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Piotr Przybylski Krystian Pyta Katarzyna Klich Wojciech Schilf Bohdan Kamieński 《Magnetic resonance in chemistry : MRC》2014,52(1-2):10-21
13C, 15N CP/MAS, including 1H–13C and 1H–15N short contact time CP/MAS experiments, and FTIR methods were applied for detailed structural characterization of ansa‐macrolides as 3‐formylrifamycin SV (1) and its derivatives (2–6) in crystal and in powder forms. Although HPLC chromatograms for 2/CH3OH and 2/CH3CCl3 were the same for rifampicin crystals dissolved in respective solvents, the UV–vis data recorded for them were different in 300–375 nm region. Detailed solid state 13C and 15N CP/MAS NMR and FTIR studies revealed that rifampicin (2), in contrast to 3‐formylrifamycin SV (1) and its amino derivatives (3–6), can occur in pure non‐ionic or zwitterionic forms in crystal and in pure these forms or a mixture of them in a powder. Multinuclear CP/MAS and FTIR studies demonstrated also that 3–6 derivatives were present exclusively in pure zwitterionic forms, both in powder and in crystal. On the basis of the solid state NMR and FTIR studies, two conformers of 3‐formylrifamycin SV were detected in powder form due to the different orientations of carbonyl group of amide moiety. The PM6 molecular modeling at the semi‐empirical level of theory, allowed visualization the most energetically favorable non‐ionic and zwitterionic forms of 1–6 antibiotics, strongly stabilized via intramolecular H‐bonds. FTIR studies indicated that the originally adopted forms of these type antibiotics in crystal or in powder are stable in standard laboratory conditions in time. The results presented point to the fact that because of a possible presence of two forms of rifampicin (compound 2), quantification of the content of this antibiotic in relevant pharmaceuticals needs caution. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Martin GE Hilton BD Irish PA Blinov KA Williams AJ 《Magnetic resonance in chemistry : MRC》2007,45(10):883-888
Utilization of long-range (1)H--(15)N heteronuclear chemical shift correlation has continually grown in importance since the first applications were reported in 1995. More recently, indirect covariance NMR methods have been introduced followed by the development of unsymmetrical indirect covariance processing methods. The latter technique has been shown to allow the calculation of hyphenated 2D NMR data matrices from more readily acquired nonhyphenated 2D NMR spectra. We recently reported the use of unsymmetrical indirect covariance processing to combine (1)H--(13)C GHSQC and (1)H--(15)N GHMBC long-range spectra to yield a (13)C--(15)N HSQC-HMBC chemical shift correlation spectrum that could not be acquired in a reasonable period of time without resorting to (15)N-labeled molecules. We now report the unsymmetrical indirect covariance processing of (1)H--(13)C GHMBC and (1)H--(15)N IMPEACH spectra to afford a (13)C--(15)N HMBC-IMPEACH spectrum that has the potential to span as many as six to eight bonds. Correlations for carbon resonances long-range coupled to a protonated carbon in the (1)H--(13)C HMBC spectrum are transferred via the long-range (1)H--(15)N coupling pathway in the (1)H--(15)N IMPEACH spectrum to afford a much broader range of correlation possibilities in the (13)C--(15)N HMBC-IMPEACH correlation spectrum. The indole alkaloid vincamine is used as a model compound to illustrate the application of the method. 相似文献
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Paramagnetic copper(II) complexes of the type [Cu(PPh3)(L)] (where L = bifunctional tridentate Schiff bases) were synthesized from the reaction of anthranillic acid with salicylaldehyde (H2L1), 2‐hydroxy‐1‐naphthaldehyde (H2L2), o‐hydroxyacetophenone (H2L3) and o‐vanillin (H2L4) with monomeric metal precursor [CuCl2(PPh3)2]. The obtained complexes were characterized by elemental analysis, magnetic susceptility and spectroscopic methods (FT‐IR, UV–vis and EPR and cyclic voltammetry). EPR and redox potential studies have been carried out to elucidate the electronic structure, nature of metal–ligand bonding and electrochemical features. EPR spectra exhibit a four line pattern with nitrogen super‐hyperfine couplings originating from imine nitrogen atom. These planar complexes possess a significant amount of tetrahedral distortion leading to a pseudo‐square planar geometry, as is evidenced from EPR properties. Cyclic voltammograms of all the complexes display quasireversible oxidations, Cu(III)? Cu(II), in the range 0.31–0.45 V and reduction peaks, Cu(II)? Cu(I),in the range ?0.29 to ?0.36 V, involving a large geometrical change and irreversible. The observed redox potentials vary with respect to the size of the chelate ring of the Schiff base ligands. Further, the catalytic activity of all the complexes has been found to be high towards the oxidation of alcohols into aldehydes and ketones in the presence of N‐methylmorpholine‐N‐oxide as co‐oxidant. The formation of high valent CuIV?O oxo species as a catalytic intermediate is proposed for the catalytic process. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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《Magnetic resonance in chemistry : MRC》2003,41(2):135-138
The proton transfer equilibrium in a series of double Schiff base derivatives of trans‐1,2‐diaminocyclohexane in solution and the solid state was studied by means of 15N NMR spectroscopy and analysis of the deuterium isotope effect on the chemical shifts Δ15N(D). The presence of a proton transfer equilibrium in the N‐2‐hydroxynaphthylidene moieties of the Schiff bases studied in the solid state at room temperature was evidenced. The results confirmed the interrelation of the two hydrogen bonds in double Schiff base derivatives of trans‐1,2‐diaminocyclohexane. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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(15)N-enriched dihydroxamic acids (HONHCO(CH(2))(n)CONHOH, n = 0, 1, and 2) were prepared and their spectra NMR ((1)H, (13)C, (15)N) recorded in dimethyl sulfoxide (DMSO) solutions with the aim of determining (15)N coupling constants ((15)N-(1)H and (15)N-(13)C). The results supplement chemical shifts published earlier and yield additional support to the structural conclusions derived from other NMR parameters. Notably, no trace of hydroximic structures could be found in the (15)N NMR spectra of these acids. The values of (15)N-(13)C coupling constants backed by theoretical calculations support the assignments made earlier for all of the major conformers and for the minor conformer of succinohydroxamic acid. The enrichment revealed that the minor component of malonodihydroxamic acid solution previously considered to be the ZE conformer is in fact the monohydroxamic acid (HOOC-CH(2)-CO-NH-OH). 相似文献
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Alan R. Katritzky Bahaa El‐Dien M. El‐Gendy Bogdan Draghici Dmytro Fedoseyenko Aziz Fadli Eric Metais 《Magnetic resonance in chemistry : MRC》2010,48(5):397-402
1H, 13C, and 15N NMR chemical shifts for pyridazines 4–22 were measured using 1D and 2D NMR spectroscopic methods including 1H? 1H gDQCOSY, 1H? 13C gHMQC, 1H? 13C gHMBC, and 1H? 15N CIGAR–HMBC experiments. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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The 1H and 13C NMR chemical shifts of the aldose reductase inhibitor 4(S)-2,3-dihydro-6-fluoro-2(R)-methylspiro[chroman-4,4'-imidazoline]-2',5'-dione, methylsorbinil, and its seven synthetic intermediates, have been completely assigned on the basis of DEPT, COSY, g-HSQC and g-HMBC. All C--F coupling constants from one-bond to four-bond in the 13C NMR spectra and H--F and H--H coupling constants from three-bond to four-bond in 1H spectra were obtained. 相似文献
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Martin GE Irish PA Hilton BD Blinov KA Williams AJ 《Magnetic resonance in chemistry : MRC》2007,45(8):624-627
There has been considerable interest over the past decade in the utilization of direct and long-range 1H- 15N heteronuclear shift correlation methods at natural abundance to facilitate the elucidation of small molecule structures. Recently, there has also been a high level of interest in the exploration of indirect covariance NMR methods. Our initial explorations in this area led to the development of unsymmetrical indirect covariance methods, which allow the calculation of hyphenated 2D NMR spectra such as 2D GHSQC-COSY and GHSQC-NOESY from the discrete component 2D NMR experiments. We now wish to report the utilization of unsymmetrical indirect covariance NMR methods for the combination of 1H- 13C GHSQC and 1H- 15N long-range (GHMBC, IMPEACH-MBC, CIGAR-HMBC, etc.) heteronuclear chemical shift correlation spectra to determine 15N- 13C correlation pathways. 相似文献
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Claramunt RM Santa María MD Sanz D Alkorta I Elguero J 《Magnetic resonance in chemistry : MRC》2006,44(5):566-570
Three N-substituted pyrazoles and three N-substituted indazoles [1-(4-nitrophenyl)-3,5-dimethylpyrazole (1), 1-(2,4-dinitrophenyl)-3,5-dimethylpyrazole (2), 1-tosyl-pyrazole (3), 1-p-chlorobenzoylindazole (4), 1-tosylinda-zole (5) and 2-(2-hydroxy-2-phenylethyl)-indazole (6)] have been studied by NMR spectroscopy in solution (1H, 13C, 15N) and in the solid state (13C, 15N). The chemical shifts have been compared with GIAO/DFT calculated absolute shieldings. Some discrepancies have been analyzed. 相似文献
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The induced codeposition mechanism of Mo, P and Ni from the solution of ammoniac citrate was studied by means of steady-state polarization, AC impedance and X-ray Photoelectron Spectroscopy (XPS). The result of electrochemical measurements proved that [NiCit(NHs)2]- is the electro-active species of nickel, though nickel ions exist mainly as [NiCit(NH3)3]? in ammoniac citrate. XPS experiments proved the existence of tetravalent molybdenum corresponding to MoO2 on the surface of mme deposits. The intermediate product, MoO2, WM probably reduced to Mo in the alloy deposit by atomic hydrogen adsorbed on the induced metal nickel. The reduction of H2PO?2 occurs through two distinctive steps with PH3 an an intermediate, which subsequently reacts with atomic hydrogen to form P in the alloy deposit. The electrodeposition mechanism was proposed in this paper. 相似文献
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Morofuji T Shimizu A Yoshida J 《Angewandte Chemie (International ed. in English)》2012,51(29):7259-7262
Pool and couple: A method for oxidative C-H/C-H cross-coupling has been developed using "radical-cation pools". Aromatic compounds react with aryl radical cations, which are generated and accumulated by low-temperature electrolysis (see scheme). This method avoids both the nonselective oxidation of substrates and oxidation of products and effects the C-H/C-H cross-coupling of aromatic compounds without metal complexes and chemical oxidants. 相似文献
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W. Schilf B. Kamie
ski Z. Rozwadowski K. Ambroziak B. Bieg T. Dziembowska 《Journal of Molecular Structure》2004,700(1-3):61
The 13C, 15N CP MAS NMR and FT-IR spectra of dioxomolybdenum (VI) complexes of trans-N,N′-bis-(R-salicylidene)-1,2-cyclohexanediamine (R=H, R=3,5-diCl, R=3,5-diBr, R=4,6-diOCH3), trans-N,N′-bis-(2-OH-naphthylidene)-1,2-cyclohexanediamine and trans-N-(salicylidene)-N′-(2-OH-naphthylidene)-1,2-cyclohexanediamine have been measured. Comparative analysis of the NMR and IR spectra of the complexes with those of the corresponding ligands has shown that the complexation of the di-Schiff bases leads to changes in the conformation of the ligands and the charge redistribution. The asymmetric structure and non-planar structure of the complexes have been suggested. 相似文献