bluuebunny/crossref_metadata_2025_split huggingface dataset:
NMR study of thermodynamic and structural properties of molecular complexes formed by metalloporphyrins and aromatic substrates
Authors: Kitaigorodski Alexander N. , Edlund Ulf 
Published: May 2005

Abstract1H NMR shifts and 13C spin–lattice relaxation rates were measured for various aromatic π‐acceptors (S) in solutions containing paramagnetic cobalt(II) and iron(III) porphyrins (P). The stability constants of P · S molecular complexes and limiting values of substrate chemical shifts in the complexes were determined from the concentration dependence of chemical shifts. The abilities of different substituents to promote complexation of aromatics with metalloporphyrins are discussed. The preferred substrate orientation in molecular complexes were derived using relative values of chemical shifts and relaxation rates induced by metalloporphyrins. Both monocyclic (benzene and pyridine derivatives) and bicyclic (naphthalene derivative) substrates tend to form ‘axially symmetric’ adducts with parallel π‐planes and the centre of the aromatic system situated in the vicinity of the porphyrin z‐axis.
High‐field magnetic resonance studies oftert‐butanol in liquid and solid phases
Authors: Aksnes D. W. , Kimtys L. L. 
Published: May 2005

Abstract1H and13C line widths and1H,2H,13C and17O spin–lattice relaxation (times (T1) oftert‐butanol (TB) were studied at a field strength of 9.4 T in the liquid and solid states (160–299 K). The NMR line width data reveal the existence of at least two crystalline forms between 160 K and the metling point (299 K). The ordered phase (solid II) is observed throughout the whole temperature region on warming, indicating that the disordered phase (solid I), observed betweenca. 210 K and the melting point, is monotropic. The line narrowing of the1H resonances for solid I, observed around 225 and 280 K, is ascribed to the onset of overall molecular tumbling and translational diffusion, respectively. The1H line width of solid II is constant between 160 and 284 K. Activation parameters for the overall molecular tumbling and/or internal methyl andtert‐butyl reorientations were obtained from theT1data. The long correlation time (75–92 ps at the melting point) and high activation energy (27–37 kJ mol−1) suggest that the overall tumbling in the disordered and liquid phases involves hydrogen‐bonded aggregates. The dynamics of the methyl group, in contrast to thetert‐butyl group, appear to be only slightly affected by change of state and phase (activation energy 11–12 kJ mol−1).
Dynamic nuclear magnetic resonance of zinc and cadmium complexes of 1,2‐propanediaminetetraacetic acid
Authors: Li Fei , Song Ruifang 
Published: May 2005

AbstractThe 1H NMR temperature dependence of the zinc(II) and cadmium(II) complexes of 1,2‐propanediaminetetraacetic acid (1,2‐PDTA) was investigated. The four AB patterns in the 1H NMR spectra of the acetates of the complexes were assigned with the aid of computer‐simulated spectra at various temperatures. The AB interchange phenomena due to nitrogen inversion were observed in the temperature range 90–148°C. The rate constants and the activation parameters were calculated. It is shown that the nitrogen‐inversion rates of the two asymmetric nitrogen atoms are different, both for Zn(1,2‐PDTA)2− and for Cd(1,2‐PDTA)2−, and that those of the nitrogen atom on the same side as the methyl group are slower. A water displacement mechanism in the process of nitrogen inversion is proposed on the basis of the kinetic data.
13C‐selective, 1H‐detected 2D {1H, 13C} correlation spectra of oligosaccharides
Authors: Poppe Leszek , van Halbeek Herman 
Published: May 2005

AbstractTwo‐dimensional 1H‐detected {1H, 13C} shift correlation spectra of oligosaccharides usually suffer from low resolution in the 13C frequency domain. This drawback can be overcome through a simple modification of the HSQC experiment, namely by implementing a selective 13C 180° pulse. It is illustrated for the mixture of the α‐and β‐anomers of the trisaccharide sialyl‐α(2→6)‐lactose that 13C‐selective HSQC allows both one‐bond and multiple‐bond {1H, 13C} correlation spectra to be obtained with high resolution in the 13C domain.
Coordination‐site exchange and solid‐state 13C NMR studies of bis(oxalato)dioxovanadate(V) ion
Authors: Lee Man‐Ho , Schaumburg Kjeld 
Published: May 2005

AbstractActivation parameters were determined for the exchange between the two types of carboxylate groups which are cis and trans to the VO bonds in the bis(oxalato)dioxovanadate(V) ion, [VO2(C2O4)2]3−. Kinetic data were obtained from the 13C NMR spectra at eleven temperatures between 268 and 306 K by the total line‐shape method. The coordination‐site exchange mechanism, involving chelate ring opening and closing in the ion, is proposed. The solid‐state 13C NMR spectra of the oxalato complexes, (NH4)3[VO2(C2O4)2]·2H2O and K3[VO2(C2O4)2]·3H2O, are also discussed in relation to the structures.
1H NMR determination of the ionization constant of a carboxylic acid group of a haem protein in mixed aqueous‐organic solvents using the super WEFT sequence
Authors: Rigby Stephen E. J. , Burch Anita M. , Moore Geoffrey R. 
Published: May 2005

Abstract1H NMR spectra of ferricytochrome c‐551 were obtained in a variety of miscible aqueous buffer‐organic solvent mixtures. The pKa of a haem carboxyl group within this protein was measured in several such solvent systems. This work was facilitated by the use of the Super water eliminated Fourier transform (SuperWEFT) technique and this was extended to the suppression of multiple solvent resonances. Nuclear Overhauser enhancement difference experiments were combined with SuperWEFT, enabling structural data to be obtained in complex solvent mixtures. The data arising from this study are relevant to the evaluation and simulation of electrostatic effects in proteins.
Compounds with bridgehead nitrogen 66—NMR spectra and stereochemistry of derivatives of 1,2,3,4,6,7,12,12b‐ octahydropyrimido [1′, 6′:1,2] pyrido [3,4‐b]indol‐2‐one and of 1,3,4,6,7,11b‐hexahydropyrimido [6,1‐a] isoquinolin‐2‐one
Authors: Crabb Trevor A. , Patel Asmita V. 
Published: May 2005

AbstractComparison of the NMR spectra of 3‐methyl‐1,2,3,4,6,7,12,12b‐octahydropyrimido [1′,6′ : 1,2]pyrido[3,4‐b] indol‐2‐one and of cis‐(H‐6, H‐12b)‐3,6‐dimethyl‐ 1,2,3,4,6,7,12,12b‐octahydropyrimido [1′,6′:1,2]pyrido[3,4‐b] indol‐2‐one shows the former to exist in solution at 25°C as an equilibrium mixture containing ca. 20% N‐inside‐cis‐ and ca. 80% trans‐fused conformers, and the latter to adopt exclusively the trans‐fused conformer. The related 3‐methyl‐ 1,3,4,6,7,11b‐ hexahydropyrimido [6,1‐a] isoquinoline‐2‐one adopts a ca. 53% trans‐fused 47% cis‐fused equilibrium.
Isolation and structural elucidation of griffithine by 1D and 2D NMR techniques
Authors: Atta‐ur‐Rahman  , Pervin Azra , Feroz M. , Perveen Shahnaz , Choudhary M. I. , Hasan Naim 
Published: May 2005

AbstractThe isolation and structure elucidation of a novel dimeric alkaloid, griffithine, from the leafy shoots of Sophora griffithii Stock (Papilionaceae) is described. The alkaloid possesses a 12‐membered ring system formed by the linking of C‐10 and C‐10′ of the alkaloid with the N‐1 and N‐1′ atoms, respectively. The structure was established on the basis of extensive 1D and 2D NMR studies. The relative stereochemistry at the chiral centres was determined by NOE difference experiments. 10‐Oxosparteine was isolated for the first time from the leafy shoots of Sophora griffithii.
Magnetic moment determination of micro‐sized solid samples by proton magnetic resonance spectroscopy. A new split peak which can be used to determine the magnetic susceptibility of solid micro samples
Authors: Furuhashi Akiko , Ono Isao , Yamasaki Akira 
Published: May 2005

AbstractThe magnetic moment of a micro‐sized solid sample can be semi‐quantitatively determined by proton magnetic resonance spectral measurement with the sample in a capillary cell coaxially placed within an NMR tube containing a suitable diamagnetic solvent with a standard such as TMS. Small signals appearing on the low‐frequency side of the main peaks can be assigned to the protons in the layer of the solution surrounding the outer surface of the coaxially placed capillary. The molar chemical shift difference of this signal splitting is proportional to the square of the magnetic moment (μ) or n(n + 2), where n is equal to the number of unpaired electrons in the sample.
Liquid‐ and solid‐state (CP‐MAS) multinuclear magnetic resonance study of some 2,5‐dihydro‐1,2,5‐oxoniastannaboratoles—carboncarbon coupling constants, 1J(13C13C), in organometallic‐substituted alkenes
Authors: Wrackmeyer Bernd , Wagner Klaus , Sebald Angelika , Merwin Lawrence H. , Boese Roland 
Published: May 2005

AbstractDerivatives of 2,5‐dihydro‐1,2,5‐oxoniastannaboratoles were studied by multinuclear magnetic resonance both in the liquid (11B, 13C, 29Si, 119Sn NMR) and solid state (13C, 29Si, 119Sn CP/MAS NMR). Together with the results of the x‐ray analysis of the 4,5,5‐triethyl‐2,5‐dihydro‐1,2,2‐trimethyl‐3‐phenyl‐1,2,5‐oxoniastannaboratole‐tetrahydrofuran adduct (1‐THF) (space group P21/c) the NMR data [chemical shifts and coupling constants J(119SnE) (E = 13C, 29Si, 119Sn)] allowed the assessment of structural features in solution and in the solid state (e.g. the weakened coordinative Sn‐O interactions in 1‐THF in solution). The 1J(13C13C) values in 4,5,5‐triethyl‐2,5‐dihydro‐1,2,2‐trimethyl‐3‐trimethylsilyl‐ and ‐3‐trimethylstannyl‐1,2,5‐oxoniastannaboratole and in some non‐cyclic alkenes bearing organometallic substituents were measured using INEPT experiments based on 3J(13C1H) long‐range coupling constants. In the presence of one boryl‐ and two stannyl groups the magnitude of 1J(13C13C) values is reduced to ca. 30 Hz. A positive sign for 2J(119Sn117Sn) in 2‐diethylboryl‐1,1‐bis(trimethylstannyl)but‐1‐ene was determined by 2D 13C1H and 2D 119Sn‐H heteronuclear shift correlations. Scalar 13C11B and 119Sn‐11B coupling has been observed for the first time in 119Sn CP‐MAS NMR spectra.
119Sn NMR study of organotin compounds having intramolecular Sn—N coordination
Authors: Jastrzebski Johann T. B. H. , Grove David M. , Boersma J. , van Koten Gerard , Ernsting Jan‐Meine 
Published: May 2005

Abstract119Sn NMR data are reported for organotin compounds containing potentially C,N‐chelating ligands capable of forming five‐ or six‐membered chelate rings. The 119Sn chemical shifts of divalent organotin compounds containing such a ligand are found at relatively high frequency. Intramolecular coordination in tetraorganotin compounds has little influence on their 119Sn chemical shifts. However, additional coordination in tri‐ and di‐organotin halides causes a large shift to lower frequency of about 100 ppm. Finally, for organotin compounds which exist as a diastereoisomeric mixture in solution, two well resolved 119Sn resonances are observed.
Detection of connectivity between equivalent carbons in a C2 molecule using isotopomeric asymmetry: Identification of hopeaphenol in Carex pumila
Authors: Kawabata Jun , Fukushi Eri , Hara Masato , Mizutani Junya 
Published: May 2005

AbstractIn the structure determination of the C2 symmetrical tetrastilbene hopeaphenol, isolated from Carex pumila, the elucidation of the C‐‐C connectivity between equivalent carbons was needed. From an isotopomeric point of view, three isotopomers, 12C12C, 12C13C and 13C13C, are present with respect to the equivalent carbons connecting each other. Among them, the the 12C12C species is undetectable and the 13C13C species is excluded owing to its low natural abundance. Therefore, only the 12C13C isotopomer is detected in 13C NMR and this species is not symmetrical. In the H12C13H system, the separate detection of 1J(CH) and 2J(CH) was achieved by the INEPT‐LSPD, COLOC and HMBC methods to demonstrate the connectivity between the equivalent carbons from the viewpoint of isotopomeric asymmetry.
Heterocyclic compounds from sugars. XIV—Structure determination and conformational analysis of the four diastereoisomeric methyl 3‐Acetyl‐5,5‐dimethyl‐2‐(D‐galacto‐pentaacetoxypentyl)‐1,3‐thiazolidine‐4‐carboxylate 1‐Oxides
Authors: Kövér Katalin E. , Györgydeàk Zoltàn 
Published: May 2005

Abstract1H and 13C NMR experiments were performed to analyse the conformation and stereochemistry of diastereomeric sulphoxides of 1,3‐thiazolidine derivatives. The conformation of the thiazolidine ring was verified by an NOE study. ASIS and 13C chemical shift data supported the sulphoxide configuration.
Quantification of partial structures in aquatic humic substances by volume integration of two‐dimensional 13C nuclear magnetic resonance spectra. Comparison of one‐ and two‐dimensional techniques
Authors: Lambert J. , Burba P. , Buddrus J. 
Published: May 2005

AbstractPartial structures of a reference groundwater humic substance were quantified by J‐resolved two‐dimensional 13C NMR spectroscopy applied in its phase‐sensitive variant. The results agree with those obtained by the one‐dimensional techniques DEPT (distortionless enhancement by polarization transfer) and SEMUT‐90 (subspectral editing using a multiple quantum trap), thus demonstrating the accuracy of both methods. However, the two‐dimensional technique is recommended, because quantification is based on only one spectrum. Quantification provides the ratio of different substructures (carbons belonging to ketones, carboxylic acids, different aromatics, carbohydrates, paraffinic C, CH, CH2 and CH3 groups) and, in combination with elemental analysis, the partition of hydrogen between C and O (83% bonded to C and 17% to O). Also, insight is obtained into the biogenesis of the humic acids. Aromatic moieties probably originate mainly from lignin rather than from other aromatic compounds. CHO moieties mainly belong to carbons in ethers and alcohols and only to a small extent to carbons in carbohydrates, as shown by comparing NMR results with gas chromatographic analysis of the carbohydrate part performed by other workers. The ratio of paraffinic CH:CH2:CH3 is about 1:1:1; the high proportion of paraffinic methyl groups cannot yet be explained.
13C magic angle spinning NMR investigations of thiourea inclusion compounds
Authors: Müller Klaus 
Published: May 2005

AbstractThiourea inclusion compounds of three monosubstituted cyclohexanes were studied by 13C magic angle spinning NMR spectroscopy. Variable‐temperature experiments were performed to evaluate the conformational and motional features of the various guest molecules. From a quantitative line‐shape analysis it is found that the halocyclohexanes with chloro and bromo substituents exist predominantly in the axial conformation whereas methylcyclohexane, as in solution, prefers the equatorial position. Generally, it could be shown that within the temperature range investigated the cyclohexane guest molecules undergo ring inversion processes with kinetic parameters almost unaffected by the host lattice.
Microcomputer prediction and assessment of substituted benzene 13C NMR chemical shifts
Authors: Hearmon Richard Angus , Liu Hok‐Ming , Laverick Simon , Tayler Paul 
Published: May 2005

AbstractA 13C NMR chemical shift prediction and spectral assessment program was written in Turbo Prolog. Based on the large data compendium of Ewing it allows the rapid assessment of the spectral–structural relationship for substituted benzene rings.
17O NMR spectra of the 1,6‐anhydro‐β‐D‐hexopyranoses and related‐compounds. Determination of configurational effects on the chemical shifts
Authors: Lauterwein Jürgen , Schulte Jürgen , Schumacher Martin , Černý Miloslav 
Published: May 2005

AbstractWell resolved natural‐abundance 17O NMR spectra of the eight 1,6‐anhydro‐β‐D‐hexopyranoses and three deoxy model compounds were recorded in aqueous solution at 90°C. The assignment of the resonances was obtained by chemical shift comparison, O‐acetylation, lanthanide shift reagents (Eu3+) and, more generally applicable, by a computational search for the minimum of the sum of the squared deviations between the observed and calculated shifts. The 17O chemical shifts were evaluated depending on the orientation of the hydroxyl groups, expressed in terms of additive γ‐ and δ‐interactions between the hydroxyl and ring ether groups. The γ‐gauche effects were dominant in a range between −7 and −20 ppm. No appreciable effects have been detected of anti‐periplanar hydroxyl groups on the 17O chemical shifts. The syn‐diaxial δ‐interaction was deshielding between hydroxyl groups, but shielding between a hydroxyl group and the bridge‐ether oxygen. A new type of interaction, a δ‐effect between equatorial hydroxyl oxygens in a planar zig‐zag arrangement, was detected. Arguments are presented suggesting that γ‐gauche effects between oxygens are not related to steric compression.
Inverse detection of broad resonances: 15N NMR spectra of boron–nitrogen compounds
Authors: Wrackmeyer Bernd , Kupče Ēriks , Köster Roland , Seidel Günter 
Published: May 2005

AbstractTwo types of proton‐detected 1H15N correlation experiments were compared with respect to the observation of 15N NMR resonances broadened by scalar relaxation of the second kind. Both single‐ and multiple‐quantum experiments gave equal 15N line widths in F1, and in all cases the inverse experiments provided a dramatic increase in sensitivity and spectrometer time‐saving compared with the direct observation of 15N resonances. Various aminoboranes [B(NHMe)3; B(NHNMe2)3; 2,3‐dihydro‐2‐methyl‐2‐boraperimidine; organo‐substituted 2,5‐dihydro‐1,2,5‐azasilaboroles; organo‐substituted 7,8‐benzo‐1‐oxa‐6‐aza‐2‐sila‐5‐bora‐3‐cyclooctene], organo‐substituted 2,5‐dihydro‐1,2,5‐azasilaboratolates, an amine–borane adduct (organo‐substituted 7,8‐benzo‐6‐oxa‐1‐aza‐2‐sila‐5‐borabicyclo[3.3.0]oct‐3‐ene), and (ligand)transition metal π‐complexes of organo‐substituted 2,5‐dihydro‐1,2,5‐azasilaboroles were studied by two‐dimensional inverse 1H{15N} NMR experiments. The straightforward application to the analysis of several mixtures suggests that this technique is promising for the investigation of oligomerization and polymerization of boron—nitrogen compounds.
Variable‐temperature high‐resolution carbon‐13 studies of molecular motion in solid bisphenol‐F diglycidyl ether
Authors: Casarini Daniele , Harris Robin K. , Kenwright Alan M. 
Published: May 2005

AbstractVariable‐temperature cross‐polarization magic‐angle spinning solid‐state 13C NMR spectra of bisphenol‐F diglycidyl ether were obtained in the temperature range 25–67°C. Dynamic phenomena are observed, and the experimental data are in accord with an inhomogeneous distribution of correlation times, perhaps related to a second‐order phase change. Single‐pulse excitation experiments under comparable conditions confirmed the presence of motional inhomogeneity, characterized by a fraction of mobile molecules within the sample. Differential scanning calorimetric measurements revealed a phase transition at ca. 50 °C.
Atropisomerism of 1‐alkylcyclohepta [b]pyrrol‐2(1H)‐ones. Isolation of the rotational isomers of 1‐(2,4‐dimethyl‐3‐pentyl)cyclohepta [b]pyrrol‐2(1H)‐one
Authors: Ikeda Yukari , Kato Nobuo , Mori Akira , Takeshita Hitoshi 
Published: May 2005

Abstract1‐Alkylcyclohepta[b]pyrrol‐2(1H)‐ones showed rotational isomerism around the CN bond. Two rotamers of the 1‐(2,4‐dimethyl‐3‐pentyl) derivative were isolable by high‐performance liquid chromatography at 0°C. The activation free energy, measured by the line‐shape analysis of the variable‐temperature NMR spectra, was 86.8 kJ mol−1 at 25°C. In a bromo derivative, a positive buttressing effect was observed.
New Pt …︁ HN bonds characterized by 15N‐filtered and 2D NOESY 1H NMR spectroscopy
Authors: Pregosin Paul S. , Rüegger Heinz , Wombacher Franz , Van Koten Gerard , Grove David M. , Wehman‐Ooyevaar Ingrid C. M. 
Published: May 2005

AbstractNew Pt …︁ HN bonding modes in two cycloplatinated complexes, [Pt(C6H4CH2NMe2‐2‐C,N)(C6H4CH2NMe2H‐2‐C,H)Br] (1) and [Pt(1‐C10H6NMe2‐8‐C,N)(1‐C10H6NMe2H‐8‐C,H)Br] (2), were characterized by 15N‐filtered and 2D NOESY 1H measurements. Both 1 and 2 show markedly different interactions of an RNMe2H+ group with a platinum centre; the 1J(15N,1H) values of 69 and 59 Hz for 1 and 2, respectively, are considerably less than those of the related free and protonated organic amine systems. The corresponding 1J(195Pt,1H) values are 72 and 180 Hz, respectively. An approach both to understanding and recognizing these Pt …︁ HN interactions is presented.
Demonstration of bicontinuous structures in microemulsions using automatic‐mode NMR (self‐)diffusion measurements
Authors: Datema K. P. , Bolt‐Westerhoff J. A. , Jaspers A. , Daane J. G. R. , Rupert L. A. M. 
Published: May 2005

AbstractThe specifications of an NMR instrument dedicated to frequency‐resolved automated Fourier transform pulsed‐field‐gradient proton NMR measurements are reported. In order to be able also to monitor accurately the slow diffusion of surfactant aggregates and polymers in automatic mode, an option for matching of the gradient pulses was developed and implemented. In a first application, the spectrometer was used to carry out NMR (self‐) diffusion measurements of microemulsions of the surfactant sodium p‐(7‐tetradecyl)benzenesulphonate in benzene and water. They indicate drastic changes in the morphology of the aggregates in the microemulsion on increasing the surfactant concentration. The aggregate morphology changes from a bicontinuous structure to hard, noninteracting spheres by increasing the surfactant concentration in the microemulsion. The bicontinuous structure, i.e. a solution which is continuous in both water and oil, is the result of a strong interaction between the microemulsion droplets (‘percolation phenomenon’). It appears that the water molecules inside the microemulsion droplets with the hard sphere character exchange rapidly, on the (NMR) time scale of 10–100 ms, with water which is dissolved in the benzene. The droplets have an apparent diameter of 56 Å.
Conformational equilibria of ephedrine and pseudoephedrine and hydrogen bonding
Authors: Tsai Helen , Roberts John D. 
Published: May 2005

AbstractProton NMR spectra suggest that the conformation with trans vicinal hydrogens is favored for ephedrine as the free base in deuterium oxide, although in non‐polar solvents, such as deuteriotrichloromethane, the gauche vicinal hydrogen conformations are favored, as has been reported previously. The conjugate acid has primarily gauche hydrogens. In contrast, the trans‐hydrogen rotamers of pseudoephedrine dominate for both the non‐protonated and protonated forms in deuterium oxide. Hydrogen bonding is unlikely to be as important as usually assumed in determining the conformational preferences of these substances.
Organometallic paramagnetic camphor complexes. EPR investigation of their formation and structures
Authors: Rebmann Andreas , Mäurer Manfred , Scheffler Klaus , Stegmann Hartmut B. 
Published: May 2005

AbstractPhotochemical reactions of camphor and other diones with carbonylmanganese or aryltin compounds lead to paramagnetic complexes. The radicals derived from Mn2(CO)10 and Mn2(CO)8(PR3)2 are formulated as sixcoordinate complexes with different structures depending on the organic moiety, and they are characterized by their EPR and ENDOR data. Under the same conditions, the tin compounds form five‐coordinate complexes in which the organic ligand occupies one equatorial and one axial position in the bipyramidal structure. Consequently, two permutation isomers are expected if camphor quinone is used as a scavenger for the photolytically generated tin radicals, independent of the structure of the trapped species. These two species can be detected by ENDOR and triple resonance experiments if the interconversion is slow with respect to the EPR time scale. Diastereomeric complexes are obtained by the formation of a second chiral centre, at the tin atom, in the course of the reaction. However, these isomers cannot be distinguished by ENDOR spectroscopy under the conditions applied.