bluuebunny/crossref_metadata_2025_split huggingface dataset:
Estimation and comparison of ζ‐potentials of silica‐based anion‐exchange type porous particles for capillary electrochromatography from electrophoretic and electroosmotic mobility
Authors: Sánchez Muñoz Orlando L. , Hernández Ever Pérez , Lämmerhofer Michael , Lindner Wolfgang , Kenndler Ernst 
Published: February 2003

AbstractMobilities of different chromatographic particles obtained from two electrokinetic methods were determined and compared. The particles were all based on porous silica, between 3 and 15 μm diameter, and were either native, or derivatized. As intermediate of chemical modification 3‐mercaptopropyl‐modified silica particles (TP‐silica) are obtained. These particles were finally transformed into weakly basic anion exchangers with O‐9‐(tert‐butylcarbamoyl)quinine (tBuCQN) as chiral selector. The electrophoretic mobility of the particles was determined from their migration velocity in an electric field using microelectrophoresis. Electrokinetic chromatography with a capillary column packed with the same particles was used to measure the electroosmotic flow generated. All measurements were carried out in background electrolytes of equal ionic strength (10−2 mol/L), at pH varying between 3.5 and 9.5. From these data a rough estimation of the ζ‐potential was made, taking Helmholtz‐Smoluchowski conditions into consideration. With both methods the ζ‐potential of the native silica particles is negative throughout, and its value increases with pH. The weakly basic tBuCQN particles have positive ζ‐potentials at pH lower than about 7.5, but exhibit a negative ζ‐potential above this pH, indicating the dominating effect of residual silanol groups at the silica surface. The ζ‐potential for these anion‐exchange particles ranged between +30 and −40 mV. The ζ‐potentials derived with electrophoresis and electroosmosis agree, showing the adequacy of the approach, although many limitations must be taken into account in the treatment of the electrokinetic phenomena in such porous systems. These restrictions in interpreting mobility and ζ‐potential were discussed.
Sieving mechanisms in polymeric matrices
Authors: Sartori Anna , Barbier Valessa , Viovy Jean‐Louis 
Published: February 2003

AbstractA critical review of the existing theoretical models and experimental evidences for sieving mechanisms during separation of macromolecules, paying particular attention to capillary electrophoresis applications is presented. Gel models (Ogston and reptation) have been successfully applied to highly entangled polymer solutions, where fast and efficient separations can occur. In order to account for the DNA/polymers collision‐interaction mechanisms during separation in dilute solutions – characterized by a poorer resolution –, approximated analytical models have been developed. An insight in the mechanism regulating the intermediate case of moderately entangled polymer solutions, for low fields and concentrations of small multiples of the overlap concentration c*, is given by the constraint release approach. This model proposes an upper limit of size separation, increasing with matrix concentration and molecular mass. Finally, the coupling between the reptative motion of the analytes and the effect of matrix constraint release very likely plays a fundamental role in the separation mechanism and requires therefore further and deeper investigation, both theoretically and experimentally.
Sample stacking revisited: A personal perspective
Authors: Chien Ring‐Ling 
Published: February 2003

AbstractOne of the major challenges in capillary electrophoresis and other miniaturization separation techniques is to maintain high detection sensitivity in the increasingly smaller dimension. Numerous on‐column sample preconcentrating procedures, based either on electrokinetic focusing or chromatographic effects, have been developed. This review will discuss some practical approaches to sample stacking from a personal perspective. Several recent developments in sample stacking on microfluidic devices are reviewed.
Eigenmobilities in background electrolytes for capillary zone electrophoresis: II. Eigenpeaks in univalent weak electrolytes
Authors: Štědrý Milan , Jaroš Michal , Včeláková Kateřina , Gaš Bohuslav 
Published: February 2003

AbstractWe analyze in detail a mathematical model of capillary zone electrophoresis (CZE) based on the conception of eigenmobilities, which are eigenvalues of the matrix tied to the linearized continuity equations. Our model considers CZE systems, where constituents are weak electrolytes and where pH of the background electrolyte may reach the full range from 0 to 14. Both hydrogen and hydroxide ions are taken into account in relations for conductivity and electroneutrality. An electrophoretic system with N constituents has N eigenmobilities. We reveal that two of the eigenmobilities have a special meaning as they exist due to the presence of hydrogen ions and hydroxide ions (in water solutions). These two eigenmobilities are responsible for the existence of two corresponding system zones (system peaks). We show that the stationary zone (injection zone, water zone, gap, peak, dip) is in many common background electrolytes composed of these two eigenzones which overlap, due to their very low electrophoretic mobility, into one zone. Other eigenmobilities give rise to system zones originating due to a possible existence of double (or multiple) coconstituents in the background electrolyte. The last group of eigenmobilities is connected with the movement of eigenzones accompanying analytes and enabling their indirect UV or conductivity detection. The model allows assessing experimentally available quantities such as effective mobility of the analyte, molar conductivity detection response, transfer ratio, and relative velocity slope and gives a picture about migration of analytes, their electromigration dispersion and signals obtained in detectors. It allows computer simulation of electropherograms and enables optimization of background electrolytes.
In the Service of the Crown
Authors: Lenz Jürgen , Thies Matthias , Schweizerhof Karl 
Published: February 2003

AbstractEach year ceramometallic dental restorations worth several hundred million euros are fabricated in Germany. However, during fabrication such restorations can be damaged by thermal stresses. Basic research is supporting the safe production of such porcelain‐fused‐to‐metal systems
A set of genes activated in differentiating smooth muscle is also activated in smooth muscle from injured arteries or atherosclerotic lesions
Authors: Jenna Lynn Ray Edward S. Moon , Leach Rebecca L. , Benson Mark R. 
Published: February 2003

AbstractWe stimulated differentiation of purified rat neural crest stem cells (NCSCs) into smooth muscle cells (SMCs) in culture, then subtracted NCSC sequences from SMC sequences to make a cDNA library specific for differentiating smooth muscle cells. Sequence analysis of the library shows that a large subset of clones is strongly associated with smooth muscle biology, confirming the overall success of the differentiation and subtraction procedures. Of this subset of clones, more than half encode proteins that have previously been shown to be upregulated in atherosclerotic or injured vascular smooth muscle as compared to normal vascular smooth muscle. Thus, a set of genes activated in differentiating smooth muscle of the neural crest lineage is also activated in atherosclerotic or injured vascular smooth muscle.
Analysis of Smoothened as a candidate gene for human holoprosencephaly
Authors: Ming Jeffrey E. , Jeng Bennie , deSauvage Frederic J. , Muenke Maximilian 
Published: February 2003

AbstractHoloprosencephaly (HPE) is the most common structural congenital forebrain malformation in humans and is associated with mental retardation and craniofacial abnormalities. In HPE, the cerebral hemispheres fail to separate into distinct right and left halves. The condition is etiologically heterogeneous, as multiple genes and environmental factors are associated with the condition. Autosomal dominant HPE can be caused by mutations in Sonic Hedgehog (SHH). Smoothened (SMOH; human gene) encodes a transmembrane protein that acts in SHH signal transduction. Because of the critical role of SMOH in the SHH pathway, we performed mutation analysis of this gene in familial and sporadic cases of HPE. Although we identified a number of nucleotide changes in SMOH in affected patients, none of these changes is likely to be pathogenic. Thus, haploinsufficiency for SMOH is unlikely to be a significant cause of human HPE in live‐born infants.
14‐Membered Cyclopeptides from Paliurus ramosissimus and P. hemsleyanus
Authors: Lin Hui‐yi , Chen Chung‐Hsiung , Chen Liu Karin C. S. , Lee Shoei‐Sheng 
Published: February 2003

AbstractSix 14‐membered cyclopeptide alkaloids, i.e., ramosines A–C, mucronine J, and lotusines A and D, were isolated from the roots of Paliurus ramosissimus, and an additional four, hemsines A–D, from the roots of P. hemsleyanus. Among these, ramosines A–C (1, 5, and 6, resp.) and hemsines A and B (7 and 8, resp.) are new bases of the amphibine‐B type, and hemsines C and D (9 and 10, resp.) are new integerrine‐type alkaloids. Additionally, ramosine C (6) represents the first 14‐membered cyclopeptide alkaloid possessing a substitution (OH) at C(13′). Their structural elucidations were based on spectral analysis and molecular‐modeling studies. Pronounced solvent effects in the 1H‐ and 13C‐NMR spectra of these two types of alkaloids were observed.
On the Reactivity of 1H‐Pyrazino[2,3‐c][1,2,6]thiadiazine 2,2‐Dioxide and Derivatives: Nucleophilic Substitution, Amination, Aldol‐Type Condensation, Oxidation, and Hydrolysis
Authors: Campillo Nuria , Páez Juan Antonio , Goya Pilar 
Published: February 2003

AbstractThe reactivity of the 1H‐pyrazino[2,3‐c][1,2,6]thiadiazine 2,2‐dioxide system, structurally related to pteridine, was studied, and a number of novel derivatives were synthesized. The chemical behaviors of these two related fused polyaza systems were compared.
Reactions of mer(exo)‐ and mer(endo)‐[Co(dien)(dapo)X]2+ Isomers (X=OH, Cl, ONO2, N3)
Authors: Browne Rebecca J. , Buckingham David A. , Clark Charles R. , McKeon Josephine A. , Jackson W. Gregory 
Published: February 2003

AbstractProperties indirectly determined, or alluded to, in previous publications on the titled isomers have been measured, and the results generally support the earlier conclusions. Thus, the common five‐coordinate intermediate generated in the OH−‐catalyzed hydrolysis of exo‐ and endo‐[Co(dien)(dapo)X]2+ (X=Cl, ONO2) has the same properties as that generated in the rapid spontaneous loss of OH− from exo‐ and endo‐[Co(dien)(dapo)OH]2+ (40±2% endo‐OH, 60±2% exo‐OH) and an unusually large capacity for capturing (R=[CoN3]/[CoOH][]=1.3; exo‐[CoN3]/endo‐[CoN3]=2.1±0.1). Solvent exchange for spontaneous loss of OH− from exo‐[Co(dien)(dapo)OH]2+ has been measured at 0.04 s−1 (k1, 0.50M NaClO4, 25°) from which similar loss from the endo‐OH isomer may be calculated as 0.24 s−1 (k2). The OH−‐catalyzed reactions of exo‐ and endo‐[Co(dien)(dapo)N3]2+ result in both hydrolysis of coordinated via an OH−‐limiting process =153 M−1 s−1; =295 M−1 s−1; KH=1.3±0.1 M−1; 0.50M NaClO4, 25.0°) and direct epimerization between the two reactants =33 M−1 s−1; =110 M−1 s−1; 1.0M NaClO4, 25.0°). Comparisons are made with other rapidly reacting CoIII‐acido systems.
Stereoselective Conversion of Aucubin into Polyfunctionalized Tetrahydro‐1H‐cyclopenta[c]furan Glucosides
Authors: Mouriès Christine , Deguin Brigitte , Koch Michel , Tillequin François 
Published: February 2003

AbstractMitsunobu reaction of 2′,3′,4′,6′,10‐penta‐O‐pivaloylaucubin (6) with phthalimide, triphenylphosphine, and diethyl azodicarboxylate gave (6R)‐6‐phthalimido‐perpivaloylbartsioside (10) (Scheme 1). Selective oxidation reactions performed with perpivaloylaucubin (12) yielded (1R)‐ and (1S)‐3(β‐D‐glucopyranosyloxy)‐1H‐cyclopenta[c]furan‐1‐carboxaldehydes 13 and 14 respectively (Scheme 2). Similarly, perpivaloyl‐6‐epiaucubin (9) and 10 afforded the corresponding (1S)‐carboxaldehyde 15 and (1R)‐carboxaldehyde 16, respectively. The protected cyclopentafuran glycosides obtained in this way are versatile synthons, which may prove useful for further chemical diversification.
Oxidative Halogenation of Aromatic Compounds with Metal Halides and Sodium Bismuthate
Authors: Muathen Hussni A. 
Published: February 2003

AbstractA new mild and efficient method for aromatic halogenation with a wide variety of halides in the presence of sodium bismuthate NaBO3 in AcOH is reported. Metal halides of groups Ia, IIa, IIIa, IVa, Va, and the first row of transition elements are suitable for this method.
Pericyclic Transformations at the Periphery of Chromen‐4‐one (=4H‐1‐Benzopyran‐4‐one): An Unusual Preference for a 1,5‐Shift of Allylic Moieties over the Ene Reaction
Authors: Singh Gurmit , Singh Gurpinder , Ishar Mohan Paul S. 
Published: February 2003

AbstractQuite unlike the reported facile ene reactions on the periphery of many related heterocyclic systems, similarly disposed moieties on the periphery of the chromen‐4‐one (=4H‐1‐benzopyran‐4‐one) system fail to undergo an ene reaction and display a rather unusual preference for an overall [1,5] shift of the allylic C‐atom. Thus, heating xylene solutions of 2‐(N‐allylanilino)‐, 2‐(N‐crotylanilino)‐, and 2‐(N‐cinnamylamino)‐substituted (E)‐(oxochromenyl)propenoates 9a–c and 2‐[allyl(benzyl)amino]‐, 2‐[benzyl(crotyl)amino]‐, and 2‐[benzyl(cinnamyl)amino]‐substituted (E)‐(oxochromenyl)propenoates 16a–c in a sealed tube at 220–230° leads to a [1,5] shift of the allylic moieties (allyl, crotyl, cinnamyl), which is followed by intramolecular cyclization involving the N‐atom and the ester function, to give the 3‐allyl‐3‐crotyl‐, and 3‐cinnamyl‐substituted‐1‐phenyl‐ or 1‐benzyl‐2H‐[1]benzopyrano[2,3‐b]pyridine‐2,5(1H)‐diones 10a–c and 17a–c. The anticipated carbonyl–ene reaction in the 2‐(N‐allylanilino)‐, 2‐(N‐crotylanilino)‐, 2‐(N‐cinnamylanilino)‐, 2‐[allyl(benzyl)amino]‐, 2‐[benzyl(crotyl)amino]‐, and 2‐[benzyl(cinnamyl)amino]‐substituted 4‐oxochromene‐3‐carboxaldehydes 8a–c and 15a–c is also not observed, and these molecules remain untransformed under identical conditions. No [1,5] shifts of benzyl, phenyl, or methyl groups are observed, even in the absence of allylic moieties, though facile [1,5]‐H shift occurs in 2‐(benzylamino)‐ and 2‐(phenylamino)‐substituted (E)‐(oxochromenyl)propenoates 23a,b, which is followed by a similar intramolecular cyclization leading to the 2H‐[1]benzopyrano[2,3‐b]pyridine‐2,5(1H)‐diones 24a,b.
Enantioselective Entry to the Homalium Alkaloid Hoprominol: Synthesis of an (R,R,R)‐Hoprominol Derivative
Authors: Ensch Corinne , Hesse Manfred 
Published: February 2003

AbstractThe diastereoselective synthesis of the N‐ and O‐protected hoprominol derivative (R,R,R)‐6 is described. The building up of the bicyclic O‐silylated and di(N‐tosylated) asymmetric scaffold 6 succeeded by convergent preparation of the two basic chiral azalactam units 7a and 7b and their subsequent iterative linking by a known method (Scheme 5). Both 4‐alkyl‐hexahydro‐1,5‐diazocin‐2(1H)‐ones 7a and 7b were prepared from the chiral β‐amino acid portions 10a and 10b, respectively, by application of a set of reactions (e.g., N‐alkylation of 10a,b and Sb(OEt)3‐assisted cyclization of the resulting open‐chain intermediates) already known. In comparison with the total syntheses of homaline (1) and homoprine (2), the newness of the described synthesis lies in the asymmetric approach to the difunctionalized fatty acid derivative 10b starting from (−)‐(S)‐malic acid (9) (Schemes 3 and 4). Key step in the preparation of 10b was the diastereoselective amination of the optically pure α,β‐unsaturated δ‐hydroxy homoallylic ester 14 via conjugate intramolecular aza‐Michael cyclization of the acylic δ‐(carbamoyloxy) intermediate 11.
On the Preparation of 2‐Substituted Cephalosporins, Part 2
Authors: Tamás László , Gunda Tamás E. , Batta Gyula , Sztaricskai Ferenc 
Published: February 2003

AbstractCephalosporin sulfoxides 1 and 2 containing an enone‐ or dienone‐type moiety at position 2 were treated with 2,3‐dimethylbuta‐1,3‐diene or diethyl azodicarboxylate to synthesize, in DielsAlder reactions, the new cephalosporin derivatives 4 and 5 with a cyclic substituent (Scheme 1). Under the same conditions, ethyl diazoacetate and diazomethane reacted differently: while reactions of 1 and 3 with the former lead to compounds 7–10 corresponding to the 1,3‐dipolar cycloaddition route (Scheme 2), diazomethane produced only enol ethers 12 and 13, respectively (Scheme 3). This difference could be rationalized by assuming two different reaction pathways: an orbital‐symmetry‐controlled concerted cycloaddition and an ionic one.
Solvation Effects in the Grignard Reaction with Carbonyl Compounds
Authors: Sassian Meeri , Tuulmets Ants 
Published: February 2003

AbstractRatios of the yields of addition and reduction products for the reactions of butylmagnesium chloride with diisopropyl ketone, methyl 2‐methylpropanoate, and isopropyl 2‐methylpropanoate in toluene were determined at different THF, diethyl ether, and tert‐butyl methyl ether contents in the Grignard reagent. Replacement of the alkoxy group in the ester leads to strikingly different results for very small additions of donors. The results are discussed in terms of the solvation of the species in the reaction mixture.
Radiation heat transfer in three‐dimensional closed space including diffuse and specular surfaces
Authors: Miyanaga Toshiyuki , Nakano Yukio 
Published: February 2003

AbstractA method of numerical calculation for radiation heat transfer in a three‐dimensional closed space including diffuse and specular surfaces was developed. To enable an analysis of the radiation heat exchange on each surface considering multiple specular reflections and obstacles to radiation in the space, an improved heat ray‐tracing method was presented to calculate view factors accurately. The method was determined to be applicable to complicated problems in test calculations using models with specular surfaces and obstacles. Continuing efforts are being applied to more realistic problems. The example examined in this paper is an infrared emitter with a parabolic specular reflector, which is a conventional electric heating apparatus. The measured result for radiant power distribution agrees well with the calculated one. The practical validity of our method was verified. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(2): 108–129, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10074
Dysregulated PTEN‐PKB and negative receptor status in human breast cancer
Authors: Shi Wei , Zhang Xinghe , Pintilie Melania , Ma Nancy , Miller Naomi , Banerjee Diponkar , Tsao Ming‐Sound , Mak Tak , Fyles Anthony , Liu Fei‐Fei 
Published: February 2003

AbstractRecent studies demonstrate that abnormalities in PTEN may be one of the most frequent genetic events observed in human cancers. PTEN dysfunction leads to tumorigenesis through unopposed survival signals mediated via activated protein kinase B (PKB), which may also be associated with hormone‐independence. We therefore investigated the relationship between PTEN‐PKB and receptor status in human breast cancer. Several molecular variables, including immunohistochemical staining for PTEN, PKB (phosphorylated on ser473), p53 and p21 were evaluated. The p53 gene was sequenced from exons 2–11. Seventy‐eight participants in a randomised breast cancer trial served as the cohort for our study. Twenty‐eight of 77 (36%) patients' tumours demonstrated absent or reduced PTEN expression; 17 of 78 (22%) tumours over‐expressed P‐PKB. A significant inverse relationship was observed between reduced PTEN and increased P‐PKB expression. Reduced PTEN also correlated with reduced ER or PR expression. None of the molecular variables correlated with survival. ER and PR negative tumours, however, experienced a significantly inferior disease‐free survival than other ER/PR status tumours. Immunohistochemical analyses of ER expression in mammary carcinomas arising in PTEN heterozygous knockout mice did not demonstrate a reduction in ER immunoreactivity, in comparison to wild‐type mice. Our data demonstrate that the PTEN–PKB pathway is abnormal in approximately ⅓ of lymph node negative breast cancer. Dysregulated PTEN‐PKB was also associated with reduced ER/PR expression, but this does not appear to be a simple direct causal relationship. These observations support the contention that dysregulation in PTEN‐PKB contributes to disease progression and hormone resistance of human breast cancer. © 2003 Wiley‐Liss, Inc.
Meat, fish and egg intake and risk of breast cancer
Authors: Holmes Michelle D. , Colditz Graham A. , Hunter David J. , Hankinson Susan E. , Rosner Bernard , Speizer Frank E. , Willett Walter C. 
Published: February 2003

AbstractIntakes of animal protein, meat, and eggs have been associated with breast cancer incidence and mortality in ecological studies, but data from long‐term prospective studies are limited. We therefore examined these relationships in the Nurses' Health Study. We followed 88,647 women for 18 years, with 5 assessments of diet by food frequency questionnaire, cumulatively averaged and updated over time. We calculated the relative risks (RR) and 95% confidence intervals (95% CI) for risk of developing invasive breast cancer, over categories of nutrient and food intake. During follow‐up, 4,107 women developed invasive breast cancer. Compared to the lowest quintile of intake, the RR and 95% CI for the highest quintile of intake were 1.02 (0.92–1.14) for animal protein, 0.93 (0.83–1.05) for red meat and 0.89 (0.79–1.00) for all meat. Results did not differ by menopausal status or family history of breast cancer. We found no evidence that intake of meat or fish during mid‐life and later was associated with risk of breast cancer. © 2003 Wiley‐Liss, Inc.
PTEN/MMAC1 gene mutation is a rare event in soft tissue sarcomas without specific balanced translocations
Authors: Saito Tsuyoshi , Oda Yoshinao , Kawaguchi Ken‐ichi , Takahira Tomonari , Yamamoto Hidetaka , Tamiya Sadafumi , Tanaka Kazuhiro , Matsuda Shuichi , Sakamoto Akio , Iwamoto Yukihide , Tsuneyoshi Masazumi 
Published: February 2003

AbstractThe tumor suppressor gene PTEN/MMAC1 was identified on chromosome 10q23.3, which is homozygously deleted in many human malignancies. The loss of chromosome 10q was also frequently reported in some types of soft tissue sarcomas. Our study was designed to investigate the frequency of PTEN/MMAC1 gene mutation and to evaluate the role of the PTEN/MMAC1 gene in the tumorigenesis of soft tissue sarcomas without specific balanced translocations. We analyzed 51 cases of soft tissue sarcomas without specific balanced translocations for PTEN/MMAC1 mutations by polymerase chain reaction‐single strand conformation polymorphism and direct sequencing. Mutations in the PTEN/MMAC1 gene were found in only 2 cases (3.9%). Both tumors with PTEN/MMAC1 mutation were leiomyosarcomas arising from the retroperitoneum and inferior vena cava, respectively. Two of 3 leiomyosarcomas arising from the intra‐abdominal cavity examined harbored mutations of this tumor suppressor gene. This result suggests that leiomyosarcomas derived from the intra‐abdominal cavity might have different tumorigenesis from those of an extremity or the trunk, from the viewpoint of PTEN/MMAC1 mutation, although PTEN/MMAC1 gene mutations are rare event in these soft tissue sarcomas. © 2003 Wiley‐Liss, Inc.