bluuebunny/crossref_metadata_2025_split huggingface dataset:
1H and 13C NMR spectroscopy of substituted bis‐1,3,4‐oxadiazoles
Authors: Tashtoush Hasan , Al‐Talib Mahmoud , Odeh Nedal 
Published: May 2005

AbstractDehydration of N,N′‐diacylalkanedioic acid dihydrazides with phosphoryl chloride gave 5,5′‐disubstituted‐2,2′‐(1,n‐alkanediyl)bis‐1,3,4‐oxadiazoles. The structures of these compounds were elucidated by 1H, 13C NMR, UV and IR spectroscopy.
ESR spin probe study of water within covalently crosslinked, dextran‐based microbead hydrogels (Sephadex® G)
Authors: Windle John J. , Scherrer Rene 
Published: May 2005

AbstractAqueous suspensions of dextran‐based Sephadex® G microbeads of progressively increasing degrees of covalent crosslinking and concomitantly decreasing water content formed a two‐phase system consisting of the waterswollen microbeads of diameter 100‐300 μm, the hydrogel phase, and of the surrounding water, the aqueous phase. These suspensions were analyzed by ESR spectroscopy using a series of small amphipathic nitroxide spin probes which partitioned between the two phases. Probe partition coefficients increased with decreasing gel water content for the more hydrophobic probes and decreased for the more hydrophilic probes. The ESR spectra of the suspensions consisted of the superposition of the spectra for the probes in the two phases. From the partition coefficients and the spectral parameters of the probes in the suspension and in the aqueous phase, relative rotational correlation times, τc, and isotropic nitrogen nuclear hyperfine splitting constants, aN, for the probes in the aqueous hydrogel interior were determined. For each probe, τc increased and aN decreased with increasing crosslinking and decreasing gel water content, indicating increasing microviscosity and decreasing dielectric constant and hydrophilicity for the gel water. The alterations in the gel water properties resulted from increasing gel matrix–water interactions and were further enhanced for water within the restricted volumes (compartments) in the most highly crosslinked hydrogels (Sephadex G‐15 and G‐10). In addition, the aN values indicated that two hydrogen bonds were formed to the nitroxide group of the probes in water and that, in the hydrogels, the hydrogen bonding contribution to aN progressively increased as the water content decreased.
The solute conformation of opioid ligands of the 4‐arylpiperidine class: α‐Promedol and related compounds
Authors: Casy Alan F. , Ogungbamila Francis O. 
Published: May 2005

AbstractThe NMR spectra (chiefly 1H) of isomeric 2,5‐ and 2,3‐dimethyl‐4‐phenyl‐4‐piperidinols, related esters and trans‐ 2,6‐dimethyl‐4‐propionyloxy‐4‐phenylpiperidine HCl (all N‐methylated) have been assigned and analysed in terms of solute conformation. Preferred forms include 4‐ax‐phenyl and 4‐eq‐phenyl chairs and, in the case of the γ‐2,3‐dimethyl‐4‐piperidinol base, a boat conformation. In several cases the existence of pairs of N‐protonated epimers has been demonstrated. The findings are important both to the conformational analysis of saturated six‐membered heterocycles and to stereoactivity analyses of opioid ligands of the 4‐arylpiperidine class.
Two‐dimensional NMR spectra of asbestinin diterpenes isolated from Briareum asbestinum (Pallas). Total stereochemical assignment by two‐dimensional NMR techniques
Authors: Rodriguez Abimael D. 
Published: May 2005

AbstractThe concerted application of two‐dimensional phase‐sensitive COSY, RELAY, ROESY and 13C‐1H shift correlation spectroscopy in the structural elucidation and stereochemical assignment of a new asbestinin diterpene, (Z‐11‐acetoxy‐4‐deoxyasbestinin‐(D), is reported. The results reveal that these two‐dimensional techniques are invaluable for the stereochemical assignment of proton resonances in the 4‐deoxyasbestinin series which overlap in 1H NMR and homonuclear correlation spectra.
Electron paramagnetic resonance, ENDOR and TRIPLE resonance study of some 9,10‐anthraquinone radicals in solution
Authors: Vuolle Mikko , Mäkelä Reijo 
Published: May 2005

AbstractEPR, ENDOR and TRIPLE resonance spectra were recorded for 1,8‐dihydroxy‐3‐methyl‐9,10‐anthraquinone and 9,10‐anthraquinone‐2‐carboxylic acid anion radicals and the 9,10‐anthraquinol‐2‐carboxylic acid cation radical. EPR spectra were recorded for the 5,8‐dideuterio‐1,4‐dideuterioxy‐9,10‐anthraquinone anion radical, the 6,7‐dideuterio‐1,4‐dideuterioxy‐9,10‐anthraquinone anion radical and the 1,4‐dihydroxy‐9,10‐anthraquinol cation radical. The coupling contants of the 1,4‐dihydroxy‐9,10‐anthraquinone anion radical were assigned by deuteriation.
Structure of Manasse's dimer from endo‐2‐hydroxyepicamphor by NOE difference spectroscopy
Authors: Banks Malcolm R. , Gosney Ian , Grant Keith J. , Reed David , Hodgson Philip K. G. 
Published: May 2005

AbstractReduction of (1R)‐(+)‐camphorquinone by zinc in acetic acid yields a mixture of endo‐2‐hydroxyepicamphor and 3‐hydroxycamphor. The former undergoes reaction in anhydrous methanol with HCl gas to furnish a stable crystalline solid, first reported in 1902. High‐resolution electron impact mass spectrometry showed the solid to be a dimer of formula C22H36O4. The 13C{1H} spectrum showed 11 discrete environments, in keeping with a symmetrical dimer. High‐field 1H NOE difference experiments were used to determine not only the connectivity but also the stereochemistry of the system. All of the NOE experiments are consistent with only one structure, that of the symmetrical dimer. In addition, 2D carbon‐proton correlation experiments (HETCOR) were used to assign unambiguously its 13C{1H} spectrum.
NMR relaxation and ESR spin probe studies of some surfactant micelles
Authors: Bratt Peter J. , Gillies Duncan G. , Krebber Angelika M. L. , Sutcliffe Leslie H. 
Published: May 2005

AbstractMulti‐frequency relaxation studies combined with the ‘two‐step’ and ‘three‐step’ models for molecular motion have been applied to a range of anionic surfactant molecules. From the internal dynamic parameters (τf and S) conclusions have been drawn about the dependence of surfactant molecular dynamics inside micelles on molecular structure, and two unusual conformations have been identified. Slow correlation time (τs) data have also been obtained for these compounds. Three deuteriated surfactant molecules were subjected to the ‘three‐step’ model and data are presented showing how the dimensions of the non‐spherical micelles vary with temperature. An ESR spin probe study has been carried out on the compounds giving probe rotational correlation times at various temperatures. Information on alkyl chain packing at or near the water/micelle interface can be obtained from the derived thermodynamic parameters.
Peptide group chemical shift computation
Authors: Herranz José , González Carlos , Rico Manuel , Nieto José L. , Santoro Jorge , Jiménez Maria A. , Bruix Marta , Neira José L. , Blanco Francisco J. 
Published: May 2005

AbstractIt has been found that protein NH protons on top of a peptide group plane experience large upfield conformation shifts. The joint analysis of this effect and other known effects of the peptide group on proton chemical shifts has led to a two‐term empirical expression for peptide group proton chemical shift computation as a function of protein backbone conformation. Both terms are expressed by McConnell's point‐dipole shielding expressions, one referred to an axis perpendicular to the peptide plane and origin in the coordinate centre of the OCN atoms and the other referred to an axis along the carbonyl bond and origin close to the oxygen atom. Values for the two constants have been determined by least‐squares fitting of the C‐α, H and amide NH chemical shifts of the protein ubiquitin. As a cross‐check on the validity of the expression, the C‐α, H and NH shifts of ribonuclease and BPTI (basic pancreatic trypsin inhibitor) have been computed. The general agreement between the observed and computed shifts and the correlation coefficients found (0.72 on average) indicate that the expression accounts for the main physical effects of the protein peptide group on the proton chemical shifts. It is shown that, together with ring current shifts, the expression explains the main characteristics of the C‐α, H and amide NH chemical shifts in proteins.
Proton NMR study on rhamnolipids produced by Pseudomonas aeruginosa
Authors: Choe Bo‐Young , Krishna N. Rama , Pritchard David G. 
Published: May 2005

AbstractThe extracellular rhamnolipids α‐L‐rhamnopyranosyl ‐ 3‐ hydroxydecanoyl ‐3‐ hydroxydecanoate and α‐L‐ rhamnopyranosyl‐(1 → 2)‐αL‐ rhamnopyranosyl ‐ 3 ‐ hydroxydecanoyl ‐ 3 ‐ hydroxydecanoate were isolated from the culture broth of Pseudomonas aeruginosa grown under growth‐limiting conditions. Proton NMR spectra of these rhamnolipids were characterized.
Substituent‐induced chemical shift 13C NMR study of substituted 2‐phenylthiazolidines
Authors: Umarani R. 
Published: May 2005

AbstractThe analysis of the 13C NMR chemical shifts of 16 substituted 2‐phenylthiazolidines shows that the 1,3‐thiazolid‐2‐yl group exerts a deshielding effect at the ipso carbon (C‐1′) and shielding effects at the ortho and para positions of the benzene ring (C‐2′ and C‐4′), and that the transmission of the resonance effect from the substituents in the phenyl ring to the benzylic carbon (C‐2) in the thiazolidine heterocycle is diminished by the polarizable nitrogen and sulphur atoms.
Signs of 19F1H and 19F13C spin–spin coupling constants mainly transmitted through space
Authors: Rae I. D. , Weigold J. A. , Contreras R. H. , Yamamoto G. 
Published: May 2005

AbstractThe details of two‐dimensional 13C1H correlated spectra have provided information about the relative signs of J(C, F) and J(F, H) for several molecules in which C, F and H are mutually coupled. Unlike signs are found for J(C, F) and J(F, H) when the coupling pathways lie approximately in the plane, but serious deviations from planarity can bring about changes in sign of J(F, H) and J(C, F).
Autoaggregation phenomena in quinine solutions
Authors: Uccello‐Barretta Gloria , Bari Lorenzo Di , Salvadori Piero 
Published: May 2005

AbstractThe coexistence of monomer and dimers of quinine was established in quinine solutions by investigating the temperature and concentration dependence of the NMR spectral parameters. Their conformations were determined by a combination of accurate 2D NOESY and proton‐selective relaxation rate measurements.
Proton NMR investigation of some substituted 1,3‐thiazolidin‐4‐ones
Authors: Woolston Christopher Richard Joseph , Lee John Barry , Swinbourne Frederick John , Thomas William Anthony 
Published: May 2005

AbstractThe 1H NMR spectra of a series of 2,3‐diaryl‐1,3‐thiazolidin‐4‐ones were measured and the ABX systems due to the heterocyclic ring protons were formally analysed. The chemical shifts and coupling constants were examined in relation to the structures concerned. The effects of S‐oxidation of these compounds on the spectral parameters were investigated. The 1H chemical shifts of 3‐benzyl‐2‐phenyl‐1,3‐thiazolidin‐4‐one and 3‐butyl‐2‐phenyl‐1,3‐thiazolidin‐4‐one suggested the presence of a preferred conformation about the NCH2 bond.
Use of 3J(13C,1H) in the stereochemical assignment of lactonic norbornene derivatives
Authors: Parella Teodor , Casas Ramon , Ortuño Rosa M. 
Published: May 2005

AbstractThe determination of 3J(13C,1H) for two sets of diastereoisomeric norbornene‐derived lactones was achieved by using fully coupled 13C spectra or the SINEPT‐2D method. The stereochemical elucidation of these compounds was performed by using long‐range carbo‐proton couplings, combined in some cases with NOE techniques and heteronuclear 2D correlations. Torsional angle dependence and the influence of γ‐substitution in the 13C‐α—C‐β—C‐gM‐1H fragment on 3J(13C,1H) values were verified in these cases.
Ab initio13C nuclear shielding calculations for some hydrocarbons using the GIAO procedure
Authors: Kurosu Hiromichi , Webb Graham A. , Ando Isao 
Published: May 2005

AbstractThe results of some ab initio GIAOCHF 13C shielding calculations for some hydrocarbons, performed with several basis sets, are reported and compared with experimental data. Optimized and experimental molecular geometries have been used in these calculations. The effect of the choice of basis set and geometric parameters on the calculated shieldings are discussed.
Thermo‐ and photochromic dyes: Spiro(indolinebenzopyrans). 2—detailed assignment of the 1H NMR spectra and structural aspects of the closed form of 1,3,3‐trimethylspiro(indoline‐2,2′‐benzopyrans)
Authors: Keum Sam‐Rok , Lee Ki‐Bong , Kazmaier Peter M. , Manderville Richard A. , Buncel Erwin 
Published: May 2005

AbstractThe proton NMR assignments for a series of 12 thermo‐ and photochromic 1,3,3‐trimethylspiro(indoline‐2,2′‐benzopyrans) dyes is reported. All of the protons in the dye molecule were assigned through a combination of homonuclear decoupling experiments and correlation spectroscopy. The relative stereochemistry of the indolino gem‐dimethyl groups was assigned so that, for the S‐epimer, the pro‐R methyl was found to resonate at 1.24 ppm while the pro‐S methyl appeared at 1.37 ppm for compound 1.
Carbon‐13 nuclear magnetic resonance relaxation study of chymotrypsin inhibitor 2 (CI‐2)
Authors: Leatherbarrow Robin J. , Matthews Stephen J. 
Published: May 2005

AbstractCarbon‐13 T1 and NOE measurements were used to study the internal motions of the single phenylalanine residue in CI‐2 and in a mutant in which an arginine residue adjacent to the Phe had been replaced with an alanine residue. Each protein was specifically enriched with [13C6‐ring]phenylalanine. The arginine to alanine modification resulted in a reduction of the order parameter, S2, from 0.39 to 0.32 for the internal motions of the aromatic ring. This is consistent with the aromatic side‐chain of Phe 69 being less restricted, as a consequence of the removal of the neighbouring bulky side chain. Wild‐type CI‐2 was also successfully enriched with [2‐13C]glycine. An average order parameter of 0.60 was obtained for the α‐carbon positions of the three glycine residues. When bound to the serine protease chymotrypsin, S2 remains unchanged within experimental error. However, the overall tumbling, derived from NMR, slows by a factor of 5, consistent with the increase in molecular weight.
Simple estimation of the conformational homogeneity of 2,5‐disubstituted‐1,3‐dithianes by means of their 1H NMR spectra
Authors: Graczyk Piotr P. , Mikolajczyk Marian 
Published: May 2005

AbstractA simple method for the correction of free energy differences, ΔG°exp, obtained via the equilibriation of 2‐substituted 5‐tert‐butyl‐1,3‐dithianes, is proposed on the basis of the 1H NMR data for diastereoisomers. It suggests, in contrast to the opinion of other workers, that these derivatives can be used in order to establish the preference of a substituent connected to the anomeric carbon atom. A simple procedure for the comparison of the amount of twist‐boat forms is also demonstrated.
NMR spectra of abieslactone and its 3‐ keto derivative
Authors: Tkachev Alexey V. 
Published: May 2005

AbstractThe carbon resonances of two naturally occurring triterpene compounds of the 9βH‐lanostane series (abieslactone and the corresponding 3‐keto derivative) have been unambiguously assigned. 2D heteronuclear chemical shift‐correlation NMR studies suggest that at least two conformations of the 3‐keto derivative are likely to be present in solution.
β‐NAD+ and its stack interaction
Authors: Zieger G. , Konrat R. , Sterk H. 
Published: May 2005

AbstractCross‐relaxation interactions between the nicotinamide moiety and the adenine moiety of NAD in D2O solution were unambiguously revealed by steady‐state NOE experiments, transient NOE experiments and synchronous nutation experiments. The experimental results, which allow a concise description in terms of auto‐relaxation and cross‐relaxation, are interpreted as the result of a stacking interaction. Studies of 13C relaxation and investigations on ternary mixtures with 6‐methylpurine give evidence for an inter‐ rather than intra‐molecular stack interaction, at least in the NMR concentration range.
Conformational analysis. Part 19—conformational analysis of 6‐deoxy‐6‐fluoro‐D‐glucose (6DFG) in solution
Authors: Abraham Raymond J. , Chambers Eric J. , Thomas W. Anthony 
Published: May 2005

AbstractThe conformation of D‐glucopyranose and 6‐deoxy‐6‐fluoro‐D‐glucose (6DFG) in solution, as determined by 1H and 19F NMR, is reviewed. The 1H NMR spectra of α‐ and β‐methyl D‐glucopyranosides and 6DFG in methanol, acetone, DMSO, and aqueous solution were acquired and fully analysed. A 19F NMR spectrum of the methanol 6DFG solution, together with a 1H COSY spectrum of α‐6DFG in methanol, were recorded. Accurate analyses of the ABC and ABCX spectra produced by the CHCH2OH and CHCH2F moieities, respectively, were performed, and from the vicinal J(H‐5,H‐6) coupling constants the populations of the three possible staggered rotamers about the C‐5C‐6 bond were calculated. The rotamer in which F is antiperiplanar to the ring O is particularly disfavoured, whereas the rotamer with F antiperiplanar to H‐5 is most favoured. This general trend was seen for both pyranose anomers in all four solvents.
A 13C T1 study of conformational and molecular mobility of mono‐ and difucosyllactoses
Authors: Ejchart Andrzej , Dabrowski Janusz 
Published: May 2005

AbstractOverall and internal motions of lactose Galβ(1 → 4)Glcα and its three fucosylated derivatives Fucα(1 → 2)Galβ(1 → 4)Glcα, Galβ(1 → 4) [Fucα(1 → 3)] Glcα and Fucα(1 → 2)Galβ(1 → 4) [Fucα(1 → 3)] Glcα were investigated in Me2SO‐d6 using the spin–lattice relaxation times of 13C nuclei, T1(13C), measured at 8.5 and 11.7T. The relaxation data of the ring carbons in lactose and the lactosyl core of its derivatives were well described by the axially symmetric motion of the molecule. However, the interpretation of the T1(13C) of ring carbons in fucose residues required the assumption of a conformational mobility about the appropriate glycosidic bonds. For this purpose, a bistable, jump model of internal motion with a varying angle between the rotation axis and the symmetry axis of the overall tumbling was developed. The internal rotation of hydroxymethyl groups in Glc and Gal residues was also analysed quantitatively; the rotation in Glc was found to be slower than that in Gal. The internal rotation of methyl groups in fucoses undergoing a complex motion was interpreted semi‐quantitatively.
Structural analysis of oligosaccharide chains of glycolipids by two‐dimensional NMR
Authors: Inagaki Fuyuhiko 
Published: May 2005

AbstractCoherence transfer methods, such as multiple‐relayed COSY and homonuclear Hartman–Hahn spectroscopy, were applied to extract subspectra of constituent monosaccharides, which allowed complete assignments of the proton resonances of oligosaccharide chains of glycolipids. The chemical structure of oligosaccharide chains of glycolipids could be determined by the combination of coherence transfer methods and NOESY experiments.
Characterization of dinitrobenzimidazoles using NOE difference and heterocorrelated NMR
Authors: Freyer Alan J. , Nissan Robin A. , Wilson William S. 
Published: May 2005

AbstractSeveral 1‐(2′,4′,6′‐trinitrophenyl)dinitrobenzimidazoles (1‐picryldinitrobenzimidazoles) were synthesized as part of an ongoing study of heterocyclic nitro compounds as energetic materials and their structure–property relationships. The 1‐picryl‐4,6‐dinitrobenzimidazoles and their 1‐methyl analogs were examined by several NMR techniques in order to confirm their structures, and assignment strategies are discussed. Nuclear Overhauser enhancement (NOE) difference spectroscopy and 1H/13C correlation experiments were used to make definitive assignments of the 1H and 13C NMR spectra. It was found that both solvent and temperature had significant effects on the chemical shifts of the benzimidazole protons. This was especially true for the 1‐picryl derivatives.
NMR study of conformation and configuration in C‐20‐substituted 5β,14β‐pregnanes, 5β‐pregn‐14‐enes and 21‐nor‐5β,14β‐pregnanes
Authors: Marat Kirk , Templeton J. F. , Ling Yangzhi 
Published: May 2005

AbstractCoupling constants and nuclear Overhauser effect measurements were used to establish the C‐20 configuration and the conformation about the C‐17C‐20 bond in a series of sixteen C‐20‐substituted 5β,14β‐pregn‐14‐enes. In the 14β‐pregnane series the conformation of the C‐17 side‐chain is variable, whereas in the pregnenes the side‐chain adopts a conformation in which H‐17 is anti to H‐20. The C‐17 side‐chain conformation of two 21‐nor‐5β,14β‐pregnanes was also determined. In the 21‐nor compounds a C‐20 hydroxyl adopts a conformation anti to H‐17, while a C‐20 nitro group is anti to C‐13.
Low‐temperature NMR of ε‐caprolactam
Authors: Borgen Gerd , Rise Frode 
Published: May 2005

AbstractThe conformation of ε‐caprolactam (1‐azacycloheptan‐2‐one) was studied by low‐temperature 2 D 1H and 13C NMR. Only one conformer was found in solution from the 13C NMR spectra recorded down to −155°C. This conformer was shown, by infrared spectroscopy, to be the same as that found in the crystals of ε‐caprolactam. A conformational process with a free energy of activation of 43 kJ mol−1, coalescence temperature −65°C, was interpreted as geminal 1H exchange. The assignments of the 13C and 1H shifts were made by 2 D NMR. Splitting of all averaged signals for geminal protons into axial and equatorial signals was demonstrated at −100°C.
1H NMR lanthanide‐induced shift investigation of highly flexible molecules—a new approach
Authors: Lehmann J. , Kleinpeter E. 
Published: May 2005

AbstractA new method for lanthanide‐induced shift (LIS) calculations of highly flexible structures was developed using molecular geometries obtained from the random variation of dihedral angles (up to ten) which are rotating freely and independently of each other. The result of the new method (program JLLISMUL) is a data set containing the specified random dihedral angles and the corresponding agreement factor R (as a criterion for the fitting of the calculated and experimental LIS values). For comparison, the same random procedure was also used for parallel force field calculations using the molecular mechanics program PIMM. The results obtained by the new method are in very good agreement with known or reported preferred conformations of five highly flexible molecules which were used as examples for examining the new strategies of obtaining the preferred conformers. The minima of both the ‘LIS R factor hyper surface’ and the ‘energy hyper surface’ are rapidly accessible.
Three‐bond 13C1H coupling constants for chrysanthemic acid and phenothrin metabolites: Detection by two‐dimensional long‐range 13C1H J‐resolution spectroscopy
Authors: Ando Tetsu , Koseki Nozomu , Toia Robert F. , Casida John E. 
Published: May 2005

AbstractTwo‐dimensional long‐range 13C1H J‐resolution spectroscopy (LRCJR) was used to measure three‐bond 13C1H coupling constants [3J(C,H)] for trans‐ and cis‐chrysanthemic acid, methyl trans‐pyrethrate and some microsomal metabolites of the trans‐chrysanthemate biophenothrin. The carbon of the methyl cis‐disposed to an attached proton shows a larger 3J(C,H) value than does the trans‐carbon for the dimethyl‐substituted cyclopropane and epoxide rings. The reverse situation applies for the analogous dimethyl vinyl grouping. The 3J(C,H) values are not altered on conversion of one of the olefinic geminal methyl groups to a hydroxymethyl or methoxycarbonyl functionality, but increase on transformation to an aldehyde. These 3J(C,H) values are in agreement previous results from long‐range CH COSY experiments, and provide a useful method for determining the stereochemistry of chrysanthemic acid derivatives.