bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observation of 201Hg NMR spectra for solid K2Hg(CN)4
Authors: Wu Gang , Wasylishen Roderick E. 
Published: May 2005

AbstractThe first observation of 201Hg NMR signals in the solid state is reported for potassium tetracyanomercurate(II), K2Hg(CN)4. NMR measurements of 201Hg and 199Hg were carried out at 4.70, 7.05 and 9.40 T. The ratio between the observed NMR frequency for 201Hg and 119Hg yields an accurate value for the ratio of their magnetogyric ratios, |γ(201Hg)/γ(199Hg) | = 0.369 1389(9). This value agrees well with that obtained from optical pumping experiments on mercury vapor in the gas phase. The 201Hg NMR line shapes observed for solid K2Hg(CN)4 are Lorentzian owing to efficient relaxation via the quadrupolar mechanism. In contrast, the corresponding 199Hg NMR line shapes are Gaussian and much narrower.
199Hg NMR of aqueous solutions of inorganic mercury salts. Chemical shifts of HgCl2 − n with n = 0–4
Authors: Klose G. , Volke F. , Peinel G. , Knobloch G. 
Published: May 2005

Abstract119Hg NMR chemical shifts of the stable mercury species HgCl with n = 0–4 were determined by a least‐squares algorithm from 199Hg chemical shifts measured in 50 mM aqueous mercury solution as a function of the chlorine concentration at 25°C. The concentrations of the corresponding mercury species in the solutions necessary in this special procedures were calculated by using published equilibrium constants. The results relative to dimethyl‐mercury are −2256 ppm (Hg2+), −1897 ppm (HgCl+), −1560 ppm (HgCl2), −1436 ppm (HgCl3−) and −1152 ppm (HgCl) with maximum errors of ±5 ppm.
Multinuclear (1H, 13C, 15N, 19F, 31P) one‐ and two‐dimensional magnetic resonance study of tert‐butylamino‐tert‐butyl‐fluorophosphane, tert‐butylimino‐tert‐butylphosphane and of its dimer formed by [1 + 2] cycloaddition
Authors: Wrackmeyer Bernd , Köhler Christian 
Published: May 2005

AbstractMultinuclear magnetic resonance studies (1H, 13C, 15N, 31P) of three phosphorus–nitrogen compounds [tert‐butylamino‐tert‐butylfluorophosphane (1), tert‐butylimino‐tert‐butylphosphane (2) and its dimer (3)], in which numerous one‐ and two‐dimensional NMR experiments [heteronuclear shift correlations based on 1J(13C1H) or 1J(15N1H) and on long‐range coupling constants 2J(13C1H), 2J(31P1H), 3J(15N1H), 3J(31P1H) and 2D inverse 1H/15N correlations] were used, led to consistent assignment of the NMR spectra. By this means, incorrect data in the literature were corrected for 1 and 3 and new 15N NMR data are reported, including isotope shifts 1Δ15/14N(31P), obtained by 31P INEPT–Hahn–echo extended (HEED) experiments. In the case of the monomeric iminophosphane 2, the largest negative value 1Δ15/14N(31P) = −144 ppb was observed. Absolute signs of numerous coupling constants across one to five bonds were determined, involving the NMR active nuclei 1H, 13C, 15N, 19F and 31P.
Determination of three‐bond 1H,1H coupling constants between the olefinic protons in cycloalkenes by means of 1H CW off‐resonance 13C NMR spectroscopy
Authors: Radeglia Reiner , Poleschner Helmut , Haufe Günter 
Published: May 2005

AbstractThe 1H CW off‐resonance decoupled 13C NMR spectra of (E)‐ and (Z)‐cycloalkenes (C5C12) were measured. The higher order 13C NMR multiplets obtained for the unsaturated carbons allow the determination of the vicinal 1H,1H coupling constant between the vinylic protons and thus the assignment of the configuration of the CH2CHCHCH2 fragment.
Chemical shift references for 77Se NMR spectroscopy. Selenous acid
Authors: Milne John 
Published: May 2005

AbstractThe temperature and concentration dépendences of the chemical shift of aqueous selenous acid were studied in order to establish a precise relationship between the shift of this convenient reference and that of dimethyl selenide. The chemical shift of saturated H2SeO3 in H2O on the Me2Se shift scale at 20°C is 1300.0 ppm and its temperature coefficient is 0.094 ppm K−1. The relationships to the chemical shifts of Me2Se in CDCl3 and SeO2 in D2O are also discussed. The results permit the correlation of 77Se NMR shifts from several sources.
Complete assignment of the 1H and 13C NMR spectra of a pentacyclo [5.4.0.02,6.03,10.05,9]undecane derivative
Authors: Cadd D. H. , Feast W. J. , Kenwright A. M. , Say J. M. 
Published: May 2005

AbstractThe production of compounds derived from intramolecular photocycloaddition reactions upon Diels–Alder adducts has received considerable attention, but assignment of the NMR spectra of the photoaddition products has proved problematic, rendering structural determination difficult. This paper reports the complete assignments of the proton and carbon NMR spectra of 11, 11‐dimethoxypentacyclo [5.4.0.02,6.03,10.O5,9] undecan‐8‐one and the assignment of the spectra of pentacyclo [5.4.0.02,6.03,10.05,9] undecan‐8,11‐dione by analogy.
Polarisation transfer between heteronuclei: Application of 31P, 15N polarisation transfer techniques in 15N NMR spectroscopy of phosphorus—nitrogen compounds
Authors: Gudat Dietrich 
Published: May 2005

AbstractA systematic study of sensitivity enhancement in 15N NMR spectra of phosphorus—nitrogen compounds by 31P, 15N polarisation transfer was performed using tris‐(dimethylamino)phosphine (1) as a model compound. The application of several multipulse techniques (refocussed and non‐refocussed INEPT, DEPT) and decoupling schemes shows that maximum enhancement was reached with the non‐refocussed INEPT sequence, whereas the performance of longer pulse sequences was deteriorated by relaxation effects. The practical application of the technique was demonstrated for the determination of 15N data of low coordinate phosphorus—nitrogen compounds (iminophosphines and imidometaphosphate ions). In favourable cases, the sensitivity gain may be comparable to that of 1H, 15N INEPT measurements via long‐range couplings. In addition to the 1D experiments, the practicability of heteronuclear correlation spectroscopy was demonstrated by the measurement of 2D 31P,15N shift‐correlated spectra of 1.
NMR of anthocyanins: Assignments and effects of exchanging aromatic protons
Authors: Pedersen Atle T. , Andersen Øyvind M. , Aksnes Dagfinn W. , Nerdal Willy 
Published: May 2005

AbstractPelargonidin‐3‐O‐β‐glucopyranoside was isolated from an acidified methanolic extract of frozen strawberries, purified by several chromatographical techniques and subjected to homo‐ and heteronuclear proton and carbon NMR analysis, including selective decoupling, DQF‐COSY, NOESY, SEFT, HMQC and HMBC. Several strategies for the unambiguous assignment of the aglycone H‐6 and H‐8 resonances are discussed. Secondary isotope effects and different deuterium exchange rates of the protons were found.
Pyramidal nitrogen inversion hindered by a strong intramolecular hydrogén bond in 2‐diethylaminomethylphenols
Authors: Denisov G. S. , Gindin V. A. , Golubev N. S. , Koltsov A. I. , Smirnov S. N. , Rospenk Koll Sobczyk M. A. And L. 
Published: May 2005

AbstractIn the 1H NMR spectra of 2‐diethylaminomethyl‐3,4,6‐trichlorophenol (1) below 260 K, an additional splitting of the CH2 signal was found, which can be ascribed to the hindered nitrogen inversion. In the molecule of the O‐methylated derivative (2) this process is fast (on the NMR time‐scale) down to 150 K. The frequencies and the activation parameters of the nitrogen inversion in (1) were measured by DNMR, which indicated that the inversion requires a preliminary stage of breaking an intramolecular hydrogen bond. The activation enthalpy, δH, of the inversion stage was evaluated as 28.5 ± 6.7 kJ mol−1.
Spectroscopic properties of free phenolic 4‐arylflavan‐3‐ols as models for natural condensed tannins
Authors: Van Zyl Pieter W. , Steynberg Jan P. , Brandt Edward V. , Ferreira Daneel 
Published: May 2005

AbstractA unique range of free phenolic 4‐arylflavan‐3‐ols consisting of four sets (3′,4′,5,7‐tetrahydroxyflavan‐3‐ol or its 5‐deoxy analogue coupled to phloroglucinol or resorcinol), each composed of three diastereomers (2,3‐trans‐3,4‐trans, 2,3‐trans‐3,4‐cis and 2,3‐cis‐3,4‐trans) were synthesized to assess their spectroscopic properties. 1H and 13C NMR and circular dichroism data are related to selected structural and stereochemical features with a view to modelling natural phenolic oligoflavanoids.
1H and 13C NMR studies of aminoglycoside antibiotics
Authors: Moloney Gerard P. , Craik David J. , Iskander Magdy N. 
Published: May 2005

Abstract1H NMR spectroscopy was used to determine the conformations of the aminoglycoside antibiotic N‐demethylclindamycin and two of its cyclic derivatives. The conformational features of these systems were determined by consideration of vicinal coupling constants and, in some cases, nuclear Overhauser enhancement (NOE) effects. 1H and 13C chemical shifts are reported and compared with previous results for the related antibiotic lincomycin. The stability of the two cyclized derivatives in aqueous solution was examined. Both cyclizations involved formation of a 4‐imidazolidinone ring. It was found that the ring system based on cyclization with formaldehyde was stable in aqueous solution, whereas that based on benzaldehyde was not.
Proton NMR study of a non‐covalent complex formed between cytochromé c peroxidase‐cyanide and tuna ferricytochrome c
Authors: Yi Qian , Satterlee James D. , Erman James E. 
Published: May 2005

AbstractA non‐covalent complex of cyanide‐ligated cytochrome c peroxidase (CcPCN) with tuna ferricytochrome c, formed in low‐concentration KNO3 solutions, was studied by proton NMR spectroscopy. Complex formation affects the ferricytochrome c spectrum similarly to the spectral changes previously observed for the corresponding complex formed using resting state cytochrome c peroxidase. The CcPCN‐tuna ferricytochrome c complex studied here is also similar to the previously studied CcPCN complexes with both horse and yeast iso‐1 ferricytochromes c. For this complex both proteins are in the low‐spin iron(III) form, which make them both paramagnetic and causes severe overlap in the proton hyperfine resonance shift region. Two‐dimensional proton NMR spectroscopy has been used to resolve this overlap and make proton resonance assignments. These results complete the set of experiments carried out on the complexes of CcPCN with three species of ferricytochrome c (hores, yeast and tuna) and reveal that as for the similar complexes of these ferricytochromes c with the resting‐state, high‐spin form of the peroxidase, the tuna results closely follow those of the horse ferricytochrome c complex. These results also extend preliminary work that revealed for the first time that cytochrome c binding was reflected in hyperfine resonance shifts of protons in the peroxidase heme pocket.
Control of the spin state of the peroxidatic haem by calcium ions in cytochrome c peroxidase from Paracoccus denitrificans: A 1H NMR study
Authors: Prazeres Susana , Moura Isabel , Moura José J. G. , Gilmour Raymond , Goodhew Celia F. , Pettigrew Graham W. 
Published: May 2005

AbstractCytochrome c peroxidase from Paracoccus denitrificans LMD 52.44 was recently identified. The enzyme contains two c‐type haems: one is reducible physiologically by cytochrome c550 from the same organism or non‐physiologically by ascorbate (high‐potential haem) and the other by dithionite (low‐potential haem). The enzymatically active form of the peroxidase is the half‐reduced enzyme state, in which the high‐potential haem is in the iron(II) state and the low‐potential haem is in the iron(III) state. It was found that the two haems interact and that the enzyme binds calcium ions near the haem sites which are necessary to promote its activation. In the oxidized form, the high‐potential haem is in a high‐spin and the low‐potential haem is in a low‐spin state. The half‐reduction of the enzyme with ascorbate‐diaminodurol changes the high‐potential haem (high‐spin) into a low‐spin state and the low‐potential haem converts from a low‐ into a high‐spin state. This high‐spin conversion of the low‐potential haem is induced by the presence of calcium ions. These processes of reduction and spin state change can be easily resolved in time by removing the calcium from the enzyme using EDTA, facilitating the observation of the intermediate form by NMR.
15N NMR assignments of (Cd2+,)2‐calbindin D9k and comparison with (Ca2+)2‐calbindin D9k. Cadmium as a substitute for calcium in calcium‐binding proteins
Authors: Akke Mikael , Forsén Sture , Chazin Walter J. 
Published: May 2005

AbstractThe amide 15N and 1H chemical shifts of (Cd2+)2‐calbindin D9k are presented. A detailed comparison is made with those of (Ca2+)2‐calbindin D9k, showing that the (Cd2+)2 and (Ca2+)2 states of the protein are very similar, with differences predominantly located in ion‐binding loop I. The present studies were carried out on the P43G mutant calbindin D9k, and corroborate previous conclusions based on a comparative analysis of the 1H chemical shifts of the (Cd2+)2 and (Ca2+)2 states of wild‐type calbindin D9k. A value for the rate constant for the dissociation of cadmium from ion‐binding loop I in calbindin D9k of koff ≈︁ 0.6 × 103 ± 0.2 × 103 was estimated by analyzing line broadening in protein samples containing equal amounts of (Cd2+)1‐ and (Cd2+)2‐calbindin D9k.
Relaxometry and paramagnetic metal ions in biological systems
Authors: Luchinat Claudio 
Published: May 2005

AbstractThis paper gives an overview of the impact of relaxometry in bioinorganic chemistry. It is taken from a lecture dedicated to Seymour H. Koenig that the author presented at the 5th Chianti Workshop in Magnetic Resonance, San Miniato, Pisa, Italy, May 30‐June 5, 1993. After a short introduction and the definition of relaxometry, the basic principles of field‐cycling relaxometry are illustrated, with reference to the Koenig‐Brown relaxometer. Through a brief survey of early relaxometric data on paramagnetic solutions dating back to the 1950s and 1960s, attention is devoted to Koenig's discovery, in the 1970s, of anomalous relaxometric profiles of metalloprotein solutions and of the theoretical problems encountered in their interpretation. Then the advances made in the 1980s in the theory of electron nucleus interactions in slowly‐rotating systems are summarized. These advances were largely due to the fruitful interactions between Koenig, Bertini and his group at the University of Florence and the author, first at the University of Florence and later at the University of Bologna. After a short digression on obtaining electron relaxation rates from relaxometric measurements and on their physical meaning, recent progresses in understanding the detailed relaxometric behaviour of aqueous solutions of paramagnetic metal ions are presented. Again, Koenig's physical insight into the phenomena is highlighted. Finally, the exciting perspectives of the 1990s in the field of contrast agents, particularly in the theoretical understanding of superparamagnets, where Koenig is again at the forefront, are briefly described.
Deuterium solid‐state NMR study of the molecular mobility and dehydration of tert‐butyl alcohol on zeolite H‐ZSM‐5
Authors: Stepanov Alexander G. , Maryasov Alexander G. , Romannikov Vyacheslav N. , Zamaraev Kirill I. 
Published: May 2005

AbstractThe molecular mobility and dehydration reaction of tert‐butyl alcohol, selectively deuteriated in the methyl groups (t‐BuOH[2 – 2H9], dTBA), absorbed on H‐ZSM‐5 zeolite was studied using 2H NMR spectroscopy. At 173–298 K two modes of fast anisotropic motion were observed for the adsorbed alcohol: rotation of CD3 groups around the CC bonds and rotation of the entire (CD3)3C fragment around the CO bond. The influence of the walls of the H‐ZSM‐5 channels on the geometry of adsorbed dTBA is small, the increase in the CD3CO angle not exceeding 2.7 ± 1.2° compared with the same angle in solid dTBA. This is explained by location of the alcohol molecules at channel intersections of the zeolite, whose dimensions exceed those of the dTBA molecule. The lifetime of the dTBA molecule at these adsorption sites exceeds 1 × 10−5 s. The observed reaction products are deuteriated water with an unusual 2H NMR lineshape and two types of butene oligomers: less mobile species with the lineshape typical of solid‐state 2H NMR and more mobile species with a liquid‐like lineshape. The number of more mobile species increases with increase in temperature. In addition, 2H NMR indicates the presence of tert‐butyl groups in the reaction products. For oligomers with a liquid‐like lineshape, the diffusion coefficient D is 3 × 10−13 m2 s−1 at 373 K, whereas for oligomers with a solid‐like lineshape D ≪ 5 × 10−14 m2 s−1 at 173‐373 K. The diffusion coefficient for the t‐BuOH molecule was estimated as D ≪ 2 × 10−14 m2 s−1 within the temperature range 173–296 K.
Nuclear quadrupole coupling constants of halogenated hydrocarbons and their relation to the natural hybrid orbitals
Authors: Zhang Yong , Li Lin‐Feng , You Xiao‐Zeng 
Published: May 2005

AbstractThe natural hybrid orbitals of halogen atoms in various halogen‐substituted alkanes and benzenes have been calculated by the Fenske–Hall MO SCF method and natural hybrid orbital theory. Four consistent parameters i, s, d and π are derived to describe the nuclear quadrupole coupling constant (QCC) of the halogen isotopes 35Cl, 81Br and 127I, with modification by the asymmetry parameter η. A semi‐empirical expression is proposed from a different point of view.
High‐resolution NMR experiments which use frequency‐selective R.F. Pulses in combination with magnetic field gradients
Authors: Bernstein Michael A. , Trimble Laird A. 
Published: May 2005

AbstractMagnetic field gradients were incorporated into the selective COSY experiment. The new gradient‐selected experiment has the expected advantages of significantly improved spectral quality resulting from better artifact suppression and the capacity to acquire spectra using fewer scans. A sample of brucine was used to evaluate the experiment and the resulting spectra were of excellent quality. These experiments may be implemented on commercial instrumentation.
Effect of stereochemistry on hydroxyl proton chemical shifts and coupling constants in carbohydrates
Authors: Adams Bruce , Lerner Laura E. 
Published: May 2005

AbstractChemical shifts and coupling constants of hydroxyl protons for a series of simple carbohydrates are reported and several trends extracted: (1) chemical shifts are relatively independent of the experimental conditions if referenced to water; (2) chemical shifts are sensitive to the orientation of the HO group and its neighbors; and (3) coupling constants fall within a relatively narrow range, which is indicative of rotational averaging. These observations suggest that NMR parameters of hydroxyl protons can provide important diagnostic information about the stereochemistry of simple carbohydrates and may prove useful for analysis of more complex compounds.
Pseudo‐triple‐resonance BIS‐HMQC experiment for the 1H‐detected measurement of couplings between rare spins
Authors: Kupče Ēriks , Lukevics Edmunds , Wrackmeyer Bernd 
Published: May 2005

AbstractImprovement in the sensitivity and accuracy of the 1H‐detected experiment for measurement of coupling constants between rare spin‐1/2 nuclei X and Y is achieved if a bi‐selective (BIS) pulse is used to excite selectively protons coupled to Y, prior to the standard 1HX HMQC experiment (BIS‐HMQC). In the 2D spectrum even very small coupling constants J(X, Y) can be measured and the signs of J(X, Y) and J(Y 1H) can be compared. High‐quality 2D spectra were obtained using post‐acquisition binomial filters. The 1H13C29Si spin systems of the methoxy group in p‐trimethoxysilyltoluene [2J(29SiO13C) = 1.3 Hz] and of the diethylamino group in bis(diethylamino)dimethylsilane [2J(29SiN13C) = 2.5 Hz] serve for demonstrating the techniques.
Irradiated nifedipine—a nitroso spin trap
Authors: Staško Andrej , Mišík Vladimir , Omelka Ladislav 
Published: May 2005

AbstractIrradiation of nifedipine yields a new nitroso spin trap which traps carbon‐centred radicals and also forms relatively stable alkoxyl radical adducts. In addition, the reaction with unsaturated lipids yield highly stable covalent nitroxide radicals.
Deuterium and 18O isotope effects on 13C chemical shifts of sterically hindered and/or intramolecularly hydrogen‐bonded o‐hydroxy acyl aromatics
Authors: Hansen Poul Erik , Ibsen Solveig N. , Kristensen Tina , Bolvig Simon 
Published: May 2005

AbstractA series of sterically hindered o‐hydroxy aromatic ketones were synthesized, including benzene, naphthalene, phenanthrene and pyrene derivatives. Deuterium isotope effects on the 13C chemical shifts of 2‐hydroxy‐1‐acenaphthone and other sterically hindered, intramolcularly hydrogen‐bonded aromatic ketones (OH exchanged) are shown to be unusual. The two‐bond isotope effects are very large. Likewise are the istope effects on CO, C1, C3 and C4 carbon resonances and some show unusual signs. These unusual effects are explained by a higher degree of twist in the deuterio than the protio compound. Steric isotope effects are also observed on OH chemical shifts of sterically hindered o‐hydroxy acetyl aromatic compounds deuteriated at the methyl group. These isotope effects show non‐additivity. For one‐bond isotope effects, 1Δ13C(18O), hydrogen bonding leads to a decrease, whereas twisting of the carbonyl group leads to an increase. Two hydrogen bonds to the same acceptor has a reduced cumulative effect. Data for sterically hindered, hydrogen‐bonded compounds are found to fall outside the correlation between δ(17O) and 1Δ13C(18O).
Proton assignment and structural features of a peptide from the chymosin‐sensitive region of bovine k‐casein determined by 2D‐NMR spectroscopy
Authors: Plowman Jeffrey E. , Smith Mark H. , Creamer Lawrence K. , Liddell Michael J. , Coddington Jan M. , Gibson Jennifer J. , Engelbretsen Darren R. 
Published: May 2005

AbstractThe peptide k‐casein(98–111) corresponding to the sequence 98–111 of bovine k‐casein (His‐Pro‐His‐Pro‐His‐Leu‐Ser‐Phe‐Met‐Ala‐Ile‐Pro‐Pro‐Lys), which includes the aspartic protease sensitive region, was analysed by 2D 1H NMR spectroscopic techniques in DMSO‐d6. The spectral peaks of all protons resolved at 400 MHz were assigned. The changes in the amide proton shifts with pH and temperature and the existence of particular cross peaks in the ROESY spectra were consistent with the central region of the peptide being in an extended chain in solution but with some type of distinct conformations at the N‐ and C‐termini. The results are not consistent with the peptide having any helical structure at either low or high pH.