Operando chemistry of catalyst surfaces during catalysis.

PubMed

Dou, Jian; Sun, Zaicheng; Opalade, Adedamola A; Wang, Nan; Fu, Wensheng; Tao, Franklin Feng

2017-04-03

Chemistry of a catalyst surface during catalysis is crucial for a fundamental understanding of mechanism of a catalytic reaction performed on the catalyst in the gas or liquid phase. Due to the pressure- or molecular density-dependent entropy contribution of gas or liquid phase of the reactants and the potential formation of a catalyst surface during catalysis different from that observed in an ex situ condition, the characterization of the surface of a catalyst under reaction conditions and during catalysis can be significant and even necessary for understanding the catalytic mechanism at a molecular level. Electron-based analytical techniques are challenging for studying catalyst nanoparticles in the gas or liquid phase although they are necessary techniques to employ. Instrumentation and further development of these electron-based techniques have now made in situ/operando studies of catalysts possible. New insights into the chemistry and structure of catalyst nanoparticles have been uncovered over the last decades. Herein, the origin of the differences between ex situ and in situ/operando studies of catalysts, and the technical challenges faced as well as the corresponding instrumentation and innovations utilized for characterizing catalysts under reaction conditions and during catalysis, are discussed. The restructuring of catalyst surfaces driven by the pressure of reactant(s) around a catalyst, restructuring in reactant(s) driven by reaction temperature and restructuring during catalysis are also reviewed herein. The remaining challenges and possible solutions are briefly discussed.

Ion Mobility Studies on the Negative Ion-Molecule Chemistry of Isoflurane and Enflurane.

PubMed

González-Méndez, Ramón; Watts, Peter; Howse, David C; Procino, Immacolata; McIntyre, Henry; Mayhew, Chris A

2017-05-01

In the present work we present an investigation of the negative ion-molecule chemistry of the anaesthetics isoflurane, ISOF, and enflurane, ENF, in an ion mobility spectrometry/mass spectrometry (IMS/MS), in both air and nitrogen. Hexachloroethane (HCE) was introduced in both air and nitrogen to produce Cl - as a reactant ion. This study was undertaken owing to uncertainties in the chemical processes, which lead to the cluster ions reported in other work (Eiceman et al. Anal. Chem. 61, 1093-1099, 1). In particular for ISOF the product ion observed was ISOF.Cl - , and it was suggested that the Cl - was formed by dissociative electron attachment (DEA) although there was mention of a chlorine containing contaminant. We show in this study that ISOF and ENF do not produce Cl - in an IMS system either by capture of free electrons or reaction with O 2 - . This demonstrates that the Cl - containing ions, reported in the earlier study, must have been the result of a chlorine containing contaminant as suggested. The failure of ISOF and ENF to undergo DEA was initially surprising given the high calculated electron affinities, but further calculations showed that this was a result of the large positive vertical attachment energies (VAEs). This experimental work has been supported by electronic structure calculations at the B3LYP level, and is consistent with those obtained in a crossed electron-molecular beam two sector field mass spectrometer. An unusual observation is that the monomer complexes of ISOF and ENF with O 2 - are relatively unstable compared with the dimer complexes. Graphical Abstract ᅟ.

Ion Mobility Studies on the Negative Ion-Molecule Chemistry of Isoflurane and Enflurane

NASA Astrophysics Data System (ADS)

González-Méndez, Ramón; Watts, Peter; Howse, David C.; Procino, Immacolata; McIntyre, Henry; Mayhew, Chris A.

2017-05-01

In the present work we present an investigation of the negative ion-molecule chemistry of the anaesthetics isoflurane, ISOF, and enflurane, ENF, in an ion mobility spectrometry/mass spectrometry (IMS/MS), in both air and nitrogen. Hexachloroethane (HCE) was introduced in both air and nitrogen to produce Cl- as a reactant ion. This study was undertaken owing to uncertainties in the chemical processes, which lead to the cluster ions reported in other work (Eiceman et al. Anal. Chem. 61, 1093-1099, 1). In particular for ISOF the product ion observed was ISOF.Cl-, and it was suggested that the Cl- was formed by dissociative electron attachment (DEA) although there was mention of a chlorine containing contaminant. We show in this study that ISOF and ENF do not produce Cl- in an IMS system either by capture of free electrons or reaction with O2 -. This demonstrates that the Cl- containing ions, reported in the earlier study, must have been the result of a chlorine containing contaminant as suggested. The failure of ISOF and ENF to undergo DEA was initially surprising given the high calculated electron affinities, but further calculations showed that this was a result of the large positive vertical attachment energies (VAEs). This experimental work has been supported by electronic structure calculations at the B3LYP level, and is consistent with those obtained in a crossed electron-molecular beam two sector field mass spectrometer. An unusual observation is that the monomer complexes of ISOF and ENF with O2 - are relatively unstable compared with the dimer complexes.

Tested Demonstrations.

ERIC Educational Resources Information Center

Gilbert, George L., Ed.

1983-01-01

Free radical chlorination of methane is used in organic chemistry to introduce free radical/chain reactions. In spite of its common occurrence, demonstrations of the reaction are uncommon. Therefore, such a demonstration is provided, including background information, preparation of reactants/reaction vessel, introduction of reactants, irradiation,…

The formation of urea in space. I. Ion-molecule, neutral-neutral, and radical gas-phase reactions

NASA Astrophysics Data System (ADS)

Brigiano, Flavio Siro; Jeanvoine, Yannick; Largo, Antonio; Spezia, Riccardo

2018-02-01

Context. Many organic molecules have been observed in the interstellar medium thanks to advances in radioastronomy, and very recently the presence of urea was also suggested. While those molecules were observed, it is not clear what the mechanisms responsible to their formation are. In fact, if gas-phase reactions are responsible, they should occur through barrierless mechanisms (or with very low barriers). In the past, mechanisms for the formation of different organic molecules were studied, providing only in a few cases energetic conditions favorable to a synthesis at very low temperature. A particularly intriguing class of such molecules are those containing one N-C-O peptide bond, which could be a building block for the formation of biological molecules. Urea is a particular case because two nitrogen atoms are linked to the C-O moiety. Thus, motivated also by the recent tentative observation of urea, we have considered the synthetic pathways responsible to its formation. Aims: We have studied the possibility of forming urea in the gas phase via different kinds of bi-molecular reactions: ion-molecule, neutral, and radical. In particular we have focused on the activation energy of these reactions in order to find possible reactants that could be responsible for to barrierless (or very low energy) pathways. Methods: We have used very accurate, highly correlated quantum chemistry calculations to locate and characterize the reaction pathways in terms of minima and transition states connecting reactants to products. Results: Most of the reactions considered have an activation energy that is too high; but the ion-molecule reaction between NH2OHNH2OH2+ and formamide is not too high. These reactants could be responsible not only for the formation of urea but also of isocyanic acid, which is an organic molecule also observed in the interstellar medium.

A corona discharge atmospheric pressure chemical ionization source with selective NO(+) formation and its application for monoaromatic VOC detection.

PubMed

Sabo, Martin; Matejčík, Štefan

2013-11-21

We have developed a new type of corona discharge (CD) for atmospheric pressure chemical ionization (APCI) for application in ion mobility spectrometry (IMS) as well as in mass spectrometry (MS). While the other CD-APCI sources are able to generate H3O(+)·(H2O)n as the major reactant ions in N2 or in zero air, the present CD-APCI source has the ability to generate up to 84% NO(+)·(H2O)n reactant ions in zero air. The change of the working gas from zero air to N2 allows us to change the major reactant ions from NO(+)·(H2O)n to H3O(+)·(H2O)n. In this paper we present the description of the new CD-APCI and discuss the processes associated with the NO(+) formation. The selective formation of NO(+)·(H2O)n reactant ions offers chemical ionization based on these ions which can be of great advantage for some classes of chemicals. We demonstrate here a significant increase in the sensitivity of the IMS-MS instrument for monoaromatic volatile organic compound (VOC) detection upon NO(+)·(H2O)n chemical ionization.

Vial OrganicTM-Organic Chemistry Labs for High School and Junior College

NASA Astrophysics Data System (ADS)

Russo, Thomas J.; Meszaros, Mark

1999-01-01

Vial Organic is the most economical, safe, and time-effective method of performing organic chemistry experiments. Activities are carried out in low-cost, sealed vials. Vial Organic is extremely safe because only micro quantities of reactants are used, reactants are contained in tightly sealed vials, and only water baths are used for temperature control. Vial Organic laboratory activities are easily performed within one 50-minute class period. When heat is required, a simple hot-water bath is prepared from a beaker of water and an inexpensive immersion heater. The low cost, ease of use, and relatively short time requirement will allow organic chemistry to be experienced by more students with less confusion and intimidation.

Polymer useful for an ion exchange membrane

DOEpatents

Liang, Siwei; Lynd, Nathaniel A.

2017-03-14

The present invention provides for a polymer formed by reacting a first reactant polymer, or a mixture of first reactant polymers comprising different chemical structures, comprising a substituent comprising two or more nitrogen atoms (or a functional group/sidechain comprising a two or more nitrogen atoms) with a second reactant polymer, or a mixture of second reactant polymers comprising different chemical structures, comprising a halogen substituent (or a functional group/sidechain comprising a halogen).

Comparing Amide-Forming Reactions Using Green Chemistry Metrics in an Undergraduate Organic Laboratory

ERIC Educational Resources Information Center

Fennie, Michael W.; Roth, Jessica M.

2016-01-01

In this laboratory experiment, upper-division undergraduate chemistry and biochemistry majors investigate amide-bond-forming reactions from a green chemistry perspective. Using hydrocinnamic acid and benzylamine as reactants, students perform three types of amide-forming reactions: an acid chloride derivative route; a coupling reagent promoted…

Pulsed discharge ionization source for miniature ion mobility spectrometers

DOEpatents

Xu, Jun; Ramsey, J. Michael; Whitten, William B.

2004-11-23

A method and apparatus is disclosed for flowing a sample gas and a reactant gas (38, 43) past a corona discharge electrode (26) situated at a first location in an ion drift chamber (24), applying a pulsed voltage waveform comprising a varying pulse component and a dc bias component to the corona discharge electrode (26) to cause a corona which in turn produces ions from the sample gas and the reactant gas, applying a dc bias to the ion drift chamber (24) to cause the ions to drift to a second location (25) in the ion drift chamber (24), detecting the ions at the second location (25) in the drift chamber (24), and timing the period for the ions to drift from the corona discharge electrode to the selected location in the drift chamber.

Neural network recognition of chemical class information in mobility spectra obtained at high temperatures

NASA Technical Reports Server (NTRS)

Bell, S.; Nazarov, E.; Wang, Y. F.; Rodriguez, J. E.; Eiceman, G. A.

2000-01-01

A minimal neural network was applied to a large library of high-temperature mobility spectra drawn from 16 chemical classes including 154 substances with 2000 spectra at various concentrations. A genetic algorithm was used to create a representative subset of points from the mobility spectrum as input to a cascade-type back-propagation network. This network demonstrated that significant information specific to chemical class was located in the spectral region near the reactant ions. This network failed to generalize the solution to unfamiliar compounds necessitating the use of complete spectra in network processing. An extended back-propagation network classified unfamiliar chemicals by functional group with a mean for average values of 0.83 without sulfides and 0.79 with sulfides. Further experiments confirmed that chemical class information was resident in the spectral region near the reactant ions. Deconvolution of spectra demonstrated the presence of ions, merged with the reactant ion peaks that originated from introduced samples. The ability of the neural network to generalize the solution to unfamiliar compounds suggests that these ions are distinct and class specific.

A SIFT study of the reactions of H2ONO+ ions with several types of organic molecules

NASA Astrophysics Data System (ADS)

Smith, David; Wang, Tianshu; Spanel, Patrik

2003-11-01

A selected ion flow tube (SIFT) study has been carried out of the reactions of hydrated nitrosonium ions, NO+H2O, which theory has equated to protonated nitrous acid ions, H2ONO+. One objective of this study was to investigate if this ion exhibits the properties of both a cluster ion and a protonated acid in their reactions with a variety of organic molecules. The chosen reactant molecules comprise two each of the following types--amines, terpenes, aromatic hydrocarbons, esters, carboxylic acids, ketones, aldehydes and alcohols. The reactant H2ONO+ (NO+H2O) ions are formed in a discharge ion source and injected into helium carrier gas where they are partially vibrationally excited and partially dissociated to NO+ ions. Hence, the reactions of the H2ONO+ ions had to be studies simultaneously with NO+ ions, the reactions of the latter ions readily being studied by selectively injecting NO+ ions into the carrier gas. The results of this study indicate that the H2ONO+ ions undergo a wide variety of reaction processes that depend on the properties of the reactant molecules such as their ionisation energies and proton affinities. These processes include charge transfer with compounds, M, that have low ionisation energies (producing M+), proton transfer with compounds possessing large proton affinities (MH+), hydride ion transfer (M---H+), alkyl radical (M---R+), alkoxide radical transfer (M---OR+), ion-molecule association (NO+H2OM) and ligand switching (NO+M), producing the ions given in parentheses.

Formation of gold and silver nanostructures within polyvinylpyrollidone (PVP) gel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kan Caixia, E-mail: cxkan@nuaa.edu.c; Wang Changshun; Zhu Jiejun

2010-04-15

Study on reduction of Au(III) and Ag(I) and the formation of Au and Ag nanostructures was performed on the gels of metal precursor and PVP polymer mixture. Some comparing samples were prepared for better understanding the role of reactants on the reduction of metal ions and further growth of nanocrystals. The results suggest that, in addition to its function of generating stable colloids, PVP not only has a reducing effect on metal ions, but also acts as a crystal growth modifier. At low temperatures, the reducing effect of PVP is strong on Ag(I) ions in AgNO{sub 3}, while the reductionmore » of complex Au(III) ions in HAuCl{sub 4} is slow, involving two steps of Au(III)->Au(I)->Au. In the study of temperature disturbance on crystal growth, Au nanoplates of new and well-defined star shape were observed. The differences in the size and shape of nanoparticles are discussed from the colloid chemistry. - Graphical abstract: If a temperature difference was introduced to the gel of Au{sup 3+}(H{sub 2}O)-PVP, large sized Au nanoplates with new and well-defined star shape were observed.« less

Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling

NASA Astrophysics Data System (ADS)

Peng, Zhe; Day, Douglas A.; Ortega, Amber M.; Palm, Brett B.; Hu, Weiwei; Stark, Harald; Li, Rui; Tsigaridis, Kostas; Brune, William H.; Jimenez, Jose L.

2016-04-01

Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O(1D), O(3P), and O3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditions via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to water vapor mixing ratio (H2O) and external OH reactivity (OHRext), as both non-OH reactants and OH scale roughly proportionally to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O(1D), O(3P), and O3 have relative contributions to volatile organic compound (VOC) consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. We define "riskier OFR conditions" as those with either low H2O (< 0.1 %) or high OHRext ( ≥ 100 s-1 in OFR185 and > 200 s-1 in OFR254). We strongly suggest avoiding such conditions as the importance of non-OH reactants can be substantial for the most sensitive species, although OH may still dominate under some riskier conditions, depending on the species present. Photolysis at non-tropospheric wavelengths (185 and 254 nm) may play a significant (> 20 %) role in the degradation of some aromatics, as well as some oxidation intermediates, under riskier reactor conditions, if the quantum yields are high. Under riskier conditions, some biogenics can have substantial destructions by O3, similarly to the troposphere. Working under low O2 (volume mixing ratio of 0.002) with the OFR185 mode allows OH to completely dominate over O3 reactions even for the biogenic species most reactive with O3. Non-tropospheric VOC photolysis may have been a problem in some laboratory and source studies, but can be avoided or lessened in future studies by diluting source emissions and working at lower precursor concentrations in laboratory studies and by humidification. Photolysis of secondary organic aerosol (SOA) samples is estimated to be significant (> 20 %) under the upper limit assumption of unity quantum yield at medium (1 × 1013 and 1.5 × 1015 photons cm-2 s-1 at 185 and 254 nm, respectively) or higher UV flux settings. The need for quantum yield measurements of both VOC and SOA photolysis is highlighted in this study. The results of this study allow improved OFR operation and experimental design and also inform the design of future reactors.

Solvent-Free Wittig Reaction: A Green Organic Chemistry Laboratory Experiment

ERIC Educational Resources Information Center

Leung, Sam H.; Angel, Stephen A.

2004-01-01

Some Wittig reactions can be carried out by grinding the reactants in a mortar with a pestle for about 20 minutes, as per investigation. A laboratory experiment involving a solvent-free Wittig reaction that can be completed in a three-hour sophomore organic chemistry laboratory class period, are developed.

Products of Dissociative Recombination in the Ionosphere

NASA Technical Reports Server (NTRS)

Cosby, Philip

1996-01-01

SRI International undertook a novel experimental measurement of the product states formed by dissociative ro-combination (DR) of C2(+), NO(+), and N2(+) as a function of both electron energy and reactant ion vibrational level. For these measurements we used a recently developed experimental technique for measuring dissociation product distributions that allows both the branching ratios to be accurately determined and the electronic and ro-vibrational state composition of the reactant ions to be specified. DR is the dominant electron loss mechanism in all regions of the ionosphere. In this process, electron attachment to the molecular ion produces an unstable neutral molecule that rapidly dissociates.

Laser Irradiation of SV40 DNA.

DTIC Science & Technology

1982-09-17

PROJECT. TASK AREA & WORK UNIT NUMBERS Laser Chemistry Division ,9epartment of Chemistry Howard University Washineton, D. C. 20059 NR-051-733. II...George Prepared for Publication in the Proceedings of the Conference on Lasers as Reactants and Probes in Chemistry ’I Howard University Department of... Howard University Washington, D. C. 20059 Jay George Department of Biochemistry Schools of Medicine and Dentistry Washington, D.. C. 2000T Modern

PMR polyimide composites for aerospace applications. [Polymerization of Monomer Reactants

NASA Technical Reports Server (NTRS)

Serafini, T. T.

1984-01-01

A novel class of addition-type polyimides has been developed in response to the need for high temperature polymers with improved processability. The new plastic materials are known as PMR (for in situ polymerization of monomer reactants) polyimides. The highly processable PMR polyimides have made it possible to realize much of the potential of high temperature resistant polymers. Monomer reactant combinations for several PMR polyimides have been identified. The present investigation is concerned with a review of the current status of PMR polyimides. Attention is given to details of PMR polyimide chemistry, the processing of composites and their properties, and aerospace applications of PMR-15 polyimide composites.

Interaction of boron cluster ions with water: Single collision dynamics and sequential etching

NASA Astrophysics Data System (ADS)

Hintz, Paul A.; Ruatta, Stephen A.; Anderson, Scott L.

1990-01-01

Reactions of mass-selected, cooled, boron cluster ions (B+n, n=1-14) with water have been studied for collision energies from 0.1 to 6.0 eV. Most work was done with D2O, however isotope effects were examined for selected reactant cluster ions. For all size clusters there are exoergic product channels, which in most cases have no activation barriers. Cross sections are generally large, however there are fluctuations with cluster size in total reactivity, collision energy dependences, and in product distributions. For small cluster ions, there is a multitude of product channels. For clusters larger than B+6, the product distributions are dominated by a single channel: Bn-1D++DBO. Under multiple collision conditions, the primary products undergo a remarkable sequence of secondary ``etching'' reactions. As these occur, boron atoms are continuously replaced by hydrogen, and the intermediate products retain the composition: Bn-mH+m. This highly efficient chemistry appears to continue unchanged as the composition changes from pure boron to mostly hydrogen. Comparison of these results is made with boron cluster ion reactions with O2 and D2, as well as reactions with water of aluminum and silicon cluster ions. Some discussion is given of the thermochemistry for these reactions, and a possible problem with the thermochemical data in the BOD/DBO system is discussed.

Nucleophilic Substitution Reactions Using Phosphine Nucleophiles: An Introduction to Phosphorus-31 NMR

ERIC Educational Resources Information Center

Sibbald, Paul A.

2015-01-01

Nuclear magnetic resonance (NMR) spectroscopy is commonly used in modern synthetic chemistry to monitor the conversion of reactants to products. Since instruction in the use of NMR spectroscopy typically does not occur until after the introduction of nucleophilic substitution reactions, organic chemistry students are not able to take advantage of…

A Conceptual Approach to Limiting-Reagent Problems

ERIC Educational Resources Information Center

Sostarecz, Michael C.; Sostarecz, Audra Goach

2012-01-01

A solid foundation of chemistry principles is only gained through a true comprehension of the material as opposed to pure memorization. One of the most fundamental concepts in chemistry is that of determining the amount of product formed in a chemical reaction when one of the reactants is limiting. To increase students' comprehension of this…

Mechanochemical Synthesis of Two Polymorphs of the Tetrathiafulvalene-Chloranil Charge Transfer Salt: An Experiment for Organic Chemistry

ERIC Educational Resources Information Center

Wixtrom, Alex; Buhler, Jessica; Abdel-Fattah, Tarek

2014-01-01

Mechanochemical syntheses avoid or considerably reduce the use of reaction solvents, thus providing green chemistry synthetic alternatives that are both environmentally friendly and economically advantageous. The increased solid-state reactivity generated by mechanical energy imparted to the reactants by grinding or milling can offer alternative…

Reactions of Azine Anions with Nitrogen and Oxygen Atoms: Implications for Titan's Upper Atmosphere and Interstellar Chemistry.

PubMed

Wang, Zhe-Chen; Cole, Callie A; Demarais, Nicholas J; Snow, Theodore P; Bierbaum, Veronica M

2015-08-26

Azines are important in many extraterrestrial environments, from the atmosphere of Titan to the interstellar medium. They have been implicated as possible carriers of the diffuse interstellar bands in astronomy, indicating their persistence in interstellar space. Most importantly, they constitute the basic building blocks of DNA and RNA, so their chemical reactivity in these environments has significant astrobiological implications. In addition, N and O atoms are widely observed in the ISM and in the ionospheres of planets and moons. However, the chemical reactions of molecular anions with abundant interstellar and atmospheric atomic species are largely unexplored. In this paper, gas-phase reactions of deprotonated anions of benzene, pyridine, pyridazine, pyrimidine, pyrazine, and s-triazine with N and O atoms are studied both experimentally and computationally. In all cases, the major reaction channel is associative electron detachment; these reactions are particularly important since they control the balance between negative ions and free electron densities. The reactions of the azine anions with N atoms exhibit larger rate constants than reactions of corresponding chain anions. The reactions of azine anions with O atoms are even more rapid, with complex product patterns for different reactants. The mechanisms are studied theoretically by employing density functional theory; spin conversion is found to be important in determining some product distributions. The rich gas-phase chemistry observed in this work provides a better understanding of ion-atom reactions and their contributions to ionospheric chemistry as well as the chemical processing that occurs in the boundary layers between diffuse and dense interstellar clouds.

Laser flash photolysis studies of atmospheric free radical chemistry using optical diagnostic techniques

NASA Technical Reports Server (NTRS)

Wine, Paul H.; Nicovich, J. M.; Hynes, Anthony J.; Stickel, Robert E.; Thorn, R. P.; Chin, Mian; Cronkhite, Jeffrey A.; Shackelford, Christie J.; Zhao, Zhizhong; Daykin, Edward P.

1993-01-01

Some recent studies carried out in our laboratory are described where laser flash photolytic production of reactant free radicals has been combined with reactant and/or product detection using time-resolved optical techniques to investigate the kinetics and mechanisms of important atmospheric chemical reactions. Discussed are (1) a study of the radical-radical reaction O + BrO yields Br + O2 where two photolysis lasers are employed to prepare the reaction mixture and where the reactants O and BrO are monitored simultaneously using atomic resonance fluorescence to detect O and multipass UV absorption to detect BrO; (2) a study of the reaction of atomic chlorine with dimethylsulfide (CH3SCH3) where atomic resonance fluorescence detection of Cl is employed to elucidate the kinetics and tunable diode laser absorption spectroscopy is employed to investigate the HCl product yield; and (3) a study of the aqueous phase chemistry of Cl2(-) radicals where longpath UV absorption spectroscopy is employed to investigate the kinetics of the Cl2(-) + H2O reaction.

Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, Zhe; Day, Douglas A.; Ortega, Amber M.

Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O( 1D), O( 3P), and O 3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditionsmore » via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to water vapor mixing ratio (H 2O) and external OH reactivity (OHR ext), as both non-OH reactants and OH scale roughly proportionally to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O( 1D), O( 3P), and O 3 have relative contributions to volatile organic compound (VOC) consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. We define “riskier OFR conditions” as those with either low H 2O (< 0.1%) or high OHR ext (≥ 100s –1 in OFR185 and > 200s –1 in OFR254). We strongly suggest avoiding such conditions as the importance of non-OH reactants can be substantial for the most sensitive species, although OH may still dominate under some riskier conditions, depending on the species present. Photolysis at non-tropospheric wavelengths (185 and 254 nm) may play a significant (> 20%) role in the degradation of some aromatics, as well as some oxidation intermediates, under riskier reactor conditions, if the quantum yields are high. Under riskier conditions, some biogenics can have substantial destructions by O 3, similarly to the troposphere. Working under low O 2 (volume mixing ratio of 0.002) with the OFR185 mode allows OH to completely dominate over O 3 reactions even for the biogenic species most reactive with O 3. Non-tropospheric VOC photolysis may have been a problem in some laboratory and source studies, but can be avoided or lessened in future studies by diluting source emissions and working at lower precursor concentrations in laboratory studies and by humidification. Photolysis of secondary organic aerosol (SOA) samples is estimated to be significant (> 20%) under the upper limit assumption of unity quantum yield at medium (1 × 10 13 and 1.5 × 10 15 photons cm –2 s –1 at 185 and 254 nm, respectively) or higher UV flux settings. Furthermore, the need for quantum yield measurements of both VOC and SOA photolysis is highlighted in this study. The results of this study allow improved OFR operation and experimental design and also inform the design of future reactors.« less

Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling

DOE PAGES

Peng, Zhe; Day, Douglas A.; Ortega, Amber M.; ...

2016-04-06

Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O( 1D), O( 3P), and O 3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditionsmore » via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to water vapor mixing ratio (H 2O) and external OH reactivity (OHR ext), as both non-OH reactants and OH scale roughly proportionally to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O( 1D), O( 3P), and O 3 have relative contributions to volatile organic compound (VOC) consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. We define “riskier OFR conditions” as those with either low H 2O (< 0.1%) or high OHR ext (≥ 100s –1 in OFR185 and > 200s –1 in OFR254). We strongly suggest avoiding such conditions as the importance of non-OH reactants can be substantial for the most sensitive species, although OH may still dominate under some riskier conditions, depending on the species present. Photolysis at non-tropospheric wavelengths (185 and 254 nm) may play a significant (> 20%) role in the degradation of some aromatics, as well as some oxidation intermediates, under riskier reactor conditions, if the quantum yields are high. Under riskier conditions, some biogenics can have substantial destructions by O 3, similarly to the troposphere. Working under low O 2 (volume mixing ratio of 0.002) with the OFR185 mode allows OH to completely dominate over O 3 reactions even for the biogenic species most reactive with O 3. Non-tropospheric VOC photolysis may have been a problem in some laboratory and source studies, but can be avoided or lessened in future studies by diluting source emissions and working at lower precursor concentrations in laboratory studies and by humidification. Photolysis of secondary organic aerosol (SOA) samples is estimated to be significant (> 20%) under the upper limit assumption of unity quantum yield at medium (1 × 10 13 and 1.5 × 10 15 photons cm –2 s –1 at 185 and 254 nm, respectively) or higher UV flux settings. Furthermore, the need for quantum yield measurements of both VOC and SOA photolysis is highlighted in this study. The results of this study allow improved OFR operation and experimental design and also inform the design of future reactors.« less

Making a molecular gas in the quantum regime

NASA Astrophysics Data System (ADS)

Ni, Kang-Kuen

2017-04-01

Ultracold molecules are exciting systems for a large range of scientific explorations including studies of novel phases of matter and precision measurement. In this talk, I will present a brief story of the first quantum gas of molecules, KRb, created under my PhD advisor, Deborah Jin, in 2008. A complete surprise was finding ultracold chemistry in such a system through measurements of reactant losses. In particular, long-range physics that determines KRb reactant collision rates, including van der Waals interactions, quantum statistics, and dipolar interactions, were studied extensively. However, the short-range behavior of these chemical reactions remains unknown. A legacy of her work is carried out in my lab at Harvard, where we are integrating physical chemistry tools with cold atom techniques to study ultracold chemistry with KRb molecules. In particular, we aim to elucidate the four-center reaction 2 KRb ->K2 + Rb2 by detecting the reaction products through ionization - both identify the product species and mapping out their complete quantum states.

High-pressure ion source combined with an in-axis ion trap mass spectrometer. 1. Instrumentation and applications

PubMed

Mathurin; Faye; Brunot; Tabet; Wells; Fuche

2000-10-15

A new combination of a dual EI/CI ion source with a quadrupole ion trap mass spectrometer has been realized in order to efficiently produce negative ions in the reaction cell. Analysis of volatile compounds was performed under negative ion chemical ionization (NICI) during a reaction period where selected reactant negative ions, previously produced in the external ion source, were allowed to interact with molecules, introduced by hyphenated techniques such as gas chromatography. The O2*-, CH3O-, and Cl- reactant ions were used in this study to ensure specific ion/molecule interactions such as proton transfer, nucleophilic displacement, or charge exchange processes, respectively leading to even-electron species, i.e., deprotonated [M - H]- molecules, diagnostic [M - R]- ions, or odd-electron M*- molecular species. The reaction orientation depends on the thermochemistry of reactions within kinetic controls. First analytical results are presented here for the trace-level detection of several contaminants under NICI/Cl- conditions. Phosphorus-containing compounds (malathion, ethyl parathion, and methyl parathion as representative for pesticides) and nitro-containing compounds (2,4,6-trinitrotoluene for explosive material) have been chosen in order to explore the analytical ability of this promising instrumental coupling.

To Model Chemical Reactivity in Heterogeneous Emulsions, Think Homogeneous Microemulsions.

PubMed

Bravo-Díaz, Carlos; Romsted, Laurence Stuart; Liu, Changyao; Losada-Barreiro, Sonia; Pastoriza-Gallego, Maria José; Gao, Xiang; Gu, Qing; Krishnan, Gunaseelan; Sánchez-Paz, Verónica; Zhang, Yongliang; Dar, Aijaz Ahmad

2015-08-25

Two important and unsolved problems in the food industry and also fundamental questions in colloid chemistry are how to measure molecular distributions, especially antioxidants (AOs), and how to model chemical reactivity, including AO efficiency in opaque emulsions. The key to understanding reactivity in organized surfactant media is that reaction mechanisms are consistent with a discrete structures-separate continuous regions duality. Aggregate structures in emulsions are determined by highly cooperative but weak organizing forces that allow reactants to diffuse at rates approaching their diffusion-controlled limit. Reactant distributions for slow thermal bimolecular reactions are in dynamic equilibrium, and their distributions are proportional to their relative solubilities in the oil, interfacial, and aqueous regions. Our chemical kinetic method is grounded in thermodynamics and combines a pseudophase model with methods for monitoring the reactions of AOs with a hydrophobic arenediazonium ion probe in opaque emulsions. We introduce (a) the logic and basic assumptions of the pseudophase model used to define the distributions of AOs among the oil, interfacial, and aqueous regions in microemulsions and emulsions and (b) the dye derivatization and linear sweep voltammetry methods for monitoring the rates of reaction in opaque emulsions. Our results show that this approach provides a unique, versatile, and robust method for obtaining quantitative estimates of AO partition coefficients or partition constants and distributions and interfacial rate constants in emulsions. The examples provided illustrate the effects of various emulsion properties on AO distributions such as oil hydrophobicity, emulsifier structure and HLB, temperature, droplet size, surfactant charge, and acidity on reactant distributions. Finally, we show that the chemical kinetic method provides a natural explanation for the cut-off effect, a maximum followed by a sharp reduction in AO efficiency with increasing alkyl chain length of a particular AO. We conclude with perspectives and prospects.

Isolation of the Copper Redox Steps in the Standard Selective Catalytic Reduction on Cu-SSZ-13

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paolucci, Christopher; Verma, Anuj A.; Bates, Shane A.

2014-10-27

Operando X-ray absorption experiments and density functional theory (DFT) calculations are reported that elucidate the role of copper redox chemistry in the selective catalytic reduction (SCR) of NO over Cu-exchanged SSZ-13. Catalysts prepared to contain only isolated, exchanged CuII ions evidence both CuII and CuI ions under standard SCR conditions at 473 K. Reactant cutoff experiments show that NO and NH3 together are necessary for CuII reduction to CuI. DFT calculations show that NO-assisted NH3 dissociation is both energetically favorable and accounts for the observed CuII reduction. The calculations predict in situ generation of Brønsted sites proximal to CuI uponmore » reduction, which we quantify in separate titration experiments. Both NO and O2 are necessary for oxidation of CuI to CuII, which DFT suggests to occur by a NO2 intermediate. Reaction of Cu-bound NO2 with proximal NH4 + completes the catalytic cycle. N2 is produced in both reduction and oxidation half-cycles.« less

Isolation of the Copper Redox Steps in the Standard Selective Catalytic Reduction on Cu-SSZ-13

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paolucci, Christopher; Verma, Anuj A.; Bates, Shane A.

2014-09-12

Operando X-ray absorption experiments and density functional theory (DFT) calculations are reported that elucidate the role of copper redox chemistry in the selective catalytic reduction (SCR) of NO over Cu-exchanged SSZ-13. Catalysts prepared to contain only isolated, exchanged CuII ions evidence both CuII and CuI ions under standard SCR conditions at 473 K. Reactant cutoff experiments show that NO and NH3 together are necessary for CuII reduction to CuI. DFT calculations show that NO-assisted NH3 dissociation is both energetically favorable and accounts for the observed CuII reduction. The calculations predict in situ generation of Brønsted sites proximal to CuI uponmore » reduction, which we quantify in separate titration experiments. Both NO and O2 are necessary for oxidation of CuI to CuII, which DFT suggests to occur by a NO2 intermediate. Reaction of Cu-bound NO2 with proximal NH4 + completes the catalytic cycle. N2 is produced in both reduction and oxidation half-cycles.« less

Multiple Ion Binding Equilibria, Reaction Kinetics, and Thermodynamics in Dynamic Models of Biochemical Pathways

PubMed Central

Vinnakota, Kalyan C.; Wu, Fan; Kushmerick, Martin J.; Beard, Daniel A.

2009-01-01

The operation of biochemical systems in vivo and in vitro is strongly influenced by complex interactions between biochemical reactants and ions such as H+, Mg2+, K+, and Ca2+. These are important second messengers in metabolic and signaling pathways that directly influence the kinetics and thermodynamics of biochemical systems. Herein we describe the biophysical theory and computational methods to account for multiple ion binding to biochemical reactants and demonstrate the crucial effects of ion binding on biochemical reaction kinetics and thermodynamics. In simulations of realistic systems, the concentrations of these ions change with time due to dynamic buffering and competitive binding. In turn, the effective thermodynamic properties vary as functions of cation concentrations and important environmental variables such as temperature and overall ionic strength. Physically realistic simulations of biochemical systems require incorporating all of these phenomena into a coherent mathematical description. Several applications to physiological systems are demonstrated based on this coherent simulation framework. PMID:19216922

Quantitative detection of RO2 radicals and other products from cyclohexene ozonolysis with ammonium-CI3-TOF and acetate-CI-API-TOF

NASA Astrophysics Data System (ADS)

Hansel, A.; Scholz, W.; Mentler, B.; Fischer, L.; Berndt, T.

2017-12-01

The performance of the novel ammonium-CI3-TOF utilizing NH4+ adduct ion chemistry to measure quantitatively first generation oxidized product molecules (OMs) as well as highly oxidized organic molecules (HOMs) was investigated for the first time. The gas-phase ozonolysis of cyclohexene served as a test system in order to evaluate the capability of the detection systems. Experiments have been carried out in the TROPOS free-jet flow system at close to atmospheric conditions. Product ion signals were simultaneously observed by the ammonium-CI3-TOF and the acetate-CI-API-TOF. Both instruments are in remarkable good agreement within a factor of two for HOMs. For OMs not containing an OOH group the acetate technique can considerably underestimate OM concentrations by 2-3 orders of magnitude. First steps of cyclohexene ozonolysis generate ten different (m/z product peaks) main products comprising 92% of observed OMs. The remaining 8% are distributed over several (m/z peaks) minor products that can be attributed to HOMs, predominately to highly oxidized RO2 radicals. Summing up, observed ammonium-CI3-TOF products yield 4.9 x 109 molecules cm-³ in excellent agreement with the amount of reacted cyclohexene of 5.0 x 109 molecules cm-³ for reactant concentrations of [O3] = 2.25 x 1012 molecules cm-³ and [cyclohexene] = 2.0 x 1012 molecules cm-³ and a reaction time of 7.9 s. NH4+ adduct ion chemistry based CIMS techniques offer a unique opportunity for complete detection of the whole product distribution, and consequently, for a much better understanding of atmospheric oxidation processes.

Detection of explosives using negative ion mobility spectrometry in air based on dopant-assisted thermal ionization.

PubMed

Shahraki, Hassan; Tabrizchi, Mahmoud; Farrokhpor, Hossein

2018-05-26

The ionization source is an essential component of most explosive detectors based on negative ion mobility spectrometry. Conventional ion sources suffer from such inherent limitations as special safety regulations on radioactive sources or generating interfering ions (for non-radioactive sources) such as corona discharge operating in the air. In this study, a new negative ion source is introduced for ion mobility spectrometry that is based on thermal ionization and operates in the air, applicable to explosives detection. Our system consists of a heating filament powered by an isolated power supply connected to negative high voltage. The ionization is assisted by doping chlorinated compounds in the gas phase using chlorinated hydrocarbons in contact with the heating element to yield Cl - reactant ions. Several chlorinated hydrocarbons are evaluated as the reagent chemicals for providing Cl- reactant ions, of which CCl 4 is identified as the best ionizing reagent. The ion source is evaluated by recording the ion mobility spectra of common explosives, including TNT, RDX, and PETN in the air. A detection limit of 150 pg is obtained for TNT. Compared to other ionization sources, the new source is found to be low-cost, simple, and long-lived, making it suited to portable explosives detection devices. Copyright © 2018 Elsevier B.V. All rights reserved.

Redox and Lewis acid-base activities through an electronegativity-hardness landscape diagram.

PubMed

Das, Ranjita; Vigneresse, Jean-Louis; Chattaraj, Pratim Kumar

2013-11-01

Chemistry is the science of bond making and bond breaking which requires redistribution of electron density among the reactant partners. Accordingly acid-base and redox reactions form cardinal components in all branches of chemistry, e.g., inorganic, organic, physical or biochemistry. That is the reason it forms an integral part of the undergraduate curriculum all throughout the globe. In an electronegativity (χ)- hardness (η) landscape diagram the diagonal χ = η line separates reducing agents from oxidizing agents as well as Lewis acids from Lewis bases. While electronegativity is related to the degree of electron transfer between two reactants, hardness is related to the resistance to that process. Accordingly the electronegativities of oxidizing agents/Lewis acids are generally greater than the corresponding hardness values and the reverse is true for reducing agents/Lewis bases. Electrophiles and nucleophiles are also expected to follow similar trends.

State-to-state chemistry for three-body recombination in an ultracold rubidium gas.

PubMed

Wolf, Joschka; Deiß, Markus; Krükow, Artjom; Tiemann, Eberhard; Ruzic, Brandon P; Wang, Yujun; D'Incao, José P; Julienne, Paul S; Denschlag, Johannes Hecker

2017-11-17

Experimental investigation of chemical reactions with full quantum state resolution for all reactants and products has been a long-term challenge. Here we prepare an ultracold few-body quantum state of reactants and demonstrate state-to-state chemistry for the recombination of three spin-polarized ultracold rubidium (Rb) atoms to form a weakly bound Rb 2 molecule. The measured product distribution covers about 90% of the final products, and we are able to discriminate between product states with a level splitting as small as 20 megahertz multiplied by Planck's constant. Furthermore, we formulate propensity rules for the distribution of products, and we develop a theoretical model that predicts many of our experimental observations. The scheme can readily be adapted to other species and opens a door to detailed investigations of inelastic or reactive processes. Copyright © 2017, American Association for the Advancement of Science.

Self-assembly of a superparamagnetic raspberry-like silica/iron oxide nanocomposite using epoxy-amine coupling chemistry.

PubMed

Cano, Manuel; de la Cueva-Méndez, Guillermo

2015-02-28

The fabrication of colloidal nanocomposites would benefit from controlled hetero-assembly of ready-made particles through covalent bonding. Here we used epoxy-amine coupling chemistry to promote the self-assembly of superparamagnetic raspberry-like nanocomposites. This adaptable method induced the covalent attachment of iron oxide nanoparticles sparsely coated with amine groups onto epoxylated silica cores in the absence of other reactants.

Step Towards Modeling the Atmosphere of Titan: State-Selected Reactions of O+ with Methane.

PubMed

Hrušák, J; Paidarová, I

2016-11-01

Methane conversion and in particular the formation of the C-O bond is one of fundamental entries to organic chemistry and it appears to be essential for understanding parts of atmospheric chemistry of Titan, but, in broader terms it might be also relevant for Earth-like exoplanets. Theoretical study of the reactions of methane with atomic oxygen ion in its excited electronic states requires treating simultaneously at least 19 electronic states. Development of a computational strategy that would allow chemically reasonable and computationally feasible treatment of the CH 4 (X)/O + ( 2 D, 2 P) system is by far not trivial and it requires careful examination of all the complex features of the corresponding 19 potential energy surfaces. Before entering the discussion of the rich (photo) chemistry, inspection of the long range behavior of the system with focus on electric dipole transition moments is required. Our calculations show nonzero probability for the reactants to decay before entering the multiple avoided crossings region of the [CH 4  + O → products] + reaction. For the CH 4 /O + ( 2 P) system non-zero transition moment probabilities occur over the entire range of considered C-O distances (up to 15 Å), while for the CH 4 /O + ( 2 D) system these probabilities are lower by one order of magnitude and were found only at C-O distances smaller than 6 Å.

Fast chemical reaction in two-dimensional Navier-Stokes flow: initial regime.

PubMed

Ait-Chaalal, Farid; Bourqui, Michel S; Bartello, Peter

2012-04-01

This paper studies an infinitely fast bimolecular chemical reaction in a two-dimensional biperiodic Navier-Stokes flow. The reactants in stoichiometric quantities are initially segregated by infinite gradients. The focus is placed on the initial stage of the reaction characterized by a well-defined one-dimensional material contact line between the reactants. Particular attention is given to the effect of the diffusion κ of the reactants. This study is an idealized framework for isentropic mixing in the lower stratosphere and is motivated by the need to better understand the effect of resolution on stratospheric chemistry in climate-chemistry models. Adopting a Lagrangian straining theory approach, we relate theoretically the ensemble mean of the length of the contact line, of the gradients along it, and of the modulus of the time derivative of the space-average reactant concentrations (here called the chemical speed) to the joint probability density function of the finite-time Lyapunov exponent λ with two times τ and τ[over ̃]. The time 1/λ measures the stretching time scale of a Lagrangian parcel on a chaotic orbit up to a finite time t, while τ measures it in the recent past before t, and τ[over ̃] in the early part of the trajectory. We show that the chemical speed scales like κ(1/2) and that its time evolution is determined by rare large events in the finite-time Lyapunov exponent distribution. The case of smooth initial gradients is also discussed. The theoretical results are tested with an ensemble of direct numerical simulations (DNSs) using a pseudospectral model.

The Role of Iron In Sporadic E Layers

NASA Astrophysics Data System (ADS)

Vondrak, T.; Woodcock, K. R. I.; Plane, J. M. C.

Sporadic E layers in the lower thermosphere are mostly composed of metallic ions, of which Fe+ is the most abundant. Because dielectric recombination (Fe+ + elec- tron) is very slow, the lifetime of Fe+ above about 100 km is at least several days. However, below this height molecular ions such as FeO+, FeO2+ and FeN2+ form in- creasingly rapidly through reactions with O3, O2 and N2, respectively. These undergo rapid dissociative recombination with electrons, causing Fe+ to be neutralised increas- ingly rapidly as a sporadic E layer descends. Indeed, this is the most likely mechanism for the formation of the sporadic neutral Fe layers that are observed by lidar. However, atomic O plays a very important role in reducing these molecular ions back to Fe+, competing with dissociative recombination and thus slowing the rate at which Fe+ is neutralised and a sporadic E layer dissipates. This paper will discuss a laboratory and modelling study of the reactions of FeO+, FeO2+ and FeN2+ with atomic O. These reactions were studied (for the first time) in a fast flow tube, using the pulsed laser ablation of a rotating iron rod as the source of Fe+ ions in the upstream section of the tube. Reactants were then added to produce molecular ions, and atomic O further downstream through a movable injector. Fe+ and the molecular ions were detected at the downstream end of the tube using a two-stage quadrupole mass spectrometer. The spectroscopy of the FeO+ ion, observed by laser induced fluorescence, will also be discussed as a candidate for future ground-based lidar studies of the ion chemistry of the lower thermosphere.

Nanopore reactive adsorbents for the high-efficiency removal of waste species

DOEpatents

Yang, Arthur Jing-Min; Zhang, Yuehua

2005-01-04

A nanoporous reactive adsorbent incorporates a relatively small number of relatively larger reactant, e.g., metal, enzyme, etc., particles (10) forming a discontinuous or continuous phase interspersed among and surrounded by a continuous phase of smaller adsorbent particles (12) and connected interstitial pores (14) therebetween. The reactive adsorbent can effectively remove inorganic or organic impurities in a liquid by causing the liquid to flow through the adsorbent. For example, silver ions may be adsorbed by the adsorbent particles (12) and reduced to metallic silver by reducing metal, such as ions, as the reactant particles (10). The column can be regenerated by backwashing with the liquid effluent containing, for example, acetic acid.

Global and Local Partitioning of the Charge Transferred in the Parr-Pearson Model.

PubMed

Orozco-Valencia, Angel Ulises; Gázquez, José L; Vela, Alberto

2017-05-25

Through a simple proposal, the charge transfer obtained from the cornerstone theory of Parr and Pearson is partitioned, for each reactant, in two channels: an electrophilic, through which the species accepts electrons, and the other, a nucleophilic, where the species donates electrons. It is shown that this global model allows us to determine unambiguously the charge-transfer mechanism prevailing in a given reaction. The partitioning is extended to include local effects through the Fukui functions of the reactants. This local model is applied to several emblematic reactions in organic and inorganic chemistry, and we show that besides improving the correlations obtained with the global model it provides valuable information concerning the atoms in the reactants playing the most important roles in the reaction and thus improving our understanding of the reaction under study.

Cycling Performance of the Iron-Chromium Redox Energy Storage System

NASA Technical Reports Server (NTRS)

Gahn, R. F.; Hagedorn, N. H.; Johnson, J. A.

1985-01-01

Extended charge-discharge cycling of this electrochemical storage system at 65 C was performed on 14.5 sq cm single cells and a four cell, 867 sq cm bipolar stack. Both the anolyte and catholyte reactant fluids contained 1 molar concentrations of iron and chromium chlorides in hydrochloric acid and were separated by a low-selectivity, cation-exchange membrane. The effect of cycling on the chromium electrode and the cation-exchange membrane was determined. Bismuth and bismuth-lead catalyzed chromium electrodes and a radiation-grafted polyethylene membrane were evaluated by cycling between 5 and 85 percent state-of-charge at 80 mA/sq cm and by periodic charge-discharge polarization measurements to 140 mA/sq cm. Gradual performance losses were observed during cycling but were recoverable by completely discharging the system. Good scale-up to the 867 sq cm stack was achieved. The only difference appeared to be an unexplained resistive-type loss which resulted in a 75 percent W-hr efficiency (at 80 mA/sq cm versus 81 percent for the 14.5 sq cm cell). A new rebalance cell was developed to maintain reactant ionic balance. The cell successfully reduced ferric ions in the iron reactant stream to ferrous ions while chloride ions were oxidized to chlorine gas.

Cycling performance of the iron-chromium redox energy storage system

NASA Technical Reports Server (NTRS)

Gahn, R. F.; Hagedorn, N. H.; Johnson, J. A.

1985-01-01

Extended charge-discharge cycling of this electrochemical storage system at 65 C was performed on 14.5 sq cm single cells and a four cell, 867 sq cm bipolar stack. Both the anolyte and catholyte reactant fluids contained 1 molar concentrations of iron and chromium chlorides in hydrochloric acid and were separated by a low-selectivity, cation-exchange membrane. The effect of cycling on the chromium electrode and the cation-exchange membrane was determined. Bismuth and bismuth-lead catalyzed chromium electrodes and a radiation-grafted polyethylene membrane were evaluated by cycling between 5 and 85 percent state-of-charge at 80 mA/sq cm and by periodic charge-discharge polarization measurements to 140 mA/sq cm. Gradual performance losses were observed during cycling but were recoverable by completely discharging the system. Good scale-up to the 867 sq cm stack was achieved. The only difference appeared to be an unexplained resistive-type loss which resulted in a 75 percent W-hr efficiency (at 80 mA/sq cm versus 81 percent for the 14.5 sq cm cell). A new rebalance cell was developed to maintain reactant ionic balance. The cell successfully reduced ferric ions in the iron reactant stream to ferrous ions while chloride ions were oxidized to chlorine gas.

Spatial atomic layer deposition for coating flexible porous Li-ion battery electrodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yersak, Alexander S.; Sharma, Kashish; Wallas, Jasmine M.

Ultrathin atomic layer deposition (ALD) coatings on the electrodes of Li-ion batteries can enhance the capacity stability of the Li-ion batteries. To commercialize ALD for Li-ion battery production, spatial ALD is needed to decrease coating times and provide a coating process compatible with continuous roll-to-roll (R2R) processing. The porous electrodes of Li-ion batteries provide a special challenge because higher reactant exposures are needed for spatial ALD in porous substrates. This work utilized a modular rotating cylinder spatial ALD reactor operating at rotation speeds up to 200 revolutions/min (RPM) and substrate speeds up to 200 m/min. The conditions for spatial ALDmore » were adjusted to coat flexible porous substrates. The reactor was initially used to characterize spatial Al2O3 and ZnO ALD on flat, flexible metalized polyethylene terephthalate foils. These studies showed that slower rotation speeds and spacers between the precursor module and the two adjacent pumping modules could significantly increase the reactant exposure. The modular rotating cylinder reactor was then used to coat flexible, model porous anodic aluminum oxide (AAO) membranes. The uniformity of the ZnO ALD coatings on the porous AAO membranes was dependent on the aspect ratio of the pores and the reactant exposures. Larger reactant exposures led to better uniformity in the pores with higher aspect ratios. The reactant exposures were increased by adding spacers between the precursor module and the two adjacent pumping modules. The modular rotating cylinder reactor was also employed for Al2O3 ALD on porous LiCoO2 (LCO) battery electrodes. Uniform Al coverages were obtained using spacers between the precursor module and the two adjacent pumping modules at rotation speeds of 25 and 50 RPM. The LCO electrodes had a thickness of ~49 um and pores with aspect ratios of ~12-25. Coin cells were then constructed using the ALD-coated LCO electrodes and were tested to determine their battery performance. The capacity of the Al2O3 ALD-coated LCO battery electrodes was measured versus the number of charge-discharge cycles. Both temporal and spatial ALD processing methods led to higher capacity stability compared with uncoated LCO battery electrodes. The results for improved battery performance were comparable for temporal and spatial ALD-coated electrodes. The next steps are also presented for scale-up to R2R spatial ALD using the modular rotating cylinder reactor.« less

Charge exchange molecular ion source

DOEpatents

Vella, Michael C.

2003-06-03

Ions, particularly molecular ions with multiple dopant nucleons per ion, are produced by charge exchange. An ion source contains a minimum of two regions separated by a physical barrier and utilizes charge exchange to enhance production of a desired ion species. The essential elements are a plasma chamber for production of ions of a first species, a physical separator, and a charge transfer chamber where ions of the first species from the plasma chamber undergo charge exchange or transfer with the reactant atom or molecules to produce ions of a second species. Molecular ions may be produced which are useful for ion implantation.

Applications of Programmable Calculators in Chemistry Classes

ERIC Educational Resources Information Center

Holdsworth, David

1977-01-01

Described is the use of calculators in two experiments. In the first, students determine the relative atomic mass of magnesium. In the second, students use a calculator to determine a constant for gaseous concentrations of two reactants and the product at equilibrium. (AJ)

DON'T BE TRICKED BY YOUR INTEGRATED RATE PLOT!

EPA Science Inventory

Reaction order can be determined from kinetic data in a variety of ways. Two methods commonly employed are comparison of initial rates (while varying reactant concentration) and plotting integrated rate expressions. Both of these are introduced in general and physical chemistry t...

Synthesis of Meso-Octamethylporphyrinogen: An Undergraduate Laboratory Mini-Scale Experiment in Organic Heterocyclic Chemistry

ERIC Educational Resources Information Center

Sobral, Abilio J. F. N.

2005-01-01

The synthesis of meso-octamethylporphyrinogen that involves a mini-scale preparation and uses acetone as reactant and also as solvent is presented. It results in a product of almost analytical grade directly from the reaction medium.

Synthesis and Study of Silver Nanoparticles

ERIC Educational Resources Information Center

Soloman, Sally D.; Bahadory, Mozghan; Jeyarajasingam, Aravindan V.; Rutkowsky, Susan A.; Boritz, Charles; Mulfinger, Lorraine

2007-01-01

A laboratory experiment was conducted in which the students synthesized yellow colloidal silver, estimate particle size using visible spectroscopy and studied aggregation effects. The students were thus introduced to nanotechnology along with other topics such as redox chemistry, limiting and excess reactants, spectroscopy and atomic size.

CHEMISTRY UNDER 'GREENER' CONDITIONS: SOLVENT-FREE SYNTHESIS USING MICROWAVE IRRADIATION

EPA Science Inventory

Solvent-free approach is emphasized that involves microwave (MW) irradiation of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable mineral supports such as alumina, silica, clay, or 'doped' surfaces which is applicable to a wide range of cleavag...

FRET-Based Nanobiosensors for Imaging Intracellular Ca²⁺ and H⁺ Microdomains.

PubMed

Zamaleeva, Alsu I; Despras, Guillaume; Luccardini, Camilla; Collot, Mayeul; de Waard, Michel; Oheim, Martin; Mallet, Jean-Maurice; Feltz, Anne

2015-09-23

Semiconductor nanocrystals (NCs) or quantum dots (QDs) are luminous point emitters increasingly being used to tag and track biomolecules in biological/biomedical imaging. However, their intracellular use as highlighters of single-molecule localization and nanobiosensors reporting ion microdomains changes has remained a major challenge. Here, we report the design, generation and validation of FRET-based nanobiosensors for detection of intracellular Ca(2+) and H⁺ transients. Our sensors combine a commercially available CANdot(®)565QD as an energy donor with, as an acceptor, our custom-synthesized red-emitting Ca(2+) or H⁺ probes. These 'Rubies' are based on an extended rhodamine as a fluorophore and a phenol or BAPTA (1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid) for H⁺ or Ca(2+) sensing, respectively, and additionally bear a linker arm for conjugation. QDs were stably functionalized using the same SH/maleimide crosslink chemistry for all desired reactants. Mixing ion sensor and cell-penetrating peptides (that facilitate cytoplasmic delivery) at the desired stoichiometric ratio produced controlled multi-conjugated assemblies. Multiple acceptors on the same central donor allow up-concentrating the ion sensor on the QD surface to concentrations higher than those that could be achieved in free solution, increasing FRET efficiency and improving the signal. We validate these nanosensors for the detection of intracellular Ca(2+) and pH transients using live-cell fluorescence imaging.

Complex Autocatalysis in Simple Chemistries.

PubMed

Virgo, Nathaniel; Ikegami, Takashi; McGregor, Simon

2016-01-01

Life on Earth must originally have arisen from abiotic chemistry. Since the details of this chemistry are unknown, we wish to understand, in general, which types of chemistry can lead to complex, lifelike behavior. Here we show that even very simple chemistries in the thermodynamically reversible regime can self-organize to form complex autocatalytic cycles, with the catalytic effects emerging from the network structure. We demonstrate this with a very simple but thermodynamically reasonable artificial chemistry model. By suppressing the direct reaction from reactants to products, we obtain the simplest kind of autocatalytic cycle, resulting in exponential growth. When these simple first-order cycles are prevented from forming, the system achieves superexponential growth through more complex, higher-order autocatalytic cycles. This leads to nonlinear phenomena such as oscillations and bistability, the latter of which is of particular interest regarding the origins of life.

CHEMISTRY UNDER NON-TRADITIONAL CONDITIONS: SOLVENT-FREE SYNTHESIS USING MICROWAVE IRRADIATION

EPA Science Inventory

A solvent-free approach that involves microwave (MW) irradiation of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable mineral supports such as alumina, silica, clay, or "doped" surfaces is presented which is applicable to a wide range of cleava...

Astrochemistry

NASA Astrophysics Data System (ADS)

Millar, T. J.

2015-08-01

In the last 40 years a wide range of molecules, including neutrals, cations and anions, containing up to 13 atoms—in addition to detections of {{\\text{C}}60} and {{\\text{C}}70} —have been found in the harsh environment of the interstellar medium. The exquisite sensitivity and very high spectral and, more recently, spatial resolution, of modern telescopes has enabled the physics of star formation to be probed through rotational line emission. In this article, I review the basic properties of interstellar clouds and the processes that initiate the chemistry and generate chemical complexity, particularly in regions of star and planet formation. Our understanding of astrochemistry has evolved over the years. Before 1990, the general consensus was that molecules were formed in binary, gas-phase, or volume, reactions, most importantly ion-neutral reactions despite the very low ionization in clouds. Since then, observations have indicated unambiguously that there is also a contribution from surface processes, particularly on the icy mantles that form around refractory grain cores in cold, dense gas. The balance between these two processes depends on particular physical conditions and can vary during the life cycle of a particular volume of interstellar cloud. The complex chemistry that occurs in space is driven mostly through interaction of the gas with cosmic ray protons, a source of ionization that enables a rich ion-neutral chemistry. In addition, I show that the interaction between the gas and the dust in cold, dense regions also leads to additional chemical complexity through reactions that take place in ices at only a few tens of degrees above absolute zero. Although densities are low compared to those in terrestrial environments, the extremely long life times of interstellar clouds and their enormous sizes, enable complex molecules to be synthesised and detected. I show that in some instances, particularly in reactions involving deuterium, the rotational populations of reactants, together with spin-selection rules, can determine the detailed abundances. Although the review is mainly focused on regions associated with star formation, I also consider chemistry in other interesting astronomical regions—in the early Universe and in the envelopes formed by mass loss during the final stages of stellar evolution.

An idealised study of the effects of small scales on chemistry in a two-dimensional turbulent flow.

NASA Astrophysics Data System (ADS)

Chaalal, F. Ait; Bartello, P.; Bourqui, M.

2009-04-01

The non-linear nature of stratospheric chemical reactions makes them sensitive to mixing and diffusion. Most stratospheric Climate-Chemistry Models neglect the effects of sub-grid flow structures on chemistry. Several previous studies have pointed out that such unresolved small scales could significantly affect the chemistry. However this problem has not been thoroughly studied from a theoretical point of view. To fulfill this gap, we investigate the interactions between advection, diffusion and chemistry for a simple bimolecular reaction between two initially unmixed reactants, within the framework of two-dimensional isotropic and homogenous turbulence. This is a highly simplified representation of quasi-isentropic mixing in the stratosphere. Our goal here is to describe and understand how the production rate of the product species is affected by the size of the smallest scales of the tracer field, as determined by the tracer diffusion coefficient ΰ. The spatial average of the prognostic equation for the product's concentration involves the covariance of the reactants. The time evolution of this covariance depends in turn on a dissipative term, and on second and third order chemical terms. The set of equations is not closed and any finite resolution model would need a parameterization of the dissipation and a closure hypothesis on the chemical terms. To study these terms, we perform ensembles of direct numerical simulations using a pseudo-spectral two-dimensional periodic model. The ensembles span different initial conditions of the flow and different tracer diffusion coefficients ΰ. Our results show a strong dependence of the total production on the diffusion coefficient. This production scales like ΰp(t) , where p(t) is a positive decreasing function of time. This scaling is very similar to the one found by Tan et al. (1998) for atmospheric flows on the deactivation of chlorine by nitrogen oxide at the southern edge of the winter time polar vortex. Furthermore, the time derivative of the reactants' covariance is found to be only very weakly dependent on the chemical reaction rate, for both slow and fast chemistries compared to the advection. The variations of the dissipation and of the chemical terms with the reaction speed compensate each other. As a consequence, the calculation of the product's concentration using the covariance of the dissipation without chemistry is a good approximation of the effect of diffusion with chemistry. Reference Tan, DGH; Haynes, PH; MacKenzie, AR; et al., Effects of fluid-dynamical stirring and mixing on the deactivation of stratospheric chlorine, Journal of Geophysical Research-Atmospheres, Volume: 103 Issue: D1 Pages: 1585-1605 (1998).

Theoretical Insights for Practical Handling of Pressurized Fluids

ERIC Educational Resources Information Center

Aranda, Alfonso; Rodriguez, Maria del Prado

2006-01-01

The practical scenarios discussed in a chemistry or chemical engineering course that use solid or liquid reactants are presented. Important ideas to be considered when handling pressurized fluids are provided and three typical examples are described to enable students develop secondary skills such as the selective search of data, identification of…

Microcomputer Calculation of Theoretical Pre-Exponential Factors for Bimolecular Reactions.

ERIC Educational Resources Information Center

Venugopalan, Mundiyath

1991-01-01

Described is the application of microcomputers to predict reaction rates based on theoretical atomic and molecular properties taught in undergraduate physical chemistry. Listed is the BASIC program which computes the partition functions for any specific bimolecular reactants. These functions are then used to calculate the pre-exponential factor of…

Mass spectrometry. [in organic ion and biorganic chemistry and medicine

NASA Technical Reports Server (NTRS)

Burlingame, A. L.; Cox, R. E.; Derrick, P. J.

1974-01-01

Review of the present status of mass spectrometry in the light of pertinent recent publications spanning the period from December 1971 to January 1974. Following an initial survey of techniques, instruments, and computer applications, a sharp distinction is made between the chemistry of organic (radical-)ions and analytical applications in biorganic chemistry and medicine. The emphasis is on the chemistry of organic (radical-)ions at the expense of inorganic, organometallic, and surface ion chemistry. Biochemistry and medicine are chosen because of their contemporary importance and because of the stupendous contributions of mass spectroscopy to these fields in the past two years. In the review of gas-phase organic ion chemistry, special attention is given to studies making significant contributions to the understanding of ion chemistry.

Surface and Interface Chemistry for Gate Stacks on Silicon

NASA Astrophysics Data System (ADS)

Frank, M. M.; Chabal, Y. J.

This chapter addresses the fundamental silicon surface science associated with the continued progress of nanoelectronics along the path prescribed by Moore's law. Focus is on hydrogen passivation layers and on ultrathin oxide films encountered during silicon cleaning and gate stack formation in the fabrication of metal-oxide-semiconductor field-effect transistors (MOSFETs). Three main topics are addressed. (i) First, the current practices and understanding of silicon cleaning in aqueous solutions are reviewed, including oxidizing chemistries and cleans leading to a hydrogen passivation layer. The dependence of the final surface termination and morphology/roughness on reactant choice and pH and the influence of impurities such as dissolved oxygen or metal ions are discussed. (ii) Next, the stability of hydrogen-terminated silicon in oxidizing liquid and gas phase environments is considered. In particular, the remarkable stability of hydrogen-terminated silicon surface in pure water vapor is discussed in the context of atomic layer deposition (ALD) of high-permittivity (high-k) gate dielectrics where water is often used as an oxygen precursor. Evidence is also provided for co-operative action between oxygen and water vapor that accelerates surface oxidation in humid air. (iii) Finally, the fabrication of hafnium-, zirconium- and aluminum-based high-k gate stacks is described, focusing on the continued importance of the silicon/silicon oxide interface. This includes a review of silicon surface preparation by wet or gas phase processing and its impact on high-k nucleation during ALD growth, and the consideration of gate stack capacitance and carrier mobility. In conclusion, two issues are highlighted: the impact of oxygen vacancies on the electrical characteristics of high-k MOS devices, and the way alloyed metal ions (such as Al in Hf-based gate stacks) in contact with the interfacial silicon oxide layer can be used to control flatband and threshold voltages.

Direct real-time detection of vapors from explosive compounds.

PubMed

Ewing, Robert G; Clowers, Brian H; Atkinson, David A

2013-11-19

The real-time detection of vapors from low volatility explosives including PETN, tetryl, RDX, and nitroglycerine along with various compositions containing these substances was demonstrated. This was accomplished with an atmospheric flow tube (AFT) using a nonradioactive ionization source coupled to a mass spectrometer. Direct vapor detection was accomplished in less than 5 s at ambient temperature without sample preconcentration. The several seconds of residence time of analytes in the AFT provided a significant opportunity for reactant ions to interact with analyte vapors to achieve ionization. This extended reaction time, combined with the selective ionization using the nitrate reactant ions (NO3(-) and NO3(-)·HNO3), enabled highly sensitive explosives detection from explosive vapors present in ambient laboratory air. Observed signals from diluted explosive vapors indicated detection limits below 10 ppqv using selected ion monitoring (SIM) of the explosive-nitrate adduct at m/z 349, 378, 284, and 289 for tetryl, PETN, RDX, and NG, respectively. Also provided is a demonstration of the vapor detection from 10 different energetic formulations sampled in ambient laboratory air, including double base propellants, plastic explosives, and commercial blasting explosives using SIM for the NG, PETN, and RDX product ions.

Synthesis of a Photoluminescent and Triboluminescent Copper(I) Compound: An Experiment for an Advanced Inorganic Chemistry Laboratory

ERIC Educational Resources Information Center

Marchetti, Fabio; Di Nicola, Corrado; Pettinari, Riccardo; Timokhin, Ivan; Pettinari, Claudio

2012-01-01

A simple synthesis is proposed from inexpensive reactants of a copper(I) derivative that exhibits strong photoluminescence and, in the crystalline form, exhibits strong triboluminescence. This laboratory provides an opportunity for introducing students to the phenomenon of triboluminescence. (Contains 1 scheme and 4 figures.)

Oxidation and Reduction Reactions in Organic Chemistry

ERIC Educational Resources Information Center

Shibley, Ivan A., Jr.; Amaral, Katie E.; Aurentz, David J.; McCaully, Ronald J.

2010-01-01

A variety of approaches to the concept of oxidation and reduction appear in organic textbooks. The method proposed here is different than most published approaches. The oxidation state is calculated by totaling the number of heterogeneous atoms, [pi]-bonds, and rings. A comparison of the oxidation states of reactant and product determine what type…

Quantum dot impregnated-chitosan film for heavy metal ion sensing and removal.

PubMed

Jaiswal, Amit; Ghsoh, Siddhartha Sankar; Chattopadhyay, Arun

2012-11-06

We report the use of biopolymer-stabilized ZnS quantum dots (Q-dots) for cation exchange reaction-based easy sensing and removal of heavy metal ions such as Hg(2+), Ag(+), and Pb(2+) in water. Chitosan-stabilized ZnS Q-dots were synthesized in aqueous medium and were observed to have been converted to HgS, Ag(2)S, and PbS Q-dots in the presence of corresponding ions. The transformed Q-dots showed characteristic color development, with Hg(2+) being exceptionally identifiable due to the visible bright yellow color formation, while brown coloration was observed in other metal ions. The cation exchange was driven by the difference in the solubility product of the reactant and the product Q-dots. The cation exchanged Q-dots preserved the morphology of the reactant Q-dots and displayed volume increase based on the bulk crystal lattice parameters. The band gap of the transformed Q-dots showed a major increase from the corresponding bulk band gap of the material, demonstrating the role of quantum confinement. Next, we fabricated ZnS Q-dot impregnated chitosan film which was used to remove heavy metal ions from contaminated water as measured using atomic absorption spectroscopy (AAS). The present system could suitably be used as a simple dipstick for elimination of heavy metal ion contamination in water.

Mechanisms by which moisture generates cocrystals.

PubMed

Jayasankar, Adivaraha; Good, David J; Rodríguez-Hornedo, Naír

2007-01-01

The purpose of this study is to determine the mechanisms by which moisture can generate cocrystals when solid particles of cocrystal reactants are exposed to deliquescent conditions (when moisture sorption forms an aqueous solution). It is based on the hypothesis that cocrystallization behavior during water uptake can be derived from solution chemistry using models that describe cocrystal solubility and reaction crystallization of molecular complexes. Cocrystal systems were selected with active pharmaceutical ingredients (APIs) that form hydrates and include carbamazepine, caffeine, and theophylline. Moisture uptake and crystallization behavior were studied by gravimetric vapor sorption, X-ray powder diffraction, and on-line Raman spectroscopy. Results indicate that moisture uptake generates cocrystals of carbamazepine-nicotinamide, carbamazepine-saccharin, and caffeine or theophylline with dicarboxylic acid ligands (oxalic acid, maleic acid, glutaric acid, and malonic acid) when solid mixtures with cocrystal reactants deliquesce. Microscopy studies revealed that the transformation mechanism to cocrystal involves (1) moisture uptake, (2) dissolution of reactants, and (3) cocrystal nucleation and growth. Studies of solid blends of reactants in a macro scale show that the rate and extent of cocrystal formation are a function of relative humidity, moisture uptake, deliquescent material, and dissolution rates of reactants. It is shown that the interplay between moisture uptake and dissolution determines the liquid phase composition, supersaturation, and cocrystal formation rates. Differences in the behavior of deliquescent additives (sucrose and fructose) are associated with moisture uptake and composition of the deliquesced solution. Our results show that deliquescence can transform API to cocrystal or reverse the reaction given the right conditions. Key indicators of cocrystal formation and stability are (1) moisture uptake, (2) cocrystal aqueous solubility, (3) solubility and dissolution of cocrystal reactants, and (4) transition concentration.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Metzler, Dominik; Li, Chen; Engelmann, Sebastian

With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching (ALE) processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO 2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C 4F 8 and CHF 3), and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J Vac Sci Technol A 32,more » 020603 (2014), and D. Metzler et al., J Vac Sci Technol A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO 2 and Si, but is limited with regard to control over material etching selectivity. Ion energy over the 20 to 30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF 3 has a lower FC deposition yield for both SiO 2 and Si, and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F 8. The thickness of deposited FC layers using CHF 3 is found to be greater for Si than for SiO 2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen whereas the chemical state of the substrate varies much less. On the other hand, for FC film deposition of 5 Å for each cycle, strong substrate surface chemical changes are seen during an etching cycle. The nature of this cyclic etching with periodic deposition of thin FC films differs significantly from conventional etching with steady-state FC layers since surface conditions change strongly throughout each cycle.« less

Characterizing fluorocarbon assisted atomic layer etching of Si using cyclic Ar/C4F8 and Ar/CHF3 plasma

NASA Astrophysics Data System (ADS)

Metzler, Dominik; Li, Chen; Engelmann, Sebastian; Bruce, Robert L.; Joseph, Eric A.; Oehrlein, Gottlieb S.

2017-02-01

With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C4F8 and CHF3) and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J. Vac. Sci. Technol., A 32, 020603 (2014) and D. Metzler et al., J. Vac. Sci. Technol., A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO2 and Si but is limited with regard to control over material etching selectivity. Ion energy over the 20-30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF3 has a lower FC deposition yield for both SiO2 and Si and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F8. The thickness of deposited FC layers using CHF3 is found to be greater for Si than for SiO2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen whereas the chemical state of the substrate varies much less. On the other hand, for FC film deposition of 5 Å for each cycle, strong substrate surface chemical changes are seen during an etching cycle. The nature of this cyclic etching with periodic deposition of thin FC films differs significantly from conventional etching with steady-state FC layers since surface conditions change strongly throughout each cycle.

Effects of different operating parameters on the particle size of silver chloride nanoparticles prepared in a spinning disk reactor

NASA Astrophysics Data System (ADS)

Dabir, Hossein; Davarpanah, Morteza; Ahmadpour, Ali

2015-07-01

The aim of this research was to present an experimental method for large-scale production of silver chloride nanoparticles using spinning disk reactor. Silver nitrate and sodium chloride were used as the reactants, and the protecting agent was gelatin. The experiments were carried out in a continuous mode by injecting the reactants onto the surface of the spinning disk, where a chemical precipitation reaction took place to form AgCl particles. The effects of various operating variables, including supersaturation, disk rotational speed, reactants flow rate, disk diameter, and excess ions, on the particle size of products were investigated. In addition, the AgCl nanoparticles were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. According to the results, smaller AgCl particles are obtained under higher supersaturations and also higher disk rotation speeds. Moreover, in the range of our investigation, the use of lower reactants flow rates and larger disk diameter can reduce the particle size of products. The non-stoichiometric condition of reactants has a significant influence on the reduction in particle aggregation. It was also found that by optimizing the operating conditions, uniform AgCl nanoparticles with the mean size of around 37 nm can be produced.

A Novel Computational Method to Reduce Leaky Reaction in DNA Strand Displacement.

PubMed

Li, Xin; Wang, Xun; Song, Tao; Lu, Wei; Chen, Zhihua; Shi, Xiaolong

2015-01-01

DNA strand displacement technique is widely used in DNA programming, DNA biosensors, and gene analysis. In DNA strand displacement, leaky reactions can cause DNA signals decay and detecting DNA signals fails. The mostly used method to avoid leakage is cleaning up after upstream leaky reactions, and it remains a challenge to develop reliable DNA strand displacement technique with low leakage. In this work, we address the challenge by experimentally evaluating the basic factors, including reaction time, ratio of reactants, and ion concentration to the leakage in DNA strand displacement. Specifically, fluorescent probes and a hairpin structure reporting DNA strand are designed to detect the output of DNA strand displacement, and thus can evaluate the leakage of DNA strand displacement reactions with different reaction time, ratios of reactants, and ion concentrations. From the obtained data, mathematical models for evaluating leakage are achieved by curve derivation. As a result, it is obtained that long time incubation, high concentration of fuel strand, and inappropriate amount of ion concentration can weaken leaky reactions. This contributes to a method to set proper reaction conditions to reduce leakage in DNA strand displacement.

Mineral induced phosphorylation of glycolate ion--a metaphor in chemical evolution

NASA Technical Reports Server (NTRS)

Kolb, V.; Zhang, S.; Xu, Y.; Arrhenius, G.

1997-01-01

Bilateral surface-active minerals with excess positive charge concentrate glycolate and trimetaphosphate ion from l0(-3) m aqueous solution to half-saturation of the internal surface sites, and induce phosphorylation of glycolate ion in the mineral with trimetaphosphate, sorbed from l0(-2) m solution. By utilizing reactants from dilute solution at near-neutral pH, and eliminating the need for participating organic nitrogen compounds, the reaction comprises several elements considered necessary for geochemical realism in models for molecular evolution.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Chen; Metzler, Dominik; Oehrlein, Gottlieb S., E-mail: oehrlein@umd.edu

Angstrom-level plasma etching precision is required for semiconductor manufacturing of sub-10 nm critical dimension features. Atomic layer etching (ALE), achieved by a series of self-limited cycles, can precisely control etching depths by limiting the amount of chemical reactant available at the surface. Recently, SiO{sub 2} ALE has been achieved by deposition of a thin (several Angstroms) reactive fluorocarbon (FC) layer on the material surface using controlled FC precursor flow and subsequent low energy Ar{sup +} ion bombardment in a cyclic fashion. Low energy ion bombardment is used to remove the FC layer along with a limited amount of SiO{sub 2} frommore » the surface. In the present article, the authors describe controlled etching of Si{sub 3}N{sub 4} and SiO{sub 2} layers of one to several Angstroms using this cyclic ALE approach. Si{sub 3}N{sub 4} etching and etching selectivity of SiO{sub 2} over Si{sub 3}N{sub 4} were studied and evaluated with regard to the dependence on maximum ion energy, etching step length (ESL), FC surface coverage, and precursor selection. Surface chemistries of Si{sub 3}N{sub 4} were investigated by x-ray photoelectron spectroscopy (XPS) after vacuum transfer at each stage of the ALE process. Since Si{sub 3}N{sub 4} has a lower physical sputtering energy threshold than SiO{sub 2}, Si{sub 3}N{sub 4} physical sputtering can take place after removal of chemical etchant at the end of each cycle for relatively high ion energies. Si{sub 3}N{sub 4} to SiO{sub 2} ALE etching selectivity was observed for these FC depleted conditions. By optimization of the ALE process parameters, e.g., low ion energies, short ESLs, and/or high FC film deposition per cycle, highly selective SiO{sub 2} to Si{sub 3}N{sub 4} etching can be achieved for FC accumulation conditions, where FC can be selectively accumulated on Si{sub 3}N{sub 4} surfaces. This highly selective etching is explained by a lower carbon consumption of Si{sub 3}N{sub 4} as compared to SiO{sub 2}. The comparison of C{sub 4}F{sub 8} and CHF{sub 3} only showed a difference in etching selectivity for FC depleted conditions. For FC accumulation conditions, precursor chemistry has a weak impact on etching selectivity. Surface chemistry analysis shows that surface fluorination and FC reduction take place during a single ALE cycle for FC depleted conditions. A fluorine rich carbon layer was observed on the Si{sub 3}N{sub 4} surface after ALE processes for which FC accumulation takes place. The angle resolved-XPS thickness calculations confirmed the results of the ellipsometry measurements in all cases.« less

Chemically-modified cellulose paper as a microstructured catalytic reactor.

PubMed

Koga, Hirotaka; Kitaoka, Takuya; Isogai, Akira

2015-01-15

We discuss the successful use of chemically-modified cellulose paper as a microstructured catalytic reactor for the production of useful chemicals. The chemical modification of cellulose paper was achieved using a silane-coupling technique. Amine-modified paper was directly used as a base catalyst for the Knoevenagel condensation reaction. Methacrylate-modified paper was used for the immobilization of lipase and then in nonaqueous transesterification processes. These catalytic paper materials offer high reaction efficiencies and have excellent practical properties. We suggest that the paper-specific interconnected microstructure with pulp fiber networks provides fast mixing of the reactants and efficient transport of the reactants to the catalytically-active sites. This concept is expected to be a promising route to green and sustainable chemistry.

Electrochemical devices utilizing molten alkali metal electrode-reactant

DOEpatents

Hitchcock, David C.; Mailhe, Catherine C.; De Jonghe, Lutgard C.

1986-01-01

Electrochemical cells are provided with a reactive metal to reduce the oxide of the alkali metal electrode-reactant. Cells employing a molten alkali metal electrode, e.g., sodium, in contact with a ceramic electrolyte, which is a conductor of the ions of the alkali metal forming the electrode, exhibit a lower resistance when a reactive metal, e.g., vanadium, is allowed to react with and reduce the alkali metal oxide. Such cells exhibit less degradation of the electrolyte and of the glass seals often used to joining the electrolyte to the other components of the cell under cycling conditions.

Electrochemical devices utilizing molten alkali metal electrode-reactant

DOEpatents

Hitchcock, D.C.; Mailhe, C.C.; De Jonghe, L.C.

1985-07-10

Electrochemical cells are provided with a reactive metal to reduce the oxide of the alkali metal electrode-reactant. Cells employing a molten alkali metal electrode, e.g., sodium, in contact with a ceramic electrolyte, which is a conductor of the ions of the alkali metal forming the electrode, exhibit a lower resistance when a reactive metal, e.g., vanadium, is allowed to react with and reduce the alkali metal oxide. Such cells exhibit less degradation of the electrolyte and of the glass seals often used to joining the electrolyte to the other components of the cell under cycling conditions.

Aminomethylation of enals through carbene and acid cooperative catalysis: concise access to β(2)-amino acids.

PubMed

Xu, Jianfeng; Chen, Xingkuan; Wang, Ming; Zheng, Pengcheng; Song, Bao-An; Chi, Yonggui Robin

2015-04-20

A convergent, organocatalytic asymmetric aminomethylation of α,β-unsaturated aldehydes by N-heterocyclic carbene (NHC) and (in situ generated) Brønsted acid cooperative catalysis is disclosed. The catalytically generated conjugated acid from the base plays dual roles in promoting the formation of azolium enolate intermediate, formaldehyde-derived iminium ion (as an electrophilic reactant), and methanol (as a nucleophilic reactant). This redox-neutral strategy is suitable for the scalable synthesis of enantiomerically enriched β(2) -amino acids bearing various substituents. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Discovering the Thermodynamics of Simultaneous Equilibria: An Entropy Analysis Activity Involving Consecutive Equilibria

ERIC Educational Resources Information Center

Bindel, Thomas H.

2007-01-01

An activity is presented in which the thermodynamics of simultaneous, consecutive equilibria are explored. The activity is appropriate for second-year high school or AP chemistry. Students discover that a reactant-favored (entropy-diminishing or endergonic) reaction can be caused to happen if it is coupled with a product-favored reaction of…

The Epoxidation of 2,5-Di-tert-butyl-1,4-benzoquinone: A Consecutive Reaction for the Physical Chemistry Laboratory.

ERIC Educational Resources Information Center

Hairfield, E. M.; And Others

1985-01-01

Reports a consecutive first-order reaction for which the concentrations of reactant, intermediate, and products can be determined simulataneously. This reaction is the epoxidation of 2,5-di-tert-butyl-1,4-benzoquinone (I) by alkaline hydroperoxidation using tert-butyl hydroperoxide and benzyltrimethylammonium hydroxide (Triton B) catalyst.…

Dissociative recombination and mutual neutralization of heavier molecular ions: C{sub 10}H{sub 8}{sup +}, WF{sub 5}{sup +}, and C{sub n}F{sub m}{sup +}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiens, Justin P.; Shuman, Nicholas S.; Viggiano, Albert A., E-mail: afrl.rvborgmailbox@kirtland.af.mil

Dissociative recombination (DR) rate coefficients for the naphthalene cation, C{sub 10}H{sub 8}{sup +}, and WF{sub 5}{sup +}, and mutual neutralization (MN) rate coefficients for these species and five C{sub n}F{sub m}{sup +} ions, were determined at 300 K using variable electron and neutral density attachment mass spectrometry (VENDAMS). DR proceeds at 9 ± 3 × 10{sup −7} cm{sup 3} s{sup −1} for C{sub 10}H{sub 8}{sup +} and at 6.1 ± 1.4 × 10{sup −7} cm{sup 3} s{sup −1} for WF{sub 5}{sup +}. Consistent with previous results, MN for the polyatomic cations with the halide anions Cl{sup −}, Br{sup −}, andmore » I{sup −} exhibits an approximate μ{sup −1/2} reduced mass dependence of the reactant partners, demonstrating that ion collision velocities influence the rate coefficients. This work is an extension of VENDAMS to systems, where low reactant concentrations are necessary to avoid significant reaction of product ions with the neutral precursor, i.e., conditions not suitable for traditional flowing afterglow measurements, as well as to ions of masses > ∼ 100 Da, which are not amenable to the study of DR in magnetic storage rings. Our results expand the sparse literature on DR and MN of heavier ions.« less

Ignition and structure of a laminar diffusion flame in a compressible mixing layer with finite rate chemistry

NASA Technical Reports Server (NTRS)

Grosch, C. E.; Jackson, T. L.

1991-01-01

The ignition and structure of a reacting compressible mixing layer is considered using finite rate chemistry lying between two streams of reactants with different freestream speeds and temperatures. Numerical integration of the governing equations show that the structure of the reacting flow can be quite complicated depending on the magnitude of the Zeldovich number. An analysis of both the ignition a diffusion flame regimes is presented using a combination of large Zeldovich number asymptotics and numerics. This allows to analyze the behavior of these regimes as a function of the parameters of the problem.

Ion transport membrane reactor systems and methods for producing synthesis gas

DOEpatents

Repasky, John Michael

2015-05-12

Embodiments of the present invention provide cost-effective systems and methods for producing a synthesis gas product using a steam reformer system and an ion transport membrane (ITM) reactor having multiple stages, without requiring inter-stage reactant injections. Embodiments of the present invention also provide techniques for compensating for membrane performance degradation and other changes in system operating conditions that negatively affect synthesis gas production.

Taking the plunge: chemical reaction dynamics in liquids.

PubMed

Orr-Ewing, Andrew J

2017-12-11

The dynamics of chemical reactions in liquid solutions are now amenable to direct study using ultrafast laser spectroscopy techniques and advances in computer simulation methods. The surrounding solvent affects the chemical reaction dynamics in numerous ways, which include: (i) formation of complexes between reactants and solvent molecules; (ii) modifications to transition state energies and structures relative to the reactants and products; (iii) coupling between the motions of the reacting molecules and the solvent modes, and exchange of energy; (iv) solvent caging of reactants and products; and (v) structural changes to the solvation shells in response to the changing chemical identity of the solutes, on timescales which may be slower than the reactive events. This article reviews progress in the study of bimolecular chemical reaction dynamics in solution, concentrating on reactions which occur on ground electronic states. It illustrates this progress with reference to recent experimental and computational studies, and considers how the various ways in which a solvent affects the chemical reaction dynamics can be unravelled. Implications are considered for research in fields such as mechanistic synthetic chemistry.

Synthesis of nanosized sodium titanates

DOEpatents

Hobbs, David T.; Taylor-Pashow, Kathryn M. L.; Elvington, Mark C.

2015-09-29

Methods directed to the synthesis and peroxide-modification of nanosized monosodium titanate are described. Methods include combination of reactants at a low concentration to a solution including a nonionic surfactant. The nanosized monosodium titanate can exhibit high selectivity for sorbing various metallic ions.

Products of Dissociative Recombination in the Ionosphere

NASA Technical Reports Server (NTRS)

Cosby, Philip

1996-01-01

SRI International undertook a novel experimental measurement of the product states formed by dissociative recombination (DR) of O2(+), NO(+), and N2(+) as a function of both electron energy and reactant ion vibrational level. For these measurements we used a recently developed experimental technique for measuring dissociation product distributions that allows both the branching ratios to be accurately determined and the electronic and rovibrational state composition of the reactant ions to be specified. DR is the dominant electron loss mechanism in all regions of the ionosphere. In this process, electron attachment to the molecular ion produces an unstable neutral molecule that rapidly dissociates. For a molecular ion such as O2(+), the dissociation recombination reaction is (1) O2(+) + e yields O + O + W. The atomic products of this reaction, in this case two oxygen atoms, can be produced in a variety of excited states and with a variety of kinetic energies, as represented by W in Eq. (1). These atoms are not only active in the neutral chemistry of the ionosphere, but are also especially important because their optical emissions are often used to infer in situ concentrations of the parent molecular ion and ambient electron densities. Many laboratory measurements have been made of DR reaction rates under a wide range of electron temperatures, but very little is known about the actual distributions among the final states of the atomic products. This lack of knowledge seriously limits the validity and effectiveness of efforts to model both natural and man-made ionospheric disturbances. Bates recently identified major deficiencies in the currently accepted branching ratios for O2(+) as they relate to blue and green line emission measurements in the nocturnal F-region. During our two-year effort, we partially satisfied our ambitious goals. We constructed and operated a variable pressure, electron-impact ion source and a high pressure, hollow-cathode discharge ion source for O2(+), NO(+), and N2(+) beams. Translational spectroscopy of the products of dissociative charge transfer in Cs vapor was used to accurately assay the composition of the O2(+) and NO(+) beams and to develop a methodology for the vibrationally controlled preparation of the ground state ion beams. Attempts to assay the N2(+) beam revealed a novel two-electron process in the charge transfer reactions. A coaxial electron gun for the DR measurements was constructed following an extensive numerical design of the fields. Tests of the gun, however, found substantial perturbations of the magnetic fields by the soft iron (CMI-C) assembly containing the Langmuir probe that locates the electron beam. Hydrogen annealing of the iron failed to eliminate the field perturbations, necessitating the removal of the probe assembly. During this work on the coaxial electron gun, we discovered that predissociated high Rydberg states of O2 could be produced by subjecting the molecules to a sudden perturbation by an electromagnetic field. This technique allowed a measurement of the product branching to the atomic limits for the lowest seven vibrational levels of O2(+).

An Enzyme Kinetics Experiment for the Undergraduate Organic Chemistry Laboratory

ERIC Educational Resources Information Center

Olsen, Robert J.; Olsen, Julie A.; Giles, Greta A.

2010-01-01

An experiment using [superscript 1]H NMR spectroscopy to observe the kinetics of the acylase 1-catalyzed hydrolysis of "N"-acetyl-DL-methionine has been developed for the organic laboratory. The L-enantiomer of the reactant is hydrolyzed completely in less than 2 h, and [superscript 1]H NMR spectroscopic data from a single sample can be worked up…

Comparative Methylation of 1,8-Dihydroxy-9,10-Anthraquinone: Chemoselectivity in the Organic Chemistry Laboratory

ERIC Educational Resources Information Center

Sereda, Grigori A.

2005-01-01

A study has shown that methylation of 1,8-dihydroxy-9,10-anthraquinone (1) with methyl tosylate is highly dependent upon reaction conditions. When the reaction is carried out by a simple heating of the reaction mixture without solvent it yields dimethyl product in a nearly quantitative yield and refluxing the same mixture of reactants in…

High pressure chemistry of red phosphorus by photoactivated simple molecules

NASA Astrophysics Data System (ADS)

Ceppatelli, Matteo; Bini, Roberto; Fanetti, Samuele; Caporali, Maria; Peruzzini, Maurizio

2013-06-01

High pressure (HP) is very effective in reducing intermolecular distances and inducing unexpected chemical reactions. In particular the photoactivation of the reactants in HP conditions can lead to very efficient and selective processes. The chemistry of phosphorus is currently based on the white molecular form. The red polymeric allotrope, despite more stable and much less toxic, has not attracted much attention so far. However, switching from the white to the red form would benefit any industrial procedure, especially from an environmental point of view. On the other side, water and ethanol are renewable, environmental friendly and largely available molecules, usable as reactants and photoactivators in HP conditions. Here we report a study on the HP photoinduced reactivity of red phosphorus with water and ethanol, showing the possibility of very efficient and selective processes, leading to molecular hydrogen and valuable phosphorus compounds. The reactions have been studied by means of FTIR and Raman spectroscopy and pressure has been generated using DAC and SAC. HP reactivity has been activated by the two-photon absorption of near-UV wavelengths and occured in total absence of solvents, catalysts and radical initiators, at room T and mild pressure conditions (0.2-1.5 GPa).

Salinity-dependent diatom biosilicification implies an important role of external ionic strength

PubMed Central

Vrieling, Engel G.; Sun, Qianyao; Tian, Mingwen; Kooyman, Patricia J.; Gieskes, Winfried W. C.; van Santen, Rutger A.; Sommerdijk, Nico A. J. M.

2007-01-01

The role of external ionic strength in diatom biosilica formation was assessed by monitoring the nanostructural changes in the biosilica of the two marine diatom species Thalassiosira punctigera and Thalassiosira weissflogii that was obtained from cultures grown at two distinct salinities. Using physicochemical methods, we found that at lower salinity the specific surface area, the fractal dimensions, and the size of mesopores present in the biosilica decreased. Diatom biosilica appears to be denser at the lower salinity that was applied. This phenomenon can be explained by assuming aggregation of smaller coalescing silica particles inside the silica deposition vesicle, which would be in line with principles in silica chemistry. Apparently, external ionic strength has an important effect on diatom biosilica formation, making it tempting to propose that uptake of silicic acid and other external ions may take place simultaneously. Uptake and transport of reactants in the proximity of the expanding silica deposition vesicle, by (macro)pinocytosis, are more likely than intracellular stabilization and transport of silica precursors at the high concentrations that are necessary for the formation of the siliceous frustule components. PMID:17563373

Thermal-energy reactions of O2(2+) ions with O2, N2, CO2, NO, and Ne

NASA Technical Reports Server (NTRS)

Chatterjee, B. K.; Johnson, R.

1989-01-01

The paper presents results of drift-tube mass-spectrometer studies of the reactivity of doubly charged molecular oxygen ions with several molecules and neon atoms. Thermal-energ rate coefficients for the reactions with the molecular reactants were found to be large, close to the limiting Langevin rates. Charge transfer with neon atoms was observed, but the measured rate coefficient was only a small fraction of the Langevin rate. It is concluded that the measured rate constants for the reactions considereed refer to vibrationally excited ions.

Method for selectively preparing evoglucosenone (LGO) and other anhydrosugars from biomass in polar aprotic solvents

DOEpatents

Huber, George W.; Cao, Fei; Dumesic, James A.; Schwartz, Thomas J.

2016-06-28

A method to produce 5-hydroxymethylfurfural (HMF) is described in which a reactant including cellulose, lignocellulose, or a combination thereof, in a reaction mixture of a polar, aprotic solvent and an acid is reacted for a time, at a temperature, and at a hydrogen ion concentration wherein at least a portion of the cellulose or lignocellulose present in the reactant is converted to HMF. The reaction mixture is initially substantially devoid of water. As the reaction proceeds, dehydration of intermediates causes the water concentration in the reaction mixture to rise to no more than about 2.0 wt % water.

Method for selectively preparing 5-hydroxymethylfurfual (HMF) from biomass in polar aprotic solvents

DOEpatents

Dumesic, James A.; Huber, George W.; Weingarten, Ronen

2016-01-26

A method to produce 5-hydroxymethylfurfural (HMF) is described in which a reactant including cellulose, lignocellulose, or a combination thereof, in a reaction mixture of a polar, aprotic solvent and an acid is reacted for a time, at a temperature, and at a hydrogen ion concentration wherein at least a portion of the cellulose or lignocellulose present in the reactant is converted to HMF. The reaction mixture is initially substantially devoid of water. As the reaction proceeds, dehydration of intermediates causes the water concentration in the reaction mixture to rise to no more than about 0.2 wt % water.

Closed end regeneration method

DOEpatents

Yang, Arthur Jing-Min; Zhang, Yuehua

2006-06-27

A nanoporous reactive adsorbent incorporates a relatively small number of relatively larger reactant, e.g. metal, enzyme, etc. particles (10) forming a discontinuous or continuous phase interspersed among and surrounded by a continuous phase of smaller adsorbent particles (12) and connected interstitial pores (14) therebetween. The reactive adsorbent can effectively remove inorganic or organic impurities in a liquid by causing the liquid to flow through the adsorbent. For example, silver ions may be adsorbed by the adsorbent particles (12) and reduced to metallic silver by reducing metal, such as irons, as the reactant particles (10). The column can be regenerated by backwashing with the liquid effluent containing, for example, acetic acid.

A Study on the Performance and Electrochemistry of Bryophyllum pinnatum Leaf (BPL) Electrochemical Cell

NASA Astrophysics Data System (ADS)

Al Mamun, Mohammad; Khan, M. I.; Sarker, M. H.; Khan, K. A.; Shajahan, M.; Professor K. A. Khan Team

2017-01-01

The study was carried out to investigate on an innovative invention, Pathor Kuchi Leaf (PKL) electrochemical cell, which is fueled with PKL sap of widely available plant called Bryophyllum pinnatum as an energy source for use in PKL battery to generate electricity. This battery, a primary source of electricity, has several order of magnitude longer shelf-lives than the traditional Galvanic cell battery, is still under investigation. In this regard, we have conducted some experiments using various instruments including Atomic Absorption Spectrophotometer (AAS), Ultra-Violet Visible spectrophotometer (UV-Vis), pH meter, Ampere-Volt-Ohm Meter (AVO Meter) etc. The AAS, UV-Vis and pH metric analysis data provided that the potential and current were produced as the Zn electrode itself acts as reductant while Cu2+ and H+ ions are behaving as oxidant. The significant influence of secondary salt on current and potential leads to the dissociation of weak organic acids in PKL juice, and subsequent enrichment to the reactant ions by the secondary salt effects. However, the liquid junction potential was not as great as minimized with the opposite transference of organic acid anions and H+ ions as their dissimilar ionic mobilities. Moreover, the large value of equilibrium constant (K) implies the big change in Gibbs free energy (ΔG), revealed the additional electrical work in presence of PKL sap. This easily fabricated high performance PKL battery can show an excellent promise during the off-peak across the country-side. Dept. of Physics and Dept. of Chemistry.

The behavior of exciplex decay processes and interplay of radiationless transition and preliminary reorganization mechanisms of electron transfer in loose and tight pairs of reactants.

PubMed

Kuzmin, Michael G; Soboleva, Irina V; Dolotova, Elena V

2007-01-18

Exciplex emission spectra and rate constants of their decay via internal conversion and intersystem crossing are studied and discussed in terms of conventional radiationless transition approach. Exciplexes of 9-cyanophenanthrene with 1,2,3-trimethoxybenzene and 1,3,5-trimethoxybenzene were studied in heptane, toluene, butyl acetate, dichloromethane, butyronitrile, and acetonitrile. A better description of spectra and rate constants is obtained using 0-0 transition energy and Gauss broadening of vibrational bands rather than the free energy of electron transfer and reorganization energy. The coincidence of parameters describing exciplex emission spectra and dependence of exciplex decay rate constants on energy gap gives the evidence of radiationless quantum transition mechanism rather than thermally activated medium reorganization mechanism of charge recombination in exciplexes and excited charge transfer complexes (contact radical ion pairs) as well as in solvent separated radical ion pairs. Radiationless quantum transition mechanism is shown to provide an appropriate description also for the main features of exergonic excited-state charge separation reactions if fast mutual transformations of loose and tight pairs of reactants are considered. In particular, very fast electron transfer (ET) in tight pairs of reactants with strong electronic coupling of locally excited and charge transfer states can prevent the observation of an inverted region in bimolecular excited-state charge separation even for highly exergonic reactions.

Consequences of atomic layer etching on wafer scale uniformity in inductively coupled plasmas

NASA Astrophysics Data System (ADS)

Huard, Chad M.; Lanham, Steven J.; Kushner, Mark J.

2018-04-01

Atomic layer etching (ALE) typically divides the etching process into two self-limited reactions. One reaction passivates a single layer of material while the second preferentially removes the passivated layer. As such, under ideal conditions the wafer scale uniformity of ALE should be independent of the uniformity of the reactant fluxes onto the wafers, provided all surface reactions are saturated. The passivation and etch steps should individually asymptotically saturate after a characteristic fluence of reactants has been delivered to each site. In this paper, results from a computational investigation are discussed regarding the uniformity of ALE of Si in Cl2 containing inductively coupled plasmas when the reactant fluxes are both non-uniform and non-ideal. In the parameter space investigated for inductively coupled plasmas, the local etch rate for continuous processing was proportional to the ion flux. When operated with saturated conditions (that is, both ALE steps are allowed to self-terminate), the ALE process is less sensitive to non-uniformities in the incoming ion flux than continuous etching. Operating ALE in a sub-saturation regime resulted in less uniform etching. It was also found that ALE processing with saturated steps requires a larger total ion fluence than continuous etching to achieve the same etch depth. This condition may result in increased resist erosion and/or damage to stopping layers using ALE. While these results demonstrate that ALE provides increased etch depth uniformity, they do not show an improved critical dimension uniformity in all cases. These possible limitations to ALE processing, as well as increased processing time, will be part of the process optimization that includes the benefits of atomic resolution and improved uniformity.

A Novel Computational Method to Reduce Leaky Reaction in DNA Strand Displacement

PubMed Central

Li, Xin; Wang, Xun; Song, Tao; Lu, Wei; Chen, Zhihua; Shi, Xiaolong

2015-01-01

DNA strand displacement technique is widely used in DNA programming, DNA biosensors, and gene analysis. In DNA strand displacement, leaky reactions can cause DNA signals decay and detecting DNA signals fails. The mostly used method to avoid leakage is cleaning up after upstream leaky reactions, and it remains a challenge to develop reliable DNA strand displacement technique with low leakage. In this work, we address the challenge by experimentally evaluating the basic factors, including reaction time, ratio of reactants, and ion concentration to the leakage in DNA strand displacement. Specifically, fluorescent probes and a hairpin structure reporting DNA strand are designed to detect the output of DNA strand displacement, and thus can evaluate the leakage of DNA strand displacement reactions with different reaction time, ratios of reactants, and ion concentrations. From the obtained data, mathematical models for evaluating leakage are achieved by curve derivation. As a result, it is obtained that long time incubation, high concentration of fuel strand, and inappropriate amount of ion concentration can weaken leaky reactions. This contributes to a method to set proper reaction conditions to reduce leakage in DNA strand displacement. PMID:26491602

Direct Real-Time Detection of Vapors from Explosive Compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ewing, Robert G.; Clowers, Brian H.; Atkinson, David A.

2013-10-03

The real-time detection of vapors from low volatility explosives including PETN, tetryl, RDX and nitroglycerine along with various compositions containing these substances is demonstrated. This was accomplished with an atmospheric flow tube (AFT) using a non-radioactive ionization source and coupled to a mass spectrometer. Direct vapor detection was demonstrated in less than 5 seconds at ambient temperature without sample pre-concentration. The several seconds of residence time of analytes in the AFT provides a significant opportunity for reactant ions to interact with analyte vapors to achieve ionization. This extended reaction time, combined with the selective ionization using the nitrate reactant ionsmore » (NO3- and NO3-•HNO3), enables highly sensitive explosives detection. Observed signals from diluted explosive vapors indicate detection limits below 10 ppqv using selected ion monitoring (SIM) of the explosive-nitrate adduct at m/z 349, 378, 284 and 289 for tetryl, PETN, RDX and NG respectively. Also provided is a demonstration of the vapor detection from 10 different energetic formulations, including double base propellants, plastic explosives and commercial blasting explosives using SIM for the NG, PETN and RDX product ions.« less

Method for dry etching of transition metals

DOEpatents

Ashby, C.I.H.; Baca, A.G.; Esherick, P.; Parmeter, J.E.; Rieger, D.J.; Shul, R.J.

1998-09-29

A method for dry etching of transition metals is disclosed. The method for dry etching of a transition metal (or a transition metal alloy such as a silicide) on a substrate comprises providing at least one nitrogen- or phosphorus-containing {pi}-acceptor ligand in proximity to the transition metal, and etching the transition metal to form a volatile transition metal/{pi}-acceptor ligand complex. The dry etching may be performed in a plasma etching system such as a reactive ion etching (RIE) system, a downstream plasma etching system (i.e. a plasma afterglow), a chemically-assisted ion beam etching (CAIBE) system or the like. The dry etching may also be performed by generating the {pi}-acceptor ligands directly from a ligand source gas (e.g. nitrosyl ligands generated from nitric oxide), or from contact with energized particles such as photons, electrons, ions, atoms, or molecules. In some preferred embodiments of the present invention, an intermediary reactant species such as carbonyl or a halide ligand is used for an initial chemical reaction with the transition metal, with the intermediary reactant species being replaced at least in part by the {pi}-acceptor ligand for forming the volatile transition metal/{pi}-acceptor ligand complex.

Method for dry etching of transition metals

DOEpatents

Ashby, Carol I. H.; Baca, Albert G.; Esherick, Peter; Parmeter, John E.; Rieger, Dennis J.; Shul, Randy J.

1998-01-01

A method for dry etching of transition metals. The method for dry etching of a transition metal (or a transition metal alloy such as a silicide) on a substrate comprises providing at least one nitrogen- or phosphorous-containing .pi.-acceptor ligand in proximity to the transition metal, and etching the transition metal to form a volatile transition metal/.pi.-acceptor ligand complex. The dry etching may be performed in a plasma etching system such as a reactive ion etching (RIE) system, a downstream plasma etching system (i.e. a plasma afterglow), a chemically-assisted ion beam etching (CAIBE) system or the like. The dry etching may also be performed by generating the .pi.-acceptor ligands directly from a ligand source gas (e.g. nitrosyl ligands generated from nitric oxide), or from contact with energized particles such as photons, electrons, ions, atoms, or molecules. In some preferred embodiments of the present invention, an intermediary reactant species such as carbonyl or a halide ligand is used for an initial chemical reaction with the transition metal, with the intermediary reactant species being replaced at least in part by the .pi.-acceptor ligand for forming the volatile transition metal/.pi.-acceptor ligand complex.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Luan; Tao, Franklin, E-mail: franklin.tao.2011@gmail.com; Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, Kansas 66045

Tracking surface chemistry of a catalyst during catalysis is significant for fundamental understanding of catalytic performance of the catalyst since it allows for establishing an intrinsic correlation between surface chemistry of a catalyst at its working status and its corresponding catalytic performance. Ambient pressure X-ray photoelectron spectroscopy can be used for in-situ studies of surfaces of different materials or devices in a gas. To simulate the gaseous environment of a catalyst in a fixed-bed a flowing gaseous environment of reactants around the catalyst is necessary. Here, we report the development of a new flowing reaction cell for simulating in-situ studymore » of a catalyst surface under a reaction condition in gas of one reactant or during catalysis in a mixture of reactants of a catalytic reaction. The homemade reaction cell is installed in a high vacuum (HV) or ultrahigh vacuum (UHV) environment of a chamber. The flowing gas in the reaction cell is separated from the HV or UHV environment through well sealings at three interfaces between the reaction cell and X-ray window, sample door and aperture of front cone of an energy analyzer. Catalyst in the cell is heated through infrared laser beam introduced through a fiber optics interfaced with the reaction cell through a homemade feedthrough. The highly localized heating on the sample holder and Au-passivated internal surface of the reaction cell effectively minimizes any unwanted reactions potentially catalyzed by the reaction cell. The incorporated laser heating allows a fast heating and a high thermal stability of the sample at a high temperature. With this cell, a catalyst at 800 °C in a flowing gas can be tracked readily.« less

Development of a reaction cell for in-situ/operando studies of surface of a catalyst under a reaction condition and during catalysis.

PubMed

Nguyen, Luan; Tao, Franklin Feng

2016-06-01

Tracking surface chemistry of a catalyst during catalysis is significant for fundamental understanding of catalytic performance of the catalyst since it allows for establishing an intrinsic correlation between surface chemistry of a catalyst at its working status and its corresponding catalytic performance. Ambient pressure X-ray photoelectron spectroscopy can be used for in-situ studies of surfaces of different materials or devices in a gas. To simulate the gaseous environment of a catalyst in a fixed-bed a flowing gaseous environment of reactants around the catalyst is necessary. Here, we report the development of a new flowing reaction cell for simulating in-situ study of a catalyst surface under a reaction condition in gas of one reactant or during catalysis in a mixture of reactants of a catalytic reaction. The homemade reaction cell is installed in a high vacuum (HV) or ultrahigh vacuum (UHV) environment of a chamber. The flowing gas in the reaction cell is separated from the HV or UHV environment through well sealings at three interfaces between the reaction cell and X-ray window, sample door and aperture of front cone of an energy analyzer. Catalyst in the cell is heated through infrared laser beam introduced through a fiber optics interfaced with the reaction cell through a homemade feedthrough. The highly localized heating on the sample holder and Au-passivated internal surface of the reaction cell effectively minimizes any unwanted reactions potentially catalyzed by the reaction cell. The incorporated laser heating allows a fast heating and a high thermal stability of the sample at a high temperature. With this cell, a catalyst at 800 °C in a flowing gas can be tracked readily.

A quantified dosing ALD reactor with in-situ diagnostics for surface chemistry studies

NASA Astrophysics Data System (ADS)

Larrabee, Thomas J.

A specialized atomic layer deposition (ALD) reactor has been constructed to serve as an instrument to simultaneously study the surface chemistry of the ALD process, and perform ALD as is conventionally done in continuum flow of inert gas. This reactor is uniquely useful to gain insight into the ALD process because of the combination of its precise, controllable, and quantified dosing/microdosing capability; its in-situ quadrupole mass spectrometer for gas composition analysis; its pair of highly-sensitive in-situ quartz crystal microbalances (QCMs); and its complete spectrum of pressures and operating conditions --- from viscous to molecular flow regimes. Control of the dose is achieved independently of the conditions by allowing a reactant gas to fill a fixed volume and measured pressure, which is held at a controlled temperature, and subsequently dosed into the system by computer controlled pneumatic valves. Absolute reactant exposure to the substrate and QCMs is unambiguously calculated from the molecular impingement flux, and its relationship to dose size is established, allowing means for easily intentionally reproducing specific exposures. Methods for understanding atomic layer growth and adsorption phenomena, including the precursor sticking probability, dynamics of molecular impingement, size of dose, and other operating variables are for the first time quantitatively related to surface reaction rates by mass balance. Extensive characterization of the QCM as a measurement tool for adsorption under realistic ALD conditions has been examined, emphasizing the state-of-the-art and importance of QCM system features required. Finally, the importance of dose-quantification and microdosing has been contextualized in view of the ALD literature, underscoring the significance of more precise condition specification in establishing a better basis for reactor and reactant comparison.

Specific interaction between negative atmospheric ions and organic compounds in atmospheric pressure corona discharge ionization mass spectrometry.

PubMed

Sekimoto, Kanako; Sakai, Mami; Takayama, Mitsuo

2012-06-01

The interaction between negative atmospheric ions and various types of organic compounds were investigated using atmospheric pressure corona discharge ionization (APCDI) mass spectrometry. Atmospheric negative ions such as O(2)(-), HCO(3)(-), COO(-)(COOH), NO(2)(-), NO(3)(-), and NO(3)(-)(HNO(3)) having different proton affinities served as the reactant ions for analyte ionization in APCDI in negative-ion mode. The individual atmospheric ions specifically ionized aliphatic and aromatic compounds with various functional groups as atmospheric ion adducts and deprotonated analytes. The formation of the atmospheric ion adducts under certain discharge conditions is most likely attributable to the affinity between the analyte and atmospheric ion and the concentration of the atmospheric ion produced under these conditions. The deprotonated analytes, in contrast, were generated from the adducts of the atmospheric ions with higher proton affinity attributable to efficient proton abstraction from the analyte by the atmospheric ion.

Catalytic Chemistry of Hydrocarbon Conversion Reactions on Metallic Single Crystals

NASA Astrophysics Data System (ADS)

Tysoe, Wilfred T.

The ability to be able to follow the chemistry of adsorbates on model catalyst surfaces has, in principle, allowed us to peer inside the “black box” of a catalytic reaction and understand the pathway. Such a strategy is most simply implemented for well-ordered single crystal model catalysts for which the catalytic reaction proceeds in ultrahigh vacuum. Thus, in order to be a good model for the supported catalyst, the single crystal should catalyze the reactions with kinetics identical to those for the supported system. This chapter focuses on catalytic systems that fulfill these criteria, namely alkene and alkyne hydrogenation and acetylene cyclotrimerization on Pd(111). The surface chemistry and geometries of the reactants in ultrahigh vacuum are explored in detail allowing fundamental insights into the catalytic reaction pathways to be obtained.

Gas-phase ion/ion reactions of peptides and proteins: acid/base, redox, and covalent chemistries

PubMed Central

Prentice, Boone M.

2013-01-01

Gas-phase ion/ion reactions are emerging as useful and flexible means for the manipulation and characterization of peptide and protein biopolymers. Acid/base-like chemical reactions (i.e., proton transfer reactions) and reduction/oxidation (redox) reactions (i.e., electron transfer reactions) represent relatively mature classes of gas-phase chemical reactions. Even so, especially in regards to redox chemistry, the widespread utility of these two types of chemistries is undergoing rapid growth and development. Additionally, a relatively new class of gas-phase ion/ion transformations is emerging which involves the selective formation of functional-group-specific covalent bonds. This feature details our current work and perspective on the developments and current capabilities of these three areas of ion/ion chemistry with an eye towards possible future directions of the field. PMID:23257901

Gas-phase ion/ion reactions of peptides and proteins: acid/base, redox, and covalent chemistries.

PubMed

Prentice, Boone M; McLuckey, Scott A

2013-02-01

Gas-phase ion/ion reactions are emerging as useful and flexible means for the manipulation and characterization of peptide and protein biopolymers. Acid/base-like chemical reactions (i.e., proton transfer reactions) and reduction/oxidation (redox) reactions (i.e., electron transfer reactions) represent relatively mature classes of gas-phase chemical reactions. Even so, especially in regards to redox chemistry, the widespread utility of these two types of chemistries is undergoing rapid growth and development. Additionally, a relatively new class of gas-phase ion/ion transformations is emerging which involves the selective formation of functional-group-specific covalent bonds. This feature details our current work and perspective on the developments and current capabilities of these three areas of ion/ion chemistry with an eye towards possible future directions of the field.

Characterizing Fluorocarbon Assisted Atomic Layer Etching of Si Using Cyclic Ar/C 4F 8 and Ar/CHF 3 Plasma

DOE PAGES

Metzler, Dominik; Li, Chen; Engelmann, Sebastian; ...

2016-09-08

With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching (ALE) processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO 2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C 4F 8 and CHF 3), and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J Vac Sci Technol A 32,more » 020603 (2014), and D. Metzler et al., J Vac Sci Technol A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO 2 and Si, but is limited with regard to control over material etching selectivity. Ion energy over the 20 to 30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF 3 has a lower FC deposition yield for both SiO 2 and Si, and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F 8. The thickness of deposited FC layers using CHF 3 is found to be greater for Si than for SiO 2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen whereas the chemical state of the substrate varies much less. On the other hand, for FC film deposition of 5 Å for each cycle, strong substrate surface chemical changes are seen during an etching cycle. The nature of this cyclic etching with periodic deposition of thin FC films differs significantly from conventional etching with steady-state FC layers since surface conditions change strongly throughout each cycle.« less

Successful photoresist removal: incorporating chemistry, conditions, and equipment

NASA Astrophysics Data System (ADS)

Moore, John C.

2002-07-01

The material make-up of photoresists span a wide polarity range and chemistry. Resists contain reactive components which are photochemically triggered to convert and condense to forms that result in a solubility change. When designing a cleaning process, a knowledge of the resist chemistry is fundamental. A DNQ/novolak system may follow a simple dissolution model under normal conditions. However, when the same resist is sent through a dry etch process, crosslinking and metallic impregnation occurs to form a residue that is insoluble by simple dissolution. The same applies for negative-tone resists, where bonds must be broken and a high chemical interaction is needed to facilitate solvent penetration. Negative resists of different chemistry, such as the benzoin/acrylic, trazine/novolak, and azide/isoprene, must be addressed separately for specific polarity and reactant requirements. When dissolving and removing these crosslinked systems, benefits in formulated chemistries such as GenSolveTM and GenCleanTM are immediately observed. Once the chemistry is identified, conditions can be optimized with process design using temperature, agitation, and rinsing to achieve a robust process with a wide process latitude.

Effects of the Ion PGM™ Hi-Q™ sequencing chemistry on sequence data quality.

PubMed

Churchill, Jennifer D; King, Jonathan L; Chakraborty, Ranajit; Budowle, Bruce

2016-09-01

Massively parallel sequencing (MPS) offers substantial improvements over current forensic DNA typing methodologies such as increased resolution, scalability, and throughput. The Ion PGM™ is a promising MPS platform for analysis of forensic biological evidence. The system employs a sequencing-by-synthesis chemistry on a semiconductor chip that measures a pH change due to the release of hydrogen ions as nucleotides are incorporated into the growing DNA strands. However, implementation of MPS into forensic laboratories requires a robust chemistry. Ion Torrent's Hi-Q™ Sequencing Chemistry was evaluated to determine if it could improve on the quality of the generated sequence data in association with selected genetic marker targets. The whole mitochondrial genome and the HID-Ion STR 10-plex panel were sequenced on the Ion PGM™ system with the Ion PGM™ Sequencing 400 Kit and the Ion PGM™ Hi-Q™ Sequencing Kit. Concordance, coverage, strand balance, noise, and deletion ratios were assessed in evaluating the performance of the Ion PGM™ Hi-Q™ Sequencing Kit. The results indicate that reliable, accurate data are generated and that sequencing through homopolymeric regions can be improved with the use of Ion Torrent's Hi-Q™ Sequencing Chemistry. Overall, the quality of the generated sequencing data supports the potential for use of the Ion PGM™ in forensic genetic laboratories.

Low Temperature ABC-Type Ru Atomic Layer Deposition through Consecutive Dissociative Chemisorption, Combustion, and Reduction Steps

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Junling; Elam, Jeffrey W.

Thermal atomic layer deposition (ALD) of noble metals is frequently performed using molecular oxygen as the nonmetal precursor to effect a combustion-type chemistry at relatively high temperatures of 300 °C. Bis(ethylcyclopentadienyl)ruthenium (Ru(EtCp)2) is one of the common used metal precursors for Ru ALD. Using Ru(EtCp)2 and oxygen as reactants, Ru ALD was acheived at near 300 °C. Here, we demonstrate that Ru ALD can proceed at as low as 150 °C by using successive exposures to oxygen and hydrogen as the co-reactants. In situ quartz crystal microbalance (QCM) and quadrupole mass spectroscopy (QMS) measurements both suggest that this ABC-type ALDmore » occurs through dissociative chemisorption, combustion, and reduction for the Ru(EtCp)2, oxygen and hydrogen steps, respectively, in a similar manner to processes using ozone and hydrogen as co-reactants reported previously. Moreover, we believe this molecular O2 and H2 based ABC-type ALD could be exploited for the ALD of other noble metals to decrease the deposition temperature and reduce oxygen impurities.« less

Distributed scaffolding: Wiki collaboration among Latino high school chemistry students

NASA Astrophysics Data System (ADS)

O'Sullivan, Edwin Duncan, Jr.

The primary purpose of this study was to evaluate if wiki collaboration among Latino high school chemistry students can help reduce the science achievement gap between Latino and White students. The study was a quasi-experimental pre/post control group mixed-methods design. It used three intact sections of a high school chemistry course. The first research question asked if there is a difference in academic achievement between a treatment and control group on selected concepts from the topics of bonding, physical changes, and chemical changes, when Latino high school chemistry students collaborate on a quasi-natural wiki project. Overall results for all three activities (Bonding, Physical Changes, and Chemical Changes) indicated no significant difference between the wiki and control group. However, students performing the chemical changes activity did significantly better than their respective control group. Furthermore, there was a significant association, with large effect size, between group membership and ability to overcome the misconception that aqueous ionic reactants in precipitation reactions exist as molecular pairs of ions. Qualitative analysis of classroom and computer lab dialogue, discussion board communication, student focus groups, teacher interviews, and wiki content attributes the better performance of the chemical changes wiki group to favorable differences in intersubjectivity and calibrated assistance, as well as learning about submicroscopic representations of precipitation reactions in multiple contexts. Furthermore, the nonsignificant result overall points to an aversion to peer editing as a possible cause. Drawing considerably on Vygotsky and Piaget, the results are discussed within the context of how distributed scaffolding facilitated medium levels of cognitive conflict. The second research question asked what the characteristics of distributed metacognitive scaffolding are when Latino high school chemistry students collaborate on a quasi-natural wiki project. Results suggested a higher frequency of metacognitive scaffolding by the teacher, over peers, for content knowledge and making connections knowledge. Teacher metacognitive scaffolding often took the form of posting discussion board questions designed to stimulate student reflection on their content or creativity. On the other hand, both teacher and peer metacognitive scaffolding for general goals knowledge and strategy knowledge was relatively infrequent. Recommendations are offered for improving teacher and peer metacognitive scaffolding.

Method of detecting defects in ion exchange membranes of electrochemical cells by chemochromic sensors

DOEpatents

Brooker, Robert Paul; Mohajeri, Nahid

2016-01-05

A method of detecting defects in membranes such as ion exchange membranes of electrochemical cells. The electrochemical cell includes an assembly having an anode side and a cathode side with the ion exchange membrane in between. In a configuration step a chemochromic sensor is placed above the cathode and flow isolation hardware lateral to the ion exchange membrane which prevents a flow of hydrogen (H.sub.2) between the cathode and anode side. The anode side is exposed to a first reactant fluid including hydrogen. The chemochromic sensor is examined after the exposing for a color change. A color change evidences the ion exchange membrane has at least one defect that permits H.sub.2 transmission therethrough.

Improving Ionic Conductivity and Lithium-Ion Transference Number in Lithium-Ion Battery Separators.

PubMed

Zahn, Raphael; Lagadec, Marie Francine; Hess, Michael; Wood, Vanessa

2016-12-07

The microstructure of lithium-ion battery separators plays an important role in separator performance; however, here we show that a geometrical analysis falls short in predicting the lithium-ion transport in the electrolyte-filled pore space. By systematically modifying the surface chemistry of a commercial polyethylene separator while keeping its microstructure unchanged, we demonstrate that surface chemistry, which alters separator-electrolyte interactions, influences ionic conductivity and lithium-ion transference number. Changes in separator surface chemistry, particularly those that increase lithium-ion transference numbers can reduce voltage drops across the separator and improve C-rate capability.

Simplified half-life methods for the analysis of kinetic data

NASA Technical Reports Server (NTRS)

Eberhart, J. G.; Levin, E.

1988-01-01

The analysis of reaction rate data has as its goal the determination of the order rate constant which characterize the data. Chemical reactions with one reactant and present simplified methods for accomplishing this goal are considered. The approaches presented involve the use of half lives or other fractional lives. These methods are particularly useful for the more elementary discussions of kinetics found in general and physical chemistry courses.

High pressure chemistry of red phosphorus by photo-activated simple molecules

NASA Astrophysics Data System (ADS)

Ceppatelli, M.; Fanetti, S.; Bini, R.; Caporali, M.; Peruzzini, M.

2014-05-01

High pressure (HP) is very effective in reducing intermolecular distances and inducing unexpected chemical reactions. In addition the photo-activation of the reactants in HP conditions can lead to very efficient and selective processes. The chemistry of phosphorus is currently based on the white molecular form. The red polymeric allotrope, despite more stable and much less toxic, has not attracted much attention so far. However, switching from the white to the red form would benefit any industrial procedure, especially from an environmental point of view. On the other side, water and ethanol are renewable, environmental friendly and largely available molecules, usable as reactants and photo-activators in HP conditions. Here we report a study on the HP photo-induced reactivity of red phosphorus with water and ethanol, showing the possibility of very efficient and selective processes, leading to molecular hydrogen and valuable phosphorus compounds. The reactions have been studied by means of FTIR and Raman spectroscopy and pressure has been generated using membrane Diamond (DAC) and Sapphire (SAC) anvil cells. HP reactivity has been activated by the two-photon absorption of near-UV wavelengths and occurred in total absence of solvents, catalysts and radical initiators, at room T and mild pressure conditions (0.2-1.5 GPa).

Comorbidity between depression and inflammatory bowel disease explained by immune-inflammatory, oxidative, and nitrosative stress; tryptophan catabolite; and gut-brain pathways.

PubMed

Martin-Subero, Marta; Anderson, George; Kanchanatawan, Buranee; Berk, Michael; Maes, Michael

2016-04-01

The nature of depression has recently been reconceptualized, being conceived as the clinical expression of activated immune-inflammatory, oxidative, and nitrosative stress (IO&NS) pathways, including tryptophan catabolite (TRYCAT), autoimmune, and gut-brain pathways. IO&NS pathways are similarly integral to the pathogenesis of inflammatory bowel disease (IBD). The increased depression prevalence in IBD associates with a lower quality of life and increased morbidity in IBD, highlighting the role of depression in modulating the pathophysiology of IBD.This review covers data within such a wider conceptualization that better explains the heightened co-occurrence of IBD and depression. Common IO&NS underpinning between both disorders is evidenced by increased pro-inflammatory cytokine levels, eg, interleukin-1 (IL-1) and tumor necrosis factor-α, IL-6 trans-signalling; Th-1- and Th-17-like responses; neopterin and soluble IL-2 receptor levels; positive acute phase reactants (haptoglobin and C-reactive protein); lowered levels of negative acute phase reactants (albumin, transferrin, zinc) and anti-inflammatory cytokines (IL-10 and transforming growth factor-β); increased O&NS with damage to lipids, proteinsm and DNA; increased production of nitric oxide (NO) and inducible NO synthase; lowered plasma tryptophan but increased TRYCAT levels; autoimmune responses; and increased bacterial translocation. As such, heightened IO&NS processes in depression overlap with the biological underpinnings of IBD, potentially explaining their increased co-occurrence. This supports the perspective that there is a spectrum of IO&NS disorders that includes depression, both as an emergent comorbidity and as a contributor to IO&NS processes. Such a frame of reference has treatment implications for IBD when "comorbid" with depression.

Whole Atmosphere Community Climate Model With Lower Ionospheric Chemistry: Improved Modeling of Nitric Acid and Active Chlorine During Energetic Particle Precipitation

NASA Astrophysics Data System (ADS)

Verronen, P. T.; Andersson, M. E.; Marsh, D. R.; Kovacs, T.; Plane, J. M. C.; Päivärinta, S. M.

2016-12-01

Energetic particle precipitation (EPP) and ion chemistry affect the neutral composition of the polar middle atmosphere. For example, production of odd nitrogen and odd hydrogen during EPP events can decrease ozone by tens of percent. However, the standard ion chemistry parameterizations used in atmospheric models neglect the effects on some important species, such as nitric acid. We present WACCM-D, a variant of the Whole Atmosphere Community Climate Model, which includes a set of lower ionosphere (D-region) chemistry: 307 reactions of 20 positive ions and 21 negative ions. Compared to the Sodankylä Ion and Neutral Chemistry (SIC), a state-of-the-art 1-D model of the D-region chemistry, WACCM-D represents the lower ionosphere well. Comparison of ion concentrations between the models shows that the WACCM-D bias is typically within ±10% or less below 70 km. At 70-90 km, when strong altitude gradients in ionization rates and/or ion concentrations exist, the bias can be larger for some ions but is still within tens of percent. We also compare WACCM-D results for the January 2005 solar proton event (SPE) to those from the standard WACCM and observations from the Aura/MLS and SCISAT/ACE-FTS instruments. The results indicate that WACCM-D improves the modeling of {HNO3}, {HCl}, {ClO}, {OH}, and {NOx} during the SPE. For example, Northern Hemispheric {HNO3} from WACCM-D shows an increase by two orders of magnitude at 40-70 km compared to WACCM, reaching 2.6 ppbv, in agreement with the observations. Based on our results, WACCM-D provides a state-of-the-art global representation of D-region ion chemistry and improves modeling of EPP atmospheric effects considerably.

The Effect of Non-equilibrium Kinetics on Oxygen Chemistry in the Interstellar Medium

NASA Technical Reports Server (NTRS)

Naduvalath, Balakrishnan

2006-01-01

It has been suggested that in photon-dominated regions, oxygen chemistry is initiated by the O+H2 yields OH+H reaction. The reaction has an energy barrier of about 0.4 eV with ground state reactants and it is slow at low temperatures. There is strong experimental evidence that vibrational excitation of the H2 molecule increases the reactivity significantly. We present extensive quantum calculations of cross sections and rate coefficients for the O+H2(v) reaction for v = 0 - 3 of the H2 molecule and show that the vibrational excitation of the molecule has a significant effect on reactivity, especially at low temperatures.

Understanding the solution phase chemistry and solid state thermodynamic behavior of pharmaceutical cocrystals

NASA Astrophysics Data System (ADS)

Maheshwari, Chinmay

Cocrystals have drawn a lot of research interest in the last decade due to their potential to favorably alter the physicochemical and biopharmaceutical properties of active pharmaceutical ingredients. This dissertation focuses on the thermodynamic stability and solubility of pharmaceutical cocrystals. Specifically, the objectives are to; (i) investigate the influence of coformer properties such as solubility and ionization characteristics on cocrystal solubility and stability as a function of pH, (ii) to measure the thermodynamic solubility of metastable cocrystals, and study the solubility differences measured by kinetic and equilibrium methods, (iii) investigate the role of surfactants on the solubility and synthesis of cocrystals, (iv) investigate the solid state phase transformation of reactants to cocrystals and the factors that influence the reaction kinetics and, (v) provide models that enable the prediction of cocrystal formation by calculating the free energy of formation for a solid to solid transformation of reactants to cocrystals. Cocrystal solubilities were measured directly when cocrystals were thermodynamically stable, while solubilities were calculated from eutectic concentration measurements when cocrystals were of higher solubility than its components. Cocrystal solubility was highly dependent on coformer solubilities for gabapentin-lactam and lamotrigine cocrystals. It was found that melting point is not a good indicator of cocrystal solubility as solute-solvent interactions quantified by the activity coefficient play a huge role in the observed solubility. Similar to salts, cocrystals also exhibit pHmax, however the salts and cocrystals have different dependencies on the parameters that govern the value of pHmax. It is also shown that cocrystals could provide solubility advantage over salts as lamotrigine-nicotinamide cocrystal hydrate has about 6 fold higher solubility relative to lamotrigine-saccharin salt. In the case of mixtures of solid reactants, it was observed that cocrystals can form spontaneously when the reactants are in physical contact and that temperature, relative humidity, and disorder in the reactants caused by mechanical stress such as milling can enhance the reaction rates. Prediction of spontaneous cocrystal formation was investigated by developing models to calculate the Gibbs free energy of formation. Thermal behavior of cocrystal reactants was investigated by calorimetry and the interaction between the reactants is explained by investigating the heats of mixing in the melt. These principles are applied on cocrystals that are divided into two categories; (i) Where the cocrystal melting point is between that of its reactants and, (ii) where the cocrystal melting point is below that of its components. Generalized equations were developed that enable the calculation of Gibbs free energy of formation from fusion temperatures, enthalpy and entropy of fusion.

Semisynthetic protein nanoreactor for single-molecule chemistry

PubMed Central

Lee, Joongoo; Bayley, Hagan

2015-01-01

The covalent chemistry of individual reactants bound within a protein pore can be monitored by observing the ionic current flow through the pore, which acts as a nanoreactor responding to bond-making and bond-breaking events. In the present work, we incorporated an unnatural amino acid into the α-hemolysin (αHL) pore by using solid-phase peptide synthesis to make the central segment of the polypeptide chain, which forms the transmembrane β-barrel of the assembled heptamer. The full-length αHL monomer was obtained by native chemical ligation of the central synthetic peptide to flanking recombinant polypeptides. αHL pores with one semisynthetic subunit were then used as nanoreactors for single-molecule chemistry. By introducing an amino acid with a terminal alkyne group, we were able to visualize click chemistry at the single-molecule level, which revealed a long-lived (4.5-s) reaction intermediate. Additional side chains might be introduced in a similar fashion, thereby greatly expanding the range of single-molecule covalent chemistry that can be investigated by the nanoreactor approach. PMID:26504203

D-region ion-neutral coupled chemistry (Sodankylä Ion Chemistry, SIC) within the Whole Atmosphere Community Climate Model (WACCM 4) - WACCM-SIC and WACCM-rSIC

NASA Astrophysics Data System (ADS)

Kovács, Tamás; Plane, John M. C.; Feng, Wuhu; Nagy, Tibor; Chipperfield, Martyn P.; Verronen, Pekka T.; Andersson, Monika E.; Newnham, David A.; Clilverd, Mark A.; Marsh, Daniel R.

2016-09-01

This study presents a new ion-neutral chemical model coupled into the Whole Atmosphere Community Climate Model (WACCM). The ionospheric D-region (altitudes ˜ 50-90 km) chemistry is based on the Sodankylä Ion Chemistry (SIC) model, a one-dimensional model containing 307 ion-neutral and ion recombination, 16 photodissociation and 7 photoionization reactions of neutral species, positive and negative ions, and electrons. The SIC mechanism was reduced using the simulation error minimization connectivity method (SEM-CM) to produce a reaction scheme of 181 ion-molecule reactions of 181 ion-molecule reactions of 27 positive and 18 negative ions. This scheme describes the concentration profiles at altitudes between 20 km and 120 km of a set of major neutral species (HNO3, O3, H2O2, NO, NO2, HO2, OH, N2O5) and ions (O2+, O4+, NO+, NO+(H2O), O2+(H2O), H+(H2O), H+(H2O)2, H+(H2O)3, H+(H2O)4, O3-, NO2-, O-, O2, OH-, O2-(H2O), O2-(H2O)2, O4-, CO3-, CO3-(H2O), CO4-, HCO3-, NO2-, NO3-, NO3-(H2O), NO3-(H2O)2, NO3-(HNO3), NO3-(HNO3)2, Cl-, ClO-), which agree with the full SIC mechanism within a 5 % tolerance. Four 3-D model simulations were then performed, using the impact of the January 2005 solar proton event (SPE) on D-region HOx and NOx chemistry as a test case of four different model versions: the standard WACCM (no negative ions and a very limited set of positive ions); WACCM-SIC (standard WACCM with the full SIC chemistry of positive and negative ions); WACCM-D (standard WACCM with a heuristic reduction of the SIC chemistry, recently used to examine HNO3 formation following an SPE); and WACCM-rSIC (standard WACCM with a reduction of SIC chemistry using the SEM-CM method). The standard WACCM misses the HNO3 enhancement during the SPE, while the full and reduced model versions predict significant NOx, HOx and HNO3 enhancements in the mesosphere during solar proton events. The SEM-CM reduction also identifies the important ion-molecule reactions that affect the partitioning of odd nitrogen (NOx), odd hydrogen (HOx) and O3 in the stratosphere and mesosphere.

Imaging dynamic fingerprints of competing E2 and SN2 reactions.

PubMed

Carrascosa, Eduardo; Meyer, Jennifer; Zhang, Jiaxu; Stei, Martin; Michaelsen, Tim; Hase, William L; Yang, Li; Wester, Roland

2017-06-21

The competition between bimolecular nucleophilic substitution and base-induced elimination is of fundamental importance for the synthesis of pure samples in organic chemistry. Many factors that influence this competition have been identified over the years, but the underlying atomistic dynamics have remained difficult to observe. We present product velocity distributions for a series of reactive collisions of the type X -  + RY with X and Y denoting the halogen atoms fluorine, chlorine and iodine. By increasing the size of the residue R from methyl to tert-butyl in several steps, we find that the dynamics drastically change from backward to dominant forward scattering of the leaving ion relative to the reactant RY velocity. This characteristic fingerprint is also confirmed by direct dynamics simulations for ethyl as residue and attributed to the dynamics of elimination reactions. This work opens the door to a detailed atomistic understanding of transformation reactions in even larger systems.The competition between chemical reactions critically affects our natural environment and the synthesis of new materials. Here, the authors present an approach to directly image distinct fingerprints of essential organic reactions and monitor their competition as a function of steric substitution.

Discovery of novel anti-HIV agents via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry-based approach.

PubMed

Gao, Ping; Sun, Lin; Zhou, Junsu; Li, Xiao; Zhan, Peng; Liu, Xinyong

2016-09-01

In recent years, a variety of new synthetic methodologies and concepts have been proposed in the search for new pharmaceutical lead structures and optimization. Notably, the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry approach has drawn great attention and has become a powerful tool for the generation of privileged medicinal skeletons in the discovery of anti-HIV agents. This is due to the high degree of reliability, complete specificity (chemoselectivity and regioselectivity), mild conditions, and the biocompatibility of the reactants. Herein, the authors describe the progress thus far on the discovery of novel anti-HIV agents via the CuAAC click chemistry-based approach. CuAAC click chemistry is a proven protocol for synthesizing triazole products which could serve as basic pharmacophores, act as replacements of traditional scaffold or substituent modification, be a linker of dual-target or dual-site inhibitors and more for the discovery of novel anti-HIV agents. What's more, it also provides convenience and feasibility for dynamic combinatorial chemistry and in situ screening. It is envisioned that click chemistry will draw more attention and make more contributions in anti-HIV drug discovery in the future.

Mass spectrometry. [in organic chemistry

NASA Technical Reports Server (NTRS)

Burlingame, A. L.; Shackleton, C. H. L.; Howe, I.; Chizhov, O. S.

1978-01-01

A review of mass spectrometry in organic chemistry is given, dealing with advances in instrumentation and computer techniques, selected topics in gas-phase ion chemistry, and applications in such fields as biomedicine, natural-product studies, and environmental pollution analysis. Innovative techniques and instrumentation are discussed, along with chromatographic-mass spectrometric on-line computer techniques, mass spectral interpretation and management techniques, and such topics in gas-phase ion chemistry as electron-impact ionization and decomposition, photoionization, field ionization and desorption, high-pressure mass spectrometry, ion cyclotron resonance, and isomerization reactions of organic ions. Applications of mass spectrometry are examined with respect to bio-oligomers and their constituents, biomedically important substances, microbiology, environmental organic analysis, and organic geochemistry.

NASA Redox Storage System Development Project

NASA Technical Reports Server (NTRS)

Hagedorn, N. H.

1984-01-01

The Redox Storage System Technology Project was jointly supported by the U.S. Department of Energy and NASA. The objectives of the project were to develop the Redox flow battery concept and to probe its technical and economic viability. The iron and chromium redox couples were selected as the reactants. Membranes and electrodes were developed for the original mode of operating at 25 C with the reactants separated by an ion-exchange membrane. Analytical capabilities and system-level operating concepts were developed and verified in a 1-kW, 13-kWh preprototype system. A subsequent change was made in operating mode, going to 65 C and using mixed reactants. New membranes and a new electrode catalyst were developed, resulting in single cell operation as high as 80 mA/sq cm with energy efficiencies greater than 80 percent. Studies indicate a likely system cost of about $75/kWh. Standard Oil of Ohio (Sohio) has undertaken further development of the Redox system. An exclusive patent license was obtained from NASA by Sohio. Transfer of Redox technology to Sohio is supported by the NASA Technology Utilization Office.

Highly efficient quenching of tris(2,2'-bipyridyl)ruthenium(II) electrochemiluminescence by ozone using formaldehyde, methylglyoxal, and glyoxalate as co-reactants and its application to ozone sensing.

PubMed

Gao, Ying; Liu, Xiaoyun; Qi, Wenjing; Gao, Wenyue; Li, Yunhui; Xu, Guobao

2015-06-21

Most electrochemiluminescence (ECL) systems require high concentrations of quencher to totally quench ECL. In this study, we found that ozone can quench tris(2,2'-bipyridyl)ruthenium(II) ECL using formaldehyde, methylglyoxal, or glyoxalate as co-reactants at a glassy carbon electrode with remarkable efficiencies even when the concentration of ozone is merely 0.25% of that of the co-reactant. The strongest quenching is observed with the tris(2,2'-bipyridyl)ruthenium(II)/formaldehyde ECL system. The tris(2,2'-bipyridyl)ruthenium(II)/formaldehyde ECL intensities decrease linearly with the ozone concentration over the range of 0.025-25 μM (r = 0.9947) with a limit of detection of 8 nM. The method is more sensitive and faster than most methods. It shows high selectivity in the presence of other ROS or oxidants and some metal ions, such as H2O2, ClO(-), Mg(2+), Ni(2+), etc. The method exhibits high recoveries for the detection of ozone in a ventilated photocopy room.

Development of ultrasonically levitated drops as microreactors for study of enzyme kinetics and potential as a universal portable analysis system

NASA Astrophysics Data System (ADS)

Scheeline, A.; Pierre, Z.; Field, C. R.; Ginsberg, M. D.

2009-05-01

Development of microfluidics has focused on carrying out chemical synthesis and analysis in ever-smaller volumes of solution. In most cases, flow systems are made of either quartz, glass, or an easily moldable polymer such as polydimethylsiloxane (Whitesides 2006). As the system shrinks, the ratio of surface area to volume increases. For studies of either free radical chemistry or protein chemistry, this is undesirable. Proteins stick to surfaces, biofilms grow on surfaces, and radicals annihilate on walls (Lewis et al. 2006). Thus, under those circumstances where small amounts of reactants must be employed, typical microfluidic systems are incompatible with the chemistry one wishes to study. We have developed an alternative approach. We use ultrasonically levitated microliter drops as well mixed microreactors. Depending on whether capillaries (to form the drop) and electrochemical sensors are in contact with the drop or whether there are no contacting solids, the ratio of solid surface area to volume is low or zero. The only interface seen by reactants is a liquid/air interface (or, more generally, liquid/gas, as any gas may be used to support the drop). While drop levitation has been reported since at least the 1940's, we are the second group to carry out enzyme reactions in levitated drops, (Weis; Nardozzi 2005) and have fabricated the lowest power levitator in the literature (Field; Scheeline 2007). The low consumption aspects of ordinary microfluidics combine with a contact-free determination cell (the levitated drop) that ensures against cross-contamination, minimizes the likelihood of biofilm formation, and is robust to changes in temperature and humidity (Lide 1992). We report kinetics measurements in levitated drops and explain how outgrowths of these accomplishments will lead to portable chemistry/biology laboratories well suited to detection of a wide range of chemical and biological agents in the asymmetric battlefield environment.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsigabu Gebrehiwet; James R. Henriksen; Luanjing Guo

Multi-component mineral precipitation in porous, subsurface environments is challenging to simulate or engineer when in situ reactant mixing is controlled by diffusion. In contrast to well-mixed systems, the conditions that favor mineral precipitation in porous media are distributed along chemical gradients, which evolve spatially due to concurrent mineral precipitation and modification of solute transport in the media. The resulting physical and chemical characteristics of a mixing/precipitation zone are a consequence of coupling between transport and chemical processes, and the distinctive properties of individual chemical systems. We examined the spatial distribution of precipitates formed in “double diffusion” columns for two chemicalmore » systems, calcium carbonate and calcium phosphate. Polyacrylamide hydrogel was used as a low permeability, high porosity medium to maximize diffusive mixing and minimize pressure- and density-driven flow between reactant solutions. In the calcium phosphate system, multiple, visually dense and narrow bands of precipitates were observed that were reminiscent of previously reported Liesegang patterns. In the calcium carbonate system, wider precipitation zones characterized by more sparse distributions of precipitates and a more open channel structure were observed. In both cases, formation of precipitates inhibited, but did not necessarily eliminate, continued transport and mixing of the reactants. A reactive transport model with fully implicit coupling between diffusion, chemical speciation and precipitation kinetics, but where explicit details of nucleation processes were neglected, was able to qualitatively simulate properties of the precipitation zones. The results help to illustrate how changes in the physical properties of a precipitation zone depend on coupling between diffusion-controlled reactant mixing and chemistry-specific details of precipitation kinetics.« less

Evaluated kinetic and photochemical data for atmospheric chemistry

NASA Technical Reports Server (NTRS)

Baulch, D. L.; Cox, R. A.; Hampson, R. F., Jr.; Kerr, J. A.; Troe, J.; Watson, R. T.

1980-01-01

This paper contains a critical evaluation of the kinetics and photochemistry of gas phase chemical reactions of neutral species involved in middle atmosphere chemistry (10-55 km altitude). Data sheets have been prepared for 148 thermal and photochemical reactions, containing summaries of the available experimental data with notes giving details of the experimental procedures. For each reaction a preferred value of the rate coefficient at 298 K is given together with a temperature dependency where possible. The selection of the preferred value is discussed, and estimates of the accuracies of the rate coefficients and temperature coefficients have been made for each reaction. The data sheets are intended to provide the basic physical chemical data needed as input for calculations which model atmospheric chemistry. A table summarizing the preferred rate data is provided, together with an appendix listing the available data on enthalpies of formation of the reactant and product species.

Observation of the adsorption and desorption of vibrationally excited molecules on a metal surface

NASA Astrophysics Data System (ADS)

Shirhatti, Pranav R.; Rahinov, Igor; Golibrzuch, Kai; Werdecker, Jörn; Geweke, Jan; Altschäffel, Jan; Kumar, Sumit; Auerbach, Daniel J.; Bartels, Christof; Wodtke, Alec M.

2018-06-01

The most common mechanism of catalytic surface chemistry is that of Langmuir and Hinshelwood (LH). In the LH mechanism, reactants adsorb, become thermalized with the surface, and subsequently react. The measured vibrational (relaxation) lifetimes of molecules adsorbed at metal surfaces are in the range of a few picoseconds. As a consequence, vibrational promotion of LH chemistry is rarely observed, with the exception of LH reactions occurring via a molecular physisorbed intermediate. Here, we directly detect adsorption and subsequent desorption of vibrationally excited CO molecules from a Au(111) surface. Our results show that CO (v = 1) survives on a Au(111) surface for 1 × 10-10 s. Such long vibrational lifetimes for adsorbates on metal surfaces are unexpected and pose an interesting challenge to the current understanding of vibrational energy dissipation on metal surfaces. They also suggest that vibrational promotion of surface chemistry might be more common than is generally believed.

Determination of ammonia in ethylene using ion mobility spectrometry

NASA Technical Reports Server (NTRS)

Cross, J. H.; Limero, T. F.; Lane, J. L.; Wang, F.

1997-01-01

A simple procedure to analyze ammonia in ethylene by ion mobility spectrometry is described. The spectrometer is operated with a silane polymer membrane., 63Ni ion source, H+ (H2O)n reactant ion, and nitrogen drift and source gas. Ethylene containing parts per billion (ppb) (v/v) concentrations of ammonia is pulled across the membrane and diffuses into the spectrometer. Preconcentration or preseparation is unnecessary, because the ethylene in the spectrometer has no noticeable effect on the analytical results. Ethylene does not polymerize in the radioactive source. Ethylene's flammability is negated by the nitrogen inside the spectrometer. Response to ammonia concentrations between 200 ppb and 1.5 ppm is near linear, and a detection limit of 25 ppb is calculated.

Composition and chemistry of Titan's thermosphere and ionosphere.

PubMed

Vuitton, V; Yelle, R V; Lavvas, P

2009-02-28

Titan has long been known to harbour the richest atmospheric chemistry in the Solar System. Until recently, it had been believed that complex hydrocarbons and nitriles were produced through neutral chemistry that would eventually lead to the formation of micrometre sized organic aerosols. However, recent measurements by the Cassini spacecraft are drastically changing our understanding of Titan's chemistry. The Ion and Neutral Mass Spectrometer (INMS) and the Cassini Plasma Spectrometer (CAPS) revealed an extraordinary complex ionospheric composition. INMS detected roughly 50 positive ions with m/z<100 and a density higher than 0.1cm-3. CAPS provided evidence for heavy (up to 350amu) positively and negatively charged (up to 4000amu) ions. These observations all indicate that Titan's ionospheric chemistry is incredibly complex and that molecular growth starts in the upper atmosphere rather than at lower altitude. Here, we review the recent progress made on ionospheric chemistry. The presence of heavy neutrals in the upper atmosphere has been inferred as a direct consequence of the presence of complex positive ions. Benzene (C6H6) is created by ion chemistry at high altitudes and its main photolysis product, the phenyl radical (C6H5), is at the origin of the formation of aromatic species at lower altitude.

The Drift, Diffusion, and Reactions of Slow Ions in Gases.

DTIC Science & Technology

1980-02-28

explaining plasma chemistry ; ionic transport data are required for the accurate determination of these rate coefficients. Observations on ionic identity and...34Studies of Ion Plasma Chemistry with Drift Tube Mass Spectrometers", Third International Symposium on Plasma Chemistry , Limoges, France, (July 1977

A Simple Analytical Model for Predicting the Detectable Ion Current in Ion Mobility Spectrometry Using Corona Discharge Ionization Sources

NASA Astrophysics Data System (ADS)

Kirk, Ansgar Thomas; Kobelt, Tim; Spehlbrink, Hauke; Zimmermann, Stefan

2018-05-01

Corona discharge ionization sources are often used in ion mobility spectrometers (IMS) when a non-radioactive ion source with high ion currents is required. Typically, the corona discharge is followed by a reaction region where analyte ions are formed from the reactant ions. In this work, we present a simple yet sufficiently accurate model for predicting the ion current available at the end of this reaction region when operating at reduced pressure as in High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) or most IMS-MS instruments. It yields excellent qualitative agreement with measurement results and is even able to calculate the ion current within an error of 15%. Additional interesting findings of this model are the ion current at the end of the reaction region being independent from the ion current generated by the corona discharge and the ion current in High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) growing quadratically when scaling down the length of the reaction region. [Figure not available: see fulltext.

A Simple Analytical Model for Predicting the Detectable Ion Current in Ion Mobility Spectrometry Using Corona Discharge Ionization Sources.

PubMed

Kirk, Ansgar Thomas; Kobelt, Tim; Spehlbrink, Hauke; Zimmermann, Stefan

2018-05-08

Corona discharge ionization sources are often used in ion mobility spectrometers (IMS) when a non-radioactive ion source with high ion currents is required. Typically, the corona discharge is followed by a reaction region where analyte ions are formed from the reactant ions. In this work, we present a simple yet sufficiently accurate model for predicting the ion current available at the end of this reaction region when operating at reduced pressure as in High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) or most IMS-MS instruments. It yields excellent qualitative agreement with measurement results and is even able to calculate the ion current within an error of 15%. Additional interesting findings of this model are the ion current at the end of the reaction region being independent from the ion current generated by the corona discharge and the ion current in High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) growing quadratically when scaling down the length of the reaction region. Graphical Abstract ᅟ.

Automated Transition State Search and Its Application to Diverse Types of Organic Reactions.

PubMed

Jacobson, Leif D; Bochevarov, Art D; Watson, Mark A; Hughes, Thomas F; Rinaldo, David; Ehrlich, Stephan; Steinbrecher, Thomas B; Vaitheeswaran, S; Philipp, Dean M; Halls, Mathew D; Friesner, Richard A

2017-11-14

Transition state search is at the center of multiple types of computational chemical predictions related to mechanistic investigations, reactivity and regioselectivity predictions, and catalyst design. The process of finding transition states in practice is, however, a laborious multistep operation that requires significant user involvement. Here, we report a highly automated workflow designed to locate transition states for a given elementary reaction with minimal setup overhead. The only essential inputs required from the user are the structures of the separated reactants and products. The seamless workflow combining computational technologies from the fields of cheminformatics, molecular mechanics, and quantum chemistry automatically finds the most probable correspondence between the atoms in the reactants and the products, generates a transition state guess, launches a transition state search through a combined approach involving the relaxing string method and the quadratic synchronous transit, and finally validates the transition state via the analysis of the reactive chemical bonds and imaginary vibrational frequencies as well as by the intrinsic reaction coordinate method. Our approach does not target any specific reaction type, nor does it depend on training data; instead, it is meant to be of general applicability for a wide variety of reaction types. The workflow is highly flexible, permitting modifications such as a choice of accuracy, level of theory, basis set, or solvation treatment. Successfully located transition states can be used for setting up transition state guesses in related reactions, saving computational time and increasing the probability of success. The utility and performance of the method are demonstrated in applications to transition state searches in reactions typical for organic chemistry, medicinal chemistry, and homogeneous catalysis research. In particular, applications of our code to Michael additions, hydrogen abstractions, Diels-Alder cycloadditions, carbene insertions, and an enzyme reaction model involving a molybdenum complex are shown and discussed.

Insight into the role of Mg2+ in hammerhead ribozyme catalysis from X-ray crystallography and molecular dynamics simulation

PubMed Central

Lee, Tai-Sung; López, Carlos Silva; Martick, Monika; Scott, William G.; York, Darrin M.

2008-01-01

Results of a series of 12 ns molecular dynamics (MD) simulations of the reactant state (with and without a Mg2+ ion), early and late transition state mimics are presented based on a recently reported crystal structure of a full-length hammerhead RNA. The simulation results support a catalytically active conformation with a Mg2+ ion bridging the A9 and scissile phosphates. In the reactant state, the Mg2+ spends significant time closely associated with the 2′OH of G8, but remains fairly distant from the leaving group O5′ position. In the early TS mimic simulation, where the nucleophilic O2′ and leaving group O5′ are equidistant from the phosphorus, the Mg2+ ion remains tightly coordinated to the 2′OH of G8, but is positioned closer to the O5′ leaving group, stabilizing the accumulating charge. In the late TS mimic simulation, the coordination around the bridging Mg2+ ion undergoes a transition whereby the coordination with the 2′OH of G8 is replace by the leaving group O5′ that has developed significant charge. At the same time, the 2′OH of G8 forms a hydrogen bond with the leaving group O5′ and is positioned to act as a general acid catalyst. This work represents the first reported simulations of the full-length hammerhead structure and TS mimics, and provides direct evidence for the possible role of a bridging Mg2+ ion in catalysis that is consistent with both crystallographic and biochemical data. PMID:19079784

From transistor to trapped-ion computers for quantum chemistry.

PubMed

Yung, M-H; Casanova, J; Mezzacapo, A; McClean, J; Lamata, L; Aspuru-Guzik, A; Solano, E

2014-01-07

Over the last few decades, quantum chemistry has progressed through the development of computational methods based on modern digital computers. However, these methods can hardly fulfill the exponentially-growing resource requirements when applied to large quantum systems. As pointed out by Feynman, this restriction is intrinsic to all computational models based on classical physics. Recently, the rapid advancement of trapped-ion technologies has opened new possibilities for quantum control and quantum simulations. Here, we present an efficient toolkit that exploits both the internal and motional degrees of freedom of trapped ions for solving problems in quantum chemistry, including molecular electronic structure, molecular dynamics, and vibronic coupling. We focus on applications that go beyond the capacity of classical computers, but may be realizable on state-of-the-art trapped-ion systems. These results allow us to envision a new paradigm of quantum chemistry that shifts from the current transistor to a near-future trapped-ion-based technology.

From transistor to trapped-ion computers for quantum chemistry

PubMed Central

Yung, M.-H.; Casanova, J.; Mezzacapo, A.; McClean, J.; Lamata, L.; Aspuru-Guzik, A.; Solano, E.

2014-01-01

Over the last few decades, quantum chemistry has progressed through the development of computational methods based on modern digital computers. However, these methods can hardly fulfill the exponentially-growing resource requirements when applied to large quantum systems. As pointed out by Feynman, this restriction is intrinsic to all computational models based on classical physics. Recently, the rapid advancement of trapped-ion technologies has opened new possibilities for quantum control and quantum simulations. Here, we present an efficient toolkit that exploits both the internal and motional degrees of freedom of trapped ions for solving problems in quantum chemistry, including molecular electronic structure, molecular dynamics, and vibronic coupling. We focus on applications that go beyond the capacity of classical computers, but may be realizable on state-of-the-art trapped-ion systems. These results allow us to envision a new paradigm of quantum chemistry that shifts from the current transistor to a near-future trapped-ion-based technology. PMID:24395054

Hunting liquid micro-pockets in snow and ice: Phase transition in salt solutions at the bulk and interface with X-ray photoelectron spectroscopy.

NASA Astrophysics Data System (ADS)

Bartels-Rausch, Thorsten; Orlando, Fabrizio; Kong, Xiangrui; Waldner, Astrid; Artiglia, Luca; Ammann, Markus; Huthwelker, Thomas

2016-04-01

Sea salt, and in particular chloride, is an important reactant in the atmosphere. Chloride in air-borne sea salt aerosol is - once chemically converted to a molecular halogen (Cl2, BrCl) and released to the atmosphere - well known as important atmospheric reactant, driving large-scale changes to the atmospheric composition and in particular to ozone levels in remote areas, but also in coastal mega cities. Similar chemistry has been proposed for sea salt deposits in polar snow covers. A crucial factor determining the overall reactivity is the local physical environment of the chloride ion. For example, the reactivity of liquid aerosols decreases significantly upon crystallization. Surprisingly, the phases of NaCl-containing systems are still under debate, partially due to the limited availability of in situ measurements directly probing the local environment at the surface of frozen NaCl-water binary systems. Using core electron spectroscopy of the oxygen atoms in water, we previously showed that these systems follow the phase rules at the air-ice interface. This finding contrasts some earlier observations, where the presence of liquid below the eutectic point of bulk solutions was postulated. In the present study, we present new electron yield near-edge X-ray absorption fine structure spectroscopy (NEXAFS) data obtained at near-ambient pressures up to 20 mbar of NaCl frozen solutions. The method is sensitive to small changes in the local environment of the chlorine atom. The measurements were performed at the PHOENIX beamline at SLS. The study indicates frapant differences in the phases of NaCl - water mixtures at temperatures blow the freezing point for the surface of the ice vs. the bulk. This has significant impact on modelling chemical reactions in snow or ice and it's environmental consequences.

Protonation of caffeine: A theoretical and experimental study

NASA Astrophysics Data System (ADS)

Bahrami, Hamed; Tabrizchi, Mahmoud; Farrokhpour, Hossein

2013-03-01

Protonation of caffeine was examined by ion mobility spectrometry equipped with two ionization sources, corona discharge (CD) and UV photoionization. Three peaks were observed in ion mobility spectrum by simultaneously running the two ionization sources. Experimental and theoretical evidence was collected to link the observed peaks to caffeine related ionic species. One peak was attributed to the M+ ion while the other two were assigned to different protonated isomers of caffeine. In the case of CD ionization source, it was observed that different sites of caffeine compete for protonation and their relative intensities, depends on the sample concentration as well as the nature of the reactant ions. The new concept of "internal proton affinity" (IPA) was defined to express the tendency of holding the added proton for each atom in a molecule.

Spatial atomic layer deposition on flexible porous substrates: ZnO on anodic aluminum oxide films and Al{sub 2}O{sub 3} on Li ion battery electrodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Kashish; Routkevitch, Dmitri; Varaksa, Natalia

2016-01-15

Spatial atomic layer deposition (S-ALD) was examined on flexible porous substrates utilizing a rotating cylinder reactor to perform the S-ALD. S-ALD was first explored on flexible polyethylene terephthalate polymer substrates to obtain S-ALD growth rates on flat surfaces. ZnO ALD with diethylzinc and ozone as the reactants at 50 °C was the model S-ALD system. ZnO S-ALD was then performed on nanoporous flexible anodic aluminum oxide (AAO) films. ZnO S-ALD in porous substrates depends on the pore diameter, pore aspect ratio, and reactant exposure time that define the gas transport. To evaluate these parameters, the Zn coverage profiles in the poresmore » of the AAO films were measured using energy dispersive spectroscopy (EDS). EDS measurements were conducted for different reaction conditions and AAO pore geometries. Substrate speeds and reactant pulse durations were defined by rotating cylinder rates of 10, 100, and 200 revolutions per minute (RPM). AAO pore diameters of 10, 25, 50, and 100 nm were utilized with a pore length of 25 μm. Uniform Zn coverage profiles were obtained at 10 RPM and pore diameters of 100 nm. The Zn coverage was less uniform at higher RPM values and smaller pore diameters. These results indicate that S-ALD into porous substrates is feasible under certain reaction conditions. S-ALD was then performed on porous Li ion battery electrodes to test S-ALD on a technologically important porous substrate. Li{sub 0.20}Mn{sub 0.54}Ni{sub 0.13}Co{sub 0.13}O{sub 2} electrodes on flexible metal foil were coated with Al{sub 2}O{sub 3} using 2–5 Al{sub 2}O{sub 3} ALD cycles. The Al{sub 2}O{sub 3} ALD was performed in the S-ALD reactor at a rotating cylinder rate of 10 RPM using trimethylaluminum and ozone as the reactants at 50 °C. The capacity of the electrodes was then tested versus number of charge–discharge cycles. These measurements revealed that the Al{sub 2}O{sub 3} S-ALD coating on the electrodes enhanced the capacity stability. This S-ALD process could be extended to roll-to-roll operation for the commercialization of S-ALD for coating Li ion battery electrodes.« less

Combinatorial computational chemistry approach for materials design: applications in deNOx catalysis, Fischer-Tropsch synthesis, lanthanoid complex, and lithium ion secondary battery.

PubMed

Koyama, Michihisa; Tsuboi, Hideyuki; Endou, Akira; Takaba, Hiromitsu; Kubo, Momoji; Del Carpio, Carlos A; Miyamoto, Akira

2007-02-01

Computational chemistry can provide fundamental knowledge regarding various aspects of materials. While its impact in scientific research is greatly increasing, its contributions to industrially important issues are far from satisfactory. In order to realize industrial innovation by computational chemistry, a new concept "combinatorial computational chemistry" has been proposed by introducing the concept of combinatorial chemistry to computational chemistry. This combinatorial computational chemistry approach enables theoretical high-throughput screening for materials design. In this manuscript, we review the successful applications of combinatorial computational chemistry to deNO(x) catalysts, Fischer-Tropsch catalysts, lanthanoid complex catalysts, and cathodes of the lithium ion secondary battery.

Ion chemistry of NOO+

NASA Astrophysics Data System (ADS)

Midey, A. J.; Fernandez, A. I.; Viggiano, A. A.; Zhang, P.; Morokuma, K.

2006-03-01

The kinetics for the reactions of NOO+ ions with neutral molecules having ionization potentials (IPs) from 9.27to15.58eV was measured in a selected ion flow tube at 298K. The NOO+ ions are produced from the reaction of N3++O2 and have been reacted with the following: NO, C6F6, CS2, CF3I, C3F6, OCS, C2H6, Xe, SO2, O3, N2O, CO2, Kr, CO, D2, and N2. Numerous types of reactions were observed with the various neutral reagents, including production of NO+ (which may involve loss of an O from the ion or addition of O to the neutral reactant, although the two channels could not be distinguished here), charge transfer, isomerization of NOO+ to ONO+, and hydride abstraction. High level theoretical calculations of the structures and energetics of the various isomers, electronic states, and transition states of NOO and NOO+ were performed to better understand the observed reactivity. All neutral species with an IP ⩽11.18eV were observed to react with NOO+ in part by charge transfer. Detailed calculations showed that the recommended adiabatic and vertical IPs of NOO are 10.4 and 11.7eV, respectively, at the MRCISD(Q)/AVQZ level of theory. The observed experimental limit for charge transfer of 11.18eV agreed well with the energetics of the final products obtained from theory if dissociation of the neutral metastable product occurred, i.e., the products were X++[O(P3)+NO(Π2)], where [O(P3)+NO(Π2)] formed via dissociation of metastable NOO. Charge exchange with neutral reagent X would, therefore, be exothermic if IP(X )<[IPad(NOO)-ΔE(O+NO)-NOO]=˜11.1eV, where IPad(NOO) is the adiabatic IP. The potential energy surface for the reaction of NOO+ with C2H6 was also calculated, indicating that two pathways for formation of HNO2+C2H5+ exist.

Reaction mechanisms for enhancing carbon dioxide mineral sequestration

NASA Astrophysics Data System (ADS)

Jarvis, Karalee Ann

Increasing global temperature resulting from the increased release of carbon dioxide into the atmosphere is one of the greatest problems facing society. Nevertheless, coal plants remain the largest source of electrical energy and carbon dioxide gas. For this reason, researchers are searching for methods to reduce carbon dioxide emissions into the atmosphere from the combustion of coal. Mineral sequestration of carbon dioxide reacted in electrolyte solutions at 185°C and 2200 psi with olivine (magnesium silicate) has been shown to produce environmentally benign carbonates. However, to make this method feasible for industrial applications, the reaction rate needs to be increased. Two methods were employed to increase the rate of mineral sequestration: reactant composition and concentration were altered independently in various runs. The products were analyzed with complete combustion for total carbon content. Crystalline phases in the product were analyzed with Debye-Scherrer X-ray powder diffraction. To understand the reaction mechanism, single crystals of San Carlos Olivine were reacted in two solutions: (0.64 M NaHCO3/1 M NaCl) and (5.5 M KHCO3) and analyzed with scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and fluctuation electron microscopy (FEM) to study the surface morphology, atomic crystalline structure, composition and amorphous structure. From solution chemistry studies, it was found that increasing the activity of the bicarbonate ion increased the conversion rate of carbon dioxide to magnesite. The fastest conversion, 60% conversion in one hour, occurred in a solution of 5.5 M KHCO3. The reaction product particles, magnesium carbonate, significantly increased in both number density and size on the coupon when the bicarbonate ion activity was increased. During some experiments reaction vessel corrosion also altered the mineral sequestration mechanism. Nickel ions from vessel corrosion led to nickel precipitation in the carbonate particles and the lack of an amorphous silica reaction layer on the olivine. It was concluded that nickel ions destabilized the silica passivation layer and led to faster growth of carbonate precipitates. Overall, nickel ions increased the reaction rate of mineral sequestration of carbon dioxide.

Chemistry and Physics of Weakly Ionized Plasmas

DTIC Science & Technology

2010-01-22

temperature: Stabilization of the reactant intermediate A.A. Viggiano, Thomas . M. Miller, Skip Williams, S.T. Arnold, J.V. Seeley , and J.F. Friedman J...16. A Theoretical Study of High Electron Affinity Sulfur Oxyfluorides FSO3, F3SO2, and F5SO Susan T. Arnold, Thomas M. Miller, and A.A. Viggiano...McSweeney, M. D. Hargus, D. M Kerr, Thomas M. Miller, and A. A. Viggiano Int. J. Mass Spectrom. 228, 541-549 (Aug 2003). 37. Reactions and

Use of column V alkyls in organometallic vapor phase epitaxy (OMVPE)

NASA Technical Reports Server (NTRS)

Ludowise, M. J.; Cooper, C. B., III

1982-01-01

The use of the column V-trialkyls trimethylarsenic (TMAs) and trimethylantimony (TMSb) for the organometallic vapor phase epitaxy (OM-VPE) of III-V compound semiconductors is reviewed. A general discussion of the interaction chemistry of common Group III and Group V reactants is presented. The practical application of TMSb and TMAs for OM-VPE is demonstrated using the growth of GaSb, GaAs(1-y)Sb(y), Al(x)Ga(1-x)Sb, and Ga(1-x)In(x)As as examples.

Do large rate coefficients for ion-polar neutral reactions have a serious effect on chemical models of dense clouds?

NASA Technical Reports Server (NTRS)

Herbst, E.; Leung, C. M.

1986-01-01

In order to incorporate large ion-polar neutral rate coefficients into existing gas phase reaction networks, it is necessary to utilize simplified theoretical treatments because of the significant number of rate coefficients needed. The authors have used two simple theoretical treatments: the locked dipole approach of Moran and Hamill for linear polar neutrals and the trajectory scaling approach of Su and Chesnavich for nonlinear polar neutrals. The former approach is suitable for linear species because in the interstellar medium these are rotationally relaxed to a large extent and the incoming charged reactants can lock their dipoles into the lowest energy configuration. The latter approach is a better approximation for nonlinear neutral species, in which rotational relaxation is normally less severe and the incoming charged reactants are not as effective at locking the dipoles. The treatments are in reasonable agreement with more detailed long range theories and predict an inverse square root dependence on kinetic temperature for the rate coefficient. Compared with the locked dipole method, the trajectory scaling approach results in rate coefficients smaller by a factor of approximately 2.5.

Effects of meteoric smoke particles on the D region ion chemistry

NASA Astrophysics Data System (ADS)

Baumann, Carsten; Rapp, Markus; Anttila, Milla; Kero, Antti; Verronen, Pekka T.

2015-12-01

This study focuses on meteor smoke particle (MSP) induced effects on the D region ion chemistry. Hereby, MSPs, represented with an 11 bin size distribution, have been included as an active component into the Sodankyä Ion and Neutral Chemistry model. By doing that, we model the diurnal variation of the negatively and positively charged MSPs as well as ions and the electron density under quiet ionospheric conditions. Two distinct points in time are studied in more detail, i.e., one for sunlit conditions (Solar zenith angle is 72°) and one for dark conditions (Solar zenith angle is 103°). We find nightly decrease of free electrons and negative ions, the positive ion density is enhanced at altitudes above 80 km and reduced below. During sunlit conditions the electron density is enhanced between 60 and 70 km altitude, while there is a reduction in negative and positive ions densities. In general, the MSP influence on the ion chemistry is caused by changes in the electron density. On the one hand, these changes occur due to nightly electron scavenging by MSPs resulting in a reduced electron-ion recombination. As a consequence positive ion density increase, especially water cluster ions are highly affected. On the other hand, the electron density is slightly increased during daytime by a MSP-related production due to solar radiation. Thus, more electrons attach to neutrals and short-lived negative ions increase in number density. The direct attachment of ions to MSPs is a minor process, but important for long living ions.

Molecular layer deposition of "vanadicone", a vanadium-based hybrid material, as an electrode for lithium-ion batteries.

PubMed

Van de Kerckhove, Kevin; Mattelaer, Felix; Dendooven, Jolien; Detavernier, Christophe

2017-04-05

Molecular layer deposition (MLD) of hybrid organic-inorganic thin films called "vanadicones" was investigated using tetrakisethylmethylaminovanadium (TEMAV) as the metal precursor and glycerol (GL) or ethylene glycol (EG) as the organic reactant. Linear and continued growth could only be achieved with GL as the organic reactant. The TEMAV/GL process displayed self-limiting reactions for both precursor and reactant pulses in the temperature range from 80 °C to 180 °C, with growth rates of 1.2 to 0.5 Å per cycle, respectively. Infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed the hybrid nature of the films. From X-ray reflectivity, the density was estimated at 2.6 g cm -3 . A series of 21 nm vanadicone films were subjected to annealing under oxidizing (air) or inert (He) atmospheres at 500 °C. During annealing in air, the film crystallized to the V 2 O 5 phase and all carbon was removed from the film. The films annealed in helium remained amorphous and retained most of their carbon content. Electrochemical measurements revealed lithium-ion activity during cyclic voltammetry in all treated films, while the as deposited film was inactive. In the 2.9 to 3.5 V vs. Li + /Li potential region, no improvement over the V 2 O 5 reference was observed. However, the helium annealed samples outperformed V 2 O 5 in terms of capacity, rate performance and cyclability when charged and discharged in the 1.0 to 3.5 V vs. Li + /Li region. This result enables the application of V x O y -based hybrid electrodes in a wider potential range without sacrificing the stability and performance.

Sample Handling and Chemical Kinetics in an Acoustically Levitated Drop Microreactor

PubMed Central

2009-01-01

Accurate measurement of enzyme kinetics is an essential part of understanding the mechanisms of biochemical reactions. The typical means of studying such systems use stirred cuvettes, stopped-flow apparatus, microfluidic systems, or other small sample containers. These methods may prove to be problematic if reactants or products adsorb to or react with the container’s surface. As an alternative approach, we have developed an acoustically-levitated drop reactor eventually intended to study enzyme-catalyzed reaction kinetics related to free radical and oxidative stress chemistry. Microliter-scale droplet generation, reactant introduction, maintenance, and fluid removal are all important aspects in conducting reactions in a levitated drop. A three capillary bundle system has been developed to address these needs. We report kinetic measurements for both luminol chemiluminescence and the reaction of pyruvate with nicotinamide adenine dinucleotide, catalyzed by lactate dehydrogenase, to demonstrate the feasibility of using a levitated drop in conjunction with the developed capillary sample handling system as a microreactor. PMID:19769373

A Pilot Study of Ion - Molecule Reactions at Temperatures Relevant to the Atmosphere of Titan.

PubMed

Zymak, Illia; Žabka, Ján; Polášek, Miroslav; Španěl, Patrik; Smith, David

2016-11-01

Reliable theoretical models of the chemical kinetics of the ionosphere of Saturn's moon, Titan, is highly dependent on the precision of the rates of the reactions of ambient ions with hydrocarbon molecules at relevant temperatures. A Variable Temperature Selected Ions Flow Tube technique, which has been developed primarily to study these reactions at temperatures within the range of 200-330 K, is briefly described. The flow tube temperature regulation system and the thermalisation of ions are also discussed. Preliminary studies of two reactions have been carried out to check the reliability and efficacy of kinetics measurements: (i) Rate constants of the reaction of CH 3 + ions with molecular oxygen were measured at different temperatures, which indicate values in agreement with previous ion cyclotron resonance measurements ostensibly made at 300 K. (ii) Formation of CH 3 + ions in the reaction of N 2 + ions with CH 4 molecules were studied at temperatures within the range 240-310 K which showed a small but statistically significant decrease of the ratio of product CH 3 + ions to reactant N 2 + ions with reaction temperature.

Crossed-beam velocity map imaging of collisional autoionization processes

NASA Astrophysics Data System (ADS)

Delmdahl, Ralph F.; Bakker, Bernard L. G.; Parker, David H.

2000-11-01

Applying the velocity map imaging technique Penning ion formation as well as generation of associative ions is observed in autoionizing collisions of metastable neon atoms (Ne* 2p5 3s 3P2,0) with ground state argon targets in a crossed molecular beam experiment. Metastable neon reactants are obtained by nozzle expansion through a dc discharge ring. The quality of the obtained results clearly demonstrates the suitability of this new, particularly straightforward experimental approach with respect to angle and kinetic energy resolved investigations of Penning processes in crossed-beam studies which are known to provide the highest level of detail.

How do video-based demonstration assessment tasks affect problem-solving process, test anxiety, chemistry anxiety and achievement in general chemistry students?

NASA Astrophysics Data System (ADS)

Terrell, Rosalind Stephanie

2001-12-01

Because paper-and-pencil testing provides limited knowledge about what students know about chemical phenomena, we have developed video-based demonstrations to broaden measurement of student learning. For example, students might be shown a video demonstrating equilibrium shifts. Two methods for viewing equilibrium shifts are changing the concentration of the reactants and changing the temperature of the system. The students are required to combine the data collected from the video and their knowledge of chemistry to determine which way the equilibrium shifts. Video-based demonstrations are important techniques for measuring student learning because they require students to apply conceptual knowledge learned in class to a specific chemical problem. This study explores how video-based demonstration assessment tasks affect problem-solving processes, test anxiety, chemistry anxiety and achievement in general chemistry students. Several instruments were used to determine students' knowledge about chemistry, students' test and chemistry anxiety before and after treatment. Think-aloud interviews were conducted to determine students' problem-solving processes after treatment. The treatment group was compared to a control group and a group watching video demonstrations. After treatment students' anxiety increased and achievement decreased. There were also no significant differences found in students' problem-solving processes following treatment. These negative findings may be attributed to several factors that will be explored in this study.

Secondary batteries with multivalent ions for energy storage

PubMed Central

Xu, Chengjun; Chen, Yanyi; Shi, Shan; Li, Jia; Kang, Feiyu; Su, Dangsheng

2015-01-01

The use of electricity generated from clean and renewable sources, such as water, wind, or sunlight, requires efficiently distributed electrical energy storage by high-power and high-energy secondary batteries using abundant, low-cost materials in sustainable processes. American Science Policy Reports state that the next-generation “beyond-lithium” battery chemistry is one feasible solution for such goals. Here we discover new “multivalent ion” battery chemistry beyond lithium battery chemistry. Through theoretic calculation and experiment confirmation, stable thermodynamics and fast kinetics are presented during the storage of multivalent ions (Ni2+, Zn2+, Mg2+, Ca2+, Ba2+, or La3+ ions) in alpha type manganese dioxide. Apart from zinc ion battery, we further use multivalent Ni2+ ion to invent another rechargeable battery, named as nickel ion battery for the first time. The nickel ion battery generally uses an alpha type manganese dioxide cathode, an electrolyte containing Ni2+ ions, and Ni anode. The nickel ion battery delivers a high energy density (340 Wh kg−1, close to lithium ion batteries), fast charge ability (1 minute), and long cycle life (over 2200 times). PMID:26365600

Nanobelt formation of magnesium hydroxide sulfate hydrate via a soft chemistry process.

PubMed

Zhou, Zhengzhi; Sun, Qunhui; Hu, Zeshan; Deng, Yulin

2006-07-13

The nanobelt formation of magnesium hydroxide sulfate hydrate (MHSH) via a soft chemistry approach using carbonate salt and magnesium sulfate as reactants was successfully demonstrated. X-ray diffraction (XRD), energy dispersion X-ray spectra (EDS), selected area electron diffraction (SAED), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis revealed that the MHSH nanobelts possessed a thin belt structure (approximately 50 nm in thickness) and a rectangular cross profile (approximately 200 nm in width). The MHSH nanobelts suffered decomposition under electron beam irradiation during TEM observation and formed MgO with the pristine nanobelt morphology preserved. The formation process of the MHSH nanobelts was studied by tracking the morphology of the MHSH nanobelts during the reaction. A possible chemical reaction mechanism is proposed.

Prebiotic chemistry in eutectic solutions at the water-ice matrix.

PubMed

Menor-Salván, César; Marín-Yaseli, Margarita R

2012-08-21

A crystalline ice matrix at subzero temperatures can maintain a liquid phase where organic solutes and salts concentrate to form eutectic solutions. This concentration effect converts the confined reactant solutions in the ice matrix, sometimes making condensation and polymerisation reactions occur more favourably. These reactions occur at significantly high rates from a prebiotic chemistry standpoint, and the labile products can be protected from degradation. The experimental study of the synthesis of nitrogen heterocycles at the ice-water system showed the efficiency of this scenario and could explain the origin of nucleobases in the inner Solar System bodies, including meteorites and extra-terrestrial ices, and on the early Earth. The same conditions can also favour the condensation of monomers to form ribonucleic acid and peptides. Together with the synthesis of these monomers, the ice world (i.e., the chemical evolution in the range between the freezing point of water and the limit of stability of liquid brines, 273 to 210 K) is an under-explored experimental model in prebiotic chemistry.

Regulation of photosensitisation processes by an RNA aptamer

NASA Astrophysics Data System (ADS)

Thoa, Tran Thi Thanh; Minagawa, Noriko; Aigaki, Toshiro; Ito, Yoshihiro; Uzawa, Takanori

2017-02-01

One of the most powerful attributes of proteins is their ability to bind to and modulate the chemistry of cofactors and prosthetic groups. Here, we demonstrated the ability of an artificial nucleic acid (an aptamer) to similarly control the functionality of a non-biological element. Specifically, we selected an RNA aptamer that binds tris(bipyridine) ruthenium (II), Ru(bpy)32+, an inorganic complex that has attracted intense interest due to its photoredox chemistry, including its ability to split water by visible light. We found that a newly discovered aptamer strongly and enantioselectively binds Λ-Ru(bpy)32+ (Kd = 65 nM) and, in doing so, selectively suppresses deactivation via energy transfer, thereby elongating the lifetime of its photo-excited state by four-fold. The ability of the aptamer to enhance this important aspect of Ru(bpy)32+ chemistry illustrates a broader point concerning the potential power of combining in vitro-created biomolecules with non-biological reactants to perform enhanced chemical reactions.

Reactions between NO/+/ and metal atoms using magnetically confined afterglows

NASA Technical Reports Server (NTRS)

Lo, H. H.; Clendenning, L. M.; Fite, W. L.

1977-01-01

A new method of studying thermal energy ion-neutral collision processes involving nongaseous neutral atoms is described. A long magnetic field produced by a solenoid in a vacuum chamber confines a thermal-energy plasma generated by photoionization of gas at very low pressure. As the plasma moves toward the end of the field, it is crossed by a metal atom beam. Ionic products of ion-atom reactions are trapped by the field and both the reactant and product ions move to the end of the magnetic field where they are detected by a quadrupole mass filter. The cross sections for charge transfer between NO(+) and Na, Mg, Ca, and Sr and that for rearrangement between NO(+) and Ca have been obtained. The charge-transfer reaction is found strongly dominant over the rearrangement reaction that forms metallic oxide ions.

Effect of surface chemistries and characteristics of Ti6Al4V on the Ca and P adsorption and ion dissolution in Hank's ethylene diamine tetra-acetic acid solution.

PubMed

Chang, E; Lee, T M

2002-07-01

This study examined the influence of chemistries and surface characteristics of Ti6Al4V on the adsorption of Ca and P species and ion dissolution behavior of the material exposed in Hank's solution with 8.0 mM ethylene diamine tetra-acetic acid at 37 degrees C. The variation of chemistries of the alloy and nano-surface characteristics (chemistries of nano-surface oxides, amphoteric OH group adsorbed on oxides, and oxide thickness) was effected by surface modification and three passivation methods (34% nitric acid passivation. 400 degrees C heated in air, and aged in 100 degrees C water). X-ray photoelectron spectroscopy and Auger electron spectroscopy were used for surface analyses. The chemistries of nano-surface oxides in a range studied should not change the capability of Ca and P adsorption. Nor is the capability affected significantly by amphoteric OH group and oxide thickness. However, passivations influence the surface oxide thickness and the early stage ion dissolution rate of the alloy. The rate-limiting step of the rate can be best explained by metal-ion transport through the oxide film, rather than hydrolysis of the film. Variation of the chemistries of titanium alloy alters the electromotive force potential of the metal, thereby affecting the corrosion and ion dissolution rate.

Assure Access to the Maritime Battlespace

DTIC Science & Technology

2012-10-22

Energy Section ( PEM Fuel Cells & Stirling Engines) Smart Battery High Pressure Gas Smart Li-Ion Battery BAA Technologies Energy Section... Fuel Cells and Advanced Reactant Storage 30 Days Endurance Ref Mission LDUUV INP Energy Plan 14 At Sea Test and Analysis At Sea Test and...undersea vehicles capable of operating near shore BAA Contracts awarded BAA Open for Competition Stirling Engine Demo UUV Fuel Cell 500hr

Chemistry Comes Alive!, Volume 4: Abstract of Special Issue 25 on CD-ROM

NASA Astrophysics Data System (ADS)

Jacobsen, Jerrold J.; Bain, Gordon; Bruce, Kara; Moore, John W.

2000-06-01

The answers can be found on p676 of the PDF version of the Table of Contents. Chemistry Comes Alive!, Volume 4 is the fourth in a series of CD-ROMs for Macintosh and Windows computers. (Chemistry Comes Alive!, Volumes 1, 2, and 3 (1-3), are also available from JCE Software.) Volume 4 contains two main topics, Reactions in Aqueous Solution and Reactions of the Elements. Chemistry truly does come to life through this collection of pictures, animations, and movies depicting chemical reactions. Topic I. Reactions in Aqueous Solution Reactions in Aqueous Solution includes video of the mixing and subsequent reaction, if any, of aqueous solutions of inorganic compounds. The compounds and ions included are listed below. Reactions with a specific compound can be accessed either by selecting the compound from an alphabetical list of the compounds or from a matrix of reactions. There are more than 200 movies of reactions from which to choose. There are also still images of each reaction. Reactions are shown in which reactants are mixed in either order; there are images of solution 2 being added to solution 1 as well as images of solution 1 being added to solution 2. In addition to videos of reactions, a quiz is available in which a matrix of unknown solutions is presented. Students attempt to identify the solutions by viewing video of each unknown solution as it is mixed with another unknown solution. Students may compare their observations from mixing the unknowns with reactions of known solutions. Topic II. Reactions of the Elements Reactions of the Elements includes video of the elements reacting with air, water, acids, and base. (This video is also used in JCE Software's popular Periodic Table Live! (4) and is included here to allow you greater freedom to use the video in your own presentations under the Chemistry Comes Alive! license.) In addition you may purchase an additional license that allows you to place all or a portion of the video on your WWW site. Contact JCE Software for more details. Chemistry Comes Alive! Volume 4: Reactions in Aqueous Solution Compounds and Ions Ammonia, NH3 Barium chloride, BaCl2 Cadmium nitrate, Cd(NO3)2 Chromium(III) chloride, CrCl3 Cobalt(II) chloride, CoCl2 Copper(II) nitrate, Cu(NO3)2 Copper(II) sulfate, CuSO4 Hydrochloric acid, HCl Iron(II) ion, Fe2+ Iron(III) ion, Fe3+ Lead(II) nitrate, Pb(NO3)2 Manganese(II) chloride, MnCl2 Mercury(I) nitrate, Hg2(NO3)2 Mercury(II) ion, Hg2+ Nickel(II) nitrate, Ni(NO3)2 Silver nitrate, AgNO3 Sodium bromide, NaBr Sodium carbonate, Na2CO3 Sodium chloride, NaCl Sodium hydroxide, NaOH Sodium iodide, NaI Sodium sulfate, Na2SO4 Sodium sulfide, Na2S Strontium chloride, SrCl2 Sulfuric acid, H2SO4 Zinc nitrate, Zn(NO3)2 About the Chemistry Comes Alive! Series In Chemistry Comes Alive!, the emphasis is on the chemistry. Reactions are shown close up. Only where scale is important can more than the demonstrator's hands be seen. Most movies in Chemistry Comes Alive! include a voice-over narration and the sound of a reaction is included when it is important. Reactions or demonstrations have been chosen because they illustrate an important aspect of chemistry, involve substances or equipment that are not available in many schools, or are hazardous or cause problems of disposal or cleanup. All are certain to stimulate students' curiosity and help them learn. The Chemistry Comes Alive! series is divided into several CD volumes on related topics as recommended by a group of chemistry educators. How to Use This CD-ROM The Chemistry Comes Alive! CD-ROMs are organized in the manner of a World Wide Web site. You access their contents with a browser such as Netscape Navigator or Microsoft Internet Explorer. Chemistry Comes Alive! Volume 4 provides links to JCE Online where you can find information about other Chemistry Comes Alive! volumes. JCE Software hopes you will let us know how you use Chemistry Comes Alive! in your classroom so that we can share with others contributed ideas, lessons, or instructional materials that utilize Chemistry Comes Alive! The movies on this CD-ROM are QuickTime movies. In addition to viewing with a WWW browser, the video can be played directly using QuickTime MoviePlayer. Images from the CD can be easily incorporated into multimedia presentations or lessons. Use of the Bookmark function of the Web browser is a particularly convenient method of organizing material for a lecture or for a student lesson. Remember that an additional license must be purchased before you place video from any CCA! volume on your local WWW server. Images of the reactions of potassium, selected from movies on Reactions of the Elements Acknowledgments Funding for Chemistry Comes Alive! was provided by the National Science Foundation, New Traditions, grant DUE-9455928 and National Science Foundation, Instructional Materials Development grant ESI-9154099. Many individuals made significant contributions to the development of this project. These include Alton Banks, North Carolina State University; Joe March, University of Alabama at Birmingham. Price and Ordering An order form is inserted in this issue that provides prices and other ordering information. If this card is not available or if you need additional information, contact JCE Software, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706-1396; phone; 608/262-5153 or 800/991-5534; fax: 608/265-8094; email: jcesoft@chem.wisc.edu. Information about all our publications (including abstracts, descriptions, updates) is available from our World Wide Web site. Literature Cited

1. Jacobsen, J. J.; Moore, J. W. Chemistry Comes Alive! Vol. 1; J. Chem. Educ. Software 1998, SP 18.
2. Jacobsen, J. J.; Moore, J. W. Chemistry Comes Alive! Vol. 2; J. Chem. Educ. Software 1998, SP 21.
3. Jacobsen, J. J.; Moore, J. W. Chemistry Comes Alive! Vol. 3; J. Chem. Educ. Software 2000, SP 23.
4. Banks, A. J.; Holmes, J. L.; Jacobsen, J. J.; Kotz, J. C.; Moore, J. W.; Robinson, W. R.; Schatz, P. F.; Tweedale, J.; Young, S. Periodic Table Live! 2nd Edition; J. Chem. Educ. Software 1999, SP17.

Super-atmospheric pressure chemical ionization mass spectrometry.

PubMed

Chen, Lee Chuin; Rahman, Md Matiur; Hiraoka, Kenzo

2013-03-01

Super-atmospheric pressure chemical ionization (APCI) mass spectrometry was performed using a commercial mass spectrometer by pressurizing the ion source with compressed air up to 7 atm. Similar to typical APCI source, reactant ions in the experiment were generated with corona discharge using a needle electrode. Although a higher needle potential was necessary to initiate the corona discharge, discharge current and detected ion signal were stable at all tested pressures. A Roots booster pump with variable pumping speed was installed between the evacuation port of the mass spectrometer and the original rough pumps to maintain a same pressure in the first pumping stage of the mass spectrometer regardless of ion source pressure. Measurement of gaseous methamphetamine and research department explosive showed an increase in ion intensity with the ion source pressure until an optimum pressure at around 4-5 atm. Beyond 5 atm, the ion intensity decreased with further increase of pressure, likely due to greater ion losses inside the ion transport capillary. For benzene, it was found that besides molecular ion and protonated species, ion due to [M + 2H](+) which was not so common in APCI, was also observed with high ion abundance under super-atmospheric pressure condition. Copyright © 2013 John Wiley & Sons, Ltd.

Photochemical Study of Silver Nanoparticles Formed from the Reduction of Silver Ions by Humic Acid

NASA Astrophysics Data System (ADS)

Leslie, Renee M.

This study focuses on the ability of silver ions and humic acid to form silver nanoparticles in the presence of UV and visible light. Silver nanoparticles have a number of industrial applications due primarily to their antimicrobial properties, but these properties pose an environmental threat. Silver nanoparticles can directly disrupt sensitive ecosystems by harming bacteria. Consumption of silver nanoparticles results in silver ions and silver nanoparticles entering waterways; the presence of silver ions raises the question of whether nanoparticles can reform in environmental waters. As our data show, silver nanoparticles can form from the reduction of silver ions by humic acid after irradiation with UV and visible light. In order to better understand the mechanism of these naturally synthesized silver nanoparticles, we investigated the effects of reactant concentration, experimental conditions and presence of ions/reactive species. We monitored silver nanoparticle growth with UV-visible spectroscopy. The evolution in time of nanoparticle size was monitored by dynamic light scattering (DLS).

Hydrated Cations in the General Chemistry Course.

ERIC Educational Resources Information Center

Kauffman, George B.; Baxter, John F., Jr.

1981-01-01

Presents selected information regarding the descriptive chemistry of the common metal ions and their compounds, including the concepts of process of solution, polar molecules, ionic size and charge, complex ions, coordination number, and the Bronsted-Lowry acid-base theory. (CS)

Determining Iron Content in Foods by Spectrophotometry.

ERIC Educational Resources Information Center

Adams, Paul E.

1995-01-01

Describes a laboratory experiment for secondary school chemistry students utilizing the classic reaction between the iron(III) ion and the thiocyanate ion. The experiment also works very well in other chemistry courses as an experience in spectrophotometric analysis. (PVD)

Synthesis of platinum nanoparticle electrocatalysts by atomic layer deposition

NASA Astrophysics Data System (ADS)

Lubers, Alia Marie

Demand for energy continues to increase, and without alternatives to fossil fuel combustion the effects on our environment will become increasingly severe. Fuel cells offer a promising improvement on current methods of energy generation; they are able to convert hydrogen fuel into electricity with a theoretical efficiency of up to 83% and interface smoothly with renewable hydrogen production. Fuel cells can replace internal combustion engines in vehicles and are used in stationary applications to power homes and businesses. The efficiency of a fuel cell is maximized by its catalyst, which is often composed of platinum nanoparticles supported on carbon. Economical production of fuel cell catalysts will promote adoption of this technology. Atomic layer deposition (ALD) is a possible method for producing catalysts at a large scale when employed in a fluidized bed. ALD relies on sequential dosing of gas-phase precursors to grow a material layer by layer. We have synthesized platinum nanoparticles on a carbon particle support (Pt/C) by ALD for use in proton exchange membrane fuel cells (PEMFCs) and electrochemical hydrogen pumps. Platinum nanoparticles with different characteristics were deposited by changing two chemistries: the carbon substrate through functionalization; and the deposition process by use of either oxygen or hydrogen as ligand removing reactants. The metal depositing reactant was trimethyl(methylcyclopentadienyl)platinum(IV). Functionalizing the carbon substrate increased nucleation during deposition resulting in smaller and more dispersed nanoparticles. Use of hydrogen produced smaller nanoparticles than oxygen, due to a gentler hydrogenation reaction compared to using oxygen's destructive combustion reaction. Synthesized Pt/C materials were used as catalysts in an electrochemical hydrogen pump, a device used to separate hydrogen fuel from contaminants. Catalysts deposited by ALD on functionalized carbon using a hydrogen chemistry were the most successful hydrogen pumping catalysts, comparable to a commercial Pt/C catalyst. Synthesized Pt/C materials were also used as PEMFC catalysts. We found the ALD catalysts with lower platinum loading to be competitive with a commercial fuel cell catalyst, especially when exhibiting similar platinum particle characteristics. The functionalized carbon helped produce smaller and more dispersed platinum particles; however, it encouraged carbon corrosion within an electrode, severing electrical connections and lowering energy production. The most suitable chemistry for competitive Pt/C catalysts was produced by platinum ALD on unmodified carbon using hydrogen as a reactant. ALD is a promising method for fabricating electrocatalysts, which could help fuel cells become an economically viable alternative to fossil fuels.

Lifecycle comparison of selected Li-ion battery chemistries under grid and electric vehicle duty cycle combinations

NASA Astrophysics Data System (ADS)

Crawford, Alasdair J.; Huang, Qian; Kintner-Meyer, Michael C. W.; Zhang, Ji-Guang; Reed, David M.; Sprenkle, Vincent L.; Viswanathan, Vilayanur V.; Choi, Daiwon

2018-03-01

Li-ion batteries are expected to play a vital role in stabilizing the electrical grid as solar and wind generation capacity becomes increasingly integrated into the electric infrastructure. This article describes how two different commercial Li-ion batteries based on LiNi0.8Co0.15Al0.05O2 (NCA) and LiFePO4 (LFP) chemistries were tested under grid duty cycles recently developed for two specific grid services: (1) frequency regulation (FR) and (2) peak shaving (PS) with and without being subjected to electric vehicle (EV) drive cycles. The lifecycle comparison derived from the capacity, round-trip efficiency (RTE), resistance, charge/discharge energy, and total used energy of the two battery chemistries are discussed. The LFP chemistry shows better stability for the energy-intensive PS service, while the NCA chemistry is more conducive to the FR service under the operating regimes investigated. The results can be used as a guideline for selection, deployment, operation, and cost analyses of Li-ion batteries used for different applications.

Grid Scale Energy Storage (Symposium EE8)

DTIC Science & Technology

2016-06-01

27709-2211 Grid-Scale Energy Storage, electrolytes, systems ntegration, Lithium - ion chemistry, Redox flow batteries REPORT DOCUMENTATION PAGE 11... Lithium - Ion Chemistry (4) Redox Flow Batteries Christopher J. Orendorff from Sandia National Laboratories kicked off the symposium on Tuesday...for redox flow batteries . SEI formation is a well-known process in standard lithium - ion battery operation; however, using aqueous electrolytes does

Chemical Aspects of Astrophysically Observed Extraterrestrial Methanol, Hydrocarbon Derivatives, and Ions.

PubMed

Olah, George A; Mathew, Thomas; Prakash, G K Surya; Rasul, Golam

2016-02-10

Astrophysically observed extraterrestrial molecular matter contains, besides hydrogen and water, methane and methanol as the most abundant species. Feasible pathways and chemical aspects of their formation as well as of derived hydrocarbon homologues and their ions (carbocations and carbanions) are discussed on the basis of observed similarities with our studied terrestrial chemistry. The preferred pathway for converting extraterrestrial methane according to Ali et al. is based on CH5(+) and Olah's related nonclassical carbonium ion chemistry. On the basis of the observed higher reactivity of methanol compared with methane in various chemical reactions, a feasible new pathway is proposed for the conversion of extraterrestrial methanol to hydrocarbons, their derivatives, and carbocations together with a possible connection with methonium ion-based chemistry.

Bioorthogonal chemistry: strategies and recent development

PubMed Central

Ramil, Carlo P.; Lin, Qing

2013-01-01

The use of covalent chemistry to track biomolecules in their native environment—a focus of bioorthogonal chemistry—has received considerable interests recently among chemical biologists and organic chemists alike. To facilitate wider adoption of bioorthogonal chemistry in biomedical research, a central effort in the last few years has been focused on the optimization of a few known bioorthogonal reactions, particularly with respective to reaction kinetics improvement, novel genetic encoding systems, and fluorogenic reactions for bioimaging. During these optimizations, three strategies have emerged, including the use of ring strain for substrate activation in the cycloaddition reactions, the discovery of new ligands and privileged substrates for accelerated metal-catalysed reactions, and the design of substrates with pre-fluorophore structures for rapid “turn-on” fluorescence after selective bioorthogonal reactions. In addition, new bioorthogonal reactions based on either modified or completely unprecedented reactant pairs have been reported. Finally, increasing attention has been directed toward the development of mutually exclusive bioorthogonal reactions and their applications in multiple labeling of a biomolecule in cell culture. In this feature article, we wish to present the recent progress in bioorthogonal reactions through the selected examples that highlight the above-mentioned strategies. Considering increasing sophistication in bioorthogonal chemistry development, we strive to project several exciting opportunities where bioorthogonal chemistry can make a unique contribution to biology in near future. PMID:24145483

Comparison of direct and alternating current vacuum ultraviolet lamps in atmospheric pressure photoionization.

PubMed

Vaikkinen, Anu; Haapala, Markus; Kersten, Hendrik; Benter, Thorsten; Kostiainen, Risto; Kauppila, Tiina J

2012-02-07

A direct current induced vacuum ultraviolet (dc-VUV) krypton discharge lamp and an alternating current, radio frequency (rf) induced VUV lamp that are essentially similar to lamps in commercial atmospheric pressure photoionization (APPI) ion sources were compared. The emission distributions along the diameter of the lamp exit window were measured, and they showed that the beam of the rf lamp is much wider than that of the dc lamp. Thus, the rf lamp has larger efficient ionization area, and it also emits more photons than the dc lamp. The ionization efficiencies of the lamps were compared using identical spray geometries with both lamps in microchip APPI mass spectrometry (μAPPI-MS) and desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS). A comprehensive view on the ionization was gained by studying six different μAPPI solvent compositions, five DAPPI spray solvents, and completely solvent-free DAPPI. The observed reactant ions for each solvent composition were very similar with both lamps except for toluene, which showed a higher amount of solvent originating oxidation products with the rf lamp than with the dc lamp in μAPPI. Moreover, the same analyte ions were detected with both lamps, and thus, the ionization mechanisms with both lamps are similar. The rf lamp showed a higher ionization efficiency than the dc lamp in all experiments. The difference between the lamp ionization efficiencies was greatest when high ionization energy (IE) solvent compositions (IEs above 10 eV), i.e., hexane, methanol, and methanol/water, (1:1 v:v) were used. The higher ionization efficiency of the rf lamp is likely due to the larger area of high intensity light emission, and the resulting larger efficient ionization area and higher amount of photons emitted. These result in higher solvent reactant ion production, which in turn enables more efficient analyte ion production. © 2012 American Chemical Society

Phosphorus-doped glass proton exchange membranes for low temperature direct methanol fuel cells

NASA Astrophysics Data System (ADS)

Prakash, Shruti; Mustain, William E.; Park, SeongHo; Kohl, Paul A.

Phosphorus-doped silicon dioxide thin films were used as ion exchange membranes in low temperature proton exchange membrane fuel cells. Phosphorus-doped silicon dioxide glass (PSG) was deposited via plasma-enhanced chemical vapor deposition (PECVD). The plasma deposition of PSG films allows for low temperature fabrication that is compatible with current microelectronic industrial processing. SiH 4, PH 3 and N 2O were used as the reactant gases. The effect of plasma deposition parameters, substrate temperature, RF power, and chamber pressure, on the ionic conductivity of the PSG films is elucidated. PSG conductivities as high as 2.54 × 10 -4 S cm -1 were realized, which is 250 times higher than the conductivity of pure SiO 2 films (1 × 10 -6 S cm -1) under identical deposition conditions. The higher conductivity films were deposited at low temperature, moderate pressure, limited reactant gas flow rate, and high RF power.

Catalytic distillation process

DOEpatents

Smith, Jr., Lawrence A.

1982-01-01

A method for conducting chemical reactions and fractionation of the reaction mixture comprising feeding reactants to a distillation column reactor into a feed zone and concurrently contacting the reactants with a fixed bed catalytic packing to concurrently carry out the reaction and fractionate the reaction mixture. For example, a method for preparing methyl tertiary butyl ether in high purity from a mixed feed stream of isobutene and normal butene comprising feeding the mixed feed stream to a distillation column reactor into a feed zone at the lower end of a distillation reaction zone, and methanol into the upper end of said distillation reaction zone, which is packed with a properly supported cationic ion exchange resin, contacting the C.sub.4 feed and methanol with the catalytic distillation packing to react methanol and isobutene, and concurrently fractionating the ether from the column below the catalytic zone and removing normal butene overhead above the catalytic zone.

Catalytic distillation process

DOEpatents

Smith, L.A. Jr.

1982-06-22

A method is described for conducting chemical reactions and fractionation of the reaction mixture comprising feeding reactants to a distillation column reactor into a feed zone and concurrently contacting the reactants with a fixed bed catalytic packing to concurrently carry out the reaction and fractionate the reaction mixture. For example, a method for preparing methyl tertiary butyl ether in high purity from a mixed feed stream of isobutene and normal butene comprising feeding the mixed feed stream to a distillation column reactor into a feed zone at the lower end of a distillation reaction zone, and methanol into the upper end of said distillation reaction zone, which is packed with a properly supported cationic ion exchange resin, contacting the C[sub 4] feed and methanol with the catalytic distillation packing to react methanol and isobutene, and concurrently fractionating the ether from the column below the catalytic zone and removing normal butene overhead above the catalytic zone.

The equilibrium of the reaction catalysed by citrate oxaloacetate-lyase

PubMed Central

Tate, S. S.; Datta, S. P.

1965-01-01

1. A method of preparation and purification of citrate oxaloacetate-lyase (EC 4.1.3.6) from Aerobacter aerogenes is described. 2. The equilibrium of this reaction has been determined at pH 8·4 and 25°. It has been shown that K, i.e. [citrate3−]/[oxaloacetateketo2−][acetate −], is 3·08±0·72, but that Kapp., i.e. [total citrate]/[total oxaloacetate][total acetate], is markedly affected by the initial concentrations of the reactants and magnesium. 3. The free-energy change during the cleavage of citrate has been calculated and compared with data from other sources. 4. The free energy of hydrolysis of acetyl-CoA has been evaluated from the present data. 5. A detailed knowledge of the interactions of the reactants with metal ions has been shown to be important in the calculation of the equilibrium constant and related thermodynamic functions. PMID:14348207

Organocatalyzed, Visible-Light Photoredox-Mediated, One-Pot Minisci Reaction Using Carboxylic Acids via N-(Acyloxy)phthalimides.

PubMed

Sherwood, Trevor C; Li, Ning; Yazdani, Aliza N; Dhar, T G Murali

2018-03-02

An improved, one-pot Minisci reaction has been developed using visible light, an organic photocatalyst, and carboxylic acids as radical precursors via the intermediacy of in situ-generated N-(acyloxy)phthalimides. The conditions employed are mild, demonstrate a high degree of functional group tolerance, and do not require a large excess of the carboxylic acid reactant. As a result, this reaction can be applied to drug-like scaffolds and molecules with sensitive functional groups, enabling late-stage functionalization, which is of high interest to medicinal chemistry.

Investigation of critical parameters controlling the efficiency of associative ionization

NASA Astrophysics Data System (ADS)

Le Padellec, A.; Launoy, T.; Dochain, A.; Urbain, X.

2017-05-01

This paper compiles our merged-beam experimental findings for the associative ionization (AI) process from charged reactants, with the aim of guiding future investigations with e.g. the double electrostatic ion storage ring DESIREE in Stockholm. A reinvestigation of the isotopic effect in H-(D-) + He+ collisions is presented, along with a review of {{{H}}}3+ and NO+ production by AI involving ion pairs or excited neutrals, and put in perspective with the mutual neutralization and radiative association reactions. Critical parameters are identified and evaluated for their systematic role in controlling the magnitude of the cross section: isotopic substitution, exothermicity, electronic state density, and spin statistics.

Paper-Based Heavy Metal Sensors from the Concise Synthesis of an Anionic Porphyrin: A Practical Application of Organic Synthesis to Environmental Chemistry

ERIC Educational Resources Information Center

Prabpal, Jutamat; Vilaivan, Tirayut; Praneenararat, Thanit

2017-01-01

Tetrakis(4-sulfonatophenyl)porphyrin (TSPP) was immobilized on patterned paper and used as a sensor for heavy metal ions in an advanced organic chemistry course. The resulting sensor could detect Hg[superscript 2+] and Cd[superscript 2+] ions colorimetrically, while Cu[superscript 2+] ion resulted in fluorescence quenching, thus demonstrating a…

Electron capture by Ne3+ ions from atomic hydrogen

NASA Astrophysics Data System (ADS)

Rejoub, R.; Bannister, M. E.; Havener, C. C.; Savin, D. W.; Verzani, C. J.; Wang, J. G.; Stancil, P. C.

2004-05-01

Using the Oak Ridge National Laboratory ion-atom merged-beam apparatus, absolute total electron-capture cross sections have been measured for collisions of Ne3+ ions with hydrogen (deuterium) atoms at energies between 0.07 and 826 eV/u . Comparison to previous measurements shows large discrepancies between 50 and 400 eV/u . Previously published molecular-orbital close-coupling (MOCC) calculations were performed over limited energy ranges, but show good agreement with the present measurements. Here MOCC calculations are presented for energies between 0.01 and 1000 eV/u for collisions with both H and D. For energies below ˜1 eV/u , an enhancement in the magnitude of both the experimental and theoretical cross sections is observed which is attributed to the ion-induced dipole attraction between the reactants. Below ˜4 eV/u , the present calculations show a significant target isotope effect.

Saturn's satellites: Potential for organic chemistry

NASA Astrophysics Data System (ADS)

Delitsky, M. L.; Lane, A. L.; Henry-Riyad, H.; Tidwell, T. T.

2003-05-01

The surfaces of the Saturnian satellites are subjected to irradiation from solar wind ions, photons, and magnetospheric ions and electrons. This bombardment will transform the chemical nature of the surfaces. At present, only water ice has been detected on their surfaces. Further studies by the Cassini spacecraft may reveal other molecules. If CO2 ice is found there, a whole panoply of new species may be detected. As nitrogen ions in the magnetosphere are thought to be an important species bombarding the satellites, Delitsky and Lane (2002) outlined the nitrogen oxides chemistry that may result from implantation of N+ into the water ice surfaces. Sittler et al (2002) showed that N+ ions originating from Titan will be enriched in the magnetospheric ion population as they move inwards towards Saturn, making the nitrogen oxides chemistry more likely. If CO2 is present, a complicated C-H-N-O chemistry may result from deposition of the N+ into a H2O/CO2 mixed ice, including nitriles, isocyanates, polymers, and amino acids. The combination of H2O/CO2 upon irradiation may also yield a complex mixture of hydrocarbons, esters, alcohols, organic acids and ketones. Possible chemical pathways and computations of their energetics will be presented. -Ref:- 1. Delitsky and Lane, Saturn's inner satellites: Ice chemistry and magnetosphere effects, JGR (Planets), Nov 2002, 3-1;; 2. Sittler et al., Energetic nitrogen ions within the inner magnetosphere of Saturn, Fall AGU meeting, Dec 2002, abstracts, pg F858, P21B-0379

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer.

PubMed

Köhler, Markus; Oßwald, Patrick; Krueger, Dominik; Whitside, Ryan

2018-02-19

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This flexible tool offers a detailed observation of chemical gas-phase kinetics in reacting flows under well-controlled conditions. The vast range of operating conditions available in a laminar flow reactor enables access to extraordinary combustion applications that are typically not achievable by flame experiments. These include rich conditions at high temperatures relevant for gasification processes, the peroxy chemistry governing the low temperature oxidation regime or investigations of complex technical fuels. The presented setup allows measurements of quantitative speciation data for reaction model validation of combustion, gasification and pyrolysis processes, while enabling a systematic general understanding of the reaction chemistry. Validation of kinetic reaction models is generally performed by investigating combustion processes of pure compounds. The flow reactor has been enhanced to be suitable for technical fuels (e.g. multi-component mixtures like Jet A-1) to allow for phenomenological analysis of occurring combustion intermediates like soot precursors or pollutants. The controlled and comparable boundary conditions provided by the experimental design allow for predictions of pollutant formation tendencies. Cold reactants are fed premixed into the reactor that are highly diluted (in around 99 vol% in Ar) in order to suppress self-sustaining combustion reactions. The laminar flowing reactant mixture passes through a known temperature field, while the gas composition is determined at the reactors exhaust as a function of the oven temperature. The flow reactor is operated at atmospheric pressures with temperatures up to 1,800 K. The measurements themselves are performed by decreasing the temperature monotonically at a rate of -200 K/h. With the sensitive MBMS technique, detailed speciation data is acquired and quantified for almost all chemical species in the reactive process, including radical species.

Growing Applications of “Click Chemistry” for Bioconjugation in Contemporary Biomedical Research

PubMed Central

Nwe, Kido

2009-01-01

Summation This update summarizes the growing application of “click” chemistry in diverse areas such as bioconjugation, drug discovery, materials science, and radiochemistry. This update also discusses click chemistry reactions that proceed rapidly with high selectivity, specificity, and yield. Two important characteristics make click chemistry so attractive for assembling compounds, reagents, and biomolecules for preclinical and clinical applications. First, click reactions are bio-orthogonal; neither the reactants nor their product's functional groups interact with functionalized biomolecules. Second, the reactions proceed with ease under mild nontoxic conditions, such as at room temperature and, usually, in water. The copper-catalyzed Huisgen cycloaddition, azide-alkyne [3 + 2] dipolar cycloaddition, Staudinger ligation, and azide-phosphine ligation each possess these unique qualities. These reactions can be used to modify one cellular component while leaving others unharmed or untouched. Click chemistry has found increasing applications in all aspects of drug discovery in medicinal chemistry, such as for generating lead compounds through combinatorial methods. Bioconjugation via click chemistry is rigorously employed in proteomics and nucleic research. In radiochemistry, selective radiolabeling of biomolecules in cells and living organisms for imaging and therapy has been realized by this technology. Bifunctional chelating agents for several radionuclides useful for positron emission tomography and single-photon emission computed tomography imaging have also been prepared by using click chemistry. This review concludes that click chemistry is not the perfect conjugation and assembly technology for all applications, but provides a powerful, attractive alternative to conventional chemistry. This chemistry has proven itself to be superior in satisfying many criteria (e.g., biocompatibility, selectivity, yield, stereospecificity, and so forth); thus, one can expect it will consequently become a more routine strategy in the near future for a wide range of applications. PMID:19538051

Imaging and controlling intracellular reactions: Lysosome transport as a function of diameter and the intracellular synthesis of conducting polymers

NASA Astrophysics Data System (ADS)

Payne, Christine

2014-03-01

Eukaryotic cells are the ultimate complex environment with intracellular chemical reactions regulated by the local cellular environment. For example, reactants are sequestered into specific organelles to control local concentration and pH, motor proteins transport reactants within the cell, and intracellular vesicles undergo fusion to bring reactants together. Current research in the Payne Lab in the School of Chemistry and Biochemistry at Georgia Tech is aimed at understanding and utilizing this complex environment to control intracellular chemical reactions. This will be illustrated using two examples, intracellular transport as a function of organelle diameter and the intracellular synthesis of conducting polymers. Using single particle tracking fluorescence microscopy, we measured the intracellular transport of lysosomes, membrane-bound organelles, as a function of diameter as they underwent transport in living cells. Both ATP-dependent active transport and diffusion were examined. As expected, diffusion scales with the diameter of the lysosome. However, active transport is unaffected suggesting that motor proteins are insensitive to cytosolic drag. In a second example, we utilize intracellular complexity, specifically the distinct micro-environments of different organelles, to carry out chemical reactions. We show that catalase, found in the peroxisomes of cells, can be used to catalyze the polymerization of the conducting polymer PEDOT:PSS. More importantly, we have found that a range of iron-containing biomolecules are suitable catalysts with different iron-containing biomolecules leading to different polymer properties. These experiments illustrate the advantage of intracellular complexity for the synthesis of novel materials.

Elusive anion growth in Titan's atmosphere: Low temperature kinetics of the C3N- + HC3N reaction

NASA Astrophysics Data System (ADS)

Bourgalais, Jérémy; Jamal-Eddine, Nour; Joalland, Baptiste; Capron, Michael; Balaganesh, Muthiah; Guillemin, Jean-Claude; Le Picard, Sébastien D.; Faure, Alexandre; Carles, Sophie; Biennier, Ludovic

2016-06-01

Ion chemistry appears to be deeply involved in the formation of heavy molecules in the upper atmosphere of Titan. These large species form the seeds of the organic aerosols responsible for the opaque haze surrounding the biggest satellite of Saturn. The chemical pathways involving individual anions remain however mostly unknown. The determination of the rates of the elementary reactions with ions and the identification of the products are essential to the progress in our understanding of Titan's upper atmosphere. We have taken steps in that direction through the investigation of the low temperature reactivity of C3N- , which was tentatively identified in the spectra measured by the CAPS-ELS instrument of the Cassini spacecraft during its high altitude flybys. The reaction of this anion with HC3N, one of the most abundant trace organics in the atmosphere, has been studied over the 49-294 K temperature range in uniform supersonic flows using the CRESU technique. The proton transfer is found to be the main exit channel (>91%) of the C315N- + HC3N reaction. It remains however indistinguishable with the non-isotopically labeled C314N- reactant. The T - 1 / 2 temperature dependence of this proton transfer reaction and its global rate are reasonably well reproduced theoretically using an average dipole orientation model. A minor exit channel, reactive detachment (< 9%), has also been uncovered, although the nature of the neutral products has not been determined. It is concluded that the C314N- + HC3N reaction cannot contribute to the growth of molecular anions in the upper atmosphere of Titan. Due to the low branching into the neutral exit channel, it cannot contribute either to the growth of neutrals even assuming a complete mass transfer.

The international water conference proceedings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guseman, J.R.

1984-10-01

This book provides information on computer applications to water chemistry control, groundwater, membrane technology, instrumentation/analytical techniques and ion exchange. Other topics of discussion include cooling water, biocontrol, the hydraulic properties of ion exchange resins, steam electric power plant aqueous discharges and colorimetric determination of trace benzotriazole or tolytriazole. Water chemistry guidelines for large steam generating power plants is discussed, as well as wastewater treatment, boiler water conditioning and ion exchange/computer related topics.

Lifecycle comparison of selected Li-ion battery chemistries under grid and electric vehicle duty cycle combinations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crawford, Alasdair J.; Huang, Qian; Kintner-Meyer, Michael C. W.

Li-ion batteries play a vital role in stabilizing the electrical grid. In this work, two different Li-ion battery chemistries based on LiNi0.8Co0.15Al0.05O2 (NCA) and LiFePO4 (LFP) cathodes have been tested under the grid duty cycles recently developed for frequency regulation (FR) and peak shaving (PS) with and without being subjected to electric vehicle (EV) drive cycles. The lifecycle comparison derived from capacity, round trip efficiency (RTE), resistance, charge/discharge energy and total utilized energy of the two battery chemistries have been discussed. The results can be used as a guideline for selection, deployment, operation and cost analyses of Li-ion batteries usedmore » for different applications.« less

Battery Research & Development Need for Military Vehicle Application

DTIC Science & Technology

2012-06-19

The charge control for lithium ion battery chemistries is different from those of flooded and sealed lead acid batteries. • The discharge control...for lithium ion battery chemistries is different from those of flooded and sealed lead acid batteries. • Battery charging voltage changes with the

Mechanism of Phenol Alkylation in Zeolite H-BEA Using In Situ Solid-State NMR Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Zhenchao; Shi, Hui; Wan, Chuan

Alkylation of phenolic compounds in the liquid phase is of fundamental and practical importance to the conversion of biomass-derived feedstocks into fuels and chemicals. In this work, the reaction mechanism for phenol alkylation with cyclohexanol and cyclohexene has been investigated on a commercial HBEA zeolite by in situ 13C MAS NMR, using decalin as the solvent. From the variable temperature 13C MAS NMR measurements of phenol and cyclohexanol adsorption on HBEA from decalin solutions, it is shown that the two molecules have similar adsorption strength in the HBEA pore. Phenol alkylation with cyclohexanol, however, becomes significantly measurable only after cyclohexanolmore » is largely converted to cyclohexene via dehydration. This is in contrast to the initially rapid alkylation of phenol when using cyclohexene as the co-reactant. 13C isotope scrambling results demonstrate that the electrophile, presumably cyclohexyl carbenium ion, is directly formed in a protonation step when cyclohexene is the co-reactant, but requires re-adsorption of the alcohol dehydration product, cyclohexene, when cyclohexanol dimer is the dominant surface species (e.g., at 0.5 M cyclohexanol concentration) that is unable to generate carbenium ion. At the initial reaction stage of phenol-cyclohexanol alkylation on HBEA, the presence of the cyclohexanol dimer species hinders the adsorption of cyclohexene at the Brønsted acid site and the subsequent activation of the more potent electrophile (carbenium ion). Isotope scrambling data also show that intramolecular rearrangement of cyclohexyl phenyl ether, the O-alkylation product, does not significantly contribute to the formation of C-alkylation products.« less

Chemistry on Stamps.

ERIC Educational Resources Information Center

Schreck, James O.

1986-01-01

Suggests how postage stamps can be incorporated into chemistry teaching. Categories considered include emergence of chemistry as a science, metric system, atoms (and molecules and ions), stoichiometry, energy relationships in chemical systems, chemical bonding, nuclear chemistry, biochemistry, geochemistry, matter (gases, liquids, and solids),…

Radical Rearrangement Chemistry in Ultraviolet Photodissociation of Iodotyrosine Systems: Insights from Metastable Dissociation, Infrared Ion Spectroscopy, and Reaction Pathway Calculations.

PubMed

Ranka, Karnamohit; Zhao, Ning; Yu, Long; Stanton, John F; Polfer, Nicolas C

2018-05-29

We report on the ultraviolet photodissociation (UVPD) chemistry of protonated tyrosine, iodotyrosine, and diiodotyrosine. Distonic loss of the iodine creates a high-energy radical at the aromatic ring that engages in hydrogen/proton rearrangement chemistry. Based on UVPD kinetics measurements, the appearance of this radical is coincident with the UV irradiation pulse (8 ns). Conversely, sequential UVPD product ions exhibit metastable decay on ca. 100 ns timescales. Infrared ion spectroscopy is capable of confirming putative structures of the rearrangement products as proton transfers from the imine and β-carbon hydrogens. Potential energy surfaces for the various reaction pathways indicate that the rearrangement chemistry is highly complex, compatible with a cascade of rearrangements, and that there is no preferred rearrangement pathway even in small molecular systems like these. Graphical Abstract.

Coloring a Superabsorbent Polymer with Metal Ions: An Undergraduate Chemistry Experiment

ERIC Educational Resources Information Center

Yaung, Jing-Fun; Chen, Yueh-Huey

2009-01-01

A novel undergraduate chemistry experiment involving superabsorbent polymers commonly used in diapers and other personal care products is described. Students observe the removal of divalent transition-metal ions from aqueous solutions by the polymers. With the procedures provided, students are able to color the superabsorbent polymers with metal…

Dissociative recombination in interstellar clouds

NASA Technical Reports Server (NTRS)

Black, John H.; Van Dishoeck, Ewine F.

1989-01-01

Molecular ions play a significant role in the chemistry and evolution of interstellar molecular clouds, even though these regions are overwhelmingly neutral. The dissociative recombination (DR) process governs the abundances of many of these ions and of related neutral species. The gas-phase ion-molecule chemistry of the simplest species is summarized, with emphasis on those problems which are most sensitive to uncertain rates or product branching ratios of DR processes. Examples of the kinds of information needed about DR processes are presented. The importance of the H3(+) ion and prospects for its direct observation are discussed.

A Glow Discharge Ion Source with Fourier Transform Ion Cyclotron Resonance Mass Spectrometric Detection

DTIC Science & Technology

1991-05-10

Hall, D . Mikrochim. Acta 1987, 1, 275. 26. Harrison, W.W.; Bentz , B.L. Prog. Analyt. Spectrosc. 1988, L19 53. 27. Harrison, W.W.; Barshick, C.M...Innovation, and Applications. ACS Symp. Series; Buchanan, M.V., Ed.; American Chemical Society: Washington, 1987; 359, p 1. 3. Wilkins, C.L.; Chowdhury, A.K...J.L. In Gas Phase Ion CheMistry; Bowers, M.T., Ed.; Academic: New York, 1984; Vol. 3, p 41. 6. Dunbar, R.C. In Gas Phase Ion Chemistry; Bowvers, M.T

Nanoporous membranes with electrochemically switchable, chemically stabilized ionic selectivity

NASA Astrophysics Data System (ADS)

Small, Leo J.; Wheeler, David R.; Spoerke, Erik D.

2015-10-01

Nanopore size, shape, and surface charge all play important roles in regulating ionic transport through nanoporous membranes. The ability to control these parameters in situ provides a means to create ion transport systems tunable in real time. Here, we present a new strategy to address this challenge, utilizing three unique electrochemically switchable chemistries to manipulate the terminal functional group and control the resulting surface charge throughout ensembles of gold plated nanopores in ion-tracked polycarbonate membranes 3 cm2 in area. We demonstrate the diazonium mediated surface functionalization with (1) nitrophenyl chemistry, (2) quinone chemistry, and (3) previously unreported trimethyl lock chemistry. Unlike other works, these chemistries are chemically stabilized, eliminating the need for a continuously applied gate voltage to maintain a given state and retain ionic selectivity. The effect of surface functionalization and nanopore geometry on selective ion transport through these functionalized membranes is characterized in aqueous solutions of sodium chloride at pH = 5.7. The nitrophenyl surface allows for ionic selectivity to be irreversibly switched in situ from cation-selective to anion-selective upon reduction to an aminophenyl surface. The quinone-terminated surface enables reversible changes between no ionic selectivity and a slight cationic selectivity. Alternatively, the trimethyl lock allows ionic selectivity to be reversibly switched by up to a factor of 8, approaching ideal selectivity, as a carboxylic acid group is electrochemically revealed or hidden. By varying the pore shape from cylindrical to conical, it is demonstrated that a controllable directionality can be imparted to the ionic selectivity. Combining control of nanopore geometry with stable, switchable chemistries facilitates superior control of molecular transport across the membrane, enabling tunable ion transport systems.Nanopore size, shape, and surface charge all play important roles in regulating ionic transport through nanoporous membranes. The ability to control these parameters in situ provides a means to create ion transport systems tunable in real time. Here, we present a new strategy to address this challenge, utilizing three unique electrochemically switchable chemistries to manipulate the terminal functional group and control the resulting surface charge throughout ensembles of gold plated nanopores in ion-tracked polycarbonate membranes 3 cm2 in area. We demonstrate the diazonium mediated surface functionalization with (1) nitrophenyl chemistry, (2) quinone chemistry, and (3) previously unreported trimethyl lock chemistry. Unlike other works, these chemistries are chemically stabilized, eliminating the need for a continuously applied gate voltage to maintain a given state and retain ionic selectivity. The effect of surface functionalization and nanopore geometry on selective ion transport through these functionalized membranes is characterized in aqueous solutions of sodium chloride at pH = 5.7. The nitrophenyl surface allows for ionic selectivity to be irreversibly switched in situ from cation-selective to anion-selective upon reduction to an aminophenyl surface. The quinone-terminated surface enables reversible changes between no ionic selectivity and a slight cationic selectivity. Alternatively, the trimethyl lock allows ionic selectivity to be reversibly switched by up to a factor of 8, approaching ideal selectivity, as a carboxylic acid group is electrochemically revealed or hidden. By varying the pore shape from cylindrical to conical, it is demonstrated that a controllable directionality can be imparted to the ionic selectivity. Combining control of nanopore geometry with stable, switchable chemistries facilitates superior control of molecular transport across the membrane, enabling tunable ion transport systems. Electronic supplementary information (ESI) available: Experimental procedures, synthesis, and characterization of molecules 1, 2 and 3. Explanation of the electrochemical method for approximating nanopore diameter. Additional XPS spectra. See DOI: 10.1039/C5NR02939B

Normal-inverse bimodule operation Hadamard transform ion mobility spectrometry.

PubMed

Hong, Yan; Huang, Chaoqun; Liu, Sheng; Xia, Lei; Shen, Chengyin; Chu, Yannan

2018-10-31

In order to suppress or eliminate the spurious peaks and improve signal-to-noise ratio (SNR) of Hadamard transform ion mobility spectrometry (HT-IMS), a normal-inverse bimodule operation Hadamard transform - ion mobility spectrometry (NIBOHT-IMS) technique was developed. In this novel technique, a normal and inverse pseudo random binary sequence (PRBS) was produced in sequential order by an ion gate controller and utilized to control the ion gate of IMS, and then the normal HT-IMS mobility spectrum and the inverse HT-IMS mobility spectrum were obtained. A NIBOHT-IMS mobility spectrum was gained by subtracting the inverse HT-IMS mobility spectrum from normal HT-IMS mobility spectrum. Experimental results demonstrate that the NIBOHT-IMS technique can significantly suppress or eliminate the spurious peaks, and enhance the SNR by measuring the reactant ions. Furthermore, the gas CHCl 3 and CH 2 Br 2 were measured for evaluating the capability of detecting real sample. The results show that the NIBOHT-IMS technique is able to eliminate the spurious peaks and improve the SNR notably not only for the detection of larger ion signals but also for the detection of small ion signals. Copyright © 2018 Elsevier B.V. All rights reserved.

Discriminant analysis of fused positive and negative ion mobility spectra using multivariate self-modeling mixture analysis and neural networks.

PubMed

Chen, Ping; Harrington, Peter B

2008-02-01

A new method coupling multivariate self-modeling mixture analysis and pattern recognition has been developed to identify toxic industrial chemicals using fused positive and negative ion mobility spectra (dual scan spectra). A Smiths lightweight chemical detector (LCD), which can measure positive and negative ion mobility spectra simultaneously, was used to acquire the data. Simple-to-use interactive self-modeling mixture analysis (SIMPLISMA) was used to separate the analytical peaks in the ion mobility spectra from the background reactant ion peaks (RIP). The SIMPLSIMA analytical components of the positive and negative ion peaks were combined together in a butterfly representation (i.e., negative spectra are reported with negative drift times and reflected with respect to the ordinate and juxtaposed with the positive ion mobility spectra). Temperature constrained cascade-correlation neural network (TCCCN) models were built to classify the toxic industrial chemicals. Seven common toxic industrial chemicals were used in this project to evaluate the performance of the algorithm. Ten bootstrapped Latin partitions demonstrated that the classification of neural networks using the SIMPLISMA components was statistically better than neural network models trained with fused ion mobility spectra (IMS).

Communication: Reactivity borrowing in the mode selective chemistry of H + CHD3 → H2 + CD3

NASA Astrophysics Data System (ADS)

Ellerbrock, Roman; Manthe, Uwe

2017-12-01

Quantum state-resolved reaction probabilities for the H + CHD3 → H2 + CD3 reaction are calculated by accurate full-dimensional quantum dynamics calculations using the multi-layer multi-configurational time-dependent Hartree approach and the quantum transition state concept. Reaction probabilities of various ro-vibrational states of the CHD3 reactant are investigated for vanishing total angular momentum. While the reactivity of the different vibrational states of CHD3 mostly follows intuitive patterns, an unusually large reaction probability is found for CHD3 molecules triply excited in the CD3 umbrella-bending vibration. This surprising reactivity can be explained by a Fermi resonance-type mixing of the single CH-stretch excited and the triple CD3 umbrella-bend excited vibrational states of CHD3. These findings show that resonant energy transfer can significantly affect the mode-selective chemistry of CHD3 and result in counter-intuitive reactivity patterns.

Reactive trajectories of the Ru2+/3+ self-exchange reaction and the connection to Marcus' theory.

PubMed

Tiwari, Ambuj; Ensing, Bernd

2016-12-22

Outer sphere electron transfer between two ions in aqueous solution is a rare event on the time scale of first principles molecular dynamics simulations. We have used transition path sampling to generate an ensemble of reactive trajectories of the self-exchange reaction between a pair of Ru 2+ and Ru 3+ ions in water. To distinguish between the reactant and product states, we use as an order parameter the position of the maximally localised Wannier center associated with the transferring electron. This allows us to align the trajectories with respect to the moment of barrier crossing and compute statistical averages over the path ensemble. We compare our order parameter with two typical reaction coordinates used in applications of Marcus theory of electron transfer: the vertical gap energy and the solvent electrostatic potential at the ions.

Liquid-assisted grinding and ion pairing regulates percentage conversion and diastereoselectivity of the Wittig reaction under mechanochemical conditions.

PubMed

Denlinger, Kendra Leahy; Ortiz-Trankina, Lianna; Carr, Preston; Benson, Kingsley; Waddell, Daniel C; Mack, James

2018-01-01

Mechanochemistry is maturing as a discipline and continuing to grow, so it is important to continue understanding the rules governing the system. In a mechanochemical reaction, the reactants are added into a vessel along with one or more grinding balls and the vessel is shaken at high speeds to facilitate a chemical reaction. The dielectric constant of the solvent used in liquid-assisted grinding (LAG) and properly chosen counter-ion pairing increases the percentage conversion of stilbenes in a mechanochemical Wittig reaction. Utilizing stepwise addition/evaporation of ethanol in liquid-assisted grinding also allows for the tuning of the diastereoselectivity in the Wittig reaction.

Numerical Analysis of Plasma Transport in Tandem Volume Magnetic Multicusp Ion Sources

DTIC Science & Technology

1992-03-01

the results of the model are qualitatively correct. Boltzmann Equation, Ion Sources, Plasma Simulation, Electron Temperature, Plasma Density, Ion Temperature, Hydrogen Ions, Magnetic Filters, Hydrogen Plasma Chemistry .

Organic chemistry on solid surfaces

NASA Astrophysics Data System (ADS)

Ma, Zhen; Zaera, Francisco

2006-07-01

Chemistry on solid surfaces is central to many areas of practical interest such as heterogeneous catalysis, tribology, electrochemistry, and materials processing. With the development of many surface-sensitive analytical techniques in the past decades, great advances have been possible in our understanding of such surface chemistry at the molecular level. Earlier studies with model systems, single crystals in particular, have provided rich information about the adsorption and reaction kinetics of simple inorganic molecules. More recently, the same approach has been expanded to the study of the surface chemistry of relatively complex organic molecules, in large measure in connection with the selective synthesis of fine chemicals and pharmaceuticals. In this report, the chemical reactions of organic molecules and fragments on solid surfaces, mainly on single crystals of metals but also on crystals of metal oxides, carbides, nitrides, phosphides, sulfides and semiconductors as well as on more complex models such as bimetallics, alloys, and supported particles, are reviewed. A scheme borrowed from the organometallic and organic chemistry literature is followed in which key examples of representative reactions are cited first, and general reactivity trends in terms of both the reactants and the nature of the surface are then identified to highlight important mechanistic details. An attempt has been made to emphasize recent advances, but key earlier examples are cited as needed. Finally, correlations between surface and organometallic and organic chemistry, the relevance of surface reactions to applied catalysis and materials functionalization, and some promising future directions in this area are briefly discussed.

Localized Elf Propagation Anomalies.

DTIC Science & Technology

1985-06-01

the above three SPEs. Those important auxiliary data are used as inputs to air- chemistry codes to calculate the electron and ion density height...horizontal magnetic intensity H is H A ( ATAR ) 1 / 2 (9 d)- 1/2 exp(-’afL- d) e- d/ 8 " 7 coso A/m, (1) where A depends on the antenna moment, frequency...those rates are input to air- chemistry equations to obtain height profiles of electron and ion densities. Calculation of ion-pair production rates

Advances in understanding the surface chemistry of lignocellulosic biomass via time-of-flight secondary ion mass spectrometry

DOE PAGES

Tolbert, Allison K.; Ragauskas, Arthur J.

2016-12-12

Overcoming the natural recalcitrance of lignocellulosic biomass is necessary in order to efficiently convert biomass into biofuels or biomaterials and many times this requires some type of chemical pretreatment and/or biological treatment. While bulk chemical analysis is the traditional method of determining the impact a treatment has on biomass, the chemistry on the surface of the sample can differ from the bulk chemistry. Specifically, enzymes and microorganisms bind to the surface of the biomass and their efficiency could be greatly impacted by the chemistry of the surface. Therefore, it is important to study and understand the chemistry of the biomassmore » at the surface. Time-of- flight secondary ion mass spectrometry (ToF-SIMS) is a powerful tool that can spectrally and spatially analyze the surface chemistry of a sample. This review discusses the advances in understanding lignocellulosic biomass surface chemistry using the ToF-SIMS by addressing the instrument parameters, biomass sample preparation, and characteristic lignocellulosic ion fragmentation peaks along with their typical location in the plant cell wall. Furthermore, the use of the ToF-SIMS in detecting chemical changes due to chemical pretreatments, microbial treatments, and physical or genetic modifications is discussed along with possible future applications of the instrument in lignocellulosic biomass studies.« less

Advances in understanding the surface chemistry of lignocellulosic biomass via time-of-flight secondary ion mass spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tolbert, Allison K.; Ragauskas, Arthur J.

Overcoming the natural recalcitrance of lignocellulosic biomass is necessary in order to efficiently convert biomass into biofuels or biomaterials and many times this requires some type of chemical pretreatment and/or biological treatment. While bulk chemical analysis is the traditional method of determining the impact a treatment has on biomass, the chemistry on the surface of the sample can differ from the bulk chemistry. Specifically, enzymes and microorganisms bind to the surface of the biomass and their efficiency could be greatly impacted by the chemistry of the surface. Therefore, it is important to study and understand the chemistry of the biomassmore » at the surface. Time-of- flight secondary ion mass spectrometry (ToF-SIMS) is a powerful tool that can spectrally and spatially analyze the surface chemistry of a sample. This review discusses the advances in understanding lignocellulosic biomass surface chemistry using the ToF-SIMS by addressing the instrument parameters, biomass sample preparation, and characteristic lignocellulosic ion fragmentation peaks along with their typical location in the plant cell wall. Furthermore, the use of the ToF-SIMS in detecting chemical changes due to chemical pretreatments, microbial treatments, and physical or genetic modifications is discussed along with possible future applications of the instrument in lignocellulosic biomass studies.« less

Protein Engineering: Development of a Metal Ion Dependent Switch

DTIC Science & Technology

2017-05-22

Society of Chemistry Royal Society of Chemistry Biochemistry PNAS Escherichia coli Journal of Biotechnology Biochemistry Nature Protocols Journal of...Molecular Biology Biochemistry Royal Society of Chemistry Proteins: Structure, Function, and Bioinformatics Journal of Molecular Biology Biophysical...Biophysical Journal Protein Science Journal of Computational Chemistry Current Opinion in Chemical Biology Royal Society of Chemistry

Rates of nickel(II) capture from complexes with NTA, EDDA, and related tetradentate chelating agents by the hexadentate chelating agents EDTA and CDTA: Evidence of a "semijunctive" ligand exchange pathway

NASA Astrophysics Data System (ADS)

Boland, Nathan E.; Stone, Alan T.

2017-09-01

Many siderophores and metallophores produced by soil organisms, as well as anthropogenic chelating agent soil amendments, rely upon amine and carboxylate Lewis base groups for metal ion binding. UV-visible spectra of metal ion-chelating agent complexes are often similar and, as a consequence, whole-sample absorbance measurements are an unreliable means of monitoring the progress of exchange reactions. In the present work, we employ capillary electrophoresis to physically separate Ni(II)-tetradentate chelating agent complexes (NiL) from Ni(II)-hexadentate chelating agent complexes (NiY) prior to UV detection, such that progress of the reaction NiL + Y → NiY + L can be conveniently monitored. Rates of ligand exchange for Ni(II) are lower than for other +II transition metal ions. Ni(II) speciation in environmental media is often under kinetic rather than equilibrium control. Nitrilotriacetic acid (NTA), with three carboxylate groups all tethered to a central amine Lewis base group, ethylenediamine-N,N‧-diacetic acid (EDDA), with carboxylate-amine-amine-carboxylate groups arranged linearly, plus four structurally related compounds, are used as tetradentate chelating agents. Ethylenediaminetetraacetic acid (EDTA) and the structurally more rigid analog trans-cyclohexaneethylenediaminetetraacetic acid (CDTA) are used as hexadentate chelating agents. Effects of pH and reactant concentration are explored. Ni(II) capture by EDTA was consistently more than an order of magnitude faster than capture by CDTA, and too fast to quantify using our capillary electrophoresis-based technique. Using NiNTA as a reactant, Ni(II) capture by CDTA is independent of CDTA concentration and greatly enhanced by a proton-catalyzed pathway at low pH. Using NiEDDA as reactant, Ni(II) capture by CDTA is first order with respect to CDTA concentration, and the contribution from the proton-catalyzed pathway diminished by CDTA protonation. While the convention is to assign either a disjunctive pathway or adjunctive pathway to multidentate ligand exchange reactions, our results indicate that a third "semijunctive" pathway is necessary to account for slow reactions progressing through Lsbnd Nisbnd Y ternary complexes. Ligand exchange pathways with NTA-type chelating agents are assigned a disjunctive pathway, while pathways with EDDA-type chelating agents are assigned a semijunctive pathway. Based upon operative mechanism(s), magnitudes of exchange rates and effects of ambient geochemical conditions can be predicted.

Influence of ligand chemistry on silver nanoparticles for colorimetric detection of Cr3+ and Hg2+ ions

NASA Astrophysics Data System (ADS)

Kailasa, Suresh Kumar; Chandel, Madhurya; Mehta, Vaibhavkumar N.; Park, Tae Jung

2018-04-01

In this work, we describe the role of ligand chemistry on the surfaces of silver nanoparticles (Ag NPs) for tuning their analytical applications. The citrate and melamine (MA) molecules were used as ligands for the surface modification of Ag NPs. The addition of Cr3+ ion in citrate-Ag NPs (Cit-Ag NPs) and of Hg2+ ion in melamine-Ag NPs (MA-Ag NPs) cause Ag NPs aggregation, and are accompanied by a color change and a red-shift. The resulting distinctly visual readouts are favorable for colorimetric detection of Cr3+ and Hg2+ ions. Under optimal conditions, the linear ranges are observed in the concentration ranges of 1.0-50.0 and of 10.0-100.0 μM, and with detection limit of 0.52 and 1.80 μM for Cr3+ and Hg2+ ions. The simultaneous detection of Cr3+ and Hg2+ ion is driven by the changing the ligand chemistry on the surfaces of Ag NPs that allows to tune their specific interactions with target analytes. Finally, the functionalized Ag NPs were successfully applied to detect Cr3+ and Hg2+ ions in water samples with satisfactory recoveries.

Ab initio study of C + H3+ reactions

NASA Technical Reports Server (NTRS)

Talbi, D.; DeFrees, D. J.

1991-01-01

The reaction C + H3+ --> CH(+) + H2 is frequently used in models of dense interstellar cloud chemistry with the assumption that it is fast, i.e. there are no potential energy barriers inhibiting it. Ab initio molecular orbital study of the triplet CH3+ potential energy surface (triplet because the reactant carbon atom is a ground state triplet) supports this hypothesis. The reaction product is 3 pi CH+; the reaction is to exothermic even though the product is not in its electronic ground state. No path has been found on the potential energy surface for C + H3+ --> CH2(+) + H reaction.

Cu-Click Compatible Triazabutadienes To Expand the Scope of Aryl Diazonium Ion Chemistry.

PubMed

Cornali, Brandon M; Kimani, Flora W; Jewett, John C

2016-10-07

Triazabutadienes can be used to readily generate reactive aryl diazonium ions under mild, physiologically relevant conditions. These conditions are compatible with a range of functionalities that do not tolerate traditional aryl diazonium ion generation. To increase the utility of this aryl diazonium ion releasing chemistry an alkyne-containing triazabutadiene was synthesized. The copper-catalyzed azide-alkyne cycloaddition ("Cu-click") reaction was utilized to modify the alkyne-containing triazabutadiene and shown to be compatible with the nitrogen-rich triazabutadiene. One of the triazole products was tethered to a fluorophore, thus enabling the direct fluorescent labeling of a model protein.

NASA preprototype redox storage system for a photovoltaic stand-alone application

NASA Technical Reports Server (NTRS)

Hagedorn, N. H.

1981-01-01

A 1 kW preprototype redox storage system underwent characterization tests and was operated as the storage device for a 5 kW (peak) photovoltaic array. The system is described and performance data are presented. Loss mechanisms are discussed and simple design changes leading to significant increases in efficiency are suggested. The effects on system performance of nonequilibrium between the predominant species of complexed chromic ion in the negative electrode reactant solution are indicated.

Fullerene ion chemistry: a journey of discovery and achievement

PubMed Central

Böhme, Diethard K.

2016-01-01

An account is provided of the extraordinary features of buckminster fullerene cations and their chemistry that we discovered in our Ion Chemistry Laboratory at York University (Canada) during a ‘golden’ period of research in the early 1990s, just after C60 powder became available. We identified new chemical ways of C60 ionization and tracked novel chemistry of C60n+ as a function of charge state (n=1–3) with some 50 different reagent molecules. We found that multiple charges enhance reaction rates and diversify reaction products and mechanisms. Strong electrostatic interactions with reagent molecules were seen to reduce barriers to carbon surface bonding and charge-separation reactions, while intramolecular Coulomb repulsion appeared to localize charge on the surface or the substituent and so influence higher order chemistry, including ‘spindle’, ‘star’, ‘fuzzy ball’, ‘ball-and-chain’ and dimer ion formation. We introduced the notion of ‘apparent’ gas-phase acidity with measurements of proton-transfer reactions of multiply charged fullerene cations. We also explored the attachment of atomic metal cations to C60 and their subsequent reactions. All these findings were applied to the possible chemistry of fullerene cations in the interstellar medium with a focus on multiply charged fullerene ion formation and the intervention of fullerene cations in fullerene derivatization and molecular synthesis, with a view to their possible future detection. This article is part of the themed issue ‘Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene’. PMID:27501972

Quantum chemistry study of dielectric materials deposition

NASA Astrophysics Data System (ADS)

Widjaja, Yuniarto

The drive to continually decrease the device dimensions of integrated circuits in the microelectronics industry requires that deposited films approach subnanometer thicknesses. Hence, a fundamental understanding of the physics and chemistry of film deposition is important to obtain better control of the properties of the deposited film. We use ab initio quantum chemistry calculations to explore chemical reactions at the atomic level. Important thermodynamic and kinetic parameters are then obtained, which can then be used as inputs in constructing first-principles based reactor models. Studies of new systems for which data are not available can be conducted as well. In this dissertation, we use quantum chemistry simulations to study the deposition of gate dielectrics for metal-oxide-semiconductor (MOS) devices. The focus of this study is on heterogeneous reactions between gaseous precursors and solid surfaces. Adsorbate-surface interactions introduce additional degrees of complexity compared to the corresponding gas-phase or solid-state reactions. The applicability and accuracy of cluster approximations to represent solid surfaces are first investigated. The majority of our results are obtained using B3LYP density functional theory (DFT). The structures of reactants, products, and transition states are obtained, followed by calculations of thermochemical and kinetic properties. Whenever experimental data are available, qualitative and/or quantitative comparisons are drawn. Atomistic mechanisms and the energetics of several reactions leading to the deposition of SiO2, Si3N4, and potential new high-kappa materials such as ZrO2, HfO2, and Al 2O3 have been explored in this dissertation. Competing reaction pathways are explored for each of the deposition reactions studied. For example, the potential energy surface (PES) for ZrO2 ALD shows that the reactions proceed through a trapping-mediated mechanism, which results in a competition between desorption and decomposition of the gaseous reactants, i.e. ZrCl4 and H2O, on the ZrO2 surface. This competition results in relatively low saturation coverage, which consequently leads to a slow growth rate and possibly affects the thickness uniformity and conformality. The insights gained are then used to systematically improve deposition reactions. For instance, from the ZrO2 ALD PES, we are able to suggest the use of high temperature and pressure to obtain higher surface coverage.

Experiences Teaching Stoichiometry to Students in Grades 10 and 11

NASA Astrophysics Data System (ADS)

Bridges, Cynthia Denise

Many students have problems learning stoichiometry, a complex mathematical chemistry concept used to determine how much product will be produced or formed from a given quantity of reactants. The problem addressed in this study was teachers' lack of understanding of how to teach stoichiometry in a Midwestern urban school district. The conceptual framework of the study was based upon constructivist theory. A qualitative narrative approach was used to obtain the perceptions of 5 high school chemistry instructors related to their experiences, successful or unsuccessful, in teaching stoichiometry to students in Grades 10 and 11. Data were gathered through face-to-face interviews, which were analyzed via an inductive approach to reveal 6 themes: a difficult subject to teach, presentation of stoichiometry, relevancy, students' reactions, barriers, and gender differences. Findings suggested the need for teachers to be knowledgeable, creative, and resourceful in their subject areas to help their students to learn stoichiometry. Findings also revealed the need for teachers to adapt their instructional strategies and modes of delivery to reflect their students' individual learning styles. Understanding how the participating teachers explained stoichiometry to their students might help other chemistry teachers to examine and adapt their own instructional styles and delivery methods of the concept. This understanding might, in term, help to improve student achievement in stoichiometry in particular and chemistry in general.

Standardization of fluorine-18 manufacturing processes: new scientific challenges for PET.

PubMed

Hjelstuen, Ole K; Svadberg, Anders; Olberg, Dag E; Rosser, Mark

2011-08-01

In [(18)F]fluoride chemistry, the minute amounts of radioactivity taking part in a radiolabeling reaction are easily outnumbered by other reactants. Surface areas become comparably larger and more influential than in standard fluorine chemistry, while leachables, extractables, and other components that normally are considered small impurities can have a considerable influence on the efficiency of the reaction. A number of techniques exist to give sufficient (18)F-tracer for a study in a pre-clinical or clinical system, but the chemical and pharmaceutical understanding has significant gaps when it comes to scaling up or making the reaction more efficient. Automation and standardization of [(18)F]fluoride PET tracers is a prerequisite for reproducible manufacturing across multiple PET centers. So far, large-scale, multi-site manufacture has been established only for [(18)F]FDG, but several new tracers are emerging. In general terms, this transition from small- to large-scale production has disclosed several scientific challenges that need to be addressed. There are still areas of limited knowledge in the fundamental [(18)F]fluoride chemistry. The role of pharmaceutical factors that could influence the (18)F-radiosynthesis and the gaps in precise chemistry knowledge are discussed in this review based on a normal synthesis pattern. Copyright © 2011 Elsevier B.V. All rights reserved.

The Quantitative Resolution of a Mixture of Group II Metal Ions by Thermometric Titration with EDTA. An Analytical Chemistry Experiment.

ERIC Educational Resources Information Center

Smith, Robert L.; Popham, Ronald E.

1983-01-01

Presents an experiment in thermometric titration used in an analytic chemistry-chemical instrumentation course, consisting of two titrations, one a mixture of calcium and magnesium, the other of calcium, magnesium, and barium ions. Provides equipment and solutions list/specifications, graphs, and discussion of results. (JM)

Combustion flame-plasma hybrid reactor systems, and chemical reactant sources

DOEpatents

Kong, Peter C

2013-11-26

Combustion flame-plasma hybrid reactor systems, chemical reactant sources, and related methods are disclosed. In one embodiment, a combustion flame-plasma hybrid reactor system comprising a reaction chamber, a combustion torch positioned to direct a flame into the reaction chamber, and one or more reactant feed assemblies configured to electrically energize at least one electrically conductive solid reactant structure to form a plasma and feed each electrically conductive solid reactant structure into the plasma to form at least one product is disclosed. In an additional embodiment, a chemical reactant source for a combustion flame-plasma hybrid reactor comprising an elongated electrically conductive reactant structure consisting essentially of at least one chemical reactant is disclosed. In further embodiments, methods of forming a chemical reactant source and methods of chemically converting at least one reactant into at least one product are disclosed.

A research in support of NASA's space science

NASA Technical Reports Server (NTRS)

Hanson, W. B.

1985-01-01

Thirty-nine papers on cosmic ray anisotropies, law energy auroral particles, helium and hydrogen airglow, ionospheric irregularities, thermospheric winds, interhemisphere ion transport, ion cyclotron heating, ion temperature morphology, ion chemistry, ion convection, and spacecraft interactions with the atmosphere and ionosphere are described.

Some aspects of metallic ion chemistry and dynamics in the mesosphere and thermosphere

NASA Technical Reports Server (NTRS)

Mathews, J. D.

1987-01-01

The relationship between the formation of sporadic layers of metallic ion and the dumping of these ions into the upper mesosphere is discussed in terms of the tidal wind, classical (i.e., windshear) and other more complex, perhaps highly nonlinear layer formation mechanisms, and a possible circulation mechanism for these ions. Optical, incoherent scatter radar, rocket, and satellite derived evidence for various layer formation mechanisms and for the metallic ion circulation system is reviewed. The results of simple one dimensional numerical model calculations of sporadic E and intermediate layer formation are presented along with suggestions for more advanced models of intense or blanketing sporadic E. The flux of metallic ions dumped by the tidal wind system into the mesosphere is estimated and compared with estimates of total particle flux of meteoric origin. Possible effects of the metallic ion flux and of meteoric dust on D region ion chemistry are discussed.

Fuel cell system blower configuration

DOEpatents

Patel, Kirtikumar H.; Saito, Kazuo

2017-11-28

An exemplary fuel cell system includes a cell stack assembly having a plurality of cathode components and a plurality of anode components. A first reactant blower has an outlet situated to provide a first reactant to the cathode components. A second reactant blower has an outlet situated to provide a second reactant to the anode components. The second reactant blower includes a fan portion that moves the second reactant through the outlet. The second reactant blower also includes a motor portion that drives the fan portion and a bearing portion associated with the fan portion and the motor portion. The motor portion has a motor coolant inlet coupled with the outlet of the first reactant blower to receive some of the first reactant for cooling the motor portion.

Effect of lead ion concentration on the structural and optical properties of nano-crystalline PbS thin films

NASA Astrophysics Data System (ADS)

Zaman, S.; Mehmood, S. K.; Mansoor, M.; Asim, M. M.

2014-06-01

PbS thin films have received considerable attention because of their potential applications in opto-electronics applications. Spontaneous reaction of lead acetate and thiourea in aqueous hydrazine hydrate has been used for depositing PbS thin films on glass substrates. Structural and optical properties of PbS thin films are greatly influenced by the morality of the reactants and crystal defects in the lattice. Our work focuses on the variation in lead ion concentration and its effect on the structural and optical properties of PbS thin films. The deposited films were analyzed using XRD, SEM, spectrophotometer and dark resistance measurement. XRD patterns indicated the formation of major phase of nano crystalline PbS with minor presence of lead oxide phase. We also noticed that peak intensity ratio of I111/I200 varied by changing the Pb ion concentration. The film thickness and dark resistance increased whereas optical band gap decreased with the decreasing Pb ion concentration. SEM scans showed that the grain size is less than 100 nm and is not affected by varying Pb ion concentration.

Perspective: Advanced particle imaging

DOE PAGES

Chandler, David W.; Houston, Paul L.; Parker, David H.

2017-05-26

This study discuss, the first ion imaging experiment demonstrating the capability of collecting an image of the photofragments from a unimolecular dissociation event and analyzing that image to obtain the three-dimensional velocity distribution of the fragments, the efficacy and breadth of application of the ion imaging technique have continued to improve and grow. With the addition of velocity mapping, ion/electron centroiding, and slice imaging techniques, the versatility and velocity resolution have been unmatched. Recent improvements in molecular beam, laser, sensor, and computer technology are allowing even more advanced particle imaging experiments, and eventually we can expect multi-mass imaging with co-variancemore » and full coincidence capability on a single shot basis with repetition rates in the kilohertz range. This progress should further enable “complete” experiments—the holy grail of molecular dynamics—where all quantum numbers of reactants and products of a bimolecular scattering event are fully determined and even under our control.« less

The influence of EI-21 redox ion-exchange resins on the secondary-coolant circuit water chemistry of vehicular nuclear power installations

NASA Astrophysics Data System (ADS)

Moskvin, L. N.; Rakov, V. T.

2015-06-01

The results obtained from testing the secondary-coolant circuit water chemistry of full-scale land-based prototype bench models of vehicular nuclear power installations equipped with water-cooled water-moderated and liquid-metal reactor plants are presented. The influence of copper-containing redox ionexchange resins intended for chemically deoxygenating steam condensate on the working fluid circulation loop's water chemistry is determined. The influence of redox ion-exchange resins on the water chemistry is evaluated by generalizing an array of data obtained in the course of extended monitoring using the methods relating to physicochemical analysis of the quality of condensate-feedwater path media and the methods relating to metallographic analysis of the state of a faulty steam generator's tube system surfaces. The deoxygenating effectiveness of the normal state turbine condensate vacuum deaeration system is experimentally determined. The refusal from applying redox ion-exchange resins in the condensate polishing ion-exchange filters is formulated based on the obtained data on the adverse effect of copper-containing redox ionexchange resins on the condensate-feedwater path water chemistry and based on the data testifying a sufficient effect from using the normal state turbine condensate vacuum deaeration system. Data on long-term operation of the prototype bench model of a vehicular nuclear power installation without subjecting the turbine condensate to chemical deoxygenation are presented.

Hydrogen ion input to the Hubbard Brook Experimental Forest, New Hampshire, during the last decade

Treesearch

Gene E. Likens; F. Herbert Bormann; John S. Eaton; Robert S. Pierce; Noye M. Johnson

1976-01-01

Being downwind of eastern and midwestern industrial centers, the Hubbard Brook Experimental Forest offers a prime location to monitor long-term trends in atmospheric chemistry. Continuous measurements of precipitation chemistry during the last 10 years provide a measure of recent changes in precipitation inputs of hydrogen ion. The weighted average pH of precipitation...

David Robichaud | NREL

Science.gov Websites

Upgrading," Green Chemistry (2018) "Group Additivity Determination for Oxygenates, Oxonium Ions ," Green Chemistry (2015) "Biomass Particle Models with Realistic Morphology and Resolved

Specification For ST-5 Li Ion Battery

NASA Technical Reports Server (NTRS)

Castell, Karen D.; Day, John H. (Technical Monitor)

2000-01-01

This Specification defines the general requirements for rechargeable Space Flight batteries intended for use in the ST-5 program. The battery chemistry chosen for this mission is lithium ion (Li-Ion).

An investigation of the solar zenith angle variation of D-region ionization

NASA Technical Reports Server (NTRS)

Ratnasiri, P. A. J.; Sechrist, C. F., Jr.

1975-01-01

Model calculations are carried out with a view to interpreting the solar zenith angle variation of D-region ionization. A model is developed for the neutral chemistry including the transport terms relating to molecular and eddy diffusion. The diurnal behavior is described of the minor neutral constituents formed in an oxygen-hydrogen-nitrogen atmosphere, in the height interval between 30 and 120 km. Computations carried out for two cases of the eddy diffusion coefficients models indicate that the constituents which are important for the D-region positive-ion chemistry do not show a significant variation with zenith angle for values up to 75 deg over the D-region heights. In the ion chemistry model, ion-pair production rates are calculated for solar X-rays between 1 A and 100 A, EUV radiations from 100 A up to the Lyman-alpha line, precipitating electrons, and galactic cosmic rays. The solar zenith angle variation of the positive-ion composition, negative-ion composition, and the electron densities are described up to 75 deg zenith angle, in the height interval between 60 and 100 km.

Fabrication of Thin Electrolytes for Second-Generation Solid Oxide Fuel Cells

DTIC Science & Technology

1999-05-05

stabilized zirconia but are equally applicable to components, have been developed. Halogen com- other oxide electrolytes. pounds such as ZrCl4 and YC13...substrates. They used ZrCl4 and an oxygen source reactant. EVD is a two-step YC13 vapor mixtures as the metal compound sources process. The first step...thin zirconia layers on ited film. In this step oxygen ions formed on the porous alumina substrates. ZrCl4 and YC13 vapor water vapor side of the

Art in Chemistry: Chemistry in Art. Second Edition

ERIC Educational Resources Information Center

Greenberg, Barbara R.; Patterson, Dianne

2008-01-01

This textbook integrates chemistry and art with hands-on activities and fascinating demonstrations that enable students to see and understand how the science of chemistry is involved in the creation of art. It investigates such topics as color integrated with electromagnetic radiation, atoms, and ions; paints integrated with classes of matter,…

Effect of Material Ion Exchanges on the Mechanical Stiffness Properties and Shear Deformation of Hydrated Cement Material Chemistry Structure C-S-H Jennite -- A Computational Modeling Study

NASA Astrophysics Data System (ADS)

Adebiyi, Babatunde Mattew

Material properties and performance are governed by material molecular chemistry structures and molecular level interactions. Methods to understand relationships between the material properties and performance and their correlation to the molecular level chemistry and morphology, and thus find ways of manipulating and adjusting matters at the atomistic level in order to improve material performance, are required. A computational material modeling methodology is investigated and demonstrated for a key cement hydrated component material chemistry structure of Calcium-Silicate-Hydrate (C-S-H) Jennite in this work. The effect of material ion exchanges on the mechanical stiffness properties and shear deformation behavior of hydrated cement material chemistry structure of Calcium Silicate Hydrate (C-S-H) Jennite was studied. Calcium ions were replaced with Magnesium ions in Jennite structure of the C-S-H gel. Different level of substitution of the ions was used. The traditional Jennite structure was obtained from the American Mineralogist Crystal Structure Database and super cells of the structures were created using a Molecular Dynamics Analyzer and Visualizer Material Studio. Molecular dynamics parameters used in the modeling analysis were determined by carrying out initial dynamic studies. 64 unit cell of C-S-H Jennite was used in material modeling analysis studies based on convergence results obtained from the elastic modulus and total energies. NVT forcite dynamics using COMPASS force field based on 200 ps dynamics time was used to determine mechanical modulus of the traditional C-S-H gel and the Magnesium ion modified structures. NVT Discover dynamics using COMPASS forcefield was used in the material modeling studies to investigate the influence of ionic exchange on the shear deformation of the associated material chemistry structures. A prior established quasi-static deformation method to emulate shear deformation of C-S-H material chemistry structure that is based on a triclinic crystal structure was used, by deforming the triclinic crystal structure at 0.2 degree per time step for 75 steps of deformation. It was observed that there is a decrease in the total energies of the systems as the percentage of magnesium ion increases in the C-S-H Jennite molecular structure systems. Investigation of effect of ion exchange on the elastic modulus shows that the elastic stiffness modulus tends to decrease as the amount of Mg in the systems increases, using either COMPASS or universal force field. On the other hand, shear moduli obtained after deforming the structures computed from the stress-strain curve obtained from material modeling increases as the amount of Mg increases in the system. The present investigations also showed that ultimate shear stress obtained from predicted shear stress---strain also increases with amount of Mg in the chemistry structure. Present study clearly demonstrates that computational material modeling following molecular dynamics analysis methodology is an effective way to predict and understand the effective material chemistry and additive changes on the stiffness and deformation characteristics in cementitious materials, and the results suggest that this method can be extended to other materials.

The activation strain model and molecular orbital theory

PubMed Central

Wolters, Lando P; Bickelhaupt, F Matthias

2015-01-01

The activation strain model is a powerful tool for understanding reactivity, or inertness, of molecular species. This is done by relating the relative energy of a molecular complex along the reaction energy profile to the structural rigidity of the reactants and the strength of their mutual interactions: ΔE(ζ) = ΔEstrain(ζ) + ΔEint(ζ). We provide a detailed discussion of the model, and elaborate on its strong connection with molecular orbital theory. Using these approaches, a causal relationship is revealed between the properties of the reactants and their reactivity, e.g., reaction barriers and plausible reaction mechanisms. This methodology may reveal intriguing parallels between completely different types of chemical transformations. Thus, the activation strain model constitutes a unifying framework that furthers the development of cross-disciplinary concepts throughout various fields of chemistry. We illustrate the activation strain model in action with selected examples from literature. These examples demonstrate how the methodology is applied to different research questions, how results are interpreted, and how insights into one chemical phenomenon can lead to an improved understanding of another, seemingly completely different chemical process. WIREs Comput Mol Sci 2015, 5:324–343. doi: 10.1002/wcms.1221 PMID:26753009

Laser Spectroscopy of Ruthenium Containing Diatomic Molecules: RuH/D and RuP.

NASA Astrophysics Data System (ADS)

Adam, Allan G.; Konder, Ricarda M.; Nickerson, Nicole M.; Linton, Colan; Tokaryk, D. W.

2015-06-01

In the last few years, the Cheung group in Hong Kong and the Steimle group in Arizona have successfully studied several ruthenium containing diatomic molecules, RuX (X =C, O, N, B, using the laser-ablation molecular jet technique. Based on this success, the UNB spectroscopy group decided to try and find the optical signatures of other RuX molecules. Using CH_3OH and PH_3 as reactant gases, the RuH and RuP diatomic molecules have been detected in surveys of the 420 - 675 nm spectral region. RuD has also been made using fully deuterated methanol as a reactant. Dispersed fluorescence experiments have been performed to determine ground state vibrational frequencies and the presence of any low-lying electronic states. Rotationally resolved spectra for these molecules have also been taken and the analysis is proceeding. The most recent results will be presented. F. Wang et al., Journal of Chemical Physics 139, 174318 (2013). N. Wang et al., Journal of Physical Chemistry A 117, 13279 (2013). T. Steimle et al., Journal of Chemical Physics 119, 12965 (2003). N. Wang et al., Chemical Physics Letters 547, 21 (2012).

Demonstration of Experimental Infrastructure for Studying Cell-to-Cell Failure Propagation in Lithium-Ion Batteries

DTIC Science & Technology

2014-09-11

LiCoO2 and LiFePO4 chemistry 18650 lithium-ion batteries were constructed and data was obtained and analyzed for abuse and failure tests. Observations...22308 Lithium-ion batteries Failure Heat propagation 18650 cells LiCoO2 LiFePO4 ii iii Contents 1.0 Background...Corp., Taipei, Taiwan) or LiFePO4 cathode chemistry (APR18650 1100mAh 3.3V, A123 Systems, Waltham, Massachusetts, USA). First, a single LiCoO2

Recent Selected Ion Flow Tube (SIFT) Studies Concerning the Formation of Amino Acids in the Gas Phase

NASA Technical Reports Server (NTRS)

Jackson, Douglas M.; Adams, Nigel G.; Babcock, Lucia M.

2006-01-01

Recently the simplest amino acid, glycine, has been detected in interstellar clouds, ISC, although this has since been contested. In order to substantiate either of these claims, plausible routes to amino acids need to be investigated. For gas phase synthesis, the SIFT technique has been employed to study simple amino acids via ion-molecule reactions of several ions of interstellar interest with methylamine, ethylamine, formic acid, acetic acid, and methyl formate. Carboxylic acid type ions were considered in the reactions involving the amines. In reactions where the carboxylic acid and methyl formate neutrals were studied, the reactant ions were primarily amine ion fragments. It was observed that the amines and acids preferentially fragment or accept a proton whenever energetically possible. NH3(+), however, uniquely reacted with the neutrals via atom abstraction to form NH4(+). These studies yielded a body of data relevant to astrochemistry, supplementing the available literature. However, the search for gas phase routes to amino acids using conventional molecules has been frustrated. Our most recent research investigates the fragmentation patterns of several amino acids and several possible routes have been suggested for future study.

Computational modeling of chemical reactions and interstitial growth and remodeling involving charged solutes and solid-bound molecules

PubMed Central

Nims, Robert J.; Maas, Steve; Weiss, Jeffrey A.

2014-01-01

Mechanobiological processes are rooted in mechanics and chemistry, and such processes may be modeled in a framework that couples their governing equations starting from fundamental principles. In many biological applications, the reactants and products of chemical reactions may be electrically charged, and these charge effects may produce driving forces and constraints that significantly influence outcomes. In this study, a novel formulation and computational implementation are presented for modeling chemical reactions in biological tissues that involve charged solutes and solid-bound molecules within a deformable porous hydrated solid matrix, coupling mechanics with chemistry while accounting for electric charges. The deposition or removal of solid-bound molecules contributes to the growth and remodeling of the solid matrix; in particular, volumetric growth may be driven by Donnan osmotic swelling, resulting from charged molecular species fixed to the solid matrix. This formulation incorporates the state of strain as a state variable in the production rate of chemical reactions, explicitly tying chemistry with mechanics for the purpose of modeling mechanobiology. To achieve these objectives, this treatment identifies the specific theoretical and computational challenges faced in modeling complex systems of interacting neutral and charged constituents while accommodating any number of simultaneous reactions where reactants and products may be modeled explicitly or implicitly. Several finite element verification problems are shown to agree with closed-form analytical solutions. An illustrative tissue engineering analysis demonstrates tissue growth and swelling resulting from the deposition of chondroitin sulfate, a charged solid-bound molecular species. This implementation is released in the open-source program FEBio (www.febio.org). The availability of this framework may be particularly beneficial to optimizing tissue engineering culture systems by examining the influence of nutrient availability on the evolution of inhomogeneous tissue composition and mechanical properties, the evolution of construct dimensions with growth, the influence of solute and solid matrix electric charge on the transport of cytokines, the influence of binding kinetics on transport, the influence of loading on binding kinetics, and the differential growth response to dynamically loaded versus free-swelling culture conditions. PMID:24558059

Computational modeling of chemical reactions and interstitial growth and remodeling involving charged solutes and solid-bound molecules.

PubMed

Ateshian, Gerard A; Nims, Robert J; Maas, Steve; Weiss, Jeffrey A

2014-10-01

Mechanobiological processes are rooted in mechanics and chemistry, and such processes may be modeled in a framework that couples their governing equations starting from fundamental principles. In many biological applications, the reactants and products of chemical reactions may be electrically charged, and these charge effects may produce driving forces and constraints that significantly influence outcomes. In this study, a novel formulation and computational implementation are presented for modeling chemical reactions in biological tissues that involve charged solutes and solid-bound molecules within a deformable porous hydrated solid matrix, coupling mechanics with chemistry while accounting for electric charges. The deposition or removal of solid-bound molecules contributes to the growth and remodeling of the solid matrix; in particular, volumetric growth may be driven by Donnan osmotic swelling, resulting from charged molecular species fixed to the solid matrix. This formulation incorporates the state of strain as a state variable in the production rate of chemical reactions, explicitly tying chemistry with mechanics for the purpose of modeling mechanobiology. To achieve these objectives, this treatment identifies the specific theoretical and computational challenges faced in modeling complex systems of interacting neutral and charged constituents while accommodating any number of simultaneous reactions where reactants and products may be modeled explicitly or implicitly. Several finite element verification problems are shown to agree with closed-form analytical solutions. An illustrative tissue engineering analysis demonstrates tissue growth and swelling resulting from the deposition of chondroitin sulfate, a charged solid-bound molecular species. This implementation is released in the open-source program FEBio ( www.febio.org ). The availability of this framework may be particularly beneficial to optimizing tissue engineering culture systems by examining the influence of nutrient availability on the evolution of inhomogeneous tissue composition and mechanical properties, the evolution of construct dimensions with growth, the influence of solute and solid matrix electric charge on the transport of cytokines, the influence of binding kinetics on transport, the influence of loading on binding kinetics, and the differential growth response to dynamically loaded versus free-swelling culture conditions.

Analytical Chemistry of Surfaces: Part III. Ion Spectroscopy.

ERIC Educational Resources Information Center

Hercules, David M.; Hercules, Shirley H.

1984-01-01

The fundamentals of two surface techniques--secondary-ion mass spectrometry (SIMS) and ion-scattering spectrometry (ISS)--are discussed. Examples of how these techniques have been applied to surface problems are provided. (JN)

Application of Ni-63 photo and corona discharge ionization for the analysis of chemical warfare agents and toxic wastes

NASA Technical Reports Server (NTRS)

Stach, J.; Adler, J.; Brodacki, M.; Doring, H.-R.

1995-01-01

Over the past decade, advances in instrumental design and refinements in the understanding of ion molecule reactions at atmospheric pressure enabled the application of Ion Mobility Spectrometry (IMS) as a simple inexpensive and sensitive analytical method for the detection of organic trace compounds. Positive and negative gas-phase ions for ion mobility spectrometry have been produced by a variety of methods, including photo-ionization, laser multi photon ionization, surface ionization, corona discharge ionization. The most common ion source used in ion mobility spectrometry is a radioactive Ni-63 foil which is favored due to simplicity, stability, convenience, and high selectivity. If reactant ions like (H2O(n)H)(+) or (H2O(n)O2)(-) dominate in the reaction region, nearly all kinds of compounds with a given proton or electron affinity; are ionized. However, the radioactivity of the Ni-63 foil is one disadvantage of this ion source that stimulates the development and application of other ionization techniques. In this paper, we report analyses of old chemical warfare agents and toxic wastes using Bruker RAID ion mobility spectrometers. Due to the modular construction of the measuring cell, the spectrometers can be equipped with different ion sources. The combined use of Ni-63, photo- and corona discharge ionization allows the identification of different classes of chemical compounds and yields in most cases comparable results.

New laboratory approach to study Titan ionospheric chemistry

NASA Astrophysics Data System (ADS)

Thissen, R.; Dutuit, O.; Pernot, P.; Carrasco, N.; Lilensten, J.; Quirico, E.; Schmitt, B.

The exploration of Titan reveals a very complex chemistry occurring in the ionospheric region of the atmosphere. In order to interpret the observations performed by the Cassini spectrometers, we need to improve our description of the ion molecule chemistry involving nitrogen and hydrocarbons. Up to now, models are based on databases compiled over the years. These are quite complete to describe the major ions, but lack of accuracy for some of them, they totally neglect the questions of isomerization or chemical functionality in the description of ionic species and still miss a lot of inputs for ionic species heavier than 50 daltons. We propose to improve the databases by systematic measurements of ion molecule reaction rates, and further structural description, by means of a high resolution mass spectrometer, allowing for MS/MS structural analysis of the ionic species. A thorough evaluation of nowadays databases by means of uncertainty propagation will lead our choice of the most important reactions to be studied. This study shall also lead to educated choice for chemistry simplification, which is mandatory in order to include the chemistry in 3D or fluid models of the atmosphere. We plan as well to use extracts from tholins as molecular source for our analysis.

A study of the dissociative recombination of CaO+ with electrons: Implications for Ca chemistry in the upper atmosphere.

PubMed

Bones, D L; Gerding, M; Höffner, J; Martín, Juan Carlos Gómez; Plane, J M C

2016-12-28

The dissociative recombination of CaO + ions with electrons has been studied in a flowing afterglow reactor. CaO + was generated by the pulsed laser ablation of a Ca target, followed by entrainment in an Ar + ion/electron plasma. A kinetic model describing the gas-phase chemistry and diffusion to the reactor walls was fitted to the experimental data, yielding a rate coefficient of (3.0 ± 1.0) × 10 -7  cm 3  molecule -1  s -1 at 295 K. This result has two atmospheric implications. First, the surprising observation that the Ca + /Fe + ratio is ~8 times larger than Ca/Fe between 90 and 100 km in the atmosphere can now be explained quantitatively by the known ion-molecule chemistry of these two metals. Second, the rate of neutralization of Ca + ions in a descending sporadic E layer is fast enough to explain the often explosive growth of sporadic neutral Ca layers.

Sunlight-initiated chemistry of aqueous pyruvic acid: building complexity in the origin of life.

PubMed

Griffith, Elizabeth C; Shoemaker, Richard K; Vaida, Veronica

2013-10-01

Coupling chemical reactions to an energy source is a necessary step in the origin of life. Here, we utilize UV photons provided by a simulated sun to activate aqueous pyruvic acid and subsequently prompt chemical reactions mimicking some of the functions of modern metabolism. Pyruvic acid is interesting in a prebiotic context due to its prevalence in modern metabolism and its abiotic availability on early Earth. Here, pyruvic acid (CH3COCOOH, a C3 molecule) photochemically reacts to produce more complex molecules containing four or more carbon atoms. Acetoin (CH3CHOHCOCH3), a C4 molecule and a modern bacterial metabolite, is produced in this chemistry as well as lactic acid (CH3CHOHCOOH), a molecule which, when coupled with other abiotic chemical reaction pathways, can provide a regeneration pathway for pyruvic acid. This chemistry is discussed in the context of plausible environments on early Earth such as near the ocean surface and atmospheric aerosol particles. These environments allow for combination and exchange of reactants and products of other reaction environments (such as shallow hydrothermal vents). The result could be a contribution to the steady increase in chemical complexity requisite in the origin of life.

Computational Investigations for Undergraduate Organic Chemistry: Predicting the Mechanism of the Ritter Reaction

NASA Astrophysics Data System (ADS)

Hessley, Rita K.

2000-02-01

In an effort to engage students more deeply in their laboratory work and provide them with valuable learning experiences in the applications and limitations of computational chemistry as a research tool, students are instructed to carry out a computational pre-lab exercise. Before carrying out a laboratory experiment that investigates the mechanism for the formation of N-t-butylbenzamide, students construct and obtain heats of formation for reactants, products, postulated reaction intermediates, and one transition state structure for each proposed mechanism. This is designed as a companion to an open-ended laboratory experiment that hones skills learned early in most traditional organic chemistry courses. The incorporation of a preliminary computational exercise enables students to move beyond guessing what the outcome of the reaction will be. It challenges them to test what they believe they "know" about such fundamental concepts as stability of carbocations, or the significance and utility of thermodynamic data relative to kinetic data. On the basis of their computations and their own experimental data, students then verify or dispute their hypothesis, finally arriving at a defensible and logical conclusion about the course of the reaction mechanism. The manner of implementation of the exercise and typical computational data are described.

Ion Chemistry in Atmospheric and Astrophysical Plasmas

NASA Technical Reports Server (NTRS)

Dalgarno, A.; Fox, J. L.

1994-01-01

There are many differences and also remarkable similarities between the ion chemistry and physics of planetary ionospheres and the ion chemistry and physics of astronomical environments beyond the solar system. In the early Universe, an expanded cooling gas of hydrogen and helium was embedded in the cosmic background radiation field and ionized by it. As the Universe cooled by adiabatic expansion, recombination occurred and molecular formation was driven by catalytic reactions involving the relict electrons and protons. Similar chemical processes are effective in the ionized zones of gaseous and planetary nebulae and in stellar winds where the ionization is due to radiation from the central stars, in the envelopes of supernovae where the ionization is initiated by the deposition of gamma-rays, in dissociative shocks where the ionization arises from electron impacts in a hot gas and in quasar broad-line region clouds where the quasar is responsible for the ionization. At high altitudes in the atmospheres of the Jovian planets, the main constituents are hydrogen and helium and the ion chemistry and physics is determined by the same processes, the source of the ionization being solar ultraviolet radiation and cosmic rays. After the collapse of the first distinct astronomical entities to emerge from the uniform flow, heavy elements were created by nuclear burning in the cores of the collapsed objects and distributed throughout the Universe by winds and explosions. The chemistry and physics became more complicated. Over 90 distinct molecular species have been identified in interstellar clouds where they are ionized globally by cosmic ray impacts and locally by radiation and shocks associated with star formation and evolution. Complex molecules have also been found in circumstellar shells of evolved stars. At intermediate and low altitudes in the Jovian atmospheres, the ion chemistry is complicated by the increasing abundance of heavy elements such as carbon, and an extensive array of complex molecules has been predicted. Reactions involving heavy elements dominate the structure of the ionspheres of the terrestrial planets and the satellites Titan and Triton.

Organic Chemistry of Meteorites

NASA Technical Reports Server (NTRS)

Chang, S.; Morrison, David (Technical Monitor)

1994-01-01

Studies of the molecular structures and C,N,H-isotopic compositions of organic matter in meteorites reveal a complex history beginning in the parent interstellar cloud which spawned the solar system. Incorporation of interstellar dust and gas in the protosolar nebula followed by further thermal and aqueous processing on primordial parent bodies of carbonaceous, meteorites have produced an inventory of diverse organic compounds including classes now utilized in biochemistry. This inventory represents one possible set of reactants for chemical models for the origin of living systems on the early Earth. Evidence bearing on the history of meteoritic organic matter from astronomical observations and laboratory investigations will be reviewed and future research directions discussed.

Selective free radical reactions using supercritical carbon dioxide.

PubMed

Cormier, Philip J; Clarke, Ryan M; McFadden, Ryan M L; Ghandi, Khashayar

2014-02-12

We report herein a means to modify the reactivity of alkenes, and particularly to modify their selectivity toward reactions with nonpolar reactants (e.g., nonpolar free radicals) in supercritical carbon dioxide near the critical point. Rate constants for free radical addition of the light hydrogen isotope muonium to ethylene, vinylidene fluoride, and vinylidene chloride in supercritical carbon dioxide are compared over a range of pressures and temperatures. Near carbon dioxide's critical point, the addition to ethylene exhibits critical speeding up, while the halogenated analogues display critical slowing. This suggests that supercritical carbon dioxide as a solvent may be used to tune alkene chemistry in near-critical conditions.

MinION Analysis and Reference Consortium: Phase 2 data release and analysis of R9.0 chemistry.

PubMed

Jain, Miten; Tyson, John R; Loose, Matthew; Ip, Camilla L C; Eccles, David A; O'Grady, Justin; Malla, Sunir; Leggett, Richard M; Wallerman, Ola; Jansen, Hans J; Zalunin, Vadim; Birney, Ewan; Brown, Bonnie L; Snutch, Terrance P; Olsen, Hugh E

2017-01-01

Long-read sequencing is rapidly evolving and reshaping the suite of opportunities for genomic analysis. For the MinION in particular, as both the platform and chemistry develop, the user community requires reference data to set performance expectations and maximally exploit third-generation sequencing. We performed an analysis of MinION data derived from whole genome sequencing of Escherichia coli K-12 using the R9.0 chemistry, comparing the results with the older R7.3 chemistry. We computed the error-rate estimates for insertions, deletions, and mismatches in MinION reads. Run-time characteristics of the flow cell and run scripts for R9.0 were similar to those observed for R7.3 chemistry, but with an 8-fold increase in bases per second (from 30 bps in R7.3 and SQK-MAP005 library preparation, to 250 bps in R9.0) processed by individual nanopores, and less drop-off in yield over time. The 2-dimensional ("2D") N50 read length was unchanged from the prior chemistry. Using the proportion of alignable reads as a measure of base-call accuracy, 99.9% of "pass" template reads from 1-dimensional ("1D")  experiments were mappable and ~97% from 2D experiments. The median identity of reads was ~89% for 1D and ~94% for 2D experiments. The total error rate (miscall + insertion + deletion ) decreased for 2D "pass" reads from 9.1% in R7.3 to 7.5% in R9.0 and for template "pass" reads from 26.7% in R7.3 to 14.5% in R9.0. These Phase 2 MinION experiments serve as a baseline by providing estimates for read quality, throughput, and mappability. The datasets further enable the development of bioinformatic tools tailored to the new R9.0 chemistry and the design of novel biological applications for this technology. K: thousand, Kb: kilobase (one thousand base pairs), M: million, Mb: megabase (one million base pairs), Gb: gigabase (one billion base pairs).

Interpretive Experiments: An Interpretive Experiment in Ion Cyclotron Resonance Spectroscopy.

ERIC Educational Resources Information Center

Burnier, R. C.; Freiser, B. S.

1979-01-01

Provides a discussion which is intended for chemistry college students on the ion cyclotron resonance (ICR) spectroscopy, the physical basis for ion cyclotron resonance, and the experimental methodology employed by ICR spectroscopists. (HM)

Some aspects of stratospheric chemical response to solar particle precipitations. I - Potential roles of N2/A3Sigma/ and ion-chemistry

NASA Technical Reports Server (NTRS)

Prasad, S. S.

1979-01-01

Large amounts of long lived N2(A3Sigma) are created by the energy degradation of precipitating solar particles. Laboratory data suggest that in the stratosphere N2(A3Sigma) are efficiently converted into N2O. Through reactions with O(1D), N2O may gradually release NO and thereby influence the long term aspects of stratospheric chemical response. During the daytime, negative ions may transform an active NO(x) into an inactive HNO3. At night both negative and positive ion chemistry generate HO(x). Omission of ionic chemistry results in considerable underestimation of O3 depletion during the initial phases of solar particle events, and thereby introduces significant error in the estimation of the nature of the prompt response.

Anion Solvation in Carbonate-Based Electrolytes

DOE PAGES

von Wald Cresce, Arthur; Gobet, Mallory; Borodin, Oleg; ...

2015-11-16

The correlation between Li + solvation and interphasial chemistry on anodes firmly established in Li-ion batteries, the effect of cation–solvent interaction has gone beyond bulk thermodynamic and transport properties and become an essential element that determines the reversibility of electrochemistry and kinetics of Li-ion intercalation chemistries. Now, most studies are dedicated to the solvation of Li +, and the solvation of anions in carbonate-based electrolytes and its possible effect on the electrochemical stability of such electrolytes remains little understood. Moreover, as a mirror effort to prior Li + solvation studies, this work focuses on the interactions between carbonate-based solvents andmore » two anions (hexafluorophosphate, PF 6–, and tetrafluoroborate, BF 4–) that are most frequently used in Li-ion batteries. The possible correlation between such interaction and the interphasial chemistry on cathode surface is also explored.« less

Correlation between surface chemistry and ion energy dependence of the etch yield in multicomponent oxides etching

NASA Astrophysics Data System (ADS)

Bérubé, P.-M.; Poirier, J.-S.; Margot, J.; Stafford, L.; Ndione, P. F.; Chaker, M.; Morandotti, R.

2009-09-01

The influence of surface chemistry in plasma etching of multicomponent oxides was investigated through measurements of the ion energy dependence of the etch yield. Using pulsed-laser-deposited CaxBa(1-x)Nb2O6 (CBN) and SrTiO3 thin films as examples, it was found that the etching energy threshold shifts toward values larger or smaller than the sputtering threshold depending on whether or not ion-assisted chemical etching is the dominant etching pathway and whether surface chemistry is enhancing or inhibiting desorption of the film atoms. In the case of CBN films etched in an inductively coupled Cl2 plasma, it is found that the chlorine uptake is inhibiting the etching reaction, with the desorption of nonvolatile NbCl2 and BaCl2 compounds being the rate-limiting step.

The reactions of SO3 with HO2 radical and H2O...HO2 radical complex. Theoretical study on the atmospheric formation of HSO5 and H2SO4.

PubMed

Gonzalez, Javier; Torrent-Sucarrat, Miquel; Anglada, Josep M

2010-03-07

The influence of a single water molecule on the gas-phase reactivity of the HO(2) radical has been investigated by studying the reactions of SO(3) with the HO(2) radical and with the H(2)O...HO(2) radical complex. The naked reaction leads to the formation of the HSO(5) radical, with a computed binding energy of 13.81 kcal mol(-1). The reaction with the H(2)O...HO(2) radical complex can give two different products, namely (a) HSO(5) + H(2)O, which has a binding energy that is computed to be 4.76 kcal mol(-1) more stable than the SO(3) + H(2)O...HO(2) reactants (Delta(E + ZPE) at 0K) and an estimated branching ratio of about 34% at 298K and (b) sulfuric acid and the hydroperoxyl radical, which is computed to be 10.51 kcal mol(-1) below the energy of the reactants (Delta(E + ZPE) at 0K), with an estimated branching ratio of about 66% at 298K. The fact that one of the products is H(2)SO(4) may have relevance in the chemistry of the atmosphere. Interestingly, the water molecule acts as a catalyst, [as it occurs in (a)] or as a reactant [as it occurs in (b)]. For a sake of completeness we have also calculated the anharmonic vibrational frequencies for HO(2), HSO(5), the HSO(5)...H(2)O hydrogen bonded complex, H(2)SO(4), and two H(2)SO(4)...H(2)O complexes, in order to help with the possible experimental identification of some of these species.

A rapid, convenient, solventless green approach for the synthesis of oximes using grindstone chemistry.

PubMed

Saikia, Lakhinath; Baruah, Jejiron Maheswari; Thakur, Ashim Jyoti

2011-10-04

Synthesis of oximes is an important reaction in organic chemistry, because these versatile oximes are used for protection, purification, and characterization of carbonyl compounds. Nitriles, amides via Beckmann rearrangement, nitro compounds, nitrones, amines, and azaheterocycles can be synthesised from oximes. They also find applications for selective α-activation. In inorganic chemistry, oximes act as a versatile ligand.Several procedures for the preparation of oximes exist, but, most of them have not addressed the green chemistry issue. They are associated with generation of pollutants, requirement of high reaction temperature, low yields, lack of a generalized procedure, etc. Hence, there is a demand for developing an efficient, convenient, and non-polluting or less polluting alternative method for the preparation of oximes. In this context, bismuth compounds are very useful as they are cheap in general, commercially available, air stable crystalline solids, safe, and non-toxic, hence easy to handle. Carbonyl compounds (aliphatic, heterocyclic, and aromatic) were converted into the corresponding oximes in excellent yields by simply grinding the reactants at room temperature without using any solvent in the presence of Bi2O3. Most importantly, this method minimizes waste disposal problems, provides a simple yet efficient example of unconventional methodology and requires short time. We have developed a novel, quick, environmentally safe, and clean synthesis of aldoximes and ketoximes under solvent-free grinding condition.

Teaching Ion-Ion, Ion-Dipole, and Dipole-Dipole Interactions

ERIC Educational Resources Information Center

Yoder, Claude H.

1977-01-01

Discusses how electrostatic interactions can be taught quantitatively through Coulomb's Law at a variety of points in a chemistry curriculum. Each type of interaction is shown at both the intramolecular and the inter-"molecular" levels. (MR)

Relationships between nitric oxide, nitroxyl ion, nitrosonium cation and peroxynitrite.

PubMed

Hughes, M N

1999-05-05

This review is concerned mainly with the three redox-related, but chemically distinct, species NO-, NO. and NO+, with greatest emphasis being placed on the chemistry and biology of the nitroxyl ion. Biochemical routes for the formation of nitroxyl ion and methods for showing the intermediacy of this species are discussed, together with chemical methods for generating nitroxyl ion in solution. Reactions of nitroxyl ion with NO., thiols, iron centres in haem and with dioxygen are reviewed The significance of the reaction between NO- and dioxygen as a source of peroxynitrite is assessed, and attention drawn to the possible significance of the spin state of the nitroxyl ion in this context. The biological significance of nitrosation and the importance of S-nitrosothiols and certain metal nitrosyl complexes as carriers of NO+ at physiological pH is stressed. Some features in the chemistry of peroxynitrite are noted.

Plastic Organic Scintillator Chemistry

NASA Astrophysics Data System (ADS)

Brightwell, C. R.; Temanson, E. S.; Febbraro, M. T.

2017-09-01

Due to their high light output, quick decay time, affordability, durability and ability to be molded, plastic organic scintillators are increasingly becoming a more viable method of particle detection. Since the plastic is composed entirely of single molecular chains with repeating units, scintillating properties remain stable despite changes in experimental conditions. Different scintillating plastics can be modified and tailored to suit specific experiments depending on a variety of requirements such as light output, scintillating wavelength, and PMT compatibility. The synthesis chemistry of a recent but well-known scintillating polyester, polyethylene naphthalate (PEN) will be presented to demonstrate how plastic organic scintillators can be modified for different particle detection experiments. PEN has been successfully synthesized at ORNL, and procedures are currently being investigated to modify PEN using different reactants and catalysts. The goal is to achieve a transparent scintillating plastic with an incorporated wavelength shifter in the chain that scintillates with a wavelength around 440 nm. The status of this project will be presented. This research is supported by the U. S. Department of Energy Office of Science.

Development of analytical procedures for coprocessing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vogh, J.W.; Anderson, R.P.

1990-05-01

Maya crude residue and Illinois No. 6 coal have been processed together over a range of reactant ratios to produce material for study of the product composition and of the coprocessing chemistry. The reaction conditions have been described in previous reports. Acid fractions have been derivatized to produce {sup 13}C tagged products suitable for NMR analysis. The acids have been identified as phenols and other oxygen acids, nitrogen acids including carbazoles, and benzylic and sulfur acids. All of the acid fractions appear to be essentially monofunctional. Base fractions were analyzed by nonaqueous titration and were shown to consist of azaarenesmore » and arylamines. Two of the distillates boiling below 175{degrees}C were analyzed by PIANO capillary gas chromatography. Maya crude petroleum fractions similar to those obtained from coprocessing products have been analyzed for carbon isotope ratios. These fractions were prepared directly from the Maya crude without application of hydrogenation or other processing chemistry. Trends indicating isotopic fractionation coprocessing to that reported earlier for coprocessing products were observed. 14 figs., 13 tabs.« less

Potential effect of ultrasound on carbohydrates.

PubMed

Bera, Smritilekha; Mondal, Dhananjoy; Martin, Jacob T; Singh, Man

2015-06-17

The use of ultrasound has emerged as one of the most useful alternative energy sources for the synthesis of carbohydrate-derived biologically and pharmaceutically potential compounds. Spectacular advances have been made in the field of sonication-assisted organic reactions, which are known for producing superior yields, enhanced reactivity of the reactant, improved stereoselectivity, and shortened reaction times. Orthogonal protection-deprotection reactions and/or modification and manipulation of functional groups in carbohydrates are common synthetic steps in carbohydrate chemistry. These reaction steps can be driven by the ultrasonic energy generated by acoustic cavitation via the formation and subsequent collapse of ultrasound-induced bubbles. The ultrasound-assisted synthesis of differently functionalised monosaccharides is useful in a wide variety of applications of carbohydrate chemistry such as the glycosylation of oligosaccharides, one pot domino reactions, thioglycoside syntheses, azidoglycoside syntheses, 1,3-dipolar cycloaddition reactions, and syntheses of natural products. This review article covers ultrasound-mediated reactions on carbohydrates that have been described in the literature since 2000. Copyright © 2015 Elsevier Ltd. All rights reserved.

Production of neutral species in Titan's ionosphere through dissociative recombination of ions

NASA Astrophysics Data System (ADS)

Plessis, Sylvain; Carrasco, Nathalie; Dobrijevic, Michel; Pernot, Pascal

2012-05-01

The production rates of neutral species by dissociative recombination (DR) of molecular ions with electrons in the ionosphere of Titan are quantified by a new model, including, for the first time, all the available kinetic data on this process. The calculation is based on the ion densities measured by the INMS instrument on Cassini orbiter during flyby T19 at 1100 km altitude. These production rates are compared with those predicted by photochemical models: we calculate that for many neutral species, DR has larger production rates than neutral chemistry. Concerning molecular growth in Titan's ionosphere, DR is shown to have two antagonistic effects: (1) a global chemical lysis of ions through C-C and C-N bond breaking (missed by the "H-loss" DR paradigm); and (2) an enhancement of the neutral chemistry by production of reactive radicals, such as C2H or NH2. Further exploration of this chemistry requires the development of ionospheric coupled models taking explicitly into account the richness of the DR process and the strong impact of ions on the budget of neutral species. This study emphasizes also the urgent need of additional experimental studies about DR of molecular ions, with two priorities: evaluation of the impact of the temperature of ions on the rates and fragmentation patterns, and the systematic study of the fragmentation patterns of CxHyNz+ ions with more than four heavy atoms (m/z > 60 u).

Method of preparing electrodes with porous current collector structures and solid reactants for secondary electrochemical cells

DOEpatents

Gay, Eddie C.; Martino, Fredric J.

1976-01-01

Particulate electrode reactants, for instance transition metal sulfides for the positive electrodes and lithium alloys for the negative electrodes, are vibratorily compacted into porous, electrically conductive structures. Structures of high porosity support sufficient reactant material to provide high cell capacity per unit weight while serving as an electrical current collector to improve the utilization of reactant materials. Pore sizes of the structure and particle sizes of the reactant material are selected to permit uniform vibratory loading of the substrate without settling of the reactant material during cycling.

Thermodynamics and Solubilities of Salts of Dipositive Ions.

ERIC Educational Resources Information Center

Riley, Gary F.; Eberhardt, William H.

1979-01-01

In this general chemistry experiment students calculate changes in free energy of formation of inorganic salts from the free energy of formation of ions. Then they test the conclusions of their calculations by mixing solutions of the ions. (BB)

Fourier Transform Mass Spectrometry.

ERIC Educational Resources Information Center

Gross, Michael L.; Rempel, Don L.

1984-01-01

Discusses the nature of Fourier transform mass spectrometry and its unique combination of high mass resolution, high upper mass limit, and multichannel advantage. Examines its operation, capabilities and limitations, applications (ion storage, ion manipulation, ion chemistry), and future applications and developments. (JN)

Application of Ion Mobility Spectrometry (IMS) in forensic chemistry and toxicology with focus on biological matrices

NASA Technical Reports Server (NTRS)

Bernhard, Werner; Keller, Thomas; Regenscheit, Priska

1995-01-01

The IMS (Ion Mobility Spectroscopy) instrument 'Ionscan' takes advantage of the fact that trace quantities of illicit drugs are adsorbed on dust particles on clothes, in cars and on other items of evidence. The dust particles are collected on a membrane filter by a special attachment on a vacuum cleaner. The sample is then directly inserted into the spectrometer and can be analyzed immediately. We show casework applications of a forensic chemistry and toxicology laboratory. One new application of IMS in forensic chemistry is the detection of psilocybin in dried mushrooms without any further sample preparation.

SO 2 oxidation in an entraining cloud model with explicit microphysics

NASA Astrophysics Data System (ADS)

Bower, K. N.; Hill, T. A.; Coe, H.; Choularton, T. W.

A model of the chemical evolution of the droplets in a hill-cap cloud is presented. The chemistry of individual droplets forming on cloud condensation nuclei of differing size and chemical composition is considered, and the take-up of species from the gas phase by the droplets is treated explicity for the droplet population. Oxidation of S(IV) dissolved in cloud droplets is assumed to be dominated by hydrogen peroxide and ozone. Hydrogen peroxide is normally found to be the dominant oxidant for the oxidation of sulphur dioxide (except in the presence of substantial concentrations of ammonia gas, which increases droplet pH and the contribution made by the oxidant ozone). The entrainment of hydrogen peroxide from above the cloud top increases the amount of sulphate produced in conditions where the reaction is otherwise oxidant limited by the availability hydrogen peroxide. These conditions occur when there are high concentrations of sulphur dioxide accompanied by low cloudwater pH values. Within droplets formed on sodium chloride aerosol, reduced levels of acidity lead to an increase in sulphate production as a result of an enhanced reaction between SO 2 and the oxidant ozone. This results in an overall higher increase in cloudwater sulphate than would be expected assuming an even distribution of all reactants amongst the droplets. In addition, concentrations of the hydrogen sulphite ion predicted to occur in the cloudwater can be substantially in excess of those predicted from the bulk cloudwater pH. This is consistent with recent observations.

A meteor ablation-cluster ion atmospheric sodium theory

NASA Technical Reports Server (NTRS)

Richter, E. S.; Sechrist, C. F., Jr.

1979-01-01

Neutral and ionic forms of sodium form narrow, well-defined layers which peak in the 90-95 km altitude region at midlatitudes. A new theory for the sodium layer is presented, which is found to be in good agreement with existing atmospheric observations as well as available laboratory measurements of rate constants. The layer is believed to result naturally from a meteor ablation source over a chemical sink with vertical transport of Na(+) playing an important role in the layer shape and variation. While the neutral chemistry is believed to consist of chemical equilibrium between Na and NaO, the ion chemistry departs from earlier studies and considers a cluster ion scheme. It is possible that higher-order cluster ions of sodium play a role in the formation of aerosols, through attachment or ion-induced nucleation processes.

Stratospheric ion and aerosol chemistry and possible links with cirrus cloud microphysics - A critical assessment

NASA Technical Reports Server (NTRS)

Mohnen, Volker A.

1990-01-01

Aspects of stratospheric ion chemistry and physics are assessed as they relate to aerosol formation and the transport of aerosols to upper tropospheric regions to create conditions favorable for cirrus cloud formation. It is found that ion-induced nucleation and other known phase transitions involving ions and sulfuric acid vapor are probably not efficient processes for stratospheric aerosol formation, and cannot compete with condensation of sulfuric acid on preexisting particles of volcanic or meteoritic origin which are larger than about 0.15 micron in radius. Thus, galactic cosmic rays cannot have a significant impact on stratospheric aerosol population. Changes in the stratospheric aerosol burden due to volcanos are up to two orders of magnitude larger than changes in ion densities. Thus, volcanic activity may modulate the radiative properties of cirrus clouds.

Novel size-dependent chemistry within ionized van der Waals clusters of 1,1-difluoroethane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coolbaugh, M.T.; Peifer, W.R.; Garvey, J.F.

1990-02-22

The authors present in this paper evidence for size-dependent cluster chemistry occurring in van der Waals clusters of 1,1-difluoroethane. Clusters of C{sub 2}H{sub 4}F{sub 2} are produced from a neat adiabatic expansion and are ionized via electron impact. In addition to the anticipated fragment ions, we observe ions with the general empirical formula of M{sub n}H{sup +} (where n {ge} 4). The reactive process that generates this species cannot be rationalized in terms of intramolecular analogues of known gas-phase bimolecular ion-molecular reactions. Hence, we fell the production of this product cluster ion represents an additional example of a brand newmore » class of ion-molecule reactions that can only occur within the unique solvated environment of the cluster.« less

Hydrated interfacial ions and electrons.

PubMed

Abel, Bernd

2013-01-01

Charged particles such as hydrated ions and transient hydrated electrons, the simplest anionic reducing agents in water, and the special hydronium and hydroxide ions at water interfaces play an important role in many fields of science, such as atmospheric chemistry, radiation chemistry, and biology, as well as biochemistry. This article focuses on these species near hydrophobic interfaces of water, such as the air or vacuum interface of water or water protein/membrane interfaces. Ions at interfaces as well as solvated electrons have been reviewed frequently during the past decade. Although all species have been known for some time with seemingly familiar features, recently the picture in all cases became increasingly diffuse rather than clearer. The current account gives a critical state-of-the art overview of what is known and what remains to be understood and investigated about hydrated interfacial ions and electrons.

Piltdown Man: Combining the Instruction of Scientific Ethics and Qualitative Analysis

NASA Astrophysics Data System (ADS)

Vincent, John B.

1999-11-01

In combination with lectures on scientific method and the problems of scientific misconduct in a freshman chemistry course at The University of Alabama, a laboratory experiment was developed to allow students to feel some of the sense of scientific discovery associated with the exposure of the Piltdown Man fraud. This is accomplished by modifying a commonly performed freshman chemistry laboratory experiment, qualitative analysis of group III metal ions. Pieces of chalk are treated with chromium, manganese, and iron to simulate the treatment used to forge the Piltdown "fossils"; students can use techniques in qualitative analysis schemes for the group III ions to determine whether the samples are "forgeries" and if so which metal ion(s) were used.

Collision-induced dissociation of diazirine-labeled peptide ions. Evidence for Brønsted-acid assisted elimination of nitrogen.

PubMed

Marek, Aleš; Tureček, František

2014-05-01

Gas-phase dissociations were investigated for several peptide ions containing the Gly-Leu* N-terminal motif where Leu* was a modified norleucine residue containing the photolabile diazirine ring. Collisional activation of gas-phase peptide cations resulted in facile N₂ elimination that competed with backbone dissociations. A free lysine ammonium group can act as a Brønsted acid to facilitate N₂ elimination. This dissociation was accompanied by insertion of a lysine proton in the side chain of the photoleucine residue, as established by deuterium labeling and gas-phase sequencing of the products. Electron structure calculations were used to provide structures and energies of reactants, intermediates, and transition states for Gly-Leu*-Gly-Gly-Lys amide ions that were combined with RRKM calculations of unimolecular rate constants. The calculations indicated that Brønsted acid-catalyzed eliminations were kinetically preferred over direct loss of N₂ from the diazirine ring. Mechanisms are proposed to explain the proton-initiated reactions and discuss the reaction products. The non-catalyzed diazirine ring cleavage and N₂ loss is proposed as a thermometer dissociation for peptide ion dissociations.

Understanding Molecular Ion-Neutral Atom Collisions for the Production of Ultracold Molecular Ions

DTIC Science & Technology

2016-06-06

Understanding Molecular Ion-Neutral Atom Collisions for the Production of Utracold Molecular Ions In the last five years, the study of ultracold...U.S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 molecular ion, quantum chemistry, atom ion interaction...Molecular Ion-Neutral Atom Collisions for the Production of Utracold Molecular Ions Report Title In the last five years, the study of ultracold molecular

A compact high resolution ion mobility spectrometer for fast trace gas analysis.

PubMed

Kirk, Ansgar T; Allers, Maria; Cochems, Philipp; Langejuergen, Jens; Zimmermann, Stefan

2013-09-21

Drift tube ion mobility spectrometers (IMS) are widely used for fast trace gas detection in air, but portable compact systems are typically very limited in their resolving power. Decreasing the initial ion packet width improves the resolution, but is generally associated with a reduced signal-to-noise-ratio (SNR) due to the lower number of ions injected into the drift region. In this paper, we present a refined theory of IMS operation which employs a combined approach for the analysis of the ion drift and the subsequent amplification to predict both the resolution and the SNR of the measured ion current peak. This theoretical analysis shows that the SNR is not a function of the initial ion packet width, meaning that compact drift tube IMS with both very high resolution and extremely low limits of detection can be designed. Based on these implications, an optimized combination of a compact drift tube with a length of just 10 cm and a transimpedance amplifier has been constructed with a resolution of 183 measured for the positive reactant ion peak (RIP(+)), which is sufficient to e.g. separate the RIP(+) from the protonated acetone monomer, even though their drift times only differ by a factor of 1.007. Furthermore, the limits of detection (LODs) for acetone are 180 pptv within 1 s of averaging time and 580 pptv within only 100 ms.

Detection of nitro-based and peroxide-based explosives by fast polarity-switchable ion mobility spectrometer with ion focusing in vicinity of Faraday detector.

PubMed

Zhou, Qinghua; Peng, Liying; Jiang, Dandan; Wang, Xin; Wang, Haiyan; Li, Haiyang

2015-05-29

Ion mobility spectrometer (IMS) has been widely deployed for on-site detection of explosives. The common nitro-based explosives are usually detected by negative IMS while the emerging peroxide-based explosives are better detected by positive IMS. In this study, a fast polarity-switchable IMS was constructed to detect these two explosive species in a single measurement. As the large traditional Faraday detector would cause a trailing reactant ion peak (RIP), a Faraday detector with ion focusing in vicinity was developed by reducing the detector radius to 3.3 mm and increasing the voltage difference between aperture grid and its front guard ring to 591 V, which could remove trailing peaks from RIP without loss of signal intensity. This fast polarity-switchable IMS with ion focusing in vicinity of Faraday detector was employed to detect a mixture of 10 ng 2,4,6-trinitrotoluene (TNT) and 50 ng hexamethylene triperoxide diamine (HMTD) by polarity-switching, and the result suggested that [TNT-H](-) and [HMTD+H](+) could be detected in a single measurement. Furthermore, the removal of trailing peaks from RIP by the Faraday detector with ion focusing in vicinity also promised the accurate identification of KClO4, KNO3 and S in common inorganic explosives, whose product ion peaks were fairly adjacent to RIP.

Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

McLuckey, Scott

2016-08-30

The overall objectives of this research effort were to expand the capabilities of spectroscopic and ion chemistry tools for the structural characterization of polyatomic ions of relevance to the broad mission of the Department of Energy. Mass spectrometry currently plays an important role in virtually all of the molecular sciences by virtue of the value of the accurate measurement of mass and the structural information that can be derived from various structural probes based on, for example, ion chemistry, ion mobility, and ion spectroscopy. Mass spectrometry has long played important roles in supporting the missions of the Department of Energymore » and its predecessor agencies, particularly in the area of isotopic analysis of nuclides. Molecular mass spectrometry has played increasingly important roles is many aspects of the production and use of energy as the nation has diversified its energy portfolio. There is an ongoing need for the expansion of the measurement capabilities associated with molecular mass spectrometry that involves both technological developments as well as improved understanding of the chemical and physical processes that take place upon ionization and ion analysis in a mass spectrometer. Advances in mass spectrometry have impacted science broadly and further advances will be required to meet the needs of current energy and environmental research. This program has historically focused on the structural characterization of polyatomic ions, usually within the context of a tandem mass spectrometry experiment. A wide variety of physical and chemical processes can take place within a mass spectrometer and advantage can be taken of such processes to enhance the quality and quantity of information that can be derived for a given chemical system of interest. For example, ions can undergo interactions with neutral molecules/atoms, light, surfaces, electrons, or oppositely charged ions. The outcomes of all such interactions can be sensitive to the structures of the ions and are therefore candidates for probes of ion structure. This program has historically focused on the chemistry and physics associated with ion/neutral interactions at both low and high translational energies, and ion/ion reactions. The former area has involved the study of ion/molecule reactions at thermal energies and the extensive study of collisional activation under a wide variety of conditions. A major area of emphasis has been collisional activation in electrodynamic ion traps. The study of gas-phase ion/ion reactions within the context of tandem mass spectrometry was initiated in this program and has grown to be a major research area in this group. Most of the focus in ion/ion chemistry has been on proton transfer and electron transfer reactions and some of the work in the previous budget period was directed, in particular, to fundamental aspects of electron transfer. Recently, the discovery of selective covalent ion/ion reactions has opened up new vistas for research that will expand significantly the capabilities of tandem mass spectrometry for the structural characterization of polyatomic ions.« less

Gradient isolator for flow field of fuel cell assembly

DOEpatents

Ernst, W.D.

1999-06-15

Isolator(s) include isolating material and optionally gasketing material strategically positioned within a fuel cell assembly. The isolating material is disposed between a solid electrolyte and a metal flow field plate. Reactant fluid carried by flow field plate channel(s) forms a generally transverse electrochemical gradient. The isolator(s) serve to isolate electrochemically a portion of the flow field plate, for example, transversely outward from the channel(s), from the electrochemical gradient. Further, the isolator(s) serve to protect a portion of the solid electrolyte from metallic ions. 4 figs.

Gradient isolator for flow field of fuel cell assembly

DOEpatents

Ernst, William D.

1999-01-01

Isolator(s) include isolating material and optionally gasketing material strategically positioned within a fuel cell assembly. The isolating material is disposed between a solid electrolyte and a metal flow field plate. Reactant fluid carried by flow field plate channel(s) forms a generally transverse electrochemical gradient. The isolator(s) serve to isolate electrochemically a portion of the flow field plate, for example, transversely outward from the channel(s), from the electrochemical gradient. Further, the isolator(s) serve to protect a portion of the solid electrolyte from metallic ions.

HI and Low Metal Ions at the Intersection of Galaxies and the CGM

NASA Astrophysics Data System (ADS)

Oppenheimer, Benjamin

2017-08-01

Over 1000 COS orbits have revealed a surprisingly complex picture of circumgalactic gas flows surrounding the diversity of galaxies in the evolved Universe. Cosmological hydrodynamic simulations have only begun to confront the vast amount of galaxy formation physics, chemistry, and dynamics revealed in the multi-ion CGM datasets. We propose the next generation of EAGLE zoom simulations, called EAGLE Cosmic Origins, to model HI and low metal ions (C II, Mg II, & Si II) throughout not just the CGM but also within the galaxies themselves. We will employ a novel, new chemistry solver, CHIMES, to follow time-dependent ionization, chemistry, and cooling of 157 ionic and molecular species, and include multiple ionization sources from the extra-galactic background, episodic AGN, and star formation. Our aim is to understand the complete baryon cycle of inflows, outflows, and gas recycling traced over 10 decades of HI column densities as well as the complex kinematic information encoded low ion absorption spectroscopy. This simulation project represents a pilot program for a larger suite of zoom simulations, which will be publicly released and lead to additional publications.

Role of adsorbed surfactant in the reaction of aryl diazonium salts with single-walled carbon nanotubes.

PubMed

Hilmer, Andrew J; McNicholas, Thomas P; Lin, Shangchao; Zhang, Jingqing; Wang, Qing Hua; Mendenhall, Jonathan D; Song, Changsik; Heller, Daniel A; Barone, Paul W; Blankschtein, Daniel; Strano, Michael S

2012-01-17

Because covalent chemistry can diminish the optical and electronic properties of single-walled carbon nanotubes (SWCNTs), there is significant interest in developing methods of controllably functionalizing the nanotube sidewall. To date, most attempts at obtaining such control have focused on reaction stoichiometry or strength of oxidative treatment. Here, we examine the role of surfactants in the chemical modification of single-walled carbon nanotubes with aryl diazonium salts. The adsorbed surfactant layer is shown to affect the diazonium derivatization of carbon nanotubes in several ways, including electrostatic attraction or repulsion, steric exclusion, and direct chemical modification of the diazonium reactant. Electrostatic effects are most pronounced in the cases of anionic sodium dodecyl sulfate and cationic cetyltrimethylammonium bromide, where differences in surfactant charge can significantly affect the ability of the diazonium ion to access the SWCNT surface. For bile salt surfactants, with the exception of sodium cholate, we find that the surfactant wraps tightly enough such that exclusion effects are dominant. Here, sodium taurocholate exhibits almost no reactivity under the explored reaction conditions, while for sodium deoxycholate and sodium taurodeoxycholate, we show that the greatest extent of reaction is observed among a small population of nanotube species, with diameters between 0.88 and 0.92 nm. The anomalous reaction of nanotubes in this diameter range seems to imply that the surfactant is less effective at coating these species, resulting in a reduced surface coverage on the nanotube. Contrary to the other bile salts studied, sodium cholate enables high selectivity toward metallic species and small band gap semiconductors, which is attributed to surfactant-diazonium coupling to form highly reactive diazoesters. Further, it is found that the rigidity of anionic surfactants can significantly influence the ability of the surfactant layer to stabilize the diazonium ion near the nanotube surface. Such Coulombic and surfactant packing effects offer promise toward employing surfactants to controllably functionalize carbon nanotubes. © 2011 American Chemical Society

Dual chemistry catalyzed by human acireductone dioxygenase

PubMed Central

Deshpande, Aditi R.; Pochapsky, Thomas C.; Petsko, Gregory A.

2017-01-01

Abstract Acireductone dioxygenase (ARD) from the methionine salvage pathway of Klebsiella oxytoca is the only known naturally occurring metalloenzyme that catalyzes different reactions in vivo based solely on the identity of the divalent transition metal ion (Fe2+ or Ni2+) bound in the active site. The iron-containing isozyme catalyzes the cleavage of substrate 1,2-dihydroxy-3-keto-5-(thiomethyl)pent-1-ene (acireductone) by O2 to formate and the ketoacid precursor of methionine, whereas the nickel-containing isozyme uses the same substrates to catalyze an off-pathway shunt to form methylthiopropionate, carbon monoxide and formate. This dual chemistry was recently demonstrated in vitro by ARD from Mus musculus (MmARD), providing the first example of a mammalian ARD exhibiting metal-dependent catalysis. We now show that human ARD (HsARD) is also capable of metal-dependent dual chemistry. Recombinant HsARD was expressed and purified to obtain a homogeneous enzyme with a single transition metal ion bound. As with MmARD, the Fe2+-bound HsARD shows the highest activity and catalyzes on-pathway chemistry, whereas Ni2+, Co2+ or Mn2+ forms catalyze off-pathway chemistry. The thermal stability of the HsARD isozymes is a function of the metal ion identity, with Ni2+-bound HsARD being the most stable followed by Co2+ and Fe2+, and Mn2+-bound HsARD being the least stable. As with the bacterial ARD, solution NMR data suggest that HsARD isozymes can have significant structural differences depending upon the metal ion bound. PMID:28062648

Roles of surface chemistry on safety and electrochemistry in lithium ion batteries.

PubMed

Lee, Kyu Tae; Jeong, Sookyung; Cho, Jaephil

2013-05-21

Motivated by new applications including electric vehicles and the smart grid, interest in advanced lithium ion batteries has increased significantly over the past decade. Therefore, research in this field has intensified to produce safer devices with better electrochemical performance. Most research has focused on the development of new electrode materials through the optimization of bulk properties such as crystal structure, ionic diffusivity, and electric conductivity. More recently, researchers have also considered the surface properties of electrodes as critical factors for optimizing performance. In particular, the electrolyte decomposition at the electrode surface relates to both a lithium ion battery's electrochemical performance and safety. In this Account, we give an overview of the major developments in the area of surface chemistry for lithium ion batteries. These ideas will provide the basis for the design of advanced electrode materials. Initially, we present a brief background to lithium ion batteries such as major chemical components and reactions that occur in lithium ion batteries. Then, we highlight the role of surface chemistry in the safety of lithium ion batteries. We examine the thermal stability of cathode materials: For example, we discuss the oxygen generation from cathode materials and describe how cells can swell and heat up in response to specific conditions. We also demonstrate how coating the surfaces of electrodes can improve safety. The surface chemistry can also affect the electrochemistry of lithium ion batteries. The surface coating strategy improved the energy density and cycle performance for layered LiCoO2, xLi2MnO3·(1 - x)LiMO2 (M = Mn, Ni, Co, and their combinations), and LiMn2O4 spinel materials, and we describe a working mechanism for these enhancements. Although coating the surfaces of cathodes with inorganic materials such as metal oxides and phosphates improves the electrochemical performance and safety properties of batteries, the microstructure of the coating layers and the mechanism of action are not fully understood. Therefore, researchers will need to further investigate the surface coating strategy during the development of new lithium ion batteries.

The biological inorganic chemistry of zinc ions.

PubMed

Krężel, Artur; Maret, Wolfgang

2016-12-01

The solution and complexation chemistry of zinc ions is the basis for zinc biology. In living organisms, zinc is redox-inert and has only one valence state: Zn(II). Its coordination environment in proteins is limited by oxygen, nitrogen, and sulfur donors from the side chains of a few amino acids. In an estimated 10% of all human proteins, zinc has a catalytic or structural function and remains bound during the lifetime of the protein. However, in other proteins zinc ions bind reversibly with dissociation and association rates commensurate with the requirements in regulation, transport, transfer, sensing, signalling, and storage. In contrast to the extensive knowledge about zinc proteins, the coordination chemistry of the "mobile" zinc ions in these processes, i.e. when not bound to proteins, is virtually unexplored and the mechanisms of ligand exchange are poorly understood. Knowledge of the biological inorganic chemistry of zinc ions is essential for understanding its cellular biology and for designing complexes that deliver zinc to proteins and chelating agents that remove zinc from proteins, for detecting zinc ion species by qualitative and quantitative analysis, and for proper planning and execution of experiments involving zinc ions and nanoparticles such as zinc oxide (ZnO). In most investigations, reference is made to zinc or Zn 2+ without full appreciation of how biological zinc ions are buffered and how the d-block cation Zn 2+ differs from s-block cations such as Ca 2+ with regard to significantly higher affinity for ligands, preference for the donor atoms of ligands, and coordination dynamics. Zinc needs to be tightly controlled. The interaction with low molecular weight ligands such as water and inorganic and organic anions is highly relevant to its biology but in contrast to its coordination in proteins has not been discussed in the biochemical literature. From the discussion in this article, it is becoming evident that zinc ion speciation is important in zinc biochemistry and for biological recognition as a variety of low molecular weight zinc complexes have already been implicated in biological processes, e.g. with ATP, glutathione, citrate, ethylenediaminedisuccinic acid, nicotianamine, or bacillithiol. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

Interfaces and Materials in Lithium Ion Batteries: Challenges for Theoretical Electrochemistry.

PubMed

Kasnatscheew, Johannes; Wagner, Ralf; Winter, Martin; Cekic-Laskovic, Isidora

2018-04-18

Energy storage is considered a key technology for successful realization of renewable energies and electrification of the powertrain. This review discusses the lithium ion battery as the leading electrochemical storage technology, focusing on its main components, namely electrode(s) as active and electrolyte as inactive materials. State-of-the-art (SOTA) cathode and anode materials are reviewed, emphasizing viable approaches towards advancement of the overall performance and reliability of lithium ion batteries; however, existing challenges are not neglected. Liquid aprotic electrolytes for lithium ion batteries comprise a lithium ion conducting salt, a mixture of solvents and various additives. Due to its complexity and its role in a given cell chemistry, electrolyte, besides the cathode materials, is identified as most susceptible, as well as the most promising, component for further improvement of lithium ion batteries. The working principle of the most important commercial electrolyte additives is also discussed. With regard to new applications and new cell chemistries, e.g., operation at high temperature and high voltage, further improvements of both active and inactive materials are inevitable. In this regard, theoretical support by means of modeling, calculation and simulation approaches can be very helpful to ex ante pre-select and identify the aforementioned components suitable for a given cell chemistry as well as to understand degradation phenomena at the electrolyte/electrode interface. This overview highlights the advantages and limitations of SOTA lithium battery systems, aiming to encourage researchers to carry forward and strengthen the research towards advanced lithium ion batteries, tailored for specific applications.

Radiation Chemistry and the Radiation Preservation of Food.

ERIC Educational Resources Information Center

Taub, Irwin A.

1981-01-01

Describes common features in the radiation chemistry of food components, and illustrates how product yields are predicted. Presents data that pertain to the radiolysis of the nitrate ion, metmyoglobin, myosin, and tripalmitin. (CS)

Perspective: Advanced particle imaging

PubMed Central

Chandler, David W.

2017-01-01

Since the first ion imaging experiment [D. W. Chandler and P. L. Houston, J. Chem. Phys. 87, 1445–1447 (1987)], demonstrating the capability of collecting an image of the photofragments from a unimolecular dissociation event and analyzing that image to obtain the three-dimensional velocity distribution of the fragments, the efficacy and breadth of application of the ion imaging technique have continued to improve and grow. With the addition of velocity mapping, ion/electron centroiding, and slice imaging techniques, the versatility and velocity resolution have been unmatched. Recent improvements in molecular beam, laser, sensor, and computer technology are allowing even more advanced particle imaging experiments, and eventually we can expect multi-mass imaging with co-variance and full coincidence capability on a single shot basis with repetition rates in the kilohertz range. This progress should further enable “complete” experiments—the holy grail of molecular dynamics—where all quantum numbers of reactants and products of a bimolecular scattering event are fully determined and even under our control. PMID:28688442

Energy gap law of electron transfer in nonpolar solvents.

PubMed

Tachiya, M; Seki, Kazuhiko

2007-09-27

We investigate the energy gap law of electron transfer in nonpolar solvents for charge separation and charge recombination reactions. In polar solvents, the reaction coordinate is given in terms of the electrostatic potentials from solvent permanent dipoles at solutes. In nonpolar solvents, the energy fluctuation due to solvent polarization is absent, but the energy of the ion pair state changes significantly with the distance between the ions as a result of the unscreened strong Coulomb potential. The electron transfer occurs when the final state energy coincides with the initial state energy. For charge separation reactions, the initial state is a neutral pair state, and its energy changes little with the distance between the reactants, whereas the final state is an ion pair state and its energy changes significantly with the mutual distance; for charge recombination reactions, vice versa. We show that the energy gap law of electron-transfer rates in nonpolar solvents significantly depends on the type of electron transfer.

Chemistry of groundwater discharge inferred from longitudinal river sampling

NASA Astrophysics Data System (ADS)

Batlle-Aguilar, J.; Harrington, G. A.; Leblanc, M.; Welch, C.; Cook, P. G.

2014-02-01

We present an approach for identifying groundwater discharge chemistry and quantifying spatially distributed groundwater discharge into rivers based on longitudinal synoptic sampling and flow gauging of a river. The method is demonstrated using a 450 km reach of a tropical river in Australia. Results obtained from sampling for environmental tracers, major ions, and selected trace element chemistry were used to calibrate a steady state one-dimensional advective transport model of tracer distribution along the river. The model closely reproduced river discharge and environmental tracer and chemistry composition along the study length. It provided a detailed longitudinal profile of groundwater inflow chemistry and discharge rates, revealing that regional fractured mudstones in the central part of the catchment contributed up to 40% of all groundwater discharge. Detailed analysis of model calibration errors and modeled/measured groundwater ion ratios elucidated that groundwater discharging in the top of the catchment is a mixture of local groundwater and bank storage return flow, making the method potentially useful to differentiate between local and regional sourced groundwater discharge. As the error in tracer concentration induced by a flow event applies equally to any conservative tracer, we show that major ion ratios can still be resolved with minimal error when river samples are collected during transient flow conditions. The ability of the method to infer groundwater inflow chemistry from longitudinal river sampling is particularly attractive in remote areas where access to groundwater is limited or not possible, and for identification of actual fluxes of salts and/or specific contaminant sources.

Impact of water chemistry on the particle-specific toxicity of copper nanoparticles to Daphnia magna.

PubMed

Xiao, Yinlong; Peijnenburg, Willie J G M; Chen, Guangchao; Vijver, Martina G

2018-01-01

Toxicity of metallic nanoparticle suspensions (NP (total) ) is generally assumed to result from the combined effect of the particles present in suspensions (NP (particle) ) and their released ions (NP (ion) ). Evaluation and consideration of how water chemistry affects the particle-specific toxicity of NP (total) are critical for environmental risk assessment of nanoparticles. In this study, it was found that the toxicity of Cu NP (particle) to Daphnia magna, in line with the trends in toxicity for Cu NP (ion) , decreased with increasing pH and with increasing concentrations of divalent cations and dissolved organic carbon (DOC). Without the addition of DOC, the toxicity of Cu NP (total) to D. magna at the LC50 was driven mainly by Cu NP (ion) (accounting for ≥53% of the observed toxicity). However, toxicity of Cu NP (total) in the presence of DOC at a concentration ranging from 5 to 50mg C/L largely resulted from the NP (particle) (57%-85%), which could be attributable to the large reduction of the concentration of Cu NP (ion) and the enhancement of the stability of Cu NP (particle) when DOC was added. Our results indicate that water chemistry needs to be explicitly taken into consideration when evaluating the role of NP (particle) and NP (ion) in the observed toxicity of NP (total) . Copyright © 2017 Elsevier B.V. All rights reserved.

Synthesis and Characterization of Calixarene Tetraethers: An Exercise in Supramolecular Chemistry for the Undergraduate Organic Laboratory

ERIC Educational Resources Information Center

Debbert, Stefan L.; Hoh, Bradley D.; Dulak, David J.

2016-01-01

In this experiment for an introductory undergraduate organic chemistry lab, students tetraalkylate tertbutylcalix[4]arene, a bowl-shaped macrocyclic oligophenol, and examine the supramolecular chemistry of the tetraether product by proton nuclear magnetic resonance (NMR) spectroscopy. Complexation with a sodium ion reduces the conformational…

The Ocean.

ERIC Educational Resources Information Center

Broecker, Wallace S.

1983-01-01

The chemistry of the ocean, whose constituents interact with those of air and land to support life and influence climate, is known to have undergone changes since the last glacial epoch. Changes in dissolved oxygen, calcium ions, phosphate, carbon dioxide, carbonate ions, and bicarbonate ions are discussed. (JN)

Precipitation chemistry - Atmospheric loadings to the surface waters of the Indian River lagoon basin by rainfall

NASA Technical Reports Server (NTRS)

Dreschel, Thomas W.; Madsen, Brooks C.; Maull, Lee A.; Hinkle, C. R.; Knott, William M., III

1990-01-01

Rain volume and chemistry monitoring as part of the Kennedy Space Center Long Term Environmental Monitoring Program included the years 1984-1987 as part of the National Atmospheric Deposition Program. Atmospheric deposition in rainfall consisted primarily of sea salt and hydrogen ion, sulfate, nitrate, and ammonium ions. The deposition of nitrogen (a principal plant nutrient) was on the order of 200-300 metric tons per year to the surface waters.

Ejection of Coulomb Crystals from a Linear Paul Ion Trap for Ion-Molecule Reaction Studies.

PubMed

Meyer, K A E; Pollum, L L; Petralia, L S; Tauschinsky, A; Rennick, C J; Softley, T P; Heazlewood, B R

2015-12-17

Coulomb crystals are being increasingly employed as a highly localized source of cold ions for the study of ion-molecule chemical reactions. To extend the scope of reactions that can be studied in Coulomb crystals-from simple reactions involving laser-cooled atomic ions, to more complex systems where molecular reactants give rise to multiple product channels-sensitive product detection methodologies are required. The use of a digital ion trap (DIT) and a new damped cosine trap (DCT) are described, which facilitate the ejection of Coulomb-crystallized ions onto an external detector for the recording of time-of-flight (TOF) mass spectra. This enables the examination of reaction dynamics and kinetics between Coulomb-crystallized ions and neutral molecules: ionic products are typically cotrapped, thus ejecting the crystal onto an external detector reveals the masses, identities, and quantities of all ionic species at a selected point in the reaction. Two reaction systems are examined: the reaction of Ca(+) with deuterated isotopologues of water, and the charge exchange between cotrapped Xe(+) with deuterated isotopologues of ammonia. These reactions are examples of two distinct types of experiment, the first involving direct reaction of the laser-cooled ions, and the second involving reaction of sympathetically-cooled heavy ions to form a mixture of light product ions. Extensive simulations are conducted to interpret experimental results and calculate optimal operating parameters, facilitating a comparison between the DIT and DCT approaches. The simulations also demonstrate a correlation between crystal shape and image shape on the detector, suggesting a possible means for determining crystal geometry for nonfluorescing ions.

The Sensitivity of Aragonite U/Ca Ratio to Seawater Carbonate Ion Concentration: Insight From Abiogenic Precipitation Experiments and Application to Coral Biomineralization

NASA Astrophysics Data System (ADS)

Decarlo, T. M.; Gaetani, G. A.; Holcomb, M.; Cohen, A. L.

2014-12-01

The U/Ca ratio of aragonite coral skeleton has been shown to correlate with both temperature and seawater carbonate chemistry. However, U/Ca has not been conclusively linked to carbonate chemistry and/or temperature in laboratory experiments. We have performed abiogenic precipitation experiments designed to evaluate the sensitivity of U partitioning between aragonite and seawater to temperature, pH, and the concentration of carbonate ion in seawater. Aragonite was precipitated from seawater by addition of carbonate alkalinity at rates set to maintain stable carbonate chemistry during precipitation. Experiments were conducted between 20-40 °C, pH 7.8-9.0, and carbonate ion concentration 600-2600 μmol kg-1. Mineralogies of the precipitates were identified by Raman spectrometry and U/Ca ratios of the bulk precipitate and fluid were determined by solution ICP-MS. Our results show that the U/Ca ratio of aragonite precipitated from an infinite reservoir of seawater decreases with increasing carbonate ion concentration, and is independent of pH and temperature. Using our abiogenic results as a basis for interpreting coral skeletal chemistry, we model the coral biomineralization process to show that the U/Ca ratio of coral skeleton reflects a calcifying fluid with carbonate ion concentration of at least 1000 μmol kg-1, several times greater than ambient seawater. Further, we show that the coral biomineralization response to environmental changes can be linked to changes in calcifying fluid composition via skeletal U/Ca ratios.

Comprehensive modeling study of ozonolysis of oleic acid aerosol based on real-time, online measurements of aerosol composition

NASA Astrophysics Data System (ADS)

Gallimore, P. J.; Griffiths, P. T.; Pope, F. D.; Reid, J. P.; Kalberer, M.

2017-04-01

The chemical composition of organic aerosols profoundly influences their atmospheric properties, but a detailed understanding of heterogeneous and in-particle reactivity is lacking. We present here a combined experimental and modeling study of the ozonolysis of oleic acid particles. An online mass spectrometry (MS) method, Extractive Electrospray Ionization (EESI), is used to follow the composition of the aerosol at a molecular level in real time; relative changes in the concentrations of both reactants and products are determined during aerosol aging. The results show evidence for multiple non-first-order reactions involving stabilized Criegee intermediates, including the formation of secondary ozonides and other oligomers. Offline liquid chromatography MS is used to confirm the online MS assignment of the monomeric and dimeric products. We explain the observed EESI-MS chemical composition changes, and chemical and physical data from previous studies, using a process-based aerosol chemistry simulation, the Pretty Good Aerosol Model (PG-AM). In particular, we extend previous studies of reactant loss by demonstrating success in reproducing the time dependence of product formation and the evolving particle size. This advance requires a comprehensive chemical scheme coupled to the partitioning of semivolatile products; relevant reaction and evaporation parameters have been refined using our new measurements in combination with PG-AM.

Multimodal Study of the Speciations and Activities of Supported Pd Catalysts During the Hydrogenation of Ethylene

DOE PAGES

Zhao, Shen; Li, Yuanyuan; Liu, Deyu; ...

2017-08-07

In this paper we describe a multimodal exploration of the atomic structure and chemical state of silica-supported palladium nanocluster catalysts during the hydrogenation of ethylene in operando conditions that variously transform the metallic phases between hydride and carbide speciations. The work exploits a microreactor that allows combined multiprobe investigations by high-resolution transmission electron microscopy (HR-TEM), X-ray absorption fine structure (XAFS), and microbeam IR (μ-IR) analyses on the catalyst under operando conditions. The work specifically explores the reaction processes that mediate the interconversion of hydride and carbide phases of the Pd clusters in consequence to changes made in the composition ofmore » the gas-phase reactant feeds, their stability against coarsening, the reversibility of structural/compositional transformations, and the role that oligomeric/waxy byproducts (here forming under hydrogen-limited reactant compositions) might play in modifying activity. The results provide new insights into structural features of the chemistry/mechanisms of Pd catalysis during the selective hydrogenation of acetylene in ethylene—a process simplified here in the use of binary ethylene/hydrogen mixtures. Finally, these explorations, performed in operando conditions, provide new understandings of structure–activity relationships for Pd catalysis in regimes that actively transmute important attributes of electronic and atomic structures.« less

Multimodal Study of the Speciations and Activities of Supported Pd Catalysts During the Hydrogenation of Ethylene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Shen; Li, Yuanyuan; Liu, Deyu

In this paper we describe a multimodal exploration of the atomic structure and chemical state of silica-supported palladium nanocluster catalysts during the hydrogenation of ethylene in operando conditions that variously transform the metallic phases between hydride and carbide speciations. The work exploits a microreactor that allows combined multiprobe investigations by high-resolution transmission electron microscopy (HR-TEM), X-ray absorption fine structure (XAFS), and microbeam IR (μ-IR) analyses on the catalyst under operando conditions. The work specifically explores the reaction processes that mediate the interconversion of hydride and carbide phases of the Pd clusters in consequence to changes made in the composition ofmore » the gas-phase reactant feeds, their stability against coarsening, the reversibility of structural/compositional transformations, and the role that oligomeric/waxy byproducts (here forming under hydrogen-limited reactant compositions) might play in modifying activity. The results provide new insights into structural features of the chemistry/mechanisms of Pd catalysis during the selective hydrogenation of acetylene in ethylene—a process simplified here in the use of binary ethylene/hydrogen mixtures. Finally, these explorations, performed in operando conditions, provide new understandings of structure–activity relationships for Pd catalysis in regimes that actively transmute important attributes of electronic and atomic structures.« less

Role of Chemical Reactivity and Transition State Modeling for Virtual Screening.

PubMed

Karthikeyan, Muthukumarasamy; Vyas, Renu; Tambe, Sanjeev S; Radhamohan, Deepthi; Kulkarni, Bhaskar D

2015-01-01

Every drug discovery research program involves synthesis of a novel and potential drug molecule utilizing atom efficient, economical and environment friendly synthetic strategies. The current work focuses on the role of the reactivity based fingerprints of compounds as filters for virtual screening using a tool ChemScore. A reactant-like (RLS) and a product- like (PLS) score can be predicted for a given compound using the binary fingerprints derived from the numerous known organic reactions which capture the molecule-molecule interactions in the form of addition, substitution, rearrangement, elimination and isomerization reactions. The reaction fingerprints were applied to large databases in biology and chemistry, namely ChEMBL, KEGG, HMDB, DSSTox, and the Drug Bank database. A large network of 1113 synthetic reactions was constructed to visualize and ascertain the reactant product mappings in the chemical reaction space. The cumulative reaction fingerprints were computed for 4000 molecules belonging to 29 therapeutic classes of compounds, and these were found capable of discriminating between the cognition disorder related and anti-allergy compounds with reasonable accuracy of 75% and AUC 0.8. In this study, the transition state based fingerprints were also developed and used effectively for virtual screening in drug related databases. The methodology presented here provides an efficient handle for the rapid scoring of molecular libraries for virtual screening.

Organic functional group transformations in water at elevated temperature and pressure: Reversibility, reactivity, and mechanisms

NASA Astrophysics Data System (ADS)

Shipp, Jessie; Gould, Ian R.; Herckes, Pierre; Shock, Everett L.; Williams, Lynda B.; Hartnett, Hilairy E.

2013-03-01

Many transformation reactions involving hydrocarbons occur in the presence of H2O in hydrothermal systems and deep sedimentary systems. We investigate these reactions using laboratory-based organic chemistry experiments at high temperature and pressure (300 °C and 100 MPa). Organic functional group transformation reactions using model organic compounds based on cyclohexane with one or two methyl groups provided regio- and stereochemical markers that yield information about reversibility and reaction mechanisms. We found rapidly reversible interconversion between alkanes, alkenes, dienes, alcohols, ketones, and enones. The alkane-to-ketone reactions were not only completely reversible, but also exhibited such extensive reversibility that any of the functional groups along the reaction path (alcohol, ketone, and even the diene) could be used as the reactant and form all the other groups as products. There was also a propensity for these ring-based structures to dehydrogenate; presumably from the alkene, through a diene, to an aromatic ring. The product suites provide strong evidence that water behaved as a reactant and the various functional groups showed differing degrees of reactivity. Mechanistically-revealing products indicated reaction mechanisms that involve carbon-centered cation intermediates. This work therefore demonstrates that a wide range of organic compound types can be generated by abiotic reactions at hydrothermal conditions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matthiesen, John; Hoff, Thomas; Liu, Chi

The production of chemicals from lignocellulosic biomass provides opportunities to synthesize chemicals with new functionalities and grow a more sustainable chemical industry. However, new challenges emerge as research transitions from petrochemistry to biorenewable chemistry. Compared to petrochemisty, the selective conversion of biomass-derived carbohydrates requires most catalytic reactions to take place at low temperatures (< 300°C) and in the condensed phase to prevent reactants and products from degrading. The stability of heterogeneous catalysts in liquid water above the normal boiling point represents one of the major challenges to overcome. Herein, we review some of the latest advances in the field withmore » an emphasis on the role of carbon materials and carbon nanohybrids in addressing this challenge.« less

Mode-Specific SN2 Reaction Dynamics.

PubMed

Wang, Yan; Song, Hongwei; Szabó, István; Czakó, Gábor; Guo, Hua; Yang, Minghui

2016-09-01

Despite its importance in chemistry, the microscopic dynamics of bimolecular nucleophilic substitution (SN2) reactions is still not completely elucidated. In this publication, the dynamics of a prototypical SN2 reaction (F(-) + CH3Cl → CH3F + Cl(-)) is investigated using a high-dimensional quantum mechanical model on an accurate potential energy surface (PES) and further analyzed by quasi-classical trajectories on the same PES. While the indirect mechanism dominates at low collision energies, the direct mechanism makes a significant contribution. The reactivity is found to depend on the specific reactant vibrational mode excitation. The mode specificity, which is more prevalent in the direct reaction, is rationalized by a transition-state-based model.

Reaction chemistry and collisional processes in multiple devices for resolving isobaric interferences in ICP-MS.

PubMed

Bandura, D R; Baranov, V I; Tanner, S D

2001-07-01

A low-level review of the fundamentals of ion-molecule interactions is presented. These interactions are used to predict the efficiencies of collisional fragmentation, energy damping and reaction for a variety of neutral gases as a function of pressure in a rf-driven collision/reaction cell. It is shown that the number of collisions increases dramatically when the ion energies are reduced to near-thermal (< 0.1 eV), because of the ion-induced dipole and ion-dipole interaction. These considerations suggest that chemical reaction can be orders of magnitude more efficient at improving the analyte signal/background ratio than can collisional fragmentation. Considerations that lead to an appropriate selection of type of gas, operating pressure, and ion energies for efficient operation of the cell for the alleviation of spectral interferences are discussed. High efficiency (large differences between reaction efficiencies of the analyte and interference ions, and concomitant suppression of secondary chemistry) might be required to optimize the chemical resolution (determination of an analyte in the presence of an isobaric interference) when using ion-molecule chemistry to suppress the interfering ion. In many instances atom transfer to the analyte, which shifts the analytical m/z by the mass of the atom transferred, provides high chemical resolution, even when the efficiency of reaction is relatively low. Examples are given of oxidation, hydroxylation, and chlorination of analyte ions (V+, Fe+, As+, Se+, Sr+, Y+, and Zr+) to improve the capability of determination of complex samples. Preliminary results are given showing O-atom abstraction by CO from CaO+ to enable the determination of Fe in high-Ca samples.

Ion exchange phenomena

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bourg, I.C.; Sposito, G.

Ion exchange phenomena involve the population of readily exchangeable ions, the subset of adsorbed solutes that balance the intrinsic surface charge and can be readily replaced by major background electrolyte ions (Sposito, 2008). These phenomena have occupied a central place in soil chemistry research since Way (1850) first showed that potassium uptake by soils resulted in the release of an equal quantity of moles of charge of calcium and magnesium. Ion exchange phenomena are now routinely modeled in studies of soil formation (White et al., 2005), soil reclamation (Kopittke et al., 2006), soil fertilitization (Agbenin and Yakubu, 2006), colloidal dispersion/flocculationmore » (Charlet and Tournassat, 2005), the mechanics of argillaceous media (Gajo and Loret, 2007), aquitard pore water chemistry (Tournassat et al., 2008), and groundwater (Timms and Hendry, 2007; McNab et al., 2009) and contaminant hydrology (Chatterjee et al., 2008; van Oploo et al., 2008; Serrano et al., 2009).« less

Addendum to "Harmony of computational quantum chemistry and experimental chemistry: Comprehensive DFT studies, microsynthesis, and characterization of mustard gas polysulfide analogues" [J. Mol. Struct. (2018) 57-62

NASA Astrophysics Data System (ADS)

Saeidian, Hamid; Faraz, Sajjad Mousavi; Mirjafary, Zohreh; Babri, Mehran

2018-07-01

Recently, Blum from OPCW laboratory investigated HD, HS2, HS3 and higher polysulfides and their corresponding reactive intermediates by using Amsterdam Density Functional (ADF) calculations [22, 23]. In his presentation, he mentioned that analysis of MO energy levels for episulfonium ions of HD, HS2 and HS3 shows that the sulfur centered LUMOs for HS2 and HS3 are LUMO+1 for HD ion; and LUMOs energy levels of HS2 and HS3 are decreased by addition of polarizable sulfur atoms. He also showed that no four-membered sulfonium ion ring structures are formed for HS2, HS3 and higher polysulfides; and episulfonium ion is the only reactive intermediate for them.

Hot electrons and radial transport in Saturn's inner magetosphere: Modeling the effects on ion chemistry

NASA Astrophysics Data System (ADS)

Fleshman, Bobby L.

The E-ring of Saturn, located just beyond the main rings at four Saturn radii, was known to be made mostly of water and its by-products before the Cassini spacecraft arrived at Saturn in 2005. Since then, Cassini has observed water geysers on the tiny moon of Enceladus ejecting ≈ 100 kg of water per second into orbit around Saturn, which most agree is the chief contributor to neutrals in the E-ring. Following several key reactions, many of these neutrals go on to populate large, tenuous structures, known as neutral clouds, extending 10s of Saturn radii. The other side of the story are the ions, which are largely created by the ionization of same neutrals sourced from Enceladus. A key distinction between the neutrals and ions is that ions are carried along by Saturn's magnetic field, and revolve around Saturn at the rotation rate of the planet, while neutrals generally have much slower Keplerian speeds. It is the study of the chemical interaction of these separate, but related populations that is the subject of this thesis. We have developed a series of models to study how the coupling of these systems affect details of the other, such as composition. The first step (Chapter 2) was the development of a water-group physical chemistry model, which includes suprathermal electrons and the effect of radial ion transport. With this "one-box" model, we are able to reproduce observed water and hydrogen ion densities in Enceladus's orbit, but only when the hot electron density is ≈ 0.5% of the total plasma density. Radial transport is found to be slow, requiring 26 days to remove ions from the orbit of Enceladus. Moving toward the development of a radial model of ion chemistry, in Chapter 4 we present a model of Saturn's neutral clouds, which are made of material outgassing from Enceladus. The effects of dissociation and charge exchange are considered, where the details of the latter prove to be of great consequence on neutral cloud morphology. The oxygen cloud is found to the most extended, followed by H2O, and finally OH. The above efforts are combined in Chapter 5, where a neutral cloud model is used to construct a radial model of ion chemistry. It is shown that neutral H2O requires more spreading than yet modeled in order to recover observed water and hydrogen ion abundances near Enceladus. The relative abundance of water-group ion species presented will be useful for analyses of CAPS-IMS data, while loss rates derived from the model can be used to improve neutral cloud models. The case is made that ion chemistry models and neutral cloud models must be developed alongside one another in order to improve understanding of these interrelated populations at Saturn.

Method of synthesizing a plurality of reactants and producing thin films of electro-optically active transition metal oxides

DOEpatents

Tracy, C.E.; Benson, D.K.; Ruth, M.R.

1985-08-16

A method of synthesizing a plurality of reactants by inducing a reaction by plasma deposition among the reactants. The plasma reaction is effective for consolidating the reactants and producing thin films of electro-optically active transition metal oxides.

Preliminary Experimental Results using a Steady State ICP Flow Reactor to Investigate Condensation Chemistry for Nuclear Forensics

NASA Astrophysics Data System (ADS)

Koroglu, Batikan; Armstrong, Mike; Cappelli, Mark; Chernov, Alex; Crowhurst, Jonathan; Mehl, Marco; Radousky, Harry; Rose, Timothy; Zaug, Joe

2016-10-01

The high temperature chemistry of rapidly condensing matter is under investigation using a steady state inductively coupled plasma (ICP) flow reactor. The objective is to study chemical processes on cooling time scales similar to that of a low yield nuclear fireball. The reactor has a nested set of gas flow rings that provide flexibility in the control of hydrodynamic conditions and mixing of chemical components. Initial tests were run using two different aqueous solutions (ferric nitrate and uranyl nitrate). Chemical reactants passing through the plasma torch undergo non-linear cooling from 10,000K to 1,000K on time scales of <0.1 to 0.5s depending on flow conditions. Optical spectroscopy measurements were taken at different positions along the flow axis to observe the in situ spatial and temporal evolution of chemical species at different temperatures. The current data offer insights into the changes in oxide chemistry as a function of oxygen fugacity. The time resolved measurements will also serve as a validation target for the development of kinetic models that will be used to describe chemical fractionation during nuclear fireball condensation. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Phase equilibria and crystal chemistry of rubidium niobates and rubidium tantalates

NASA Technical Reports Server (NTRS)

Minor, D. B.; Roth, R. S.; Parker, H. S.; Brower, W. S.

1977-01-01

The phase equilibria relations and crystal chemistry of portions of the Rb2O-Nb2O5 and Rb2O-Ta2O5 systems were investigated for structures potentially useful as ionic conductors. A hexagonal tungsten bronze-type (HTB) structure was found in both systems as well as three hexagonal phases with mixed HTB-pyrochlore type structures. Ion exchange experiments between various alkali ions are described for several phases. Unit cell dimensions and X-ray diffraction powder patterns are reported.

Semiempirical and ab initio Calculations of Charged Species Used in the Physical Organic Chemistry Course.

ERIC Educational Resources Information Center

Gilliom, Richard D.

1989-01-01

Concentrates on the semiempirical methods MINDO/3, MNDO, and AMI available in the program AMPAC from the Quantum Chemistry Program Exchange at Indiana University. Uses charged ions in the teaching of computational chemistry. Finds that semiempirical methods are accurate enough for the general use of the bench chemist. (MVL)

Method of synthesizing a plurality of reactants and producing thin films of electro-optically active transition metal oxides

DOEpatents

Tracy, C. Edwin; Benson, David K.; Ruth, Marta R.

1987-01-01

A method of synthesizing electro-optically active reaction products from a plurality of reactants by inducing a reaction by plasma deposition among the reactants. The plasma reaction is effective for consolidating the reactants and producing thin films of electro-optically active transition metal oxides.

A Hands-On Activity Incorporating the Threefold Representation on Limiting Reactant

ERIC Educational Resources Information Center

Gonza´lez-Sa´nchez, Ange´lica M.; Ortiz-Nieves, Edgardo L.; Medina, Zuleikra

2014-01-01

Many students share the common belief that the limiting reactant in a chemical reaction is the reactant in the smallest quantity of material. To help students overcome this difficulty a hands-on activity for the limiting reactant concept was developed. The activity incorporates the three levels of representation (macroscopic, submicroscopic, and…

Hydrochemical evaluation and identification of geochemical processes in the shallow and deep wells in the Ramganga Sub-Basin, India.

PubMed

Rajmohan, Natarajan; Patel, Neelam; Singh, Gaurav; Amarasinghe, Upali A

2017-09-01

Groundwater samples were collected from 44 wells in the Ramganga Sub-Basin (RSB), India, and analysed for major ions, nutrients and trace metals. The primary goal of this study is to evaluate the hydrochemistry and to identify the geochemical processes that govern the water chemistry in the shallow and deep tube wells in the study area using geochemical methods. The knowledge of changes in hydrochemistry of the aquifers is important for both groundwater recharge and use in the region. This study found that there are substantial differences of water chemistry between shallow and deep wells. In the shallow wells, the average concentrations of total dissolved solid (TDS), Na, K, Ca, Mg, HCO 3 , Cl, SO 4 , NO 3 , PO 4 , F, Cu, Mn, Fe and Cr are twofold higher than the deep wells. The concentrations of dissolved silica in the groundwater do not vary with the depth, which implies that the variation in the water chemistry is not due to mineral dissolution alone. Major ion ratios and saturation indices suggest that the water chemistry is predominantly controlled by dissolution of carbonate minerals, silicate weathering and ion exchange reactions. Thermodynamic evaluation (ion activity ratios and stability filed diagrams) indicates that the kaolinite and gibbsite controlled the water chemistry in the both shallow and deep wells. In addition, the groundwater chemistry in the shallow wells is affected by the vertical infiltration of contaminated water from surface contamination sources and nitrification process. In the deep wells, absence of NO 3 and low concentrations of Cl, SO 4 , PO 4 and F imply the role of regional flow and denitrification in the groundwater. Results concluded that proper management plan is necessary to protect the shallow aquifer in the RSB since shallow aquifer pumping is less expensive than the deeper one.

Physicochemical variation of mica surface by low energy ion beam irradiation

NASA Astrophysics Data System (ADS)

Bhowmik, Dipak; Karmakar, Prasanta

2018-05-01

We report the transformation of smooth and hydrophilic mica surface to a patterned and hydrophobic surface by 12 keV Ar+ and N+ ion bombardment at oblique ion incidence. Periodic ripple pattern has been found on the mica surface when nitrogen like lighter or argon like heavier ions are bombarded at an angle 60° with respect to the surface normal. During ion bombardment the different components of multi-elemental mica are eroded at different rate; as a result surface chemistry is changed, as well as a surface ripple pattern is developed on the surface due to the generation of surface instabilities. The change of surface chemistry and presence of pattern change the hydrophilic nature of the mica surface. X-ray photoelectron spectroscopy (XPS) study of irradiated mica surface shows that the upper K atoms are sputtered most. The vertical and lateral dimensions of the surface patterns are controlled by varying the ion fluence. Contact angle measurement of un-irradiated and irradiated mica surface shows a certain change from hydrophilicity to hydrophobicity. The physicochemical changes of mica surface due to Ar+ and N+ ion bombardment have been discussed.

Molecular complexes in close and far away

PubMed Central

Klemperer, William; Vaida, Veronica

2006-01-01

In this review, gas-phase chemistry of interstellar media and some planetary atmospheres is extended to include molecular complexes. Although the composition, density, and temperature of the environments discussed are very different, molecular complexes have recently been considered as potential contributors to chemistry. The complexes reviewed include strongly bound aggregates of molecules with ions, intermediate-strength hydrogen bonded complexes (primarily hydrates), and weakly bonded van der Waals molecules. In low-density, low-temperature environments characteristic of giant molecular clouds, molecular synthesis, known to involve gas-phase ion-molecule reactions and chemistry at the surface of dust and ice grains is extended here to involve molecular ionic clusters. At the high density and high temperatures found on planetary atmospheres, molecular complexes contribute to both atmospheric chemistry and climate. Using the observational, laboratory, and theoretical database, the role of molecular complexes in close and far away is discussed. PMID:16740667

Titan's Complex Chemistry: Insights from the Lab

NASA Astrophysics Data System (ADS)

Horst, Sarah

2018-06-01

The Cassini-Huygens mission revealed Titan to be a complex world with physical processes reminiscent of other terrestrial planets, but chemistry that is unlike anywhere else in the Solar System. Titan's complex atmospheric chemistry converts N2 and CH4 into numerous, abundant organic molecules ranging from relatively simple hydrocarbons to ions with mass to charge ratios up to 10,000 amu/q. The molecules eventually settle to the surface where they can participate in and be modified by geological processes such as aeolian and fluvial erosion or undergo subsequent chemistry in Titan's lakes and seas or impact craters and potential cryovolcanic flows. From the processes leading to massive ion formation in the atmosphere to the behavior of saltating organic sands on the surface, laboratory experiments are playing a pivotal role in understanding Titan and expanding our understanding of planetary processes into new, exciting phase space.

Dissociative properties of 1,1,1,2-tetrafluoroethane obtained by computational chemistry

NASA Astrophysics Data System (ADS)

Hayashi, Toshio; Ishikawa, Kenji; Sekine, Makoto; Hori, Masaru

2018-06-01

The electronic properties and dissociative channels of the alternative to the CCl2F2 (CFC-12) refrigerant, 1,1,1,2-tetrafluoroethane (HFC-134a) with a low global warming potential (GWP, 1430), were revealed by computational chemistry. The results show that CF3 + and CHF2 + ions are mainly produced by ionization. The CF3CH2 + ion is produced by ion pair formation and by direct ionization in the energy region higher than approximately 15 eV, but also in small amounts by the ionization of the dissociated CF3CH2 radical. This information is useful for etching process engineers in leading-edge semiconductor manufacturing.

Aromatic polyimides containing a dimethylsilane-linked dianhydride

NASA Technical Reports Server (NTRS)

St.clair, Anne K. (Inventor); St.clair, Terry L. (Inventor); Pratt, J. Richard (Inventor)

1989-01-01

A high-temperature stable, optically transparent, low dielectric aromatic polyimide is prepared by chemically combining equimolar quantities of an aromatic dianhydride reactant and an aromatic diamine reactant, which are selected so that one reactant contains at least one Si(CH3)2 group in its molecular structure, and the other reactant contains at least one -CF3 group in its molecular structure. The reactants are chemically combined in a solvent medium to form a solution of a high molecular weight polyamic acid, which is then converted to the corresponding polyimide.

Aromatic polyimides containing a dimethylsilane-linked dianhydride

NASA Technical Reports Server (NTRS)

St. Clair, Anne K. (Inventor); St. Clair, Terry L. (Inventor); Pratt, J. Richard (Inventor)

1992-01-01

A high-temperature stable, optically transparent, low dielectric aromatic polyimide is prepared by chemically combining equimolar quantities of an aromatic dianhydride reactant and an aromatic diamine reactant, which are selected so that one reactant contains at least one Si(CH.sub.3).sub.2 group in its molecular structure, and the other reactant contains at least one --CH.sub.3 group in its molecular structure. The reactants are chemically combined in a solvent medium to form a solution of a high molecular weight polyamic acid, which is then converted to the corresponding polyimide.

Comparison between cylindrical and prismatic lithium-ion cell costs using a process based cost model

NASA Astrophysics Data System (ADS)

Ciez, Rebecca E.; Whitacre, J. F.

2017-02-01

The relative size and age of the US electric vehicle market means that a few vehicles are able to drive market-wide trends in the battery chemistries and cell formats on the road today. Three lithium-ion chemistries account for nearly all of the storage capacity, and half of the cells are cylindrical. However, no specific model exists to examine the costs of manufacturing these cylindrical cells. Here we present a process-based cost model tailored to the cylindrical lithium-ion cells currently used in the EV market. We examine the costs for varied cell dimensions, electrode thicknesses, chemistries, and production volumes. Although cost savings are possible from increasing cell dimensions and electrode thicknesses, economies of scale have already been reached, and future cost reductions from increased production volumes are minimal. Prismatic cells, which are able to further capitalize on the cost reduction from larger formats, can offer further reductions than those possible for cylindrical cells.

On the Chemistry of Hydrides of N Atoms and O+ Ions

NASA Astrophysics Data System (ADS)

Awad, Zainab; Viti, Serena; Williams, David A.

2016-08-01

Previous work by various authors has suggested that the detection by Herschel/HIFI of nitrogen hydrides along the low-density lines of sight toward G10.6-0.4 (W31C) cannot be accounted for by gas-phase chemical models. In this paper we investigate the role of surface reactions on dust grains in diffuse regions, and we find that formation of the hydrides by surface reactions on dust grains with efficiency comparable to that for H2 formation reconciles models with observations of nitrogen hydrides. However, similar surface reactions do not contribute significantly to the hydrides of O+ ions detected by Herschel/HIFI that are present along many sight lines in the Galaxy. The O+ hydrides can be accounted for by conventional gas-phase chemistry either in diffuse clouds of very low density with normal cosmic-ray fluxes or in somewhat denser diffuse clouds with high cosmic-ray fluxes. Hydride chemistry in dense dark clouds appears to be dominated by gas-phase ion-molecule reactions.

Roles of Bulk and Surface Chemistry in the Oxygen Exchange Kinetics and Related Properties of Mixed Conducting Perovskite Oxide Electrodes

PubMed Central

Perry, Nicola H.; Ishihara, Tatsumi

2016-01-01

Mixed conducting perovskite oxides and related structures serving as electrodes for electrochemical oxygen incorporation and evolution in solid oxide fuel and electrolysis cells, respectively, play a significant role in determining the cell efficiency and lifetime. Desired improvements in catalytic activity for rapid surface oxygen exchange, fast bulk transport (electronic and ionic), and thermo-chemo-mechanical stability of oxygen electrodes will require increased understanding of the impact of both bulk and surface chemistry on these properties. This review highlights selected work at the International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, set in the context of work in the broader community, aiming to characterize and understand relationships between bulk and surface composition and oxygen electrode performance. Insights into aspects of bulk point defect chemistry, electronic structure, crystal structure, and cation choice that impact carrier concentrations and mobilities, surface exchange kinetics, and chemical expansion coefficients are emerging. At the same time, an understanding of the relationship between bulk and surface chemistry is being developed that may assist design of electrodes with more robust surface chemistries, e.g., impurity tolerance or limited surface segregation. Ion scattering techniques (e.g., secondary ion mass spectrometry, SIMS, or low energy ion scattering spectroscopy, LEIS) with high surface sensitivity and increasing lateral resolution are proving useful for measuring surface exchange kinetics, diffusivity, and corresponding outer monolayer chemistry of electrodes exposed to typical operating conditions. Beyond consideration of chemical composition, the use of strain and/or a high density of active interfaces also show promise for enhancing performance. PMID:28773978

Relationships determining the toxicity of major ion mixtures to Ceriodaphnia dubia

EPA Science Inventory

Significant impacts to aquatic systems can occur due to increases in major ions (Na, K, Ca, Mg, Cl, SO4, HCO3) from various anthropogenic activities, these impacts varying with both the specific combination of ions that are elevated and the chemistry of the background water. A s...

An ICR study of ion-molecule reactions of PH(n)+ ions. [of importance to interstellar chemistry, using ion cyclotron resonance techniques

NASA Technical Reports Server (NTRS)

Thorne, L. R.; Anicich, V. G.; Huntress, W. T.

1983-01-01

The reactions of PH(n)+ ions (n = 0-3) were examined with a number of neutrals using ion-cyclotron-resonance techniques. The reactions examined have significance for the distribution of phosphorus in interstellar molecules. The results indicate that interstellar molecules containing the P-O bond are likely to be more abundant than those containing the P-H bond.

Heavy Ion Formation in Titan's Ionosphere: Magnetospheric Introduction of Free Oxygen and Source of Titan's Aerosols?

NASA Technical Reports Server (NTRS)

Sittler, E. C., Jr.; Hartle, R. E.; Cooper, J. F.; Johnson, R. E.; Coates, A.; dePater, imke; Strom, Daphne; Simoes, F.; Steele, A.; Robb, F.

2007-01-01

With the recent discovery of heavy ions, positive and negative, by the Cassini Plasma Spectrometer (CAPS) instrument in Titan's ionosphere, it reveals new possibilities for aerosol formation at Titan and the introduction of free oxygen to the aerosol chemistry from Saturn's magnetosphere with Enceladus as the primary oxygen source. One can estimate whether the heavy ions in the ionosphere are of sufficient number to account for all the aerosols, under what conditions are favorable for heavy ion formation and how they are introduced as seed particles deeper in Titan's atmosphere where the aerosols form and eventually find themselves on Titan's surface where unknown chemical processes can take place. Finally, what are the possibilities with regard to their chemistry on the surface with some free oxygen present in their seed particles?

Processes regulating watershed chemical export during snowmelt, fraser experimental forest, Colorado

USGS Publications Warehouse

Stottlemyer, R.

2001-01-01

In the Central Rocky Mountains, snowfall dominates precipitation. Airborne contaminants retained in the snowpack can affect high elevation surface water chemistry during snowmelt. At the Fraser Experimental Forest (FEF), located west of the Continental Divide in Central Colorado, snowmelt dominates the annual hydrograph, and accounts for >95% of annual stream water discharge. During the winters of 1989-1993, we measured precipitation inputs, snowpack water equivalent (SWE) and ion content, and stream water chemistry every 7-10 days along a 3150-3500 m elevation gradient in the subalpine and alpine Lexen Creek watershed. The study objectives were to (1) quantify the distribution of SWE and snowpack chemical content with elevation and aspect, (2) quantify snowmelt rates, temperature of soil, snowpack, and air with elevation and aspect, and (3) use change in upstream-downstream water chemistry during snowmelt to better define alpine and subalpine flowpaths. The SWE increased with elevation (P - 3??C) temperatures throughout winter which resulted in significant snowpack ion loss. By snowpack PWE in mid May, the snowpack had lost almost half the cumulative precipitation H+, NH4+, and SO42- inputs and a third of the NO3- input. Windborne soil particulate inputs late in winter increased snowpack base cation content. Variation in subalpine SWE and snowpack ion content with elevation and aspect, and wind redistribution of snowfall in the alpine resulted in large year-to-year differences in the timing and magnitude of SWE, PWE, and snowpack ion content. The alpine stream water ion concentrations changed little during snowmelt indicating meltwater passed quickly through surface porous soils and was well mixed before entering the stream. Conversely, subalpine stream water chemistry was diluted during snowmelt suggesting much melt water moved to the stream as shallow subsurface lateral flow. Published by Elsevier Science B.V.

The inorganic side of chemical biology.

PubMed

Lippard, Stephen J

2006-10-01

Bioinorganic chemistry remains a vibrant discipline at the interface of chemistry and the biological sciences. Metal ions function in numerous metalloenzymes, are incorporated into pharmaceuticals and imaging agents, and inspire the synthesis of catalysts used to achieve many chemical transformations.

Speeding Up Sigmatropic Shifts-To Halve or to Hold.

PubMed

Tantillo, Dean J

2016-04-19

Catalysis is common. Rational catalyst design, however, is at the frontier of chemical science. Although the histories of physical organic and synthetic organic chemistry boast key chapters involving [3s,3s] sigmatropic shifts, catalysis of these reactions is much less common than catalysis of ostensibly more complex processes. The comparative dearth of catalysts for sigmatropic shifts is perhaps a result of the perception that transition state structures for these reactions, like their reactants, are nonpolar and therefore not amenable to selective stabilization and its associated barrier lowering. However, as demonstrated in this Account, transition state structures for [3s,3s] sigmatropic shifts can in fact have charge distributions that differ significantly from those of reactants, even for hydrocarbon substrates, allowing for barriers to be decreased and rates increased. In some cases, differences in charge distribution result from the inclusion of heteroatoms at specific positions in reactants, but in other cases differences are actually induced by catalysts. Perhaps surprisingly, strategies for complexation of transition state structures that remain nonpolar are also possible. In general, the strategies for catalysis employed can be characterized as involving either mechanistic intervention, where a catalyst induces a change from the concerted mechanism expected for a [3s,3s] sigmatropic shift to a multistep process (cutting the transformation into halves or smaller pieces) whose overall barrier is decreased relative to the concerted process, or transition state complexation, where a catalyst simply binds (holds) more tightly to the transition state structure for a [3s,3s] sigmatropic shift than to the reactant, leading to a lower barrier in the presence of the catalyst. Both of these strategies can be considered to be biomimetic in that enzymes frequently induce multistep processes and utilize selective transition state stabilization for the steps involved. In addition, transition state complexation was the principle around which catalytic antibodies were originally designed. The field of catalysis of sigmatropic shifts is now ready for rational design. The studies described here all provide evidence for the origins of rate acceleration, derived in large part from the results of quantum chemical calculations, that can now be applied to the design of new catalysts for [3s,3s] and other sigmatropic shifts.

Design of biomimetic catalysts by molecular imprinting in synthetic polymers: the role of transition state stabilization.

PubMed

Wulff, Günter; Liu, Junqiu

2012-02-21

The impressive efficiency and selectivity of biological catalysts has engendered a long-standing effort to understand the details of enzyme action. It is widely accepted that enzymes accelerate reactions through their steric and electronic complementarity to the reactants in the rate-determining transition states. Thus, tight binding to the transition state of a reactant (rather than to the corresponding substrate) lowers the activation energy of the reaction, providing strong catalytic activity. Debates concerning the fundamentals of enzyme catalysis continue, however, and non-natural enzyme mimics offer important additional insight in this area. Molecular structures that mimic enzymes through the design of a predetermined binding site that stabilizes the transition state of a desired reaction are invaluable in this regard. Catalytic antibodies, which can be quite active when raised against stable transition state analogues of the corresponding reaction, represent particularly successful examples. Recently, synthetic chemistry has begun to match nature's ability to produce antibody-like binding sites with high affinities for the transition state. Thus, synthetic, molecularly imprinted polymers have been engineered to provide enzyme-like specificity and activity, and they now represent a powerful tool for creating highly efficient catalysts. In this Account, we review recent efforts to develop enzyme models through the concept of transition state stabilization. In particular, models for carboxypeptidase A were prepared through the molecular imprinting of synthetic polymers. On the basis of successful experiments with phosphonic esters as templates to arrange amidinium groups in the active site, the method was further improved by combining the concept of transition state stabilization with the introduction of special catalytic moieties, such as metal ions in a defined orientation in the active site. In this way, the imprinted polymers were able to provide both an electrostatic stabilization for the transition state through the amidinium group as well as a synergism of transition state recognition and metal ion catalysis. The result was an excellent catalyst for carbonate hydrolysis. These enzyme mimics represent the most active catalysts ever prepared through the molecular imprinting strategy. Their catalytic activity, catalytic efficiency, and catalytic proficiency clearly surpass those of the corresponding catalytic antibodies. The active structures in natural enzymes evolve within soluble proteins, typically by the refining of the folding of one polypeptide chain. To incorporate these characteristics into synthetic polymers, we used the concept of transition state stabilization to develop soluble, nanosized carboxypeptidase A models using a new polymerization method we term the "post-dilution polymerization method". With this methodology, we were able to prepare soluble, highly cross-linked, single-molecule nanoparticles. These particles have controlled molecular weights (39 kDa, for example) and, on average, one catalytically active site per particle. Our strategies have made it possible to obtain efficient new enzyme models and further advance the structural and functional analogy with natural enzymes. Moreover, this bioinspired design based on molecular imprinting in synthetic polymers offers further support for the concept of transition state stabilization in catalysis.

Streamwater chemistry and nutrient budgets for forested watersheds in New England: variability and management implications

Treesearch

J.W. Hornbeck; S.W. Bailey; D.C. Buso; J.B. Shanley

1997-01-01

Chemistry of precipitation and streamwater and resulting input-output budgets for nutrient ions were determined concurrently for three years on three upland, forested watersheds located within an 80 km radius in central New England. Chemistry of precipitation and inputs of nutrients via wet deposition were similar among the three watersheds and were generally typical...

Effect of thermal expansion on the stability of two-reactant flames

NASA Technical Reports Server (NTRS)

Jackson, T. L.

1986-01-01

The full problem of flame stability for the two-reactant model, which takes into account thermal expansion effects for all disturbance wave lengths, is examined. It is found that the stability problem for the class of two-reactant flames is equivalent to the stability problem for the class of one-reactant flames with an appropriate interpretation of Lewis numbers.

Apparatus and method for depositing coating onto porous substrate

DOEpatents

Isenberg, Arnold O.; Zymboly, Gregory E.

1986-01-01

Disclosed is an apparatus for forming a chemically vapor deposited coating on a porous substrate where oxygen from a first gaseous reactant containing a source of oxygen permeates through the pores of the substrate to react with a second gaseous reactant that is present on the other side of the substrate. The apparatus includes means for controlling the pressure and flow rate of each gaseous reactant, a manometer for measuring the difference in pressure between the gaseous reactants on each side of the substrate, and means for changing the difference in pressure between the gaseous reactants. Also disclosed is a method of detecting and closing cracks in the coating by reducing the pressure difference between the two gaseous reactants whenever the pressure difference falls suddenly after gradually rising, then again increasing the pressure difference on the two gases. The attack by the by-products of the reaction on the substrate are reduced by maintaining the flow rate of the first reactant through the pores of the substrate.

A facile approach toward transition metal oxide hierarchical structures and their lithium storage properties.

PubMed

Zhang, Cuimiao; Chen, Jing; Zeng, Yi; Rui, Xianhong; Zhu, Jixin; Zhang, Wenyu; Xu, Chen; Lim, Tuti Mariana; Hng, Huey Hoon; Yan, Qingyu

2012-06-21

A simple, non-template, non-surfactant and environmentally friendly hydrothermal method is presented based on the controlled release of the reactants into the reaction solvents to induce slow nucleation and growth of three-dimensional hierarchical nanostructures of transition metal oxides. This method is a general approach, which can be used to prepare Co(3)O(4), CuO, and Ni(OH)(2)/NiO. These metal oxides with hierarchical nanostructures can be used as anode materials for lithium-ion batteries with good Li storage performance, e.g. high specific capacities and stable cyclability.

The Generation of Dehydroalanine Residues in Protonated Polypeptides: Ion/Ion Reactions for Introducing Selective Cleavages

NASA Astrophysics Data System (ADS)

Peng, Zhou; Bu, Jiexun; McLuckey, Scott A.

2017-09-01

We examine a gas-phase approach for converting a subset of amino acid residues in polypeptide cations to dehydroalanine (Dha). Subsequent activation of the modified polypeptide ions gives rise to specific cleavage N-terminal to the Dha residue. This process allows for the incorporation of selective cleavages in the structural characterization of polypeptide ions. An ion/ion reaction within the mass spectrometer between a multiply protonated polypeptide and the sulfate radical anion introduces a radical site into the multiply protonated polypeptide reactant. Subsequent collisional activation of the polypeptide radical cation gives rise to radical side chain loss from one of several particular amino acid side chains (e.g., leucine, asparagine, lysine, glutamine, and glutamic acid) to yield a Dha residue. The Dha residues facilitate preferential backbone cleavages to produce signature c- and z-ions, demonstrated with cations derived from melittin, mechano growth factor (MGF), and ubiquitin. The efficiencies for radical side chain loss and for subsequent generation of specific c- and z-ions have been examined as functions of precursor ion charge state and activation conditions using cations of ubiquitin as a model for a small protein. It is noted that these efficiencies are not strongly dependent on ion trap collisional activation conditions but are sensitive to precursor ion charge state. Moderate to low charge states show the greatest overall yields for the specific Dha cleavages, whereas small molecule losses (e.g., water/ammonia) dominate at the lowest charge states and proton catalyzed amide bond cleavages that give rise to b- and y-ions tend to dominate at high charge states. [Figure not available: see fulltext.

A new approach in dry technology for non-degrading optical and EUV mask cleaning

NASA Astrophysics Data System (ADS)

Varghese, Ivin; Smith, Ben; Balooch, Mehdi; Bowers, Chuck

2012-11-01

The Eco-Snow Systems group of RAVE N.P., Inc. has developed a new cleaning technique to target several of the advanced and next generation mask clean challenges. This new technique, especially when combined with Eco-Snow Systems cryogenic CO2 cleaning technology, provides several advantages over existing methods because it: 1) is solely based on dry technique without requiring additional complementary aggressive wet chemistries that degrade the mask, 2) operates at atmospheric pressure and therefore avoids expensive and complicated equipment associated with vacuum systems, 3) generates ultra-clean reactants eliminating possible byproduct adders, 4) can be applied locally for site specific cleaning without exposing the rest of the mask or can be used to clean the entire mask, 5) removes organic as well as inorganic particulates and film contaminations, and 6) complements current techniques utilized for cleaning of advanced masks such as reduced chemistry wet cleans. In this paper, we shall present examples demonstrating the capability of this new technique for removal of pellicle glue residues and for critical removal of carbon contamination on EUV masks.

Impact constraints on the environment for chemical evolution and the continuity of life

NASA Technical Reports Server (NTRS)

Oberbeck, Verne R.; Fogleman, Guy

1990-01-01

The moon and the earth were bombarded heavily by planetesimals and asteroids that were capable of interfering with chemical evolution and the origin of life. This paper explores the frequency of giant terrestrial impacts able to stop prebiotic chemistry in the probable regions of chemical evolution. The limited time available between impacts disruptive to prebiotic chemistry at the time of the oldest evidence of life suggests the need for a rapid process for chemical evolution of life. On the other hand, rapid chemical evolution in cloud systems and lakes or other shallow evaporating water bodies would have been possible because reactants could have been concentrated and polymerized rapidly in this environment. Thus life probably could have originated near the surface between frequent surface-sterilizing impacts. There may not have been continuity of life depending on sunlight because there is evidence that life, existing as early as 3.8 Gyr ago, may have been destroyed by giant impacts. The first such organisms on earth were probably not the ancestors of present life.

Gold surfaces and nanoparticles are protected by Au(0)-thiyl species and are destroyed when Au(I)-thiolates form.

PubMed

Reimers, Jeffrey R; Ford, Michael J; Halder, Arnab; Ulstrup, Jens; Hush, Noel S

2016-03-15

The synthetic chemistry and spectroscopy of sulfur-protected gold surfaces and nanoparticles is analyzed, indicating that the electronic structure of the interface is Au(0)-thiyl, with Au(I)-thiolates identified as high-energy excited surface states. Density-functional theory indicates that it is the noble character of gold and nanoparticle surfaces that destabilizes Au(I)-thiolates. Bonding results from large van der Waals forces, influenced by covalent bonding induced through s-d hybridization and charge polarization effects that perturbatively mix in some Au(I)-thiolate character. A simple method for quantifying these contributions is presented, revealing that a driving force for nanoparticle growth is nobleization, minimizing Au(I)-thiolate involvement. Predictions that Brust-Schiffrin reactions involve thiolate anion intermediates are verified spectroscopically, establishing a key feature needed to understand nanoparticle growth. Mixing of preprepared Au(I) and thiolate reactants always produces Au(I)-thiolate thin films or compounds rather than monolayers. Smooth links to O, Se, Te, C, and N linker chemistry are established.

Gold surfaces and nanoparticles are protected by Au(0)–thiyl species and are destroyed when Au(I)–thiolates form

PubMed Central

Reimers, Jeffrey R.; Ford, Michael J.; Halder, Arnab; Ulstrup, Jens; Hush, Noel S.

2016-01-01

The synthetic chemistry and spectroscopy of sulfur-protected gold surfaces and nanoparticles is analyzed, indicating that the electronic structure of the interface is Au(0)–thiyl, with Au(I)–thiolates identified as high-energy excited surface states. Density-functional theory indicates that it is the noble character of gold and nanoparticle surfaces that destabilizes Au(I)–thiolates. Bonding results from large van der Waals forces, influenced by covalent bonding induced through s–d hybridization and charge polarization effects that perturbatively mix in some Au(I)–thiolate character. A simple method for quantifying these contributions is presented, revealing that a driving force for nanoparticle growth is nobleization, minimizing Au(I)–thiolate involvement. Predictions that Brust–Schiffrin reactions involve thiolate anion intermediates are verified spectroscopically, establishing a key feature needed to understand nanoparticle growth. Mixing of preprepared Au(I) and thiolate reactants always produces Au(I)–thiolate thin films or compounds rather than monolayers. Smooth links to O, Se, Te, C, and N linker chemistry are established. PMID:26929334

3D-Printing inside the Glovebox: A Versatile Tool for Inert-Gas Chemistry Combined with Spectroscopy.

PubMed

Lederle, Felix; Kaldun, Christian; Namyslo, Jan C; Hübner, Eike G

2016-04-01

3D-Printing with the well-established 'Fused Deposition Modeling' technology was used to print totally gas-tight reaction vessels, combined with printed cuvettes, inside the inert-gas atmosphere of a glovebox. During pauses of the print, the reaction flasks out of acrylonitrile butadiene styrene were filled with various reactants. After the basic test reactions to proof the oxygen tightness and investigations of the influence of printing within an inert-gas atmosphere, scope and limitations of the method are presented by syntheses of new compounds with highly reactive reagents, such as trimethylaluminium, and reaction monitoring via UV/VIS, IR, and NMR spectroscopy. The applicable temperature range, the choice of solvents, the reaction times, and the analytical methods have been investigated in detail. A set of reaction flasks is presented, which allow routine inert-gas syntheses and combined spectroscopy without modifications of the glovebox, the 3D-printer, or the spectrometers. Overall, this demonstrates the potential of 3D-printed reaction cuvettes to become a complementary standard method in inert-gas chemistry.

Molecular processes in a high temperature shock layer

NASA Technical Reports Server (NTRS)

Guberman, S. L.

1984-01-01

Models of the shock layer encountered by an Aeroassisted Orbital Transfer Vehicle require as input accurate cross sections and rate constants for the atomic and molecular processes that characterize the shock radiation. From the estimated atomic and molecular densities in the shock layer and the expected residence time of 1 m/s, it can be expected that electron-ion collision processes will be important in the shock model. Electron capture by molecular ions followed by dissociation, e.g., O2(+) + e(-) yields 0 + 0, can be expected to be of major importance since these processes are known to have high rates (e.g., 10 to the -7th power cu/cm/sec) at room temperature. However, there have been no experimental measurements of dissociative recombination (DR) at temperatures ( 12000K) that are expected to characterize the shock layer. Indeed, even at room temperature, it is often difficult to perform experiments that determine the dependence of the translational energy and quantum yields of the product atoms on the electronic and vibrational state of the reactant molecular ions. Presented are ab initio quantum chemical studies of DR for molecular ions that are likely to be important in the atmospheric shock layer.

Chemistry Notes

ERIC Educational Resources Information Center

School Science Review, 1972

1972-01-01

Short articles on the kinetics of the hydrogen peroxide-iodide ion reaction, simulation of fluidization catalysis, the use of Newman projection diagrams to represent steric relationships in organic chemistry, the use of synthetic substrates for proteolytic enzyme reactions, and two simple clock reactions"--hydrolysis of halogenoalkanes and…

Chemistry Notes

ERIC Educational Resources Information Center

School Science Review, 1976

1976-01-01

Describes several chemistry projects, including solubility, formula for magnesium oxide, dissociation of dinitrogen tetroxide, use of 1-chloro-2, 4-dinitrobenzene, migration of ions, heats of neutralizations, use of pocket calculators, sonic cleaning, oxidation states of manganese, and cell potentials. Includes an extract from Chemical Age on…

Protons and Hydroxide Ions in Aqueous Systems.

PubMed

Agmon, Noam; Bakker, Huib J; Campen, R Kramer; Henchman, Richard H; Pohl, Peter; Roke, Sylvie; Thämer, Martin; Hassanali, Ali

2016-07-13

Understanding the structure and dynamics of water's constituent ions, proton and hydroxide, has been a subject of numerous experimental and theoretical studies over the last century. Besides their obvious importance in acid-base chemistry, these ions play an important role in numerous applications ranging from enzyme catalysis to environmental chemistry. Despite a long history of research, many fundamental issues regarding their properties continue to be an active area of research. Here, we provide a review of the experimental and theoretical advances made in the last several decades in understanding the structure, dynamics, and transport of the proton and hydroxide ions in different aqueous environments, ranging from water clusters to the bulk liquid and its interfaces with hydrophobic surfaces. The propensity of these ions to accumulate at hydrophobic surfaces has been a subject of intense debate, and we highlight the open issues and challenges in this area. Biological applications reviewed include proton transport along the hydration layer of various membranes and through channel proteins, problems that are at the core of cellular bioenergetics.

Are clusters important in understanding the mechanisms in atmospheric pressure ionization? Part 1: Reagent ion generation and chemical control of ion populations.

PubMed

Klee, Sonja; Derpmann, Valerie; Wißdorf, Walter; Klopotowski, Sebastian; Kersten, Hendrik; Brockmann, Klaus J; Benter, Thorsten; Albrecht, Sascha; Bruins, Andries P; Dousty, Faezeh; Kauppila, Tiina J; Kostiainen, Risto; O'Brien, Rob; Robb, Damon B; Syage, Jack A

2014-08-01

It is well documented since the early days of the development of atmospheric pressure ionization methods, which operate in the gas phase, that cluster ions are ubiquitous. This holds true for atmospheric pressure chemical ionization, as well as for more recent techniques, such as atmospheric pressure photoionization, direct analysis in real time, and many more. In fact, it is well established that cluster ions are the primary carriers of the net charge generated. Nevertheless, cluster ion chemistry has only been sporadically included in the numerous proposed ionization mechanisms leading to charged target analytes, which are often protonated molecules. This paper series, consisting of two parts, attempts to highlight the role of cluster ion chemistry with regard to the generation of analyte ions. In addition, the impact of the changing reaction matrix and the non-thermal collisions of ions en route from the atmospheric pressure ion source to the high vacuum analyzer region are discussed. This work addresses such issues as extent of protonation versus deuteration, the extent of analyte fragmentation, as well as highly variable ionization efficiencies, among others. In Part 1, the nature of the reagent ion generation is examined, as well as the extent of thermodynamic versus kinetic control of the resulting ion population entering the analyzer region.

Exciplex formation in bimolecular photoinduced electron-transfer investigated by ultrafast time-resolved infrared spectroscopy.

PubMed

Koch, Marius; Letrun, Romain; Vauthey, Eric

2014-03-12

The dynamics of bimolecular photoinduced electron-transfer reactions has been investigated with three donor/acceptor (D/A) pairs in tetrahydrofuran (THF) and acetonitrile (ACN) using a combination of ultrafast spectroscopic techniques, including time-resolved infrared absorption. For the D/A pairs with the highest driving force of electron transfer, all transient spectroscopic features can be unambiguously assigned to the excited reactant and the ionic products. For the pair with the lowest driving force, three additional transient infrared bands, more intense in THF than in ACN, with a time dependence that differs from those of the other bands are observed. From their frequency and solvent dependence, these bands can be assigned to an exciplex. Moreover, polarization-resolved measurements point to a relatively well-defined mutual orientation of the constituents and to a slower reorientational time compared to those of the individual reactants. Thanks to the minimal overlap of the infrared signature of all transient species in THF, a detailed reaction scheme including the relevant kinetic and thermodynamic parameters could be deduced for this pair. This analysis reveals that the formation and recombination of the ion pair occur almost exclusively via the exciplex.

Synthesis of Fe3O4@nickel-silicate core-shell nanoparticles for His-tagged enzyme immobilizing agents

NASA Astrophysics Data System (ADS)

Shin, Moo-Kwang; Kang, Byunghoon; Yoon, Nam-Kyung; Kim, Myeong-Hoon; Ki, Jisun; Han, Seungmin; Ahn, Jung-Oh; Haam, Seungjoo

2016-12-01

Immobilizing enzymes on artificially fabricated carriers for their efficient use and easy removal from reactants has attracted enormous interest for decades. Specifically, binding platforms using inorganic nanoparticles have been widely explored because of the benefits of their large surface area, easy surface modification, and high stability in various pH and temperatures. Herein, we fabricated Fe3O4 encapsulated ‘sea-urchin’ shaped nickel-silicate nanoparticles with a facile synthetic route. The enzymes were then rapidly and easily immobilized with poly-histidine tags (His-tags) and nickel ion affinity. Porous nickel silicate covered nanoparticles achieved a high immobilization capacity (85 μg mg-1) of His-tagged tobacco etch virus (TEV) protease. To investigate immobilized TEV protease enzymatic activity, we analyzed the cleaved quantity of maltose binding protein-exendin-fused immunoglobulin fusion protein, which connected with the TEV protease-specific cleavage peptide sequence. Moreover, TEV protease immobilized nanocomplexes conveniently removed and recollected from the reactant by applying an external magnetic field, maintained their enzymatic activity after reuse. Therefore, our newly developed nanoplatform for His-tagged enzyme immobilization provides advantageous features for biotechnological industries including recombinant protein processing.

A cluster ion chemistry for the mesospheric sodium layer

NASA Technical Reports Server (NTRS)

Richter, E. S.; Sechrist, C. F., Jr.

1979-01-01

A cluster ion chemistry for sodium is developed which relates the Na(+) profile to the Na profile using reactions involving Na(+).N2, Na(+).CO2, and Na(+).H2O. Removal of sodium from the mesosphere is accomplished by the formation of higher order clusters of the form Na(+).(H2O)n which presumably precipitate to the lower atmosphere. This sink is most effective in the 80-85 km altitude range. The chemical equilibrium model is applied to experimental observations of the Na and Na(+) layers.

Dehydration Polymerization for Poly(hetero)arene Conjugated Polymers.

PubMed

Mirabal, Rafael A; Vanderzwet, Luke; Abuadas, Sara; Emmett, Michael R; Schipper, Derek

2018-02-18

The lack of scalable and sustainable methods to prepare conjugated polymers belies their importance in many enabling technologies. Accessing high-performance poly(hetero)arene conjugated polymers by dehydration has remained an unsolved problem in synthetic chemistry and has historically required transitional-metal coupling reactions. Herein, we report a dehydration method that allows access to conjugated heterocyclic materials. By using the technique, we have prepared a series of small molecules and polymers. The reaction avoids using transition metals, proceeds at room temperature, the only required reactant is a simple base and water is the sole by-product. The dehydration reaction is technically simple and provides a sustainable and straightforward method to prepare conjugated heteroarene motifs. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Venusian atmospheric equilibrium chemistry at the Pioneer Venus anomalous event altitude

NASA Technical Reports Server (NTRS)

Craig, Roger A.

1994-01-01

No convincing explanation for the anomalous behavior of the Atmospheric Structure Experiment temperature sensors at approximately 13 km altitude has been found. It occurred on all of the widely-spaced probes, in a similar fashion. A preliminary effort has been made to determine atmospheric chemical species which might be present at 13 km. The purpose of this effort is to initiate suggestions of possible chemical interactions and to explore the effects of the presence of possible metal reactants including condensation. Equilibrium fractions of chemical species were calculated at a variety of conditions. Baseline calculations were made for the altitudes near 13 km. For comparison calculations were also made at 13 km but with the introduction of plausible metal atoms.

A coordination chemistry study of hydrated and solvated cationic vanadium ions in oxidation states +III, +IV, and +V in solution and solid state

PubMed Central

Krakowiak, Joanna; Lundberg, Daniel

2012-01-01

The coordination chemistry of hydrated and solvated vanadium(III), oxovanadium(IV), and dioxovanadium(V) ions in the oxygen donor solvents water, dimethylsulfoxide (dmso) and N,N′-dimethylpropyleneurea (dmpu) has been studied in solution by EXAFS and large angle X-ray scattering (LAXS) and in solid state by single crystal X-ray diffraction and EXAFS. The hydrated vanadium(III) ion has a regular octahedral configuration with a mean V-O bond distance of 1.99 Å. In the hydrated and dimethylsulfoxide solvated oxovanadium(IV) ions vanadium binds strongly to an oxo group at ca. 1.6 Å. The solvent molecule trans to the oxo group is very weakly bound, at ca. 2.2 Å, while the remaining four solvent molecules, with a mean V-O bond distance of 2.0 Å, form a plane slightly below the vanadium atom; the mean O=V-Operp bond angle is ca. 98°. In the dmpu solvated oxovanadium(IV) ion, the space demanding properties of the dmpu molecule leaving no solvent molecule in the trans position to the oxo group which reduces the coordination number to 5. The O=V-O bond angle is consequently much larger, 106°, and the mean V=O and V-O bond distances decrease to 1.58 and 1.97 Å, respectively. The hydrated and dimethylsulfoxide solvated dioxovanadium(V) ions display a very distorted octahedral configuration with the oxo groups in cis position with mean V=O bond distances of 1.6 Å and a O=V=O bond angle of ca. 105°. The solvent molecules trans to the oxo groups are weakly bound, at ca. 2.2 Å, while the remaining two have bond distances of 2.02 Å. The experimental studies of the coordination chemistry of hydrated and solvated vanadium(III,IV,V) ions are complemented by summarizing previously reported crystal structures to yield a comprehensive description of the coordination chemistry of vanadium with oxygen donor ligands. PMID:22950803

Nuclear chemistry. Annual report, 1974

DOE Office of Scientific and Technical Information (OSTI.GOV)

Conzett, H.E.; Edelstein, N.M.; Tsang, C.F.

1975-07-01

The 1974 Nuclear Chemistry Annual Report contains information on research in the following areas: nuclear science (nuclear spectroscopy and radioactivity, nuclear reactions and scattering, nuclear theory); chemical and atomic physics (heavy ion-induced atomic reactions, atomic and molecular spectroscopy, photoelectron spectroscopy and hyperfine interactions); physical, inorganic, and analytical chemistry (x-ray crystallography, physical and inorganic chemistry, geochemistry); and instrumentation. Thesis abstracts, 1974 publication titles, and an author index are also included. Papers having a significant amount of information are listed separately by title. (RWR)

Simulating Dynamic Equilibria: A Class Experiment

NASA Astrophysics Data System (ADS)

Harrison, John A.; Buckley, Paul D.

2000-08-01

A first-order reversible reaction is simulated on an overhead projector using small coins or discs. A simulation is carried out in which initially there are 24 discs representing reactant A and none representing reactant B. At the end of each minute half of the reactant A discs get converted to reactant B, and one quarter of the reactant B discs get converted to reactant A discs. Equilibrium is established with 8 A discs and 16 B discs, and no further net change is observed as the simulation continues. Another simulation beginning with 48 A discs and 0 B discs leads at equilibrium to 16 A discs and 32 B discs. These results illustrate how dynamic equilibria are established and allow the introduction of the concept of an equilibrium constant. Le Châtelier's principle is illustrated by further simulations.

Investigations on the photoreactions of phenothiazine and phenoxazine in presence of 9-cyanoanthracene by using steady state and time resolved spectroscopic techniques.

PubMed

Bardhan, Munmun; Mandal, Paulami; Tzeng, Wen-Bih; Ganguly, Tapan

2010-09-01

By using electrochemical, steady state and time resolved (fluorescence lifetime and transient absorption) spectroscopic techniques, detailed investigations were made to reveal the mechanisms of charge separation or forward electron transfer reactions within the electron donor phenothiazine (PTZH) or phenoxazine (PXZH) and well known electron acceptor 9-cyanoanthracene (CNA). The transient absorption spectra suggest that the charge separated species formed in the excited singlet state resulted from intermolecular photoinduced electron transfer reactions within the donor PTZH (or PXZH) and CNA acceptor relaxes to the corresponding triplet state. Though alternative mechanisms of via formations of contact neutral radical by H-transfer reaction have been proposed but the observed results obtained from the time resolved measurements indicate that the regeneration of ground state reactants is primarily responsible due to direct recombination of triplet contact ion-pair (CIP) or solvent-separated ion-pair (SSIP).

Interface confined hydrogen evolution reaction in zero valent metal nanoparticles-intercalated molybdenum disulfide

PubMed Central

Chen, Zhongxin; Leng, Kai; Zhao, Xiaoxu; Malkhandi, Souradip; Tang, Wei; Tian, Bingbing; Dong, Lei; Zheng, Lirong; Lin, Ming; Yeo, Boon Siang; Loh, Kian Ping

2017-01-01

Interface confined reactions, which can modulate the bonding of reactants with catalytic centres and influence the rate of the mass transport from bulk solution, have emerged as a viable strategy for achieving highly stable and selective catalysis. Here we demonstrate that 1T′-enriched lithiated molybdenum disulfide is a highly powerful reducing agent, which can be exploited for the in-situ reduction of metal ions within the inner planes of lithiated molybdenum disulfide to form a zero valent metal-intercalated molybdenum disulfide. The confinement of platinum nanoparticles within the molybdenum disulfide layered structure leads to enhanced hydrogen evolution reaction activity and stability compared to catalysts dispersed on carbon support. In particular, the inner platinum surface is accessible to charged species like proton and metal ions, while blocking poisoning by larger sized pollutants or neutral molecules. This points a way forward for using bulk intercalated compounds for energy related applications. PMID:28230105

Pure rhombohedral Bi1-x EuxPO4 nano-/micro-structures: fast synthesis, shape evolution and luminescence properties.

PubMed

Yu, Dongyan; Liang, Yujun; Zhang, Mengfei; Li, Guogang; Yan, Chunjie

2016-02-01

BiPO4 and Eu-doped BiPO4 crystals were synthesized via a simple precipitation route at room temperature, employing Bi(NO3)3 and (NH4)2HPO4 as the reactants, Eu2O3 as the dopant and citric acid as a template. X-ray powder diffraction analyses showed that pure rhombohedral BiPO4 form was obtained, and was the preferential orientation growth of the crystal. Field emission scanning electron microscope observations showed that the concentration of Bi(3+) obviously changed the products' morphologies from nanosphere, hollow sphere to hexagonal prism. The acidity of the solution and the contents of citric acid and Eu(3+) ion tailored the size of the final crystals. Effects of concentration of Eu(3+) ion on the luminescence emission intensity were also investigated. Copyright © 2015 John Wiley & Sons, Ltd.

Investigation of the graphene-electrolyte interface in Li-air batteries: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Pavlov, S. V.; Kislenko, S. A.

2018-01-01

In this work the behavior of the main reactants (Li+, O2) of the oxygen reduction reaction (ORR) in acetonitrile solvent near the multi-layer graphene edge has been studied. It was observed by molecular dynamics simulations that the concentration distributions of the Li+ and O2 represent a “chessboard” structure. It was ascertained that the concentrations of the lithium ions and oxygen molecules reach their maximum values near the graphene edges pushed out from the surface, which may act as nucleation centers for the formation of crystalline products of the ORR. The maps of the free energy were estimated for the Li+ and O2. Energy optimal trajectories for the adsorption of oxygen molecules and lithium ions were found. Moreover, the distributions of the electric potential were obtained near the following carbon surfaces: single- and multi-layer graphene edge, graphene plane, which shows the qualitative differences in the double-layer structure.

Thermonuclear Reaction Rate of T(t,2n) α Measured in ICF Plasmas

NASA Astrophysics Data System (ADS)

Brune, C. R.; Casey, D. T.; Caggiano, J. A.; Hatarik, R.; McNabb, D. P.; Sayre, D. B.; Smalyuk, V. A.; Bacher, A. D.; Frenje, J. A.; Gatu-Johnson, M.; Zylstra, A. B.; Couder, M.

2014-09-01

Measurements of charged-particle reactivity have been performed in inertial confinement fusion experiments at the National Ignition Facility. Time-of-flight detectors were used to measure neutrons from the T(t,2n) and T(d,n) reactions produced by implosions with tritium-filled targets (0.1% deuterium). Along with the measured target fuel composition and reactant ion temperature, the well-known T(d,n) reactivity was used to convert the measured neutron yields into a T(t,2n) reactivity. The ion temperature was determined to be 3.3(3) keV, corresponding to an effective energy of 16 keV. In comparison to accelerator measurements of the low-energy T(t,2n) cross section, the source of all previous data, our experiment has resulted in T(t,2n) data with better statistics and lower backgrounds.

The Role of Oxygen in the Formation of TNT Product Ions in Ion Mobility Spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daum, Keith Alvin; Atkinson, David Alan; Ewing, Robert Gordon

2002-03-01

The atmospheric pressure ionization of 2,4,6-trinitrotoluene (TNT) in air yields the (TNT-H)- product ion. It is generally accepted that this product ion is formed by the direct proton abstraction of neutral TNT by O2- reactant ions. Data presented here demonstrate the reaction involves the formation of an intermediate (TNT·O2)-, from the association of either TNT+O2- or TNT-+O2. This intermediate has two subsequent reaction branches. One of these branches involves simple dissociation of the intermediate to TNT-; the other branch is a terminal reaction that forms the typically observed (TNT-H)- ion via proton abstraction. The dissociation reaction involving electron transfer tomore » TNT- appeared to be kinetically favored and prevailed at low concentrations of oxygen (less than 2%). The presence of significant amounts of oxygen, however, resulted in the predominant formation of the (TNT-H)- ion by the terminal reaction branch. With TNT- in the system, either from direct electron attachment or by simple dissociation of the intermediate, increasing levels of oxygen in the system will continue to reform the intermediate, allowing the cycle to continue until proton abstraction occurs. Key to understanding this complex reaction pathway is that O2- was observed to transfer an electron directly to neutral TNT to form the TNT-. At oxygen levels of less than 2%, the TNT- ion intensity increased with increasing levels of oxygen (and O2-) and was larger than the (TNT-H)- ion intensity. As the oxygen level increased from 2 to 10%, the (TNT-H)- product ion became predominant. The potential reaction mechanisms were investigated with an ion mobility spectrometer, which was configured to independently evaluate the ionization pathways.« less

Influence of Microheterogeneous Environments of Sodium Dodecyl Sulfate on the Kinetics of Oxidation of l-Serine by Chloro and Chlorohydroxo Complexes of Gold(III).

PubMed

Maiti, Krishnendu; Sen, Pratik K; Barik, Anil K; Pal, Biswajit

2018-06-21

The oxidation of l-serine by chloro and chlorohydroxo complexes of gold(III) was spectrophotometrically investigated in acidic buffer media in the absence and presence of the anionic surfactant sodium dodecyl sulfate (SDS). The oxidation rate decreases with increase in either [H + ] or [Cl - ]. Gold(III) complex species react with the zwitterionic form of serine to yield acetaldehyde (principal reaction product) through oxidative decarboxylation and subsequent deamination processes. A reaction pathway involving one electron transfer from serine to Au(III) followed by homolytic cleavage of α-C-C bond with the concomitant formation of iminic cation intermediate has been proposed where Au(III) is initially reduced to Au(II). The surfactant in the submicellar region exhibits a catalytic effect on the reaction rate at [SDS] ≤ 4 mM; however, in the postmicellar region an inhibitory effect was prominent at [SDS] ≥ 4 mM. The catalytic effect below the critical micelle concentration (cmc) may be attributable to the electrostatic attraction between serine and SDS that, in turn, enhances the nucleophilicity of the carboxylate ion of the amino acid. The inhibition effect beyond cmc has been explained by considering the distribution of the reactant species between the aqueous and the micellar pseudophases that restricts the close association of the reactant species. The thermodynamic parameters Δ H 0 and Δ S 0 associated with the binding between serine and SDS micelle were calculated to be -14.4 ± 2 kJ mol -1 and -6.3 ± 0.5 J K -1 mol -1 , respectively. Water structure rearrangement and micelle-substrate binding play instrumental roles during the transfer of the reactant species from aqueous to micellar pseudophase.

Effect of the calcium to phosphorus ratio on the setting properties of calcium phosphate bone cements.

PubMed

Vlad, M D; Gómez, S; Barracó, M; López, J; Fernández, E

2012-09-01

α-Tricalcium phosphate (α-TCP) has become the main reactant of most experimental and commercial ceramic bone cements. It has calcium-to-phosphorus (Ca/P) ratio of 1.50. The present study expands and reports on the microstructures and mechanical properties of calcium phosphate (CP) cements containing sintered monolithic reactants obtained in the interval 1.29 < Ca/P < 1.77. The study focuses on their cement setting and hardening properties as well as on their microstructure and crystal phase evolution. The results showed that: (a) CP-cements made with reactants with Ca/P ratio other than 1.50 have longer setting and lower hardening properties; (b) CP-cements reactivity was clearly affected by the Ca/P ratio of the starting reactant; (c) reactants with Ca/P < 1.50 were composed of several phases, calcium pyrophosphate and α- and β-TCP. Similarly, reactants with Ca/P > 1.50 were composed of α-TCP, tetracalcium phosphate and hydroxyapatite; (d) only the reactant with Ca/P = 1.50 was monophasic and was made of α-TCP, which transformed during the setting into calcium deficient hydroxyapatite; (e) CP-cements developed different crystal microstructures with specific features depending on the Ca/P ratio of the starting reactant.

Improvement in ionization efficiency of direct analysis in real time-mass spectrometry (DART-MS) by corona discharge.

PubMed

Sekimoto, Kanako; Sakakura, Motoshi; Kawamukai, Takatomo; Hike, Hiroshi; Shiota, Teruhisa; Usui, Fumihiko; Bando, Yasuhiko; Takayama, Mitsuo

2016-08-02

Herein it is shown that a combination of direct analysis in real time (DART) with a corona discharge system consisting of only a needle electrode easily improves DART ionization efficiency. Positive and negative DC corona discharges led to a formation of abundant excited helium atoms as well as the reactant ions H3O(+)(H2O)n and O2˙(-) in the DART analyte ionization area. These phenomena resulted in an increase in the absolute intensities of (de)protonated analytes by a factor of 2-20 over conventional DART. The other analyte ions detected in this corona-DART system (i.e., molecular ions, fragment ions, oxygenated (de)protonated analytes, dehydrogenated deprotonated analytes, and negative ion adducts) were quite similar to those obtained from DART alone. This indicates a lack of side reactions due to the corona discharge. The change in the relative intensities of individual analyte-related ions due to the combination of a corona discharge system with DART suggests that there is no effect of the abundant excited helium in the analyte ionization area on the fragmentation processes or enhancement of oxidation due to hydroxyl radicals HO˙. Furthermore, it was found that the corona-DART combination can be applied to the highly sensitive analysis of n-alkanes, in which the alkanes are ionized as positive ions via hydride abstraction and oxidation, independent of the type of alkane or the mass spectrometer used.

Sensitivity of Ocean Chemistry and Oxygen Change to the Uncertainty in Climate Change

NASA Astrophysics Data System (ADS)

Cao, L.; Wang, S.; Zheng, M.; Zhang, H.

2014-12-01

With increasing atmospheric CO2 and climate change, global ocean is undergoing substantial physical and biogeochemical changes. In particular, changes in ocean oxygen and carbonate chemistry have great implication for marine biota. There is considerable uncertainty in the projections of future climate change, and it is unclear how the uncertainty in climate change would affect the projection of ocean oxygen and carbonate chemistry. To examine the effect of climate change on ocean oxygen and carbonate chemistry, we used an Earth system model of intermediate complexity to perform simulations that are driven by atmospheric CO2 concentration pathway of RCP 8.5 with climate sensitivity varying from 0.0°C to 4.5 °C. Climate change affects carbonate chemistry and oxygen mainly through its impact on ocean temperature, ocean ventilation, and concentration of dissolved inorganic carbon and alkalinity. Our simulations show that climate change mitigates the decrease of carbonate ions at the ocean surface but has negligible effect on surface ocean pH. Averaged over the whole ocean, climate change acts to decrease oxygen concentration but mitigates the CO2-induced reduction of carbonate ion and pH. In our simulations, by year 2500, every degree increase of climate sensitivity warms the ocean by 0.8 °C and reduces ocean-mean dissolved oxygen concentration by 5.0%. Meanwhile, every degree increase of climate sensitivity buffers CO2-induced reduction in ocean-mean carbonate ion concentration and pH by 3.4% and 0.02 units, respectively. Our study demonstrates different sensitivities of ocean temperature, carbonate chemistry, and oxygen, in terms of both the sign and magnitude, to the amount of climate change, which have great implications for understanding the response of ocean biota to climate change.

Plasma chemistry study of PLAD processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin Shu; Brumfield, Kyle; Liu, Lequn Jennifer

2012-11-06

Plasma doping (PLAD) shows very different impurity profiles compared to the conventional beam-line-based ion implantations due to its non-mass separation property and plasma environment. There is no simulation for PLAD process so far due to a lack of a dopant profile model. Several factors determine impurity profiles of PLAD process. The most significant factors are: plasma chemistry and deposition/etching characteristics of multi-ion species plasmas. In this paper, we present plasma chemistry and deposition/etching characteristics of PLAD processes versus co-gas dilutions. Four dopant plasmas including B{sub 2}H{sub 6}, BF{sub 3}, AsH{sub 3}, and PH{sub 3}, and two non-dopant plasmas including CH{submore » 4} and GeH{sub 4} are studied and demonstrated.« less

Substantial difference in target surface chemistry between reactive dc and high power impulse magnetron sputtering

NASA Astrophysics Data System (ADS)

Greczynski, G.; Mráz, S.; Schneider, J. M.; Hultman, L.

2018-02-01

The nitride layer formed in the target race track during the deposition of stoichiometric TiN thin films is a factor 2.5 thicker for high power impulse magnetron sputtering (HIPIMS), compared to conventional dc processing (DCMS). The phenomenon is explained using x-ray photoelectron spectroscopy analysis of the as-operated Ti target surface chemistry supported by sputter depth profiles, dynamic Monte Carlo simulations employing the TRIDYN code, and plasma chemical investigations by ion mass spectrometry. The target chemistry and the thickness of the nitride layer are found to be determined by the implantation of nitrogen ions, predominantly N+ and N2+ for HIPIMS and DCMS, respectively. Knowledge of this method-inherent difference enables robust processing of high quality functional coatings.

Gas-Phase Oxidation via Ion/Ion Reactions: Pathways and Applications

NASA Astrophysics Data System (ADS)

Pilo, Alice L.; Zhao, Feifei; McLuckey, Scott A.

2017-06-01

Here, we provide an overview of pathways available upon the gas-phase oxidation of peptides and DNA via ion/ion reactions and explore potential applications of these chemistries. The oxidation of thioethers (i.e., methionine residues and S-alkyl cysteine residues), disulfide bonds, S-nitrosylated cysteine residues, and DNA to the [M+H+O]+ derivative via ion/ion reactions with periodate and peroxymono-sulfate anions is demonstrated. The oxidation of neutral basic sites to various oxidized structures, including the [M+H+O]+, [M-H]+, and [M-H-NH3]+ species, via ion/ion reactions is illustrated and the oxidation characteristics of two different oxidizing reagents, periodate and persulfate anions, are compared. Lastly, the highly efficient generation of molecular radical cations via ion/ion reactions with sulfate radical anion is summarized. Activation of the newly generated molecular radical peptide cations results in losses of various neutral side chains, several of which generate dehydroalanine residues that can be used to localize the amino acid from which the dehydroalanine was generated. The chemistries presented herein result in a diverse range of structures that can be used for a variety of applications, including the identification and localization of S-alkyl cysteine residues, the oxidative cleavage of disulfide bonds, and the generation of molecular radical cations from even-electron doubly protonated peptides. [Figure not available: see fulltext.

Modularized Production of Value-Added Products and Fuels from Distributed Waste Carbon-Rich Feedstocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weber, Robert S.; Holladay, Johnathan E.

Here, we have adapted and characterized electrolysis reactors to complement the conversion of regional- and community-scale quantities of waste into fuel or chemicals. The overall process must be able to contend with a wide range of feedstocks, must be inherently safe, and should not rely on external facilities for co-reactants or heat rejection and supply. Our current approach is based on the upgrading of bio-oil produced by the hydrothermal liquefaction (HTL) of carbon-containing waste feedstocks. HTL can convert a variety of feedstocks into a bio-oil that requires much less upgrading than the products of other ways of deconstructing biomass. Wemore » are now investigating the use of electrochemical processes for the further conversions needed to transform the bio-oil from HTL into fuel or higher value chemicals. We, and others, have shown that electrochemical reduction can offer adequate reaction rates and at least some of the necessary generality. In addition, an electrochemical reactor necessarily both oxidizes (removes electrons) on one side of the reactor and reduces (adds electrons) on the other side. Therefore, the two types of reactions could, in principle, be coupled to upgrade the bio-oil and simultaneously polish the water that is employed as a reactant and a carrier in the upstream HTL. Here, we overview a notional process, the possible conversion chemistry, and the economics of an HTL-electrochemical process.« less

Modularized Production of Value-Added Products and Fuels from Distributed Waste Carbon-Rich Feedstocks

DOE PAGES

Weber, Robert S.; Holladay, Johnathan E.

2018-05-22

Here, we have adapted and characterized electrolysis reactors to complement the conversion of regional- and community-scale quantities of waste into fuel or chemicals. The overall process must be able to contend with a wide range of feedstocks, must be inherently safe, and should not rely on external facilities for co-reactants or heat rejection and supply. Our current approach is based on the upgrading of bio-oil produced by the hydrothermal liquefaction (HTL) of carbon-containing waste feedstocks. HTL can convert a variety of feedstocks into a bio-oil that requires much less upgrading than the products of other ways of deconstructing biomass. Wemore » are now investigating the use of electrochemical processes for the further conversions needed to transform the bio-oil from HTL into fuel or higher value chemicals. We, and others, have shown that electrochemical reduction can offer adequate reaction rates and at least some of the necessary generality. In addition, an electrochemical reactor necessarily both oxidizes (removes electrons) on one side of the reactor and reduces (adds electrons) on the other side. Therefore, the two types of reactions could, in principle, be coupled to upgrade the bio-oil and simultaneously polish the water that is employed as a reactant and a carrier in the upstream HTL. Here, we overview a notional process, the possible conversion chemistry, and the economics of an HTL-electrochemical process.« less

Porous Core-Shell Nanostructures for Catalytic Applications

NASA Astrophysics Data System (ADS)

Ewers, Trevor David

Porous core-shell nanostructures have recently received much attention for their enhanced thermal stability. They show great potential in the field of catalysis, as reactant gases can diffuse in and out of the porous shell while the core particle is protected from sintering, a process in which particles coalesce to form larger particles. Sintering is a large problem in industry and is the primary cause of irreversible deactivation. Despite the obvious advantages of high thermal stability, porous core-shell nanoparticles can be developed to have additional interactive properties from the combination of the core and shell together, rather than just the core particle alone. This dissertation focuses on developing new porous core-shell systems in which both the core and shell take part in catalysis. Two types of systems are explored; (1) yolk-shell nanostructures with reducible oxide shells formed using the Kirkendall effect and (2) ceramic-based porous oxide shells formed using sol-gel chemistry. Of the Kirkendall-based systems, Au FexOy and Cu CoO were synthesized and studied for catalytic applications. Additionally, ZnO was explored as a potential shelling material. Sol-gel work focused on optimizing synthetic methods to allow for coating of small gold particles, which remains a challenge today. Mixed metal oxides were explored as a shelling material to make dual catalysts in which the product of a reaction on the core particle becomes a reactant within the shell.

Potential surfaces for O atom-polymer reactions

NASA Technical Reports Server (NTRS)

Laskowski, B. C.; Jaffe, R. L.

1987-01-01

Ab initio quantum chemistry methods are used to study the energetics of interactions of O atoms with organic compounds. Polyethylene (CH2)n has been chosen as the model system to study the interactions of O(3P) and O(1D) atoms with polymers. In particular, H abstraction is investigated and polyethylene is represented by a C3 (propane) oligomeric model. The gradient method, as implemented in the GRADSCF package of programs, is used to determine the geometries and energies of products and reactants. The saddle point, barrier geometry is determined by minimizing the squares of the gradients of the potential with respect to the internal coordinates. To correctly describe the change in bonding during the reaction at least a two configuration MCSCF (multiconfiguration self consistent field) or GVB (generalized valence bond) wave function has to be used. Basis sets include standard Pople and Dunning sets, however, increased with polarization functions and diffuse p functions on both the C and O atoms. The latter is important due to the O(-) character of the wave function at the saddle point and products. Normal modes and vibrational energy levels are given for the reactants, saddle points and products. Finally, quantitative energetics are obtained by implementing a small CAS (complete active space) approach followed by limited configuration interaction (CI) calculations. Comparisons are made with available experimental data.

F region above Kauai - Measurement, model, modification

NASA Technical Reports Server (NTRS)

Johnson, C. Y.; Sjolander, G. W.; Oran, E. S.; Young, T. R.; Bernhardt, P. A.; Da Rosa, A. V.

1980-01-01

Results of the Lagopedo II experiment conducted from Kauai, Hawaii to investigate the ionospheric modification that occurs when rocket combustion products are introduced into the O(+)-rich F region are presented. The experiment involved the detonation of a chemical explosion in the F2 peak accompanied by rocket-borne measurements of ion composition and electron content in the vicinity of the explosion. The experimental data is found to be in good agreement with the predictions of a model of the nighttime ion densities in the midlatitude laminar ionosphere, with the exception of N2(+) densities before the explosion. H2O(+) and H3O(+) currents produced by considerable H2O outgassing from the rocket are used to determine a H3O(+)/H2O(+) dissociative recombination rate averaging 1.6 to 1.08, depending on model assumptions. At the time of the explosion, an ionic void 1 km in radius is observed, the boundary of which is characterized by a steep gradient in ionic densities. Evidence of variations in the concentrations of ambient ion species, new reactant species and ionic depletion by sweeping is also obtained.

Statistical modeling of competitive threshold collision-induced dissociation

NASA Astrophysics Data System (ADS)

Rodgers, M. T.; Armentrout, P. B.

1998-08-01

Collision-induced dissociation of (R1OH)Li+(R2OH) with xenon is studied using guided ion beam mass spectrometry. R1OH and R2OH include the following molecules: water, methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol. In all cases, the primary products formed correspond to endothermic loss of one of the neutral alcohols, with minor products that include those formed by ligand exchange and loss of both ligands. The cross-section thresholds are interpreted to yield 0 and 298 K bond energies for (R1OH)Li+-R2OH and relative Li+ binding affinities of the R1OH and R2OH ligands after accounting for the effects of multiple ion-molecule collisions, internal energy of the reactant ions, and dissociation lifetimes. We introduce a means to simultaneously analyze the cross sections for these competitive dissociations using statistical theories to predict the energy dependent branching ratio. Thermochemistry in good agreement with previous work is obtained in all cases. In essence, this statistical approach provides a detailed means of correcting for the "competitive shift" inherent in multichannel processes.

Observations of Carbon Isotopic Fractionation in Interstellar Formaldehyde

NASA Technical Reports Server (NTRS)

Wirstrom, E. S.; Charnley, S. B.; Geppert, W. D.; Persson, C. M.

2012-01-01

Primitive Solar System materials (e.g. chondrites. IDPs, the Stardust sample) show large variations in isotopic composition of the major volatiles (H, C, N, and O ) even within samples, witnessing to various degrees of processing in the protosolar nebula. For ex ample. the very pronounced D enhancements observed in IDPs [I] . are only generated in the cold. dense component of the interstellar medium (ISM), or protoplanetary disks, through ion-molecule reactions in the presence of interstellar dust. If this isotopic anomaly has an interstellar origin, this leaves open the possibility for preservation of other isotopic signatures throughout the form ation of the Solar System. The most common form of carbon in the ISM is CO molecules, and there are two potential sources of C-13 fractionation in this reservoir: low temperature chemistry and selective photodissociation. While gas-phase chemistry in cold interstellar clouds preferentially incorporates C-13 into CO [2], the effect of self-shielding in the presence of UV radiation instead leads to a relative enhancement of the more abundant isotopologue, 12CO. Solar System organic material exhibit rather small fluctuations in delta C-13 as compared to delta N-15 and delta D [3][1], the reason for which is still unclear. However, the fact that both C-13 depleted and enhanced material exists could indicate an interstellar origin where the two fractionation processes have both played a part. Formaldehyde (H2CO) is observed in the gas-phase in a wide range of interstellar environments, as well as in cometary comae. It is proposed as an important reactant in the formation of more complex organic molecules in the heated environments around young stars, and formaldehyde polymers have been suggested as the common origin of chondritic insoluable organic matter (IOM) and cometary refractory organic solids [4]. The relatively high gas-phase abundance of H2CO observed in molecular clouds (10(exp- 9) - 10(exp- 8) relative to H2) makes it feasible to observe its less common isotopologues. As a step in our investigation of C-13 fractionation patterns in the ISM, we here present comparisons between observations of the C-13 fraction in formaldehyde, and chemical fractionation models.

User's guide to PHREEQC (Version 2) : a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations

USGS Publications Warehouse

Parkhurst, David L.; Appelo, C.A.J.

1999-01-01

PHREEQC version 2 is a computer program written in the C programming language that is designed to perform a wide variety of low-temperature aqueous geochemical calculations. PHREEQC is based on an ion-association aqueous model and has capabilities for (1) speciation and saturation-index calculations; (2) batch-reaction and one-dimensional (1D) transport calculations involving reversible reactions, which include aqueous, mineral, gas, solid-solution, surface-complexation, and ion-exchange equilibria, and irreversible reactions, which include specified mole transfers of reactants, kinetically controlled reactions, mixing of solutions, and temperature changes; and (3) inverse modeling, which finds sets of mineral and gas mole transfers that account for differences in composition between waters, within specified compositional uncertainty limits.New features in PHREEQC version 2 relative to version 1 include capabilities to simulate dispersion (or diffusion) and stagnant zones in 1D-transport calculations, to model kinetic reactions with user-defined rate expressions, to model the formation or dissolution of ideal, multicomponent or nonideal, binary solid solutions, to model fixed-volume gas phases in addition to fixed-pressure gas phases, to allow the number of surface or exchange sites to vary with the dissolution or precipitation of minerals or kinetic reactants, to include isotope mole balances in inverse modeling calculations, to automatically use multiple sets of convergence parameters, to print user-defined quantities to the primary output file and (or) to a file suitable for importation into a spreadsheet, and to define solution compositions in a format more compatible with spreadsheet programs. This report presents the equations that are the basis for chemical equilibrium, kinetic, transport, and inverse-modeling calculations in PHREEQC; describes the input for the program; and presents examples that demonstrate most of the program's capabilities.

The catalytic effect of H2O on the hydrolysis of CO32- in hydrated clusters and its implication in the humidity driven CO2 air capture.

PubMed

Xiao, Hang; Shi, Xiaoyang; Zhang, Yayun; Liao, Xiangbiao; Hao, Feng; Lackner, Klaus S; Chen, Xi

2017-10-18

The hydration of ions in nanoscale hydrated clusters is ubiquitous and essential in many physical and chemical processes. Here we show that the hydrolysis reaction is strongly affected by relative humidity. The hydrolysis of CO 3 2- with n = 1-8 water molecules is investigated using an ab initio method. For n = 1-5 water molecules, all the reactants follow a stepwise pathway to the transition state. For n = 6-8 water molecules, all the reactants undergo a direct proton transfer to the transition state with overall lower activation free energy. The activation free energy of the reaction is dramatically reduced from 10.4 to 2.4 kcal mol -1 as the number of water molecules increases from 1 to 6. Meanwhile, the degree of hydrolysis of CO 3 2- is significantly increased compared to the bulk water solution scenario. Incomplete hydration shells facilitate the hydrolysis of CO 3 2- with few water molecules to be not only thermodynamically favorable but also kinetically favorable. We showed that the chemical kinetics is not likely to constrain the speed of CO 2 air capture driven by the humidity-swing. Instead, the pore-diffusion of ions is expected to be the time-limiting step in the humidity driven CO 2 air capture. The effect of humidity on the speed of CO 2 air capture was studied by conducting a CO 2 absorption experiment using IER with a high ratio of CO 3 2- to H 2 O molecules. Our result is able to provide valuable insights into designing efficient CO 2 air-capture sorbents.

Complexities of Focused Ion Beam Preparation of Electron-Transparent Sections for Meteorite Studies

NASA Astrophysics Data System (ADS)

Ishii, H. A.; Bradley, J. P.; Teslich, N.

2012-09-01

Focused Ion Beam is increasingly used to prepare site-specific, electron-transparent sections for meteorite micro-texture and -chemistry studies. We discuss technical challenges and frequently-overlooked FIB artifacts relevant to meteorite analyses.

Visualizing Chemistry: Investigations for Teachers.

ERIC Educational Resources Information Center

Ealy, Julie B.; Ealy, James L., Jr.

This book contains 101 investigations for chemistry classrooms. Topics include: (1) Physical Properties; (2) Reactions of Some Elements; (3) Reactions Involving Gases; (4) Energy Changes; (5) Solutions and Solubility; (6) Transition Metals and Complex Ions; (7) Kinetics and Equilibrium; (8) Acids and Bases; (9) Oxidation-Reduction; (10)…

The Conjugate Acid-Base Chart.

ERIC Educational Resources Information Center

Treptow, Richard S.

1986-01-01

Discusses the difficulties that beginning chemistry students have in understanding acid-base chemistry. Describes the use of conjugate acid-base charts in helping students visualize the conjugate relationship. Addresses chart construction, metal ions, buffers and pH titrations, and the organic functional groups and nonaqueous solvents. (TW)

Mars aqueous chemistry experiment

NASA Technical Reports Server (NTRS)

Clark, Benton C.; Mason, Larry W.

1993-01-01

The Mars Aqueous Chemistry Experiment (MACE) is designed to conduct a variety of measurements on regolith samples, encompassing mineral phase analyses, chemical interactions with H2O, and physical properties determinations. From these data, much can be learned or inferred regarding the past weathering environment, the contemporaneous soil micro-environments, and the general chemical and physical state of the Martian regolith. By analyzing both soil and duricrust samples, the nature of the latter may become more apparent. Sites may be characterized for comparative purposes and criteria could be set for selection of high priority materials on future sample return missions. Progress for the first year MACE PIDDP is reported in two major areas of effort: (1) fluids handling concepts, definition, and breadboard fabrication and (2) aqueous chemistry ion sensing technology and test facility integration. A fluids handling breadboard was designed, fabricated, and tested at Mars ambient pressure. The breadboard allows fluid manipulation scenarios to be tested under the reduced pressure conditions expected in the Martian atmosphere in order to validate valve operations, orchestrate analysis sequences, investigate sealing integrity, and to demonstrate efficacy of the fluid handling concept. Additional fluid manipulation concepts have also been developed based on updated MESUR spacecraft definition. The Mars Aqueous Chemistry Experiment Ion Selective Electrode (ISE) facility was designed as a test bed to develop a multifunction interface for measurements of chemical ion concentrations in aqueous solution. The interface allows acquisition of real time data concerning the kinetics and heats of salt dissolution, and transient response to calibration and solubility events. An array of ion selective electrodes has been interfaced and preliminary calibration studies performed.

Mars aqueous chemistry experiment

NASA Astrophysics Data System (ADS)

Clark, Benton C.; Mason, Larry W.

1993-06-01

The Mars Aqueous Chemistry Experiment (MACE) is designed to conduct a variety of measurements on regolith samples, encompassing mineral phase analyses, chemical interactions with H2O, and physical properties determinations. From these data, much can be learned or inferred regarding the past weathering environment, the contemporaneous soil micro-environments, and the general chemical and physical state of the Martian regolith. By analyzing both soil and duricrust samples, the nature of the latter may become more apparent. Sites may be characterized for comparative purposes and criteria could be set for selection of high priority materials on future sample return missions. Progress for the first year MACE PIDDP is reported in two major areas of effort: (1) fluids handling concepts, definition, and breadboard fabrication and (2) aqueous chemistry ion sensing technology and test facility integration. A fluids handling breadboard was designed, fabricated, and tested at Mars ambient pressure. The breadboard allows fluid manipulation scenarios to be tested under the reduced pressure conditions expected in the Martian atmosphere in order to validate valve operations, orchestrate analysis sequences, investigate sealing integrity, and to demonstrate efficacy of the fluid handling concept. Additional fluid manipulation concepts have also been developed based on updated MESUR spacecraft definition. The Mars Aqueous Chemistry Experiment Ion Selective Electrode (ISE) facility was designed as a test bed to develop a multifunction interface for measurements of chemical ion concentrations in aqueous solution. The interface allows acquisition of real time data concerning the kinetics and heats of salt dissolution, and transient response to calibration and solubility events. An array of ion selective electrodes has been interfaced and preliminary calibration studies performed.

General theory of multistage geminate reactions of isolated pairs of reactants. I. Kinetic equations.

PubMed

Doktorov, Alexander B; Kipriyanov, Alexey A

2014-05-14

General matrix approach to the consideration of multistage geminate reactions of isolated pairs of reactants depending on reactant mobility is formulated on the basis of the concept of "effective" particles. Various elementary reactions (stages of multistage reaction including physicochemical processes of internal quantum state changes) proceeding with the participation of isolated pairs of reactants (or isolated reactants) are taken into account. Investigation has been made in terms of kinetic approach implying the derivation of general (matrix) kinetic equations for local and mean probabilities of finding any of the reaction species in the sample under study (or for local and mean concentrations). The recipes for the calculation of kinetic coefficients of the equations for mean quantities in terms of relative coordinates of reactants have been formulated in the general case of inhomogeneous reacting systems. Important specific case of homogeneous reacting systems is considered.

Processing of ammonia-containing ices by heavy ions and its relevance to outer Solar System surfaces

NASA Astrophysics Data System (ADS)

Pilling, Sergio; Seperuelo Duarte, Eduardo; da Silveira, Enio F.; Domaracka, Alicja; Balanzat, Emmanuel; Rothard, Hermann; Boduch, Philippe

Ammonia-containing ices have been detected or postulated as important components of the icy surfaces of planetary satellites (e.g. Enceladus, Miranda), in the outer Solar System objects (e.g. Charon, Quaoar) and in Oort cloud comets. We present experimental studies of the interaction of heavy, highly-charged, and energetic ions with ammonia-containing ices (pure NH3 ; NH3 :CO; NH3 :H2 O and NH3 :H2 O:CO) in an attempt to simulate the physical chemistry induced by heavy-ion cosmic rays and heavy-ion solar wind particles at outer Solar System surfaces. The measurements were performed inside a high vacuum chamber at the heavy-ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds) in Caen, France. The gas samples were deposited onto a polished CsI substrate previously cooled to 13 K. In-situ analysis was performed by a Fourier transform infrared spectrometer (FTIR) at different ion fluences. The dissociation cross-section and sputtering yield of ammonia and other ice compounds have been determined. Half-life of frozen ammonia due to heavy ion bombardment at different Solar System surfaces has been estimated. Radiolysis products have been identified and their implications for the chemistry on outer Solar System surfaces are discussed.

Taking Advantage of a Corrosion Problem to Solve a Pollution Problem

ERIC Educational Resources Information Center

Palomar-Ramirez, Carlos F.; Bazan-Martinez, Jose A.; Palomar-Pardave, Manuel E.; Romero-Romo, Mario A.; Ramirez-Silva, Maria Teresa

2011-01-01

Some simple chemistry is used to demonstrate how Fe(II) ions, formed during iron corrosion in acid aqueous solution, can reduce toxic Cr(VI) species, forming soluble Cr(III) and Fe(III) ions. These ions, in turn, can be precipitated by neutralizing the solution. The procedure provides a treatment for industrial wastewaters commonly found in…

Investigating the Intercalation Chemistry of Alkali Ions in Fluoride Perovskites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yi, Tanghong; Chen, Wei; Cheng, Lei

Reversible intercalation reactions provide the basis for modern battery electrodes. In spite of the decades of exploration of electrode materials, the potential for materials in the nonoxide chemical space with regards to intercalation chemistry is vast and rather untested. Transition metal fluorides stand out as an obvious target. To this end, we report herein a new family of iron fluoride-based perovskite cathode materials A xK 1–xFeF 3 (A = Li, Na). By starting with KFeF 3, approximately 75% of K+ ions were subsequently replaced by Li + and Na + through electrochemical means. X-ray diffraction and Fe X-ray absorption spectroscopymore » confirmed the existence of intercalation of alkali metal ions in the perovskite structure, which is associated with the Fe 2+/3+ redox couple. A computational study by density functional theory showed agreement with the structural and electrochemical data obtained experimentally, which suggested the possibility of fluoride-based materials as potential intercalation electrodes. Our study increases our understanding of the intercalation chemistry of ternary fluorides, which could inform efforts toward the exploration of new electrode materials.« less

Investigating the Intercalation Chemistry of Alkali Ions in Fluoride Perovskites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yi, Tanghong; Chen, Wei; Cheng, Lei

Reversible intercalation reactions provide the basis for modern battery electrodes. Despite decades of exploration of electrode materials, the potential for materials in the nonoxide chemical space with regards to intercalation chemistry is vast and rather untested. Transition metal fluorides stand out as an obvious target. To this end, we report herein a new family of iron fluoride-based perovskite cathode materials A xK 1–xFeF 3 (A = Li, Na). By starting with KFeF 3, approximately 75% of K + ions were subsequently replaced by Li + and Na + through electrochemical means. X-ray diffraction and Fe X-ray absorption spectroscopy confirmed themore » existence of intercalation of alkali metal ions in the perovskite structure, which is associated with the Fe 2+/3+ redox couple. A computational study by density functional theory showed agreement with the structural and electrochemical data obtained experimentally, which suggested the possibility of fluoride-based materials as potential intercalation electrodes. This study increases our understanding of the intercalation chemistry of ternary fluorides, which could inform efforts toward the exploration of new electrode materials.« less

Investigating the Intercalation Chemistry of Alkali Ions in Fluoride Perovskites

DOE PAGES

Yi, Tanghong; Chen, Wei; Cheng, Lei; ...

2017-01-20

Reversible intercalation reactions provide the basis for modern battery electrodes. In spite of the decades of exploration of electrode materials, the potential for materials in the nonoxide chemical space with regards to intercalation chemistry is vast and rather untested. Transition metal fluorides stand out as an obvious target. To this end, we report herein a new family of iron fluoride-based perovskite cathode materials A xK 1–xFeF 3 (A = Li, Na). By starting with KFeF 3, approximately 75% of K+ ions were subsequently replaced by Li + and Na + through electrochemical means. X-ray diffraction and Fe X-ray absorption spectroscopymore » confirmed the existence of intercalation of alkali metal ions in the perovskite structure, which is associated with the Fe 2+/3+ redox couple. A computational study by density functional theory showed agreement with the structural and electrochemical data obtained experimentally, which suggested the possibility of fluoride-based materials as potential intercalation electrodes. Our study increases our understanding of the intercalation chemistry of ternary fluorides, which could inform efforts toward the exploration of new electrode materials.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vorotilin, V. P., E-mail: VPVorotilin@yandex.ru

A generalization of the theory of chemical transformation processes under turbulent mixing of reactants and arbitrary values of the rate of molecular reactions is presented that was previously developed for the variant of an instantaneous reaction [13]. The use of the features of instantaneous reactions when considering the general case, namely, the introduction of the concept of effective reaction for the reactant volumes and writing a closing conservation equation for these volumes, became possible due to the partition of the whole amount of reactants into “active” and “passive” classes; the reactants of the first class are not mixed and reactmore » by the mechanism of instantaneous reactions, while the reactants of the second class approach each other only through molecular diffusion, and therefore their contribution to the reaction process can be neglected. The physical mechanism of reaction for the limit regime of an ideal mixing reactor (IMR) is revealed and described. Although formally the reaction rate in this regime depends on the concentration of passive fractions of the reactants, according to the theory presented, the true (hidden) mechanism of the reaction is associated only with the reaction of the active fractions of the reactants with vanishingly small concentration in the volume of the reactor. It is shown that the rate constant of fast chemical reactions can be evaluated when the mixing intensity of reactants is much less than that needed to reach the mixing conditions in an IMR.« less

NREL Research Overcomes Major Technical Obstacles in Magnesium-Metal

Science.gov Websites

Chunmei Ban are co-authors of the Nature Chemistry white paper, "An Artificial Interphase Enables corresponding author of the paper, "An Artificial Interphase Enables Reversible Magnesium Chemistry in an artificial solid-electrolyte interphase from polyacrylonitrile and magnesium-ion salt that

Heteroditopic receptors for ion-pair recognition.

PubMed

McConnell, Anna J; Beer, Paul D

2012-05-21

Ion-pair recognition is a new field of research emerging from cation and anion coordination chemistry. Specific types of heteroditopic receptor designs for ion pairs and the complexity of ion-pair binding are discussed to illustrate key concepts such as cooperativity. The importance of this area of research is reflected by the wide variety of potential applications of ion-pair receptors, including applications as membrane transport and salt solubilization agents and sensors. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemistry in Titan

NASA Astrophysics Data System (ADS)

Plessis, S.; Carrasco, N.; Pernot, P.

2009-04-01

Modelling the chemical composition of Titan's ionosphere is a very challenging issue. Latest works perform either inversion of CASSINI's INMS mass spectra (neutral[1] or ion[2]), or design coupled ion-neutral chemistry models[3]. Coupling ionic and neutral chemistry has been reported to be an essential feature of accurate modelling[3]. Electron Dissociative Recombination (EDR), where free electrons recombine with positive ions to produce neutral species, is a key component of ion-neutral coupling. There is a major difficulty in EDR modelling: for heavy ions, the distribution of neutral products is incompletely characterized by experiments. For instance, for some hydrocarbon ions only the carbon repartition is measured, leaving the hydrogen repartition and thus the exact neutral species identity unknown[4]. This precludes reliable deterministic modelling of this process and of ion-neutral coupling. We propose a novel stochastic description of the EDR chemical reactions which enables efficient representation and simulation of the partial experimental knowledge. The description of products distribution in multi-pathways reactions is based on branching ratios, which should sum to unity. The keystone of our approach is the design of a probability density function accounting for all available informations and physical constrains. This is done by Dirichlet modelling which enables one to sample random variables whose sum is constant[5]. The specifics of EDR partial uncertainty call for a hierarchiral Dirichlet representation, which generalizes our previous work[5]. We present results on the importance of ion-neutral coupling based on our stochastic model. C repartition H repartition (measured) (unknown ) → C4H2 + 3H2 + H .. -→ C4 . → C4H2 + 7H → C3H8. + CH C4H+9 + e- -→ C3 + C .. → C3H3 + CH2 + 2H2 → C2H6 + C2H2 + H .. -→ C2 + C2 . → 2C2H2 + 2H2 + H (1) References [1] J. Cui, R.V. Yelle, V. Vuitton, J.H. Waite Jr., W.T. Kasprzak, D.A. Gell, H.B. Niemann, I.C.F. Müller-Wodarg, N. Borggren, G.G. Fletcher, E.L. Patrick, E. Raaen, and B.A. Magee. Analysis of Titan's neutral upper atmosphere from Cassini ion neutral mass spectrometer measurements. Icarus, In Press, Accepted Manuscript:-, 2008. [2] V. Vuitton, R. V. Yelle, and M.J. McEwan. Ion chemistry and N-containing molecules in Titan's upper atmosphere. Icarus, 191:722-742, 2007. [3] V. De La Haye, J.H. Waite Jr., T.E. Cravens, I.P. Robertson, and S. Lebonnois. Coupled ion and neutral rotating model of Titan's upper atmosphere. Icarus, 197(1):110 - 136, 2008. [4] J. B. A. Mitchell, C. Rebrion-Rowe, J. L. Le Garrec, G. Angelova, H. Bluhme, K. Seiersen, and L. H. Andersen. Branching ratios for the dissociative recombination of hydrocarbon ions. I: The cases of C4H9+ and C4H5+. International Journal of Mass Spectrometry, 227(2):273-279, June 2003. [5] N. Carrasco and P. Pernot. Modeling of branching ratio uncertainty in chemical networks by Dirichlet distributions. Journal of Physical Chemistry A, 11(18):3507-3512, 2007.

Diurnal variations of Titan's ionosphere

NASA Astrophysics Data System (ADS)

Cui, J.; Galand, M.; Yelle, R. V.; Vuitton, V.; Wahlund, J.-E.; Lavvas, P. P.; Müller-Wodarg, I. C. F.; Cravens, T. E.; Kasprzak, W. T.; Waite, J. H.

2009-06-01

We present our analysis of the diurnal variations of Titan's ionosphere (between 1000 and 1300 km) based on a sample of Ion Neutral Mass Spectrometer (INMS) measurements in the Open Source Ion (OSI) mode obtained from eight close encounters of the Cassini spacecraft with Titan. Although there is an overall ion depletion well beyond the terminator, the ion content on Titan's nightside is still appreciable, with a density plateau of ˜700 cm-3 below ˜1300 km. Such a plateau is a combined result of significant depletion of light ions and modest depletion of heavy ones on Titan's nightside. We propose that the distinctions between the diurnal variations of light and heavy ions are associated with their different chemical loss pathways, with the former primarily through “fast” ion-neutral chemistry and the latter through “slow” electron dissociative recombination. The strong correlation between the observed night-to-day ion density ratios and the associated ion lifetimes suggests a scenario in which the ions created on Titan's dayside may survive well to the nightside. The observed asymmetry between the dawn and dusk ion density profiles also supports such an interpretation. We construct a time-dependent ion chemistry model to investigate the effect of ion survival associated with solid body rotation alone as well as superrotating horizontal winds. For long-lived ions, the predicted diurnal variations have similar general characteristics to those observed. However, for short-lived ions, the model densities on the nightside are significantly lower than the observed values. This implies that electron precipitation from Saturn's magnetosphere may be an additional and important contributor to the densities of the short-lived ions observed on Titan's nightside.

Mass spectrometry. [review of techniques

NASA Technical Reports Server (NTRS)

Burlingame, A. L.; Kimble, B. J.; Derrick, P. J.

1976-01-01

Advances in mass spectrometry (MS) and its applications over the past decade are reviewed in depth, with annotated literature references. New instrumentation and techniques surveyed include: modulated-beam MS, chromatographic MS on-line computer techniques, digital computer-compatible quadrupole MS, selected ion monitoring (mass fragmentography), and computer-aided management of MS data and interpretation. Areas of application surveyed include: organic MS and electron impact MS, field ionization kinetics, appearance potentials, translational energy release, studies of metastable species, photoionization, calculations of molecular orbitals, chemical kinetics, field desorption MS, high pressure MS, ion cyclotron resonance, biochemistry, medical/clinical chemistry, pharmacology, and environmental chemistry and pollution studies.

Method for forming H2-permselective oxide membranes

DOEpatents

Gavalas, George R.; Nam, Suk Woo; Tsapatsis, Michael; Kim, Soojin

1995-01-01

Methods of forming permselective oxide membranes that are highly selective to permeation of hydrogen by chemical deposition of reactants in the pore of porous tubes, such as Vycor.TM. glass or Al.sub.2 O.sub.3 tubes. The porous tubes have pores extending through the tube wall. The process involves forming a stream containing a first reactant of the formula RX.sub.n, wherein R is silicon, titanium, boron or aluminum, X is chlorine, bromine or iodine, and n is a number which is equal to the valence of R; and forming another stream containing water vapor as the second reactant. Both of the reactant streams are passed along either the outside or the inside surface of a porous tube and the streams react in the pores of the porous tube to form a nonporous layer of R-oxide in the pores. The membranes are formed by the hydrolysis of the respective halides. In another embodiment, the first reactant stream contains a first reactant having the formula SiH.sub.n Cl.sub.4-n where n is 1, 2 or 3; and the second reactant stream contains water vapor and oxygen. In still another embodiment the first reactant stream containing a first reactant selected from the group consisting of Cl.sub.3 SiOSiCl.sub.3, Cl.sub.3 SiOSiCl.sub.2 OSiCl.sub.3, and mixtures thereof and the second reactant stream contains water vapor. In still another embodiment, membrane formation is carried out by an alternating flow deposition method. This involves a sequence of cycles, each cycle comprising introduction of the halide-containing stream and allowance of a specific time for reaction followed by purge and flow of the water vapor containing stream for a specific length of time. In all embodiments the nonporous layers formed are selectively permeable to hydrogen.

Method for forming H2-permselective oxide membranes

DOEpatents

Gavalas, G.R.; Nam, S.W.; Tsapatsis, M.; Kim, S.

1995-09-26

Methods are disclosed for forming permselective oxide membranes that are highly selective to permeation of hydrogen by chemical deposition of reactants in the pore of porous tubes, such as Vycor{trademark} glass or Al{sub 2}O{sub 3} tubes. The porous tubes have pores extending through the tube wall. The process involves forming a stream containing a first reactant of the formula RX{sub n}, wherein R is silicon, titanium, boron or aluminum, X is chlorine, bromine or iodine, and n is a number which is equal to the valence of R; and forming another stream containing water vapor as the second reactant. Both of the reactant streams are passed along either the outside or the inside surface of a porous tube and the streams react in the pores of the porous tube to form a nonporous layer of R-oxide in the pores. The membranes are formed by the hydrolysis of the respective halides. In another embodiment, the first reactant stream contains a first reactant having the formula SiH{sub n}Cl{sub 4{minus}n} where n is 1, 2 or 3; and the second reactant stream contains water vapor and oxygen. In still another embodiment the first reactant stream containing a first reactant selected from the group consisting of Cl{sub 3}SiOSiCl{sub 3}, Cl{sub 3}SiOSiCl{sub 2}OSiCl{sub 3}, and mixtures thereof and the second reactant stream contains water vapor. In still another embodiment, membrane formation is carried out by an alternating flow deposition method. This involves a sequence of cycles, each cycle comprising introduction of the halide-containing stream and allowance of a specific time for reaction followed by purge and flow of the water vapor containing stream for a specific length of time. In all embodiments the nonporous layers formed are selectively permeable to hydrogen. 11 figs.

The general theory of multistage geminate reactions of isolated pairs of reactants. III. Two-stage reversible dissociation in geminate reaction A + A ↔ C ↔ B + B.

PubMed

Kipriyanov, Alexey A; Kipriyanov, Alexander A; Doktorov, Alexander B

2016-04-14

Specific two-stage reversible reaction A + A ↔ C ↔ B + B of the decay of species C reactants by two independent transition channels is considered on the basis of the general theory of multistage reactions of isolated pairs of reactants. It is assumed that at the initial instant of time, the reacting system contains only reactants C. The employed general approach has made it possible to consider, in the general case, the inhomogeneous initial distribution of reactants, and avoid application of model concepts of a reaction system structure (i.e., of the structure of reactants and their molecular mobility). Slowing of multistage reaction kinetics as compared to the kinetics of elementary stages is established and physically interpreted. To test approximations (point approximation) used to develop a universal kinetic law, a widely employed specific model of spherical particles with isotropic reactivity diffusing in solution is applied. With this particular model as an example, ultimate kinetics of chemical conversion of reactants is investigated. The question concerning the depths of chemical transformation at which long-term asymptotes are reached is studied.

The general theory of multistage geminate reactions of isolated pairs of reactants. III. Two-stage reversible dissociation in geminate reaction A + A↔C↔B + B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kipriyanov, Alexey A.; Kipriyanov, Alexander A.; Doktorov, Alexander B.

2016-04-14

Specific two-stage reversible reaction A + A↔C↔B + B of the decay of species C reactants by two independent transition channels is considered on the basis of the general theory of multistage reactions of isolated pairs of reactants. It is assumed that at the initial instant of time, the reacting system contains only reactants C. The employed general approach has made it possible to consider, in the general case, the inhomogeneous initial distribution of reactants, and avoid application of model concepts of a reaction system structure (i.e., of the structure of reactants and their molecular mobility). Slowing of multistage reactionmore » kinetics as compared to the kinetics of elementary stages is established and physically interpreted. To test approximations (point approximation) used to develop a universal kinetic law, a widely employed specific model of spherical particles with isotropic reactivity diffusing in solution is applied. With this particular model as an example, ultimate kinetics of chemical conversion of reactants is investigated. The question concerning the depths of chemical transformation at which long-term asymptotes are reached is studied.« less

Probing Molecular Ions With Laser-Cooled Atomic Ions

DTIC Science & Technology

2017-10-11

Sept. 23, 2015 Precision Chemical Dynamics and Quantum Control of Ultracold Molecular Ion Reactions , Cold Molecular Ions at the Quantum limit (COMIQ...ken.brown@chemistry.gatech.edu This work solved an old mystery about the lifetime of Ca+ due to reactions with background gases in laser-cooling experiments...Relative to other alkaline earths, Ca+ had a much slower reaction rate. We discovered the reason is that the Doppler cooling laser is near

Smart molecules for imaging, sensing and health (SMITH).

PubMed

Smith, Bradley D

2015-01-01

This autobiographical review provides a personal account of the author's academic journey in supramolecular chemistry, including brief summaries of research efforts in membrane transport, molecular imaging, ion-pair receptors, rotaxane synthesis, squaraine rotaxanes, and synthtavidin technology. The article concludes with a short perspective of likely future directions in biomedical supramolecular chemistry.

Chemistry--The Big Picture

ERIC Educational Resources Information Center

Cassell, Anne

2011-01-01

Chemistry produces materials and releases energy by ionic or electronic rearrangements. Three structure types affect the ease with which a reaction occurs. In the Earth's crust, "solid crystals" change chemically only with extreme heat and pressure, unless their fixed ions touch moving fluids. On the other hand, in living things, "liquid crystals"…

Filtrates & Residues: A "Semimicro" Spectrophotometric Determination of the Ksp of Silver Acetate at Various Temperatures.

ERIC Educational Resources Information Center

Liebermann, John, Jr.; Yun, Ki J.

1988-01-01

Examines a solubility laboratory experiment using silver acetate and spectrophotometers for an Advanced Placement chemistry course. Covers experimental procedure, analysis of saturated solutions, and a discussion of chemistry involved. Includes an absorbance curve for silver ions and solution preparation suggestions. (ML)

Sudoku Puzzles as Chemistry Learning Tools

ERIC Educational Resources Information Center

Crute, Thomas D.; Myers, Stephanie A.

2007-01-01

A sudoku puzzle was designed that incorporated lists of chemistry terms like polyatomic ions, organic functional groups or strong nucleophiles that students need to learn. It was found that students enjoyed solving such puzzles and also such puzzles made the boring tasks of memorizing basic chemical terms an exciting one.

Throughfall chemistry beneath Quercus rubra: atmospheric, foliar, and soil chemistry considerations

Treesearch

Theodor D. Leininger; W.E. Winner

1988-01-01

Concentrations of inorganic ions were measured in bulk rainfall and bulk throughfall collected beneath northern red oak (Quercus rubra L.) trees growing in fertile, limestone-derived soil and less fertile sandstone/shale-derived soil. Rainfall passing through the crowns at both sites was enriched with SO2-4...

Advances in membrane technology for the NASA redox energy storage system

NASA Technical Reports Server (NTRS)

Ling, J. S.; Charleston, J.

1980-01-01

Anion exchange membranes used in the system serve as a charge transferring medium as well as a reactant separator and are the key enabling component in this storage technology. Each membrane formulation undergoes a series of screening tests for area-resistivity, static (non-flow) diffusion rate determination, and performance in Redox systems. The CDIL series of membranes has, by virtue of its chemical stability and high ion exchange capacity, demonstrated superior properties in the redox environment. Additional resistivity results at several acid and iron solution concentrations, iron diffusion rates, and time dependent iron fouling of the various membrane formulations are presented in comparison to past standard formulations.

Study on reaction mechanism by analysis of kinetic energy spectra of light particles and formation of final products

NASA Astrophysics Data System (ADS)

Giardina, G.; Mandaglio, G.; Nasirov, A. K.; Anastasi, A.; Curciarello, F.; Fazio, G.

2018-05-01

The sensitivity of reaction mechanism in the formation of compound nucleus (CN) by the analysis of kinetic energy spectra of light particles and of reaction products are shown. The dependence of the P CN fusion probability of reactants and W sur survival probability of CN against fission at its deexcitation on the mass and charge symmetries in the entrance channel of heavy-ion collisions, as well as on the neutron numbers is discussed. The possibility of conducting a complex program of investigations of the complete fusion by reliable ways depends on the detailed and refined methods of experimental and theoretical analyses.

Effect of argon and hydrogen on deposition of silicon from tetrochlrosilane in cold plasmas

NASA Technical Reports Server (NTRS)

Manory, R. R.; d.

1985-01-01

The roles of Ar and H2 on the decomposition of SiCl4 in cold plasma were investigated by Langmuir probes and mass spectrometry. Decomposition of the reactant by Ar only has been found to be very slow. In presence of H2 in the plasma SiCl4 is decomposed by fast radical-molecule reactions which are further enhanced by Ar due to additional ion-molecule reactions in which more H radicals are produced. A model for the plasma-surface interactions during deposition of mu-Si in the Ar + H2 + SiCl4 system is presented.

Hydrolysis Studies and Quantitative Determination of Aluminum Ions Using [superscript 27]Al NMR: An Undergraduate Analytical Chemistry Experiment

ERIC Educational Resources Information Center

Curtin, Maria A.; Ingalls, Laura R.; Campbell, Andrew; James-Pederson, Magdalena

2008-01-01

This article describes a novel experiment focused on metal ion hydrolysis and the equilibria related to metal ions in aqueous systems. Using [superscript 27]Al NMR, the students become familiar with NMR spectroscopy as a quantitative analytical tool for the determination of aluminum by preparing a standard calibration curve using standard aluminum…

Studies of the Chemistry of the Nightside Ionosphere of Venus

NASA Technical Reports Server (NTRS)

Fox, J.L.

1992-01-01

During the tenure of this grant, we have been looking into the chemistry of the nightside ionosphere of Venus with a view toward elucidating the relative roles of electron precipitation and plasma transport as sources of the nightside ionosphere. Secondary goals have included determining the densities of minor species on the nightside, and verifying the relative normalization of the Pioneer Venus orbiter ion mass spectrometer (OIMS) and orbiter neutral mass spectrometer (ONMS) in the photochemical equilibrium region. Our studies have involved a combination of numerical modeling and analysis of the Pioneer Venus UADS data base, specifically data from the OIMS, ONMS and electron temperature probe (OETP). We have set up a one-dimensional model of the Venus nightside ionosphere, in which downward fluxes of atomic ions are introduced at the upper boundary to simulate transport of ions from the dayside. Our model shows that the densities of mass-28 ions (CO+ + N+) resulting from an influx of atomic ions from the dayside are quite small, due to the high ionization potentials of CO and N2 that make chemical production difficult.

Critical Loads of Acid Deposition for Wilderness Lakes in the Sierra Nevada (California) Estimated by the Steady-State Water Chemistry Model

Treesearch

Glenn D. Shaw; Ricardo Cisneros; Donald Schweizer; James O. Sickman; Mark E. Fenn

2014-01-01

Major ion chemistry (2000-2009) from 208 lakes (342 sample dates and 600 samples) in class I and II wilderness areas of the Sierra Nevada was used in the Steady-State Water Chemistry (SSWC) model to estimate critical loads for acid deposition and investigate the current vulnerability of high elevation lakes to acid deposition. The majority of the lakes were dilute (...

Single photon ionization and chemical ionization combined ion source based on a vacuum ultraviolet lamp for orthogonal acceleration time-of-flight mass spectrometry.

PubMed

Hua, Lei; Wu, Qinghao; Hou, Keyong; Cui, Huapeng; Chen, Ping; Wang, Weiguo; Li, Jinghua; Li, Haiyang

2011-07-01

A novel combined ion source based on a vacuum ultraviolet (VUV) lamp with both single photon ionization (SPI) and chemical ionization (CI) capabilities has been developed for an orthogonal acceleration time-of-flight mass spectrometer (oaTOFMS). The SPI was accomplished using a commercial 10.6 eV krypton discharge lamp with a photon flux of about 10(11) photons s(-1), while the CI was achieved through ion-molecule reactions with O(2)(+) reactant ions generated by photoelectron ionization at medium vacuum pressure (MVP). To achieve high ionization efficiency, the ion source pressure was elevated to 0.3 mbar and the photoionization length was extended to 36 mm. As a result, limits of detection (LODs) down to 3, 4, and 6 ppbv were obtained for benzene, toluene, and p-xylene in MVP-SPI mode, and values of 8 and 10 ppbv were obtained for toluene and chloroform, respectively, in SPI-CI mode. As it is feasible to switch between MVP-SPI mode and SPI-CI mode rapidly, this system is capable of monitoring complex organic mixtures with a wide range of ionization energies (IEs). The analytical capacity of this system was demonstrated by measuring dehydrogenation products of long-chain paraffins to olefins through direct capillary sampling and drinking water disinfection byproducts from chlorine through a membrane interface.

Atmospheric pressure flow reactor: Gas phase chemical kinetics under tropospheric conditions without wall effects

NASA Technical Reports Server (NTRS)

Koontz, Steven L. (Inventor); Davis, Dennis D. (Inventor)

1991-01-01

A flow reactor for simulating the interaction in the troposphere is set forth. A first reactant mixed with a carrier gas is delivered from a pump and flows through a duct having louvers therein. The louvers straighten out the flow, reduce turbulence and provide laminar flow discharge from the duct. A second reactant delivered from a source through a pump is input into the flowing stream, the second reactant being diffused through a plurality of small diffusion tubes to avoid disturbing the laminar flow. The commingled first and second reactants in the carrier gas are then directed along an elongated duct where the walls are spaced away from the flow of reactants to avoid wall interference, disturbance or turbulence arising from the walls. A probe connected with a measuring device can be inserted through various sampling ports in the second duct to complete measurements of the first and second reactants and the product of their reaction at selected XYZ locations relative to the flowing system.

THE ACUTE TOXICITY OF MAJOR ION SALTS TO CERIODAPHNIA DUBIA: I. INFLUENCE OF BACKGROUND WATER CHEMISTRY

PubMed Central

Mount, David R.; Erickson, Russell J.; Highland, Terry L.; Hockett, J. Russell; Hoff, Dale J.; Jenson, Correne T.; Norberg-King, Teresa J.; Peterson, Kira N.; Polaske, Zach; Wisniewski, Stephanie

2018-01-01

The ions Na+, K+, Ca2+, Mg2+, Cl−, SO42−, and HCO3−/CO32− (referred to here as “major ions”) are present in all fresh waters and are physiologically required by aquatic organisms, but can increase to harmful levels from a variety of anthropogenic activities. It is also known that the toxicities of major ion salts can vary depending on the concentrations of other ions, and understanding these relationships is key to establishing appropriate environmental limits. In this paper we present a series of experiments with Ceriodaphnia dubia to evaluate the acute toxicity of twelve major ion salts and to determine how toxicity of these salts varies as a function of background water chemistry. All salts except CaSO4 and CaCO3 were acutely toxic below saturation, with the lowest LC50s found for K salts. All ten salts that showed toxicity also showed some degree of reduced toxicity as the ionic content of the background water increased. Experiments that independently varied Ca:Mg ratio, Na:K ratio, Cl:SO4 ratio, and alkalinity/pH demonstrated that Ca concentration was the primary factor influencing the toxicities of Na and Mg salts, while the toxicities of K salts were primarily influenced by the concentration of Na. These experiments also indicated multiple mechanisms of toxicity and suggested important aspects of dosimetry: the toxicities of K, Mg, and Ca salts were best related to the chemical activity of the cation, while the toxicities of Na salts also reflected an influence of the anions and were well correlated with osmolarity. Understanding these relationships between major ion toxicity and background water chemistry should aid in the development of sensible risk assessment and regulatory standards. PMID:27167636

Calcium carbonate precipitation rate as a function of ion ratio in the presence & absence of Sr2+

NASA Astrophysics Data System (ADS)

Gebrehiwet, T.; Beig, M. S.; Fujita, Y.; Redden, G. D.; Smith, R. W.

2010-12-01

Tsigabu Gebrehiwet 1*, Mikala Beig 2, Yoshiko Fujita 3, George Redden 3 and Robert W. Smith 1 1University of Idaho, 1776 Science Center Dr, Idaho Falls,ID, 83402 (*tgebrehiwet@uidaho.edu; smithbob@uidaho.edu ) 27963 Grasmere Dr.Boulder, CO 80301(mbeig@alumni.rice.edu) 3Idaho National Laboratory, MS 2208, Idaho Falls, ID 83415 (Yoshiko.Fujita@inl.gov; George.Redden@inl.gov) Engineered in situ precipitation of calcium carbonate is a proposed strategy for remediating toxic or radioactive metals (e.g., Sr2+)in subsurface environments as well as for modifying the physical properties (e.g., stiffness, permeability) of geomedia. Inducing the precipitation reaction will likely involve manipulating the geochemical conditions by adding calcium, (bi)carbonate, or both, and relying on mixing of the two reactants. Under these conditions, the ratio of Ca2+ to CO32- will vary with distance from the mixing interface, and for most or all of the porous medium, a 1:1 stoichiometry between calcium and carbonate is unlikely to be achieved. Indeed, in engineered systems where rapid treatment is an important objective, very steep ion concentration gradients may be generated, which would result in local reactant ratios varying from very small to very large over short distances, depending on the mixing geometry and particular chemical composition of the mixing fluids. This in turn has an impact on the rate of mineral precipitation. Typically, the rate of calcium carbonate precipitation is expressed with an affinity-based rate law of the type: Rate = k(Ω-1)n, where k is a rate constant, Ω is the saturation state for the mineral (e.g., calcite), and n is an empirical reaction order. The saturation state Ω is defined as the ratio of the ion activity product to the mineral solubility product. In this expression, the rate is simply dependent on the value of Ω; the actual activities of the individual ions (Ca2+ and CO32-) do not appear in the expression. In support of the development of engineered calcite precipitation schemes for contaminant immobilization, we have conducted experiments on CaCO3 precipitation kinetics under constant composition conditions where the supersaturation state (Ω) with respect to calcite is held constant at 12.8, but the ion activity ratio (Ca2+:CO32-) is varied. The objective is to examine the effect of the ion ratio on the mineral precipitation rate and on the distribution coefficient for co-precipitated Sr (DexSr). Our results to date indicate that precipitation rates vary by up to a factor of two with the maximum rate occurring at r=0.23, where r is carbonate to calcium ions ratio. In addition, although the extent of variation in the DexSr values is similar to that for the calcite precipitation rate, we have observed low correlation between strontium distribution coefficients and precipitation rates.

Ion mobility spectrometric analysis of vaporous chemical warfare agents by the instrument with corona discharge ionization ammonia dopant ambient temperature operation.

PubMed

Satoh, Takafumi; Kishi, Shintaro; Nagashima, Hisayuki; Tachikawa, Masumi; Kanamori-Kataoka, Mieko; Nakagawa, Takao; Kitagawa, Nobuyoshi; Tokita, Kenichi; Yamamoto, Soichiro; Seto, Yasuo

2015-03-20

The ion mobility behavior of nineteen chemical warfare agents (7 nerve gases, 5 blister agents, 2 lachrymators, 2 blood agents, 3 choking agents) and related compounds including simulants (8 agents) and organic solvents (39) was comparably investigated by the ion mobility spectrometry instrument utilizing weak electric field linear drift tube with corona discharge ionization, ammonia doping, purified inner air drift flow circulation operated at ambient temperature and pressure. Three alkyl methylphosphonofluoridates, tabun, and four organophosphorus simulants gave the intense characteristic positive monomer-derived ion peaks and small dimer-derived ion peaks, and the later ion peaks were increased with the vapor concentrations. VX, RVX and tabun gave both characteristic positive monomer-derived ions and degradation product ions. Nitrogen mustards gave the intense characteristic positive ion peaks, and in addition distinctive negative ion peak appeared from HN3. Mustard gas, lewisite 1, o-chlorobenzylidenemalononitrile and 2-mercaptoethanol gave the characteristic negative ion peaks. Methylphosphonyl difluoride, 2-chloroacetophenone and 1,4-thioxane gave the characteristic ion peaks both in the positive and negative ion mode. 2-Chloroethylethylsulfide and allylisothiocyanate gave weak ion peaks. The marker ion peaks derived from two blood agents and three choking agents were very close to the reactant ion peak in negative ion mode and the respective reduced ion mobility was fluctuated. The reduced ion mobility of the CWA monomer-derived peaks were positively correlated with molecular masses among structurally similar agents such as G-type nerve gases and organophosphorus simulants; V-type nerve gases and nitrogen mustards. The slope values of the calibration plots of the peak heights of the characteristic marker ions versus the vapor concentrations are related to the detection sensitivity, and within chemical warfare agents examined the slope values for sarin, soman, tabun and nitrogen mustards were higher. Some CWA simulants and organic solvents gave the ion peaks eluting at the similar positions of the CWAs, resulting in false positive alarms. Copyright © 2015 Elsevier B.V. All rights reserved.

Structural evolution of fluorinated graphene upon molten-alkali treatment probed by X-ray absorption near-edge structure spectroscopy

NASA Astrophysics Data System (ADS)

Liang, Xianqing; Pan, Deyou; Lao, Ming; Liang, Shuiying; Huang, Dan; Zhou, Wenzheng; Guo, Jin

2017-05-01

The structural evolution of fluorinated graphene (FG) nanosheets upon molten-alkali treatment has been systematically investigated utilizing X-ray absorption near-edge structure (XANES) spectroscopy. It is found that the hydroxyl groups can progressively displace fluorine atoms to form covalent bonds to the graphene sheets under designed molten-alkali condition. The XANES spectra also reveal the formation of epoxide groups through intramolecular dehydration of neighbouring hydroxyl groups after substitution reaction. At high alkali-FG weight ratio, the restoration of the π-conjugated structure in graphene sheets can be observed due to the gradual decomposition of epoxide groups. Our experimental results indicate that the surface chemistry and electronic structure of hydroxyl-functionalized FG (HFG) can be readily tuned by varying the ratio of reactants.

Spontaneous Mirror Symmetry Breaking in the Aldol Reaction and its Potential Relevance in Prebiotic Chemistry

NASA Astrophysics Data System (ADS)

Mauksch, Michael; Wei, Shengwei; Freund, Matthias; Zamfir, Alexandru; Tsogoeva, Svetlana B.

2010-02-01

The origin of the single chirality of most biomolecules is still a great puzzle. Carbohydrates could form in the formose reaction, which is proposed to be autocatalytic and contains aldol reaction steps. Based on our earlier observation of organoautocatalysis and spontaneous enantioenrichment in absence of deliberate chiral influences in the aldol reaction of acetone and p-nitrobenzaldehyde we suggest that a similar effect might be present also in the aldol reactions involved in gluconeogenesis. Herein we show that reactant precipitation observed in our earlier reported experiments does not affect the asymmetric autocatalysis in the aldol reaction we studied. We explain the phenomenon of spontaneous mirror symmetry breaking in such organocatalytic homogenous systems qualitatively by non-linear reaction network kinetics and classical transition state theory.

Simulating the fidelity and the three Mg mechanism of pol η and clarifying the validity of transition state theory in enzyme catalysis.

PubMed

Yoon, Hanwool; Warshel, Arieh

2017-08-01

Pol η belongs to the important Y family of DNA polymerases that can catalyze translesion synthesis across sites of damaged DNA. This activity involves the reduced fidelity of Pol η for 8-oxo-7,8-dhyedro-2'-deoxoguanosin(8-oxoG). The fundamental interest in Pol η has grown recently with the demonstration of the importance of a 3rd Mg2+ ion. The current work explores both the fidelity of Pol η and the role of the 3rd metal ion, by using empirical valence bond (EVB) simulations. The simulations reproduce the observed trend in fidelity and shed a new light on the role of the 3rd metal ion. It is found that this ion does not lead to a major catalytic effect, but most probably plays an important role in reducing the product release barrier. Furthermore, it is concluded, in contrast to some implications, that the effect of this metal does not violate transition state theory, and the evaluation of the catalytic effect must conserve the molecular composition upon moving from the reactant to the transition state. Proteins 2017; 85:1446-1453. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Molecular Studies of Complex Soil Organic Matter Interactions with Metal Ions and Mineral Surfaces using Classical Molecular Dynamics and Quantum Chemistry Methods

NASA Astrophysics Data System (ADS)

Andersen, A.; Govind, N.; Laskin, A.

2017-12-01

Mineral surfaces have been implicated as potential protectors of soil organic matter (SOM) against decomposition and ultimate mineralization to small molecules which can provide nutrients for plants and soil microbes and can also contribute to the Earth's elemental cycles. SOM is a complex mixture of organic molecules of biological origin at varying degrees of decomposition and can, itself, self-assemble in such a way as to expose some biomolecule types to biotic and abiotic attack while protecting other biomolecule types. The organization of SOM and SOM with mineral surfaces and solvated metal ions is driven by an interplay of van der Waals and electrostatic interactions leading to partitioning of hydrophilic (e.g. sugars) and hydrophobic (e.g., lipids) SOM components that can be bridged with amphiphilic molecules (e.g., proteins). Classical molecular dynamics simulations can shed light on assemblies of organic molecules alone or complexation with mineral surfaces. The role of chemical reactions is also an important consideration in potential chemical changes of the organic species such as oxidation/reduction, degradation, chemisorption to mineral surfaces, and complexation with solvated metal ions to form organometallic systems. For the study of chemical reactivity, quantum chemistry methods can be employed and combined with structural insight provided by classical MD simulations. Moreover, quantum chemistry can also simulate spectroscopic signatures based on chemical structure and is a valuable tool in interpreting spectra from, notably, x-ray absorption spectroscopy (XAS). In this presentation, we will discuss our classical MD and quantum chemistry findings on a model SOM system interacting with mineral surfaces and solvated metal ions.

Modulating macrophage polarization with divalent cations in nanostructured titanium implant surfaces

NASA Astrophysics Data System (ADS)

Lee, Chung-Ho; Kim, Youn-Jeong; Jang, Je-Hee; Park, Jin-Woo

2016-02-01

Nanoscale topographical modification and surface chemistry alteration using bioactive ions are centrally important processes in the current design of the surface of titanium (Ti) bone implants with enhanced bone healing capacity. Macrophages play a central role in the early tissue healing stage and their activity in response to the implant surface is known to affect the subsequent healing outcome. Thus, the positive modulation of macrophage phenotype polarization (i.e. towards the regenerative M2 rather than the inflammatory M1 phenotype) with a modified surface is essential for the osteogenesis funtion of Ti bone implants. However, relatively few advances have been made in terms of modulating the macrophage-centered early healing capacity in the surface design of Ti bone implants for the two important surface properties of nanotopography and and bioactive ion chemistry. We investigated whether surface bioactive ion modification exerts a definite beneficial effect on inducing regenerative M2 macrophage polarization when combined with the surface nanotopography of Ti. Our results indicate that nanoscale topographical modification and surface bioactive ion chemistry can positively modulate the macrophage phenotype in a Ti implant surface. To the best of our knowledge, this is the first demonstration that chemical surface modification using divalent cations (Ca and Sr) dramatically induces the regenerative M2 macrophage phenotype of J774.A1 cells in nanostructured Ti surfaces. In this study, divalent cation chemistry regulated the cell shape of adherent macrophages and markedly up-regulated M2 macrophage phenotype expression when combined with the nanostructured Ti surface. These results provide insight into the surface engineering of future Ti bone implants that are harmonized between the macrophage-governed early wound healing process and subsequent mesenchymal stem cell-centered osteogenesis function.

Liquid Water Transport in the Reactant Channels of Proton Exchange Membrane Fuel Cells

NASA Astrophysics Data System (ADS)

Banerjee, Rupak

Water management has been identified as a critical issue in the development of PEM fuel cells for automotive applications. Water is present inside the PEM fuel cell in three phases, i.e. liquid phase, vapor phase and mist phase. Liquid water in the reactant channels causes flooding of the cell and blocks the transport of reactants to the reaction sites at the catalyst layer. Understanding the behavior of liquid water in the reactant channels would allow us to devise improved strategies for removing liquid water from the reactant channels. In situ fuel cell tests have been performed to identify and diagnose operating conditions which result in the flooding of the fuel cell. A relationship has been identified between the liquid water present in the reactant channels and the cell performance. A novel diagnostic technique has been established which utilizes the pressure drop multiplier in the reactant channels to predict the flooding of the cell or the drying-out of the membrane. An ex-situ study has been undertaken to quantify the liquid water present in the reactant channels. A new parameter, the Area Coverage Ratio (ACR), has been defined to identify the interfacial area of the reactant channel which is blocked for reactant transport by the presence of liquid water. A parametric study has been conducted to study the effect of changing temperature and the inlet relative humidity on the ACR. The ACR decreases with increase in current density as the gas flow rates increase, removing water more efficiently. With increase in temperature, the ACR decreases rapidly, such that by 60°C, there is no significant ACR to be reported. Inlet relative humidity of the gases does change the saturation of the gases in the channel, but did not show any significant effect on the ACR. Automotive powertrains, which is the target for this work, are continuously faced with transient changes. Water management under transient operating conditions is significantly more challenging and has not been investigated in detail. This study begins to investigate the effects of changing operating conditions on liquid water transport through the reactant channels. It has been identified that rapidly increasing temperature leads to the dry-out of the membrane and rapidly cooling the cell below 55°C results in the start of cell flooding. In changing the operating load of the PEMFC, overshoot in the pressure drop in the reactant channel has been identified for the first time as part of this investigation. A parametric study has been conducted to identify the factors which influence this overshoot behavior.

Baking Soda Science.

ERIC Educational Resources Information Center

Science Activities, 1994

1994-01-01

Discusses the basic principles of baking soda chemistry including the chemical composition of baking soda, its acid-base properties, the reaction of bicarbonate solution with calcium ions, and a description of some general types of chemical reactions. Includes a science activity that involves removing calcium ions from water. (LZ)

Cation Hydration Constants by Proton NMR: A Physical Chemistry Experiment.

ERIC Educational Resources Information Center

Smith, Robert L.; And Others

1988-01-01

Studies the polarization effect on water by cations and anions. Describes an experiment to illustrate the polarization effect of sodium, lithium, calcium, and strontium ions on the water molecule in the hydration spheres of the ions. Analysis is performed by proton NMR. (MVL)

Chemical Reactions Triggered Using Electrons Photodetached from "Clean" Distributions of Anions Deposited in Cryogenic Matrices via Counterion Codeposition.

PubMed

Ludwig, Ryan M; Moore, David T

2014-09-04

Application of matrix isolation spectroscopy to ionic species is typically complicated by the presence of neutral contaminants during matrix deposition. Herein we demonstrate that simultaneous deposition of balanced currents of counterions with mass-selected ions of interest generates "clean" distributions of matrix-isolated metal carbonyl anions, where the only bands appearing in the CO-stretching region of the vibrational spectrum arise from ions. (Neutrals are initially absent.) Photodetachment by mild irradiation with visible light leads to complete conversion of the anions into their corresponding neutral species. The photodetached electrons, in turn, initiate covalent chemistry, inducing C-C bond formation following electron-capture by CO van der Waals dimers to produce trans-OCCO(-). The initial clean distribution of ions enables clear connections to be drawn between the spectral changes occurring at each experimental step, thus demonstrating the potential of the counterion codeposition technique to facilitate detailed studies of chemistry involving ions and electron transfer in cryogenic matrices.

Cometary MHD and chemistry

NASA Technical Reports Server (NTRS)

Wegmann, R.; Schmidt, H. U.; Huebner, W. F.; Boice, D. C.

1987-01-01

An MHD and chemical comet-coma model was developed, applying the computer program of Huebner (1985) for the detailed chemical evolution of a spherically expanding coma and the program of Schmidt and Wegman (1982) and Wegman (1987) for the MHD flow of plasma and magnetic field in a comet to the Giotto-mission data on the ion abundances measured by the HIS ion mass spectrometer. The physics and chemistry of the coma are modeled in great detail, including photoprocesses, gas-phase chemical kinetics, energy balance with a separate electron temperature, multifluid hydrodynamics with a transition to free molecular flow, fast-streaming atomic and molecular hydrogen, counter and cross streaming of the ionized species relative to the neutral species in the coma-solar wind interaction region with momentum exchange by elastic collisions, mass-loading through ion pick-up, and Lorentz forces of the advected magnetic field. The results, both inside and outside of the contact surface, are discussed and compared with the relevant HIS ion mass spectra.

Reversible Redox Chemistry of Azo Compounds for Sodium-Ion Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Chao; Xu, Gui-Liang; Ji, Xiao

Sustainable sodium-ion batteries (SSIBs) using renewable organic electrodes are promising alternatives to lithium-ion batteries for the large-scale renewable energy storage. However, the lack of high-performance anode material impedes the development of SSIBs. Herein, we report a new type of organic anode material based on azo group for SSIBs. Azobenzene-4,4'-dicarboxylic acid sodium salt is used as a model to investigate the electrochemical behaviors and reaction mechanism of azo compound. It exhibits a reversible capacity of 170 mAhg -1 at 0.2C. When current density is increased to 20C, the reversible capacities of 98 mAhg -1 can be retained for 2000 cycles, demonstratingmore » excellent cycling stability and high rate capability. The detailed characterizations reveal that azo group acts as an electrochemical active site to reversibly bond with Na +. The reversible redox chemistry between azo compound and Na ions offer opportunities for developing longcycle-life and high-rate SSIBs.« less

Reversible Redox Chemistry of Azo Compounds for Sodium-Ion Batteries

DOE PAGES

Luo, Chao; Xu, Gui-Liang; Ji, Xiao; ...

2018-01-29

Sustainable sodium-ion batteries (SSIBs) using renewable organic electrodes are promising alternatives to lithium-ion batteries for the large-scale renewable energy storage. However, the lack of high-performance anode material impedes the development of SSIBs. Herein, we report a new type of organic anode material based on azo group for SSIBs. Azobenzene-4,4'-dicarboxylic acid sodium salt is used as a model to investigate the electrochemical behaviors and reaction mechanism of azo compound. It exhibits a reversible capacity of 170 mAhg -1 at 0.2C. When current density is increased to 20C, the reversible capacities of 98 mAhg -1 can be retained for 2000 cycles, demonstratingmore » excellent cycling stability and high rate capability. The detailed characterizations reveal that azo group acts as an electrochemical active site to reversibly bond with Na +. The reversible redox chemistry between azo compound and Na ions offer opportunities for developing longcycle-life and high-rate SSIBs.« less

Oxygen redox chemistry without excess alkali-metal ions in Na2/3[Mg0.28Mn0.72]O2.

PubMed

Maitra, Urmimala; House, Robert A; Somerville, James W; Tapia-Ruiz, Nuria; Lozano, Juan G; Guerrini, Niccoló; Hao, Rong; Luo, Kun; Jin, Liyu; Pérez-Osorio, Miguel A; Massel, Felix; Pickup, David M; Ramos, Silvia; Lu, Xingye; McNally, Daniel E; Chadwick, Alan V; Giustino, Feliciano; Schmitt, Thorsten; Duda, Laurent C; Roberts, Matthew R; Bruce, Peter G

2018-03-01

The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds as promising high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion and charge compensation by transition-metal (TM) ions. The additional capacity is provided through charge compensation by oxygen redox chemistry and some oxygen loss. It has been reported previously that oxygen redox occurs in O 2p orbitals that interact with alkali ions in the TM and alkali-ion layers (that is, oxygen redox occurs in compounds containing Li + -O(2p)-Li + interactions). Na 2/3 [Mg 0.28 Mn 0.72 ]O 2 exhibits an excess capacity and here we show that this is caused by oxygen redox, even though Mg 2+ resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygen redox. We also show that, unlike the alkali-rich compounds, Na 2/3 [Mg 0.28 Mn 0.72 ]O 2 does not lose oxygen. The extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen, which promotes oxygen loss, whereas Mg 2+ remains in Na 2/3 [Mg 0.28 Mn 0.72 ]O 2 , which stabilizes oxygen.

Influence of biocompatible metal ions (Ag, Fe, Y) on the surface chemistry, corrosion behavior and cytocompatibility of Mg-1Ca alloy treated with MEVVA.

PubMed

Liu, Yang; Bian, Dong; Wu, Yuanhao; Li, Nan; Qiu, Kejin; Zheng, Yufeng; Han, Yong

2015-09-01

Mg-1Ca samples were implanted with biocompatible alloy ions Ag, Fe and Y respectively with a dose of 2×10(17)ionscm(-2) by metal vapor vacuum arc technique (MEVVA). The surface morphologies and surface chemistry were investigated by SEM, AES and XPS. Surface changes were observed after all three kinds of elemental ion implantation. The results revealed that the modified layer was composed of two sublayers, including an outer oxidized layer with mixture of oxides and an inner implanted layer, after Ag and Fe ion implantation. Y ion implantation induced an Mg/Ca-deficient outer oxidized layer and the distribution of Y along with depth was more homogeneous. Both electrochemical test and immersion test revealed accelerated corrosion rate of Ag-implanted Mg-1Ca and Fe-implanted Mg-1Ca, whereas Y ion implantation showed a short period of protection since enhanced corrosion resistance was obtained by electrochemical test, but accelerated corrosion rate was found by long period immersion test. Indirect cytotoxicity assay indicated good cytocompatibility of Y-implanted Mg-1Ca. Moreover, the corresponding corrosion mechanisms involving implanting ions into magnesium alloys were proposed, which might provide guidance for further application of plasma ion implantation to biodegradable Mg alloys. Copyright © 2015 Elsevier B.V. All rights reserved.

Oxygen redox chemistry without excess alkali-metal ions in Na2/3[Mg0.28Mn0.72]O2

NASA Astrophysics Data System (ADS)

Maitra, Urmimala; House, Robert A.; Somerville, James W.; Tapia-Ruiz, Nuria; Lozano, Juan G.; Guerrini, Niccoló; Hao, Rong; Luo, Kun; Jin, Liyu; Pérez-Osorio, Miguel A.; Massel, Felix; Pickup, David M.; Ramos, Silvia; Lu, Xingye; McNally, Daniel E.; Chadwick, Alan V.; Giustino, Feliciano; Schmitt, Thorsten; Duda, Laurent C.; Roberts, Matthew R.; Bruce, Peter G.

2018-03-01

The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds as promising high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion and charge compensation by transition-metal (TM) ions. The additional capacity is provided through charge compensation by oxygen redox chemistry and some oxygen loss. It has been reported previously that oxygen redox occurs in O 2p orbitals that interact with alkali ions in the TM and alkali-ion layers (that is, oxygen redox occurs in compounds containing Li+-O(2p)-Li+ interactions). Na2/3[Mg0.28Mn0.72]O2 exhibits an excess capacity and here we show that this is caused by oxygen redox, even though Mg2+ resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygen redox. We also show that, unlike the alkali-rich compounds, Na2/3[Mg0.28Mn0.72]O2 does not lose oxygen. The extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen, which promotes oxygen loss, whereas Mg2+ remains in Na2/3[Mg0.28Mn0.72]O2, which stabilizes oxygen.

Atomistic Structure, Strength, and Kinetic Properties of Intergranular Films in Ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garofalini, Stephen H

2015-01-08

Intergranular films (IGFs) present in polycrystalline oxide and nitride ceramics provide an excellent example of nanoconfined glasses that occupy only a small volume percentage of the bulk ceramic, but can significantly influence various mechanical, thermal, chemical, and optical properties. By employing molecular dynamics computer simulations, we have been able to predict structures and the locations of atoms at the crystal/IGF interface that were subsequently verified with the newest electron microscopies. Modification of the chemistry of the crystal surface in the simulations provided the necessary mechanism for adsorption of specific rare earth ions from the IGF in the liquid state tomore » the crystal surface. Such results had eluded other computational approaches such as ab-initio calculations because of the need to include not only the modified chemistry of the crystal surfaces but also an accurate description of the adjoining glassy IGF. This segregation of certain ions from the IGF to the crystal caused changes in the local chemistry of the IGF that affected fracture behavior in the simulations. Additional work with the rare earth ions La and Lu in the silicon oxynitride IGFs showed the mechanisms for their different affects on crystal growth, even though both types of ions are seen adhering to a bounding crystal surface that would normally imply equivalent affects on grain growth.« less

Chemistry in acetone complexes of metal dications: a remarkable ethylene production pathway.

PubMed

Wu, Jianhua; Liu, Dan; Zhou, Jian-Ge; Hagelberg, Frank; Park, Sung Soo; Shvartsburg, Alexandre A

2007-06-07

Electrospray ionization can generate microsolvated multiply charged metal ions for various metals and ligands, allowing exploration of chemistry within such clusters. The finite size of these systems permits comparing experimental results with accurate calculations, creating a natural laboratory to research ion solvation. Mass spectrometry has provided much insight into the stability and dissociation of ligated metal cations. While solvated singly charged ions tend to shrink by ligand evaporation, solvated polycations below a certain size exhibit charge reduction and/or ligand fragmentation due to organometallic reactions. Here we investigate the acetone complexes of representative divalent metals (Ca, Mn, Co, Ni, and Cu), comparing the results of collision-induced dissociation with the predictions of density functional theory. As for other solvated dications, channels involving proton or electron transfer compete with ligand loss and become dominant for smaller complexes. The heterolytic C-C bond cleavage is common, like in DMSO and acetonitrile complexes. Of primary interest is the unanticipated neutral ethylene loss, found for all metals studied except Cu and particularly intense for Ca and Mn. We focus on understanding that process in the context of competing dissociation pathways, as a function of metal identity and number of ligands. According to first-principles modeling, ethylene elimination proceeds along a complex path involving two intermediates. These results suggest that chemistry in microsolvated multiply charged ions may still hold major surprises.

Click chemistry-mediated cyclic cleavage of metal ion-dependent DNAzymes for amplified and colorimetric detection of human serum copper (II).

PubMed

Li, Daxiu; Xie, Jiaqing; Zhou, Wenjiao; Jiang, Bingying; Yuan, Ruo; Xiang, Yun

2017-11-01

The determination of the level of Cu 2+ plays important roles in disease diagnosis and environmental monitoring. By coupling Cu + -catalyzed click chemistry and metal ion-dependent DNAzyme cyclic amplification, we have developed a convenient and sensitive colorimetric sensing method for the detection of Cu 2+ in human serums. The target Cu 2+ can be reduced by ascorbate to form Cu + , which catalyzes the azide-alkyne cycloaddition between the azide- and alkyne-modified DNAs to form Mg 2+ -dependent DNAzymes. Subsequently, the Mg 2+ ions catalyze the cleavage of the hairpin DNA substrate sequences of the DNAzymes and trigger cyclic generation of a large number of free G-quadruplex sequences, which bind hemin to form the G-quadruplex/hemin artificial peroxidase to cause significant color transition of the sensing solution for sensitive colorimetric detection of Cu 2+ . This method shows a dynamic range of 5 to 500 nM and a detection limit of 2 nM for Cu 2+ detection. Besides, the level of Cu 2+ in human serums can also be determined by using this sensing approach. With the advantages of simplicity and high sensitivity, such sensing method thus holds great potential for on-site determination of Cu 2+ in different samples. Graphical abstract Sensitive colorimetric detection of copper (II) by coupling click chemistry with metal ion-dependentDNAzymes.

System and process for biomass treatment

DOEpatents

Dunson, Jr., James B; Tucker, III, Melvin P; Elander, Richard T; Lyons, Robert C

2013-08-20

A system including an apparatus is presented for treatment of biomass that allows successful biomass treatment at a high solids dry weight of biomass in the biomass mixture. The design of the system provides extensive distribution of a reactant by spreading the reactant over the biomass as the reactant is introduced through an injection lance, while the biomass is rotated using baffles. The apparatus system to provide extensive assimilation of the reactant into biomass using baffles to lift and drop the biomass, as well as attrition media which fall onto the biomass, to enhance the treatment process.

Chemical approach for controlling nadimide cure temperature and rate

NASA Technical Reports Server (NTRS)

Lauver, R. W. (Inventor)

1985-01-01

Polyimide resins suitable for use as composite matrix materials are formed by copolymerization of maleic and norbornenyl end-capped monomers and oligomers. The copolymers can be cured at temperatures under about 300 C. by controlling the available concentration of the maleic end-capped reactant. This control can be achieved by adding sufficient amounts of said maleic reactant, or by chemical modification of either copolymer, to increase Diels-Alder retrogression of the norbornenyl-capped reactant and/or holding initiation and polymerization to a rate compatible with the availability of the maleic-capped reactant.

Chemical approach for controlling nadimide cure temperature and rate

NASA Technical Reports Server (NTRS)

Lauver, R. W. (Inventor)

1984-01-01

Polyimide resins suitable for use as composite matrix materials are formed by copolymerization of maleic and norbornenyl endcapped monomers and oligomers. The copolymers can be cured at temperatures under about 300 C by controlling the available concentration of the maleic capped reactant. This control can be achieved by adding sufficient amounts of said maleic reactant, or by chemical modification of either copolymer, so as to either increase Diels-Alder retrogression of the norbornenyl capped reactant and/or holding initiation and polymerization to a rate compatible with the availability of the maleic capped reactant.

Chemical approach for controlling nadimide cure temperature and rate

NASA Technical Reports Server (NTRS)

Lauver, R. W. (Inventor)

1985-01-01

Polyimide resins suitable for use as composite matrix materials are formed by copolymerization of maleic and norbornenyl endcapped monomers and oligomers. The copolymers can be cured at temperatures under about 300 C by controlling the available concentration of the maleic endcapped reactant. This control is achieved by adding sufficient amounts of said maleic reactant or by chemical modification of either copolymer, to either increase Diels-Alder retrogression of the norbornenyl capped reactant and/or hold initiation and polymerization to a rate compatible with the availability of the maleic capped reactant.

Method for predicting enzyme-catalyzed reactions

DOEpatents

Hlavacek, William S.; Unkefer, Clifford J.; Mu, Fangping; Unkefer, Pat J.

2013-03-19

The reactivity of given metabolites is assessed using selected empirical atomic properties in the potential reaction center. Metabolic reactions are represented as biotransformation rules. These rules are generalized from the patterns in reactions. These patterns are not unique to reactants but are widely distributed among metabolites. Using a metabolite database, potential substructures are identified in the metabolites for a given biotransformation. These substructures are divided into reactants or non-reactants, depending on whether they participate in the biotransformation or not. Each potential substructure is then modeled using descriptors of the topological and electronic properties of atoms in the potential reaction center; molecular properties can also be used. A Support Vector Machine (SVM) or classifier is trained to classify a potential reactant as a true or false reactant using these properties.

Gas-Phase Ion Chemistry in Interstellar, Circumstellar, and Planetary Environments

NASA Astrophysics Data System (ADS)

Demarais, Nicholas J.

In the last century, astronomers, physicists, and chemists have shown that the environments of space are complex. Although we have learned a great amount about the interstellar medium, circumstellar medium, and atmospheres of other planets and moons, many mysteries still remain unsolved. The cooperation of astronomers, modelers, and chemists has lead to the detection of over 180 molecules in the interstellar and circumstellar medium, and the evolution of the new scientific field of astrochemistry. Gas-phase ion chemistry can determine the stability of ions in these complex environments, provide chemical networks, and guide searches for new interstellar molecules. Using the flowing afterglow-selected ion flow tube (FA-SIFT), we have characterized the reactions of positive and negative ions that are important in a variety of astrochemical environments. The detection of CF+ in photodissociation regions highlights the importance of fluorinated species in the interstellar medium. The viability of CF+ as a possible diffuse interstellar band (DIB) carrier is discussed as related to reactions with neutral molecules in various interstellar conditions; the reactions of CF+ with twenty-two molecules of interstellar relevance were investigated. The chemical reactions of HCNH+ with H2, CH 4, C2H2, and C2H4 were reexamined to provide insight into the overprediction of HCNH+ in Titan's ionosphere by current astrochemical models. In addition, this work suggests other chemical reactions that should be included in the current models to fully describe the destruction rates of HCNH+ in Titan's ionosphere. The reactions of polycyclic aromatic hydrocarbon (PAH) ions with H atoms and other small molecules were carried out to determine the stability of these species. In diffuse regions, where the photon flux is high, PAH cations are the dominant ionization state. This work continues our previous research to include PAHs of differing geometries as well as nitrogen-containing PAHs. Extension to larger PAH cations was made possible by the integration of the laser induced acoustic desorption (LIAD) source with the FA-SIFT. In addition, in dense environments, where the photon flux is low, anionic PAHs may exist. The detection of negative ions in the past 10 years has highlighted the importance of their inclusion in astrochemical models. We have investigated the chemistry of deprotonated PAHs with molecules of interstellar relevance to determine their chemical stability in dense regions of the interstellar and circumstellar medium. In addition to PAH anions, H- is an important species in dense interstellar environments. While the reaction of hydride anion has been recognized as a critical mechanism in the initial cooling immediately after the Big Bang, H- + H → H2 + e-, chemistry with neutral molecules was largely unknown. The chemistry of H- with various classes of organic molecules was investigated and conclusions are drawn based on reaction mechanisms.

Mechanism of Gaseous Detonation Propagation Through Reactant Layers Bounded by Inert Gas

NASA Astrophysics Data System (ADS)

Houim, Ryan

2017-11-01

Vapor cloud explosions and rotating detonation engines involve the propagation of gaseous detonations through a layer of reactants that is bounded by inert gas. Mechanistic understanding of how detonations propagate stably or fail in these scenarios is incomplete. Numerical simulations were used to investigate mechanisms of gaseous detonation propagation through reactant layers bounded by inert gas. The reactant layer was a stoichiometric mixture of C2H4/O2 at 1 atm and 300K and is 4 detonation cells in height. Cases where the inert gas temperature was 300, 1500, and 3500 K will be discussed. The detonation failed for the 300 K case and propagated marginally for the 1500 K case. Surprisingly, the detonation propagated stably for the 3500 K case. A shock structure forms that involves a detached shock in the inert gas and a series of oblique shocks in the reactants. A small local explosion is triggered when the Mach stem of a detonation cell interacts with the compressed reactants behind one of these oblique shocks. The resulting pressure wave produces a new Mach stem and a new triple point that leads to a stable detonation. Preliminary results on the influence of a deflagration at the inert/reactant interface on the stability of a layered detonation will be discussed.

Hydrogeochemical processes controlling changes in fluoride ion concentration within alluvial and hard rock aquifers in a part of a semi-arid region of Northern India

NASA Astrophysics Data System (ADS)

Singh, Priyadarshini; Ashthana, Harshita; Rena, Vikas; Kumar, Pardeep; Mukherjee, Saumitra

2017-04-01

Geochemical signatures from alluvial and hard rock aquifers in a part of Northern India elucidate the chemical processes controlling fluctuations in fluoride ion concentration linked to changes in major ion groundwater chemistry. Majority of samples from the hard rock and the alluvial aquifers for pre-monsoon show both carbonate and silicate weathering, ion exchange, evaporation and rock water interaction as the processes controlling major ion chemistry whereas for post monsoon samples, contribution of silicate weathering and ion exchange process were observed. Evaporative processes causing the increase in Na+ ion concentration in premonsoon enhance the reverse ion exchange processes causing increase in Ca2+ ions which impedes fluorite mineral dissolution in the premonsoon groundwater samples within the study area. Alternately, it is observed that the removal of Ca2+ ion from solution plays a key role in increase in fluorite mineral dissolution despite its saturation in groundwater in the postmonsoon samples. Also, ion exchange process on clay surfaces is more pronounced in the postmonsoon samples leading to the uptake of Ca2+ ion upon release of Na+ and K+ ion in solution. Ca2+ ion concentration is inversely correlated with F- ion concentration in both the aquifers in the postmonsoon season validating the role of calcite precipitation as a major reason for the fluoride ion increase. Moreover, increase in silicate weathering in the postmonsoon samples leads to increase in clay particles acting as suitable sites for ion exchange enhancing Ca2+ removal from groundwater. Cationic dominance of Na+ ion in the post monsoon samples also validates the occurrence of this process. Collectively, these processes set the ideal conditions for increase in the fluoride ion concentration particularly in the alluvium aquifer waters in the postmonsoon season Keywords: geochemistry, ion-exchange, rock-water interaction, mineral dissolution, weathering.

Reactive Transport Modeling of Induced Calcite Precipitation Reaction Fronts in Porous Media Using A Parallel, Fully Coupled, Fully Implicit Approach

NASA Astrophysics Data System (ADS)

Guo, L.; Huang, H.; Gaston, D.; Redden, G. D.; Fox, D. T.; Fujita, Y.

2010-12-01

Inducing mineral precipitation in the subsurface is one potential strategy for immobilizing trace metal and radionuclide contaminants. Generating mineral precipitates in situ can be achieved by manipulating chemical conditions, typically through injection or in situ generation of reactants. How these reactants transport, mix and react within the medium controls the spatial distribution and composition of the resulting mineral phases. Multiple processes, including fluid flow, dispersive/diffusive transport of reactants, biogeochemical reactions and changes in porosity-permeability, are tightly coupled over a number of scales. Numerical modeling can be used to investigate the nonlinear coupling effects of these processes which are quite challenging to explore experimentally. Many subsurface reactive transport simulators employ a de-coupled or operator-splitting approach where transport equations and batch chemistry reactions are solved sequentially. However, such an approach has limited applicability for biogeochemical systems with fast kinetics and strong coupling between chemical reactions and medium properties. A massively parallel, fully coupled, fully implicit Reactive Transport simulator (referred to as “RAT”) based on a parallel multi-physics object-oriented simulation framework (MOOSE) has been developed at the Idaho National Laboratory. Within this simulator, systems of transport and reaction equations can be solved simultaneously in a fully coupled, fully implicit manner using the Jacobian Free Newton-Krylov (JFNK) method with additional advanced computing capabilities such as (1) physics-based preconditioning for solution convergence acceleration, (2) massively parallel computing and scalability, and (3) adaptive mesh refinements for 2D and 3D structured and unstructured mesh. The simulator was first tested against analytical solutions, then applied to simulating induced calcium carbonate mineral precipitation in 1D columns and 2D flow cells as analogs to homogeneous and heterogeneous porous media, respectively. In 1D columns, calcium carbonate mineral precipitation was driven by urea hydrolysis catalyzed by urease enzyme, and in 2D flow cells, calcium carbonate mineral forming reactants were injected sequentially, forming migrating reaction fronts that are typically highly nonuniform. The RAT simulation results for the spatial and temporal distributions of precipitates, reaction rates and major species in the system, and also for changes in porosity and permeability, were compared to both laboratory experimental data and computational results obtained using other reactive transport simulators. The comparisons demonstrate the ability of RAT to simulate complex nonlinear systems and the advantages of fully coupled approaches, over de-coupled methods, for accurate simulation of complex, dynamic processes such as engineered mineral precipitation in subsurface environments.

Low-Energy Mutual Neutralization Studies for Early Universe Hydrogen Chemistry

NASA Astrophysics Data System (ADS)

Urbain, Xavier

2010-03-01

Low-energy interactions between light ions, as they occur in low density plasmas, are ideally studied under merged-beam conditions. This was the motivation for building the dual-source setup in operation at UCL, Louvain-la-Neuve, since the early eighties. Although initially developed for the study of charge exchange [1], mutual neutralization and transfer ionization, this machine has produced a host of total cross section measurements for a wide variety of associative ionization and other reactive processes involving charged reactants, from H^+ to CO^+, in collision with H^-, D^-, C^- and O^- [2]. A recent paper by Glover et al. [3] has revived the interest for mutual neutralization studies, by stressing the need of the astrophysical community for a precise determination of the low-energy cross section of the H^+/H^- reaction. The mutual neutralization acts as a sink for negative ions which otherwise dominate the primordial formation of H2 by associative detachment with ground state H. Absolute measurements in the range 5 meV to 5 eV are needed to rule out earlier experimental work [4] contradicting the most recent theoretical predictions [5]. Our setup is currently modified to incorporate coincident imaging techniques, giving access to differential cross sections besides the branching among accessible neutral channels. Mutual neutralization reactions of H^- with H2^+ and H3^+ will also be investigated, for the role they play in laboratory plasmas [6].[4pt] [1] S. Sz"ucs, M. Karemera, M. Terao, and F. Brouillard, J. Phys. B 17, 1613 (1983).[0pt] [2] E. A. Naji et al., J. Phys. B 31, 4887 (1998), A. Le Padellec et al., J. Chem. Phys., 124, 154304 (2006) and references therein.[0pt] [3] S. C. Glover, D. W. Savin, and A.-K. Jappsen , Astrophys. J. 640, 553 (2006). [0pt] [4] J. Moseley, W. Aberth, and J. R. Peterson, Phys. Rev. Lett. 24, 435 (1970).[0pt] [5] M. Stenrup, å. Larson, and N. Elander, Phys. Rev. A 79, 012713 (2009).[0pt] [6] M. J. J. Eerden et al., Phys. Rev. A 51, 3362 (1995).

Effect of Material Ion Exchanges on the Mechanical Stiffness Properties and Shear Deformation of Hydrated Cement Material Chemistry Structure C-S-H Jennit - A Computational Modeling Study

DTIC Science & Technology

2014-01-01

Study Material properties and performance are governed by material molecular chemistry structures and molecular level interactions. Methods to...understand relationships between the material properties and performance and their correlation to the molecular level chemistry and morphology, and thus...find ways of manipulating and adjusting matters at the atomistic level in order to improve material performance are required. A computational material

Low temperature oxidation of benzene and toluene in mixture with n-decane

PubMed Central

Herbinet, Olivier; Husson, Benoit; Ferrari, Maude; Glaude, Pierre-Alexandre; Battin-Leclerc, Frédérique

2013-01-01

The oxidation of two blends, benzene/n-decane and toluene/n-decane, was studied in a jet-stirred reactor with gas chromatography analysis (temperatures from 500 to 1100 K, atmospheric pressure, stoichiometric mixtures). The studied hydrocarbon mixtures contained 75% of aromatics in order to highlight the chemistry of the low-temperature oxidation of these two aromatic compounds which have a very low reactivity compared to large alkanes. The difference of behavior between the two aromatic reactants is highly pronounced concerning the formation of derived aromatic products below 800 K. In the case of benzene, only phenol could be quantified. In the case of toluene, significant amounts of benzaldehyde, benzene, and cresols were also formed, as well as several heavy aromatic products such as bibenzyl, phenylbenzylether, methylphenylbenzylether, and ethylphenylphenol. A comparison with results obtained with neat n-decane showed that the reactivity of the alkane is inhibited by the presence of benzene and, to a larger extent, toluene. An improved model for the oxidation of toluene was developed based on recent theoretical studies of the elementary steps involved in the low-temperature chemistry of this molecule. Simulations using this model were successfully compared with the obtained experimental results. PMID:23762017

Theoretical characterization of gas-phase thermolysis products of ethane-1,2-diol, 2-chloroethanol and 2-fluoroethanol

NASA Astrophysics Data System (ADS)

Osman, Osman I.; Elroby, Shabaan A. K.; Hilal, Rifaat H.; Aziz, Saadullah G.

2013-03-01

The transition structures and the activation energies for the possible thermal elimination of H2O, HF and HCl from ethane-1,2-diol, 2-fluoroethanol and 2-chloroethanol respectively, were investigated. The relative stabilities and associated barrier heights of syn and anti vinyl alcohol isomers and their acetaldehyde tautomer were estimated. HF, DFT/B3LYP and MP2 methods at 3-21G, 6-31+G(d), 6-311++G(d,p) and aug-cc-pvdz basis sets were applied to identify the stationary points of the studied systems. The optimized geometries and electronic energies of reactants, transition states and products were analyzed. The dependence of these properties upon the theoretical level was discussed. A concerted proton release and a hydroxide or halide ion expulsion mechanism was proposed to account for the thermal rearrangement of reactants to products. A thorough understanding of syn vinyl alcohol preference is provided by performing natural bond orbital (NBO) analysis. The oxygen atom lone pair (LP) and periplanar hyperconjugative effects are responsible for this preference. It was suggested that the LP hyperconjugative interactions with the C=C σ and π antibonds were the most important origin of the structural differences between the two vinyl alcohol isomers.

Small-Sized Mg–Al LDH Nanosheets Supported on Silica Aerogel with Large Pore Channels: Textural Properties and Basic Catalytic Performance after Activation

PubMed Central

Wang, Yusen; Wang, Xiaoxia; Feng, Xiaolan; Ye, Xiao; Fu, Jie

2018-01-01

Layered double hydroxides (LDHs) have been widely used as an important subset of solid base catalysts. However, developing low-cost, small-sized LDH nanoparticles with enhanced surface catalytic sites remains a challenge. In this work, silica aerogel (SA)-supported, small-sized Mg–Al LDH nanosheets were successfully prepared by one-pot coprecipitation of Mg and Al ions in an alkaline suspension of crushed silica aerogel. The supported LDH nanosheets were uniformly dispersed in the SA substrate with the smallest average radial diameter of 19.2 nm and the thinnest average thickness of 3.2 nm, both dimensions being significantly less than those of the vast majority of LDH nanoparticles reported. The SA/LDH composites also showed large pore volume (up to 1.3 cm3·g) and pore diameter (>9 nm), and therefore allow efficient access of reactants to the edge catalytic sites of LDH nanosheets. In a base-catalyzed Henry reaction of benzaldehyde with nitromethane, the SA/LDH catalysts showed high reactant conversions and favorable stability in 6 successive cycles of reactions. The low cost of the SA carrier and LDH precursors, easy preparation method, and excellent catalytic properties make these SA/LDH composites a competitive example of solid-base catalysts. PMID:29462941

Small-Sized Mg-Al LDH Nanosheets Supported on Silica Aerogel with Large Pore Channels: Textural Properties and Basic Catalytic Performance after Activation.

PubMed

Wang, Lijun; Wang, Yusen; Wang, Xiaoxia; Feng, Xiaolan; Ye, Xiao; Fu, Jie

2018-02-16

Layered double hydroxides (LDHs) have been widely used as an important subset of solid base catalysts. However, developing low-cost, small-sized LDH nanoparticles with enhanced surface catalytic sites remains a challenge. In this work, silica aerogel (SA)-supported, small-sized Mg-Al LDH nanosheets were successfully prepared by one-pot coprecipitation of Mg and Al ions in an alkaline suspension of crushed silica aerogel. The supported LDH nanosheets were uniformly dispersed in the SA substrate with the smallest average radial diameter of 19.2 nm and the thinnest average thickness of 3.2 nm, both dimensions being significantly less than those of the vast majority of LDH nanoparticles reported. The SA/LDH composites also showed large pore volume (up to 1.3 cm3·g) and pore diameter (>9 nm), and therefore allow efficient access of reactants to the edge catalytic sites of LDH nanosheets. In a base-catalyzed Henry reaction of benzaldehyde with nitromethane, the SA/LDH catalysts showed high reactant conversions and favorable stability in 6 successive cycles of reactions. The low cost of the SA carrier and LDH precursors, easy preparation method, and excellent catalytic properties make these SA/LDH composites a competitive example of solid-base catalysts.

Research Advances: Nitric Oxide Synthase Reduces Cr(VI); The Chemistry of Popcorn: It's All About "Pop-Ability"; Nanotubes May Help Heal Broken Bones; New Method Unites Organic Materials and Nanotechnology

NASA Astrophysics Data System (ADS)

King, Angela G.

2005-12-01

An enzyme can reduce chromium ions and increase toxicity. Chemistry may reduce the number of unpopped kernels. Nanotubes provide scaffolding for bone growth. A new method will aid fabrication of drug-delivery agents.

Supramolecular Based Membrane Sensors

PubMed Central

Ganjali, Mohammad Reza; Norouzi, Parviz; Rezapour, Morteza; Faridbod, Farnoush; Pourjavid, Mohammad Reza

2006-01-01

Supramolecular chemistry can be defined as a field of chemistry, which studies the complex multi-molecular species formed from molecular components that have relatively simpler structures. This field has been subject to extensive research over the past four decades. This review discusses classification of supramolecules and their application in design and construction of ion selective sensors.

An Attenuated Total Reflectance Sensor for Copper: An Experiment for Analytical or Physical Chemistry

ERIC Educational Resources Information Center

Shtoyko, Tanya; Zudans, Imants; Seliskar, Carl J.; Heineman, William R.; Richardson, John N.

2004-01-01

A sensor experiment which can be applied to advanced undergraduate laboratory course in physical or analytical chemistry is described along with certain concepts like the demonstration of chemical sensing, preparation of thin films on a substrate, microtitration, optical determination of complex ion stoichiometry and isosbestic point. It is seen…

Ionic Strength Effect on the Rate of Reduction of Hexacyanoferrate (III) by Ascorbic Acid: A Physical Chemistry Laboratory Experiment.

ERIC Educational Resources Information Center

Watkins, Kenneth W.; Olson, June A.

1980-01-01

Describes a physical chemistry experiment that allows students to test the effect of ionic strength on the rates of a reaction between ions. The reduction of hexacyanoferrate III by ascorbic acid is detailed. Comparisons with the iodine clock reaction are made. (CS)

Clearcutting affects stream chemistry in the White Mountains of New Hampshire

Treesearch

C. Wayne Martin; Robert S. Pierce; Gene E. Likens; F. Herbert Bormann; F. Herbert Bormann

1986-01-01

Commercial clearcutting of northern hardwood forests changed the chemistry of the streams that drained from them. By the second year after cutting, specific conductance doubled, nitrate increased tenfold, calcium tripled, and sodium, magnesium, and potassium doubled. Chloride and ammonium did not change; sulfate decreased. Concentrations of most ions returned to...

Use of a Card Sort Task to Assess Students' Ability to Coordinate Three Levels of Representation in Chemistry

ERIC Educational Resources Information Center

Irby, Stefan M.; Phu, Andy L.; Borda, Emily J.; Haskell, Todd R.; Steed, Nicole; Meyer, Zachary

2016-01-01

There is much agreement among chemical education researchers that expertise in chemistry depends in part on the ability to coordinate understanding of phenomena on three levels: macroscopic (observable), sub-microscopic (atoms, molecules, and ions) and symbolic (chemical equations, graphs, etc.). We hypothesize this "level-coordination…

Synergetic topography and chemistry cues guiding osteogenic differentiation in bone marrow stromal cells through ERK1/2 and p38 MAPK signaling pathway.

PubMed

Zhang, Xinran; Li, Haotian; Lin, Chucheng; Ning, Congqin; Lin, Kaili

2018-01-30

Both the topographic surface and chemical composition modification can enhance rapid osteogenic differentiation and bone formation. Till now, the synergetic effects of topography and chemistry cues guiding biological responses have been rarely reported. Herein, the ordered micro-patterned topography and classically essential trace element of strontium (Sr) ion doping were selected to imitate topography and chemistry cues, respectively. The ordered micro-patterned topography on Sr ion-doped bioceramics was successfully duplicated using the nylon sieve as the template. Biological response results revealed that the micro-patterned topography design or Sr doping could promote cell attachment, ALP activity, and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). Most importantly, the samples both with micro-patterned topography and Sr doping showed the highest promotion effects, and could synergistically activate the ERK1/2 and p38 MAPK signaling pathways. The results suggested that the grafts with both specific topography and chemistry cues have synergetic effects on osteogenic activity of BMSCs and provide an effective approach to design functional bone grafts and cell culture substrates.

Single-Molecule Reaction Chemistry in Patterned Nanowells

PubMed Central

2016-01-01

A new approach to synthetic chemistry is performed in ultraminiaturized, nanofabricated reaction chambers. Using lithographically defined nanowells, we achieve single-point covalent chemistry on hundreds of individual carbon nanotube transistors, providing robust statistics and unprecedented spatial resolution in adduct position. Each device acts as a sensor to detect, in real-time and through quantized changes in conductance, single-point functionalization of the nanotube as well as consecutive chemical reactions, molecular interactions, and molecular conformational changes occurring on the resulting single-molecule probe. In particular, we use a set of sequential bioconjugation reactions to tether a single-strand of DNA to the device and record its repeated, reversible folding into a G-quadruplex structure. The stable covalent tether allows us to measure the same molecule in different solutions, revealing the characteristic increased stability of the G-quadruplex structure in the presence of potassium ions (K+) versus sodium ions (Na+). Nanowell-confined reaction chemistry on carbon nanotube devices offers a versatile method to isolate and monitor individual molecules during successive chemical reactions over an extended period of time. PMID:27270004

Methane chemistry involved in a low-pressure electron cyclotron wave resonant plasma discharge

NASA Astrophysics Data System (ADS)

Morrison, N. A.; William, C.; Milne, W. I.

2003-12-01

Radio frequency (rf) generated methane plasmas are commonly employed in the deposition of hydrogenated amorphous carbon (a-C:H) thin films. However, very little is known about the rf discharge chemistry and how it relates to the deposition process. Consequently, we have characterized a low-pressure methane plasma and compared the results with those obtained theoretically by considering the steady-state kinetics of the chemical processes present in a low-pressure plasma reactor, in order to elucidate the dominant reaction channels responsible for the generation of the active precursors required for film growth. Mass spectrometry measurements of the gas phase indicated little variation in the plasma chemistry with increasing electron temperature. This was later attributed to the partial saturation of the electron-impact dissociation and ionization rate constants at electron temperatures in excess of ˜4 eV. The ion densities in the plasma were also found to be strongly dependent upon the parent neutral concentration in the gas phase, indicating that direct electron-impact reactions exerted greater influence on the plasma chemistry than secondary ion-neutral reactions.

Diurnal variations of Titan

NASA Astrophysics Data System (ADS)

Cui, J.; Galand, M.; Yelle, R. V.; Vuitton, V.; Wahlund, J.-E.; Lavvas, P. P.; Mueller-Wodarg, I. C. F.; Kasprzak, W. T.; Waite, J. H.

2009-04-01

We present our analysis of the diurnal variations of Titan's ionosphere (between 1,000 and 1,400 km) based on a sample of Ion Neutral Mass Spectrometer (INMS) measurements in the Open Source Ion (OSI) mode obtained from 8 close encounters of the Cassini spacecraft with Titan. Though there is an overall ion depletion well beyond the terminator, the ion content on Titan's nightside is still appreciable, with a density plateau of ~700 cm-3 below ~1,300 km. Such a plateau is associated with the combination of distinct diurnal variations of light and heavy ions. Light ions (e.g. CH5+, HCNH+, C2H5+) show strong diurnal variation, with clear bite-outs in their nightside distributions. In contrast, heavy ions (e.g. c-C3H3+, C2H3CNH+, C6H7+) present modest diurnal variation, with significant densities observed on the nightside. We propose that the distinctions between light and heavy ions are associated with their different chemical loss pathways, with the former primarily through "fast" ion-neutral chemistry and the latter through "slow" electron dissociative recombination. The INMS data suggest day-to-night transport as an important source of ions on Titan's nightside, to be distinguished from the conventional scenario of auroral ionization by magnetospheric particles as the only ionizing source on the nightside. This is supported by the strong correlation between the observed night-to-day ion density ratios and the associated ion lifetimes. We construct a time-dependent ion chemistry model to investigate the effects of day-to-night transport on the ionospheric structures of Titan. The predicted diurnal variation has similar general characteristics to those observed, with some apparent discrepancies which could be reconciled by imposing fast horizontal thermal winds in Titan's upper atmosphere.

The Chemistry of Deposit Formation in Distillate Fuels,

DTIC Science & Technology

1986-01-01

identified as groups of multiple isomers of the alkylphenols , alkylnaphthols and alkylphenylphenols listed in Table VI. Ion chromatograms for isomers...matching was achieved. For example, Figure 8 shows the reconstructed ion chromatogram for m/z 136 (C3- alkylphenols ), which corresponds to peak cluster 13 in

The radiation chemistry of nuclear reactor decontaminating reagents

NASA Astrophysics Data System (ADS)

Sellers, Robin M.

Processes involved in the radiation chemistry of some typical nuclear reactor decontaminating reagents including complexing, reducing and oxidising agents are described. It is concluded that radiation-induced decomposition is only likely to be a problem with dilute formulations, and/or with minor additives such as corrosion inhibitors which are not protected from attack by the other constituents. Addition of a "sacrificial" compound may be necessary to overcome this. The importance of considering loss of function, rather than the decomposition rate of the starting material, is emphasised. Reagents based on low oxidation state metal ions (LOMI) can be regenerated by the radiation field in the presence of formate ion.

Ab Initio Calculations Applied to Problems in Metal Ion Chemistry

NASA Technical Reports Server (NTRS)

Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Partridge, Harry; Arnold, James O. (Technical Monitor)

1994-01-01

Electronic structure calculations can provide accurate spectroscopic data (such as molecular structures) vibrational frequencies, binding energies, etc.) that have been very useful in explaining trends in experimental data and in identifying incorrect experimental measurements. In addition, ab initio calculations. have given considerable insight into the many interactions that make the chemistry of transition metal systems so diverse. In this review we focus on cases where calculations and experiment have been used to solve interesting chemical problems involving metal ions. The examples include cases where theory was used to differentiate between disparate experimental values and cases where theory was used to explain unexpected experimental results.

Laboratory chemistry relevant to understanding and modeling the ionosphere of Titan.

PubMed

Adams, Nigel G; Mathews, L Dalila; Osborne, David

2010-01-01

Laboratory data have a dual and critical role in interpreting information obtained from the Cassini spacecraft in its passes through the Titan ionosphere. Firstly, in situ mass spectra are obtained by Cassini and their conversion into atmospheric molecular composition requires chemical modeling to create agreement between the observed mass spectra and those determined from the models. Secondly, once agreement is obtained, then the chemical model can be considered to represent the evolution of the Titan atmosphere. As a contribution to these endeavors in the past, laboratory measurements have been made in the Selected Ion Flow Tube (SIFT) of the reactions of a series of ring molecules with the important ionospheric ion CH3+. These reactions showed that a dominant reaction channel is association. In the present study, this work has been extended to reactions of another important Titan ion C3H3+. These ion-molecule reactions have also been studied at room temperature using a SIFT. Reactions have been studied in detail with benzene, toluene and pyridine and show again that association is very important. The loss of ionization in the ionosphere is then controlled by electron-ion dissociative recombination of the association ions and their progeny. The recombination reactions have been studied as a function of temperature (300 to 550 K) using a flowing afterglow. These combined data have been used to develop a subset of the chemistry and test its viability. They have indicated that association of the important Titan ions with the abundant nitrogen, followed by switching of the nitrogen for the ring compounds, can build up larger species, perhaps resulting in multi-rings. Recombination of such species can affect the ionization balance and provide species which can contribute to the parallel neutral chemistry. Species are suggested that should be looked for in the in situ mass spectra.

Assessment of hydrogeochemical status of groundwater in a coastal region of Southeast coast of India

NASA Astrophysics Data System (ADS)

Chidambaram, S.; Sarathidasan, J.; Srinivasamoorthy, K.; Thivya, C.; Thilagavathi, R.; Prasanna, M. V.; Singaraja, C.; Nepolian, M.

2018-03-01

A study was conducted in a coastal region of Cuddalore district of Tamil Nadu, India, to identify the hydrogeochemical processes controlling the groundwater chemistry. The major geological units of the study area are sandstone, clay, alluvium, and laterite soils of Tertiary and Quaternary age. A total of 64 groundwater samples were measured for major ions and stable isotopes. Higher electrical conductivity values indicate the poor quality groundwater along the coastal region. Saline water intrusion mainly affects the hydrochemical composition of the aquifer water reflected by Na-Cl-type waters. Cl-/(Cl- + HCO3 -) ratio also indicates the mixing of fresh groundwater with saline water. The results of δD and δ18O analyses show that isotopic compositions of groundwater ranges from - 7.7 to - 2.1‰ for δ18O and from - 55.6 to - 18.5‰ for δD. Correlation and factor analysis were carried out to find the association of ions and to determine the major factors controlling the groundwater chemistry of the region. The study indicates that ion exchange, weathering, salt water intrusion along the coast, and anthropogenic impacts are the major controlling factors for the groundwater chemistry of the region.

Cryogenic reactant storage for lunar base regenerative fuel cells

NASA Technical Reports Server (NTRS)

Kohout, Lisa L.

1989-01-01

There are major advantages to be gained by integrating a cryogenic reactant storage system with a hydrogen-oxygen regenerative fuel cell (RFC) to provide on-site electrical power during the lunar night. Although applicable to any power system using hydrogen-oxygen RFC's for energy storage, cryogenic reactant storage offers a significant benefit whenever the sun/shade cycle and energy storage period approach hundreds of hours. For solar power installations on the moon, cryogenic reactant storage reduces overall specific mass and meteoroid vulnerability of the system. In addition, it offers synergistic benefits to on-site users, such as availability of primary fuel cell reactants for surface rover vehicles and cryogenic propellants for OTV's. The integration involves processing and storing the RFC reactant streams as cryogenic liquids rather than pressurized gases, so that reactant containment (tankage per unit mass of reactants) can be greatly reduced. Hydrogen-oxygen alkaline RFC's, GaAs photovoltaic (PV) arrays, and space cryogenic processing/refrigeration technologies are assumed to be available for the conceptual system design. Advantages are demonstrated by comparing the characteristics of two power system concepts: a conventional lunar surface PV/RFC power system using pressurized gas storage in SOA filament wound pressure vessels and, that same system with gas liquefaction and storage replacing the pressurized storage. Comparisons are made at 20 and 250 kWe. Although cryogenic storage adds a processing plant (drying and liquefaction) to the system plus 30 percent more solar array to provide processing power, the approximate order of magnitude reduction in tankage mass, confirmed by this analysis, results in a reduction in overall total system mass of approximately 50 percent.

Influence of the reactant carbon-hydrogen-oxygen composition on the key products of the direct gasification of dewatered sewage sludge in supercritical water.

PubMed

Gong, Miao; Zhu, Wei; Fan, Yujie; Zhang, Huiwen; Su, Ying

2016-05-01

The supercritical water gasification of ten different types of dewatered sewage sludges was investigated to understand the relationship between sludge properties and gasification products. Experiments were performed in a high-pressure autoclave at 400°C for 60 min. Results showed that gasification of sewage sludge in supercritical water consists mainly of a gasification reaction, a carbonization reaction and a persistent organic pollutants synthesis reaction. Changes in the reactant C/H/O composition have significant effects on the key gasification products. Total gas production increased with increasing C/H2O of the reactant. The char/coke content increased with increasing C/H ratio of the reactant. A decrease in the C/O ratio of the reactant led to a reduction in polycyclic aromatic hydrocarbon formation. This means that we can adjust the reactant C/H/O composition by adding carbon-, hydrogen-, and oxygen-containing substances such as coal, algae and H2O2 to optimize hydrogen production and to inhibit an undesired by-product formation. Copyright © 2016 Elsevier Ltd. All rights reserved.

Molecular Layer Deposition for Surface Modification of Lithium-Ion Battery Electrodes

DOE PAGES

Ban, Chunmei; George, Steven M.

2016-10-21

This review presents the MLD process and its outstanding attributes for electrochemical applications and is inspired by recent successes in applying molecular layer deposition (MLD) to stabilize lithium-ion (Li-ion) electrodes. Furthermore, this review discusses various MLD materials and their implementation in Li-ion electrodes. The rationale behind these emerging uses of MLD is examined to motivate future efforts on the fundamental understanding of interphase chemistry and the development of new materials for enhanced electrochemical performance.

Exploring Cryogenic Focused Ion Beam Milling as a Group III-V Device Fabrication Tool

DTIC Science & Technology

2013-09-01

boiling, triple , and critical points of the elements” in CRC Handbook of Chemistry and Physics, 92nd ed., Boca Raton, FL: CRC press, 2011-2012, p. 4...The most widely used ion source in FIB instruments is a gallium (Ga) liquid metal ion source (LMIS) [4]. Gallium is attractive as an ion source...Figure 3b. EDS spectra were captured at different points across the patterned region of the room temperature milled sample, as indicated in Figure 4

Learning to predict chemical reactions.

PubMed

Kayala, Matthew A; Azencott, Chloé-Agathe; Chen, Jonathan H; Baldi, Pierre

2011-09-26

Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles, respectively, are not high throughput, are not generalizable or scalable, and lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry data set consisting of 1630 full multistep reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top-ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of nonproductive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal ( http://cdb.ics.uci.edu) under the Toolkits section.

Learning to Predict Chemical Reactions

PubMed Central

Kayala, Matthew A.; Azencott, Chloé-Agathe; Chen, Jonathan H.

2011-01-01

Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles respectively are not high-throughput, are not generalizable or scalable, or lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry dataset consisting of 1630 full multi-step reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval, problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of non-productive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal (http://cdb.ics.uci.edu) under the Toolkits section. PMID:21819139

Predictive beyond-mean-field rate equations for multisite lattice–gas models of catalytic surface reactions: CO oxidation on Pd(100)

DOE PAGES

Liu, Da -Jiang; Zahariev, Federico; Gordon, Mark S.; ...

2016-11-29

Tailored multisite lattice–gas (msLG) models are developed for CO oxidation on Pd(100) at low-pressures. These models include multiple adsorption site types and superlattice adlayer ordering due to short-range exclusion for highly mobile reactant adspecies. However, they are simplified to neglect longer-range weaker adspecies interactions, so that the key energetic parameters are the CO desorption barrier and the reaction barrier. We discuss existing density functional theory results for these energies and present additional analysis for CO adsorption. After also including an appropriate nontrivial specification of the dynamics of adsorption onto mixed reactant adlayers, we develop rate equations for the reaction kinetics.more » Our formulation goes beyond traditional mean-field (MF) Langmuirian treatments by accounting for multiple adsorption sites and for the strong spatial correlations associated with superlattice ordering. Specifically, we utilize factorization approximations based on appropriate site motifs, and also Padé resummation of exact low-coverage expansions for sticking coefficients. Our beyond-MF rate equations are successful in accurately predicting key aspects of reactive steady-state behavior, and thus expand the utility of rate equation formulations in surface chemistry. This is confirmed by comparison with precise kinetic Monte Carlo simulation results. Furthermore, we not only assess bistability and criticality observed for CO oxidation but also find more complex multistability associated with symmetry-breaking transitions in high-coverage CO adlayers.« less

Mass transfer and carbon isotope evolution in natural water systems

USGS Publications Warehouse

Wigley, T.M.L.; Plummer, Niel; Pearson, F.J.

1978-01-01

This paper presents a theoretical treatment of the evolution of the carbon isotopes C13 and C14 in natural waters and in precipitates which derive from such waters. The effects of an arbitrary number of sources (such as dissolution of carbonate minerals and oxidation of organic material) and sinks (such as mineral precipitation, CO2 degassing and production of methane), and of equilibrium fractionation between solid, gas and aqueous phases are considered. The results are expressed as equations relating changes in isotopic composition to changes in conventional carbonate chemistry. One implication of the equations is that the isotopic composition of an aqueous phase may approach a limiting value whenever there are simultaneous inputs and outputs of carbonate. In order to unambiguously interpret isotopic data from carbonate precipitates and identify reactants and products in reacting natural waters, it is essential that isotopic changes are determined chiefly by reactant and product stoichiometry, independent of reaction path. We demonstrate that this is so by means of quantitative examples. The evolution equations are applied to: 1. (1) carbon-14 dating of groundwaters; 2. (2) interpretation of the isotopic composition of carbonate precipitates, carbonate cements and diagenetically altered carbonates; and 3. (3) the identification of chemical reaction stoichiometry. These applications are illustrated by examples which show the variation of ??C13 in solutions and in precipitates formed under a variety of conditions involving incongruent dissolution, CO2 degassing, methane production and mineral precipitation. ?? 1978.

From D-sorbitol to five-membered bis(cyclo-carbonate) as a platform molecule for the synthesis of different original biobased chemicals and polymers.

PubMed

Furtwengler, Pierre; Avérous, Luc

2018-06-14

Bis(cyclo-carbonate) was successfully synthesized from D-sorbitol (Sorb-BisCC) through an environmentally friendly process with dimethyl carbonate (DMC) as a reactant. In agreement with green chemistry principles, solvent free reactions were catalyzed and took place at low temperature. The reaction yield was increased until 50%, with the use of 1.3.5-triazabicyclo[4.4.0]dec-5-ene as catalyst and a continuous DMC feed to limit the side-reactions or the loss of reactant by azeotropic flux with a reactional subsidiary product. The obtained Sorb-BisCC is a remarkable platform molecule which could compete with others polycyclic platform molecules (isosorbide). Sorb-BisCC can be e.g., used to synthesize different chemicals such as short and long polyols, or novel biobased non-isocyanate polyurethanes (NIPU). Two Sorb-BisCC molecules have been coupled to obtain novel cyclic diols with pendant side chains. Polyether polyols were also obtained by anionic ring opening polymerization. According to the synthesis conditions, these synthetized polyether polyols range from partially to highly cross-linked materials. Finally, NIPU were synthesized with short and biobased fatty diamines. These different modifications and synthesis highlight the versatility of the Sorb-BisCC and demonstrated its high potential as building block. Sorb-BisCC can be considered as a platform molecule to open the way to different original and biobased chemical architectures.

Carbon dioxide-soluble polymers and swellable polymers for carbon dioxide applications

DOEpatents

DeSimone, Joseph M.; Birnbaum, Eva; Carbonell, Ruben G.; Crette, Stephanie; McClain, James B.; McCleskey, T. Mark; Powell, Kimberly R.; Romack, Timothy J.; Tumas, William

2004-06-08

A method for carrying out a catalysis reaction in carbon dioxide comprising contacting a fluid mixture with a catalyst bound to a polymer, the fluid mixture comprising at least one reactant and carbon dioxide, wherein the reactant interacts with the catalyst to form a reaction product. A composition of matter comprises carbon dioxide and a polymer and a reactant present in the carbon dioxide. The polymer has bound thereto a catalyst at a plurality of chains along the length of the polymer, and wherein the reactant interacts with the catalyst to form a reaction product.

Mechanism of Zn Insertion into Nanostructured δ-MnO 2 : A Nonaqueous Rechargeable Zn Metal Battery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Sang-Don; Kim, Soojeong; Li, Dongguo

2017-05-19

Unlike the more established lithium-ion based energy storage chemistries, the complex intercalation chemistry of multivalent cations in a host lattice is not well understood, especially the relationship between the intercalating species solution chemistry and the prevalence and type of side reactions. Among multivalent metals, a promising model system can be based on nonaqueous Zn2+ ion chemistry. Several examples of these systems support the use of a Zn metal anode, and reversible intercalation cathodes have been reported. This study utilizes a combination of analytical tools to probe the chemistry of a nanostructured delta-MnO2 cathode in association with a nonaqueous acetonitrile-Zn(TFSI)(2) electrolytemore » and a Zn metal anode. As many of the issues related to understanding a multivalent battery relate to the electrolyte electrode interface, the high surface area of a nanostructured cathode provides a significant interface between the electrolyte and cathode host that maximizes the spectroscopic signal of any side reactions or minor mechanistic pathways. Numerous factors affecting capacity fade and issues associated with the second phase formation including Mn dissolution in heavily cycled Zn/delta-MnO2 cells are presented including dramatic mechanistic differences in the storage mechanism of this couple when compared to similar aqueous electrolytes are noted.« less

Infrared Spectrometry of Inorganic Salts

ERIC Educational Resources Information Center

Ackermann, Martin N.

1970-01-01

Describes a general chemistry experiment which uses infrared spectroscopy to analyze inorganic ions and thereby serves to introduce an important instrumental method of analysis. Presents a table of eight anions and the ammonium ion with the frequencies of their normal modes, as well as the spectra of three sulfate salts. (RR)

Fun with Ionic Compounds

ERIC Educational Resources Information Center

Logerwell, Mollianne G.; Sterling, Donna R.

2007-01-01

Ionic bonding is a fundamental topic in high school chemistry, yet it continues to be a concept that students struggle to understand. Even if they understand atomic structure and ion formation, it can be difficult for students to visualize how ions fit together to form compounds. This article describes several engaging activities that help…

Chemistry Within Molecular Clusters

DTIC Science & Technology

1992-06-01

reactions, and only occur within van der Waals clusters. 23 They include the generation of (C2H4F2),>4H+ ions from 1,1- difluoroethane clusters, 4 the...of fragment ions, and identification of the molecule must be made by the characteristic fragmentation pattern. The mass spectrum of 1,1- difluoroethane

Chemistry within Molecular Clusters

DTIC Science & Technology

1992-05-29

within van der Waals clusters. 23 They include the generation of (C2H4F 2),,>4H+ ions from 1,1- difluoroethane clusters, 24 the generation of (CH 3...fragment ions, and identification of the molecule must be made by the characteristic fragmentation pattern. The mass spectrum of 1,1- difluoroethane (DFE

Collisional Detachment of Anions using Fourier Transform Mass Spectrometry

DTIC Science & Technology

1992-12-01

cross section. which itself may be the object of the measurement. Two pressure gauges are employed to monitor system pressure: a standard nude ion...Transform Ion Cyclotron Res- onance Mass Spectrometry: The Teen Years," Analytical Chemistry, 63:215A-229A (February 1991). 88. Marshall, Alan G., et al

The Physics and Chemistry of Small Translucent Molecular Clouds. VII. SO + and H 2S

NASA Astrophysics Data System (ADS)

Turner, B. E.

1996-09-01

In this third paper on sulfur species, we have conducted a survey of SO+ (two transitions) and H2S (one transition) in our standard samples of 11 cirrus cores and 27 Clemens-Barvainis translucent objects whose structures and chemistry have been studied earlier in this series. SO+(2II½, J = 3/2-1/2) is seen weakly in 12 objects, while H2S (110 -101) is detected quite strongly in 31 objects. These results are modeled in terms of our previous hydrostatic equilibrium and n ˜r-α structures together with other chemical and physical properties derived earlier. The typical H2S fractional abundance is large, ˜1 × 10-8, and increases monotonically with increasing extinction in the 1.2-2.7 mag range (edge-to-center). Thus H2S displays the same characteristic transition between diffuse and dense cloud chemistry as do SO, SO2, CS, HCS +, HCO +, and other species studied in this series. By contrast, the SO + abundances are small, 1 × 10-9, and exhibit a marginal decrease with increasing extinction. The simple ion-molecule network as used by Turner for sulfur chemistry includes the sulfur hydride species and predicts the observed parameters of SO+ but predicts an H2S abundance 2 orders of magnitude less than observed. Of the 10 species presently analyzed in detail in the translucent cores, H2S is only the second (along with H2CO) that fails to be explained in detail by quiescent cloud ion-molecule chemistry. Various catalytic models of H2S on grains are discussed. Photocatalysis of H2S is found capable of producing the observed abundances but only for sizable accreted mantles. Other types of surface chemistry are also successful but are close to the limits of possible efficiencies. We have detected OCS and H2CS in one object, CB 17, with abundances of 1 × 10-9 and 7 × 10-9 respectively. Our ion-molecule model has been expanded to include OCS and H2CS chemistry. We find that the model fits observed abundances within a factor of 3 for both species.

What is the fundamental ion-specific series for anions and cations? Ion specificity in standard partial molar volumes of electrolytes and electrostriction in water and non-aqueous solvents.

PubMed

Mazzini, Virginia; Craig, Vincent S J

2017-10-01

The importance of electrolyte solutions cannot be overstated. Beyond the ionic strength of electrolyte solutions the specific nature of the ions present is vital in controlling a host of properties. Therefore ion specificity is fundamentally important in physical chemistry, engineering and biology. The observation that the strengths of the effect of ions often follows well established series suggests that a single predictive and quantitative description of specific-ion effects covering a wide range of systems is possible. Such a theory would revolutionise applications of physical chemistry from polymer precipitation to drug design. Current approaches to understanding specific-ion effects involve consideration of the ions themselves, the solvent and relevant interfaces and the interactions between them. Here we investigate the specific-ion effects trends of standard partial molar volumes and electrostrictive volumes of electrolytes in water and eleven non-aqueous solvents. We choose these measures as they relate to bulk properties at infinite dilution, therefore they are the simplest electrolyte systems. This is done to test the hypothesis that the ions alone exhibit a specific-ion effect series that is independent of the solvent and unrelated to surface properties. The specific-ion effects trends of standard partial molar volumes and normalised electrostrictive volumes examined in this work show a fundamental ion-specific series that is reproduced across the solvents, which is the Hofmeister series for anions and the reverse lyotropic series for cations, supporting the hypothesis. This outcome is important in demonstrating that ion specificity is observed at infinite dilution and demonstrates that the complexity observed in the manifestation of specific-ion effects in a very wide range of systems is due to perturbations of solvent, surfaces and concentration on the underlying fundamental series. This knowledge will guide a general understanding of specific-ion effects and assist in the development of a quantitative predictive theory of ion specificity.

Gas Phase Ion-Molecule Chemistry of Carbon, Nitrogen and Oxygen Compounds.

DTIC Science & Technology

1985-01-29

silyl anions aza allyl anion) phosphide anion sulfides) Reactivity; nitrite estersj electron affinityMechanism’, sulfur dioxidej. (cont’d) M L..J A6*rAcr...use of silane chemistry to attack a problem of fundamental importance to all organic chemistry, the relative acidity of the alkanes.20 While it is well...alkane lost are a measure of the relative acidity of RH. For example, because ethane is lost less easily than methane, we believe that the ethyl anion

Perspectives on Computational Organic Chemistry

PubMed Central

Streitwieser, Andrew

2009-01-01

The author reviews how his early love for theoretical organic chemistry led to experimental research and the extended search for quantitative correlations between experiment and quantum calculations. The experimental work led to ion pair acidities of alkali-organic compounds and most recently to equilibria and reactions of lithium and cesium enolates in THF. This chemistry is now being modeled by ab initio calculations. An important consideration is the treatment of solvation in which coordination of the alkali cation with the ether solvent plays a major role. PMID:19518150

Chemistry WebBook

National Institute of Standards and Technology Data Gateway

SRD 69 NIST Chemistry WebBook (Web, free access)   The NIST Chemistry WebBook contains: Thermochemical data for over 7000 organic and small inorganic compounds; thermochemistry data for over 8000 reactions; IR spectra for over 16,000 compounds; mass spectra for over 33,000 compounds; UV/Vis spectra for over 1600 compounds; electronic and vibrational spectra for over 5000 compounds; constants of diatomic molecules(spectroscopic data) for over 600 compounds; ion energetics data for over 16,000 compounds; thermophysical property data for 74 fluids.

Chemistry in cometary comae

NASA Technical Reports Server (NTRS)

Irvine, W. M.; Dickens, J. E.; Lovell, A. J.; Schloerb, F. P.; Senay, M.; Bergin, E. A.; Jewitt, D.; Matthews, H. E.

1998-01-01

Significant gas-phase chemistry occurs in the comae of bright comets, as is demonstrated here for the case of Comet Hale-Bopp. The abundance ratio of the two isomers, hydrogen cyanide and hydrogen isocyanide, is shown to vary with heliocentric distance in a way that is consistent with production of HNC by ion-molecule chemistry initiated by the photoionization of water. Likewise, the first maps of emission from HCO+ show an abundance and an extended distribution that are consistent with the same chemical model.

pH responsive label-assisted click chemistry triggered sensitivity amplification for ultrasensitive electrochemical detection of carbohydrate antigen 24-2.

PubMed

Zheng, Yun; Zhao, Lihua; Ma, Zhanfang

2018-05-15

Sensitivity amplification strategy by implementing click chemistry in the construction of biosensing interface can efficiently improve the performance of immunosensor. Herein, we developed a sandwich-type amperometric immunosensor for ultrasensitive detection of carbohydrate antigen 24-2 (CA 242) based on pH responsive label-assisted click chemistry triggered sensitivity amplification strategy. The sensitivity of amperometric immunosensor relies on the current response differences (ΔI) caused by per unit concentration target analyte. The pH responsive Cu 2+ -loaded polydopamine (CuPDA) particles conjugated with detection antibodies were employed as labels, which can release Cu(II) ions by regulating pH. In the presence of ascorbic acid (reductant), Cu(II) ions were reduced to Cu(I) ions. Azide-functionalized double-stranded DNA (dsDNA) as signal enhancer was immobilized on the substrate through Cu + -catalyzed azide/alkyne cycloaddition reaction. With the help of the click reaction, the ΔI caused by target was elevated prominently, resulting in sensitivity amplification of the immunosensor. Under optimal condition, the proposed immunosensor exhibited excellent performance with linear range from 0.0001 to 100 U mL -1 and ultralow detection limit of 20.74 μU mL -1 . This work successfully combines click chemistry with pH-responsive labels in sandwich-type amperometric immunosensor, providing a promising sensitivity amplification strategy to construct immunosensing platform for analysis of other tumor marker. Copyright © 2018 Elsevier B.V. All rights reserved.

Facile synthesis of Li2S-P2S5 glass-ceramics electrolyte with micron range particles for all-solid-state batteries via a low-temperature solution technique (LTST)

NASA Astrophysics Data System (ADS)

Choi, Sunho; Lee, Sewook; Park, Jongyeop; Nichols, William T.; Shin, Dongwook

2018-06-01

A lithium ion conductive 75Li2Sṡ25P2S5 glass-ceramics electrolyte is, for the first time, successfully synthesized via a new low-temperature solution technique (LTST) and compared to the conventional mechanical-milling technique. Both samples are composed of the highly lithium ion conductive thio-LISICON III analog phase. Due to the uniform dispersion of reactants in an organic liquid, the use of LTST produced significantly smaller and more uniform particle sizes (2.2 ± 1.68 μm) resulting in a 6.5 times higher specific surface area compared to the mechanically-milled sample. A pronounced enhancement of both the rate capability and cyclability is demonstrated for the LTST solid electrolyte sample due to the more intimate contact with the LiCoO2 active material. Furthermore, the LTST sample shows excellent electrochemical stability throughout the potential range of -1 to 5 V. These results suggest that the proposed technique using the optimized LTST process is promising for the preparation of 75Li2Sṡ25P2S5 solid electrolytes for use in advanced Li-ion batteries.

Combustion chemistry and flame structure of furan group biofuels using molecular-beam mass spectrometry and gas chromatography – Part II: 2-Methylfuran

PubMed Central

Tran, Luc-Sy; Togbé, Casimir; Liu, Dong; Felsmann, Daniel; Oßwald, Patrick; Glaude, Pierre-Alexandre; Fournet, René; Sirjean, Baptiste; Battin-Leclerc, Frédérique; Kohse-Höinghaus, Katharina

2013-01-01

This is Part II of a series of three papers which jointly address the combustion chemistry of furan and its alkylated derivatives 2-methylfuran (MF) and 2,5-dimethylfuran (DMF) under premixed low-pressure flame conditions. Some of them are considered to be promising biofuels. With furan as a common basis studied in Part I of this series, the present paper addresses two laminar premixed low-pressure (20 and 40 mbar) flat argon-diluted (50%) flames of MF which were studied with electron-ionization molecular-beam mass spectrometry (EI-MBMS) and gas chromatography (GC) for equivalence ratios φ=1.0 and 1.7, identical conditions to those for the previously reported furan flames. Mole fractions of reactants, products as well as stable and reactive intermediates were measured as a function of the distance above the burner. Kinetic modeling was performed using a comprehensive reaction mechanism for all three fuels given in Part I and described in the three parts of this series. A comparison of the experimental results and the simulation shows reasonable agreement, as also seen for the furan flames in Part I before. This set of experiments is thus considered to be a valuable additional basis for the validation of the model. The main reaction pathways of MF consumption have been derived from reaction flow analyses, and differences to furan combustion chemistry under the same conditions are discussed. PMID:24518895