bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of rCBF by diffusible signals: An analysis of constraints on diffusion and elimination
Authors: Friston K. J.
Published: May 2005

Local changes in cerebral hemodynamics are observed within a few hundred milliseconds of changes in neural activity. If hemodynamic responses are mediated by passive diffusion of a spatial signal (from the site of neural activity to the microvessels) then the dynamics of the response suggest a lower limit on the signal's apparent diffusion and elimination. The aim of this work was to estimate these limits and narrow the field of possible candidate substances.

A simple biophysical simulation was used to examine how the time course of concentration changes in a spatial signal, at the site of action (microvessels), depends on key diffusion parameters (source geometry, apparent diffusion and elimination half‐life). The simulations suggested (1) that the rise in signal concentration is mostly a function of source geometry and diffusion. Conversely falls in concentration depend on elimination and (2) even when sources are very sparsely distributed Nitric Oxide would have a sufficiently fast diffusion and elimination to signal the early components of activity‐dependent hemodynamic response by passive diffusion. © 1995 Wiley‐Liss, Inc.
Surface modification of interconnected porous scaffolds
Authors: Liu Xiaohua , Won Youngjun , Ma Peter X.
Published: June 2005

Surface properties of scaffolds play an important role in cell adhesion and growth. Biodegradable poly(α‐hydroxy acids) have been widely used as scaffolding materials for tissue engineering; however, the lack of functional groups is a limitation. In this work, gelatin was successfully immobilized onto the surface of poly(α‐hydroxy acids) films and porous scaffolds by a new entrapment process. The surface composition and properties were examined using attenuated total reflection–Fourier transform infrared spectroscopy (ATR‐FTIR), X‐ray photoelectron spectra (XPS), and contact angle measurements. Control over the amount of entrapped gelatin was achieved by varying the solvent composition, the duration of soaking, the concentration of gelatin in solution, and chemical crosslinking. The amount of entrapped gelatin increased with the ratio of dioxane/water in the solvent mixture used. Chemical crosslinking after physical entrapment considerably increased the amount of retained gelatin on the surface of poly(α‐hydroxy acids). Osteoblasts were cultured on these films and scaffolds. The surface modification significantly improved cell attachment and proliferation. Cell numbers on the surface‐modified films and scaffolds were significantly higher than those on controls 4 h and 1 day after cell seeding. The osteoblasts showed higher proliferation on surface‐modified scaffolds than on the control during 4 weeks of in vitro cultivation. More collagen fibers and other cell secretions were deposited on the surface‐modified scaffolds than on the control scaffolds. This novel surface treatment strategy provides a convenient and universal way to modify the surface properties of three‐dimensional scaffolds and thus promote cell adhesion and proliferation for tissue engineering. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005
Comparison of one‐dimensional and two‐dimensional functionally graded materials for the backing shell of the cemented acetabular cup
Authors: Hedia H. S.
Published: June 2005

Among the factors that have been suggested as contributing to the failure of a total joint replacement are stress shielding and the subsequent bone resorption. Recent studies have shown that when a backing shell made from a Ti alloy is used, high stresses are generated in the cement at the edges of the cup, and low stresses are generated at the dome of the bone in the acetabulum; thus, the bone at the dome suffers stress shielding and the cement edge suffers high stresses. The aim of this study was to investigate the effect of using a functionally graded material (FGM), instead of Ti alloy, for the backing shell (BS) on the stress distribution in the BS–cement–bone system. Finite‐element and optimization techniques were used to obtain the optimal distribution of materials in the tangential direction only of the backing (1D FGM) as well as in the tangential and radial directions of the backing (2D FGM). It was found that the stress distribution in the BS–cement–bone system was about the same, regardless of whether the BS was fabricated from a 1D or 2D FGM. The stress‐shielding factor in the bone at the dome of the acetabulum and the maximum von Mises stress in cement at the cement interfaces for 1D and 2D FGM were reduced by about 51%, 69%, and 50%, respectively, compared to the case when the shell was fabricated from a Ti alloy. The optimal elastic modulus of the 1D FGM was obtained with the materials graded from HA at the dome of the acetabulum to a Ti alloy at the rim of the shell. The optimal elastic modulus of the 2D FGM was obtained with the materials graded from Ti alloy at the right edge of the rim, to Bioglass 45S5 at the left edge of the rim, and to HA at the dome of the shell. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2005
Protective effect of NAC on formaldehyde‐containing–ZOE‐based root‐canal‐sealers–induced cyclooxygenase‐2 expression and cytotoxicity in human osteoblastic cells
Authors: Huang Fu‐Mei , Chou Lin Shin‐Shen , Chou Ming‐Yung , Chang Yu‐Chao
Published: June 2005

Cyclooxygenase‐2 (COX‐2) is an inducible enzyme believed to be responsible for prostaglandin synthesis at site of inflammation. Recently, the activation of COX‐2 expression may be one of the important pathogenesis of root‐canal‐sealers–induced periapical inflammation. However, little is known about whether chemical interaction can modulate the COX‐2 expression and cytotoxicity induced by formaldehyde‐containing–ZOE‐based root canal sealers. The aim of this study was to investigate the effects of antioxidants such as catalase, superoxide dismutase (SOD), and N‐acetyl‐L‐cysteine (NAC) on N2‐ and endomethasone‐induced COX‐2 mRNA gene and cytotoxicity in human osteoblastic cell line U2OS cells. Our data demonstrated that both formaldehyde‐containing–ZOE‐based root canal sealers were found to induce COX‐2 mRNA gene expression in U2OS cells. The addition of glutathione (GSH) precursor NAC led to decrease the induction of COX‐2 mRNA gene expression and cytotoxicity by both N2 and Endomethasone (p < 0.05). However, catalase and SOD lacked the ability to prevent cytotoxicity and COX‐2 mRNA gene expression induced by N2 and Endomethasone (p > 0.05). The data presented here demonstrated that the activation of COX‐2 mRNA gene expression may be one of the pathogenesis of formaldehyde‐containing–ZOE‐based root‐canal‐sealers–induced periapical inflammation. In addition, GSH depletion, but not the attack of oxygen free radicals, could be the mechanism for cytotoxicity and COX‐2 mRNA gene expression induced by formaldehyde‐containing–ZOE‐based root canal sealers. NAC appears as a useful agent in protecting cell damage mediated by formaldehyde‐containing–ZOE‐based root canal sealers. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2005
Histone H4 post‐translational modifications in chordate mitotic and endoreduplicative cell cycles
Authors: Spada Fabio , Chioda Mariacristina , Thompson Eric M.
Published: June 2005

Histone post‐translational modifications mark distinct structural and functional chromatin states but little is known of their involvement in the progression of different cell cycle types across phylogeny. We compared temporal and spatial dynamics of histone H4 post‐translational modifications during both mitotic and endoreduplicative cycles of the urochordate, Oikopleura dioica, and proliferating mammalian cells. Endocycling cells showed no signs of chromosome condensation or entry into mitosis. They exhibited an evolution of replication patterns indicative of reduced chromatin compartmentalization relative to proliferating mammalian cells. In the latter cells, published cell cycle profiles of histone H4 acetylated at lysine 16 (H4AcK16) or dimethylated at lysine 20 (H4Me2K20) are disputed. Our results, using different, widely used H4AcK16 antibodies, revealed significant antibody‐specific discrepancies in spatial and temporal cell cycle regulation of this modification, with repercussions for interpretation of previous immunofluorescence and immunoprecipitation data based on these reagents. On the other hand, three different antibodies to H4Me2K20 revealed similar cell cycle profiles of this modification that were conserved throughout the mitotic cell cycle in urochordate and mammalian cells, with accumulation at mitosis and a decrease during S‐phase. H4Me2K20 also cycled in endocycles, indicating that dynamics of this modification are not strictly constrained by the mitotic phase of the cell cycle and suggesting additional roles during G‐ and S‐phase progression. This article contains Supplementary Material available at http://www.mrw.interscience.wiley.com/suppmat/0730‐2312/suppmat/2005/95/spada.html. © 2005 Wiley‐Liss, Inc.
Andrograpanin, a compound isolated from anti‐inflammatory traditional Chinese medicine Andrographis paniculata, enhances chemokine SDF‐1α‐induced leukocytes chemotaxis
Authors: Ji Li‐Li , Wang Zhu , Dong Fang , Zhang Wen‐Bo , Wang Zheng‐Tao
Published: June 2005

Andrographis paniculata is a traditional Chinese medicine (TCM) that has been effectively used for treatment of infection, inflammation, cold, fever, and diarrhea in China. However, mechanism of its therapeutic function is not well known. In the current study, we showed one of its components, andrograpanin, could enhance chemokine stromal cell‐derived factor‐1α (SDF‐1α) induced chemotaxis in Jurkat and THP‐1 cells. Further study demonstrated that this kind of effect was CXC chemokine receptor‐4 (CXCR4) specific, since andrograpanin could not enhance other chemokines, such as RANTES, monocyte chemotactic protein‐1 (MCP‐1), etc. induced cell chemotaxis. Mechanisms of andrograpanin exerting its effect were not directly in the receptor and G protein coupling level because it had no effect on the binding of SDF‐1 to CXCR4, SDF‐1 induced G protein activation and adenyly cyclase inhibition. However, receptor internalization might be involved, since we found it significantly reduced SDF‐1α‐induced CXCR4 internalization. © 2005 Wiley‐Liss, Inc.
The ab initio limit quartic force field of BH3
Authors: Schuurman Michael S. , Allen Wesley D. , Schaefer Henry F.
Published: June 2005

The complete quartic force field of BH3 has been converged to the ab initio limit by extrapolation of core‐valence correlation‐consistent basis set series (cc‐pCVXZ, X = T, Q, 5) of all‐electron CCSD(T) (coupled‐cluster singles and doubles with perturbative triples) energy points. Additional computations including full coupled‐cluster treatments through quadruple excitations (CCSDTQ), scalar relativistic effects, and diagonal Born–Oppenheimer corrections (DBOC) were concurrently executed. Within second‐order vibrational perturbation theory (VPT2) our quartic force field yields the fundamental frequencies ν1 = 2502.3 cm−1, ν2 = 1147.2 cm−1, ν3 = 2602.1 cm−1, and ν4 = 1196.5 cm−1, in excellent agreement with observed gas‐phase fundamentals, displaying a mean absolute error of only 0.3 cm−1. Our converged prediction for the equilibrium bond length of BH3 is re = 1.1867 Å. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1106–1112, 2005
Representation of Zn(II) complexes in polarizable molecular mechanics. Further refinements of the electrostatic and short‐range contributions. Comparisons with parallel ab initio computations
Authors: Gresh Nohad , Piquemal Jean‐Philip , Krauss Morris
Published: June 2005

We present refinements of the SIBFA molecular mechanics procedure to represent the intermolecular interaction energies of Zn(II). The two first‐order contributions, electrostatic (EMTP), and short‐range repulsion (Erep), are refined following the recent developments due to Piquemal et al. (Piquemal et al. J Phys Chem A 2003, 107, 9800; and Piquemal et al., submitted). Thus, EMTP is augmented with a penetration component, Epen, which accounts for the effects of reduction in electronic density of a given molecular fragment sensed by another interacting fragment upon mutual overlap. Epen is fit in a limited number of selected Zn(II)–mono‐ligated complexes so that the sum of EMTP and Epen reproduces the Coulomb contribution Ec from an ab initio Hartree–Fock energy decomposition procedure. Denoting by S, the overlap matrix between localized orbitals on the interacting monomers, and by R, the distance between their centroids, Erep is expressed by a S2/R term now augmented with an S2/R2 one. It is calibrated in selected monoligated Zn(II) complexes to fit the corresponding exchange repulsion Eexch from ab initio energy decomposition, and no longer as previously the difference between (Ec + Eexch) and EMTP. Along with the reformulation of the first‐order contributions, a limited recalibration of the second‐order contributions was carried out. As in our original formulation (Gresh, J Comput Chem 1995, 16, 856), the Zn(II) parameters for each energy contribution were calibrated to reproduce the radial behavior of its ab initio HF counterpart in monoligated complexes with N, O, and S ligands. The SIBFA procedure was subsequently validated by comparisons with parallel ab initio computations on several Zn(II) polyligated complexes, including binuclear Zn(II) complexes as in models for the Gal4 and β‐lactamase metalloproteins. The largest relative error with respect to the RVS computations is 3%, and the ordering in relative energies of competing structures reproduced even though the absolute numerical values of the ab initio interaction energies can be as large as 1220 kcal/mol. A term‐to‐term identification of the SIBFA contributions to their ab initio counterparts remained possible even for the largest sized complexes. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1113–1130, 2005
Airway gene transfer using cationic emulsion as a mucosal gene carrier
Authors: Kim Tae Woo , Chung Hesson , Kwon Ick Chan , Sung Ha Chin , Shin Byung Chul , Jeong Seo Young
Published: May 2005

Background

Delivery of genes to airway mucosa would be a very valuable method for gene therapy and vaccination. However, there have been few reports on suitable gene delivery systems for administration. In this study, we use a cationic emulsion system, which is physically stable and facilitates the transfer of genes in the presence of up to 90% serum, as a mucosal gene carrier.

Methods and results

Cationic lipid emulsion was formulated with squalene and 1,2‐dioleoyl‐sn‐glycero‐3‐trimethylammoniumpropane (DOTAP) as major components. Emulsions formed stable complexes with DNA and protected and transferred DNA to target cells against DNase I digestion in the presence of mucosal destabilizers such as heparin sulfate (a polysaccharide of the glycosaminoglycan family in mucosa) and Newfectan (a natural lung extract of bovine) in an in vitro system. In contrast, commercial liposomes and counter liposomes, made with an identical lipid composition of emulsions, failed. After in vivo intranasal instillation, the cationic emulsion showed at least 200 times better transfection activity than the liposomal carriers in both nasal tissue and lung.

Conclusions

These findings show that cationic emulsions can mediate gene transfection into airway epithelium, making it a good choice for transferring therapeutic genes and for genetic vaccination against an pathogenic infection via an airway route. Copyright © 2005 John Wiley & Sons, Ltd.
Regular orientable embeddings of complete bipartite graphs
Authors: Kwak Jin Ho , Kwon Young Soo
Published: June 2005

In this paper, it will be shown that the isomorphism classes of regular orientable embeddings of the complete bipartite graph Kn,n are in one‐to‐one correspondence with the permutations on n elements satisfying a given criterion, and the isomorphism classes of them are completely classified when n is a product of any two (not necessarily distinct) prime numbers. For other n, a lower bound of the number of those isomorphism classes of Kn,n is obtained. As a result, many new regular orientable embeddings of the complete bipartite graph are constructed giving an answer of Nedela‐Škoviera's question raised in 12. © 2005 Wiley Periodicals, Inc. J Graph Theory
On graphs whose Laplacian matrices have distinct integer eigenvalues
Authors: Fallat Shaun M. , Kirkland Stephen J. , Molitierno Jason J. , Neumann M.
Published: June 2005

In this paper, we investigate graphs for which the corresponding Laplacian matrix has distinct integer eigenvalues. We define the set Si,n to be the set of all integers from 0 to n, excluding i. If there exists a graph whose Laplacian matrix has this set as its eigenvalues, we say that this set is Laplacian realizable. We investigate the sets Si,n that are Laplacian realizable, and the structures of the graphs whose Laplacian matrix has such a set as its eigenvalues. We characterize those i < n such that Si,n is Laplacian realizable, and show that for certain values of i, the set Si,n is realized by a unique graph. Finally, we conjecture that Sn,n is not Laplacian realizable for n ≥ 2 and show that the conjecture holds for certain values of n. © 2005 Wiley Periodicals, Inc. J Graph Theory
Analysis of normal human fetal eye lens crystallins by high‐performance liquid chromatography/mass spectrometry
Authors: He Shuming , Pan Suhua , Wu Kaili , Amster I. Jonathan , Orlando Ron
Published: May 2005

High‐performance liquid chromatography/mass spectrometry (HPLC/MS) was used to characterize the water‐soluble and water‐insoluble fractions of human fetal eye lens crystallins. This age group was selected since their crystallins are not expected to have accumulated significant amounts of either age‐ or cataract‐related post‐translational modifications owing to their young age. This analysis permitted the identification and determination of the extent of post‐translational modifications for a range of crystallins in a single procedure. The excellent agreement between the calculated and experimental molecular weights from HPLC/MS implies that the published sequences for the crystallins αA2, αB2, βA3, βB2 and γC are correct. This agreement also demonstrates that these proteins do not contain any previously undetected post‐translational modifications. In addition, the molecular weights for many crystallins with unknown sequences and/or post‐translational modifications were determined to within several mass units. This appears to be the first reported analysis of the post‐translational modifications occurring in crystallins from this age group. By providing the molecular weights of the native human crystallins, this study provides a baseline for future comparisons of the age‐ and cataract‐related post‐translational modifications of human lens crystallins.
Structurally‐selective gas‐phase ion‐molecule reactions of dibenzo‐16‐crown‐5 compounds
Authors: Liou Chien‐Chung , Isbell John , Wu Hui‐Fen , Brodbelt Jennifer S. , Bartsch Richard A. , Lee Jong Chan , Hallman Johnny L.
Published: May 2005

Steric and substituent effects can play large roles in influencing the outcomes of organic reactions. In this work, the use of ion‐molecule reactions of dibenzo‐16‐crown‐5 compounds (lariat ethers) by tandem mass spectrometry to probe the influence of the pendant groups on the selectivity of their gas‐phase reactions was evaluated. Lariat ethers are macrocyclic ethers with pendant substituents that have been developed as new types of hosts for molecular recognition. Dimethyl ether (DME) was the reactant chosen because of its well characterized reactivity with various organic substrates possessing different functional groups. Only those dibenzo‐16‐crown‐5 compounds with no or at most one substituent at the center carbon of the three‐carbon bridge form the diagnostic [M + 13]+ product ion through a methylene substitution process. Dibenzo‐16‐crown‐5 compounds with geminal substituents on the center carbon of the three‐carbon bridge form the [M + 45]+ ion, but not the characteristic [M + 13]+ ion. Causative factors may be steric blocking of the reaction pathway by the geminal groups or a requirement for the presence of at least one hydrogen on the center carbon of the three‐center bridge for formation of the [M + 13]+ ion. CAD, deuterium labelling, molecular orbital calculations and comparisons with model compounds provide additional information about the reaction pathways.
Special feature: Tutorial. Translational energy spectrocopy
Authors: Brenton Anthony Gareth
Published: May 2005

The technique of translational energy spectroscopy (TES) is described, whereby a collision of a fast ion (a few keV in energy) with a neutral target gas can reveal spectroscopic information on the states of the participating species. Information on the dynamics of the collision, lifetimes of species, collision cross‐sections and populations of states can be revealed. Classification of collisional processes amenable to TES are given together with simple aspects of relevant collision theory, an appraisal of quantum selection rules for collisions, a description of typical high resolution instrumentation and two simple examples of TES experiments.
Gas‐phase H–D exchange reactions of protonated amino acids and peptides with ND3
Authors: Dookeran Nyla N. , Harrison Alex G.
Published: May 2005

The gas‐phase H‐D exchange reactions of protonated amino acids and small peptides with ND3 have been studied for reactions occurring in the quadrupole collision cell of a hybrid BEqQ mass spectrometer (B = magnetic sector, E = electric sector, q = quadrupole collision cell, Q = quadrupole mass analyzer). Protonated amino acids RCH(NH2)COOH· H+, including those with hydroxyl, carboxyl, and amine functions in the R group, exchange all active hydrogens readily. The amide hydrogens of protonated glutamine and asparagine exchange less readily as does the N‐bonded hydrogen of the imidazole ring of histidine. The phenolic hydrogen of protonated tyrosine and tyrosine‐containing peptides does not undergo significant exchange. Protonated arginine undergoes only limited exchange with ND3 and arginine‐containing peptides are essentially unreactive with ND3. Although simple protonated di‐ and tripeptides exchange all active hydrogens readily, peptides with amide groups in the side‐chain exchange the last two hydrogens slowly. Mechanisms for exchange of the active hydrogens are discussed in relation to the proton affinities of the various sites of the amino acids and the potential and limitations of the method for counting the labile hydrogens of unknown peptides is assessed.
Alumatrane revisited: Distribution of oligomeric ions in electron impact ionization, chemical ionization and liquid secondary ion mass spectra
Authors: Bartlett Michael G. , Burns Scot A. , Bruce David A. , Busch Kenneth L.
Published: May 2005

Oligomeric ions formed from aluminium 2,2′,2″‐nitriltriethoxide (alumatrane) are present in electron impact (EI) ionization, chemical ionization (CI), direct‐exposure probe chemical ionization (DCI) and liquid secondary ion (LSI) mass spectra. These oligomeric ions are most pronounced in the LSI mass spectrum, extending from monomeric to heptameric ions. The oligomeric ions exist there in the forms [Mn + H]+ and [Mn + (AIO)a + (Al2O3)b]+ where the sum of a and b can be as high as 5. In contrast to previous interpretations of EI and CI results, the LSI mass spectral data do not support a special stability for either the dimeric or tetrameric gas‐phase forms of alumatrane.
Oligosaccharide characterization using collision‐induced dissociation fast atom bombardment mass spectrometry: Evidence for internal monosaccharide residue loss
Authors: Kováčik V. , Hirsch J. , Kováč P. , Heerma W. , Thomas‐Oates J. , Haverkamp J.
Published: May 2005

The protonated and sodium cationized pseudomolecular ions of a series of reducing and non‐reducing oligosaccharides possessing aldopentopyranosyl, 6‐deoxyaldohexopyranosyl, ketohexofuranosyl, 4‐O‐methyl glucuronopyranosyl methyl ester and N‐acetyl 2‐deoxyglucopyranosylamine units were studied using collision‐induced dissociation (CID) fast atom bombardment (FAB) mass spectrometry. The CID spectra of the [M + H]+ ions provide information about the sequence of the monosaccharide units, while dissociation of the [M + Na]+ ions by two‐bond ring cleavage processes gives rise to fragment ions which allow differentiation of 1 → 2 and 1 → 4 linkages. The influence of the structure of the constituent monosaccharides on the dissociation of the [M + H]+ and [M + Na]+ ions is discussed. An unusual type of fragmentation, which we suggest involves the elimination of internal monosaccharides residues, has not only been observed in the FAB mass spectra but also in the unimolecular decomposition and CID spectra of both [M + H]+ ions and oxonium ions from several oligosaccharides containing monosaccharide residues with different masses.
Special feature: Tutorial. Glow discharge mass spectrometry: Trace element determinations in solid samples
Authors: King F. L. , Teng J. , Steiner R. E.
Published: May 2005

Glow discharge mass spectrometry (GDMS) is a mature, versatile technique for the direct determination of trace elements in a variety of materials. The technique is an extension of the earliest forms of mass spectrometry. Processes inherent to the glow discharge, namely cathodic sputtering coupled with Penning ionization, yield an ion population from which semi‐quantitative results can be directly obtained. Quantification in GDMS is achieved both through standard elemental mass spectrometric procedures and more innovative approaches. The analytical performance of GDMS compares favorably with competing elemental mass spectrometric methods and newer experiments use this ionization method for both molecular and elemental analysis. As with any analytical technique, the future of GDMS lies in improvements with respect to instrumental implementation and extension to new areas of application. If the method is to remain competitive, commercial GDMS systems must incorporate advances in mass spectrometric technology to increase analytical performance while decreasing the size, complexity and cost of the technique. Continued efforts to develop improved quantitation procedures are needed to provide greater accuracy. The method should continue to mature as sustained efforts demonstrate its utility in the solution of new and more varied problems.
Negative‐ion fast atom bombardment tandem mass spectrometry of sodium salts of monensins and related compounds
Authors: Havlíček Vladimír , Ryska Miroslav , Pospíšil Stanislav
Published: May 2005

The negative‐ion collisionally induced dissociation fast atom bombardment mass spectra of sodium salts of monensins A and B, their 3‐O‐demethyl derivatives, laidlomycin and 26‐deoxylaidlomycin are reported. The nature of the R3 substituent appears to be important for the formation of sodium‐containing product ions. Fragment ion series observed in the mass spectra of the [M − H]− ions of monensins are characterized by alkali metal retention. In contrast to monensins, the product ions observed in the corresponding spectra of laidlomycins are sodium free. The affinity of monensins to alkali metals is a useful feature that may be used for the structure determination of unknown monensins, their metabolites and derivates. The structure of a novel natural monensin was elucidated based on its mass spectrometric behaviour.
Charged vs. neutral nucleobase loss from multiply charged oligonucleotide anions
Authors: McLuckey Scott A. , Vaidyanathan Gopalakrishnan , Habibi‐Goudarzi Sohrab
Published: May 2005

Tandem mass spectra of a variety of adenine‐containing deoxynucleic acid anions obtained using collisional activation in a quadrupole ion trap are described. Data are reported for singly charged mono‐, di‐ and trinucleotide species, and also for multiply charged anions derived from tri‐, tetra‐, penta‐ and hexanucleotides. Attention is focused on the first step in the unimolecular decomposition of these species, namely the loss of the nucleobase. Specifically, the competition between the loss of the nucleobase as a neutral versus its loss as an anion is addressed within the context of a proposed proton‐bound intermediate consisting of the nucleobase and a phosphodiester linkage. The data are interpreted on the basis of the energy surface involved in the break‐up of the proton‐bound intermediate, which can explain why the competition between loss of a neutral versus charged base is strongly dependent upon the charge of the parent ion.
Matrix‐assisted laser desorption/ionization mass spectrometry of phospholipids
Authors: Harvey D. J.
Published: May 2005

Phosphatidylcholine, lysophosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylglycerol, phosphatidylinositol, phosphatidic acid and cardiolipin were examined by matrix‐assisted laser desorption/ionization mass spectrometry on both a time‐of‐flight and a magnetic sector instrument using several substituted cinnamic acids, benzoic acids and substituted coumarins as matrices. All of these phospholipids gave signals, with the strongest responses being obtained from α‐cyano‐4‐hydroxycinnamic acid, esculetin (6,7‐dihydroxycoumarin) and 2,5‐dihydroxybenzoic acid (2,5‐DHB). In the positive‐ion mode, most compounds produced mixtures of [M + H]+, [M + Na]+ and [M + K]+ ions from both the free acids and from the sodium salts to give a complex mixture of ions. The spectra were considerably simpler in the negative‐ion mode, where the molecular ion region contained mainly [M − H]− ions. Spectral simplification was also achieved in the positiveion mode by methylation with diazomethane to prevent salt formation. This procedure had the additional advantage of converting phosphatidylethanolamine and phosphatidylserine into their corresponding quaternary derivatives with a consequent gain in detection sensitivity. Fragmentation involving cleavages around the phosphate group was common, with the diacyl‐containing ion produced by loss of the substituted phosphate moiety being particularly abundant. Fragmentation appeared to be strongly dependent on the nature of the matrix and, particularly, on the presence or absence of water in the matrix solvent. With spectra recorded on the magnetic sector instrument, additional fragment ions produced by losses of the acyl groups were seen. These latter ions provided some information regarding the distribution of carbon atoms between the acyl chains.
Application of time‐of‐flight mass spectrometry to the analysis of phototransformation products of diclofenac in water under natural sunlight
Authors: Agüera A. , Pérez Estrada L. A. , Ferrer I. , Thurman E. M. , Malato S. , Fernández‐Alba A. R.
Published: June 2005

Exact mass capabilities of time‐of‐flight (TOF) mass spectrometry along with other mass spectrometric techniques have been evaluated to elucidate a complete range of dichlofenac phototransformation products. Photolysis experiments with diclofenac in water under direct solar irradiation were performed to characterise the main phototransformation products generated and to determine their stability. Photolysis experiments were performed in both demineralised water and reconstructed standard freshwater. Samples were extracted before analysis by solid phase extraction (SPE) with Oasis® HLB and MAX cartridges. Separation and identification of the transformation products were accomplished by the combined use of gas chromatography‐mass spectrometry (GC/MS) and liquid chromatography coupled with time‐of‐flight mass spectrometry (LC/TOFMS). Both techniques provided complementary information that enabled the identification of 13 phototransformation products. Six of them were identified by GC/MS through the structural information provided by the full scan mass spectra obtained under electron impact (EI) ionisation and the confirmation of the molecular mass provided by positive chemical ionisation (PCI) analyses. Accurate mass measurements obtained by LC/TOFMS provided the elucidation of seven polar transformation products. The low mass error observed (<2 ppm) enabled the assignment of highly probable empirical formulas as well as identification of a process dimerisation route. The photoproducts identified demonstrated that photolysis of diclofenac occurs by two main routes. One is the consequence of the initial photocyclisation of diclofenac into carbazole derivatives. The other route goes through the initial decarboxilation of diclofenac and further oxidation of the alkyl‐chain, which are typical photolytic process reactions. The main photoproduct identified was 8‐chloro‐9H‐carbazole‐1yl‐acetic acid. Copyright © 2005 John Wiley & Sons, Ltd.
Electrospray tandem mass spectrometric analysis of zeaxanthin and its oxidation products
Authors: Prasain Jeevan Kumar , Moore Ray , Hurst John S. , Barnes Stephen , van Kuijk Frederik J. G. M.
Published: June 2005

Carotenoids have been implicated in protection of the eye from light‐mediated photo‐toxicity caused by free radicals. Under conditions of normal oxidative stress the carotenoids serve as protective antioxidants; however, when the oxidative stress exceeds the antioxidant capacity, carotenoids can be oxidized into numerous cleavage products. The determination and identification of oxidized carotenoids in biological samples remains a major challenge due to the small sample size and low stability of these compounds. We investigated the reaction of various zeaxanthin cleavage products with O‐ethyl hydroxylamine to evaluate their levels in a biological sample. For this, a sensitive and specific electrospray tandem mass spectrometry (ESI‐MS/MS) was developed, avoiding the classical lower sensitive and specific HPLC‐UV and fluorescence absorption methods. Protonated molecules [M + H]+ of carotenoids upon collision‐induced dissociation produced a number of structurally characteristic product ions. A series of complicated clusters of product ions differing in 14 (CH2)and 26 (C2H2)Da was characteristic of the polyene chain of intact carotenoids. All carotenoid ethyl oximes of zeaxanthin cleavage products were characterized by the losses of 60 and 61 Da in their MS/MS spectra. Through the application of the LC/MS/MS method, we identified two oxime derivatives of 3‐hydroxy‐β‐ionone and 3‐hydroxy‐14′‐apocarotenal with protonated molecules at m/z 252 and m/z 370 respectively, in a human eye sample. Copyright © 2005 John Wiley & Sons, Ltd.
Online microdialysis‐dynamic nanoelectrospray ionization‐mass spectrometry for monitoring neuropeptide secretion
Authors: Jakubowski Jennifer A. , Hatcher Nathan G. , Sweedler Jonathan V.
Published: June 2005

Although mass spectrometric approaches offer a sensitive method for identifying cell–cell signaling peptides, the high salt‐containing environment of extracellular solutions often complicates characterization of these microscale samples. Accordingly, we have developed a miniature hollow‐fiber microdialysis device optimized for desalting small‐volume neuronal samples online, with the device directly connected to a modified dynamic nanoelectrospray ionization assembly interfaced with an ion trap mass spectrometer. Improvements over existing designs include placement of a capillary insert within the microdialysis fiber to minimize volume, as well as the use of a microinjector that enables 1 µl sample injections. We present detailed evaluation of peptide recoveries within the microdialysis fiber by liquid chromatography–electrospray ionization–ion trap–mass spectrometry analysis of tissue homogenate in artificial seawater with and without microdialysis. Analyte recoveries after microdialysis ranged from 6 to 78% with higher recoveries of more hydrophilic peptides, while little correlation between mass and percentage recovery was observed in the range studied (2000 to 6000 Da). Recoveries of peptides were the lowest for the analytes with the highest initial mass spectrometry signal intensity. Finally, we illustrate the utility of this microdialysis device for desalting neuropeptides secreted from preparations of the peptidergic bag cell neurons of the marine mollusk, Aplysia californica. Without microdialysis, the high concentration of salts (∼0.5 M) prevented detection of peptides, whereas following online microdialysis–dynamic nanoelectrospray mass spectrometry of stimulated releasate, three peptides (acidic peptide, acidic peptide 1‐24 and δ‐bag cell peptide) were detected. Copyright © 2005 John Wiley & Sons, Ltd.
Covalent modification of actin by 4‐hydroxy‐trans‐2‐nonenal (HNE): LC‐ESI‐MS/MS evidence for Cys374 Michael adduction
Authors: Aldini Giancarlo , Dalle‐Donne Isabella , Vistoli Giulio , Maffei Facino Roberto , Carini Marina
Published: June 2005

We demonstrate for the first time, by a combined mass spectrometric and computational approach, that G‐ and F‐actin can be covalently modified by the lipid‐derived aldehyde, 4‐hydroxy‐trans‐2‐nonenal, providing information on the molecular mass of modified protein and the mechanism and site of adduction.

ESI‐MS analysis of actin treated with different molar ratios of HNE (1 : 1 to 1 : 20) showed the formation of a protein derivative in which there was an increase of 156 Da (42028 Da) over native actin (41872 Da), consistent with the adduction of one HNE residue through Michael addition. To identify the site of HNE adduction, G‐ and F‐actin were stabilized by NaBH4 reduction and digested with trypsin. LC‐ESI‐MS/MS analysis in data‐dependent scan mode of the resulting peptides unequivocally indicated that Cys374 is the site of HNE adduction. Computational studies showed that the reactivity of Cys374 residue is due to a significant accessible surface and substantial thiol acidity due to the particular microenvironment surrounding Cys374. Copyright © 2005 John Wiley & Sons, Ltd.
Screening for unknown synthetic steroids in human urine by liquid chromatography‐tandem mass spectrometry
Authors: Thevis Mario , Geyer Hans , Mareck Ute , Schänzer Wilhelm
Published: June 2005

Chemically modified steroids (designer steroids), including tetrahydrogestrinone and norbolethone, pose a threat to the integrity of the sport community. These compounds have recently been detected in urine specimens from athletes, resulting in temporary or permanent suspension from amateur and/or professional competition. Triple quadrupole mass spectrometers enable doping control laboratories to screen for unknown, anabolic, androgenic steroids utilizing precursor ion scans. On the basis of common dissociation patterns of steroids with common structural features, characteristic product ions were selected to serve as diagnostic markers for previously unidentified drugs or drug metabolites in human urine samples. An assay was established to complement standard screening procedures. Urine specimens were enzymically hydrolyzed, partitioned into ether, concentrated, and analyzed by precursor ion scanning. Spectra from samples fortified with eight standard compounds (methyltestosterone, ethyltestosterone, 1‐testosterone, gestrinone, dihydrogestrinone, tetrahydrogestrinone, norbolethone, and propyltrenbolone) and one deuterium‐labeled analog (d4‐tetrahydrogestrinone) at 50 ng/ml of urine, had precursor ion peaks other than those from common endogenous steroids. Subsequent product ion scan experiments on precursor ions of peaks of unknown origin provided structural identification of the unknown compounds. Copyright © 2005 John Wiley & Sons, Ltd.
Balance of xanthophylls molecular and protonated molecular ions in electrospray ionization
Authors: Guaratini Thais , Vessecchi Ricardo , Pinto Ernani , Colepicolo Pio , Lopes Norberto P.
Published: June 2005

This paper reports the chemical evidence of the balance between radical molecular ions and protonatedmolecules of xanthophylls (an oxygen‐containing carotenoid) with a conjugated π‐system (polyene) and oxygen as a heteroatom in ESI and HRESI mass spectrometry. The ionization energy of neutral xanthophylls was calculated by semi‐empirical methods. The results were compared with those previously published for carotenoids and retinoids, which have also been shown in ESI‐MS to form M+• and [M + H]+, respectively. This study demonstrates, for the first time, the correlation of an extended conjugation and the presence of oxygen in the formation and balance of M+• or [M + H]+ for the carotenoids, neoxanthin, lutein, violaxanthin and zeaxanthin. Copyright © 2005 John Wiley & Sons, Ltd.
Effect of nitrogen nutrition on salt tolerance of Pisum sativum during vegetative growth
Authors: de Almeida Paula Figueira Etelvina M. , Nunes Caldeira Gustavo C.
Published: June 2005

The influence of different nitrogen (N) forms on salt tolerance of Pisum sativum L. was investigated. Plants of the pea cultivar “Resal” were subjected to 0 (control) or 90 mM NaCl and one of the following nitrogen forms: 5 mM mineral N supplied as either NO$ _3^- $, NH$ _4^+ $, or NH4NO3 or N supplied by biological N2 fixation (inoculated with Rhizobium leguminosarum bv. viciae). Root and shoot biomass were determined 15, 30, 45, and 60 d after emergence, and Na+, K+, and Cl– concentrations were determined by capillary electrophoresis. Nitrogen sources induced significant differences in plant growth and in ion accumulation and distribution and in differentially affected salt tolerance. In the absence of salt, the largest biomass accumulation was obtained with NH4NO3. In the presence of NaCl, NO$ _3^- $‐fed plants experienced less salt toxicity than plants supplied with other N sources, as indicated by lower Na+ and Cl– and higher K+ concentrations in the shoot. The results also suggest that it is possible to establish an effective symbiosis under saline conditions, provided that a salt‐tolerant Rhizobium isolate with good N2‐fixing ability is used. The use of the appropriate N‐fertilizer source can enhance the growth of Pisum sativum. Hence, NH4NO3 may be preferably used under non‐saline and NO$ _3^- $ under moderately saline conditions.
Root turnover of faba beans (Vicia faba L.) and its interaction with P and K supply
Authors: Steingrobe Bernd
Published: June 2005

An increased root turnover can be a mechanism of improved nutrient‐uptake efficiency. The objectives of this study were to investigate P and K efficiency of faba beans (Vicia faba L.), to determine their root growth and root turnover, and to assess the relevance of root turnover on P and K uptake at limited supply. Faba beans were grown as part of a long‐term fertilization experiment on fertilized plots (control) and plots that had not received any P or K fertilizer for 16 years (P0, K0). Although the unfertilized soils were low and very low in their P‐ and K‐supply level, respectively, no differences in shoot‐dry‐matter production occurred compared to the control. However, relative K concentration in dry matter of the K0 plants (control plants = 100) decreased during the experiment and was only 60% of the control at the final harvest. This indicated a high K‐utilization efficiency of faba bean. Relative phosphorus concentration increased in the P0 treatment and was not different from the control at the last harvest, indicating an improvement in P‐uptake efficiency with time. The size of the standing root system determined by sequential auger sampling (net development) was not influenced by P and K supply. Total root production as measured by the ingrowth‐core method was about 6 times higher than the average size of the standing root system and even increased under low‐K conditions. This indicated a fast root turnover. Modeling soil nutrient transport and uptake revealed that calculated uptake of the control was up to 48% higher when root turnover was taken into account, compared to calculations based on the net development of the root systems. This is due to a better soil exploitation. Under K shortage, root turnover resulted in a 117% higher calculated uptake, which was close to measured K uptake. Root turnover was also of benefit for P uptake, but calculated P uptake was significantly less than measured, indicating that root turnover was of little importance for P uptake of faba beans.
Diffusive flux of cationic micronutrients in two Oxisols as affected by low‐molecular‐weight organic acids and cover‐crop residue
Authors: Pegoraro Rodinei F. , Silva Ivo R. , Novais Roberto F. , Mendonça Eduardo S. , Alvarez Victor Hugo , Nunes Flancer N. , Fonseca Frederico M. , Smyth Thomas J.
Published: June 2005

Low‐molecular‐weight organic acids with one or more carboxylic groups are ubiquitous. In soils, they can originate from leaching of plants, litter decomposition, plant‐roots exudation, and microbial activity. Their presence in the soil may favor the formation of soluble organo‐metallic complexes that improve the transport of Zn, Cu, Fe, and Mn to plant‐root surfaces via diffusion. The current study sought to determine if some of the organic acids (OA) in soils and a cover‐crop residue influence the diffusive flux (DF) of Zn, Cu, Mn, and Fe. Two OA were added to two Oxisols (Typic Haplustox): a clayey Dark Red Latosol (DRL) and a sandy‐loam Red Yellow Latosol (RYL). Acetic and citric acid were added to achieve concentrations of 0, 250, 500, 1000, and 2000 mmol (m3 soil)–1. The effect of adding plant material (pearl millet) on the soil DF of the cationic micronutrients was also determined. Soil diffusive flux was evaluated by incubating positively charged and negatively charged exchange‐resin membranes with the soil in PVC diffusion chambers for 15 d. Desorption of Zn, Cu, Fe, Mn, and OA from the resins was performed with 0.5 mol l–1 HCl. The results demonstrated that the DF of the cationic micronutrients increased with the addition of organic acid. The DF of Zn and Mn occurred mostly towards the cationic resin, whereas the diffusive flux of Cu and Fe occurred mostly towards the anionic resin. Apparently, the dissolution of oxides and/or complexation of micronutrients adsorbed to the solid phase or in the soil solution contributed to the obtained results. Citric acid was more efficient than acetic acid in maintaining a larger DF value for Zn, Cu, and Fe. The addition of millet plant material to the soil increased the DF in the following order: Mn > Cu > Fe > Zn; Mn moved towards the cationic resin, and the other micronutrients moved towards the anionic resin. These findings suggest that organic compounds play an important role in the short‐distance transport of cationic micronutrients in highly weathered soils.
The umbric epipedon in the N Apennines, Italy—an example from the Vallombrosa Forest
Authors: Sanesi Guido , Certini Giacomo
Published: June 2005

The umbric epipedon is a diagnostic surface horizon recognized by both the World Reference Base for Soil Resources and the U.S. Soil Taxonomy. It is mainly characterized by a dark color, a moderate to high content of OM, and a base saturation of less than 50%. In the N Apennines, Central Italy, forest soils over 600–700 m a.s.l. often have this epipedon. This paper stresses the morphological, chemical, and biological properties of the epipedon, specifically in the Vallombrosa Forest, where considerable work has been done in the last decade. Here, the umbric epipedon forms on sandstone, in high forests of Abies alba, Fagus sylvatica, and Castanea sativa. It does not have homogeneous properties throughout its thickness and often is divided into two distinct genetic horizons, A1 and A2. The A1 horizon is thinner, darker, and richer in OM, more base‐saturated, and biologically more active than the underlying A2 horizon. The mean residence time of the bulk OM amounts to about a century in the A1 horizon, versus half a millennium in the A2. In both A1 and A2 horizons, the non‐humic fraction prevails in the OM; this could account for the high susceptibility of the umbric epipedon to degrade when the forest is clear‐cut or undergoes extensive uprooting due to windstorms or heavy snow loads. Significant discrepancies between the two A horizons have been found in regard to the microbial community. Umbric epipedons which developed under different tree species show minor differences, mainly concerning the microbial community.