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CO Groups (co + groups)
Selected AbstractsComparison of Isoelectronic Heterometallic and Homometallic Binuclear Cyclopentadienylmetal Carbonyls: The Iron,Nickel vs. the Dicobalt SystemsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2008Jun D. Zhang Abstract The heterometallic binuclear cyclopentadienylironnickel carbonyl compounds Cp2FeNi(CO)n (n = 3, 2, 1; Cp = ,5 -C5H5) have been studied by density functional theory (BP86) for comparison with the isoelectronic homometallic dicobalt derivatives Cp2Co2(CO)n. The FeNi tricarbonyl is shown to be the doubly bridged isomer Cp2Fe(CO)Ni(,-CO)2 with an Fe,Ni distance of 2.455 Å (BP86), in accord with experiment and in contrast to Cp2Co2(CO)3 where singly and triply bridged but not doubly bridged isomers are found. The dicarbonyl compounds Cp2FeNi(,-CO)2 and Cp2Co2(,-CO)2 both have analogous doubly bridged structures with M=M distances around 2.35 Å, suggesting formal M=M double bonds. The monocarbonyl compounds have analogous singly bridged axial structures Cp2FeNi(,-CO) and Cp2Co2(,-CO) with metal,metal distances in the range 2.05 Å (M2 = Co2) to 2.12 Å (M2 = FeNi) consistent with the formal M,M triple bonds required for the favored 18-electron configuration. Open-shell states of Cp2FeNi(,-CO) are found to have even lower energies than the closed-shell structure, which indicates that the ground state of Cp2FeNi(,-CO) might be a high spin structure. However, the global minimum for the monocarbonyl is found to be a singlet "hot dog" perpendicular Cp2NiFe(CO) structure with a terminal CO group bonded to the iron atom. Other higher energy perpendicular structures are also found for Cp2FeNi(CO)n (n = 3, 2, 1) with terminal CO groups and bridging Cp rings. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Synthesis of Cyclic Peptides by Photochemical Decarboxylation of N -Phthaloyl Peptides in Aqueous SolutionHELVETICA CHIMICA ACTA, Issue 12 2002The synthesis of a variety of cyclic peptides from N -phthaloyl-protected di-, tri-, tetra-, and pentapeptides with different aminocarboxylic acid tethers by photodecarboxylation , initiated by intramolecular electron transfer , has been explored in aqueous media. The progress and the chemoselectivity of the follow-up processes after CO2 extrusion were traced by the respective pH/time-profiles, as well as by the overall change in pH after completion of the reaction. The competition between cyclization and simple oxidative decarboxylation depends on spacer length and geometry, H-bonding interaction between the electron accepting phthalimide CO groups and amide H-atoms, as well as the geometric reorganization coupled with the radical combination step and the formation of the lactam rings. With progressing reaction, hydrolysis of the phthalimide chromophore becomes an increasingly important side reaction due to the constant increase in pH. The use of phosphate-buffered aqueous media consequently improved the cyclization yields. The ground-state interactions between amide groups and the terminal COO, group with the imide CO groups were studied for the model system [N -(phthaloyl)glycyl]sarcosine (1) by NMR spectroscopy where the amide (E/Z)-equilibrium depends on the presence of carboxylate vs. free carboxylic acid, demonstrating the role of H-bonding and metal coordination. [source] Dye,fiber interactions in PET fibers: Hydrogen bonding studied by IR-spectroscopyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Karen De Clerck Abstract Dye,fiber interactions are studied in poly (ethylene terephthalate) fibers by FT-IR spectroscopy. It is shown for the first time that DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) serves as an easy applicable and accurate technique for the study of fibrous structures. This article focuses on the possible hydrogen bond interactions in the dye,fiber system, where the PET fibers are dyed with anthraquinone-based disperse dyes. The dyes and related anthraquinone structures are studied in both the dilute solution state, the solid state, and as present in the PET fibers. It is proven that 1-amino anthraquinones show strong "chelate-type" intramolecular hydrogen bonding in all three states. In the fibers an important supplementary intermolecular hydrogen bonding with the CO groups in the PET fiber is observed. The extend of hydrogen bonding seems to be prone to dye concentration variations. Further analysis by modulated differential scanning calorimetry links the hydrogen bonding to an intrinsic plasticizing effect of the dyes affecting the dye diffusion process. This thus offers a tool for the fundamental understanding of the dyeing process and possible observed differences in dyeing behavior in dye,fiber systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Characteristics of hydrogen bond formation between sugar and polymer in freeze-dried mixtures under different rehumidification conditions and its impact on the glass transition temperatureJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2008Koreyoshi Imamura Abstract The characteristics of hydrogen bond formation between trehalose and polyvinylpyrrolidone (PVP) in amorphous mixtures at different hydration states were quantitatively investigated. Amorphous trehalose,PVP mixtures were prepared by freeze-drying and equilibrated at different relative humidities (RH). Infrared (IR) spectra of the trehalose,PVP mixtures were obtained by Fourier transform IR spectroscopy,(FTIR) and the IR band corresponding to CO groups of PVP was deconvolved into the component bands responsible for CO groups that were free and restricted by hydrogen bonds, to estimate the degree of the trehalose,PVP interactions. The FTIR analysis indicated that approximately 80% of the CO groups of PVP formed hydrogen bonds with trehalose in the presence of more than 3 g of trehalose per gramme of PVP, independent of the RH. IR analysis of the OH stretching vibration of the sugar demonstrated that the presence of PVP lead to an increase in the free hydroxyl groups of trehalose that did not form hydrogen bonds at RH 0%. On the other hand, the water sorption behavior of the trehalose,PVP mixtures suggested that rehumidification diminished the effect of PVP on increasing the free OH groups. Thus a peculiar relationship may exist between Tg, RH and the composition of the mixture: The presence of PVP increased Tg at RHs 0 and above 23% but decreased Tg at 11%. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:1301,1312, 2008 [source] Synthesis of Nanocrystalline Lanthanum Strontium Manganite Powder by the Urea,Formaldehyde Polymer Gel Combustion RouteJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2006Kuttan Prabhakaran Nanocrystalline lanthanum strontium manganite (LSM) powder has been synthesized by combustion of a transparent gel obtained by the polymerization of methylol urea and urea in a solution containing La3+, Sr2+, and Mn2+ (LSM ions). Chemistry of the transparent urea,formaldehyde (UF) polymer gel formation and structure of the gel have been proposed such that the LSM ions act in between the growing UF polymer chains by interacting through NH, OH, and CO groups by co-ordination and prevent polymer self-assembly through inter-chain hydrogen bonding as evidenced from infrared spectrum. Thermally stable structures formed by the decomposition of UF polymer below 300°C undergo combustion in the presence of nitrate oxidant in a temperature range from 350°,450°C. A perovskite LSM phase has been formed by self-sustained combustion of the dried gel initiated with little kerosene. The powder obtained after deagglomeration and calcination at 600°C for 2 h has a D50 value of 0.19 ,m, and the particles are aggregates of crystallites 10,25 nm in size. [source] Effect of Functionalized Carbon Nanotubes on Molecular Interaction and Properties of Polyurethane CompositesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 19 2006Nanda Gopal Sahoo Abstract Summary: Functionalized MWNTs were incorporated into PU by solution mixing to improve the mechanical and thermal properties of composites. A homogeneous dispersion of MWNTs was successfully achieved in PU matrix as evidenced by scanning electron microscopy. It may be attributed to the hydrogen bonds existing between CO groups of hard segments of PU chains and COOH groups of the MWNT-COOH. The incorporation of the MWNTs effectively enhanced the crystallization of the PU matrix through heterogeneous nucleation, and the nucleation effect was more evident at 10 wt.-% functionalized MWNTs as compared to other composite systems. Mechanical properties of the PU-MWNTs composites were assessed as a function of MWNT concentration and dispersion of MWNT in PU matrix. The most significant improvement in mechanical properties was obtained, e.g., 740% increase in modulus and 180% increase in tensile strength over pure PU with 20% MWNT content. The thermal stability of composites due to thermal gravimetric measurements was significantly improved. A possible interaction of H-bonding existed between PU chain and MWNT-COOH. [source] Aplanarity of CO3 groups: a theoretical investigationACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2000Björn Winkler Density functional theory-based calculations have been used to demonstrate that the aplanarity of CO groups in some carbonates such as dolomite, CaMg(CO), aragonite, CaCO, and norsethite, BaMg(CO), is a ground-state property. This distortion stabilizes dolomite by ,500,J,mol. Up to at least 6,GPa, the aplanarity of CO groups in dolomite is independent of pressure. In aragonite the aplanarity increases slightly on increasing pressure, while a significant tilting of the CO groups occurs. The calculations do not support previous findings of anomalously low values for the pressure derivative of the bulk moduli, , of aragonite and dolomite. Instead, the computed pressure dependences of the unit-cell volumes correspond to = 5.0,(5) for aragonite and = 4,(1) for dolomite, when fitted with a third-order Birch,Murnaghan equation-of-state. [source] Spectroscopic study on structure of horseradish peroxidase in water and dimethyl sulfoxide mixtureBIOPOLYMERS, Issue 2 2002Yasushi Maeda Abstract The structure of horseradish peroxidase (HRP) in phosphate buffered saline (PBS)/dimethyl sulfoxide (DMSO) mixed solvents at different compositions is investigated by IR, electronic absorption, and fluorescence spectroscopies. The fluorescence spectra and the amide I spectra of ferric HRP [HRP(Fe3+)] show that overall structural changes are relatively small up to 60% DMSO. Although the amide I band of HRP(Fe3+) shows a gradual change in the secondary structure and a decrease in the contents of , helices, its fluorescence spectra indicate that the distance between the heme and Trp173 is almost constant. In contrast, the changes in the positions of the Soret bands for resting HRP(Fe3+) and catalytic intermediates (compounds I and II) and the IR spectra at the CO stretching vibration mode of carbonyl ferrous HRP [HRP(Fe2+)-CO] show that the microenvironment in the distal heme pocket is altered, even with low DMSO contents. The large reduction of the catalytic activity of HRP even at low DMSO contents can be attributed to the structural transition in the distal heme pocket. In PBS/DMSO mixtures containing more than 70 vol % DMSO, HRP undergoes large structural changes, including a large loss of the secondary structure and a dissociation of the heme from the apoprotein. The presence of the components of the amide I band that can be assigned to strongly hydrogen bonding amide CO groups at 1616 and 1684 cm,1 suggests that the denatured HRP may aggregate through strong hydrogen bonds. © 2002 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 67: 107,112, 2002 [source] Carbon Monoxide Has Direct Toxicity on the Myocardium Distinct from Effects of Hypoxia in an Ex Vivo Rat Heart ModelACADEMIC EMERGENCY MEDICINE, Issue 1 2008Selim Suner MD Abstract Objectives:, Carbon monoxide (CO) toxicity causes significant central nervous system and cardiac injury. Although the neurological damage caused by CO toxicity is extensively described, the mechanisms underlying myocardial insult are unclear. The authors used an externally perfused isolated rat heart model to examine the effects of a physiological saline solution (Krebs Henseleit HEPES, KHH) aerated with CO on cardiac function. Methods:, Fifteen rats were equally divided into three groups: the control group (KHH + 100% O2), the nitrogen control group (KHH + 70% O2, 30% N2), and the CO group (KHH + 70% oxygen, 30% CO). Left ventricular peak systolic pressure (LVPsP), end diastolic pressure (LVEdP), and coronary perfusion pressure were measured while the isolated heart was paced and perfused on a modified Langendorf apparatus. Results:, Left ventricular generated pressure (LVGP = LVPsP , LVEdP) decreased in the nitrogen control and CO groups compared to the control group. There was higher LVGP in the recovery phase between the nitrogen control group compared to the CO group. Both groups had increased lactic acid levels in the experimental phase. Conclusions:, Carbon monoxide with hypoxia and hypoxemic hypoxia both result in similar depression of cardiac function. Hearts poisoned with CO with hypoxia do not recover function to the extent that hearts rendered hypoxic with nitrogen do when perfused with 100% oxygen after the insult. This suggests that CO causes direct myocardial toxicity distinct from the effects of hypoxia. [source] Analysis of a Pentacoordinate Iron Dicarbonyl as Synthetic Analogue of the Hmd or Mono-Iron Hydrogenase Active Site,CHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2010Tianbiao Liu Abstract Pentacoordinate iron dicarbonyls, (NS)Fe(CO)2P (NS=2-amidothiophenylate, P=PCy3 (4), PPh3, (5), and P(OEt)3 (6)) were prepared as potential biomimetics of the active site of the mono-iron hydrogenase, [Fe]-H2ase. Full characterization including X-ray diffraction, density functional theory (DFT) computations, and Mössbauer studies for complexes 5 and 6 find that, despite similar infrared v(CO) pattern and absorption frequencies as the active site of the [Fe]-H2ase, the geometrical distortions towards trigonal bipyramidal, the negative isomer shift parameters, and the differences in CO-uptake reactivity are due to the "non-innocence" of the NS ligand. Ligand-based protonation with a strong acid, HBF4,Et2O, interrupted the extensive ,-delocalization over Fe and NS ligand of complex 4 and switched on CO uptake (1,bar) to form a CO adduct, mer -[(H-NS)Fe(CO)3(PCy3)]+ or 4(CO)-H+. The extrinsic CO is reversibly removed on deprotonation with Et3N to regenerate complex 4. In a 13CO atmosphere, concomitant CO uptake by 4 -H+ and exchange with intrinsic CO groups provide a facile route to 13C-labeled 4(CO)-H+ and, upon deprotonation, 13C-labeled complex 4. DFT calculations show substantial Fe character in the LUMO of 4 -H+ typical of the d6 FeII in a regular square-pyramidal geometry. Thus, the Lewis acidity of 4 -H+ makes it amenable for CO binding, whereas the dianionic NS ligand renders the iron center of 4 insufficiently electrophilic and largely of FeI character. [source] Infrared Study of Intercomponent Interactions in a Switchable Hydrogen-Bonded RotaxaneCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2008Dhiredj Abstract The macrocycle in rotaxane 1 is preferentially hydrogen bonded to the succinamide station in the neutral form, but can be moved to the naphthalimide station by one-electron reduction of the latter. The hydrogen bonding between the amide NH groups of the macrocycle and the CO groups in the binding stations in the thread was studied with IR spectroscopy in different solvents in both states. In addition, the solvent effect on the vibrational frequencies was analyzed; a correlation with the solvent acceptor number (AN) was observed. The conformational switching upon reduction could be detected by monitoring the hydrogen-bond-induced shifts of the ,(CO) frequencies of the CO groups of the succinamide and the reduced naphthalimide stations. The macrocycle was found to shield the encapsulated station from the solvent: wavenumbers of ,(CO) bands of the CO groups residing inside the macrocycle cavity remain unaffected by the solvent polarity. [source] Casearin X, Its Degradation Product and Other Clerodane Diterpenes from Leaves of Casearia sylvestris: Evaluation of Cytotoxicity against Normal and Tumor Human CellsCHEMISTRY & BIODIVERSITY, Issue 1 2010André Gonzaga, Santos Abstract An EtOH extract of the leaves of Casearia sylvestris afforded new clerodane diterpene, casearin X, together with the known compounds casearins B, D, L, and O, and caseargrewiin F. Casearin X degraded to the corresponding dialdehyde when stored in CDCl3. The diterpenes isolated were cytotoxic to human cancer cell lines, with caseargrewiin F being the most active and the new clerodane, casearin X, the second active compound with IC50 values comparable to the positive control doxorubicin. All isolated diterpenes showed lower activities against normal human cells than against cancer cell lines, which might indicate a possible selective action on cancer cells. Casearin X dialdehyde was not cytotoxic to cancer cells indicating that the occurrence of these CO groups at C(18) and C(19) is incompatible with the cytotoxic activity. [source] Spectroscopic rationalization of the separation abilities of decaproline chiral selector in dichloromethane,isopropanol solvent mixtureCHIRALITY, Issue 2 2007Peng Zhang Abstract A chiral column, with decaproline as the chiral selector, has broad chiral selectivity. To understand the separation mechanism of this chiral column, multiple spectroscopic techniques, including optical rotation, electronic circular dichroism, infrared absorption and vibrational circular dichroism, have been used here to study the conformation of the decaproline oligomer in isopropanol(IPA)/dichloromethane(DCM) mixtures. These studies indicate that decaproline oligomer adopts polyproline II conformation in IPA/DCM solvent system (0% IPA , 100% IPA). Hydrogen bonding interactions between CO groups of decaproline and IPA molecules increase as the content of IPA in the solvent mixture increases up to 60% and become less significant from then onwards. These spectroscopic observations are found to have a good correlation with the enantiomeric separation of racemic 2,2,2-trifluoro-1-[10-(2,2,2-trifluoro-1-hydroxy-ethyl-anthracen-9-yl]-ethanol by the decaproline column. Chirality 2006. © 2006 Wiley-Liss, Inc. [source] | |||||||||||||