bluuebunny/crossref_metadata_2025 huggingface dataset:
Bonding States of He, Ne and Ar in Solid C60
Authors: Ichimura Kenji , Imaeda Kenichi , Inokuchi Hiroo
Published: June 2003

He, Ne and Ar are intercalated in a lattice of C60 under the conditions of ambient temperature and pressure. The mass-analyzed thermal desorption reveals that rare gases are desorbed above 400 K and their desorption amounts are not in impurity level but in stoichiometric level. X-Ray photoelectron spectra in the C1s and valence band regions show different peak profiles. These results indicate that He, Ne and Ar atoms in a C60 lattice are in the bonding state.
Electron Spin-Echo Envelope Modulation Spectral Properties of Amidate Nitrogen Coordinated to Oxovanadium(IV) Ion
Authors: Fukui Kôichi , Fujii Hiroshi , Ohya-Nishiguchi Hiroaki , Kamada Hitoshi
Published: June 2003

Electron spin-echo envelope modulation (ESEEM) measurements have been performed for a VO2+-amidate complex, [VIVO(hybeb)]2− (H4hybeb = 1,2-bis(2-hydroxybenzamido)benzene). ESEEM spectroscopic properties of the amidate 14N nucleus have been characterized for the first time (|Aiso| = 6.70 MHz; e2qQ/h = 2.5 MHz, η = 0.04) to provide a basis for the studies of vanadium-peptide interactions. The electronic structure of the amidate nitrogen is discussed.
2-Bromo-1-ethyl Pyridinium Tetrafluoroborate (BEP): A Powerful Coupling Reagent for N-Methylated Peptide Synthesis
Authors: Li Peng , Xu Jie Cheng
Published: June 2003

2-Bromo-1-ethyl pyridinium tetrafluoroborate (BEP) was firstly utilized to the synthesis of peptides containing N-methyl amino acid residues both in solution and solid phase, and demonstrated high reactivity, low racemization and excellent yields, which were approved by the successful synthesis of a series of oligopeptides and hindered peptide fragments, such as the 8-11 segment of Cyclosporine A and the pentapeptide moiety of Dolastatin 15.
Pyrolytic Formation of C19 Isoprenoid Hydrocarbons from Dihydrophytol: in Relation to the Genesis of Pristane in Petroleum
Authors: Ishiwatari Mariko , Yamada Keita , Ishiwatari Ryoshi
Published: June 2003

This study was concluded to elucidate a pathway for formation of C19 isoprenoid hydrocarbons (isops) in petroleum from chlorophylls. C19 isops are predominantly produced when dihydrophytol is heated at 320 °C for a period ranging from 1 to 5 h under vacuum while C20 isops are predominantly produced when chlorophyll a or phytol is heated. A radical chain reaction of decomposition of dihydrophytol is proposed as plausible pathway for producing C19 isops.
Separation and Concentration of Trace Lead by Coprecipitation with Yttrium Phosphate
Authors: Kagaya Shigehiro , Araki Yasuko , Hasegawa Kiyoshi
Published: June 2003

Yttrium phosphate coprecipitates quantitatively lead and iron(III) and hardly does chromium(III), manganese(II), cobalt, nickel, copper, and zinc and alkali and alkaline earth metals at pH about 3. The determination of lead separated and concentrated by the coprecipitation was demonstrated using flame atomic absorption spectrometry.
Voltammetric Behaviors of Lectin-Sugar Binding Using Au Electrode Modified with Galactosamine
Authors: Sugawara Kazuharu , Ueda Ken , Kuramitz Hideki , Hoshi Suwaru , Akatsuka Kunihiko , Tanaka Shunitz
Published: June 2003

Voltammetric behaviors of binding between soybean agglutinin (SBA) having sites for galactosamine and the sugar were investigated. A self-assembled monolayer (SAM) of galactosamine was designed on an Au electrode surface, and SBA-galactosamine interaction was monitored through ferrocyanide ion as marker. Electrode responses of ferrocyanide ion decreased with increasing the concentrations of the SBA. This is because SBA selectively combines to sugar part on the electrode surface. To confirm the binding, voltammetric behaviors of several lectins not having sites for galactosamine were compared to that of SBA.
Preparation of Plate-shaped Crystals of Li2MnO3 by Reaction at a Solid/LiCl-Flux/Air Interface in a Tilted Crucible
Authors: Tang Weiping , Kanoh Hirofumi , Ooi Kenta
Published: June 2003

Plate-shaped crystals of Li2MnO3, red-colored with glossy surface, were obtained over a tilted crucible by LiCl flux evaporation at 923 K for 5 days. The growth of the Li2MnO3 crystal plates proceeded at the interface of three phases, i.e. the LiCl flux, the precipitated powder, and the atmosphere on the tilted crucible. The moving solid-liquid-air interface due to the continuous evaporation of LiCl flux plays an important role in the growth of Li2MnO3 crystal plate.
Formation of Zirconacyclohexadienes from Zirconacyclopentadienes and LiCHClSiR3
Authors: Xi Zhenfeng , Huo Shouquan , Noguchi Yoshinori , Takahashi Tamotsu
Published: June 2003

Six-membered zirconacyclohexadienes were formed by insertion of LiCHClSiR3 into zirconacyclopentadienes.
Highly Diastereoselective Photochromic Cyclization of a Bisthienylfulgide
Authors: Yokoyama Yasushi , Sagisaka Toshiya , Yamaguchi Yoshiro , Yokoyama Yayoi , Kiji Jitsuo , Okano Tamon , Takemoto Akiko , Mio Shin-ya
Published: June 2003

A fulgide, 3,4-bis[1-(2,5-dimethyl-3-thienyl)ethylidene]-3,4-dihydro-2,5-furandione, was synthesized by Pd-catalyzed carbonylation of the corresponding 2-butyne-1,4-diol derivative. UV-irradiation to the ZZ-form in toluene resulted in the formation of two diastereomeric colored forms by way of EE- and EZ-forms. The colored form from the EE-form was predominant in 90% de.
A Density Functional Study for Hydrogen Bond Energy by Employing Real Space Grids
Authors: Takahashi Hideaki , Hori Takumi , Wakabayashi Tadafumi , Nitta Tomoshige
Published: June 2003

In order to examine the efficiency of a nobel real space grid method for density functional theory (DFT) calculations, the hydrogen bond energy of the water dimer was computed. It was demonstrated that the real space grid augmented by double grid near the atomic core can yield a realistic hydrogen bond energy curve of the water dimer.
Ni-Catalyzed Homocoupling of 3-Halopropenoates in the Presence of Water: Formation of Hexendioates
Authors: Kotora Martin , Matsumura Hiroshi , Takahashi Tamotsu
Published: June 2003

Homocoupling of (Z)-3-halopropenoates using a catalytic amount of NiCl2 and Zn in the presence of water in pyridine afforded a mixture of (Z)- and (E)-3-hexenedioates.
Reaction of a Stable Silylene–Isocyanide Complex with Nitrile Oxides: A New Approach to the Generation of a Silanone
Authors: Takeda Nobuhiro , Tokitoh Norihiro , Okazaki Renji
Published: June 2003

An overcrowded silanone [Tbt(Mes)Si=O; Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Mes = mesityl] (8) was generated via intermediary 1,2,4-oxazasiletes by the reaction of a stable silylene–isocyanide complex with nitrile oxides. In a THF solution, silanone 8 underwent intramolecular cyclization with migration of a trimethylsilyl group in Tbt group to the oxygen atom of the Si=O double bond.
Addition of Dichloro- and Dibromocarbene to 1,2-Diphenylcyclobutene
Authors: Wagner Robert A , Weber Jürgen , Brinker Udo H
Published: June 2003

1,2-Diphenylcyclobutene (7) was reacted with dibromo- and dichlorocarbene, both generated via three different methods. 1,3-Diphenyl-2-halocyclopenta-1,3-dienes 12 were isolated which result from addition of the dihalocarbenes to the cyclobutene double bond of 7. A cationic cyclopropyl-allyl rearrangement (CCA) in gem-dihalobicyclopentanes 8 leads to 2,3-dihalocyclopentenes 9, which under the reaction conditions are dehydrohalogenated to 12. A second carbene addition and rearrangement afford aromatic compounds 11 and 16.
Preparation, Structures and Properties of Novel Mono- and Trinuclear Iron(III) Complexes with Mixed Ligands
Authors: Nakamura Toshio , Kuranuki Etsuko , Niwa Kenshin , Fujiwara Manabu , Matsushita Takayuki
Published: June 2003

Novel mono- and trinuclear iron(III) complexes with mixed ligands, FeIII(acac)(N-PhO-sal)(MeOH) 1 and FeIII3(acac)(N-PhO-sal)4  2 have been prepared and characterized, where acacH and N-PhOH-salH denote acetylacetone and N-2-hydroxyphenyl-salicylideneamine, respectively. The variable temperature magnetic susceptibilities (2-350 K) for complex 2 indicate that there is an intramolecular antiferromagnetic interaction among the iron(III) ions, and that spin-crossover behavior may take place from S = 5/2, 5/2 and 5/2 ground states to S = 1/2, 5/2 and 1/2 (Fe1, Fe2 and Fe1*) near 60 K and below.
Association and Guest-induced Dissociation of a Novel α-Helix Peptide Bearing Pyrene and γ-Cyclodextrin in the Side Chains
Authors: Hossain Mohammed Akhter , Hamasaki Keita , Mihara Hisakazu , Ueno Akihiko
Published: June 2003

A designed α-helix peptide, γ-PR17, which bears γ-cyclodextrin (γ-CD) and pyrene units, exhibits both monomer and excimer emissions, indicating that γ-PR17 forms an association dimer that could be dissociated upon addition of hyodeoxycholic acid as a guest for γ-CD.
Dramatic Increase in Thermal Stability by Partial Phenylethynylation at the Silicon Center in Poly[(dihydrosilylene)-1,3-phenylene]
Authors: Reddy Poreddy Narsi , Hayashi Teruyuki , Tanaka Masato , Itoh Masayoshi
Published: June 2003

Partial ethynylation of the Si-H in poly[(dihydrosilylene)(1,3-phenylene)] dramatically increases thermal stability of the polymer. The Td5 value observed for [SiH1.44(C≡CPh)0.56(1,3-C6H4)]n is 820 °C, which is much higher than the value (586 °C) of a commercial polyimide (Kapton, DuPont).
A New Feature of Bifunctional Catalysis. Cyclodextrins Bearing Two Imidazole Moieties as Hydrolysis Enzyme Model
Authors: Lee Woo-Sang , Ueno Akihiko
Published: June 2003

β-Cyclodextrin derivatives bearing two imidazole rings at AC, AD glucose residues (AC and AD isomers) exhibit much higher catalytic activity in hydrolysis of p-nitrophenyl acetate than AB isomer, showing a bell-shaped pH profile with a peak at pH 7.2. They accelerate the hydrolysis of Boc-alanine-p-nitrophenyl ester with remarkable d-substrate preference.
Carrier Mobilities in a Regioregular Poly(3-octylthiophene) Film at Various Oxidation Stages
Authors: Kunugi Yoshihito , Harima Yutaka , Yamashita Kazuo , Ohta Nobuaki , Ito Sotaro
Published: June 2003

Apparent mobilities of positive charge carriers in a regioregular poly(3-octylthiophene) film in varying oxidation states were successfully evaluated by using electrochemical techniques. Electrochemical ClO4− doping caused a decrease of the mobility by about one order of magnitude until the doping level reached about 2%. Further electrochemical doping resulted in the drastic increase of the mobilities up to 0.5 cm2 V−1 s−1 at a maximum doping level of 23%.
Preparation of Highly Dispersed Cu on TiO2 Using Cu(II) Complexes
Authors: Nagashima Koji , Kokusen Hisao , Ueno Norieda , Matsuyoshi Ayako , Kosaka Tomomi , Hasegawa Miki , Hoshi Toshihiko , Ebitani Kohki , Kaneda Kiyotomi , Aritani Hirofumi , Hasegawa Sadao
Published: June 2003

TiO2-supported Cu samples were prepared by using several Cu precursors, and isolated Cu2+ ions and their behavior of thermal reduction were evaluated by means of ESR spectroscopy. Only 50% of Cu2+ were reduced to Cu+ or Cu0 by using cupric nitrate as a precursor. Highly dispersed Cu ions on TiO2 could be obtained by using Cu2+ complexes (Cu(acac)2 and Cu(dbm)2) as a precursor.
The Fast Photovoltaic Response from Multilayer by Alternate Layer-by-layer Assembly of Polycation and Bacteriorhodopsin
Authors: Li Meiling , Li Baofang , Jiang Long , Tussila Tapio , Tkachenko Nikolai , Lemmetyinen Helge
Published: June 2003

A thin multilayer film, formed by alternate deposition of poly(dimethyldiallylammonium chloride) (PDAC) and bacteriorhodopsin (bR) (pH = 9), generated a photovoltage with defined polarities upon one flash excitation. Three time constants of 2.59 µs, 13.64 µs and 58.03 µs fitting to the kinetics of photovoltage were assigned to the decay of K, L1 and L2 intermediates of bR photocycle respectively. The positive photovoltage accompanying the formation of M indicated that the cytoplasmic side of PM fragments was directed toward the substrate.
Photochromism of Bis Schiff Base N,N′-Bis(Salicylidene)-1,2-Cyclohexanediamine
Authors: Zhao Jianzhang , Zhao Bing , Liu Juzheng , Ren Aimin , Feng Jikang
Published: June 2003

The photochromism of N,N′-bis(salicylidene)-1,2-cyclohexanediamine was studied by time-dependent UV-Vis absorption spectra, fluorescence spectra and INDO/SCI methods. The photo-product was determined to be the two-proton-transferred cis-keto form.
Synthesis of Pentamethyl-monohydro[60]fullerene C60Me5H and Its Use as Cyclopentadienyl-Type Ligand Precursor
Authors: Sawamura Masaya , Toganoh Motoki , Kuninobu Yoichiro , Kato Seiichi , Nakamura Eiichi
Published: June 2003

Pentamethyl-monohydro[60]fullerene C60Me5H has been synthesized through five-fold addition of methylcopper reagent to C60. The anion C60Me5− generated by deprotonation of C60Me5H forms organometallic complexes with K+ and Tl+ ions with stronger metal-carbon interaction than that in the corresponding pentaphenylated ligand C60Ph5−.
Effect of Molecular Sieves and Methanol on the endo-Selectivity in La(Otf)3-catalyzed Cyclization of 5-Hydroxy-2-methoxymethyl-1,2-epoxide System
Authors: Tokiwano Tetsuo , Fujiwara Kenshu , Murai Akio
Published: June 2003

Molecular sieves improved the reproducibility of the cyclization catalyzed by La(Otf)3 in the 5-hydroxy-2-methoxymethyl-1,2-epoxide system, and addition of methanol raised the desired endo-selectivity.
Synthesis and Crystal Structure of a Water-soluble Gold(I) Complex, {K3[Au(mba)2]}2 Formed by 2-Mercaptobenzoic Acid (H2mba), with Aurophilic Interaction in the Solid-State
Authors: Nomiya Kenji , Noguchi Ryusuke , Sakurai Tomohiro
Published: June 2003

Medicinally active, water-soluble and anionic gold(I) complex {K3[Au(mba)2]}2  1 formed by 2-mercaptobenzoic acid (H2mba) was isolated and its crystal structure determined. The molecular structure in the solid-state comprised a dimeric (AuS2)2 core through a short gold(I)-gold(I) contact (3.1555(7) Å), i.e., the aurophilic interaction.
Crystallization of Newly Synthesized Syndiotactic Graft Copolymers
Authors: Senoo Kazunobu , Endo Kiyoshi , Murakami Syozo , Tosaka Masatoshi
Published: June 2003

Crystallization behavior of newly synthesized syndiotactic graft copolymers of polystyrene having side chains of atactic polystyrene (APS) or of polyisoprene were studied. The APS side chains were found to have rather strong effect to prevent crystallization of the main chain of syndiotactic polystyrene.
Enhancing the NO/C3H8/O2 Reaction by Using H2 over Ag/Al2O3 Catalysts under Lean-Exhaust Conditions
Authors: Satokawa Shigeo
Published: June 2003

We examine the effect of H2 on the selective reduction of NO by C3H8 over Ag/Al2O3 catalysts under lean-exhaust conditions. The NO reduction activity caused by C3H8 at low temperature (590-760 K) is greatly increased by adding H2 in the presence of excess oxygen and water vapor.
Electrochemistry of Poly(3,4‐alkylenedioxythiophene) Derivatives
Authors: Groenendaal L. , Zotti G. , Aubert P.‐H. , Waybright S.M. , Reynolds J.R.
Published: June 2003

An overview of the electrochemistry of poly(3,4‐alkylenedioxythiophene)s (PXDOTs) is presented. As a class of conducting and electroactive polymers that can exhibit high and quite stable conductivities, a high degree of optical transparency as a conductor, and the ability to be rapidly switched between conducting doped and insulating neutral states, PXDOTs have attracted attention across academia and industry. Numerous fundamental aspects are addressed here in detail, ranging from the electrochemical synthesis of PXDOTs, a variety of in‐situ characterization techniques, the broad array of properties accessible, and morphological aspects. Finally, two electrochemically‐driven applications, specifically electrochromism and chemical sensors of PXDOTs are discussed.
Strong Optical Limiting of Soluble Axially Substituted Gallium and Indium Phthalocyanines
Authors: Chen Y. , Fujitsuka M. , O'Flaherty S.M. , Hanack M. , Ito O. , Blau W.J.
Published: June 2003

Optical limiting in In‐ and Ga‐phthalocyanines exhibits a range of saturation densities and absorption cross‐section ratios. Substitution of the p‐trifluoromethylphenyl group at the central metal in tBu4PcGaCl and tBu4PcInCl reduces the saturation energy density by a factor of >3. Tailorable optical limiting properties are shown in the Figure, which plots the nonlinear absorption coefficient as a function of intensity for the five compounds studied.
Highly Efficient Red Electrophosphorescent Devices Based on Iridium Isoquinoline Complexes: Remarkable External Quantum Efficiency Over a Wide Range of Current
Authors: Su Y.‐J. , Huang H.‐L. , Li C.‐L. , Chien C.‐H. , Tao Y.‐T. , Chou P.‐T. , Datta S. , Liu R.‐S.
Published: June 2003

Outstanding performance as an emissive dopant in organic light‐emitting devices is shown by red phosphorescent iridium complexes based on an isoquinoline framework (such as that shown in the Figure). Remarkably high efficiency can be maintained in the devices at high currents with a negligible effect from either triplet–triplet (T–T) annihilation or saturation of the excited states.
Soluble Microcapsules Assembled Stepwise from Weak Polyelectrolytes Using Acid‐Decomposable Cores
Authors: Gao C.‐Y. , Möhwald H. , Shen J.‐C.
Published: June 2003

Decomposable microcapsules with tunable permeability, loading, and release properties—with potential applications as chemical reservoirs and for controlled drug release—have been fabricated by assembly of weak polyelectrolytes on melamine formaldehyde templates followed by removal of the cores at low pH by precise control of the time of acid treatment. The Figure shows capsules before (left) and after (right) treatment with 0.1 M HCl.
Tunable and Latchable Liquid Microlens with Photopolymerizable Components
Authors: Yang S. , Krupenkin T.N. , Mach P. , Chandross E.A.
Published: June 2003

A novel liquid microlens with photopolymerizable components is described (see Figure). When the lens is in liquid form, both its position and curvature can be reversibly tuned through electrowetting. After the liquid microlens is precisely aligned on the substrate, it is exposed to UV light to initiate polymerization and thus lock its position and shape.
Photonic Papers and Inks: Color Writing with Colorless Materials
Authors: Fudouzi H. , Xia Y.
Published: June 2003

A photonic paper/ink system for color writing on and with colorless materials is described. The “paper” is a 3D crystal of polymer beads embedded in an elastomer matrix made of poly(dimethylsiloxane) (PDMS), and the “ink” is a liquid (e.g., a silicone fluid or organic solvent) capable of swelling the matrix, changing the lattice constant and hence wavelength of light diffracted (see Figure and cover).
Titelbild: Expanding the Functional Group Compatibility of Small‐Molecule Microarrays: Discovery of Novel Calmodulin Ligands (Angew. Chem. 21/2003)
Authors: Barnes‐Seeman David , Park Seung Bum , Koehler Angela N. , Schreiber Stuart L.
Published: May 2003

Mikroarrays aus kleinen Molekülen ermöglichen die robuste und skalierbare Suche nach Ligand‐Protein‐Wechselwirkungen. Das Titelbild zeigt das Protein Calmodulin im Komplex mit einem kleinen Molekül, das mithilfe der neuartigen “Slide‐Capture”‐Methode auf einer Glasoberfläche immobilisiert wurde. Mehr über diese Technik und ihre Anwendung erfahren Sie in der Zuschrift von S. L. Schreiber et al. auf S. 2478ff.
Higher‐Order Organization by Mesoscale Self‐Assembly and Transformation of Hybrid Nanostructures
Authors: Cölfen Helmut , Mann Stephen
Published: May 2003

The 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

The 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

The 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

In 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

Measurements 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

Although 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

The 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

Ti 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

The 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

Three 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

The 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

In 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

The 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

The 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

Large 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

The 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

We 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

The 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

During 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

Direct 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

The 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.
Structural and spectral studies on gypsum crystals under simulated conditions of phosphoric acid production with and without organic and inorganic additives
Authors: Rashad M. M. , Baioumy H. M. , Abdel‐Aal E. A.
Published: June 2003

In the dihydrate process to produce phosphoric acid, phosphate ore [Ca10F2(PO4)6] is leached with sulfuric and weak phosphoric acids to produce phosphoric acid and gypsum as a by‐product. Crystallization of gypsum occurs as the leaching is taking place. The effect of organic and inorganic additives on the structure and spectrum of gypsum crystals under simulated conditions of phosphoric acid production is studied using x‐ray diffraction and infrared spectroscopy. Structure and spectrum of formed gypsum crystals in the absence of additives are slightly different from the standard gypsum crystals (card No. 6‐0046), which reflect the effect of preparation medium on the crystal structure of gypsum crystals. Presence of additives such as cetyl trimethyl ammonium bromide and 1,2‐dihydroxybenzene‐3,5‐disulfonic acid, Al3+ and Mg2+ increase the crystallinity of gypsum, while presence of additives such as citric acid and sodium dodecyl sulfate decrease the crystallinity of gypsum. Presence of Al3+ and Mg2+ as additives lead to the formation of calcium sulfate hemihydrate beside calcium sulfate dihydrate. Presence of sodium dodecyl sulfate as an additive inhibits the crystallization of gypsum and leads to the formation of anhydrite and calcium sulfate hemihydrate.
X‐ray interferometric investigation of homogeneity of substances
Authors: Drmeyan H. R.
Published: June 2003

The influence of inhomogeneous distribution of substance density on interference patterns of X‐rays is investigated. It is shown experimentally that during preliminary transition of superposing Roentgen waves through samples with inhomogeneous distribution of substance density, irregular phase shifts occur in these waves, leading to disappearance of interference patterns. Special two‐ and three crystal interferometers are developed for such investigations.
Optical and opto‐electronic properties of polycrystalline Cd0.96Zn0.04Te thin films
Authors: Sridharan M. , Narayandass Sa. K. , Mangalaraj D. , Lee Hee Chul
Published: June 2003

Cd0.96Zn0.04Te thin films are deposited onto thoroughly cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation. The films are found to have good stoichiometry as analyzed by Rutherford Backscattering Spectrometry. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the films evaluated by AFM is 3.7 nm. The pseudodielectric‐function spectra, ε(E) = ε1(E) + i ε2(E) at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E1, E1+ Δ1 and E2 critical points. The band gap energy of the films measured by optical transmittance measurement is 1.523 eV. The PL spectrum of the films shows intense emission due to free and bound exciton recombination and no emission associated with crystal imperfection and deeper impurity levels. The PL line shapes give indications of the high quality of the layers.
Negative T cell costimulation and islet tolerance
Authors: Gao Wenda , Demirci Gülçin , Li Xian Chang
Published: June 2003

Activation of self‐reactive T cells that specifically destroy the pancreatic β‐cells is one of the hallmarks in the development of type 1 diabetes. Thus, for prevention and treatment of this autoimmune disease, approaches to induce and maintain T cell tolerance toward the β‐cells, especially in islet transplantation, have been actively pursued. Noticeably, many of the recent protocols for inducing transplant tolerance involve blockade of positive T cell costimulation extrinsically. Though highly effective in prolonging graft survival, these strategies alone might not be universally sufficient to achieve true tolerance. As the mystery of the suppressive and regulatory T cells unfolds, it is becoming appreciated that exploiting the intrinsic molecular and cellular mechanisms that turn off an immune response would perhaps facilitate the current protocols in establishing T cell tolerance. In this perspective, here we summarize the recent findings on the negative costimulation pathways, in particular, the newly identified PD‐1 : PD‐L interactions. On the basis of these observations, we propose a new principle of curtailing pathogenic T cell response in which blockade of positive T cell costimulation is reinforced by concurrent engagement of the negative costimulation machinery. Such a strategy may hold greater hope for therapeutic intervention of transplant rejection and autoimmune diseases. Copyright © 2003 John Wiley & Sons, Ltd.