bluuebunny/crossref_metadata_2025 huggingface dataset:
Induced intramolecularity in the reference reaction can be responsible for the low effective molarity of intramolecular general acid–base catalysis
Authors: Pascal Robert
Published: October 2002

Whereas intramolecular catalysis by nucleophilic groups can be associated with values of effective molarities ranging from 105 to 108 M in the absence of strain, values below 10 M are usually observed for general acid–base catalysis. Based on the grounds that the efficiency of intramolecular reactions is related to the entropic disadvantage of bimolecular reactions, this low efficiency is usually explained by a loose transition state for proton transfer that is diffusion limited in the thermodynamically favorable direction. However, the transient formation of a hydrogen bond at an electronegative center provides another possibility that can account for the low efficiency of general acid–base catalysis when the reaction is not diffusion limited. Any proton transfer at a site that forms hydrogen bonds to the solvent and that is concerted with a slower process is likely to take place along a hydrogen bond with the catalyst and thus to have an intramolecular character. As a result, low benefits can be earned from further intramolecularity. This analysis has important consequences for intramolecular and enzymatic proton transfers to and from carbon atoms. Owing to the absence or the weak strength of hydrogen bonds capable of inducing intramolecularity in the non‐catalyzed mechanism, high effective molarities could be recovered. As a result, the existence of strong hydrogen bonds with carbon acids would no longer be needed to account for the high effective molarities that have been observed in some cases for intramolecular proton transfer to or from carbon. Moreover, the introduction of new concepts such as short, strong hydrogen bonds (low‐barrier hydrogen bonds) to account for the high efficiency of enzymatic proton abstraction from carbon would not be necessary. Copyright © 2002 John Wiley & Sons, Ltd.
Dual influence of lithium chloride on the anionic propagation of polystyryllithium in ethereal solvents
Authors: Verheyden Hilde , Van Lierde Paul , Szwarc Michael , Litvinenko Galina , Van Beylen Marcel
Published: October 2002

The addition of lithium chloride (LiCl) to a solution of polystyryllithium (PStLi) in tetrahydropyran (THP) reduces the rate of propagation of PStLi at a low concentration of the latter but accelerates it at higher concentrations of PStLi. Moreover, the addition of LiCl, which is dimeric in ethereal solutions, increases the conductance of PStLi solutions in tetrahydrofuran (THF) and THP to a much greater extent than expected from the separate conductances of PStLi and LiCl, which is itself even less dissociated than PStLi. These phenomena are fully explained by the dual action of LiCl. Below a certain concentration of PStLi, the dissociation, not of LiCl as such, as claimed before, but of its solvated dimer into free Li+ ions and ClLiCl− triple ions provides Li+ ions that repress the ionic dissociation of PStLi by a common ion effect. This, in turn, diminishes the concentration of free polystyryl anions, which are the dominating species responsible for the propagation of PStLi, resulting in retardation. However, at higher concentrations of PStLi, Li+ ions produced by its dissociation are scavenged by the scavenging action of LiCl dimers, producing quintuple cations. This reduces the concentration of free Li+ ions and, therefore, increases the concentration of the reactive free polystyryl anions, resulting in an acceleration of the propagation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2148–2157, 2002
Living cationic polymerization route to poly(oligooxyethylene carbonate) vinyl ethers
Authors: Feit Ben‐Ami , Halak Baruch
Published: October 2002

The addition of dialkyl (R = Me or Et) carbonates to poly(oxyethylene)‐based solid polymeric electrolytes resulted in enhanced ionic conductivities. Relatively high conductivities in lithium batteries with solutions of lithium salts in di(oligooxyethylene) carbonates such as R(OCH2CH2)nOC(O)O(CH2CH2O)mR (R = Et, n = 1, 2, or 3, m = 0, 1, 2, or 3) and related carbonates were obtained. In this respect, related comb‐shaped poly(oligooxyethylene carbonate) vinyl ethers of the type CH2CH(OR) were prepared [R = (OCH2CH2)nOC(O)O(CH2CH2O)mR′; (1) n = 2 or 3, m = 0, R′ = Et; (2) n = 2 or 3; m = 3, R′ = Me]. The direct preparation of derived target polymers of this class by polymerization of the corresponding vinyl ether‐type monomers could not be achieved because of a rapid in situ decarboxylative decomposition of these monomers (as formed) during the final step of their synthesis. Instead, a prepolymer was prepared by a living cationic polymerization of CH2CH(OCH2CH2)nOC(O)CH3 (n = 2 or 3). The hydrolysis of its pendant ester groups, followed by the reaction of the hydrolyzed prepolymer with each of several alkyl chloroformates of the type ClC(O)O(CH2CH2O)mR′ (m = 0, 2, or 3, R′ = Me or Et) resulted in the corresponding target polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2171–2183, 2002
Cationic copolymerization of indene with styrene derivatives: Synthesis of random copolymers of indene with high molecular weight
Authors: Kanaoka Shokyoku , Ikeda Nobuyuki , Tanaka Akira , Yamaoka Hitoshi , Higashimura Toshinobu
Published: October 2002

Random copolymers with high molecular weights of indene and p‐methylstyrene (pMeSt) were synthesized by cationic polymerization with trichloroacetic acid/tin tetrachloride in CH2Cl2 at low temperatures. When indene and pMeSt (1:1 v/v), for example, were polymerized at −40 °C, both monomers were consumed at very similar rates to give a copolymer with high molecular weight [number‐average molecular weight (Mn): 8–9 × 104]. This is indeed quite unexpected behavior for the combination of these two monomers because pMeSt polymerized over 1000 times faster than indene in the homopolymerization under the reaction conditions previously described. The product copolymer of indene and pMeSt had a random monomer sequence in it that was confirmed by NMR analyses and thermal‐property measurements. In sharp contrast with pMeSt, styrene and p‐chlorostyrene, which have no electron‐donating groups on the phenyl ring, led to low molecular weight polymers (Mn < 10,000) in the copolymerization with indene (1:1 v/v). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2449–2457, 2002
Block copolyesters of poly(pentamethylene p,p′‐bibenzoate) and poly(tetramethylene adipate)
Authors: Tsai Ruey‐Shi , Lee Yu‐Der , Tsai Hong‐Bing
Published: October 2002

Hydroxy‐terminated poly(pentamethylene p,p′‐bibenzoate) oligomers with different molecular weights were prepared. The poly(pentamethylene p,p′‐bibenzoate) oligomers showed rather high crystallinity, and some of them exhibited a monotropic smectic phase. Block copolyesters with hard segments of poly(pentamethylene p,p′‐bibenzoate) and soft segments of poly(tetramethylene adipate) were prepared by coupling the poly(pentamethylene p,p′‐bibenzoate) oligomer and a poly(tetramethylene adipate)glycol with methylene‐4,4′‐diphenylene diisocyanate in solution. The block copolyesters were characterized by IR, 1H NMR, differential scanning calorimetry, a polarized microscope, and X‐ray diffraction. The thermal transitions of the block copolyesters were dependent on the composition and the molecular weight of the poly(pentamethylene p,p′‐bibenzoate) oligomer used. The hard segments in the block copolyesters showed no liquid crystallinity and exhibited rather low crystallinity or were even amorphous. The molecular weight of the poly(pentamethylene p,p′‐bibenzoate) oligomer used influences the glass‐transition temperature and crystalline properties of the soft segments in the block copolyesters significantly. The effect on the glass‐transition temperature of the soft segments is described as the difference in miscibility between the hard and soft segments. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2626–2636, 2002
Facile synthesis of comb, star, and graft polymers via reversible addition–fragmentation chain transfer (RAFT) polymerization
Authors: Quinn John F. , Chaplin Rodney P. , Davis Thomas P.
Published: October 2002

Reversible addition–fragmentation chain transfer (RAFT) polymerization has been shown to be a facile means of synthesizing comb, star, and graft polymers of styrene. The precursors required for these reactions were synthesized readily from RAFT‐prepared poly(vinylbenzyl chloride) and poly(styrene‐co‐vinylbenzyl chloride), which gave intrinsically well‐defined star and comb precursors. Substitution of the chlorine atom in the vinylbenzyl chloride moiety with a dithiobenzoate group proceeded readily, with a minor detriment to the molecular weight distribution. The kinetics of the reaction were consistent with a living polymerization mechanism, except that for highly crowded systems, there were deviations from linearity early in the reaction due to steric hindrance and late in the reaction due to chain entanglement and autoacceleration. A crosslinked polymer‐supported RAFT agent was also prepared, and this was used in the preparation of graft polymers with pendant polystyrene chains. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2956–2966, 2002
Structure‐property relationships for a series of amorphous partially aliphatic polyimides
Authors: Eichstadt Amy E. , Ward Thomas C. , Bagwell Melanie D. , Farr Isaac V. , Dunson Debra L. , McGrath James E.
Published: October 2002

High molecular weight, soluble, amorphous, partially aliphatic polyimides were successfully synthesized using an ester acid high‐temperature solution imidization route, which allows one to control desired glass‐transition (Tg) and processing temperatures. This method involves the prereaction of aromatic dianhydrides with ethanol and a tertiary amine catalyst to form ester acids, followed by the addition of diamines. Subsequent thermal reaction forms fully cyclized polyimides. This reaction pathway eliminates the need for anhydrous solvents and overcomes the problem of salt formation commonly observed for nucleophilic, more‐basic aliphatic amines when utilizing the traditional polyamic acid synthesis route. The molar ratio of aromatic‐to‐aliphatic diamines was varied to generate a series of copolyimides with the chosen dianhydride and tailor the physical properties for specific adhesive applications. This series of copolyimides was characterized by their molecular weight, Tg, thermal stability, coefficient of thermal expansion, refractive index, and dielectric constant. Structure‐property relationships were established. The γ and β sub‐Tg viscoelastic properties were researched to understand their molecular origins. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1503–1512, 2002
Gel polymer electrolytes prepared with porous membranes based on an acrylonitrile/methyl methacrylate copolymer
Authors: Min Hyo‐Sik , Kang Dong‐Wan , Lee Doo‐Yeon , Kim Dong‐Won
Published: October 2002

Porous membranes based on acrylonitrile/methyl methacrylate copolymer were prepared by a phase‐inversion method. Microstructures of the porous membranes were controlled through the variation of the evaporation drying time before immersion in a nonsolvent bath. Gel polymer electrolytes were prepared from these porous membranes via soaking in an organic electrolyte solution. They encapsulated the electrolyte solution well without solvent leakage and maintained good mechanical properties that allowed the preparation of thin films (∼23 μm). These systems showed acceptable ionic conductivity values (>6.0 × 10−4 S/cm) at room temperature and sufficient electrochemical stability over 4.4 V that allowed applications in lithium‐ion polymer batteries. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1496–1502, 2002
Information exchange in oncology outpatient clinics: source, valence and uncertainty
Authors: Rogers Margaret , Todd Chris
Published: October 2002

A large literature of doctor–patient communication exists, yet little is known about how symptom information is communicated in cancer care. This qualitative study explores the exchange of symptom and clinical information between cancer patients and oncologists in outpatient clinics of a regional teaching hospital. Verbatim transcripts of consultations between 14 doctors and 43 post‐treatment follow‐up patients from eight consultants' clinics were subjected to analytic induction and microinteractional analysis techniques. Findings from these analyses indicate that information about patients was accorded varying relevance by doctors depending upon its source, valence and certainty. Doctors' requests for information was contingent upon certainty of clinical information. Symptom information was elicited from patients only when clinical information with high certainty was unavailable. If negative patient information was volunteered, it was not addressed when positive clinical information was present and cancer treatment was not indicated. It appears that information in outpatient oncology consultations is organised according to a hierarchy and is used to make treatment decisions and not primarily for symptom management. Copyright © 2002 John Wiley & Sons, Ltd.
Unusual cause of chronic cough in a four‐year‐old cured by uvulectomy
Authors: Najada Abdelhamid , Weinberger Miles
Published: October 2002

A 4‐year‐old boy had a history of persistent barking cough unresponsive to medical treatment since infancy. He described a feeling of something in his throat. When investigated by flexible fiberoptic bronchoscopy, the only abnormality was the uvula resting in contact with the epiglottis. The cough was no longer present after uvulectomy. Pediatr Pulmonol. 2002; 34:144–146. © 2002 Wiley‐Liss, Inc.
Hormones and prostate cancer: Current perspectives and future directions
Authors: Hsing Ann W. , Reichardt Juergen K.V. , Stanczyk Frank Z.
Published: October 2002

Prostate cancer is the most commonly diagnosed non‐skin cancer in men in most western countries. Despite the high morbidity and mortality from prostate cancer, its etiology remains obscure. Although compelling laboratory data suggest a role for androgens in prostate carcinogenesis, most epidemiologic data on humans are inconclusive. To provide insights and directions for future epidemiologic research on hormones and prostate cancer, this review focuses on current perspectives of serum‐based studies and polymorphisms in relevant hormone‐related genes. We highlight the importance of methodologic studies and investigations of hormone levels in the prostatic tissue to help clarify the often‐contradictory data on serologic studies. We recommend careful analysis and cautious interpretation of studies of genetic markers, including repeats and single nucleotide polymorphisms (SNPs), as false positive and negative results may arise in many current and future studies with limited statistical power and non‐representative samples from the population. The review also highlights the reasons to perform functional analyses of SNPs, a critical and often under‐appreciated component of molecular epidemiologic investigations.

The time is ripe for large‐scale multidisciplinary investigations that incorporate molecular genetics, biochemistry, histopathology, and endocrinology into traditional epidemiologic studies. Such collaboration will lead to a deeper understanding of the etiologic pathways of prostate cancer, ultimately yielding better preventive, diagnostic, and therapeutic strategies. Prostate 52:213–235, 2002. Published 2002 Wiley‐Liss, Inc.
Pathway heterogeneity in protein folding
Authors: Fernández Ariel , Colubri Andrés
Published: October 2002

We generate ab initio folding pathways in two single‐domain proteins, hyperthermophile variant of protein G domain (1gb4) and ubiquitin (1ubi), both presumed to be two‐state folders. Both proteins are endowed with the same topology but, as shown in this work, rely to a different extent on large‐scale context to find their native folds. First, we demonstrate a generic feature of two‐state folders: A downsizing of structural fluctuations is achieved only when the protein reaches a stationary plateau maximizing the number of highly protected hydrogen bonds. This enables us to identify the folding nucleus and show that folding does not become expeditious until a topology is generated that is able to protect intramolecular hydrogen bonds from water attack. Pathway heterogeneity is shown to be dependent on the extent to which the protein relies on large‐scale context to fold, rather than on contact order: Proteins that can only stabilize native secondary structure by packing it against scaffolding hydrophobic moieties are meant to have a heterogeneous transition‐state ensemble if they are to become successful folders (otherwise, successful folding would be too fortuitous an event.) We estimate mutational Φ values as ensemble averages and deconvolute individual‐route contributions to the averaged two‐state kinetic picture. Our results find experimental corroboration in the well‐studied chymotrypsin inhibitor (CI2), while leading to verifiable predictions for the other two study cases. Proteins 2002;48:293–310. © 2002 Wiley‐Liss, Inc.
Identification of the N‐terminal functional domains of Cdk5 by molecular truncation and computer modeling
Authors: Zhang Jianwen , Luan Chi‐Hao , Chou Kuo‐Chen , Johnson Gail V.W.
Published: October 2002

Cyclin dependent kinase (Cdk) 5, an atypical member of the Cdk family, plays a fundamental role in the development of the nervous system, and may also be involved in the pathogenesis of certain neurodegenerative diseases. Further, Cdk5 is activated by the specific regulatory proteins p39, p35, or p25 rather than cyclins, and in contrast to other members of the Cdk family is not involved in the progression of the cell cycle. A three‐dimensional computer model of Cdk5‐p25‐ATP has been generated previously [Chou et al., Biochem Biophys Res Commun 1999;259:420–428], providing a structural basis for the study of the mechanisms of Cdk5 activation. To assess the predicted ATP and p25 binding domains at the N‐terminal of Cdk5, two mutants of Cdk5 were prepared in which amino acids 9–15 (Δ9–15) or 9–47 (Δ9–47) were deleted. The results of these studies clearly demonstrate that an N‐terminal loop and the PSSALRE helix are indispensable for Cdk5‐p25 interactions, and amino acids 9–15 are necessary for ATP binding but are not involved in Cdk5‐p25 interactions. Predicted models of Δ9‐15 Cdk5 and Δ9‐47 Cdk5 were generated, and were used to interpret the experimental data. The experimental and molecular modeling results confirm and extend specific aspects of the original predicted computer model, and may provide useful information for the design of highly selective inhibitors of Cdk5, which could be used in the treatment of certain neurodegenerative conditions. Proteins 2002;48:447–453. © 2002 Wiley‐Liss, Inc.
Studies on heat processing and storage of seer fish curry in retort pouches
Authors: Shankar C. N. Ravi , Gopal T. K. Srinivasa , Vijayan P. K.
Published: October 2002

Seer fish in curry medium packed in locally manufactured retort pouches, having a three‐layer configuration of thickness 12.5 µm polyester/12.5 µm aluminium foil/80 µm cast polypropylene was processed in a steam/air mixture over a pressure retort. About 210 g fish curry, having 110 g fish slices, was packed in a retort pouch of size 17 cm × 15.5 cm, each fitted with a thermocouple. Time–temperature data were collected during heat processing using an Ellab data recorder FO and cook value integrator. The heat penetration characteristics were determined using a mathematical method. The fh value was 25 min with a FO value of 11.5 and cook value of 95 min. These samples remained in good condition for up to 24 months at room temperature. Copyright © 2002 John Wiley & Sons, Ltd.
Theoretical study of insoluble polymer monolayers
Authors: Ivanova A. , Tadjer A. , Radoev B.
Published: October 2002

Several oligomers of biodegradable polymers (polycaprolactone and polylactic acid) were theoretically investigated at the gas–water interface. A combined Monte Carlo–semiempirical computational scheme was suggested. It proved to reproduce successfully the most essential properties of the monolayer, such as dipole moment and area/monomer. These calculations were used for prediction of the most probable molecular conformation at the interface. Moreover, an effective normal component of the monolayer dielectric constant was estimated and can be used for description of the dielectric behavior of different insoluble monolayers. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Vibronic polarons: Self‐trapping, local rotation, and band features
Authors: Andreev A. G. , Ivanovich M. D. , Georgiev M.
Published: October 2002

We revisit basic theoretical concepts of local and itinerant vibronic polarons in crystals. The following results may be regarded as novel: (1) The electron self‐trapping rate to a small polaron is calculated via the reaction rate method; subsequently, self‐trapped on‐center small polarons relax to an off‐center vibronic polaron state. (2) The general vibronic Hamiltonian is redefined so as to incorporate both local and itinerant behavior and pairing into bipolarons or Cooper pairs. (3) The planar rotation and diametral tunneling of an off‐center polaron around and across its centrosymmetrical site are dealt with to adiabatic approximation. (4) Variational calculations are made for vibronic polarons itinerant along 1‐D chains by means of a two‐band extension of Merrifield's ansatz. This investigation of vibronic polarons is undertaken in view of their presumed role in high‐temperature superconductivity and colossal magnetoresistance. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Relaxation of quantum hydrodynamic modes
Authors: Bittner Eric R. , Maddox Jeremy B. , Burghardt Irene
Published: October 2002

In this article, we develop a series of hierarchical mode‐coupling equations for the momentum cumulants and moments of the density matrix for a mixed quantum system. Working in the Lagrange representation, we show how these can be used to compute quantum trajectories for dissipative and nondissipative systems. This approach is complementary to the de Broglie–Bohm approach in that the moments evolve along hydrodynamic/Lagrangian paths. In the limit of no dissipation, the paths are the Bohmian paths. However, the “quantum force” in our case is represented in terms of momentum fluctuations and an osmotic pressure. Representative calculations for the relaxation of a harmonic system are presented to illustrate the rapid convergence of the cumulant expansion in the presence of a dissipative environment. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Improved embedded molecular cluster model
Authors: Shidlovskaya E. K.
Published: October 2002

We demonstrate that boundary effects (i.e., displacements of the cluster boundary atoms from their lattice sites and the difference between effective charges of the perfect crystal atoms and those of the cluster atoms in the case of a cluster with no point defect in it) in an embedded molecular cluster (EMC) model can be radically reduced. A new embedding scheme is proposed. It includes search for the structural elements (SE) of which perfect crystal is composed, use of corresponding to these SE expression for the total energy, and application of the degree of localization of equations consistent with the wave functions of the cluster. To get equations for the cluster wave functions, the problem of varied subsystem in the field of the frozen remaining part of the whole electron system” is investigated in the framework of a one‐electron approximation. The consideration is general for every task of this type. Homogeneous equations resulting directly from variation of the total energy expression are obtained and transformed to the eigenvalue problem equations. Orthogonality constraints are not imposed during variation. A particular case of the equations describing mutually orthogonal one‐electron wave functions of the cluster staying nonorthogonal to those of the remaining crystal is found. A proposed embedding scheme is realized in the CLUSTER code based on the calculation scheme of the semiempirical INDO method. Boundary effects both in the standard (cluster in the field of the infinite lattice of nonpoint spherical charges) and new embedding scheme are investigated, calculating the clusters of LiF, MgO, NaCl, KCl, and AgCl crystals. Significant reduction of the boundary effects in the new embedding scheme is achieved. Reasons for the boundary effects are discussed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Numerical method to solve chemical differential‐algebraic equations
Authors: Çelik Ercan , Karaduman Erdal , Bayram Mustafa
Published: October 2002

In this article, the solution of a chemical differential‐algebraic equation model of general type F(y, y′, x) = 0 has been done using MAPLE computer algebra systems. The MAPLE program is given in the Appendix. First we calculate the Power series of the given equations system, then we transform it into Padé series form, which gives an arbitrary order for solving chemical differential‐algebraic equation numerically. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Quantitative determination of polar and ionic compounds in petroleum fractions by atmospheric pressure chemical ionization and electrospray ionization mass spectrometry
Authors: Roussis Stilianos G. , Fedora James W.
Published: October 2002

The capabilities of atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) methods for quantitative analysis of polar and ionic compounds in petroleum fractions have been examined. The requirements of the analysis for sensitivity, linear dynamic range, and structural characterization have been discussed. ESI was found to be approximately two orders of magnitude more sensitive than APCI and is most suitable for the detection of analytes in weak concentrations. Equivalent relative linear dynamic ranges were observed by the two methods (at least three orders of magnitude). For the relatively high analyte concentrations examined here (e.g., 1–100 ppm or higher), the absolute area counts increased linearly with the analyte amount only in APCI, making this method more attractive for quantitative liquid chromatography/mass spectrometry (LC/MS) applications. Nevertheless, a wider range of ionic compounds can be detected by ESI than by APCI. Copyright © 2002 John Wiley & Sons, Ltd.
Analysis of estrogenic contaminants in river water using liquid chromatography coupled to ion trap based mass spectrometry
Authors: Benijts Tom , Dams Riet , Günther Wolfgang , Lambert Willy , Leenheer André De
Published: October 2002

A precise and reliable method, using liquid chromatography combined with ion trap based mass spectrometry, for the determination of three endogenous estrogens, namely, estrone, estradiol, and estriol, and two synthetic estrogens, ethinyl estradiol and diethylstilbestrol, in environmental water samples was developed. Optimization of the parameter settings of the ion source and mass analyzer as well as evaluation of solvent composition were carried out by continuous introduction of standards through a syringe pump. In negative ion mode the electrospray ionization source gave acceptable results. The optimum solvent used consisted of water/acetonitrile, with no volatile bases or buffers added. A simple, off‐line, manual solid‐phase extraction method was developed for sample preparation of environmental water samples. Recoveries were over 86% for all compounds. The method was validated and found to be linear, selective, and robust. For analysis of a 50‐mL sample, the limit of detection (LOD) ranged from 3.2 to 10.6 ng/L for all compounds, and the limit of quantitation (LOQ) from 10.6 to 35.0 ng/L. Within‐day (n = 5) and total (n = 5) reproducibility were investigated at three different concentration levels and ranged from 6.2 to 9.5% and 9.4 to 12.1%, respectively. Finally, the method was applied to real‐world samples. Copyright © 2002 John Wiley & Sons, Ltd.
Direct surface analysis of fungal species by matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Valentine Nancy B. , Wahl Jon H. , Kingsley Mark T. , Wahl Karen L.
Published: October 2002

In this study various methods of sample preparation and matrices were investigated to determine optimum collection and analysis criteria for fungal analysis by matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS). Intact spores and/or hyphae of Aspergillus niger, Rhizopus oryzae, Trichoderma reesei and Phanerochaete chrysosporium were analyzed by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS). The fungal samples were applied to the MALDI sample target as untreated, sonicated, or acid/heat treated samples, or blotted directly from the fungal culture with double‐stick tape. Ferulic acid or sinapinic acid matrix solution was layered over the dried samples and analyzed by MALDI‐MS. Statistical analysis showed that simply using double‐stick tape to collect and transfer to a MALDI sample plate typically worked as well as the other preparation methods, and required the least sample handling. Copyright © 2002 John Wiley & Sons, Ltd.
Studying protein‐carbohydrate interactions by amide hydrogen/deuterium exchange mass spectrometry
Authors: King Daniel , Lumpkin Michelle , Bergmann Carl , Orlando Ron
Published: October 2002

Protein‐carbohydrate interactions play a significant role in biological processes. Presented here is the novel application of amide hydrogen/deuterium exchange mass spectrometry (amide exchange‐MS) to the study of the interaction between a protein and its carbohydrate substrate. The degree of deuterium incorporation into hen egg lysozyme was monitored with and without substrate to verify that a carbohydrate can provide sufficiently stable protection of the amide hydrogen atoms in a protein's backbone from exchange with deuterated solvent. The substrate protected a number of amide hydrogens from exchange, implying that protein‐carbohydrate binding systems will be compatible with amide exchange‐MS. Endopolygalacturonase‐II (EPG‐II) from Aspergillus niger, a pectin‐degrading enzyme, was chosen as the first carbohydrate‐binding system to be extensively studied using quenched amide exchange‐MS. Monitoring the changes in deuterium incorporation of EPG‐II in the presence and absence of an oligomer of galacturonic acid implied the location of substrate binding. This study demonstrates the ability of amide exchange‐MS to investigate protein‐carbohydrate interactions. Copyright © 2002 John Wiley & Sons, Ltd.
Study of structural characteristic features of phenanthriondolizidine alkaloids by fast atom bombardment with tandem mass spectrometry
Authors: Xiang Yun , Abliz Zeper , Li Li‐jun , Huang Xue‐shi , Yu Shi‐shan
Published: October 2002

The mass spectrometric behavior of phenanthroindolizidine alkaloids has been investigated in detail by positive ion fast atom bombardment tandem mass spectrometry (FAB‐MS/MS) combined with collision‐induced dissociation (CID). The fragmentation has been correlated with the skeleton structure and positions of substituents. The product ions arising from retro‐Diels‐Alder cleavages differ clearly for compounds with different skeletons. The substituents at C‐14 were observed to markedly influence the fragmentation pathway of [M + H]+ ions. A diversity of dissociation behavior initiated by the variation of substituents on the aromatic ring was also observed in the CID spectra. Product ions resulting from loss of CH4 were obtained for compounds in which both C‐6 and C‐7 are occupied by methoxy groups. FAB‐MS/MS spectra can reflect the connection between the fragmentation behavior and structural features of these phenanthroindolizidine alkaloids rapidly and effectively, and should prove to be a powerful method to determine the structures of related compounds. Copyright © 2002 John Wiley & Sons, Ltd.
Temporal changes in macroinvertebrate assemblages following experimental flooding in permanent and temporary wetlands in an Australian floodplain forest
Authors: Hillman T.J. , Quinn G.P.
Published: October 2002

The River Murray, Australia, is a highly regulated river from which almost 80% of mean annual flow is removed for human use, primarily irrigated agriculture. Consequent changes to the pattern and volume of river flow are reflected in floodplain hydrology and, therefore, the wetting/drying patterns of floodplain wetlands. To explore the significance of these changes, macroinvertebrate samples were compared between permanent and temporary wetlands following experimental flooding in a forested floodplain of the River Murray. Weekly samples from two permanent wetlands and four associated temporary sites were used to track changes in macroinvertebrate assemblage composition. Non‐metric multidimensional scaling was used to ordinate the macroinvertebrate data, indicating consistent differences between the biota of permanent and temporary wetlands and between the initial and later assemblages in the temporary sites. There were marked changes over time, but little sign that the permanent and temporary assemblages were becoming more alike over the 25‐week observation period. The apparent heterogeneity of these systems is of particular importance in developing river management plans which are likely to change flooding patterns. Such plans need to maintain a mosaic of wetland habitats if floodplain biodiversity is to be supported. Copyright © 2002 John Wiley & Sons, Ltd.
Performance of a fishway system in a major South American dam on the Parana River (Argentina–Paraguay)
Authors: Oldani Norberto O. , Baigún Claudio R. M.
Published: October 2002

Successful design and operation of fish passage systems are important to protect fish communities from impacts of hydroelectric dams in the Río de la Plata River basin. We evaluated the performance of an elevator lift system to pass adult fish through Yacyretá dam on the Paraná River between 1995 and 1998, both for mechanical reliability and performance. The elevator lift system was mechanically inoperative 30–38% of the time during the October–December period of greatest fish migration. Target species represented 30% of total fish number in gillnet samples in the tailwater, but constituted only 10% of the total number of fish transferred. Fish collected within the system were dominated by Pimelodus clarias (>69%), although this species represented less than 10% of captures in experimental gillnets set in the tailwater. Prochilodus lineatus, a key species, represented less than 5% of transferred fish, but constituted 22.1% of tailwater samples. Estimated number of fish transferred per year ranged between 1 210 000 (1995) and 3 610 000 (1996) with biomass ranging from 631 to 1989 tons, respectively. We estimated a fish passage efficiency of 1.88% for all species and 0.62% for target species. At this efficiency, transferred species would increase the total fish yield in the reservoir by as much as 4.9 kg/ha/year, but only 0.5 kg/ha/year for target species. We conclude that fish transfer efficiency is inadequate to maintain populations of target species in the Paraná River system. We identify critical research needs to improve the passage of fish at dams. Copyright © 2002 John Wiley & Sons, Ltd.
A systems approach to river restoration: a case study in the lower Seine valley, France
Authors: Poudevigne I. , Alard D. , Leuven R. S. E. W. , Nienhuis P. H.
Published: October 2002

Restoration of regulated rivers presents fundamental challenges because of the complexity and adaptive nature of riverine ecosystems. It is now agreed that restoration strategies need to restore the system as a whole (structure, function and dynamics). Most studies are faced with the same difficulties concerning the right scale for restoration actions, the representative attributes of the riverine system and the measures capable of surveying restoration action impacts.

This work proposes an approach to river restoration borrowed from the conceptual and theoretical background of landscape ecology. Leaning on experience on biodiversity restoration along the Lower Seine river, we propose a systemic approach based on the hierarchical nature of riverine systems. This approach suggests that like any system, riverine ecosystems can be simplified into basic units which are complementary and integrated in a hierarchical structure. Simplification leads to focusing on one component of the ecosystem at a relevant scale of space and time (organization level). Here, we focus on two attributes of this ecosystem at different scales: community organization and landscape organization. These organization measures, realized at different observation scales, provide insight to the ecological response of the system in time. They are measures of the stability of the system and can provide effective tools for predicting or following the impact of restoration actions on riverine landscapes. Copyright © 2002 John Wiley & Sons, Ltd.
Effect of flow‐related substrate alteration on physical habitat: a case study of the endemic river loach Sinogastromyzon puliensis (Cypriniformes, Homalopteridae) downstream of Chi‐Chi Diversion Weir, Chou‐Shui Creek, Taiwan
Authors: Wu Fu‐Chun , Wang Chi‐Fang
Published: October 2002

This paper addresses the variation of substrate status with flow in the framework of habitat simulation. The Physical Habitat Simulation System (PHABSIM) was developed as a tool for water management and has become one of the most popular methods worldwide. Despite its many advantages, the variation of channel properties with flow is not addressed in PHABSIM. We modified PHABSIM by incorporating a sub‐program that can perform substrate analyses under five different schemes for evaluating the substrate suitability. These schemes include the conventional methods to specify the substrate attribute (scheme 1) and to use the mean grain size of the original bed material for determining the substrate suitability (scheme 2), or employ the threshold conditions for sediment entrainment to evaluate the nominal grain size of the stable substrate (schemes 3–5). As a case study, Sinogastromyzon puliensis in Chou‐Shui Creek (Taiwan) is selected as the target species for the habitat simulation. For schemes 1 and 2, the substrate attribute specified for each cell of a cross‐section does not change with flow. The nominal grain size of the stable armour material (scheme 5) is generally greater than the nominal grain sizes of the above‐critical bed material (scheme 3) and the static armour layer (scheme 4). The simulation results indicate that the suitability values specified in scheme 1 and the resulting habitat area are on the optimistic side, whereas scheme 2 tends to undervalue the suitability of the hydraulically worked substrate. The overall variation trends of the weighted usable area (or percentage usable area) curves for different substrate schemes are similar, especially in the in‐phase regions of the water velocity and depth. The results of this study appear to imply that the flow‐related habitat analyses are not usually sensitive to substrate. Copyright © 2002 John Wiley & Sons, Ltd.
The development of preservice chemistry teachers' pedagogical content knowledge
Authors: Van Driel Jan H. , Jong Onno De , Verloop Nico
Published: October 2002

This study investigated the development of pedagogical content knowledge (PCK) within a group of 12 preservice chemistry teachers (all M.Sc.) during the first semester of their one‐year post‐graduate teacher education program. The study focused on PCK with respect to a central issue in science teaching, that is, the relation between observable phenomena, like chemical reactions, and macroscopic properties (e.g., boiling point, solubility) on the one hand, and their interpretation in terms of corpuscular characteristics on the other hand (macro–micro). For secondary school students, shifting mentally between the macro and micro levels is usually problematic, whereas their teachers are often unaware of students' learning difficulties in this domain. The collection of data involved two written questionnaires, interviews with each preservice teacher and their respective mentors, and an audio recording of a specific workshop session in the teacher education program. Results indicated a growing awareness among the preservice teachers concerning the need, in teaching situations, to explicitly relate the macro and micro levels to each other. Moreover, the importance of the careful and consistent use of language was noticed by many preservice teachers. The growth of PCK was influenced mostly by the preservice teachers' teaching experiences. Also, the workshop contributed substantially. Finally, for some preservice teachers, their mentors had influenced the growth of PCK. Implications for science teacher education are discussed. © 2002 Wiley Periodicals, Inc. Sci Ed 86:572–590, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/sce.10010
Disease prevalence estimations based on contact registrations in general practice
Authors: Hoogenveen Rudolf , Westert Gert , Dijkgraaf Marcel , Schellevis François , de Bakker Dinny
Published: October 2002

This paper describes how to estimate the prevalence of chronic diseases in a population using data from contact registrations in general practice with a limited time length. Instead of using only total numbers of observed patients adjusted for the length of the observation period, we propose the use of (i) the time of the first contact of patients, (ii) the joint total numbers of patients and contacts, and (iii) the sets of patients in distinct time intervals, to generate prevalence rate estimates. The three new prevalence rate estimators have been developed assuming either a homogeneous or a parameterized heterogeneous patient population. Systematic and stochastic components of the estimators have been analysed by cross‐validation for five chronic diseases using data from the Dutch ‘Study on Chronic Conditions’. The results show that the first two estimators work well for diseases with a relatively structured visiting behaviour, such as hypertension and diabetes mellitus, assuming a time‐constant contact rate and homogeneous patient population. For diseases such as ischaemic heart disease, chronic non‐specific respiratory diseases and osteoarthritis, that do not satisfy these assumptions, the methods generally result in underestimations. Copyright © 2002 John Wiley & Sons, Ltd.
When are technologies disruptive? a demand‐based view of the emergence of competition
Authors: Adner Ron
Published: October 2002

By identifying the possibility that technologies with inferior performance can displace established incumbents, the notion of disruptive technologies, pioneered by Christensen (1997), has had a profound effect on the way in which scholars and managers approach technology competition. While the phenomenon of disruptive technologies has been well documented, the underlying theoretical drivers of technology disruption are less well understood. This article identifies the demand conditions that enable disruptive dynamics. By examining how consumers evaluate technology and how this evaluation changes as performance improves, it offers new theoretical insight into the impact of the structure of the demand environment on competitive dynamics. Two new constructs—preference overlap and preference symmetry—are introduced to characterize the relationships among the preferences of different market segments. The article presents a formal model that examines how these relationships lead to the emergence of different competitive regimes. The model is analyzed using computer simulation. The theory and model results hold implications for understanding the dynamics of disruptive technologies and suggest new indicators for assessing disruptive threats. Copyright © 2002 John Wiley & Sons, Ltd.
Second step algorithms in the Burrows–Wheeler compression algorithm
Authors: Deorowicz Sebastian
Published: October 2002

In this paper we focus our attention on the second step algorithms of the Burrows–Wheeler compression algorithm, which in the original version is the Move To Front transform. We discuss many of its replacements presented so far, and compare compression results obtained using these replacements. Then we propose a new algorithm that yields a better compression ratio than the previous algorithms. Copyright © 2001 John Wiley & Sons, Ltd.
Chiral Proton Donor Reagents: Tin Tetrachloride—Coordinated Optically Active Binaphthol Derivatives
Authors: Ishibashi Hideaki , Ishihara Kazuaki , Yamamoto Hisashi
Published: October 2002

The Lewis acid–assisted chiral Brønsted acids (chiral LBAs), which are prepared from tin tetrachloride and optically active binaphthol derivatives, are highly effective chiral proton donor reagents for enantioselective protonation and biomimetic polyene cyclization. These chiral LBAs can directly protonate various silyl enol ethers and ketene disilyl acetals to give the corresponding α‐aryl or α‐halo ketones and α‐arylcarboxylic acids, respectively, with high enantiomeric excess (up to 98% ee). A catalytic version of enantioselective protonation was also achieved using stoichiometric amounts of 2,6‐dimethylphenol and catalytic amounts of monomethyl ether of optically active binaphthol in the presence of tin tetrachloride. The biomimetic cyclization of simple isoprenoids to polycyclic isoprenoids using chiral LBA is also described. This is the first example of a chiral Brønsted acid–induced enantioselective ene cyclization in synthetic chemistry. Geranyl phenyl ethers, o‐geranylphenols, and homogeranylphenol derivatives were directly cyclized in the presence of (R)‐binaphthol derivatives and tin tetrachloride (up to 90% ee). Compounds bearing a farnesyl group could also be cyclized under the same conditions to give the natural products (−)‐ambrox® and (−)‐chromazonarol, and (−)‐tetracyclic polyprenoids of sedimentary origin. These chiral LBAs recognize the prochiral face of a trisubstituted terminal olefin and site selectively generate carbocations on the substrates. © 2002 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 2: 177–188,2002: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.10020
The Art of Acetylenic Scaffolding: Rings, Rods, and Switches
Authors: Brøndsted Nielsen Mogens , Diederich François
Published: October 2002

Acetylenic scaffolding with derivatives of tetraethynylethene (TEE, 3,4‐diethynylhex‐3‐ene‐1,5‐diyne) and (E)‐1,2‐diethynylethene (DEE, (E)‐hex‐3‐ene‐1,5‐diyne) provides carbon‐rich compounds with interesting physicochemical properties. Thus, these modules are building blocks for monodisperse, linearly π‐conjugated oligomers [polytri(acetylene)s, PTAs] extending in length beyond 10nm, and for large, macrocyclic, all‐carbon cores (dehydroannulenes and expanded radialenes) exhibiting strong chromophoric properties. The advanced materials' properties were strongly influenced by the presence of electron‐donating substituents at the lateral positions, decreasing the decreasing the (HOMO–LUMO) gap in both PTAs and expanded radialenes. Arylated TEEs were found to undergo photochemically induced cis–trans isomerization, paving the way for applications as light‐driven molecular switches in optoelectronic devices. Derivatives of 1,3‐diethynylallene are new modules that offer the prospect of scaffolding in an orthogonal manner; that is, they represent precursors for helical oligomers. © 2002 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 2: 189–198,2002: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.10022