bluuebunny/crossref_metadata_2025_split huggingface dataset:
RF nonlinear interactions in living cells–I: Nonequilibrium thermodynamic theory
Authors: Balzano Quirino , Sheppard Asher 
Published: September 2003

AbstractSome biological experiments report effects that depend on low frequency modulation of a radiofrequency (RF) carrier. Such effects require nonlinear responses in biological preparations, which we show could be observed with great generality by the unique frequency signatures that would appear in the scattered RF energy. Following Illinger [Illinger (1982): Bioelectromagnetics 3:9–16], we considered a two part physical system. The greater part, dominated by the properties of water, interacts linearly with the RF field and is described by equilibrium thermodynamics. However, another, much smaller part, e.g., certain biological molecules and molecular subgroups, supports nonlinear interactions and is described by nonequilibrium thermodynamics. For example, a nonlinear interaction might result from scattering of RF photons from oscillators located in a region of strong field gradients, such as at membrane surfaces. A second nonlinear mechanism could appear if stress (elastic) waves were launched within the confines of the exposure vessel by RF heating. Amplitude modulation at angular frequency Ω of a carrier wave with angular frequency ω (Ω ≪ ω) produces two peaks in elastic stress in the cell structure during each period; that is, there is “full‐wave demodulation.” As a result of coherent nonlinear charge motion, modulation products could appear at frequencies ω ± 2Ω and, in general, at ω ± n 2Ω (n = 1, 2,…) if vibrational harmonics at 2 nΩ also are excited. Although in principle microwaves can alter the stability of a thermodynamic system by pumping a chemical transition, the degree of nonlinear coupling required for an observable instability is so great that its probability is effectively zero, unless field intensity is extremely high. A companion paper suggests an extremely sensitive method and the related instrumentation for detection of the spectrum scattered by living cells during exposure to amplitude modulated RF energy. Bioelectromagnetics 24:473–482, 2003. © 2003 Wiley‐Liss, Inc.
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

AbstractThermophysiological 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

AbstractThis 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

AbstractExperiments 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

AbstractWe 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

AbstractCyclohexadiene‐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

AbstractA 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

AbstractA 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

AbstractProperties 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

AbstractThe 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

AbstractDepolymerization 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

AbstractA 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

AbstractThe 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

AbstractA 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.