveals nonproductive misfolded intermediates.  

PubMed

Many native proteins occasionally form partially unfolded forms (PUFs), which can be detected by hydrogen/deuterium exchange and NMR spectroscopy. Knowledge about these metastable states is required to better understand the onset of folding-related diseases. So far, not much is known about where PUFs reside within the energy landscape for protein folding. Here, four PUFs of the relatively large apoflavodoxin (179 aa) are identified. Remarkably, at least three of them are partially misfolded conformations. The misfolding involves side-chain contacts as well as the protein backbone. The rates at which the PUFs interconvert with native protein have been determined. Comparison of these rates with stopped-flow data positions the PUFs in apoflavodoxin's complex folding energy landscape. PUF1 and PUF2 are unfolding excursions that start from native apoflavodoxin but do not continue to the unfolded state. PUF3 and PUF4 could be similar excursions, but their rates of formation suggest that they are on a dead-end folding route that starts from unfolded apoflavodoxin and does not continue all of the way to native protein. All PUFs detected thus are off the protein's productive folding route. PMID:16537490

Bollen, Yves J M; Kamphuis, Monique B; van Mierlo, Carlo P M

2006-03-14

321

HD Desktop: an integrated platform for the analysis and visualization of H/D exchange data  

PubMed Central

Here we describe an integrated software platform titled HD Desktop designed specifically to enhance the analysis of hydrogen/deuterium exchange (HDX) mass spectrometry data. HD Desktop integrates tools for data extraction with visualization components within a single web-based application. The interface design enables users to navigate from the peptide view to the sample and experiment levels, tracking all manipulations while updating the aggregate graphs in real time. HD Desktop is integrated with a relational database designed to provide performance enhancements, as well as a robust model for data storage and retrieval. Additional features of the software include retention time determination, which is achieved with the use of theoretical isotope fitting; here, we assume that the best theoretical fit will occur at the correct retention time for any given peptide. Peptide data consolidation for the rendering of data in 2D was realized by automating known and novel approaches. Designed to address broad needs of the HDX community, the platform presented here provides an efficient and manageable workflow for HDX data analysis and is freely available as a web tool at the project home page http://hdx.florida.scripps.edu.

Pascal, Bruce D.; Chalmers, Michael J.; Busby, Scott A.; Griffin, Patrick R.

2009-01-01

322

DMSO exchange on [Gd(DMSO)8]3+—a variable pressure17O NMR study  

NASA Astrophysics Data System (ADS)

Variable temperature (at 9.4 and 14.1 T) and pressure (at 9.4 T) 17O NMR relaxation and chemical shift experiments have been performed on DMSO solutions of [Gd(DMSO)8]3+. It has been found that DMSO exchange is more than two orders of magnitude slower than water exchange (kex298 = 6.2 × 106 s-1 for [Gd(DMSO)8]3+/8.3 × 108 s-1 for [Gd(H2O)8]3+). Comparison of activation volumes (DgrVDagger = +8.2 cm3 s-1 for [Gd(DMSO)8]3+/-3.3 cm3 s-1 for [Gd(H2O)8]3+) shows that activation modes are different for solvent exchange on [Gd(DMSO)8]3+ and [Gd(H2O)8]3+: DMSO exchange follows a dissociative activation mode in contrast to H2O exchange which follows an associative activation mode. This change in activation mode is explained by the increase in molecular volume from H2O to DMSO.

Dessapt, Rémi; Helm, Lothar; Merbach, AndrA~© E.

2004-04-01

323

Factors Affecting Outcome in Acute Hypertriglyceridemic Pancreatitis Treated with Plasma Exchange: An Observational Cohort Study  

PubMed Central

Objectives The optimal therapy for hypertriglyceridemic acute pancreatitis, especially the role of plasma exchange (PE), is not entirely clear. The aim of our large, single-center, observational, cohort study was to analyze the factors affecting outcome in hypertriglyceridemic pancreatitis treated with PE. Methods We included 111 episodes of hypertriglyceridemic pancreatitis treated with PE, which occurred in 103 different patients. The Acute Physiology and Chronic Health Evaluation (APACHE) II score, triglycerides, delay to first PE, and PE treatment details were retrospectively obtained from the patients’ records. The main outcome measures were length of hospitalization and in-hospital mortality. Results The patients were 47±9 years old and the median APACHE II score at first PE was 4 (inter-quartile range (IQR) 2–7). There was a seasonal variation in the incidence of hypertriglyceridemic pancreatitis, and the recurrence rate was 1.6% per year. Triglycerides at presentation did not correlate with APACHE II or influence the outcome. The mean reduction in triglycerides during PE was 59% (from 44±31 to 18±15 mmol/l), which was twice the reduction observed during conservative treatment (27% daily). The median hospital stay was 16 days (IQR 10–24) and in-hospital mortality was 5%. The median delay to first PE was 35 hours (IQR 24–52), and there was no difference in mortality in the early and late PE groups (7% vs. 6%, p?=?0.79). The group with citrate anticoagulation during PE had a significantly lower mortality than the group with heparin anticoagulation (1% vs. 11%, p?=?0.04), and citrate was an independent predictor also in the multivariate model (p?=?0.049). Conclusions PE effectively reduced serum triglycerides faster than could be expected with conservative treatment. The delay in PE therapy did not influence survival. We found that citrate anticoagulation during PE was associated with reduced mortality, which should be confirmed in a randomized study.

Gubensek, Jakob; Buturovic-Ponikvar, Jadranka; Romozi, Karmen; Ponikvar, Rafael

2014-01-01

324

Concurrent studies of enhanced heat transfer and materials in ocean thermal heat exchangers  

NASA Astrophysics Data System (ADS)

Vertical shell and tube condensors and evaporators with axially ridged tubes produce high heat fluxes under OTEC conditions. Shell side pressure drop is inconsequential and there are only minimal problems associated with the operation of large exchangers. Yet the cost effectiveness of ridged tube units is reduced by added material and labor costs to the point where the possible advantages of these exchangers must lie in such areas as ease of cleaning and decreased buoyancy. Units built from vertically ridged plates or sheets give promise of reducing fabricating costs while retaining the thermal and hydrodynamic benefits of ridged tubes. The dynamics of closed OTEC power cycles are dominated by the dynamics of the evaporator and condenser. Mathematical modeling of several candidate exchangers shows the OTEC cycle to be stable and bypass valve control to be a relatively fast and smooth method of turbine speed control.

Bothfus, R. R.

1981-04-01

325

Plasma-exchange treatment for severe carbamazepine intoxication: A case study.  

PubMed

Acute poisoning is an important cause of morbidity and mortality during childhood. This manuscript reports the positive outcome of a pediatric case with a history of accidental carbamazepine intake treated using plasma exchange. A 3-year-old male presented with severe carbamazepine intoxication. He was comatose and had generalized tonic clonic seizure, ventricular tachycardia, and hypotension. Although he did not respond to classical therapies, we performed two sessions of plasma exchange. The patient recovered rapidly and was discharged from the hospital six days from the time of carbamazepine ingestion with no complication or neurologic impairment. Plasma exchange can be performed safely in very small children, and it might be the first line treatment, particularly for intoxication with drugs that have high plasma-protein-binding properties. J. Clin. Apheresis 29:178-180, 2014. © 2013 Wiley Periodicals, Inc. PMID:24136443

Kozanoglu, Ilknur; Kahveci, Suat; Asma, Suheyl; Yeral, Mahmut; Noyan, Aytul; Boga, Can; Ozdogu, Hakan

2014-06-01

326

Dynamic NMR study of ligand exchange reactions in U(VI)-phosphonic acid systems  

SciTech Connect

The rates of hydrogen ion exchange on phosphonic acid ligands and that of phosphonate ligand exchange on selected uranyl-phosphonate complexes have been investigated by dynamic NMR spectroscopy. The spin-spin relaxation time (ln(1/T{sub 2})) for H{sup +} exchange on the fee ligands exhibits a parabolic dependence on reciprocal temperature (1/T (K{sup {minus}1})). The empirical fit parameters are correlated with the activation parameters ({Delta}H{sup *}, {Delta}S{sup *}, {Delta}C{sub p}{sup *}) by adapting the statistical mechanical framework developed by Braibanti et al. to the Eyring activated complex theory. The correlation of the apparent activation enthalpy with temperature indicates that 6--11 water molecules participate in the transition from reactants to activated complex for ligand proton exchange reactions, depending on the ligand. Mechanistic details of ligand exchange reactions of phosphonic acid complexants onto the corresponding uranium(VI) complexes are not fully developed, but the negative values for {Delta}S{sup *} imply increased order in the transition to the activated complex. Though {Delta}H{sup *} for ligand exchange covers a range of 15 kJ/mol, the free energy of activation ({Delta}G{sup *}) is nearly constant for the series of ligands, implying substantial entropy compensation in the activation process. Application of the Marcus relationship defines a correlation between {Delta}G{sup *} and the thermodynamic stability ({Delta}G{degree}) for the 1:2 uranyl complexes with methanediphosphonic acid and 1-hydroxyethane-1,1-diphosphonic acid.

Muntean, J.V.; Nash, K.L.; Rickert, P.G.; Sullivan, J.C. [Argonne National Lab., IL (United States). Chemistry Div.] [Argonne National Lab., IL (United States). Chemistry Div.

1999-05-06

327

Two-dimensional Pulsed EPR Studies of Vanadium-Exchanged ZSM-5  

SciTech Connect

The pulsed electron paramagnetic resonance (EPR) technique of hyperfine sublevel correlation spectroscopy (HYSCORE) was used to obtain structural information about vanadium(VO2+) exchanged ZSM-5. HYSCORE spectra were obtained for vanadium exchanged ZSM-5 before and after dehydration and after adsorption of ammonia. For the hydrated samples, proton hyperfine coupling constants were measured and assigned to equatorial water ligands with orientations perpendicular and parallel to the equatorial plane. Nitrogen hyperfine coupling constants for adsorbed ammonia were also determined from the HYSCORE spectra. The results were compared with previous density functional theory (DFT) calculations of hyperfine coupling constants for vanadyl model complexes.

Woodworth, James F.; Bowman, Michael K.; Larsen, Sarah C.

2004-10-14

328

Asymmetric GUVs Prepared by M?CD-Mediated Lipid Exchange: An FCS Study  

PubMed Central

We report a simple method to obtain stable asymmetric giant unilamellar vesicles (GUVs). Fluorescence correlation spectroscopy was used to quantitatively characterize vesicle properties. After brain sphingomyelin (bSM) was exchanged into dioleoylphosphatidylcholine (DOPC) GUVs, lateral diffusion in the bSM-containing outer leaflet decreased, whereas that in the DOPC-containing inner leaflet was largely unchanged, confirming asymmetry and a lack of coupling between the physical states of the inner and outer leaflets. In contrast, after bSM was exchanged into brain phosphatidylcholine vesicles, lateral diffusion decreased in both leaflets. Thus, asymmetric GUVs should be useful for investigating the molecular mechanisms behind interleaflet coupling.

Chiantia, Salvatore; Schwille, Petra; Klymchenko, Andrey S.; London, Erwin

2011-01-01

329

Experimental and Modeling Study of Ion Exchange Between Aqueous Solutions and the Zeolite Mineral Clinoptilolite  

Microsoft Academic Search

Ion-exchange experiments were conducted at 25°C between the zeolite mineral clinoptilolite and aqueous solutions of Na+\\/Sr2+ (0.005, 0.05, and 0.5 N), K+\\/Sr2+ (0.05N), and K+\\/Ca2+ (0.05 N). The isotherm data were used to derive equilibrium constants and Gibbs energies for the ion-exchange reactions and Margules parameters for the zeolite solid solution. The Margules model, in combination with the Pitzer equations

Roberto T. Pabalan; F. Paul Bertetti

1999-01-01

330

Study of the Behavior of Inorganic Ion Exchangers in the Treatment of Medium Active Effluents. Pt. 5. The Encapsulation of Inorganic Ion Exchangers in Cement.  

National Technical Information Service (NTIS)

This report describes some results obtained for a generic program of work for the Department of the Environment on the potential application of inorganic ion exchangers for the treatment of medium active effluents. The results from a preliminary investiga...

G. W. Beaven J. E. Cross E. W. Hooper

1988-01-01

331

Retrospective Study of Rapid-Exchange Monorail Versus Over-the-Wire Technique for Femoropopliteal Angioplasty  

SciTech Connect

PurposeThe purpose of this study was to compare procedural outcome of rapid-exchange (RX) monorail versus conventional over-the-wire (OTW) technique for femoropopliteal angioplasty.Materials and MethodsDemographic data, procedure details, angioplasty success, and complications of 328 consecutive percutaneous transluminal angioplasties (PTAs) were collected from a prospective database and retrospectively analyzed. Procedure details included duration of fluoroscopy, area-dose product, amount of contrast agent, sheath sizes, access route, length of stenosis, presence of total occlusion, technical and anatomical success (residual stenosis <30% in the absence of complications), need for bail-out stenting, and periprocedural complications. The RX technique alone was used in 102 of 328 cases (31%); the OTW technique, in 226 of 328 of cases (68%).ResultsTechnical success was 98% for the RX versus 95.4% for the OTW technique (p = 0.2). A significantly greater number of stents had to be implanted due to angioplasty failure when the OTW technique was used (RX, 5.9%; OTW, 13.7%; p = 0.04). There were no significant differences in fluorocopy time, dose-area product, or amount of contrast medium used. The RX system facilitated the use of smaller sheath sizes (5 Fr = 38% and 6 Fr = 59% for RX versus 5 Fr = 16.8% and {>=}6 Fr = 82.5% for OTW) but showed only a tendency toward lower overall complication rates (16.6% [17/102] in the RX group versus 19.9% [45/226] in the OTW group; p = 0.09). There was no effect on length of hospitalization. RX monorail systems were not associated with higher procedural costs when compared to conventional OTW technique.ConclusionWe conclude that RX monorail systems seem to enhance the technical success of femoropopliteal angioplasty. Although smaller sheath sizes can be used due to the lower profile of the RX systems, there is only a tendency toward lower complication rates.

Jahnke, Thomas, E-mail: jahnke@prontomail.com; Schaefer, Jost Philipp; Bolte, Hendrik; Schaefer, Fritz; Michalek, Jens; Charalambous, Nicholas [University Hospital Schleswig-Holstein, Klinik fuer Diagnostische Radiologie (Germany); Sapoval, Marc [Radiologie Vasculaire, Hopital Europeen Georges Pompidou (France); Mueller-Huelsbeck, Stefan [University Hospital Schleswig-Holstein, Klinik fuer Diagnostische Radiologie (Germany)

2008-09-15

332

Ethanolamine base exchange in astrocyte primary cultures: localization and developmental studies.  

PubMed

The enzymatic activities of ethanolamine base exchange (EBEE) and CDP-ethanolamine: 1,2-diacylglycerol ethanolamine phosphotransferase (EPT) were investigated during the growth of rat astrocyte primary cultures. From the 16th day, cells ceased to divide (2.0 X 10(6) cells per culture dish); the total phospholipid (PL) content increased 1.5 fold between the 16th and 24th day (0.20 to 0.30 mumol per mg protein) but the amount of ethanolamine phospholipid (28% of PL content) remained constant. Whereas the specific activity (pmol/min X mg protein) of EPT reached a plateau at 16 days in culture and remained constant (400) thereafter, that of EBEE increased up to the 19th day (190) and decreased gradually to a basal level (75) at the 24th day. EBEE activity was not detected in plasma membranes isolated from 16, 19 and 24 days astrocyte cultures. Sub-cellular fractionation and determination of EBEE specific activities showed that the 104 X 10(3) g fraction (P4) was 4.8 and 8.8 fold enriched at the 16th day and 24th day respectively as compared to the whole cell homogenate (50 and 75). The 7 X 10(3) g (P2) and 17 X 10(3) g (P3) fractions were 8.4 and 7.0 fold enriched respectively at the 19 day in culture. The percentages of the enzymatic activity in the different subcellular fractions were 30, 57.2 and 25.7 for P2 and 39.2, 2.6 and 39.8 for P4 at 16, 19 and 24 days in culture respectively. The activity remained constant in P3 (23%) and was negligible in P1 (6%). Ultrastructural studies revealed that P2 and P3 were enriched in mitochondria while P4 contained essentially microsomes.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:3037404

Mersel, M; el-Achkar, P; Hindelang, C; Mandel, P; Van Dorsselaer, A; Freysz, L

1987-04-01

333

Optimizing Exchange Transfusion for Severe Unconjugated Hyperbilirubinemia: Studies in the Gunn Rat  

PubMed Central

Background Severe unconjugated hyperbilirubinemia carries the risk of neurotoxicity. Phototherapy (PT) and exchange transfusion (ET) are cornerstones in the treatment of unconjugated hyperbilirubinemia. Studies to improve ET efficacy have been hampered by the low application of ET in humans and by the lack of an in vivo model. The absence of an appropriate animal model has also prevented to determine the efficacy of adjunct or alternative treatment options such as albumin (Alb) administration. Aim To establish an in vivo model for ET and to determine the most effective treatment (combination) of ET, PT and Alb administration. Methods Gunn rats received either PT, PT+Alb, ET, ET+PT, ET+PT+Alb or sham operation (each n?=?7). ET was performed via the right jugular vein in ?20 min. PT (18 µW/cm2/nm) was started after ET or at T0. Albumin i.p. injections (2.5 g/kg) were given after ET or before starting PT. Plasma unconjugated bilirubin (UCB), plasma free bilirubin (Bf), and brain bilirubin concentrations were determined. Results We performed ET in 21 Gunn rats with 100% survival. At T1, ET was profoundly more effective in decreasing both UCB ?44%, p<0.01) and Bf ?81%, p<0.05) than either PT or PT+Alb. After 48 h, the combination of ET+PT+Alb showed the strongest hypobilirubinemic effect (?54% compared to ET). Conclusions We optimized ET for severe unconjugated hyperbilirubinemia in the Gunn rat model. Our data indicate that ET is the most effective treatment option, in the acute as well as the follow-up situation.

Schreuder, Andrea B.; Vanikova, Jana; Vitek, Libor; Havinga, Rick; Ahlfors, Charles E.; Hulzebos, Christian V.; Verkade, Henkjan J.

2013-01-01

334

ION EXCHANGE  

EPA Science Inventory

The IONEX program's name is a contraction of "ion exchange." The IONEX program performs calculations related to removing radium and/or uranium from water with the ion exchange process. IONEX provides a quick method of calculating whether a proposed ion exchange process will m...

335

Tank 241-AZ-102 SuperLig 639 Technetium Ion Exchange Eluate Evaporation Study  

Microsoft Academic Search

As part of the Hanford River Protection Project (RPP), the Savannah River Technology Center (SRTC) has conducted tests on the pretreatment and vitrification of a radioactive waste sample from Hanford Tank 241-AZ-102. The original, AZ-102 sample which was received at SRTC was characterized and filtered to remove entrained solids.1 The sample was then passed sequentially through ion exchange columns containing

2001-01-01

336

EPR Studies of Spin-Spin Exchange Processes: A Physical Chemistry Experiment.  

ERIC Educational Resources Information Center

Theoretical background, experimental procedures, and analysis of experimental results are provided for an undergraduate physical chemistry experiment on electron paramagnetic resonance (EPR) linewidths. Source of line broadening observed in a spin-spin exchange process between radicals formed in aqueous solutions of potassium peroxylamine…

Eastman, Michael P.

1982-01-01

337

A numerical and experimental study of chevron, corrugated-plate heat exchangers  

Microsoft Academic Search

In this work, the widely used chevron corrugated-plate heat exchanger was simulated, and the three-dimensional temperature, pressure, and velocity fields were obtained. From the temperature field we can see that in the first zone, the temperature gradient increases gradually and get the maximum; in the central of the flow, the temperature gradient becomes smaller again. The highest temperature appears around

Xiao-Hong Han; Li-Qi Cui; Shao-Jie Chen; Guang-Ming Chen; Qin Wang

2010-01-01

338

Development of a direct contact heat exchanger, phase 1 study report  

Microsoft Academic Search

Electric power generation from geothermal brine requires, first, bringing the hot brine to the surface and then converting the heat to electric power. Binary conversion schemes were proposed, with the heat transfer between the brine and the working organic fluid taking place in a conventional tube and shell heat exchanger. If the brine is heavily laden with dissolved solids, however,

R. Manvi

1978-01-01

339

1H NMR studies of electron exchange rate of Pseudomonas aeruginosa azurin.  

PubMed Central

T1 values of the His-35 C-2 proton resonance of reduced Pseudomonas aeruginosa azurin were determined at 25 degrees C and pH values 4.5, 7.3, and 9.0 in the presence of different fractional amounts of oxidized azurin. The C-2 proton of His-35 undergoes very rapid spin relaxation in oxidized azurin because of its close proximity to the paramagnetic copper. In the presence of oxidized protein, the T1 values of this proton in reduced azurin depend on the lifetime of the reduced protein. From the T1 data, the electron self-exchange rate constant for azurin was calculated to be 1.4 X 10(4) M-1 X s-1, 4.3 X 10(3) M-1 X s-1, and 6.0 X 10(3) M-1 X s-1 at pH values 4.5, 7.3, and 9, respectively. At pH 7.3, the C-2 proton of His-35 is in slow exchange between the imidazole and imidazolium forms and gives rise to two separate resonances at 9.39 and 8.00 ppm. By using these two resonances, the electron self-exchange rate constants were determined separately for the two species of azurin for which the His-35 residue is in the imidazole or the imidazolium forms; results showed that both species participate in self-exchange of electrons with equal efficiency.

Ugurbil, K; Mitra, S

1985-01-01

340

Monte Carlo study of a two-compartment exchange model of diffusion†  

PubMed Central

Multisite exchange models have been applied frequently to quantify measurements of transverse relaxation and diffusion in living tissues. Although the simplicity of such models is attractive, the precise relationship of the model parameters to tissue properties may be difficult to ascertain. Here, we investigate numerically a two-compartment exchange (Kärger) model as applied to diffusion in a system of randomly packed identical parallel cylinders with permeable walls, representing cells with permeable membranes, that may serve particularly as a model for axons in the white matter of the brain. By performing Monte Carlo simulations of restricted diffusion, we show that the Kärger model may provide a reasonable coarse-grained description of the diffusion-weighted signal in the long time limit, as long as the cell membranes are sufficiently impermeable, i.e. whenever the residence time in a cell is much longer than the time it takes to diffuse across it. For larger permeabilities, the exchange time obtained from fitting to the Kärger model overestimates the actual exchange time, leading to an underestimated value of cell membrane permeability.

Fieremans, Els; Novikov, Dmitry S.; Jensen, Jens H.; Helpern, Joseph A.

2010-01-01

341

Structure and energy landscape of a photoswitchable peptide: A replica exchange molecular dynamics study  

Microsoft Academic Search

A replica exchange molecular dy- namics (REMD) simulation of a bicyclic azobenzene peptide in explicit dimethyl sulfoxide solution is presented in order to characterize the conforma- tional structures and energy landscape of a photo- switchable peptide. It is shown that an enhanced- sampling technique such as the REMD method is essential to obtain a converged conformational sam- pling of the

Phuong H. Nguyen; Yuguang Mu; Gerhard Stock

2005-01-01

342

"Actually, I Wanted to Learn": Study-Related Knowledge Exchange on Social Networking Sites  

ERIC Educational Resources Information Center

Social media open up multiple options to add a new dimension to learning and knowledge processes. Particularly, social networking sites allow students to connect formal and informal learning settings. Students can find like-minded people and organize informal knowledge exchange for educational purposes. However, little is known about in which way…

Wodzicki, Katrin; Schwammlein, Eva; Moskaliuk, Johannes

2012-01-01

343

Advanced Coal-Fueled Combustor/Heat Exchanger Technology Study. Final Report, March 1977--June 1978.  

National Technical Information Service (NTIS)

This report is concerned principally with the design of coal-fired combustor/heat exchangers suitable for inputting the heat to base-loaded, closed-cycle, gas turbine, 350 MWe, central station power generation systems. A wide variety of CCGT cycles are ev...

1978-01-01

344

ION EXCHANGE STUDIES ON ACID LEACH LIQUORS FROM DURANGO RESIDUES. Topical Report  

Microsoft Academic Search

Acid leach liquor from Durango residues was treated with ion exchange ; resins for uranium recovery in columnwise operation. Several competitive resins ; were used to determine maximum recovery of uranium under varying conditions of ; pH, degree of reduction, dilution, and flow rate. The results obtained indicate ; that the liquor should be reduced to a potential of approximately

Pickwick; F. Jr

1954-01-01

345

Reaction mechanism and nuclear correlations study by low energy pion double charge exchange.  

National Technical Information Service (NTIS)

In pion double-charge-exchange (DCX) reactions, a positive (negative) pion is incident on a nucleus and a negative (positive) pion emerges. These reactions are of fundamental interest since the process must involve at least two nucleons in order to conser...

Z. Weinfeld

1993-01-01

346

Study of the Possible Relationship of Intrauterine or Exchange Transfusion of Blood to Leukemia in Children.  

National Technical Information Service (NTIS)

The case records of 339 children with acute leukemia between 1965 and 1974 were reviewed for a history of intrauterine or exchange transfusions. Children with other types of neoplasms were used as controls. In addition, the histories of 85 children with n...

M. Haghbin

1977-01-01

347

Optimization of baffl ec onfigurations to prevent aeroacoustic instabilities in heat exchangers: a preliminary study  

Microsoft Academic Search

It is well known that gas heat exchangers are prone to aeroacoustic instabilities, which often lead to severe noise levels, structural vibrations and fatigue. These are unacceptable, as they threaten the component integrity and expose the plant workers to excessive noise levels. Such phenomenon is due to a cooperative interplay between the Karman vortices generated by the cross-flow and the

Miguel Moreira; José Antunes; Martins Paulino; Heitor Pina

348

Ferromagnetic resonance studies of exchange coupled ultrathin Py/Cr/Py trilayers  

NASA Astrophysics Data System (ADS)

Magnetic properties of ultrathin Py/Cr/Py trilayers have been investigated as a function of Cr spacer layer thickness by using ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques. The Cr spacer layer thickness was increased from 4 to 40 A? with 1 A? steps to determine the dependence of interlayer exchange coupling between ferromagnetic layers on the spacer layer thickness. Two strong and well resolved peaks were observed which correspond to a strong (acoustic) and weak (optic) modes of magnetization precession in the effective dc field due to the exciting external microwave field as the external dc field orientation comes close to the film normal. The separation of the two modes in the field axis depends on the thickness of Cr spacer layer. An interchange in the relative positions of the acoustic and optic modes has been observed for a particular thickness of Cr spacer layer as well. A computer program for magnetically exchange coupled N magnetic layers was written to simulate the experimental FMR spectra and to obtain the magnetic parameters of ultrathin Py/Cr/Py trilayers. FMR data have been analyzed from every aspect by using this program and interlayer exchange coupling constant was calculated for the prepared structures. It was found that the relative position of the peaks depends on the nature (sign) of the interlayer exchange coupling between ferromagnetic layers through Cr spacer layer. In Py/Cr/Py trilayers, strength of the interlayer exchange coupling constant oscillates and changes its sign with Cr spacer layer thickness with a period of about 11 A?.

Topkaya, R.; Erkovan, M.; Öztürk, A.; Öztürk, O.; Akta?, B.; Özdemir, M.

2010-07-01

349

A multicenter study of noncompliance with continuous ambulatory peritoneal dialysis exchanges in US and Canadian patients.  

PubMed

Recent evidence suggested that noncompliance (NC) with continuous ambulatory peritoneal dialysis (CAPD) exchanges may be more common in US than in Canadian dialysis centers. This issue was investigated using a questionnaire-based method in 656 CAPD patients at 14 centers in the United States and Canada. NC was defined as missing more than one exchange per week or more than two exchanges per month. Patients were ensured of the confidentiality of their individual results. Mean patient age was 56 +/- 16 years, 52% were women, and 39% had diabetes. The overall admitted rate of NC was 13%, with a rate of 18% in the United States and 7% in Canada (P < 0.001). NC was more common in younger patients (P < 0.0001), those without diabetes (P < 0.001), and employed patients (P < 0.05). It was also more common in black and Hispanic than in Asian and white patients (P < 0.001). NC was more common in patients prescribed more than four exchanges daily (P < 0.0001) but was not affected by dwell volume. On multiple regression analysis, the independent predictors of NC, in order of importance, were being prescribed more than four exchanges per day, black race, being employed, younger age, and not having diabetes. Being treated in a US unit did not quite achieve significance as a multivariate independent predictor. These findings suggest that NC is not uncommon in CAPD patients and is more frequent in US than in Canadian patients. However, country of residence is less powerful as a predictor of NC than a variety of other demographic and prescription factors. PMID:10692278

Blake, P G; Korbet, S M; Blake, R; Bargman, J M; Burkart, J M; Delano, B G; Dasgupta, M K; Fine, A; Finkelstein, F; McCusker, F X; McMurray, S D; Zabetakis, P M; Zimmerman, S W; Heidenheim, P

2000-03-01

350

The adsorption of nitrogen oxides and water on rare-earth ion-exchanged ZSM-5: a density functional study  

Microsoft Academic Search

In this study, we present the adsorption behavior of NO, NO2 and H2O on trivalent rare-earth ion-exchanged ZSM-5 (RE-ZSM-5; RE=La, Ce, Nd, Sm, Gd and Dy) using density functional theory. The results show that Ce-ZSM-5 is more effective for the activation of NOx than La-ZSM-5 and Nd-ZSM-5, which is in good agreement with experimental results. The present investigation also suggests

Y. Luo; Xiaohong Wan; Yuki Ito; Seiichi Takami; Momoji Kubo; Akira Miyamoto

2002-01-01

351

Classical trajectory studies of alkali atom-alkali dimer exchange reactions : Na Li2 and Li Na2  

Microsoft Academic Search

The endoergic and exoergic alkali atom-alkali dimer exchange reactions, Na+Li2-->NaLi+Li and Li+Na2-->LiNa+Na, have been studied using classical trajectory methods on LEPS surfaces exhibiting shallow potential wells at small internuclear separations. For both systems the total reaction cross section, collision lifetime, differential reaction cross section and product energy disposal were calculated for a range of initial collisional energies. Comparison with the

J. C. Whitehead

1976-01-01

352

Numerical study of an ion-exchanged glass waveguide using both two-dimensional and three-dimensional models  

Microsoft Academic Search

A numerical study is carried out to compare the two-dimensional (2-D) case and three-dimensional (3-D) case for the modelling of an ion-exchanged glass waveguide. It is shown that different waveguide widths on the photomask correspond to different ion concentration distributions after an annealing process. A numerical example is presented of two waveguide sections with different widths indicates that due to

Pengfei Wang; Yuliya Semenova; Jie Zheng; Qiang Wu; Agus Muhamad Hatta; Gerald Farrell

2011-01-01

353

Numerical Study of an Ion-Exchanged Glass Waveguide Using Both Two-Dimensional and Three-Dimensional Models  

Microsoft Academic Search

A numerical study is carried out to compare the two-dimensional (2-D) case and three-dimensional (3-D) case for the modelling of an ion-exchanged glass waveguide. It is shown that different waveguide widths on the photomask correspond to different ion concentration distributions after an annealing process. A numerical example is presented of two waveguide sections with different widths indicates that due to

Pengfei Wang; Yuliya Semenova; Jie Zheng; Qiang Wu; Agus Hatta; Gerald Farrell

2010-01-01

354

Surface magnetic phase transition of the double-exchange ferromagnet: Schwinger-boson mean-field study  

SciTech Connect

Surface magnetic phase transition of a double-exchange model for colossal magnetoresiscance manganites is studied using a Schwinger-boson mean-field method. About three unit cell wide surface layers are identified. The magnetic moment in these layers decreases more rapidly than that in the bulk when temperature is increased. This behavior is consistent with experimental observations. Are also discussed implication to the tunneling magnetoresistance effect using manganites and possible improvement of the magnetoresistance effect near bulk Curie temperature.

Okamoto, Satoshi [ORNL

2009-01-01

355

Solid-state NMR studies of methanol-to-aromatics reaction over silver exchanged HZSM-5 zeolite  

Microsoft Academic Search

Solid-state NMR spectroscopy was used to study the conversion of methanol to aromatics (MTA) over silver exchanged HZSM-5 zeolites. It is the silver oxide rather than silver cation that plays a crucial role for the MTA reaction. The aromatic products (mainly toluene and benzene) are formed at the expense of the small alkanes (mainly propane and isobutane). AgZSM-5 zeolite calcined

Danlin Zeng; Jun Yang; Jiqing Wang; Jun Xu; Yongxia Yang; Chaohui Ye; Feng Deng

2007-01-01

356

Exchange interaction in binuclear complexes with rare-earth and copper ions: A many-body model study  

Microsoft Academic Search

We have used a many-body model Hamiltonian to study the nature of the magnetic ground state of heterobinuclear complexes involving rare-earth and copper ions. We have taken into account all diagonal repulsions involving the rare-earth 4f and 5d orbitals and the copper 3d orbital. In addition, we have included direct exchange interaction, crystal field splitting of the rare-earth atomic levels

Indranil Rudra; C. Raghu; S. Ramasesha

2002-01-01

357

A comparative study of linear and non-linear regression analysis for ammonium exchange by clinoptilolite zeolite  

Microsoft Academic Search

Ammonium ion exchange from aqueous solution using clinoptilolite zeolite was investigated at laboratory scale. Batch experimental studies were conducted to evaluate the effect of various parameters such as pH, zeolite dosage, contact time, initial ammonium concentration and temperature. Freundlich and Langmuir isotherm models and pseudo-second-order model were fitted to experimental data. Linear and non-linear regression methods were compared to determine

Dogan Karadag; Yunus Koc; Mustafa Turan; Mustafa Ozturk

2007-01-01

358

The Effectiveness of the Picture Exchange Communication System (PECS) for Children with Autism Spectrum Disorder (ASD): A South African Pilot Study  

ERIC Educational Resources Information Center

This study investigated the effects of introducing the Picture Exchange Communication System (PECS) on the frequency of requesting and commenting and the length of verbal utterances of two children with autism spectrum disorder (ASD) who presented with some spoken language, but limited use of language in communicative exchanges. A mixed research…

Travis, Julia; Geiger, Martha

2010-01-01

359

International Trade Price Stickiness and Exchange Rate Pass-through in Micro Data: A Case Study on US-China Trade.  

National Technical Information Service (NTIS)

The interaction between the exchange rate regime, trade rms' price-setting behavior, and exchange rate pass-through (ERPT) is an important topic in international economics. This paper studies this using a goods-level dataset of US-China trade prices colle...

D. Nam J. Wang J. Wu M. Kim

2013-01-01

360

Spectroscopic studies of Fe(III) ion-exchanged ETS-10 and ETAS-10 molecular sieves  

SciTech Connect

Two new titanium silicate molecular sieves, designated ETS-10 and ETAS-10, have been ion-exchanged with Fe(III). Both products exhibit prominent EPR signals, at g = 6.0 and 4.3, that are assigned to populations of ferric iron on the surface and in the interior cavities, respectively, of the molecular sieve microcrystals. Corollary XPS measurements on these samples indicate that a substantial fraction of the surface iron is present as Fe(II). Chemical modification procedures have been explored in an effort to produce ion-exchanged materials containing no exterior iron. Acid treatment (pH 1.0) proved to be an effective means of achieving this goal in the case of ETS-10-based materials. ETAS-10-based samples do not retain their crystallinity under these conditions. 35 refs., 4 figs., 2 tabs.

Sommerfeld, D.A.; Ellis, W.R. Jr.; Eyring, E.M. [Univ. of Utah, Salt Lake City, UT (United States)] [and others

1992-11-26

361

A comparative study of chelating and cationic ion exchange resins for the removal of palladium(II) complexes from acidic chloride media.  

PubMed

The increasing demand for palladium for technological application requires the development of ion exchange chromatography. Recently ion exchange chromatography has developed largely as a result of new types of ion exchangers available on the market of which two types are widely applied. One of them are selective (chelating) and modified ion exchangers and the other one are liquid exchangers. Two types of ion exchange resins such as chelating (Lewatit TP 214, Purolite S 920) and cationic (Chelite S, Duolite GT 73) ion exchangers are used for the recovery of palladium(II) complexes from chloride media (0.1-2.0M HCl-1.0M NaCl-0.0011 M Pd(II); 0.1-2.0M HCl-2.0M NaCl-0.0011M Pd(II)). The influence of concentration of hydrochloric acid, sodium chloride as well as the phase contact time on the degree of recovery of palladium(II) complexes was studied. Moreover, the amount of palladium(II) chlorocomplexes sorbed onto ion exchangers, the working ion exchange capacities and the weight and bed distribution coefficients were calculated in order to judge which of two types of resins possesses the best performance towards palladium(II) complexes. PMID:18980805

Hubicki, Zbigniew; Wo?owicz, Anna

2009-05-30

362

Sorption of levulinic acid onto weakly basic anion exchangers: Equilibrium and kinetic studies  

Microsoft Academic Search

The equilibrium and dynamics of levulinic acid sorption on two weakly basic anion exchangers, in free base form, in single-component aqueous solutions were investigated. Adsorption isotherms such as Langmuir, Sips, Radke–Prausnitz, and Toth were applied to correlate the experimental data in the temperature range 285–315 K. Modeling results showed that the Toth model is the best one to correlate the sorption

Bao-Jian Liu; Qi-Long Ren

2006-01-01

363

Conceptual design study for the HCRF direct contact heat exchanger modification  

Microsoft Academic Search

The conceptual design of sieve trays for modifying the HCRF direct contact heat exchanger was developed as follows. The models of the prior work, EG&G subcontract No. K-7752, were extended and modified so the predicted heat transfer coincided with the experimental data of the 60 KW Raft River tests conducted by EG&G. Using these models, a hole diameter of 0.25

E. F. Wahl

1984-01-01

364

The Relationship between Corporate Governance Indicators and Firm Value : A Case Study of Karachi Stock Exchange  

Microsoft Academic Search

We investigated whether differences in quality of firm-level corporate governance can explain the firm-level performance in a cross-section of companies listed at Karachi Stock Exchange. Therefore, we analysed the relationship between firm-level value as measured by Tobins Q and total Corporate Governance Index (CGI) and three sub-indices : Board, Shareholdings and Ownership, and Disclosures and Transparency for a sample of

Attiya Y. Javed; Robina Iqbal

2007-01-01

365

A gas-exchange study of photosynthesis and isoprene emission in Quercus rubra L  

Microsoft Academic Search

We have investigated the signals which affect the rate of isoprene emission from photosynthesizing leaves of red oak (Quercus rubra L.) using analytical gas-exchange techniques, chlorophyll-fluorescence measurements, and inhibitor feeding. Isoprene emission\\u000a increased with increasing photon flux density at low CO2 but much less so at high CO2 partial pressure. Photosynthetic CO2 assimilation exhibited the opposite behavior. In CO2-free air,

Francesco Loreto; Thomas D. Sharkey

1990-01-01

366

Study of superparamagnetic clusters in Co2+-exchanged NaY zeolite  

Microsoft Academic Search

Magnetic properties of Co2+-exchanged NaY zeolite have been investigated using a dc magnetization technique. In the presence of low applied magnetic fields, a difference between zero-field-cooled and field-cooled magnetizations is observed below ~3.4 K. At T>5 K, the M vs H\\/T curves superimpose and these curves could be fitted well using the Langevin function, which yields a saturation moment of

M. D. Mukadam; S. M. Yusuf; R. Sasikala; S. K. Kulshreshtha

2006-01-01

367

Study of superparamagnetic clusters in Co2+-exchanged NaY zeolite  

Microsoft Academic Search

Magnetic properties of Co2+-exchanged NaY zeolite have been investigated using a dc magnetization technique. In the presence of low applied magnetic fields, a difference between zero-field-cooled and field-cooled magnetizations is observed below ?3.4 K. At T>5 K, the M vs H?T curves superimpose and these curves could be fitted well using the Langevin function, which yields a saturation moment of

M. D. Mukadam; S. M. Yusuf; R. Sasikala; S. K. Kulshreshtha

2006-01-01

368

Study by XPS of different conditioning processes to improve the cation exchange in clinoptilolite  

Microsoft Academic Search

We report the X-ray photoelectron spectroscopy (XPS) analysis of natural clinoptilolite from a mine in Sonora, México. From these measurements we determined the chemical state and binding energy of the elements in the zeolite framework and of those in the extra framework sites. The analysis was done on natural clinoptilolite and on cation-exchanged clinoptilolites with Na+ and NH4+ ions. Complementary

D. Ruiz-Serrano; M. Flores-Acosta; E. Conde-Barajas; D. Ramírez-Rosales; J. M. Yáñez-Limón; R. Ramírez-Bon

2010-01-01

369

A model theoretical study on ligand exchange reactions of CooA.  

PubMed

Rr-CooA is a CO-sensor heme protein, where binding of CO with the heme group stimulates a transcriptional activator activity of CooA. In this process, the heme undergoes a series of ligand exchanges. In the ferric form, the heme has Cys75 and Pro2 as the axial ligands. In the reduced ferrous form, the heme has His77 instead of Cys75 as an axial ligand with Pro2. Only in the reduced form, CooA can bind CO that replaces Pro2. Model calculations are carried out to elucidate the ligand exchange reactions of CooA. The coordinated proline is found to be the neutral, protonated form. The ligand exchange of cysteine for histidine is reproduced by a relatively small model. This exchange would be mainly due to difference in stability of the non-bonding sulfur p-orbital in Cys75 between the ferric and ferrous states. The selectivity of gas molecules among CO, NO, and O2 in the proteins is explained by the relative stability of products for Rr-CooA. This is also the case for Ch-CooA, where the amino group of the N-terminus and a histidine are coordinated to the iron ion both in the ferric and ferrous states. The ability to bind the gas molecules is a little stronger in Rr-CooA than in Ch-CooA. In the ferric form of Rr-CooA, heme is deformed to a ruffled form whereas heme is planar in the ferrous form, which leads to a red-shifted Q-band in the former. PMID:23511331

Ishida, Toshimasa; Aono, Shigetoshi

2013-04-28

370

Numerical study on the operational performance of spray column direct contact heat exchangers  

Microsoft Academic Search

Spray columns have received considerable attention as direct contact heat exchangers due to their potential high throughput,\\u000a as well as their near perfect counterflow operations if one-dimensional flow is obtainable. In practice, the degree of success\\u000a in obtaining one-dimensional flow has depended on the design of the injectors for the disperse and continuous phases. In the\\u000a past, the design of

Chong Bo Kim; H. R. Jacobs

1987-01-01

371

An experimental study of a three-phase, direct-contact heat exchanger  

Microsoft Academic Search

An experimental pilot scale three-phase, direct-contact heat exchanger was constructed and tested. Experiments were performed using normal pentane as the dispersed phase and water as the continuous phase. The inlet water temperatures ranged from 75 to 88°C, and the inlet pentane temperatures varied from 23 to 38°C. The volumetric heat transfer coefficient, hold-up and heat flow-rate are functions of pentane

J. Siqueiros; O. Bonilla

1999-01-01

372

Atom exchange between aqueous Fe(II) and goethite: an Fe isotope tracer study.  

PubMed

The reaction of aqueous Fe(II) with Fe(III) oxides is a complex process, comprising sorption, electron transfer, and in some cases, reductive dissolution and transformation to secondary minerals. To better understand the dynamics of these reactions, we measured the extent and rate of Fe isotope exchange between aqueous Fe(II) and goethite using a 57Fe isotope tracer approach. We observed near-complete exchange of Fe atoms between the aqueous phase and goethite nanorods over a 30-day time period. Despite direct isotopic evidence for extensive mixing between the aqueous and goethite Fe, no phase transformation was observed, nor did the size or shape of the goethite rods change appreciably. High-resolution transmission electron microscopy images, however, appear to indicate that some recrystallization of the goethite particles may have occurred. Near-complete exchange of Fe between aqueous Fe(II) and goethite, coupled with negligible change in the goethite mineralogy and morphology, suggests a mechanism of coupled growth (via sorption and electron transfer) and dissolution at separate crystallographic goethite sites. We propose that sorption and dissolution sites are linked via conduction through the bulk crystal, as was recently demonstrated for hematite. Extensive mixing between aqueous Fe(II) and goethite, a relatively stable iron oxide, has significant implications for heavy metal sequestration and release (e.g., arsenic and uranium), as well as reduction of soil and groundwater contaminants. PMID:19320165

Handler, Robert M; Beard, Brian L; Johnson, Clark M; Scherer, Michelle M

2009-02-15

373

Studies in the reaction-separation method for the preparation of barium chloride from barite using ion exchange  

SciTech Connect

The authors report the application of an ion-exchange process as a reaction-separation strategy for the preparation of barium chloride from barite ore and sodium chloride. Experimental studies were carried out to evaluate the process efficiency and purity/yield of barium chloride using a strong acid cation-exchange resin, Tulsion T-42. The effects of various process parameters such as concentration of barium sulfide and concentration of sodium chloride were investigated, and optimization of the experimental variables was attempted. The results indicate the developed strategy to be attractive and an alternative route to existing processes. The methodology developed has large potential for the inorganic chemical process industry in general.

Gokarn, A.N.; Gaikwad, A.G.; Phalak, C.A.; Bhandari, V.M. [National Chemical Lab., Pune (India). Chemical Engineering Div.] [National Chemical Lab., Pune (India). Chemical Engineering Div.

1999-06-01

374

Report on the round table session on: Near surface analysis and charge exchange studies with high-resolution spectrographs  

NASA Astrophysics Data System (ADS)

This note is a report on the round table session on near-surface analysis and charge exchange studies with high-resolution spectrographs, with contributions from: H.D. Carstanjen, Max-Planck Institut für Metallforschung, Stuttgart, Germany (see separate contribution to these proceedings, H.D. Carstanjen, Overview of existing high resolution spectrographs.). P. Sigmund, Physics Department, Odense University, Denmark (see separate contribution to these proceedings, P. Sigmund, L. Glazov, Energy loss and charge exchange: Statistics and atomistics.). W.M. Arnoldbik, Debye Institute, Utrecht University, The Netherlands G. Dollinger, Technical University Munich, Germany K. Kimura, Department of Engineering Science, Kyoto University, Japan O. Kruse, Forschungszentrum Rossendorf, Dresden, Germany T. Gustafsson, Dept. of Physics and Astronomy, Rutgers University, Piscataway, USA I. Yamada, Dept of Ion Beam Engineering, Kyoto University, Japan R. Behrisch, Max Planck Institut für Plasmaphysik, Garching, Germany

Boerma, D. O.

1998-03-01

375

The Benefits of Past and Current Regional Hydroclimate Projects to the Third Pole Environment (TPE) Water and Energy Exchanges Studies  

NASA Astrophysics Data System (ADS)

To improve understanding of the various processes at work on spatial and temporal scales from regional to global the Regional Hydroclimate Projects (RHP's) are established as part of the Global Energy and Water Exchanges (GEWEX)Project to link the regional observations and process understanding to the global scale. This is done through exchange of observations, data, modeling, transferability studies etc. In this presentation the series of RHP's that were underway over North and South America, Europe and Asia continuously from the early 1990's up to the present will be examined, the reasons they were established, how they evolved and how they are evolving or are likely to evolve in the future, with an emphasis on where they can and should benefit similar work proposed for the TPE. The results will be presented in the context of the World Climate Research Programme (WCRP) Grand Challenge related to the development of a water strategy that addresses the issue of past and future changes in Water, in general, and the GEWEX science question on global water resource systems, in particular. This material will address issues associated with how changes in land surface and hydrology influence past and future changes in water availability and security, how new observations lead to improvements in water management and how models become better in global and regional climate predictions and projections of precipitation and how these outcomes relate to the TPE Water and Energy Exchanges Studies.

Benedict, Sam; van Oevelen, Peter

2014-05-01

376

Kinetics and utilization studies of the oxygen reduction and hydrogen oxidation reactions in a proton exchange membrane fuel cell  

NASA Astrophysics Data System (ADS)

The current/voltage relation of a proton exchange membrane fuel cell (PEMFC) has been austerely studied through carefully designed experiments to support models developed theoretically using kinetic, thermodynamic and mass transport principles. In order to develop a complete model description of voltage losses for a PEMFC gas phase mass transport free environment, individual experiments on; (i) the kinetics of the hydrogen oxidation reaction (HOR); (ii) the kinetic dependence of the oxygen reduction reaction (ORR), occurring on a PVC catalyst, on oxygen partial pressure and cell temperature; (iii) the voltage loss associated with proton transport and distribution of the oxygen reduction reaction in a porous proton exchange membrane fuel cell cathode; (iv) the effect of relative humidity, or water content, on the kinetics of the oxygen reduction reaction were performed. These studies revealed that; (i) the voltage loss associated with the HOR is negligible due to its very high exchange current density (235--600 mA/cm2), (ii) the exchange current density, activation energy, and reaction order for the ORR are 2.5 x 10-8 A/cm2, 67 kJ/mol, and 0.5 respectively, (iii) the voltage loss resulting from a balance of proton transport and oxygen reduction reaction kinetics can be precisely predicted using a simple figure (4.2), which was developed from a solution to the conservation of charge equation in the cathode electrode and (iv) the effect of RH on ORR kinetics is negligible above 60% relative humidity. A PEMFC model that can accurately depict the voltage loss associated with each of the above material/process relationships was developed using differential cell experiments (i.e., experiments in which concentrations of reactants and products varied in only the through plane direction) and corresponding simplified 1-D models.

Neyerlin, Kenneth Charles (K. C.)

377

Study of Np(V) Sorption by Ionic Exchange on Na, K, Ca and Mg-Montmorillonite  

NASA Astrophysics Data System (ADS)

The transport behavior of actinides in soil and ground water are highly influenced by clay minerals due to their ubiquity in the environment, reactivity and colloidal properties. Neptunium(V) has been introduced in the environment as a result of nuclear weapons testing [e.g. 1, 2] and is a radionuclide of potential interest for safety assessment of high level radioactive waste disposal because its long half-life and high toxicity [3]. Surface complexation and ionic exchange have been identified as Np(V) sorption mechanisms onto montmorillonite. At pH below 5, Np(V) sorption is mainly attributed to ionic exchange. This study examines Np(V) ion exchange on Na, K, Ca and Mg forms of montmorillonite. Experiments were carried out using 237Np concentrations between 2 x 10-8 M and 5 x 10-6 M at three different ionic strengths 0.1, 0.01 and 0.001M. The pH was maintained at 4.5. Np(V) sorption to montmorillonite homoionized with monovalent cations (Na and K) demonstrated a markedly different behavior to that observed for montmorillonite homoionized with divalent cations (Ca and Mg). Np sorption to Na and K-montmorillonite was greater than Np sorption to Ca and Mg-montmorillonite. Isotherms with Na and K-montmorillonite showed a strong dependence on ionic strength: the percentage of Np adsorbed was near zero at 0.1M ionic strength, but increased to 30% at 0.001 M ionic strength. This suggests ionic exchange is the main Np adsorption mechanism under the experimental conditions investigated. Dependence on ionic strength was not observed in the Np sorption isotherms for Ca and Mg-montmorillonite indicating a low exchange capacity between Np and divalent cations. Modeling of the sorption experimental data will allow determination of the Na+?NpO2+ and K+?NpO2+ ionic exchange constants on montmorillonite. References: [1] A. R. Felmy; K. J. Cantrell; S. D. Conradson, Phys. Chem. Earth 2010, 35, 292-297 [2] D. K. Smith; D. L. Finnegan; S. M. Bowen, J. Environ. Radioact. 2003, 67, (1), 35-51 [3] N. Kozai; T. Ohnuki; S. Muraoka, J. Nucl. Sci. Technol. 1993, 30, (11), 1153-1159 This work was funded by U. S. DOE Office of Biological & Environmental Sciences, Subsurface Biogeochemistry Research Program, and performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Security, LLC under Contract DE-AC52-07NA27344. A. Benedicto was supported by a Spanish Ministry of Science and Innovation 'FPI' pre-doctoral contract in CIEMAT (Spain). LLNL-ABS-570160

Benedicto, A.; Begg, J.; Zhao, P.; Kersting, A. B.; Zavarin, M.

2012-12-01

378

Higher Education Exchange, 2005  

ERIC Educational Resources Information Center

The "Higher Education Exchange" is part of a movement to strengthen higher education's democratic mission and foster a more democratic culture throughout American society. Working in this tradition, the "Higher Education Exchange" publishes case studies, analyses, news, and ideas about efforts within higher education to develop more democratic…

Brown, David W., Ed; Witte, Deborah, Ed.

2005-01-01

379

Higher Education Exchange, 2010  

ERIC Educational Resources Information Center

"Higher Education Exchange" publishes case studies, analyses, news, and ideas about efforts within higher education to develop more democratic societies. Contributors to this issue of the "Higher Education Exchange" examine whether institutions of higher learning are doing anything to increase the capacity of citizens to shape their future.…

Brown, David W., Ed.; Witte, Deborah, Ed.

2010-01-01

380

Higher Education Exchange, 2008  

ERIC Educational Resources Information Center

"Higher Education Exchange" publishes case studies, analyses, news, and ideas about efforts within higher education to develop more democratic societies. Contributors to this issue of the "Higher Education Exchange" examine whether institutions of higher learning are doing anything to increase the capacity of citizens to shape their future.…

Brown, David W., Ed.; Witte, Deborah, Ed.

2008-01-01

381

Higher Education Exchange, 2007  

ERIC Educational Resources Information Center

"Higher Education Exchange" publishes case studies, analyses, news, and ideas about efforts within higher education to develop more democratic societies. Contributors to this issue of the "Higher Education Exchange" discuss the concept of growing public scholars; each contribution incorporates a student component. Articles include: (1) "Foreword"…

Brown, David W., Ed.; Witte, Deborah, Ed.

2007-01-01

382

Higher Education Exchange, 2004  

ERIC Educational Resources Information Center

The Higher Education Exchange is part of a movement to strengthen higher education's democratic mission and foster a more democratic culture throughout American society. Working in this tradition, the Higher Education Exchange publishes case studies, analyses, news, and ideas about efforts within higher education to develop more democratic…

Brown, David W., Ed; Witte, Deborah, Ed.

2004-01-01

383

Higher Education Exchange, 2012  

ERIC Educational Resources Information Center

"Higher Education Exchange" publishes case studies, analyses, news, and ideas about efforts within higher education to develop more democratic societies. Contributors to this issue of the "Higher Education Exchange" examine whether institutions of higher learning are doing anything to increase the capacity of citizens to shape their future.…

Brown, David W., Ed.; Witte, Deborah, Ed.

2012-01-01

384

Higher Education Exchange, 2011  

ERIC Educational Resources Information Center

"Higher Education Exchange" publishes case studies, analyses, news, and ideas about efforts within higher education to develop more democratic societies. Contributors to this issue of the "Higher Education Exchange" examine whether institutions of higher learning are doing anything to increase the capacity of citizens to shape their future.…

Brown, David W., Ed.; Witte, Deborah, Ed.

2011-01-01

385

Ion exchange and dehydration experimental studies of clinoptilolite: Implications to zeolite dating  

SciTech Connect

Variable effects were noted on the argon (Ar) and potassium (K) contents of clinoptilolite fractions used in ion-exchange and dehydration experiments. The K contents of clinoptilolite fractions were differently affected during cation exchange with Ca-, Cs-, K-, and Na-chloride solutions. Ar was generally less affected during these experiments, except for a Na-clinoptitolite fraction exchanged for five days. Loss of Ar during organic heavy-liquid treatment and cleaning using acetone and deionized water does occur, as indicated by comparing the amounts of radiogenic Ar of treated and untreated fractions. Moreover, a regular decrease in radiogenic Ar contents was noted in clinoptilolite fractions during dehydration experiments at different temperatures for 16 hours. Comparable losses do not occur from saturated samples that were heated in 100 C for more than five months. Water appears to play a vital role in stabilizing the clinoptilolite framework structure and in the retention of Ar. The radiogenic Ar depletion pattern noted in clinoptilolite fractions dehydrated in unsaturated environment at different temperatures is similar to variations in the amount of radiogenic Ar observed in clinoptilolite samples from the unsaturated zone of an altered tuff. These results can be used to evaluate the extent of zeolitic water (and hence Ar) retention in unsaturated geologic settings. The utility of alkali zeolites (e.g., phillipsite, clinoptilolite, and mordenite) from low-temperature, open-hydrologic alteration as potential dateable minerals was evaluated using the K/Ar method as part of the Yucca Mountain Site Characterization Project, which is evaluating Yucca Mountain, Nevada, as a potential high-level radioactive waste repository site.

WoldeGabriel, G.

1995-02-01

386

Kinetic study on the reaction between CO2-CO and wustite using the isotope exchange method  

NASA Astrophysics Data System (ADS)

To investigate the reaction between CO2-CO and wustite using the isotope exchange method at 1073, 1173, 1273, and 1373 K, the experiment apparatus was designed to simulate the fluidized bed. The chemical rate constant was estimated by considering the effect of gas phase mass transfer on the reaction. It is found that the chemical rate constant is inversely decreased with the increase in the ratio of CO2/CO by volume. The activation energy of reaction is in a linear relationship with the ratio of CO2/CO by volume, and the average activation energy is 155.37 kJ/mol.

Zhang, Teng; Hu, Xiao-jun; Chou, Kuo-Chih

2013-02-01

387

Spin-polarized tunneling study of s-f exchange in superconductors  

SciTech Connect

Spin-polarized tunneling into the side of an Al film covered with a submonolayer of Gd reveals the presence of the localized Ruderman-Kittel-Kasuya-Yosida spin polarization in the normal state and its absence in the superconducting state. This result is attributed to the fact that the long-range part of the spin susceptibility in the superconductor vanishes at low temperature. The exchange constant is derived from the Zeeman splitting of the superconductor density of states, and its value agrees with that obtained from the Abrikosov-Gor'kov theory.

Tkaczyk, J.E.; Tedrow, P.M.

1988-09-05

388

Quantitating the statistical distribution of deuterium incorporation to extend the utility of H/D exchange MS data.  

PubMed

Measuring the statistical distribution of deuterium incorporated into enzymatically derived peptide fragments provides a valuable dimension to hydrogen/deuterium exchange mass spectrometry data. In this paper, we will discuss our improvement to the linear least-squares method for determining this distribution, through the addition of "zeroes" to the end of the deuterated isotopic envelope, to partially compensate for data truncation due to finite instrumental signal-to-noise ratios. The value of the distribution is demonstrated in a simple experimental example, where the linearity between average deuteration and percent D2O used to label test peptides hides a more complex relationship between the site-labeling probability and the total number of sites. This method offers the opportunity to resolve cases where a single peptide experiences distinct, independent biochemical states with each bearing a unique average deuteration; this can occur when a protein is modified to substoichiometric levels. From the experimentally determined distribution of a heterogeneously deuterated peptide, it was possible to extract the average deuteration of each component of the mixture. PMID:16383329

Chik, John K; Vande Graaf, Jaclyn L; Schriemer, David C

2006-01-01

389

Double-exchange model study of multiferroic RMnO3 perovskites  

SciTech Connect

In this proceeding, recent theoretical investigations by the authors on the multiferroic RMnO3 perovskites are briefly reviewed at first. Using the double-exchange model, the realistic spiral spin order in undoped manganites such as TbMnO3 and DyMnO3 is well reproduced by incorporating a weak nextnearest neighbor superexchange ( 10% of nearest neighbor superexchange) and moderate Jahn-Teller distortion. The phase transitions from the A-type antiferromagnet (as in LaMnO3), to the spiral phase (as in TbMnO3), and finally to the E-type antiferromagnet (as in HoMnO3), with decreasing size of the R ions, were also explained. Moreover, new results of phase diagram of the three-dimensional lattice are also included. The ferromagnetic tendency recently discovered in the LaMnO3 and TbMnO3 thin films is explained by considering the substrate stress. Finally, the relationship between our double-exchange model and a previously used J1-J2-J3 model is further discussed from the perspective of spin wave excitations.

Dong, Shuai [ORNL; Yu, Rong [ORNL; Yunoki, Seiji [RIKEN, Japan; Liu, J.-M. [Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing; Dagotto, Elbio R [ORNL

2009-01-01

390

Enhancing the quality of H/D exchange measurements with mass spectrometry detection in disulfide-rich proteins using electron capture dissociation.  

PubMed

Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) has become a potent technique to probe higher-order structures, dynamics, and interactions of proteins. While the range of proteins amenable to interrogation by HDX MS continues to expand at an accelerating pace, there are still a few classes of proteins whose analysis with this technique remains challenging. Disulfide-rich proteins constitute one of such groups: since the reduction of thiol-thiol bonds must be carried out under suboptimal conditions (to minimize the back-exchange), it frequently results in incomplete dissociation of disulfide bridges prior to MS analysis, leading to a loss of signal, inadequate sequence coverage, and a dramatic increase in the difficulty of data analysis. In this work, the dissociation of disulfide-linked peptide dimers produced by peptic digestion of the 80 kDa glycoprotein transferrin in the course of HDX MS experiments is carried out using electron capture dissociation (ECD). ECD results in efficient cleavage of the thiol-thiol bonds in the gas phase on the fast LC time scale and allows the deuterium content of the monomeric constituents of the peptide dimers to be measured individually. The measurements appear to be unaffected by hydrogen scrambling, even when high collisional energies are utilized. This technique will benefit HDX MS measurements for any protein that contains one or more disulfides and the potential gain in sequence coverage and spatial resolution would increase with disulfide bond number. PMID:24820935

Bobst, Cedric E; Kaltashov, Igor A

2014-06-01

391

Membrane protein dynamics: limited lipid control  

Microsoft Academic Search

Correlation of lipid disorder with membrane protein dynamics has been studied with infrared spectroscopy, by combining data characterizing lipid phase, protein structure and, via hydrogen-deuterium (H\\/D) exchange, protein dynamics. The key element was a new measuring scheme, by which the combined effects of time and temperature on the H\\/D exchange could be separated. Cyanobacterial and plant thylakoid membranes, mammalian mitochondria

Balázs Szalontai

2009-01-01

392

Leach studies on cement-solidified ion exchange resins from decontamination processes at operating nuclear power stations  

SciTech Connect

The effects of varying pH and leachant compositions on the physical stability and leachability of radionuclides and chelating agents were determined for cement-solidified decontamination ion-exchange resin wastes collected from two operating commercial light water reactors. Small scale waste-form specimens were collected during waste solidifications performed at the Brunswick Steam Electric Plant Unit 1 and at the James A. FitzPatrick Nuclear Power Station. The collected specimens were leach tested, and their compressive strength was measured in accordance with the Nuclear Regulatory Commission's Technical Position on Waste Form'' (Revision 1), from the Low-Level Waste Management Branch. Leachates from these studies were analyzed for radionuclides, selected transition metals, and chelating agents to assess the leachability of these waste form constituents. Leachants used for the study were deionized water, simulated seawater, and groundwater compositions similar to those found at Barnwell, South Carolina and Hanford, Washington. Results of this study indicate that initial leachant pH does not affect leachate pH or releases from cement-solidified decontamination ion-exchange resin waste forms. However, differences in leachant composition and the presence of chelating agents may affect the releases of radionuclides and chelating agents. In addition, results from this study indicate that the cumulative releases of radionuclides and chelating agents observed for forms that disintegrated were similar to those for forms that maintained their general physical integrity.

McIsaac, C.V.; Akers, D.W.; McConnell, J.W.; Morcos, N.

1992-01-01

393

Leach studies on cement-solidified ion exchange resins from decontamination processes at operating nuclear power stations  

SciTech Connect

The effects of varying pH and leachant compositions on the physical stability and leachability of radionuclides and chelating agents were determined for cement-solidified decontamination ion-exchange resin wastes collected from two operating commercial light water reactors. Small scale waste-form specimens were collected during waste solidifications performed at the Brunswick Steam Electric Plant Unit 1 and at the James A. FitzPatrick Nuclear Power Station. The collected specimens were leach tested, and their compressive strength was measured in accordance with the Nuclear Regulatory Commission`s ``Technical Position on Waste Form`` (Revision 1), from the Low-Level Waste Management Branch. Leachates from these studies were analyzed for radionuclides, selected transition metals, and chelating agents to assess the leachability of these waste form constituents. Leachants used for the study were deionized water, simulated seawater, and groundwater compositions similar to those found at Barnwell, South Carolina and Hanford, Washington. Results of this study indicate that initial leachant pH does not affect leachate pH or releases from cement-solidified decontamination ion-exchange resin waste forms. However, differences in leachant composition and the presence of chelating agents may affect the releases of radionuclides and chelating agents. In addition, results from this study indicate that the cumulative releases of radionuclides and chelating agents observed for forms that disintegrated were similar to those for forms that maintained their general physical integrity.

McIsaac, C.V.; Akers, D.W.; McConnell, J.W.; Morcos, N.

1992-08-01

394

Quantum statistical study of O + O2 isotopic exchange reactions: cross sections and rate constants.  

PubMed

Using a wave packet based statistical model, we compute cross sections and thermal rate constants for various isotopic variants of the O + O2 exchange reaction on a recently modified ab initio potential energy surface. The calculation predicts a highly excited rotational distribution and relatively cold vibrational distribution for the diatomic product. A small but important threshold effect was identified for the (16)O + 18O2 reaction, which is suggested to contribute to the experimentally observed negative temperature dependence of the rate ratio, k(18O + 16O2)/k(16O + 18O2). Despite reasonable agreement with quasiclassical trajectory results, however, the calculated thermal rate constants are smaller than experimental measurements by a factor from 2 to 5. The experimentally observed negative temperature dependence of the rate constants is not reproduced. Possible reasons for the theory-experiment discrepancies are discussed. PMID:16623456

Lin, Shi Ying; Guo, Hua

2006-04-27

395

Experimental Background Studies in the Two Photon Exchange (TPE) Experiment at Jefferson Lab  

SciTech Connect

This work is based on the improvement of an existing simulation for the two photon exchange (TPE) experiment at Jefferson Lab developed within the GEANT4 framework. This experiment will determine the ratio of the positron-proton elastic scattering cross section and the electron-proton elastic scattering cross section with high precision. To accomplish this measurement requires the use of a variety of devices and complex arrangements, creating background particles that manage to reach the detector system (CLAS). A number of test runs have identified the sources of background in the detector guided by previous simulations. Even so, the remaining background can be reduced considerably by the microscopic identification and locating of the background sources performed by our new simulation.

Pena, Cristian; Brooks, W. K.; Hakobyan, Hayk [Universidad Tecnica Federico Santa Maria, Valparaiso (Chile)

2010-08-04

396

Effect of exchangeable cation on the swelling property of 2:1 dioctahedral smectite--a periodic first principle study.  

PubMed

We used both localized and periodic calculations on a series of monovalent (Li+, Na+, K+, Rb+, Cs+) and divalent (Mg2+, Ca2+, Sr2+, Ba2+) cations to monitor their effect on the swelling of clays. The activity order obtained for the exchangeable cations among all the monovalent and divalent series studied: Ca2+ > Sr2+ > Mg2+ > Rb+ > Ba2+ > Na+ > Li+ > Cs+ > K+. We have shown that, in case of dioctahedral smectite, the hydroxyl groups play a major role in their interaction with water and other polar molecules in the presence of an interlayer cation. We studied both type of clays, with a different surface structure and with/without water using a periodic calculation. Interlayer cations and charged 2:1 clay surfaces interact strongly with polar solvents; when it is in an aqueous medium, clay expands and the phenomenon is known as crystalline swelling. The extent of swelling is controlled by a balance between relatively strong swelling forces and electrostatic forces of attraction between the negatively charged phyllosilicate layer and the positively charged interlayer cation. We have calculated the solvation energy at the first hydration shell of an exchangeable cation, but the results do not correspond directly to the experimental d-spacing values. A novel quantitative scale is proposed with the numbers generated by the relative nucleophilicity of the active cation sites in their hydrated state through Fukui functions within the helm of the hard soft acid base principle. The solvation effect thus measured show a perfect match with experiment, which proposes that the reactivity index calculation with a first hydration shell could rationalize the swelling mechanism for exchangeable cations. The conformers after electron donation or acceptance propose the swelling mechanism for monovalent and divalent cations. PMID:15268498

Chatterjee, Abhijit; Ebina, Takeo; Onodera, Yoshio; Mizukami, Fujio

2004-02-15

397

Kitchen Appliance Upgrades Improve Water Efficiency at DOD Exchange Facilities: Best Management Practice Case Study #11: Commercial Kitchen Equipment (Brochure)  

SciTech Connect

The Exchange, formerly the Army and Air Force Exchange Service (AAFES), is a joint military activity and the U.S. Department of Defense?s (DOD) oldest and largest retailer. The Exchange is taking a leadership role in water efficiency improvements in their commercial kitchens by integrating water efficiency concepts into the organization?s overall sustainability plan and objectives.

Not Available

2011-09-01

398

Use of Space-borne Observations to Study Air-Sea CO2 Exchange  

NASA Astrophysics Data System (ADS)

Atmosphere-ocean exchange of CO2 is driven by the difference in CO2 partial pressure across the air-sea interface, and is proportional to wind speed and turbulent mixing in the boundary layers. Globally, the air-sea CO2 flux averages ~90 PgC/yr. The imbalance between the CO2 invasion and outgassing, ~1-2 PgC/yr currently, constitutes the oceanic uptake of anthropogenic CO2. The magnitudes of these fluxes have been inferred from other tracers and from models; their direct measurement has been difficult, because of the sparsity of high-frequency wind and pCO2 observations. The only global distribution of air-sea CO2 flux has been compiled by Takahashi (1999) using available ship-board measurements of pCO2 and climatological winds. This approach provides a first estimate of the air-sea exchange. As the product of the mean wind and mean pCO2 is different from the mean of the product, there has to be uncertainties associated with air-sea fluxes derived using conventional ship-board measurements. Space-borne observations like QuikSCAT provide twice-daily near-real-time information of the wind vector over the ocean surface. At this writing, global, high-frequency observations of pCO2 are beyond current measurement capabilities. In this paper, we use the NCAR coupled atmosphere-ocean carbon-climate general circulation model to investigate variability of pCO2 in the surface waters, and variability in the air-sea flux. We present a parameterization of pCO2 variation and air-sea CO2 flux using remotely observable parameters such as sea surface temperature from TMI, TRMM and MODIS, and wind speed and wind stress curl from QuikSCAT. Such a parameterization permits the assessment of sampling uncertainty in the estimation of the air-sea flux, and an independent estimate of the oceanic sink for CO2.

Fung, I.; Doney, S.

2001-12-01

399

Influence of 8-Oxoguanosine on the Fine Structure of DNA Studied with Biasing-Potential Replica Exchange Simulations  

SciTech Connect

Chemical modification or radiation can cause DNA damage, which plays a crucial role for mutagenesis of DNA, carcinogenesis, and aging. DNA damage can also alter the fine structure of DNA that may serve as a recognition signal for DNA repair enzymes. A new, advanced sampling replica-exchange method has been developed to specifically enhance the sampling of conformational substates in duplex DNA during molecular dynamics (MD) simulations. The approach employs specific biasing potentials acting on pairs of pseudodihedral angles of the nucleic acid backbone that are added in the replica simulations to promote transitions of the most common substates of the DNA backbone. The sampled states can exchange with a reference simulation under the control of the original force field. The application to 7,8-dihydro-8oxo-guanosine, one of the most common oxidative damage in DNA indicated better convergence of sampled states during 10 ns simulations compared to 20 times longer standard MD simulations. It is well suited to study systematically the fine structure and dynamics of large nucleic acids under realistic conditions, including explicit solvent and ions. The biasing potential-replica exchange MD simulations indicated significant differences in the population of nucleic acid backbone substates in the case of 7,8-dihydro-8oxo-guanosine compared to a regular guanosine in the same sequence context. This concerns both the ratio of the B-DNA substates BI and BII associated with the backbone dihedral angles ? and z but also coupled changes in the backbone dihedral angles a and g. Such differences may play a crucial role in the initial recognition of damaged DNA by repair enzymes.

Kara, Mahmut; Zacharias, Martin W.

2013-03-05

400

Estuary/ocean exchange and tidal mixing in a Gulf of Maine Estuary: A Lagrangian modeling study  

NASA Astrophysics Data System (ADS)

A Lagrangian particle method embedded within a 2-D finite element code, is used to study the transport and ocean-estuary exchange processes in the well-mixed Great Bay Estuarine System in New Hampshire, USA. The 2-D finite element model, driven by residual, semi-diurnal and diurnal tidal constituents, includes the effects of wetting and drying of estuarine mud flats through the use of a porous medium transport module. The particle method includes tidal advection, plus a random walk model in the horizontal that simulates sub-grid scale turbulent transport processes. Our approach involves instantaneous, massive [O(500,000)] particle releases that enable the quantification of ocean-estuary and inter-bay exchanges in a Markovian framework. The effects of the release time, spring-neap cycle, riverine discharge and diffusion strength on the intra-estuary and estuary-ocean exchange are also investigated. The results show a rather dynamic interaction between the ocean and the estuary with a fraction of the exiting particles being caught up in the Gulf of Maine Coastal Current and swept away. Three somewhat different estimates of estuarine residence time are calculated to provide complementary views of estuary flushing. Maps of residence time versus release location uncover a strong spatial dependency of residence time within the estuary that has very important ramifications for local water quality. Simulations with and without the turbulent random walk show that the combined effect of advective shear and turbulent diffusion is very effective at spreading particles throughout the estuary relatively quickly, even at low (1 m 2/s) diffusivity. The results presented here show that a first-order Markov Chain approach has applicability and a high potential for improving our understanding of the mixing processes in estuaries.

Bilgili, Ata; Proehl, Jeffrey A.; Lynch, Daniel R.; Smith, Keston W.; Swift, M. Robinson

2005-12-01

401

Videotape Exchange  

ERIC Educational Resources Information Center

Describes a videotape exchange between students in a New York City school and a classroom of students in Charleston, South Carolina, explaining what the students learned about themselves and others from the personally-made tapes. (RB)

Mack, Teresa

1975-01-01

402

CO2 adsorption in mono-, di- and trivalent cation-exchanged metal-organic frameworks: a molecular simulation study.  

PubMed

A molecular simulation study is reported for CO(2) adsorption in rho zeolite-like metal-organic framework (rho-ZMOF) exchanged with a series of cations (Na(+), K(+), Rb(+), Cs(+), Mg(2+), Ca(2+), and Al(3+)). The isosteric heat and Henry's constant at infinite dilution increase monotonically with increasing charge-to-diameter ratio of cation (Cs(+) < Rb(+) < K(+) < Na(+) < Ca(2+) < Mg(2+) < Al(3+)). At low pressures, cations act as preferential adsorption sites for CO(2) and the capacity follows the charge-to-diameter ratio. However, the free volume of framework becomes predominant with increasing pressure and Mg-rho-ZMOF appears to possess the highest saturation capacity. The equilibrium locations of cations are observed to shift slightly upon CO(2) adsorption. Furthermore, the adsorption selectivity of CO(2)/H(2) mixture increases as Cs(+) < Rb(+) < K(+) < Na(+) < Ca(2+) < Mg(2+) ? Al(3+). At ambient conditions, the selectivity is in the range of 800-3000 and significantly higher than in other nanoporous materials. In the presence of 0.1% H(2)O, the selectivity decreases drastically because of the competitive adsorption between H(2)O and CO(2), and shows a similar value in all of the cation-exchanged rho-ZMOFs. This simulation study provides microscopic insight into the important role of cations in governing gas adsorption and separation, and suggests that the performance of ionic rho-ZMOF can be tailored by cations. PMID:22332962

Chen, Y F; Nalaparaju, A; Eddaoudi, M; Jiang, J W

2012-02-28

403

X-ray spectroscopic study of charge exchange phenomena in plasma-wall interaction  

NASA Astrophysics Data System (ADS)

Jets of energetic ions launched at laser-burnt-through foils represent an efficient tool for investigation of plasma interaction with solid surfaces (plasma-wall interaction, PWI) and for description of transient phenomena occurring close to the walls. Highly charged ions approaching the secondary target interpenetrate the near surface layer, collide with the counter-propagating matter and capture a large number of electrons. This results in a creation of atoms in highly excited Rydberg states or hollow ions with multiple inner vacancies; plasma jet and target ions may also undergo charge exchange (CE) processes. We report PWI experiments with Al/Si(PMMA) and Al/C targets irradiated at normal or oblique laser incidence. The distinct dip structures observed in red wings of Al Ly? self-emission is interpreted in terms of CE between C6+ and Al12+ in the near-wall zone. The spectroscopic identification of CE phenomena is supported by results of analytical and numerical calculations.

Renner, O.; Krouský, E.; Šmíd, M.; Liska, R.; Váchal, P.; Khattak, F. Y.; Dalimier, E.; Oks, E.

2013-11-01

404

The grammar of exchange: a comparative study of reciprocal constructions across languages.  

PubMed

Cultures are built on social exchange. Most languages have dedicated grammatical machinery for expressing this. To demonstrate that statistical methods can also be applied to grammatical meaning, we here ask whether the underlying meanings of these grammatical constructions are based on shared common concepts. To explore this, we designed video stimuli of reciprocated actions (e.g., "giving to each other") and symmetrical states (e.g., "sitting next to each other"), and with the help of a team of linguists collected responses from 20 languages around the world. Statistical analyses revealed that many languages do, in fact, share a common conceptual core for reciprocal meanings but that this is not a universally expressed concept. The recurrent pattern of conceptual packaging found across languages is compatible with the view that there is a shared non-linguistic understanding of reciprocation. But, nevertheless, there are considerable differences between languages in the exact extensional patterns, highlighting that even in the domain of grammar semantics is highly language-specific. PMID:21713188

Majid, Asifa; Evans, Nicholas; Gaby, Alice; Levinson, Stephen C

2011-01-01

405

Exchange-dominated eigenmodes in sub-100 nm permalloy dots: A micromagnetic study at finite temperature  

NASA Astrophysics Data System (ADS)

Micromagnetic simulations at room temperature (300 K) have been carried out in order to analyse the magnetic eigenmodes (frequency and spatial profile) in elliptical dots with sub-100 nm lateral size. Features are found that are qualitatively different from those typical of larger dots because of the dominant role played by the exchange-energy. These features can be understood most simply in terms of nodal planes defined relative to the orientation of the static magnetization. A new, generalized labeling scheme is proposed that simplifies discussion and comparison of modes from different geometries. It is shown that the lowest-frequency mode for small dots is characterized by an in-phase precession of spins, without nodal planes, but with a maximum amplitude at the edges. This mode softens at an applied switching field with magnitude comparable to the coercive field and determines specific aspects of magnetization reversal. This characteristic behavior can be relevant for optimization of microwave assisting switching as well as for maximizing interdot coupling in dense arrays of dots.

Carlotti, G.; Gubbiotti, G.; Madami, M.; Tacchi, S.; Stamps, R. L.

2014-05-01

406

The Grammar of Exchange: A Comparative Study of Reciprocal Constructions Across Languages  

PubMed Central

Cultures are built on social exchange. Most languages have dedicated grammatical machinery for expressing this. To demonstrate that statistical methods can also be applied to grammatical meaning, we here ask whether the underlying meanings of these grammatical constructions are based on shared common concepts. To explore this, we designed video stimuli of reciprocated actions (e.g., “giving to each other”) and symmetrical states (e.g., “sitting next to each other”), and with the help of a team of linguists collected responses from 20 languages around the world. Statistical analyses revealed that many languages do, in fact, share a common conceptual core for reciprocal meanings but that this is not a universally expressed concept. The recurrent pattern of conceptual packaging found across languages is compatible with the view that there is a shared non-linguistic understanding of reciprocation. But, nevertheless, there are considerable differences between languages in the exact extensional patterns, highlighting that even in the domain of grammar semantics is highly language-specific.

Majid, Asifa; Evans, Nicholas; Gaby, Alice; Levinson, Stephen C.

2010-01-01

407

TRENTA Facility for Trade-Off Studies Between Combined Electrolysis Catalytic Exchange and Cryogenic Distillation Processes  

SciTech Connect

One of the most used methods for tritium recovery from different sources of tritiated water is based on the combination between Combined Electrolysis Catalytic Exchange (CECE) and Cryogenic Distillation (CD) processes. The development, i.e. configuration, design and performance testing of critical components, of a tritium recovery system based on the combination CECE-CD is essential for both JET and ITER. For JET, a Water Detritiation System (WDS) is not only needed to process tritiated water which has already been accumulated from operation, but also for the tritiated water which will be generated during decommissioning. For ITER, the WDS is one of the key systems to control the tritium content in the effluents streams, to recover as much tritium as possible and consequently to minimize the impact on the environment. A cryogenic distillation facility with the aim to investigate the trade-off between CECE-CD, to validate different components and mathematical modelling software is current under development at Tritium Laboratory Karlsruhe (TLK) as an extension of the existing CECE facility.

Cristescu, I. [Forschungszentrum Karlsruhe (Germany); Cristescu, I.R. [Forschungszentrum Karlsruhe (Germany); Doerr, L. [Forschungszentrum Karlsruhe (Germany); Glugla, M. [Forschungszentrum Karlsruhe (Germany); Hellriegel, G. [Forschungszentrum Karlsruhe (Germany); Schaefer, P. [Forschungszentrum Karlsruhe (Germany); Welte, S. [Forschungszentrum Karlsruhe (Germany); Kveton, O.; Murdoch, D

2005-07-15

408

Three Dimensional Computational Study on Proton Exchange Membrane Fuel Cell by Operation Conditions  

NASA Astrophysics Data System (ADS)

A single-phase, fully three-dimensional simulation model for a proton exchange membrane(PEM) fuel cell was used to examine the interdigitated flow field with electrochemical reaction and ion, electron, and water transport(electro-osmotic drag flux and back diffusion flux) through the polymer membrane. The numerical results showed that the fuel cell with an interdigitated flow field resulted in better performance than a fuel cell with a conventional flow field due to its strong convective transport across gas diffusion layer(GDL). However, the pressure drop in an interdigitated flow field is much greater than in conventional flow field. To investigate the effect of relative humidity on the performance of a PEM fuel cell, the humidification condition was set to 100% at the anode flow field and was changed by 0-100% at the cathode flow field. Maximum power density was obtained for a 70% humidified condition at the cathode where the oxygen concentration is moderately high while maintaining high ion conductivity at the polymer membrane.

Lee, Pil Hyong; Park, Bong Il; Hwang, Sang Soon

409

Studies on biologically induced corrosion in heat exchanger systems at the Savannah River Plant, Aiken, SC  

SciTech Connect

Biological fouling and corrosion of stainless steel tubes in the heat exchangers in nuclear reactors at the Savannah River Plant have caused decreased heat transfer efficiency and reduced operational life. This report addresses the microbiology and chemistry of the films present on these tubes, and the relation of this data to the corrosion of the tube material (304L stainless steel). Very few microorganisms other than bacteria were found in the biofilm. Bacteria capable of producing H/sub 2/S, organic acids, anaerobic conditions, and slime have all been isolated from these films. All of these have been implicated in corrosion processes. The most remarkable chemical finding was the inability to detect chloride in the film around areas of presumed chloride induced stress corrosion cracking. Three model systems were used to test the fouling and corrosion potential of metal specimens under a variety of environmental conditions including various biocide regimes. Using these systems, potential improvements in the use of chlorine as a biocidal agent have been observed. It was also shown that larger bacterial populations (including viable and killed cells) were associated with corroded areas as compared to noncorroded areas on the same specimen.

Pope, D.H. (Rensselaer Polytechnic Inst., Troy, NY); Soracco, R.J.; Wilde, E.W.

1982-07-01

410

Studies of sorbent\\/ion-exchange materials for the removal of radioactive strontium from liquid radioactive waste and high hardness groundwaters  

Microsoft Academic Search

Different sorbents were studied in terms of their full-scale applicability for radioactive strontium removal in low-level liquid radioactive waste (LLRW) management. The following types of sorbent\\/ion-exchange materials were investigated: natural zeolite–clinoptilolite, modified natural clinoptilolite, synthetic zeolites, new synthetic crystalline materials selective to strontium, ion-exchange resins, and modified fiber sorbents. Simulated solutions for experimental tests were prepared according to the composition

Dmitry V Marinin; Garrett N Brown

2000-01-01

411

Comparison of Two ESI MS Based H/D Exchange Methods for Extracting Protein Folding Energies  

PubMed Central

In this report, the model proteins staphylococcal nuclease and ubiquitin were used to test the applicability of two new hydrogen/deuterium exchange (HX) electrospray ionization mass spectrometry (ESI-MS) methods for estimating protein folding energies. Both methods use the H/D exchange of globally protected amide protons (amide protons which are buried in the hydrophobic core) to elucidate protein folding energies. One method is a kinetic-based method and the other is equilibrium-based. The first method, the HX ESI-MS kinetic-based approach is conceptually identical to SUPREX (stability of unpurified proteins from rates of H/D exchange) method but is based on ESI-MS rather than MALDI-MS (matrix assisted laser desorption mass spectrometry). This method employs the time-dependence of H/D exchange using various denaturant concentrations to extract folding energies. Like SUPREX, this approach requires the assumption of EX2 exchange kinetics. The second method, which we call a protein equilibrium population snapshot (PEPS) by HX ESI-MS uses data collected only for a single time point (usually the shortest possible) to obtain a snapshot of the open and closed populations of the protein. The PEPS approach requires few assumptions in the derivation of the equations used for calculation of the folding energies. The extraction of folding energies from mass spectral data is simple and straightforward. The PEPS method is applicable for proteins that follow either EX1 or EX2 HX mechanisms. In our experiments the kinetic-based method produced less accurate ?GH2O and mGdHCl values for wild-type staphylococcal nuclease and mutants undergoing H/D exchange by EX1, as would be expected. Better results were obtained for ubiquitin which undergoes HX by an EX2 mechanism. Using the PEPS method we obtained ?GH2O and mGdHCl values that were in good agreement with literature values for both staphylococcal nuclease (EX1) and ubiquitin (EX2). We also show that the observation of straight lines in linear extrapolation method (LEM) plots is not a reliable indicator of the validity of the data obtained using the LEM approach.

Liyanage, Rohana; Devarapalli, Nagarjuna; Puckett, Latisha M.; Phan, N. H.; Gidden, Jennifer; Stites, Wesley E.; Lay, Jackson O.

2010-01-01

412

Quantal Study of the Exchange Reaction for N + N2 using an ab initio Potential Energy Surface  

NASA Technical Reports Server (NTRS)

The N + N2 exchange rate is calculated using a time-dependent quantum dynamics method on a newly determined ab initio potential energy surface (PES) for the ground A" state. This ab initio PES shows a double barrier feature in the interaction region with the barrier height at 47.2 kcal/mol, and a shallow well between these two barriers, with the minimum at 43.7 kcal/mol. A quantum dynamics wave packet calculation has been carried out using the fitted PES to compute the cumulative reaction probability for the exchange reaction of N + N2(J=O). The J - K shift method is then employed to obtain the rate constant for this reaction. The calculated rate constant is compared with experimental data and a recent quasi-classical calculation using a LEPS PES. Significant differences are found between the present and quasiclassical results. The present rate calculation is the first accurate 3D quantal dynamics study for N + N2 reaction system and the ab initio PES reported here is the first such surface for N3.

Wang, Dunyou; Stallcop, James R.; Huo, Winifred M.; Dateo, Christopher E.; Schwenke, David W.; Partridge, Harry; Kwak, Dochan (Technical Monitor)

2002-01-01

413

Space charge and aeroelectric flows in the exchange layer: An experimental and numerical study  

NASA Astrophysics Data System (ADS)

Experimental research on the turbulent transport of aeroelectrical field inhomogeneities and modeling of the formation of the dynamic electrical layer in the PBL has been carried out. The transport of aeroelectric inhomogeneities was detected on the basis of field observations during electrodynamics campaigns in the seasons of 2006-2011. Investigations of a dynamic component of the boundary layer electric field are carried out in terms of numerical modeling of spatially heterogeneous turbulent transport of space charge. The modeling of aeroelectric field dynamics is executed by means of a method of probe structures. The response of the aeroelectric field to the transport of aeroelectrical turbulence is investigated. Observations of the aeroelectric field intensity, the vertical profiles of wind speed and direction and the heights of a layer with a temperature inversion are used as input model parameters. Basic model parameters of space charge distributions are analyzed. It is shown that the evolution of an aeroelectrical vertical electric field profile is defined by the formation of dynamic electrical layers in the lower atmosphere. Estimations of the interrelation of aeroelectric field dynamics and trends of meteorological parameters are adduced for boundary layer conditions. It is shown that the velocity of transfer of aeroelectric field heterogeneities is defined by the velocities of space charge transport in electrical layers of the boundary layer. The influence of the large-scale wind velocity structure to the space charge spatial distributions is investigated. It is shown that the space-time aeroelectric field dynamics are due to the integrated contribution of the transfer of electric space charge. From the results of electric field observations the numerical estimation of space charge transport in the exchange layer is performed.

Anisimov, S. V.; Galichenko, S. V.; Shikhova, N. M.

2014-01-01

414

A portable hydro-thermo-mechanical loading cell for in situ small angle neutron scattering studies of proton exchange membranes.  

PubMed

A portable hydro-thermo-mechanical loading cell has been designed to enable in situ small angle neutron scattering (SANS) studies of proton exchange membranes (PEMs) under immersed tensile loadings at different temperatures. The cell consists of three main parts as follows: a letter-paper-size motor-driven mechanical load frame, a SANS friendly reservoir that provides stable immersed and thermal sample conditions, and a data acquisition and control system. The ex situ tensile tests of Nafion 212 membranes demonstrated a satisfactory thermo-mechanical testing performance of the cell for either dry or immersed conditions at elevated temperatures. The in situ SANS tensile measurements on the Nafion 212 membranes immersed in D2O at 70 °C proved the feasibility and capability of the cell for small angle scattering study on deformation behaviors of PEM and other polymer materials under hydro-thermo-mechanical loading. PMID:24182171

Yu, Dunji; An, Ke; Gao, Carrie Y; Heller, William T; Chen, Xu

2013-10-01

415

Design study of a coal-fired thermionic (THX) topped power plant. Volume IV. Thermionic heat exchanger design and costing  

SciTech Connect

This volume deals with the details of how thermionic conversion works, and how it is used in a coal-fired furnace to achieve power plant efficiencies of 45%, and overall costs of 36.3 mills/kWh. A review of the fundamental technical aspects of thermionic conversion is given. The overall Thermionic Heat Exchanger (THX) design, the heat pipe design, and the interaction of the heat pipes with the furnace are presented. Also, the operational characteristics of thermionic converters are described. Details on the computer program used to perform the parametric study are given. The overall program flow is reviewed along with the specifics of how the THX subroutine designed the converter to match the conditions imposed. Also, input costs and variables effecting the THX's performance are detailed. The efficiencies of the various power plants studied are given as a function of the air preheat temperature, size of the power plant, and thermionic level of performance.

Dick, R.S.; Britt, E.J.

1980-10-15

416

Magnetic properties of exchange biased and of unbiased oxide/permalloy thin layers: a ferromagnetic resonance and Brillouin scattering study.  

PubMed

Microstrip ferromagnetic resonance and Brillouin scattering are used to provide a comparative determination of the magnetic parameters of thin permalloy layers interfaced with a non-magnetic (Al(2)O(3)) or with an antiferromagnetic oxide (NiO). It results from our microstructural study that no preferential texture is favoured in the observed polycrystalline sublayers. It is shown that the perpendicular anisotropy can be monitored using an interfacial surface energy term which is practically independent of the nature of the interface. In the interval of thicknesses investigated (5-25 nm) the saturation magnetization does not significantly differ from the reported one in bulk permalloy. In-plane uniaxial anisotropy and exchange bias anisotropy are also derived from the study of the dynamic magnetic excitations and compared with our independent evaluations using conventional magnetometry. PMID:21386581

Zighem, F; Roussigné, Y; Chérif, S-M; Moch, P; Ben Youssef, J; Paumier, F

2010-10-13

417

First-principles studies of interlayer exchange coupling in (Ga, Cr)N-based diluted magnetic semiconductor multilayers  

NASA Astrophysics Data System (ADS)

Interlayer exchange coupling (IEC) in a series model diluted magnetic semiconductor multilayer consisting of two magnetic (Ga, Cr)N layers separated by non-doped or Mg-doped GaN non-magnetic spacers has been studied by first-principles calculations. The effects of the spacer thickness and hole doping to the IEC were studied systematically. For the GaN spacers without Mg doping, the IEC between two magnetic (Ga, Cr)N layers is always ferromagnetic and is clarified as an intrinsic character of the Ruderman-Kittle-Kasuya-Yoshida interaction based on a two-band model for a gapped system. For the Mg-doped GaN spacers, the IEC is antiferromagnetic, and the antiferromagnetic IEC is stable with increasing the spacer thickness.

Luo, M.; Sun, F.; Tang, Z.

2013-02-01

418

First-principles studies of interlayer exchange coupling in (Ga, Co)N-based diluted magnetic semiconductor multilayers  

NASA Astrophysics Data System (ADS)

Interlayer exchange coupling (IEC) in a series model diluted magnetic semiconductor (DMS) multilayer consisting of two magnetic (Ga, Co)N layers separated by non-doped or Mg-doped GaN non-magnetic spacers has been studied by first-principles calculations. The effects of the spacer thickness and hole doping to the IEC were studied systematically. It is observed that (1) for the GaN spacers without Mg doping, the IEC between two magnetic (Ga, Co)N layers is always ferromagnetic, which is clarified as an intrinsic character of the Ruderman-Kittle-Kasuya-Yoshida (RKKY) interaction based on a two-band model for a gapped system; and (2) for the Mg-do