bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of peptides by liquid chromatography/electrospray ionization mass spectrometry using silver nitrate as a post‐column complexant
Authors: Cheguillaume Ghislain , Buchmann William , Desmazières Bernard , Tortajada Jeanine 
Published: March 2004

AbstractTwo model peptides, des‐Arg1‐bradykinin (DAB) and bradykinin (B), were cationized by Ag+ after their separation by reversed‐phase liquid chromatography (RPLC) prior to mass spectrometry (MS). Silver nitrate solution was used as a post‐column reagent. The RPLC and MS experimental conditions were optimized using flow injection in order to obtain sufficiently abundant silver adducts to permit MS/MS experiments. The use of water–methanol with 0.1% formic acid as mobile phase allowed a good chromatographic separation of the two peptides with a polymeric stationary phase and sufficiently abundant silver‐containing adducts, [M + Ag + H]2+ and [M + 2Ag]2+. The gas‐phase dissociation of [DAB + Ag + H]2+ and [DAB + 2Ag]2+ led to interpretable mass spectra during the on‐line cationization experiment. Most of the ions obtained by dissociating [DAB + Ag + H]2+ and [DAB + 2Ag]2+ species are silver‐containing ions but the ions produced depend on the parent. The ions coming from the dissociation of the doubly charged silver adducts [DAB + Ag + H]2+ or [DAB + 2Ag]2+ are of interest compared with those coming from the singly charged silver species or doubly charged protonated species. The fragmentation of the doubly charged silver adducts provides ions over the entire mass range. Although the presence of several prolines in des‐Arg1‐bradykinin prevents the formation of some expected ions, the observation of triplets [an−H + Ag]+, [bn−H + Ag]+ and [bn + OH + Ag]+ produced by the dissociation of on‐line Ag+‐cationized peptides could contribute to greater success of automatic sequencing of peptides. Copyright © 2004 John Wiley & Sons, Ltd.
Determination of fatty acid positions in native lipid A by positive and negative electrospray ionization mass spectrometry
Authors: Sforza Stefano , Silipo Alba , Molinaro Antonio , Marchelli Rosangela , Parrilli Michelangelo , Lanzetta Rosa 
Published: March 2004

AbstractLipid A is the endotoxic principle of the lipopolysaccharide fraction from Gram‐negative bacteria. It is involved in the elicitation of cytokine production that leads to massive inflammation and to septic shock as a lethal consequence. For this reason, the structural elucidation of lipopolysaccharides from toxic Gram‐negative bacteria is an important and complicated task, mainly owing to its natural heterogeneity. Here, a new methodology to infer the distribution of the primary and secondary acyl residues is described, based on electrospray ionization mass spectrometry (ESI‐MS) of intact lipid A under high cone voltage in order to achieve in‐source fragmentation. Under these conditions, acyl fragmentation is induced and a different regioselective cleavage of secondary fatty acids is observed in positive and negative ESI‐MS, allowing the rapid identification of the lipid A structure. Copyright © 2004 John Wiley & Sons, Ltd.
Comparison of sustained off‐resonance irradiation collisionally activated dissociation and multipole storage‐assisted dissociation for top‐down protein analysis
Authors: Keller Karin M. , Brodbelt Jennifer S. , Hettich Robert L. , Berkel Gary J. Van 
Published: March 2004

AbstractTandem mass spectrometric data acquired for small (8–18 kDa) intact proteins by sustained off‐resonance irradiation collisionally activated dissociation (SORI‐CAD) and multipole storage‐assisted dissociation (MSAD) were compared, and the results indicate that the two activation methods do not always provide the same fragmentation patterns. In MSAD experiments, the charge state distribution made available by the ionization conditions may dictate the range of fragment ions that can be generated. In addition, conditions of high space charge within the hexapole impair transmission and/or trapping of high m/z species, which can result in loss of important precursor and product ions. Finally, the non‐resonant nature of activation in MSAD can provide access to secondary dissociation processes that are not available by SORI. Because of these considerations, MSAD is less reliable than SORI for generating sequence tag data. However, it appears that MSAD samples ‘preferred’ cleavage processes (i.e. those occurring at D and P residues) just as well as SORI, which implies that MSAD data may be somewhat more compatible with search algorithms that utilize unprocessed fragment ion masses. Copyright © 2004 John Wiley & Sons, Ltd.
Identification of the hydrolysis products of AlCl3·6H2O by electrospray ionization mass spectrometry
Authors: Sarpola Arja , Hietapelto Vesa , Jalonen Jorma , Jokela Jukka , Laitinen Risto S. 
Published: March 2004

AbstractThe hydrolysis reactions of AlCl3 in 0.1 M aqueous solutions at pH 3.27–4.20 were monitored by electrospray ionization time‐of‐flight mass spectrometry (ESI‐ToF MS) as a function of time. The cationic and anionic ESI mass spectra of aluminum(III) solutions gave strong evidence of the presence of a variety of monomeric and polymeric complexes. Competition between the OH− and Cl− ligands within the same aluminum core was observed. The influence of the sample cone voltage on the product distribution was also explored. The optimum sample cone voltage for the cationic spectra was 70 V. For the anionic spectra no optimum sample cone voltage was found and the appearance of the anionic spectra was strongly dependent on the sample cone voltage within the whole range explored. Copyright © 2004 John Wiley & Sons, Ltd.
A novel class of chemically modified iodo‐containing resins: design, synthesis and application to mass spectrometry‐based proteome analysis
Authors: Zhang Li , Guo Yin‐Long , Liu Han‐Qing 
Published: March 2004

AbstractA novel class of chemically modified iodo‐containing resins with isotope‐labeled tagging for mass spectrometry‐based proteome analysis is described. This iodo‐containing resin contains a thiol‐reactive group that is used to capture the cysteine (Cys)‐containing peptides from peptide mixtures, one ‘tag’ amino acid, and an aminomethyl polystyrene resin with Rink Amide Linker. The ‘tag’ amino acid is synthesized in both heavy and light isotope‐coded forms and therefore permits the direct relative quantification of peptides/proteins through mass spectrometric analysis. In the iodo‐containing resin strategy, the Cys‐containing peptides of two samples covalently captured by either light or heavy iodo‐containing resin were mixed and washed extensively under stringent conditions. Then the Cys‐containing peptides were retrieved by acid‐catalyzed elution. Finally, the eluted peptides were directly analyzed by micro liquid chromatography/mass spectrometry for identification and relative quantification. The iodo‐containing resins were synthesized by a simple but effective method. Their abilities to identify and quantify the Cys‐containing part in two samples were proved by the analysis of mixtures of amino acids, peptides and proteins. Copyright © 2004 John Wiley & Sons, Ltd.
Method of moments modelling of cylindrical microwave integrated circuits interconnections
Authors: Al Salameh M. S. , Olaimat A. M. 
Published: March 2004

AbstractIn this paper, a numerical technique suitable for characterizing a wide variety of interconnection configurations printed on cylindrical surfaces, is presented. The interconnection lines may have either finite or infinitesimal cross‐sections. To model cylindrical interfaces, suitable space‐domain integral equations are formulated to represent the potential on conductors and electric field at dielectric interfaces. The solution of the integral equations is then obtained numerically by applying the method of moments (MOM). The objective of this approach is to determine the capacitance matrix of cylindrical interconnection systems with different configurations. From the capacitance matrix, other quantities such as characteristic impedance, coupling coefficient and effective permittivity can be determined. The numerical technique described in this paper is implemented as a general computer program. Various circular cylindrical as well as elliptical cylindrical structures have been solved including microstrip lines and coplanar waveguide lines. The results obtained compare very well with other published data. Copyright © 2004 John Wiley & Sons, Ltd.
Input resistance is voltage dependent due to activation of Ih channels in rat CA1 pyramidal cells
Authors: Surges Rainer , Freiman Thomas M. , Feuerstein Thomas J. 
Published: March 2004

AbstractThe contribution of the hyperpolarization‐activated cation current (Ih) to input resistance (RN) and resting potential (RP) was investigated during whole‐cell patch‐clamp recordings in CA1 pyramidal cells of rat hippocampal slices. In current‐clamp mode, RN was determined at different membrane potentials. RN decreased with increasing hyperpolarization, from about 260 MΩ to 140 MΩ at potentials of about −60 mV and −110 mV, respectively. Both the potential of half‐maximal reduction of RN and the potential of half‐maximal Ih activation (determined in voltage‐clamp mode) were approximately −90 mV. The analysis of the voltage sag indicative of Ih activation revealed a preferential activity of Ih channels in a voltage range between −70 and −95 mV. ZD7288 (50 μM), a specific Ih blocker, led to a hyperpolarization by about 4.8 mV, increased RN by approximately 45% within a potential range between −65 and −80 mV, and abolished the voltage dependence of RN. Gabapentin (GBP, 100 μM), an Ih channel agonist, led to a depolarization by about 2.4 mV and reduced RN by about 20% within a potential range between −65 and −80 mV. In conclusion, our data show that RN is voltage dependent due to Ih channel activation and that Ih channels are preferentially active at voltages between −70 and −95 mV. Furthermore, we demonstrated that RN can be modulated by antiepileptic drugs such as GBP, which may partly explain its antiepileptic effect as due to decreasing the sensitivity to excitatory input. © 2004 Wiley‐Liss, Inc.
Mulching effects on phosphorus and sulfur concentrations in a Miamian soil in central Ohio, USA
Authors: Saroa G. S. , Lal R. 
Published: March 2004

AbstractIn addition to nitrogen (N), phosphorus (P) and sulfur (S) elements are also essential to conversion of biomass carbon into soil humus. Therefore, soil analyses were done on two long‐term mulching experiments initiated in 1989 and 1996 on a Crosby silt loam (Aeric Ochraqualf or Stagnic Luvisol) soil in central Ohio to assess P and S dynamics in soil for different rates of mulching. Mulch treatments were 0, 8 and 16 Mg ha−1 y−1 without any crop cultivation. Our objectives were to assess: (i) the effect of different mulch rates on P and S concentrations, and soil organic carbon sequestration; (ii) association of available and total P and S with different particle size fractions; and (iii) temporal changes in available and total P and total S concentrations within aggregate and particle size fractions with duration of mulching. Soil samples from 0 to 5 and 5 to 10 cm depths were obtained in November 2000. Mulch rate significantly increased Bray‐P in 0 to 5 and 5 to 10 cm depths but had no significant effect on total P after 4 years of mulching. Total P concentration in the 5 to 10 cm layer increased significantly with mulch application after 11 years, but the total S concentration was not affected. Total P in aggregates>2 mm size at 5 to 10 cm depth was significantly higher than whole soil after 11 years of mulching. More than 50 per cent of the total P was associated with clay fraction, and P concentration increased with duration of mulching. The enrichment factor for total P was in the order: clay>sand>silt. Total S concentration in aggregates increased with increase in aggregate size for both depths, and was in the order: clay>sand>silt. The clay fraction accounted for 48 per cent of total S after 4 years of mulching and 50 per cent after 11 years of mulching. The enrichment factor of S in clay and sand fractions increased with duration of mulching and with depth for clay, and decreased for sand. The C:P and C:S ratios decreased both with duration of mulching and particle size. Availability of P and S is essential for humification of carbon input in crop residue mulch. Copyright © 2004 John Wiley & Sons, Ltd.
Erosion Induced Controllable Release of Gliclazide Encapsulated Inside Degradable Polymeric Particles
Authors: Zhao Yue , Chen Wenna , Cai Qing , Wang Shenguo , Bo Jun , Wu Chi 
Published: March 2004

AbstractSummary: The microphase inversion of water‐insoluble poly(L‐lactide), “poly[(L‐lactide)‐co‐glycolide] and polylactide‐block‐poly(ethylene oxide)‐block‐polylactide from THF to water can result in narrowly distributed stable particles. Gliclazide, a commercial drug, can be encapsulated inside during the process. The formation and degradation of such particles was studied by laser light scattering. In comparison with the corrosion of a bulk material, the degradation of each particle is so fast that we only detect the decrease of the particle number, not the corrosion of individual particles. Therefore, the degradation is a “one‐by‐one” random process, just like the chemical reaction of molecules in solution. The disappearing rate of the particle number is nearly independent of time, ideal for the controlled release of drugs encapsulated inside. The amount of encapsulated gliclazide depends on the copolymer's hydrophobicity (composition), while the releasing rate mainly is, directly related to the disappearing rate of the particles. The correlation between the fluorescence intensity and the degradation was used to study the kinetics of gliclazide releasing. The releasing pattern is controllable with a proper choice of the drug loading, copolymer composition, pH and temperature.image
Biosynthesis and Compositional Regulation of Poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyhexanoate)] in Recombinant Ralstonia eutropha Expressing Mutated Polyhydroxyalkanoate Synthase Genes
Authors: Tsuge Takeharu , Saito Yu , Kikkawa Yoshihiro , Hiraishi Tomohiro , Doi Yoshiharu 
Published: March 2004

AbstractSummary: A new strategy for bacterial polyhydroxyalkanoate (PHA) production by recombinant Ralstonia eutropha PHB−4 harboring mutated PHA synthase genes (phaCAc) from Aeromona caviae was investigated. The strain harboring wild‐type phaCAc gene produced a PHA copolymer consisting of (R)‐3‐hydroxybutyrate and (R)‐3‐hydroxyhexanoate [P(3HB‐co‐3HHx)] with 3.5 mol‐% of 3HHx fraction from soybean oil. When the mutants of phaCAc gene were applied to this production system, 3HHx fraction in copolymers was varied in the range of 0–5.1 mol‐%. Thus, the regulation of PHA copolymer compositions has been achieved by the use of mutated PHA synthase genes.Relationship between PHA synthase activity and 3HHx fraction in P(3HB‐co‐3HHx).imageRelationship between PHA synthase activity and 3HHx fraction in P(3HB‐co‐3HHx).
Ring‐Opening Polymerization of L‐Lactide and Preparation of Its Microsphere in Supercritical Fluids
Authors: Pack Ji Won , Kim Soo Hyun , Park Soo Young , Lee Youn‐Woo , Kim Young Ha 
Published: March 2004

AbstractSummary: The ring‐opening polymerization of L‐lactide initiated by stannous octoate was carried out in supercritical chlorodifluoromethane (scR22) at various reaction conditions (time and temperature) and reactant concentrations (initiator, monomer, and solvent). The monomer conversion increased to ca. 70% on increasing the reaction time to 1 h. The molecular weight of the poly(L‐lactide) (PLLA) product also increased to ca. 160 000 g · mol−1 over the same period. Increasing reaction temperature from 90 to 130 °C resulted in increased monomer conversion and PLLA molecular weight. A series of polymerizations conducted at various 1‐dodecanol and stannous octoate concentrations suggested that stannous octoate does not act as an initiator by itself, and that the tin‐alkoxide formed from 1‐dodecanol and stannous octoate serves as the initiating species in scR22. While enhancements of the monomer conversion and PLLA molecular weight were observed with increasing monomer concentration, the chlorodifluoromethane concentration had the opposite on both. After the polymerization, PLLA microspheres were prepared in situ by using a continuous supercritical antisolvent process without residual organic solvent and monomer to yield highly purified microspheres for environmental and biomedical applications.Relation between monomer conversion (○) and poly(L‐lactide) molecular weight (•).imageRelation between monomer conversion (○) and poly(L‐lactide) molecular weight (•).
Fermentative Production of Chemicals That Can Be Used for Polymer Synthesis
Authors: Lee Sang Y. , Hong Soon H. , Lee Seung H. , Park Si J. 
Published: March 2004

AbstractSummary: The fermentative production of chemicals that can be used as monomers for the synthesis of polymers has become an important topic in biotechnology research because of the limited nature of petroleum and environmental issues. In particular, the fermentative production of metabolites such as dicarboxylic acids, amino acids, and diols, which are suitable as building blocks for subsequent polymerization, has attracted much attention. Various wild‐type and metabolically engineered microorganisms have been developed for the efficient production of these chemicals from renewable resources. In addition, the development of fermentation strategies to achieve the highest possible productivities has been another focus of research, considering that these monomers should be produced at costs low enough to compete with petroleum‐derived ones. In this paper, the metabolic pathways leading to the synthesis of such important monomers including succinic acid, lactic acid, fumaric acid, propan‐1,2‐diol, and propan‐1,3‐diol are reviewed. In addition, the metabolic engineering and fermentation strategies for their production are reviewed.image
Biodegradable Water Absorbent Synthesized from Bacterial Poly(amino acid)s
Authors: Kunioka Masao 
Published: March 2004

AbstractSummary: Biodegradable hydrogels prepared by γ‐irradiation from microbial poly(amino acid)s have been studied. pH‐Sensitive hydrogels were prepared by the γ‐irradiation of poly(γ‐glutamic acid) (PGA) produced by Bacillus subtilis and poly(ε‐lysine) (PL) produced by Streptomyces albulus in aqueous solutions. When the γ‐irradiation dose was 19 kGy or more, and the concentration of PGA in water was 2 wt.‐% or more, transparent hydrogels could be produced. For the 19 kGy dose, the produced hydrogel was very weak, however, the specific water content (wt. of absorbed water/wt. of dry hydrogel) of this PGA hydrogel was approximately 3 500. The specific water content decreased to 200, increasing when the γ‐irradiation dose was over 100 kGy. Under acid conditions or upon the addition of electrolytes, the PGA hydrogels shrunk. The PGA hydrogel was pH‐sensitive and the change in the volume of the hydrogel depended on the pH value outside the hydrogel in the swelling medium. This PGA hydrogel was hydrodegradable and biodegradable. A new novel purifier reagent (coagulant), made from the PGA hydrogels, for contaminated turbid water has been found and developed by Japanese companies. A very small amount of this coagulant (only 2 ppm in turbid water) with poly(aluminum chloride) can be used for the purification of turbid water.A PL aqueous solution also can change into a hydrogel by γ‐irradiation. The specific water content of the PL hyrdogel ranged from 20 to 160 depending on the preparation conditions. Under acid conditions, the PL hydrogel swelled because of the ionic repulsion of the protonated amino groups in the PL molecules. The rate of enzymatic degradation of the respective PL hydrogels by a neutral protease was much faster than the rate of simple hydrolytic degradation.image
Grafting of Polystyrene onto Poly(butyl acrylate) and Polystyrene Backbones Using Functionalized Methacrylates
Authors: Böhme Karsten , Peppers Michel , Schmidt‐Naake Gudrun 
Published: March 2004

AbstractSummary: Grafting of terminal epoxide‐functionalized polystyrene onto poly[styrene‐co‐(2‐hydroxyethyl methacrylate)] or poly[(butyl acrylate)‐co‐(2‐hydroxyethyl methacrylate)] backbones was carried out by coupling reactions catalyzed by boron trifluoride. The functionalized backbones were prepared by free radical copolymerization of 2‐hydroxyethyl methacrylate (HEMA) with styrene or butyl acrylate. For the synthesis of terminal functionalized polymer chains a side reaction of the TEMPO‐mediated free radical polymerization of methacrylates could be used successfully to convert TEMPO‐terminated polymers into terminal epoxide‐functionalized polymers by the use of glycidyl methacrylate. The number of epoxide units attached to the backbone was directly related to the TEMPO concentration during the disproportionation reaction. Taking P(S‐co‐HEMA) as well as P(BuA‐co‐HEMA) backbones in coupling reactions with different epoxy‐functionalized polystyrenes in the presence of boron trifluoride, graft polymers with up to 7 and 37 side chains per backbone were produced.Molecular weight distribution curves of a linking experiment between P(BuA‐co‐HEMA) backbones and epoxide‐functionalized polystyrene side chains.magnified imageMolecular weight distribution curves of a linking experiment between P(BuA‐co‐HEMA) backbones and epoxide‐functionalized polystyrene side chains.
Stable Free Radical Polymerization Kinetics of Alkyl Acrylate Monomers Using in situ FTIR Spectroscopy: Influence of Hydroxyl‐Containing Monomers and Additives
Authors: Lizotte Jeremy R. , Long Timothy E. 
Published: March 2004

AbstractSummary: The homopolymerization and copolymerization of various alkyl acrylate monomers was studied under stable free radical polymerization (SFRP) conditions using in situ FTIR spectroscopy to monitor polymerization kinetics. The IR absorbance corresponding to the CH deformation of the monomer (968 cm−1) was measured to determine monomer conversion in real‐time fashion. The monomer disappearance profiles were subsequently converted to pseudo‐first order kinetic plots. Altering the alkyl ester chain length and configuration did not reveal a significant trend in the resulting polymerization kinetics. However, addition of 2‐hydroxyethyl acrylate (HEA) to a polymerization of n‐butyl acrylate (nBA) substantially accelerated the rate of total monomer conversion, increasing the observed rate constant almost two times. 1H NMR spectroscopy also showed that the resulting HEA/nBA copolymers were enriched with the HEA monomer. Moreover, a similar but enhanced effect was also observed upon the addition of small amounts of dodecanol to an n‐butyl acrylate homopolymerization resulting in more than a doubling of the observed rate constant.Resonance forms associated with the DEPN nitroxide and stabilization resulting from hydrogen bonding.magnified imageResonance forms associated with the DEPN nitroxide and stabilization resulting from hydrogen bonding.