bluuebunny/crossref_metadata_2025_split huggingface dataset:
Link between biological signaling and increased enantioseparations of acids using glycopeptide antibiotics
Authors: Reilly J. , Sanchez‐Felix M. , Smith N.W. 
Published: October 2003

AbstractThe vancomycin analog A82846B has been shown to provide excellent selectivity as a chiral recognition agent for some acidic test analytes in capillary electrophoresis (CE) and high‐performance liquid chromatography (HPLC). In both modes A82846B outperforms vancomycin as a chiral selector. A82846B has enhanced antibacterial activity data in comparison to vancomycin, which is probably due to the increased dimerization constant of over 100 in magnitude in comparison to vancomycin. The link between the electrophoretic and chromatographic separations observed and the biological activity of A82846B is discussed. Dimerization of A82846B in solution was proposed as a theory as to why A82846B gave such enhanced separations for acidic racemates. Further literature and experimental studies support the theory. Chirality 15:731–742, 2003. © 2003 Wiley‐Liss, Inc.
Absolute configuration determination of chiral molecules in the solution state using vibrational circular dichroism
Authors: Freedman Teresa B. , Cao Xiaolin , Dukor Rina K. , Nafie Laurence A. 
Published: October 2003

AbstractAdvances in the measurement, calculation, and application of vibrational circular dichroism (VCD) for the determination of absolute configuration are described. The purpose of the review is to provide an up‐to‐date perspective on the capability of VCD to solve problems of absolute stereochemistry for chiral molecules primarily in the solution state. The scope of the article covers the experimental methods needed for the accurate measurement of VCD spectra and the theoretical steps required to systematically deduce absolute configuration. Determination of absolute configuration of a molecule by VCD requires knowledge of its conformation or conformational distribution, and hence VCD analysis necessarily provides solution‐state conformation information, in many cases available by no other method, as an additional benefit. Comparisons of the advantages and limitations of VCD relative to other available chiroptical methods of analysis are also presented. Chirality 15:743–758, 2003. © 2003 Wiley‐Liss, Inc.
Photoreaction of a racemate proceeding through radical or ion pairs. The effect of circularly polarized light on the enantiomeric excess of recovered reactant
Authors: Pagni Richard M. , Bartmess John 
Published: October 2003

AbstractA simple theory has been developed to explain how circularly polarized light will affect the outcome of a photoreaction of a racemic substrate proceeding through ion pairs or radical pairs. One can calculate the enantiomeric excess and amount of recovered substrate at any stage of the reaction. Chirality 15:772‐776, 2003. © 2003 Wiley‐Liss, Inc.
G‐quartet self‐assembly under osmotic pressure: remote control by vesicle shrinking rather than stress
Authors: Sakai Naomi , Matile Stefan 
Published: October 2003

AbstractDoes osmotic pressure stimulate assembly or disassembly of supramolecules in vesicles? Self‐assembly was conceivable as intravesicular response to osmotic shrinking upon application of extravesicular overpressure, whereas disassembly was conceivable as a response to bilayer stress in hyperosmotic vesicles. Self‐assembly of guanosine 5′‐monophosphates (GMPs) into G‐quartets was selected to investigate the nature of remote control of supramolecular chemistry within vesicles by osmotic pressure. Using circular dichroism spectroscopy to selectively detect G‐quartets, we found that extravesicular overpressure stimulates intravesicular self‐assembly, whereas underpressure stimulates disassembly. G‐quartet self‐assembly by osmotic pressure exhibited ion‐selective metal‐cation templation, as expected. The key conclusions are that supramolecular chemistry within vesicles is governed by vesicle shape rather than vesicle stress and that detection of osmotic pressure by CD spectroscopy is an interesting alternative to the commonly used methods based on fluorescence self‐quenching. Chirality 15:766–771, 2003. © 2003 Wiley‐Liss, Inc.
Using stereocartography for predicting efficacy of stereoinduction by chiral catalysts
Authors: Lipkowitz Kenny B. , Sakamoto Taka , Stack Jonathan 
Published: October 2003

AbstractA computational method called stereocartography is used to examine regions around chiral catalysts that are most stereoinducing during Diels‐Alder reactions. Geometries and atomic charges of catalysts are first generated quantum mechanically. The transition state of the reaction being catalyzed is then computed quantum mechanically and those enantiomeric transition states are used as probes to determine where around the catalyst stereoinduction is optimal. A description of how to treat catalysts with multiple conformations is given. In this article seven catalysts containing a variety of ligand motifs and metals were evaluated. The hypothesis that the region of maximum stereoinduction must be spatially coincident with the site of chemistry for a catalyst to be efficient is upheld. Chirality 15:759–765, 2003. © 2003 Wiley‐Liss, Inc.
A novel L‐neopentylglycine derivative as auxiliary for copper‐catalyzed asymmetric Michael reactions
Authors: Christoffers Jens , Schuster Katja 
Published: October 2003

AbstractL‐Neopentylglycine diethylamide (4a). was prepared from the new unnatural amino acid L‐neopentylglycine (1). The utilization of amide 4a as a chiral auxiliary in the copper(II)‐catalyzed asymmetric Michael reaction was investigated in comparison with L‐valine diethylamide (4b). Cyclic β‐oxocarboxylates 7 react with 4a and 4b to give the respective enaminoesters 8, which were converted with methyl vinyl ketone (9) in the presence of 10 mol% Cu(OAc)2 · H2O at room temperature in acetone to yield the optically active Michael addition products (R)‐10a, b with high selectivity independent of the starting enamine. In the case of the seven‐membered β‐oxocarboxylate 7c, however, the valine‐derived enamine 8f led to higher enantioselectivity for product 10c. Despite the bulkiness of the neopentyl group, the isopropyl group with an α‐branch has a better stereoinducing effect. Chirality 15:777–782, 2003. © 2003 Wiley‐Liss, Inc.
Enantioseparation of chiral alcohols by complex formation and subsequent supercritical fluid extraction
Authors: Székely Edit , Simándi Béla , Fogassy Elemér , Kemény Sándor , Kmecz Ildikó 
Published: October 2003

AbstractThe very first application of supercritical fluid extraction (SFE) on enantioseparation of alcohols is discussed. Resolution of three chiral alcohols (trans‐2‐chloro‐cyclohexanol, trans‐2‐bromo‐cyclohexanol, and trans‐2‐iodo‐cyclohexanol) were performed by partial complexation with (−)‐O,O′‐dibenzoyl‐(2R,3R)‐tartaric acid monohydrate (DBTA). DBTA formed diastereomeric complexes with all S,S‐enantiomers stable enough to extract the unreacted alcohols with supercritical carbon dioxide. Resolution efficiency increased with the size of halogen substituents, and by the proper selection of molar ratio, pure (−)‐R,R‐trans‐2‐iodo‐cyclohexanol (ee > 99%, yield: 39%) or (+)‐S,S‐trans‐2‐iodo‐cyclohexanol (ee = 98%, yield: 8%) were prepared in one process step. Achieved resolution efficiency values were much higher in all resolution procedures than in any other known enantioseparation of these racemic compounds. The developed method offers an environmentally friendly, efficient alternative of currently applied resolution processes, also on a preparative scale. Chirality 15:783–786, 2003. © 2003 Wiley‐Liss, Inc.
Absolute configuration of (−)‐2,6‐dimethyl‐10‐(p‐tolyl)‐2,6(E)‐undecadiene from Cistus monspeliensis
Authors: Pietsch Martin , König Wilfried A. , Joulain Daniel 
Published: October 2003

Abstract(−)‐2,6‐Dimethyl‐10‐(p‐tolyl)‐2,6(E)‐undecadiene (1) is a major constituent in the essential oil of Cistus monspeliensis, an aromatic shrub common in Mediterranian countries. 1 was isolated by column chromatography, subjected to ozonolyses, and the absolute configuration was determined by enantioselective gas chromatographic correlation with the ozonolysis product of the sesquiterpene hydrocarbon ar‐curcumene with known absolute configuration. Chirality 15:794–798, 2003. © 2003 Wiley‐Liss, Inc.
Effects from hydrogen bonding and rigidity on selectivity in tartaric acid‐based chiral selectors for enantioselective liquid chromatography
Authors: Oxelbark Joakim , Sellén Inga‐Britt 
Published: October 2003

AbstractTartaric acid‐based selectors 1 ((R,R)‐O,O′‐Bis(dimethylbenzoyl)‐N,N′‐diallyl‐N,N′‐dimethyl tartaramide) and 2 ((R,R)‐N‐allyl‐O,O′‐bis(dimethylbenzoyl) tartarimide) were synthesized, immobilized on silica, and evaluated as chiral stationary phases in enantioselective chromatography. Comparison with the commercially available column Kromasil‐CHI‐1, based on selector 3 ((R,R)‐O,O′‐Bis(dimethylbenzoyl)‐N,N′‐diallyl tartaramide) resulted in the conclusion that amide NH functions are essential to chiral recognition on this sorbent. Furthermore, NH functions contribute significantly to retention of analytes except for alcohols. It was also found that flexibility of the benzoyl moieties is essential to selectivity. Chirality 15:787–793, 2003. © 2003 Wiley‐Liss, Inc.
Trennmethoden für Graphit‐Nanoröhren
Authors: Groß Michael 
Published: October 2003

AbstractStellen Sie sich eine einzelne Schicht von graphitartig angeordneten Kohlenstoffatomen vor — ein perfektes Wabenmuster aus lauter gleichseitigen Sechsecken. Wenn man diese Ebene zu einem Zylinder aufrollt, erhält man Graphit‐Nanoröhren. Je nachdem, in welcher Richtung man gerollt hat, werden diese Röhren metallische oder Halbleiter‐Eigenschaften haben.
Kleinste Chips für Handys
Authors: Borchard‐Tuch Claudia 
Published: October 2003

AbstractSeit ihrer Einführung vor über 20 Jahren sind Mobiltelefone auf eine handliche Größe geschrumpft. Hierzu hat die Miniaturisierung ihrer wichtigsten Bauelemente — der Chips — entscheidend beigetragen. Damit verbunden sind deutlich gestiegene Ansprüche an deren strukturelle Homogenität und Oberflächenstruktur sowie die Reinheit der Elektronik‐Chemikalien.
Cytoarchitecture, topography, and descending supraspinal projections in the anterior central nervous system of Branchiostoma lanceolatum
Authors: Ekhart Daniel , Korf Horst‐Werner , Wicht Helmut 
Published: October 2003

AbstractThe central nervous system (CNS) of the chordate amphioxus (Branchiostoma lanceolatum) is divisible into a spinal cord and an anterior portion in some ways equivalent to the brain of craniates. The present study reports on this anterior portion, with respect to general topography, cytoarchitecture, and cells that give rise to descending supraspinal projections. The anterior portion of the CNS is located adjacent to the first four myomeres and rostral to the first giant cell of Rohde—it can be divided into several regions that differ with respect to their cytoarchitecture. The tip of the neural tube is formed by a small anterior vesicle; caudally, there is a much larger region that is intercalated between the anterior vesicle and the first cell of Rohde. This intercalated region, in turn, consists of three subdivisions: an anterior subdivision adjacent to myomere 1, an intermediate subdivision adjacent to myomere 2, and a posterior one adjacent to myomeres 3 and 4. After injections of tracers into the spinal cord a large number of cells were labeled in the intercalated region. The spinally projecting cells were not evenly distributed: their number was decreased in the center of the intermediate subdivision. These subdivisions, which have previously not been noted, may be aligned with the expression domains of regulatory genes (e.g., AmphiOtx, AmphiHox) in larval lancelets. In particular, the center of the intermediate subdivision may correspond to a “nonHox/nonOtx” domain in the CNS of the larva. A similar embryonic domain occurs in the brain of craniates in which it develops into the isthmus cerebri that separates mid‐ and hindbrain. A close structural and topographical inspection of the corresponding region of adult lancelets reveals, however, that this region is not the homolog of an isthmus, but a uniquely derived, autapomorphic feature of lancelets. J. Comp. Neurol. 466:319–330, 2003. © 2003 Wiley‐Liss, Inc.
Aging of the human cerebellum: A stereological study
Authors: Andersen Birgitte Bo , Gundersen Hans Jørgen G. , Pakkenberg Bente 
Published: October 2003

AbstractCerebella from 19 normal Caucasian males, ages 19–84 years, were studied using stereological methods. Cerebellum was divided into four different regions: the anterior and posterior lobe, the vermis, and the flocculonodular lobe. Total volume of the cerebellar cortex and white matter, cerebellar surface area, total Purkinje and granule cell number, and the distribution of the volumes of the Purkinje cells and their nuclei were estimated in all four regions. The global white matter was reduced by 26% with age; the mean volume of the Purkinje cell body was decreased by 33% with no decrease in the volume of the Purkinje cell nuclei. A tendency towards a 16% total cerebellar volume loss was seen without a concomitant neuron loss. No global Purkinje or granule cell loss was detected with age, total Purkinje cell number being 28 × 106 (coefficient of variation, CV = 0.16) and total granule cell number 109 × 109 (CV = 0.17). However, a significant change was observed with age in the anterior lobe, where a selective 40% loss of both Purkinje and granule cells was found. Furthermore, a 30% loss of volume, mostly due to a cortical volume loss, was recorded in the anterior lobe, which is predominantly involved in motor control. J. Comp. Neurol. 466:356–365, 2003. © 2003 Wiley‐Liss, Inc.
Local commissural interneurons integrate information from intersegmental coordinating interneurons
Authors: Mulloney Brian , Hall Wendy M. 
Published: October 2003

AbstractThe information that coordinates movements of swimmerets on different segments of the crayfish abdomen is conducted by interneurons that originate in each abdominal ganglion. These interneurons project axons to neighboring ganglia and beyond. To discover the anatomy of these axons in their target ganglia, we used Neurobiotin and dextran‐Texas Red microelectrodes to fill them near their targets. Coordinating axons coursed through these target ganglia close to the midline and extended only a few short branches that did not approach the lateral neuropils. Two of the three types of coordinating axons made direct synaptic connections with a class of local commissural interneurons that relayed the information to targets in the swimmeret pattern‐generating circuits. These commissural interneurons, named here ComInt 1 neurons, followed a particular route to cross the midline and reach their targets. ComInt 1 neurons were nonspiking; they received EPSPs from the coordinating axons near the midline and transmitted this information to their targets in the lateral neuropils using graded transmission. The output of each ComInt 1 was restricted to a single local circuit and had opposite effects on the power‐stroke and return‐stroke motor neurons driven by that circuit. ComInt 1 neurons were direct postsynaptic targets of both descending and ascending coordinating axons that originated in other anterior and posterior ganglia. Because of phase differences in the impulses in these different coordinating axons, their signals arrived simultaneously at each ComInt 1. We discuss these findings in the context of alternative models of the intersegmental coordinating circuit. J. Comp. Neurol. 466:366–376, 2003. © 2003 Wiley‐Liss, Inc.
Consequences of interspecies antennal imaginal disc transplantation on organization of olfactory glomeruli and pheromone blend discrimination
Authors: Vickers Neil J. , Poole Kathy , Linn Charles E. 
Published: October 2003

AbstractThe antennal imaginal disc was transplanted between male larvae of two different heliothine moth species, Heliothis virescens (HV) and Helicoverpa zea (HZ). Males of these species respond to distinct pheromone blends, have different peripheral and central olfactory neuron specificities, as well as distinct arrangements of antennal lobe olfactory glomeruli, in the specialized male macroglomerular complex (MGC). After pupal development and adult eclosion, unilateral (with one antennal disc left intact) and bilateral antennal transplant males were assayed in a wind tunnel to both species' pheromone blends to determine their ability to discriminate between the two signals. The postmetamorphic developmental effects of interspecific transplantation upon the primary olfactory centers in the moth brain were then examined in these same individuals. Behavioral tests showed that both types of unilateral transplant continued to exhibit upwind anemotactic flight to the normal recipient blend with occasional flights to the donor blend. In contrast, bilateral transplants preferred the HV pheromone blend regardless of the direction of transplant, with some males of each type also responding to the HZ blend. Neuroanatomic evaluation of the MGC revealed that the donor arrangement of MGC glomeruli was induced in 73% HZ donor to HV recipient transplants and 56% of the reciprocal transplant. Surprisingly, several V‐Z bilateral transplant males responded to both HV and HZ pheromone blends and had two HV MGC structures. This behavioral outcome was unexpected, because responses to the HV blend are mediated by inputs that are normally antagonistic to HZ males and the normal HV antenna lacks olfactory receptor neurons capable of responding to the essential minor pheromone component of the HZ blend. These data indicate a plasticity in developmental pathways regulating the expression of peripheral olfactory receptor neurons and in the glomerular processing of species‐specific olfactory information. J. Comp. Neurol. 466:377–388, 2003. © 2003 Wiley‐Liss, Inc.
Stereologic analysis of estrogen receptor alpha (ERα) expression in rat hypothalamus and its regulation by aging and estrogen
Authors: Chakraborty Tandra R. , Hof Patrick R. , Ng Laurie , Gore Andrea C. 
Published: October 2003

AbstractThe estrogen receptor alpha (ERα) in the hypothalamus plays important roles in the regulation of reproductive development, physiology, and behavior. However, the expression of the ERα may change during aging or in response to varying estrogen levels. The present study measured changes in the numbers of ERα‐expressing cells in specific hypothalamic and preoptic nuclei of ovariectomized female Sprague‐Dawley rats at three ages (young [3–4 months], middle‐aged [10–12 months], or old [24–26 months]) and with or without estrogen replacement. Numbers of ERα‐immunoreactive neurons were quantified in four regions relevant to reproductive function: the anteroventral periventricular nucleus (AVPV), medial preoptic nucleus (MPN), arcuate nucleus (ARH), and ventromedial nucleus (VMN), using an unbiased stereologic approach. In the AVPV and VMN, significant age‐related increases in the numbers of ERα‐expressing cells from the middle‐aged to the old group were detected, and no differences were observed in the MPN and ARH, indicating that ERα neuron number is maintained or even elevated during aging. No significant effects of estrogen on ERα cell number were detected in any of the four regions studied. Therefore, ERα cell number in the rat hypothalamus and preoptic area changes with aging in a region‐specific manner. J. Comp. Neurol. 466:409–421, 2003. © 2003 Wiley‐Liss, Inc.
Nanoscopic Structure of a Metallo‐supramolecular Polyelectrolyte–Amphiphile Complex, Elucidated by X‐ray Scattering and Molecular Modeling
Authors: Meister Annette , Förster Günter , Thünemann Andreas F. , Kurth Dirk G. 
Published: October 2003

AbstractA combination of molecular modeling and X‐ray scattering was used to elucidate the structure of the metallosupramolecular polyelectrolyte–amphiphile complex (PAC) self‐assembled from FeII, 1,4‐bis(2,2′:6′,2″‐terpyridin‐4′‐yl)benzene, and dihexadecyl phosphate (DHP). An approximate structure of the semi‐ordered material was derived from the analysis of the X‐ray scattering data. The experimental data provided sufficient input for obtaining a useful starting configuration for molecular modeling. Various models of the supramolecular architecture are presented and discussed in terms of their total energies and scattering patterns. In an iterative approach each level of the structural hierarchy was refined until satisfactory agreement of calculated and experimental scattering patterns was reached. The remarkable sensitivity of the simulated scattering curves to even the smallest structural changes at all length scales restricts the arbitrariness of modeling. The final model of PAC consists of flat lamellae of alternating strata of interdigitated DHP monolayers and nematically ordered polyelectrolyte chains.
Locating Dynamic Species with X‐ray Crystallography and NMR Spectroscopy: Acetone in p‐tert‐Butylcalix[4]arene
Authors: Udachin Konstantin A. , Enright Gary D. , Ratcliffe Christopher I. , Ripmeester John A. 
Published: October 2003

AbstractThe exact location and orientation of dynamic species in structural studies continues to be a serious challenge, yet it is of paramount importance in modeling guest–host interactions so as to improve our understanding of the multiple weak interactions that govern many chemical and biological processes. The acetone guest in the tBC (p‐tert‐butylcalixarene) host presents such a challenge, as initial guest positions obtained from single crystal X‐ray diffraction (XRD) are incompatible with the 2H NMR spectrum. A detailed consideration of the diffraction data showed that more complicated structural models could be constructed that were consistent with the NMR data and still yielded satisfactory diffraction residuals. These models agree that one acetone methyl group is inserted into the deep cavity, and that it exchanges with the second methyl group outside. The outside methyl group in turn can switch positions with the carbonyl group, but the distribution of the methyl and carbonyl groups over the two sites is not equal. One factor that poses additional difficulty in deciding between models is whether the actual space group is tetragonal (P4/n), or twinned monoclinic (P2/n). All of the structural models considered here disagree substantially with the one proposed in an earlier publication.
Micelle and Solvent Relaxation in Aqueous Sodium Dodecylsulfate Solutions
Authors: Fernandez Patrick , Schrödle Simon , Buchner Richard , Kunz Werner 
Published: October 2003

AbstractDielectric spectra have been measured for aqueous sodium dodecylsulfate (SDS) solutions up to 0.1 mol L−1 at 25 °C over the frequency range 0.005≤ν GHz−1≤89. The spectra exhibit two relaxation processes at approximately 0.03 GHz and 0.2 GHz associated with the presence of micelles in addition to the dominant solvent relaxation process at approximately 18 GHz and a small contribution at approximately 1.8 GHz due to H2O molecules hydrating the micelles. Detailed analysis reveals that the micelles bind 20 water molecules per SDS unit, but not as strongly as trimethylalkylammonium halide surfactants do. The relaxation times and amplitudes of both micelle relaxation processes can be simultaneously analysed with the theory of Grosse, yielding the effective volume of a SDS unit in the micelle and the lateral diffusion coefficient of the bound counterions. The findings of this investigation fully corroborate recent molecular dynamics simulations on structure and dynamics of SDS micelles.