bluuebunny/crossref_metadata_2025_split huggingface dataset:
Higher‐Order Organization by Mesoscale Self‐Assembly and Transformation of Hybrid Nanostructures
Authors: Cölfen Helmut , Mann Stephen 
Published: May 2003

AbstractThe organization of nanostructures across extended length scales is a key challenge in the design of integrated materials with advanced functions. Current approaches tend to be based on physical methods, such as patterning, rather than the spontaneous chemical assembly and transformation of building blocks across multiple length scales. It should be possible to develop a chemistry of organized matter based on emergent processes in which time‐ and scale‐dependent coupling of interactive components generate higher‐order architectures with embedded structure. Herein we highlight how the interplay between aggregation and crystallization can give rise to mesoscale self‐assembly and cooperative transformation and reorganization of hybrid inorganic–organic building blocks to produce single‐crystal mosaics, nanoparticle arrays, and emergent nanostructures with complex form and hierarchy. We propose that similar mesoscale processes are also relevant to models of matrix‐mediated nucleation in biomineralization.
Imaging magnetographs for high‐resolution solar observations in the visible and near‐infrared wavelength region
Authors: Denker C. , Didkovsky L. , Ma J. , Shumko S. , Varsik J. , Wang J. , Wang H. , Goode P.R. 
Published: May 2003

AbstractThe Coudé feed of the vacuum telescope (apertureD= 65 cm) at the Big Bear Solar Observatory (BBSO) is currently completely remodelled to accommodate a correlation tracker and a high‐order Adaptive Optics (AO) system. The AO system serves two imaging magnetograph systems located at a new optical laboratory on the observatory's 2ndfloor. The InfraRed Imaging Magnetograph (IRIM) is an innovative magnetograph system for near‐infrared (NIR) observations in the wavelength region from 1.0μm to 1.6μm. The Visible‐light Imaging Magnetograph (VIM) is basically a twin of IRIM for observations in the wavelength range from 550 nm to 700 nm. Both instruments were designed for high spatial and high temporal observations of the solar photosphere and chromosphere. Real‐time data processing is an integral part of the instruments and will enhance BBSO's capabilities in monitoring solar activity and predicting and forecasting space weather.
Evolution of temperature in granule and intergranular space
Authors: Koza J. , Bellot Rubio L.R. , Kučera A. , Hanslmeier A. , Rybák J. , Wöhl H. 
Published: May 2003

AbstractThe temporal evolution of temperature in a dissolving granule and in an adjacent intergranular space is presented. The semi‐empirical evolutionary models have been calculated using an inversion method applied to 4‐min time series of Stokes I spectral line profiles. The models are presented in the form of the functional dependence of temperature T(log τ5, t) on optical depth τ5 at 500 nm and time t. The observed disappearance of the granule is accompanied with overall cooling of the granular photosphere. Temperature changes greater than 100 K have been found in deeper (log τ5 ≥ 0) and upper layers (log τ5 ≤ –2) whereas the intermediate layers are thermally stable. The intergranular space, which is 2 arcsec off the granule, keeps the temperature structure of the layers from log τ5 = 0.5 to log τ5 = –2 without global evolutionary changes except short‐term and spatially confined heating. Finally, the significant temperature changes in the upper layers (log τ5 ≤ 2.5) observed during the time interval of 4 min are found to be typical for the granular and intergranular photosphere.
Two‐dimensional speckle spectroscopy of Hα features
Authors: Al N. , Hirzberger J. , Kneer F. 
Published: May 2003

AbstractIn May 2002, the solar chromosphere was observed with a two‐dimensional spectrometer which is mounted in the German Vacuum Tower Telescope (VTT) at the Observatorio del Teide/Tenerife. The aim of this observation was to investigate the fine structure of the solar chromosphere seen in Hα. We took narrow‐band filtergrams (Δλ ≈ 72 mÅ) by scanning through this line. Broad‐band images taken strictly simultaneously with the narrow‐band filtergrams were restored by speckle methods. The instantaneous optical transfer function from this restoration procedure was used for the reconstruction of the narrow‐band images. Some results of this high spatial resolution observation are presented below.
Visual and photoelectric measurements of the solar diameter (1972‐2002): Methods and results
Authors: Wittmann A.D. 
Published: May 2003

AbstractMeasurements of the solar diameter using both visual and photoelectric drift scan techniques have been made since 1972 using two almost identical 45‐cm Gregory‐Coudé telescopes at Locarno/Switzerland and Izaña/Tenerife. The method, in which a time measurement substitutes an angular measurement, is especially suited to obtain about 30 measurements of the absolute solar semidiameter per day. During the years 1972–2002 a total of 10996 visual timing measurements have been made on 320 observing days, an additional 1373 photoelectric recordings have been obtained on 117 observing days. The data were used to study the long‐term behaviour of the solar semidiameter R at unit distance and its possible variations. No fluctuations dR in excess of about ±0.05″ have been found, neither long‐term nor short‐term. The photoelectric semidiameter, which refers to the continuum at λ ≈ 585 nm, is Rphot = (959.89 ± 0.12)″. The visual semidiameter, which refers to the footpoint of the limb intensity profile at λ ≈ 550 nm, is Rvis = (960.62 ± 0.02)″.
Synthesis of Cytidine Ribonucleotides by Stepwise Assembly of the Heterocycle on a Sugar Phosphate
Authors: Ingar Abdul‐Aziz , Luke Richard W. A. , Hayter Barry R. , Sutherland John D. 
Published: June 2003

AbstractAlthough various syntheses of the nucleic acid bases exist and ribose is a product of the formose reaction, no prebiotically plausible methods for attaching pyrimidine bases to ribose to give nucleosides have been described. Kinetic and thermodynamic factors are thought to mitigate against such condensation reactions in aqueous solution. This inability to produce pyrimidine nucleosides and hence nucleotides is a major stumbling block of the “RNA World” hypothesis and has led to suggestions of alternative nucleic acids as evolutionary precursors to RNA. Here, we show that a process in which the base is assembled in stages on a sugar phosphate can produce cytidine nucleotides. The sequential action of cyanamide and cyanoacetylene on arabinose‐3‐phosphate produces cytidine‐2′,3′‐cyclophosphate and arabinocytidine‐3′‐phosphate.
Alkyne Migration in Alkylidene Carbenoid Species: A New Method of Polyyne Synthesis
Authors: Eisler Sara , Chahal Navjot , McDonald Robert , Tykwinski Rik R. 
Published: June 2003

AbstractThe synthesis of conjugated polyyne structures via a modification of the Fritsch–Buttenberg–Wiechell (FBW) rearrangement is reported. Our adaptation provides for the 1,2‐migration of an alkyne in a carbene/carbenoid intermediate that is conveniently effected via lithium–halogen exchange with the appropriate dibromo‐olefinic precursor. This rearrangement is quite rapidly accomplished under mild conditions (hexane solution, −78 °C), and the seemingly high migratory aptitude of the alkynyl moiety provides for efficient rearrangement. This, in turn, allows for multiple rearrangements in a single molecule, greatly facilitating the construction of highly unsaturated substrates. This procedure is exploited for the rapid synthesis of symmetrical and unsymmetrical 1,3,5‐hexatriynes, extended polyynes, and aryl polyyne building blocks. Most significantly, many of these structures have been or would be difficult to access via more traditional transition metal catalyzed homo‐ or cross‐coupling techniques.
Unprecedented Living Olefin Polymerization Derived from an Attractive Interaction between a Ligand and a Growing Polymer Chain
Authors: Mitani Makoto , Nakano Takashi , Fujita Terunori 
Published: June 2003

AbstractTi complexes incorporating fluorine‐containing phenoxy–imine chelate ligands (fluorinated Ti‐FI catalysts) have been demonstrated to induce an unprecedented living polymerization effect with both ethylene and propylene, through an attractive interaction between the fluorine atom in the ligand and a β‐hydrogen atom on the growing polymer chain. With the aid of this attractive interaction, highly controlled living ethylene polymerization, highly‐syndiospecific living propylene polymerization, the synthesis of unique block copolymers from ethylene and propylene, and the catalytic production of monodisperse polyethylene and Zn‐terminated polyethylene have been realized. The attractive interaction provides a conceptually new strategy for the achievement of controlled living olefin polymerization.
BaP4Te2—A Ternary Telluride with PTe Bonds and a Structural Fragment of Black Phosphorus
Authors: Jörgens Stefan , Johrendt Dirk , Mewis Albrecht 
Published: June 2003

AbstractThe new telluride BaP4Te2 was synthesized in form of gleaming black needles by heating stochiometric mixtures of the elements to 475 °C for 100 h. The crystal structure was determined by single‐crystal Xray methods. BaP4Te2 crystallizes orthorhombically, space group Pnma with a=16.486(8), b=6.484(2), c=7.076(4) Å, and Z=4. A main feature of the so far unknown crystal structure type are P4Te2 chains that consist of condensed six‐membered rings of phosphorus. These strands are equivalent to a structural fragment of black phosphorus, in which each of the lateral atoms is connected to a tellurium atom. The chains running along [0 1 0] are separated from each other by barium atoms, that is, linked through BaTe and BaP bonds. BaP4Te2 is an electron precise compound according to the Zintl concept, and the formula can be split ionically as follows: BaP4Te2≡Ba2+(P0)4(Te−)2. The remarkable TeP bonds have been analyzed by electronic structure calculations using the electron localization function (ELF) and the crystal orbital Hamiltonian population (COHP) methods.
Enantioseparation of racemic 4‐aryl‐3,4‐dihydro‐2(1H)‐pyrimidones on chiral stationary phases based on 3,5‐dimethylanilides of N‐(4‐alkylamino‐3,5‐dinitro)benzoyl L‐α‐amino acids
Authors: Kontrec Darko , Vinković Vladimir , Šunjić Vitomir , Schuiki Birgit , Fabian Walter M.F. , Kappe C. Oliver 
Published: May 2003

AbstractThree novel chiral packing materials for high‐performance liquid chromatography were prepared by covalently binding of (2S)‐N‐(3,5‐dimethylphenyl)‐2‐[(4‐chloro‐3,5‐dinitrophenyl)carbonylamino]propan‐amide (7), (2S)‐N‐(3,5‐dimethylphenyl)‐2‐[(4‐chloro‐3,5‐dinitrophenyl)carbonylamino]‐4‐methylpentanamide (8), and (2S)‐N‐(3,5‐dimethylphenyl)‐2‐[(4‐chloro‐3,5‐dinitrophenyl)carbonyl‐amino]‐2‐phenylacetamide (9) to aminopropyl silica. The resulting chiral stationary phases (CSPs 1–3) proved effective for the resolution of racemic 4‐aryl‐3,4‐dihydro‐2(1H)‐pyrimidone derivatives (TR 1–14). The mechanism of their enantioselection, supported by the elution order of (S)‐TR 13 and (R)‐TR 13 and molecular modeling of the complex of the slower running (S)‐TR 13 with CSP 1 is discussed. Chirality 15:550–557, 2003. © 2003 Wiley‐Liss, Inc.
Chiral discrimination of 2‐arylalkanoic acids by (1S,2S)‐1‐aminoindan‐2‐ol and (1S,2S)‐2‐aminoindan‐1‐ol: Correlation of the relative configuration of the amino and hydroxy groups with the pattern of a supramolecular hydrogen‐bond network in the less‐soluble diastereomeric salt
Authors: Kinbara Kazushi , Katsumata Yoshiyuki , Saigo Kazuhiko 
Published: May 2003

AbstractThe diastereomeric resolution of 2‐arylalkanoic acids with enantiopure trans‐1‐aminoindan‐2‐ol and trans‐2‐aminoindan‐1‐ol were studied. Enantiopure trans‐1‐aminoindan‐2‐ol had a moderate resolving ability for 2‐arylalkanoic acids having a naphthyl group as an aryl substituent at the α‐position, while enantiopure trans‐2‐aminoindan‐1‐ol had a moderate‐to‐high resolving ability for a wide variety of the acids having a methyl group as an alkyl substituent at the α‐position. The crystal structures of the corresponding less‐soluble salts revealed that a reinforced columnar hydrogen‐bond network was formed in the less‐soluble salts with trans‐1‐aminoindan‐2‐ol, while a rather stable hydrogen‐bond sheet was generated with the assistance of water molecules in the less‐soluble salts with trans‐2‐aminoindan‐1‐ol. These results suggest that not only the relative configuration but also the position of the hydrogen‐bonding groups in resolving agents have a considerable effect on the structure of the less‐soluble salts. The difference in favorable hydrogen‐bond structure determined the adaptivity to the structural feature of target racemic 2‐arylalkanoic acids in the resolution by trans‐1‐aminoindan‐2‐ol and trans‐1‐aminoindan‐2‐ol, respectively. Chirality 15:564–570, 2003. © 2003 Wiley‐Liss, Inc.
Effect of constituting amino acid residue numbers on molecularly imprinted chiral recognition sites
Authors: Kondo Yoshiko , Morita Yukihiro , Fujimoto Atushi , Tounai Masahiko , Kimura Satoshi , Yoshikawa Masakazu 
Published: May 2003

AbstractIn the present study, the effect of constituting amino acid residue numbers of oligopeptide derivatives, which are candidate materials to construct molecular recognition sites, on chiral recognition ability was investigated. Chiral recognition sites were formed from oligopeptide derivatives, of which constituting amino acid residue numbers were three to six, by adopting an alternative molecular imprinting. It was made clear that the number four, in other words, the tetrapeptide derivative, is the best candidate material to form a chiral recognition site. Chirality 15:498–503, 2003. © 2003 Wiley‐Liss, Inc.
Chiroptical properties and synthesis of enantiopure cis and trans Pterocarpan Skeleton
Authors: Kiss Loránd , Kurtán Tibor , Antus Sándor , Bényei Attila 
Published: May 2003

AbstractThe first enantioselective synthesis of trans‐(6aS,11aR)‐pterocarpan [(+)‐2] and its conversion to cis‐(6aS,11aS)‐pterocarpan [(+)‐1] was achieved starting from racemic 2′‐benzyloxyflavanone (rac‐3). Their stereochemistry was deduced by X‐ray analysis of the ketal intermediate (–)‐5a. The CD study of (+)‐1 and (+)‐2 allows the configurational assignment of similar pterocarpan derivatives by CD spectroscopy. Chirality 15:558–563, 2003. © 2003 Wiley‐Liss, Inc.
Diastereoselective [2+2] photocycloaddition of chiral cyclohexenonecarboxylates to ethylene
Authors: Tsutsumi Ken , Endou Katsunori , Furutani Akinori , Ikki Tomomi , Nakano Hiroaki , Shintani Takuya , Morimoto Tsumoru , Kakiuchi Kiyomi 
Published: May 2003

AbstractThe diastereoselective [2+2] photocycloaddition of cyclohexenonecarboxylates containing various chiral auxiliaries to ethylene is described. The effect of the auxiliary, reaction temperature, and solvent on diastereoselectivity was examined. The (−)‐8‐(p‐methoxyphenyl)menthyl group was found to be the most effective chiral auxiliary. The photoreaction of (−)‐8‐(p‐methoxyphenyl)menthyl cyclohexenonecarboxylate in methylcyclohexane at −78°C gave the corresponding bicyclo[4.2.0]octanone derivative in 81% diastereomeric excess (d.e.). The extent of diastereoselectivity was found to be closely related to the most stable π‐stack conformation of the starting cyclohexenones. Chirality 15:504–509, 2003. © 2003 Wiley‐Liss, Inc.
Preparation of enantiomeric gossypol by crystallization
Authors: Dowd Michael K. 
Published: May 2003

AbstractLarge enantiomorphic crystals of gossypol‐acetone (1:3) were grown from acetone solutions of rac‐gossypol‐acetic acid (1:1) at 4°C. By controlling the initial gossypol concentration, crystallization time, and solution volume, single crystals were grown that weighed >50 mg, equivalent to >37 mg of enantiomeric gossypol. Even larger crystals were possible, but it was difficult to produce these reliably without contamination of the antipode. Essentially all of the acetone within the crystal form was removed by storing the crystals under vacuum for 3–4 days. By employing these techniques, gram quantities of enantiomeric gossypol were prepared in high chemical and optical purity. Based on measured and reported optical rotations, the optical purity of samples prepared by crystallization was greater than the optical purity of samples prepared by chromatographic separation of gossypol‐amine diastereomers. The principal limitation of crystallization as a preparative method is the need to determine the chirality and purity of each product crystal. Nevertheless, the method competes favorably with preparative‐scale chromatographic procedures. Chirality 15:486–493, 2003. Published 2003 Wiley‐Liss, Inc.
Enantiomeric separation by HPLC of 1,4‐dihydropyridines with vancomycin as chiral selector
Authors: Boatto Gianpiero , Nieddu Maria , Faedda Maria Virginia , de Caprariis Paolo 
Published: May 2003

AbstractThe macrocyclic antibiotics represent a relatively new class of chiral selectors in CE, HPLC, and TLC. We have examined the use of the macrocyclic antibiotic vancomycin as a chiral selector in HPLC for the separation of 1,4‐dihydropyridines (DHPs) calcium antagonists (CAs). Chromatographic data of six 1,4‐dihydropyridine calcium channel blockers obtained on the vancomycin chiral stationary phase (Chirobiotic V) were compared with those obtained on an α1‐acid glycoprotein (AGP) HPLC stationary phase. Optimization of pH and organic modifier was carried out in order to modulate the retention properties of each system. All chiral neutral DHPs were resolved on the AGP column, whereas on Chirobiotic V only basic DHPs showed a split peak. The analytical chromatographic procedure on Chirobiotic V proved suitable for semipreparative separation, since the separation factor on the analytical column was high enough to obtain pure enantiomers with high yields. Chirality 15:494–497, 2003. © 2003 Wiley‐Liss, Inc.
Racemization and degradation of thioridazine and thioridazine 2‐sulfone in human plasma and aqueous solutions
Authors: Masetto de Gaitani Cristiane , Martinez Alexandre Souto , Bonato Pierina Sueli 
Published: May 2003

AbstractWe present two methods for the enantioselective analysis of thioridazine (THD) and thioridazine 2‐sulfone (THD 2‐SO2) in human plasma based on liquid–liquid extraction with diethyl ether and chiral resolution of the enantiomers on Chiralpak AD and Chiralcel OD‐H columns, respectively. After validation, the methods were used to study the degradation and racemization of both drug and metabolite. Our results showed that both enantiomers of THD and THD 2‐SO2 were stable at varying temperatures, pH, and ionic strengths; however, solubility problems for THD and THD 2‐SO2 enantiomers were observed, mainly at pH 8.5. The influence of light on the stability of the THD and THD 2‐SO2 enantiomers was also studied. Degradation of the THD enantiomers was observed under UV light (254 and 366 nm) while THD 2‐SO2 enantiomers were stable at these wavelengths and also when exposed to visible light. Chirality 15:479–485, 2003. © 2003 Wiley‐Liss, Inc.
First asymmetric synthesis of (–)‐lintetralin via intramolecular Friedel‐Crafts‐type cyclization
Authors: Enders Dieter , del Signore Giuseppe , Berner Otto Mathias 
Published: May 2003

AbstractThe asymmetric synthesis of an aryltetralin lignan, (–)‐lintetralin, was achieved with an overall yield of 29% with seven steps. Key features of the synthesis are an asymmetric Strecker reaction, a diastereoselective Michael addition of the lithiated amino nitrile product to 5H‐furan‐2‐one, and an intramolecular carbocationic cyclization to provide the desired ring skeleton with the correct configuration. Chirality 15:510–513, 2003. © 2003 Wiley‐Liss, Inc.
Synthesis and reactivity of N‐protected‐α‐amino aldehydes
Authors: Gryko Dorota , Chałko Joanna , Jurczak Janusz 
Published: May 2003

AbstractDuring the last decade α‐amino aldehydes have attracted widespread attention as the important natural source of chiral substrates useful in stereocontrolled organic synthesis. They are of special interest due to their ready availability in both enantiomeric forms from natural sources, as well as their pronounced versatility, due to the presence of both the formyl group and suitably protected amino functionality in the molecule. These bifunctional compounds exhibit a valuable dual reactivity, which has been utilized in a broad range of synthetic applications. Chirality 15:514–541, 2003. © 2003 Wiley‐Liss, Inc.
Stereoselective metabolism of metoprolol: Enantioselectivity of α‐hydroxymetoprolol in plasma and urine
Authors: Cerqueira Paula Macedo , Cesarino Evandro José , Bertucci Carlo , Bonato Pierina Sueli , Lanchote Vera Lucia 
Published: May 2003

AbstractDirect stereoselective separation on chiral stationary phase was developed for HPLC analysis of the four stereoisomers of α‐hydroxymetoprolol in human plasma and urine. Plasma samples were prepared using solid‐phase extraction columns and urine samples were prepared by liquid–liquid extraction. The stereoisomers were separated on a Chiralpak® AD column at 24°C with fluorescence detection and a mobile phase consisting of a mixture of hexane:ethanol:isopropanol:diethylamine (88:10.2:1.8:0.2) for plasma samples and hexane:ethanol:diethylamine (88:12:0.2) for urine samples. Calibration curves for the individual stereoisomers were linear within the concentration range of 2.0–200 ng/ml plasma or 0.125–25 μg/ml urine. The methods were validated with intra‐ and interday variations less than 15%. The absolute configuration of the pure stereoisomers were assigned by circular dichroism spectra. The methods were employed to determine the concentrations of α‐hydroxymetoprolol stereoisomers in a metabolism study of multiple‐dose administration of racemic metoprolol to hypertensive patients phenotyped as extensive metabolizers of debrisoquine. We observed stereo‐selectivity in the α‐hydroxymetoprolol formation favoring the new 1′R chiral center from both metoprolol enantiomers (AUC0–241′R1′S = 3.02). The similar renal clearances (ClR) of the four stereoisomers demonstrated absence of stereoselectivity in their renal excretion. (–)‐(S)‐metoprolol was slightly more α‐hydroxylated than its antipode (AUC0–242S/2R = 1.19), suggesting that this pathway is not responsible for plasma accumulation of this enantiomer in humans. Chirality 15:542–549, 2003. © 2003 Wiley‐Liss, Inc.
Optimization of thermal conditions during crystal growth in a multi‐zone resistance furnace
Authors: Lin K. , Dold P. , Benz K.W. 
Published: June 2003

AbstractThe thermal condition is one the of most important control parameters for crystal growth. In this paper we present an effective numerical method in detail for optimizing thermal conditions in multi‐zone crystal growth facilities, especially for crystal growth by the float zone (FZ) technique. A furnace function Ω is introduced to integrate the character of a growth furnace into a linear equation system. The desired power distribution can be therefore approached by solving the linear equation system iteratively. An expert systemlike algorithm has been developed in order to obtain a more suitable solution for practical applications. This method was used to investigate thermal parameters for experiments of SiGe/GeSi single crystal growth by the FZ technique. It is an individual program which can be combined with any commercial finite element/finite volume (FE/FV) program such as FIDAPTM.