bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of hyperfine‐shifted 1H resonances in oxidized and reduced putidaredoxin, an Fe2S2 ferredoxin from Pseudomonas putida
Authors: Ratnaswamy Gayathri , Pochapsky Thomas C. 
Published: May 2005

AbstractHyperfine‐shifted 1H resonances in the two accessible oxidation states of putidaredoxin (Pdx), an Fe2S2 ferredoxin from Pseudomonas putida, were observed and their temperature dependence and relaxation times measured using rapid‐recycle NMR methods. As with other Fe2S2 ferredoxins, the hyperfine‐shifted resonances observed in oxidized (Fe3+−Fe3+) Pdx exhibit anti‐Curie behavior, their signals moving away from the diamagnetic region with increasing temperature. The hyperfine‐shifted resonances of reduced Pdx (Fe3+−Fe2+) exhibit Curie‐type behavior, and closely resemble the appearance and behavior of the hyperfine shifted resonances of human ferredoxin (HFdx), with which Pdx shares significant sequence and functional homology. Electron self‐exchange is slow on the 1H chemical shift time‐scale, as half‐reduced samples of Pdx exhibit hyperfine‐shifted resonances characteristic of both forms.
Two‐dimensional 1H NMR spectroscopy of paramagnetic haem models of the cytochromes: Successes, failures and unanswered questions
Authors: Simonis Ursula , Lin Qing , Tan Helming , Barber R. Andrew , Walker F. Ann 
Published: May 2005

AbstractAs part of an effort to assign completely the1H resonances of the pyrrole protons of model haems, the NOESY spectra of a series of unsymmetrically phenyl‐substituted derivatives of a low‐spin paramagnetic haem model complex tetraphenylporphyrinatoiron (III)bis(N‐methylimidazole), [TPPFe(N‐Meim)2]+, for which the COSY spectra have been reported previously, were recorded in CD2Cl2 or CDCl3 at temperatures of 30 to −35°C using a variety of mixing times. Fourphenomena of importance to the understanding of the cross‐correlation patterns obtained in the NOESY spectra of these paramagnetic complexes were observed: (1) NOE cross peaks can be detected for these intermediate molecular weight complexes, even in non‐viscous solvents; (2) for some complexes only one set of NOE cross peaks different from those previously observed in the COSY maps were obtained, whereas for other complexes two sets were observed; (3) cross correlations between protons in the same pyrrole ring (i.e. cross peaks previously observed in the COSY maps) were observed in the NOESY spectra of some complexes, but not of others; and (4) at ambient temperature, where axial ligand exchange is detectable through cross peaks between the methyl resonances of free and coordinated N‐methylimidazole, additional sets of cross correlations between pairs of pyrrole protons, not observed at −35°C, were detecte d. Each of these phenomena is discussed and questions are raised concerning the cross‐relaxation pathways leading to the observed NOESY maps of these paramagnetic complexes. At the present state of development of two‐dimensional NMR studies of these paramagnetic model haem complexes, the electron density distribution in the orbital utilized for spin delocalization can be delineated (with some cautionary notes), but there still remains some ambiguity in the assignment of the fourpyrrole proton resonances of these mono‐ortho‐substituted tetraphenylporphyrinatoiron(III)complexes.
Investigation of the dynamics of cyclodextrins and their inclusion complexes in water by deuterium NMR
Authors: Azaroual‐Bellanger Nathalie , Perly Bruno 
Published: May 2005

AbstractDeuterium NMR and relaxation data are presented to investigate the state of β‐cyclodextrin in aqueous solution and to derive dynamic parameters for inclusion complexes. Labelled host and guest molecules were used, and dedicated pulse sequences are proposed for improving the deuterium spectra in terms of reduction of artifacts and of solvent peak(s) and also in terms of total duration of the experiments. This technique was used to investigate the state of β‐cyclodextrin in aqueous solution and to derive important information regarding the degree of dynamic coupling between host and guest in inclusion complexes.
Determination of the quadrupole coupling from featureless line shapes
Authors: Hepp M. A. , Man P. P. , Trokiner A. , Fraissard J. 
Published: May 2005

AbstractNMR nutation and quadrupole echo experiments were used to determine the quadrupole frequency (ωQ) of 87Rb (I = 3/2) in a single crystal of RbCaF3. Since RbCaF3 has a cubic unit cell above 195 K, there is no second‐order quadrupole shift and the spectrum is rather featureless. By fitting the response of 87Rb, as a function of pulse duration, to the predicted response we were able to determine that the average ωQ/2π = 4.5 kHz in this sample. Discrepancies in the agreement between the theory and the experiment for the echo response were attributed to differential relaxation of the central and satellite transitions.
Determination of three‐dimensional structure of nervosin in solution by two‐dimensional nuclear magnetic resonance spectroscopy
Authors: Yang Yanwu , Xu Xiaolong , Wang Dehua , Qian Baogong 
Published: May 2005

AbstractTwo‐dimensional NMR techniques were used to obtain a complete proton spectral assignment of nervosin, a natural product with medicinal interest isolated from a Chinese herbal medicine. The full relaxation matrix analysis method was used to process the NOE matrix of nervosin. The three‐dimensional structure in solution was calculated by the combination of the WUPH and WUPH‐S methods, based on NMR experimental data, with molecular mechanics energy minimization calculation. The result indicated that the solution structure of nervosin is similar to the x‐ray structure.
Identification of modified natural porphyrin isomers: 1H and 13C NMR assignments by NOESY and reverse heteronuclear shift correlation
Authors: Bondon Arnaud , Autret Marie , Simonneaux Gérard 
Published: May 2005

AbstractThe efficiency of two‐dimensional homonuclear 1H1H NOE spectroscopy in characterizing and fully assigning the 1H NMR spectra of several isomers of meso‐ or ring‐substituted deuteroporphyrins is demonstrated. The carbon resonances of the skeleton and the substituents were fully assigned using two‐dimensional reverse heteronuclear shift correlation spectroscopy.
NMR conformational analysis of complexes of the carboxylic ionophore nigericin with Na+ and K+
Authors: Beloeil Jean‐Claude , Biou Valérie , Dauphin Gérard , Garnier Jean , Morellet Nelly , Vaufrey Françoise 
Published: May 2005

AbstractThe conformations of the complexes formed by the ionophore nigericin with Na+ and K+ in CDCl3 solution determined by ROESY NMR and distance geometry computations are in good agreement with the X‐ray crystallographic data. The structures with the Na+ ion are more compact than those with the K+ ion, as the latter have a wider cage for the ion.
Stereospecific assignment of exocyclic methylene protons in panose by 13C‐filtered 1D TOCSY
Authors: Poppe Leszek , Sheng Shuqun , van Halbeek Herman 
Published: May 2005

AbstractThe C‐6‐methylene protons in the internal glucosyl unit of panose, D‐Glc‐α(1 → 6)‐D‐Glc‐α(1 → 4)‐D‐Glc(α,β), were stereospecifically assigned. The assignment strategy involved the measurement of the long‐range 3J(C‐4, H‐6R) and 3J(C‐4,H‐6S) coupling constants for this residue in panose, with natural 13C isotope abundance, using a newly designed 13C‐filtered 1D TOCSY experiment.
Variable‐temperature 13C CP/MAS study of (Me3Sn)2CO3
Authors: Kümmerlen Jörg , Sebald Angelika 
Published: May 2005

AbstractSolid (Me3Sn)2CO3, 1, forms polymeric zig‐zag chains were bidentate magnified image units (containing a tetrahedral Me3Sn group) connect trigonal‐bipyramidal Me3SnO2 units which form the polymeric backbone. Both the tetrahedral and the trigonal‐bipyramidal Me3Sn moiety in solid 1 undergo 2π/3 reorientation around their respective SnO bonds at ambient temperature. Although 13C cross‐polarization magic angle spinning (CP/MAS) spectra of 1 are strongly temperature dependent in the temperature range 160–383 K, neither lineshape analysis of these exchange‐broadened 13C spectra nor 13C 2D exchange spectroscopy allows the extraction of meaningful kinetic data for solid 1. Owing to severe overlap problems in the various 13C CP/MAS spectra and because of the apparent vastly different 2π/3 jump rates for the two different Me3Sn units in solid 1, only combined information from variable‐temperature/variable‐r.f. irradiation strength 13C CP/MAS experiments in conjunction with consideration of geometric information from single‐crystal x‐ray diffraction yields an estimate of the respective activation energies for the 2π/3 jump processes of the trigonal‐bipyramidal Me3Sn(1) unit (Ea = 22.1 ± 2.4 kJ mol−1) and of the tetrahedral Me3Sn(2) unit (Ea ≈︁ 50 kJ mol−1) in solid 1.
13C NMR spectra of allosteric effectors of hemoglobin
Authors: Ostrowski Stanislaw , Priebe Waldemar , Burke Thomas G. 
Published: May 2005

AbstractCarbon‐13 NMR studies were performed for a series of allosteric effectors of hemoglobin. Spectral assignments were made by comparison of 1H‐decoupled 13C spectra; for selected cases, 2D HETCOR experiments were applied. High regularity in the chemical shifts of the similar fragments of these structures was found.
NMR spectra and configuration of biochromophoric compounds with norbornylogue spacer
Authors: Touillaux R. , Jiwan J.‐L. Habib , Soumillion J.‐Ph. 
Published: May 2005

AbstractThe determination of the structure and configuration of bichromophoric compounds with a norbornylogue spacer is presented on the basis of the 1H and 13C chemical shifts and vicinal HH coupling constants.
Methoxy group conformation effects on 13C NMR parameters in 1‐cis‐methoxy‐ and 1‐trans‐methoxy‐1,3‐trans‐butadiene
Authors: Esteban Angel L. , Galache Maria P. , Diez Ernesto , Biekofsky Rodolfo R. , Contreras Rubén H. 
Published: May 2005

AbstractThe proton‐coupled 13C NMR spectra of 1‐trans‐methoxy‐ (2) and 1‐cis‐methoxy‐1,3‐trans‐butadiene (3) are consistent with a methoxy heavy atom planar conformation with s‐syn and s‐anti orientations, respectively. Ab initio 6–31G* calculations confirmed such conformations. They were taken as model compounds to determine the influence of electrostatic interactions on the methoxy 13C NMR parameters. A shielding increase of 4 ppm is observed in 2, with respect to 3, for the OMe 13C chemical shift in an s‐syn conformation and is ascribed to the attraction between the methyl and vinyl moieties as proposed by Li and Chesnut. The methyl 1J(C,H) coupling is not affected by this interaction, showing that the carbon 2p electrons are more polarizable than those in the 2s orbital.
Electronic interactions implied by the non‐additivity of carbon‐13 substituent parameters in 2‐substituted cyclohexanones
Authors: Basso Ernani A. , Kaiser Carlos , Rittner Roberto , Lambert Joseph B. 
Published: May 2005

AbstractThe carbon‐13 chemical shifts were assigned for all ring positions in cyclohexanone and 4‐tert‐butylcyclohexanone with H, F, Cl, Br, I, MeO, MeS, MeSe, Me2N, Me or tert‐butyl in the 2‐position. The substituent‐induced shifts were calculated by difference from unsubstituted cyclohexanone or 4‐tert‐butylcyclohexanone. Both stereoisomers (cis and trans) were available for the 4‐tert‐butylcyclohexanones in all but one case. Comparison of the substituent‐induced shifts for the cis (equatorial 2‐substituent) and trans (axial 2‐substituent) isomers provides stereochemical insight into the interactions between the 2‐substituent and the carbonyl group that bring about non‐additivity of the substituent effects. In the 2‐equatorial isomer, the dipole–dipole interaction between the functional groups causes non‐additivities for the C‐2 carbon that depend largely on the electronegativity of the 2‐substituent. In the 2‐axial isomer, hyperconjugation or other orbital interactions between the groups cause non‐additivities for the C‐2 carbon that depend largely on the polarizability in addition to the electronegativity of the 2‐substituent.
183W NMR spectroscopy of W(VI) imidoaryl and imidoalkyl complexes using inverse detection based on non‐specific long‐range interactions
Authors: Macchioni Alceo , Pregosin Paul S. , Rüegger Heinz , van Koten Gerard , van der Schaaf Paul A. , Abbenhuis Rob A. T. M. 
Published: May 2005

Abstract183W NMR spectra for a series of octahedral W(VI) imidophenyl, ‘WNPh’ and W(VI) imidoethyl, ‘WNEt,’ complexes were obtained using inverse detection based on non‐specific long‐range interactions. The metal couples to both the ortho and para protons of the NPh moiety (four and six bonds, respectively). The 183W shift is shown to be sensitive to the nature of the ligand and the coordination number. The effect of geometric isomerism on δ183W is shown to be several hundred ppm. Some δ14N and δ15N and 1J(183W,15N) data are reported. A number of new geometric isomers, involving the position of the NR ligand with respect to the remaining ligands, have been identified.
Conformational analysis. Part 20—conformational analysis of 4‐deoxy‐4‐fluoro‐D‐glucose and 6‐deoxy‐6‐fluoro‐D‐galactose in solution
Authors: Abraham Raymond J. , Chambers Eric J. , Thomas W. Anthony 
Published: May 2005

AbstractThe 1H and 19F NMR spectra of the α‐ and β‐pyranose anomers of 4‐deoxy‐4‐fluoro‐D‐glucose (4FG) and 6‐deoxy‐6‐fluoro‐D‐galactose (6FGA) in methanol‐d4, DMSO‐d6, acetone‐d6 and D2O solution are reported. Computer analysis of the ABMX spectra of the CHCH2F fragments gives accurate vicinal HH and HF coupling constants. An iterative computational analysis of the observed vicinal couplings in this fragment for 6FG, 6FGA and other molecules allows the determination of both the individual rotamer couplings and the rotamer populations. Consideration of the derived rotamer couplings strongly suggests that the correct assignment for the prochiral C‐6 methylene protons in 6FG is that with the 6S proton having the larger coupling to H‐5. This is the reverse of the assignment of these protons in D‐glucose. In contrast, the assignment of these protons in 6FGA follows that given previously for D‐galactose. The relative energies for the conformations about the C‐5C‐6 bond for 4FG, 6FG and 6FGA are given from the derived rotamer populations. For 6FGA the rotamer in which the fluorine is antiperiplanar to C‐4 is particularly favoured. For 4FG the rotamer with OH anti‐periplanar to the ring O is highly unfavoured, but the other two rotamers are of almost equal energy. Consideration of the effect of replacing hydroxyl by fluorine in these molecules indicates that any hydrogen bonding involving the C‐4 or C‐6 hydroxyls plays little part in determining the conformer energies of glucose or galactose in polar solutions.
Stereochemistry of 4‐amino‐(D3)‐trishomocubanes. NMR study of 3‐phenyl‐4‐amino‐(D3)‐trishomocubane
Authors: Oliver D. W. , Dekker T. G. , Wessels P. L. 
Published: May 2005

AbstractAmino compounds of the highly symmetrical (D3)‐trishomocubane were recently shown to possess promising biological activities, i.e. antiviral and antiparkinson. This series was synthesized via a modified Ritter reaction. The unique hydrocarbon skeleton of these compounds has a D3 point group symmetry with a propeller shape. Several geometrical isomers are possible for the derivatives of (D3)‐trishomocubane. This paper reports the complete 1H and 13C NMR assignments and the configuration at C‐4 of one of the most promising compounds of the present series, i.e. 3‐phenyl‐4‐amino‐(D3)‐trishomocubane. The 13C NMR spectrum of this amine indicates the presence of only one geometrical isomer for the compound. NOE experiments on the fully assigned 1H NMR spectrum show that this isomer has the 3S4S/3R4R configuration, and not the 3S4R/3R4S configuration. These results indicate that the Ritter rearrangement proceeds stereospecifically and that it provides a facile method for the synthesis of (D3)‐trishomocuban‐4‐amines from tertiary alcohols of pentacyclo[5.4.0.02,6.03,10.05,9] undecan‐8‐ol.
NMR study of the inclusion complex formed between γ‐cyclodextrin and TmDOTP5−
Authors: Sherry A. Dean , Zarzycki Ryszard , Geraldes Carlos F. G. C. 
Published: May 2005

AbstractThe host–guest complex formed in aqueous solution between γ‐cyclodextrin (γ‐CD) and the macrocyclic paramagnetic shift reagent TmDOTP5− was examined by NMR spectroscopy. Paramagnetic lanthanide‐induced shifts (LIS) and spin‐lattice relaxation rate enhancements in the proton resonances of γ‐CD on binding of TmDOTP5− were used to define the position of the guest anion within the host cavity. A proportionality constant which relates pseudo‐contact shifts induced by TmDOTP5− to the geometrical position of each ligand nucleus (previously determined from a LIS study of the TmDOTP5− complex) was used to determine a fully bound LIS value for each γ‐CD proton. These values, in combination with experimental LIS data from TmDOTP5− titrations at constant γ‐CD concentration, were then used to obtain the association constant for the host‐guest complex (3.9–4.5 mol l−1). These constants were indicative of a weak host‐guest interaction and consistent with the location of the TmDOTP5− binding site reported by the LIS values well above the center of the γ‐CD cavity.
1H and 13C NMR of substituted dibenzo‐14‐crown‐4 ethers
Authors: Chen Zhihong , Sachleben Richard A. 
Published: May 2005

AbstractDibenzo‐14‐crown‐4 and eight substituted dibenzo‐14‐crown‐4‐ethers were studied by 1D and 2D 1H and 13C NMR and their chemical shifts are reported.
Isotope effects on the 13C chemical shift and carbon–proton coupling constant in dichloromethane
Authors: Sergeyev N. M. , Sergeyeva N. D. , Raynes W. T. 
Published: May 2005

AbstractCarbon–proton and carbon–deuteron coupling constants were measured in the isotopomers CH2Cl2, CHDCl2 and CD2Cl2. The primary and secondary isotope effects on the carbon–proton coupling are −0.60 (±0.05) and −0.25 (±0.01) Hz, respectively. The deuterium‐induced 13C isotope shifts proved to be almost linearly dependent on the number of deuterium atoms, although there is a small but significant non‐additivity.
Conformational studies on phosphorus‐containing macrocycles
Authors: Boese R. , Boetzel R. , Hägele G. 
Published: May 2005

AbstractH,H and P,H coupling constants and variable‐temperature 1H and 13C NMR spectra and 13C T1 values for some macrocyclic dithiophosphonic esters are presented to show that these compounds possess reduced flexibility in comparison with crown ethers. The NMR spectroscopic results are supported by an x‐ray structure which shows a highly strained ring system.
Solution and solid‐state structural chemistry of tungsten pyrazolylborate π‐allyl complexes: 2D 183W and 1H NOESY NMR studies
Authors: Pregosin Paul S. , Macchioni Alceo , Templeton Joseph L. , White Peter S. , Feng Shaoguang 
Published: May 2005

Abstract2D1H NOESY and inverse detected 183W NMR measurements for the pseudo‐octahedral η3‐allyl complexes W(CO)2(Tp′)(η3‐CH2CHCDPh) (1) and W(CO)2(Tp′)(η3‐CH2CHCHCH3) (2), where Tp′ = hydridotris(3,5‐dimethylpyrazolyl)borate are reported. The observed solution structure for 1 differs from that found in the solid‐state via x‐ray diffraction (isomers can arise due to allyl rotation and/or coordination of either allyl face). Crystal data for 1: WC26H31BN6O3, space group P21/c, a = 9.775(1) Å, b = 17.360(2) Å, c = 16.144(5) Å, β = 102.26(2)°, V = 2677(1) Å3, Z = 4.
Total assignment of the 1H and 13C chemical shifts for a mixture of cis‐ and trans‐p‐hydroxycinnamoyl esters of taraxerol with the aid of high‐resolution, 13C‐detected, 13C1H shift correlation spectra
Authors: McLean Stewart , Reynolds William F. , Yang Ji‐Ping , Jacobs Helen , Jean‐Pierre Laurent L. 
Published: May 2005

AbstractA mixture of two slowly interconverting isomeric compounds was isolated from Bernardia laurentii and identified as the trans‐ and cis‐p‐hydroxycinnamoyl esters of the triterpene taraxerol. Their 13C and 1H NMR spectra were totally assigned with the aid of concerted two‐dimensional NMR experiments. Not all assignments could be made using HMQC and HMBC owing to the limited 13C resolution and severe spectral crowding. However, the assignments could be made unambiguously by HETCOR and FLOCK experiments, relying on the superior 13C resolution of the 13C‐detected experiments. Comparison of 13C spectral assignments for a series of eight pentacyclic triterpenes with identical A and B ring structures but differences in C, D and/or E rings illustrates the risks and limitations of the use of model compounds for spectral assignments.
Data for the characterization of the geometrical isomers of β‐sulphinylenamines
Authors: Kozerski L. , Kawȩcki R. , Hansen P. E. 
Published: May 2005

AbstractNOE experiments at low temperature were used to establish the structure of the E‐ and Z‐isomers of the enamine ButSOCHCHNHBut. The NOE experiments revealed large intermolecular NOE effects between E‐ and Z‐isomers indicating the formation of dimers of specific orientation. NH chemical shifts and their temperature dependence showed that the E‐ and Z‐ isomers behave differently. The NH chemical shifts of the former go to higher frequencies on lowering the temperature, whereas the opposite holds for the (Z)‐NH resonance. Similar trends are found on increasing the concentration. The orientation around the C1N bond can be probed by 3J(H1,NH) or by 1J(N,H). The 15N chemical shifts were also investigated in a series of β‐sulphinylenamines. They are mainly dominated by α‐ and β‐effects and show only a slight dependence on the E/Z isomerism, which seems to indicate a weak hydrogen bond in the Z‐isomer at high concentration. Pertinent NMR parameters are now available for a general structure determination of geometrical isomers of β‐sulphinylenamines.
Spin trapping of sterically unhindered phenoxyl radicals with nitrosobenzene and nitrosodurene
Authors: Omelka Ladislav , Kováčová Jana 
Published: May 2005

AbstractUnhindered phenols were oxidized with PbO2 in the presence of nitrosobonzene and nitrosodurene. The phenoxyl radicals generated are trapped in their resonance form as ortho‐carbon‐centred radicals. Depending on the substitution of the spin trap, two types of aminoxyl radicals are formed. Stable diarylaminoxyls are the final products of the spin‐trapping reaction with nitrosodurene. The adducts of the ortho‐carbon‐centred phenoxyl radicals with nitrosobenzene are rapidly rearranged to the phenoxazine‐10‐oxyl radicals, the only radical products observed. Some exceptions to this rule are discussed. Radical products were characterized by their EPR parameters.
1H and 13C nuclear magnetic resonance studies of pyrazolo [c]‐ and pyrazolo [b]phenothiazines
Authors: Boyer G. , Galy J. P. , Faure R. , Barbe J. 
Published: May 2005

AbstractThe complete assignment of the 1H and 13C NMR spectra of eight Pyrazolo[b]‐ and pyrazolo[c]phenothiazines was performed using 1H detected one‐bond heteronuclear multiple quantum coherence (HMQC) and long‐range (two and three bonds) heteronuclear multiple quantum bond connectivity (HMBC) experiments. 1H and 13C NMR chemical shifts are also reported for some N‐arylindazoles
29Si and 13C NMR spectra of trimethylsilylated amino acids
Authors: Schraml Jan , Kvíčalová Magdalena , Schwarzová Iveta , Velíšek Jan 
Published: May 2005

AbstractThe 29Si and 13C NMR chemical shifts are reported for trimethylsilyl derivatives of 25 amino acids, the majority of which occur naturally as protein constituents of foodstuffs. The 29Si chemical shifts in trimethylsilyl esters of amino acids roughly correlate linearly with the pK values of the parent amino acid. No such simple correlations were found for the shifts in the fully trimethylsilylated amino acids. The 29Si chemical shifts of various functionalities encountered fall into distinct spectral regions, but the shifts of (CH3)3SiN or (CH3)3SiOOC groups alone are not sufficiently characteristic to identify the acid but their combination is in most cases.