bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of misoptimization of the BIRD pulse on one‐bond modulation effects in long‐range heteronuclear chemical shift correlation spectra
Authors: Salazar Miguel , Soltero Luis R. , Zektzer Andrew S. , Martin Gary E. 
Published: May 2005

AbstractBIRD pulses have been shown to provide an effective means of decoupling one‐bond modulation of long‐range response intensity. It is not possible to optimize the BIRD pulse effectively when there is a range of one‐bond coupling constants. To examine the effects of misoptimization of the fixed delays (τ) in the BIRD pulse, the simple alkaloid norharmane was employed. Long‐range heteronuclear correlation spectra were recorded using a modified pulse sequence containing a BIRD pulse midway through the Δ2 interval. The experiment was optimized for 10.3 and 11.1 Hz, which correspond to a valley and a peak in the response intensity curve when the experiment is performed without the BIRD pulse midway through Δ2. The delays in the BIRD pulse were variously optimized for values ranging from 80 to 175 Hz. The results suggest that the BIRD pulse is effective in decoupling one‐bond modulations of response intensity even when the τ delays are grossly misoptimized for the one‐bond coupling constantin question.
Identification of the b, d, and e analogs of vitamin B12 as monocarboxylic acids by 15N NMR spectroscopy
Authors: Difeo Thomas J. , Schiksnis Robert A. , Kohli Rakesh K. , Opella Stanley J. , Nath Amar 
Published: May 2005

Abstract15N NMR spectra of b−, d−, and e‐cyanocobalamin (vitamin B12) and the products of their amidation with 15N‐labeled ammonia show that these analogs are monocarboxylic acids of vitamin B12 which result from hydrolysis at the respective propionamide groups.
13C NMR studies of 2‐ and 3‐methyl‐ and 2‐ and 3‐formyl‐indoles. Nitro and phenyl derivatives
Authors: Erra‐Balsells R. , Frasca A. R. 
Published: May 2005

Abstract13C chemical shifts are reported for a series of nitro and phenyl derivatives of 2‐ and 3‐methylindoles and 2‐ and 3‐formylindoles, measured in DMSO‐d6. The 13C substituent chemical shift (SCS) data are discussed and compared with 1H SCS data.
1H and 13 NMR study of the structure of 3‐N‐(4‐ and 5‐benzimidazolyl or benztriazolyl)amino derivatives of prop‐2‐enoic acid in the liquid and solid states
Authors: Goljer Igor , Milata Viktor , Ilavský Dušan 
Published: May 2005

AbstractBenzimidazole‐ and benzotriazole‐amino derivatives of prop‐2‐enoic acid were studied by 1H NMR spectroscopy in the liquid state and by 13C NMR spectroscopy in the liquid and solid states. The spectra shows tautomerism of the benzimidazole and benzotriazole rings, E‐Z isomerism of the double bond of the propenoic acid substituent and the conformation around the amino NHCH bond. The formation of an intramolecular hydrogen bond between the amino proton and the COOR group of propenoic acid is discussed. The structures of the derivatives are presented on the basis of the 13C CP‐MAS NMR spectra in the solid state.
Configuration and solvent‐dependent conformation of thiaprotoberberines
Authors: Sohár P. , Fodor L. , Szabó J. , Bernáth G. 
Published: May 2005

AbstractThe C‐13 configurations of several 13‐carboxy‐ and 13‐carbalkoxy‐thiaprotoberbanes were determined and evidence of the solvent dependence of their conformations was provided by 1H and 13C NMR and DNOE measurements.
The pyrethrins and related compounds 36—1H and 13C NMR spectra of cis‐ and trans‐aryl‐substituted cyclo‐pentanoid alcohols and of their pyrethroidal esters
Authors: Janes Norman F. , Khambay Bhupinder P. S. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of a range of 1‐, 2‐ and 3‐pheny1, ‐benzyl and ‐phenethyl substituted cyclopentanols and cyclopentylmethyl alcohols and related unsaturated compounds are reported, and assigned using heteronuclear shift correlations. Shift profiles for simple cis‐ and trans‐1,3‐disubstituted cyclopentanes are shown to apply also to those with bulkier substituents, and thence stereochemistries can be assigned to isomeric components in mixtures.
Electron paramagnetic resonance study of the complex formed between copper and 1‐[2(S)‐3‐mercapto‐2‐methylpropionyl]‐L‐proline (Captopril) in solid and aqueous solution
Authors: Evans Jeffrey C. , Morris Caroline R. , Rees Sian B. , Rowlands Christopher C. , Williams David R. 
Published: May 2005

AbstractEPR spectroscopy was used to elucidate the nature of the interaction between copper and the antihypertensive agent 1‐[2(S)‐3‐mercapto‐2‐methylpropionyl]‐L‐proline (Captopril) in both solid and aqueous solutions. The EPR spectra indicate that binding to copper(II) occurs via the ligand oxygens rather than the thiol moieties, and that the EPR‐detectable copper is greatly reduced on complexation. The EPR parameters for the solid copper(II) complexes are in the range g∥ = 2.374−2.386, g⟂ = 2.076−2.086 and A = 13.5 mT, and the parameters for the aqueous solutions are giso = 2.107−2.129 and A = 7.1−8.6 mT.
13C NMR studies on the structure of aminosulfonic acids in dimethyl sulfoxide and water
Authors: Benoit Robert L. , Boulet Danielle , Fréchette Monique 
Published: May 2005

AbstractThe 13C NMR spectra of three aminosulfonic acids (HA) [p‐aminobenzenesulfonic acid (sulfanilic acid), amino‐methanesulfonic acid and 2‐aminoethanesulfonic acid (taurine)] and their anions (A−) and cations (H2A+) were obtained using aqueous H2SO4, fuming H2SO4 and Me2SO solutions of trifluoromethanesulfonic acid. The chemical shifts of HA, A− and H2A+ and the protonation and deprotonation shifts of HA are compared with corresponding data for related amines and sulfonic acids in Me2SO and water. Our results indicate that the three aminosulfonic acids are essentially zwitterionic in Me2SO.
2‐phenylisatogen: A study of molecular dynamics using 13C NMR spin‐lattice relaxation times
Authors: Stoddart Barry , Hooper Malcolm 
Published: May 2005

Abstract13C NMR spin‐lattice relaxation times (T1) were measured for 2‐phenylisatogen in CDCl3 solution. The nonequivalence of the T1 values for the various protonated carbons in this molecule indicates that molecular motion is anisotropic. Analysis of the T1 data using the Woessner formalism for axially symmetric ellipsoids yields a set of diffusion coefficients for overall and internal motion. The phenyl ring undergoes internal motion relative to the larger isatogen ring system. A variable‐temperature study of T1 behaviour in the range 301−363 K indicates that the major motions of the molecule have identical activation energies, viz. 10.5 ± 0.5 kJ mol−1, and that the ratios of derived diffusion coefficients remain constant with temperature. These results suggest that solvent interactions play a major role in controlling the motions of the molecule.
Principal component analysis of the 13C NMR shifts of norbornyl derivatives
Authors: Tostes J. G. Ribeiro , Seidl P. R. , Bruns R. E. 
Published: May 2005

AbstractPrincipal component analysis was applied to the 13C NMR chemical shifts of the seven carbon atoms of the norbornyl framework for 75 molecules. Two two‐dimensional principal component projections are shown to be sufficient to distinguish the main electronic and steric substituent effects contributing to these shifts. These effects allow a comparison of the (three‐, four‐ and five‐membered) ring and non‐ring substituents and their influence on the shifts of carbon atoms of the norbornyl framework. Four classes of molecules, each with characteristic chemical behaviour, are identified. Exo‐endo class discrimination and exo‐endo patterns of isomer pairs are emphasized, especially with regard to cyclic substituents on norbornyl systems.
13C chemical shift non‐equivalence in methylene carbons of monosubstituted cyclohexanes
Authors: Ito Hiroshi , Renaldo Alfred F. , Johnson Robert D. , Ueda Mitsuru 
Published: May 2005

AbstractMonosubstituted cyclohexanes were synthesized by addition of a cyclohexyl radical to olefins bearing different substituents at the α‐position. Six distinct methylene 13C resonances were observed, indicating that the methylene carbons located at the 2 and 6 positions and at the 3 and 5 positions are not magnetically equivalent. This magnetic non‐equivalence (anisochronism) observed in the monosubstituted cyclohexanes is due to the introduction of an asymmetric center β to the prochiral C‐1 ring carbon.
Studies on systems of salts and mixed solvents 35—27 Al NMR investigations of AlCl3‐water‐N,N‐dimethylformamide solutions using the solid‐state MAS technique
Authors: Hallas E. , Emons H.‐H. , Siedler M. , Thomas B. 
Published: May 2005

AbstractConventional liquid‐state 27Al NMR spectra of concentrated solutions of the AlCl3‐water‐N,N‐dimethyl‐N‐Dimethylformamide formamide system contain comparatively broad non‐structured lines. Application of MAS leads to a reduction in the line width and a structuring of the spectra. This allowed the experimental determination of the chemical shifts of [Al(H2O)6−x(DMF)x]3+ (x = 0−6) mixed‐ligand complexes. The investigations demonstrate an example of the applicability to liquids of the NMR MAS technique, which was originally developed for solids. They underline the existence, in a reduced form, of ‘solid‐type’ interactions within the investigated solutions.
13C NMR studies of some tricyclo[3.2.1.02,4]octanes
Authors: Wilt James W. , Peeran Mehboob , Ramakrishnan Subramanian , Crumrine David S. 
Published: May 2005

AbstractThe 13C NMR chemical shifts for a series of exo‐ and endo‐3,3‐diphenyltricyclo[3.2.1.02,4]octanes are reported. Comparisons with the parent exo‐ and endo‐tricyclo[3.2.1.02,4]octanes and with bicyclo[2.2.1]heptanes show that most of the chemical shifts are additive. Substituent effect constants are presented for the tricyclo[3.2.1.02,4]octyl system. Pronounced deshielding effects are seen in the endo series for C‐6 and −7 of the alkene endo‐3,3‐diphenyltricyclo[3.2.1.02,4]oct‐6‐ene, the epoxide endo‐3,3‐diphenyltricyclo[3.2.1.02,4]octan‐6,7‐exo‐oxide, and the tetracyclic exo‐3,3‐diphenyltetracyclo[3.3.1.02,406,8]nonane. The chemical shifts of C‐3 and −8 are diagnostic for endo vs. exo substitution.
2D heteronuclear NOE spectroscopy with full ω1 decoupling. A method for elimination of 13C1H coupling dependence
Authors: Kövér Katalin E. , Batta Gy. 
Published: May 2005

Abstract‘Constant‐time’ experiments are proposed for heteronuclear 2D NOE spectroscopy which provide full decoupling in the ω1 dimension. The heteronuclear coupling modulation of signal intensities is removed by a slight modification of the basic constant‐time experiments. This new sequence seems to be appropriate for routine applications.
Involvement of exciplexes in the photolysis of aliphatic ketones in deuteriochloroform: CIDNP evidence
Authors: Zhang Mao‐Xi , Liu Zhong‐Li , Wu Lung‐Min , Liu You‐Cheng 
Published: May 2005

AbstractPhotolysis of 4‐acetyl‐4‐ethoxyformylcyclohexanone and 4‐acetyl‐4‐phenylcyclohexanone in deuteriochloroform showed an unusual polarization which suggests that a singlet exciplex of the ketone with deuteriochloroform may be involved in the Norrish type I reaction.
Solid‐state NMR study of a series of aminophosphonic acids
Authors: Harris Robin K. , Merwin Lawrence H. , Hägele Gerhard 
Published: May 2005

AbstractHigh‐resolution 31P, 15N and 13C NMR spectra have been obtained for nine solid aminophosphonic acids under conditions of high‐power decoupling, cross‐polarization and magic‐angle spinning. The NMR evidence shows that the asymmetric unit is a single molecule in all cases, which is consistent with the available diffraction studies. Phosphorus‐31 shielding tensor components determined from static and slow‐spinning MAS spectra are given for a number of the compounds.
Complete 1H and 13C NMR assignment of two α‐isosparteine salts by the use of two‐dimensional NMR spectroscopy
Authors: Simeonov Mario F. , Spassov Stefan L. , Duddeck Helmut , Majchrzak‐Kuczyńska Urszula , Skolik Jerzy 
Published: May 2005

AbstractTwo‐dimensional phase‐sensitive homo‐ and hetero‐nuclear shift correlation methods, in addition to homo‐ and hetero‐nuclear relayed coherence transfer, COLOC and NOESY experiments, were used to obtain a complete proton and 13C assignment of α‐isosparteine methiodide and α‐isosparteine methylene diiodide.
Lanthanide‐induced shifts in the 1H NMR spectra of N,N‐dimethylformamide and N, N‐dimethylacetamide: Limitations of the point methyl model
Authors: Ladd J. A. 
Published: May 2005

AbstractThe shifts induced in the 1H NMR spectra of N,N‐dimethylformamide and N,N‐dimethylacetamide by Pr(fod)3, have been measured by the reciprocal method and the results analysed using various models of the substrate molecules. Only those models which take full account of the stereochemistry of the methyl groups give a reasonable description of the induced shifts. It is also demonstrated that there is only one time‐averaged position of the lanthanide ion in the framework of the substrate molecule which adequately fits the experimental results.
Tellurium‐125 NMR investigations on coordination compounds of tellurium(II) with unsaturated dithio, thioseleno and diseleno ligands
Authors: Dietzsch Wolfgang , Olk Ruthmaria , Hoyer Eberhard , Meiler Wolfgang , Robien Wolfgang 
Published: May 2005

Abstract125Te NMR spectra of tellurium(II) complexes containing dithiolene or other unsaturated 1,1‐dithio, 1,1‐thioseleno or 1,1‐diseleno ligands are reported. According to their chemical shift values, the complexes can be divided into three groups, well separated by several hundred ppm.
Quantitative analysis and determination of the enantiomeric purity of glycerides by 13C NMR spectroscopy. Application to the lipase‐catalysed transesterification of triacylglycerides
Authors: Rabiller Claude , Maze Françoise 
Published: May 2005

Abstract13C NMR spectroscopy can be used for the quantitative analysis of mixtures of glycerides and the enantiomeric purity can be determined by using Eu(hfbe)3‐d reagent. This technique was applied to the study of the reaction mixture obtained from the transesterification of tributyrin catalysed by My‐lipase (Candida cylindracea). A ‘preference’ of this lipase for the pro‐R ester function of tributyrin is demonstrated.
Effect of methylation on the association ability of purine and pyrimidine in aqueous solutions. A 1H NMR chemical shift study
Authors: Aradi Ferenc , Földesi András 
Published: May 2005

AbstractThe self‐association of 6‐methylpurine and 4‐methylpyrimidine and their hetero‐association with caffeine and theophylline in deuterium oxide at 35°C were studied by measuring the concentration‐dependent changes in proton chemical shift. The association parameters were calculated using simple and competitive dimer models. The self‐association constants for 6‐methylpurine and 4‐methylpyrimidine were found to be 2.24 ± 0.07 and 0.200 ± 0.007 1 mol−1, respectively, and the hetero‐association constants could be ordered in the decreasing series caffeine‐6‐methylpurine (4.85 ± 0.12 1 mol−1) > theophylline‐6‐methylpurine (4.11 ± 0.15 1 mol−1) > caffeine‐4‐methylpyrimidine (1.45 ± 0.13 1 mol−1) > theophylline‐4‐methylpyrimidine (0.98 ± 0.10 1 mol−1). The equilibrium constants imply that methylation enhances the association ability and the upfield dimer shifts can be interpreted in terms of a stacking‐like interaction.
Linear and angular effects on the 1H and 13C NMR spectra of tricyclic aromatic ketones formally derived from tetralone
Authors: Buchanan G. W. , Tong P. T. , Wightman R. H. , Dawson B. A. 
Published: May 2005

AbstractComplete unambiguous assignments of 1H and 13C chemical shifts for α‐tetralone, a related dihydroanthracenone and two related dihydrophenanthrones are presented. Data are based on results of 400 MHz 1H−1H and 1H−13C COSY experiments, and permit an evaluation of linear vs. angular endo and exo ketone orientation on the NMR parameters.
6Li J‐modulated 13C spin‐echo spectra. Selective observation of alkyllithium aggregates
Authors: Thomas Ruthanne D. , Ellington Donald H. 
Published: May 2005

AbstractA 13C spin‐echo technique with gated 6Li decoupling has been developed for the selective observation of different alkyllithium aggregates, (RLi)n. The spectral editing technique is based on the fact that both the multiplicity of the 13C resonance and the magnitude of the observed 13C6Li coupling are a function of the number of coupled 6Li nuclei. The method was shown to differentiate between three types of tert‐butyllithium‐6Li: dimers, fluxional tetramers and non‐fluxional tetramers.
Assignment of phosphate groups and determination of P,H coupling constants in the DNA fragment d(CGTACG) by 31P 2D NMR experiments
Authors: Ragg Enzio , Mondell Rosanna , Garbesi Anna , Colonna Francesco P. , Battistini Carlo , Vioglio Sergio 
Published: May 2005

Abstract2D 31P/1H correlation spectroscopy has been used to assign individual phosphates in the self‐complementary DNA fragment d(CGTACG), which is present in solution as a B‐DNA type double helix. 31P chemical shift variation with temperature and with the base sequence has been studied, and evidence is given of a steric clash between purines in the minor groove, affecting the chemical shift of the innermost TpA phosphate. For this hexanucleotide there is a good correlation of 31P shifts with both the helical twist (∑1) and roll angle (∑2) Calladine‐Dickerson sum functions. Different types of linear correlations, also including data from other nuclotides, have been performed. The results show that it is more appropriate to consider the change in chemical shifts as it occurs during melting rather than the actual 31P shifts. An interesting correlation was also found between 31P chemical shifts and P,H‐3′ coupling constants.
Partial editing in heteronuclear J‐resolved solid‐state NMR spectroscopy
Authors: Tekely P. , Brondeau J. , Retournard A. , Canet D. 
Published: May 2005

AbstractA solid‐state analogue of the double echo sequence and gated decoupling used previously for the determination of carbon multiplicities in liquids is described; it was applied to the simplification and assignment of 13C CP‐MAS spectra in solids. This procedure permits partially edited 13C CP‐MAS subspectra to be obtained directly by means of distinct experiments performed under an identical length of the evolution period.
13C NMR of coumarins I: 3‐(1,1‐Dimethylallyl) derivatives
Authors: Macís F. A. , Massanet G. M. , Rodriguez‐Luis F. , Salvá J. 
Published: May 2005

AbstractThe 13C NMR data of nine 3‐(1,1‐dimethylallyl)coumarins are reported and compared with those of the corresponding C‐3 unsubstituted compounds. A spectro‐scopic criterion for distinguishing C‐3 alkylated dihydrofurano‐ from dihydro‐pyrano‐coumarins is proposed.
Reaction of dibenzalcyclohexanone with hydroxylamine hydrochloride. 2D NMR elucidation of the structure of the products
Authors: Dlaz Eduardo , Barrios Héctor , Ortiz Benjamin , Sánchez‐Obregón Rubén , Yuste Francisco , Reynolds W. F. , Aguilera Jose Luis , Caballero Efrén 
Published: May 2005

AbstractThe reaction of dibenzalcyclohexanone with hydroxylamine hydrochloride affords three compounds: the oxime of 2‐benzylidenecyclohexanone (2), 3‐phenyl‐7‐benzylidene‐3,3a,4,5,6,7‐hexahydro‐2,1‐benzisoxazole (3) and 3‐phenyl‐3,3a,4,5,6,7‐hexahydro‐2,1‐benzisoxazole‐7‐spiro‐2′‐(3′‐phenylaziridine) (4). Their structures were deduced by 2D NMR analysis. Single‐crystal x‐ray diffraction was used to confirm the structure and stereochemistry of 4. A possible mechanism for this reaction is proposed.
Full assignments of the 1H and 13C NMR spectra of the antibiotic kirromycin (mocimycin)
Authors: Barber Jill , Derome Andrew E. , Howard Tina D. , Lian Luyun , Tebb Graham 
Published: May 2005

AbstractThe 1H nuclear magnetic resonance spectra of kirromycin in acetone‐d6 and in buffered D2O have been assigned using a range of one‐ and two‐dimensional NMR techniques. The 13C NMR spectrum of kirromycin in acetone‐d6 has also been assigned, and compared with the 13C NMR spectrum of its N‐methyl analogue, aurodox.
13C and 1H NMR study of structure and structural dynamics of tautomeric 2‐ethoxycarbonylthiolane‐3‐thiones
Authors: Duus Fritz 
Published: May 2005

Abstract2‐Ethoxycarbonylthiolane‐3‐thione (1) and its 5‐methyl, 5‐phenyl, 5,5‐dimethyl and 4,5‐dimethyl derivatives (2–5) were studied in solution by 13C and 1H NMR spectroscopy, using solvents of various polarity. Compounds 1–4 exist entirely in the tautomeric (Z)‐enethiol form, i.e. they are in fact 2‐ethoxycarbonyl‐3‐mercapto‐4,5‐dihydrothiophenes (1C‐4C), apparently irrespective of their molecular surroundings. Compound 5 exists predominantly as the pair of enantiomeric (and hence NMR‐indistinguishable) 2‐ethoxycarbonyl‐3‐mercapto‐4,5‐dimethyl‐4,5‐dihydrothiophenes having a trans location of their ring‐methyl groups, i.e. 5C(4R, 5R) and 5C(4S, 5S). The diastereomeric counterparts 5C(4R, 5S)/5C(4S, 5R) are observable as minor constituents, co‐existing with the former in a double two‐step equilibrium system, involving tautomeric 2‐ethoxycarbonyl‐3‐mercapto‐4,5‐dimethyl‐2,5‐dihydrothiophenes as intermediates.The 13C chemical shifts of C‐4 and C‐5 of the unsubstituted and mono‐ and di‐methyl‐substituted 4,5‐dihydrothiophenes (1C, 2C, 4C, 5C) are describable in terms of additive methyl‐substituent shielding.The observed solvent‐induced displacement of the mercapto proton chemical shift is interpreted in terms of the solvent's ability to effect pertubation of the intramolecular S—H ⃛O hydrogen bonding.Vicinal couplings between ring protons at C‐4 and C‐5 are influenced by substitution at C‐4 and C‐5, and also by the nature (polarity) of the solvent used. The measured coupling constants have been rationalized in terms of the conformational mobility of the 4,5‐dihydrothiophene framework. A methyl group at C‐5 has little significance for conformational preference. A phenyl group at C‐5 preferentially occupies the near‐equatorial position. The conformational equilibrium of the trans‐4,5‐dimethyl‐4,5‐dihydrothiophenes 5C(4R, 5R)/5C(4S, 5S) apparently depends on the solvent's polarity, a more polar solvent favouring the conformer having near‐diaxial methyl groups.
Proton‐detected C,H correlation NMR techniques for the complete assignment of all proton and carbon resonances of a cyclic peptide
Authors: Hofmann Mechtild , Gehrke Matthias , Bermel Wolfgang , Kessler Horst 
Published: May 2005

AbstractThe assignment of the proton and carbon spectra of the cyclic peptide cyclo(‐Phe1‐Pro2‐Thr3‐Lys(Z)4‐Trp5‐Phe6‐) was accomplished by the application of multiple quantum proton‐detected heteronuclear correlation spectroscopy. Since the proton spectrum shows severe overlap, the carbon chemical shifts were used to disentangle the proton resonances. The methodology described is useful even in cases where only limited quantities of materials are available.The combination of (i) a proton decoupled C,H correlation spectrum and (ii) a (not decoupled) H‐relayed C,H correlation gave the assignments of all CHn groups. The non‐protonated carbons, i.e. the carbonyl carbons of the peptide bond, were assigned with a C,H correlation optimized for long‐range couplings, an experiment that also gave helpful information about the conformational features of the hexapeptide.The cyclic peptide contains a Phe‐Pro cis‐peptide bond forming a βVI‐like bend and a β‐turn about the amino acids Thr‐Lys‐Trp‐Phe. Although the conventional discussion of NMR parameters indicates a strong preference for one conformation, the quantitative evaluation of NOE‐derived distances in restrained MD calculations proves that the type of β‐turn in the last‐mentioned region is not unique. Whereas the MD calculations converge to a βII' turn, the vicinal proton coupling constants are in better agreement with type βI. Thus a dynamic equilibrium of the backbone is proposed.