bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multi‐frequency, variable‐temperature and high‐pressure study of carbon‐13 spin—lattice relaxation in tetraoctyltin
Authors: Gillies Duncan G. , Matthews Stephen J. , Sutcliffe Leslie H. 
Published: May 2005

AbstractCarbon‐13 NMR spin–lattice relaxation times, T1, and nuclear Overhauser effect data were obtained for neat tetra‐n‐octyltin at 22.5 and 100.6 MHz over a wide temperature range. T1 values were also measured at 25.16 MHz at pressures up to 211 MPa. The ambient‐pressure data were fitted to the ‘model‐free’ two‐correlation time spectral density with a temperature‐dependent order parameter, S2. The pressure data were interpreted by assuming that internal motions of the octyl chain are independent of pressure while the overall (tumbling) motion and S2 are pressure dependent. The values of the motional parameters for tetra‐n‐octyltin lie in the ranges expected for compounds containing long n‐alkyl chains. The results show that this approach is applicable to complex liquids such as synthetic lubricants of the polydecene type.
13C NMR chemical shifts of ω‐haloalkyl‐trimethylsilyl and ‐tert‐butyldimethylsilyl ethers
Authors: Poleschner Helmut , Heydenreich Matthias 
Published: May 2005

AbstractThe 13C NMR chemical shifts of Me3SiO(CH2)n(1, X = I, n = 2–6, 8, 10; 2, X = Br, n = 2, 4, 6, 8, 10; 3, X = Cl, n = 2, 4, 6; 4, X = F, n = 6) and t‐BuMe2SiO(CH2)n(5, X = I, n = 2–4; 6, X = Cl, n = 4) are presented and assigned.
Water signal suppression by T2‐relaxation enhancement promoted by Dy(III) complexes
Authors: Aime Silvio , Botta Mauro , Barbero Luca , Uggeri Fulvio , Fedeli Franco 
Published: May 2005

AbstractA novel method for water signal suppression in 1H NMR spectra is proposed for biological systems. It is based on the acquisition of a spin–echo spectrum in the presence of Dy(III) complexes, which cause a marked decrease of the water proton T2 through the modulation of ΔωM (chemical shift difference between the bulk and coordinated water resonance) by τM (time associated with the exchange between the two sites).
1H NMR T1(min) data and structure in a series of rhenium polyhydride complexes and the contribution of M‐H dipole–dipole relaxation
Authors: Luo Xiao‐Liang , Howard Judith A. K. , Crabtree Robert H. 
Published: May 2005

AbstractThe unusual species [ReH5(H2){P(p‐tolyl)3}2], for which a neutron diffraction study shows an intermediate HH bond distance of 1.357 Å, is studied by variable‐temperature 1H NMR spin‐lattice (T1) relaxation time measurements. The T1 relaxation rate goes through a maximum at low temperature and the resulting T1 (min) value is 66 ms. This is within the range of T1(min) values found for classical ReH7L2 complexes, so H2 complexes with such long HH bond distances are undetectable by the T1 method. The observed T1(min) value is compared with that calculated from the neutron diffraction data. We consider not only the usual proton–proton dipole–dipole (HHDD) contributions to the relaxation but also the metal‐hydride dipole–dipole (MHDD) contributions. The latter are shown to be negligible for most transition metals, but not for Nb, V, Re, Mn, Co and Ta. Inclusion of the MHDD contributions leads to better agreement between the calculated and observed T1(min) values for a series of rhenium polyhydride complexes. The MHDD relaxation also accounts for most of the disparity previously noted between the calculated and observed T1(min) values for Re2H8(PEt2Ph)4.
Interactions of aminoglycosides with phosphatidylinositol: A 15N nuclear magnetic resonance study
Authors: Schanck André , Brasseur Robert , Mingeot‐Leclercq Marie‐Paule , Tulkens Paul M. 
Published: May 2005

AbstractThe 15N NMR spectra of eight aminoglycosides were interpreted. The effect of mixing 20 mol.% of various aminoglycosides with phosphatidylinositol in aqueous dispersion was studied by 15N NMR, and correlations were found between the degree of interaction of the aminoglycoside for phosphatidylinositol and the calculated energy of interaction of the antibiotic with the negatively charged phospholipid and the inhibitory potency of the drug towards lysosomal phospholipase A1, a critical parameter in the nephrotoxic potential of aminoglycosides.
13C NMR substituent effects in aliphatic systems: Principal component analysis and correlations with electronegativities
Authors: Zalewski Romuald I. , Schneider Hans‐Jörg , Buchheit Ulrich 
Published: May 2005

AbstractPrincipal component (PC) or factor analysis was applied to 13C substituent effects (literature SCS values) in α to δ positions of 47 aliphatic frameworks with 4–13 different substituents X. Two PC terms for each substituent X are sufficient to describe 99.3% of all C‐α shifts within < ± 0.6 ppm, even in the largest data matrix containing 13 × 47 = 611 shifts; shifts in β. γ and δ positions require a third PC term for a similar percentage SCS accuracy. Scaling problems with the different order of magnitudes between α to δ SCS variations are avoided by analysing the corresponding data sets separately; this approach, together with the large data base, leads to a dominating first PC term for C‐α which unambiguously correlates with substituent electronegativities (EN), in contrast to an earlier factor analysis. The same result is obtained by direct comparison of α‐SCS with different EN scales, including for the first time group electronegativities. PCs for β to γ SCS indicate only less consistent trends, which again agree partially with results from direct correlations, but not with EN values. The present PC analysis did not include stereochemical descriptors, but furnishes clear distinctions between clusters of (pseudo‐) equatorially or axially substituted compounds. The PC loadings for C‐α also lead to the unambiguous distinction of primary, secondary, tertiary and quaternary carbon atoms.
Determination of the conformation in solution of three 1,2‐3,4‐Di‐O‐methylenepyranoses: NMR and molecular mechanics studies
Authors: Giraud Bouchra , Nouguier Robert , Jaime Carlos , Virgili Albert 
Published: May 2005

AbstractThe conformational analysis of three 1,2‐3,4‐di‐O‐Methylenepyranoses was carried out using NMR (coupling constants and homonuclear Overhauser effect) and theoretical (MM2 calculations) methods. A preferred twist–boat conformation was found.
Measurement of inter‐proton distances from cross‐relaxation rates determined by a selective null inversion–recovery NMR method
Authors: Liu Maili , Farrant R. Duncan , Lindon John C. 
Published: May 2005

AbstractAn efficient method of measuring proton spin–lattice cross‐relaxation rates in small molecules is proposed. The method involves measuring the difference in relaxation rates in a non‐selective experiment and in one with all resonances except one of interest inverted. This procedure yields cross‐relaxation rates between this nucleus and all other nuclei. These rates are independent of the effects of non‐excited heteronuclei and of non‐dipolar contributions and can be used to determine relative inter‐proton distances. The method was tested using 7‐azaindole and compared favourably with the standard NOE method for estimating proton proximities requiring less data acquisition time.
Structural elucidation of two major metabolites of crisnatol in the rat by NMR and mass spectrometry
Authors: Shockcor John P. , Patel Dipak K. , Johnson Robert L. , Taylor Lester C. E. , Chandrasurin Pisal 
Published: May 2005

AbstractNMR and mass spectral data are presented in support of the structures of two metabolites of crisnatol, 2‐[(6‐chrysenylmethyl)amino]‐2‐methylpropane‐1,3‐diol, a novel DNA intercalator currently undergoing Phase II clinical trials as an anticancer agent. Elucidation of the structures of the major rat urinary metabolite as trans‐1,2‐dihydro‐1,2‐dihydroxycrisnatol, and the major rat fecal metabolite as 1‐hydroxycrisnatol, using 2D NMR techniques are described.
Comparison of the Woessner and the ‘model‐free’ approaches for the analysis of carbon‐13 spin–lattice relaxation data for methyl groups
Authors: Gillies Duncan G. , Matthews Stephen J. , Sutcliffe Leslie H. 
Published: May 2005

AbstractCarbon‐13 NMR relaxation data obtained for methyl groups in two dicyclohexane compounds were used to compare the Woessner and ‘model‐free’ approaches. It is shown that the extra flexibility offered by the latter leads to a more successful analysis of the data.
1H NMR model studies of amphotericin B: Comparison of x‐ray and NMR stereochemical data
Authors: Sowiński Pawel , Pawlak Jan , Borowski Edward , Gariboldi Pierluigi 
Published: May 2005

Abstract1H NMR data for amphotericin B methoxycarbonylmethylamide extracted from DQF‐COSY, ROESY and 1D spectra were compared with x‐ray data for amphotericin B. The conformation of amphotericin B in solution was identical with that found by x‐ray analysis in the solid state. Most of the relay artifacts observed in the ROESY spectrum were recognized, and their pathways of formation were assigned.
Lanthanide‐induced shifts in the 17O NMR spectra of 1,6‐anhydro‐β‐D‐hexopyranoses. Evidence for tridentate complexing
Authors: Schulte J. , Lauterwein J. 
Published: May 2005

AbstractThe complexation of four 1,6‐anhydro‐β‐D‐hexopyranoses with europium(III) was studied in aqueous solution by natural abundance 17O NMR. The paramagnetic ion induced contact shifts of individual hydroxy and ether resonances to low frequency. A clear indication of tridentate complexes was obtained, proving the involvement of the oxygen atom of the anhydro ring in talosan and mannosan and that of the pyranose ring in glucosan.
Conformation of adenosine 5′‐phosphate in solution, deduced from experimental and simulated proton T1 values
Authors: Shibata Susumu 
Published: May 2005

AbstractA computer program developed for the simulation of proton spin‐lattice relaxation times (T1) was applied to the conformational analysis of adenosine 5′‐phosphate (5′‐AMP) in neutral D2O solution. The T1 values of all the non‐exchangeable protons of 5′‐AMP were calculated from the atomic coordinates of the hydrogens and the rotational correlation times by numerically solving a simultaneous differential equation for all the proton magnetizations of the molecule. However, no single conformation gave a good enough agreement between the calculated and observed T1 values. 5′‐AMP in solution must therefore be in conformational equilibrium.The equilibrium around the C‐4′–C‐5′ bond was fixed as gauche‐trans (16%), gauche‐gauche (68%) and trans‐gauche (16%) from the spin coupling constant. A correlation was found to exist between two conformational equilibria, anti ⇌ syn and 2′‐endo ⇌ 3′‐endo. The best agreement between the calculated and observed T1 values was obtained for an equilibrium between three conformers, 2′‐endo‐anti (Z = 60°) 40–53%, 3′‐endo‐anti (Z = 30°) 18–28% and 2′‐endo‐syn (Z = 220–260°) 27–30%. This equilibrium was consistent with all the currently available information about the conformation of 5′‐AMP in solution. 5′‐AMP exists only in the anti conformation in the crystal. This is similar to our results that the anti is the major conformation at 58–81%, but the syn conformer also exists as 19–42% in solution.
13C chemical shifts and 1H‐13C coupling constants of N‐phenyl‐, N‐p‐fluorophenyl‐ and N‐o‐nitrophenylpyrazoles
Authors: Begtrup Mikael , Vedsø Per , Cabildo Pilar , Claramunt Rosa Maria , Elguero Jose , Meutermans Wim 
Published: May 2005

AbstractThe 13C chemical shifts and some 1H13C coupling constants of twelve N‐arylpyrazoles are reported. The assignments were made by using the effects of a fluorine substituent and two‐dimensional techniques.
Determination of absolute values of dipolar cross‐relaxation rates for ligands bound to macromolecules using double‐selective T1
Authors: Gaggelli Elena , Valensin Gianni , Kushnir Tamir , Navon Gil 
Published: May 2005

AbstractMeasuring double‐selective and single‐selective proton relaxation rates has been shown to provide directly the dipolar cross‐relaxation rate of any pair of protons in a ligand molecule. The same measurements for a ligand exchanging between a free and a macromolecule‐bound state yield the cross‐relaxation rate of the bound ligand provided that the rate of exchange is relatively fast, thus allowing one to obtain dynamic and conformational features of the bound ligand. As an example, rigid binding of sulphisomidine to bovine serum albumin has been demonstrated.
Multinuclear magnetic resonance and x‐ray diffraction studies of aminonitropyridines
Authors: Kolehmainen Erkki , Laihia Katri , Rissanen Kari , Rasala Danuta , Gawinecki Ryszard 
Published: May 2005

AbstractThe 15N NMR spectra for 21 aminonitropyridines were measured and their chemical shifts assigned. The 1H and 13C NMR chemical shifts and spin–spin coupling constants were also determined for 16 compounds of this series. In order to relate the structural properties of nitramino groups and their 15N NMR chemical shifts in 2‐ and 4‐nitramino‐3‐nitropyridines, which differ remarkably from all other amino groups studied, low‐temperature 1H NMR, 17O NMR, comparative INEPT and IR spectroscopic studies were carried out. In addition, the x‐ray crystal structure of 2‐nitramino‐3‐nitropyridine was determined. Comparative spectroscopic studies showed that the nitramino derivatives exhibit different characteristics to the other compounds studied. Based on the x‐ray structural data, the nitramino group differs markedly from separate aryl‐bound amino and nitro groups. The nitramino group does not exhibit prototropic tautomerism in the crystalline state. This is in agreement with the small variation in the 15N NMR chemical shifts of the pyridine nitrogen, which excludes the prevalence of pyridinium ions. Among the four NMR nuclei studied, 15N seems to possess the best predictive power regarding the exceptional properties of the nitramino group.
31P and 13C NMR spectra of cyclohexylphenylphosphines, tricyclohexylphosphine and triphenylphosphine
Authors: Schraml Jan , Čapka Martin , Blechta Vratislav 
Published: May 2005

Abstract13C and 31P NMR chemical shifts and coupling constants are reported and assigned for the two cyclohexylphenylphosphines, tricyclohexylphosphine and triphenylphosphine. The 13C NMR spectra of all compounds except dicyclohexylphenylphosphine could be assigned on the basis of APT experiments, substituent effects on the chemical shifts and the values of the 13C31P spin–spin coupling constants. The 13C NMR spectrum of dicyclohexylphenylphosphine, which shows six non‐equivalent (both in chemical shift and in spin–spin coupling) cyclohexyl carbons, was completely assigned on the basis of one‐bond and long‐range 13C13C 2D INADEQUATE experiments. The variable‐temperature spectra indicate a hindered motion in this compound. The one‐bond 13C13C spin–spin coupling constants of the cyclohexyl carbons vary only slightly with the distance from the substituent. An increase in the 31P chemical shift with an increasing number of cyclohexyl groups parallels the increasing catalytic activity of rhodium complexes containing the studied molecules as ligands.
15N NMR study of tetrazoles
Authors: Naumenko Valentina N. , Koren Andrei O. , Gaponik Pavel N. 
Published: May 2005

AbstractA natural abundance 15N NMR study was carried out on a series of 1‐ and 2‐mono‐ and 1,5‐ and 2,5‐disubstituted tetrazoles in different media. An erroneous assignment given in the literature for 2,5‐disubstituted tetrazoles was corrected using MNDO molecular orbital calculations and the analysis of changes in the 15N chemical shifts on protonation. Earlier assignments for 1‐ and 2‐mono‐ and 1,5‐disubstituted tetrazoles were confirmed by the same means and by the use of 15N,H couplings. Direct proof that N‐4 is the protonation site is presented, to our knowledge for the first time.
Phenindamine and its analogues and precursors: NMR evidence of structure and configuration
Authors: Casy Alan F. , Hussain Rohannah B. , Upton Christopher 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of analogues of the antihistaminie agent phenindamine and its precursors are interpreted in terms of structure and geometry. Points of interest are the conformations of 4‐piperidinol and dihydro‐1‐pyrindene(diene) intermediates, and the configuration of the hexahydro analogue of phenindamine and its corresponding product of equilibration. Results of an antihistamine evaluation test are presented.
High‐resolution proton‐detected 2D HEHAHA correlation experiments with spin–echo discrimination of long‐range correlations
Authors: Gibbs Andrew , Morris Gareth A. 
Published: May 2005

AbstractRecent work has shown that broadband heteronuclear Hartmann—Hahn coherence transfer is an efficient alternative to pulsed coherence transfer methods. A new technique for heteronuclear long‐range correlation between 13C and protons, making use of proton detection and an extended mixing period, is described, which can have sensitivity and resolution advantages over current techniques. Efficient regiospecific correlation is shown in a model system, menthol, and the use of a modulated spin‐‐echo for the simultaneous determination of one‐bond and long‐range correlations is demonstrated.
Complete assignment of the 1H, 13C and 15N spectra of bradykinin derivatives
Authors: Zerbe Oliver , Welsh John H. , Robinson John A. , Von Philipsborn Wolf‐Gang 
Published: May 2005

AbstractThe complete assignment of the 1H, 13C and 15N spectra of bradykinin derivatives is presented. The proton assignments were performed using COSY, TOCSY and ROESY experiments, whereas the heteronuclei were assigned using inverse correlation experiments.
NMR and 14N NQR spectra. Structure of the crystalline products from the nitrosation of phosphorylacetaldehydes
Authors: Pavlov Valeriy A. , Smith John A. S. , Zjablikova Tatjana A. 
Published: May 2005

Abstract14N NQR and NMR spectroscopy were used to show that, in the solid phase, the products of nitrosation of phosphorylacetaldehydes are a mixture of dimers of 1‐(dialkoxyphosphoryl)‐1‐nitrosoethen‐2‐ols and dialkoxyphosphorylacetaldnitrones. The stabilization of the nitrone form is probably made possible by a high degree of conjugation and by the way the dimeric molecules are packed in the crystal, which causes them to be held in fixed positions. When the dimeric 1‐(dialkoxyphosphoryl)‐1‐nitrosoethen‐2‐ols and dialkoxyphosphorylacetaldnitrones are dissolved, they undergo aldo‐enol, nitroso‐oxime and nitrone‐oxime tautomerism, converting gradually into monomeric aldehyde oximes which exist in E‐ and Z‐isomeric forms. The ratios of dimeric nitroso‐enol, nitrone‐enol and monomeric aldehyde oxime forms can be measured by NMR and depend on the solvent, concentration and temperature.
Synthesis and evaluation of fluorinated calcium chelators with enhanced relaxation characteristics
Authors: Levy Louis A. , Murphy Elizabeth , Raju Bore , London Robert E. 
Published: May 2005

AbstractThe fluorinated calcium ion chelator 5F BAPTA [1,2‐bis(2‐amino‐5‐fluorophenoxy)ethane‐N, N, N′, N′‐tetra‐acctic acid] was used for the determination of cytosolic Ca2+ ion levels in cells and tissues by 19F NMR. The possibility of enhancing the sensitivity of these measurements by modifying the relaxation behavior of the chelator was evaluated. These strategies involved the design of a chelator with reduced T1 value viz. 5F RBAPTA {1,2‐bis [2‐amino‐4‐(1‐carboxy‐2‐methyl‐2‐propyl)‐5‐fluorophenoxy]ethane‐N, T, N′, N‐tetraacetic acid}, and the evaluation of chelator with slower exchange characteristics, viz 5F BenzEGTA [1‐(2‐amino‐5‐fluorophenoxy)‐2‐(2‐aminoethoxy)ethane‐N, N, N′, N′‐tetraacetic acid]. Both analogs exhibit chemical shift differences on calcium complexation which are similar to those of the parent compound, 5F BAPTA. In the case of BenzEGTA, a considerably greater pH dependence of the apparent calcium, dissociation constant, KD, also results from the presence of a tertiary amine with a pK value above the physioligical range. Additionally, the synthetic approach used for RBAPTA can lead to wide variety of derivatives with variable chemical, biochemical and NMR properties.
Applications of gradient‐selective COSY and DQCOSY to brucine and gibberellic acid
Authors: Carpenter T. A. , Colebrook L. D. , Hall L. D. , Pierens G. K. 
Published: May 2005

AbstractHigh‐quality gradient‐selective COSY spectra were recorded at 300 MHz for brucine and gibberellic acid and double‐quantum filtered gradient‐selective COSY spectra for brucine, using a single‐frequency, high‐resolution 1H probe modified by the addition of an unshielded z‐gradient coil set. Data were efficiently recorded using buffered acquisition with a single transient per increment in 1t, in times much lower than those required for phase‐cycled COSY, and with no loss of information. Gradient‐selective COSY90, COSY45 and long‐range COSY45 experiments, and the correlations leading to chemical shift assignments for gibberellic acid, are reported.
Assignment of the 1H and 13C NMR spectra of naphtho [1′,2′:4,5]thieno[2,3‐c]quinoline using two‐dimensional NMR spectroscopy
Authors: Castle Lyle W. , Zektzer Andrew S. , Johnston Milton D. 
Published: May 2005

AbstractThe 1H NMR spectrum of naphtho [1′,2′:4,5]thieno[2,3‐c]quinoline is highly congested because all the protons are in an aromatic environment, and the structure of the molecule is nearly symmetric. With this in mind, the assignment of the 1H and 13C NMR spectra of this compound obtained using two‐dimensional NMR spectroscopy is reported.
Deuterium isotope effects on 13C nuclear shielding of amino and acetamido compounds. Tautomerism and intramolecular hydrogen bonding
Authors: Hansen Poul Erik , Kolonicny Alois , Lycka Antonin 
Published: May 2005

AbstractDeuterium isotope effects on 13C nuclear shielding were investigated for a series of o‐amino and acetamido azo compounds and for amino‐ and acetamido‐9,10‐anthra‐ and leucoanthraquinones. A variety of these compounds form intramolecular hydrogen bonds and are possibly tautomeric in nature. Deuterium isotope effects on 13C chemical shifts were used to probe both the tautomerism and the nature of the hydrogen bond. Deuterium isotope effects over two bonds reflect the strength of the hydrogen bond. In general, isotope effects do not depend on the solvent and, in this study, are independent of temperature. In the acetamido compounds isotope effects on the internal aromatic carbons, 2ΔCar(ND), vary much more than the 2ΔCO(ND) values of the external carbonyl carbon. Plots of 2Δ vs. δ(H) accordingly show different slopes. Investigations of these types of compounds allow a correlation between the hydrogen‐bond enthalpy and 2ΔCO(ND) of amides. 2ΔCO(ND) values therefore form a basis for extending the use of deuterium isotope effects to, for example, biomolecules. Diamino‐9,10‐leucoanthraquinone represents, to our knowledge, the first case of a compound in which isotope effects from both a hydrogen‐bonded and a free ND deuterium can be observed. Bis(phenylamino)leucoanthraquinone exhibits interesting equilibrium isotope effects over many bonds. Many of these isotope effects are non‐additive. Hydrogen bonding is discussed in general, based on these observations.
Structural elucidation of disubstituted nortricyclenes through vicinal 13C, 1H coupling constants
Authors: Gridnev I. D. , Leshcheva I. F. , Sergeyev N. M. , Chertkov V. A. 
Published: May 2005

AbstractVicinal 13C, 1H coupling constants were used to establish the configuration of a 3,5‐disubstituted notricyclene. The assignment procedure is supported by independent measurements of 13C, 2H coupling constants in 3‐ deuterionortricyclene and confirmed by 1H, 1H NOE data for exo‐3‐N‐acetylamino‐exo‐5‐pivaloylnortricyclene.