bluuebunny/crossref_metadata_2025 huggingface dataset:
The radial distribution function in planetary nebulae
Authors: Phillips J.P.
Published: April 2003

We have investigated the variation of planetary nebula number densities as a function of nebular radius, taking account of uncertainties arising from interstellar extinction. We find that the trend is composed of two components: one (a “spike” component) located at radii R < 0.035 pc, and the other (a “plateau” component) extending to larger radii. The plateau component appears to follow a Gaussian fall‐off law with scale radius R0 = 0.28 pc. It is shown that this latter trend is not consistent with the assumption that larger shells are optically thin and density bounded. Rather, it seems likely thatmany of the larger sources have appreciable Lyman continuum optical depths and are ionization bounded. The deduced variation in N(R) then suggests that the velocities of the ionization fronts increase with radius. The nature of the spike component is less easy to fathom, and this may arise as a result of sharply lower ionization front velocities at radii R < 0.035 pc, or through contraction of the shells following a down‐turn in central star luminosities.
The total‐to‐selective extinction ratio determined from near IR photometry of OB stars
Authors: Wegner W.
Published: April 2003

The paper presents an extensive list of the total to selective extinction ratios R calculated from the infrared magnitudes of 597 O and B stars using the extrapolation method. The IR magnitudes of these stars were taken from the literature. The IR colour excesses are determined with the aid of “artificial standards” – Wegner (1994). The individual and mean values of total to selective extinction ratios R differ in most cases from the average value R= 3.10 ±0.05 – Wegner (1993) in different OB associations. The relation between total to selective extinction ratios R determined in this paper and those calculated using the “method of variable extinction” and the Cardelli et al. (1989) formulae is discussed. The R values presented in this paper can be used to determine individual absolute magnitudes of reddened OB stars with known trigonometric parallaxes.
An oscillating model suggestion for 63 Her
Authors: Kiziloğlu N. , Kirbiyik H. , Civelek R.
Published: April 2003

An attempt has been made towards explaining the observed frequencies in 63 Her. The evolution of rotating stars of 1.96, 1.98, 2.00, 2.05 and 2.10 M⊙ have been studied up to a point where stellar parameters match the observed luminosity and effective temperature of 63 Her. Radial and nonradial adiabatic oscillation frequencies were obtained in low harmonic degrees ( l = 0,1,2,3 ). One radial and three nonradial frequency values that match with the observed values were found for the model of mass 2.00 M⊙.
The integral Newton's and MacLaurin's theorems in tensor form
Authors: Caimmi R.
Published: April 2003

The current paper deals with the investigation of the gravitational potential of heterogeneous ellipsoids and its extension to the tensor potential, since little attention has been given to this point in the last century. In this view, both integral Newton's and integral MacLaurin's theorems are formulated in tensor form. The generalization is extended to heterogeneous homeoids and focaloidally striated ellipsoids, respectively. A discontinuity in the tensor potential is found across a homogeneous, infinitely thin focaloid, which vanishes in the spherical limit. The potential‐energy tensors related to focaloidally striated ellipsoids are expressed in integral form, depending on the density profile. All the results are particularized to the spherical limit, for which both Newton's and MacLaurin's theorems hold. With the aim of illustrating the procedure, an explicit calculation of the potential‐energy tensors is outlined in the special case of homogeneous, spherical configurations. Finally, an application is made to the Coma cluster of galaxies.
Groups of symmetries in the two‐body problem associated to Einstein's PN field
Authors: Mioc V.
Published: April 2003

The two‐body problem associated to a spherical post‐Newtonian (PN) field with Einsteinian parameterization is revisited from the single standpoint of symmetries. The corresponding vector fields, in Hamiltonian and standard polar coordinates, or in collision‐blow‐up and infinity‐blow‐upMcGehee‐type coordinates, present symmetries that form diffeomorphic commutative groups endowed with a Boolean structure. The existence of such symmetries is of much help in understanding characteristics of the global flow, or in finding symmetric periodic orbits in more complex problems depending on a small parameter.
UBV and vbyβ stellar photometry in the eastern part of M31
Authors: Kurtev R.G.
Published: April 2003

We present UBV and the first vbyβ Strömgren stellar photometry in a field centered on the stellar association OB31 in the Eastern part of the Andromeda galaxy. The ages of the stellar populations are determined from the colormagnitude diagrams using the latest theoretical isochrones. HR diagram for all stars in the area is constructed. The mass of the brightest blue star is about 60ℳ︁⊙ and for the brightest red star is about 20ℳ︁⊙. The slope of the Stellar Initial Mass Function (IMF) for blue stars is –2.0±0.1 which is similar to that of other nearby galaxies.We investigate the stellar content of three van den Bergh associations as well as that of some new OB associations determined by cluster analysis. Ages of the van den Bergh associations are 4Myr for OB31 and 6Myr for OB32, OB34 and OB35. Eight blue supergiant candidates are isolated from the rest of the stars by using suitable color‐color diagrams in Strömgren system. The results from UBV and Strömgren uvby photometry are compared.
Statistical method for distance determination of a stellar group
Authors: Sharaf M.A. , Kamal F.Y.
Published: April 2003

In this paper, we developed statistical method for distance determination of a stellar group. The method depends on the assumption that, the stars scatter around a mean magnitude in a Gaussian distribution. The mean apparent magnitude of the stars is then expressed in terms of the frequency function of the apparent magnitudes, so as to correct for observational incompleteness at the faint end. The problem reduces to the solution of a highly transcendental equation for a given apparent magnitude parameter α. Computational algorithm of the method is illustrated and the numerical solutions of the basic equation are given for some values of α .
Metallicity distributions of globular cluster systems in galaxies
Authors: Eerik H. , Tenjes P.
Published: April 2003

We collected a sample of 100 galaxies for which different observers have determined colour indices of globular cluster candidates. The sample includes representatives of galaxies of various morphological types and different luminosities. Colour indices (in most cases (V–I), but also (B–I) and (C–T1)) were transformed into metallicities [Fe/H] according to a relation by Kissler‐Patig (1998). These data were analysed with the KMM software in order to estimate similarity of the distribution with uni‐ or bimodal Gaussian distribution. We found that 45 of 100 systems have bimodal metallicity distributions. Mean metallicity of the metal‐poor component for these galaxies is 〈[Fe/H]〉 = –1.40 ± 0.02, of the metalrich component 〈[Fe/H]〉 = –0.69 ± 0.03. Dispersions of the distributions are 0.15 and 0.18, respectively. Distribution of unimodal metallicities is rather wide. These data will be analysed in a subsequent paper in order to find correlations with parameters of galaxies and galactic environment.
Time‐series photometric spot modelling – VI. A new computer code and its application to 23 years of photometry of the active giant IM Pegasi
Authors: Ribárik G. , Oláh K. , Strassmeier K.G.
Published: April 2003

We present and apply a new computer program named SpotModeL to analyze single and multiple bandpass photometric data of spotted stars. It is based on the standard analytical formulae from Budding and Dorren. The program determines the position, size, and temperature of up to three spots by minimizing the fit residuals with the help of the Marquardt‐Levenberg non‐linear least‐squares algorithm. We also expand this procedure to full time‐series analysis of differential data, just as real observations would deliver. If multi‐bandpass data are available, all bandpasses can be treated simultaneously and thus the spot temperature is solved for implicitly. The program may be downloaded and used by anyone. In this paper, we apply our code to an ≈23 year long photometric dataset of the spotted RS CVn giant IM Peg. We extracted and modelled 33 individual light curves, additionally, we fitted the entire V dataset in one run. The resulting spot parameters reflect the long term light variability and reveal two active longitudes on the substellar point and on the antipode. The radius and longitude of the dominant spot show variations with 29.8 and 10.4 years period, respectively. Our multicolour data suggests that the spot temperature is increasing with the brightening of the star. The average spot temperature from V, IC is 3550 ± 150 K or approximately 900 K below the effective temperature of the star.
Black holes as parts of entangled systems
Authors: Basini G. , Capozziello S. , Longo G.
Published: April 2003

A possible link between EPR‐type quantum phenomena and astrophysical objects like black holes, under a new general definition of entanglement, is established. A new approach, involving backward time evolution and topology changes, is presented bringing to a definition of the system black hole‐worm hole‐white hole as an entangled system.
Effect of food on gastrointestinal transit of liquids in cynomolgus monkeys
Authors: Kondo Hiromu , Watanabe Takashi , Yokohama Shigeharu , Watanabe Jun
Published: April 2003

We investigated the gastrointestinal transit of liquids, as well as various gastric pH profiles, in fed cynomolgus monkeys. Twelve grams of a biscuit‐type solid food were provided 1 h before the test. The acetaminophen method was used to determine the gastric half‐emptying time (t50%), which provided an estimate of the gastric emptying rate. The gastric emptying rate of liquids was significantly reduced after food intake in monkeys. The mean t50% value was 143.5 min and comparable to that of humans after eating. However, there was a large variability in the t50% between individual animals as shown by the coefficient of variance of approximately 80%. Next, the median oro‐caecal transit time in fed monkeys was determined to be 1.8 h, using the sulfasalazine‐sulfapyridine method. There was no significant difference in oro‐caecal transit time between unfed and fed monkeys; thus, food intake has no significant effect on the oro‐caecal transit time of liquids in either monkeys or humans. However, the oro‐caecal transit time in humans is about 2 h longer than that in monkeys. Our experiments using several different foods suggested that the typical human gastric pH profile could not be simulated in fed monkeys. Copyright © 2003 John Wiley & Sons, Ltd.
Does stereoselective lymphatic absorption contribute to the enantioselective pharmacokinetics of halofantrine In Vivo?
Authors: Shackleford David M. , Porter Christopher J. H. , Charman William N.
Published: April 2003

Halofantrine (Hf) is a chiral, lipophilic phenanthrene methanol antimalarial which exhibits both enantioselective plasma pharmacokinetics and extensive lymphatic absorption when administered postprandially. In order to determine whether enantioselective lymphatic absorption contributes to the previously reported enantioselective pharmacokinetics of Hf, lymph samples collected from thoracic duct‐cannulated dogs dosed with racemic Hf (100 mg, administered postprandially) were assayed with a chiral HPLC method capable of quantifying the relative amounts of (+)‐ and (−)‐Hf. During the period when the majority (>95%) of Hf transport into lymph occurred (0–5 h post dose), essentially equal amounts of the two enantiomers were present in the intestinal lymph. At later times (e.g. 5–12 h post dose), there was a steady increase in the fraction of (+)‐Hf present in lymph. The trends evident at later time points most likely reflect an increase in the proportion of (+)‐Hf present in systemic blood, (resulting from enantioselective systemic metabolism) and a corresponding increase in (+)‐Hf in the thoracic lymph by equilibration of drug across blood and lymphatic capillaries, as opposed to enantioselective lymphatic transport per se. This study was the first to examine the possibility of stereoselectivity in lymphatic transport, however, the data suggest that drug absorption (at least in the case of halofantrine) via the intestinal lymphatics is not enantioselective. Copyright © 2003 John Wiley & Sons, Ltd.
Interfacial effect of extremely low frequency electromagnetic fields (EM‐ELF) on the vaporization step of carbon dioxide from aqueous solutions of body simulated fluid (SBF)
Authors: Beruto D.T. , Botter R. , Perfumo F. , Scaglione S.
Published: April 2003

Spontaneous processes in an aqueous solution of body simulated fluid (SBF) were monitored in closed vessel for a period of 1 month at 310 K, at atm pressure, and initial pH of 7.2, both with and without exposure to a square pulsed extremely low frequency electromagnetic fields (EM‐ELF) of 250 μT, repeated at 75 Hz. The most important findings are that the SBF surface tension (γ), evaluated under the EM‐ELF field, is lower than the corresponding value measured without EM‐ELF at any time. Furthermore, the pH of the exposed SBF is always more basic than that of the unexposed solution. As a consequence, when the EM‐ELF is applied, calcium phosphate salts do not precipitate from the SBF solution for a period as long as 30 days. Behind all these experimental evidences there is only one mechanism: the vaporisation from the SBF‐air interface of the CO2(aq) dissolved into the aqueous electrolyte solution. Thermodynamic analysis of these results establish that, at any given time, the difference, Δ, between the measured surface tensions with and without EM‐ELF applied, gives the work of the electromagnetic forces to change the extent at which the CO2(aq) adsorbs at the liquid‐air interface. It has been demonstrated that the work supply per second and per unit of area by the electromagnetic forces, 3.73 × 10−10 mJ/s cm2, is very near to the experimental slope in the plot Δ vs. t 1.7 × 10−10 mJ/s cm2. This leads to the conclusion that the EM‐ELF fields have an interfacial effect on the concentration value of the CO2 (aq) at the SBF‐air interface. Because of that, the EM‐ELF field is enhancing the CO2 vaporisation rate; thus any other steps, which are a consequence of this mechanism, are changing. These results allow explanation of previous experiments concerning the precipitation of calcium carbonate from flowing hydrogen carbonate aqueous solution in the temperature range 353–373 K at a pressure of 0.1 MPa under the effect of static magnetic fields. Bioelectromagnetics 24:251‐261, 2003. © 2003 Wiley‐Liss, Inc.
No influence of magnetic fields on cell cycle progression using conditions relevant for patients during MRI
Authors: Schiffer Ilka B. , Schreiber Wolfgang G. , Graf Robert , Schreiber Elke M. , Jung Detlev , Rose Dirk M. , Hehn Manfred , Gebhard Susanne , Sagemüller Jens , Spieß Hans W. , Oesch Franz , Thelen Manfred , Hengstler Jan G.
Published: April 2003

The purpose of this study was to examine whether exposure to magnetic fields (MFs) relevant for magnetic resonance imaging (MRI) in clinical routine influences cell cycle progression in two tumor cell lines in vitro. HL60 and EA2 cells were exposed to four types of MFs: (i) static MF of 1.5 and 7.05 T, (ii) extremely low frequency magnetic gradient fields (ELFMGFs) with ± 10 mT/m and 100 Hz, as well as ± 100 mT/m and 100 Hz, (iii) pulsed high frequency MF in the radiofrequency (RF) range (63.6 MHz, 5.8 μT), and (iv) a combination of (i–iii). Exposure periods ranged from 1 to 24 h. Cell cycle distribution (G0/G1, S, and G2/M phases) was analyzed by flow cytometry. Cell cycle analysis did not reveal differences between the exposed and the control cells. As expected, positive controls with irradiated (8 Gy) HL60 and EA2 cells showed a strong G2/M arrest. Using conditions that are relevant for patients during MRI, no influence of MFs on cell cycle progression was observed in these cell lines. Care was taken to control secondary parameters of influence, such as vibration by the MR scanner or temperature to avoid false positive results. Bioelectromagnetics 24:241‐250, 2003. © 2003 Wiley‐Liss, Inc.
1439 MHz pulsed TDMA fields affect performance of rats in a T‐maze task only when body temperature is elevated
Authors: Yamaguchi Hironori , Tsurita Giichirou , Ueno Shoogo , Watanabe Soichi , Wake Kanako , Taki Masao , Nagawa Hirokazu
Published: April 2003

This study sought to clarify the effects of exposure to electromagnetic waves (EMW) used in cellular phones on learning and memory processes. Sprague–Dawley rats were exposed for either 1 h daily for 4 days or for 4 weeks to a pulsed 1439 MHz time division multiple access (TDMA) field in a carousel type exposure system. At the brain, average specific absorption rate (SAR) was 7.5 W/kg, and the whole body average SAR was 1.7 W/kg. Other subjects were exposed at the brain average SAR of 25 W/kg and the whole body average SAR of 5.7 W/kg for 45 min daily for 4 days. Learning and memory were evaluated by reversal learning in a food rewarded T‐maze, in which rats learned the location of food (right or left) by using environmental cues. The animals exposed to EMW with the brain average SAR of 25 W/kg for 4 days showed statistically significant decreases in the transition in number of correct choices in the reversal task, compared to sham exposed or cage control animals. However, rats exposed to the brain average SAR of 7.5 W/kg for either 4 days or for 4 weeks showed no T‐maze performance impairments. Intraperitoneal temperatures, as measured by a fiber optic thermometer, increased in the rats exposed to the brain average SAR of 25 W/kg but remained the same for the brain average SAR of 7.5 W/kg. The SAR of a standard cellular phone is restricted to a maximum of 2 W/kg averaged over 10 g tissue. These results suggest that the exposure to a TDMA field at levels about four times stronger than emitted by cellular phones does not affect the learning and memory processes when there are no thermal effects. Bioelectromagnetics 24:223–230, 2003. © 2003 Wiley‐Liss, Inc.
Effects of 50 Hz magnetic fields on fMLP‐induced shape changes in invertebrate immunocytes: The role of calcium ion channels
Authors: Gobba Fabriziomaria , Malagoli Davide , Ottaviani Enzo
Published: April 2003

Plasma membrane Ca2+ channels in immunocytes from the mussel Mytilus galloprovincialis exposed to 50 Hz sine wave magnetic fields (MFs) of various strengths were studied. At levels of 300 μT and above, MFs reduce shape changes in immunocytes induced by the chemotactic substance N‐formyl‐Meth‐Leu‐Phe, and this effect involves L‐type Ca2+ channels. Upon the addition of the Ca2+ blocker verapamil to molluscan immunocytes exposed to MFs results in a synergistic cytotoxic action, while in the presence of the Ca2+ opener SDZ‐202, 791, a reactivation of the cells is observed. This suggests that, as previously reported for potassium channels, the damage to Ca2+ channels induced by short exposure to MF at appropriate intensities is not permanent. Bioelectromagnetics 24:277–282, 2003. © 2003 Wiley‐Liss, Inc.
Radio frequency electromagnetic field exposure in humans: Estimation of SAR distribution in the brain, effects on sleep and heart rate
Authors: Huber Reto , Schuderer Jürgen , Graf Thomas , Jütz Kathrin , Borbély Alexander A , Kuster Niels , Achermann Peter
Published: April 2003

In two previous studies we demonstrated that radiofrequency electromagnetic fields (RF EMF) similar to those emitted by digital radiotelephone handsets affect brain physiology of healthy young subjects exposed to RF EMF (900 MHz; spatial peak specific absorption rate [SAR] 1 W/kg) either during sleep or during the waking period preceding sleep. In the first experiment, subjects were exposed intermittently during an 8 h nighttime sleep episode and in the second experiment, unilaterally for 30 min prior to a 3 h daytime sleep episode. Here we report an extended analysis of the two studies as well as the detailed dosimetry of the brain areas, including the assessment of the exposure variability and uncertainties. The latter enabled a more in depth analysis and discussion of the findings. Compared to the control condition with sham exposure, spectral power of the non‐rapid eye movement sleep electroencephalogram (EEG) was initially increased in the 9–14 Hz range in both experiments. No topographical differences with respect to the effect of RF EMF exposure were observed in the two experiments. Even unilateral exposure during waking induced a similar effect in both hemispheres. Exposure during sleep reduced waking after sleep onset and affected heart rate variability. Exposure prior to sleep reduced heart rate during waking and stage 1 sleep. The lack of asymmetries in the effects on sleep EEG, independent of bi‐ or unilateral exposure of the cortex, may indicate involvement of subcortical bilateral projections to the cortex in the generation of brain function changes, especially since the exposure of the thalamus was similar in both experiments (approx. 0.1 W/kg). Bioelectromagnetics 24:262‐276, 2003. © 2003 Wiley‐Liss, Inc.
Effect of a 902 MHz electromagnetic field emitted by mobile phones on human cognitive function: A replication study
Authors: Haarala Christian , Björnberg Linda , Ek Maria , Laine Matti , Revonsuo Antti , Koivisto Mika , Hämäläinen Heikki
Published: April 2003

Our study was a replication and extension with methodological improvements to a previous study on effects of the electromagnetic field (EMF) emitted by a 902 MHz mobile phone on human cognitive functioning. Improvements on the previous study included multicentre testing and a double blind design. A total of 64 subjects (32 men and 32 women) in two independent laboratories performed a battery of 9 cognitive tasks twice: while the EMF was on and while it was off. Reaction times (RTs) and accuracy were recorded. The order of exposure and tasks was counterbalanced across subjects and gender. There were no statistically significant differences in performance between genders or laboratories. Although the RTs and the accuracy of answers were very similar to those of our previous study, our previous results were not replicated. We concluded that EMF had no effect on RTs or on the accuracy of the subjects' answers. Further, our results indicate that our EMF had no immediate effect on human cognitive functioning or that such effects are so small that they are observed on behavior only occasionally. Bioelectromagnetics 24:283–288, 2003. © 2003 Wiley‐Liss, Inc.
Mouse circadian rhythm before the Kobe earthquake in 1995
Authors: Yokoi Sayoko , Ikeya Motoji , Yagi Takeshi , Nagai Katsuya
Published: April 2003

Mouse circadian diagrams recorded at Osaka University showed unusual mouse behavior before the Kobe earthquake on January 17th, 1995. The locomotive activities on January 16th showed drastic increases, several times above the standard deviation, during both sleep and active periods, indicating that mice perceived of some preseismic signals. Bioelectromagnetics 24:289–291, 2003. © 2003 Wiley‐Liss, Inc.
On the human body's inductive features: A comment on “Bioelectrical parameters…” by A.L. Lafargue et al.
Authors: Gluskin Emanuel
Published: April 2003

The original article to which this Comment refers was published in Bioelectromagnetics 23:450–454Bioelectromagnetics (2002) 23(5) 450–454
Developmental toxicity evaluation of ELF magnetic fields in Sprague–Dawley rats
Authors: Chung Moon‐Koo , Kim Jong‐Choon , Myung Sung‐Ho , Lee Dong‐Il
Published: April 2003

To identify possible effects of horizontally polarized magnetic field (MF) exposure on maintenance of pregnancy and embryo‐fetal development, an MF exposure system was designed and constructed and 96 time‐mated female Sprague–Dawley (SD) rats (24/group) received continuous exposure to 60 Hz MF at field strengths of 0 (sham control) and 5, 83.3, or 500 μT (50, 833, or 5000 mG). Dams received MF or sham exposures for 22 h/day on gestational day 6–20. MF was monitored continuously throughout the study. There were no evidences of maternal toxicity or developmental toxicity in any MF exposed groups. Mean maternal body weight, organ weights, and hematological and serum biochemical parameters in groups exposed to MF did not differ from those in sham control. No exposure related differences in fetal deaths, fetal body weight, and placental weight were observed between MF exposed groups and sham control. External, visceral, and skeletal examination of fetuses demonstrated no significant differences in the incidence of fetal malformations between MF exposed and sham control groups. In conclusion, exposure of pregnant rats to 60 Hz at MF strengths up to 500 μT during gestation day 6–20 did not produce any biologically significant effect in either dams or fetuses. Bioelectromagnetics 24:231‐240, 2003. © 2003 Wiley‐Liss, Inc.
The Role of Community Colleges in Offering Baccalaureates in tEacher Education: An Emerging Possibility
Authors: Furlong Thomas E.
Published: April 2003

This chapter describes the efforts of St. Petersburg College (formerly St. Petersburg Junior College) to offer teacher education baccalaureate degrees in elementary education, in special education, and in secondary education in math and science.
Community College Roles in Teacher Education: Current Approaches and Future Possibilities
Authors: Townsend Barbara K. , Ignash Jan M.
Published: April 2003

This chapter examines the current role of community colleges in preservice and in‐service teacher education, including the development of the associate of arts degree in teacher education, the community college baccalaureate in teacher education, and alternative certification programs. Factors influencing future trends and predictions and recommendations about the community college's future role are also discussed.
Transfer Issues in Preservice Undergraduate Teacher Education Programs
Authors: Lindstrom Joyce , Rasch Katherine D.
Published: April 2003

The national teacher shortage has made it imperative for two‐ and four‐year colleges to collaborate in facilitating transfer of education majors. This chapter focuses on some of the challenges to transfer and articulation in Missouri.
A New Degree for the Community College: The Associate of Arts in Teaching
Authors: McDonough Maureen L.
Published: April 2003

The development of the Associate of Arts in Teaching degree in Maryland represents an outcomes‐based, statewide articulation of the two‐year degree in elementary education to public and private four‐year institutions.
High School, Community Colleges, and Universities: Partners in Teacher Education and National Efforts
Authors: Gaskin Fred , Helfgot Steven R. , Parsons Sue , Solley Anna
Published: April 2003

This chapter focuses on the activities and outcomes of the Teacher Education Partnership Commission in Arizona and the efforts of the newly formed National Association of Community College Teacher Education Programs.
Predominantly σ‐Bonded Metal Carbonyl Cations (σ‐Carbonyls): New Synthetic, Structural, and Bonding Concepts in Metal Carbonyl Chemistry
Authors: Willner Helge , Aubke Friedhelm
Published: April 2003

Predominantly σ‐bonded metal carbonyl cations (σ‐carbonyls) are conveniently generated in the Lewis superacid SbF5 or the conjugate Brønsted–Lewis superacid HFSbF5, primarily by solvolytic or reductive carbonylations. Thermally stable salts are formed with the fluoroantimonate(V) ions [SbF6]− and [Sb2F11]−. The salts are characterised by analytical, structural, spectroscopic and computational methods. Most homoleptic carbonyl cations have very regular geometries, comensurate with their d‐electron configurations: linear (d10), square planar (d8) or octahedral(d6). The cations with metals in oxidation states of +2 or +3 are termed “superelectrophilic”. Extended molecular structures form by significant interionic CF contacts with electrophilic carbon as acceptor. To account for all experimental observations, a conceptually simple synergetic bonding model is proposed. An outlook at anticipated future developments based on very recent results is provided.
Hexacyanometalate Molecular Chemistry: Heptanuclear Heterobimetallic Complexes; Control of the Ground Spin State
Authors: Marvaud Valérie , Decroix Caroline , Scuiller Ariane , Guyard‐Duhayon Carine , Vaissermann Jacqueline , Gonnet Florence , Verdaguer Michel
Published: April 2003

Following a bottom‐up approach to nanomaterials, we present a rational synthetic route from hexacyanometalates [M(CN)6]3− (M=CrIII, CoIII) cores to well‐defined heptanuclear complexes. By changing the nature of the metallic cations and using a localised orbital model it is possible to control and to tune the ground state spin value. Thus, with M=CrIII, d3, S=3/2, three heptanuclear species were built and characterised by mass spectrometry in solution, by single‐crystal X‐ray diffraction and by powder magnetic susceptibility measurements, [CrIII(CNM′Ln)6]9+ (M′=CuII, NiII, MnII, Ln=polydentate ligand), showing spin ground states SG=9/2 [CuII], with ferromagnetic interactions JCr,Cu=+45 cm−1, SG=15/2 [NiII] and JCr,Ni=+17.3 cm−1, SG=27/2 [MnII], with an antiferromagnetic interaction JCr,Mn=−9 cm−1, (interaction Hamiltonian ℋ︁=−JCr,M [SCrΣiSM(i)], i=1–6). With M=CoIII, d6, S=0, the heptanuclear analogues [CoIII(CN−M′Ln)6]9+ (M′=CuII, NiII, MnII) were similarly synthesised and studied. They present a singlet ground state and allow us to evaluate the weak antiferromagnetic coupling constant between two next‐nearest neighbours M′CoM′.
Hexacyanometalate Molecular Chemistry: Di‐, Tri‐, Tetra‐, Hexa‐ and Heptanuclear Heterobimetallic Complexes; Control of Nuclearity and Structural Anisotropy
Authors: Marvaud Valérie , Decroix Caroline , Scuiller Ariane , Tuyèras Fabien , Guyard‐Duhayon Carine , Vaissermann Jacqueline , Marrot Jérome , Gonnet Florence , Verdaguer Michel
Published: April 2003

Following a bottom‐up approach to nanomaterials, we present a rational synthetic route to high‐spin and anisotropic molecules based on hexacyanometalate [M(CN)6]3− cores. Part 1 of this series was devoted to isotropic heptanuclear clusters; herein, we discuss the nuclearity and the structural anisotropy of nickel(II) derivatives. By changing either the stoichiometry, the nature of the terminal ligand, or the counterion, it is possible to tune the nuclearity of the polynuclear compounds and therefore to control the structural anisotropy. We present the synthesis and the characterisation by mass spectrometry, X‐ray crystallography and magnetic susceptibility of bi‐, tri‐, tetra‐, hexa‐ and heptanuclear species [M(CN)n(CNM′L)6−n]m+ (with n=0–5; M=CrIII, CoIII, M′=NiII; L=pentadentate ligand). Thus, with M=CrIII, d3, S=3/2, a dinuclear complex [CrIII(CN)5(CNNiLn)]9+, (Ln=polydentate ligand) was built and characterised, showing a spin ground state, SG=5/2, with a ferromagnetic interaction JCr,Cu=+18.5 cm−1. With M=CoIII (d6, S=0) were built di‐, tri‐, tetra‐, hexa and hepanuclear CoNi species: CoNi, CoNi2, CoNi3, CoNi5 and CoNi6. By a first approximation, they behave as one, two, three, five and six isolated nickel(II) complexes, respectively, but more accurate studies allow us to evaluate the weak antiferromagnetic coupling constant between two next‐nearest neighbours M′‐Co‐M′.
Organic Chemistry on Cold Molecular Films: Kinetic Stabilization of SN1 and SN2 Intermediates in the Reactions of Ethanol and 2‐Methylpropan‐2‐ol with Hydrogen Bromide
Authors: Park Seong‐Chan , Maeng Kye‐Won , Kang Heon
Published: April 2003

We prepared thin molecular films of ethanol and 2‐methylpropan‐2‐ol on Ru(001) substrates at temperature of 100–150 K and examined their reactivity toward HBr. The reaction intermediates and products formed at the surfaces were unambiguously identified by the techniques of Cs+ reactive ion scattering (RIS) and low‐energy sputtering. The reaction on the ethanol surface produced protonated ethanol, which is stabilized on the surface and does not proceed to further reactions. On the 2‐methylpropan‐2‐ol surface, protonated alcohol [(CH3)3COH2+] and carbocation [(CH3)3C+] were formed with the respective yield of 20 and 78 %. Alkyl bromides, which are the final products of the corresponding reactions in liquid solvents, have extremely small yields on these surfaces (< 0.3 % for ethyl bromide and 2 % for tert‐butyl bromide). The results indicate that the reactions on frozen films are characterized by kinetic control, stabilization of ionic intermediates (protonated alcohols and tert‐butyl cation), and effective blocking of the charge recombination steps in SN1 and SN2 paths. The implication of these findings for the molecular evolution process in interstellar medium is also discussed.
Binding Site Optimisation for Artificial Enzymes by Diffusion NMR of Small Molecules
Authors: Atkinson Catherine E. , Aliev Abil E. , Motherwell William B.
Published: April 2003

A binding site optimisation protocol for the design of artificial enzymes based on “small molecule–small molecule” binding studies by diffusion NMR is presented. Since the reaction chosen was the hydrolysis of ester 1 ([4‐(4‐carboxy‐1‐oxobutyl)‐aminobenzyl]‐phenethyl ester), an analogous phosphonate ester 2 ([4‐(4‐carboxy‐1‐oxobutyl)‐aminobenzyl]‐phosphonic phenethyl ester) was selected as a suitable transition state analogue (TSA). The key objective of the NMR studies was to find a unit with functional groups capable of binding to the acidic sites of the TSA. Nine dipeptides, mainly with basic and hydroxyl groups, were used and their affinity to the TSA was studied by measuring the change in the diffusion coefficient, Dpep, upon binding by pulse field gradient NMR. The value of Dpep at 298 K in D2O at pD 5, 7 and 10 was measured both in free solution, and mixtures containing one dipeptide and the TSA. As both components are low molecular weight species with M < 500, a TSA‐to‐dipeptide ratio of 10:1 was used to detect significant changes in Dpep. The results revealed that dipeptides with basic residues show higher affinity to the TSA than those with hydroxyl or aliphatic side chains in aqueous solutions. The dipeptide showing the most significant relative change in Dpep was H‐Arg‐Arg‐OH, and the binding constant was estimated to be 86 L M−1 by measuring Dpep at varying concentrations of the TSA. In addition, binding of the TSA to a new water‐soluble polymer with a polyallylamine backbone and randomly distributed Arg‐Arg binding sites was examined, and the binding constant was estimated to be ≥1500 L M−1. As confirmed by further catalytic activity tests, polymers containing Arg‐Arg as a binding site are capable of significant rate accelerations in the hydrolysis of ester 1.
Cover Picture: The First Self‐Assembled Trimetallic Lanthanide Helicates Driven by Positive Cooperativity (Chem. Eur. J. 8/2003)
Authors: Floquet Sébastien , Ouali Nadjet , Bocquet Bernard , Bernardinelli Gérald , Imbert Daniel , Bünzli Jean‐Claude G. , Hopfgartner Gérard , Piguet Claude
Published: April 2003

The cover picture shows the emergence of the first self‐assembled trimetallic lanthanide helicate in which positive cooperativity overcomes strong intermetallic electrostatic repulsions occurring between the metals. The D3 symmetry of the final edifice provides two different metallic sites that are insensitive to the relative orientation of the ligand strands. This unique feature offers novel perspectives for the rational programming of magnetic and optical properties in polymetallic lanthanide complexes. An investigation on the influence of the fine tuning of crystal‐field parameters on multicentre paramagnetic NMR spectra and luminescence is reported by C. Piguet et al. on p. 1860 ff.
Natural Abundance Deuterium NMR Spectroscopy in Polypeptide Liquid Crystals as a New and Incisive Means for the Enantiodifferentiation of Chiral Hydrocarbons
Authors: Lesot Philippe , Sarfati Muriel , Courtieu Jacques
Published: April 2003

Polymeric chiral liquid‐crystalline solvents based on homopolypeptides are of interest with the view to discriminate between enantiomeric pairs of chiral hydrocarbons using proton‐decoupled deuterium one‐ and two‐dimensional NMR spectroscopy at natural abundance level. This method offers the major advantage that neither chemical modification nor isotopic labelling of the solutes to be studied is required. Chiral differentiation between optical isomers is observed through a difference in residual deuterium quadrupolar splittings. The spectroscopic separations and the S/N ratio from the spectra are usually large enough to measure the enantiomeric excess with an accuracy varying between 5 to 10 %. This analytical approach is successfully applied to a large collection of chiral, rigid or flexible unsaturated as well as saturated hydrocarbons, including cases of axial chirality, atropoisomerism, and moieties existing as a mixture of enantiomers interconverting by ring inversion. Using the results reported in literature, a systematic comparison with other analytical strategies (NMR, GC, HPLC, VCD) is made and discussed. Also, a tentative proposal to rationalise the various results in terms of chiral differentiation and enantioselective shape recognition is presented. We show that this original tool provides an attractive and incisive alternative to the existing analytical techniques for studying nonfunctionalised chiral materials.
Unique Coordination of Two CC Double Bonds to an Electron‐Deficient Lead Center
Authors: Müller Thomas , Bauch Christian , Bolte Michael , Auner Norbert
Published: April 2003

Reaction of bis(cyclopentenemethyl)diethylplumbane (2) with trityl cation leads to the formation of the plumbyl cation bis(cyclopentenemethyl)plumbylium (1), in which the positively charged lead atom interacts with the two CC double bonds of the cyclopentene ligands. The plumbyl cation1is characterized by NMR spectroscopy (δ(207Pb)=807 ppm,δ(13C(CC))= 136.1 ppm,1J(Pb,CC)=14.4 Hz) and Xray crystallography. The structure of1reveals a distorted trigonal‐bipyramidal coordination sphere for the lead atom with a unique coordination of two CC double bonds in apical positions. According to quantum‐mechanical calculations (MP2/6‐311G(d,p) (C, H), SDD (Pb)//MP2/6‐31G(d), SDD (Pb)) this interaction stabilizes1by 28.3 kcal mol−1relative to the tricoordinated plumbylium ion10. An “atoms in molecules” (AIM) analysis indicates a π‐type interaction between the lead atom and the CC double bonds, reminiscent of that in the 2norbornyl cation.
Ethene/Norbornene Copolymerization with Palladium(II) α‐Diimine Catalysts: From Ligand Screening to Discrete Catalyst Species
Authors: Kiesewetter Jens , Kaminsky Walter
Published: April 2003

Sixteen palladium(II) α‐diimine catalysts were investigated in a screening‐like procedure for the copolymerization of ethene with norbornene. The resulting copolymers were characterized by 13C NMR spectroscopy, differential scanning calorimetry, gel permeation chromatography, and viscosimetry. The degree of incorporation of norbornene in the polymer chain is very high for most of the catalysts. To validate the results achieved in the screening, two catalysts, [{ArNCHCHNAr}Pd(Me)(CH3CN)]BArf4 (1 b′; Ar=2,6‐Me2C6H3, BArf4=B[3,5‐C6H3(CF3)2]4) and [{ArNC(CH3)C(CH3)NAr}Pd(Me)(CH3CN)]BArf4 (2 c′; Ar=2,6‐iPr2C6H3), were synthesized as discrete catalytically active species, and their copolymerization behavior was investigated in detail. In agreement with the screening results, 1 b′ incorporates norbornene much better in the polymer chain than ethene, a property that has no analogue in metallocene catalysts.
Double Bonds in Motion: Bis(oxazolinylmethyl)pyrroles and Their Metal‐Induced Planarization to a New Class of Rigid Chiral C2‐symmetric Complexes
Authors: Mazet Clément , Gade Lutz H.
Published: April 2003

The synthesis of a new class of chiral C2‐symmetric tridentate Ndonor ligands, a series of 2,5‐bis(2‐oxazolinylmethyl)pyrroles, was achieved in four steps starting from the known 2,5‐bis(trimethylammoniomethyl)pyrrole diiodide (1). Reaction of 1 with NaCN in dimethyl sulfoxide gave 2,5‐bis(cyanomethyl)pyrrole (2) cleanly, which was then cyclized with amino alcohols to give the 2,5‐bis(2‐oxazolinylmethyl)pyrroles 3 a–c (3 a: bis[2‐(4,4′‐dimethyl‐5‐hydrooxazolyl)methyl]pyrrole; 3 b: (S,S)‐bis[2‐(4‐isopropyl‐4,5‐dihydrooxazolyl)methyl]pyrrole; 3 c: (S,S)‐bis[2‐(4‐tertiobutyl‐4,5‐dihydrooxazolyl)methyl]pyrrole). Metallation of 3 a–c with one molar equivalent of tBuLi and their subsequent reaction with a stoichiometric amount of [PdCl2(cod)] (cod=cyclooctadiene) gave the palladium(II) complexes 4 a–c. Whereas the arrangement of the Ndonor atoms in the crystallographically characterized complex 4 a is almost ideally square planar, all three heterocycles in the ligand are twisted out of the coordination plane, leading to a chiral conformation of the complex. Attempts to freeze out these two conformers in solution at 200 K (NMR) failed, and this suggests that the activation barrier for conformational racemization is significantly below 10 kcal mol−1. The palladium‐induced shift of two double bonds as well as the porphyrinogen/porphyrin‐type oxidation of the complexes 4 a–c led to the planarization of the 2,5‐bis(oxazolinylmethyl)pyrrolide ligands in the palladium(II) complexes 5 a–c, 6 b, and 6 c, and to the formation of rigid chiral C2‐symmetric systems as shown by Xray diffraction studies. The formation of the conjugated system of double bonds in this transformation is accompanied by the emergence of an intra‐ligand chromophore. This is evident in the absorption spectrum of 6 c which displays an intense band with a maximum at 485 nm attributable to an intra‐ligand π*←π transition and a characteristic vibrational progression of ν≈1350 cm−1. Complexes 4 b and 4 c were tested in the catalytic asymmetric Michael addition of ethyl 2cyanopropionate to methyl vinylketone (catalyst loading: 1 mol %) and were found to give maximum ee values of 43 % (4 b) and 21 % (4 c) at low conversions.
Modulation of a Supramolecular Bowl and Pot by Changing Solvent Systems and/or Metal/Ligand Ratios
Authors: Park Seong Jin , Lee Jae Woo , Sakamoto Shigeru , Yamaguchi Kentaro , Hong Jong‐In
Published: April 2003

A resorcin[4]arene‐based ligand 2 a with four pyrimidine substituents at the upper rim was synthesized, and the generation of different metal‐mediated superstructures from the same ligand and metal ions utilizing the unfavorable incorporation of the third and fourth PdII ions to ligand 2 a was investigated. The supramolecular bowl 3 a, which comes from a 1:2 combination of ligand 2 a and [Pd(en)(NO3)2], was obtained in water even though excess of PdII complexes were employed. By adding methanol, the supramolecular pot 4 gradually formed, which was the major product when the ratio of mixed solvent reached methanol/water=5:1 (v/v). Host–guest complexation phenomena of 3 a toward several aromatic carboxylates were demonstrated by isothermal titration calorimetry (ITC) and by 1H NMR spectroscopy; both the enthalpy gain from electrostatic and hydrophobic interactions, and the entropy gain from desolvation cooperatively contribute to the binding of anionically charged guests. The crystal structure of supramolecular pot 4 shows direct evidence for the hydrogen bonding between water and the aromatic π electrons in the solid state. The modulation between supramolecular bowl 3 a and pot 4 was also made possible by changing the metal/ligand ratios in aqueous methanol solution as well as by varying the water content of the mixed solvent.
Helical Polymer‐Anchored Porphyrin Nanorods
Authors: de Witte Pieter A. J. , Castriciano Mariangela , Cornelissen Jeroen J. L. M. , Monsù Scolaro Luigi , Nolte Roeland J. M. , Rowan Alan E.
Published: April 2003

Well‐defined arrays of porphyrins attached to a rigid polyisocyanide backbone have been synthesized and their physical and optical properties studied. The helical polymers are rigidified by an inter‐side chain hydrogen‐bonded network and have an average mass of 1.1×106 Daltons and a polydispersity index of 1.3. Each of the polymer strands contains four columns of around 200 stacked porphyrins and has an overall length of 87 nm. The chromophores are arranged in a left‐handed helical fashion along the polymer backbone. Photophysical studies show that at least 25 porphyrins within one column are excitationally coupled.
Homochiral Oligopeptides by Chiral Amplification within Two‐Dimensional Crystalline Self‐Assemblies at the Air–Water Interface; Relevance to Biomolecular Handedness
Authors: Weissbuch Isabelle , Zepik Helmut , Bolbach Gérard , Shavit Edna , Tang Mao , Jensen Torben R. , Kjaer Kristian , Leiserowitz Leslie , Lahav Meir
Published: April 2003

A possible role that might have been played by ordered clusters at interfaces for the generation of homochiral oligopeptides under prebiotic conditions has been probed by a catalyzed polymerization of amphiphilic activated α‐amino acids, in racemic and chiral non‐racemic forms, which had self‐assembled into two‐dimensional (2D) ordered crystallites at the air–aqueous solution interface. As model systems we studied Nε‐stearoyl‐lysine thioethyl ester (C18‐TE‐Lys), γ‐stearyl‐glutamic thioethyl ester (C18‐TE‐Glu), Nα‐carboxyanhydride of γ‐stearyl‐glutamic acid (C18‐Glu NCA) and γ‐stearyl‐glutamic thioacid (C18‐thio‐Glu). According to in‐situ grazing incidence Xray diffraction measurements on the water surface, (R,S)‐C18‐TE‐Lys, (R,S)‐C18‐TE‐Glu, and (R,S)‐C18‐Glu‐NCA amphiphiles self‐assembled into ordered racemic 2D crystallites. Oligopeptides 2–12 units long were obtained at the air–aqueous solution interface after injection of appropriate catalysts into the water subphase. The experimental relative abundance of oligopeptides with homochiral sequence generated from (R,S)‐C18‐TE‐Lys and (R,S)‐C18‐TE‐Glu, as determined by mass spectrometry on enantioselectively deuterium‐labeled samples, was found to be significantly larger than that obtained from (R,S) C18‐thio‐Glu which polymerizes randomly. An efficient chiral amplification was obtained in the polymerization of non‐racemic mixtures of C18‐Glu‐NCA since the monomer molecules in the racemic 2D crystallites are oriented such that the reaction occurs between heterochiral molecules related by glide symmetry to yield heterochiral oligopeptides whereas the enantiomer in excess, in the enantiomorphous crystallites, yield oligopeptides of a single handedness.
Spontaneously Organizing Metal Connectors as Supramolecular Structure Directors of Two‐ and Three‐Dimensional Organometallic Assemblies
Authors: Eckhardt Rolf , Hanika‐Heidl Hilka , Fischer R. Dieter
Published: April 2003

The supramolecular interplay of Me3Sn+ and [M(CN)2n]n− ions (n=3 and 4) with either 4,4′‐bipyridine (bpy), trans‐bis(4‐pyridyl)ethene (bpe) or 4cyanopyridine (cpy) in the presence of H2O has been investigated for the first time. Crystal structures of the six novel assemblies: [(Me3Sn)4MoIV(CN)8⋅2 H2O⋅bpy] (8) and [(Me3Sn)4MoIV(CN)8⋅2 H2O⋅bpe] (8 a; isostructural), [(Me3Sn)3FeIII(CN)6⋅4 H2O⋅bpy] (9), [(Me3Sn)3CoIII(CN)6⋅3 H2O⋅3/2 bpy] (10), [(Me3Sn)4FeII(CN)6⋅H2O⋅3/2 bpy] (11), and [(Me3Sn)4RuII(CN)6⋅2 H2O⋅3/2 cpy] (12) are presented. H2O molecules are usually coordinated to tin atoms and involved in two significant OH⋅⋅⋅N hydrogen bonds, wherein the nitrogen atoms belong either to bpy (bpe, cpy) molecules or to Mcoordinated cyanide ligands. Extended supramolecular assemblies such as ‐CN→Sn(Me3)←O(H⋅⋅⋅)H⋅⋅N(L)N⋅⋅HO(H⋅⋅⋅)→Sn(Me3)←NC‐ (L=bpy, bpe or cpy) function as efficient metal connectors (or spacers) in the structures of all six compounds. Only in the three‐dimensional framework of 11, one third of all bpy molecules is involved in coordinative N→Sn bonds. The supramolecular architecture of 9 involves virtually non‐anchored (to cyanide N atoms), Me3Sn+ units with a strictly planar SnC3 skeleton, and two zeolitic H2O molecules. Pyrazine (pyz) is surprisingly reluctant to afford assemblies similar to 8–12, however, the genuine host–guest systems [(Me3Sn)4Mo(CN)8⋅0.5pyz] and [(Me3Sn)4Mo(CN)8⋅pym] (pym=pyrimidine) could be isolated and also structurally characterized.