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Carbonyl Carbon (carbonyl + carbon)
Terms modified by Carbonyl Carbon Selected AbstractsFormation of Pyridazinium Salts by Azo Coupling of N -Substituted 3-Amino-1-phenylbut-2-en-1-ones and Diazonium SaltsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 24 2004Abstract Treatment of 3-(2,4-dimethoxyphenylamino)- and 3-methylamino-1-phenylbut-2-en-1-ones with some benzenediazonium tetrafluoroborates gives, besides the usual azo coupling products [i.e., 3-(substituted imino)-1-phenylbutane-1,2-diones 2-(4-substituted phenylhydrazones) and 2-(4-methoxyphenyldiazenyl)-3-methylamino-1-phenylbut-2-en-1-one, respectively], the previously unreported 1,4,5,6-tetrasubstituted pyridazinium tetrafluoroborates. The pyridazinium salts have been identified by X-ray analysis and by their 1H, 13C, 15N, 11B and 19F NMR spectra. Their formation is most probably the result of nucleophilic attack on the carbonyl carbon by the nitrogen of the hydrazone group and subsequent dehydration. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Quantitative solid-state 13C NMR spectroscopy of organic matter fractions in lowland rice soilsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2004R. J. Smernik Summary Spin counting on solid-state 13C cross-polarization (CP) nuclear magnetic resonance (NMR) spectra of two humic fractions isolated from tropical lowland soils showed that only 32,81% of potential 13C NMR signal was detected. The observability of 13C NMR signal (Cobs) was higher in the mobile humic acid (MHA) than in the calcium humate (CaHA) fraction, and increased with increasing intensity of irrigated rice cropping. NMR observability appeared to be related to the nature of the organic carbon, with phenol- and methoxyl-rich samples having the higher values of Cobs. The Bloch decay (BD) technique provided more quantitatively reliable 13C NMR spectra, as evidenced by values of Cobs in the range 91,100% for seven of the eight humic fractions studied. The BD spectra contained considerably more aryl and carbonyl signal, and less O,alkyl and alkyl signal, with the greatest differences between CP and BD spectra observed for the samples with low Cobs(CP). The causes of low CP observability were investigated using the spectral editing technique RESTORE ( REstoration of Spectra via TCH and T One Rho (T1,H) Editing). Rapid T1,H relaxation was found to be primarily responsible for the under-representation of carbonyl carbon, whereas inefficient cross-polarization was primarily responsible for the under-representation of aryl carbon in CP spectra. Proton NMR relaxation rates T1H and T1,H were found to correlate with other NMR properties and also with cropping management. Non-uniform rates of T1H relaxation in two of the CaHA fractions enabled the generation of proton spin relaxation editing subspectra. [source] (R,S)-Azolides as Novel Substrates for Lipase-Catalyzed Hydrolytic Resolution in Organic SolventsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Pei-Yun Wang Abstract Azolides, that is, N -acylazoles, as versatile acylation reagents are well characterized in the literature, in which the azole structure can not only act as a better leaving group but also make the carbonyl carbon more electrophilic and susceptible to nucleophilic attack. It is therefore desirable to combine this unique property and lipase resolution ability in the development of a new resolution process for preparing optically pure carboxylic acids. With the Candida antarctica lipase B (CALB) - catalyzed hydrolysis of (R,S)- N -profenylazoles in organic solvents as the model system, (R,S)- N -profenyl-1,2,4-triazoles instead of their corresponding ester analogues were exploited as the best substrates for preparing optically pure profens, i.e., 2-arylpropionic acids. The structure-reactivity correlations for the (R,S)-azolides in water-saturated methyl tert -butyl ether (MTBE) at 45,°C coupled with a thorough kinetic analysis were further employed for elucidating the rate-limiting formation of a tetrahedral adduct without CN bond breaking or with moderate CN bond breaking concerted with CO bond formation in the acylation step. The advantages of easy substrate preparation, high enzyme reactivity and enantioselectivity, and easy recovery of the product and remaining substrate by aqueous extraction demonstrate the potential of using (R,S)-azolides as novel substrates for the enzymatic resolution process. [source] Polymer electrolyte membranes having sulfoalkyl grafts into ETFE film prepared by radiation-induced copolymerization of methyl acrylate and methyl methacrylateJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009Truong Thi Hanh Abstract Polymer electrolyte membranes (PEMs) containing alkylsulfonic acid grafts can be prepared by radiation-induced graft copolymerization of methyl acrylate (MA) and methyl methacrylate (MMA) into a poly(ethylene- co -tetrafluoroethylene) film followed by sulfonation of the MA units in the copolymer grafts using an equimolar complex of chlorosulfonic acid and 1,4-dioxane (ClSO3H-Complex). PEMs with MA/MMA copolymer grafts that are 33%,79% MA units were prepared by preirradiation with a dose of 20 kGy and grafting in bulk comonomers at 60°C. The grafted films are treated with ClSO3H-Complex to obtain PEMs with ion exchange capacity of 0.36-0.81 mmol/g (sulfonation degrees of 20%,40%) and proton conductivity of 0.04-0.065 S/cm. These values can be controlled by changing the MA content the sulfonation occurring at an ,-carbonyl carbon. The PEMs with higher MMA content showed higher durability in water (80°C) and under oxidative conditions (3% H2O2) at 60°C. This is because the PMMA grafts in the PEMs have no proton at an ,-carbonyl carbon, which is considered to be a trigger of the degradation of grafting polymers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] A comparison of quantum chemical models for calculating NMR shielding parameters in peptides: Mixed basis set and ONIOM methods combined with a complete basis set extrapolationJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2006Seongho Moon Abstract This article compares several quantum mechanical approaches to the computation of chemical shielding tensors in peptide fragments. First, we describe the effects of basis set quality up to the complete basis set (CBS) limit and level of theory (HF, MP2, and DFT) for four different atoms in trans N -methylacetamide. For both isotropic shielding and shielding anisotropy, the MP2 results in the CBS limit show the best agreement with experiment. The HF values show quite a different tendency to MP2, and even in the CBS limit they are far from experiment for not only the isotropic shielding of carbonyl carbon but also most shielding anisotropies. In most cases, the DFT values differ systematically from MP2, and small basis-set (double- or triple-zeta) results are often fortuitously in better agreement with the experiment than the CBS ones. Second, we compare the mixed basis set and ONIOM methods, combined with CBS extrapolation, for chemical shielding calculations at a DFT level using various model peptides. From the results, it is shown that the mixed basis set method provides better results than ONIOM, compared to CBS calculations using the nonpartitioned full systems. The information studied here will be useful in guiding the selection of proper quantum chemical models, which are in a tradeoff between accuracy and cost, for shielding studies of peptides and proteins. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 825,836, 2006 [source] Molecular mechanics (MM4) calculations on carbonyl compounds part I: aldehydesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2001Charles H. Langley Abstract Aliphatic aldehydes have been studied with the aid of the MM4 force field. The structures, moments of inertia, vibrational spectra, conformational energies, barriers to internal rotation, and dipole moments have been examined for six compounds (nine conformations). MM4 parameters have been developed to fit the indicated quantities to the wide variety of experimental data. Ab initio (MP2) and density functional theory (B3LYP) calculations have been used to augment and/or replace experimental data, as appropriate. Because more, and to some extent, better, data have become available since MM3 was developed, it was anticipated that the overall accuracy of the information calculated with MM4 would be better than with MM3. The best single measure of the overall accuracy of a force field is the accuracy to which the moments of inertia of a set of compounds (from microwave spectroscopy) can be reproduced. For all of the 20 moments (seven conformations) experimentally known for the aldehyde compounds, the MM4 rms error is 0.30%, while with MM3, the most accurate force field presently available, the rms error over the same set is 1.01%. The calculation of the vibrational spectra was also improved overall. For the four aldehydes that were fully analyzed (over a total of 78 frequencies), the rms errors with MM4 and MM3 are 18 and 38 cm,1, respectively. These improvements came from several sources, but the major ones were separate parameters involving the carbonyl carbon for formaldehyde, the alkyl aldehydes and the ketones, and new crossterms featured in the MM4 force field that are not present in the MM3 version. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1396,1425, 2001 [source] Formulation considerations for proteins susceptible to asparagine deamidation and aspartate isomerizationJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2006Aditya A. Wakankar Abstract The asparagine (Asn) deamidation and aspartate (Asp) isomerization reactions are nonenzymatic intra-molecular reactions occurring in peptides and proteins that are a source of major stability concern in the formulation of these biomolecules. The mechanisms for the deamidation and isomerization reactions are similar since they both proceed through an intra-molecular cyclic imide (Asu) intermediate. The formation of the Asu intermediate, which involves the attack by nitrogen of the peptide backbone on the carbonyl carbon of the Asn or the Asp side chain, is the rate-limiting step in both the deamidation and the isomerization reactions at physiological pH. In this article, the influence of factors such as formulation conditions, protein primary sequence, and protein structure on the reactivity of Asn and Asp residues in proteins are reviewed. The importance of formulation conditions such as pH and solvent dielectric in influencing deamidation and isomerization reaction rates is addressed. Formulation strategies that could improve the stability of proteins to deamidation and isomerization reactions are described. The review is intended to provide information to formulation scientists, based on protein sequence and structure, to predict potential degradative sites on a protein molecule and to enable formulation scientists to set appropriate formulation conditions to minimize reactivity of Asn and Asp residues in protein therapeutics. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95:2321,2336, 2006 [source] Disubstituted 4(3H) Quinazolones: A Novel Class of Antitumor AgentsCHEMICAL BIOLOGY & DRUG DESIGN, Issue 3 2009Vikas Srivastava A series of disubstituted 4(3H) quinazolines were designed for potential application in tumors. Firstly, N -benzoyl anthranilic acid is formed, which undergoes cyclization in the presence of pyridine. Subsequently, nucleophilic attack by semicarbazide on the carbonyl carbon gives 2-substituted 3-carbamido 4(3H) quinazolones, which gives final compound with appropriate substitution. The final as well as intermediate products were confirmed by NMR, FT-IR, and mass spectrometry. In vitro toxicity was performed with different cell lines and showed that the connection of hydrophilic styryl to quinazoline moiety increases its efficacy. [source] Mechanistic Investigation of Chiral Phosphoric Acid Catalyzed Asymmetric Baeyer,Villiger Reaction of 3-Substituted Cyclobutanones with H2O2 as the OxidantCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2010Senmiao Xu Dr. Abstract The mechanism of the chiral phosphoric acid catalyzed Baeyer,Villiger (B,V) reaction of cyclobutanones with hydrogen peroxide was investigated by using a combination of experimental and theoretical methods. Of the two pathways that have been proposed for the present reaction, the pathway involving a peroxyphosphate intermediate is not viable. The reaction progress kinetic analysis indicates that the reaction is partially inhibited by the ,-lactone product. Initial rate measurements suggest that the reaction follows Michaelis,Menten-type kinetics consistent with a bifunctional mechanism in which the catalyst is actively involved in both carbonyl addition and the subsequent rearrangement steps through hydrogen-bonding interactions with the reactants or the intermediate. High-level quantum chemical calculations strongly support a two-step concerted mechanism in which the phosphoric acid activates the reactants or the intermediate in a synergistic manner through partial proton transfer. The catalyst simultaneously acts as a general acid, by increasing the electrophilicity of the carbonyl carbon, increases the nucleophilicity of hydrogen peroxide as a Lewis base in the addition step, and facilitates the dissociation of the OH group from the Criegee intermediate in the rearrangement step. The overall reaction is highly exothermic, and the rearrangement of the Criegee intermediate is the rate-determining step. The observed reactivity of this catalytic B,V reaction also results, in part, from the ring strain in cyclobutanones. The sense of chiral induction is rationalized by the analysis of the relative energies of the competing diastereomeric transition states, in which the steric repulsion between the 3-substituent of the cyclobutanone and the 3- and 3,-substituents of the catalyst, as well as the entropy and solvent effects, are found to be critically important. [source] | ||||||||||