bluuebunny/crossref_metadata_2025 huggingface dataset:
Micelle and Solvent Relaxation in Aqueous Sodium Dodecylsulfate Solutions
Authors: Fernandez Patrick , Schrödle Simon , Buchner Richard , Kunz Werner
Published: October 2003

Dielectric 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.
Anchoring Fe Ions to Amorphous and Crystalline Oxides: A Means To Tune the Degree of Fe Coordination
Authors: Berlier Gloria , Bonino Francesca , Zecchina Adriano , Bordiga Silvia , Lamberti Carlo
Published: October 2003

We report on an IR spectroscopic study on the room‐temperature adsorption of NO on different iron(II)‐containing siliceous matrices. Fe2+ hosted inside the channels of MFI‐type zeolites (Fe‐ZSM‐5 and Al‐free Fe‐silicalite) exhibits pronounced coordinative unsaturation, as witnessed by the capability to form, at 300 K, [Fe2+(NO)], [Fe2+(NO)2] and [Fe2+(NO)3] complexes with increasing NO equilibrium pressure. Fe2+ hosted on amorphous supports (high surface area SiO2 and MCM‐41) sinks more deeply into the surface of the siliceous support and thus exhibits less pronounced coordinative unsaturation: only [Fe2+(NO)2] complexes were observed, even at the highest investigated NO equilibrium pressures. Activation at higher temperature (1073 K) of the Al‐free Fe‐silicalite sample resulted in the appearance of Fe2+ species similar to those observed on SiO2 and MCM‐41, and this suggests that local (since not detectable by X‐ray diffraction) amorphisation of the environment around Fe2+ anchoring sites occurs. The fact that this behaviour is not observed on the Fe‐ZSM‐5 sample activated at the same temperature suggests that framework Al species (and their negatively charged oxygen environment) have an important role in anchoring extraframework Fe2+ species. Such an anchoring phenomenon will prevent a random migration of iron species, with subsequent aggregation and loss of coordinative unsaturation. These observations can thus explain the higher catalytic activity of the Fe‐ZSM‐5 system in one‐step benzene to phenol conversion when compared with the parent, Al‐free, Fe‐silicalite system with similar Fe content. The nature of the support and the activation temperature can therefore be used as effective means to tune the degree of Fe coordination.
Excited‐State Proton‐Relay Dynamics of 7‐Hydroxyquinoline Embedded in a Solid Matrix of Poly(2‐hydroxyethyl methacrylate)
Authors: Kwon Oh‐Hoon , Doo Hyungie , Lee Young‐Shin , Jang Du‐Jeon
Published: October 2003

Excited 7‐hydroxyquinoline embedded in a solid matrix of poly(2‐hydroxyethyl methacrylate) undergoes a proton‐relay reaction efficiently to form its keto tautomer. However, the reaction mechanism depends on the torsional conformation and the microscopic environment of the molecule at the moment of excitation. Whereas the bridged cis‐enol form undergoes proton relay immediately on absorption of a photon to produce its tautomeric keto species, the unbridged cis form requires 120 ps for bridge formation via solvent reorganization prior to proton relay. Furthermore, the trans form needs 1000 ps for tautomerization because it requires an activated (11 kJ mol−1) torsional motion to change into its cis form prior to bridge formation and proton relay. Torsional motion rather than solvent reorganization determines the proton relay rate of the trans‐form of the molecule.
Structural Forces near Phase Transitions of Liquid Crystals
Authors: Kočevar Klemen , Muševič Igor
Published: October 2003

The structure of the fragile liquid‐crystalline phases has a strong impact on the forces between bodies immersed in a liquid crystal (LC). We have equipped an atomic force microscope with a precise temperature control and measured various liquid‐crystalline structural forces at temperatures close to the phase transitions. The observed forces agree well with predictions of Landau–de Gennes phenomenological theory of LCs, even at a nanoscale length. In addition to this, we have observed a molecular layer, adsorbed on the surfactant‐covered glass surface, and determined its thickness and elastic properties.
A Theoretical Study of the UV/Visible Absorption and Emission Solvatochromic Properties of Solvent‐Sensitive Dyes
Authors: Han Wen‐Ge , Liu Tiqing , Himo Fahmi , Toutchkine Alexei , Bashford Donald , Hahn Klaus M. , Noodleman Louis
Published: October 2003

Using the density‐functional vertical self‐consistent reaction field (VSCRF) solvation model, incorporated with the conductor‐like screening model (COSMO) and the self‐consistent reaction field (SCRF) methods, we have studied the solvatochromic shifts of both the absorption and emission bands of four solvent‐sensitive dyes in different solutions. The dye molecules studied here are: S‐TBA merocyanine, Abdel‐Halim's merocyanine, the rigidified aminocoumarin C153, and Nile red. These dyes were selected because they exemplify different structural features likely to impact the solvent‐sensitive fluorescence of “push‐pull”, or merocyanine, fluorophores. All trends of the blue or red shifts were correctly predicted, comparing with the experimental observations. Explicit H‐bonding interactions were also considered in several protic solutions like H2O, methanol and ethanol, showing that including explicit H‐bonding solvent molecule(s) in the calculations is important to obtain the correct order of the excitation and emission energies. The geometries, electronic structures, dipole moments, and intra‐ and intermolecular charge transfers of the dyes in different solvents are also discussed.
Cover Picture: Experimental Detection of the H2NO3 Radical (ChemPhysChem 10/2003)
Authors: Cacace Fulvio , de Petris Giulia , Troiani Anna
Published: October 2003

The cover pictures shows…︁‥the mass spectrum of nitrogen hydroxide oxide, the H2NO3. radical, which was discovered by neutralization reionization mass spectrometry (NRMS) and characterized as a relatively long‐lived (over 1 μs) metastable species. The discovery required the availability of the appropriate charged precursor that fortunately had previously been prepared by this group (1989) as a result of their sustained interest in gas‐phase ion chemistry of nitrates, nitrites and related molecules. Cacace et al. found that protonation of nitric acid by strong Brønsted acids yields, in addition to the H2ONO2+ ion, smaller amounts of the less stable (HO)2NO+ isomer, namely charged nitrogen hydroxide oxide. This result has allowed the present discovery by NRMS (yellow trace), whereas NRMS of the H2ONO2+ ion does not result in detectable H2NO3. neutral species (green trace). The importance of nitrogen hydroxide oxide stems from its relevance to a variety of research areas, from the reduction of the NO32− anion, to atmospheric chemistry, radiolysis of nuclear‐waste solutions, the charge‐transfer mechanism of aromatic nitration, etc. Find out more in the communication by Cacace et al. on pp. 1128–131.
Theoretical Search for Anions Possessing Large Electron Binding Energies
Authors: Sobczyk Monika , Sawicka Agnieszka , Skurski Piotr
Published: October 2003

The vertical electron detachment energies (VDE) of several anions were calculated at the OVGF level with 6‐311++G(d) basis sets. The negatively charged species studied were chosen based on the observation that the largest electron binding energies for such systems are expected to be found for the anions whose neutral parents are polynuclear superhalogens. The largest vertical electron binding energy of 12.63 eV was found for Ta3F16−, and this is the largest excess electron binding energy of a molecular system reported in the literature thus far. Moreover, the VDEs of 12.63 and 12.20 eV calculated for Ta3F16− and As3F16−, respectively, exceed the upper limit for the excess electron binding energy (thought to be 12 eV). Several other anions were also found [at the OVGF/6‐311++G(d) level] to possess very large VDEs (i.e. Al2Br7−: 7.08 eV, Al2Cl7−: 7.75 eV, Al2F7−: 11.16 eV, P2F11−: 10.95 eV, V2F11−: 10.98 eV, As2F11−: 11.43 eV, and Ta2F11−: 11.84 eV). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Structures of the Octahedral Persulfuranes H4SF2, H2SF4, Me2SH4 and Me2SF4, and Activation Enthalpies for Their cis/trans Isomerization
Authors: Steudel Yana , Steudel Ralf
Published: October 2003

Eight hypothetical persulfurane molecules of the type X2SY4 (X, Y = H, F, Me) have been studied by ab initio MO calculations at the G3(MP2) level of theory. Depending on the substituents either the cis or the trans isomers of these octahedral molecules are most stable. While H4SF2 is most stable as the cis isomer, the global minimum structures of H2SF4, Me2SH4, and Me2SF4 are the trans isomers. The enthalpy differences between the corresponding isomers are in the range 7−53 kJ·mol−1. The transition states for the intramolecular cis ⇋ trans isomerization have been located in all cases. Starting from the global minimum geometries the activation enthalpies (ΔH#298) for this isomerization are in the range 199−263 kJ·mol−1, indicating rather rigid structures. Therefore, it should be possible to isolate both isomers at low to moderate temperatures. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Chain‐Like Tetra‐, Penta‐ and Heptanuclear Cyanide‐Bridged Complexes by Attachment of Organometallic Cyanides to M2, M3 and M5 Units
Authors: Sheng Tianlu , Appelt Ralf , Comte Virginie , Vahrenkamp Heinrich
Published: October 2003

Attachment of the “ligands” [Cp(dppe)Fe‐CN], [Cp(PPh3)2Ru‐CN], [Cp(CO)2Fe‐CN] and [(CO)5M‐CN]−, (where M = Cr, Mo, W) to the polymetallic centres [Ru2(OAc)4]+, [Co3(dpa)4]2+ and [Ni5(tdpa)4]2+ yielded two tetra‐, three penta‐ and five heptanuclear complexes with chain‐like linear arrangements of the metal ions and the bridging cyanide ligands, as proved by the structure determination of [Ni5(tdpa)4{Cp(dppe)2Fe‐CN}2](PF6)2. IR and CV data show that the Ru2, Co3 and Ni5 centres of these complexes withdraw electron density from the external organometallic units. This prevents electronic interactions between the two terminal metal ions, yet allows multistep one‐ and two‐electron redox processes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis and Characterization of Oxorhenium and Oxotechnetium Complexes with a Novel Tetradentate N3O Bifunctional Agent
Authors: Papachristou Maria , Pirmettis Ioannis , Siatra‐Papastaikoudi Theodora , Pelecanou Maria , Tsoukalas Charalambos , Raptopoulou Catherine P. , Terzis Aris , Chiotellis Efstratios , Papadopoulos Minas
Published: October 2003

The novel tetradentate N3O bifunctional agent 3‐hydroxy‐4‐[2‐(2′‐pyridinecarboxamido)acetylamino]benzoic acid (1), reacts with [Bu4N][ReOCl4] or [Bu4N][99gTcOCl4] in EtOH resulting in neutral and stable oxorhenium 2 or oxotechnetium‐99 g 3 complexes. Both complexes were characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy. X‐ray analysis of 2 showed that the rhenium atom is pentacoordinate presenting a distorted square‐pyramidal coordination geometry. The analogous oxotechnetium‐99m complex 4 was also prepared quantitatively by the reaction of ligand 1 with Na99mTcO4 in isotonic saline using tin chloride as reducing agent. Its identity was established by chromatographic comparison to the oxorhenium 2 and oxotechnetium 3 complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A Binuclear Copper(II) Acetate Complex Showing a 3D Supramolecular Network with Hydrophilic Pockets: Its Unusual Magnetic Behaviour
Authors: Fondo Matilde , García‐Deibe Ana M. , Sanmartín Jesús , Bermejo Manuel R. , Lezama Luis , Rojo Teófilo
Published: October 2003

The binuclear complex [Cu2L(OAc)]·6H2O (1) {H3L = 2‐(2‐hydroxyphenyl)‐1,3‐bis[4‐(2‐hydroxyphenyl)‐3‐azabut‐3‐enyl]‐1,3‐imidazolidine} which shows an unusual magnetic superexchange behaviour, acts as a building block for a novel three‐dimensional metal‐organic framework, with hydrophilic pockets. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Selective Aromatic N‐Substitution with N‐(4‐Tolyl)hydroxylamine by Addition of Polar Aprotic or Diethereal Solvent
Authors: Takeuchi Hiroshi , Tateiwa Jun‐ichi , Hata Suguru , Tsutsumi Keisuke , Osaki Yoshinori
Published: October 2003

Amination of anisole and toluene with N‐(4‐tolyl)hydroxylamine in trifluoroacetic acid was tuned to regioselectively provide the corresponding diarylamine by partial replacement of trifluoroacetic acid with a polar aprotic or a diethereal solvent. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A Radical Version of the Bromo‐ and the Iodocyclization of Bis(homoallylic) Alcohols — The Synthesis of Halogenated Tetrahydrofurans by Stereoselective Alkoxyl Radical Ring Closures
Authors: Hartung Jens , Kneuer Rainer , Laug Stefanie , Schmidt Philipp , Špehar Kristina , Svoboda Ingrid , Fuess Hartmut
Published: October 2003

A new synthesis of bromo‐ and iodomethyl‐substituted tetrahydrofurans has been devised. The sequence starts with the conversion of aryl‐functionalized bis(homoallylic) alcohols1intoN‐alkenoxythiazole‐2(3H)‐thiones6or pyridine‐2(1H)‐thiones7. When photolyzed in the presence of appropriate trapping reagents, thiones6and7efficiently liberated substituted 4‐penten‐1‐oxyl radicals2, which underwent synthetically useful 5‐exo‐trig cyclizations. Cyclized radicals3were trapped with BrCCl3or an adequate iodine atom donor (eithern‐C4F9I or diethyl 2‐iodo‐2‐methyl malonate) to provide halocyclization products4or5. This strategy has been applied for the synthesis of 3‐, 4‐, or 5‐phenyl‐substituted 2‐(1‐bromo‐1‐methylethyl)tetrahydrofurans4a−c(75−90%, 36−96%de), which were not attainable as major products from polar, for example NBS‐mediated, bromocyclizations. Aryl‐substituted 2‐iodomethyl tetrahydrofurans5(46−80%) were prepared in a similar way starting fromN‐alkenoxypyridine‐2(1H)‐thiones7and a suitable iodine atom donor. Diastereomerically pure iodidescis‐5andtrans‐5served as starting materials for a stereochemical analysis of disubstituted tetrahydrofurans by NMR spectroscopy and X‐ray diffraction analysis. The results of this investigation clarified that all new alkoxyl radical cyclizations followed in terms of regio‐ and diastereoselectivity the general guidelines which had been established for this type of ring‐closure reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
3‐Nitrocoumarin Amidines: A New Synthetic Strategy for Substituted [1]Benzopyrano[3,4‐d]imidazol‐4(3H)‐ones
Authors: Beccalli Egle M. , Contini Alessandro , Trimarco Pasqualina
Published: October 2003

A new synthesis of substituted [1]benzopyrano[3,4‐d]imidazol‐4(3H)‐ones, starting from 3‐nitrocoumarin N‐functionalized amidines 3, has been developed. When the 3‐nitro‐amidines 3 were treated with NaBH4 in the presence of 10% palladium on charcoal, 2‐substituted [1]benzopyrano[3,4‐d]imidazol‐4(3H)‐ones 4 were produced. Structure elucidation of compounds 4 revealed that they exist as one of the three possible tautomeric structures (i.e., 4dα). Alkylation of 4d to give 6, as well as NOE experiments on 6 and energy calculations allowed the most favoured structure of the 4 derivatives to be identified. Alternatively, the reduction of the 3‐nitro‐amidines 3 by triethyl phosphite, through a nitrene intermediate, cyclization and a [1.5] sigmatropic shift, yielded 2‐morpholino‐3‐alkyl‐[1]benzopyrano[3,4‐d]imidazol‐4(3H)‐ones 7. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Episulfidation of trans‐Cyclooctene with an 1,2,4‐Oxadithiolane
Authors: Adam Waldemar , Bargon Rainer M. , Mloston Grzegorz
Published: October 2003

The dipolar cycloaddition of thiobenzophenone S‐oxide (1) and 2,2,4,4‐tetramethyl‐3‐thioxocyclobutanone (2) generates the labile 1,2,4‐oxadithiolane I, which in the presence of trans‐cyclooctene (3) affords trans‐episulfide (9). In this direct sulfur transfer, the oxathiirane II and/or the dithiirane IV, both derived from the 1,2,4‐oxadithiolane I, are proposed as elusive episulfidating agents. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A Tunable One‐Step N,N′‐Disubstitution of 1,4,8,11‐Tetraazacyclotetradecane with Acrylamide
Authors: Fensterbank Hélène , Berthault Patrick , Larpent Chantal
Published: October 2003

N,N′‐disubstitution of cyclam without the use of protecting groups was investigated. This macrocycle reacted with two equivalents of a Michael acceptor in chloroform to yield as a major isolated compound the 1,8 di‐N,N′‐substituted macrocycle. Running the same reaction in the presence of one equivalent of para‐toluenesulfonic acid led to the 1,11‐di‐N,N′‐substituted macrocycle as the major product. Each regioisomer has been isolated and fully characterized. The observed regioselectivity is discussed with respect to the reactivity of the unprotonated or protonated monoalkylated intermediate. A site of protonation for the latter intermediate is deduced from an NMR study. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Recent Advances in the Synthesis of Spermine and Spermidine Analogs of the Shark Aminosterol Squalamine
Authors: Brunel Jean Michel , Letourneux Yves
Published: October 2003

Great attention has recently been focused on the shark aminosterol squalamine (1) because of its important antimicrobial and antiangiogenic activities. Herein, we present the different series of spermine and spermidine analogs that have been synthesized. Many of the squalamine mimics demonstrate a broad spectrum activity against microorganisms. Squalamine is currently undergoing Phase II clinical trials in cancer patients. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of Differently Disubstituted 2,2′‐Bipyridines by a Modified Negishi Cross‐Coupling Reaction
Authors: Lützen Arne , Hapke Marko , Staats Holger , Bunzen Jens
Published: October 2003

A general practical approach to a number of differently disubstituted 2,2′‐bipyridines from substituted 2‐bromo‐ and 2‐chloropyridines by application of modified Negishi cross‐coupling conditions has been developed. These 2,2′‐bipyridines carry versatile functional groups that can be elaborated further, as demonstrated for some examples. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
New One‐Pot Synthesis of 3‐Alkyl‐ and 3‐(ψ‐Hydroxyalkyl)oxindoles from Isatins
Authors: Volk Balázs , Simig Gyula
Published: October 2003

A new and efficient one‐pot procedure has been developed for the synthesis of 3‐alkyl‐ and 3‐(ψ‐hydroxyalkyl)oxindoles from isatins by treatment with alcohols and diols in the presence of Raney nickel, under hydrogen atmosphere. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Chagosensine, a New Chlorinated Macrolide from the Red Sea Sponge Leucetta chagosensis
Authors: Řezanka Tomáš , Hanuš Lumír , Dembitsky Valery M.
Published: October 2003

Chagosensine, a sixteen‐membered chlorinated macrolide, was isolated from the Red Sea calcareous sponge Leucetta chagosensis. Its structure was elucidated mainly on the basis of NMR spectroscopic data. The relative and absolute configurations were determined by analysis of 1H and 13C NMR, NOESY, and CD data, by the modified Mosher’s method, and by using degradation products. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A Flexible Asymmetric Synthesis of anti‐1,2‐Sulfanyl Amines
Authors: Enders Dieter , Moll Alexander , Schaadt Annette , Raabe Gerhard , Runsink Jan
Published: October 2003

An efficient and flexible asymmetric synthesis of various protected anti‐1,2‐sulfanyl amines bearing two adjacent stereogenic centres is described. Key steps are the diastereoselective α‐alkylation of α‐sulfanylated acetaldehyde‐SAMP‐hydrazones with various electrophiles and subsequent nucleophilic 1,2‐addition of organocerium reagents to the hydrazone CN double bond. The resulting hydrazines were converted into the title compounds with excellent diastereomeric and enantiomeric excesses (de and ee values ⩾ 96%) by reductive N,N bond cleavage to remove the chiral auxiliaries and protection of the amino functions. The relative and absolute configurations were determined by NOE experiments and X‐ray structure analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Organic Chemistry of Vitamin D Analogues (Deltanoids)
Authors: Posner Gary H. , Kahraman Mehmet
Published: October 2003

An increasing number of synthetic vitamin D analogues (deltanoids) are now being used as sensitive molecular biology probes and also as new drug candidates and new drugs for treatment of various human diseases. The design and stereocontrolled synthesis of such new deltanoids are guided by considering catabolism inhibition and by using large steroidal chirons and small steroid‐derived chirons. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Azido/Tetrazole Tautomerism in 2‐Azidoadenine β‐D‐Pentofuranonucleoside Derivatives
Authors: Lioux Thierry , Gosselin Gilles , Mathé Christophe
Published: October 2003

The β‐D‐ribofuranoside derivative of 2‐azidoadenine and its 2′‐deoxy‐, 2′,3′‐dideoxy‐ and 2′,3′‐dideoxy‐2′,3′‐didehydro counterparts have been synthesized. All these compounds were obtained through the preparation of their 2‐chloro precursors. These were converted into their 2‐hydrazino derivatives, which upon treatment with sodium nitrate in acid medium gave the target nucleosides. The azido/tetrazole tautomerism observed in such nucleoside analogues was studied in detail. The compounds were also tested for their activity against HIV and HBV, but did not show significant antiviral effects. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Electrophilic Cyclization of 1,6‐Dienes Containing an Allylsilane Moiety − Enantioselective Synthesis of cis‐ and trans‐γ‐Irone
Authors: Beszant Stephen , Giannini Elios , Zanoni Giuseppe , Vidari Giovanni
Published: October 2003

In this paper, we report the first examples of Lewis acid and mercuric trifluoroacetate promoted cyclizations of 1,6‐dienes containing an allylsilane moiety. Mercuric trifluoroacetate has been proved to be the reagent of choice leading to methylenecyclohexane derivatives in good yields and with complete regioselectivity albeit with poor diastereoselectivity. Using this methodology a stereodivergent synthesis of enantiomerically pure (−)‐(2S,6R)‐cis‐γ‐irone and (−)‐(2S,6S)‐trans‐γ‐irone, two precious aroma constituents, has been accomplished. This represents an innovative approach with respect to previous syntheses of γ‐irones. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of Dihydrodiosgenin Glycosides as Mimetics of Bidesmosidic Steroidal Saponins
Authors: Suhr René , Lahmann Martina , Oscarson Stefan , Thiem Joachim
Published: October 2003

The focus of this work is the synthesis of bidesmosidic saponin mimetics. Therefore, dihydrodiosgenin derivatives, which differ from the natural compounds by reduction of the 22‐(hemi) acetal were used as glycosyl acceptors. In preliminary studies, the dihydrodiosgenin glycosides 16, 17 and 19, as well as trisaccharide 22, were synthesized. The acceptors 10 and 14 were subjected to DMTST‐mediated glucosylation for the synthesis of the chacotriose‐substituted compound 3. For a selective 2,4‐di‐rhamnosylation of the dihydrodiosgenin glucopyranoside, differentiation of the glucose OH groups was achieved by selective benzoylation with 1‐(benzoyloxy)benzotriazole. Reaction of the 3,6‐di‐O‐benzoate 32 with the perbenzoylated ethyl thiorhamnopyranoside donor 15 gave the 2,4‐di‐rhamnosylated compound 33, together with the mono‐rhamnosylated derivative. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Transannular Cyclization in Cyclodecenes: The Case Study of Melampolides
Authors: Neukirch Hannes , Guerriero Antonio , D’Ambrosio Michele
Published: October 2003

The structures of products formed by electrophilic transannular cyclization (ETC) in medium‐ring compounds are affected by several parameters. The melampolides, (cis,trans)‐cyclodeca‐1(10),5‐diene terpenes, undergo ring closure only under Lewis acid conditions. The transannular distance proves to be a key factor. Molecular mechanics calculations suggest that the cis ring junction of products is formed through a less populated conformer. ETC has chemical significance because it may play an important role in the pharmacological action of sesquiterpene lactones. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Copper(II)‐Catalyzed Oxidation of Alcohols to Carbonyl Compounds with Hydrogen Peroxide
Authors: Velusamy Subbarayan , Punniyamurthy Tharmalingam
Published: October 2003

Copper(II) complex 1 efficiently catalyses the oxidation of alcohols to the corresponding carboxylic acid analogues and ketones in the presence of H2O2 in high yields. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Efficient Synthesis of Differently Protected Lanthionines via β‐Bromoalanine Derivatives
Authors: Zhu Xiangming , Schmidt Richard R.
Published: October 2003

Lanthionines, thioether‐linked alanines, are readily available from differently protected β‐bromoalanine and cysteine derivatives under phase‐transfer conditions at pH 8.5. Racemisation or elimination of starting materials or products was not observed. Also base‐sensitive protecting groups, such as, for instance, the Fmoc group, were compatible with this procedure, thus conveniently permitting the synthesis of orthogonally protected lanthionines. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Asymmetric Synthesis of α,γ‐Substituted γ‐Sultones via Allylation of Chiral Lithiated Sulfonates
Authors: Enders Dieter , Harnying Wacharee , Vignola Nicola
Published: October 2003

The first auxiliary controlled asymmetric synthesis of enantiopure α,γ‐substituted γ‐sultones via α‐allylation of lithiated sulfonates by using 1,2:5,6‐di‐O‐isopropylidene‐α‐D‐allofuranose as chiral auxiliary is described. The high asymmetric inductions of the α‐allylations were reached in good to excellent yields. Successive epimerization‐free cleavage of the auxiliary and diastereoselective ring closure of the sulfonic acid intermediates in a one‐pot procedure led to the title compounds in good to excellent yields and diastereo‐ and enantiomeric excesses (de, ee ≥ 98%). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Chemistry of Tonghaosu Analogs: Novel Acid‐Catalyzed Nucleophilic Addition to the Dienyl Acetal System
Authors: Yin Biao‐Lin , Wu Wen‐Min , Hu Tai‐Shan , Wu Yu‐Lin
Published: October 2003

The acid‐catalyzed nucleophilic addition reaction of spiroketal enol ether‐containing tonghaosu analogs 2 was explored. Soft nucleophiles, such as mercaptans, alcohols and heteroaromatic compounds, gave rise exclusively to 1,6‐adducts, while harder nucleophiles, such as Grignard reagents, afforded mixtures of 1,2‐ and 1,6‐adducts. The reaction with cysteine and glutathione, which might be related to the mode of action of insect antifeeding, also took place smoothly. Friedel−Crafts dimerization reactions of 10 and 11 gave the dimers 12 and 13 respectively. By comparison of 1H NMR spectroscopic data, we also suggest that the structure of compound 9 reported in the literature for a natural product is revised to that of compound 13. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A Mild and Versatile Method for Palladium‐Catalyzed Cross‐Coupling of Aryl Halides in Water and Surfactants
Authors: Arcadi Antonio , Cerichelli Giorgio , Chiarini Marco , Correa Mariano , Zorzan Daniel
Published: October 2003

Various aqueous surfactants proved to be excellent media for carrying out palladium‐catalyzed Suzuki−Miyaura cross‐coupling reactions under mild conditions. The dehalogenation side reaction, which is usually a drawback with the aqueous protocol, was not observed. The concentration of the surfactant in water played a pivotal role for the reaction outcome. Smooth cross‐coupling of iodoanisole and a variety of aryl bromides, including electron‐rich derivatives, with aryl boronic acids occurred at room temperature in high yields either with [Pd(PPh3)4] or Pd/C as catalyst. The water‐surfactant Pd/C system combines high activity under ambient conditions (air), easy separation and recyclability. Palladium acetate was found to be effective in cross‐coupling of the less reactive aryl chlorides at 100 °C. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The First Crystal Structure of a Halogenated Higher Fullerene, C78Br18, Obtained by Bromination of a Fullerene Mixture
Authors: Troyanov Sergey I. , Kemnitz Erhard
Published: October 2003

Simple bromination of a fullerene mixture allowed the separation of C78 from other fullerenes in form of crystalline C78Br18. The first X‐ray single‐crystal structure of a halogenated higher fullerene, C78Br18, revealed that the addition pattern of 18 bromine atoms on the C78 cage corresponds to a partial retention of the conjugated double bond systems and the formation of isolated C−C double bonds. Evidently, even a separation of the C2v and D3 isomers of C78 occurred in the course of bromination and precipitation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of Theophylline and 6‐Thiotheophylline 7‐Ribosyl Nucleosides
Authors: Rico‐Gómez Rodrigo , Rodríguez‐González Angel , Ríos‐Ruíz Josefa , Nájera Francisco , López‐Romero J. Manuel
Published: October 2003

The syntheses of theophylline and thiotheophylline 7‐ribopyranose and 7‐ribofuranose nucleosides, both by direct coupling of the base and the sugar and by construction of the imidazole ring, are reported. The conformational syn/anti equilibrium of the peracetyl derivatives was studied by molecular mechanics and by the low‐temperature line‐shape/1H NMR method. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Vicarious Nucleophilic Substitution of (Chloroalkyl)oxazolines with Nitroarenes: Synthesis of (Nitrobenzyl)oxazolines
Authors: Florio Saverio , Lorusso Patrizia , Granito Catia , Ronzini Ludovico , Troisi Luigino
Published: October 2003

2‐Chloroalkyloxazolines 1a and 1b react with nitroarenes in the presence of tBuOK in DMSO to give, upon acidic quenching, substituted nitroaryloxazolines 2a, 2b, 3a, 9, 10, 11a−d, 12−19, and 21−22, probably by vicarious nucleophilic substitution (VNS). The reaction of 1a is poorly regioselective, while that of 1b is completely para regioselective, thus showing that the coupling is sterically controlled. Trapping of the carbanionic intermediate B of the VNS reaction with electrophiles furnished α,α‐disubstituted (nitrobenzyl)oxazolines 4−7. Attempts to trap B with PhCHO failed: the [(p‐nitrophenyl)oxazolinyl]ethanol 8 was obtained. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Stereocontrol of the Intramolecular Diels−Alder Reaction by Internal Hydrogen Bonding
Authors: Cayzer Tory N. , Paddon‐Row Michael N. , Sherburn Michael S.
Published: October 2003

A novel approach for exo/endo stereocontrol of intramolecular Diels−Alder reactions is described. Substrates carrying a hydroxymethyl group attached to the diene and an ester group attached to the dienophile participate in hydrogen bonding in the transition state. This non‐covalent interaction causes either a significant enhancement or diminution in the observed kinetic endo/exo product ratio. Thus, the parent pentadienyl maleate 12 undergoes intramolecular Diels−Alder reaction to give an approx. 5:1 mixture of trans‐ and cis‐fused bicyclic cycloadducts, whereas the C2‐hydroxymethyl analogue 1 delivers a 1:1 ratio of products. In contrast, the parent pentadienyl fumarate 13 gives a 3:2 trans:cis ratio, which is improved to 9:1 in the C2‐hydroxymethyl analogue 4. These stereoselectivities are accurately predicted from transition structure populations calculated using B3LYP/6‐31+G(d) theory. The presence of an intramolecular H‐bond confers a transannular Diels−Alder‐like appearance upon the transition states of these reactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Construction of Consecutive Chiral Non‐Racemic Quaternary and Tertiary Carbon Centers: A Short Synthetic Route to (−)‐Acetomycin
Authors: Uenishi Jun′ichi , Kawatsura Motoi , Ikeda Daiji , Muraoka Nobuhiro
Published: October 2003

Regio‐ and diastereoselective nucleophilic substitution of 2‐methylacetoacetate with a chiral non‐racemic π‐allyl Pd complex creates consecutive chiral non‐racemic quaternary and tertiary carbon centers. σ‐Bond formation between the re‐face of the π‐allyl Pd complex and the re‐face of the enol acetoacetate was controlled by the o‐(diphenylphosphanyl)arylcarboxylic acid ligand selectively. (−)‐Acetomycin was synthesized in seven steps using this key approach. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cover Picture: Recent Advances in the Synthesis of Spermine and Spermidine Analogs of the Shark Aminosterol Squalamine (Eur. J. Org. Chem. 20/2003)
Authors: Brunel Jean Michel , Letourneux Yves
Published: October 2003

The cover picture shows, the dogfish shark Squalus Acanthias from which the aminosterol squalamine has been isolated. Squalamine has been characterized as a water‐soluble cationic steroid exhibiting potent antimicrobial activity against fungi, protozoa fungi, protozoa and both Gram‐negative and Gram‐positive bacteria. Details on the different series of spermine and spermidine analogs synthesized as well as comparison of their pharmacological properties are discussed in the Microreview by J. M. Brunel and Y. Letourneux on p. 3897 ff.
Evaluation of mutagenic activity in an extract of pepper tree stem bark (Schinus terebinthifolius Raddi)
Authors: de Carvalho Maria Cleide Ribeiro Dantas , Barca Francisco Napoleão Túlio Varela , Agnez‐Lima Lucymara Fassarella , de Medeiros Sílvia Regina Batistuzzo
Published: October 2003

An extract (decoction) from pepper tree stem bark (Schinus terebinthifolius Raddi) is widely used in Brazil as a topical antiinflammatory agent and to cicatrize wounds. The extract contains catechin, tannins, terpenes, flavonoids, and saponins; of these components, both mutagenic potential and antioxidant properties have been ascribed to flavonoids. The mutagenicity of some flavonoids is believed to be associated with the formation of reactive oxygen species and seems to depend on the number and position of hydroxyl groups. In the present study, we evaluated an extract of S. terebinthifolius in a series of cell‐free and bacterial assays in order to determine its genotoxic potential. The extract was negative in a cell‐free plasmid DNA test, indicating that it did not directly break DNA. Positive results, however, were obtained in the SOS chromotest, in a forward mutagenesis assay employing CC104 and CC104mutMmutY strains of Escherichia coli, and in the Salmonella reversion assay, using strains TA97, TA98, TA100, and TA102. All the bacterial tests were performed without exogenous metabolic activation due to the topical use of this preparation. The results indicate that pepper tree stem bark extract produces DNA damage and mutation in bacteria, and that oxidative damage may be responsible for the genotoxicity. Environ. Mol. Mutagen. 42:185–191, 2003. © 2003 Wiley‐Liss, Inc.
Structure–activity relationships for the mutagenicity and carcinogenicity of simple and α‐β unsaturated aldehydes
Authors: Benigni Romualdo , Passerini Laura , Rodomonte Andrea
Published: October 2003

Aldehydes are important industrial compounds that are used for the synthesis of chemicals and pharmaceuticals and as solvents, food additives, and disinfectants. Because of their reactivity, aldehydes are able to interact with electron‐rich biological macromolecules and adverse health effects have been reported, including general toxicity, allergenic reactions, mutagenicity, and carcinogenicity. The cost, time, and number of animals necessary to adequately screen these chemicals places serious limitations on the number of aldehydes whose health potential can be studied and points to the need of using alternative methods for assessing, at least in a preliminary way, the risks associated with the use of aldehydes. A method of choice is the study of quantitative structure–activity relationships (QSARs). In the present work, we present QSAR models for the mutagenicity and carcinogenicity of simple aldehydes and α‐β unsaturated aldehydes. The models point to the role of electrophilicity, bulkiness, and hydrophobicity in the genotoxic activity of the aldehydes and lend themselves to the prediction of the activity of other untested chemicals of the same class. Environ. Mol. Mutagen. 42:136–143, 2003. © 2003 Wiley‐Liss, Inc.
Methylated trivalent arsenicals as candidate ultimate genotoxic forms of arsenic: Induction of chromosomal mutations but not gene mutations
Authors: Kligerman Andrew D. , Doerr Carolyn L. , Tennant Alan H. , Harrington‐Brock Karen , Allen James W. , Winkfield Ernest , Poorman‐Allen Patricia , Kundu Bijit , Funasaka Kunihiro , Roop Barbara C. , Mass Marc J. , DeMarini David M.
Published: October 2003

Arsenic is a prevalent human carcinogen whose mutagenicity has not been characterized fully. Exposure to either form of inorganic arsenic, AsIII or AsV, can result in the formation of at least four organic metabolites: monomethylarsonic acid, monomethylarsonous acid (MMAIII), dimethylarsinic acid, and dimethylarsinous acid (DMAIII). The methylated trivalent species, as well as some of the other species, have not been evaluated previously for the induction of chromosome aberrations, sister chromatid exchanges (SCE), or toxicity in cultured human peripheral blood lymphocytes; for mutagenicity in L5178Y/Tk+/‐ mouse lymphoma cells or in the Salmonella reversion assay; or for prophage‐induction in Escherichia coli. Here we evaluated the arsenicals in these assays and found that MMAIII and DMAIII were the most potent clastogens of the six arsenicals in human lymphocytes and the most potent mutagens of the six arsenicals at the Tk+/‐ locus in mouse lymphoma cells. The dimethylated arsenicals were also spindle poisons, suggesting that they may be ultimate forms of arsenic that induce aneuploidy. Although the arsenicals were potent clastogens, none were potent SCE inducers, similar to clastogens that act via reactive oxygen species. None of the six arsenicals were gene mutagens in Salmonella TA98, TA100, or TA104; and neither MMAIII nor DMAIII induced prophage. Our results show that both methylated AsV compounds were less cytotoxic and genotoxic than AsV, whereas both methylated AsIII compounds were more cytotoxic and genotoxic than AsIII. Our data support the view that MMAIII and DMAIII are candidate ultimate genotoxic forms of arsenic and that they are clastogens and not gene mutagens. We suggest that the clastogenicity of the other arsenicals is due to their metabolism by cells to MMAIII or DMAIII. Environ. Mol. Mutagen. 42:192–205, 2003. Published 2003 Wiley‐Liss, Inc.
Computation of moving boundaries and interfaces and stabilization parameters
Authors: Tezduyar Tayfun E.
Published: October 2003

The interface‐tracking and interface‐capturing techniques we developed in recent years for computation of flow problems with moving boundaries and interfaces rely on stabilized formulations such as the streamline‐upwind/Petrov–Galerkin (SUPG) and pressure‐stabilizing/Petrov–Galerkin (PSPG) methods. The interface‐tracking techniques are based on the deforming‐spatial‐domain/stabilized space–time formulation, where the mesh moves to track the interface. The interface‐capturing techniques, typically used with non‐moving meshes, are based on a stabilized semi‐discrete formulation of the Navier–Stokes equations, combined with a stabilized formulation of the advection equation governing the time‐evolution of an interface function marking the interface location. We provide an overview of the interface‐tracking and interface‐capturing techniques, and highlight how we determine the stabilization parameters used in the stabilized formulations. Copyright © 2003 John Wiley & Sons, Ltd.
Fast preconditioned multigrid solution of the Euler and Navier–Stokes equations for steady, compressible flows
Authors: Caughey David A. , Jameson Antony
Published: October 2003

New versions of implicit algorithms are developed for the efficient solution of the Euler and Navier–Stokes equations of compressible flow. The methods are based on a preconditioned, lower‐upper (LU) implementation of a non‐linear, symmetric Gauss‐Seidel (SGS) algorithm for use as a smoothing algorithm in a multigrid method. Previously, this method had been implemented for flows in quasi‐one‐dimensional ducts and for two‐dimensional flows past airfoils on boundary‐conforming ‘O’‐type grids for a variety of symmetric limited positive (SLIP) spatial approximations, including the scalar dissipation and convective upwind split pressure (CUSP) schemes. Here results are presented for both inviscid and viscous (laminar) flows past airfoils on boundary‐conforming ‘C’‐type grids. The method is significantly faster than earlier explicit or implicit methods for inviscid problems, allowing solution of these problems to the level of truncation error in three to five multigrid cycles. Viscous solutions still require as many as twenty multigrid cycles. Copyright © 2003 John Wiley & Sons, Ltd.
The distinctive CFD challenges of computational rheology
Authors: Walters K. , Webster M. F.
Published: October 2003

In this general lecture, we shall first outline the way computationalnon‐Newtonian fluid mechanics differs from conventional computational fluid dynamics (CFD). We do this by briefly outlining the major historical developments in this relatively new field of science, which is conveniently called Computational Rheology. To illustrate essential features, we limit the discussion to the Oldroyd B, UCM and Phan‐Thien/Tanner constitutive models. In order to provide a serious challenge to existing numerical codes, we describe some recent unpublished experimental results on flow through a contraction of constant viscosity (Boger) and also shear‐thinning elastic liquids. Both planar and axisymmetric contractions are of interest, and pressure drops and observed flow structures provide the relevant points of contact between experiment and numerical prediction. Numerical codes developed at UWS involving a hybrid finite‐element/finite‐volume scheme for Oldroyd B and Phan‐Thien/Tanner constitutive models are applied to the contraction‐flow problems and an encouraging agreement is demonstrated between theory and experiment. Specifically, the dramatic experimental differences between flow in planar and axisymmetric contractions and between constant viscosity and shear‐thinning polymer solutions are mirrored in the numerical predictions, at least in a qualitative sense. Notwithstanding these encouraging developments, the review ends with a realistic assessment of the challenges still awaiting computational rheologists, with particular reference to the choice of constitutive model and the possibility of further refinements to the numerical techniques. Copyright © 2003 John Wiley & Sons, Ltd.
A multigrid accelerated time‐accurate inviscid compressible fluid flow solution algorithm employing mesh movement and local remeshing
Authors: Sørensen K. A. , Hassan O. , Morgan K. , Weatherill N. P.
Published: October 2003

An implicit scheme for the time accurate solution of three dimensional compressible fluid flow problems with moving boundaries on unstructured tetrahedral meshes is described. The numerical scheme is nominally second order accurate in both space and time and satisfies a geometric conservation law. For improved computational performance, the implicit equation system is solved by explicit iteration with multigrid acceleration. For the multigrid implementation, the coarse meshes are automatically generated by an agglomeration technique. The change in the solution domain geometry with time is handled by moving the mesh using a spring analogy scheme, with local remeshing performed in regions of reduced mesh quality. Copyright © 2003 John Wiley & Sons, Ltd.
Numerical modelling of free‐surface flows in ship hydrodynamics
Authors: Bulgarelli U. P. , Lugni C. , Landrini M.
Published: October 2003

Current trends in the investigation of ship hydrodynamics are reviewed with emphasis on the problem of wave‐body interaction. This includes the classical seakeeping problem and as a special case, the problem of prediction for the drag encountered by a ship advancing in calm water. Specific issues related to the numerical treatment of the air–water interface are examined, with emphasis on the modelling of wave breaking. The discussion on the large‐scale modelling of the flow around ships is focused on the prediction of wave loads, ship motions and resistance in calm water. Copyright © 2003 John Wiley & Sons, Ltd.
Evapotranspiration and runoff in a forest watershed, western Japan
Authors: Shimizu A. , Shimizu T. , Miyabuchi Y. , Ogawa Y.
Published: October 2003

A Note has been published for this article in Hydrological Processes 18(4) 2004, 825.

Both water and heat balances were studied in a conifer plantation watershed in south‐west Japan, within the warm‐temperate East Asia monsoon area. Forest cover in the watershed consists mainly of Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecyparis obtusa) plantations. Precipitation and runoff have been observed since 1991, so evapotranspiration can be compared with the water balance. Two meteorological observation towers were built to monitor evapotranspiration in the watershed. The annual average precipitation, amount of runoff and losses were 2166, 1243 and 923 mm, respectively. The evapotranspiration (latent heat flux) agreed well with the water balance losses. The average annual evapotranspiration at the tower built in the centre of the watershed was 902 mm; evapotranspiration at the other tower, further upslope, was 875 mm. The observed evapotranspiration was 39% to 40% of the average precipitation (2166 mm). The mean net radiation was c. 2·6 GJ m−2 year−1, and is considered a representative value of the net radiation (Rn) in coniferous plantations in this region. This region is classified in the humid zone based on the ratio of net radiation (Rn) to the energy required to evaporate the rainfall (λR). The mean annual evaporation of canopy‐intercepted water was 356 mm or about 15% of the average precipitation. Copyright © 2003 John Wiley & Sons, Ltd.