Chloro- and phenoxy-phosphines in frustrated Lewis pair additions to alkynes

The reaction of tBu(C(6)H(4)O(2))P, with the borane B(C(6)F(5))(3) gives rise to NMR data consistent with the formation of the classical Lewis acid-base adduct tBu(C(6)H(4)O(2))P(B(C(6)F(5))(3)) (1). In contrast, the NMR data for the corresponding reactions of tBu(C(20)H(12)O(2))P and Cl(C(20)H(12)O(2))P with B(C(6)F(5))(3) were consistent with the presence of equilibria between free phosphine and borane and the corresponding adducts. Nonetheless, in each case, the adducts tBu(C(20)H(12)O(2))P(B(C(6)F(5))(3)) (2) and Cl(C(20)H(12)O(2))P(B(C(6)F(5))(3)) (3) were isolable. The species 1 reacts with PhCCH to give the new species tBu(C(6)H(4)O(2))P(Ph)C=CHB(C(6)F(5))(3) (4) in near quantitative yield. In an analogous fashion, the addition of PhCCH to solutions of the phosphines tBu(C(20)H(12)O(2))P, tBuPCl(2) and (C(6)H(3)(2,4-tBu(2))O)(3)P each with an equivalent of B(C(6)F(5))(3) gave rise to L(Ph)C=CHB(C(6)F(5))(3) (L = tBu(C(20)H(12)O(2))P 5, tBuPCl(2)6 and (C(6)H(3)(2,4-tBu(2))O)(3)P 7). X-Ray data for 1, 2, 6 and 7 are presented. The implications of these findings are considered.     

Two routes to vesicle formation: metal-ligand complexation and ionic interactions

Two routes to vesicle formation were designed to prepare uni- and multilamellar vesicles in salt-free aqueous solutions of surfactants. The formation of a surfactant complex between a double-chain anionic surfactant with a divalent-metal ion as the counterion and a single-chain zwitterionic surfactant with the polar group of amine-oxide group is described for the first time as a powerful driving force for vesicle-phases constructed from salt-free mixtures of aqueous surfactant solutions. As a typical example, a Zn(2+)-induced charged complex fluid, vesicle-phase has been studied in aqueous mixtures of tetradecyldimethylamine oxide (C(14)DMAO) and zinc 2,2-dihydroperfluorooctanoate [Zn(OOCCH(2)C(6)F(13))(2)]. This ionically charged vesicle-phase formed due to surfactant complexation has interesting rheological properties and is not shielded by excess salts because there are no counterions in the solution. Such a vesicle-phase of surfactant complex is important for many applications; for example, the vesicle-phase was further used to produce in situ the vesicle-phase of the salt-free cationic/anionic (catanionic) surfactants, C(14)DMAOH(+)-(-)OOCCH(2)C(6)F(13). The salt-free catanionic vesicle-phase could be produced through injecting H(2)S gas into the C(14)DMAO/Zn(OOCCH(2)C(6)F(13))(2) vesicle-phase, because the zwitterionic surfactant C(14)DMAO can be charged by the H(+) released from H(2)S to become a cationic surfactant and Zn(2+) was precipitated as ZnS. After the ZnS precipitates were removed from C(14)DMAO/Zn(OOCCH(2)C(6)F(13))(2) solutions, the final mixed solution does not contain excess salts as do other cationic/anionic surfactant systems. Both the C(14)DMAO-Zn(OOCCH(2)C(6)F(13))(2) complex and the resulting catanionic C(14)DMAOH(+)-(-)OOCCH(2)C(6)F(13) solution are birefringent Lalpha-phase solutions that consist of uni- and multilamellar vesicles. Ring-shaped semiconductor ZnS materials with encapsulated ZnS precipitates and regular spherical ZnS particles were prepared, which resulted in a transition from vesicles composed of metal-ligand complexes to vesicles held together by ionic interactions in the salt-free aqueous systems. This strategy should provide a new method to prepare inorganic materials. The present routes to form vesicles solve a problem: how to prepare nanomaterials using surfactant self-assembly, with structure controlled not by the growing material, but by the phase behavior of the surfactants.     

A facile and novel route to unprecedented manganese C4 cumulenic complexes

The theoretically characterized (DFT) C4 cumulenic species Mn(C5H4R)(dmpe) [=C=C=C=C(SnPh3)2] was obtained by photolysis of the C(sp2)-Sn bond in the vinylidene complex Mn(C5H4R)(dmpe)[=C=C(SnPh3)-C[triple bond]CSnPh3], which in turn was prepared by a thermal reaction from MnC5H4R(dmpe)(C7H8) and Ph3Sn-C4-SnPh3.     

Novel approach to the analysis and use of fullerenes in capillary electrophoresis

The analysis and use of fullerenes in capillary electrophoresis (CE) was investigated. Sodium dodecyl sulfate (SDS) was used to solubilize fullerenes C60, C70, and a mixture of C60 and C70 in water. The behavior of the solutions of the C60- and C70-SDS complexes was examined by CE with on-line UV-Vis diode array detection. This study included the use of a C60-SDS complex as a new method of micellar electrokinetic chromatography (MEKC) for the separation of polycyclic aromatic hydrocarbons (PAHs) using CE with uniwavelength detection. Since SDS micelles act as a pseudostationary phase in which the PAH compounds partition with their hydrophobic interior, the addition of C60 within the micelles enhanced separation of the PAHs. The preliminary results using C60-MEKC with SDS were compared to those obtained with MEKC with SDS. The capillary electrophoretic separations were performed in 10 mM borate-phosphate buffer with 100 mM SDS at pH 9.5.     

Electron attachment to higher fullerenes and to Sc3N@C80

We report on attachment of free electrons to fullerenes C(n) (n = 60, 70, 76, 78, 80, 82, 84, 86) and to Sc(3)N@C(80). The attachment cross sections exhibit a strong resonance at 0 eV for all species. The overall shape of the anion yield versus electron energy is quite similar for the higher fullerenes, with a minimum around 1 eV and a maximum which gradually shifts from 6 eV for C(60) to approximately 4 eV for large n. The endohedral Sc(3)N@C(80) exhibits a particularly shallow minimum and a maximum below 4 eV. We model autoionization of the anions with due consideration of the internal energy distributions. The relatively low electron affinity of Sc(3)N@C(80) is reflected in its reduced ion yield at higher attachment energies.     

Photochemical and discharge-driven pathways to aromatic products from 1,3-butadiene

A detailed study of the photochemical and discharge-driven pathways taken by gas-phase 1,3-butadiene has been carried out. Photolysis or discharge excitation was initiated inside a short reaction tube attached to the outlet of a pulsed valve. Bath gas temperatures near 100 K were achieved in the reaction tube by the constrained expansion of the gas mixture into the tube, simulating temperatures of relevance in Titan's atmosphere. Photolysis of 1,3-butadiene was initiated at 218 nm with a laser pulse that counter-propagated the reaction tube. Discharge excitation was carried out using discharge electrodes imbedded in the reaction tube walls, enabling the study of the photochemical and discharge products under similar conditions. Products were detected using either single-photon VUV photoionization (118 nm = 10.5 eV) or resonant two-photon ionization (R(2)PI) spectroscopy in a time-of-flight mass spectrometer. Emphasis was placed on characterization of the aromatic products formed, since these may be of particular relevance to Titan's atmosphere, where benzene has been positively identified and 1,3-butadiene is projected as the principle pathway to its formation. Consistent with previous studies of the photodissociation of 1,3-butadiene, C(3)H(3) + CH(3) is the dominant primary product formed. Under the temperature-pressure conditions present in the reaction tube (T approximately 75-100 K, P = 50 mbar), C(6)H(6) is the dominant secondary photochemical product formed. A 1:1 C(4)H(6):C(4)D(6) mixture was used to prove that the C(6)H(6) product was formed by recombination of two C(3)H(3) radicals; however, a careful search for benzene revealed none, indicating that less than 1% of the C(6)H(6) formed in the reaction tube is benzene. This is consistent with expectations for these temperatures and pressures based on previous modeling of propargyl recombination. Two aromatic products were observed from the photochemistry: ethylbenzene and 3-phenylpropyne. Plausible pathways leading to these products are proposed. In the discharge, C(3)H(3) + CH(3) are also identified as significant primary neutral products and C(6)H(6) as a dominant higher-mass product. In this case, the C(6)H(6) was identified as benzene via its R2PI spectrum, appearing with intensity about 10 times larger than any other aromatic formed in the discharge. R2PI spectra of a total of about 15 aromatic products were recorded from the 1,3-butadiene discharge, among them toluene; styrene; phenylacetylene; o-, m-, and p-xylene; ethylbenzene; indane; indene; beta-methylstyrene; and naphthalene. Previously unidentified spectra in the m/z 142 and 144 mass channels were positively identified as the 1,3- and 1,4-isomers of phenylcyclopentadiene and the analogous 1-phenylcyclopentene.     

Liquid-phase force field and dipole moment derivatives with respect to internal coordinates of benzene

This paper presents an analysis of the infrared vibrational intensities found for C(6)H(6), C(6)D(6) and C(6)H(5)D in the liquid phase, motivated in part by the quite marked intensity differences between the fundamentals of C(6)H(6) and C(6)D(6) in the liquid, and between corresponding vibrations in the liquid and gas phases. The analysis is carried out under the harmonic approximation and results from a determination of the force field for liquid C(6)H(6), C(6)D(6) and C(6)H(5)D. The force constants for the liquid-phase are presented and compared to those in the literature for the gas-phase. Previously reported experimental intensities are used along with the eigenvectors of the force field analysis to determine the dipole moment derivatives with respect to symmetry and internal coordinates. The dipole moment derivatives with respect to internal coordinates obtained are partial differentialmicro/ partial differentials=0.38+/-0.02DebyeA(-1), partial differentialmicro/ partial differentialt=0.24+/-0.01, partial differentialmicro/ partial differentialbeta=0.26+/-0.01, and partial differentialmicro/ partial differentialgamma=0.64+/-0.03DebyeA(-1). There is very little difference between the dipole moment derivatives with respect to internal coordinates obtained from non-linear least squares fitting of the two D(6h) isotopomers and those obtained from non-linear least squares fitting of the three isotopomers. The results show that there is significant intensity sharing in the CH stretch region of C(6)H(5)D between the fundamental and combination bands.     

Isotopic fractionation of endogenous anabolic androgenic steroids and its relationship to doping control in sports

The use of gas chromatography (GC)-combustion (C)-isotope ratio mass spectrometry (IRMS) demonstrates that a single oral administration of dehydroepiandrosterone (DHEA, 100 mg) to a male subject significantly lowers the 13C content of etiocholanolone (Et) and androsterone (A) in the subject's urine. The difference in carbon isotope ratio (d13C per thousand) values between Et and A increases from 1.6 per thousand at the time of administration to 5.1 per thousand at 26 h post-administration, indicating preferential metabolism of administered DHEA to form Et in relation to A. Multiple oral administrations of DHEA to a male subject reveals lower d13C values during the excretion period of Et (-31.7 per thousand to -34.6 per thousand) and A (-31.4 per thousand to -33.0 per thousand) to that of the d13C value of the administered DHEA (-31.3 per thousand). Reference distributions of d13C Et and d13C A constructed from normal athlete populations within Australia and New Zealand show a small natural discrimination against 13C in the formation of Et relative to A (mean=0.3 per thousand, n=167, p=0.007). Amplified differences between d13C Et and d13C A, and in vivo 13C depletion measured by GC-C-IRMS are shown to be potentially useful for doping control.     

Kinetics and mechanism of addition of benzylamines to benzylidene-1,3-indandiones in acetonitrile

Nucleophilic addition reactions of benzylamines (BA; XC6H4CH2NH2) to benzylidene-1,3-indandiones (BID; YC6H4CH=C(C=O)2C6H4) have been studied in acetonitrile at 25.0 degrees C. The rate is first-order with respect to BA and BID, and no base catalysis is observed. The structure-reactivity behaviors (k2, rhoX, betaX, and betaY) are intermediate between the two series of addition reactions of BA to beta-nitrostyrene (NS) and benzylidenemalononitrile (BMN) in acetonitrile. The normal kinetic isotope effects, kH/kD > 1.0, involving deuterated BAs (XC6H4CH2ND2) are smaller than those for the reactions of NS and BMN suggesting a somewhat looser bond formation in the transition state. The reaction is predicted to proceed in a single step with concurrent C(alpha)-N bond formation and proton transfer to C(beta). A hydrogen-bonded, four-center type cyclic transition state is proposed.     

Atomic layer deposition and chemical vapor deposition precursor selection method application to strontium and barium precursors

A new selection method for atomic layer deposition (ALD) or chemical vapor deposition (CVD) precursors is proposed and tested. Density functional theory was used to simulate Sr and Ba precursors, and several precursors were selected and used to grow films via ALD as test cases for the precursor selection method. The precursors studied were M(x)2 (M = Sr, Ba; x = tetramethylheptanedionate (tmhd), acetylacetonate (acac), hexafluoroacetylacetonate (hfac), cyclopentadienyl (H(5)C(5)), pentamethylcyclopentadienyl (Me(5)C(5)), n-propyltetramethylcyclopentadienyl (PrMe(4)C(5)), tris(isopropylcyclopentadienyl) (Pr(3)(i)H(2)C(5)), tris(isopropylcyclopentadienyl)(THF) (Pr(3)(i)H(2)C(5))(OC(4)H(8)), tris(isopropylcyclopentadienyl)(THF)2 (Pr(3)(i)H(2)C(5))(OC(4)H(8))2, tris(tert-butylcyclopentadienyl) (Bu(3)(t)H(2)C(5)), tris(tert-butylcyclopentadienyl)(THF) (Bu(3)(t)H(2)C(5))(OC(4)H(8)), heptafluoro-2,2-dimethyl-3,5-octanedionate (fod)). The energy required to break bonds between the metal atom and the ligands was calculated to find which precursors react most readily. In the case of tmhd and Cp precursors, the energy required to break bonds in the precursor ligand was studied to evaluate the most likely mechanism of carbon incorporation into the film. Trends for Ba and Sr followed each other closely, reflecting the similar chemistry among alkaline earth metals. The diketonate precursors have stronger bonds to the metals than the Cp precursors, but weaker bonds within the ligand, explaining the carbon contamination found in experimentally grown films. Atomic layer deposition of SrO was tested with Sr(tmhd)2 and Sr(PrMe(4)Cp)2 and oxygen, ozone, and water as oxygen sources. No deposition was measured with tmhd precursors, and SrO films were deposited with PrMe(4)Cp with a source temperature of 200 degrees C and at substrate temperatures between 250 and 350 degrees C with growth rates increasing for oxygen sources in this order: O2 < H2O < O2 + H2O. The experimental results support the predictions based upon calculations: PrMe(4)Cp and Me(5)Cp precursors are expected to be the best precursors among those studied for Ba and Sr film growth.     

Temporary anion states and dissociative electron attachment to isothiocyanates

The temporary anion states of isothiocyanates CH3CH2=C=S (and CH3CH2N=C=O for comparison), C6H5CH2N=C=S, and C6H5N=C=S are characterized experimentally in the gas phase for the first time by means of electron transmission spectroscopy (ETS). The measured vertical electron attachment energies (VAEs) are compared with the virtual orbital energies of the neutral-state molecules supplied by MP2 and B3LYP calculations with the 6-31G* basis set. The calculated energies, scaled with empirical equations, reproduce satisfactorily the experimental VAEs. The first VAE is also closely reproduced as the total energy difference between the anion and neutral states calculated at the B3LYP/6-31+G* level. Due to mixing between the ring and N=C=S pi-systems, C6H5N=C=S possesses the best electron-acceptor properties, and its lowest-lying anion state is largely localized at the benzene ring. The anion states with mainly pi*C=S and pi*N=C character lie at higher energy than the corresponding anion states of noncumulated pi-systems. However, the electron-acceptor properties of isothiocyanates are found to be notably larger than those of the corresponding oxygen analogues (isocyanates). The dissociative electron attachment (DEA) spectra show peaks close to zero energy and at 0.6 eV, essentially due to NCS- negative fragments. In spite of the energy proximity of the first anion state in phenyl isothiocyanate to the DEA peak, the zero-energy anion current in the benzyl derivative is about 1 order of magnitude larger.     

A streamlined approach to the analysis of volatile fatty acids and its application to the measurement of whole-body flux

Volatile fatty acids (VFAs) are produced in the human colon by the bacterial breakdown of carbohydrates that escape digestion and absorption in the small intestine. They have important local and systemic effects on gastrointestinal and nutritional functions. Measuring their production is difficult because of inaccessibility of sampling sites and low circulating concentrations. Stable isotope tracer techniques are a way to measure VFA production but require measurement of isotope dilution in blood and other biological fluids. We have developed a streamlined and robust method to measure the concentration and enrichment of [(2)H]-labelled VFAs by gas chromatography/mass spectrometry (GC/MS) and [(13)C]-labelled VFAs by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Both types of analysis were carried out on the same samples allowing multiple tracer studies to be conducted. Good accuracy and repeatability were found for GC/MS analysis of [(2)H]-labelled VFAs. Careful handling of the background contribution, especially acetate, allowed quantitation of concentration and enrichment within the analysis. GC/C/IRMS analysis of [(13)C] VFAs was also achieved with good accuracy and repeatability. This methodology was used to determine whole-body acetate production in two subjects using multiple tracers ([(2)H(3)]- and [1-(13)C]acetate) and blood and urine sampling. Whole-body acetate flux was similar when measured either with [(2)H(3)]- or [1-(13)C]acetate, and when flux was determined from plasma or urine tracer enrichment. This new method will permit rapid and accurate measurement of VFA flux using [(2)H]- and/or [(13)C]-labelled VFAs as tracers. Measurements of the contribution of colonic VFA production to whole-body VFA flux are now possible.     

Dissociative electron attachment to furan, tetrahydrofuran, and fructose

We study dissociative electron attachment to furan (FN) (C(4)H(4)O), tetrahydrofuran (THF) (C(4)H(8)O), and fructose (FRU) (C(6)H(12)O(6)) using crossed electron/molecular beams experiments with mass spectrometric detection of the anions. We find that FN and THF are weak electron scavengers and subjected to dissociative electron attachment essentially in the energy range above 5.5 eV via core excited resonances. In striking contrast to that, FRU is very sensitive towards low energy electrons generating a variety of fragment ions via a pronounced low energy feature close to 0 eV. These reactions are associated with the degradation of the ring structure and demonstrate that THF cannot be used as surrogate to model deoxyribose in DNA with respect to the attack of electrons at subexcitation energies (<3 eV). The results support the picture that in DNA the sugar moiety itself is an active part in the initial molecular processes leading to single strand breaks.     

Terminal vanadium-neopentylidyne complexes and intramolecular cross-metathesis reactions to generate azametalacyclohexatrienes

Four-coordinate vanadium complexes containing a terminal neopentylidyne functionality have been prepared by two consecutive alpha-hydrogen abstraction reactions both of which were induced by one-electron oxidations. Among these vanadium-alkylidyne complexes are the neutral and the cation (Nacnac)VCtBu(OTf) and [(Nacnac)VCtBu(THF)]+, respectively (Nacnac- = [Ar]NC(CH3)CHC(CH3)N[Ar], Ar = 2,6-(CHMe2)2C6H3). The vanadium-alkylidynes have been characterized by 1H, 13C, 51V NMR spectroscopy and single-crystal X-ray diffraction and are consistent with a short VC bond. These alkylidynes were found to transform to azametalacyclohexatriene systems via an intramolecular cross-metathesis reaction. Kinetic studies of the transformation of (Nacnac)VCtBu(OTf) in C7D8 reveal the formation of the azametalacyclohexatriene to be independent of solvent (toluene vs THF) and the reaction to be first order in vanadium (k = 3.30(5) x 10-5 s-1 at 80 degrees C, with activation parameters DeltaH= 25.4(3) kcal/mol, DeltaS = -6(3) cal/molK). High-level DFT calculations on the full model suggest an intramolecular mechanism invoking only one transition state. The overall thermodynamic driving force for the reaction (DeltaG) in solution phase was estimated to be -21.3 kcal/mol.     

13C/12C isotope labeling to study carbon partitioning and dark respiration in cereals subjected to water stress

Despite the relevance of carbon (C) loss through respiration processes (with its consequent effect on the lower C availability for grain filling), little attention has been given to this topic. Literature data concerning the role of respiration in cereals are scarce and these have been produced using indirect methods based on gas‐exchange estimations. We have developed a new method based on the capture of respired CO₂ samples and their analysis by gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS). In order to analyse the main processes involved in the C balance during grain filling (photosynthesis, respiration, allocation and partitioning) the ambient isotopic ¹³C/¹²C composition (δ¹³C) of the growth chamber was modified during this period (δ¹³C ca. ?12.8 ± 0.3‰ to ca. ?20.0 ± 0.2‰). The physiological performance, together with the C allocation on total organic matter (TOM) and respiration of wheat (Triticum aestivum L., var. Califa sur) and two hybrids, tritordeum (X Tritordeum Asch. & Graebn line HT 621) and triticale (X Triticosecale Wittmack var. Imperioso), were compared during post‐anthesis water stress. In spite of the larger ear DM/total ratio, especially under drought conditions, the grain filling of triticale and wheat was mainly carried out with pre‐anthesis C, while the majority of C assimilated during post‐anthesis was invested in respiration processes. In the case of wheat and tritordeum, the C balance data suggested a reallocation during grain filling of photoassimilates stored prior to anthesis from shoot to ear. Furthermore, the lower percentage of labeled C on respired CO₂ of droughted tritordeum plants, together with the lower plant biomass, explained the fact that those plants had more C available for grain filling. Copyright © 2009 John Wiley & Sons, Ltd.     

Remarkable reactions of cyclooctatetraene diiron-bridging carbyne complexes with amino and amido compounds: nucleophilic addition to and breaking of the cyclooctatetraene ring

The reactions of the cationic, diiron-bridging carbyne complexes [Fe(2)(mu-CAr)(CO)(4)(eta(8)-C(8)H(8))]BF(4) (1, Ar=C(6)H(5); 2, Ar=p-CH(3)C(6)H(4); 3, Ar=p-CF(3)C(6)H(4)) with LiN(C(6)H(5))(2) in THF at low temperature gave novel N-nucleophilic-addition products, namely, the neutral, diiron-bridging carbyne complexes [Fe(2)(mu-CAr)(CO)(4)(eta(7)-C(8)H(8)N(C(6)H(5))(2))] (4, Ar=C(6)H(5); 5, Ar=p-CH(3)C(6)H(4); 6, Ar=p-CF(3)C(6)H(4))). Cationic bridging carbyne complexes 1-3 react with (C(2)H(5))(2)NH, (iC(3)H(7))(2)NH, and (C(6)H(11))(2)NH under the same conditions with ring cleavage of the COT ligand to produce the novel diiron-bridging carbene inner salts [Fe(2)[mu-C(Ar)C(8)H(8)NR(2)](CO)(4)] (7, Ar=C(6)H(5), R=C(2)H(5); 8, Ar=p-CH(3)C(6)H(4), R=C(2)H(5); 9, Ar=p-CF(3)C(6)H(4), R=C(2)H(5); 10, Ar=C(6)H(5), R=iC(3)H(7); 11, Ar=p-CH(3)C(6)H(4), R=iC(3)H(7); 12, Ar=p-CF(3)C(6)H(4), R=iC(3)H(7); 13, Ar=C(6)H(5), R=C(6)H(11); 14, Ar=p-CH(3)C(6)H(4), R=C(6)H(11), 15, Ar=p-CF(3)C(6)H(4), R=C(6)H(11)). Piperidine reacts similarly with cationic carbyne complex 3 to afford the corresponding bridging carbene inner salt [Fe(2)[mu-C(Ar)C(8)H(8)N(CH(2))(5)](CO)(4)] (16). Compound 9 was transformed into a new diiron-bridging carbene inner salt 17, the trans isomer of 9, by heating in benzene. Unexpectedly, the reaction of C(6)H(5)NH(2) with 2 gave a novel COT iron-carbene complex [Fe(2)[=C(C(6)H(4)CH(3)-p)NHC(6)H(5)](mu-CO)(CO)(3)(eta(8)-C(8)H(8))] (18). However, the analogous reactions of 2-naphthylamine with 2 and of p-CF(3)C(6)H(4)NH(2) with 3 produce novel chelated iron-carbene complexes [Fe(2)[=C(C(6)H(4)CH(3)-p)NC(10)H(7)](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (19) and [Fe(2)[=C(C(6)H(4)CF(3)-p)NC(6)H(4)CF(3)-p](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (20), respectively. Compound 18 can also be transformed into the analogous chelated iron-carbene complex [Fe(2)[=C(C(6)H(4)CH(3)-p)NC(6)H(5)](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (21). The structures of complexes 6, 9, 15, 17, 18, and 21 have been established by X-ray diffraction studies.     

Beyond-thermal-equilibrium" conversion of methane to acetylene and hydrogen under pulsed corona discharge

At ambient temperature and pressure, C2H2 and H2 are the dominating products from pure methane conversion under pulsed corona discharge (PCD). When the energy density of 194-1788 kJ/mol was applied, 7%-30% of C2H2 yield and 6%-35% of H2 yield per pass have been obtained. These results are higher than the maximum thermodynamic yield of C2H2 (5.1%) and H2 (3.8%) at 100 kPa and 1100 K, respectively. Thereby, pulsed corona discharge is a very effective tool for "beyond-thermal-equilibrium" conversion of methane to C2H2 and H2 at ambient temperature and pressure. In the PCD energy density range of 339-822 kJ/mol, the carbon distribution of the methane conversion products is found to be: C2H2 86%-89%, C2H6 4%-6%, C2H4 4%-6%, C3 -2%, C4 -1%. Through comparison of the product from pure methane, ethane and ethylene conversion at the same discharge conditions, it can be concluded that three pathways may be responsible for the C2H2 formation via CHx radicals produced from the collisions of CH4 molecules with energi     

Stereospecific Photoredox-Catalyzed Vinylations to Functionalized Alkenes and C-Glycosides**

We report an efficient radical-mediated C−C coupling through photoredox-catalyzed reactions of 4-alkyl-dihydropyridines (DHPs) and vinylbenziodoxol(on)es (VBX, VBO). This transition-metal-free and mild photocatalytic method has excellent functional group tolerance and affords vinylated products in good yields, with complete retention of the alkene configuration. The utility of the methodology is demonstrated by the diastereoselective synthesis of C-vinyl glycosides. Preliminary mechanistic studies suggest that the C−C bond formation is stereospecific and proceeds through a concerted radical coupling transition state.     

Theoretical studies on the smallest fullerene: from monomer to oligomers and solid States

Hybrid B3LYP and density-functional-based tight-binding (DFTB) computations on the solid-state structures and electronic properties of the C(20) fullerene monomer and oligomers are reported. C(20) cages with C(2), C(2h), C(i), D(3d), and D(2h) symmetries have similar energies and geometries. Release of the very high C(20) strain is, in theory, responsible for the ready oligomerization and the formation of different solid phases. Open [2+2] bonding is preferred both in the oligomers and in the infinite one-dimensional solids; the latter may exhibit metallic character. Two types of three-dimensional solids, the open [2+2] simple cubic and the body-centered cubic (bcc) forms, are proposed. The energy of the latter is lower due to the better oligomer bonding. The open [2+2] simple cubic solid should be a conductor, whereas the bcc solids are insulators. The most stable three-dimensional solid-state structure, an anisotropically compressed form of the bcc solid, has a HOMO-LUMO gap of approximately 2 eV and a larger binding energy than that of the proposed C(36) solid.     

New synthetic approach to paullones and characterization of their SIRT1 inhibitory activity

A series of 7,12-dihydroindolo[3,2-d][1]benzazepine-6(5H)-ones (paullones) substituted at C9/C10 (Br) and C2 (Me, CF(3), CO(2)Me) have been synthesized by a one-pot Suzuki-Miyaura cross-coupling of an o-aminoarylboronic acid and methyl 2-iodoindoleacetate followed by intramolecular amide formation. Other approaches to the paullone scaffold based on Pd-catalyzed C-H activation were unsuccessful. In vitro enzymatic assay with recombinant human SIRT-1 indicated a strong inhibitory profile for the series, in particular the analogue with a methoxycarbonyl group at C2 and a bromine at C9. These compounds are, in general, inducers of granulocyte differentiation of the U937 acute leukemia cell line and cause a marked increase in pre-G1 of the cell cycle.