bluuebunny/crossref_metadata_2025_split huggingface dataset:
On‐line LC‐GC method for determination of isomers of nervonic acid in meat‐derived food
Authors: Barcarolo Robertino , Bau Andrea , Moreno Josefa Barrero , Dimitrova Burya , Anklam Elke 
Published: October 2003

AbstractAn on‐line liquid chromatography‐gas chromatography (LC‐GC) method for determination of the cis/trans isomers of nervonic acid in meat‐derived food is described. The technique used a home‐assembled LC‐GC coupled system. A simple LC clean‐up procedure using an analytical gel permeation (5 μm) column and 1% ethyl acetate in hexane as mobile phase has proved to be suitable for the isolation and purification of fatty acid methyl esters from the meat matrix. Use of a silica gel (5 μm) pre‐column improved the separation of cis/trans nervonic acid from cholesterol and the more polar constituents of the extracted fraction. GC analyses were performed using a non‐polar GC column and mass spectrometry (MS) for identification of the analytes and flame ionization detector (FID) for quantification of the compounds studied. Excellent linearity with correlation coefficients higher than 0.999 in the range of 0.05–10 μg mL–1 nervonic acid and a good repeatability with relative standard deviation (RSD) values generally lower than 4% was obtained. The method developed provides a high sensitivity for trace analysis of the cis/trans isomers of nervonic acid and enables complete automation.
Open tubular liquid chromatographic separations using an aptamer stationary phase
Authors: Clark Stacey L. , Remcho Vincent T. 
Published: October 2003

AbstractAptamers are oligonucleotides which are isolated in vitro based on their affinity for a target molecule. These molecules hold promise for use in analytical methods which rely on molecular recognition. In this study, we report the immobilization of an RNA aptamer on the inner walls of fused silica capillaries. Due to the small size of these molecules, the resulting surface coverage of these capillaries made them suitable for use in open tubular liquid chromatographic studies. These capillaries also exhibited stability when an organic modifier was added to the mobile phase. These characteristics of aptamers make them desirable over traditional affinity chromatography stationary phases.
Multi‐compound methods for the detection of pharmaceutical residues in various waters applying solid phase extraction (SPE) and gas chromatography with mass spectrometric (GC‐MS) detection
Authors: Reddersen Kirsten , Heberer Thomas 
Published: October 2003

AbstractThis paper describes two highly sensitive analytical methods for the unambiguous determination of pharmaceutical residues and related polar contaminants in environmental water samples. Both analytical methods use solid phase extraction (SPE), chemical derivatization, and detection of the analytes by capillary gas chromatography‐mass spectrometry (GC‐MS) with selected ion monitoring (SIM). Using the two methods, a total of 19 pharmaceuticals and 7 related polar contaminants, most of them pesticides, can be detected and quantified down to the low ng/L range in sewage, surface, ground, and drinking water. Recoveries between 70 and 110% and standard deviations of less than 15% were determined for 21 analytes when applying the analytical method that uses pentafluorobenzyl bromide (PFBBr) for derivatization. The second method, which employs N‐(t‐butyldimethylsilyl)‐N‐methyltrifluoroacetamide (MTBSTFA) for derivatization was found to be slightly less sensitive and reproducible but it also permitted the analysis of several other environmentally important compounds such as the antiepileptic drugs carbamazepine or primidone. From spiking experiments, limits of detection (LODs) between less than 1 and 10 ng/L and limits of quantification (LOQs) between 1 and 40 ng/L were calculated.
Polymer‐bound cellulose phenylcarbamate derivatives as chiral stationary phases for enantioselective HPLC
Authors: Ling Frank , Brahmachary Enugurthi , Xu Mingcheng , Svec Frantisek , Fréchet Jean M. J. 
Published: October 2003

AbstractNovel chiral stationary phases (CSP) have been prepared by coating the internal surface of monodisperse macroporous poly(2‐aminoethyl methacrylate‐co‐ethylene dimethacrylate) beads with dimethylphenylcarbamate derivatives of regenerated cellulose. The coating was achieved either by simple adsorption or by chemical bonding using a diisocyanate linker. Separation of enantiomers in normal‐phase HPLC mode was used to evaluate the enantioselectivity of all CSPs. The influence of the properties of the polymer support such as pore size, pore volume, and content of the amine functionalities, reaction and separation conditions such as weight ratio of modified cellulose selector to polymer beads, amount of diisocyanate crosslinker, and the composition of the mobile phase on chiral discrimination and chromatographic resolution were also systematically investigated. The CSPs prepared by chemical anchoring were more stable and a wider range of solvents including dichloromethane could be used for the separations. Compared to the coated‐type CSPs, the chemically bonded stationary phases enabled the enantioseparations of a larger number of racemates and exhibited enantioselectivity fully comparable to their counterparts prepared using porous silica as a support. However, the benefits of tailored macroporous polymer supports demonstrated earlier with brush‐type CSPs did not enhance the performance of the chiral stationary phases prepared from cellulose‐based selectors.
Analysis of tramadol in pharmaceutical preparations by high performance thin layer chromatography
Authors: Meyyanathan S. N. , Kumar Pradeep , Suresh B. 
Published: October 2003

AbstractA new simple, precise, rapid, and selective high‐performance thin layer chromatography (HPTLC) method has been developed for the analysis of tramadol in pharmaceutical formulations. The method uses chlorzoxazone as an internal standard. The stationary phase was silica gel 60F254 prewashed with methanol; ethyl acetate‐methanol‐ammonia solution 7 + 1 + 0.5 (v/v) was used as mobile phase. Detection and quantification were performed densitometrically at λ = 275 nm. The linear range of the analysis was 1.0–2.5 μg and the percentage recovery was 104.6%.
Enantiomeric resolution of some human aldosterone synthase [CYP 11 B2] inhibitors on derivatized polysaccharide chiral stationary phases
Authors: Aboul‐Enein Hassan Y. , Hefnawy Mohamed M. , Ehmer Peter B. , Hartmann Rolf W. 
Published: October 2003

AbstractAldosterone synthase (CYP 11 B2) is a mitochrondrial cytochrome P450 enzyme catalyzing the last steps of aldosterone production in the adrenal cortex. A new pharmacological approach for the treatment of the aldosterone‐induced effects in congestive heart failure and all forms of hyperaldosteronism could be achieved through the use of (CYP 11 B2) inhibitors. The chiral resolution of some of active compounds, namely 1‐(4‐pyridyl(methyl)tetralin (I)), 7‐chloro‐1‐(1‐imidazolyl)tetralin (II), and 5‐hydroxy‐2‐(4‐pyridylmethyl)indane (III), on various polysaccharide derivative chiral stationary phases, namely Chiralcel OD, OJ, OC, and Chiralpak AD and AS, in normal phase mode was achieved. The mobile phase used was hexane/2‐propanol/triethylamine (9 : 1 : 0.1 v/v/v). The flow rate of the mobile phase was 0.8 mL/min and the wavelengths of detection of compounds I, II, and III were set at 288, 271, and 254 nm, respectively. The chromatographic parameters: retention factor (k), selectivity (α), and resolution factor (Rs) were calculated. The chiral recognition mechanisms between these analytes and chiral selectors are discussed.
A trifluoropropyl‐containing silphenylene–siloxane terpolymer for high temperature gas chromatography
Authors: Mayer Bernhard X. , Rauter Walfried , Kählig Hanspeter , Zöllner Peter 
Published: October 2003

AbstractA silanol terminated tetramethyl‐p‐silphenylene–3,3,3‐trifluoropropylmethyl, dimethyl siloxane terpolymer was prepared by a condensation reaction. Its chemical composition and microstructure were characterized by 1H and 29Si nuclear magnetic resonance spectroscopy. The polymer was coated on fused silica capillary columns in order to evaluate its gas chromatographic properties. At moderate temperatures its selectivity is similar to that of medium polarity stationary phases; at high temperatures, however, the interactions between stationary phase and unsaturated triacylglycerols are reduced to such an extent that the typical GC behavior of an apolar phase could be observed. Furthermore, the columns showed high separation efficiency and a good inertness of the fused silica surface. Relatively low column bleed permitted a maximum allowable operating temperature of 360°C. These capillary columns were used to determine the distribution of the carbon numbers of triacylglycerols in extracts of human subcutaneous adipose tissue. Thermal treatment of the columns at 400°C leads to a high degree of immobilization associated with reduced column bleed and a slightly changed selectivity, which indicates that a crosslinking process has taken place. Nevertheless, decreased separation efficiency and the thermal instability of the trifluoropropyl group would indicate that the capillary columns should be used at temperatures < 380°C.
Experimental evaluation of possible side effects of intra‐operative photodynamic therapy on rabbit blood vessels and nerves
Authors: Kübler Alexander C. , Stenzel W. , Rühling M. , Meul B. , Fischer J.‐H. 
Published: October 2003

AbstractBackground and ObjectivesTumours of the head and neck show a high local tumour recurrence rate ranging between 7 and 30% despite combined treatment modalities. To improve these data, photodynamic therapy (PDT) might be used as an additional treatment besides surgery and radio‐chemotherapy. Intra‐operative PDT has been proposed to “sterilise” the tumour bed after surgical tumour resection in order to kill any remaining tumour cells which are responsible for local tumour recurrences. Often, during head and neck surgery, large blood vessels and important nerve structures are exposed and could potentially be harmed by intra‐operative PDT. Despite the fact that mTHPC is the most commonly used photosensitiser for head and neck tumours, there are no data on potential detrimental side effects of intra‐operative PDT onto these vital structures. The purpose of this study was to use a maximal treatment protocol in rabbit observing possible damage to the blood vessels and nerve structures and thus judge the most severe event that could happen in patients.Study Design/Materials and MethodsIn rabbits the large blood vessels and nerve structures at the neck and at the groin area were surgically exposed and treated by mTHPC‐mediated intra‐operative PDT. Various treatment parameters (drug‐light interval, light dosage, follow up interval) were modified in order to find the critical treatment parameters which might cause maximum tissue effects. The intention was to define the most severe clinical complications which could be expected from mTHPC mediated intra‐operative PDT.ResultsThe most severe tissue reactions were found at a drug dosage of 0.3 mg/kg, a drug‐light interval of 24 hours and a light dosage of 20 J/cm2. Complete necrosis was found for the muscles, fat and connective tissue within the entire treatment field. Blood vessels demonstrated severe oedema, media‐hyperplasia or loosening of the endothelial layer leading to various degrees of local thrombosis but no break down of the vessel wall or any rupture was noted. Most nerves were altered by a 75% demyelisation but this did not result in any clinical symptoms.ConclusionsOur results have shown that mTHPC mediated intra‐operative PDT used with a maximal treatment protocol (very high doses and very short drug‐light intervals) has significant histological impact onto all tissue structures, but did not show any clinical symptoms in rabbits. mTHPC mediated intra‐operative PDT seems to be a promising and a safe treatment option which could complement existing treatment modalities in order to improve total survival rate of tumour patients. Lasers Surg. Med. 33:247–255, 2003. © 2003 Wiley‐Liss, Inc.
Influence of an optically thick water layer on the bond‐strength of composite resin to dental enamel after IR laser ablation
Authors: Staninec Michal , Xie John , Le Charles Q. , Fried Daniel 
Published: October 2003

AbstractBackground and ObjectivesSeveral studies of hard tissue ablation with Er:YAG lasers have shown that the addition of an optically thick water layer (∼1 mm) added to the surface of dental enamel before each incident laser pulse, profoundly influences the rate and efficiency of ablation and the resulting surface morphology. The objective of this study was the determination of laser parameters which result in clinically useful bond strengths without the need for phosphoric acid etching. The hypothesis to be tested was that laser irradiation through a relatively thick layer of water would result in a surface to which composite could be bonded with bond strength similar to surfaces etched with phosphoric acid. This hypothesis is predicated on the assumption that the water prevents the formation of non‐apatite calcium phosphate phases on the enamel surface.Materials and MethodsIn this study, a calibrated syringe pump and a motion control system were used to uniformly treat flat enamel surfaces using free‐running Er:YAG laser pulses with and without water, and 9.6 μm CO2 laser pulses on a dry surface for comparison. The rate of water delivery that resulted in the most efficient ablation was determined by profiling the resulting laser incisions using optical coherence tomography. In addition, enamel surfaces of 5 × 5 mm2 were uniformly treated and the resulting surface morphology was examined using synchrotron radiation‐fourier transform infrared spectroscopy (SR‐FTIR), and optical and electron microscopy. The influence of the modified surface morphology on the adhesion of composite resin was investigated.ResultsThe shear‐bond strength of composite bonded to enamel surfaces irradiated at intensities clinically relevant for caries removal approached values measured for conventional acid etching when the water delivery rate was optimized.ConclusionsThis study demonstrates that composite restorative materials can be directly bonded to laser prepared surfaces without the necessity of further surface preparation and acid etching and that the addition of a thick water layer (∼1 mm) prevents the formation of undesirable CaP phases that compromise adhesion to restorative materials. Lasers Surg. Med. 33:264–269, 2003. © 2003 Wiley‐Liss, Inc.
The role of ring‐ring equilibria in thermodynamically controlled polycondensations
Authors: Kricheldorf Hans R. 
Published: October 2003

AbstractThermodynamically controlled polycondensations (TCPs) involve rapid equilibration reactions, such as transesterification, transamidation, etc. An important component of these equilibration reactions is the reversible formation of cyclic oligomers and polymers by “back‐biting”. Therefore, TCPs were described in the previous literature in terms of ring‐chain equilibria. The present study presents a complementary theory saying that ring‐chain equilibria automatically include ring‐ring equilibria which gain in importance with higher conversions because the molar ratio of rings versus linear chains rapidly increases. At 100% conversion, all reaction products will be cycles and the ring‐ring equilibria limit the chain growth. Several polycondensations cited from the literature are discussed in the light of the new theory.
Nonstoichiometric polycondensation I. synthesis of polythioether from dibromomethane and 4,4′‐thiobisbenzenethiol
Authors: Iimori Hirokazu , Shibasaki Yuji , Ando Shinji , Ueda Mitsuru 
Published: October 2003

AbstractHigh molecular weight poly(phenylene thioether) (3) was successfully obtained by the polycondensation of 4,4′‐thiobisbenzenethiol (1) and dibromomethane (2) with a variety of feed ratios in the presence of 1,8‐diazabicyclo[5,4,0]undec‐7‐ene (DBU) in 1‐methyl‐2‐pyrrolidinone (NMP) at 75°C. The resulting polymer showed the maximum inherent viscosity (ηinh) of 0.50 dL/g in 4 h when 1.5 equivalents excess of 2 was used. The model reaction using benzenethiol (4) and dichloromethane (5) in the presence of DBU in deuterated dimethylsulfoxide (DMSO‐d6) at 25°C indicated that the rate of the second nucleophilic displacement reaction (k2) is 61 times faster than that of the first one (k1). The maximum of theoretical molecular weights calculated at various stoichiometric imbalance (S) under the condition of k2/k1 = 61 showed a good agreement with the experimental molecular weights at specific polymerization times.
Polyaddition reaction in a dispersed medium: elaboration of new core‐shell polyurethane particles
Authors: Chambon Pierre , Radhakrishnan Bindushree , Cloutet Eric , Papon Eric , Cramail Henri 
Published: October 2003

AbstractThe elaboration in a dispersed organic medium of calibrated polyurethane particles with a core‐shell structure is presented in this paper. The objective could be achieved by using a series of reactive steric stabilizers of the type ω‐(OH)x‐poly(n‐butyl acrylate), ‐polystyrene, ‐polysiloxane or ‐polybutadiene (x=1 or 2) that play the role of surfmers during the polyaddition reaction between ethylene glycol and tolylene‐2,4‐diisocyanate, in cyclohexane as a dispersant medium. The final size of the polyurethane particles (0,5‐10 μm) was found to be a function of the steric stabilizer characteristics (nature, molar mass and concentration) and of the addition procedure of the different reactants. These novel particles constituted of a polyurethane core and various shells depending on the stabilizer used exhibit specific and original properties.
Control of macromolecular architecture of polyamides by poly‐functional agents. 2. Use of oligomerization in polycondensation study
Authors: Yuan Cuiming , Di Silvestro Giuseppe , Speroni Franco , Guaita Cesare , Zhang Haichun 
Published: October 2003

AbstractIn the first paper of the series, a statistical model for star‐branched polycondenzation of AB type monomers in the presence of a polyfunctional agent RAf was completely developed. The analytical expressions obtained for the number‐average (D̄P̄n̄) and weight‐average (D̄P̄w̄) degree of polymerization, and the dispersion index (D) for whole polymer species, linear and star macromolecular chains, are now derived as function of the feed and of end‐group analysis. Also the important molecular parameter, mole fraction of star‐branched polymer, can be evaluated. Some numerical examples are presented. It is illustrated that the molecular weight properties of the linear and star‐branched polymers in the mixture of the products, very important factors for the application of this kind of polymeric materials, can be determined starting from the feed and terminal group analysis.Polymerization and oligomerization of 6‐aminocaproic acid were carried out in the presence of trimesic (T3) acid and 2,2,6,6‐tetra(β‐carboxyethyl)cyclohexanone (T4) and EDTA as tri‐ and terra‐functional agents. The molecular weights calculated are in good agreement with those obtained by Size Exclusion Chromatography (SEC), end group analysis and NMR spectra.
Synthesis and characterization of semifluorinated polymers and block copolymers
Authors: Pospiech Doris , Komber Hartmut , Voigt Dieter , Jehnichen Dieter , Häußler Liane , Gottwald Antje , Kollig Wolfram , Eckstein Kathrin , Baier Angela , Grundke Karina 
Published: October 2003

AbstractThe goal of the investigation presented here was to evaluate the influence of semifluorinated side chains on the bulk structure and the surface properties of polysulfones with different chain structure. Thus, segmented block copolymers consisting of polysulfone and semifluorinated aromatic polyester segments as well as polysulfones having semifluorinated side chains randomly distributed over the polymer backbone were synthesized and characterized. Oxydecylperfluorodecyl side chains were used because of their strong tendency for self‐organization. The influence of the chain architecture on the self‐organization as well as on the surface properties, particularly the wetting behavior, was examined. It could be shown that despite of the higher self‐organizing tendency of block copolymers the surface properties of both polymer types are comparable and depend only on the concentration of side chains.
Synthesis of well‐defined poly(p‐benzamide) from chain‐growth polycondensation and its application to block copolymers
Authors: Yokozawa Tsutomu , Ogawa Miyuki , Sekino Atsushi , Sugi Ryuji , Yokoyama Akihiro 
Published: October 2003

AbstractPoly(p‐benzamide) with a defined molecular weight and a low polydispersity and block copolymers containing this well‐defined aramide was synthesized. Phenyl 4‐(4‐octyloxybenzylamino)benzoate (1b) polymerized at room temperature in the presence of base and phenyl 4‐nitrobenzoate (2a) as an initiator in a chain‐growth polycondensation manner to give well‐defined aromatic polyamides having the 4‐octyloxybenzyl groups as a protecting group on nitrogen in an amide. It was confirmed by a model reaction that deprotection of this protecting group proceeded completely with trifluoroacetic acid (TFA) without breaking the amide linkage. The utility of this approach to poly(p‐benzamide) with a low polydispersity was demonstrated by the synthesis of block copolymers of poly(p‐benzamide) and poly(N‐octyl‐p‐benzamide) or poly(ethylene glycol). The SEM images of the supramolecular assemblies of the former block copolymer showed μm‐sized bundles and aggregates of flake structures.
Cyclizations in hyperbranched aliphatic polyesters and polyamides
Authors: Chikh Linda , Arnaud Xavier , Guillermain Céline , Tessier Martine , Fradet Alain 
Published: October 2003

AbstractHyperbranched aliphatic polyesters of 2,2′‐bis‐(hydroxymethyl) propanoic acid and hyperbranched aliphatic polyamides obtained from new carboxy‐ and amino‐functionalized caprolactams were studied by NMR spectroscopy and MALDI‐TOF mass spectrometry. Ring‐chain equilibria taking place through intramolecular hydroxy‐ester, carboxy‐amide or amine‐amide interchanges and leading to the formation of cyclic branches or end‐groups were found to exert a predominant influence on the molar mass of these hyperbranched polymers. A number of intra‐ or intermolecular side reactions, such as the formation of ethers in polyesters and the formation of anhydrides, imides, amidines and secondary amines in polyamides were also detected and resulted in polymer crosslinking on prolonged heating. The existence of such ring‐chain equilibria and side‐reactions make the control of hyperbranched polymer structure much more difficult than generally accepted.
Lyotropic para‐linked aromatic poly(amic ethyl ester)s
Authors: Neuber Christian , Giesa Reiner , Schmidt Hans‐Werner 
Published: October 2003

AbstractThe synthesis, characterization and application of lyotropic precursor polymers for polyimides, poly(amic ethyl ester)s (PAE) are presented. By the use of non‐coplanar and para‐linked monomers, rigid‐rod PAEs are synthesized in a typical polycondensation reaction yielding liquid crystalline solutions at concentrations of 30‐40 wt% in NMP at 100°C. These lyotropic solutions permit for the first time the fabrication of orientation PAE layers by shear which are thermally converted to the corresponding polyimide. The bulk orientation in the thin films is characterized by spectroscopic methods. In addition the lyotropic solution is spun into fibers in a dry‐jet wet spinning process. The obtained fiber orientation is characterized by tensile tests and wide angle X‐ray scattering.