bluuebunny/crossref_metadata_2025 huggingface dataset:
Point-Counterpoint of Sphingosine 1-Phosphate Metabolism
Authors: Saba Julie D. , Hla Timothy
Published: April 2004

Sphingosine 1-phosphate (S1P), an evolutionarily conserved bioactive lipid mediator, is now recognized as a potent modulator of cell regulation. In vertebrates, S1P interacts with cell surface G protein-coupled receptors of the EDG family and induces profound effects in a variety of organ systems. Indeed, an S1P receptor agonist is undergoing clinical trials to combat immune-mediated transplant rejection. Recent information on S1P receptor biology suggests potential utility in the control of cardiovascular processes, including angiogenesis, vascular permeability, arteriogenesis, and vasospasm. However, studies from diverse invertebrates, such as yeast,
Dictyostelium
,
Drosophila
, and
Caenorhabditis elegans
have shown that S1P is involved in important regulatory functions in the apparent absence of EDG S1P receptor homologues. Metabolic pathways of S1P synthesis, degradation, and release have recently been described at the molecular level. Genetic and biochemical studies of these enzymes have illuminated the importance of S1P signaling systems both inside and outside of cells. The revelation of receptor-dependent pathways, as well as novel metabolic/intracellular pathways has provided new biological insights and may ultimately pave the way for the development of novel therapeutic approaches for cardiovascular diseases.
Impedance‐type approximations of the P–P elastic reflection coefficient: Modeling and AVO inversion
Authors: Santos Lúcio T. , Tygel Martin
Published: April 2004

The normal‐incidence elastic compressional reflection coefficient admits an exact, simple expression in terms of the acoustic impedance, namely the product of the P‐wave velocity and density, at both sides of an interface. With slight modifications a similar expression can, also exactly, express the oblique‐incidence acoustic reflection coefficient. A severe limitation on the use of these two reflection coefficients in analyzing seismic reflection data is that they provide no information on shear‐wave velocities that refer to the interface. We address the natural question of whether a suitable impedance concept can be introduced for which arbitrary P–P reflection coefficients can be expressed in a form analogous to their acoustic counterparts. Although no closed‐form exact solution exists, our analysis provides a general framework for which, under suitable restrictions of the medium parameters, possible impedance functions can be derived. In particular, the well‐established concept of elastic impedance and the recently introduced concept of reflection impedance can be better understood. Concerning these two impedances, we examine their potential for modeling and for estimating the AVO indicators of intercept and gradient. For typical synthetic examples, we show that the reflection impedance formulation provides consistently better results than those obtained using the elastic impedance.
Elicitation of Probabilities Using Competitive Scoring Rules
Authors: Kilgour D. Marc , Gerchak Yigal
Published: April 2004

Several forecasters predict the probability of an event, and then make or receive payments contingent on their predictions and on whether the event actually occurs. The payment functions generalize the concept of scoring rule to a competitive setting. We allow for exogenously determined subsidies to each forecaster, and require that the scheme be anonymous, neutral, and truth-inducing. By centering each forecaster's payment at the average payment to all other forecasters, we construct competitive scoring rules that reward the better predictors. Applications include multiparty betting and fixed-budget surveys to determine subjects' truthful probability assessments. We discuss when forecasters would voluntarily participate in such a competition, and relate our results to the scoring rules proposed by De Finetti (1974) for eliciting probabilities.
Speaking of Decisions: Precise Decision Language
Authors: Howard Ronald A.
Published: April 2004

This paper presents the current state of evolution of a language for teaching and practicing decision analysis that may avoid confusion of students, clients, and ourselves. Many of the terms currently used are inaccurate, arcane, or unnecessary. Restricting decision language to terms that are accurate, familiar, and fundamental contributes to clarity of thought and understanding. To illustrate the type of changes advocated, I propose replacing dependence with relevance, expectation with e-value, utility with u-value, and eschewing subjective probability, confidence, uncertainty about probability, any distinction between risk and uncertainty, and states of nature. I show how to incorporate the new terminology in teaching and practice.
Precise Decision Language
Authors: Smith James E.
Published: April 2004

Howard (2004) proposes a “precise decision language” that aims to improve clarity of discussion and thought about decision making and decision modeling. While I applaud Howard's goals, I think it is important that our language be consistent with the terminology currently used in the many fields related to decision analysis. On these grounds, I argue against some of Howard's proposed changes.
Prospects for a Decision Language
Authors: Kirkwood Craig W.
Published: April 2004

In “Speaking of Decisions: Precise Decision Language,” Howard (2004) discusses important issues about the terminology and concepts of decision analysis. A unified decision language could clarify communications across the diverse communities interested in decision analysis, but the diversity of these stakeholders makes achieving such a unified language an ambitious goal. Many of the concepts that Howard discusses predate decision analysis or are widely used in other fields. Those other fields will not change their terminology, and it is unlikely that modifying terminology for these concepts within decision analysis would provide sufficient benefits to outweigh the costs associated with potentially isolating ourselves from related fields.
Note—Commonality Strategies: Value Drivers and Equivalence with Flexible Capacity and Inventory Substitution
Authors: Van Mieghem Jan A.
Published: April 2004

Commonality strategies assemble different products from at least one common component and one other product-specific component. The distinguishing feature of commonality, i.e., the presence of dedicated components to be assembled with a common component, is shown to be mathematically inconsequential in the sense that the unified commonality problem for two products can be reduced to an equivalent substitution flexibility problem without those dedicated components. This significant simplification provides the first general, closed-form condition for commonality adoption and identifies its value drivers. Commonality is optimal even for perfectly correlated demands if products have sufficiently different margins. This introduces the "revenue-maximization option" of commonality as a second benefit that is independent of the traditional risk-pooling benefit. "Pure commonality" strategies are never optimal unless complexity costs are introduced. Dual sourcing, externalities, and operational hedging features of commonality are discussed.
Dynamic Conversion Behavior at E-Commerce Sites
Authors: Moe Wendy W. , Fader Peter S.
Published: April 2004

This paper develops a model of conversion behavior (i.e., converting store visits into purchases) that predicts each customer's probability of purchasing based on an observed history of visits and purchases. We offer an individual-level probability model that allows for different forms of customer heterogeneity in a very flexible manner. Specifically, we decompose an individual's conversion behavior into two components: one for accumulating visit effects and another for purchasing threshold effects. Each component is allowed to vary across households as well as over time. Visit effects capture the notion that store visits can play different roles in the purchasing process. For example, some visits are motivated by planned purchases, while others are associated with hedonic browsing (akin to window shopping); our model is able to accommodate these (and several other) types of visit-purchase relationships in a logical, parsimonious manner. The purchasing threshold captures the psychological resistance to online purchasing that may grow or shrink as a customer gains more experience with the purchasing process at a given website. We test different versions of the model that vary in the complexity of these two key components and also compare our general framework with popular alternatives such as logistic regression. We find that the proposed model offers excellent statistical properties, including its performance in a holdout validation sample, and also provides useful managerial diagnostics about the patterns underlying online buyer behavior.
A real‐life event enhances the accuracy of preschoolers' recall
Authors: Thierry Karen L. , Spence Melanie J.
Published: March 2004

Children's memory and susceptibility to misinformation about a real‐life and video event were examined. Eighty‐six three‐ to four‐year‐olds and five‐ to six‐year‐olds observed an event either in real life or on video. Immediately afterward, they freely recalled the event and answered misleading questions about central and descriptive information. Three‐ to four‐year‐olds in the video condition were less likely to accurately recall descriptive information than three‐ to four‐year‐olds in the live condition and five‐ to six‐year‐olds in either condition. Children in the video condition were less accurate in response to misleading questions than those in the live condition. When video condition three‐ to four‐year‐olds in Experiment 2 were asked nonmisleading questions that prompted them for descriptive information, they recalled descriptors less accurately than those in the live condition. These results have particularly important implications for studies that utilize video events when investigating children's eyewitness memory. Copyright © 2004 John Wiley & Sons, Ltd.
Secrecy and suggestibility: are children's memories for secrets less suggestible than other memories?
Authors: Wilson J. Clare , Powell Martine B. , Raju Sadhana , Romeo Rosanna
Published: March 2004

Adult secrecy research has found a memory‐enhancing effect for information kept secret as the secret is mentally rehearsed each time the adult is required to prevent it being reported (e.g. Lane & Wegner, 1994). The present study examined possible memory‐enhancing effects of children keeping information secret. Two hundred and thirty two five to eight year olds took part in a puppet‐making task. During the task the puppet‐maker sprayed glitter onto the puppets. Half the children were told to keep a secret (that the spray had been taken from Disneyland) and the other half (the control group) were merely told the spray was from Disneyland. One week later the children were interviewed either by the puppet‐maker (the secret‐giver) or by the puppet‐maker's friend (the secret‐novice). The five to six year olds showed no effect of the secret condition, whereas the seven to eight year olds made significantly less errors in their free recall in the secret condition compared to the control condition. There was no effect of the secret condition on children's suggestibility to leading questions. However, both age groups were significantly more suggestible when interviewed by the secret‐giver. Finally, both age groups showed a recall deficit in the secret condition. Copyright © 2004 John Wiley & Sons, Ltd.
Earwitnesses: effects of speech duration, retention interval and acoustic environment
Authors: Kerstholt José H. , Jansen Noortje J. M. , Van Amelsvoort Adri G. , Broeders A. P. A.
Published: March 2004

An experiment was conducted to investigate the reliability of voice lineups. More specifically, the experiment was designed to look into the effects of retention interval (an immediate test or after a week), speech duration (30 or 70 s) and acoustic environment (indoors or indoors and outdoors) on speaker identification accuracy. In addition, the relation between confidence assessments of both participants and test assistant on the one hand and identification accuracy was explored. A total of 361 participants heard the target voice in one of four exposure conditions (short or long text and speech samples recorded only indoors or indoors and outdoors). Half the participants were tested immediately after exposure to the target voice and half 1 week later. The results show that the target was correctly identified in 42% of cases. In the target‐absent condition there were 51% false alarms. Acoustic environment did not affect identification accuracy. There was an interaction between speech duration and retention interval in the target‐absent condition. When listeners were tested after a week, they made fewer false identifications if the speech sample was long. No effects were found when participants were tested immediately. Only the confidence scores of the test assistant had predictive value. Taking the confidence score of the test assistant into account therefore increases the diagnostic value of the identity parade. Copyright © 2004 John Wiley & Sons, Ltd.
Nanoporous Ultra‐Low‐κ Fluoropolymer Composite Films via Plasma Polymerization of Allylpentafluorobenzene and Magnetron Sputtering of Poly(tetrafluoroethylene)
Authors: Fu G. D. , Zhang Y. , Kang E.‐T. , Neoh K.‐G.
Published: March 2004

Fluoropolymer composite films with nanoporous morphology and dielectric constants less than 2.0, consisting of plasma‐polymerized allylpentafluorobenzene (pp‐APFB) nanospheres and magnetron sputter‐deposited poly(tetrafluoroethylene) (s‐PTFE) dense layers, have been prepared on hydrogen‐terminated Si(100) (H‐Si) substrates (see Figure).
α‐Hydroxylation of β‐Dicarbonyl Compounds
Authors: Christoffers Jens , Baro Angelika , Werner Thomas
Published: March 2004

The most convenient and direct route to α‐hydroxy‐β‐dicarbonyl compounds is the oxidation of readily accessible 1,3‐dicarbonyls. Hence, this type of oxidation is an intensively investigated field. In this short review, we present and compare α‐hydroxylations using various oxidants such as peracids (Rubottom oxidation), dimethyldioxirane or molecular oxygen. From an economical and ecological point of view, metal‐catalyzed air oxidations are optimal at least for cyclic β‐dicarbonyls. For asymmetric α‐hydroxylations only chiral sulfonyloxaziridines are available to date. Thus, there is still a need for significant development in this area.
Ruthenium‐Catalyzed Asymmetric Alkene Epoxidation with tert‐Butyl Hydroperoxide as Oxidant
Authors: Bhor Santosh , Tse Man Kin , Klawonn Markus , Döbler Christian , Mägerlein Wolfgang , Beller Matthias
Published: March 2004

A ruthenium‐catalyzed asymmetric epoxidation of various olefins using tert‐butyl hydroperoxide (TBHP) as the oxidant is reported. By applying ruthenium(pyridinebisoxazoline)‐(pyridinedicarboxylate) complexes 1 [Ru(pybox)(pydic), 1] as catalysts, aromatic and aliphatic olefins yielded the corresponding epoxides at room temperature in good to excellent yields and enantioselectivities up to 65% ee. Slow addition of the stoichiometric oxidant significantly improved the yield and the chemoselectivity of the reaction.
Oxidations Catalyzed by Metallocorroles
Authors: Gross Zeev , Gray Harry B.
Published: March 2004

Metallocorroles, in particular those containing chromium, manganese, and iron, have been found to be efficient catalysts for oxidation reactions. This review deals with work on hydrocarbon oxidations after the 1999 advance made in corrole synthesis that sparked the Technion‐Caltech collaborative program.
Hydrogen Peroxide Oxygenation of Alkanes Including Methane and Ethane Catalyzed by Iron Complexes in Acetonitrile
Authors: Shul'pin Georgiy B. , Nizova Galina V. , Kozlov Yuriy N. , Gonzalez Cuervo Laura , Süss‐Fink Georg
Published: March 2004

This paper describes an investigation of the alkane oxidation with hydrogen peroxide in acetonitrile catalyzed by iron(III) perchlorate (1), iron(III) chloride (2), iron(III) acetate (3) and a binuclear iron(III) complex with 1,4,7‐triazacyclononane (4). The corresponding alkyl hydroperoxides are the main products. Nevertheless in the kinetic study of cyclohexane oxidation, the concentrations of oxygenates (cyclohexanone and cyclohexanol) were measured after reduction of the reaction solution with triphenylphosphine (which converts the cyclohexyl hydroperoxide to the cyclohexanol). Methane and ethane can be also oxidized with TONs up to 30 and 70, respectively. Chloride anions added to the oxidation solution with 1 activate the perchlorate iron derivative in acetonitrile, whereas the water as additive inactivates 2 in the H2O2 decomposition process. Pyrazine‐2‐carboxylic acid (PCA) added to the reaction mixture decreases the oxidation rate if 1 or 2 are used as catalysts, whereas compounds 3 and 4 are active as catalysts only in the presence of small amount of PCA. The investigation of kinetics and selectivities of the oxidations demonstrated that the mechanisms of the reactions are different. Thus, in the oxidations catalyzed by the 1, 3+PCA and 4+PCA systems the main oxidizing species is hydroxyl radical, and the oxidation in the presence of 2 as a catalyst has been assumed to proceed (partially) with the formation of ferryl ion, (FeIVO)2+. In the oxidation catalyzed by the 4+PCA system (TONs attain 240) hydroxyl radicals were generated in the rate‐determining step of monomolecular decomposition of the iron diperoxo adduct containing one PCA molecule. A kinetic model of the process which satisfactorily describes the whole set of experimental data was suggested. The constants of supposed equilibriums and the rate constant for the decomposition of the iron diperoxo adduct with PCA were estimated.
A Simple and Highly Selective Biomimetic Oxidation of Alcohols and Epoxides with N‐Bromosuccinimide in the Presence of β‐Cyclodextrin in Water
Authors: Krishnaveni N. Srilakshmi , Surendra K. , Rama Rao K.
Published: March 2004

A simple, mild and highly efficient biomimetic oxidation of various alcohols and epoxides with N‐bromosuccinimide (NBS) catalyzed by β‐cyclodextrin in water has been developed. A series of alcohols and epoxides were oxidized selectively at room temperature in excellent yields. This method is a direct one‐pot synthesis under mild conditions using water as solvent and has many advantages over the existing methodologies.
Fluorinated Silica Gels Doped with TPAP as Effective Aerobic Oxidation Catalysts in Dense Phase Carbon Dioxide
Authors: Ciriminna Rosaria , Campestrini Sandro , Pagliaro Mario
Published: March 2004

Hybrid organic‐inorganic fluorinated silica glasses doped with the ruthenium species TPAP (tetra‐n‐propylammonium perruthenate) are effective catalysts for the aerial oxidation of benzyl alcohol to benzaldehyde in dense phase CO2. Moderate silica fluorination (10%) by short‐chain fluoroalkyl‐containing monomers in the sol‐gel polycondensation with TMOS affords highly active catalysts which at 75 °C and 220 bar selectively dehydrogenate the alcohol with oxygen as primary oxidant. Both the activity and the stability of the fluorinated materials vary with the degree of fluorination and the nature of the fluoroalkyl residue attached to the silica polymeric network. An explanation of the behaviour of doped sol‐gel oxides in supercritical carbon dioxide is proposed which is thought to be of general validity for future practical applications to heterogeneously catalysed aerobic oxidations eliminating the current need for both organic solvents and stoichiometric oxidants.
Aerobic Oxidation of 1‐Phenylethanol Catalyzed by Palladaheterocycles
Authors: Paavola Sari , Zetterberg Krister , Privalov Timofei , Csöregh Ingeborg , Moberg Christina
Published: March 2004

Cyclometallated palladium compounds with pyridine were shown to serve as more efficient catalysts for the aerobic oxidation of 1‐phenylethanol than a previously investigated analogue with an oxazoline ring. Substituents with different electronic properties in the phenyl ring were shown to exhibit an only minor influence on the reactivity of the catalytic system. The first step in the reaction consists of the splitting of the acetate bridge in the dimeric starting complex and coordination of a ligand to palladium. By ab initio calculations it was shown that, in the presence of solvent, a complex with pyridine was more stable than that with the alcohol, whereas the opposite situation was found in the gas phase. The complex with coordinated alcohol was stabilized by hydrogen bonding. Good agreement was found between the computed structure and the X‐ray structure of the initial palladaheterocycle 1.
Synthesis of Naphthalenediols by Aerobic Oxidation of Diisopropylnaphthalenes Catalyzed by N‐Hydroxyphthalimide (NHPI)/α,α′‐Azobisisobutyronitrile (AIBN)
Authors: Aoki Yasuhiro , Sakaguchi Satoshi , Ishii Yasutaka
Published: March 2004

Naphthalenediols were successfully synthesized in a one‐pot reaction through the oxidation of diisopropylnaphthalenes with air catalyzed by N‐hydroxyphthalimide (NHPI) combined with α,α′‐azobisisobutyronitrile (AIBN) followed by decomposition with sulfuric acid. Thus, the oxidation of 2,6‐diisopropylnaphthalene with air (20 atm) in the presence of AIBN (3 mol %) and NHPI (10 mol %) in CH3CN at 75 °C for 21 h followed by treatment with 0.3 M H2SO4 gave 2,6‐naphthalenediol in 92% yield.
Biocatalytic Oxidation of Primary and Secondary Alcohols
Authors: Kroutil Wolfgang , Mang Harald , Edegger Klaus , Faber Kurt
Published: March 2004

Driven by the immaturity of many organic oxidation reactions and the necessity for ‘green’ chemical processes, biocatalytic redox processes are being investigated with increasing intensity in order to tap the full potential of the excellent chemo‐, regio‐ and enantioselectivity of enzymes. Despite their unmatched advantage in view of environmental aspects, the requirement of cofactors and the availability of redox enzymes able to tolerate high concentrations of organic (co)substrates sets limitations. However, during the past years, an increasing number of applications to the bio‐oxidation of primary and secondary alcohols with novel redox enzymes have been developed. This review gives an overview on the different methods and their potential and limits.
Photooxygenation in Polystyrene Beads with Covalently and Non‐Covalently Bound Tetraarylporphyrin Sensitizers
Authors: Griesbeck Axel G. , El‐Idreesy Tamer T. , Bartoschek Anna
Published: March 2004

Two reaction protocols are described which involve the use of polymer supports as reaction media for photooxygenation processes: 1) The use of polystyrene beads (PS) loaded with tetraphenyl‐ (TPP) or tetratolylporphyrin (TTP), swollen with the substrate in an appropriate organic solvent and subsequent irradiation under air. Products were isolated simply by dissolution in alcoholic solvents and filtration. 2) Covalently linked tetrastyrylporphyrin in polystyrene‐divinylbenzene beads were synthesized by emulsifier‐free emulsion polymerization and directly used for the photooxygenation protocol described above. The latter alternative allows also the use of less polar solvents for the extraction of the oxygenation products from the polymer beads. From the sensitizer loading degree, an optimal substrate/sensitizer molar ratio of 1,000–2,000 was determined and recyclization is possible for at least five times resulting in a minimum turnover number (with respect to the sensitizer TTP) of 5×104 (after five cycles). Both approaches were applied to the ene reaction of singlet oxygen with citronellol (1), the regioisomeric pinenes 3 and 5, and the allylic alcohols 9a–c, respectively, as well as to the [4+2]‐cycloadditions of singlet oxygen to sorbinol (7) and the chiral diene 11.
Microbial Transformations, 56. Preparative Scale Asymmetric Baeyer–Villiger Oxidation using a Highly Productive “Two‐in‐One” Resin‐Based in situ SFPR Concept
Authors: Hilker Iris , Alphand Véronique , Wohlgemuth Roland , Furstoss Roland
Published: March 2004

An efficient preparative scale process for achieving asymmetric Baeyer–Villiger oxidation – a reaction still very difficult to perform using conventional chemistry – is described. This process is based on a biocatalytic whole cells strategy – using a recombinant E. coli strain overexpressing cyclohexanone monooxygenase (CHMO) – combined with a “two‐in‐one” in situ “substrate feeding and product removal” concept (SFPR) using an adsorbent resin. The most efficient resin out of fourteen tested was used in three types of bioreactors (conventional, recycle and bubble column) that were compared. The best one proved to be the bubble column reactor, where 25 g (0.23 M) of rac‐bicyclo[3.2.0]hept‐2‐en‐6‐one could be totally transformed using a one‐litre vessel with a volumetric productivity of about 1 g L−1 h−1 (i.e., 7.7 mmol L−1 h−1). This led to the production of the two corresponding regioisomeric lactones, which were both obtained in excellent enantiomeric purity (ee>98%) and high preparative yield (84%). To our knowledge, these results represent the best example of a (highly productive) preparative scale asymmetric Baeyer–Villiger oxidation.
The Complex Synergy of Water in the Metal/Bromide Autoxidation of Hydrocarbons Caused by Benzylic Bromide Formation
Authors: Partenheimer Walt
Published: March 2004

One of the most active and selective catalysts in homogeneous liquid phase oxidation using molecular oxygen (O2) is a mixture of cobalt, manganese and bromide salts in acetic acid. It has been used to produce hundreds of different carboxylic acids in high yield and purity including the commercial production of terephthalic acid from p‐xylene. Water is normally a by‐product in these reactions and it is shown here that its concentration is an important reaction variable. In anhydrous acetic acid, with reagents with sufficiently strong electron‐withdrawing substitutents (toluene, 4‐carboxytoluene, 4‐chlorotoluene), all of the active bromide becomes inactive via benzylic bromide formation. The Co/Mn/Br catalyst is therefore converted to a Co/Mn catalyst which is dubbed ‘catalyst failure’ because of its undesirable characteristics of lower activity, decreased selectivity especially towards over‐oxidation and color formation. For 4‐chlorotoluene, increasing the water concentration to 5 weight % initially decreases the rate of reaction but eventually is more active and selective because the oxidation and hydrolysis of the benzylic bromide allows for sufficient active catalytic bromide. It is shown that benzylic bromides do not ‘promote’ the reaction and that both oxidation and solvolysis of the benzylic bromide occurs during autoxidation. During polymethylbenzene oxidation, benzylic bromide formation occurs only with the most reactive methyl group. The complex factors during metal/bromide autoxidation – some favored by increased water concentration and others detrimental – are outlined.
Catalytic Enantioselective Oxidation of Alkanes and Alkenes Using (Salen)Manganese Complexes Bearing a Chiral Binaphthyl Strapping Unit
Authors: Murahashi Shun‐Ichi , Noji Satoru , Komiya Naruyoshi
Published: March 2004

A (salen)manganese(III) complex bearing a chiral binaphthyl strapping unit catalyzes the enantioselective hydroxylation of indane (up to 34% ee) and the epoxidation of alkenes (up to 93% ee) with iodosylbenzene.
Biomimetic Chemical Catalysts in the Oxidative Activation of Drugs
Authors: Bernadou Jean , Meunier Bernard
Published: March 2004

An overview of the biomimetic catalysts used in the oxidative activation of drugs is given, with an emphasis on the use of synthetic metalloporphyrins as models of cytochrome P450 to mimic the in vivo metabolism of pharmaceuticals. In addition, a special focus is directed towards the recent results from the authors' group on the oxidative activation of isoniazid, an antitubercular drug.
Aerobic Oxidation of Cycloalkanes, Alcohols and Ethylbenzene Catalyzed by the Novel Carbon Radical Chain Promoter NHS (N‐Hydroxysaccharin)
Authors: Baucherel Xavier , Gonsalvi Luca , Arends Isabel W. C. E. , Ellwood Simon , Sheldon Roger A.
Published: March 2004

Replacement of Ishii's N‐hydroxyphthalimide (NHPI) with the novel carbon radical chain promoter N‐hydroxysaccharin (NHS) affords, in combination with metal salts, notably Co, or other additives, selective catalytic autoxidation of hydrocarbons, alcohols and alkylbenzenes under mild conditions (25–100 °C, O2 1 atm). The effects of solvent, temperature and the nature of the additives were investigated to give an optimised oxidation protocol for the various systems. The NHS/Co combination was more reactive than NHPI/Co in the autoxidation of cycloalkanes. In contrast, the opposite order of reactivity was observed in the autoxidation of ethylbenzene and alcohols. It is suggested, on the basis of bond dissociation energy (BDE) considerations, that this is a result of a change in the rate‐limiting step with the more reactive ethylbenzene and alcohol substrates. In the autoxidation of the model cycloalkane, cyclododecane, the best results (90% selectivity to a 4 : 1 mixture of alcohol and ketone at 24% conversion) were obtained with NHS/Co(acac)3 in PhCF3 at 80 °C. Competition experiments revealed that, in contrast to what is commonly believed, formation of the dicarboxylic acid by ring opening is not a result of further oxidation of the ketone product. It is suggested that ring opened products are a result of ß‐scission of the cycloalkoxy radical formed via (metal‐catalysed) decomposition of the hydroperoxide. This is suppressed in the presence of NHS (or NHPI) which efficiently scavenge the alkoxy radicals.
In situ Formation of Peracetic Acid in Iron‐Catalyzed Epoxidations by Hydrogen Peroxide in the Presence of Acetic Acid
Authors: Fujita Megumi , Que Lawrence
Published: March 2004

Iron complexes (tpa)Fe(OTf)2 (1) and (bpmen)Fe(OTf)2 (2) [tpa=tris‐(2‐pyridylmethyl)amine; bpmen=N,N′‐bis‐(2‐pyridylmethyl)‐N,N′‐dimethyl‐1,2‐ethylenediamine] were found to catalyze the in situ formation of AcOOH from H2O2 and AcOH in the course of olefin oxidations. While oxidation of cyclooctene by H2O2 catalyzed by 1 gives nearly equimolar epoxide and cis‐diol products, introduction of AcOH to the reaction greatly enhances the selectivity for epoxidation. The resulting product distribution is nearly identical to that of cyclooctene oxidation by AcOOH catalyzed by 1. The in situ generation of AcOOH from H2O2 and AcOH in epoxidation catalyzed by some iron complexes opens a possibility to attain AcOOH‐type efficiency of epoxidation using H2O2 as a terminal oxidant.
Kinetic Studies of Olefin Epoxidation with Hydrogen Peroxide in 1,1,1,3,3,3‐Hexafluoro‐2‐propanol Reveal a Crucial Catalytic Role for Solvent Clusters
Authors: Berkessel Albrecht , Adrio Jens A.
Published: March 2004

The epoxidation of cyclooctene and 1‐octene with hydrogen peroxide was studied kinetically in HFIP (1,1,1,3,3,3‐hexafluoro‐2‐propanol)/1,4‐dioxane mixtures. In the case of cyclooctene, no additional catalyst was applied, whereas the epoxidation of 1‐octene was run in the presence of phenylarsonic acid as catalyst. For both reaction types, two kinetic regimes can be distinguished: at low HFIP concentration (nHFIP/ntotal≤0.15), both the catalyzed and the uncatalyzed reaction show first order dependence on the HFIP concentration. This result is interpreted by the HFIP “charge template” for the uncatalyzed epoxidation (as postulated by Shaik and Neumann) and by the formation of an arsonic acid mono‐HFIP ester for the catalyzed reaction. At high HFIP concentration (nHFIP/ntotal≥0.5), both reaction types are up to ca. 5 orders of magnitude faster and show ca. 12th order dependence on the HFIP concentration. We propose that the dramatic accelerations observed at high HFIP concentrations are brought about by HFIP clusters. Based on literature data (Fioroni, Roccatano, Hong, Suhm), it is concluded that the epoxidation reactions studied here take place in a HFIP coordination sphere comprising ca. 12 HFIP molecules, and that this coordination sphere effects the enormous increases in epoxidation rates. This mechanistic model bears resemblance to enzymatic reactions taking place in and being catalyzed by a protein matrix.
Solid Materials as Sources for Synthetically Useful Singlet Oxygen
Authors: Wahlen Joos , De Vos Dirk E. , Jacobs Pierre A. , Alsters Paul L.
Published: March 2004

Solid materials can generate 1O2 (1Δg) either by irradiation of an immobilized dye in the presence of oxygen, or by catalytic decomposition of H2O2. The methods for obtaining such solid catalysts are described, and the usefulness of the obtained materials in preparative 1O2 oxygenations (“ene” hydroperoxidation, [2+2]‐ and [4+2]‐cycloaddition) is discussed, particularly with respect to substrate scope, solvent scope, reusability and productivity of the catalyst, regioselectivity and chemoselectivity of the oxidation.
Radiational hardening of poly(vinylidene fluoride)–poly(methyl methacrylate)–polystyrene ternary blends
Authors: Mishra A. K. , Agrawal P. , Bajpai R.
Published: March 2004

Specimens of poly(vinylidene fluoride) (PVDF)–poly(methyl methacrylate) (PMMA)–polystyrene (PS) polyblends with different weight percentage ratios of the three polymers were prepared with the solution cast technique. The effect of γ irradiation on the Vicker's microhardness was studied. Among the three pure polymers, PVDF, PMMA, and PS, the γ irradiation imparted crosslinking in PVDF, thereby causing radiational hardening. In the cases of PMMA and PS, the effect of irradiation exhibited a predominance of both the scissioning and crosslinking processes in different ranges of doses. Moreover, at a dose of 5 Mrad, in both PMMA and PS, maximum radiational crosslinking was observed. The effect of γ irradiation seemed to stabilize beyond 15 Mrad in PVDF and beyond 20 Mrad in PMMA and PS. Microhardness measurements on ternary blends of PVDF, PMMA, and PS revealed that the blend with low contents of PMMA, that is, up to 5 wt %, yielded softening, whereas increasing the content of PMMA beyond 5 wt % produced a hardened material because of radiational crosslinking, and a higher content of PMMA in the blend facilitated this crosslinking. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3107–3111, 2004
Ultraviolet light treatment of thin high‐density polyethylene films monitored with a quartz crystal microbalance
Authors: Øiseth Sofia Kihlman , Krozer Anatol , Lausmaa Jukka , Kasemo Bengt
Published: March 2004

Ultraviolet (UV) treatment is an effective method for modification of the surface properties of polymeric materials. In this study, the effects of the ozone‐generating UV light treatment of thin high‐density polyethylene (HDPE) films were monitored with the quartz crystal microbalance (QCM) technique both in the presence of ozone and without it. The films were further characterized by X‐ray photoelectron spectroscopy, optical microscopy, and atomic force microscopy. We found that the ozone not only modified the surface properties of the HDPE films but also etched away the polymer layer. An average etching rate of 0.48 nm/min was determined. UV light exposure of the polymer film in an argon atmosphere resulted only in minor degradation of the films; the presence of ozone was needed to cause the destruction and loss of material. The QCM technique was a straightforward method for the monitoring of the kinetics of the ablation induced by the UV–ozone treatment process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2833–2839, 2004
Syntheses of hydroxypropyl methylcellulose phthalate gels in organic solvents by radiation crosslinking
Authors: Xu Ling , Nagasawa Naotsugu , Yoshii Fumio , Kume Tamikazu
Published: March 2004

Cellulose gels were prepared through the crosslinking of hydroxypropyl methylcellulose phthalate (HPMCP) with electron‐beam irradiation in concentrated organic solvent solutions. The effects of the solvent species, polymer concentration, and irradiation dose on the formation of the gels were investigated. Some organic solvents, such as alcohols with short alkyl chains, alkyl acetates, and ketones, were found to be suitable as media for the radiation crosslinking of the polymer. The prepared HPMCP gels showed excellent swelling in various organic solvents with medium hydrogen‐bonding abilities, such as pyridine, cresol (meta), acetic acid, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, 1,4‐dioxane, acetone, methyl ethyl ketone, methyl acetate, and chloroform. In an acetone/water mixture, the swelling ratio was significantly dependent on the solvent composition because of the coexistence of both hydrophilic and hydrophobic moieties in HPMCP. These results suggest that HPMCP gels have the potential to be superabsorbents for various kinds of organic solvents. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3002–3007, 2004
Dependence of optical properties on the preparation methods of poly[(9,9′‐dialkylfluorene‐2,7‐diyl)‐alt‐(1,3,4‐oxadiazole‐2,5‐diyl)]
Authors: Yang Nam Choul , Lee Chang Ik , Kim Jong Kyu , Suh Dong Hack
Published: March 2004

A blue‐light‐emissive fluorene‐based polyoxadiazole, an n‐type polyfluorene derivative, was synthesized by both one‐step and two‐step methods. Directly polymerized poly[(9,9′‐didodecylfluorene‐2,7‐diyl)‐alt‐(1,3,4‐oxadiazole‐2,5‐diyl)] (PFOx‐DP) exhibited a higher molecular weight and a more efficient photoluminescence quantum yield than poly[(9,9′‐didodecylfluorene‐2,7‐diyl)‐alt‐(1,3,4‐oxadiazole‐2,5‐diyl)] (PFOx) prepared via a polyhydrazide precursor, poly[9,9′‐didodecylfluorene‐2,7‐(2,5‐dihydrazide‐ 1,3,4‐oxadiazole). Both polymers, differently prepared, showed similar photoluminescent properties in 1,2‐dichloroethane. However, in a film state, the influence of the interchain interactions on the photoluminescence of PFOx with the lower molecular weight was larger than on the photoluminescence of PFOx‐DP. The electron‐deficient property of an oxadiazole group in the polymer backbone resulted in low‐lying highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of −6.29 and −3.26eV, respectively, of the polymer suitable for electron‐transport/hole‐blocking layers and emissive layers in multilayer electroluminescence devices. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3112–3118, 2004
Functional barriers in PET recycled bottles. Part II. Diffusion of pollutants during processing
Authors: Pennarun P. Y. , Ngono Y. , Dole P. , Feigenbaum A.
Published: March 2004

Recycled plastics may be polluted by various chemicals available to consumers. When such materials are used to manufacture packaging materials intended to be in direct contact with food, these pollutants may migrate into food. The use of multilayer structures with a virgin polymer layer as a functional barrier may prevent such migration. This work deals with the possible diffusion of pollutants into and through the virgin layer during processing at high temperatures. A test is designed to measure diffusion coefficients in elastomeric and glassy polymers, in their molten state; 2.5‐dimethoxyacetophenone was used as a surrogate pollutant, and its concentration profiles are monitored by UV microscopy. Based on diffusion coefficients and on activation energies, glassy polymers appear to be much better barriers than polyolefins, even in their molten state. We then focus on poly(ethylene terephthalate) (PET) bottle preforms, processed by injection molding. In a first approach, a worst case situation was simulated by numerical analysis, using both overestimated diffusion coefficient values and very low values of activation energy. It appears that migration into foodstuffs through functional barriers can only be observed with unrealistic high diffusion coefficients and low activation energies. These results were confirmed by experimental determination of the concentration gradients of model pollutants in multilayer structures. It appears that little diffusion occurs, despite at a very high temperature. The effects of temperature and thickness of the functional barrier are discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2859–2870, 2004
Behavior of poly(ethylene‐co‐olefin) polymers as elastomeric materials
Authors: López‐Manchado Miguel Angel , Valle Marcela , Sapunar Rodrigo , Quijada Raúl
Published: March 2004

The properties of two new ethylene‐α‐olefin copolymers, namely, ethylene–1‐hexene copolymer (EHC) and ethylene–1‐octadecene copolymers (EOC), synthesized via metallocene catalysts were evaluated. The copolymerization was carried out in an autoclave reactor with Et(Indenyl)2ZrCl2/methylaluminoxane as a catalyst system. These single‐site catalysts (metallocene type) allow one to obtain very homogeneous copolymers with excellent control of the molecular weight distribution and proportion of comonomer incorporation. So, copolymers with 18 mol % comonomer in the case of EHC and 12 mol % for EOC were shaped, and activities around 100,000 kg of polymer mol−1 of Zr bar−1 h−1 were reached. The properties of these copolymers were compared with other commercial elastomers, such as ethylene–propylene copolymers synthesized by Ziegler–Natta catalysts and an ethylene–octene copolymer obtained via metallocene catalysts. The results show that these new copolymers, in particular, EOC, had excellent elastomeric properties. Furthermore, they had a relatively low viscosity, which implied a good response during processing. Moreover, the effectiveness of these copolymers as impact modifiers for polyolefins was also studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3008–3015, 2004
Particle size distribution control in emulsion polymerization
Authors: Sood Ashwini
Published: March 2004

Effects of the operating policies—the initial initiator amount; the initial emulsifier amount; the monomer addition mode: batch or semibatch; and the monomer addition rate under “monomer‐starved conditions” for the control of particle size distribution (PSD)—were studied through a model that simulates batch and semibatch reactor operations in conventional emulsion polymerization. The population balance model incorporates both the nucleation stage and the growth stage. The full PSDs were reported, which have normally been omitted in earlier studies. It was shown through simulations that the broadness of the distributions, both initial (obtained after the end of nucleation) and final (after complete conversion of monomer), can be controlled by the initial initiator amount and the emulsifier amount. The higher initiator amounts and the lower emulsifier amounts favor narrower initial and final distributions. The shape of the initial PSDs and the trends in the average size and range were preserved with subsequent addition of monomer in the batch or in the semibatch mode, although the final PSD was always considerably narrower than that of the initial PSD. The addition of monomer in the semibatch mode gave narrower distribution compared to that of the batch mode, and also, lower monomer addition rates gave narrower distributions (larger average sizes), which was a new result. It was further shown through simulations that, under monomer‐starved conditions, the reaction rate closely matched the monomer feed rate. These conclusions are explained (1) qualitatively—the shorter the length of the nucleation stage and the larger the length of the growth stage (provided the number of particles remains the same), the narrower is the distribution; and (2) mathematically—in terms of the “self‐sharpening” effect. Experimental evidence in favor of the self‐sharpening effect was given by analyzing the experimental particle size distributions in detail. The practical significance of this work was proposed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2884–2902, 2004
Diffusion of unreacted monomers detected by ATR FTIR spectroscopy in a photosensitive printing plate after the photoreaction
Authors: Sakaguchi Yoshimitsu , Kawahara Keizo , Yamada Takatoshi , Okazaki Yasuyuki , Imahashi Satoshi
Published: March 2004

A water‐developable flexographic printing plate consisting of poly(acrylonitrile‐co‐butadiene), polybutadiene, and carboxylated polyurethane as a polymer matrix, hexanediol dimethacrylate and polybutadiene diacrylate as reactive monomers, and benzildimethylketal as a photoinitiator was prepared and its photoreaction followed by structural change caused by the diffusion of unreacted monomers was characterized. Analysis combined 13C‐NMR and attenuated total reflection (ATR) FTIR showed the photoreaction occurred predominantly at the surface of exposure to the light at first, and then the reaction proceeded to the direction of the opposite surface with an increase in the exposure time. Diffusion of unreacted monomers after the photoreaction from the unexposed side to the exposed side was monitored by ATR FTIR. The diffusivity of unreacted monomers was dependent on the extent of photoreaction in the plate and the molecular weight of diffusing monomers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2903–2907, 2004
Immobilization of lipase on hydrogels: Structural aspects of polymeric matrices as determinants of enzyme activity in different physical environments
Authors: Chauhan Ghanshyam S. , Mahajan Swati , Sddiqui Khalid M. , Gupta Reena
Published: March 2004

Well‐defined and characterized polymeric matrices showing close chemical similarities but wide differences in water uptake and swellability in aqueous medium were used for lipase immobilization. Biphasic networks of 2‐hydroxypropylcellulose (HPC) were synthesized with acrylamide (AAm), methacrylamide (MAAm),N‐isopropylacrylamide (N‐i‐PAAm), and 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPSA) and simultaneously crosslinked withN,N‐methylene bisacrylamide in aqueous medium by using simultaneous γ‐radiation technique. Lipase enzyme was produced from a mesophilic bacterial isolate (HBK‐8) and was immobilized onto all the matrices by adsorption method. The activity of the immobilized enzyme was optimized for pH, temperature, and amount of crude enzyme and effect of dehydration. High relative activity for the immobilized enzymes was observed and loss of activity with time was minimal; reusability was found to be good. The activity of the immobilized enzyme was also observed to be good in both esterification and hydrolysis of esters. In the present study, lipase immobilization, hydrolysis ofp‐nitrophenyl palmitate, and optimum pH and temperature for substrate hydrolysis were evaluated for different matrices to study polymer structure and enzyme activity relationship in diverse physical environments. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3135–3143, 2004
Emulsifier‐minor emulsion copolymerization of BA‐MMA‐St‐MAA (or AA)‐N‐MA
Authors: Tang Linsheng , Yang Jingwei , Zhang Shufeng , Yang Jinzong , Wu Yumin
Published: March 2004

A novel emulsion polymerization technique referred to as emulsifier‐minor emulsion polymerization was achieved by the copolymerization of methyl methacrylate, butyl acrylate, and styrene (MMA‐BA‐St) with a combination of water‐soluble ionic monomers [methacrylic acid (MAA) or acrylic acid (AA)] and nonionic monomers (N‐methylol acrylamide). In the technique, water‐soluble monomers play a crucial role in the stabilization of the latex particles as they can be bound to the particle surface and form a hydrate protective layer, which exhibits steric and/or electrostatic effects to prevent particle coagulation. The minor but over its critical micelle concentration emulsifier sodium alkylated diphenyl ether disulfonate (DSB) results in the nucleation of particles mainly by the micelle nucleation mechanism and thus determines the polymerization rate, the particle size, and the number. The film water resistance of the latices can be improved, and the foaming capacity of can be lowered by using technique instead of conventional emulsion polymerization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2923–2929, 2004