bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of polyphenylquinoxaline copolymers via aromatic nucleophilic substitution reactions of an A‐B quinoxaline monomer
Authors: Klein Daniel J. , Korleski Joseph E. , Harris Frank W.
Published: August 2002

A self‐polymerizable quinoxaline monomer (A‐B) has been synthesized and polymerized via aromatic nucleophilic substitution reactions. An isomeric mixture of self‐polymerizable quinoxaline monomers—2‐(4‐hydroxyphenyl)‐3‐phenyl‐6‐fluoroquinoxaline and 3‐(4‐hydroxyphenyl)‐2‐phenyl‐6‐fluoroquinoxaline—was polymerized in N‐methyl‐2‐pyrrolidinone (NMP) to afford high molecular weight polyphenylquinoxaline (PPQ) with intrinsic viscosities up to 1.91 dL/g and a glass‐transition temperature (Tg) of 251 °C. A series of comonomers was polymerized with A‐B to form PPQ/polysulfone (PS), PPQ/polyetherether ketone (PEEK), and PPQ/polyethersulfone (PES) copolymers. The copolymers readily obtained high intrinsic viscosities when fluorine was displaced in NMP under reflux. However, single‐electron transfer (SET) side reactions, which limit molecular weight, played a more dominant role when chlorine was displaced instead of fluorine. SET side reactions were minimized in the synthesis of PPQ/PS copolymers through mild polymerization conditions in NMP for longer polymerization times. Thus, the Tg's of PES (Tg = 220 °C), PEEK (Tg = 145 °C), and PS (Tg = 195 °C) were raised through the incorporation of quinoxaline units into the polymer. Copolymers with high intrinsic viscosities resulted in all cases, except in the case of PPQ/PEEK copolymers when 4,4′‐dichlorobenzophenone was the comonomer. © 2001 John Wiley & Sons, Inc. J Polym Sci A Part A: Polym Chem 39: 2037–2042, 2001
Star‐polymer synthesis via radical reversible addition–fragmentation chain‐transfer polymerization
Authors: Stenzel‐Rosenbaum Martina , Davis Thomas P. , Chen Vicki , Fane Anthony G.
Published: August 2002

Polystyrene stars were synthesized by reversible addition–fragmentation chain‐transfer (RAFT) polymerization using hexakis(thiobenzoylthiomethyl)benzene (I) as a hexafunctional RAFT agent at 80, 100, and 120 °C. The polymerizations conformed to pseudo‐first‐order kinetic behavior. The molecular weight distributions displayed characteristics consistent with a living radical process. A number of salient features were observed in the molecular weight distributions with the star distribution accompanied by a linear polymer‐chain distribution and shoulders on the distributions that can be attributed to radical–radical‐termination events. The evidence suggests that high temperatures are required to activate all the RAFT active sites on I, and a hypothesis proposes that there is significant steric hindrance in the initial stages of the RAFT process with I. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2777–2783, 2001
Structure and morphology development in syndiotactic polypropylene during isothermal crystallization and subsequent melting
Authors: Wang Zhi‐Gang , Wang Xue‐Hui , Hsiao Benjamin S. , Phillips Roger A. , Medellin‐Rodriguez Francisco J. , Srinivas Srivatsan , Wang Howard , Han Charles C.
Published: August 2002

Structure and morphology development during the isothermal crystallization and subsequent melting of syndiotactic polypropylene (sPP) was studied with differential scanning calorimetry (DSC), time‐resolved simultaneous small‐angle X‐ray scattering (SAXS), and wide‐angle X‐ray diffraction (WAXD) methods with synchrotron radiation. The morphology of sPP isothermally crystallized at 100 °C for 3 h was also characterized with transmission electron microscopy (TEM). Time‐ and temperature‐dependent parameters such as the long period (L), crystal lamellar thickness (lc), amorphous layer thickness (la), scattering invariant (Q), crystallinity (Xc), lateral crystal sizes (L200 and L010), and unit cell dimensions (a and b) were extracted from the SAXS and WAXD data. Results indicate that the decreases in L and lc with time are probably due to the formation of thinner crystal lamellae, and the decreases in a and b are due to crystal perfection. The changes in the morphological parameters (Q, Xc, L, and lc) during subsequent melting exhibited a two‐stage process that was consistent with the multiple melting peaks observed in DSC. The two high‐temperature peaks can be attributed to the melting of primary lamellae (at lower temperatures) and recrystallized lamellae (at higher temperatures). An additional minor peak, located at the lowest temperature, was also visible and was related to the melting of thin and defective secondary lamellae. TEM results are consistent with the SAXS data, which supports the assignment of the larger value (l1) from the correlation function analysis as lc. WAXD showed that the thermal expansion was greater along the b axis than the a axis during melting. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2982–2995, 2001
Spherulitic growth rates and morphology of absorbable poly(p‐dioxanone) homopolymer and its copolymer by hot‐stage optical microscopy
Authors: Andjelić Saša , Jamiolkowski Dennis , McDivitt James , Fischer Jerome , Zhou Jack
Published: August 2002

Hot‐stage optical microscopy was used to study the crystal morphology, nucleation, and spherulitic growth rates of poly(p‐dioxanone) (PDS) homopolymer and an 89/11 PDS/glycolide segmented block copolymer. A wide range of crystallization conditions were experimentally accessible, allowing the inspection of various morphological features and accurate estimations of characteristic growth parameters, including radial growth and nucleation rates. Although the regime analysis of the crystallization kinetics indicated no breaks in the growth rate curve, the isothermal data were in excellent agreement with the Hoffman–Lauritzen theory. Spherulitic growth rates obtained from optical measurements are compared with values of the half‐time of crystallization determined earlier by differential scanning calorimetry. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3073–3089, 2001
Free volume, glass transition, and degree of branching in metallocene‐based propylene/α‐olefin copolymers: Positron lifetime, density, and differential scanning calorimetric studies
Authors: Dlubek G. , Bamford D. , Rodriguez‐Gonzalez A. , Bornemann S. , Stejny J. , Schade B. , Alam M. A. , Arnold M.
Published: August 2002

Positron annihilation lifetime spectroscopy (PALS), density, and differential scanning calorimetric (DSC) measurements were used to study systematically the variation of the glass‐transition temperature (Tg) and the size v and number density Nh of local free volumes in n‐alkyl‐branched polypropylenes. The samples were metallocene‐catalyzed propylene copolymers with different α‐olefins (from C4 to C16) and a different α‐olefin content (between 0 and 20 mol %). From the total specific volume and crystallinity the specific volume of the amorphous phase Va was estimated and used to calculate the fractional free (hole) volume h and value of Nh. The variations of Tg, v, Va, h, and Nh were related to the degree (number and length) of branching. Tg decreases and v increases linearly with the number and length of n‐alkyl branches. This behavior was attributed to an increased segmental mobility caused by branching. Both values, Tg and v, follow linear master curves as a function of the degree of branching (DB) if this is defined as the number of all side‐chain carbons with respect to a total of 1000 (main‐chain and side‐chain) carbons. Only propylene/1‐butene copolymers deviated from these relations. A linear relation between v and Tg was also found. The number density of holes was estimated to be Nh = 0.49(±0.07) nm−3 and Nh′ = 0.58(±0.11) × 1021 g−1, respectively. It shows a slight variation with the DB, which is also seen in the behavior of the specific volume Va. This variation was explained by the appearance of sterical hindrances resulting from short‐chain branches that may prevent an efficient packing of the chains. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 434–453, 2002; DOI 10.1002/polb.10108
Mechanism for the phase transition of poly(butylene terephthalate)
Authors: Takahashi Yasuhiro , Murakami Kei , Nishikawa Sumiyo
Published: August 2002

The α and β forms of poly(butylene terephthalate) transform reversibly by elongation and relaxation. The conformation change occurs in the tetramethylene glycol part, from GGTGG conformation to TSTS̄T conformation. In this study, by using a doubly oriented sample, we measured the positions, intensities, and half‐widths of the (100) and (010) reflections of the α and β forms of poly(butylene terephthalate) with a position‐sensitive proportional counter system. During the transformation, the molecules translate only slightly. These slight molecular translations, or distortions, accumulate, and the crystallite of the α form breaks into the small crystallites of the β form as the α–β transformation proceeds, and the crystallite of the α form grows with the relaxation of the distortion accumulated in the crystal and amorphous regions and on the crystallite surface as the β–α transformation proceeds. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 765–771, 2002
Diffusion of small molecules through modified poly(vinyl chloride) membranes
Authors: Tiemblo P. , Guzmán J. , Riande E. , Mijangos C. , Herrero M. , Espeso J. , Reinecke H.
Published: August 2002

The transport properties of a set of four copolymers based on poly(vinyl chloride) (PVC) have been studied. The nucleophilic substitution of chlorine atoms with 4‐mercaptophenol sodium salt, 2‐thionaphthalene, 4‐(1‐adamantyl) thiophenol, and thiophenolate sodium salt as the nucleophiles has been performed, from low conversion levels (3%) to high levels (40%), and the permeability, solubility, and diffusivity of oxygen, nitrogen, carbon dioxide, and methane have been measured. The introduction of bulky groups to the PVC chain leads to chain separation and results in large increases in the free volume at conversions up to 10%. This brings about a 5‐fold increase in the diffusion coefficients that is almost independent of the bulkiness of the substituent. Solubility is little affected and instead tends to decrease as substitution progresses. The substitution of more than 10% of the chlorine atoms does not result in an improvement in the transport properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 964–971, 2002
Transport of toluene/methyl ethyl ketone mixtures in polyisobutylene
Authors: Hong Seong U. , Barbari Timothy A.
Published: August 2002

In this study, the diffusion behavior of methyl ethyl ketone (MEK)/toluene mixtures, with MEK molar fractions (x1) in the liquid source lower than 0.2, in polyisobutylene (PIB) was investigated with vapor‐sorption Fourier transform infrared attenuated total reflectance (FTIR‐ATR) spectroscopy. FTIR‐ATR Fickian diffusion models for both binary and ternary systems were used to determine diffusion coefficients. Obtained diffusion coefficients for MEK from the binary diffusion model did not agree with those determined previously for the diffusion of MEK/toluene mixtures, with x1 > 0.2, in PIB. When the ternary diffusion model was used, the main‐term and cross‐term diffusion coefficients of MEK were comparable. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 908–914, 2001
Frequency‐dependent conductivity of interpenetrating polymer network composites of polypyrrole–poly(vinyl acetate)
Authors: Bhattacharyya S. , Saha S. K. , Chakravorty M. , Mandal B. M. , Chakravorty D. , Goswami K.
Published: August 2002

The frequency‐dependent conductivity of interpenetrating polymer network composites of polypyrrole (PPy) and poly(vinyl acetate) (PVAc) synthesized by FeCl3‐impregnated PVAc films being dipped into solutions of pyrrole in water was investigated over a frequency range of 100 Hz to 2 MHz and a temperature range of 110–300 K. For specimens with a PPy content less than the percolation threshold, the quantum mechanical tunneling of electrons was the conduction mechanism. For specimens with a higher PPy content, correlated barrier hopping of electrons appeared to be operative. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1935–1941, 2001
Glass‐formation kinetics of miscible blends of atactic polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide)
Authors: Robertson Christopher G. , Wilkes Garth L.
Published: August 2002

We present a detailed investigation of the kinetics associated with the glass transitions of miscible blends composed of atactic polystyrene (a‐PS) and poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO). According to both dynamic mechanical analysis and differential scanning calorimetry, relaxation times displayed an enhanced temperature dependence (i.e., more fragile or more cooperative behavior) for the blends compared with additive behavior based on the responses of neat a‐PS and PPO. This is consistent with the notion that specific interactions between the blend components heighten the intermolecular cooperativity. The compositional dependence of fragility provided insight into physical aging results for the properties of volume and enthalpy. The combination of our research and a previously reported pressure–volume–temperature study by Zoller and Hoehn (J Polym Sci Polym Phys Ed 1982, 20, 1385) provided evidence that the observation of increased glassy densities for the blends compared with those of the pure polymers was kinetic in origin and was not a feature of the thermodynamics of miscibility. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2118–2129, 2001
Replacement of thrombin residue G184 with Lys or Arg fails to mimic Na+ binding
Authors: Roy Dolly Banerjee , Rose Thierry , Di Cera Enrico
Published: August 2002

Na+ binding to thrombin enhances the catalytic activity toward numerous synthetic and natural substrates. The bound Na+ is located in a solvent channel 16 Å away from the catalytic triad, and connects with D189 in the S1 site through an intervening water molecule. Molecular modeling indicates that the G184K substitution in thrombin positions the protonated ϵ‐amino group of the Lys side‐chain to replace the bound Na+. Likewise, the G184R substitution positions the guanidinium group of the longer Arg side‐chain to replace both the bound Na+ and the connecting water molecule to D189. We explored whether the G184K or G184R substitution would replace the bound Na+ and yield a thrombin derivative stabilized in the highly active fast form. Both the G184K and G184R mutants lost sensitivity to monovalent cations, as expected, but their activity toward a chromogenic substrate was compromised up to 200‐fold as a result of impaired diffusion into the S1 site and decreased deacylation rate. Interestingly, both G184K and G184R substitutions compromised cleavage of procoagulant substrates fibrinogen and PAR1 more than that of the anticoagulant substrate protein C. These findings demonstrate that Na+ binding to thrombin is difficult to mimic functionally with residue side‐chains, in analogy with results from other systems. Proteins 2001;43:315–318. © 2001 Wiley‐Liss, Inc.
Efficacy and residues of phloxine B and uranine for the suppression of Mediterranean fruit fly in coffee fields
Authors: Licudine Jocelyn A , McQuate Grant T , Cunningham Roy T , Liquido Nicanor J , Li Qing X
Published: August 2002

The field efficacy of a bait containing phloxine B, uranine and Provesta 621 protein was tested against Mediterranean fruit fly (Ceratitis capitata; Medfly) by aerial and ground spraying in about 84 ha of coffee fields in Kauai, Hawaii, USA. Concurrently, soil and crop samples were collected from the aerially sprayed field and its unsprayed control field for residue studies. Efficacy of the sprays was assessed through trapping with both protein‐baited and trimedlure‐baited traps and through the infestation level of coffee cherries collected at least three‐quarters ripe. The C capitata population was low at the start of the aerial and ground spray studies, but dramatically increased in the control fields. This increase coincided with initial ripening of coffee cherries. During times of peak population levels, C capitata populations were reduced by more than 91% in the ground‐sprayed field and 99% in the aerial‐sprayed field, relative to the populations in their respective control fields and based on protein‐baited trap catches. Results of residue analyses indicated that uranine dissipated quickly compared with phloxine B on coffee and soil. Coffee samples collected at pre‐spray periods had phloxine B residues of 7.2–25.5 ng g−1 on berries. Phloxine B concentrations were much higher on coffee leaves (163–1120 ng g−1). Lower concentrations of the dye were found from coffee samples collected during rainy days. Average phloxine B concentrations immediately after spraying were 56 and 2840 ng g−1 in coffee berries and leaves, respectively. Dissipation of phloxine B on berries was fast, with a half‐life (t1/2) of 3 days. Dissipation of phloxine B on leaves was fitted to two linear phases: the initial (0–4 days) with a shorter t1/2 of 3 days and the later phase (4–28 days) with a longer t1/2 of 15 days. Average concentrations of phloxine B in the top soil ranged from 50 to 590 ng g−1 at pre‐spray. Phloxine B initial concentration (770 ng g−1) reached a plateau immediately after the last spraying, but showed a steady decline over time with t1/2 of 16 days. Fast dissipation of the dyes in the field indicates that these chemicals may be environmentally compatible and therefore a promising alternative for fruit fly control.

© 2001 Society of Chemical Industry
Active packaging as an opportunity to create package design that reflects the communicational, functional and logistical requirements of food products
Authors: Meroni Anna
Published: August 2002

The packaging of industrial food products is the most important means of transmitting a product's image and taste value. When the nature of its interface and its contents are the product of carefully planned imaging, the product has notable advantages in defining its image and product identity. Modern food trends dictate an ever‐increasing amount of services: The so‐called ‘functional packaging’ and ‘active packaging’ are prime examples of this service. The greatest innovation within this category of products consists literally of their interaction with food. These features create numerous fallbacks within all stages of the life‐cycle of a product, requiring a complex and multidisciplinary evaluation. The evaluation strategy of services which this packaging will offer to the consumer is still to be defined, and still to be identified within the key applications are the interests of the intermediary links of the production process. This requires the evaluation of the semantic and communicative aspects of the packaging which tend to be confused with the foodstuffs, the individualization of appropriate user profiles, control of logistical and location aspect of production, and a careful analysis of a comprehensive environmental balance, all issues that are parts of the objectives of the European project, Actipak. It is hoped, therefore, that the elaboration of these packaging systems will become a motive to try out a more knowledgeable and systematic design process for foodstuffs, in which innovative technology is used to provide effective benefits to the consumer. Copyright © 2000 John Wiley & Sons, Ltd.
Partition experimental designs for sequential processes: Part I—First‐order models
Authors: Perry Leonard A. , Montgomery Douglas C. , Fowler John W.
Published: August 2002

The output quality or performance characteristics of a product often depend not only on the effect of the factors in the current process but on the effect of factors from preceding processes. Statistically‐designed experiments provide a systematic approach to study the effects of multiple factors on process performance by offering a structured set of analyses of data collected through a design matrix. One important limitation of experimental design methods is that they have not often been applied to multiple sequential processes. The objective is to create a first‐order experimental design for multiple sequential processes that possess several factors and multiple responses. The first‐order design expands the current experimental designs to incorporate two processes into one partitioned design. The designs are evaluated on the complexity of the alias structure and their orthogonality characteristics. The advantages include a decrease in the number of experimental design runs, a reduction in experiment execution time, and a better understanding of the overall process variables and their influence on each of the responses. Copyright © 2001 John Wiley & Sons, Ltd.
Structural properties of PbTiO3 and PbZrxTi1−xO3: A quantum‐chemical study
Authors: Stashans Arvids , Zambrano Cesar , Sanchez Alfredo , Procel Luis Miguel
Published: August 2002

We investigate the structural and electronic properties of pure and Zr‐doped PbTiO3 crystals. The nature of atomic relaxation around the Zr impurity is studied through quantum‐chemical simulations based on the Hartree–Fock theory and a periodic large unit cell model adopted within the so‐called intermediate neglect of differential overlap approximation. The most stable defect configurations are predicted for different impurity concentrations. The results obtained are compared with those from other theoretical studies and a number of experimental measurements carried out on this technologically important perovskite‐type crystal. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Quantum chemical study of the reaction mechanism of ozone and methane with fluorine and chlorine atoms
Authors: Li Lai‐Cai , Wang Jing , Wang Xin , Tian An‐Min , Wong Ning‐Bew
Published: August 2002

Ab initio calculations of the potential energy surface for the F + O3 and Cl + O3 reactions have been performed using the G3 and G3MP2 methods, which optimize the geometry configuration of reactants, products, intermediates, and transition states. The results show that fluorine atoms react with ozone as violently as chlorine atoms. At the same time, we have studied the reaction mechanisms of F atoms and Cl atoms with methane. It is found that fluorine atoms prefer to react with methane and chlorine atoms with ozone when there is competition between ozone and methane. Therefore, we can reasonably explain why chlorine atoms play the main role of reactants depleting ozone, while the more active fluorine atoms deplete less ozone. © 2002 Wiley Periodicals, Inc.; DOI 10.1002/qua.10119
Examination of several density functionals in numerical Kohn–Sham calculations for atoms
Authors: Andrae Dirk , Brodbeck Ralf , Hinze Juergen
Published: August 2002

We studied several exchange‐only and exchange–correlation energy density functionals in numerical, i.e., basis‐set‐free, nonrelativistic Kohn–Sham calculations for closed‐shell 1S states of atoms and atomic ions with N electrons, where 2≤N≤120. Accurate total energies are presented to serve as reference data for algebraic approaches, as do the numerical Hartree–Fock results, which are also provided. Gradient‐corrected exchange‐only functionals considerably improve the total energies obtained from the usual local density approximation, when compared to the Hartree–Fock results. Such an improvement due to gradient corrections is not seen in general for highest orbital energies, neither for exchange‐only results (to be compared with Hartree–Fock results), nor for exchange–correlation results (to be compared with experimental ionization energies). © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 227–241, 2001
Theoretical study of CnCl, CnCl+, CnCl− (n=1–7) clusters
Authors: Largo Antonio , Cimas Alvaro , Redondo Pilar , Barrientos Carmen
Published: August 2002

A theoretical study of CnCl, CnCl+, and CnCl− (n=1–7) clusters has been carried out. Predictions for their electronic structures, dipole moments, and vibrational frequencies have been made at the B3LYP/6‐311G(d) level. According to our calculations the lowest‐lying geometry of all these species (with the only exception of neutral C3Cl) is predicted to be either a linear or quasi‐linear structure with chlorine located at the end of the carbon chain. CnCl clusters all have doublet ground states, whereas the anionic clusters, with the only exception of CCl−, all have singlet ground states. For CnCl+ species, n‐even clusters have triplet ground states whereas n‐odd ones have singlet ground states. An even–odd parity effect (n‐even clusters more stable than n‐odd ones) is found for both the neutral and anionic species, whereas in the case of the cations the alternation in stability is reversed. The ionization potential (IP) and electron affinity (EA) also exhibit regular variations with the size of the cluster, with n‐even clusters having both higher IP and EA than n‐odd ones. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 127–135, 2001
Evaluation of protein modification during anti‐viral heat bioprocessing by electrospray ionization mass spectrometry
Authors: Smales C. Mark , Pepper Duncan S. , James David C.
Published: August 2002

During the preparation of therapeutic plasma and recombinant protein biopharmaceuticals heat‐treatment is routinely applied as a means of viral inactivation. However, as most proteins denature and aggregate under heat stress, it is necessary to add thermostabilizing excipients to protein formulations destined for anti‐viral heat‐treatment in order to prevent protein damage. Anti‐viral heat‐treatment bioprocessing therefore requires that a balance be found between the bioprocessing conditions, virus kill and protein integrity. In this study we have utilized a simple model protein, β‐lactoglobulin, to investigate the relationship between virucidal heat‐treatment conditions (protein formulation and temperature) and the type and extent of protein modification in the liquid state. A variety of industrially relevant heat‐treatments were undertaken, using formulations that included sucrose as a thermostabilizing excipient. Using liquid chromatography/electrospray ionization mass spectrometry (LC/ESI‐MS) we show here that protein modifications do occur with increasingly harsh heat‐treatment. The predominant modification under these conditions was protein glycation by either glucose or fructose derived from hydrolyzed sucrose. Advanced glycation end products and additional unidentified products were also present in β‐lactoglobulin protein samples subjected to extended heat‐treatment. These findings have implications for the improvement of anti‐viral heat‐treatment bioprocesses to ensure the safety and efficacy of protein biopharmaceuticals. Copyright© 2001 John Wiley & Sons, Ltd.
Perturbation of ion trajectories by resonant excitation leads to occurrence of ghost peaks
Authors: Favre Amelie , Gonnet Florence , Tabet Jean‐Claude
Published: August 2002

We have shown in a recent paper (Kocher F, Favre A, Gonnet F, Tabet JC J. Mass Spectrom. 1998; 33: 921) that under particular ion trapping conditions, i.e. space charge, artefacts called ghost peaks were displayed in mass spectra and isolation spectra. All experimental factors which modified the space‐charge strength, influenced the intensities of the ghost peaks. It was demonstrated that only the injected ions having qz ≤0.25 (βz ≤ 2/11) at the beginning of the analytical scan step gave rise to the formation of such artefact peaks. In fact, the ion cloud defocused by space charge was subjected to high‐order multipole fields (e.g. 22‐pole, Wang Y, Schubert M, Franzen J, Proc. 44th ASMS Conf. Mass Spectrom. and Allied Topics, Portland OR, 1996; p. 131), so that the trajectories of the analysed ions were destabilized thus affecting the ion ejection which then occurred at qz = 0.908 (βz = 1, natural boundary). However, ions having 0.25 (βz ≤ 2/11) ≤qz ≤0.45 (βz ≤ 1/3), at the beginning of the analytical scan step, were not destabilized, and were correctly ejected where the axial modulation was applied (βz ≤ 1/3). Thus, under extreme space‐charge conditions, the ion excursion increased, the influence of the non‐linear resonance at βz = 2/11 was enhanced, ion excursion was more enhanced, and the ions were not ejected at βz = 1/3 but at βz = 1.

We shown here that, again under the influence of the non‐linear resonance at βz = 2/11, under space‐charge conditions the ion excursion increased, and the application of a resonant excitation dramatically enhanced this ion excursion, compared to only the isolation step as was performed in the previous work. This led to these ions not being ejected at βz = 1/3 but rather at βz = 1, and thus being displayed as ghost peaks in the collisionally induced dissociation (CID) spectra. This behavior could take place for other working ejection points, which occur at non‐linear resonances (e.g. βz = 2/11 as well as βz = 2/3). Copyright © 2001 John Wiley & Sons, Ltd.
Combining energy‐dependent electrospray ionisation with tandem mass spectrometry for the analysis of inorganic compounds
Authors: Dyson Paul J. , Hearley Andrew K. , Johnson Brian F. G. , McIndoe J. Scott , Langridge‐Smith Patrick R. R. , Whyte Christopher
Published: August 2002

The recently developed technique of energy‐dependent electrospray ionisation mass spectrometry (EDESI‐MS) has been implemented on a triple quadrupole mass spectrometer such that fragmentation occurs in the collision cell rather than at the skimmer cone. This modification enables a superior two‐dimensional map of the collision voltage versus mass‐to‐charge ratio to be generated, providing unambiguous peak assignments. This latest enhancement to the technique is referred to as energy‐dependent electrospray ionisation tandem mass spectrometry (EDESI‐MS/MS). In the present work the technique has been applied to investigate the sequential removal of ligands from the inorganic mixed‐metal anionic cluster compound [Ru5CoC(CO)16]−, which serves to illustrate the advantages of this approach. Copyright © 2001 John Wiley & Sons, Ltd.
Proteomics of gluten: mapping of subunit 1 Ax2* in Cheyenne cultivar by matrix‐assisted laser desorption/ionization
Authors: Cozzolino Rosaria , Giorgi Sabrina Di , Fisichella Salvatore , Garozzo Domenico , Lafiandra Domenico , Palermo Angela
Published: August 2002

This paper reports results on the verification of the 1Ax2* high molecular weight glutenin subunit sequence in Cheyenne cultivar. The gene sequence of the protein is known but recently some text changes have been made, and furthermore until now no characterization of post‐translational modifications has been reported. The two published sequences, named I and II, differ in four residues at positions 23, 208, 475, and 611. The first sequence contains 20 Arg and 6 Lys residues, producing 26 tryptic fragments, since the Arg109‐Pro110 bond is generally not cleaved by trypsin. The second sequence contains 19 Arg and 6 Lys residues, producing 25 tryptic peptides, again because of the Arg109‐Pro110 bond. Both sequences generate two cyanogen bromide fragments. Matrix‐assisted laser desorption/ionization analysis of the tryptic digest of the high‐MW glutenin subunit 1Ax2* resulted in the identification of 24 out of the 26 expected peptides for sequence I, a sequence coverage of 99.5%. These results were sufficient to rule out sequence II and any protein glycosylation and any other post‐translational modifications to within the detection limits of the method. It was found that the choice of matrix considerably influenced the sequence coverage in peptide mapping. Copyright © 2001 John Wiley & Sons, Ltd.
Atmospheric pressure matrix‐assisted laser desorption/ionization ion trap mass spectrometry of sulfonic acid derivatized tryptic peptides
Authors: Keough T. , Lacey M. P. , Strife R. J.
Published: August 2002

Atmospheric pressure matrix‐assisted laser desorption/ionization (AP‐MALDI) and ion trap mass spectrometry have been used to study the fragmentation behavior of native peptides and peptide derivatives prepared for de novo sequencing applications. Sulfonic acid derivatized peptides were observed to fragment more extensively and up to 28 times more efficiently than the corresponding native peptides. Tandem mass spectra of native peptides containing aspartic or glutamic acids are dominated by cleavage on the C‐terminal side of the acidic residues. This significantly limits the amount of sequence information that can be derived from those compounds. The MS/MS spectra of native tryptic peptides containing oxidized Met residues show extensive loss of CH3SOH and little sequence‐specific fragmentation. On the other hand, the tandem mass spectra of derivatized peptides containing Asp, Glu and oxidized Met show much more uniform fragmentation along the peptide backbone. The AP‐MALDI tandem mass spectra of some derivatized peptides were shown to be qualitatively very similar to the corresponding vacuum MALDI postsource decay mass spectra, which were obtained on a reflector time‐of‐flight instrument. However, the ion trap mass spectrometer offers several advantages for peptide sequencing relative to current reflector time‐of‐flight instruments including improved product ion mass measurement accuracy, improved precursor ion selection and MSn. These latter capabilities were demonstrated with solution digests of model proteins and with in‐gel digests of 2D‐gel separated proteins. Copyright © 2001 John Wiley & Sons, Ltd.
Gas‐phase ion/molecule reactions between dimethoxyphosphonium ions and aromatic hydrocarbons
Authors: Leclerc Eric , Buchmann William , Taphanel Marie‐Hélène , Morizur Jean‐Pierre
Published: August 2002

Ion/molecule reactions between O=P(OCH3)2+ phosphonium ions and six aromatic hydrocarbons (benzene, toluene, 1,2,4‐trimethylbenzene, naphthalene, acenaphthylene and fluorene) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH3)2+ phosphonium ions, formed by electron impact from neutral trimethyl phosphite, were found to react with aromatic hydrocarbons (ArHs) to give (i) an adduct [ArH, O=P(OCH3)2]+ and (ii) for ArHs which have an ionization energy below or equal to 8.14 eV, a radical cation ArH+· by charge transfer reaction. Collision‐induced dissociation experiments, which produce fragment ions other than the O=P(OCH3)2+ ions, indicate that the adduct ions are covalent species. Isotope‐labeled ArHs were used to elucidate fragmentation mechanisms. The charge transfer reactions were investigated using density functional theory at the B3LYP/6‐311 + G(3df,2p)//B3LYP/6‐31G(d,p) level of theory. The potential energy surface obtained from B3LYP/6‐31G(d,p) calculations for the reaction between O=P(OCH3)2+ and benzene is described. Copyright © 2002 John Wiley & Sons, Ltd.
A QFT framework for nonlinear robust stability
Authors: Baños Alfonso , Barreiro Antonio , Gordillo Francisco , Aracil Javier
Published: August 2002

The problem of deriving conditions for a stabilizing linear compensator in a uncertain nonlinear control system is addressed, for some types of memoryless nonlinearities like the saturation or the dead zone. The approach is to incorporate to QFT conditions given by the application of harmonic balance and multiplier techniques, providing the designer with a very transparent tool for synthesizing nonlinear stabilizing compensators, balancing between different possible alternatives. Copyright © 2002 John Wiley & Sons, Ltd.
Epitaxial phenomena across length and time scales
Authors: Vvedensky D. D.
Published: August 2002

The morphological evolution of an epitaxial film results from atomistic processes such as adatom motion and step–adatom interactions asserting their influence over the macroscopic length and time scales of the growth front. Modelling epitaxial phenomena thus necessitates making a compromise between the detailed information provided by first‐principles methods and the computational flexibility afforded by methods such as Monte‐Carlo simulations and continuum equations of motion, in which atomistic processes are replaced by coarse‐grained effective kinetics. We will review the various approaches that are available for modelling epitaxial phenomena using the (001) surfaces of III–V compound semiconductors as a case study, with a view to making direct comparisons with experimental measurements and to establishing a methodology that is capable of incorporating all pertinent length and time scales. Copyright © 2001 John Wiley & Sons, Ltd.
Correlation coefficient estimation involving a left censored laboratory assay variable
Authors: Lyles Robert H. , Fan Dongjie , Chuachoowong Rutt
Published: August 2002

When assessing a correlation between two exposure or biological marker variables, one sometimes encounters the problem of indeterminate values for one of the variables due to an assay detection limit. In this event, investigators often report correlation coefficients computed after removing the pairs involving non‐detectable values, or after substituting some small constant for those values. These ad hoc practices can lead to bias in both point and confidence interval estimates of the true correlation coefficient. To address this issue, we consider two parametric techniques for estimating the correlation in the presence of left censoring for one of the variables. The first is a maximum likelihood approach, and the second is an adaptation of multiple imputation motivated primarily by potential benefits in confidence interval coverage. Both of the estimators studied reduce to the standard Pearson's correlation coefficient in the event of no censoring, and hence are valid in cases where this measure would be appropriate for the complete data. We assess these approaches empirically and contrast them with ad hoc methods for estimating the correlation between cervicovaginal human immunodeficiency virus (HIV) viral load measurements and CD4+ lymphocyte counts from HIV positive women enrolled in a clinical trial conducted in Bangkok, Thailand. Copyright © 2001 John Wiley & Sons, Ltd.
Testing abnormality in the spatial arrangement of cells in the corneal endothelium using spatial point processes
Authors: Díaz M. E. , Ayala G. , Quesada S. , Martínez‐Costa L.
Published: August 2002

The study of central corneal endothelium morphology is important in Ophthalmology. Some of the pathologies that could compromise endothelial cell morphology are trauma, cataract, surgery, use of contact lenses, corneal dystrophies or degenerations. The quantitative analysis of cell shape and cellular pattern is more sensitive in detecting subtle changes in endothelial morphology than cell density measurement or cell area analysis. In this paper, the morphology of the central cornea, the most important area from the point of view of vision, is studied through an associated bivariate spatial point pattern: the centroids of the cells and the triple points, that is, the points where three different cells converge. Nine different summary descriptors (widely used in the statistical analysis of spatial point patterns) have been used: the empty space distribution function; the nearest neighbour distribution function and Ripley's 𝒦‐function for each type of point separately (centroids and triple points), plus the corresponding three versions of these functions in the bivariate case. A control sample with similar age and cell density and no known abnormality is associated to each patient. The above descriptors are calculated for the patient and the controls. Each descriptive of the patient is compared with the corresponding descriptors from the controls by means of a graphical analysis and a formal test. Some patients presenting different pathologies are analysed in detail. Endothelia considered morphologically abnormal by visual inspection, which were not detected by hexagonality or density analysis, could be distinguished from control endothelia by these new descriptors. Copyright 2001 John Wiley & Sons, Ltd.
Role of ultrasonography in the staging of gastrointestinal neoplasms
Authors: Neumaier Carlo Emanuele , Cittadini Giuseppe , Grasso Andrea , Dahmane M'hamed
Published: August 2002

This article reviews the capabilities and limits of ultrasonography (US) in the staging of gastrointestinal neoplasms. US is a well‐established tool in the investigation of abdominal diseases. Its role is very important in the first approach to liver, gallbladder, biliary, and pancreatic diseases, but its abilities for accurate staging may be limited by various factors, which will be discussed. In the evaluation of the stomach and intestine, US is rarely utilized, but it can occasionally demonstrate an unsuspected gastrointestinal mass that usually must be evaluated further with specific techniques (endoscopy and barium studies) to confirm the diagnosis and to perform an accurate staging (with endosonography and computed tomography). Semin. Surg. Oncol. 20:86–90, 2001. © 2001 Wiley‐Liss, Inc.
Role of the surgeon as a variable in the treatment of rectal cancer
Authors: Hermanek Paul , MD Peter J. Hermanek,
Published: August 2002

Increasingly, data are being accumulated on the influence of intersurgeon variability on outcome after curative surgical treatment of rectal carcinoma. Thus, today the individual surgeon has to be considered as an independent factor influencing locoregional recurrence, as well as survival rates. In general, higher local control and survival can be expected for specialized colorectal surgeons. There are no clear correlations between surgical volume and outcome. Interinstitutional variability in treatment results reflects intersurgeon variability, but analysis is generally more difficult because of a lack of homogeneity with respect to different confounding factors. There are several factors in surgical technique that are important for long‐term outcome. Of greatest apparent importance is the adequacy of mesorectal excision (for carcinomas of the middle and lower third, total mesorectal excision; for carcinomas of the upper third, mesorectal excision down to a mesorectal plane 5 cm distal to the gross tumor margin detected by the surgeon in situ). Furthermore, intraoperative local tumor spillage (tumor perforation during mobilization, incision into the tumor), en bloc resection technique, skill, and the extent of regional lymphadenectomy may influence outcome. For quality assurance, detailed operative reports are required, as well as histopathology examinations concerning indicators of surgical oncologic quality discernable from the resection specimens. In future clinical trials of multimodal treatment of rectal cancer, quality assurance of surgery and pathology is necessary for consideration of the surgeon and surgical technique prognostic factors. Semin. Surg. Oncol. 19:329–335, 2000. © 2000 Wiley‐Liss, Inc.
Decreased calcineurin and increased phosphothreonine‐DARPP‐32 in the striatum of rats behaviorally sensitized to methamphetamine
Authors: Lin Xian‐Hao , Hashimoto Takeshi , Kitamura Noboru , Murakami Naoya , Shirakawa Osamu , Maeda Kiyoshi
Published: August 2002

We investigated changes in signal transduction via calcineurin (CaN) in the striatum of rats behaviorally sensitized to methamphetamine (Meth). The rats were injected with Meth (4 mg/kg, s.c.) five times a week for 3 weeks and then were given a challenge dose of Meth (2 mg/kg, s.c.). Seven days after the challenge test, we determined the levels of CaN Aα and Aβ by Western blotting. We further immunoquantified DARPP‐32 (dopamine‐ and cAMP‐regulated phosphoprotein, mw 32,000) and phosphothreonine‐DARPP‐32, which can be dephosphorylated at threonine sites by CaN. We found that both CaN Aα and Aβ were significantly decreased in the particulate fractions but were not changed in the soluble fractions from the striatum of Meth‐sensitized rats as compared with control rats. The same findings were observed in the striatum of rats 6 h after the injection of PCP (10 mg/kg, s.c.). In the striatum of Meth‐sensitized rats, phosphothreonine‐DARPP‐32 immunoreactivities significantly increased, but DARPP‐32 immunoreactivities were not significantly different from those of the control rats. These results indicate that the activity of signal transduction via CaN is functionally decreased in the striatum of Meth‐sensitized rats. Synapse 44:181–187, 2002. © 2002 Wiley‐Liss, Inc.
Comparison of paired‐pulse facilitation of AMPA and NMDA synaptic currents in the lateral amygdala
Authors: Zinebi Fatiha , Russell Rex T. , McKernan Margaret , Shinnick‐Gallagher Patricia
Published: August 2002

Stimulating thalamic fibers exiting from the internal capsule evokes a glutamatergic excitatory postsynaptic current (EPSC) recorded in vitro with patch electrodes in neurons of the rat lateral amygdala (LA). The purpose of this study is to compare paired‐pulse facilitation (PPF), a form of short‐term synaptic plasticity, of AMPA and NMDA receptor‐mediated EPSCs. Analysis of PPF at this synapse is important since, in fear‐conditioned animals, PPF reflects an enhanced transmitter release but the amplitude of only AMPA EPSCs is facilitated. PPF magnitude of the composite EPSC is a result of both AMPA and NMDA receptor activation; however, the characteristics of AMPA and NMDA PPF are dissimilar. Specifically, the NMDA EPSC shows greater PPF (NMDA PPF) than does the AMPA EPSC whether measuring the NMDA PPF magnitude in an AMPA antagonist/Mg2+‐free solution or by subtracting the AMPA EPSC from the composite EPSC in normal Mg2+. Presynaptic NMDA receptors neither influence AMPA PPF nor account for the difference between the NMDA and AMPA PPF. Another difference was that removal of inhibitory tone enhanced AMPA PPF, while it had mixed effects on NMDA PPF. Furthermore, AMPA PPF was independent of stimulus intensity and postsynaptic voltage, unlike the NMDA PPF. Another dissimilarity was that the amplitudes of pairs of AMPA EPSCs were not correlated, suggesting presynaptic mechanisms. In contrast, NMDA PPF was dependent on stimulus intensity and postsynaptic voltage and the amplitudes of paired NMDA EPSCs had a positive correlation, suggesting a postsynaptic influence. Both AMPA and NMDA PPF were influenced by GABA inhibition and this could be a factor in the magnitude disparity. These data show that AMPA and NMDA PPF have different characteristics and contribute to the composite PPF in the thalamic to lateral amygdala pathway. Synapse 42:115–127, 2001. © 2001 Wiley‐Liss, Inc.
Methylenetetrahydrofolate reductase: A common human polymorphism and its biochemical implications
Authors: Matthews Rowena G.
Published: August 2002

Methlenetetrahydrofolate (CH2‐H4folate) is required for the conversion of homocysteine to methionine and of dUMP to dTMP in support of DNA synthesis, and also serves as a major source of one carbon unit for purine biosynthesis. This review presents biochemical studies of a human polymorphism in methylenetetrahydrofolate reductase, which catalyzes the reaction shown below. The mutation decreases the flux of CH2‐H4folate into CH3‐H4folate, and is associated with both beneficial and deleterious effects that can be traced to the molecular effect of the substitution of alanine 222 by valine. © 2002 The Japan Chemical Journal Forum and John Wiley & Sons, Inc. Chem Rec 2: 4–12, 2002
Issues, Examples, and Challenges in Formative Assessment
Authors: Hunt Earl , Pellegrino James W.
Published: August 2002

Formative assessment, in which the assessment is integrated within instruction and aimed at increasing learning, can replace summative assessment in many situations. Two programs of formative assessment are described: DIANOSER and SMART.