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921.
Mass spectrometry is a widely used method to obtain information about the structures of molecules. This technique was introduced to beginning first-year organic chemistry students as an experiment that focused on the identification of the molecular ion from experimental data. After students had correctly identified the molecular ion in their samples, they learn other information that can be deduced from the molecular ion. 相似文献
922.
Bijan Das Rabindra N. Roy Kenneth S. Pitzer Darin R. Gregory Stephanie A. Kiefer 《Journal of solution chemistry》2000,29(3):289-297
A comprehensive equation for the thermodynamic properties of the systemGaCl3-HCl-H2O at 25°C in the ion-interaction (Pitzer) equation form has been generatedon the basis of a recent and comprehensive array of electrochemical cellmeasurements of the HCl activity at total stoichiometric ionic strengths from 0.01 to 3.0mol-kg–1. Alternate equations with and without explicit consideration of thehydrolyzed product GaOH2+ as a separate species have been tested. Excellentagreement is obtained between the calculated and measured cell potentials forthe formulation, which includes GaOH2+ as an additional species. The effect offurther hydrolysis as well as that of complex formation has been found to benegligible. While a satisfactory set of Pitzer parameters has been found, it wasnot possible to obtain a unique thermodynamic representation for this systembecause of large uncertainties in the first hydrolysis constant of Ga(III) and becauseof redundancies and intrinsic correlations between some of the Pitzer parameters.Deceased December 26, 1997 相似文献
923.
The application of modulated temperature programs to thermomechanical analysis can be used to separate the reversible nature
of thermal expansion from irreversible deformation arising from creep under the applied load or changes in dimensions due
to relaxation of orientation. The effect of experimental variables and calibration are described. Modulated temperature TMA
allows the time-dependent nature of thermal expansivity to be studied. Measurements made under compression afford a means
of measuring the thermal expansivity of soft specimens independently of initial load. Application of these principles to scanning
thermal microscopy leads to a novel method of generating image contrast based upon local changes thermal expansivity of a
specimen.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
924.
The study of factors affecting human fertility is an important problem affording interesting statistical and computational challenges. Analyses of human fertility rates must cope with extra variability in fecundability parameters as well as a host of covariates ranging from the obvious, such as coital frequency, to the subtle, like the smoking habits of the female’s mother. In retrospective human fecundity studies, researchers ask couples the time required to conceive. This time-to-pregnancy data often exhibits digit preference bias, among other problems. We introduce computationally intensive models with sufficient flexibility to represent such bias and other causes yielding a similar lack of monotonicity in conception probabilities. 相似文献
925.
Synthesis of C-aryl-Δ-glycopyranosides via uncatalyzed addition of triarylindium reagents to glycals
Sarah Price 《Tetrahedron letters》2004,45(27):5197-5201
2,3-Unsaturated-C-aryl glycopyranosides are important intermediates in the synthesis of medicinally important C-aryl glycosides. Treatment of glycal acetates with triarylindiums in ether at room temperature gives good yields of C-aryl-Δ2,3-glycosides of predominantly α-configuration. The mechanism of this reaction likely involves the formation of an oxocarbenium ion intermediate via indium(III) Lewis acid-assisted ionization of the glycal C.3 acetate. Coupling of trivinyl- and tris(alkynyl)indiums with glycals similarly led to C-vinyl- and C-alkynyl-Δ2,3-glycosides in good yield. 相似文献
926.
Gabriele Kociok‐Köhn Kieran C. Molloy Gareth J. Price Douglas R. G. Smith 《Journal of heterocyclic chemistry》2016,53(1):64-68
The structures of 1,3 bis‐(allyl)cytosinium bromide ( 1 ), 7,9 bis‐(allyl)adeninium bromide hydrate ( 2 ) and 3‐(butenyl)adeninium bromide ( 3 ) have been determined. 1 is dimeric via N―H…Br hydrogen bonds, which further associate into ribbons via weaker C―H…Br interactions. 2 is also dimeric, now from N―H…N hydrogen bonds, which build up further through a complex array of hydrogen bonds involving both the anion and water of crystallization (O―H…N, O―H…Br, C―H…Br). 3 does not dimerise but forms polymeric sheets via a series of N―H…N, C―H…N and C―H…Br hydrogen bonds. 相似文献
927.
Xiaoyu Zhou Dr. Gregory A. Price Dr. Glenn J. Sunley Prof. Dr. Christophe Copéret 《Angewandte Chemie (International ed. in English)》2023,62(52):e202314274
Cobalt-based catalysts are well-known to convert syngas into a variety of Fischer–Tropsch (FTS) products depending on the various reaction parameters, in particular particle size. In contrast, the reactivity of these particles has been much less investigated in the context of CO2 hydrogenation. In that context, Surface organometallic chemistry (SOMC) was employed to synthesize highly dispersed cobalt nanoparticles (Co-NPs) with particle sizes ranging from 1.6 to 3.0 nm. These SOMC-derived Co-NPs display significantly different catalytic performances under CO2 hydrogenation conditions: while the smallest cobalt nanoparticles (1.6 nm) catalyze mainly the reverse water-gas shift (rWGS) reaction, the larger nanoparticles (2.1–3.0 nm) favor the expected methanation activity. Operando X-ray absorption spectroscopy shows that the smaller cobalt particles are fully oxidized under CO2 hydrogenation conditions, while the larger ones remain mostly metallic, paralleling the observed difference of catalytic performances. This fundamental shift of selectivity, away from methanation to reverse water-gas shift for the smaller nanoparticles is noteworthy and correlates with the formation of CoO under CO2 hydrogenation conditions. 相似文献
928.
Super water- and oil-repellent surfaces on intrinsically hydrophilic and oleophilic porous silicon films 总被引:3,自引:0,他引:3
Cao L Price TP Weiss M Gao D 《Langmuir : the ACS journal of surfaces and colloids》2008,24(5):1640-1643
We demonstrate that porous Si films fabricated by a convenient gold-assisted electroless etching process, which possess a hierarchical porous structure consisting of micrometer-sized asperities superimposed onto a network of nanometer-sized pores, are able to induce a superhydrophobic phenomenon on an intrinsically hydrophilic hydrogen-terminated Si surface and a superoleophobic phenomenon on an intrinsically oleophilic self-assembled monolayer-coated Si surface. Through comparison with porous Si films consisting of vertically aligned straight pores, which are hydrophilic and oleophilic, we show that an overhang structure resulting from the hierarchical porous structure is essential to preventing water and oil from penetrating the texture of the films and inducing the observed macroscopic superhydrophobic and superoleophobic phenomena. 相似文献
929.
Anderson AS Dattelbaum AM Montaño GA Price DN Schmidt JG Martinez JS Grace WK Grace KM Swanson BI 《Langmuir : the ACS journal of surfaces and colloids》2008,24(5):2240-2247
We report a general procedure to prepare functional organic thin films for biological assays on oxide surfaces. Silica surfaces were functionalized by self-assembly of an amine-terminated silane film using both vapor- and solution-phase deposition of 3'-aminopropylmethyldiethoxysilane (APMDES). We found that vapor-phase deposition of APMDES under reduced pressure produced the highest quality monolayer films with uniform surface coverage, as determined by atomic force microscopy (AFM), ellipsometry, and contact angle measurements. The amine-terminated films were chemically modified with a mixture of carboxylic acid-terminated poly(ethylene glycol) (PEG) chains of varying functionality. A fraction of the PEG chains (0.1-10 mol %) terminated in biotin, which produced a surface with an affinity toward streptavidin. When used in pseudo-sandwich assays on waveguide platforms for the detection of Bacillus anthracis protective antigen (PA), these functional PEG surfaces significantly reduced nonspecific binding to the waveguide surface while allowing for highly specific binding. Detection of PA was used to validate these films for sensing applications in both buffer and complex media. Ultimately, these results represent a step toward the realization of a robust, reusable, and autonomous biosensor. 相似文献
930.
Delgado R Félix V Lima LM Price DW 《Dalton transactions (Cambridge, England : 2003)》2007,(26):2734-2745
A series of the most common chelators used in magnetic resonance imaging (MRI) and in radiopharmaceuticals for medical diagnosis and tumour therapy, H(4)dota, H(4)teta, H(8)dotp and H(8)tetp, is examined from a chemical point of view. Differences between 12- and 14-membered tetraazamacrocyclic derivatives with methylcarboxylate and methylphosphonate pendant arms and their chelates with divalent first-series transition metal and trivalent lanthanide ions are discussed on the basis of their thermodynamic stability constants, X-ray structures and theoretical studies. 相似文献