bluuebunny/crossref_metadata_2025 huggingface dataset:
What treatment for early‐stage glottic carcinoma among adult patients: CO2 endolaryngeal laser excision versus standard fractionated external beam radiation is superior in terms of cost utility?
Authors: Higgins Kevin M.
Published: September 2010

Objectives/Hypothesis:

To determine which treatment for Tis/T1 glottic carcinoma among adult patients, transoral CO2 laser excision (TOL) versus external beam radiation (XRT), is superior in terms of cost utility.

Study Design:

Cost‐utility analysis.

Methods:

Six head‐to‐head comparison studies and 22 consecutive case series were identified to examine oncologic control. The case series were pooled as a composite group. Primary end points were local control (LC), laryngectomy‐free survival (LFS), and overall survival (OS). Objective and subjective voice‐quality measures were secondary end points. Third‐party payer perspective was adopted for cost‐utility analysis. Operational and capital costs were determined with the microcosting method. Rollback calculations and quality adjusted life years (QALYs) were calculated with decision‐tree modeling.

Results:

There were no significant differences between TOL surgery and XRT with respect to LC (odds ratio [OR], 0.81; 95% confidence interval [CI], 0.51‐1.3) and LFS (OR, 0.84, 95% CI, 0.42‐1.66). The weighted mean difference for OS was 0.03. There were no objective differences for measures of voice quality. Decision‐tree analysis was undertaken using mean 5‐year local control initial probabilities. CO2 laser cost $2475.65/case (US $2407.32/case), generating 1.663 QALYs, whereas radiation cost $4965.85/case (US $4828.79/case), generating 1.506 QALYs. This contrasts initial upstream costs for CO2 laser (∼$1889/case, ∼US $1836.86/case) and radiation (∼$2454.70/case, ∼US $2386.95/case).

Conclusions:

This meta‐analysis shows that there is no clear difference in oncologic outcome between TOL surgery and XRT. There is a trend for improved post‐treatment voice quality with XRT, although the clinical significance of this is questionable. TOL surgery dominates XRT from a cost‐utility standpoint primarily because of the enhanced downstream affordability of salvage treatment. Laryngoscope, 2011
Enhanced efficiency of polymeric solar cells via alignment of carbon nanotubes
Authors: Radbeh Roshanak , Parbaile Emilien , Chakaroun Mohamad , Ratier Bernard , Aldissi Matt , Moliton André
Published: September 2010

Carbon nanotubes (CNTs) are well‐known electron acceptor materials for use in optoelectronic devices due to their appropriate electronic properties. In this work, we report on their use as a part of the multi‐component active layer in organic solar cells to provide better transport of photogenerated charges. To optimize transport, orientation of CNTs perpendicular to the electrodes of solar cells with an active layer of poly(3‐hexylthiophene)–CNT–(6,6‐phenyl C61 butyric acid methyl ester) (P3HT–CNT–PCBM) composite is preferable. In order to achieve this preferred orientation by applying an electric field on the device electrodes, polarization of CNT solutions was studied using dielectric spectroscopy. We find that an improved orientation can be achieved with a high‐frequency AC electric field due to the alternating force exerted rapidly on field‐induced dipoles of the nanotubes. Following these experiments, the orientation method was applied to organic solar cells with a sandwich structure in which the active layer consists of P3HT–CNT–PCBM. The electric field was applied continuously on the electrodes during annealing at a temperature near the glass transition of the polymer matrix. We demonstrate that a significant increase in cell performance (i.e. open‐circuit voltage = 0.61 V, efficiency = 4.53%, fill factor = 0.46) can be achieved, which may signify a better path created by the oriented nanotubes for carrier transport to the electrodes. Copyright © 2010 Society of Chemical Industry
Subcellular fractionation methods and strategies for proteomics
Authors: Lee Yie Hou , Tan Hwee Tong , Chung Maxey C. M.
Published: September 2010

Developments in subcellular fractionation strategies have provided the means to profile and analyze the protein composition of organelles and cellular structures by proteomics. Here, we review the application of classical (e.g. density gradient centrifugation) and emerging sophisticated techniques (fluorescent‐assisted organelle sorting) in the fractionation, and statistical/bioinformatics tools for the prediction of protein localization in subcellular proteomics. We also review the validation methods currently used (such as microscopy, RNA interference and multiple reaction monitoring) and discuss the importance of verification of the results obtained in subcellular proteomics. Finally, the numerous challenges facing subcellular proteomics including the dynamics of organelles are being examined. However, complementary approaches such as modern statistics, bioinformatics and large‐scale integrative analysis are beginning to emerge as powerful tools to proteomics for analyzing subcellular organelles and structures.
Possibility of non‐adiabatic level crossing by DFT study of tautomerism and potential energy surfaces in of 3‐hydroxy‐5‐(pyrimidin‐2‐yl)‐2H‐pyrrol‐2‐one and its tautomer
Authors: Tavakol Hossein , Sabzyan Hassan
Published: September 2010

3‐Hydroxy‐5‐(pyrimidin‐2‐yl)‐2H‐pyrrol‐2‐one (HYPO, T1) and 2‐hydroxy‐5‐(pyrimidine‐2‐yl)‐3H‐pyrrole‐3‐one (HYPO, T2) have designed in this research to study potential energy curves for their dynamic motions and possibility of crossing between levels. Study of tautomerism shows that T1 tautomer is more stable than T2 (about 5.83 kJ/mol). Dynamic study of possible motions show rate constants (highest possible) equal to 8.82 M/s for tautomerism, 1.70 × 109 M/s for relative rotation of ring (rr) and 3.67 × 106 M/s for rotation of OH bond (br). Moreover, variations of orbital populations, NBO charges, hybridations, and acceptor–donor interactions in IRC steps have been investigated to study the possibility of non‐adiabatic crossing between tautomerism and ring rotation potential energy curves. The data showed that in spite of the fact that these two potentials share three common points, these two potential curves cannot have non‐adiabatic crossing because of different symmetries and a large difference between their barrier energies. Copyright © 2010 John Wiley & Sons, Ltd.
Formation of long‐range stripe patterns with sub‐10‐nm half‐pitch from directed self‐assembly of block copolymer
Authors: Takenaka Mikihito , Aburaya Shusuke , Akasaka Satoshi , Hasegawa Hirokazu , Hadjichristidis Nikos , Sakellariou George , Tada Yasuhiko , Yoshida Hiroshi
Published: September 2010

We have demonstrated directed self‐assembly of poly(styrene‐b‐dimethylsiloxiane) (PS‐b‐PDMS) down to sub‐10‐nm half‐pitch by using grating Si substrate coated with PDMS. The strong segregation between PS and PDMS enables us to direct the self‐assembly in wide grooves of the grating substrate up to 500 nm in width. This process can be applied to form various type of sub‐10‐nm stripe pattern along variety of grating shape. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010
Integrated prediction of the effect of mutations on multiple protein characteristics
Authors: Johnston Michael A. , Søndergaard Chresten R. , Nielsen Jens Erik
Published: September 2010

Site‐directed mutagenesis is routinely used in modern biology to elucidate the functional or biophysical roles of protein residues, and plays an important role in the field of rational protein design. Over the past decade, a number of computational tools have been developed that can predict the effect of point mutations on a protein's biophysical characteristics. However, these programs usually provide predictions for only a single characteristic. Furthermore, online versions of these tools are often impractical to use for examination of large and diverse sets of mutants. We have created a new web application, (http://enzyme.ucd.ie/PEAT_SA), that can simultaneously predict the effect of mutations on stability, ligand affinity and pK
a values. PEAT‐SA also provides an expanded feature‐set with respect to other online tools which includes the ability to obtain predictions for multiple mutants in one submission. As a result, researchers who use site‐directed mutagenesis can access state‐of‐the‐art protein design methods with a fraction of the effort previously required. The results of benchmarking PEAT‐SA on standard test‐sets demonstrate that its accuracy for all three prediction types compares well to currently available tools. We illustrate PEAT‐SA's potential by using it to investigate the influence of mutations on the activity of Subtilisin BPN′. This example demonstrates how the ability to obtain a wide range of information from one source, that can be combined to obtain deeper insight into the influence of mutations, makes PEAT‐SA a valuable service to both experimental and computational biologists. Proteins 2010. © 2010 Wiley‐Liss, Inc.
Subcontracting work via social networks: migrant Latino Labour and the rebuilding of New Orleans
Authors: Blue Sarah A. , Drever Anita I.
Published: September 2010

The unprecedented destruction caused by Hurricane Katrina attracted tens of thousands of Latino migrants to work in clean‐up and reconstruction jobs in the New Orleans area. This study uses a survey of Latino workers in New Orleans and interviews from various actors involved in the recruitment and hiring of migrant labour – including employers, subcontractors, and the workers themselves – to explore how migrant networks function. In particular, it highlights the key role of migrant entrepreneur subcontractors in drawing new migrants and securing them jobs in unfamiliar destinations. This is of conceptual importance to migration theory because it highlights the need to expand the dominant concept of social networks to include employers, recruiters, and other migrant service‐providers. Latino migration to New Orleans provides insight into the complexity of contemporary network migration, including the overlapping roles of friend, family, and employer. Copyright © 2010 John Wiley & Sons, Ltd.
Comparative studies on transport and magnetotransport behaviour of as‐deposited and ex situ annealed A‐type antiferromagnetic Nd0.45Sr0.55MnO3 films
Authors: Zhang Q. , Zhang Y. Q. , Zhu Y. L. , Cho J. H. , Zhang Z. D.
Published: September 2010

Magnetic, transport and magnetotransport properties of A‐type antiferromagnetic Nd0.45Sr0.55MnO3 films with different thicknesses grown on SrTiO3 (100) have been investigated before and after ex situ annealing processes. In contrast to the bulk system, all as‐deposited films exhibit insulating behaviour due to the local Jahn–Teller distortion induced by in‐plane tensile strain. The annealing process only induces an insulator–metal transition in ultrathin film with a thickness of 16 nm, resulting in metallically conductive behaviour and the transport properties similar to those of the bulk. This may be ascribed to the cooperative influences of changes in oxygen content and strain‐induced ${\rm d}_{x^{2} {-} y^{2} } $‐type orbital order owing to the annealing process. When a magnetic field of 70 kOe is applied, the metallic behaviour appears in a broad temperature range in the annealed film with 16 nm thickness and, the metallic behaviour is also observed in the annealed film with 32 nm thickness. The different effects of the external magnetic field on the transport properties of as‐deposited and annealed Nd0.45Sr0.55MnO3 films are discussed.
A systematic study of optical and Raman spectra of peapod‐based DWNTs
Authors: Botka Bea , Pekker Áron , Botos Ákos , Kamarás Katalin , Hackl Rudi
Published: September 2010

We followed the preparation of double‐walled carbon nanotubes (DWNTs) from fullerene peapods by optical and Raman spectroscopy in a systematic way. 1.4 nm average diameter nanotubes were opened by oxidation in air, and filled with C60 by sublimation. The peapods were converted to DWNTs by annealing at 1250 °C. As a reference, a control sample was also prepared, where the same sequence of treatments was applied but no C60 was added. We monitored each preparation step from pristine nanotubes to DWNTs by Raman and wide range FIR‐UV transmission spectroscopy. Both free carrier absorption and interband transitions decrease in intensity in DWNTs, indicating that there cannot be significant charge transfer between the outer and the inner tube. Fullerene features show up in the peapod optical spectra, but the transitions of inner tubes are not observed in the DWNT spectra. In the Raman spectra of peapods, the radial breathing modes (RBMs) of the nanotubes show clear changes. Beside the shifts that were reported earlier, the linewidths of the components become smaller. The RBMs of the outer tubes are shifted back to their original position when the peapods are converted to DWNTs.
Investigation of hydrogenated HiPCo nanotubes by infrared spectroscopy
Authors: Németh Katalin , Pekker Áron , Borondics Ferenc , Jakab Emma , Nemes Norbert M. , Kamarás Katalin , Pekker Sándor
Published: September 2010

Two different reductive synthetic methods were applied to hydrogenate the sidewalls of HiPCo single‐walled carbon nanotubes (SWNTs). In the first one, the reductive agent was melted potassium which doped and exfoliated the nanotube bundles, so that before hydrogenation all of the tubes had been converted to metallic ones. In the second method, doping occurred just before hydrogenation by naphthalenide radical anions. The products were characterized by wide range infrared (30–52 000 cm−1) spectroscopy with special emphasis on the selectivity of the two methods. We found that in the first case the controlling factor is the bandgap, and in the second case the diameter. This difference suggests the importance of the π–π interaction between naphthalenide and the nanotube surface.
Electrocorrosion properties of multiwall carbon nanotubes
Authors: Cherstiouk O. V. , Kuznetsov V. L. , Simonov A. N. , Mazov I. N. , Elumeeva K. V. , Moseva N. S.
Published: September 2010

The electrochemical corrosion properties of a set of multiwalled carbon nanotubes (MWCNT) with different average diameters (〈d〉 = 7–22 nm) and conventional carbon black Vulcan XC‐72 were studied potentiostatically in 2 M H2SO4 at 80 °C. Effects of grinding and high‐temperature treatment (2800 °C) in inert gas on the corrosion stability of MWCNT were also examined. Excitation of MWCNTs with large 〈d〉 in activator mill results in local disruption of the fine structure of the NTs and increase of the corrosion current densities. No rupture and changes of the corrosion behaviour occur for MWCNTs with lower 〈d〉 after grinding. High‐temperature treatment of MWCNTs leads to removal of amorphous carbon and defects from the surface of the materials and results in drastic decrease of the reactivity of the surface of the materials towards electrocorrosion. The ABET‐weighted corrosion current densities of the MWCNTs are significantly lower than that of conventional XC‐72 material evidencing of their higher stability towards electrocorrosion.
Two New Xanthones from Hypericum sampsonii and biological activity of the isolated compounds
Authors: Xin Wen‐Bo , Mao Zhu‐Jun , Jin Gui‐Lin , Qin Lu‐Ping
Published: September 2010

Phytochemical investigation of the CH2Cl2 extract of the aerial part of Hypericum sampsonii yielded two new prenylated xanthones, hypericumxanthone A and B, together with three known xanthones. Their structures were elucidated by analysis of physical and spectral (UV, IR, mass and NMR) data and comparison of spectroscopic data with those reported previously. All these compounds were evaluated for in vitro antibacterial activity against methicillin‐resistant Staphylococcus aureus (MRSA). Two new compounds were also tested for their cytotoxicity against human breast (MCF‐7), hepatoma (HepG2), colon (HT‐29) and lung (A549) tumour cell lines. Two new compounds showed moderate antibacterial activities at minimum inhibitory concentrations (MIC) of 16 and 32 µg/mL, respectively, whereas the positive standard antibacterial drug, vancomycin, showed an MIC of 8 µg/mL. The other compounds were inactive against MRSA. In addition, hypericumxanthone B showed weak inhibitory activities against four human tumour cell lines. Copyright © 2010 John Wiley & Sons, Ltd.
Oral administration of Aloe vera and honey reduces walker tumour growth by decreasing cell proliferation and increasing apoptosis in tumour tissue
Authors: Tomasin Rebeka , Cintra Gomes‐Marcondes Maria Cristina
Published: September 2010

Cancer is diagnosed in approximately 11 million people and is responsible for almost 8 million deaths worldwide every year. Research in cancer control has shown the importance of co‐adjuvant therapies. Aloe vera may reduce tumour mass and metastasis rates, while honey may inhibit tumour growth. This study verified the influence of Aloe vera and honey on tumour growth and in the apoptosis process by assessing tumour size, the cell proliferation rate (Ki67‐LI) and Bax/Bcl‐2 expression at 7, 14 and 20 days after Walker 256 carcinoma implant in Wistar rats distributed into two groups: the WA group – tumour‐bearing rats that received a gavage with a 670 µL/kg dose of Aloe vera and honey solution daily, and the CW group – tumour‐bearing rats which received only a 0.9% NaCl solution. The effect of Aloe vera and honey against tumour growth was observed through a decrease in relative weight (%) and Ki67‐LI in tumours from the WA group compared with those from the CW group. The Bax/Bcl‐2 ratio increased in tumours from the WA group at all tested timepoints. These data suggest Aloe vera and honey can modulate tumour growth by reducing cell proliferation and increasing apoptosis susceptibility. Copyright © 2010 John Wiley & Sons, Ltd.
Product defect rate confidence bound with attribute and variable data
Authors: Kang Lulu , Brenneman William A.
Published: September 2010

The upper confidence bound for a product defect rate is a very important index for evaluating the production process in industry. In this paper, we provide a bootstrap methodology to construct a (1−α)100% upper confidence bound for the overall defect rate of a product whose quality assessment involves multiple pass/fail binary data and multiple continuous data. When only the pass/fail data are included we propose using a bootstrap method which is consistent with the Clopper–Pearson one‐sided confidence interval. When only the continuous data are included the BCa bootstrap method is recommended. These two methods are combined to provide an upper confidence bound for the overall defect rate of the product when multiple pass/fail binary data and multiple continuous data are present. All methods are clearly stated in algorithmic form, investigated through simulation and demonstrated using example data sets. In the simulation studies and examples the proposed algorithms show great advantages in both coverage probability and computational efficiency. Copyright © 2010 John Wiley & Sons, Ltd.
Autoxidation of cyclohexene catalysed by a rhodium complex
Authors: van Vugt Barry H. , Drenth W.
Published: September 2010

RhCl(PPh3)3 is used in the catalytic reaction between cyclohexene and oxygen in benzene at 30°. 2‐Cyclohexen‐1‐yl hydroperoxide is formed almost quantitatively. The reaction has an induction period during which the phosphine of the rapidly formed RhCl(PPh3)2.O2 is oxidized. The induction period is eliminated by addition of peroxide, which oxidizes the phosphine rapidly. Added Ph3P and phenols have inhibiting properties; they irreversibly change and deactivate the catalyst. Part of the rhodium is present in an esr‐active form, RhII.O−2. The reaction is zero order in O2 and of the order 1.42 in cyclohexene, while the order in Rh varies between 0.50 and 0.64.

All these observations as well as literature data are critically evaluated. They do not permit of a decision being made between a radical chain and a coordination‐sphere mechanism. Thus, the rather general belief that this reaction follows a radical chain path is not based on solid reasoning.
Photoreactions of aromatic compounds. XXXVI, Nucleophilic photosubstitution reactions of some derivatives of imidazole and pyrazole
Authors: Oldenhof C. , Cornelisse J.
Published: September 2010

Nucleophilic photosubstitution of nitro derivatives of 1‐methylimidazole and 1‐methylpyrazole strongly depends on the position of the nitro group. In the imidazole series the 5‐nitro compound is the most reactive isomer: photochemical replacement of the nitro group by cyano or methoxy proceeds in good yield, thus providing useful methods for the preparation of 5‐cyano‐ and 5‐methoxy‐1‐methylimidazole. Of the nitro‐substituted 1‐methylpyrazoles, the 3‐nitro derivative is the most reactive isomer: photocyanation yields equal amounts of 1‐methyl‐3‐nitro:4‐cyanopyrazole and 1 ‐methyl‐3‐nitrosopyrazole. Some of the reactions proceed by normal bimolecular aromatic photo‐substitution; others bear resemblance to the photoreactions of methoxy‐benzenes and ‐naphthalenes in which a cation radical is intermediate. Anodic cyanation of some derivatives of imidazole and pyrazole is also investigated.
Molecular‐mechanics and ‐dynamics simulations of trivalent europium complexes of calix[4]arene derivatives and a bislariat diazacrown ether
Authors: van Veggel Frank C. J. M. , Reinhoudt David N.
Published: September 2010

Molecular‐mechanics (MM) and molecular‐dynamics (MD) simulations (in MeOH) were performed on Eu3+ complexes of two derivatized calix[4]arenes (2b and 2d) and a bislariat diazacrown ether (3). The Quanta/CHARMm Lennard‐Jones parameters of Ca2+ proved suitable as a model for the Lennard‐Jones parameters of Eu3+. The radial distribution function (RDF) of Eu3+ … MeOH (O) agrees well with experimental data. The MD of 2b · Eu3+ showed that the phenolic oxygens cannot compete with the solvent, although they are preorganized. Three molecules of MeOH are within the first coordination shell. The MD of 2d · Eu3+ showed two transitions. After the first the Eu3+ was coordinated by one molecule of MeOH and after the second by three molecules of MeOH. The pyridine ring was not involved in coordination to Eu3+, which explained the measured lifetimes and derived coordination shells in methanol. The calculations on 3 · Eu3+ revealed that the conformation with the pendant arms in an anti configuration is unlikely to exist in solution, whereas the syn form calculated by MM rearranged to a structure with two molecules of MeOH in the first coordination sphere. This is consistent with experimental data, which show that the two dominant species in methanol solution have two molecules of MeOH coordinated to the Eu3+. All calculations were performed with the Quanta/CHARMm package.
Synthesis of nitroxide containing polyenes: Two chemically modified retinals and their interaction with bacterioopsin
Authors: Groesbeek M. , Lugtenburg J.
Published: September 2010

The synthesis and spectroscopic characterization of two retinal analogues is described, the paramagnetic 3‐pyrrolin‐1‐yloxy analogue 1 and its diamagnetic equivalent, the 3‐pyrroline analogue 2. Various aspects of the synthesis of the aminoxy group containing polyenes are discussed. Upon interaction with bacterioopsin, both 1 and 2 are incorporated in the protein and form a system with λmax 459 nm. Neither of the two bacteriorhodopsin analogues is photoactive. ESR spectroscopy data of the system containing 1 show that the ring part of the chromophore in the protein is rigidly fixed in orientation.
Reactivity and regioselectivity in the reaction of allylsilanes and some analogous all‐carbon alkenes with sulfur trioxide
Authors: Cerfontain Hans , Kramer Johannes B. , Schonk Ruud M. , Bakker Bert H.
Published: September 2010

Sulfonations of the 1‐(trimethylsilyl)alk‐2‐enes 1a‐12a, the 1‐(trimethylsilyl)‐ω‐phenyl‐alk‐2‐enes 13a–18a, the triisopropylsilylalk‐2‐enes 19a–21a, 1‐(trimethylsilyl)penta‐2,4‐diene (22a), and the allylsilane 23a with sulfur trioxide were studied in the temperature range ‐60 to 25°C using dichloromethane‐d2 as solvent and 1.5 mol‐equiv. of dioxane‐d8 relative to the amount of SO3 as reactivity moderator. For comparison, the sulfonation of the all carbon analogues 24a–27a were also studied. Reaction of the 1‐(trialkylsilyl)alk‐2‐enes 1a–11a and 13a–17a with SO3 at −60°C all afford the corresponding trialkylsilyl‐alk‐1‐ene‐3‐sulfonate esters c within 20 min in yields of > 95%. 1‐(Trimethylsilyl)‐2‐cycloheptylideneethane (12a) at −60°C gives a mixture of the trimethylsilyl sulfonate ester 12c and the isomeric 1‐(trimethylsilyl)‐2‐(1‐cycloheptenyl)ethane‐2‐sulfonic acid (12f) in a molar ratio of 4:6. With 1‐(trimethylsilyl)‐2‐(1,2,3,4‐tetrahydro‐1‐naphthylidene)‐ ethane (18a) the exclusive product is 1‐(trimethylsilyl)‐2‐(3,4‐dihydro‐1‐naphthyl)ethane‐2‐sulfonic acid (18f). Direct NMR evidence for the formation of β‐sultones as initial intermediates was observed in the sulfonation of the 1‐(trimethylsilyl)‐2‐cycloalkylideneethanes 11a and 12a. Upon sulfonation of the 1‐(triisopropylsilyl)‐alk‐2‐enes 19a–21a at — 60°C the initial products are the β‐sultone 20b‐II and the carbyl sulfates 19h‐II and 21h–II, of which the relative yields depend on the amount of SO3 employed. The SO3 sulfonation of 1‐(trimethylsilyl)penta‐2,4‐diene (22a) gives trimethylsilyl penta‐1,3‐diene‐5‐sulfonate (22i). The three homologous non‐silicon containing 1‐ cycloalkylidenehexanes 24a–26a at — 60°C afford the respective 1‐cycloalkylhexane‐1,1′‐sultones 24b‐III–26b‐III which, at higher temperatures, isomerize to give the 1‐(cycloalk‐1′‐enyl)hexane‐1‐ sulfonic acids 24m–26m. 1‐Methylene‐1,2,3,4‐tetrahydronaphthalene (27a) reacts with SO3 at −60°C to give (3,4‐dihydro‐1‐naphthyl)methanesulfonic acid (27o). Treatment of the various products containing a trialkylsilyl sulfonate ester substituent with aqueous KOH gives quantitatively the corresponding potassium sulfonate salts.

Mechanisms for the formation of the various products are suggested and the observed selectivities are discussed.
The lowest triplet state of tetradecahexaenal
Authors: Kok Peter , Groenen Edgar J. J.
Published: September 2010

The lowest triplet state, T0, of all‐trans‐tetradecahexaenal has been investigated by means of electron‐spin‐echo spectroscopy in a magnetic field and in zero field. The directions of the principal axes and the eigenvalues of the fine‐structure tensor have been determined. The triplet state corresponds to a π π* excitation. In zero field, T0 is populated predominantly through the upper spin sublevel which is found to decay fastest. Comparison of the relative energies and the decay rates of the sublevels of T0 with those obtained previously for shorter polyenals reveals that both the zero‐field splitting and the logarithm of the decay rates are inversely proportional to the total number of double bonds.
Excited‐state intramolecular charge transfer in donor/acceptor‐substituted aromatic hydrocarbons and in biaryls. The significance of the redox potentials of the D/A subsystems
Authors: von Der Haar Thomas , Hebecker Axel , Il'Ichev Yurii , Jiang Yun‐Bao , Kühnle Wolfgang , Zachariasse Klaas A.
Published: September 2010

The energy of the charge transfer (CT) emission maximum of a series of dual fluorescent 4‐aminobenzonitriles in diethyl ether and acetonitrile does not show a correlation with the redox potentials of the amino (D) and benzonitrile (A) subgroups. It is therefore concluded that these electron donor and acceptor subgroups cannot be treated in the same way as the A and D molecules in exciplexes1(A−D+). This means that in the intramolecular charge transfer (ICT) state of the aminobenzonitriles, a considerable electronic coupling between the A−and D+parts exists, in contradiction with the twisted intramolecular charge transfer (TICT) hypothesis. For 9,9′‐bianthryl, 10‐cyano‐9,9′‐bianthryl and 10,10′‐dicyano‐9,9′‐bianthryl, photostationary and time‐resolved measurements are presented, which show that the influence of the cyano substituents on the ICT reaction in the excited state can be understood by considering the redox potentials of the anthryl groups. The introduction of an additional cyano group in an aminobenzonitrile, however, leads to the disappearance of ICT and dual fluorescence, indicating that the photophysics of these molecules cannot be understood on the basis of the redox potentials of the D and A constituents.
Selectivity in the direction of photoisomerization reactions in liquid‐crystalline guest‐host systems
Authors: Meier Herbert , Lifka Thorsten , Müller Klaus
Published: September 2010

E ⇄ Z photoisomerization reactions of stilbenes la‐c were studied in liquid‐crystalline (LC) phases and in the corresponding isotropic melts. Whereas viscosity has a moderate influence on the photostationary states, a strong effect caused by the regular incorporation of the stilbene molecules in the LC phases was observed. The direction of the isomerization can be reversed, up to the case of a one‐way isomerization Z → E for the tailored guest‐host system 1b/BS. Such an LC‐matrix effect is of typical highly ordered (smectic) phases with free volumina which are strictly limited by hydrophobic interactions; it could not be detected in a much more mobile nematic phase. Textures based on the birefringence of doped LC phases, differential‐scanning‐calorimetry (DSC) measurements and phase‐dependent absorption spectra were used for the interpretation.
Stereochemical features of meta photocycloadducts derived from 3‐alkyl‐4‐phenoxybut‐1‐enes
Authors: van der Eycken Erik , de Keukeleire Denis , de Bruyn André , van der Eycken Johan , Gilbert Andrew
Published: September 2010

3‐Alkyl‐4‐phenoxybut‐1‐enes (alkyl: methyl, isopropyl, tert‐butyl) on excitation at 254 nm in cyclohexane give rise to 4‐alkyl‐2‐oxatetracyclo[5.4.0.01,8.05,11]undec‐ 9‐enes via intramolecular meta photocycloaddition. Prevailing stereochemical features are the configuration of the alkyl group at C‐4 and the conformation of the tetrahydropyran ring contained in the tetracyclic system. These are revealed by detailed 1H‐NMR analysis and interpretation of the coupling constants. Whereas the alkyl group at C‐4 invariably occurs in the exo configuration, the conformation of the tetrahydropyran ring depends on the bulkiness of the alkyl substituent. Thus, the C‐4 methyl group occupies an equatorial position in a chair conformation, while a flattened chair conformation accomodates appropriately the C‐4 isopropyl group in the pertaining structure. The required equatorial position of the tert‐butyl group at C‐4, on the other hand, forces the tetrahydropyran ring into a boat conformation, thereby alleviating steric constraints.
Photoaddition reactions of 1,3‐dioxin‐4‐ones
Authors: Graalfs Heiner , Mattay Jochen
Published: September 2010

Irradiation of 1,3‐dioxin‐4‐ones having l‐menthone as a chiral auxiliary in the 2‐position in 1,3‐dioxolane and oxolane, respectively, affords adducts with good facial selectivities. The benzophenone‐initiated photoaddition of isopropanol is also investigated.
Photochemical rearrangement of 2‐(N‐allyl‐N‐alkylamino)cyclohex‐2‐enones
Authors: Meyer Catherine , Pete Jean‐Pierre , Piva Olivier
Published: September 2010

Irradiation at 366 nm of 2‐(N‐allyl‐N‐alkylamino)cyclohex‐2‐enones led, surprisingly, to very unstable 1‐azaspiro[2.5]octan‐4‐ones rather than to the expected [2 + 2] intramolecular photo‐cycloaddition. The corresponding alcohols could be isolated in good yield by reduction of the crude reaction mixture. When the reaction was carried out in a mixture of acetone/D2O (9/1), incorporation of one deuterium atom was observed. The proposed mechanism involves an intramolecular γ‐H abstraction in the primary step, followed by the molecular rearrangement of a 7‐azabicyclo[4.2.0]octan‐1‐ol intermediate.
Kinetic salt effects in the quenching of the excited state of the tris(2,2′‐bipyridine)ruthenium(II) complex by 2‐methylanthraquinone
Authors: Frank Rudolf , Rau Hermann
Published: September 2010

In the title system, quenching rate constants kq were determined as a function of c(Et4NClO4), c(NaClO4), and c(LiClO4) in acetonitrile solution. A general and a specific salt effect on kq can be distinguished. The 2‐methylanthraquinone radical anion produced by the photoinduced electron transfer forms strong associates with Na+ and even stronger ones with Li+, the formation constants of these complexes being determined from electrochemical measurements. Transient absorption spectra of the methylanthraquinone radical anion and of its associates with Na+ and Li+ are presented. The rate constant of the electron transfer step could be determined in selected systems and effΔG° values of the electron transfer step were developed. Apparent activation parameters ΔH≠, ΔS≠, and ΔG≠ were determined from the kq data. The negative values of ΔH≠ can be rationalized by the mechanism of the photoinduced electron transfer reaction. The back electron transfer in the successor complex to the ground state molecules shows Marcus‐inverted behaviour.
Role of an electron‐transfer chain reaction in the unusual photochemical formation of five‐coordinated anions [Mn(CO)3(α‐diimine)]− from fac‐[Mn(X)(CO)3(α‐diimine)] (X = halide) at low temperatures
Authors: Hartl František , Rossenaar Brenda D. , Stor Gerard J. , Stufkens Derk J.
Published: September 2010

The 16e− radicals [Mn(CO)3(α‐diimine)] are the key transients in the complex mechanism of formation of five‐coordinated anions [Mn(CO)3(α‐diimine)]− in 2‐MeTHF at 135K by visible excitation of the complexes fac‐[Mn(X)(CO)3(α‐diimine)] [X = halide; α‐diimine = 2,2′‐ bipyridine (bpy), pyridine‐2‐carbaldehyde N‐isopropylimine (iPr‐PyCa), and pyridine‐2‐carbaldehyde N‐p‐tolylimine (pTol‐PyCa)] into their low‐energy MLCT/XLCT transitions. This article describes the as yet unresolved electron‐transfer step in the mechanism which converts the radicals [Mn(CO)3(α‐diimine)] into the corresponding anions. Cyclic voltammetry and IR spectroelectro‐chemistry in optically transparent thin‐layer electrochemical cells were employed at variable temperatures in order to study the temperature‐dependent stability of the radicals [Mn(CO)3(α‐diimine)], their redox properties and their interaction with a coordinating solvent (Sv) to give the 18e− adducts fac‐[Mn(Sv)(CO)3(α‐diimine)]. The latter radicals are strong reductors capable of electron transfer to their five‐coordinated precursors which are quite stable at temperatures below 220K. This behaviour was demonstrated in the complex fac‐[Mn(Cl)(CO)3(bpy)] and the related complexes fac‐[Mn(Br)(CO)3(iPr‐DAB)] and fac‐[Mn(PrCN)(CO)3(iPr‐DAB)]+(PrCN = n‐ butyronitrile; iPr‐DAB = N, N′‐diisopropyl‐1,4‐diaza‐1,3‐butadiene

Chem. Abstracts name: N, N′‐diisopropyl‐ethane‐1,2 diimine (iPr‐ED)

which were used as reference. The (spectro)electrochemical results have revealed that the formation of [Mn(CO)3(α‐diimine)]− in the course of the above photoreaction is most probably accompanied by parallel generation of the cations fac‐[Mn(Sv)(CO)3(α‐diimine)]+. The cations in turn react back with the free halide to give the starting complex fac‐[Mn(X)(CO)3(α‐diimine)], thereby closing the catalytic cycle. The overall mechanism of the formation of [Mn(CO)3(α‐diimine)]− from the neutral Mn(halide) complexes can therefore be viewed as a photo‐assisted/ETC reaction. No anions [Mn(CO)3(α‐diimine)]− are formed in the presence of excess PR3 which is reasonably ascribed to a complete conversion of the 16e− transients [Mn(CO)3(α‐diimine)] into the stable 18e− adducts fac‐[Mn(PR3)(CO)3(α‐diimine)], the final photoproducts observed in this case.
Photolytic behaviour of tricarbonyl[(1,2,5,6‐η)‐cycloocta‐1,5‐diene]iron in solution and low‐temperature matrices
Authors: Grevels Friedrich‐Wilhelm , Klotzbücher Werner E. , Russell Graham , Schaffner Kurt
Published: September 2010

The photo‐induced isomerization of Fe(CO)3[(1,2,5,6‐η)‐1,5‐COD] (1) yields Fe(CO)3[(1,2,3,4‐η)‐1,3‐COD] (2) with a quantum yield of Φ 0.04 ± 0.005 (λexc 405 nm). Photolysis of 1 in low‐temperature matrices generates the fragment Fe(CO)2[(1,2,5,6‐η)‐1,5‐COD] (3) as the only primary photoproduct observed by conventional IR spectroscopy. The species 3 is also produced upon laser‐flash photolysis (λexc 308 nm) of 1 in solution at ambient temperature, as detected by time‐resolved IR spectroscopy. Accordingly, 12CO/ 13CO exchange occurs upon photolysis of 1 in the presence of 13CO. However, the isomerized complex 2 is initially formed without 13CO incorporation, thus discounting the possible involvement of the dicarbonyl fragment 3 in this process. It is concluded that photolytic generation of the de‐chelated species Fe(CO)3[(1,2‐η)‐1,5‐COD)] (4) is the initial step in the photo‐induced isomerization of 1 to 2.
The dipolar 1,3 cycloaddition of C,N‐dialkylnitrone to olefins with hydroxyl group and the derivatives
Authors: Naito Takeaki , Shirakawa Mitsuko , Ikai Miho , Ninomiya Ichiya , Kiguchi Toshiko
Published: September 2010

The reaction rate and stereoselectivity of intermolecular dipolar 1,3 cycloaddition of the C,N‐dialkylnitrone to olefins with hydroxyl groups and their derivatives were found to depend upon the type of hydroxyl group. The rate is accelerated in the order: magnesium alkoxide (OMgBr); free hydroxyl group (OH); ether (OR). Selectivities are improved moderately when magnesium alkoxide is used.
Synthesis and Diels‐Alder reaction of 5β‐methyl‐β‐dihydrothebaine and its 6‐demethoxy analogue (chemistry of opium alkaloids, Part XLII)
Authors: de Grauw M. , Muller E. F. , Woudenberg R. H. , Maat L.
Published: September 2010

The scission of the 4,5α‐epoxy bridge of 5β‐methylthebaine (2) and 5β‐methyl‐6‐demethoxythebaine (5), yielded 5β‐methyl‐β‐dihydrothebaine (4) and 5β‐methyl‐6‐demethoxy‐β‐dihydrothebaine (6), respectively. The scission was carried out by zinc reduction in a potassium hydroxide solution. It took place with retention of the 6,8‐diene system and the configuration at the C‐5 atom. To perform the Diels‐Alder reaction on 4, the hydroxyl substituent at C‐4 had to be protected with a phenyl group, yielding 5β‐methyl‐4‐O‐phenyl‐β‐dihydrothebaine (7). The Diels‐Alder reaction of 7 was carried out in boiling ethyl propenoate for three weeks. Two 6β,14β‐ethenomorphinans (8 and 9) were obtained. For the Diels‐Alder reaction of 6 no protection of the hydroxyl substituent at C‐4 was necessary. Cycloaddition gave after one day two 6β,14β‐ethenomorphinans (10 and 11).
Synthesis and characterization of a novel macrocyclic ligand containing nine donor atoms
Authors: Giovenzana G. B. , Jommi G. , Pagliarin R. , Sisti M. , Aime S. , Botta M. , Crich S. Geninatti
Published: September 2010

The synthesis of a novel macrocyclic ligand containing nine potential coordination sites (six nitrogens and three oxygens) formed by a triazacyclododecane ring trisubstituted with CH2CH2N(CH2Ph)CH2COOH groups is reported. The protonation scheme of this ligand has been elucidated by measuring the proton NMR shifts of the various methylenic resonances upon changing the pH of the solution. This ligand affords stable metal complexes with Cd2+ ion, whose 1H‐ and 13C‐NMR spectra suggest a remarkable kinetic inertia and stereochemical rigidity.
Reaction of D‐fructose, D‐glucose and inulin with alcohols in the presence of iodine; a novel glycosidation procedure
Authors: Verhart Cor G. J. , Fransen Carel T. M. , Zwanenburg Binne , Chittenden Gordon J. F.
Published: September 2010

An efficient procedure for the glycosidation of D‐fructose and D‐glucose catalyzed by iodine is described. The reaction yields mainly alkyl glycofuranosides. Treatment of inulin under similar conditions leads to inter‐glycosidic bond cleavage and to formation of alkyl D‐fructofuranosides. The reaction conditions are particularly mild and relatively selective.
Asymmetric induction in kinetically controlled zirconium‐catalysed Meerwein‐Ponndorf‐Verley reductions
Authors: Krohn Karsten , Knauer Birgit
Published: September 2010

Twelve chiral ligands 718 were tested in the new kinetically controlled variation of zirconium alkoxide catalysed Meerwein‐Ponndorf‐Verley reduction of 2′‐chloroacetophenone (2) using rac‐4 as the reducing alcohol (Scheme 3). The tetraaryl‐1,3‐dioxolanes 11 (ca. 30% enantiomeric excess, ee) and the triphenylethanediol 14 (62% ee, 99% yield) gave the best results. A relatively low dependence on the amount of the catalyst (aluminum alkoxide gave no asymmetric induction) and the ligand excess was observed compared with a very high dependence on incubation time of Zr(OtBu)4 with the chiral ligand 14 and also on the reaction temperature.
Synthesis and properties of a series of strained [2.2]paracyclophane‐4,15‐disulfonimides
Authors: van Lindert Helen C. A. , van Doorn Johannes A. , Bakker Bert H. , Cerfontain Hans
Published: September 2010

The series of N‐alkyl‐, N‐cycloalkyl‐, N‐allyl‐, N‐benzyl‐, and N‐phenyl‐[2.2]paracyclophane‐4,15‐disulfonimides 4b − 4m was synthesized, starting from [2.2]paracyclophane ([2.2]PCP) (1). The initial step is sulfonation of 1 with chlorosulfuric acid to give [2.2]PCP‐4,15‐disulfonic anhydride (2) in 97% yield. Subsequent reaction of 2 with the appropiate primary amine quantitatively affords the corresponding alkylammonium 4‐(alkylsulfamoyl)[2.2]PCP‐15‐sulfonate salt (3) which, upon treatment with phosphoric anhydride in dichloromethane, gives the corresponding N‐alkyl[2.2]PCP‐4,15‐disulfonimide 4 in yields up to 56%. The parent [2.2]PCP‐4,15‐disulfonimide (4a) was obtained by pyrolysis of N‐isopropyl‐ (4d), N‐cyclopentyl‐ (4h), and N‐cyclohexyl[2.2]PCP‐4,15‐disulfonimide (4i) at 200°C for 20 min in almost quantitative yields with simultaneous expulsion of the corresponding alkene.

As determined by X‐ray analysis, the distances between the two p‐phenylene rings are the same for the 4,15‐disulfonimide 4a and the corresponding 4,15‐disulfonic anhydride 2, but they are both significantly different from those of the N‐isopropyl derivative 4d. The sum of the three bond angles around N is ≈︁ 5° smaller for 4d than 4a as result of non‐bonded interaction between the methyls of the isopropyl and the neighbouring sulfonyl oxygens. Evidence for non‐bonded interaction was also obtained from dynamic 1H‐NMR studies on the N‐cyclohexyl and N‐phenyl derivatives 4i and 4l, the barrier of rotation around the C‐N bond of 4l at 353K, i.e. the temperature of coalescence, being 71 kJ.mol−1.

Pyrolysis of crystals of N‐isopropyl‐, N‐cyclopentyl‐ and N‐cyclohexyl‐[2.2]PCP‐4,15‐disulfonimide (4d, 4h and 4i) in an argon or nitrogen atmosphere at 200‐210°C for 20 min leads to the formation of [2.2]PCP‐4,15‐disulfonimide (4a) in yields of > 95% under the simultaneous expulsion of the corresponding alkene. Under the same conditions the corresponding N‐propyl, N‐cyclopropyl and N‐allyl derivatives 4c, 4e and 4f were found to be stable.

The homogeneous thermolysis of the N‐alkyl[2.2]PCP‐4,15‐disulfonimides 4c − 4i in DMSO as solvent, leading to the formation of [2.2]PCP‐4,15‐disulfonimide (4a), was studied quantitatively and appeared to exhibit first order kinetics. At 105‐150°C, the first order rate coefficients decrease in the order N‐cyclopentyl (4h) > N‐cyclohexyl (4i) > N‐isopropyl (4d) >> N‐allyl (4f) >> N‐propyl (4c); the N‐cyclopropyl derivative 4e does not yield any disulfonimide 4a. The mechanism of the thermolysis of the N‐alkyl[2.2]PCP‐4,15‐disulfonimides is discussed, and the differences in rate are explained in terms of (i) differences in the C(α)‐H bond strengths of the N‐alkyl moiety and (ii) relief of steric strain for the intramolecularly overcrowded disulfonimides 4d, 4h and 4i.
Electron transfer as a possible initial step in nucleophilic addition elimination reactions between (radical) anions and carbonyl compounds in the gas phase
Authors: Staneke Paul O. , Ingemann Steen , Nibbering Nico M. M.
Published: September 2010

The reactions of the HO−, CH3S−, CH2S− and CH2  C(CH3)CH2− ions with three ketones (CF3COR; R  CH3, CF3, C6H5) and three esters of trifluoroacetic acid (CF3CO2R; R  CH3, C2H5 and C6H5) have been studied with use of Fourier Transform Ion Cyclotron Resonance (FT‐ICR) mass spectrometry. All four negative ions react exclusively by proton transfer with CF3COCH3. With the other substrates, the HO− ion reacts by various pathways, such as proton transfer, SN2 substitution, E2 elimination and attack on the carbonyl group. The CH3S− ion is unreactive towards CF3COC6H5 but is able to react by hydride transfer, SN2, E2 and/or carbonyl attack with the remaining neutral species. The CH2S− radical anion reacts by electron transfer to afford stable molecular radical anions of CF3COCF3 and CF3COC6H5, whereas the main reaction with the two esters, CF3CO2CH3 and CF3CO2C2H5, is dissociative electron transfer leading to CF3CO2− and CF3− ions. The CH2C(CH3)CH2− anion displays a more complex reactivity pattern involving electron transfer, SN2, E2 as well as attack on the carbonyl group. Direct evidence for the occurrence of electron transfer as the initial step in an overall BAC2 type process has not been obtained for the systems studied. The reaction of the CH2S− ion with CF3CO2C6H5 was observed, however, to yield exclusively a CF3COCHS−. radical anion. Based upon the absence of a BAC2 process in the reaction of CH2S− with the methyl and ethyl esters of trifluoroacetic acid in combination with the facile occurrence of electron transfer from this radical anion, it is suggested that the CF3COCHS−. ion is formed by an initial electron transfer followed by coupling between the CH2S molecule and the CF3CO2C6H5− radical anion and subsequent loss of C6H5OH from the collision complex.
Ring expansion of norpenicillin to 3‐norcephalosporin
Authors: van der Klein Pieter A. M. , Castelijns Judith , Hirs Hans G. J. , Verweij Jan , de Vroom Erik
Published: September 2010

The Morin ring expansion of penicillin 1‐oxides to cephalosporins has been extended to norpenicillin 1‐oxides. To this end, both the norpenicillin sulfoxide moiety and the methyl group should be β‐oriented. Norpenicillin 1‐oxides are prepared from properly protected exomethylene penam derivatives using hydrogen on palladium/carbon and oxidation with 3‐chloroperoxybenzoic acid or peroxyacetic acid.
Metal‐binding affinity of a series of bis(2‐pyridylalkyl)amines immobilized on silica
Authors: Hoorn H.J. , de Joode P. , Driessen W.L. , Reedijk J.
Published: September 2010

Four potentially tridentate bis(2‐pyridylalkyl)amines, differing in the number of methylene groups in the alkyl chain, have been coupled to the epoxy‐containing bifunctional spacer (3‐glycidoxypropyl)trimethoxysilane (GLYMO) and subsequently grafted onto silica. These ion exchangers were characterized by solid‐state CP‐MAS 13C‐NMR and elemental analyses. The obtained ligand concentrations varied from 0.29‐0.63 mmol/g ion exchanger. With the only exception of Alfa‐GLYMO‐bis(2‐pyridyl)amine, which showed a very low capacity for any of the metal ions tested, these ion‐exchange materials selectively absorbed Cu2+, with a maximum capacity of 0.22‐0.59 mmol/g ion exchanger at pH 5.6, from aqueous solutions containing a mixture of the divalent metal ions Cu2+, Ni2+, Co2+, Cd2+ and Zn2+. The metal‐uptake capacities and distribution coefficients established at different pH, correlate with the length of the alkyl bridge in the chelating ligand. The longer the alkyl spacer the lower the capacity and the metal‐ligand complex stability at lower pH. The use of strong chelating tridentate N‐donor ligands greatly increases the ligand occupation by metal ions. The Cu2+ uptake varies strongly with pH in the case of Alfa‐GLYMO‐bis[2‐(2‐pyridyl) ethyl]amine.