bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cross‐polarization for quadrupolar nuclei—proton to molybdenum‐95
Authors: Edwards John C. , Ellis Paul D. 
Published: May 2005

AbstractHigh‐field, 95Mo, solid‐state nuclear magnetic resonance spectra of (NH4)6Mo7O24 · 4H2O and (Bu4N)2Mo2O7 were obtained using solid‐echo techniques together with 1H cross‐polarization and dipolar decoupling. The results show that reliable second‐order powder line shapes can be obtained with excellent cross‐polarization enhancements of 66–86% of maximum theoretical enhancement. The lower than maximum enhancements are due to the relatively long TIS values, which are similar in magnitude to the TH1ρ values. Experiments were performed which reveal the dynamics involved in the cross‐polarization process, including measurement of the cross‐relaxation time constant and the 1H and 95Mo rotating‐frame spin‐lattice relaxation times. It was found that the principal relaxation process causing low gain in the observed signal was the 1H T1ρ, which was found to be on the order of 23–24 ms. The experimental results obtained indicate that selective cross‐polarization dynamics occur in molybdenum cluster species with inequivalent molybdenum sites. The 95Mo rotating‐frame spin‐lattice relaxation rate is long in comparison with the other relaxation processes, making molybdenum a good cross‐polarization candidate but precluding the use of multiple contact cross‐polarization.
1H and 13C NMR studies of isomerism in hydroxamic acids
Authors: Brown David A. , Glass William K. , Mageswaran Rajeswary , Mohammed Salima Ali 
Published: May 2005

Abstract1H and 13C NMR studies of N‐methyl‐substituted hydroxamic acids, RCON(CH3)OH (R = CH3, C2H5 and C6H5), show that the series exhibits cis–trans isomerism about the CN bond. The Z/E ratio increases in the series CH3 < C2H5 < n‐C5H11 < n‐C6H13 for a given solvent, indicating that steric interaction between R and the OH group is more important than that between R and the CH3 group. In DMSO‐d6 the Z isomer is preferentially stabilized by solvation, whereas in C6D6 and toluene‐d8 the unsolvated E form is thermodynamically more stable, as predicted by ab initio molecular orbital calculations. (12) At high concentrations (in CDCl3, CD2Cl2, C6D6 and toluene‐d8) the E isomer may also be stabilized by intermolecular association. In the O‐methyl‐substituted series, RCONHOCH3 (R = CH3, C6H5), although the Z isomer predominates in all solvents, at low temperatures there is evidence for enolic forms.
Study of the distribution of the π‐electrons in push‐pull alkenes by 1H and 13C NMR spectroscopy
Authors: Fischer G. , Rudorf W.‐D. , Kleinpeter E. 
Published: May 2005

AbstractPush‐pull alkenes with variable structure were investigated with respect to the influence of the different substituents at the central C,C double bond on the dynamic behaviour of this type of compound. 1H and 13C NMR spectroscopic investigations were carried out for ketene‐S,S‐, ‐S,N‐ and ‐N,N‐acetals. HMO calculations were employed to discuss the related π‐electron density distributions.
An explanation of anomalous artifact intensity in fully 1H–1H decoupled two‐dimensional chemical shift correlation spectroscopy
Authors: Bain Alex D. , Burton Ian W. , Carpenter Katharine , Reynolds William F. 
Published: May 2005

AbstractTwo‐dimensional heteronuclear chemical shift correlation experiments which attempt decoupling in f1 have been shown to give artifacts in strongly coupled systems. In particular, COLOC and HETRES experiments on methylene groups show an artifact midway between the two proton lines. This paper provides an explanation of the artifact intensity behaviour with respect to the strength of coupling between the methylene protons. Experimental results on 1,2‐dibromoethylbenzene are presented, and theoretical calculations were carried out on the COLOC experiment and a mathematical model was developed which predicted the artifact appearance and intensity. Simulations were also performed using the simulation program SIMPLTN to verify the experimental and theoretical results.
13C NMR spectra of the models for the end‐group analysis of polybutadiene
Authors: Podkorytov I. S. , Lubnin A. V. 
Published: May 2005

AbstractThe 13C NMR spectra of models for the initial and terminal monomeric unit diads of polybutadiene are interpreted. The models are C10H18, diolefins, separated from the mixture of oligomers which are formed in the reaction of buta‐1,3‐diene with ethyllithium and a proton donor. A version of the INADEQUATE pulse sequence with DEPT polarization transfer and a selective DANTE read pulse is described and used for assignment.
Structure of the De‐O‐acetylated glucuronoxylomannan from Cryptococcus neoformans serotype D, as determined by 2D NMR spectroscopy
Authors: Skelton Marshall A. , Cherniak Robert , Poppe Leszek , van Halbeek Herman 
Published: May 2005

AbstractThe primary structure of the de‐O‐acetylated glucuronoxylomannan isolated from Cryptococcus neoformans serotype D was characterized de novo by NMR spectroscopy. Assignment of the 1H and 13C spectra of the polysaccharide involved a combination of 2D NMR experiments including double‐quantum‐filtered {1H,1H} COSY, {1H,1H} TOCSY and 1H‐detected {1H,13C} heteronuclear multiple quantum coherence spectroscopy. The sequence of the glycosyl residues, including the linkage positions, was deduced by {1H,1H} rotating‐frame NOE (ROESY) spectroscopy. The serotype‐D glucuronoxylomannan was found to be a branched polymer with a repeating pentasaccharide unit of the following structure: magnified image.
Influence of gauche interactions on the substituent effects on carbon‐13 chemical shifts in six‐membered ring compounds
Authors: Rajan K. Pandia , Manimekalai A. 
Published: May 2005

Abstract13C NMR spectra of six epimeric substituted 4‐hydroxypiperidines and two corresponding piperidines were recorded. Substituent parameters for equatorial methyl, gem‐dimethyl, equatorial hydroxy and axial hydroxy groups were calculated from the 13C chemical shifts of these compounds and several other six‐membered ring compounds. The effects of nearby substituents on these parameters were examined. It is concluded that the magnitude and even the sign of the α effect is modified by the presence of nearby substituents. It was found that gauche interactions play an important role in determining the magnitude of the α effect. However, the β effect is not influenced by the nearby substituents except for the gem‐dimethyl group. The magnitude of the γ effect is almost independent of the nearby substituents.
13C, 6Li and 7Li NMR T1 and T1ρ study of ion‐pair dynamics and structure of lithium fluorenide
Authors: Sethson Ingmar , Eliasson Bertil , Edlund Ulf 
Published: May 2005

AbstractThe rate of interconversion between tight and loose ion pairs of lithium fluorenide in 2‐methyltetrahydrofuran was determined from 7Li relaxation in the rotating frame. The rate constant for the tight to loose ion‐pair interconversion at −60°C is 2.3 × 104 s−1 and for the reverse process 2.6 × 103 s−1. The 13C relaxation times (T1) of the fluorenyl anion, adjusted for viscosity changes, do not change significantly with the ion‐pair structure. The electric quadrupole relaxation contribution to the 7Li T1 was derived from 6Li and 7Li T1 measurements. Lower limits of 7Li quadrupole splitting constants (QSCs) were obtained from the 7Li quadrupolar and the 13C dipole‐dipole relaxation times. The QSC values are in the range 37–200 kHz and appear to reflect changes in the ion‐pair structure, with a low value corresponding to a solvent‐separated ion pair. The higher value for the contact ion pair is in agreement with a structure where the anion disrupts the symmetrical coordination of solvent molecules around the cation. A decreased QSC and a shortened 13C T1 at high temperature for the diethyl ether solution may be caused by aggregation.
Study of fluorinated blowing agents in polyurethane foams by fast magic angle spinning fluorine‐19 NMR spectroscopy
Authors: Jackson Peter , Carr Robert H. 
Published: May 2005

AbstractUsing magic angle spinning 19F NMR, it has been possible to identify gaseous chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) blowing agents trapped in the cells of test samples of polyurethane foam. On spinning the samples at rates greater than 10 kHz, further signals have been observed corresponding to rigidly held CFC and HCFC molecules absorbed in the solid polymer. Differences are seen between a sample taken from the centre of a foam block and a sample taken from the block edge, possibly indicating some localized decomposition of the blowing agent(s) within the solid polymer.
59Co and 99Ru NMR investigation of heterometallic carbonyl clusters. Reactivity of [MCo3(CO)12]− (M = Fe, Ru) towards NO+; formation of RuCo3(CO)11(NO) and FeCo2(μ3‐NH)(CO)9
Authors: Braunstein Pierre , Rosé Jacky , Granger Pierre , Richert Thierry 
Published: May 2005

AbstractA series of mixed‐metal carbonyl clusters containing Co and Ru atoms was investigated by 59Co NMR and, for the first time in cluster chemistry, by 99Ru NMR. These techniques were successfully used to follow the reactivity of these complexes towards nitrosylation by NO+. Whereas [NEt4] [RuCo3(CO)12] reacts with [NO]BF4 with the formation of RuCo3(CO)11(NO), which subsequently fragments into RuCo2(CO)11 and Co(CO)3(NO), [NEt4] [FeCo3(CO)12] leads inter alia to FeCo2(μ3‐NH)(CO)9, in which the coordinated NO ligand has been reduced.
Synthesis, tautomerism and stereochemistry of spiropyrazolines
Authors: Tóth Gábor , Lévai Albert , Duddeck Helmut 
Published: May 2005

Abstract1,3‐Dipolar cycloaddition of (E)‐ and (Z)‐arylidene‐1‐tetralone derivatives affords trans‐ and cis‐spiro‐1‐pyrazolines, respectively, regio‐ and stereo‐selectively in a one‐step reaction. These rearrange into spiro‐2‐pyrazolines on proton catalysis. The relative configurations and conformations of the spiropyrazolines were elucidated by different NMR methods.
Complete 1H and 13C NMR spectral assignment of patchoulenone, a tricyclic sesquiterpene ketone
Authors: Hisham A. , Wray V. , Pieters L. , Claeys M. , Dommisse R. , Vlietinck A. 
Published: May 2005

AbstractA tricyclic sesquiterpene ketone, patchoulenone, was isolated from the hexane extract of the root bark of Uvaria narum Wall. (Annonaceae). Its structural elucidation was based on detailed 2D NMR spectroscopy, leading to the complete assignment of the 1H and 13C NMR spectra.
Stereochemical study of anagyrine‐type quinolizidine alkaloids by 15N and 2D NMR spectroscopy
Authors: Liu Zimin , Yang Li , Jia Zhongjian , Chen Jihong 
Published: May 2005

AbstractThe configurations of anagyrine, thermopsine and two other anagyrine‐type quinolizidine alkaloids were revised using 15N and 2D NMR in a 400 MHz NMR study. Their 1H and 13C NMR chemical shifts are given in detail.
Interpretation of the 13C NMR spectra of thirteen methoxycarbonylpyridines and some of their derivatives
Authors: Jokela Reija 
Published: May 2005

AbstractThe 13C NMR spectra of thirteen methoxycarbonylpyridine derivatives and two pyridine lactones are interpreted. The substituent increments for the methoxycarbonyl group in 2‐, 3‐ and 4‐substituted pyridines are reported.
Determination by NMR methods of the structure and stereochemistry of astellatol, a new and unusual sesterterpene
Authors: Sadler Ian H. , Simpson Thomas J. 
Published: May 2005

AbstractThe full structure of astellatol, a new complex sesterterpene isolated from Aspergillus variecolor, was determined solely by the use of one‐ and two‐dimensional NMR techniques. The carbon skeleton was deduced from a two‐dimensional INADEQUATE spectrum, and the proton shifts were deduced from a two‐dimensional CH correlation (HMQC) experiment. Analysis of a two‐dimensional proton DQFCOSY spectrum and a series of homonuclear NOE difference spectra allowed the determination of the full stereochemistry.
Two‐dimensional NMR spectra of hydrolysable tannins which form equilibrium mixtures
Authors: Yoshida Takashi , Hatano Tsutomu , Okuda Takuo 
Published: May 2005

AbstractThe structures of hydrolysable tannins, each existing as an equilibrium mixture due to tautomerization at the sugar core(s) or at the dehydrohexahydroxydiphenoyl group (five‐ and six‐membered hemiacetal forms) in the molecule, were elucidated by NMR, employing 2D NMR techniques (COSY, NOESY, 1H13C long‐range COSY, etc.), on derivatives which avoid the spectral complication due to equilibration.
C‐19 configurational assignments in some morphine derivatives by homonuclear NOE
Authors: Batta Gy. , Gunda T. E. , Szabó Z. , Berényi S. , Gulyás Gy. , Makleit S. 
Published: May 2005

AbstractAzidolysis‐thermolysis of C‐19 diastereomer tosyl esters of morphine derivatives resulted in the formation of a new substituted 4‐azatetracyclo [4.4.02,4.03,8] decane ring system. As the course of such transformations depends on the chirality of C‐19, its relative configuration was determined both in the starting materials and in the new compounds. To this end a semiquantitative 1H{1H} NOE interpretation was combined with MMX molecular mechanics. Interestingly, both in the starting materials with a rotating C‐7—C‐19 bond and in the fairly rigid aziridine ring‐containing products, the same (H‐8α{19‐Me}) NOE effects were the most informative on the stereochemistry. In addition full a priori 1H and 13C assignments of 13 compounds are presented.
Solution conformation of mono‐ and difucosyllactoses as revealed by rotating‐frame NOE‐based distance mapping and molecular mechanics and molecular dynamics calculations
Authors: Ejchart Andrzej , Dabrowski Janusz , von der Lieth Claus‐Wilhelm 
Published: May 2005

AbstractThe solution conformation of two fucosyllactoses, Fucα(1 → 2)Galβ(1 → 4)Glcα,β and Galβ(1 → 4) [Fucα(1 → 3)] Glcα,β, and a difucosyllactose, Fucα(1 → 2)Galβ(1 → 4)[Fucα(1 → 3)]Glcα,β, were investigated in Me2SO‐d6 with the use of distance mapping, molecular mechanics (MM) energy minimization and molecular dynamics (MD) simulations. The distance mapping procedure, which was based on rotating‐frame NOE constraints involving C‐ and O‐linked protons, and hydrogen bonding constraints, suggested the occurrence of two conformations for each of the fucose residues. The MM calculations resulted in two minima that were located reasonably near to the regions demarcated in the Θ, Ψ conformational space by distance mapping; 500 ps MD trajectories showed transitions between two conformations characterized by glycosidic angles Θ and Ψ that only deviated insignificantly from those found by the first two methods. No similar transitions were observed for the Galβ14Glc linkage.
Ab initio IGLO study of the syn/anti dependence of the 13C NMR chemical shifts in simple amides
Authors: Jiao Ding , Barfield Michael , Hruby Victor J. 
Published: May 2005

AbstractThe syn/anti dependences of the alkyl 13C chemical shifts provide a useful probe of stereochemistry around the amide bonds in peptides and proteins. To investigate these dependences the ab initio IGLO method was used to obtain the 13C chemical shielding for the following series of amide molecules as models for the peptide bond: syn‐ and anti‐N‐methylformamide (NMF), cis‐ and trans‐N‐methylacetamide (NMA), N,N‐dimethylformamide (DMF) and N,N‐dimethylacetamide (DMA). Molecular geometries for shielding calculations are optimized ones at the HF/6–31G* level. Good correlations were observed between the calculated 13C chemical shift results and the experimental data. The syn/anti dependence of 13C chemical shifts around amide bonds is perdicted either with double‐ζ or triple‐ζ quality basis sets. Based on an analysis of the paramagnetic bond contributions (PBC) to the chemical shieldings, it is concluded that the syn/anti dependence of the 13C chemical shifts in amides arises almost entirely from the PBC of the syn and anti NC bonds, and is completely analogous to the electronic origin for the cis/trans γ‐effect in hydrocarbons.
1H, 13C and 15N NMR study of N1‐alkyl‐N2‐arylthioureas
Authors: Wawer Iwona , Koleva Vera 
Published: May 2005

Abstract13C and 15N NMR chemical shifts were measured for N1‐alkyl‐N2‐arylthioureas. The absence of decoalescence of the N1‐alkyl group carbon signals down to 190 K, the europium‐induced chemical shifts and the molecular mechanics calculations indicate that the preferred conformation is E,Z. Solvent effects suggest that N1‐alkyl‐N2 arylthioureas exist as dimers, forming an eight‐membered ring hydrogen bonded complex. In N1, N1‐dimethyl‐N2‐phenylthiourea the barrier to rotation around the CN1 bond is 47 kJ mol−1 (from 13C NMR, in CD2Cl2). The upfield N1‐CH3 signal in both the 1H and 13C NMR spectra results from the methyl group anti to the CS and the low‐field signal from the syn methyl group.
Multinuclear magnetic resonance study of oxaziridines
Authors: Čudić Mane , Herrmann Rudolf 
Published: May 2005

AbstractNMR data (13C, 15N, 17O) for the three ring atoms of various oxaziridines are compared. Their significance for the prediction of the enantioselectivity of the oxidation of sulphides by chiral oxaziridines is discussed.
Conformational characteristics of kessane studied by 600 MHz 1H NMR and molecular mechanics
Authors: Lankhorst Peter P. , van Beek Teris A. , Haasnoot Cornelis A. G. 
Published: May 2005

AbstractThe conformational characteristics of kessane were investigated by means of 600 MHz 1H NMR spectroscopy and molecular mechanics (MM2) calculations. Accurate vicinal 1H1H coupling constants were obtained by means of extensive computer simulations. These experimental values were compared with coupling constants calculated by the combined use of MM2 calculations and the generalized Karplus equation. It is shown that kessane adopts a single conformation in solution which is only slightly different from the conformation predicted by the MM2 calculations. The cyclopentane ring of kessane is characterized by a pure 1E conformation. The cycloheptane ring adopts a conformation which is situated precisely between the twist‐chair TC9 and the chair C5 conformation on the pseudo‐rotational pathway of the seven‐membered ring.
1H and 13C NMR data for 2‐O‐, 3‐O‐and 2,3‐di‐O‐glycosylated methyl α‐and β‐D‐galactopyranosides
Authors: Shashkov Alexander S. , Nifant'ev Nikolay E. , Amochaeva Vera Yu. , Kochetkov Nikolay K. 
Published: May 2005

Abstract1H and 13C NMR data for a series of 2‐O‐, 3‐O‐ and 2,3‐di‐O‐glycosylated methyl α‐and β‐D‐gluco‐ and β‐D‐galactopyrano‐sides are presented. The glycosylation effects on the spectra of disaccharides and the deviations from additivity values in the spectra of trisaccharides were determined.
13C NMR data for several cyclolignans
Authors: Feliciano A. San , Del Corral J. M. Miguel , Gordaliza M. , Castro M. A. 
Published: May 2005

Abstract13C NMR shielding data for 100 naturally occurring and hemisynthetic cyclolignans are tabulated. Some of them have been compiled from the literature. The data have been assigned on the basis of 2D heteronuclear 1H‐13C correlations.
Water exchange on [Gd(H2O)8]3+ and [Gd(PDTA)(H2O)2]‐ in aqueous solution: A variable‐pressure, ‐temperature and ‐magnetic field 17O NMR study
Authors: Micskei Károly , Powell D. Hugh , Helm Lothar , Brücher Ernö , Merbach André E. 
Published: May 2005

Abstract17O NMR longitudinal and tranverse relaxation rates and chemical shifts were measured at variable temperature at three magnetic fields (1.4, 4.7 and 9.4 T) for aqueous solutions of the complexes [Gd(H2O)8]3+ and [Gd(PDTA)(H2O)2]−. The transverse relaxation rates and chemical shifts were analysed in the light of recent EPR line width measurements to obtain the parameters for water exchange kinetics: k = (8.30 ± 0.95) × 108 and (1.02 ± 0.10) × 108 s−1, ΔH‡ = 14.9 ± 1.3 and 11.0 ± 1.4 kJ mol−1 and ΔS‡ = −24.1 ± 4.1 and −54.6 ± 4.6 J K−1 mol−1 for [Gd(H2O)8]3+ and [Gd(PDTA)(H2O)2]−, respectively. The longitudinal relaxation rates were used to obtain the parameters for the rotation time of the complexes: τ = (2.9 ± 0.2) × 10−11 and (7.9 ± 0.3) × 10−11 s and Ec = 15.1 ± 1.5 and 19.2 ± 1.1 kJ mol−1 for [Gd(H2O)8]3+ and [Gd(PDTA)(H2O)2]−, respectively. The 17O NMR transverse relaxation rates were measured at variable pressure, and were used to determine the activation volumes for the water exchange process: ΔV0‡ = −3.3 ± 0.2 and −1.5 ± 0.5 cm3 mol−1 for [Gd(H2O)8]3 + and [Gd(PDTA)(H2O)2]−, respectively. It can be concluded that water exchange occurs via an associative limiting A mechanism for [Gd(H2O)8]3 + (without excluding Ia) and an associative interchange, Ia, mechanism for [Gd(PDTA)(H2O)2]−. These water exchange kinetic and mechanistic results are compared with those for the heavy Ln3+ aqua ions and the Gd3+ complexes with DTPA5− and DOTA4−.
1H 3D NOE‐NOE spectrum of met‐cyanomyoglobin: The first 3D NMR spectrum of a paramagnetic protein
Authors: Banci Lucia , Bermel Wolfgang , Luchinat Claudio , Pierattelli Roberta , Tarchi Dario 
Published: May 2005

AbstractA 3D NOE‐NOE spectrum of the paramagnetic protein met‐cyanomyoglobin has been successfully obtained. The protein shows hyperfine shifted signals. Planes at their frequencies show clean cross peaks with signals of nearby protons. Connectivities can be detected in‐plane at frequencies corresponding to hyperfine broadened signals beneath the diamagnetic envelope, whose connectivities may be difficult to observe otherwise. The limits of observability of cross peaks are discussed by means of spectral simulations.
1H, 2H and 19F NMR spectroscopy of a novel iron(II) tetradentate cysteine‐peptide complex having only one δ isomer. Detection of two isomers in coordination of CysXYCys bidentate peptide ligands to iron(II) ion
Authors: Sun Wei‐yin , Ueyama Norikazu , Nakamura Akira 
Published: May 2005

AbstractAn Fe(II) complex with Z‐Ala‐CysProLeuCysGlyNHC6H4mF (Z = benzoxylcarbonyl) having an invariant bidentate peptide ligand, CysKYCys, in rubredoxins was synthesized. The contact‐shifted 1H, 2H and 19F NMR signals of (Et4N)2[Fe(ZAlacysProLeucysGlyNHC6H4mF)2] (1) in acetonitrile‐d3 or acetonitrile at 30°C indicate the existence of two isomers (δ and λ) in the solution of bidentate complex 1 with different orientations of the bidentate peptide ligand to a tetrahedral Fe(II) ion. A novel tetradentate cysteine‐containing peptide ligand, cis‐1,2‐cyclohexylene(COAlaCysProLeuCysGlyNHC6H4mF)2, is designed by energy minimum calculations and synthesized. Its Fe(II) complex, (Et4N)2[Fe(cis‐1,2‐cyclohexylene(CO‐Ala‐cys‐Pro‐Leu‐cys‐Gly‐NH‐C6H4‐m‐F)2)], showed only set of contact‐shifted 1H, 2H and 19F NMR signals of Cys CβH2 due to the preferable formation of the δ isomer.
Oxygen‐17 NMR studies of N‐nitrosamines
Authors: Cerioni Giovanni , Giumanini Angelo G. , Verardo Giancarlo , Dahn Hans 
Published: May 2005

AbstractNatural abundance 17O NMR data for seven aliphatic, nine cyclic and thirteen aromatic N‐nitrosamines, recorded at room temperature in acetonitrile, are reported. Differences in chemical shifts among and within the three groups are discussed in terms of electronic and steric effects. The σ+ value for the N‐nitrosamine group was estimated. A comparison between amides and N‐nitrosamines was made.
The 2D QUADSHIFT experiment: Separation of deuterium chemical shifts and quadrupolar couplings by two‐dimensional solid‐state MAS NMR spectroscopy
Authors: Chandrakumar Narayanan , von Fircks Gero , Günther Harald 
Published: May 2005

AbstractThe two‐dimensional QUADSHIFT experiment is introduced, which permits the separation of chemical shifts and quadrupolar couplings in solid‐state magic angle spinning NMR spectra of powder samples. The technique was applied to partially deuteriated norcamphor and camphor under slow magic angle spinning. Double quantum chemical shift resolutions down to 0.2 ppm were achieved, with double quantum linewidths in the range 6–12 Hz. Separation and correlation of deuterium chemical shifts and quadrupolar couplings is demonstrated for individual sites.