bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved 2D inverse proton detected C,H correlation NMR techniques for the total assignment of carbon resonances of a highly delta opioid receptor agonist peptide
Authors: Kövér Katalin E. , Prakash Om , Hruby Victor J. 
Published: May 2005

AbstractAssignment of the 13C resonances of the highly delta opioid receptor selective cyclic peptide magnified image enkephalin (DPDPE) was accomplished by using single‐quantum inverse proton detected 2D heteronuclear correlation spectroscopy. The pulse sequences described provided better sensitivity and resolution than the corresponding, commonly used, multiple‐quantum evolution experiments, since during the SQ‐evolution period there is no line broadening due to scalar and dipolar 1H‐1H interactions. The proton detected C,H correlation spectrum, in combination with the H‐TOCSY relay C,H correlation, gave the assignment of all protonated carbons. The C,H correlation optimized for long‐range coupling gave the assignments of all non‐protonated carbons, such as the carbonyl carbons of the peptide bonds. These spectra also allowed the sequential assignment of this molecule.
Carbon‐13 NMR spectra of tetracyclododecanes: Evidence for upfield δ and ε steric effects
Authors: Seidl Peter Rudolf , Leal Kátia Zaccur , Costa Valentim Emilio Uberti , Möllmann Maria Elisabeti Stapoelbroek 
Published: May 2005

Abstract13C NMR spectra of 36 endo–endo, exo–endo and exo–exo tetracyclic fused norbornyl compounds are interpreted. Stereochemical influences on 1H and 13C chemical shifts are compared and discussed. Only upfield δ and ε effects are observed.
Multifrequency ESR and NMR analysis of the metal–ATP interaction
Authors: Marchettini Nadia , Pogni Rebecca , Basosi Riccardo , Tiezzi Enzo 
Published: May 2005

AbstractMultifrequency ESR analysis allows a new interpretation of the correlation times involved in nuclear relaxation. In this study the metal‐ATP interaction, so important in ecosystem energy mechanisms, was interpreted in the light of new multifrequency ESR and NMR experimental data. ESR spectra of the Mn(II)‐ATP complex were recorded at 2–4 GHz (S‐band), 9 GHz (X‐band) and 35 GHz (Q‐band). A loop‐gap resonator was used to enhance the ηQ0 product at low frequencies. The ESR line shapes at different temperatures and frequencies led to the interpretation of the predominant relaxation mechanism involved. The NMR relaxation rates, also recorded at different temperatures and frequencies, are discussed in terms of a motional model taking into account a distribution of correlation times. Structural and dynamic features were analysed in order to determine the effective correlation time contributing to nuclear paramagnetic relaxation. A comprehensive analysis of the multifrequency ESR spectra is crucial for the correct interpretation of the NMR spectra and of the metal–ATP interaction.
Method for the quantification of silicon‐29 NMR spectra, developed for viscous silicate solutions
Authors: Bahlmann Elke K. F. , Harris Robin K. , Say Barry J. 
Published: May 2005

AbstractA method is described for obtaining quantitative intensity data from solution‐state spectra by a combination of coaxial tubes and sample replacement to take account of spectrometer electronic effects. The protocol was applied to two sodium silicate solutions of high silica content, and it is shown that there is no ‘invisible’ silica at the concentrations studied.
Gradient selection in inverse heteronuclear correlation spectroscopy
Authors: Willker Wieland , Leibfritz Dieter , Kerssebaum Rainer , Bermel Wolfgang 
Published: May 2005

AbstractAfter a brief theoretical description, new gradient‐selected, proton‐detected heteronuclear correlation sequences are introduced. The gs‐HMBC and gs‐Relayed‐HMQC are closely related to the original gs‐HMQC proposed by Hurd and John. A new approach to obtain pure absorption line shapes in gradient selected spectroscopy is used to measure phase‐sensitive gs‐HMQC spectra, to carry out multiplicity editing in HSQC spectra and to distinguish direct and long‐range correlations in HMQC/HSQC–TOCSY spectra.
‘Through‐space’ hydrogen–fluorine, carbon‐fluorine and fluorine–fluorine spin–spin coupling in 2‐phenyl‐3‐alkyl‐4,5,6,7‐tetrahydroindazoles
Authors: Lyga John W. , Henrie Robert N. , Meier Gary A. , Creekmore R. William , Patera Russell M. 
Published: May 2005

Abstract1H, 13C and 19F NMR experiments for a series of 3‐alkyl‐2‐phenyl‐4,5,6,7‐tetrahydroindazoles revealed a six‐bond through‐space coupling between the ortho‐fluorine and the hydrogen or fluorine atom of the position 3‐alkyl group. This was further supported by NOE experiments. Molecular mechanics calculations on a representative structure indicated that several low energy conformers met the fluorine‐carbon distance constraint suggested by the NMR data, and dynamic annealing experiments produced a conformer which was in complete agreement with the NMR data. This through‐space interaction is speculated to be a result of repulsion between N‐1 of the tetrahydroindazole and the ortho‐fluorine lone pair electrons.
Carbon‐13 NMR investigation of some substituted 1,3‐thiazolidin‐4‐ones
Authors: Woolston Christopher Richard Joseph , Lee John Barry , Swinbourne Frederick John 
Published: May 2005

AbstractThe 13C NMR spectra of a series of 2,3‐diaryl‐1,3‐thiazolidin‐4‐ones were measured and the resonance signals produced by the methylene, methine and carbonyl groups of the heterocyclic ring assigned. The variations in their chemical shifts were examined and the influence of S‐oxidation was investigated. 3‐Benzyl‐2‐phenyl‐1,3‐thiazolidin‐4‐one, 3‐butyl‐2‐phenyl‐1,3‐thiazolidin‐4‐one and 2,3‐diphenyl‐5‐methyl‐1,3‐thiazolidin‐4‐one were also examined, the last compound being shown to exist as a mixture of isomers. T1 relaxation times were determined for three thiazolidinones and related to structural effects.
E–Z isomerism of anilinomethylenemalonic acid derivatives
Authors: Bünz C. , Heber D. , Holzgrabe U. , Sürig U. 
Published: May 2005

AbstractThe temperature and concentration dependence of the 1H NMR spectra of four anilinomethylenemalonic acid derivatives were determined in CDCl3 and DMSO‐d6 to assign the E–Z isomers and to investigate the formation of intra‐ and intermolecular hydrogen bonds. Chemical shifts and coupling constants in the 13C NMR spectra correspond with the results of the 1H NMR investigations in the case of the cyanoacetate ester derivative. Contradictory results for the acetoacetate derivative were found by semi‐empirical calculations.
Eburnane‐14‐spiro heterocycles. Synthesis and stereostructure determination by NMR spectroscopy
Authors: Nemes András , Sohár Pál , Kövesdi István , Czibula László , Csehi Attila , Kreidl János 
Published: May 2005

AbstractNew spiroheterocyclic systems, eburnane‐14‐spiro‐5′‐oxazolidinedione, eburnane‐14‐spiro‐4′‐imidazolidinedione and related compounds were prepared by reacting vincamine stereoisomers or 14‐desoxy‐14‐aminovincamines with alkyl isocyanates. Stereostructures of the new compounds were proved by 1H and 13C NMR spectroscopy, including DR, DNOE, DEPT and 2D HSC measurements.
Structure determination of a new saponin from the plant Alphitonia zizyphoides by NMR spectroscopy
Authors: Perera Premila , Andersson Rolf , Bohlin Lars , Andersson Cristina , Li Du , Owen Noel L. , Dunkel Reinhard , Mayne Charles L. , Pugmire Ronald J. , Grant David M. , Cox Paul A. 
Published: May 2005

AbstractHigh‐field NMR experiments, including the 2D INADEQUATE technique coupled with a computerized spectral analysis, were used to determine the full structure of a new saponin extracted from a plant (Alphitonia zizyphoides) found in the Samoan rain forests. The saponin, which shows significant pharmacological activity, consists of an aglycone framework of six rings (three saturated six‐membered rings, two oxygen‐containing five‐membered rings and a five‐membered carbon ring) to which are attached four sugar units and a six‐carbon side‐chain. The INADEQUATE experiment, which was carried out on 60 mg of sample, provided absolute confirmation of the assignments for 35 of the possible 53 CC bonds from the 13C–13C connectivities.
17O NMR spectroscopy: Study of intramolecular hydrogen bonding in phenols and salicylaldehydes
Authors: Boykin David W. , Chandrasekaran S. , Baumstark A. L. 
Published: May 2005

AbstractNatural abundance 17O NMR data for fifteen 2‐ and 4‐substituted phenols, ten 3‐and 5‐substituted 2‐hydroxybenzaldehydes and eight 3‐substituted benzaldehydes, recorded at 75°C in acetonitrile are reported. The chemical shift change due to intramolecular hydrogen bonding for the phenolic oxygen was found to be 10–14 ppm shielding. In acetonitrile, the 17O NMR chemical shift for phenol signals was insensitive to added water up to water concentrations of 0.5 mole fraction. The 17O NMR chemical shifts of the 4‐substituted phenols gave an excellent correlation (r = 0.990) with anisole 17O NMR data; the data also correlated moderately well with σ− (r = 0.974). The chemical shifts of the 3‐substituted benzaldehydes were correlated with σ+ values (r = 0.991). A plot of the carbonyl chemical shift data for the substituted 2‐hydroxybenzaldehydes versus the carbonyl data for 3‐substituted benzaldehydes gave a slope of 0.87 and with r = 0.960. The plot of the 4‐substituted phenol data with that for OH of the corresponding 2‐hydroxybenzaldehydes gave a slope of 1.04 with r = 0.996. Proton to oxygen coupling for the phenolic group of several of the intramolecular hydrogen bonded systems was observed directly [J(OH) = 58–92 Hz]. MM2 and MOPAC calculations predict that the hydrogen bond distances and angles for the substituted 2‐hydroxybenzaldehydes and the partial atomic charges for the carbonyl groups (AMI) were essentially constant. After corrections for electronic effects the chemical shift changes due to hydrogen bonding for the donor (ΔδHBD) and acceptor (ΔδHBA) of the carbonyl–phenol intramolecular bonding system were 5–12 and 30 ± 2 ppm, respectively. The ΔδHBA value was between those for keto and ester acceptors consistent with the relative basicity of the aldehyde group. The ΔδHBD value was substantially larger than those for phenolic donors to keto and ester groups.
1H and 13C NMR assignments with coordination‐induced shift calculations of carbon σ‐bonded ortho‐metalated rhodium(III) and iridium(III) complexes
Authors: Garces Fred O. , Watts Richard J. 
Published: May 2005

AbstractComplete 1H and 13C NMR assignments and coordination‐induced shift [CIS, δ(complex) – δ(free ligand)] calculations for carbon σ‐bonded ortho‐metalated rhodium(III) and iridium(III) complexes are described. NMR parameters are used as probes of van der Waals interactions and ring current anisotropy in the ligand's environmental framework and to monitor σ‐donation and π‐back‐bonding within the ligand in this family of ortho‐metalated complexes. CIS measurements indicate large charge redistribution within the ligands as a result of ortho‐metalation to the rhodium(III) or iridium(III) cationic metal centers. The pulse sequences, attached proton test (APT), 1H1H homonuclear correlation spectroscopy (COSY), single‐frequency off‐resonance decoupling (SFORD) and 1H13C heteronuclear correlation spectroscopy (HETCOR), were utilized to assign all proton and carbon resonances of [Rh(ppy)2Cl]2, [Ir(ppy)2Cl]2, [Ir(ptpy)2Cl]2, [Ir(mppy)2Cl]2, [Rh(ppy)2bpy]+, [Ir(ppy)2bpy]+, [Ir(ptpy)2bpy]+ and [Ir(mppy)2bpy]+, where ppy is 2‐phenylpyridine, ptpy is 2‐(p‐tolyl)pyridine, mppy is 3‐methyl‐2‐phenylpyridine and bpy is 2,2′‐bipyridine.
Conformation of ethane‐1,2‐diol from analysis of its NMR spectrum obtained using gradient‐enhanced inverse detection
Authors: Salman S. R. , Farrant R. D. , Sanderson P. N. , Lindon J. C. 
Published: May 2005

AbstractThe 1H NMR spectrum of [13C]ethane‐1,2‐diol was measured at natural abundance using the 1H13C inverse‐detected HMQC method with magnetic field gradients. A limited solvent and temperature dependence study was undertaken and the vicinal 1H1H coupling constants were related to those in model compounds. It is shown that the trans rotamer is significantly populated, in contradiction to some recent theoretical and experimental studies.
Substituent effects on ESR parameters of α‐phenyl‐N‐tert‐butylnitrone spin adducts. Resolution enhancement and mass spectrometry
Authors: Pan Kai , Lin Chiou‐Rong , Ho Tong‐Ing 
Published: May 2005

AbstractThe combination of high‐performance liquid chromatography (HPLC) and ESR spectrometry was used to isolate the free radicals produced by the reaction of a Grignard reagent with 15 substituted α‐Phenyl‐N‐tert‐butylnitrone. Long‐range hyperfine splitting constants (hfsc) were obtained by the resolution enhancement method. Linear correlation studies between hfsc and Hammett σp constants are reported. Dual‐parameter correlations using σR and σI were also studied. The mass spectra for the HPLC‐isolated spin adducts and their fragmentation patterns are reported.
1H and 13C NMR studies of proton transfer in intramolecular hydrogen bonds in substituted 2‐diethylaminomethylphenol N‐oxides
Authors: Brzezinski Bogumił , Brycki Bogumił , Maciejewska‐Urjasz Hanna , Zundel Georg 
Published: May 2005

AbstractEleven substituted 2‐diethylaminomethylphenol N‐oxides were studied in CDCl3 solutions by 1H and 13C NMR spectroscopy. The 1H chemical shifts of the intramolecular hydrogen‐bonded proton and the Δ14 values obtained from the 13C signals were considered as a function of the pKa values of the parent phenols. The 1H chemical shift of the hydrogen‐bonded proton shows a maximum at pKa ≈ 7. This result agrees well with the turning point of the curve if Δ14 is plotted as a function of the pKa of the parent phenols. All these results agree well with recently obtained Fourier transform IR results. With the system with the strongest hydrogen bond (pKa ≈ 7) a broad, flat, single‐minimum proton potential or a double‐minimum proton potential with a small barrier is present. With this system the deshielding of the proton in the intramolecular hydrogen bond is strongest.
Solution structures of [IrH2(1,5‐cyclooctadiene) (bisphosphine)](CF3SO3) complexes. Homo‐ and heteronuclear long‐range couplings from hydride and phosphorus spins to cyclooctadiene protons
Authors: Hälg Werner J. , Öhrström Lars R. , Rüegger Heinz , Venanzi Luigi M. 
Published: May 2005

AbstractThe solution structures of the two all‐cis stereoisomers of [IrH2(COD)((−)‐chiraphos)](CF3SO3) and the four all‐cis stereoisomers of [IrH2(COD)((−)‐norphos)](CF3SO3) [COD = cycloocta‐1,5‐diene, (−)‐chiraphos = 2S,3S‐bis(diphenyl‐ phosphino)butane, (−)‐norphos = 2R,3R‐bis(diphenylphosphino)norbornene] were assigned on the basis of various one‐ and two‐dimensional correlation methods. The rationalization of a specifically observed scalar coupling interaction between one of the hydrides and a methylene proton of the cyclooctadiene moiety required an assignment of all the relevant protons including their stereochemical relationship. Analogous long‐range coupling pathways were also found for the heteronuclear interactions nJ(P,H) and an interpretation of the origin of these scalar couplings is provided in the form of an expansion of the known geometric dependence of allylic and homoallylic couplings.
13C NMR spectra of trimethylsilylated secondary steroid alcohols
Authors: Schraml Jan , Čermák Jan , Kasal Alexander 
Published: May 2005

AbstractThe 13C NMR chemical shifts of 39 trimethylsilylated secondary steroid alcohols are presented. The compounds include both 5α‐ and 5β‐steroid skeletons and the trimethylsiloxy groups are attached at various positions both in α‐ and β‐configurations.
Analysis of long‐range through‐space couplings via an intramolecular hydrogen bond
Authors: Rae Ian D. , Weigold Josephine A. , Contreras Rubén H. , Biekofsky Rodolfo R. 
Published: May 2005

Abstract2‐Fluorobenzamide and its N‐methyl derivative show spin‐spin couplings between the aromatic fluorine and the nitrogen and carbon of the amide group, which are absent in the corresponding N,N‐dimethylamide. The N‐methyl compound, in which there is a hydrogen bond between the fluorine and the amide hydrogen, also shows fluorine couplings to the nuclei of the methyl group, and these are diminished for solutions of the amide in polar solvents. Such couplings are absent in the N,N‐dimethylamide, which does, however, show fluorine couplings to the proximate methyl group. Calculations at the INDO level employing the IPPP method give reasonable agreement with the magnitudes of the observed 4J(F,N) values in the N‐methylamide and show that the Fermi contact contributions are dominant and that the spin information is transmitted mainly through the hydrogen bond.
Conformations and conformational interconversions of enantholactam
Authors: Borgen Gerd , Dale Johannes , Rise Frode 
Published: May 2005

AbstractThe conformational properties of enantholactam (1‐azacyclooctane‐2‐one) in solution were studied by 1H and 13C NMR at various temperatures. Only the cis‐isomer is present and it occurs in two different conformations in the ratio 3:2, as observed by 13C NMR at − 133°C. In the temperature range − 50 to − 140°C, two conformational processes were observed. A low energy process was visible in both the 1H and the 13C NMR spectra with coalescence temperature ca. − 110°C and a free energy of activation of 30 kJ mol−1, identified as interconversion between the two conformations. A higher energy process was visible in the 1H but not in the 13C NMR spectrum with coalescence temperature ca. − 96°C and free energy of activation 35 kJ mol−1. This process was identified as geminal 1H exchange. A conformational interconversion scheme for partial and full site exchange of protons and carbon atoms, explaining the variable‐temperature NMR results, is proposed.
High‐resolution solid‐state 13C CP/MAS NMR study of scleroglucan hydration
Authors: Bardet M. , Rousseau A. , Vincendon M. 
Published: May 2005

AbstractScleroglucan is a branched poiysaccharide, soluble in water. Solid‐state and solution 13C NMR were used to follow the fixation of water molecules on anhydrous scleroglucan and the evolution of the scleroglucan—water complex from the solid state to the gel and solution state. Determination of both chemical shift values and relaxation times (T, T1pH and T1C) for anhydrous and hydrated scleroglucans permit the observation of a transition between the two forms. The fixation of water leads to an increase in the solid‐state order, in the form of a triple‐helix association, and at the same time an increase in the interchain distance and in the molecular motion. The gel state obtained for a water‐scleroglucan composition of 90:10 is characterized by an important macromolecular rigidity which implies the use of the solid‐state NMR techniques. Solution 13C NMR can be utilized to characterize the primary structure and the triple‐helix random‐coil conformational transition.
Variable‐temperature NMR studies of 2,6‐dihydroxy acylaromatic compounds. Deuterium isotope effects on chemical shifts, isotopic perturbation of equilibrium and barriers to rotation
Authors: Hansen Poul Erik , Christoffersen Morten , Bolvig Simon 
Published: May 2005

AbstractA series of 2,6‐dihydroxy acylaromatic compounds were investigated to characterize the rotational and hydrogen bonding properties of the carbonyl group. Deuterium isotope effects on 1H and 13C chemical shifts due to deuteriation of OH groups were determined at both ambient and low temperature. In the latter case isotope effects on chemical shifts of the individual rotamers can be determined. Deuteriation of one of the OH groups may lead to isotopic perturbation of the tautomeric equilibrium of the carbonyl group and the two hydroxyl groups. The perturbation was found to be larger in ketones than in esters. Complete band shape analysis of the OH resonances of the esters and ketones in a temperature interval above and below the coalescence temperature led to ΔG≠, AH≠ and ΔS≠ values for various concentrations of added THF‐d8. ΔS≠ was found to be strongly negative. Temperature coefficients for the shift of the OH resonances showed large variations for esters and ketones owing to the different hydrogen bond patterns. The esters have two intramolecular hydrogen bonds, one strong and an additional weaker one between the OH and OR groups. The second OH group of the ketones was shown to point primarily towards C‐5. Increasing amounts of THF‐d8 increased the amount of this rotamer. The anisotropy of the XCO group at C‐2, C‐6 was shown to lead to a low‐field shift of C‐2, very different from that found for CO groups without hydrogen bonds. The anisotropy caused by OH groups can also be estimated. On the basis of the thermodynamic parameters, a model for the rotation of the ester group is suggested. The rate‐determining step involves both intramolcular hydrogen bonds, which are twisted out of the ring plane to form hydrogen bonds to the solvent or other hydrogen bond acceptors.
Solvent versus substituent effects on the nitrogen NMR shielding of the nitro‐group in substituted benzenes
Authors: Witanowski Michal , Sicinska Wanda , Biedrzycka Zenobia , Webb Graham A. 
Published: May 2005

AbstractIntermolecular effects are shown to induce a variation of about 5 ppm in the nitrogen NMR shieldings of aromatic nitro groups. The latter turn out to be comparable to those exerted by substituents in nitrobenzene derivatives in solutions in a given solvent. Substituent effects on the NO2 nitrogen shielding in nitro benzenes, in a given solvent, seem to reflect contributions from the so‐called field‐inductive effects on the electron charge distribution in such systems, and are insensitive to the resonance effects concerned with the delocalized pπ‐electron systems involved.
One‐dimensional multiple quantum filtration 1H NMR spectra of a 15‐mer DNA Duplex modified by the carcinogen 4‐aminobiphenyl
Authors: Cho Bongsup P. , Beland Frederick A. , Marques M. Matilde 
Published: May 2005

AbstractThe selective detection of the arylamine aromatic protons in a 15‐mer DNA duplex modified by the carcinogen 4‐aminobiphenyl was accomplished using one‐dimensional multiple quantum filtration experiments.
Electron spin resonance spectroscopy of free radicals
Authors: Fairhurst Shirley A. , Sutcliffe Leslie H. , Preston Keith F. , Banister Arthur J. , Partington Andrew S. , Rawson Jeremy M. , Passmore Jack , Schriver Melbourne J. 
Published: May 2005

AbstractSolution and powder ESR spectra of the 4‐trifluoromethyl‐1,2,3,5‐dithiadiazolyl and 4‐pentafluorophenyl‐1,2,3,5‐dithiadiazolyl free radicals were analysed. Comparison of the ESR parameters with those obtained for the protonated equivalents shows that fluorination produces a drift of unpaired electron spin density away from the nitrogen 2px orbitals towards sulphur 3px orbitals (x is the direction perpendicular to the heterocyclic ring), consistent with an increase in electronegativity of the substituent. The fluorinated radicals dimerize more readily than their protonated counterparts.
Complete 1H (600 MHz) and 13C NMR spectral assignments of 3,4‐bis [(3,4‐dimethoxyphenyl)‐methyl]dihydro‐(3R‐trans)‐2(3H)‐furanone (matairesinol dimethyl ether), a naturally occurring dibenzylbutyrolactone lignan
Authors: Chimichi Stefano , Cosimelli Barbara , Bambagiotti‐Alberti Massimo , Coran Silvia A. , Vincieri Franco F. 
Published: May 2005

AbstractThe concerted applications of a variety of one‐ and two‐dimensional NMR techniques (COSY, NOESY, HETCOR, COLOC, etc.) to the structural elucidation of the natural 3,4‐bis[(3,4‐dimethoxyphenyl)methyl]dihydro‐(3R‐trans)‐2(3H)‐furanone, isolated from Oenanthe aquatica fruits, in CDCl3 solution are reported. The magnitude of the 1H,1H coupling constants obtained from the simulated spectrum together with a series of homonuclear NOE difference spectra were used to determine the full stereochemistry of the system.