Distribution by Scientific Domains
Distribution within Chemistry

Kinds of C2

  • group c2
  • monoclinic space group c2
  • new c2
  • novel c2
  • space group c2

  • Terms modified by C2

  • c2 domain
  • c2 level
  • c2 monitoring
  • c2 symmetry

  • Selected Abstracts

    Laser plasma plume kinetic spectroscopy of the nitrogen and carbon species

    Z. Zelinger
    Abstract The formation and decay of carbon and nitrogen atoms, CN radicals and C2 molecules were monitored using spatial- and time-resolved emission spectroscopy in a plasma plume formed during laser ablation of a graphite target in nitrogen atmosphere. A simple exponential model was used to explain the effect of the individual chemical reactions and plasma dynamics on the measured kinetic characteristics. The succession of emissions C , N , CN was observed in the time-resolved spectra, supporting the suggestion that the CN radical is formed mainly by the direct reaction C + N , CN or C2 + N2 , 2CN. The formation of CN radical was enhanced by the additional generation of atomic nitrogen through the RF discharge. ( 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Synthesis and crystal structure determination of 6,7-dihydro-2-methoxy-4-(substituted)-5H -benzo[6,7]cyclohepta[1,2- b ]pyridine-3-carbonitrile

    A. M. Moustafa
    Abstract The compounds 6,7-dihydro-2-methoxy-4-(4-methylphenyl)-5H -benzo[6.7]cyclohepta[1,2 -b ]pyridine-3-carbonitrile (compound IIIa) and 4-(4-chlorophenyl)-6,7-dihydro-2-methoxy-5H -benzo[6,7]cyclohepta[1,2- b ]pyridine-3-carbonitrile (compound IIIb) were synthesized and their structures have been determined from three dimensional X-ray data using direct method and refined by full matrix least squares with anisotropic thermal parameters for non-hydrogen atoms to conventional R(gt) of 0.036 and 0.038 for the two compounds respectively. For compound (IIIa) the crystals are monoclinic, space group Cc, with a=11.2909 (5) , b=17.7755(8) , c=9.1437(4) and ,=95.428(3), while the crystals of the second compound (IIIb) are triclinic, space group P1, with a=8.7465(3), b=10.3958(3), c=10.9011(4), ,= 108.3870(10), ,=101.3741(12), ,=97.9594(12). The molecular structure of the two compounds have nearly the same configuration, where the cyclohepta ring takes the boat shape and the methoxy and the carbonitrile groups are attached at the same position C2 and C8. The difference occurs only at the position C4, where the substituent is methylphenyl for compound (IIIa) and chlorophenyl for the other. The bond lengths, valency angles and the hydrogen bonding were calculated and fully discussed. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    An audit of ,equivocal' (C3) and ,suspicious' (C4) categories in fine needle aspiration cytology of the breast

    CYTOPATHOLOGY, Issue 4 2001
    R. A. Deb
    An audit of ,equivocal' (C3) and ,suspicious' (C4) categories in fine needle aspiration cytology of the breast We have audited the frequency of use and outcome of the ,equivocal/atypia probably benign' (C3) and ,suspicious of malignancy' (C4) category for breast cytology in our Unit. A total of 14 935 cytological specimens were reported by at least one of the three pathologists with a special interest in breast pathology, according to five categories of the NHSBSP guidelines for cytology reporting, 1992; 3.7% (555 cases) and 3.9% (587 cases) of cases were classified as equivocal (C3) and suspicious (C4), respectively, giving a total rate (C3 + C4) of 7.6%. Of the C3 cases, 68% were subsequently benign and 32% were malignant. Of the C4 cases, 19% were subsequently benign and 81% malignant. The commonest benign lesions in both categories were fibroadenomas (7.6% of C3 and 19.8% of C4), fibrocystic change (14.3% of C3 and 12.5% of C4), radial scars (6.2% of C3 and 10.4% of C4) and papillomas (6.2% of C3 and 6.3% of C4). Of the malignant lesions (particularly those classified as C3), a high proportion were low grade or special type cancers. The categories of atypia probably benign (C3) and suspicious of malignancy (C4) in breast cytology provide a strategy for classification of problematic or uncertain cases; this maintains the predictive value of the benign (C2) and malignant (C5) categories, and allows separation of these difficult cases into clinically useful groups with differing probabilities of malignancy. [source]

    Insulin-like growth factors, hepatocyte growth factor and transforming growth factor-, in mouse tongue myogenesis

    Akira Yamane
    Many reports have shown that tongue striated muscles have several unique characteristics not found in other skeletal muscles such as limb and trunk. Several peptide growth factors are reported to play important roles in skeletal myogenesis. In this article, the roles of insulin-like growth factors (IGF), hepatocyte growth factor (HGF) and transforming growth factor (TGF)-, in mouse tongue myogenesis were studied using an organ culture system of the mandible or tongue obtained from mouse embryos. It was found that IGF-I promotes the differentiation of tongue myoblasts. HGF plays an essential role in the migration and proliferation of tongue myogenic cells, and inhibits the differentiation of tongue myoblasts. TGF-, does not play an essential role in the proliferation of tongue myogenic cells, but does promote the early differentiation of tongue myoblasts. The role of IGF-I in the differentiation of tongue myoblasts, and that of HGF in the migration, proliferation and differentiation of tongue myogenic cells appear to be almost identical to their roles in the myogenesis of limb and cultured myogenic cell lines. However, the role of TGF-, in the proliferation and differentiation of tongue myogenic cells appears to be different from its role in the myogenesis of limb and cultured myogenic cell lines such as C2 and L6. [source]

    Subclinical vascular alterations in young adults with type 1 diabetes detected by arterial tonometry

    I. Barchetta
    Abstract Background Diabetes mellitus is characterized by a very high prevalence of atherosclerotic disease. Aims of this study were to determine arterial compliance parameters in type 1 diabetes (T1D) patients as an expression of early pre-clinical endothelial dysfunction and to evaluate the impact of glucose exposure parameters such as the duration of diabetes and glycosylated haemoglobin (HbA1c) on the risk of developing alterations in vascular compliance. Methods 23 patients with uncomplicated type 1 diabetes (mean age: 32.78 9.06 years, mean disease duration: 10.78 7.51 years, mean HbA1c levels: 7.7 1.9) and 26 age- and sex-matched healthy subjects (mean age: 32.3 8.51 years) were recruited. In these subjects, we evaluated arterial compliance by calibrated tonometry (HDI/Pulsewave CR-2000). Parameters included the following: large artery elasticity (C1), small artery elasticity (C2), systemic vascular resistance (SVR) and total vascular impedance (TVI). Results Patients with longer duration of T1D (>10 years) showed significant alterations in C2 (4.97 2.7 mL/mmHg 100) and in SVR (1464.67 169.16 dina s cm,5) when compared with both healthy individuals (C2: 8.28 2.67 mL/mmHg 100, p = 0.001; SVR: 1180.58 151.55 dina s cm,5, p = 0.01) and patients with recent-onset disease (,10 years) (C2: 10.02 3.6 mL/mmHg 100, p < 0.001; SVR: 1124.18 178.5 dina s cm,5, p < 0.000). Both disease duration and HbA1c independently predicted impaired arterial compliance. Conclusions Young adult T1D patients with no signs of disease complication have detectable vessel wall abnormalities, particularly of small arteries, suggestive of hyperglycaemia-related early endothelial dysfunction. Copyright 2009 John Wiley & Sons, Ltd. [source]

    The Auxiliary Substrate Concept: From simple considerations to heuristically valuable knowledge

    Wolfgang Babel
    Abstract Microorganisms are used in biotechnology. They are either (i) aim and purpose of a process, e.g. with the production of single cell proteins, or (ii) mean to an end insofar as they serve as a catalyst or "factory" for syntheses (e.g. of products of primary and secondary metabolism, of enzymes and antibiotics) or for the degradation and detoxification of harmful organics and inorganics. In all cases, the efficiency and velocity, finally the productivity, are parameters which essentially determine the economy of the processes. Therefore, search for approaches to optimize these processes is a permanent task and challenge for scientists and engineers. It is shown that the auxiliary substrate concept is suitable to increase the yield coefficients. It is based on the energetic evaluation of organics, on the knowledge that organics as sources of carbon and energy for growth are deficient in ATP and/or reducing equivalents, and says that it is possible to improve the carbon conversion efficiency up to the carbon metabolism determined upper limit. The latter is determined by inevitable losses of carbon along the way of assimilation and anabolism and amounts to about 85% for so-called glycolytic substrates, e.g. glucose, methanol, and to about 75% for gluconeogenetic substrates, e.g. C2 -substrates (acetic acid, hexadecane). The approach is explained and some experimental examples are presented. By simultaneous utilization of an extra energy source (auxiliary substrate) the yield coefficient can be increased (i) in glucose from about 0.5 to 0.7,g/g (by means of formate), (ii) in acetate from 0.34,0.4 to 0.5,0.65,g/g (by means of formate and thiosulfate, respectively), and (iii) in hexadecane from about 0.94 to 1.26,g/g (by means of formate). The precalculated yield coefficients and mixing ratios agree well with the experimentally attained ones. The approach is easily feasible and economically valuable. [source]

    The Prestige oil spill.


    Abstract In vitro biodegradation of the Prestige heavy fuel oil has been carried out using two microbial consortia obtained by enrichment in different substrates to simulate its environmental fate and potential utility for bioremediation. Different conditions, such as incubation time (i.e., 20 or 40 d), oil weathering, and addition of an oleophilic fertilizer (S200), were evaluated. Weathering slowed down the degradation of the fuel oil, probably because of the loss of lower and more labile components, but the addition of S200 enhanced significantly the extension of the biodegradation. n -Alkanes, alkylcyclohexanes, alkylbenzenes, and the two- to three-ring polycyclic aromatic hydrocarbons (PAHs) were degraded in 20 or 40 d of incubation of the original oil, whereas the biodegradation efficiency decreased for higher PAHs and with the increase of alkylation. Molecular markers were degraded according to the following sequence: Acyclic isoprenoids < diasteranes < C27 -steranes < ,,-steranes < homohopanes < monoaromatic steranes < triaromatic steranes. Isomeric selectivity was observed within the C1 - and C2 -phenanthrenes, dibenzothiophenes, pyrenes, and chrysenes, providing source and weathering indices for the characterization of the heavy oil spill. Acyclic isoprenoids, C27 -steranes, C1 - and C2 -naphthalenes, phenanthrenes, and dibenzothiophenes were degraded completely when S200 was used. The ratios of the C2 - and C3 -alkyl homologues of fluoranthene/pyrene and chrysene/benzo[a]anthracene are proposed as source ratios in moderately degraded oils. The 4-methylpyrene and 3-methylchrysene were refractory enough to serve as conserved internal markers in assessing the degradation of the aromatic fraction in a manner similar to that of hopane, as used for the aliphatic fraction. [source]

    Anaerobic transformation of compounds of technical toxaphene.


    Abstract Technical toxaphene (Melipax) and the single compounds of technical toxaphene (CTTs) 2,2,5- endo, 6- exo, 8,8,9,10- octachlorobornane (B8-806), 2,2,5- endo, 6- exo, 8,9,9,10-octachlorobornane (B8-809), 2,2,5,5,8,9,9,10,10-nonachlorobornane (B9- 1025), 2- endo, 3- exo, 5- endo, 6- exo, 8,8,9,10,10-nonochlorobornane (B9-1679), 2- endo, 3- exo, 5- endo, 6- exo, 8,9,10,10-octachlorobornane (B8-1414), 2- endo, 3- exo, 5- endo, 6- exo, 8,8,9,10-octachlorobornane (B8-1412), and 2- exo, 3- endo, 5- exo, 9,9,10,10-heptachlorobornane (B7-1453) were treated with suspensions of the anaerobic bacterium Dehalospirillum multivorans. After 7 d, more than 50% of technical toxaphene was transformed, and the relative amount of early eluting CTTs increased. After 16 d, only 2- exo, 3- endo, 6- exo, 8,9,10-hexachlorobornane (B6-923), 2- endo, 3- exo, 5- endo, 6- exo, 8,9,10-heptachlorobornane (B7-1001), and a few minor penta- and hexachloro-CTTs were detected in the samples. The result of the transformation was comparable with observations in naturally contaminated sediments and soil. However, the performance with D. multivorans was more simple and reproducible, as well as faster, than use of soil, sediment, or anaerobic sewage sludge. In agreement with reports in the literature, reductive dechlorination at geminal chlorine atoms (gem -Cls) was found to be the major CTT transformation pathway. Experiments conducted with CTTs and gem -Cls at both primary and secondary carbons clarified that the initial Cl -> H substitution takes place at the secondary carbon C2. Furthermore, the 2- endo -Cl position was preferably substituted with hydrogen. In the case of B8-806, the dechlorination at the secondary carbon C2 was approximately 20-fold faster than the subsequent, slow reduction at the primary carbon C8. The three different formerly unknown heptachloro-CTTs, 2- exo, 3- endo, 6- exo, 8,9,9,10-heptachlorobornane (B7-1473), 2- exo, 3- endo, 6- endo, 8,9,9,10-hepatchlorobornane (B7-1461), and 2- exo, 3- endo, 6- exo, 8,8,9,10-heptachlorobornane (B7-1470) were found as intermediates of the B8-806/809 transformation. Treatment of B9-1679 with D. multivorans indicated that gem -Cls on the bridge (C8 and C9) are dechlorinated faster than gem -Cls on the bridgehead (C10). [source]

    Effects of Valproate on Acylcarnitines in Children with Epilepsy Using ESI-MS/MS

    EPILEPSIA, Issue 1 2007
    Tamara Werner
    Summary:,Purpose: To determine the influence of valproate (VPA) treatment on acylcarnitines in children with epilepsy. Methods: Determination of acylcarnitines (including free carnitine and acylcarnitines from C2 to C18) in dried blood spot specimens using tandem-mass spectrometry. Longitudinal study of changes in acylcarnitines in children under VPA treatment without pretreatment (group 1) or with pretreatment with other antiepileptic drugs (group 2) before the start of VPA treatment at an early and a late treatment interval (12,66, 90,260 days after the beginning of treatment, respectively). Cross-sectional comparison of these two VPA groups and of a group receiving carbamazepine monotherapy (group 3) with controls. Results: Acylcarnitines in epileptic patients before VPA therapy did not differ from control values. In group 1, decreases of C0 (,26%), C2 (,12%), C16 (,31%), C18 (,41%), Ctotal (,10%), increases of C5OH (+31%), C8 (+33%) in the early treatment interval, and decreases of C16 (,21%), C18 (,42%), and increases of C2 (+26%), C5OH (+44%) in the late treatment interval were significant. In group 2, both in the longitudinal and the cross-sectional study, only a decrease of C18 (,41%, ,43%, respectively) in the late treatment interval was found. In group 3, no significant changes have been observed. Conclusions: We could prove changes in acylcarnitine subspecies, which were associated with VPA treatment in children with epilepsy. The treatment interval with the most marked changes coincides with the interval of highest risk for VPA-induced hepatotoxicity. The observed specific acylcarnitine pattern might point to the impaired intermediary metabolism that is responsible for VPA-induced hepatotoxicity. [source]

    New Coordination Modes of L -Ascorbic Acid and Dehydro- L -ascorbic Acid as Dianionic Chelating Ligand for Platinum

    Paola Bergamini
    Abstract A variety of coordination modes of L -ascorbic acid as an anionic bidentate ligand has been exploited to prepare platinum(II) complexes 1,7 that contain phosphanes or R,R -dach (1R,2R -diaminocyclohexane) as neutral ligands in which O2, O3, O5, O6 and C2 act as anionic donating functionalities. An alternative synthetic route to known O2,O3 complexes is proposed, and their solubility in water has been enhanced by introducing PTA (1,3,5-triaza-7-phosphaadamantane) as a neutral ligand. A new coordination mode of ascorbic acid (O2 and O3 protected) as an O5,O6-diolate chelating ligand has been characterised in solution by NMR spectroscopy and in the solid state by X-ray crystallography. The first example of a platinum complex that contains dehydroascorbic acid, 7, has also been prepared and its X-ray crystal structure has been determined. The antiproliferative activity in vitro of complexes 1,7 has been tested, and the best values were obtained for the DHA complex 7, which was found to be more active than cisplatin on both a cisplatin-sensitive and a cisplatin-resistant cell line.( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    [Bis(guanidine)]zinc Complexes and Their Application in Lactide Polymerisation

    Janna Brner
    Abstract The bis(guanidine)-stabilised zinc complexes [N1,N2 -bis(1,3-dimethylimidazolidin-2-ylidene)ethane-1,2-diamine]dichloridozinc(II), [Zn(DMEG2e)Cl2] (C1), diacetato[N1,N2 -bis(1,3-dimethylimidazolidin-2-ylidene)ethane-1,2-diamine]zinc(II),[Zn(DMEG2e)(CH3COO)2] (C2), and bis[N1,N2 -bis(1,3-dimethylimidazolidin-2-ylidene)ethane-1,2-diamine]zinc(II) bis(trifluoromethanesulfonate), [Zn(DMEG2e)2](CF3SO3)2 (C3), have been synthesised and completely characterised by means of X-ray structure analysis, NMR spectroscopy and mass spectrometry. These [bis(guanidine)]zinc complexes were investigated regarding their activity in the bulk polymerisation of D,L -lactide. It could be shown that these compounds are able to act as initiators for lactide polymerisation, and polylactides with molecular weights (Mw) of around 18000,59000 g/mol could be obtained. Variation of the reaction temperature revealed that the molecular weights decrease with increasing temperature. Additionally, the correlation of the intrinsic viscosity with the molecular weight demonstrates that the obtained polymers are linear and structurally homogeneous.( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    A Rearrangement of Azobenzene upon Interaction with an Aluminum(I) Monomer LAl {L = HC[(CMe)(NAr)]2, Ar = 2,6- iPr2C6H3}

    Hongping Zhu
    Abstract Reaction of LAl (1) or [LAl{,2 -C2(SiMe3)2}] (2) {L = HC[(CMe)(NAr)]2, Ar = 2,6- iPr2C6H3} with azobenzene affords a five-membered ring compound [LAl{N(H)- o -C6H4N(Ph)}] (3). In the formation of 3 a three-membered intermediate [LAl(,2 -N2Ph2)] (A) is suggested by a [1 + 2] cycloaddition reaction; A is not stable and further rearranges to 3. DFT calculations on similar compounds with modified L' {L' = HC[(CMe)(NPh)]2} show that the complexation energy of the reaction of L'Al with azobenzene to form [L'Al(,2 -N2Ph2)] is about,39 kcal,mol,1, and the best estimate of the energy difference between [L'Al(,2 -N2Ph2)] and [L'Al{N(H)- o -C6H4N(Ph)}] is,76 kcal,mol,1. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Phenomenological diversity of spinal reflexes in brain death

    J. F. Spittler
    In brain death, spinal reflexes and automatisms are observed which may cause irritation and even doubt in the diagnosis. In the literature there are no dedicated descriptions of the diversity and of neuroanatomical considerations. In 278 examinations of 235 patients for the determination of brain death, on 42 occasions obvious spinal reflexes and/or spinal automatisms were observed in 27 brain dead bodies. Because they were not systematically searched for, minute forms have probably been missed. The reflexes (R) and automatisms (A) are described according to the time of observation in relation to the development of brain death, the presumable spinal localization and the possible phylogenetical interpretation. Especially disquieting examples are discussed in more detail, e.g. monophasic EndotrachealSuction,ThoracicContraction-R supposedly switched in segments C2,6 or TrapeziusPinch,ShoulderProtrusion-R conveyed by the accessory nerve (terminology according to the scheme: for the reflexes, Trigger-Response-R: for the automatisms, Movement-A). After these experiences a more thorough examination showed frequent observations of rather minute forms of spinal reflexes, as well as automatisms and even the Lazarus sign (in possibly more than two thirds of the examinations). An estimation of the factual frequency would necessitate special attention to those much more frequent but less obvious minute spinal reflexes and automatisms. [source]

    Ketopinic Acid Derived Bis(hydroxy amides) as Cheap, Chiral Ligands for the Enantioselective Ethylation of Aromatic Aldehydes

    Toms de las Casas Engel
    Abstract Readily accessible, C2 - and pseudo- C2 -symmetric bis(hydroxy amides), derived from commercially available (+)-ketopinic acid and protic diamines, are promising, cheap, chiral ligands for the synthetically valuable, enantioselective addition of organozinc reagents to carbon electrophiles. A series of ligands of this type, having key structural differences, has been synthesized and tested in the enantioselective ethylation of benzaldehydes and (E)-cinnamaldehyde, in order to gain information on the origin of ligand efficiency. The results obtained allow for the definition of a privileged structural pattern for the design of improved cheap ligands and support interesting models proposed for both the acting catalytic species and the controlling transition states. The most efficient ligands proved to be less efficient than commercially available (,)-MIB; nevertheless, an impressive efficiency level was obtained, which should sustain interest in this cheap type of ligands. [source]

    Palladium-Catalyzed C2 or C5 Direct Arylation of 3-Formylthiophene Derivatives with Aryl Bromides

    Jia Jia Dong
    Abstract The system Pd(OAc)2/dppb was found to be an efficient catalyst precursor for the direct arylation of 3-formylthiophene derivatives. When using 3-formylthiophene, the 2-arylated thiophenes were obtained with regioselectivities of 76,86,%, whereas the arylation of 3-formylthiophene diethyl acetal gave the 5-arylated thiophenes with regioselectivities of 64,88,%. These reactions were performed by using only 0.1 mol-% of the catalyst. Moreover, this procedure has been found to be tolerant to a variety of functional groups on the aryl bromide such as formyl, propionyl, benzoyl, nitrile, or nitro. [source]

    Organocatalytic Enantioselective Michael Addition of 4-Hydroxycoumarin to ,,,-Unsaturated Ketones: A Simple Synthesis of Warfarin

    Zhenhua Dong
    Abstract A type of C2 -symmetric secondary amine amide catalysts were developed for the asymmetric Michael addition of 4-hydroxycoumarin to ,,,-unsaturated ketones. A series of important biologically and pharmaceutically active compounds were obtained in excellent yields (up to 99,%) with high enantioselectivities (up to 89,%,ee) under mild conditions. In addition, enantiopure product could be obtained by a single recrystallization. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Chiral Primary Amine,Polyoxometalate Acid Hybrids as Asymmetric Recoverable Iminium-Based Catalysts

    Jiuyuan Li
    Abstract A new strategy for the immobilization of iminium organocatalysts through the acid,base assembly of multidentate chiral primary amines and solid polyacids is presented. A suitable structurally distinctive C2 -symmetric chiral primary amine (CPA) was identified in this study and the optimal CPA,POM hybrid obtained catalyzed the Diels,Alder cycloaddition of ,-substituted acroleins in high yields and fair-to-high selectivity under aqueous conditions. The primary amine in the metal,organic-framework (MOF)-like catalyst acted as the catalytic center as well as multidentate basic centers, whereas phosphotungstic acid played dual roles as both catalyst anchors and modulators of the activity and stereoselectivity. Furthermore, the MOF-like catalyst showed both high reactivity and physical stability and thus could be recycled and reused six times with only a small loss of activity and selectivity. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Chiral Concave Imidazolinium Salts as Precursors to Chiral Concave N -Heterocyclic Carbenes,

    Ole Winkelmann
    Abstract Imidazolinium moieties have been incorporated into bimacrocycles to generate precursors for concave N -heterocyclic carbenes (NHCs). By using one symmetrically substituted benzene bridgehead and one naphthalene bridgehead devoid of local C2 -symmetry, axially chiral concave imidazolinium ions have been obtained. Starting from 2,7-dihydroxy-1-nitronaphthalene (7), the phenol groups have been transformed to 4-pentenyl ethers 8, and the nitro group was then reduced to the corresponding amine 9. Next, 9 and a 2,6-bis(alkenyloxy)aniline 10 were connected by an oxalic acid linker. After reduction of the diamide 13 to diamine 14, a bridge was installed with triethyl orthoformate to give a tetraalkenyl-substituted imidazolinium salt 15. Ring-closing metathesis of 15 followed by hydrogenation of the products 16 yielded the bimacrocyclic salts 17 in 9,18,% overall yield (based on 7), giving amounts up to >300 mg. The configurational stability of 17 was investigated by NMR using chiral enantiopure anions TRISPHAT 18 and BINPHAT 19 as stereodynamic probes.( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Diastereoselective Alkylation of (Arene)tricarbonylchromium and Ferrocene Complexes Using a Chiral, C2 -Symmetrical 1,2-Diamine as Auxiliary

    Alexandre Alexakis
    No abstract is available for this article. [source]

    Synthesis of An Enantioenriched C2 -Symmetric Molecule by a Chiral-Base-Mediated Kinetic Resolution of an (Arene)tricarbonylchromium(0) Complex

    M. Paola Castaldi
    Abstract Trimethylsilyl substituents have been used to control the conformational preferences of a 1,2-disubstituted (arene)tricarbonylchromium(0) complex. The kinetic resolution of the mono-methyl derivative ()- 11 using a chiral base/iodomethane quench sequence led to the synthesis of the enantioenriched C2 -symmetric bis-ether (+)- 13. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    Stereoselective Construction of a Highly Functionalized Taxoid ABC-Ring System: the C2,C9 Oxa-Bridge Approach

    Sylvain Hamon
    Abstract The goal of this investigation is to assemble the 20-carbon unit 1 of the taxoid diterpene skeleton with a high level of stereocontrol by means of a three-reaction sequence developed in this laboratory. The strategy involves seven C,C bond-forming operations together with eighteen functional group transformations, circumventing the stereoselectivity issue altogether. Furthermore, there is no isomer formation and hence no need for chromatographic separation. A temporary oxa-bridge (C2/C9) was used as a problem-solving approach. The key step in the planned sequence was based on achieving the last C,C bonding between C11 and C12, following a successful C11 functionalization. X-ray analyses of 8b, 17, 18, 19, 20, and 21, together with extensive use of 800 MHz 1H (200 MHz 13C) NMR spectra, support the suggested structures. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Diastereoselective Alkylation of (Arene)tricarbonylchromium and Ferrocene Complexes Using a Chiral, C2 -Symmetrical 1,2-Diamine as Auxiliary

    Alexandre Alexakis
    Abstract The aminal of (benzaldehyde)tricarbonylchromium and en-antiopure bipyrrolidine undergoes diastereoselective ortho -metallation with butyllithium. Quenching with various electrophiles, followed by hydrolysis of the aminal, affords ortho -substituted (benzaldehyde)tricarbonylchromium compounds with high ee (91,99,%). When quenched with Ph2PCl, a new chiral P,N-bidentate ligand is obtained, which shows efficiency in Pd- and Cu-catalysed reactions. The aminal of ferrocenecarbaldehyde could also be formed, but the ortho -deprotonation occurs with only moderate diastereoselectivity (70,%). ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Stereodivergent Syntheses of Highly Substituted Enantiopure 4-Alkoxy-3,6-dihydro-2H -1,2-oxazines by Addition of Lithiated Alkoxyallenes to Carbohydrate-Derived Aldonitrones

    Matthias Helms
    Abstract Additions of lithiated alkoxyallenes to D -glyceraldehyde-based nitrones 1 and 2 did not provide the expected hydroxylamine derivatives. Instead, a novel [3+3] cyclization process furnished 4-alkoxy-3,6-dihydro-2H -1,2-oxazines 9,14 with excellent syn selectivities and in moderate to good yields. Through precomplexation of the nitrones the corresponding anti -configured 1,2-oxazines 9, 10 and 13 could be obtained with high stereoselectivity. The reactions of nitrones 3,6, derived from D -erythrose or D -threose, generally proceeded less diastereoselectively, but reasonable yields of anti -configured 1,2-oxazines such as anti - 17 and anti - 19 could be obtained under Lewis acid promotion conditions. This was also the case for reactions of the D -arabinose-derived nitrone 7, which provided the anti -1,2-oxazines 23 and 24 with excellent diastereoselectivity and in good yields. Bis-nitrone 8 and lithiated methoxyallene furnished a mixture of six compounds, among which the major componentwas the C2 -symmetric syn/syn -1,2-oxazine 29. The diastereoselectivities of these reactions are interpreted on the basis of Dondoni's model for reactions between organolithium compounds and nitrones. The mechanisms for formation of 1,2-oxazines and of side products are discussed. The method introduced here seems to be of broad applicability and an excellent tool for diastereoselective chain elongation of carbohydrate derivatives, affording stereodefined precursors of aminopolyols and other highly functionalized compounds. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    A C2 -Chiral Bis(amidinium) Catalyst for a Diels,Alder Reaction Constituting the Key Step of the Quinkert,Dane Estrone Synthesis

    Svetlana B. Tsogoeva
    Abstract A novel C2 -chiral bis(amidinium) salt 12 has been synthesised from 5-(tert -butyl)isophthalic acid. The hydrogen-bond-mediated association of dienophiles 3a and 3b with the chiral host molecule 12 accelerates the Diels,Alder reactions with diene 2 by more than three orders of magnitude. In addition, enantioselective formation of the desired adducts is observed under catalysis with 12. Good ratios of 4a(b) + ent - 4a(b)/5a(b) + ent - 5a(b) from 1:10 to 1:22 were found in all reactions. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Effect of organic matter applications on 13C-NMR spectra of humic acids of soil

    S. Dou
    Summary Much attention has been paid to improving soil fertility with organic matter (OM) application, which not only deals with organic wastes and protects the environment, but also maintains soil fertility and increases crop yields. Much research has also been on the effects of OM applications on the soil's physical, chemical and biological properties, but relatively less attention has been spent on humic substance (HS). In order to clarify the mechanism of improving soil fertility by applying OM, we analysed the changes of structural characteristics of humic acid (HA) from OM applications to soils by 13C-NMR, chemical analysis, thermal analysis, optical properties, IR and fluorescence spectroscopy. Samples of a brown soil (Paleudalf) and a paddy soil (an anthropogenic soil originating from Udifluvents) were collected from the plough layer of the long-term field experiment at Shenyang Agricultural University and Liaoning Provincial Alkali-Saline Soil Institute, respectively. Both field experiments included three treatments each: (i) brown soil, zero-treatment (CKbr) and two pig manure (PM) applications (O1 and O2) at annual rates of 0.9 t ha,1 and 1.8 t ha,1 of organic carbon, respectively; and (ii) paddy soil, zero-treatment (CKpad), pig manure (Op) and rice straw (Or) at annual rates of 2.62 t ha,1 and 1.43 t ha,1 of organic carbon, respectively. An incubation experiment was also carried out to test the field experiment on the brown soil, namely four treatments: zero-treatment (CKc), and three pig manure applications at rates of 30 g kg,1 (C1), 50 g kg,1 (C2) and 70 g kg,1 (C3), respectively. The total incubation was 180 days. The results indicated that number-average molecular weights (Mn), total acidity, aromaticity, excitation maximum wavelength (,Exmax), and the heat ratio of the high to moderate temperature exothermic regions (H3/H2) of the HA all decreased after OM application. The degree of activation (AD), the absorption intensity ratio of 2920 cm,1 to 1720 cm,1 in infrared spectra (IR2920/1720), alkyl C and O-alkyl C of the HA increased. The HA structure tended to become simpler and more aliphatic. [source]

    The one-level functional equation of multi-rate loss systems

    Harro L. Hartmann
    Motivated by the discrete multi-rate Kaufmann,Roberts recurrence relations, we derive a functional equation (FE), which covers nonintegral states. This FE implies a unique effective step parameter d, which defines an equivalent one-level recurrence depth, or bit-rate, at each state under progress. This state-dependent depth results from the equality requirement of the multi-rate and the one-level model in the moment-generating function transform domain. By this method it is possible to model d by a few moments of the original multi-rate statistic. In this case we obtain an explicit FE solution covering the entire (global) state space. Next we verify that the resulting state probability density incorporates iteratively enumerated discrete state probabilities, including the state-dependent depth. With a system capacity C the iterations then need time complexities between O(C) and O(C2). In contrast to this each FE state, is performed at a time complexity O(1). By the efficient coverage of the whole state space, fast optimizations of multi-rate networks and multi-resource systems can be improved. Copyright 2003 AEI. [source]

    An Alternative Approach to Constructing Solution Processable Multifunctional Materials: Their Structure, Properties, and Application in High-Performance Organic Light-Emitting Diodes

    Shanghui Ye
    Abstract A new series of full hydrocarbons, namely 4,4,-(9,9,-(1,3-phenylene)bis(9H -fluorene-9,9-diyl))bis(N,N -diphenylaniline) (DTPAFB), N,N,-(4,4,-(9,9,-(1,3-phenylene)bis(9H -fluorene-9,9-diyl))bis(4,1-phenylene))bis(N -phenylnaphthalen-1-amine) (DNPAFB), 1,3-bis(9-(4-(9H -carbazol-9-yl)phenyl)-9H -fluoren-9-yl)benzene, and 1,3-bis(9-(4-(3,6-di- tert -butyl-9H -carbazol-9-yl)phenyl)-9H -fluoren-9-yl)benzene, featuring a highly twisted tetrahedral conformation, are designed and synthesized. Organic light-emitting diodes (OLEDs) comprising DNPAFB and DTPAFB as hole transporting layers and tris(quinolin-8-yloxy)aluminum as an emitter are made either by vacuum deposition or by solution processing, and show much higher maximum efficiencies than the commonly used N,N,-di(naphthalen-1-yl)- N,N,-diphenylbiphenyl-4,4,-diamine device (3.6 cd A,1) of 7.0 cd A,1 and 6.9 cd A,1, respectively. In addition, the solution processed blue phosphorescent OLEDs employing the synthesized materials as hosts and iridium (III) bis[(4,6-di-fluorophenyl)-pyridinato-N, C2] picolinate (FIrpic) phosphor as an emitter present exciting results. For example, the DTPAFB device exhibits a brightness of 47 902 cd m,2, a maximum luminescent efficiency of 24.3 cd A,1, and a power efficiency of 13.0 lm W,1. These results show that the devices are among the best solution processable blue phosphorescent OLEDs based on small molecules. Moreover, a new approach to constructing solution processable small molecules is proposed based on rigid and bulky fluorene and carbazole moieties combined in a highly twisted configuration, resulting in excellent solubility as well as chemical miscibility, without the need to introduce any solubilizing group such as an alkyl or alkoxy chain. [source]

    Improving thermostability and catalytic activity of pyranose 2-oxidase from Trametes multicolor by rational and semi-rational design

    FEBS JOURNAL, Issue 3 2009
    Oliver Spadiut
    The fungal homotetrameric flavoprotein pyranose 2-oxidase (P2Ox; EC catalyses the oxidation of various sugars at position C2, while, concomitantly, electrons are transferred to oxygen as well as to alternative electron acceptors (e.g. oxidized ferrocenes). These properties make P2Ox an interesting enzyme for various biotechnological applications. Random mutagenesis has previously been used to identify variant E542K, which shows increased thermostability. In the present study, we selected position Leu537 for saturation mutagenesis, and identified variants L537G and L537W, which are characterized by a higher stability and improved catalytic properties. We report detailed studies on both thermodynamic and kinetic stability, as well as the kinetic properties of the mutational variants E542K, E542R, L537G and L537W, and the respective double mutants (L537G/E542K, L537G/E542R, L537W/E542K and L537W/E542R). The selected substitutions at positions Leu537 and Glu542 increase the melting temperature by approximately 10 and 14 C, respectively, relative to the wild-type enzyme. Although both wild-type and single mutants showed first-order inactivation kinetics, thermal unfolding and inactivation was more complex for the double mutants, showing two distinct phases, as revealed by microcalorimetry and CD spectroscopy. Structural information on the variants does not provide a definitive answer with respect to the stabilizing effects or the alteration of the unfolding process. Distinct differences, however, are observed for the P2Ox Leu537 variants at the interfaces between the subunits, which results in tighter association. [source]

    Properties of pyranose dehydrogenase purified from the litter-degrading fungus Agaricus xanthoderma

    FEBS JOURNAL, Issue 3 2007
    Magdalena Kujawa
    We purified an extracellular pyranose dehydrogenase (PDH) from the basidiomycete fungus Agaricus xanthoderma using ammonium sulfate fractionation and ion-exchange and hydrophobic interaction chromatography. The native enzyme is a monomeric glycoprotein (5% carbohydrate) containing a covalently bound FAD as its prosthetic group. The PDH polypeptide consists of 575 amino acids and has a molecular mass of 65 400 Da as determined by MALDI MS. On the basis of the primary structure of the mature protein, PDH is a member of the glucose,methanol,choline oxidoreductase family. We constructed a homology model of PDH using the 3D structure of glucose oxidase from Aspergillus niger as a template. This model suggests a novel type of bi-covalent flavinylation in PDH, 9- S -cysteinyl, 8-,- N3-histidyl FAD. The enzyme exhibits a broad sugar substrate tolerance, oxidizing structurally different aldopyranoses including monosaccharides and oligosaccharides as well as glycosides. Its preferred electron donor substrates are d -glucose, d -galactose, l -arabinose, and d -xylose. As shown by in situ NMR analysis, d -glucose and d -galactose are both oxidized at positions C2 and C3, yielding the corresponding didehydroaldoses (diketoaldoses) as the final reaction products. PDH shows no detectable activity with oxygen, and its reactivity towards electron acceptors is rather limited, reducing various substituted benzoquinones and complexed metal ions. The azino-bis-(3-ethylbenzthiazolin-6-sulfonic acid) cation radical and the ferricenium ion are the best electron acceptors, as judged by the catalytic efficiencies (kcat/Km). The enzyme may play a role in lignocellulose degradation. [source]

    DAP kinase activity is critical for C2 -ceramide-induced apoptosis in PC12 cells

    FEBS JOURNAL, Issue 1 2002
    Mutsuya Yamamoto
    Exposure of PC12 cells to C2 -ceramide results in dose-dependent apoptosis. Here, we investigate the involvement of death-associated protein (DAP) kinase, initially identified as a positive mediator of the interferon-,-induced apoptosis of HeLa cells, in the C2 -ceramide-induced apoptosis of PC12 cells. DAP kinase is endogenously expressed in these cells. On exposure of PC12 cells to 30 m C2 -ceramide, both the total (assayed in the presence of Ca2+/calmodulin) and Ca2+/calmodulin-independent (assayed in the presence of EGTA) DAP kinase activities were transiently increased 5.0- and 12.2-fold, respectively, at 10 min, and then decreased to 1.7- and 3.4-fold at 90 min. After 10 min exposure to 30 m C2 -ceramide, the Ca2+/calmodulin independent activity/ total activity ratio increased from 0.22 to 0.60. These effects were dependent on the C2 -ceramide concentration. C8 -ceramide, another active ceramide analog, also induced apoptosis and activated DAP kinase, while C2 -dihydroceramide, an inactive ceramide analog, failed to induce apoptosis and increase DAP kinase activity. Furthermore, transfection studies revealed that overexpression of wild-type DAP kinase enhanced the sensitivity to C2 - and C8 -ceramide, while a catalytically inactive DAP kinase mutant and a construct containing the death domain and C-terminal tail of DAP kinase, which act in a dominant-negative manner, rescued cells from C2 -, and C8 -ceramide-induced apoptosis. These findings demonstrate that DAP kinase is an important component of the apoptotic machinery involved in ceramide-induced apoptosis, and that the intrinsic DAP kinase activity is critical for ceramide-induced apoptosis. [source]