bluuebunny/crossref_metadata_2025 huggingface dataset:
A theoretical explanation for the retention mechanism of ion exclusion chromatography
Authors: Głód Bronisław K. , Baumann Marc
Published: November 2003

Ion Exclusion Chromatography is classically used for the separation of weak acid anions. Dilute strong acids (e.g. sulphuric or perchloric acid) or just water are used as eluents. To increase the exclusion effect, strong cation exchangers, characterized by high concentration of functional groups, are applied. The inner column volume of commercially available columns is increased by increasing their size in comparison to traditional ones (usually 300×7.8 mm ID). The description of the retention mechanism of this technique implicitly assumes that both mobile and stationary phases are typical aqueous solutions, and their dielectric constants are thus equal. This equality implies the equality of solute dissociation constants in both phases. Another implicit assumption is that the dead‐ and inner volumes of the column are constant, and independent of the mobile phase composition. The present paper shows that stationary and mobile phases are generally characterized by different physicochemical parameters. Thus, they cannot be considered as regular aqueous solutions. Additionally, we show that weak cation exchanger resins, which are characterized by a relatively small concentration of the functional groups, and weak acid based buffers can also be used in IEC. This would expand the possible applications of this method and enable, for example, the separation of strong acids (anions). The influence of ionic strength on the retention and dead‐ and inner column volumes is also discussed. Finally we also briefly describe the retention mechanism of Electrostatic Ion Chromatography.
Ultra‐rapid non‐equilibrium solid‐phase microextraction at elevated temperatures and direct coupling to mass spectrometry for the analysis of lidocaine in urine
Authors: van Hout Mischa W. J. , Jas Vincent , Niederländer Harm A. G. , de Zeeuw Rokus A. , de Jong Gerhardus J.
Published: November 2003

Solid‐phase microextraction (SPME) has been directly coupled to an ion‐trap mass spectrometer (MS) for the determination of the model compound lidocaine in urine, hereby applying MS/MS [fragmentation of [M + H]+ (m/z 235) to a fragment with m/z 86]. The throughput of samples has been increased using non‐equilibrium SPME with polydimethylsiloxane (PDMS) fibers. The effect of temperature on the sorption and the desorption was studied. Elevated temperatures during sorption (65°C) and desorption (55°C) had a considerable influence on the speed of the extraction. The desorption was carried out with a home‐made desorption chamber allowing thermostating. Only 1 min sorption and 1 min desorption were performed, after which MS detection took place, resulting in a total analysis time of 3 min. Detection limits below 1 ng/mL could be obtained despite yields of only 2.1 and 1.5% for a 100‐ and a 30‐μm PDMS‐coated fiber, respectively. Furthermore, the determination of lidocaine in urine had acceptable reproducibilities, i.e., relative standard deviations (RSDs) below 10%. A limit of quantitation (RSD < 15%) of about 1 ng/mL was obtained. No extra wash step of the extraction fiber was required after desorption if a 30‐μm coating was used, whereas not all the analyte was desorbed from the 100‐μm coating in a single desorption. Therefore, the SPME‐MS/MS system with a 30‐μm PDMS‐coated fiber for rapid non‐equilibrium SPME at elevated temperatures has interesting potential for high‐throughput analysis of biological samples.
A comparative study of hospitality and tourism graduates in Australia and Hong Kong
Authors: King Brian , McKercher Bob , Waryszak Robert
Published: November 2003

This paper evaluates the career experiences and perceptions of graduates from the School of Hotel and Tourism Management at the Hong Kong Polytechnic University and the School of Hospitality, Tourism and Marketing at Victoria University in Melbourne, Australia towards the programmes that they undertook. The two cohorts of graduates exhibited broadly similar career histories and expressed similar attitudes towards the quality, strengths and weaknesses of their respective programmes. In both cases, female students dominate the graduate cohort and about half of the respondents were found to have left the tourism or hospitality field within 3–5 years after graduation. Graduates believe that their general business and general education subjects play a stronger role in acquiring their first and current jobs than specialist tourism, hotel management and food service subjects. The findings highlight the challenge facing the university sector in attempting to balance the desire to provide a broadly grounded liberal education with the student desire for practical training. Copyright © 2003 John Wiley & Sons, Ltd.
In the air again: frequent flyer relationship programmes and business travellers' quality of life
Authors: Long Mary M. , Clark Sylvia D. , Schiffman Leon G. , McMellon Charles
Published: November 2003

This research explores whether frequent flyer programmes somehow add to the quality of life of the frequent business traveller (defined in this study as business flyers who had flown round trip 26 or more times in the past 12 months). A questionnaire was mailed to subscribers of a newsletter for members of frequent air and hotel programmes. Results indicated that frequent flyer programmes contribute positively to frequent business travellers' lifestyles and to their quality of life, perhaps by countervailing some of the negative aspects of frequent business travel. Copyright © 2003 John Wiley & Sons, Ltd.
Economic aspects and the Summer Olympics: a review of related research
Authors: Kasimati Evangelia
Published: November 2003

As the Summer Olympics are growing with larger media coverage and sponsorship, host cities have started to attach great importance to the tourism and other likely economic effects that occur by staging such a special event. As a result, a number of studies have been conducted to consider the various economic implications on the hosts. This paper examines and evaluates methods and assumptions used by the economic studies. It also comparesex‐antemodels and forecasts with theex‐postapproach. The aim is to improve the information available to policy makers and potential future hosts of Summer Olympics and other mega‐events. Copyright © 2003 John Wiley & Sons, Ltd.
Domestic tourism destination choices — a choice modelling analysis
Authors: Huybers Twan
Published: November 2003

Tourism destinations compete with each other to attract visitors. Although international tourism has received a lot of attention, domestic tourism remains the mainstay for many destinations. To inform the basis on which destinations compete, an understanding of the determinants of destination choices is required. In this paper, the discrete choice modelling method is applied to investigate the determining factors underlying the short‐break holiday destination choices of prospective tourists from Melbourne, Australia. The results from an estimated nested logit model indicate the relative importance of a number of destination and trip attributes and respondent characteristics. The model results are used to simulate the effects on destinations' market shares resulting from various changes in attributes and tourist characteristics. Copyright © 2003 John Wiley & Sons, Ltd.
Novel Semi‐Fluorinated Poly(ether imide)s Derived From 4‐(p‐Aminophenoxy)‐3‐trifluoromethyl‐4′‐aminobiphenyl
Authors: Kute Vijay , Banerjee Susanta
Published: November 2003

An unsymmetrical diamine monomer 4‐(p‐aminophenoxy)‐3‐trifluoromethyl‐4′‐aminobiphenyl has been synthesized successfully. This monomer leads to the synthesis of different novel poly(ether imide)s when reacted with different dianhydrides like pyromellatic dianhydride (PMDA), benzophenone tetracarboxylic acid dianhydride (BTDA), 2,2‐bis(3,4‐dicarboxyphenyl) hexafluoropropane (6FDA), and oxy diphthalic anhydride (ODA). The poly(ether imide) prepared from this monomer on reaction with 6FDA is soluble in several organic solvents such as N‐methylpyrolidinone (NMP), dimethylformamide (DMF), N,N‐dimethylacetamide (DMAc), tetrahydrofuran (THF), and CHCl3. The poly(ether imide)s prepared from BTDA and ODA are soluble in NMP, DMF, and DMAc but not in THF or CHCl3, whereas the polymer prepared from PMDA is soluble only in NMP. The water uptake value for these poly(ether imide) films is very low (0.2–0.5%), and exhibited low dielectric constants (2.81 at 1 MHz). The polymers exhibited high thermal stability up to 532 °C in air for 5% weight loss, and high glass transition temperatures up to 288 °C. The polymer exhibited high tensile strength up to 135 MPa, modulus 3.2 GPa, and elongation at break up to 25%, depending on the exact polymer structure.

The structure of the poly(ether imide) synthesised from 4‐(p‐aminophenoxy)‐3‐trifluoromethyl‐4′‐aminobiphenyl and 2,2‐bis(3,4‐dicarboxyphenyl) hexafluoropropane. This polymer was soluble in many organic solvents.

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The structure of the poly(ether imide) synthesised from 4‐(p‐aminophenoxy)‐3‐trifluoromethyl‐4′‐aminobiphenyl and 2,2‐bis(3,4‐dicarboxyphenyl) hexafluoropropane. This polymer was soluble in many organic solvents.
Novel Superlattices via Blending of Asymmetric Triblock Terpolymers with Diblock Copolymers
Authors: Jiang Shimei , Göpfert Astrid , Abetz Volker
Published: November 2003

The formation of superlattices in blends of a series of asymmetric BSV triblock terpolymers and symmetric SV or VC diblock copolymers is investigated with S being polystyrene, B being poly(1,2‐butadiene), V being poly(2‐vinylpyridine), and C being poly(cyclohexyl methacrylate). All of these triblock terpolymers and diblock copolymers by themselves self‐assemble into lamellae. Apart from various core shell morphologies, in these blends some new unexpected superstructures were obtained.

A TEM micrograph of a 50/50 blend of B30S58V with S45V.

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A TEM micrograph of a 50/50 blend of B30S58V with S45V.
Influence of particle shape and angularity on the behaviour of granular materials: a numerical analysis
Authors: Nouguier‐Lehon C. , Cambou B. , Vincens E.
Published: November 2003

This paper analyses the influence of grain shape and angularity on the behaviour of granular materials from a two‐dimensional analysis by means of a discrete element method (Contact Dynamics). Different shapes of grains have been studied (circular, isotropic polygonal and elongated polygonal shapes) as well as different initial states (density) and directions of loading with respect to the initial fabric. Simulations of biaxial tests clearly show that the behaviour of samples with isotropic particles can be dissociated from that of samples with anisotropic particles. Indeed, for isotropic particles, angularity just tends to strengthen the behaviour of samples and slow down either local or global phenomena. One of the main results concerns the existence of a critical state for isotropic grains characterized by an angle of friction at the critical state, a critical void ratio and also a critical anisotropy. This critical state seems meaningless for elongated grains and the behaviour of samples generated with such particles is highly dependent on the direction of loading with respect to the initial fabric. The study of local variables related to fabric and particle orientation gives more information. In particular, the coincidence of the principal axes of the fabric tensor with those of the stress tensor is sudden for isotropic particles. On the contrary, this process is gradually initiated for elongated particles. Copyright © 2003 John Wiley & Sons, Ltd.
Micro‐mechanical simulation of geotechnical problems using massively parallel computers
Authors: Washington David W. , Meegoda Jay N.
Published: November 2003

This paper demonstrates that the architecture of a massively parallel computer can be adapted for micro‐mechanical simulations of a Geotechnical problem. The Discrete Element Method was used on a massively parallel supercomputer to simulate Geotechnical boundary value problems. For the demonstration, a triaxial test was simulated using an algorithm titled ‘TRUBAL for Parallel Machines (TPM)’ based on the discrete element method (DEM). In this trial demonstration, the inherent parallelism within DEM algorithm is shown. Then a comparison is made between the parallel algorithm (TPM) and the serial algorithm (TRUBAL) to show the benefits of this research. TPM showed substantial improvement in performance with increasing number of processors when compared with TRUBAL using single processor. Copyright © 2003 John Wiley & Sons, Ltd.
Age‐related differences in synaptic plasticity following muscle unloading
Authors: Deschenes Michael R. , Wilson Meredith H.
Published: November 2003

The objective of the present investigation was to determine the effects of muscle unloading—a form of subtotal disuse— on the morphology of the neuromuscular junction (NMJ) in younger and aged animals. Sixteen aged (22 months) and 16 young adult (8 months) male Fischer 344 rats were assigned to control and hindlimb suspension (HS) conditions (n = 8/group). At the conclusion of the 4 week experimental period, soleus muscles were collected, and immunofluorescent procedures were used to visualize acetylcholine (ACh) vesicles and receptors, nerve terminal branching, as well as NCAM and NT‐4 expression. Quantitative analyses revealed that aged controls displayed significant (p < 0.05) reductions in area and perimeter length of ACh vesicle and receptor regions, without affecting nerve terminal branch number or length. In contrast to younger NMJs, which were resilient to the effects of unloading, NMJs of aged HS rats demonstrated significant expansion of ACh vesicle and receptor dimensions compared to aged controls. Qualitative analyses of NCAM staining indicated that aging alone somewhat increased this molecule's expression (aged controls > young controls). Among the four groups, however, the greatest amount of NCAM content was detected among aged HS muscles, matching the degree of synaptic plasticity exhibited in those muscles. Unlike NCAM, the expression of NT‐4 did not appear to differ among the treatment groups. These data suggest that although young adult muscle maintains normal NMJ structure during prolonged exposure to unloading, aged NMJs experience significant adaptation to that stimulus. © 2003 Wiley Periodicals, Inc. J Neurobiol 57: 246–256, 2003
Newly proliferated cells in the adult male amygdala are affected by gonadal steroid hormones
Authors: Fowler Christie D. , Freeman Marc E. , Wang Zuoxin
Published: November 2003

Gonadal steroid hormones play an important role in the proliferation, survival, and activation of neurons. The present study was performed to examine the effects of testosterone and its metabolites on newly proliferated cells in the amygdala of adult male meadow voles (Microtus pennsylvanicus). Treatment with testosterone propionate (TP) in castrated males resulted in plasma testosterone levels similar to males following mating. TP‐treated males displayed a significant increase in the density of cells labeled with a cell proliferation marker (BrdU) in the amygdala. Treatment with estradiol benzoate (EB) exerted a similar effect as TP on the density of BrdU‐labeled cells, whereas 5α‐dihydrotestosterone (DHT) was ineffective. A larger proportion (≈44%) of the BrdU‐labeled cells in the amygdala displayed a neuronal phenotype, and a lesser percentage (≈35%) displayed a glial progenitor phenotype; however, treatment effects were not found in either population of cells. Hormonal effects appeared to be site‐specific as no group differences were found in the dentate gyrus of the hippocampus or ventromedial hypothalamus. Finally, a time course study indicated that BrdU‐labeled cells in the amygdala are present as early as 30 min following an acute injection of BrdU. Together, these data suggest that gonadal steroid hormones influence the number of newly proliferated cells in the amygdala, most likely by acting through an estrogenic mechanism, and these effects may be exerted on locally proliferating progenitors within the amygdala. © 2003 Wiley Periodicals, Inc. J Neurobiol 57: 257–269, 2003
Gain‐of‐function screen identifies a role of the Src64 oncogene in Drosophila mushroom body development
Authors: Nicolaï Maryse , Lasbleiz Christelle , Dura Jean‐Maurice
Published: November 2003

Mushroom bodies (MB) are substructures in the Drosophila brain that are essential for memory. At present, MB anatomy is rather well described when compared to other brain areas, and elucidation of the genetic control of the development and projection patterns of MB neurons will be important to the understanding of their functions. We have performed a gain‐of‐function screen in order to identify genes that are involved in MB development. We drove expression of genes in MB neurons by crossing 2407 GAL4‐driven UY element lines to lines containing an MB GAL4 source and UAS‐GFP elements, and looked for defects in the MB structure. We have molecularly identified the genomic regions adjacent to the 26 positive UY insertions and found 18 potential genes that exhibit adult MB gain‐of‐function phenotypes. The proteins encoded by these candidate genes include, as well as genes with yet unknown function, transcription factors (e.g., tramtrack), nanos RNA‐binding protein, microtubule‐severing protein, vesicle trafficking proteins, axon guidance receptor, and the Src64 cytoplasmic protein tyrosine kinase. These genes are involved in key features of neuron cell biology. In three cases, tramtrack, nanos, and Src64, we show that the open reading frame located directly downstream of the UY P element is indeed the expressed target gene. Loss‐of‐function mutations of both ttk and Src64 lead to MB phenotypes proving that these genes are involved in the genetic control of MB development. Moreover, Src64 is shown here to act in a cell‐autonomous fashion and is likely to interact with the previously‐identified linotte/derailed receptor tyrosine kinase in MB development. © 2003 Wiley Periodicals, Inc. J Neurobiol 57: 291–302, 2003
Excess FoxG1 causes overgrowth of the neural tube
Authors: Ahlgren Sara , Vogt Peter , Bronner‐Fraser Marianne
Published: November 2003

The winged helix transcription factor FoxG1 (Bf‐1, qin) plays multiple roles in the development of the telencephalon, with different parts of the protein affecting either proliferation or differentiation. We examined the consequences of over‐expression, via retroviral expression, of FoxG1 on the growth of different regions of the chicken brain. Excess expression of FoxG1 caused a thickening of the neuroepithelium, and ultimately large outgrowths of the telencephalon and mesencephalon. In contrast, the myelencephalon appeared unaffected, exhibiting normal apoptosis and growth characteristics. A DNA binding defective form of FoxG1 did not exhibit these abnormalities, suggesting that these effects are due to FoxG1's function as a transcriptional repressor. To examine the means by which excess FoxG1caused overgrowth of the brain, we examined alterations in cell proliferation and death. No increase in proliferation was noted in any portion of the neural tube, rather a significant decrease in neuroepithelial apoptosis was seen. These results demonstrate a previously unrecognized role for winged helix factors in the regulation of neural cell apoptosis. © 2003 Wiley Periodicals, Inc. J Neurobiol 57: 337–349, 2003
Serotonin patterns locomotor network activity in the developing zebrafish by modulating quiescent periods
Authors: Brustein Edna , Chong Mabel , Holmqvist Bo , Drapeau Pierre
Published: November 2003

Developing neural networks follow common trends such as expression of spontaneous, recurring activity patterns, and appearance of neuromodulation. How these processes integrate to yield mature, behaviorally relevant activity patterns is largely unknown. We examined the integration of serotonergic neuromodulation and its role in the functional organization of the accessible locomotor network in developing zebrafish at behavioral and cellular levels. Locally restricted populations of serotonergic neurons and their projections appeared in the hindbrain and spinal cord of larvae after hatching (≈day 2). However, 5‐HT affected the swimming pattern only from day 4 on, when sustained spontaneous swimming appeared. 5‐HT and its agonist quipazine increased motor output by reducing intervals of inactivity, observed behaviorally (by high‐speed video) and in recordings from spinal neurons during fictive swimming (by whole‐cell current clamp). 5‐HT and quipazine had little effect on the properties of the activity periods, such as the duration of swim episodes and swim frequency. Further, neuronal input resistance, rheobasic current, and resting potential were not affected significantly. The 5‐HT antagonists methysergide and ketanserin decreased motor output by prolonging the periods of inactivity with little effect on the active swim episode or neuronal properties. Our results suggest that 5‐HT neuromodulation is integrated early in development of the locomotor network to increase its output by reducing periods of inactivity with little effect on the activity periods, which in contrast are the main targets of 5‐HT neuromodulation in neonatal and adult preparations. © 2003 Wiley Periodicals, Inc. J Neurobiol 57: 303–322, 2003
Vestibular Schwann cells are a distinct subpopulation of peripheral glia with specific sensitivity to growth factors and extracellular matrix components
Authors: Bartolami Sylvain , Augé Christelle , Travo Cécile , Ventéo Stéphanie , Knipper Marlies , Sans Alain
Published: November 2003

Vestibular nerve Schwann cells are predisposed to develop schwannoma. While knowledge concerning this condition has greatly improved, little is known about properties of normal vestibular Schwann cells. In an attempt to understand this predisposition, we evaluated cell density regulation and proliferative features of these cells taken from 6‐day‐old rats. Data were compared to those obtained with sciatic Schwann cells. In both vestibular and sciatic 7‐day‐old cultures, Schwann cells appear as bipolar or flattened cells. However, sciatic and vestibular cells greatly differ in other aspects: on poly‐L‐lysine coating, sciatic cells specifically synthesize myelin basic protein, while expression of P0 mRNAs is restricted to some vestibular cells. Laminin increases sciatic cell density but not that of vestibular cells. Fibronectin selectively enhances the proliferation of vestibular Schwann cells and lacks an effect on sciatic ones. Comparison of cell density changes between sciatic and vestibular cells shows that they are sensitive to two different sets of growth factors. Progesterone and FGF‐2 combined with forskolin selectively enhance the cell density of sciatic glia, while IGF‐1 and GDNF specifically increase vestibular cell density. Furthermore, BrdU incorporation assays indicate that GDNF is also a mitogen for vestibular cells. Altogether, vestibular Schwann cells display phenotypic features and responsiveness to exogenous signals that are significantly different from sciatic Schwann cells, suggesting that vestibular glia form a subpopulation of Schwann cells. © 2003 Wiley Periodicals, Inc. J Neurobiol 57: 270–290, 2003
B‐type Eph receptors and ephrins induce growth cone collapse through distinct intracellular pathways
Authors: Mann Fanny , Miranda Elena , Weinl Christine , Harmer Emma , Holt Christine E.
Published: November 2003

Forward and reverse signaling mediated by EphB tyrosine kinase receptors and their transmembrane ephrin‐B ligands play important roles in axon pathfinding, yet little is known about the intracellular pathways involved. Here we have used growth cones from the ventral (EphB receptor‐bearing) and dorsal (ephrin‐B‐bearing) embryonic Xenopus retina to investigate the signaling mechanisms in both forward and reverse directions. We report that unclustered, but not clustered, EphB2 ectodomains trigger fast (5–10 min) transient collapse responses in growth cones. This collapse response is mediated by low levels of intracellular cyclic GMP and requires proteasome function. In contrast, clustered, but not unclustered, ephrin‐B1 ectodomains cause slow (30–60 min) growth cone collapse that depends on high cGMP levels and is insensitive to inhibition of the proteasomal pathway. Upon receptor‐ligand binding, endocytosis occurs in the reverse direction (EphB2‐Fc into dorsal retinal growth cones), but not the forward direction, and is also sensitive to proteasomal inhibition. Endocytosis is functionally important because blocking of EphB2 internalization inhibits growth cone collapse. Our data reveal that distinct signaling mechanisms exist for B‐type Eph/ephrin‐mediated growth cone guidance and suggest that endocytosis provides a fast mechanism for switching off signaling in the reverse direction. © 2003 Wiley Periodicals, Inc. J Neurobiol 57: 323–336, 2003
Cisco Systems puts its HR programs and processes on line and reaps big productivity gains
Authors: Wittman Brit
Published: November 2003

As the leading provider of Internet networking technology, Cisco Systems practices what it preaches. It has
relentlessly sought ways to use its own intranet to communicate instantly and consistently with its 34,000 worldwide
employees, to enable managers to conduct most HR transactions on line, and to allow employees to update and access
an array of employment and benefits information. Cisco's on‐line HR and communications tools have
produced impressive productivity gains, but as importantly, they are an invaluable means for reinforcing a common
culture and unifying a globally dispersed workforce. © 2003 Cisco Systems, Inc.
The aging workforce raises new talent management issues for employers
Authors: Rappaport Anna , Bancroft Ed , Okum Lauren
Published: November 2003

With Baby Boomers aging and fewer thirty‐somethings in the employment ranks, the graying of the
workforce is right around the corner. With it will come a host of issues—loss of human capital, talent
shortages, ageism, and culture clash among them—that will force employers to rethink many of their
practices for acquiring and managing talent. Employers can take specific steps now to cushion the impact of the
aging of their workforce, and those who act too late may find themselves at a competitive disadvantage.
© 2003 Wiley Periodicals, Inc.
Orientation of platelets in multilayered nanocomposite polymer films
Authors: Malwitz Matthew M. , Lin‐Gibson Sheng , Hobbie Erik K. , Butler Paul D. , Schmidt Gudrun
Published: November 2003

The orientation of platelets in micro‐meter‐thick polymer‐clay nanocomposite films was investigated with small‐angle neutron scattering (SANS), small‐angle X‐ray scattering (SAXS), and wide‐angle X‐ray diffraction (WAXD). The films with various clay contents (15–60% by mass fraction) were prepared by a layer‐by‐layer approach from polymer‐clay solutions that led to the formation of a high degree of orientation in both polymer and clay platelets. Shear‐induced orientation of polymer‐clay solutions is compared with the orientation of polymer‐clay films. SANS, SAXS, and WAXD, with beam configurations in and perpendicular to the spread direction of the film, were used to determine the structure and orientation of platelets. In all films, the clay platelets oriented preferentially in the plane of the film. The observed differences in semidilute solutions, with clay surface normal parallel to the vorticity direction, versus bulk films and with clay surface normal parallel to the shear gradient direction at clay mass fractions of 40 and 60%, were attributed to the collapses of clay platelet during the drying process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3237–3248, 2003
Long‐lived excitons up to 1 μs in GaN/AlN self‐assembled quantum dots
Authors: Kako S. , Miyamura M. , Hoshino K. , Arakawa Y.
Published: November 2003

We report the observation of long‐lived excitons in GaN/AlN self‐assembled quantum dots at the temperature of 3.5 K. The PL decay time strongly increases and reaches μs order with increasing size of the QDs. This strongly suggests that the PL decay is almost free from non‐radiative processes and dominated by radiative recombination processes in the GaN QDs. The increase of the PL decay time with increasing size of the QDs originates from the reduction of the oscillator strength due to the strong built‐in electric field in the GaN/AlN heterostructures. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of ketotifen and its conjugated metabolite in human plasma by liquid chromatography/tandem mass spectrometry: application to a pharmacokinetic study
Authors: Chen Xiaoyan , Zhong Dafang , Liu Dan , Wang Yingwu , Han Ying , Gu Jingkai
Published: November 2003

A sensitive and specific liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for the investigation of the pharmacokinetics of ketotifen and its major metabolite, ketotifen N‐glucuronide, in human plasma. The plasma samples were treated by liquid–liquid extraction and analyzed using LC/MS/MS with an electrospray ionization interface. Diphenhydramine was used as the internal standard. The method had a lower limit of quantitation of 10 pg/mL for ketotifen, which offered increased sensitivity, selectivity and speed of analysis, compared with existing methods. The intra‐ and inter‐day precision were measured to be below 8.2% and accuracy between −2.4% and 3.4% for all QC samples. Incubation of the plasma samples with β‐glucuronidase allowed the quantitation of ketotifen N‐glucuronide. This quantitation method was successfully applied to a pharmacokinetic study of ketotifen and its major metabolite after oral administration of 2 mg ketotifen fumarate to 16 healthy volunteers. Copyright © 2003 John Wiley & Sons, Ltd.
Characterization of ammonium chloride derivatives by salt clustering in electrospray mass spectrometry
Authors: Charles Laurence , Chiron Julien , Galy Jean‐Pierre
Published: November 2003

Clustering of ammonium chloride salts was studied using an electrospray source to characterize the form, mono‐ vs. dihydrochloride, of organic compounds by mass spectrometry. This new way of taking advantage of cluster formation is applied to aminomethylacridines as their storage requires the synthesis of such derivatives. Both positive and negative cluster mass spectra were obtained and allowed the determination of the nature of the hydrochloride forms as the salt mass is straightforwardly derived from the mass of the cluster monomer, calculated from singly and multiply charged ion distributions. The identity of the counterion is confirmed from the mass of the ionic moieties in the clusters. Copyright © 2003 John Wiley & Sons, Ltd.
Electrospray mass spectrometric investigation of the binding of cis‐parinaric acid to bovine beta‐lactoglobulin and study of the ligand‐binding site of the protein using limited proteolysis
Authors: Imre Tímea , Zsila Ferenc , Szabó Pál T.
Published: November 2003

The binding property of parinaric acid, a polyunsaturated fatty acid, to bovine β‐lactoglobulin, has been studied by electrospray ionization mass spectrometry. Stable complexation was observed under acidic conditions in a molar ratio of 1:1. Competitive complexation experiments were performed using saturated and unsaturated fatty acid standards with different chain lengths and number of double bonds to study the specificity of the interaction. It can be concluded that formation of the parinaric acid–lactoglobulin complex is preferred even if the molar concentration of the other fatty acids is ten times higher. In cases of specific complex formation the protein must have an active site that is a good acceptor for the ligand molecule. Limited trypsinolysis was performed on the lactoglobulin molecule to identify which part is responsible for the complexation. An intermediate tryptic fragment with molecular mass of 5200 Da was found to have the same ability to bind parinaric acid as the intact protein. This disulfide‐bonded residue, [41‐70]S‐S[149‐162], might thus be involved in the specific complexation of parinaric acid to β‐lactoglobulin. This conclusion is consistent with previous information on this binding site. Copyright © 2003 John Wiley & Sons, Ltd.
Electron ionization mass spectrometry of citrus limonoids
Authors: Tian Qingguo , Li Dan , Barbacci Damon , Schwartz Steven J. , Patil Bhimanagouda S.
Published: November 2003

Electron ionization (EI) mass spectrometry was used to differentiate four structurally closely related citrus limonoid aglycones, including limonin, nomilin, obacunone, and deacetylnomilin. The limonoids were isolated and purified from citrus seeds. Structures of major fragment ions were elucidated by high‐resolution mass spectrometry (HRMS) and fragmentation pathways were proposed. The fragmentation patterns observed in the EI spectra can be used as important references for the positive characterization of limonoid aglycones. Copyright © 2003 John Wiley & Sons, Ltd.
Two new organic reference materials for δ13C and δ15N measurements and a new value for the δ13C of NBS 22 oil
Authors: Qi Haiping , Coplen Tyler B. , Geilmann Heike , Brand Willi A. , Böhlke J. K.
Published: November 2003

Analytical grade L‐glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L‐glutamic acid reference materials with substantially different 13C and 15N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L‐glutamic acid and has a δ13C value of −26.24‰ relative to VPDB and a δ15N value of −4.52‰ relative to N2 in air. USGS41 was prepared by dissolving analytical grade L‐glutamic acid with L‐glutamic acid enriched in 13C and 15N. USGS41 has a δ13C value of +37.76‰ and a δ15N value of +47.57‰. The δ13C and δ15N values of both materials were measured against the international reference materials NBS 19 calcium carbonate (δ13C = +1.95‰), L‐SVEC lithium carbonate (δ13C = −46.48‰), IAEA‐N‐1 ammonium sulfate (δ15N = 0.43‰), and USGS32 potassium nitrate (δ15N = 180‰) by on‐line combustion continuous‐flow and off‐line dual‐inlet isotope‐ratio mass spectrometry. Both USGS40 and USGS41 are isotopically homogeneous; reproducibility of δ13C is better than 0.13‰, and that of δ15N is better than 0.13‰ in 100‐μg amounts. These two isotopic reference materials can be used for (i) calibrating local laboratory reference materials, and (ii) quantifying drift with time, mass‐dependent fractionations, and isotope‐ratio‐scale contraction in the isotopic analysis of various biological materials. Isotopic results presented in this paper yield a δ13C value for NBS 22 oil of −29.91‰, in contrast to the commonly accepted value of −29.78‰ for which off‐line blank corrections probably have not been quantified satisfactorily. Published in 2003 by John Wiley & Sons, Ltd.
A direct injection high‐throughput liquid chromatography tandem mass spectrometry method for the determination of a new orally active αvβ3 antagonist in human urine and dialysate
Authors: Zeng Wei , Wang Amy Qiu , Fisher Alison L. , Musson Donald G.
Published: November 2003

A generic high‐throughput liquid chromatography (HTLC) tandem mass spectrometry (MS/MS) assay for the determination of compound I in human urine and dialysate (hemodialysis) was developed and validated. By using the HTLC on‐line extraction technique, sample pretreatment was not necessary. The sample was directly injected onto a narrow bore large particle size extraction column (50 × 1.0 mm, 60 μm) where the sample matrix was rapidly washed away using a high flow rate (5 mL/min) aqueous mobile phase while analytes were retained. The analytes were subsequently eluted from the extraction column onto an analytical column using an organic‐enriched mobile phase prior to mass spectrometric detection. The analytes were then eluted from the analytical column to the mass spectrometer for the determination. The linear dynamic range was 2.0–6000 ng/mL for the urine assay and 0.1–300 ng/mL for the dialysate assay. Intraday accuracy and precision were evaluated by analyzing five replicates of calibration standards at all concentrations used to construct the standard curve. For the urine assay, the precision (RSD%, n = 5) ranged from 1.9 to 8.0% and the accuracy ranged from 87.8 to 105.2% of nominal value. For the dialysate assay, the precision (RSD%, n = 5) ranged from 1.1 to 10.0% and the accuracy from 94.5 to 105.2% of nominal value. In‐source fragmentation of the acyl glucuronide metabolite (compound III) did not interfere with the determination of parent compound I. The developed HTLC/MS/MS methodology was specific for compound I in the presence of compound III. Column life‐time is increased and sample analysis time is decreased over traditional reversed‐phase methods when direct injection assays for urine and dialysate are coupled with the technology of HTLC. Copyright © 2003 John Wiley & Sons, Ltd.
Gas chromatography/mass spectrometry for the characterization of organic materials in frescoes of the Momumental Cemetery of Pisa (Italy)
Authors: Bonaduce Ilaria , Colombini Maria Perla
Published: November 2003

The paper deals with the application of two analytical procedures, based respectively on on‐line pyrolysis in the presence of hexamethyldisilazane followed by gas chromatography/mass spectrometric analysis (Py/GC/MS) and on selective extractions and microwave‐assisted hydrolysis followed by GC/MS determination. These procedures give reliable data on the organic composition of micro‐samples; moreover, when applied to the same micro‐sample, they give comparable data on natural substances, and complementary information on synthetic compounds and degradation products. The two methods were used to characterise the organic matter present in several samples taken from scenes of the frescoes ‘Giudizio Universale’ and the ‘Ascensione’ by Bonamico Buffalmacco in the Monumental Cemetery of Pisa. The observed hydrophobicity of their surfaces, which hampers traditional means of restoration, is explained by the formation of a polymeric network due to reactions between a synthetic polymer used as adhesive, the proteinaceous material (animal glue and casein), and formaldehyde. Copyright © 2003 John Wiley & Sons, Ltd.
Dual isotope and isotopomer ratios of N2O emitted from a temperate grassland soil after fertiliser application
Authors: Bol R. , Toyoda S. , Yamulki S. , Hawkins J. M. B. , Cardenas L. M. , Yoshida N.
Published: November 2003

The N2O and N2 fluxes emitted from a temperate UK grassland soil after fertiliser application (equivalent to 25 and 75 kg N ha−1) were simultaneously measured, using a new automated soil incubation system, which replaces soil atmosphere (N2 dominated) with a He+O2 mixture. Dual isotope and isotopomer ratios of the emitted N2O were also determined. Total N2O and N2 fluxes were significantly lower (P < 0.001) in the control (0 kg N) than in the 25 and 75 kg N treatments. The total N2O flux was significantly higher (P < 0.001) in the 75 kg N than in the 25 kg N treatment. The general patterns of N2O and N2 fluxes were similar for both fertiliser treatments. The total gaseous N loss in the control treatment was nearly all N2, whereas in the fertiliser treatment more N2O than N2 was emitted from the soil. The ratio N2O/N2 fluxes as measured during the experiment suggested three phases in N2O production, in phase 1 nitrification > denitrification, in phase 2 denitrification > nitrification, and in phase 3 denitrification (and total denitrification) ≫ nitrification. Dual δ15N and δ18O isotope and isotopomer (δ15Nα and δ15Nβ) value ratios of emitted N2O also pointed towards an increasing dominance of the production of N2O by denitrification and total denitrification. The site preference value from the soil‐emitted N2O was lower than the troposphere value. This confirmed that the enhanced troposphere N2O site preference could result from back injection of N2O from the stratosphere. The measurements of N2O/N2 flux ratio and the isotopic content of emitted N2O pointed, independently, to similar temporal trends in N2O production processes after fertiliser application to grassland soil. This confirmed that both measurements are suitable diagnostic tools to study the N2O production process in soils. Copyright © 2003 John Wiley & Sons, Ltd.
The fragmentations of [M–H]− anions derived from underivatised peptides. The side‐chain loss of H2S from Cys. A joint experimental and theoretical study
Authors: Bilusich Daniel , Brinkworth Craig S. , McAnoy Andrew M. , Bowie John H.
Published: November 2003

Loss of H2S is the characteristic Cys side‐chain fragmentation of the [MH]− anions of Cys‐containing peptides. A combination of experiment and theory suggests that this reaction is initiated from the Cys enolate anion as follows: RNH‐−C(CH2SH)CONHR′ Ø [RNHC(CH2)CONHR′ (HS−)] Ø [RNHC(CH2)CO‐HNR′‐H]−+H2S. This process is facile. Calculations at the HF/6‐31G(d)//AM1 level of theory indicate that the initial anion needs only ≥20.1 kcal mol−1 of excess energy to effect loss of H2S. Loss of CH2S is a minor process, RNHCH(CH2SH)CON−‐R′ Ø RNHCH(CH2S−)CONHR′ Ø RNH −CHCONHR+CH2S, requiring an excess energy of ≥50.2 kcal mol−1. When Cys occupies the C‐terminal end of a peptide, the major fragmentation from the [M–H]− species involves loss of (H2S+CO2). A deuterium‐labelling study suggests that this could either be a charge‐remote reaction (a process which occurs remote from and uninfluenced by the charged centre in the molecule), or an anionic reaction initiated from the C‐terminal CO2− group. These processes have barriers requiring the starting material to have an excess energy of ≥79.6 (charge‐remote) or ≥67.1 (anion‐directed) kcal mol−1, respectively, at the HF/6‐31G(d)//AM1 level of theory. The corresponding losses of CH2O and H2O from the [MH]− anions of Ser‐containing peptides require ≥35.6 and ≥44.4 kcal mol−1 of excess energy (calculated at the AM1 level of theory), explaining why loss of CH2O is the characteristic side‐chain loss of Ser in the negative ion mode. Copyright © 2003 John Wiley & Sons, Ltd.
Synthesis and physicochemical characteristics of a liver‐targeted conjugate of fluorodeoxyuridine monophosphate with lactosaminated human albumin
Authors: Stefano Giuseppina Di , Tubaro Michela , Lanza Marcella , Boga Carla , Fiume Luigi , Traldi Pietro
Published: November 2003

In previous experiments fluorodeoxyuridine monophosphate (FUdRMP) was conjugated with lactosaminated human albumin (L‐HSA). Fluorodeoxyuridine (FUdR) is an anticancer agent and L‐HSA is a hepatotropic carrier of drugs obtained by the covalent linkage of lactose residues to the albumin molecule. The conjugate was synthesised via the imidazolide of FUdRMP at alkaline pH. Peripheral venous administration of L‐HSA‐FUdRMP produced enhanced FUdR levels in hepatic blood and might accomplish a non‐invasive loco‐regional chemotherapy of liver micrometastases. In the present paper some physicochemical characteristics of L‐HSA‐FUdRMP are reported. Polyacrylamide gel electrophoresis indicated that the coupling reaction did not cause covalent aggregation of the L‐HSA molecules. 31P NMR spectra of the conjugate showed that FUdRMP was linked to L‐HSA by phosphoamide bonds to lysine and histidine residues, and the area of the peak due to the lysine bond represented more than 80% of the spectrum of L‐HSA‐FUdRMP. MALDI analysis revealed a partial degradation of the peptide backbone of the conjugate which could not be detected using other methods of analysis. The degradation was not caused by the coupling of lactose molecules to albumin, but rather a consequence of FUdRMP conjugation with L‐HSA. This fragmentation was dependent on the pH of the medium used for the FUdRMP coupling reaction. By decreasing the pH to 7.5, conjugates were obtained with a lower drug load but with a substantially reduced fragmentation, which should be preferred for a clinical use of L‐HSA‐FUdRMP. Copyright © 2003 John Wiley & Sons, Ltd.
Structural identification of new glycolipids based on cyclodextrin using high‐resolution positive and negative electrospray ionization mass spectrometry
Authors: Moutard Stephane , Djedaïni‐Pilard Florence , Meudal Sophie , Luijten Wim , Perly Bruno , Pilard Serge
Published: November 2003

In the continuing challenge to increase the performance of cyclodextrins (CDs) for various applications, new phospholipidyl‐cyclodextrin derivatives showing improved self‐organization properties in water have been synthesized, as new carriers for drug vectorization, starting from natural β‐cyclodextrin. Due to the important chemical modifications of the original cyclic oligosaccharide molecules, simple nuclear magnetic resonance (NMR) experiments do not easily lead to both an unambiguous assignment of the structures and to a rapid evaluation of the purity of the final products. However, positive and negative ion electrospray ionization (ESI‐MS) in combination with accurate mass measurements and tandem mass spectrometry (MS/MS) led to the positive structural identification of the first series of these new amphiphilic compounds. Copyright © 2003 John Wiley & Sons, Ltd.
Quadrupole mass filters with octopole fields
Authors: Ding Chuanfan , Konenkov N. V. , Douglas D. J.
Published: November 2003

The performance of quadrupole mass filters with added octopole fields in the range 2.0–4.0% has been investigated. The added fields are much greater than those normally added to conventional rod sets by mechanical tolerances or construction errors. Quadrupole rod sets with added octopole fields were constructed with round rods by making one pair of rods greater in diameter than the other pair. For positive ions, resolution at half height of only about 200 is possible if the negative direct current (dc) output of the quadrupole power supply is connected to the smaller rods. If the positive dc output of the quadrupole power supply is connected to the smaller rods, the resolution improves dramatically; a resolution at half height of 5800 has been observed with a rod set with 2.6% added octopole field. For negative ions the best resolution is obtained with the polarity of the dc reversed, i.e. with the negative dc applied to the smaller rods. These findings are unexpected in view of the literature that argues that to obtain high mass resolution with quadrupole mass filters, higher order multipoles must be kept as small as possible. Numerical simulations of peak shapes agree qualitatively with experiments. Simulation of the boundaries of the first stability region for positive ions shows that when the positive dc is applied to the smaller rods, the addition of a 2.0% octopole field causes the boundaries to shift slightly but the boundaries are well defined, and the tip of the stability region remains sharp. When the positive dc is applied to the larger rods, the boundaries of the stability region move out and become diffuse. For instruments that require a rod set that can be used both as a linear trap and a mass filter, these rod sets may offer improved trap performance while still being capable of providing conventional mass analysis. Copyright © 2003 John Wiley & Sons, Ltd.