bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two‐dimensional 1H NMR studies on Desulfovibrio gigas ferredoxins. Assignment of the iron‐sulfur cluster cysteinyl ligand protons
Authors: Macedo Anjos L. , Palma P. Nuno , Moura Isabel , Legall Jean , Wray Victor , Moura José J. G. 
Published: May 2005

Abstract1D and 2D 1H NMR studies are reported on the oxidized and reduced [4Fe‐4S] cluster of Desulfovibrio gigas ferredoxin I (Fdl). Several low‐field contact shifted resonances (fast relaxing) are assigned to β‐CH2 and α‐CH coordinated cysteinyl residues. NOESY patterns (supported by 1D NOE experiments) resolves four pairs of geminal β‐CH2 protons at low‐field. The cluster ligands are assigned non‐specifically to Cys8, Cys11, Cys14 and Cys50, based on the X‐ray structural analysis available for the oligomeric form, FdII, that contains a single [3Fe‐4S] cluster. It was indicated in this case that Cys11 is not bound to the trinuclear cluster but is tilted towards the solvent. The presence of four pairs of geminal β‐CH2 protons for FdI unambiguously proves the occupancy of the fourth site of the [3Fe‐4S] complex and implies the coordination of the Cys11 at the cluster. Analysis of the oxidized form of FdII, using the same methodology as described for FdI, supports the presence of three cysteinyl ligands in the [3Fe‐4S] core. Further, the combined use of the X‐ray coordinates enables the specific assignment of the three cysteinyl ligands of the cluster, extending a previous assignment of Cys50. In addition, very broad resonances were detected for the reduced form of FdII in the low‐field region around 200 ppm and in the high field region around −80 ppm.
Two‐dimensional 1H NMR studies of Ca(II)‐binding site in proteins using paramagnetic lanthanides(III) as probes and Yb(III)‐substituted bovine α‐lactalbumin as an example
Authors: Ming Li‐june 
Published: May 2005

AbstractSubstitution of Yb3+ for the Ca2+ in bovine α‐lactalbumin affords a derivative that gives rise to several isotropically shifted 1H NMR signals in the range 80 to − 35 ppm in D2O. Despite the broadness of the isotropically shifted features, cross signals in both NOESY and COSY spectra have been detected. Several Asp residues in the metal‐binding loop can be recognized in the 2D 1H NMR spectra of this derivative, showing cross signals among the protons of a CβH2CαH moiety. This paper reports 2D 1H NMR studies of a paramagnetic lanthanide(III)‐substituted Ca2+−containing protein that may serve as a model for future NMR studies of other biochemically significant Ca2+ proteins.
Spin—spin couplings between 13C nuclei in five‐membered heteroaromatic ring systems
Authors: Witanowski Michal , Biedrzycka Zenobia 
Published: May 2005

AbstractA set of 14 1J(CC) spin—spin coupling constants are reported for 11 five‐membered heteroaromatic molecules, including all relevant diazole, triazole, oxazole, oxadiazole, thiazole and thiadiazole systems. The couplings show a clear distinction between carbon—carbon bonds which are formally double or single, respectively. There seems to be no correlation of the couplings with the bond lengths concerned, in spite of some apparent trends. Potential applications of the couplings are discussed in assessing the aromaticity of five‐membered heterocycles.
Long‐range carbon–proton couplings in strychnine
Authors: Blechta Vratislav , del Río‐Portilla Federico , Freeman Ray 
Published: May 2005

AbstractLong‐range 13C,H NMR coupling constants were measured in strychnine at 400 MHz by a method that employs selective excitation of individual 13C sites under decoupled conditions followed by polarization transfer to protons. The sensitivity was improved by performing eight simultaneous soft‐pulse experiments coded (±) according to a Hadamard matrix and later separated by reference to the same matrix. The antiphase 13C,H splittings were measured by J‐doubling performed in the frequency domain.
Binding modes of the distamycin analogue FCE‐24517 to d(CGTATACG)2. 1H and 13C sequence‐specific assignments
Authors: Mazzini Stefania , Musco Giovanna , Ragg Enzio , Penco Sergio 
Published: May 2005

AbstractThe interaction of an analogue of distamycin, FCE‐24517, with the ‘AT‐rich’ DNA fragment d(CGTATACG)2, was studied in solution by the combined usage of 2D techniques, TOCSY, NOESY, ROESY and 13C/1H shift correlation experiments. The formation of the complex destroys the C2 symmetry of the double helix, leading to a doubling of the nucleotide resonances. Proton and carbon atoms were assigned in the complex in terms of specific strand and residue. The imino protons of the base pairs, involved in hydrogen bonding and the H‐2 protons of adenine moieties, were determinant for defining the binding sites of the drug. The presence of multiple equilibrium reactions was proved by means of NOESY and ROESY spectra, where all the chemical‐exchange cross peaks were analysed. The FCE‐24517 signals in the complex were attributed and some stereospecific assignments performed. Two sets of resonances for FCE were identified, showing that the drug exists in two different chemical environments, corresponding to two different modes of binding in slow chemical exchange. Significant intermolecular NOE interactions between the drug and the nucleotide have allowed the binding sites in the minor groove of the DNA fragment to be located.
1H, 13C, 17O NMR and IR spectroscopic study of all methyl chloropropanoates
Authors: Kolehmainen Erkki , Korhonen Ilpo O. O. , Kauppinen Reijo 
Published: May 2005

Abstract1H, 13C and 17O NMR chemical shifts, nJ(H,H) and nJ(C,H) spin‐spin coupling constants and IR absorption maxima and intensities for the most characteristic bands of methyl propanoate and all eleven chloropropanoic acid methyl esters are reported.
Conformation of tricyclo [4.3.1.12,5]undec‐3‐en‐10‐one
Authors: Camps Pelayo , Vázquez Santiago , Jaime Carlos , Virgili Albert 
Published: May 2005

AbstractA high preference for the boat conformation of tricyclo[4.3.1.12,5]undec‐3‐en‐10‐one was established on the basis of 1H NMR spectroscopy with the aid of molecular mechanics calculations (MM3 program).
Secondary isotope effect on the 19F shielding in xenon and krypton difluorides in solution
Authors: Jokisaari Jukka P. , Ingman L. Petri , Schrobilgen Gary J. , Sanders Jeremy C. P. 
Published: May 2005

AbstractThe effects of the various xenon and krypton isotopes on the nuclear shielding of 19F in xenon and krypton difluoride in solution were studied by 19F NMR spectroscopy. For both molecules, linear relationships were observed between the one‐bond secondary isotope shift of the 19F nucleus, 1Δ; 19F(m′/128Xe) and 1Δ 19F(m′/78Kr), and the relative mass factor, (m′ − m)/m′, and also between the shifts and the quadratic mean bond displacement, 〈(Δr)2〉. On the basis of the latter correlation and the linear relationship between 〈Δr〉 and 〈(Δr)2〉 for the linear combination of the first and second derivatives of the 19F shielding, the values −1742 and −5804 ppm Å−2, respectively, were determined. Further, the temperature dependence of the 129Xe and 19F chemical shifts and the 129Xe, 19F indirect spin‐spin coupling of XeF2 were determined. The 129Xe chemical shift is extremely sensitive to temperature with Δδ/ΔT = −0.4718 ppm K−1, whereas for 19F Δδ/ΔT = +0.0042 ppm K−1. In contrast, the 129Xe, 19F indirect spin–spin coupling is independent of temperature over the range 243–303 K, the mean value being 5644.2 ± 0.6 Hz.
77Se, 13C and 1H NMR spectra of phenylselenenyl azide and chloride addition products of methylenecyclohexane and cyclohexene
Authors: Boyko Walter J. , Duarte Franco J. , Giuliano Robert M. 
Published: May 2005

AbstractThe 77Se, 13C and 1H NMR spectra of the products of phenylselenenyl azide and chloride addition to methylenecyclohexane and cyclohexene are presented. Scalar couplings between 77Se and 1H/13C allowed the absolute assignment of the regioisomers in the 1H and 13C spectra. Low‐temperature 77Se NMR was used to determine the conformer ratios for 1‐azidomethyl‐ and 1‐chloromethyl‐1‐phenylselenenylcyclohexane anti‐Markovnikov addition products.
Nuclear magnetic resonance imaging as a probe of the freezing—thawing phenomena of liquids in heterogeneous systems
Authors: Fyfe Colin A. , Isbell Stephanie A. , Burlinson Nicolas E. 
Published: May 2005

AbstractNMR microscopic imaging is shown to be an excellent probe of the freezing and thawing phenomena of liquids in heterogeneous chemical systems, and, in addition, is capable of monitoring the freezing‐thawing of mixed solvent systems. In the model mixed solvent system Me2SO–water, the chemical shift specific slice selective (C4S) imaging technique is used to obtain the spatial distributions of the concentrations and mobilities of the two individual solvents in test samples. Measurements of relaxation parameters make it possible to choose values of imaging parameters TE and TR to ensure quantitative reliability of the images. Images of test samples generated at various temperatures demonstrate the qualitative relationship between image intensity and the Me2SO–water phase diagram. This series of experiments verifies that NMR microscopic imaging will be a powerful tool for the study of liquids within solid matrices, and in particular of cryoprotectant solvents in biological systems.
Deuterium isotope effects as evidence for substituent perturbation of the π‐electron frame in benzanilides
Authors: Morales‐Ríos Martha S. , Pérez‐Alvarez Víctor , Joseph‐Nathan Pedro , Zepeda L. Gerardo 
Published: May 2005

AbstractDeuterium isotope effects on 13C nuclear shielding, nΔC(D), transmitted across a D‐labelled nitrogen atom were investigated for a series of para‐substituted benzanilides. The two two‐bond isotope shifts, 2ΔC(D) are perturbed essentially in a trough‐bond manner by change of the contribution of mesomeric structures. The magnitudes of 2Δ(CO) and 2Δ(C‐1′) are found to be mutually interdependent as evidenced by the linear relationships between the average values of 2Δ(CO) and 2Δ(C‐1′) with 1H(NH) chemical shifts and with 15N SCS. This behaviour is interpreted as resulting from a cross‐conjugated transmission pathway involving the carbons sharing the D‐labelled nitrogen.
Carbon‐13 NMR studies on azolopyridines. 3—the isothiazolopyridine systems
Authors: Chimichi Stefano , Cosimelli Barbara , Tedeschi Piero , Ponticelli Fabio 
Published: May 2005

AbstractAll four fully aromatic isothiazolopyridine isomers have been synthesized, their 13C spectra have been assigned and all one‐bond and long‐range 13C1H coupling constants have been determined.
17O NMR spectra of vinyl ethers
Authors: Taskinen Esko , Hellman Jaakko 
Published: May 2005

AbstractThe 17O NMR spectra of 58 α,β‐unsaturated (vinyl) ethers were recorded in CDCl3 solution. The dependence of the chemical shift on the number and position of alkyl substituents in the vinyl moiety and on the nature and bulkiness of the alkoxy group was explored. The oxygen chemical shifts proved to be sufficiently sensitive to structural factors to make 17O NMR spectroscopy a useful tool in the investigation of the electronic and spatial structures of vinyl ethers.
Simple technique for temperature calibration of a MAS probe for solid‐state NMR spectroscopy
Authors: Aliev Abil E. , Harris Kenneth D. M. 
Published: May 2005

AbstractA simple method is reported for temperature calibration of a magic angle spinning probe for solid‐state NMR spectroscopy. The method is an extension of that developed by van Geet for temperature calibration of liquid‐state NMR probes, and consists of measuring the frequency difference (Δν) between the resonances for the methyl and hydroxyl protons of methanol in the 1H NMR spectrum of a sample of tetrakis(trimethylsilyl)silane soaked in liquid methanol. The successful application of this method for temperature calibration was demonstrated from an assessment, from high‐resolution solid‐state 13C NMR spectroscopy, of the phase transition temperatures for solid tetrakis(trimethylsilyl)silane and for solid 2,2‐dimethylpropane‐1,3‐diol.
Steric effects induced by solvent association. 29Si NMR chemical shifts in trimethylsiloxysteroids controlled by solvent accessible surface
Authors: Kasal A. , Schraml J. , Čermák J. 
Published: May 2005

AbstractChemical shifts of silicon‐29 in 39 trimethylsiloxy derivatives of 5α‐ and 5β‐androstanes reported here satisfy an empirical linear correlation with terms describing molecular geometry. The steric 29Si chemical shifts are controlled by association of the silyl ethers with the hydrogen bonding solvent. The chemical shifts measured in dilute solutions show a dependence on the surface of the oxygen atom accessible to the solvent for hydrogen bonding. The steric upfield shifts are due to steric hindrance to hydrogen bonding which itself produces downfield shifts.
Diamagnetic lanthanide tris‐β‐diketonates as ‘dissolving’ reagents
Authors: Komarov Igor V. , Kornilov Mikhail Yu. , Turov Aleksandr V. 
Published: May 2005

AbstractIt is proposed to use diamagnetic lanthanide tris‐β‐diketonates as auxilliary reagents to promote solubilization of organic compounds in low‐polarity solvents, thereby enhancing the NMR spectral sensitivity. For such a purpose the lanthanum complexes with fluorinated β‐diketonate ligands were shown to be the most suitable. These tris‐β‐diketonates form adducts with compounds possessing ‘hard’ Lewis base functional groups, and the adducts are more soluble than their components. The effect of the lanthanum complexes on paramagnetic shifts induced by lanthanide shift reagents was examined. A considerable increase in the shifts values was found in the presence of some lanthanum tris‐β‐diketonates.
Substituted methyl 5β‐cholan‐24‐oates. I—17O NMR spectral characterization
Authors: Kolehmainen Erkki , Kaartinen Mari , Kauppinen Reijo , Kotoneva Jari , Lappalainen Kari , Lewis Philip T. , Seppälä Raimo , Sundelin Jukka , Vatanen Virpi 
Published: May 2005

AbstractMethyl esters of four common bile acids, 3α‐hydroxy‐5‐β‐cholan‐24‐oic (lithocholic) acid, 3α, 7α‐dihydroxy‐5β‐cholan‐24‐oic (chenodeoxycholic) acid, 3α,12α‐dihydroxy‐5β‐cholan‐24‐oic (deoxycholic) acid and 3α,7α,12α‐trihydroxy‐5β‐cholan‐24‐oic (cholic) acid, and 14 acetylated, trifluoroacetylated, mesylated and oxo derivatives of methyl 5β‐cholan‐24‐oates were prepared and their 17O NMR spectra recorded. In spite of their relatively high molecular masses and the rigid molecular structure of the steroid skeleton, most of the oxygens included in these structures gave well resolved 17O NMR resonance lines at natural abundance in 0.25–0.5 M acetonitrile solutions at 75°C. In agreement with the present 17O NMR results, molecular mechanics calculations revealed that a hydroxy substituent located at the 3α‐position clearly differs from the hydroxyls at the 7α‐ and 12α‐positions. This is due to the fact that the 3α‐hydroxyl possessing only two γ‐carbons at antiperiplanar positions is less shielded than the other hydroxyls influenced also by the shielding effects of γ‐gauche carbons. The spectral deconvolution of the overlapping signals of the 7α‐ and 12α‐hydroxyls is based on a computer‐aided method or on chemical substitutions. The oxo groups located at the longitudinal (3‐oxo) vs. transversal (7‐ and 12‐oxo) axes of the steroid framework show very different quadrupolar relaxation properties and 17O NMR linewidths owing to the strong anisotropy of overall molecular motion. In contrast, the 17O NMR linewidths of all 3α‐, 7α‐ and 12α‐hydroxyls are very similar and clearly smaller than those of the corresponding oxo groups, revealing that their quadrupolar relaxation is merely determined by their internal rotation rather than by the overall molecular motion.
1H and 13C NMR studies of the self‐association of chlorpromazine hydrochloride in aqueous solution
Authors: Attwood David , Waigh Roger , Blundell Ross , Bloor Debra , Thévand André , Boitard Elizabeth , Dubès Jean‐Paul , Tachoire Henri 
Published: May 2005

AbstractThe 1H NMR spectrum of chlorpromazine hydrochloride was fully assigned at 400 MHz. Similarly, the 13C NMR spectrum was assigned unambiguously using two‐dimensional NMR. Measurements of chemical shift as a function of concentration in D2O showed appreciable changes of shift of both protons and carbons which were apparent even at solution concentrations two orders of magnitude lower than the critical micelle concentration (CMC). The relative magnitude of the shifts of the aromatic protons and carbons on dilution below the CMC were compatible with vertical stacking of the molecules in an off‐set manner such that maximum overlap of the chlorinated rings occurred. Proton chemical shift data were interpreted using a stepwise association model to quantify the extent of association in the pre‐CMC region.
ESR spectra of 4‐phenyl‐1,2,3,5‐diselenadiazolyl, PhCN2Se2·, and the first diselenadiazolyl metal complex, Pt[PhCN2Se2][PPh3]2
Authors: Rawson Jeremy M. , Banister Arthur J. , May Iain 
Published: May 2005

AbstractAnisotropic ESR spectra (THF, frozen glass, 77 K) of PhCN2Se2˙ provide valuable information about the electronic structure of the diselenadiazolyl radical. Reaction of PhCN2Se2˙ with Pt(PPh3)3 in CH2Cl2 yielded the first diselenadiazolyl–metal complex, Pt[PhCN2Se2][PPh3]2. The electronic structures of both compounds are described in comparison with their sulphur analogues and the isoelectronic SN2E2+˙ radicals (E = S, Se).
Variable‐temperature and pH studies of a DNA minor groove binder, Hoechst 32985, by 1H NMR spectroscopy
Authors: Cross Keith J. , Embrey Kevin J. , Coles Murray , Bicknell Wendy , Craik David J. 
Published: May 2005

Abstract1H NMR spectra of the dipiperazine‐based DNA minor groove binding compound Hoechst 32985 indicate that at room temperature and low pH (2.90) a single conformation is detected. This is attributed to the form in which both piperazine rings are protonated at the N‐methyl and the bulky methyl and aromatic groups are in an equatorial arrangement. The aliphatic regions of the spectra broaden considerably with an increase in either temperature or pH, indicating the presence of a dynamic exchange process. This process results in interchange of axial and equatorial environments of the piperazine ring protons and is attributed to combined ring and nitrogen inversions. Analysis of the variable‐temperature spectra for a solution at pH 2.90 allowed a Gibb's free energy of activation (ΔG‡) of 69.4±0.4 kJ mol−1 to be calculated for this process.
13C and 19F NMR spectra of a series of laterally fluorinated mesogens
Authors: Loubser Christa 
Published: May 2005

Abstract13C and 19F NMR spectra of a series of mesogenic compounds, (S)‐4‐n‐octyloxy‐fluorobiphenyl‐4′‐yl fluoro‐4‐(2‐fluoro‐octanoyloxy)benzoates, were determined in solution. The effect of fluoro substitution in various positions on the 13C and 19F chemical shifts was studied. 13C, 19F and 19F, 19F scalar coupling constants are given.
Complete assignment of the 1H and 13C NMR spectra of deoxyhemigossypol derivatives
Authors: Alam T. M. , Rosay M. , Deck L. , Royer R. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of the deoxyhemigossypol derivatives 4‐isopropyl‐2,3‐dimethoxy‐6‐methylnaphthalene, 4‐isopropyl‐2,3‐dimethoxy‐6‐methyl‐1‐naphthaldehyde and 2,3‐dihydroxy‐4‐isopropyl‐6‐methyl‐1‐naphthaldehyde were assigned using one‐ and two‐dimensional NMR techniques, including DEPT, 1H NOE and 1H13C HETCORR spectroscopy.
Proton and carbon‐13 NMR and conformation in solution of some amorphanes (quinghaosu derivatives)
Authors: Marsaioli Anita J. , Fujiwara Fred Y. , Foglio Mary Ann , Sharapin Nikolai , Zhang Jin‐Sheng 
Published: May 2005

AbstractThe total proton and carbon‐13 NMR assignments of quinghaosu I, II and V isolated from Artemisia annua cultivated in Brazil and of the synthetic derivatives quinghaosu alkene, ketone and epoxy are reported. The conformations and conformational equilibria of these compounds in solution were obtained from the spectral data and molecular mechanics calculations.
13C NMR chemical shifts of heterocycles. Empirical substituent effects in 5‐halomethyl‐5‐hydroxy‐4,5‐dihydroisoxazoles
Authors: Martins Marcos A. P. , Martins Anna C. L. 
Published: May 2005

AbstractEvaluation by empirically derived equations for the substituent effect (α, β, γ, δ) on the 13C NMR chemical shifts for C‐3, C‐4, C‐5 and halomethyl‐substituent carbon (C‐6) in 5‐halomethyl‐5‐hydroxy‐4,5‐dihydroisoxazoles (where C‐3 substituent=H), alkyl or phenyl, C‐4 substituent=H, alkyl or heteroalkyl and C‐5 substituent (=dior trihalomethyl), taking as reference 5‐trichloromethyl‐5‐hydroxy‐4,5‐dihydroisoxazole, is reported. From the calculated values for the α, β, γ and δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds.
Study of halogen exchange in allyltin trihalides by two‐dimensional 119Sn EXSY NMR
Authors: Pianet Isabelle , Fouquet Eric , Pereyre Michel , Gielen Marcel , Kayser François , Biesemans Monique , Willem Rudolph 
Published: May 2005

Abstract(2‐Ethoxycarbonyl)crotylbromodichlorostannane (1) and (2‐ethoxycarbonyl)allylbromodichlorostannane (2), two compounds with formula RSnCl2Br, were shown by 2D phase‐sensitive EXSY 119Sn NMR to undergo halogen exchange, resulting in equilibrium mixtures of RSnCl3, RSnCl2Br, RSnClBr2 and RSnBr3. The unidirectional pseudo‐first‐order rate constants were determined by two different methods, the initial rate and the exchange matrix resolution approaches. The data show that the exchange proceeds by single halogen exchange, probably occurring through an intermediate involving two organotin trihalide moieties, as evidenced from the linear dependence of the pseudo‐first‐order rate constants on concentration. The mechanism is briefly discussed.
Restricted rotation of the phenyl group in β‐hydroxyphosphonates: Dynamic NMR and semiempirical studies
Authors: Vassilev Nikolay G. , Dimitrov Valentin S. 
Published: May 2005

AbstractFree energies of activation, ΔG, for the rotation of the phenyl group in the range of 46.06–63.25 kJ mol−1 were observed in some model β‐hydroxyphosphonates. These barriers were found to depend on the type of substituents at the phosphorus atom and on the substituents at the β‐position with respect to the phenyl ring. The steric origin of this observation is discussed. Dynamic NMR studies were performed in order to determine the activation parameters for the exchange process. For that purpose, variable‐temperature 1H and 13C NMR spectra were treated by non‐iterative, iterative and iterative double‐fit procedures. MNDO, AM1 and PM3 theoretical calculations of the barriers for three of the compounds studied are reported and results are compared with the experiments. It is found that the PM3 results are very close to the experimental data.
Nuclear magnetic resonance spectral analysis of three isomeric 2,3,5‐trisubstituted N‐methylpiperidines
Authors: Kotzamani Heleni K. , Stamos Ioannis K. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of three stereoisomeric 2‐(p‐chlorophenylthiomethyl)‐3‐(3‐methoxyphenyl)‐5‐carbomethoxy‐N‐methylpiperidines were analysed in terms of configuration and solute conformation. These studies together with 2D J‐resolved, 2D‐COSY and 2D 1H13C‐correlated spectra demonstrate the existence of 2a‐3a‐5e, 2e‐3a‐5e and 2e‐3e‐5e chair conformations