bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermophysiological consequences of whole body resonant RF exposure (100 MHz) in human volunteers
Authors: Adair Eleanor R. , Mylacraine Kevin S. , Allen Stewart J.
Published: September 2003

Thermophysiological responses of heat production and heat loss were measured in seven adult volunteers (six males and one female, aged 31–74 years) during 45 min dorsal exposures of the whole body to 100 MHz continuous wave (CW) radio frequency (RF) energy. Three power densities (PD) (average PD = 4, 6, and 8 mW/cm2; whole body specific absorption rate [SAR] = 0.068 [W/kg]/[mW/cm2]) were tested in each of three ambient temperatures (Ta = 24, 28, and 31 °C), as well as in Ta controls (no RF). A standardized protocol (30 min baseline, 45 min RF or sham exposure, 10 min baseline) was used. Measured responses included esophageal and seven skin temperatures, metabolic heat production, local sweat rate, and local skin blood flow. No changes in metabolic heat production occurred under any test condition. Unlike published results of similar exposures at 450 and 2450 MHz, local skin temperatures, even those on the back that were irradiated directly, changed little or not at all during 100 MHz exposures. The sole exception was the temperature of the ankle skin, which increased by 3–4 °C in some subjects at PD = 8 mW/cm2. During the 45 min RF exposure, esophageal temperature showed modest changes (range = −0.15 to 0.13 °C) and never exceeded 37.2 °C. Thermoregulation was principally controlled by appropriate increases in evaporative heat loss (sweating) and, to a lesser extent, by changes in skin blood flow. Because of the deep penetration of RF energy at this frequency, effectively bypassing the skin, these changes must have been stimulated by thermal receptors deep in the body rather than those located in the skin. Bioelectromagnetics 24:489–501, 2003. Published 2003 Wiley‐Liss, Inc.
Empirical and theoretical dosimetry in support of whole body resonant RF exposure (100 MHz) in human volunteers
Authors: Allen Stewart J. , Adair Eleanor R. , Mylacraine Kevin S. , Hurt William , Ziriax John
Published: September 2003

This study reports the dosimetry performed to support an experiment that measured physiological responses of volunteer human subjects exposed to the resonant frequency for a seated human adult at 100 MHz. Exposures were performed in an anechoic chamber which was designed to provide uniform fields for frequencies of 100 MHz or greater. A half wave dipole with a 90° reflector was used to optimize the field at the subject location. The dosimetry plan required measurement of transmitter harmonics, stationary probe drift, field strengths as a function of distance, electric and magnetic field maps at 200, 225, and 250 cm from the dipole antenna, and specific absorption rate (SAR) measurements using a human phantom, as well as theoretical predictions of SAR with the finite difference time domain (FDTD) method. On each exposure test day, a measurement was taken at 225 cm on the beam centerline with a NBS E field probe to assure consistently precise exposures. A NBS 10 cm loop antenna was positioned 150 cm to the right, 100 cm above, and 60 cm behind the subject and was read at 5 min intervals during all RF exposures. These dosimetry measurements assured accurate and consistent exposures. FDTD calculations were used to determine SAR distribution in a seated human subject. This study reports the necessary dosimetry for work on physiological consequences of human volunteer exposures to 100 MHz. Bioelectromagnetics 24:502–509, 2003. Published 2003 Wiley‐Liss, Inc.
Effects of 50 Hz electromagnetic field exposure on apoptosis and differentiation in a neuroblastoma cell line
Authors: Pirozzoli M.C. , Marino C. , Lovisolo G.A. , Laconi C. , Mosiello L. , Negroni A.
Published: September 2003

Experiments were carried out to assess whether a magnetic field of 50 Hz and 1 mT can influence apoptosis and proliferation in the human neuroblastoma cell line LAN‐5. TUNEL assays and poly‐ADP ribose polymerase (PARP) expression analysis were performed to test apoptosis induction, and the WST‐1 assay was used to calculate the proliferation index in a long term exposure. No alterations were found in cellular ability to undergo programmed cell death, but a small increase in the proliferation index was evidenced after 7 days of continuous exposure. Also, a slight and transient increase of B‐myb oncogene expression was detected after 5 days of exposure. Combined exposures of cells to EMF and to chemical agents which interfere with proliferation, such as the differentiative agent retinoic acid and the apoptotic inducer camptothecin, showed an antagonistic effect of magnetic fields against the differentiation of the LAN‐5 cells and a protective effect towards apoptosis. Bioelectromagnetics 24:510–516, 2003. © 2003 Wiley‐Liss, Inc.
Phase I clinical study of a static magnetic field combined with anti‐neoplastic chemotherapy in the treatment of human malignancy: Initial safety and toxicity data
Authors: Salvatore Joseph R. , Harrington Joanne , Kummet Thomas
Published: September 2003

We have completed the lowest level of exposure in a Phase I study, designed to establish the safety and toxicity of the combination of a static magnetic field (SMF) and antineoplastic chemotherapy in patients with advanced malignancy. The SMF application is carefully controlled by applying the magnet to the patient only in our clinic during chemotherapy administration. No increase in the severity of chemotherapy toxicity as measured by white blood cell count and platelet count was seen in the participants exposed to SMF compared to the historical control subjects. These data have permitted the next group of subjects to be treated at the next dose level. Bioelectromagnetics 24:524–527, 2003. Published 2003 Wiley‐Liss, Inc.
(S,S)‐2,3‐Dihydroxy‐2,3‐dihydrobenzoic Acid: Microbial Access with Engineered Cells of Escherichia coli and Application as Starting Material in Natural‐Product Synthesis
Authors: Franke Dirk , Lorbach Volker , Esser Simon , Dose Christian , Sprenger Georg A. , Halfar Markus , Thömmes Jörg , Müller Rolf , Takors Ralf , Müller Michael
Published: September 2003

Cyclohexadiene‐trans‐5,6‐diols such as (S,S)‐2,3‐dihydroxy‐2,3‐dihydrobenzoic acid (2,3‐trans‐CHD) have been shown to be of importance as chiral starting materials for the syntheses of bioactive substances, especially for the syntheses of carbasugars. By using methods of metabolic‐pathway engineering, the Escherichia coli genes entB and entC, which encode isochorismatase and isochorismate synthase, were cloned and over‐expressed in E. coli strains with a deficiency of entA, which encodes 2,3‐dihydroxybenzoate synthase. A 30‐fold increase in the corresponding EntB/EntC enzyme activities affects the accumulation of 2,3‐trans‐CHD in the cultivation medium. Although the strains did not contain deletions in chorismate‐utilising pathways towards aromatic amino acids, neither chorismate nor any other metabolic intermediates were found as by‐products. Fermentation of these strains in a 30 L pH‐controlled stirred tank reactor showed that 2,3‐trans‐CHD could be obtained in concentrations of up to 4.6 g L−1. This demonstrates that post‐chorismate metabolites are accessible on a preparative scale by using techniques of metabolic‐pathway engineering. Isolation and separation from fermentation salts could be performed economically in one step through anion‐exchange chromatography or, alternatively, by reactive extraction. Starting from 2,3‐trans‐CHD as an example, we established short syntheses towards new carbasugar derivatives.
Kinetic versus Thermodynamic Control During the Formation of [2]Rotaxanes by a Dynamic Template‐Directed Clipping Process
Authors: Horn Matthias , Ihringer Johannes , Glink Peter T. , Stoddart J. Fraser
Published: September 2003

A template‐directed dynamic clipping procedure has generated a library of nine [2]rotaxanes that have been formed from three dialkylammonium salts—acting as the dumbbell‐shaped components—and three dynamic, imino bond‐containing, [24]crown‐8‐like macrocycles—acting as the ring‐shaped components—which are themselves assembled from three dialdehydes and one diamine. The rates of formation of these [2]rotaxanes differ dramatically, from minutes to days depending on the choice of dialkylammonium ion and dialdehyde, as do their thermodynamic stabilities. Generally, [2]rotaxanes formed by using 2,6‐diformylpyridine as the dialdehyde component, or bis(3,5‐bis(trifluoromethyl)benzyl)ammonium hexafluorophosphate as the dumbbell‐shaped component, assembled the most rapidly. Those rotaxanes containing this particular electron‐deficient dumbbell‐shaped unit, or 2,5‐diformylfuran units in the macroring, were the most stable thermodynamically. The relative thermodynamic stabilities of all nine of the [2]rotaxanes were determined by competition experiments that were monitored by 1H NMR spectroscopy.
Helical Supramolecular Aggregates Based on Ureidopyrimidinone Quadruple Hydrogen Bonding
Authors: Hirschberg J. H. K. Ky , Koevoets Rolf A. , Sijbesma Rint P. , Meijer E. W.
Published: September 2003

A series of mono‐ and bifunctional compounds 2–7, based on the ureido pyrimidinone quadruple hydrogen bonding unit, was prepared to study the mode of aggregation of these compounds in the bulk and in solution. Compounds 2–7 exhibit thermotropic liquid crystalline properties, as evidenced by differential scanning calorimetry and optical polarization microscopy. The presence of an ordered hexagonal discotic (Dho) phase of 2 a was confirmed by X‐ray diffraction on an aligned sample. In chloroform, the bifunctional compounds form cyclic dimers at millimolar concentrations, and these dimers exist in equilibrium with linear species above a critical concentration, which may be from 6 mM to greater than 260 mM, depending on the structure of the spacer. Circular dichroism measurements in chloroform did not show a Cotton effect. Dodecane solutions of compounds 3, 4 b, and 7 b display a Cotton effect at the absorption band of the phenyl‐pyrimidinone unit. Amplification of chirality was observed in mixtures of 7 a and 7 b, but not in mixtures of 4 a and 4 b, indicating that 7 a and 7 b form mixed polymeric aggregates with a helical architecture in dodecane solution, whereas 4 a and 4 b do not. The Cotton effect is lost upon increasing the temperature. Half of the helicity is lost at 25 °C for 3 and at 60 °C for 4 b, suggesting that 3, bearing the shorter spacer, forms less stable columns than 4 b. Compound 7 b loses half of its helicity at 45 °C. Compounds 2 b, 5, and 6 do not exhibit helical organization, as evidenced by the absence of Cotton effects.
Zwitterionic Silenes: Interesting Goals for Synthesis?
Authors: Ottosson Henrik
Published: September 2003

Properties of silenes, as a function of increased reversal of the SiC bond polarity, have been examined through quantum‐chemical calculations. The aim of this study was to identify silenes that can be of general interest for organic synthesis. The calculations were carried out primarily with the B3LYP hybrid density functional method, but also with the CASSCF, MP2, MP4(SDQ), and CCSD(T) methods. The study was performed on Z2SiCXY compounds which were divided into three sets that differ with regard to their Si substituents (Z), and with their C substituents (X and Y) varying from weakly to strongly π‐electron‐donating groups. The charge at the Si atom (q(Si)) was used as a measure of the extent of reversed silicon–carbon bond polarity. For each of the three sets, the variation in silicon–carbon bond lengths (rSiC) and extent of Si pyramidalization (ΣSi) in relation to q(Si) follow three separate curves. Silenes with strongly π‐electron‐donating X and Y groups are completely described by zwitterionic (reverse‐polarized) resonance structures. Such zwitterionic silenes are singly (SiC) rather than doubly bonded (SiC), and have a distinctly pyramidal Si atom due to negative charge localization. These silenes also have much lower heats of dimerization than the parent silene. Finally, inversion barriers of zwitterionic silenes are increased by electron‐withdrawing substituents, and this enables computational design of silenes with their Si atoms as chiral centers. It is hoped that such chiral zwitterionic silenes can find use in organic synthesis.
Synthesis and Characterization of New Five‐Coordinate Platinum Nitrosyl Derivatives: Density Functional Theory Study of Their Electronic Structure
Authors: Ara Irene , Forniés Juan , García‐Monforte María Angeles , Menjón Babil , Sanz‐Carrillo Rosa María , Tomás Milagros , Tsipis Athanassios C. , Tsipis Constantinos A.
Published: September 2003

The neutral, five‐coordinate platinum nitrosyl compounds [Pt(C6F5)3(L)(NO)] (2) [L=CNtBu (2 a), NC5H4Me‐4 (2 b), PPhMe2 (2 c), PPh3 (2 d) and tht (2 e)] have been prepared by the reaction of [NBu4][Pt(C6F5)3(L)] (1) with NOClO4 in CH2Cl2. The ionic compound [N(PPh3)2][Pt(C6F5)4(NO)] (4) has been prepared in a similar way starting from the homoleptic species [N(PPh3)2]2[Pt(C6F5)4] (3). Compounds 2 and 4 are all diamagnetic with {PtNO}8 electronic configuration and show ν(NO) stretching frequencies at around 1800 cm−1. The crystal and molecular structures of 2 c and 4 have been established by X‐ray diffraction methods. The coordination environment for the Pt center in both compounds can be described as square pyramidal (SPY‐5). Bent nitrosyl coordination is observed in both cases with Pt‐N‐O angles of 120.1(6) and 130.2(7)° for 2 c and 4, respectively. The bonding mechanism of the nitrosyl ligand coordinated to various model [PtIIR4]2− (R=H, Me, Cl, CN, C6F5 or C6Cl5) and [Pt(C6F5)3(L)]− (L=CNMe, PH3) systems has been studied by density functional calculations at the B3LYP level of theory, using the SDD basis set. The R4Pt–NO and (C6F5)3(L)Pt–NO interactions generally involve two components: i) a direct Pt–NO bonding interaction and ii) multicenter‐bonding interactions between the N atom of the NO ligand and the donor atoms of the R and L ligands. Moreover, with the more complex R groups, C6F5 or C6Cl5, a third component has been found to arise, which involves multicenter electrostatic interactions between the positively charged NO ligand and the negatively charged halo‐substituents in the ortho‐position of the C6X5 groups (X=F, Cl). The contribution of each component to the PtNO bonding in R4PtNO and (C6F5)3(L)PtNO compounds seems to be modulated by the electronic and steric effects of the R and L ligands.
Depolymerization of Poly(2,6‐dimethyl‐1,4‐phenylene oxide) under Oxidative Conditions
Authors: Saito Kei , Masuyama Toru , Oyaizu Kenichi , Nishide Hiroyuki
Published: September 2003

Depolymerization of an engineering plastic, poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO), was accomplished by using 2,6‐dimethylphenol (DMP) under oxidative conditions. The addition of an excess amount of DMP to a solution of PPO in the presence of a CuCl/pyridine catalyst yielded oligomeric products. When PPO (Mn=1.0×104, Mw/Mn=1.2) was allowed to react with a sufficient amount of DMP, the molecular weight of the product decreased to Mn=4.9×102 (Mw/Mn=1.5). By a prolonged reaction with the oxidant, the oligomeric product was repolymerized to produce PPO essentially identical to the starting material, making the oligomer useful as a reusable resource. During the depolymerization reaction, an intermediate phenoxyl radical was observed by ESR spectroscopy. Kinetic analysis showed that the rate of the oxidation of PPO was about 10 times higher than that of DMP. These results show that a monomeric phenoxyl radical attacks the polymeric phenoxyl to induce the redistribution via a quinone ketal intermediate, leading to the substantial decrease in the molecular weight of PPO, which is much faster than the chain growth.
Templated Synthesis of a Rotaxane with a [Ru(diimine)3]2+ Core
Authors: Pomeranc Didier , Jouvenot Damien , Chambron Jean‐Claude , Collin Jean‐Paul , Heitz Valérie , Sauvage Jean‐Pierre
Published: September 2003

A rotaxane containing a ruthenium bisphenanthroline complex, acting as an axis, and a macrocycle incorporating a 2,2′‐bipyridine (bpy) unit, threaded by the axis, has been synthesized. The bisphenanthroline ligand is such that its ruthenium(II) complexes possess a clearly identified axis, making such compounds ideal components of rotaxanes constructed around an octahedral ruthenium(II) center, which serves as a template. The ring is threaded by the axial ruthenium(II) precursor complex, to afford the corresponding pseudorotaxane in moderate yield. The X‐ray structure analysis of this compound reveals the threaded nature of the complex. The length of the threaded ring (35 atoms in the periphery) is too short to allow easy threading of the axis through the macrocycle. As a consequence, an isomer is also obtained for which the axial ruthenium complex is attached in an exo fashion. 1H NMR studies have been carried out, which reveal various conformational equilibria for the pseudorotaxane. Light‐induced decoordination of the bpy‐containing cyclic fragment was shown to be quantitative and to lead to the free ring and the axial ruthenium(II) complex, regardless of the starting compound (pseudorotaxane or exo isomer). Finally, the real rotaxane could be prepared, although it could not be separated from its exo isomer.
A Combined Spectroscopic and Theoretical Study of a Series of Conformationally Restricted Hexapeptides Carrying a Rigid Binaphthyl–Nitroxide Donor–Acceptor Pair
Authors: Pispisa Basilio , Mazzuca Claudia , Palleschi Antonio , Stella Lorenzo , Venanzi Mariano , Wakselman Michel , Mazaleyrat Jean‐Paul , Rainaldi Mario , Formaggio Fernando , Toniolo Claudio
Published: September 2003

The structural features of a series of linear hexapeptides of general formula Boc‐B‐Ar‐T‐Am‐OtBu, where A is L‐Ala or Aib (α‐aminoisobutyric acid), B is (R)‐Bin, a binaphthyl‐based Cα,α‐disubstituted Gly residue, T is Toac, a nitroxide spin‐labeled Cα,α‐disubstituted Gly, and r+m=4, were investigated in methanol solution by fluorescence, transient absorption, IR and CD spectroscopic studies, and by molecular mechanics calculations. These peptides are denoted as B‐T/r‐m, to emphasize the different position of Toac with respect to that of the Bin fluorophore in the amino acid sequence. The rigidity of the B‐T donor–acceptor pair and of the Aib‐rich backbone allowed us to investigate the influence of the interchromophoric distance and orientation on the photophysics of the peptides examined. The excited state relaxation processes of binaphthyl were investigated by time‐resolved fluorescence and transient absorption experiments. Dynamic quenching of the excited singlet state of binaphthyl by Toac was successfully interpreted by the Förster energy transfer model, provided that the mutual orientation of the chromophores is taken into account. This implies that interconversion among conformational substates, which involves puckering of the Toac piperidine ring, is slow on the time scale of the transfer process, that is slower than 5 ns. By comparison of the experimental and theoretical data, the type of secondary structure (right‐handed 310 helix) from the B‐T/r‐m peptides in solution was determined; this would not have been achievable by using the CD and NMR data only, as the data are not diagnostic in this case. Static quenching was observed in all peptides examined but B‐T/1‐3, where the effect can be ascribed to a non‐fluorescent complex. Among the computed low‐energy conformers of these peptides, there is one structure exhibiting a NO.–naphthalene center‐to‐center distance <6 Å, which might be assigned to this complex. The overall results emphasize the versatility of fluorescence experiments in 3D‐structural studies in solution.
Temperature Dependence of X‐ and Q‐Band EPR Spectra of the Dinuclear Manganese(II) Complex [(NO2Bpmp)Mn2(μ‐OAc)2]+: Determination of the Exchange Constant and of the Spin Parameters for the S=1, 2, and 3 Spin States
Authors: Blanchard Sébastien , Blain Guillaume , Rivière Eric , Nierlich Martine , Blondin Geneviève
Published: September 2003

A new dinuclear manganese(II) complex was synthesised with the biscompartimental ligand 2,6‐bis[bis(2‐pyridylmethyl)aminomethyl]‐4‐nitrophenol (NO2BpmpH) and characterised by X‐ray crystallography. Magnetic susceptibility measurements revealed that the two high‐spin MnII ions are antiferromagnetically coupled with a singlet‐to‐triplet separation of 7.2 cm−1. The powder EPR spectra were recorded for both X‐ and Q‐bands between 1.8 K and 35 K. A detailed analysis of these spectra led to the determination of three out of five individual spin‐state zero‐field splitting parameters. From the proposed simulations, the exchange coupling constant J and the intermetallic distance have been computed.
Mechanism of Aromatic Hydroxylation by an Activated FeIVO Core in Tetrahydrobiopterin‐Dependent Hydroxylases
Authors: Bassan Arianna , Blomberg Margareta R. A. , Siegbahn Per E. M.
Published: September 2003

The chemical pathways leading to the hydroxylated aromatic amino acids in phenylalanine and tryptophan hydroxylases have been investigated by means of hybrid density functional theory. In the catalytic core of these non‐heme iron enzymes, dioxygen reacts with the pterin cofactor and is likely to be activated by forming an iron(IV)O complex. The capability of this species to act as a hydroxylating intermediate has been explored. Depending on the protonation state of the ligands of the metal, two different mechanisms are found to be energetically possible for the hydroxylation of phenylalanine and tryptophan by the high‐valent iron–oxo species. With a hydroxo ligand the two‐electron oxidation of the aromatic ring passes through a radical, while an arenium cation is involved when a water replaces the hydroxide. After the attack of the activated oxygen on the substrate, it is also found that a 1,2‐hydride shift (known as an NIH shift) generates a keto intermediate, which can decay to the true product through an intermolecular keto–enol tautomerization. The benzylic hydroxylation of 4‐methylphenylalanine by the FeIVO species has also been investigated according to the rebound mechanism. The computed energetics lead to the conclusion that FeIVO is capable not only of aromatic hydroxylation, but also of benzylic hydroxylation.
Fluorous Biphasic Catalysis: Synthesis and Characterization of Copper(I) and Copper(II) Fluoroponytailed 1,4,7‐Rf‐TACN and 2,2′‐Rf‐Bipyridine Complexes—Their Catalytic Activity in the Oxidation of Hydrocarbons, Olefins, and Alcohols, Including Mechanistic Implications
Authors: Contel María , Izuel Cristina , Laguna Mariano , Villuendas Pedro R. , Alonso Pablo J. , Fish Richard H.
Published: September 2003

In this contribution on fluorous biphasic catalysis (FBC), we present the synthesis and characterization of new copper complexes, and define their role, as precatalysts, in the FBC oxidation of hydrocarbons, olefins, and alcohols. Thus the previously reported, but poorly characterized, fluoroponytailed ligand, 2,2′‐Rf‐bipyridine (Rf=‐(CH2)3C8F17) 2, as well as the new CuII fluoroponytailed carboxylate synthon complex [Cu(C8F17(CH2)2CO2)2] 3, will be addressed. Moreover, the reaction of previously described ligands, 1,4,7‐Rf‐TACN 1, or 2,2′‐Rf‐bipyridine 2 with 3 afforded new perfluoroheptane‐soluble CuII complexes, [Cu(C8F17(CH2)2CO2)2(Rf‐tacn)] 4 and [Cu(C8F17(CH2)2CO2)2(Rf‐bpy)] 5, respectively. The reaction of 1 with [Cu(CH3CN)4]PF6 or [CuCl] provided new CuI complexes, which could be isolated and fully characterized as [Cu(Rf‐tacn)X′]X, in which X=PF6 (6) or X′=Cl (7) (soluble in perfluoroheptane). The CuII and CuI complexes, 4–7, were characterized by elemental analysis, mass spectrometry, and IR, diffuse reflectance UV/Vis, and EPR spectroscopies; complex 7 was also characterized by 1H and 19F{1H} NMR spectroscopy. Complexes 4 and 5, as well as 6 and 7 generated in situ, were evaluated as precatalysts for hydrocarbon and olefin functionalization. The oxidation reactions of these substrates in the presence of the necessary oxidants, tert‐butyl hydroperoxide (TBHP) and oxygen gas, proceeded under FBC conditions for 5, 7, and CuI salts with 2. However, the complexes with ligand 2 could not be recycled, owing to significant ligand dissociation. The CuII complex 4, with the ligand 1, provide the oxidation of 4‐nitrobenzyl alcohol to 4‐nitrobenzaldehyde under single‐phase FBC conditions at 90 °C with TEMPO (2,2,6,6‐tetramethylpiperidinyl‐1‐oxy) and O2; the precatalyst 4, can be utilized for an additional four catalytic cycles without loss of activity. Plausible mechanisms concerning these FBC oxidation reactions will be discussed.
A New Enzyme Model For Enantioselective Esterases Based On Molecularly Imprinted Polymers
Authors: Emgenbroich Marco , Wulff Günter
Published: September 2003

An efficient enzyme model exhibiting enantioselective esterase activity was prepared by using molecular imprinting techniques. The enantiomerically pure phosphonic monoesters 4 L and 5 L were synthesized as stable transition‐state analogues. They were used as templates connected by stoichiometric noncovalent interactions to two equivalents of the amidinium binding site monomer 1. After polymerization and removal of the template, the polymers were efficient catalysts for the hydrolysis of certain nonactivated amino acid phenylesters (2 L, 2 D, 3 L, 3 D) depending on the template used. Imprinted catalyst IP4 (imprinted with 4 L) enhanced the hydrolysis of the corresponding substrate 2 L by a factor of 325 relative to that of a buffered solution. Relative to a control polymer containing the same functionalities, prepared without template 4 L, the enhancement was still about 80‐fold, showing the highest imprinting effect up to now. In cross‐selectivity experiments a strong substrate selectivity of higher than three was found despite small differences in the structure of the substrate and template. Plots of initial velocities of the hydrolysis versus substrate concentration showed typical Michaelis–Menten kinetics with saturation behavior. From these curves, the Michaelis constant KM and the catalytic constant kcat can be calculated. The enantioselectivity shown in these values is most interesting. The ratio of the catalytic efficiency kcat/KM, between the hydrolysis of 2 L‐ and 2 D‐substrate with IP4, is 1.65. This enantioselectivity derives from both selective binding of the substrate (KML/KMD=0.82), and from selective formation of the transition state (kcatL/kcatD=1.36). Thus, these catalysts give good catalysis as well as high imprinting and substrate selectivity. Strong competitive inhibition is caused by the template used in imprinting. This behavior is also quite similar to the behavior of natural enzymes, for which these catalysts are good models.
Diastereoselective Conjugate Addition to Chiral α,β‐Unsaturated Carbonyl Systems in Aqueous Media: An Enantioselective Entry to α‐ and γ‐Hydroxy Acids and α‐Amino Acids
Authors: Suárez Rosa M. , Pérez Sestelo José , Sarandeses Luis A.
Published: September 2003

The stereoselectivity of the ultrasonically induced zinc—‐copper conjugate addition of iodides to chiral α,β‐unsaturated carbonyl systems under aqueous conditions was studied. Alkyl iodides add diastereoselectively to methylenedioxolanone 1 and methyleneoxazolidinone 2 to afford the 1,4‐addition products in good yields (38–95 %) and with high diastereomeric excess (44–90 % de). The 1,4‐addition to chiral γ,δ‐dioxolanyl‐α,β‐unsaturated esters 3–5 also proceeds with good yields (51–99 %). The diastereoselectivity is dependent on the geometry of the olefin: the Z isomer 3 gives high diastereoselectivity, while the reactions with the E isomer 4 are nonstereoselective. The reaction proceeds with excellent chemoselectivity and allows the use of iodides bearing ester, hydroxy, and amino groups. Since the 1,4‐addition products can be readily hydrolyzed, this methodology constitutes a novel entry for the enantioselective synthesis of α‐ and γ‐hydroxy acids and α‐amino acids in aqueous media. The results obtained support the radical mechanism proposed by Luche, and represent one of the few examples of a radical stereoselective conjugate addition in aqueous medium.
Waste‐Free and Facile Solid‐State Protection of Diamines, Anthranilic Acid, Diols, and Polyols with Phenylboronic Acid
Authors: Kaupp Gerd , Naimi‐Jamal M. Reza , Stepanenko Vladimir
Published: September 2003

Phenylboronic acid (2) reacts quantitatively by ball‐milling in the solid state with o‐phenylendiamine, 1,8‐diaminonaphthalene, anthranilic acid, pyrocatechol, pyrogallol, pinacol, bicyclic cis‐diols, mannitol, and inositol to form the five‐ or six‐membered cyclic phenylboronic amides or esters. Catalysts or other auxiliaries are strictly excluded as they are not required and would have to be removed after the reactions. These varied model reactions provide pure protected products without the necessity of further purifying workup and the potential for protection chemistry is demonstrated. Some of the reactions can also be quantitatively performed if stoichiometric mixtures of the reactants are co‐ground or co‐milled and heated to appropriate temperatures either below the eutectics or above the melting points. The temperatures are much higher in the latter case. Similar reactions in solution suffer from less than 100 % yield of the mostly sensitive compounds that are difficult to purify and thus create much waste. The hydrolysis (deprotection) conditions of the products are rather mild in most cases. Therefore, this particularly easy access to heteroboroles, heteroborolanes, heteroborinones, heteroborines, and heteroborinines is highly valuable for their more frequent use in protective syntheses.
Soluble Carbon Nanotubes
Authors: Tasis Dimitrios , Tagmatarchis Nikos , Georgakilas Vasilios , Prato Maurizio
Published: September 2003

Carbon nanotubes have attracted great interdisciplinary interest because of their unique structure and properties. However, carbon‐nanotube research is challenged by several problems, such as: i) mass production of material, ii) control of length, diameter, and chirality, and iii) manipulation for use in diverse technological fields. Issues regarding the synthesis and purification as well as the functionalization and solubilization of carbon nanotubes are relevant topics in this rapidly growing field. In this paper, covalent and noncovalent approaches to functionalized and solubilized nanotubes are examined in detail, with particular emphasis on the change of properties that accompany the chemical modification.
Computation of Aromatic C3N4 Networks and Synthesis of the Molecular Precursor N(C3N3)3Cl6
Authors: Vodak David T. , Kim Kibum , Iordanidis Lykourgos , Rasmussen Paul G. , Matzger Adam J. , Yaghi Omar M.
Published: September 2003

The successful synthesis and structural characterization of molecules that represent segments of extended solids is a valuable strategy for learning metric and stereochemical characteristics of those solids. This approach has been useful in cases in which the solids are particularly difficult to crystallize and thus their atomic connectivity and overall structures become difficult to deduce with X‐ray diffraction techniques. One such class of materials is the covalently linked CxNy extended solids, where molecular analogues remain largely absent. In particular, structures of C3N4 solids are controversial. This report illustrates the utility of a simple molecule, N(C3N3)3Cl6, in answering the question of whether triazine based C3N4 phases are layered or instead they adopt 3D structures. Here, we present density functional calculations that clearly demonstrate the lower stability of graphitic C3N4 relative to 3D analogues.
From Central to Helical Chirality: Synthesis of P and M Enantiomers of [5]Helicenequinones and Bisquinones from (SS)‐2‐(p‐Tolylsulfinyl)‐ 1,4‐benzoquinone
Authors: Carreño M. Carmen , García‐Cerrada Susana , Urbano Antonio
Published: September 2003

The reaction of 1,4‐divinyl‐1,3‐cyclohexadiene, 5,8‐dimethoxy‐ or tert‐butyldimethylsilyloxy‐3‐vinyl‐1,2‐dihydrophenanthrene or 6‐vinyl‐7,8‐dihydro‐1,4‐phenanthrenequinone with an excess of enantiopure (SS)‐2‐(p‐tolylsulfinyl)‐1,4‐benzoquinone (2) led to the direct formation of enantioenriched dihydro[5]helicenequinones or bisquinones (50→98 % ee). A domino Diels–Alder cycloaddition/sulfoxide elimination/partial aromatization process occurs, being the absolute configuration of the final helicene defined in the aromatization step. Both M and P helimers are accessible through a stepwise enantiodivergent process if the pentacyclic dihydroaromatic intermediate resulting in the two first steps is aromatized in the presence of (±)‐2, DDQ, CAN or DBU.
Solvatochromic Azamethine Dyes for Probing the Polarity of Gold‐Cluster‐Functionalized Silica Particles
Authors: Spange Stefan , Kunzmann Dagmar , Sens Rüdiger , Roth Isabelle , Seifert Andreas , Thiel Werner R.
Published: September 2003

Azamethine dyes of the merocyanine type [4‐(N,N‐di‐n‐butylamino)‐2‐methylphenyl]{2,4‐di‐keto‐3‐[N′‐(n‐hexyl)]‐5‐cyano‐6‐methyl‐3‐pyridinio}‐1‐azamethine (1) and [4‐(N,N‐diethylamino)‐2‐(N′‐tert‐butylcarboxy)‐amidophenyl]‐{2,4‐diketo‐3‐[N″‐(n‐hexyl)]‐5‐cyano‐6‐methyl‐3‐pyridinio}‐1‐azamethine (2) have been used as surface‐polarity indicators for gold‐cluster‐functionalized silica particles. Their UV/Vis absorption maxima range from about λ=600 to 700 nm as a function of solvent polarity and are clearly separated from the surface plasmon UV/Vis absorption band of gold (λ≈520–540 nm). Solvatochromism of both dyes has been investigated in 26 solvents of different polarity. The positive solvatochromic band shifts of 1 and 2 can be well expressed in terms of the empirical Kamlet–Taft solvent polarity parameters α and π*. They are mainly sensitive to the dipolarity/polarizability (π* term; 70–75 %) and HBD (hydrogen‐bond donating) acidity (α term) of the solvent. Both dyes adsorb readily on functionalized silica samples from solutions in 1,2‐dichloroethane or cyclohexane. The surface polarities of gold‐cluster‐functionalized silica particles, with and without co‐adsorbed L‐cysteine and poly(ethylenimine), have been investigated by using these solvatochromic dyes. The specific interaction of dye 2 with cysteine has been examined independently by quantum‐chemical calculations by using the AM1 and PM3 methods.
Employing the Structural Diversity of Nature: Development of Modular Dipeptide‐Analogue Ligands for Ruthenium‐Catalyzed Enantioselective Transfer Hydrogenation of Ketones
Authors: Pastor Isidro M. , Västilä Patrik , Adolfsson Hans
Published: September 2003

A library of novel dipeptide‐analogue ligands based on the combination of tert‐butoxycarbonyl(N‐Boc)‐protected α‐amino acids and chiral vicinal amino alcohols were prepared. These highly modular ligands were combined with [{RuCl2(p‐cymene)}2] and the resulting metal complexes were screened as catalysts for the enantioselective reduction of acetophenone under transfer hydrogenation conditions using 2‐propanol as the hydrogen donor. Excellent enantioselectivity of 1‐phenylethanol (up to 98 % ee) was achieved with several of the novel catalysts. Although most of the ligands contained two stereocenters, it was demonstrated that the absolute configuration of the product alcohol was determined by the configuration of the amino acid part of the ligand. Employing ligands based on L‐amino acids generated S‐configured products, and catalysts based on D‐amino acids favored the formation of the R‐configured alcohol. The combination N‐Boc‐L‐alanine and (R)‐phenylglycinol (Boc‐L‐Ab) or its enantiomer (N‐Boc‐D‐alanine and (S)‐phenylglycinol, Boc‐D‐Aa) proved to be the best ligands for the reduction process. Transfer hydrogenation of a number of aryl alkyl ketones were evaluated and excellent enantioselectivity, up to 96 % ee, was obtained.
How Nucleophilic Are Diazo Compounds?
Authors: Bug Thorsten , Hartnagel Manfred , Schlierf Clemens , Mayr Herbert
Published: September 2003

The kinetics of the reactions of benzhydryl cations with eight diazo compounds 1 a–g were investigated photometrically in dichloromethane. The nucleophilicity parameters N and slope parameters s of these diazo compounds were derived from the equation log k (20 °C)=s (E+N) and compared with the nucleophilicities of other π systems (alkenes, arenes, silyl enol ethers, silyl ketene acetals). It is shown that the nucleophilic reactivities of diazo compounds cover more than ten orders of magnitude, being comparable to that of styrene on the low reactivity end and to that of enamines on the high reactivity end. The rate‐determining step of these reactions is the electrophilic attack at the diazo‐carbon atom to yield diazonium ions, which rapidly lose nitrogen.
Highly Substituted Azulene Dyes as Multifunctional NLO and Electron‐Transfer Compounds
Authors: Lambert Christoph , Nöll Gilbert , Zabel Manfred , Hampel Frank , Schmälzlin Elmar , Bräuchle Christoph , Meerholz Klaus
Published: September 2003

Two highly substituted azulene derivatives were synthesised by Pd‐mediated dimerisation from the corresponding tolan species. One azulene derivative (2) has donor functionalities (dianisylaminophenyl and dianisylamino) in the 1‐, 2‐, 3‐ and 6‐positions, while the other (1) has donors (dianisylaminophenyl) in the 2‐ and 6‐positions and acceptors (nitrophenyl) in the 1‐ and 3‐positions. Each azulene derivative shows strong bond length alternation in the solid state, determined by X‐ray crystal analysis, and an intense CT band around 450–500 nm in its UV/Vis spectrum. The first‐order hyperpolarisability of 1 and of 2 was measured by hyper‐Rayleigh scattering and is about that of disperse red DR1. Both azulene derivatives show multiple oxidation processes. The intramolecular adiabatic ET behaviour of the mixed valence radical cations of 1 and of 2 was investigated by UV/Vis/NIR spectroelectrochemistry. The intervalence‐CT band of 1+ could be analysed by the Generalised Mulliken–Hush theory, which yields an electronic coupling V=1140 cm−1 for the optically induced adiabatic hole transfer.
Synthesis, X‐ray Crystal Structure, UV/Visible Linear and Nonlinear (Optical Limiting) Spectral Properties of Symmetrical and Unsymmetrical Porphyrazines with Annulated 1,2,5‐Thiadiazole and 1,4‐Diamyloxybenzene Moieties
Authors: Donzello Maria Pia , Ercolani Claudio , Gaberkorn Anna A. , Kudrik Evgenij V. , Meneghetti Moreno , Marcolongo Gabriele , Rizzoli Corrado , Stuzhin Pavel A.
Published: September 2003

Co‐cyclization of 1,2,5‐thiadiazole‐3,4‐dicarbonitrile and 3,6‐diamyloxyphthalodinitrile in the presence of magnesium or lithium amylate in amyl alcohol leads to mixtures containing the Mg derivatives of the symmetrical species tetrakis(1,2,5‐thiadiazolo)porphyrazine, (S4)PzH2, and tetrakis(1,4‐diamyloxybenzo)porphyrazine, (A4)PzH2, and the low‐symmetry macrocycles bearing peripheral 1,2,5‐thiadiazole and 1,4‐diamyloxybenzene rings in the ratio 1:3, 2:2 (cis and trans), and 3:1, that is, (SA3)PzH2, (S2A2)PzH2, (SASA)PzH2, and (S3A)PzH2, respectively. The basic Mg materials were converted to the corresponding free‐base macrocycles by treatment with CF3COOH. The species were separated from the mixtures by chromatography, either as Mg complexes or demetalated materials. With results on (S4)PzH2 and (SA3)PzH2 in hand, including crystallographic work on the latter, a general chemical physical investigation has been carried out of all the symmetrical and unsymmetrical free‐base macrocycles. The structures of the species (S2A2)PzH2 and (A4)PzH2. were elucidated by single‐crystal X‐ray crystallography. The effect of the progressive variation of the macrocyclic structure along the series, from the symmetrical (S4)PzH2 to its symmetrical partner (A4)PzH2 via the low‐symmetry 3:1, 2:2 (cis and trans), and 1:3 macrocycles, was studied by IR, 1H NMR, and UV/Vis linear and nonlinear (optical limiting) measurements. The results are interpreted on the basis of intra‐ and intermolecular interactions between the electron‐deficient 1,2,5‐thiadiazole and the electron‐donating 1,4‐diamyloxybenzene moieties.
Molybdenum Amido Complexes with Single MoN Bonds: Synthesis, Structure, and Reactivity
Authors: Morales Dolores , Pérez Julio , Riera Lucía , Riera Víctor , Miguel Daniel , Mosquera Marta E. G. , García‐Granda Santiago
Published: September 2003

Reactions of the complex [MoCl(η3‐C3H4‐Me‐2)(CO)2(phen)] (1) (phen=1,10‐phenanthroline) with potassium arylamides were used to synthesize the amido complexes [Mo(N(R)Ar)(η3‐C3H4‐Me‐2)(CO)2(phen)] (R=H, Ar=Ph, 2 a; R=H, Ar=p‐tolyl, 2 b; R=Me, Ar=Ph; 2 c). For 2 b the MoN(amido) bond length (2.105(4) Å) is consistent with it being a single bond, with which the metal attains an 18‐electron configuration. The reaction of 2 b with HOTf affords the amino complex [Mo(η3‐C3H4‐Me‐2)(NH2(p‐tol))(CO)2(phen)]OTf (3‐OTf). Treatment of 3‐OTf with nBuLi or KN(SiMe3)2 regenerates 2 b. The new amido complexes react with CS2, arylisothiocyanates and maleic anhydride. A single product corresponding to the formal insertion of the electrophile into the MoN(amido) bond is obtained in each case. For maleic anhydride, ring opening accompanied the formation of the insertion product. The reaction of 2 b with maleimide affords [Mo(η3‐C3H4‐Me‐2){NC(O)CHCHC(O)}(CO)2(phen)] (7), which results from simple acid–base metathesis. The reaction of 2 b with (p‐tol)NCO affords [{Mo(η3‐C3H4‐Me‐2)(CO)2(phen)}2(η2‐MoO4)] (8), which corresponds to oxidation of one third of the metal atoms to MoVI. Complex 8 was also obtained in the reactions of 2 b with CO2 or the lactide 3,6‐dimethyl‐1,4‐dioxane‐2,5‐dione. The structures of the compounds 2 b, 3‐OTf, [Mo(η3‐C3H4‐Me‐2){SC(S)(N(H)Ph)}(CO)2(phen)] (4), [Mo(η3‐C3H4‐Me‐2){SC(N(p‐tol))(NH(p‐tol))}(CO)2(phen)] (5 a), and [Mo(η3‐C3H4‐Me‐2){OC(O)CHCHC(O)(NH(p‐tol))}(CO)2(phen)] (6), 7, and 8 (both the free complex and its N,N′‐di(p‐tolyl)urea adduct) were determined by X‐ray diffraction.
Li3[ScN2]: The First Nitridoscandate(III)—Tetrahedral Sc Coordination and Unusual MX2 Framework
Authors: Niewa Rainer , Zherebtsov Dmitri A. , Leoni Stefano
Published: September 2003

Li3[ScN2] was prepared from Li3N with Sc or ScN in a nitrogen atmosphere at 1020 K as a light yellow powder with an optical band gap of about 2.9 eV. The crystal structure was refined based on X‐ray and neutron powder diffraction data (Ia$\bar 3$, Z=16, X‐ray diffraction: Rprofile=0.078, RBragg=0.070; Neutron diffraction: Rprofile=0.077, RBragg=0.074; Rietfeld: a=1003.940(8) pm, Guinier: a=1004.50(3) pm). Li3[ScN2] is an isotype of Li3[AlN2] and Li3[GaN2] and crystallizes in an ordered superstructure of the Li2O structure type, leading to a three‐dimensional framework of all‐vertex‐sharing tetrahedra ${^{3}_{\infty }}$[ScN${_{4/2}^{3-}}$]. Li is displaced from the center of a tetrahedron of N atoms in the direction of one trigonal face. Li3[ScN2] decomposes above 1050 K to form ScN and Li3N. Calculations of the periodic nodal surface (PNS) and of the electron localization function (ELF) support the picture of a covalent ScN network separated from isolated Li cations, whereby scandium d orbitals are involved in the chemical bonding.
Origin of the Regio‐ and Stereoselectivity in Palladium‐Catalyzed Electrophilic Substitution via Bis(allyl)palladium Complexes
Authors: Wallner Olov A. , Szabó Kálmán J.
Published: September 2003

Palladium‐catalyzed allylic substitution of aryl allyl chlorides with aromatic and heteroaromatic aldehydes was performed in the presence of hexamethylditin. This procedure involves palladium‐catalyzed formation of transient allylstannanes followed by generation of a bis(allyl)palladium intermediate, which subsequently reacts with the aldehyde electrophile. The catalytic substitution reaction proceeds with high regio‐ and stereoselectivity. The stereoselectivity is affected by the steric and electronic properties of the allylic substituents. Various functionalities including NO2, COCH3, Br, and F groups are tolerated under the applied catalytic conditions. Density functional calculations at the B3PW91/DZ+P level of theory were applied to study the steric and electronic effects controlling the regio‐ and stereoselectivity of the electrophilic addition. The development of the selectivity was studied by modeling the various bis(allyl)palladium species occurring in the palladium‐catalyzed substitution of cinnamyl chloride with benzaldehyde. It was found that the electrophilic attack proceeds via a six‐membered cyclic transition state, which has a pronounced chair conformation. The regioselectivity of the reaction is controlled by the location of the phenyl group on the η1‐allyl moiety of the complex. The stereoselectivity of the addition process is determined by the relative configuration of the phenyl substituents across the developing carbon–carbon bond. The lowest energy path corresponds to the formation of the branched allylic isomer with the phenyl groups in anti configuration, which is in excellent agreement with the experimental findings.
Tetrameric, Trititanium(IV)‐Substituted Polyoxotungstates with an α‐Dawson Substructure as Soluble Metal‐Oxide Analogues: Molecular Structure of the Giant “Tetrapod” [(α‐1,2,3‐P2W15Ti3O62)4{μ3‐Ti(OH)3}4Cl]45−
Authors: Sakai Yoshitaka , Yoza Kenji , Kato Chika Nozaki , Nomiya Kenji
Published: September 2003

The preparation and structural characterization of the novel polyoxoanion [(α‐1,2,3‐P2W15Ti3O62)4{μ3‐Ti(OH)3}4Cl]45− (1 a; abbreviated to {TiO6}16; FW ∼16 000) which consists of four tri‐TiIV‐1,2,3‐substituted α‐Dawson substructures, four Ti(OH)3 bridging groups, and one encapsulated Cl− ion, are described. A water‐soluble, all‐inorganic composition compound of the tetrameric Ti‐O‐Ti‐bridged anhydride form, NaxH45−x[1 a]⋅y H2O (1; x=16–19, y=60–70), which was afforded by the reaction of the tri‐lacunary Dawson polyoxotungstate Na12[B‐α‐P2W15O56]⋅19 H2O with an excess of TiCl4 in aqueous solution, was obtained as analytically pure, homogeneous colorless crystals. Single‐crystal X‐ray structure analysis revealed that 1 a was an inorganic, giant “tetrapod”‐shaped molecule (inscribed to a sphere with a diameter of ∼32 Å) with approximately Td symmetry, in which the 16 edge‐ and/or corner‐shared TiO6 octahedra were contained. This number of TiO6 octahedra was larger than that found in other titanium(IV)‐substituted polyoxotungstates. Complex 1 was characterized by complete elemental analysis, TG/DTA, FTIR, UV/Vis absorption, and solution (31P and 183W) NMR spectroscopy. The longest wavelength band in the UV/Vis absorption spectra of 1 in water was attributed to the O→TiIV ligand‐to‐metal charge‐transfer (LMCT) transition: the wavelength of the LMCT band increased linearly as the number of TiO6 octahedra contained in the Keggin and Dawson polyoxoanions increased. The Tin chromophores formed in the Keggin and Dawson polyoxotungstates are water‐soluble analogues of solid TiO2 or SrTiO3 as light‐semiconductors and photocatalysts.
Cover Picture: Li3[ScN2]: The First Nitridoscandate(III)—Tetrahedral Sc Coordination and Unusual MX2 Framework (Chem. Eur. J. 17/2003)
Authors: Niewa Rainer , Zherebtsov Dmitri A. , Leoni Stefano
Published: September 2003

The cover picture shows a section of the crystal structure of the first nitridoscandate Li3[ScN2], in which for the first time Sc is observed in tetrahedral coordination. A the periodic nodal surface (PNS: grey mesh) separates Li+ atoms from the ${^{3}_{\infty }}$[ScN${_{4/2}^{3-}}$] network. Two isosurfaces of the electron localization function (ELF) at η=0.85 (light yellow) and η=0.74 (transparent orange) show the structuring of the outer‐core localization domain of Sc and the valence localization domain of N, respectively. For more details, see the paper by R. Niewa et al. on p. 4255 ff.