bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlation between 27Al and 71Ga NMR chemical shifts
Authors: Bradley Susan M. , Howe Russell F. , Kydd Ronald A. 
Published: May 2005

AbstractA linear relationship has been found to exist between the aluminum‐27 and gallium‐71 NMR chemical shifts of a series of structurally analogous aluminum and gallium compounds having only oxygen in the first metal coordination spheres; δ71Ga = 2.83(δ27Al) − 4.50. This relationship allows the prediction of 71Ga chemical shifts for such gallium compounds from the 27Al values already known for their aluminum analogues, and also a greater understanding of observed 71Ga chemical shifts.
Tautomerism in 2‐hydroxy‐1‐naphthaldehyde schiff bases in solution and the solid state investigated using 13C NMR spectroscopy
Authors: Salman S. R. , Lindon J. C. , Farrant R. D. , Carpenter T. A. 
Published: May 2005

Abstract13C and 1H NMR spectra of six Schiff bases formed from 2‐hydroxy‐1‐naphthaldehyde and substituted anilines were measured and assigned in a variety of solvents. Based on the 13C chemical shifts and 3J(CH,NH), the ratio of the keto‐amine and phenol‐imine tautomers was derived using both 13C chemical shifts and 1H−1H coupling constants, the two methods giving comparable results. The solid‐state 13C NMR spectra of two of these Schiff bases were also measured and interpreted. Based on chemical shift assignments from solution NMR, which showed a relationship between certain shifts and the proportions of the tautomers, it has been shown that these compounds exist essentially as the keto‐amine form in the solid, the tautomer previously shown to be the more thermodynamically stable.
Factors affecting the line widths and signal‐to‐noise ratios of the 13C CP/MAS spectra of proteins
Authors: Belton Peter S. , Gil Ana M. , Tanner Stephen F. 
Published: May 2005

AbstractTypically the 13C CP/MAS spectra of proteins have low signal‐to‐noise ratios and broad lines, which considerably degrade the value of such spectra. The origins of these effects were examined using a model protein, lysozyme. The effects of hydration, relaxation time and crystallinity were systematically investigated. It is concluded that low signal‐to‐noise ratios are the result of the typically low density of protein preparations and not an intrinsic magnetic resonance phenomenon, and that line broadening is principally the result of poor molecular packing in noncrystalline protein preparations.
Structure of oxidatively damaged nucleic acid adducts: PH dependence of the 13C NMR spectra of 8‐oxoguanosine and 8‐oxoadenosine
Authors: Cho Bongsup P. 
Published: May 2005

Abstract13C NMR spectra of two C‐8‐oxo purine nucleosides, 8‐oxoguanosine and 8‐oxoadenosine, were recorded as a function of pH. The pH dependence of 13C chemical shifts and 13C‐1H coupling constants associated with the purine carbon resonances was analyzed to probe the sites and extent of ionization and protonation of these oxidatively damaged nucleic acid adducts. In the course of this study, it was found that the C‐2′ and C‐3′ resonances of the ribofuranosyl sugar ring can be conveniently assigned on the basis of their unique pH‐independent 1H‐coupling spectral patterns in aqueous solution.
Conformational analysis of four β‐methylphenylalanine stereoisomers in a bioactive peptide by z‐filtered relay NMR spectroscopy
Authors: Kövér Katalin E. , Jiao Ding , Fang Sunan , Hruby Victor J. 
Published: May 2005

AbstractThe rotamer populations around the C‐α—C‐β bond of amino acid residues with one β‐proton can be calculated from homonuclear and heteronuclear vicinal coupling constants. The measurement of long‐range heteronuclear coupling constants, however, suffers from the inherent low sensitivity of the heteronuclear multiple bond experiments. In this paper it is demonstrated that z‐filtered homonuclear and heteronuclear relay spectroscopy provides a sensitive and accurate means for the evaluation of conformationally important vicinal coupling constants. Side‐chain conformations of the four stereoisomers of β‐methylphenylalanine residues in synthetic octapeptide analogues of CCK‐8 were derived from the measured coupling constants. This information is not easily available from conformational analysis based on simple steric considerations.
Direct analysis of the ABX spin system in two symmetrical diphosphonates: Comparison with two‐dimensional methods
Authors: Harris R. K. , Jones M. S. , Kenwright A. M. 
Published: May 2005

AbstractThe results of the direct analysis of the ABX spin system present in two symmetrical diphosphonates containing a single vinylic 13C nucleus are presented. This allows a comparison to be made with the two‐dimensional methods used by Beckmann et al. Significant differences are found in the results obtained: the need to recognize the existence of isotopic chemical shifts is emphasized.
1H NMR spectra of some 4,5‐dihydro‐1,2,4‐triazol‐5‐ones
Authors: Ikizler A. Aykut , Ikizler Aysun , Yüksek Haydar 
Published: May 2005

AbstractThirty 3‐substituted‐ and 3,4‐disubstituted‐4,5‐dihydro‐1,2,4‐triazol‐5‐ones (seven being new compounds) were synthesized and their proton magnetic resonance spectra were measured in trifluoroacetic acid (TFA). The protonation shifts observed on comparison of the spectra run in DMSO‐d6 and TFA were attributed to an amidinium‐type resonance of the resulting cations in the acidic medium.
Electron‐transfer self‐exchange of trimethylphosphine‐modified cytochrome c: NMR study and kinetics using spin‐lattice relaxation times
Authors: Legrand Nathalie , Bondon Arnaud , Simonneaux Gérard , Schejter Abel 
Published: May 2005

AbstractThe binding of trimethylphosphine to the axial position of the haeme iron in modified cytochrome c by alkylation of methionine was studied by NMR spectroscopy. Electron self‐exchange was determined by spin‐lattice relaxation time (T1) measurement. The rate is 7.5 × 103 1 mol−1 s−1 at 25°C in 0.1 M phosphate buffer (pH 7.0). Two‐dimensional transfer spectroscopy was used to locate haeme methyl resonances in both iron(II) and iron(III) complexes of modified cytochrome c.
Sequential assignments by 1H 2D NMR of oxidized ferredoxins from Clostridium pasteurianum and Clostridium acidurici
Authors: Gaillard Jacques , Moulis Jean‐marc , Kümmerle Rainer , Meyer Jacques 
Published: May 2005

AbstractA 1H 2D NMR investigation of the oxidized 2[4Fe‐4S] ferredoxins from Clostridium pasteurianum and C. acidurici was carried out. Sequential assignments through standard HOHAHA and NOESY procedures were obtained for the 2–7, 23–36 and 52–55 sequence segments of both proteins. Additional assignments of the 15–17 and 44–46 segments, linking the clusters, and of a few other residues were made by taking advantage of sequence differences between the two proteins. In summary, only the immediate vicinity of the cysteine ligands could not be identified by the procedure. In these small 2[4Fe‐4S] ferredoxins, a large proportion of the resonances is sensitive to the presence of the paramagnetic centres and does not easily display NOE correlations. Nevertheless, long‐range NOE peaks that could be observed shed light on the solution structure of these proteins. The close interaction between the N‐ and C‐termini, previously evidenced by x‐ray crystallography, was confirmed for both proteins in solution. Small differences between the ferredoxins from C. pasteurianum and C. acidurici were detected in the flexible and variable external 25–30 loop and also in the region separating the clusters. These differences may correlate with small dissimilarities previously observed between some properties of these ferredoxins.
Two‐dimensional 1H NMR studies of paramagnetic bimetallic mixed‐metal complexes
Authors: Wang Zhigang , Holman Theodore R. , Que Lawrence 
Published: May 2005

AbstractSynthetic dinuclear mixed‐metal complexes have proved useful as models for metal‐substituted dinuclear iron‐oxo proteins. However, a detailed assignment of their paramagnetically shifted proton NMR resonances has thus far been difficult to achieve. In the light of the significant role of two‐dimensional (2D) NMR techniques in establishing the bond connectivities in diamagnetic molecules, COSY studies were performed on a series of complexes, [Fe(II)M(II)BPMP(O2CCH2CH3)2]+ {BPMP = 2,6‐bis [bis(2‐pyridylmethyl)aminomethyl]‐4‐methylphenol, M  Mn, Co and Zn}, taking advantage of the short electronic relaxation time of Fe(II). The resonances from the four distinct pyridine rings of each of the three complexes were unambiguously assigned based on the bond‐correlated cross signals in the 2D spectra due to the (α‐)β‐γ‐β′ pyridyl proton connectivities. The resonances from the two bridging ligands of these complexes were also unambiguously assigned based on the same approach. Together with longitudinal relaxation time (T1) measurements, the 2D data allow the assignment of all the paramagnetically shifted proton resonances of all the three bimetallic complexes.
Assignment of Pseudo‐contact‐shifted 1H NMR resonances in the EF site of Yb3 +‐substituted rabbit parvalbumin through a combination of 2D techniques and magnetic susceptibility tensor determination
Authors: Capozzi Francesco , Cremonini Mauro Andrea , Luchinat Claudio , Sola Marco 
Published: May 2005

AbstractPseudo‐contact‐shifted 1H NMR resonances of rabbit parvalbumin substituted with Yb3+ at the Ca2+ EF site have been sequence‐specific assigned by a combination of 2D techniques and magnetic susceptibility tensor determination. By taking the X‐ray structure of the homologous carp protein as a starting point, the sequence‐specific assignment proceeded in a stepwise fashion. The first resonances assigned on the basis of their unique connectivity pattern were used to make a first coarse determination of the X‐tensor parameters; the latter were used to guess the identity of further hyperfine‐shifted resonances, which were then checked through 2D connectivities and in turn allowed us to improve the reliability of the X‐tensor parameters. This cyclic procedure was repeated until virtually all pseudo‐contact‐shifted resonances were assigned. In the last steps the X‐tensor parameters did not change appreciably. The orientation of the tensor was found to be very similar to that previously proposed for the homologous Yb3+−substituted protein from carp. Modest discrepancies between some calculated and experimental shift values in the present system were found to be due mainly to structural differences between the present protein and the homologous protein whose x‐ray structure was used as model and, to a lesser extent, to indetermination in the diamagnetic shift values. The success of the analysis and the univocal solution for the X‐tensor parameters under these conditions show that the above procedure is robust enough to permit both signal assignment and X‐tensor determination even when the structural data are only a rough approximation of the actual structure. These findings may open the way to the development of a systematic use of pseudo‐contact shifts as constraints for MD refinement of solution structures of paramagnetic metalloproteins.
Complete assignment of 1H and 13C NMR spectra of chlorobenzanthrones
Authors: Takekawa Minoru , Aoki Junji , Iwashima Satoshi , Ueda Toyotoshi 
Published: May 2005

Abstract1H and 13C NMR studies were carried out on benzanthrone and 3‐, 4‐, 6‐, 8‐, 9‐, 10‐ and 11‐chlorobenzanthrone. Complete assignments of proton and carbon resonances were made with the aid of HH‐COSY, NOESY, CH‐COSY and HMBC techniques. Substitution effects of a chlorine atom are not large, but give a systematic change particularly in 13C shift values. The anomalous downfield shift of the H‐1 signal in 11‐chlorobenzanthrone was explained by the electrostatic attraction between the electronegative Cl atom, based on the result of an MNDO‐PM3 calculation.
13C CP/MAS NMR study of a phenyl group rotation in the solid state using T1ρ, lineshape and 2D EXSY measurements
Authors: Riddell Frank G. , Bremner Murray , Strange John H. 
Published: May 2005

AbstractA combination of solid‐state 13C CP/MAS NMR methods was used to study the rates of rotation of the phenyl group in 3,5‐dimethyl‐1‐phenylhex‐1‐yn‐3‐ol. The methods used were T1ρ measurements, lineshape analysis and 2D exchange spectroscopy over the temperature range 219–284 K. The rates of rotation obtained from the lineshape and 2D EXSY methods give an energy of activation of 58.6 ± 3.0 kJ mol−1. In good agreement with this, the T1ρ measurements give an activation energy for the rotation of 58.7 ± 3.6 kJ mol−1. The two sets of data are shown to be compatible, within experimental error, with a calculated value for the dipolar carbon–hydrogen interaction (B) from an assumed molecular geometry.
1H, 19F and 13C NMR spectral data of fifteen gyrase inhibitors and some metabolites
Authors: Holzgrabe Ulrike , Branch Sarah K. 
Published: May 2005

AbstractAnalyses of 1H and 13C NMR spectra of 15 gyrase inhibitors were carried out using mainly the hydrogen—fluorine and the carbon‐fluorine coupling constants. 19F NMR chemical shifts were obtained for pefloxacin and its metabolites.
1H NMR study of the diastereomeric forms of the protease inhibitor antipain
Authors: Hoebeke Johan , Busatto‐Samsoen Catherine , Davoust Daniel , Lebrun Evelyne 
Published: May 2005

AbstractAntipain [(1‐carboxy‐2‐phenylethyl)carbamoyl‐L‐arginyl‐L‐valyl‐DL‐arginal] is a potent inhibitor of papain and related proteases. The assignment of 1H NMR signals of the interconverting forms in equilibrium in aqueous solution at pH 5.8 were investigated using two‐dimensional DQF‐COSY, DOUBLE‐RELAYED‐COSY, HOHAHA and ROESY nuclear magnetic resonance techniques. The assignments of protons of several forms in equilibrium of the D‐ and L‐arginal antipain isomers were determined in aqueous solution at 300 K, and their corresponding stereochemistry is tentatively proposed. Addition of equimolar amounts of papain resulted in spectral changes and chemical shifts which are compatible with enzyme‐L‐carbinolamine interactions.
Substituent effects and stereochemistry in 125Te NMR spectroscopy. Diorganyltellurium dihalides and some tellurides and ditellurides
Authors: Duddeck Helmut , Biallaβ Armin 
Published: May 2005

Abstract125Te, 19F and 13C NMR data for 33 compounds containing tellurium substituents are presented. The 125Te chemical shifts in (PhTeCl2)R compounds are between δ = 878 and 1023; in corresponding (PhTeF2)R compounds they are 220 to 360 ppm larger. Effects of substituents and conformational interconversions (dynamic 125Te NMR) are discussed. Several diastereomers were identified in (PhTeCl2)R derivatives which are stable at room temperature and differ in the configuration at the tellurium atom (restricted pseudo‐rotation). It is shown that 125Te is a well suited nucleus for chiral recognition.
NMR conformational studies of fenamate non‐steroidal anti‐inflammatory drugs
Authors: Munro Sharon L. A. , Craik David J. 
Published: May 2005

Abstract1H and 13C NMR spectra of the non‐steroidal anti‐inflammatory drugs mefenamic acid, meclofenamic acid and flufenamic acid were assigned and the solution dynamics and conformations of the compounds were probed by the analysis of NMR chemical shifts, temperature coefficients, 3J(C,H) coupled constants, nuclear Overhauser enhancement (NOE) effects and saturation transfer experiments. At low concentrations the anthranilic acid derivatives (the fenamates) exist as monomer units with intramolecular hydrogen bonding between the amine proton and the carboxylic acid group. At concentrations of 10 mM and above, solution aggregates exist. The intermolecular association does not disrupt the intramolecular NH…OC hydrogen bonding, resulting in a similar conformation for mefenamic and flufenamic acids at both low and high concentrations. Meclofenamic acid has an additional intramolecular hydrogen bond, resulting in a slightly different conformation to the other two fenamates. The results from this conformational study are of potential value in molecular and pharmacophore modelling studies on the bioactive conformations of these drugs.
Characterization of the dibutylstannylene derivative of pyridoxine by proton detected 2D heteronuclear correlation NMR
Authors: Kayser François , Biesemans Monique , Gielen Marcel , Willem Rudolph 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of pyridoxine (vitamin B6) and its dibutylstannylene derivative were assigned from proton detected 1H13C heteronuclear multiple bond correlation (1H13C HMBC) spectra.
Spectral separation of two very closely related organic compounds by 1D TOCSY
Authors: Kanthimathi T. , Moorthy Y. V. S. Narayana , Pillai C. N. , Subramanian S. 
Published: May 2005

AbstractThe use of one‐dimensional total correlation spectroscopy (1D TOCSY) combined with the z‐filtration technique to generate pure phase subspectra of individual isomers from the spectrum of the corresponding mixture without any chemical separation of the mixture is described. A straightforward spectral assignment is achieved for the isomers obtained on lithium aluminium hydride reduction of 2,7‐dioxatetracyclo[3.3.04,9.08,11] undeca‐3,6‐dione (dilactone) by studying the subspectrum of each isomer as a function of the propagation time of magnetization through the network of coupled protons.
1H and 13C NMR structural studies in solution of oxotechnetium(V) complexes with N,N‐bis(2‐mercaptoethyl)‐N′,N′‐diethylethylenediamine and N,N‐bis(2‐mercaptoethyl)‐2‐ethylthioethylamine
Authors: Stassinopoulou C. I. , Pelecanou M. , Mastrostamatis S. , Chiotellis E. 
Published: May 2005

AbstractThe complete assignments of the 1H and 13C resonances of three TcOLX complexes of oxotechnetium(V)‐99 with H2L=N,N‐bis(2‐mercaptoethyl)‐N′,N′‐diethylethylenediamine or N,N‐bis(2‐mercaptoethyl)‐2‐ethylthioethylamine and X=p‐methoxythiophenolate or chloride ions are reported. Chemical shifts are influenced by the proximity of protons and carbons to the coordinated heteroatoms and by their orientation with respect to the TcO core. The NMR spectra at room temperature are the result of motionally averaged conformations.
13C NMR spectroscopy of some 20‐ketopregnanes
Authors: Garcia José Alberto Ruiz , Navarro Fernando A. Verdecia , Castro HermáN T. Vélez 
Published: May 2005

AbstractThe 13C NMR spectra of 21 20‐ketopregnanes were examined and assigned. The substituent effects on the 13C chemical shifts are discussed on the basis of comparisons with published spectra of some closely related compounds.
High resolution 1H NMR studies of cyclic N‐nitrosamines
Authors: Milewska M. J. , Poloński T. 
Published: May 2005

AbstractMolecular modeling by molecular mechanics (MM2) calculations were used to predict conformational preferences of cyclic N‐nitrosamines. The results were compared with 1H NMR data. The observed geminal coupling constants 2J were considerably stronger for syn than for anti α‐methylene protons and thus appear to be very useful for configurational predictions. The long‐range 4J couplings across the nitrogen atom were observed directly from the 1D spectra.
Empirical group electronegativities for vicinal NMR proton–proton couplings along a CC bond: Solvent effects and reparameterization of the Haasnoot equation
Authors: Altona Cornelis , Francke Robert , de Haan Rudy , Ippel Johannes H. , Daalmans Godefridus J. , Hoekzema Aldert J. A. Westra , van Wijk John 
Published: May 2005

AbstractEmpirical group electronegativities (substituent parameters λi), valid for 3J(HH) in saturated HCCH fragments, were derived from the coupling to methyl in substituted ethanes and isopropyl derivatives according to the equation

In contrast to earlier work, it was found advantageous to differentiate between the λi values of hydrogen acting as substituent in CH3 as compared with H in CH2. Special attention was paid to solvent effects, in particular the influence of D2O, on the vicinal couplings and thus on λi. The previously derived λi values remain valid in all common organic solvents but a special effect of D2O on λ is manifest in cases where the α‐substituent carries one or two non‐conjugated lone pairs of electrons that readily act as hydrogen bond acceptors: Δλ= −0.11 ± 0.03 for NH2, NHR, NR2, OH, OR, R = alkyl. Protonation of NH2 to give NH3+ lowers λi by 0.28 units. The λi values for the nucleic acid bases (Ade, Gua, Ura, Thy, Cyt), as determined from the N‐isopropyl derivatives, are 0.56 ± 0.01 irrespective of the solvent. Secondary amides display similar values. The parameters of the Haasnoot equation, originally derived with the aid of a Pauling‐type electronegativity scale, were reoptimized on the basis of the present λi scale; the previous overall r.m.s. error of 0.48 Hz now drops to 0.36 Hz and separate parameterization of HCCH fragments with different substitution patterns appears to be no longer necessary.
Water exchange on the light lanthanide aqua ions [Pr(H2O)9]3+ and [Nd(H2O)9]3 +: A variable temperature and magnetic field 17O NMR study
Authors: Powell D. Hugh , Merbach André E. 
Published: May 2005

Abstract17O NMR relaxation rate measurements were made on aqueous perchlorate solutions of the light lanthanide ions Nd3+ and Pr3+, with the aim of measuring the kinetics of water exchange on these ennea aqua ions. Variable‐temperature results at three magnetic fields show that the ‘kinetic’ effect is not the only contribution to the difference between the transverse and longitudinal relaxation rates. The results at high magnetic field allow lower limits, k ⩾ 5 × 108 S−1 and k ⩾ 4 × 108 s−1, to be determined for water exchange rates at 298.15 K on [Nd(H2O)9]3+ and [Pr(H2O)9]3+, respectively. These limits are consistent with our current understanding of water exchange on the lanthanide aqua ions, based on the change of relative stability of the ennea and octa aqua ions across the series.
31P and 77Se CP/MAS and 31P CPECHO solid‐state NMR studies of bis(dineopentoxy‐thiophosphoryl) diselenide and disulphide
Authors: Potrzebowski Marek J. 
Published: May 2005

AbstractThe principal elements δii of 31P and 77Se chemical shift tensors for the structural analogues bis(dineopentoxythiophosphoryl) diselenide (1) and bis(dineopentoxythiophosphoryl) disulphide (2) were calculated from spinning sideband intensities employing the MASNMR program. From analysis of the 31P NMR data it was concluded that replacement of sulphur by selenium has little influence on shielding parameters, anisotropy Δδ and span Ω. The asymmetry η and skew k are very similar if the geometry of SPXXPS unit (X = S, Se) is not changed. 77Se NMR data are discussed in terms of PSeSeP unit geometry. The static spectra were recorded employing the CPECHO pulse sequence. It was found that this technique is useful both for the lineshape analysis and the calculation of the second moment. The experimental values of M2d are 0.387 kHz2 for diselenide 1 and 0.495 kHz2 for disulphide 2. These values are consistent with those calculated from the van Vleck equation for polycrystalline materials.