bluuebunny/crossref_metadata_2025_split huggingface dataset:
An infrared spectroscopic study of CO and NO adsorption on bimetallic Pd‐Rh/SiO2 catalysts
Authors: Mergler Y.J. , Ramsaransing D.R.G. , Nieuwenhuys B.E. 
Published: September 2010

AbstractPure Pd/SiO2, pure Rh/SiO2, and bimetallic PdRh/SiO2 catalysts, with Pd and Rh in the atomic ratios of 75/25 at% and 50/50 at%, were studied by means of infrared (IR) spectroscopy. Spectra of adsorbed CO and NO were recorded in the temperature range from 298 to 573K. The IR spectra obtained for the bimetallic catalysts exhibit characteristic features of both Pd and Rh. The results point to the presence of alloy crystallites with properties between those of the constituent metals. Most likely the PdRh(1:1)/SiO2 catalyst consists of small Rh clusters or atoms, surrounded by Pd, whereas for the PdRh(3:1)/SiO2 catalyst the surface consists primarily of Pd. However, in the presence of NO, Rh migrates to the surface, due to the dissociation of NO and the concomitant oxidation of the metal particles. No indication of mixed sites, consisting of both Pd and Rh atoms, was found. The results are compared with those previously reported for Pt‐Rh catalysts.
Direct imaging of catalytic surface reactions in the field‐ion microscope: The oxidation of hydrogen on platinum
Authors: Block J.H. , Drachsel W. , Gorodetskii V.V. 
Published: September 2010

AbstractA field‐ion microscope (FIM) was used in the investigation of hydrogen oxidation at temperatures between 300 K and 430 K and pressures of p(O2) = 5 · 10−4 mbar, p(H2) = 3 · 10−4 to 7 · 10−4 mbar. The H2O molecules produced act as an imaging gas and display the catalytically active surface area. The structure‐sensitive H2O formation was studied under steady‐state conditions or in the oscillatory regime or in form of chemical waves. The displacement of Pt lattice atoms is spectacular in the Pt(100) plane, where the transformation from (1 × 1) Pt(100) to hex Pt(100) can be directly imaged.
Adsorption of biacetyl on Rh/SiO2 catalysts: An FTIR study
Authors: Beutel Tilman , Moroz Boris L. , Knözinger Helmut 
Published: September 2010

AbstractBiacetyl (butane‐2,3‐dione) adsorbs to silica via H bonding. Splitting of the central C‐C bond occurs on adsorption on Rh particles in Rh/SiO2 catalysts. The resulting surface‐acetyl species seems to undergo rapid decomposition even at temperatures below 300K and leads to the formation of chemisorbed CO and methyl fragments. Based on the principle of microscopic reversibility, it is concluded that acetyl species may be formed under catalytic conditions from chemisorbed CO and methyl species by migratory insertion of CO into the metal‐carbon bond of a chemisorbed methyl fragment.
The effect of propane activation over Ga‐modified H‐ZS M‐5 catalysts
Authors: Ivanova Irina I. , Derouane Eric G. , Blom Niels , Hamid Sharifah B. Abdul 
Published: September 2010

AbstractIn situ 13C MAS NMR was used to investigate the influence of total and partial pressure of propane on the initial stages of its conversion over a Ga/H‐MFI catalyst (2‐13C). Propane was the labelled reactant. Different pressures were achieved by varying the amounts of propane and of nitrogen as diluent in the cell. The nature of primary and secondary labelled reaction products depends on total pressure. High total and partial pressures of propane enhance bimolecular primary formation of n‐butane and isobutane via a BREST (Bifunctional Reaction Step) mechanism1. Low total pressure leads to methane and polymeric fragments as primary products. A reaction pathway including the formation of a polymeric hydrocarbon‐chain intermediate is proposed to account for secondary isobutane formation at low pressure. The influence of pressure on reaction equilibria and kinetics and on adsorption and exchange processes is discussed.
A model for the enantioselective hydrogenation of pyruvate catalysed by alkaloid‐modified platinum
Authors: Simons K.E. , Meheux P.A. , Griffiths S.P. , Sutherland I.M. , Johnston P. , Wells P.B. , Carley A.F. , Rajumon M.K. , Roberts M.W. , Ibbotson A. 
Published: September 2010

AbstractA LEED and XPS study of the adsorption of naphthalene, quinoline, and 10,11‐dihydrocinchonidine on Pt(111) at 300K has shown that only naphthalene forms an ordered ad‐layer, and that quinoline and the alkaloid adsorb in a disordered state and without decomposition. These experiments do not support the hypothesis of ordered adsorption of alkaloid that forms the basis of the template model for the interpretation of enantioselectivity in Pt‐catalysed pyruvate hydrogenation. The model is accordingly reviewed. Molecular modelling studies show that a highly specific 1:1 interaction between cinchonidine (or cinchonine) and pyruvate interprets the observed sense of the enantioselectivity, provided relative energy relationships derived for purely inter‐molecular interactions are valid for the same molecules in the adsorbed state. Moreover, the ‘product’ of this 1:1 interaction is a satisfactory precursor to the H‐bonded state considered responsible for the greatly enhanced rate that always accompanies enantioselective reaction over cinchona‐modified Pt. The previously published dependencies of optical yield on (a) surface concentration of adsorbed cinchonidine modifier, and (b) modifier composition for mixtures of quinine and quinidine, are shown to be in quantitative agreement with the proposed 1:1 interaction model and at variance with the ordered adsorption model. Catalysts modified and used under strictly anaerobic conditions show negligible activity and enantioselectivity demonstrating that oxygen plays a crucial role in successful catalyst preparation. XPS experiments confirm that adsorption of cinchonidine from air‐saturated ethanolic solution on Pt(111) provides an adlayer containing both alkaloid and adsorbed oxygen. (S)‐(‐)‐1‐benzyl‐pyrrolidine‐2‐methanol, various configurations of ephedrine, D‐and L‐histidine and the methyl esters of D‐ and L‐tryptophan have been examined as modifiers for supported Pt. Although there is evidence that these compounds can provide chiral direction to pyruvate hydrogenation, rate enhancement is slight and enantioselectivity is correspondingly low.
The reaction of α‐amino‐substituted diphenylphosphine oxide anions with elemental sulfur and selenium: A new route to thio‐ and selenoamides
Authors: Otten P.A. , van der Gen A. 
Published: September 2010

AbstractThe lithiated anions of α‐amino‐substituted diphenylphosphine oxides 1, in which R can be hydrogen, aryl, alkyl and alkenyl, react with two equivalents of sulfur or selenium to form thio‐ and selenoamides, which can be isolated in good to excellent yields in most cases. The optimal reaction conditions (temperature and time) were found to depend both on the phosphine oxide used and on the chalcogene. A mechanism is presented which accounts for the stoichiometry of the reaction.
Synthesis of oxygen‐substituted N‐alkyl 1‐deoxynojirimycin derivatives: Aza sugar α‐glucosidase inhibitors showing antiviral (HIV‐1) and immunosuppressive activity
Authors: van den Broek L.A.G.M. , Vermaas D.J. , van Boeckel C.A.A. , Rotteveel F.T.M. , Zandberg P. , van Kemenade F.J. , Miedema F. , Butters T.D. , Tan M.C.C.A. , Ploegh H.L. 
Published: September 2010

AbstractThe synthesis of a series of six less‐lipophilic analogues of the α‐glucosidase inhibitor N‐decyl‐1‐deoxynojirimycin (N‐decyl‐dNM, 5) is described. With the incorporation of a single oxygen atom, particularly at position seven in the N‐decyl side‐chain to give N‐(7‐oxadecyl)‐dNM (8), the therapeutic ratio (α‐glucosidase I inhibitory activity over toxicity in HepG2 cells) increases considerably. Compound 8 inhibits purified porcine liver α‐glucosidase I with an IC50 value of 0.28 μM. The position of the oxygen atom in the N‐decyl side‐chain is of importance since N‐(3‐oxadecyl)‐dNM (7) is less active than 8 and, moreover, is toxic to HepG2 cells at 3 mM. Subsequently, the synthesis of eight ester derivatives of N‐(7‐oxadecyl)‐dNM is described. All of these ester analogues are less active α‐glucosidase inhibitors than the parent compound 8 in HepG2 cells. The compounds were further analyzed for antiviral and immunomodulatory activity in vitro. It is found that the most potent α‐glucosidase I inhibitor from this study N‐(7‐oxadecyl)‐dNM (8) inhibits HIV‐1‐induced syncytia formation and lymphocyte proliferation in vitro. Finally, compound 8 was investigated in vivo. N‐(7‐Oxadecyl)‐dNM (8) reduced adjuvant‐induced arthritis in rats making this compound a potential candidate for treating autoimmune diseases like rheumatoid arthritis.
Sonochemistry: Theory and applications
Authors: Pestman Jolanda M. , Engberts Jan B. F. N. , de Jong Feike 
Published: September 2010

AbstractUltrasound can be used in chemistry to increase both reaction rates and yields of products. Most effects of ultrasound on chemical reactions are due to cavitation: the formation and collapse of small bubbles in the solvent. In this review, we first outline the physical background of cavitation, and discuss its dependence on factors such as sound intensity and frequency, solvent and temperature. The impact of ultrasound on chemical reactions is considered for homogeneous reactions and for heterogeneous liquid‐solid systems. The first area is mainly illustrated by a discussion of the effect of ultrasound on polymerization and depolymerization reactions, the second by selected examples in organic synthesis. The tendency of ultrasound to change reaction mechanisms in favour of homolytic (instead of heterolytic) pathways, is also briefly discussed. The specific preference for a particular pathway under sonochemical conditions, different from that under mechanical stirring has been termed “sonochemical switching”. Ultrasonic equipment for lab‐scale experiments are compared, and some practical “tricks and traps” are given.
On the stability of S‐(alkylsulfanyl) cysteine derivatives during solid‐phase synthesis
Authors: Rietman B. H. , Peters R. F. R. , Tesser G. I. 
Published: September 2010

AbstractN‐Acetyl‐S‐(alkylsulfanyl)cysteine benzyl esters were synthesized as models for N‐acylated S‐(alkylsulfanyl)cysteine residues linked via an ester bond to a solid phase. The S‐protections involved were: the ethylsulfanyl, the well‐established tert‐butylsulfanyl and the newly developed tritylsulfanyl group. We investigated the chemical behaviour of the disulfides in reagents commonly applied in solid‐phase peptide synthesis using the Fmoc strategy (Fmoc SPPS). It was found that the tritylsulfanyl group as a thiol protection is comparable with the tert‐butylsulfanyl group in these respects. It is stable in trifluoroacetic acid and is rapidly reduced by thiols and phosphines. For all three cysteine esters rapid racemization was observed in piperidine (25%) in DMF, the amides being chirally stable. The demonstrated chiral instability of cysteine esters has consequences for the solid‐phase synthesis of peptides using the Fmoc protocol.
Coulomb‐induced intramolecular exciplex formation in semiflexible donor‐bridge‐acceptor compounds in nonpolar solvents as a function of temperature
Authors: Wegewijs B. , Ng A. K. F. , Verhoeven J. W. 
Published: September 2010

AbstractThe mechanism of exciplex formation of two donor‐bridge–acceptor compounds, both containing a strong donor ‐ acceptor pair interconnected by a piperidine ring, was studied in nonpolar solvents as a function of temperature. Fluorescence spectra at low temperature in methylcyclohexane show that in both compounds the exciplex is formed via the harpooning mechanism, i.e. long‐range charge separation leading to an extended charge‐transfer state, followed by Coulomb‐induced folding to the exciplex state. The kinetic link between these two emissive states could be established by studying their transient fluorescence curves. Furthermore, the activation energy of the folding process was estimated from the decay rates of the extended charge‐transfer state in various solvents. An interpretation of the observed activation energies in terms of Kramers theory is presented, which gives an indication of the relative importance of internal steric effects and solvent viscosity on the dynamics of the folding process.
Formation of the 1,3‐Oxazepine ring system during the oxidation of an alcohol with activated dimethyl sulfoxide
Authors: Belle David Din , Tolvanen Arto , Lounasmaa Mauri 
Published: September 2010

AbstractAlcohol 3, an intermediate in indole alkaloid synthesis, was converted to the ox‐azepinoindoloquinolizine 5 by oxidation with DMSO activated by the sulfur trioxide/pyridine complex. The ring closure proceeds through the common oxidation side‐product, methylthiomethyl ether 4.
The Cossee mechanism: Migratory insertion reactions in palladium phosphine‐phosphinite complexes
Authors: van Leeuwen Piet W. N. M. , Roobeek Kees F. 
Published: September 2010

AbstractMethylpalladium complexes containing phosphine‐phosphinite bidentate ligands 1‐3 undergo stepwise insertions of carbon monoxide and norbornadiene. The 31P NMR spectra prove that a true migration pathway is the mechanism for this reaction.
2‐(Trifluoromethyl)piperazine: Synthesis and characterization using NMR and X‐ray photoelectron spectroscopy
Authors: Jenneskens Leonardus W. , Mahy Jan , de Brabander‐van den Berg Ellen M. M. , van der Hoef Ineke , Lugtenburg Johan 
Published: September 2010

AbstractThe synthesis of 2‐(trifluoromethyl)piperazine (1) is reported. 1H NMR spectroscopy shows that in the chair‐type piperazine ring the CF3 group occupies an equatorial position. X‐ray photoelectron spectroscopy of solid 1 reveals that the CF3 group induces a secondary (β) chemical shift of 1.5 eV on the C 1s core binding energy of its nearest neighbour carbon atom. The results are supported by semi‐empirical PM3 and HAM/3 calculations.
Dispiroketals in synthesis (Part 16): Functionalised dispiroketals as new chiral auxiliaries; the synthesis of dihydroxylated dispiroketals in optically pure form and their application as bifunctional, C2‐symmetrical, chiral auxiliaries for highly stereoselective Michael additions
Authors: Bezuidenhoudt Barend C. B. , Castle Grant H. , Innes Jean E. , Ley Steven V. 
Published: September 2010

AbstractA range of rigid, architecturally complex diols derived from dispiroketals have been synthesised. A bifunctional, C2‐symmetrical, chiral auxiliary derived from these dihydroxylated dispiroketals has been used to induce a high degree of asymmetry in Michael additions of cuprates to a variety of di‐α, β‐unsaturated ester systems.
Synthesis of enantiomerically pure tricarbonylchromium(0) complexes of ortho substituted styrenes from (S)‐α‐Methylbenzylamine
Authors: Christian Paul W. N. , Gibson Susan E. , Gil Richard , Jones P. Caroline V. , Marcos Carlos F. , Prechtl Frank , Wierzchleyski Adam T. 
Published: September 2010

AbstractTricarbonylchromium(0) complexes of sulfur, phosphorus, silicon, iodine, tin and carbon substituted (S)‐(α‐methylbenzyl)dimethylamines are oxidized by dimethyldioxirane to enantiomerically pure tricarbonylchromium(0) complexes of substituted styrenes; the reactions proceed via a chemoselective oxidation of the tertiary amines to their N‐oxides, one of which was isolated, and a subsequent Cope reaction.
Synthesis of chiral (phosphinoaryl)oxazolines, a versatile class of ligands for asymmetric catalysis
Authors: Koch Guido , Lloyd‐Jones Guy C. , Loiseleur Olivier , Pfaltz Andreas , Prétôt Roger , Schaffner Silvia , Schnider Patrick , von Matt Peter 
Published: September 2010

AbstractEnantiomerically pure 2‐[2‐(diphenylphosphino)aryl]oxazolines are readily prepared from 2‐bromobenzonitrile by transmetalation with BuLi, subsequent reaction with chloro‐diphenylphosphine and conversion of the resulting phosphinoaryl nitrile to the oxazoline by treatment with a chiral amino alcohol in the presence of ZnCl2. An alternative synthesis is based on the orthometalation of 2‐aryloxazolines followed by reaction with chlorodiphenylphosphine.
Synthesis of dipeptides containing α‐substituted amino acids; their use as chiral ligands in Lewis‐acid‐catalyzed reactions
Authors: Kaptein Bernard , Monaco Vania , Broxterman Quirinus B. , Schoemaker Hans E. , Kamphuis Johan 
Published: September 2010

AbstractL‐α‐Methylphenylalanine, obtained by enzymatic resolution of the corresponding racemic amide with amidase from Ochrobactrum anthropi NCIMB 40321, was used in the synthesis of dipeptides containing α‐substituted amino acids. The 2‐hydroxynaphthalene‐1‐carboxaldehyde Schiff bases of the dipeptides (1 and 2) were tested as Ti(IV) and Al(III) complexes in asymmetric Lewis‐acid‐catalyzed reactions. Only the Al(III) complex of 2 showed moderate enantioselectivity in the cyanation reaction of benzaldehyde with TMS‐CN.
Alkali‐cation transport through supported liquid membranes mediated by solvent‐linked carriers
Authors: Visser Herman C. , Vink Remco , Snellink‐Ruel Bianca H. M. , Kokhuis Simone B. M. , Harkema Sybolt , de Jong Feike , Reinhoudt David N. 
Published: September 2010

AbstractNeutral macrocyclic alkali‐cation receptors have been covalently linked to one or more molecules of the membrane solvent 2‐nitrophenyl n‐octyl ether (NPOE). These compounds are all highly lipophilic and soluble in NPOE. The flux of alkali‐perchlorate salts through supported liquid membranes (SLMs) has been optimized by variation of the carrier content in the membrane and the temperature. With all carriers, the optimum flux is reached at carrier contents of about 20% (w/w) in NPOE. Above this carrier content the flux decreases because of an increase in the viscosity of the membrane solutions. Relatively low activation energies for transport indicate that the transport is diffusion‐limited. The excellent compatibility between the carriers and the membrane solvent leads to very stable membranes (NPOE/Accurel®). The mechanism of alkali perchlorate transport has been investigated by variation of the source‐phase salt activity and the carrier concentration. Indications about ion pair formation and 2/1 carrier/cation complexation have been obtained from variation of the carrier concentration and transport selectivity measurements.
Hydrocarbons and chloroaromatics from anilines and n‐butyl nitrite
Authors: Giumanini Angelo G. , Verardo Giancarlo , Gorassini Fausto , Strazzolini Paolo 
Published: September 2010

AbstractA single reagent, i.e. n‐butyl nitrite, can be used to oxidize an aromatic amine, or the corresponding N‐methylene derivative, to a diazo compound followed by its subsequent reduction to hydrocarbon in a single batch. Alternatively, a chloro derivative can be obtained if carbon tetrachloride is used as the solvent. The reactions appear to be general and complete product identification was accomplished.
Synthesis of a potential enzyme‐specific inhibitor of squalene synthase
Authors: Valentijn A. R. P. M. , de Haan R. , Hagens S. , de Kant E. , van der Marel G. A. , Cohen L. H. , van Boom J. H. 
Published: September 2010

AbstractA multi‐step synthesis of phosphinylphosphonate analogue 12 of the proposed farnesyl‐farnesyl‐enzyme (FFE) intermediate in the enzymatic conversion of farnesyl pyrophosphate to squalene is described. In addition, evidence is presented of the inhibitory effect of 12 on squalene synthase.
Synthesis and crystal structure of [Bu4N][Ni(mdt)2], a novel nickel dithiolene complex (H2mdt = 2H‐1,3‐dithiole‐4,5‐dithiol)
Authors: Veldhuizen Yvonne S. J. , Veldman Nora , Spek Anthony L. , Haasnoot Jaap G. , Reedijk Jan 
Published: September 2010

Abstract[Bu4N][Ni(mdt)2] (H2mdt = 2H‐1,3‐dithiole‐4,5‐dithiol) has been prepared in a three‐step synthesis from [Bu4N]2[Zn(dmit)2] (H2dmit = 2‐thione‐1,3‐dithiole‐4,5‐dithiol). The crystal structure is reported which shows that the Ni(mdt)2 anion is distorted significantly from planarity.
A family firm variant of the behavioral agency theory
Authors: Lim Elizabeth N. K. , Lubatkin Michael H. , Wiseman Robert M. 
Published: September 2010

AbstractThere is currently a debate in the literature regarding whether family firm ownership fosters or discourages risk‐taking activities. In this article, we propose a contingency framework that shifts the focus of investigation: instead of asking whether family firms tend to be risk takers, we suggest specific ownership conditions under which privately owned family‐managed firms are more likely to engage in risk taking. We do so by integrating concepts from the behavioral agency model and a resource‐based concept known as familiness to advance a base proposition that explains the effects of different ownership structures (controlling ownership, sibling partnership, and cousin consortium) on risk‐taking behaviors in family firms. Then, drawing insights from the family firm and household economics literatures, we discuss the contingent effects of three distinct forms of altruism (parental, paternalistic, and psychosocial) on the base proposition. The framework advances our current understanding of risk taking in family businesses in two ways: first, by proposing how and when risk‐taking behaviors differ across these firms; and second, by offering a variant of the base behavioral agency model that is better suited for explaining risk taking at family firms. Copyright © 2010 Strategic Management Society.
A modeling framework for the analysis of HPV incidence and persistence: A semi‐parametric approach for clustered binary longitudinal data analysis
Authors: Kong Xiangrong , Gray Ronald H. , Moulton Lawrence H. , Wawer Maria , Wang Mei‐Cheng 
Published: September 2010

AbstractHuman papillomavirus (HPV) infection is a common sexually transmitted disease of growing public health importance, and over 40 genotypes have been identified in genital infections. Current HPV cohort studies often follow participants at pre‐determined visits, such as every 6 months, and data generated from such epidemiology studies can be described as clustered longitudinal binary data where correlation arises in two ways: the directionless clustering due to the multiple genotypes tested within an individual, and the temporal correlation among the repeated measurements on the same genotype along time. Current analyses for identification of risk factors associated with HPV incidence and persistence often either do not fully utilize information in the data set or ignore the correlation between the multiple genotypes. Given the scientific definition of incidence and persistence, conditional probability modeling provides us a natural mathematical tool. We thus present a semi‐parametric regression model for such data where full specification of the joint multivariate binary distribution is avoided by using conditioning argument to handle the temporal correlation and GEE to account for the correlation between the multiple genotypes. The model is applied to the HPV data from the Rakai male circumcision (MC) trial to evaluate the as‐treated efficacy of MC and also identify modifiable risk factors for incidence and persistence of oncogenic HPV types in men. A simulation study is performed to provide empirical information on the number of individuals that is needed for satisfactory power and estimation accuracy of the association parameter estimates in future studies. Copyright © 2010 John Wiley & Sons, Ltd.