bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Pyrolytic and Kinetic Behaviour of β,δ′‐Dioxo‐Stabilised Phosphorus Ylides: Convenient Preparation of γ,δ‐Alkynyl Ketones and 2,3‐Functionalised Butadienes
Authors: Aitken R. Alan , Al‐Awadi Nouria A. , Balkovich Mark E. , Bestmann Hans Jürgen , Clem Oliver , Gibson Scott , Groß Andreas , Kumar Ajith , Röder Thomas
Published: February 2003

Both ketone‐ and ester‐stabilised phosphorus ylides undergo Michael addition to vinyl ketones to give the β,δ′‐dioxo ylides 3 and 5, respectively, although in the latter case careful temperature control is required to avoid an undesired side‐reaction. Under conditions of flash vacuum pyrolysis at 650 °C the ylides 3 generally undergo Ph3PO extrusion to afford the γ,δ‐alkynyl ketones 14, although these are found to partly undergo a secondary fragmentation. In contrast, the ylides 5 react under the same conditions to give the synthetically useful 1,3‐dienes 20 by way of cyclobutenes. Rate constants for the reaction of selected ylides 3 and 5 are reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Measuring the impact of US research consortia
Authors: Sakakibara Mariko , Branstetter Lee
Published: February 2003

This paper empirically evaluates the impact of the US Advanced Technology Program‐sponsored consortia on the ex‐post research productivity of participating firms. We find that there is a positive association between the intensity of participation in research consortia and the overall research productivity of participants. We also find a positive impact of consortia on the research productivity of participants in the technological areas targeted by the consortia. This positive impact is higher when the average technological proximity of participants is high. There is evidence that large, R&D intensive firms tend to benefit more from participation in consortia. Copyright © 2003 John Wiley & Sons, Ltd.
Sulphur isotopes in palaeodietary studies: a review and results from a controlled feeding experiment
Authors: Richards M. P. , Fuller B. T. , Sponheimer M. , Robinson T. , Ayliffe L.
Published: February 2003

Recent advances in mass spectrometry now allow relatively routine measurements of sulphur isotopes (δ34S) in small samples (>10 mg) of tissue from archaeological human, plant, and faunal samples. δ34S values of human and faunal bone collagen can indicate residence or migration and can provide palaeodietary information. Here we present a review of applications of sulphur isotopes to archaeological materials, and we also present preliminary results from one of the few controlled feeding experiments undertaken for sulphur isotopes. This study indicates that there is relatively little fractionation (−1‰ ) between diet and body protein (keratin) δ34S values for modern horses on a protein adequate C3 plant diet. In contrast, horses fed a possible low protein C4 feed have a diet to hair fractionation of +4‰ that could be the result of the input of endogenous sulphur from the recycling of body proteins. Copyright © 2003 John Wiley & Sons, Ltd.
Polyethylene cross‐linking by two different methods reduces acetabular liner wear in a hip joint wear simulator
Authors: D'Lima Darryl D. , Hermida Juan C. , Chen Peter C. , Colwell Clifford W.
Published: February 2003

Advances in cross‐linking have led to the development of wear resistant ultrahigh molecular weight polyethylene for total joint replacement. This study compared wear reduction by two different cross‐linking methods as measured in a hip wear simulator. One highly cross‐linked polyethylene was treated with 7.5 Mrad gamma irradiation with post‐irradiation annealing and a sterilization dose of 2.5 Mrad (10 Gamma), while the other used 9.5 Mrad warm irradiation with 10 MeV electron‐beam (9.5 EB). Liners of the same design, made from nominally cross‐linked (gamma sterilized) polyethylene were also tested. Gravimetric wear analysis was performed every 500,000 cycles for 5,000,000 cycles. After correcting for weight gain due to water absorption, the nominally cross‐linked liners demonstrated mean wear rates of 15.7 (±1.7) and 12.5 (±1.0) mg/million cycles. Both highly cross‐linked polyethylene liners demonstrated significantly less wear than their respective controls (with mean wear rates of 1.5 (±1.2) and –1.4 (±1.5) mg/million cycles). The 9.5 EB liners gained weight presumably due to increased fluid absorption, in addition to that measured in loaded–soaked control implants. Any wear occurring was therefore assumed to have been more than offset by weight gain. Highly cross‐linked polyethylene was significantly more wear resistant than non‐ or nominally cross‐linked polyethylene. The differences in wear rates between the two highly cross‐linked polyethylene designs (9.5 EB or 10 Gamma) are probably too small to be clinically significant. © 2003 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.
Central hemodynamic responses during serial exercise tests in heart failure patients using implantable hemodynamic monitors
Authors: Ohlsson Å. , Steinhaus D. , Kjellström B. , Ryden L. , Bennett T.
Published: February 2003

Introduction:

Exercise testing is commonly used in patients with congestive heart failure for diagnostic and prognostic purposes. Such testing may be even more valuable if invasive hemodynamics are acquired. However, this will make the test more complex and expensive and only provides information from isolated moments. We studied serial exercise tests in heart failure patients with implanted hemodynamic monitors allowing recording of central hemodynamics.

Methods:

Twenty‐one NYHA Class II–III heart failure patients underwent maximal exercise tests and submaximal bike or 6‐min hall walk tests to quantify their hemodynamic responses and to study the feasibility of conducting exercise tests in patients with such devices.

Results:

Patients were followed for 2–3 years with serial exercise tests. During maximal tests (n=70), heart rate increased by 52±19 bpm while SvO2 decreased by 35±10% saturation units. RV systolic and diastolic pressure increased 29±11 and 11±6 mmHg, respectively, while pulmonary artery diastolic pressure increased 21±8 mmHg. Submaximal bike (n=196) and hall walk tests (n=172) resulted in SvO2 changes of 80 and 91% of the maximal tests, while RV pressures ranged from 72 to 79% of maximal responses.

Conclusions:

An added potential value of implantable hemodynamic monitors in heart failure patients may be to quantitatively determine the true hemodynamic profile during standard non‐invasive clinical exercise tests and to compare that to hemodynamic effects of regular exercise during daily living. It would be of interest to study whether such information could improve the ability to predict changes in a patient's clinical condition and to improve tailoring patient management.
Molecular beam study of the H2–D2 exchange reaction on stepped platinum crystal surfaces: Dependence on reactant angle of incidence
Authors: Salmeron M. , Gale R. J. , Somorjai G. A.
Published: February 2003

The exchange reaction H2+D2→2HD was studied as a function of the angle of incidence (polar and azimuthal) of the beam of reactants on two stepped platinum surfaces, the Pt(S) -[6(111) × (111)] and Pt(S) -[5(111) × (111)]. The reaction probability was found to depend markedly on the direction of approach of the reactants to the step structure. The production of HD is highest when the reactants strike the open side of the step structure, decreasing by approximately a factor of 2 when the inner corner of the step is shadowed. These variations are intimately related to the geometry of the stepped surfaces and cannot be attributed to an activation energy barrier for adsorption. The observed dependence can be accounted for in a simple model, assigning different activities for H–H bond breaking to the step and terrace sites. For the best fit with the experimental data we find that the activity of a step site is seven times that of a terrace site at normal incidence.
A 125Te and 129I Mössbauer study of tellurium–selenium and tellurium–sulfur phases
Authors: Jones C. H. W. , Mauguin M.
Published: February 2003

The 125Te Mössbauer absorption and 129I Mössbauer emission spectra of the alloys Te1−xSex (0<x<0.9) and Te1−xSx (0<x<0.98) have been recorded. Evidence is presented that in the Te1−xSex system the 129I impurity atom serves as a more sensitive probe than the parent tellurium atom to changes in lattice environment with changing composition of the alloy. The 129I results provide evidence for the formation of copolymer chains at the Te0.5Se0.5 composition. Results for the Te1−xSx system are also briefly discussed.
Far-infrared absorption by ices Ih and Ic at 4.3 °K and the powder diffraction pattern of ice Ic
Authors: Bertie John E. , Jacobs Stephen M.
Published: February 2003

The far-infrared spectra of H2O and D2O ices Ih and Ic at 4.3 °K are reported. Many weak features are observed and for ice Ih are shown to correspond well with features in the published Raman spectra. Differences between the spectra of ices Ih and Ic are reported for the first time; they are due to the different crystal structures and can be understood in more detail from published calculations of dispersion curves and densities of translational vibrational states. These results and the Raman spectra provide much information with which to test calculations of the translational vibrations in ice I. Extra lines in powder diffraction patterns of ice Ic have generally been attributed to ice Ih impurity. From the measurements reported in this work it is suggested that this may not be the case.
Radiative and radiationless transitions in oxalyl fluoride resulting from single vibronic level excitation
Authors: Baronavski A. P. , McDonald J. R.
Published: February 2003

The excited state dynamics of oxalyl fluoride resulting from single vibronic level excitation of the 1Au←1Ag transition are reported. Excitation near the origin of the transition leads to radiative decay with a lifetime of ∼25 μsec. Unimolecular dissociation due to an avoided curve crossing onsets at ∼965 cm−1 above the O–O band. Bimolecular self-quenching rates are measured at several wavelengths for the lower 1Au state. Near the origin this process is likely dominated by collision-induced intersystem crossing to a phosphorescing triplet level. At levels within ∼1 kT of the dissociation limit, collision-induced predissociation may become competitive with the intersystem crossing process.
p120 Catenin Is Required for Growth Factor–dependent Cell Motility and Scattering in Epithelial Cells
Authors: Cozzolino Mauro , Stagni Venturina , Spinardi Laura , Campioni Nadia , Fiorentini Carla , Salvati Erica , Alemà Stefano , Salvatore Anna Maria
Published: February 2003

Cadherin-mediated cell–cell adhesion is dynamically modulated during epithelial–mesenchymal transition triggered by activation of receptor tyrosine kinases (RTK) in epithelial cells. Several cadherin-binding proteins have been identified that control cell–cell adhesion. However, the mechanisms by which intercellular adhesion and cell motility are coregulated are still unknown. Here, we delineate a hitherto uncharted cooperation between RTKs, RhoA GTPase, and p120 catenin in instructing a motile behavior to epithelial cells. We found that expression of an N-terminus–deleted p120 catenin in a variety of epithelial cell types, including primary keratinocytes, effectively competes for endogenous p120 at cadherin binding sites and abrogates EGF-stimulated cell motility as well as HGF-induced cell scattering. The deleted mutant also inhibits the PI3K-dependent RhoA activation ensuing receptor activation. Conversely, we also show that the ectopic expression of full-length p120 in epithelial cells promotes cytoskeletal changes, stimulates cell motility, and activates RhoA. Both motogenic response to p120 and RhoA activation require coactivation of signaling downstream of RTKs as they are suppressed by ablation of the Ras/PI3K pathway. These studies demonstrate that p120 catenin is a necessary target of RTKs in regulating cell motility and help define a novel pathway leading to RhoA activation, which may contribute to the early steps of metastatic invasion.
Distinct Developmental Function of TwoCaenorhabditis elegansHomologs of the Cohesin Subunit Scc1/Rad21
Authors: Mito Yoshiko , Sugimoto Asako , Yamamoto Masayuki
Published: February 2003

Cohesin, which mediates sister chromatid cohesion, is composed of four subunits, named Scc1/Rad21, Scc3, Smc1, and Smc3 in yeast. Caenorhabditis elegans has a single homolog for each of Scc3, Smc1, and Smc3, but as many as four for Scc1/Rad21 (COH-1, SCC-1/COH-2, COH-3, and REC-8). Except for REC-8 required for meiosis, function of these C. elegans proteins remains largely unknown. Herein, we examined their possible involvement in mitosis and development. Embryos depleted of the homolog of either Scc3, or Smc1, or Smc3 by RNA interference revealed a defect in mitotic chromosome segregation but not in chromosome condensation and cytokinesis. Depletion of SCC-1/COH-2 caused similar phenotypes. SCC-1/COH-2 was present in cells destined to divide. It localized to chromosomes in a cell cycle-dependent manner. Worms depleted of COH-1 arrested at either the late embryonic or the larval stage, with no indication of mitotic dysfunction. COH-1 associated chromosomes throughout the cell cycle in all somatic cells undergoing late embryogenesis or larval development. Thus, SCC-1/COH-2 and the homologs of Scc3, Smc1, and Smc3 facilitate mitotic chromosome segregation during the development, presumably by forming a cohesin complex, whereas COH-1 seems to play a role important for development but unrelated to mitosis.
Multifactor dimensionality reduction software for detecting gene–gene and
gene–environment interactions
Authors: Hahn Lance W. , Ritchie Marylyn D. , Moore Jason H.
Published: February 2003

Motivation: Polymorphisms in human genes are being described in remarkable numbers. Determining which polymorphisms and which environmental factors are associated with common, complex diseases has become a daunting task. This is partly because the effect of any single genetic variation will likely be dependent on other genetic variations (gene–gene interaction or epistasis) and environmental factors (gene–environment interaction). Detecting and characterizing interactions among multiple factors is both a statistical and a computational challenge. To address this problem, we have developed a multifactor dimensionality reduction (MDR) method for collapsing high-dimensional genetic data into a single dimension thus permitting interactions to be detected in relatively small sample sizes. In this paper, we describe the MDR approach and an MDR software package.

Results: We developed a program that integrates MDR with a cross-validation strategy for estimating the classification and prediction error of multifactor models. The software can be used to analyze interactions among 2–15 genetic and/or environmental factors. The dataset may contain up to 500 total variables and a maximum of 4000 study subjects.

Availability: Information on obtaining the executable code, example data, example analysis, and documentation is available upon request.

Contact: moore@phg.mc.vanderbilt.edu

Supplementary information: All supplementary information can be found at http://phg.mc.vanderbilt.edu/Software/MDR.

* To whom correspondence should be addressed.
WiGID: wireless genome information database
Authors: Ursing Björn M.
Published: February 2003

Summary: WiGID, wireless genome information database, is a new application for mobile internet and can be reached through wireless application protocol (WAP). The main purpose of WiGID is to give easy access to information on completely sequenced genomes. Genome entries in WiGID can be queried by the number of open reading frames (ORFs), genus and species name and year published. Initial search results are linked to information on the full entry.

Availability: WiGID can be accessed through WAP at http://wigid.cgb.ki.se/index.wml and through the regular internet at http://wigid.cgb.ki.se.

Contact: bjorn.ursing@cgb.ki.se

* To whom correspondence should be addressed.
A literature-based method for assessing the functional
coherence of a gene group
Authors: Raychaudhuri Soumya , Altman Russ B.
Published: February 2003

Motivation: Many experimental and algorithmic approaches in biology generate groups of genes that need to be examined for related functional properties. For example, gene expression profiles are frequently organized into clusters of genes that may share functional properties. We evaluate a method, neighbor divergence per gene (NDPG), that uses scientific literature to assess whether a group of genes are functionally related. The method requires only a corpus of documents and an index connecting the documents to genes.

Results: We evaluate NDPG on 2796 functional groups generated by the Gene Ontology consortium in four organisms: mouse, fly, worm and yeast. NDPG finds functional coherence in 96, 92, 82 and 45% of the groups (at 99.9% specificity) in yeast, mouse, fly and worm respectively.

Availability: Contact authors.

Contact: russ.altman@stanford.edu

* To whom correspondence should be addressed.
Leader Proteinase of
Beet Yellows Virus
Functions in Long-Distance Transport
Authors: Peng Chih-Wen , Napuli Alberto J. , Dolja Valerian V.
Published: February 2003

The 66-kDa leader proteinase (L-Pro) of the
Beet yellows virus
(BYV) possesses a nonconserved N-terminal domain and a conserved, papain-like C-terminal domain. Previous work revealed that the N-terminal domain functions in RNA amplification, whereas the C-terminal domain is required for autoproteolysis. Alanine-scanning mutagenesis was applied to complete the functional analysis of L-Pro throughout the virus life cycle. This analysis indicated that the C-terminal domain of L-Pro, in addition to being required for proteolysis, also functions in RNA amplification and that these two functions are genetically separable. Examination of the role of L-Pro in BYV cell-to-cell movement revealed that none of the 20 examined replication-competent mutants was movement defective. In contrast, six of the L-Pro mutations affected the long-distance transport of BYV to various degrees, whereas three mutations completely abolished the transport. Because these mutations were located throughout the protein molecule, both domains of L-Pro function in virus transport. We conclude that in addition to previously identified functions of L-Pro, it also serves as the BYV long-distance transport factor.
A New Hybrid System Capable of Efficient Lentiviral Vector Production and Stable Gene Transfer Mediated by a Single Helper-Dependent Adenoviral Vector
Authors: Kubo Shuji , Mitani Kohnosuke
Published: February 2003

To achieve efficient and sustained gene expression, we developed a new lentivirus/adenovirus hybrid vector (LA vector) that encodes sequences required for production of a human immunodeficiency virus-based lentiviral vector (i.e., a lentiviral vector, a
gag/pol/rev
expression cassette, a tetracycline-inducible envelope cassette, and the tetracycline-inducible transcriptional activator cassette) in a single helper-dependent adenovirus vector backbone. Via either transfection or infection, human cell lines transduced with the LA vector produced a lentiviral vector in a doxycycline-dependent manner at titers up to 10
5
to 10
6
green fluorescent protein transducing units per ml, which are comparable to the titers obtained by conventional multiple plasmid transfection methods. Efficient spread and persistent expression of the transgene were observed in cells maintained in long-term culture that had been infected with the LA vector. Furthermore, when cocultured with adherent cells infected with the LA vector, the human T-cell leukemia cell line was successfully transduced with a marker gene. This LA vector possesses the advantages of efficient gene transfer from an adenoviral vector and stable integration from a lentiviral vector; therefore, it might have potential for a variety of gene therapy applications.
The Avian Retrovirus Avian Sarcoma/Leukosis Virus Subtype A Reaches the Lipid Mixing Stage of Fusion at Neutral pH
Authors: Earp Laurie J. , Delos Sue E. , Netter Robert C. , Bates Paul , White Judith M.
Published: February 2003

We previously showed that the envelope glycoprotein (EnvA) of avian sarcoma/leukosis virus subtype A (ASLV-A) binds to liposomes at neutral pH following incubation with its receptor, Tva, at ≥22°C. We also provided evidence that ASLV-C fuses with cells at neutral pH. These findings suggested that receptor binding at neutral pH and ≥22°C is sufficient to activate Env for fusion. A recent study suggested that two steps are necessary to activate avian retroviral Envs: receptor binding at neutral pH, followed by exposure to low pH (W. Mothes et al., Cell
103:
679-689, 2000). Therefore, we evaluated the requirements for intact ASLV-A particles to bind to target bilayers and fuse with cells. We found that ASLV-A particles bind stably to liposomes in a receptor- and temperature-dependent manner at neutral pH. Using ASLV-A particles biosynthetically labeled with pyrene, we found that ASLV-A mixes its lipid envelope with cells within 5 to 10 min at 37°C. Lipid mixing was neither inhibited nor enhanced by incubation at low pH. Lipid mixing of ASLV-A was inhibited by a peptide designed to prevent six-helix bundle formation in EnvA; the same peptide inhibits virus infection and EnvA-mediated cell-cell fusion (at both neutral and low pHs). Bafilomycin and dominant-negative dynamin inhibited lipid mixing of Sindbis virus (which requires low pH for fusion), but not of ASLV-A, with host cells. Finally, we found that, although EnvA-induced cell-cell fusion is enhanced at low pH, a mutant EnvA that is severely compromised in its ability to support infection still induced massive syncytia at low pH. Our results indicate that receptor binding at neutral pH is sufficient to activate EnvA, such that ASLV-A particles bind hydrophobically to and merge their membranes with target cells. Possible roles for low pH at subsequent stages of viral entry are discussed.
Detecting Occult Coronary Disease in a High-Risk Asymptomatic Population
Authors: Blumenthal Roger S. , Becker Diane M. , Yanek Lisa R. , Aversano Thomas R. , Moy Taryn F. , Kral Brian G. , Becker Lewis C.
Published: February 2003

Background—

Exercise stress testing alone or with perfusion imaging is the standard screening method to determine the presence of obstructive coronary artery disease (CAD) in people with chest pain. In asymptomatic individuals with a family history of premature CAD, it is unclear whether abnormalities on these functional exercise tests represent significant coronary disease.

Methods and Results—

An abnormal exercise test, thallium scan, or both occurred in 153 (21%) of 734 asymptomatic siblings of persons with documented CAD, of whom 105 underwent coronary angiography with quantitative analysis of stenosis severity. Overall, 95% had coronary atherosclerosis, but only 39% had 1 or more stenoses with ≥50% narrowing. Of 30 siblings in whom the exercise test and perfusion scan were both abnormal, 70% had ≥50% stenoses. The mean stenosis in arteries that fed perfusion defects was only 43±31%, and 68% of such stenoses were <50%. However, in 71% of all defects, the location matched arteries with the most severe stenoses.

Conclusions—

In asymptomatic persons with a family history of CAD, abnormal exercise scintigraphy identifies predominantly mild coronary atherosclerosis. Perfusion defects may be caused by coronary vasomotor dysfunction in addition to atherosclerotic plaque.
Efficient transduction of primary human B lymphocytes and nondividing myeloma B cells with HIV-1–derived lentiviral vectors
Authors: Bovia Fabrice , Salmon Patrick , Matthes Thomas , Kvell Krisztian , Nguyen Tuan H. , Werner-Favre Christiane , Barnet Marc , Nagy Monika , Leuba Florence , Arrighi Jean-François , Piguet Vincent , Trono Didier , Zubler Rudolf H.
Published: February 2003

We studied the transduction of primary human B lymphocytes and myeloma cells with lentiviral vectors. In peripheral blood B cells that had been activated with helper T cells (murine thymoma EL-4 B5) and cytokines, multiply attenuated HIV-1–derived vectors pseudotyped with vesicular stomatitis virus (VSV) G-envelope protein achieved the expression of green fluorescence protein (GFP) in 27% ± 12% (mean ± 1 SD; median, 27%) of B cells in different experiments. When compared in parallel cultures, the transducibility of B cells from different donors exhibited little variation. The human cytomegalovirus (CMV) promoter gave 4- to 6-fold higher GFP expression than did the human elongation factor-1α promoter. A murine retroviral vector pseudotyped with VSV G protein proved inefficient even in mitotically active primary B cells. B cells freshly stimulated with Epstein-Barr virus were also transducible by HIV vectors (24% ± 9%), but B cells activated with CD40 ligand and cytokines resisted transduction. Thus, different culture systems gave different results. Freshly isolated, nondividing myeloma cells were efficiently transduced by HIV vectors; for 6 myelomas the range was 14% to 77% (median, 28%) GFP+ cells. HIV vectors with a mutant integrase led to no significant GFP signal in primary B or myeloma cells, suggesting that vector integration was required for high transduction. In conclusion, HIV vectors are promising tools for studies of gene functions in primary human B cells and myeloma cells for the purposes of research and the development of gene therapies.
Donor CMV serostatus has no impact on CMV viremia or disease when prophylactic granulocyte transfusions are given following allogeneic peripheral blood stem cell transplantation
Authors: Vij Ravi , DiPersio John F. , Venkatraman Partha , Trinkaus Kathryn , Goodnough Lawrence T. , Brown Randy A. , Khoury Hanna J. , Devine Steven M. , Oza Aarti , Shenoy Shalini , Blum William , Adkins Douglas
Published: February 2003

We studied the impact of donor cytomegalovirus (CMV) serologic status on CMV viremia and disease when prophylactic granulocyte colony-stimulating factor (G-CSF)–mobilized granulocyte transfusions (GTs) were given following allogeneic peripheral blood stem cell (AlloPBSC) transplantation. A cohort of 83 patients who received 2 prophylactic GTs from ABO-compatible stem cell donors following AlloPBSC transplantation was compared with a cohort of 142 patients who did not. AlloPBSC donors were eligible for granulocyte donation irrespective of their CMV serostatus. Recipients received no prophylactic therapy for CMV. Donor CMV serostatus had no impact on CMV viremia and disease in the 2 cohorts. Our data show that in an era of effective surveillance and preemptive therapy for CMV, AlloPBSC recipients can safely receive 2 transfusions of prophylactic G-CSF–mobilized granulocyte components from CMV-seropositive AlloPBSC donors. This knowledge may help expand the donor pool in areas with a high prevalence of CMV in the general population.
Antibiotika‐Resistenz: Struktur eines Transporterproteins
Authors: Groß Michael
Published: February 2003

Bakterienstämme, die gegen zahlreiche Medikamente resistent sind, stellen die Medizin vor immer größere Herausforderungen. Seit den 1990er Jahren weiß man, dass die dafür verantwortlichen Resistenzgene nicht nur zwischen Stämmen sondern sogar zwischen verschiedenen Arten leichter weitergereicht werden können, als man vermutet hatte. Um so dringender wird die Aufgabe, die in der Natur existierenden Resistenzen umfassend zu verstehen und direkt bei der Entwicklung neuer Antibiotika zu berücksichtigen.
Highlights aus Liebigs Experimentalvorlesung
Authors: Schwedt Georg
Published: February 2003

Liebigs Geburtstag jährt sich am 12. Mai 2003 zum 200. Mal. Aus diesem Anlass werden einzelne Experimente bzw. Versuchsreihen, die noch heute eine grundlegende Bedeutung haben, aus seiner in Gießen entwickelten Experimentalvorlesung vorgestellt. Sie stammen aus dem im Nachlass seines Sohnes, des Arztes Georg von Liebig (1827—1903), im Jahre 1906 aufgefundenen Vorlesungsbuch, das 1983 veröffentlicht wurde.
Champagnerschäume
Authors: Först Johannes Otto
Published: February 2003

Chemische Experimente mit Alltagsgegenständen faszinieren Schüler besonders. Das nachstehende Experiment entstand in der Chemie‐AG eines Gymnasiums bei der Untersuchung von Säuren und ihren Eigenschaften.
A CNDO/S study on the electronic structure of some methyl and phenyl substituted pyryliums
Authors: Bigelow Richard W.
Published: February 2003

The semiempirical molecular orbital CNDO/S spectral parameterization of Del Bene and Jaffe has been used to elucidate the electronic structure of a series of methyl and phenyl substituted pyrylium cations. This study demonstrates that the CNDO/S technique, without additional parameterization, provides a quantitative basis for the understanding of various ground and excited singlet state properties of the five pyrylium molecules considered. Of particular importance is the favorable comparison of experimental and calculated relative oscillator strengths and the magnitude and direction of shifts of the singlet transitions. The nature of the low-lying singlet states are further elucidated through a study of the calculated wavefunctions. Comparisons of potential energy diagrams for the interaction of the ground and excited state static charge density distributions with a negative test charge demonstrates that the nature of the transition could be important in the determination of relative spectral sensitization properties.
The molecular and crystal structure of squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione) at 121 °C: A neutron diffraction study
Authors: Hollander F. J. , Semmingsen D. , Koetzle T. F.
Published: February 2003

The molecular and crystal structure of squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione) has been determined by neutron diffraction techniques at 121°C, a temperature above that of the monoclinic to tetragonal phase transition (∼100°C). The high-temperature structure is in space group I4/m, a=c=6.137(2) Å, b=5.337(2) Å. Least-squares refinement has been carried out with 25 variable parameters and 276 reflections, to yield an unweighted R value (on F2) of 0.042. The squaric acid molecule has point symmetry 4/m, and the hydrogen atom is ’’disordered’’ about the inversion center at the midpoint of the O⋅⋅⋅O hydrogen bond. Hydrogen-bonding parameters are O–H 1.014(4), H⋅⋅⋅O 1.536(5) Å, O⋅⋅⋅O 2.548(2) Å, & O–H⋅⋅⋅O 176.2(6) °. The tetragonal structure corresponds closely to that obtained from the atomic parameters determined in the monoclinic phase at 25°C, by averaging over the pseudofourfold symmetry.
Decay kinetics of the delayed fluorescence of aromatic compounds
Authors: Bazin M. , Aubailly M. , Santus R.
Published: February 2003

The decay kinetics of the isothermal recombination fluorescence (ITF) contributing to the delayed fluorescence emission (DF) of the indole ring in water–alcohol glasses at 77 K have been analyzed from 10 msec to several seconds. The experimental decay of the ITF intensity can be fitted by a theoretical relationship derived from the well-known phenomenological Debye–Edwards law [I(delayed emission) ∝t−m]. It confirms that as previously shown the uv induced ITF and the ITP (isothermal recombination phosphorescence) are produced by the same mechanism, i.e., electron–cation isothermal recombination which consequently is independent of the excitation mode.
Photosensitization processes in molecular solids
Authors: Grammatica S. , Mort J.
Published: February 2003

Experiments relating to the photosensitization process in molecular solids are discussed. The studies deal with molecularly doped polymers which offer the advantage of controlled dye (sensitizer) –transport molecule separation and the ability to change the nature of the sensitizer and transport molecule. The photosensitization is shown to be controlled by the dye–transport molecule separation. Experimentally this requires the elimination of the associated transport limitations caused by the inevitable increase in the separation between transport molecules. Additional experiments involving the xerographic discharge of dye/transport molecule doped polymers overcoated with an a-Se sensitizing layer reveal the dual sensitizing and trapping role that dye molecules can play.
Rotational correlations in rough sphere fluids
Authors: Kapral Raymond , Desai Rashmi C.
Published: February 2003

The coupling of the angular velocity of a test rough sphere to the collective modes of the surrounding bath of rough spheres is studied as a function of the mass and diameter of the test sphere using renormalized kinetic theory. As the diameter of the tagged particle increases, the collective contribution to the relaxation changes from a situation where coupling to the fluid transverse angular velocity field dominates to one in which coupling to the transverse linear velocity field dominates. As the mass of the test particle increases, the collective contribution becomes increasingly sensitive to the nonhydrodynamic states which appear in the kinetic theory. The long time behavior of the angular velocity correlation function and the associated memory kernels are found to have interesting dependence on the test sphere diameter. The results are used to elucidate some features of the hydrodynamic character of microscopic relaxation processes.
The interaction of inversion with other vibrations in ammonia
Authors: Cress Daniel H. , Quade C. Richard
Published: February 2003

The inversion energy levels of NH3, ND3, NH2D, and NHD2 have been calculated on the basis of the theory for the interaction of a large amplitude internal motion with other vibrations. A single parameter potential energy function that is the same for all isotopic species has been used for the ground state of the other vibrations which, as determined in this work, is given by V (α) =33 120 cm−1 (α−αo)2, with r=1.014 A and αo=106.78°. The agreement between calculated and observed energies is remarkably good, and it is clear that what has previously been presumed to be a dependence of the inversion potential energy upon isotopic species can be accounted for from the interaction with the other vibrations. The inversion frequencies of NH3 and ND3 in the excited states for the other vibrations have been calculated from the introduction of a large amplitude coordinate dependence into the force constants for the other vibrations. This calculation uses a four parameter model and the results are as good, if not better, than those from the eight parameter model used previously.
Steady-state kinetics of diffusionless first order phase transformations
Authors: Chan Sai-Kit
Published: February 2003

An attempt is made to describe the kinetics of diffusionless first order phase transformations in terms of the time-dependent Landau–Ginzburg equation. A steady-state solution to the equation is presented such that an interface may propagate with a shape-preserving profile under constant supercooling. The laws of growth and dissolution are derived and their condition of validity is discussed. The results provide a plausible basis for the interpretation of the kinetics of displacive transformations in solids and of certain first order transformations in liquid crystals.
ESR of diphenylantimony radical in a triphenylantimony single crystal
Authors: Cook W. Thomas , Vincent James S.
Published: February 2003

Ultraviolet irradiation of a single crystal of triphenylantimony produces an antimony centered radical with an anisotropic 121Sb coupling having principal absolute values of 704, 352, and 352 MHz and a g tensor with the same principal axis as the hyperfine interaction and components of 1.998, 2.045, and 2.065. This radical has been assigned to the diphenyl antimony radical with approximately zero s and 0.7 p character. The linewidth of the spectra are consistent with unresolved hyperfine structure due to spin density delocalized on the phenyl rings.
Energy transfer in collisions of excited Na atoms with NO molecules
Authors: Silver Joel A. , Blais N. C. , Kwei G. H.
Published: February 2003

Measurements of scatterng angle and product velocity distributions are reported for a crossed molecular beam study of excited Na atoms and NO molecules. These results provide evidence that most of the electronic energy is partitional between relative translation and vibration f the NO molecule. (AIP).
Assignment of the triplet factor group states of benzene
Authors: Trommsdorff H. P. , Castro G.
Published: February 2003

The pure electronic 1Ag–3B1u transition of crystalline benzene has been measured by photoexcitation techniques. Polarization and Zeeman measurements on single crystals provide the following assignment of the factor group states (energies relative to the mean value): B3u−7.8 cm−1, Au−0.3 cm−1, B1u+2.6 cm−1, B2u+5.5 cm−1. These results are in contradiction with the most recent calculations performed within the neutral exciton model. The relative intensity of the factor group states suggests that other crystal states do contribute to the transition.
A spectral analysis method of obtaining molecular spectra from classical trajectories
Authors: Noid D. W. , Koszykowski M. L. , Marcus R. A.
Published: February 2003

Vibrational classical trajectories of anharmonic molecules are used here to obtain the classical vibrational autocorrelation function and, via a Fourier transform, the power (or infrared) spectrum of the dynamical variables. In the vibrationally quasiperiodic regime the spectrum consists of sharp lines, for any given initial amplitude. The initial amplitudes are chosen semiclassically. The spectral lines are compared with quantum mechanical calculations for systems with two and three coordinates, with excellent agreement. The method is also useful for obtaining a classical spectrum in the ergodic regime; the spectral lines are then ’’broad’’ rather than narrow. The method can be used in the analysis of trajectories for unimolecular reactions, infrared multiphoton dissociations, and for obtaining molecular spectra from force fields. The spectral analysis itself has implications for the theory of unimolecular reactions.
Normal coordinate analysis of the MNb2O6 series of columbite structure (M=Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd)
Authors: Husson E. , Repelin Y. , Dao Nguyen Quy , Brusset H.
Published: February 2003

Normal coordinate analysis of the MNb2O6 series of columbite structure (M=Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd) was carried out and the results obtained permitted the assignment of all the observed vibrational bands of the columbite series. It is also shown that the force fields of the columbite series are very similar when cations are changed. The variations are interpreted as due to the mass, the electronegativity, and the positions of the cations in the periodic table. The order of the bonds is also given.
Short range antiferromagnetic coupling in bis(N,N-dialkyldithiocarbamato) ironIII halides
Authors: Petrouleas V. , Malliaris Angelos
Published: February 2003

Several bis(N,N-dialkyldithiocarbamato) ironIII have been studied by Mössbauer spectroscopy in the presence of external magnetic fields. The spectra have shown strong evidence of dimeric antiferromagnetic coupling between the molecular units in the crystal lattice. The dimeric coupling occurs through superexchange interacton between different molecules. The magnitude of the coupling constant JD, which was estimated from the magnetically perturbed Mössbauer spectra, was found to be of the order of 0.25–0.50 K for the complexes studied here.
Energy transfer in A 2Σ+ OH. I. Rotational
Authors: Lengel Russell K. , Crosley David R.
Published: February 2003

We have used a frequency doubled, tunable dye laser to excite individual v′, N′, J′ levels of the A 2Σ+ state of the OH molecule. The fluorescence emitted in the presence of known pressures of various fill gases has permitted the determination of collisionally induced population changes, and hence state-to-state energy transfer rates. Here are reported results on rotational energy transfer within v′=0, using six different initially pumped levels for N2 as a collision partner, and two each for H2 and Ar. It is found that the rates are fast (5×10−10 cm3 sec−1 for a typical total transfer rate with N2), that a process having ΔN =ΔJ occurs faster than one where ΔN≠ΔJ, and that multiquantum transfer rates are nearly as large as single quantum transfer rates.
Analysis of torsional spectra of molecules with two internal C3v rotors. VIII. The torsional potential function of dimethylsulfide
Authors: Durig J. R. , Griffin M. G.
Published: February 2003

The Raman spectrum of gaseous dimethylsulfide has been recorded between 50 and 3500 cm−1. The region from 300 to 400 cm−1 was recorded with a resolution of 2 cm−1. The far infrared spectrum has been recorded from 100 to 400 cm−1 with a resolution of 0.25 cm−1. Considerable torsional data are reported and used to characterize the torsional potential function based on a semirigid model. The average effective V3 was found to be 659±3 cm−1 (1.89 kcal/mole). The cosine–cosine coupling term V33 was found to be 146±8 (0.42 kcal/mole) and the sine–sine term V′33 has a value of −22±3 cm−1 (−0.06 kcal/mole). These data are compared to the corresponding quantities obtained from microwave data. Comparisons are also given to similar quantities obtained for other molecules.
Coadsorption of CO2 and O2 on MgO: An experimental and theoretical ESR study
Authors: Taarit Y. Ben , Vedrine J.C. , Naccache C. , de Montgolfier Ph. , Meriaudeau P.
Published: February 2003

A paramagnetic species attributed to an anionic coadsorbate of CO2 and O2 has been identified on an uv irradiated MgO surface. Its ESR parameters are as follows: gx=g1=2.040±0.001, gy=g2=2.0072±0.0005, and gz=2.0015±0.0005; Cx ?4 Oe, Cy=3.5±0.5 Oe, and Cz=2.8±0.3 Oe for 13C hyperfine tensor, and Caz=100 Oe and Cbz=50 Oe for 17O hyperfine splittings from molecular oxygen; the corresponding Cy and Cx components were too small to be determined. A theoretical approach to such a species has been made using the CNDO II/SP method. We have studied first the direct interaction of CO2 with O−2 in the gas phase, and then various models for the adsorbed species. The one that best fitted the experimental data corresponded to a species parallel to the surface with a CO2–O2 distance equal to 1.5 Å. We suggest that interaction of the O−2 unit with both CO2 and surface ions is necessary in order to obtain theoretical results in qualitative agreement with experimental data.
Quenching of benzene fluorescence in pulsed proton irradiation: Dependence on proton energy
Authors: Miller J. H. , West M. L.
Published: February 2003

Dilute solutions of benzene in cyclohexane were irradiated with subnanosecond pulses of protons from a 2 MV accelerator. Changes in the time resolved emission at 285 nm were studied as a function of proton energy. The initial rate of fluorescence decay is energy dependent and always greater than that observed with ultraviolet radiation. As time after irradiation increases, the decay rate approaches the uv value. A model based upon quenching by transient species in the proton track is used to analyze the data. The analysis suggests that the energy dependence of the initial decay rate results from the effect of proton stopping power on the initial quencher concentration.
Power generation in coherent anti-Stokes Raman spectroscopy with focused laser beams
Authors: Shaub W. M. , Harvey A. B. , Bjorklund G. C.
Published: February 2003

Focusing effects for nonlinear power generation are explicitly discussed for coherent anti-Stokes Raman spectroscopy (CARS). It is shown that very tight focusing only increases CARS power generation by about a factor of 4, while an extra λ−2 dependence introduced by focusing implies CARS signals scale with wavelength in the same manner as do the signals in normal spontaneous Raman scattering. Axial power generation in a gas phase medium is illustrated, and a modified plane wave approximation function is developed to analyze this behavior for loose focusing cases.
The Raman spectrum of NaCN under hydrostatic pressure
Authors: Dultz W. , Krause H. , Winchester L. W.
Published: February 2003

We have measured the Raman spectrum of NaCN in the two orthorhombic low temperature phases under hydrostatic pressure up to 6 kbar. At the order–disorder phase transition from the disordered phase D252h to the ordered phase D132h the unit cell doubles and new phonon bands fold from the zone boundary to the center and appear in the Raman spectrum. We analyze the transition group theoretically and assign the different phonon bands in the Raman spectrum. The pressure shift of the CN− librational mode is larger than the shift of the lattice modes, which supports our band assignment. We estimate the mode Grüneisen parameters using an approximated value for the bulk modulus of NaCN and compare the results with the averaged Grüneisen parameter of NaCl.
An analytical theory of vibrational relaxation for anharmonic molecules under strongly pumped conditions
Authors: Lam S. H.
Published: February 2003

An analytical theory of vibrational relaxation is presented showing explicitly the effects of the strength of the pumping, the anharmonicity of the energy level spacings, and the VV and VT kinetic rate models. The quasiequilibrium population distribution, the loci of the Treanor–Plateau boundary and the Plateau–Boltzmann knee, the nominal magnitude of the plateau, the ground-level vibrational temperature, and the rates of vibrational quanta and energy dissipations are obtained. A method for deducing quantitative information on kinetic rates at high quantum numbers from measured population distributions is suggested.
High pressure luminescence studies of localized excitations in ZnS doped with Pb2+ and Mn2+
Authors: House G. L. , Drickamer H. G.
Published: February 2003

High pressure luminescence measurements have been made on ZnS doped with Pb+2 and Mn+2. The data include changes in peak energy and shape, integrated intensities, and lifetimes. These localized emissions are treated in terms of a single configuration coordinate model. For Pb+2 the emission peak shifted to lower energy by a moderate amount and narrowed. For excitation in the Pb+2 absorption the intensity was independent of pressure, which is consistent with the fact that the energy barrier for radiationless return to the ground state was high at all pressures. For excitation in the ZnS absorption edge the intensity decreased significantly with pressure above about 80 kbar. Data on shifts of the conduction band with pressure would indicate that one is approaching a transition from a direct to indirect transition at high pressure so that decrease in emission intensity may be associated with decreased absorption efficiency. The Mn+2 emission peak shifted strongly to lower energy with increasing pressure. The direction and magnitude of the shift were consistent with the predictions of ligand field theory. The intensity doubled in 100 kbar, while the lifetime decreased by roughly a factor of 2. These results could be described in terms of a model for a phonon assisted transition. In addition, peak location, intensity, and lifetime measurements were made on ZnS:Pb:Mn. There is clear evidence of energy transfer by exchange, but in addition there is a nonradiative process in the doubly doped crystal which affects both intensities and lifetimes.