bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental appraisal of solvent effects on internal rotation barriers and stabilization energies of disubstituted methyl radicals
Authors: Mordi Raphael C. , Walton John C.
Published: May 2005

The EPR spectra of aminopropynyl and aminocyanomethyl radicals were recorded in a variety of solvents with different dielectric constants. For the former radical the spectra showed exchange broadening due to restricted rotation about the H2NC˙ bond. Arrhenius parameters for the bond rotation, i.e. for the interconversion of the two rotamers, were obtained by computer simulation of the exchange‐broadened spectra. The rotational barrier height was found to change only marginally in solvents with dielectric constants ranging from 2.1 to 37.5. For both radicals the temperature dependences of the α(NH2) values also indicated little change in their H2NC˙ rotation barriers in solvents of differing polarity. Because rotation barriers are directly related to the stabilization energies (SE) of the radicals, it was concluded that solvent polarity has little effect on the SE of a capto‐datively substituted radical.
Synthesis and configurational assignment of epimeric 22‐hydroxy‐, 23, 24‐acetylenic, olefinic or epoxy steroids using carbon‐13 NMR Spectroscopy
Authors: Hazra Braja G. , Pore Vandana S. , Joshi Padmakar L. , Padalkar Sharmila N. , Deshpande Shubhada A , Rajamohanan Pattuparambil R.
Published: May 2005

Stereoisomers of steroidal 22‐hydroxy‐23‐acetylenic, 23‐olefinic and 23, 24‐isomeric epoxides were synthesized from C‐22 aldehydes and their 13C NMR spectra were analysed. A correlation regarding the combined effect of the 22‐hydroxy and 23, 24‐substituents on the stereochemistry of the attached groups at C‐22, ‐23 and ‐24 is derived.
13C nuclear magnetic resonance data for methyl 3,4‐disubstituted benzoates
Authors: Varma R. S. , Shukla Amita
Published: May 2005

The 13C NMR spectral assignments and 1J(C,H) spin–spin coupling constants for methyl 4‐anilino‐3‐nitrobenzoate, methyl 4‐p‐chloroanilino‐3‐nitrobenzoate, methyl 4‐p‐toluidino‐3‐nitrobenzoate, methyl 4‐p‐ anisidino‐3‐nitrobenzoate, methyl 4‐hydroxy‐ 3‐methoxybenzoate and methyl 3,4‐dimethoxybenzoate are reported.
Determination of the structure of alkoxysilane polymers in solution by natural abundance two dimensional 29Si‐29Si INEPT DQF COSY NMR
Authors: Lux Philippe , Brunet Francine , Desvaux Hervé , Virlet Joseph
Published: May 2005

In order to determine the nature and the structure of polymers formed by condensation of alkoxysilanes, a two‐dimensional INEPT double quantum filtered COSY NMR experiment was developed to observe 29Si29Si correlations at 29Si natural abundance. This experiment was tested on a mixture containing a trimer, [(CH3)3SiO]2Si(CH3)2, and a tetramer, [(CH3)3SiOSi(CH3)2]2O. This 2D INEPT DQF COSY experiment was then used to investigate the nature and the structure of the polymers which are formed in the early stages of the condensation reaction of diethoxydimethylsilane (DEDMS) in a DEDMS–water mixture containing a small amount of water at low pH (1.0).
Complete 1H and 13C resonance assignments of stereoisomeric 3α,6,7,12α‐tetrahydroxycholanoic acids by two‐dimensional shift‐correlated NMR
Authors: Iida Takashi , Chang Frederic C. , Mushiake Kumiko , Goto Junichi , Nambara Toshio
Published: May 2005

Complete 1H and 13C NMR resonance assignments were carried out for six stereoisomeric 6,7‐glycol derivatives of deoxycholic acid as their methyl esters (four being in the 5β‐series and two in the 5α‐series). In addition to conventional 1D NMR methods, 2D shift‐correlated NMR techniques (1H1H COSY, 1H1H NOESY and 1H13C HETCOR) were used for the signal assignments. Several 1H and 13C resonances have been reassigned from those previously reported. Substituent effects of the 6,7‐glycol moieties on the proton and carbon resonances were clarified and used in the structural elucidation of these compounds.
Chemical shift anisotropy of the anomeric protons in α‐ and β‐D‐glucose
Authors: Poppe Leszek , van Halbeek Herman
Published: May 2005

Values for the chemical shift anisotropies of the α‐ and β‐anomeric protons in [1‐13C]‐D‐glucose were measured by ortho‐ROESY and SLOESY experiments using non‐selective and selective 1H spin‐locking by DANTE pulse trains, respectively. The experiments were performed under the condition ωHτo ≈ 1, in order to enhance cross‐correlated cross‐relaxation due to interference between 1H chemical shift anisotropy and 1H‐13C dipolar interactions. Assuming axial symmetry for the 1H chemical shift tensor, chemical shift anisotropy values of ΔσH‐1(α) ≈ −6.1 ppm and ΔσH‐1(β) ≈ −2.4 ppm were obtained.
Use of indirect 199Hg NMR detection for aromatic mercury compounds of biological interest
Authors: Neirinck Vincent , Robert Danielle , Nardin Robert
Published: May 2005

When vanillin (4‐hydroxy‐3‐methoxbenzaldehyde) and syringaldehyde (4‐hydroxy‐3,5‐dimethoxybenzaldehyde) react with Hg(OAc)2, selective monomercuration occurs on the aromatic ring. The three 3J, 4J and 5(199Hg,1H) coupling constants of phenylmercury acetate were used as 1/2J delays in the 1D inverse 1H 199Hg, sequence applied to 5‐acetoxymercuriovanillin and 2‐acetoxymercuriosyringaldehyde, the edited proton spectra obtained for each nJ(199Hg, 1H) coupling gave the value of n and the J(199Hg, 1H) coupling constants, and therefore yielded information about the position of the mercury substitution on the aromatic ring. A 2D 199Hg,1H shift correlation with 1H detection was applied in the case of phenylmercury acetate, using the mean value of the three J couplings; the 3J and 4J couplings were clearly resolved. As vanillin and syringaldehyde are representative monomer models of lignin, the indirect detection of 199Hg is then an appropriate method to determine the aromatic substitution pattern, which is a key point in lignin structural elucidation.
1H, 13C, 15N, 113Cd, 2D 15N1H and solid‐state 13C CP/MAS NMR of Hg and Cd complexes of 4(1H)‐quinazolinone‐2,3‐dihydro‐2‐thioxo
Authors: Martínez‐Martínez Francisco Javier , Ariza‐Castolo Armando , Ramos‐Nava Victor , Barba‐Behrens Norah , Contreras Rosalinda
Published: May 2005

The Cd(II) and Hg(II) complexes of 4(1H)‐quinazolinone‐2,3‐dihydro‐2‐thioxo (1) and the free ligand were studied by 1D and 2D multinuclear magnetic resonance in solution and 13C cross polarization magic angle spinning NMR in the solid state. Compound 1 adopts only one of five possible tautomeric structures in solution, namely the thiouracyl‐like structure. It was found that the metal atom is linked to two molecules of deprotonated 1 by N‐1 and coordinated by the sulphur atom. The compounds retain the same structure in the solid state and in dimethyl sulphoxide solution.
Correlation between 27Al and 71Ga NMR chemical shifts
Authors: Bradley Susan M. , Howe Russell F. , Kydd Ronald A.
Published: May 2005

A linear relationship has been found to exist between the aluminum‐27 and gallium‐71 NMR chemical shifts of a series of structurally analogous aluminum and gallium compounds having only oxygen in the first metal coordination spheres; δ71Ga = 2.83(δ27Al) − 4.50. This relationship allows the prediction of 71Ga chemical shifts for such gallium compounds from the 27Al values already known for their aluminum analogues, and also a greater understanding of observed 71Ga chemical shifts.
Tautomerism in 2‐hydroxy‐1‐naphthaldehyde schiff bases in solution and the solid state investigated using 13C NMR spectroscopy
Authors: Salman S. R. , Lindon J. C. , Farrant R. D. , Carpenter T. A.
Published: May 2005

13C and 1H NMR spectra of six Schiff bases formed from 2‐hydroxy‐1‐naphthaldehyde and substituted anilines were measured and assigned in a variety of solvents. Based on the 13C chemical shifts and 3J(CH,NH), the ratio of the keto‐amine and phenol‐imine tautomers was derived using both 13C chemical shifts and 1H−1H coupling constants, the two methods giving comparable results. The solid‐state 13C NMR spectra of two of these Schiff bases were also measured and interpreted. Based on chemical shift assignments from solution NMR, which showed a relationship between certain shifts and the proportions of the tautomers, it has been shown that these compounds exist essentially as the keto‐amine form in the solid, the tautomer previously shown to be the more thermodynamically stable.
Factors affecting the line widths and signal‐to‐noise ratios of the 13C CP/MAS spectra of proteins
Authors: Belton Peter S. , Gil Ana M. , Tanner Stephen F.
Published: May 2005

Typically the 13C CP/MAS spectra of proteins have low signal‐to‐noise ratios and broad lines, which considerably degrade the value of such spectra. The origins of these effects were examined using a model protein, lysozyme. The effects of hydration, relaxation time and crystallinity were systematically investigated. It is concluded that low signal‐to‐noise ratios are the result of the typically low density of protein preparations and not an intrinsic magnetic resonance phenomenon, and that line broadening is principally the result of poor molecular packing in noncrystalline protein preparations.
Structure of oxidatively damaged nucleic acid adducts: PH dependence of the 13C NMR spectra of 8‐oxoguanosine and 8‐oxoadenosine
Authors: Cho Bongsup P.
Published: May 2005

13C NMR spectra of two C‐8‐oxo purine nucleosides, 8‐oxoguanosine and 8‐oxoadenosine, were recorded as a function of pH. The pH dependence of 13C chemical shifts and 13C‐1H coupling constants associated with the purine carbon resonances was analyzed to probe the sites and extent of ionization and protonation of these oxidatively damaged nucleic acid adducts. In the course of this study, it was found that the C‐2′ and C‐3′ resonances of the ribofuranosyl sugar ring can be conveniently assigned on the basis of their unique pH‐independent 1H‐coupling spectral patterns in aqueous solution.
Conformational analysis of four β‐methylphenylalanine stereoisomers in a bioactive peptide by z‐filtered relay NMR spectroscopy
Authors: Kövér Katalin E. , Jiao Ding , Fang Sunan , Hruby Victor J.
Published: May 2005

The rotamer populations around the C‐α—C‐β bond of amino acid residues with one β‐proton can be calculated from homonuclear and heteronuclear vicinal coupling constants. The measurement of long‐range heteronuclear coupling constants, however, suffers from the inherent low sensitivity of the heteronuclear multiple bond experiments. In this paper it is demonstrated that z‐filtered homonuclear and heteronuclear relay spectroscopy provides a sensitive and accurate means for the evaluation of conformationally important vicinal coupling constants. Side‐chain conformations of the four stereoisomers of β‐methylphenylalanine residues in synthetic octapeptide analogues of CCK‐8 were derived from the measured coupling constants. This information is not easily available from conformational analysis based on simple steric considerations.
Direct analysis of the ABX spin system in two symmetrical diphosphonates: Comparison with two‐dimensional methods
Authors: Harris R. K. , Jones M. S. , Kenwright A. M.
Published: May 2005

The results of the direct analysis of the ABX spin system present in two symmetrical diphosphonates containing a single vinylic 13C nucleus are presented. This allows a comparison to be made with the two‐dimensional methods used by Beckmann et al. Significant differences are found in the results obtained: the need to recognize the existence of isotopic chemical shifts is emphasized.
1H NMR spectra of some 4,5‐dihydro‐1,2,4‐triazol‐5‐ones
Authors: Ikizler A. Aykut , Ikizler Aysun , Yüksek Haydar
Published: May 2005

Thirty 3‐substituted‐ and 3,4‐disubstituted‐4,5‐dihydro‐1,2,4‐triazol‐5‐ones (seven being new compounds) were synthesized and their proton magnetic resonance spectra were measured in trifluoroacetic acid (TFA). The protonation shifts observed on comparison of the spectra run in DMSO‐d6 and TFA were attributed to an amidinium‐type resonance of the resulting cations in the acidic medium.
Electron‐transfer self‐exchange of trimethylphosphine‐modified cytochrome c: NMR study and kinetics using spin‐lattice relaxation times
Authors: Legrand Nathalie , Bondon Arnaud , Simonneaux Gérard , Schejter Abel
Published: May 2005

The binding of trimethylphosphine to the axial position of the haeme iron in modified cytochrome c by alkylation of methionine was studied by NMR spectroscopy. Electron self‐exchange was determined by spin‐lattice relaxation time (T1) measurement. The rate is 7.5 × 103 1 mol−1 s−1 at 25°C in 0.1 M phosphate buffer (pH 7.0). Two‐dimensional transfer spectroscopy was used to locate haeme methyl resonances in both iron(II) and iron(III) complexes of modified cytochrome c.
Sequential assignments by 1H 2D NMR of oxidized ferredoxins from Clostridium pasteurianum and Clostridium acidurici
Authors: Gaillard Jacques , Moulis Jean‐marc , Kümmerle Rainer , Meyer Jacques
Published: May 2005

A 1H 2D NMR investigation of the oxidized 2[4Fe‐4S] ferredoxins from Clostridium pasteurianum and C. acidurici was carried out. Sequential assignments through standard HOHAHA and NOESY procedures were obtained for the 2–7, 23–36 and 52–55 sequence segments of both proteins. Additional assignments of the 15–17 and 44–46 segments, linking the clusters, and of a few other residues were made by taking advantage of sequence differences between the two proteins. In summary, only the immediate vicinity of the cysteine ligands could not be identified by the procedure. In these small 2[4Fe‐4S] ferredoxins, a large proportion of the resonances is sensitive to the presence of the paramagnetic centres and does not easily display NOE correlations. Nevertheless, long‐range NOE peaks that could be observed shed light on the solution structure of these proteins. The close interaction between the N‐ and C‐termini, previously evidenced by x‐ray crystallography, was confirmed for both proteins in solution. Small differences between the ferredoxins from C. pasteurianum and C. acidurici were detected in the flexible and variable external 25–30 loop and also in the region separating the clusters. These differences may correlate with small dissimilarities previously observed between some properties of these ferredoxins.
Two‐dimensional 1H NMR studies of paramagnetic bimetallic mixed‐metal complexes
Authors: Wang Zhigang , Holman Theodore R. , Que Lawrence
Published: May 2005

Synthetic dinuclear mixed‐metal complexes have proved useful as models for metal‐substituted dinuclear iron‐oxo proteins. However, a detailed assignment of their paramagnetically shifted proton NMR resonances has thus far been difficult to achieve. In the light of the significant role of two‐dimensional (2D) NMR techniques in establishing the bond connectivities in diamagnetic molecules, COSY studies were performed on a series of complexes, [Fe(II)M(II)BPMP(O2CCH2CH3)2]+ {BPMP = 2,6‐bis [bis(2‐pyridylmethyl)aminomethyl]‐4‐methylphenol, M  Mn, Co and Zn}, taking advantage of the short electronic relaxation time of Fe(II). The resonances from the four distinct pyridine rings of each of the three complexes were unambiguously assigned based on the bond‐correlated cross signals in the 2D spectra due to the (α‐)β‐γ‐β′ pyridyl proton connectivities. The resonances from the two bridging ligands of these complexes were also unambiguously assigned based on the same approach. Together with longitudinal relaxation time (T1) measurements, the 2D data allow the assignment of all the paramagnetically shifted proton resonances of all the three bimetallic complexes.
Assignment of Pseudo‐contact‐shifted 1H NMR resonances in the EF site of Yb3 +‐substituted rabbit parvalbumin through a combination of 2D techniques and magnetic susceptibility tensor determination
Authors: Capozzi Francesco , Cremonini Mauro Andrea , Luchinat Claudio , Sola Marco
Published: May 2005

Pseudo‐contact‐shifted 1H NMR resonances of rabbit parvalbumin substituted with Yb3+ at the Ca2+ EF site have been sequence‐specific assigned by a combination of 2D techniques and magnetic susceptibility tensor determination. By taking the X‐ray structure of the homologous carp protein as a starting point, the sequence‐specific assignment proceeded in a stepwise fashion. The first resonances assigned on the basis of their unique connectivity pattern were used to make a first coarse determination of the X‐tensor parameters; the latter were used to guess the identity of further hyperfine‐shifted resonances, which were then checked through 2D connectivities and in turn allowed us to improve the reliability of the X‐tensor parameters. This cyclic procedure was repeated until virtually all pseudo‐contact‐shifted resonances were assigned. In the last steps the X‐tensor parameters did not change appreciably. The orientation of the tensor was found to be very similar to that previously proposed for the homologous Yb3+−substituted protein from carp. Modest discrepancies between some calculated and experimental shift values in the present system were found to be due mainly to structural differences between the present protein and the homologous protein whose x‐ray structure was used as model and, to a lesser extent, to indetermination in the diamagnetic shift values. The success of the analysis and the univocal solution for the X‐tensor parameters under these conditions show that the above procedure is robust enough to permit both signal assignment and X‐tensor determination even when the structural data are only a rough approximation of the actual structure. These findings may open the way to the development of a systematic use of pseudo‐contact shifts as constraints for MD refinement of solution structures of paramagnetic metalloproteins.
Complete assignment of 1H and 13C NMR spectra of chlorobenzanthrones
Authors: Takekawa Minoru , Aoki Junji , Iwashima Satoshi , Ueda Toyotoshi
Published: May 2005

1H and 13C NMR studies were carried out on benzanthrone and 3‐, 4‐, 6‐, 8‐, 9‐, 10‐ and 11‐chlorobenzanthrone. Complete assignments of proton and carbon resonances were made with the aid of HH‐COSY, NOESY, CH‐COSY and HMBC techniques. Substitution effects of a chlorine atom are not large, but give a systematic change particularly in 13C shift values. The anomalous downfield shift of the H‐1 signal in 11‐chlorobenzanthrone was explained by the electrostatic attraction between the electronegative Cl atom, based on the result of an MNDO‐PM3 calculation.
13C CP/MAS NMR study of a phenyl group rotation in the solid state using T1ρ, lineshape and 2D EXSY measurements
Authors: Riddell Frank G. , Bremner Murray , Strange John H.
Published: May 2005

A combination of solid‐state 13C CP/MAS NMR methods was used to study the rates of rotation of the phenyl group in 3,5‐dimethyl‐1‐phenylhex‐1‐yn‐3‐ol. The methods used were T1ρ measurements, lineshape analysis and 2D exchange spectroscopy over the temperature range 219–284 K. The rates of rotation obtained from the lineshape and 2D EXSY methods give an energy of activation of 58.6 ± 3.0 kJ mol−1. In good agreement with this, the T1ρ measurements give an activation energy for the rotation of 58.7 ± 3.6 kJ mol−1. The two sets of data are shown to be compatible, within experimental error, with a calculated value for the dipolar carbon–hydrogen interaction (B) from an assumed molecular geometry.
1H, 19F and 13C NMR spectral data of fifteen gyrase inhibitors and some metabolites
Authors: Holzgrabe Ulrike , Branch Sarah K.
Published: May 2005

Analyses of 1H and 13C NMR spectra of 15 gyrase inhibitors were carried out using mainly the hydrogen—fluorine and the carbon‐fluorine coupling constants. 19F NMR chemical shifts were obtained for pefloxacin and its metabolites.
1H NMR study of the diastereomeric forms of the protease inhibitor antipain
Authors: Hoebeke Johan , Busatto‐Samsoen Catherine , Davoust Daniel , Lebrun Evelyne
Published: May 2005

Antipain [(1‐carboxy‐2‐phenylethyl)carbamoyl‐L‐arginyl‐L‐valyl‐DL‐arginal] is a potent inhibitor of papain and related proteases. The assignment of 1H NMR signals of the interconverting forms in equilibrium in aqueous solution at pH 5.8 were investigated using two‐dimensional DQF‐COSY, DOUBLE‐RELAYED‐COSY, HOHAHA and ROESY nuclear magnetic resonance techniques. The assignments of protons of several forms in equilibrium of the D‐ and L‐arginal antipain isomers were determined in aqueous solution at 300 K, and their corresponding stereochemistry is tentatively proposed. Addition of equimolar amounts of papain resulted in spectral changes and chemical shifts which are compatible with enzyme‐L‐carbinolamine interactions.
Substituent effects and stereochemistry in 125Te NMR spectroscopy. Diorganyltellurium dihalides and some tellurides and ditellurides
Authors: Duddeck Helmut , Biallaβ Armin
Published: May 2005

125Te, 19F and 13C NMR data for 33 compounds containing tellurium substituents are presented. The 125Te chemical shifts in (PhTeCl2)R compounds are between δ = 878 and 1023; in corresponding (PhTeF2)R compounds they are 220 to 360 ppm larger. Effects of substituents and conformational interconversions (dynamic 125Te NMR) are discussed. Several diastereomers were identified in (PhTeCl2)R derivatives which are stable at room temperature and differ in the configuration at the tellurium atom (restricted pseudo‐rotation). It is shown that 125Te is a well suited nucleus for chiral recognition.
NMR conformational studies of fenamate non‐steroidal anti‐inflammatory drugs
Authors: Munro Sharon L. A. , Craik David J.
Published: May 2005

1H and 13C NMR spectra of the non‐steroidal anti‐inflammatory drugs mefenamic acid, meclofenamic acid and flufenamic acid were assigned and the solution dynamics and conformations of the compounds were probed by the analysis of NMR chemical shifts, temperature coefficients, 3J(C,H) coupled constants, nuclear Overhauser enhancement (NOE) effects and saturation transfer experiments. At low concentrations the anthranilic acid derivatives (the fenamates) exist as monomer units with intramolecular hydrogen bonding between the amine proton and the carboxylic acid group. At concentrations of 10 mM and above, solution aggregates exist. The intermolecular association does not disrupt the intramolecular NH…OC hydrogen bonding, resulting in a similar conformation for mefenamic and flufenamic acids at both low and high concentrations. Meclofenamic acid has an additional intramolecular hydrogen bond, resulting in a slightly different conformation to the other two fenamates. The results from this conformational study are of potential value in molecular and pharmacophore modelling studies on the bioactive conformations of these drugs.
Characterization of the dibutylstannylene derivative of pyridoxine by proton detected 2D heteronuclear correlation NMR
Authors: Kayser François , Biesemans Monique , Gielen Marcel , Willem Rudolph
Published: May 2005

The 1H and 13C NMR spectra of pyridoxine (vitamin B6) and its dibutylstannylene derivative were assigned from proton detected 1H13C heteronuclear multiple bond correlation (1H13C HMBC) spectra.
Two‐dimensional 13C, 11B correlation spectroscopy
Authors: Fäcke Thomas , Berger Stefan
Published: May 2005

The first examples of two‐dimensional 2D 13C,11B correlation NMR are shown. The advantages and limitations of this new application of heteronuclear COSY type spectra are discussed
Spectral separation of two very closely related organic compounds by 1D TOCSY
Authors: Kanthimathi T. , Moorthy Y. V. S. Narayana , Pillai C. N. , Subramanian S.
Published: May 2005

The use of one‐dimensional total correlation spectroscopy (1D TOCSY) combined with the z‐filtration technique to generate pure phase subspectra of individual isomers from the spectrum of the corresponding mixture without any chemical separation of the mixture is described. A straightforward spectral assignment is achieved for the isomers obtained on lithium aluminium hydride reduction of 2,7‐dioxatetracyclo[3.3.04,9.08,11] undeca‐3,6‐dione (dilactone) by studying the subspectrum of each isomer as a function of the propagation time of magnetization through the network of coupled protons.
1H and 13C NMR structural studies in solution of oxotechnetium(V) complexes with N,N‐bis(2‐mercaptoethyl)‐N′,N′‐diethylethylenediamine and N,N‐bis(2‐mercaptoethyl)‐2‐ethylthioethylamine
Authors: Stassinopoulou C. I. , Pelecanou M. , Mastrostamatis S. , Chiotellis E.
Published: May 2005

The complete assignments of the 1H and 13C resonances of three TcOLX complexes of oxotechnetium(V)‐99 with H2L=N,N‐bis(2‐mercaptoethyl)‐N′,N′‐diethylethylenediamine or N,N‐bis(2‐mercaptoethyl)‐2‐ethylthioethylamine and X=p‐methoxythiophenolate or chloride ions are reported. Chemical shifts are influenced by the proximity of protons and carbons to the coordinated heteroatoms and by their orientation with respect to the TcO core. The NMR spectra at room temperature are the result of motionally averaged conformations.
13C NMR spectroscopy of some 20‐ketopregnanes
Authors: Garcia José Alberto Ruiz , Navarro Fernando A. Verdecia , Castro HermáN T. Vélez
Published: May 2005

The 13C NMR spectra of 21 20‐ketopregnanes were examined and assigned. The substituent effects on the 13C chemical shifts are discussed on the basis of comparisons with published spectra of some closely related compounds.
High resolution 1H NMR studies of cyclic N‐nitrosamines
Authors: Milewska M. J. , Poloński T.
Published: May 2005

Molecular modeling by molecular mechanics (MM2) calculations were used to predict conformational preferences of cyclic N‐nitrosamines. The results were compared with 1H NMR data. The observed geminal coupling constants 2J were considerably stronger for syn than for anti α‐methylene protons and thus appear to be very useful for configurational predictions. The long‐range 4J couplings across the nitrogen atom were observed directly from the 1D spectra.
Empirical group electronegativities for vicinal NMR proton–proton couplings along a CC bond: Solvent effects and reparameterization of the Haasnoot equation
Authors: Altona Cornelis , Francke Robert , de Haan Rudy , Ippel Johannes H. , Daalmans Godefridus J. , Hoekzema Aldert J. A. Westra , van Wijk John
Published: May 2005

Empirical group electronegativities (substituent parameters λi), valid for 3J(HH) in saturated HCCH fragments, were derived from the coupling to methyl in substituted ethanes and isopropyl derivatives according to the equation

In contrast to earlier work, it was found advantageous to differentiate between the λi values of hydrogen acting as substituent in CH3 as compared with H in CH2. Special attention was paid to solvent effects, in particular the influence of D2O, on the vicinal couplings and thus on λi. The previously derived λi values remain valid in all common organic solvents but a special effect of D2O on λ is manifest in cases where the α‐substituent carries one or two non‐conjugated lone pairs of electrons that readily act as hydrogen bond acceptors: Δλ= −0.11 ± 0.03 for NH2, NHR, NR2, OH, OR, R = alkyl. Protonation of NH2 to give NH3+ lowers λi by 0.28 units. The λi values for the nucleic acid bases (Ade, Gua, Ura, Thy, Cyt), as determined from the N‐isopropyl derivatives, are 0.56 ± 0.01 irrespective of the solvent. Secondary amides display similar values. The parameters of the Haasnoot equation, originally derived with the aid of a Pauling‐type electronegativity scale, were reoptimized on the basis of the present λi scale; the previous overall r.m.s. error of 0.48 Hz now drops to 0.36 Hz and separate parameterization of HCCH fragments with different substitution patterns appears to be no longer necessary.
Water exchange on the light lanthanide aqua ions [Pr(H2O)9]3+ and [Nd(H2O)9]3 +: A variable temperature and magnetic field 17O NMR study
Authors: Powell D. Hugh , Merbach André E.
Published: May 2005

17O NMR relaxation rate measurements were made on aqueous perchlorate solutions of the light lanthanide ions Nd3+ and Pr3+, with the aim of measuring the kinetics of water exchange on these ennea aqua ions. Variable‐temperature results at three magnetic fields show that the ‘kinetic’ effect is not the only contribution to the difference between the transverse and longitudinal relaxation rates. The results at high magnetic field allow lower limits, k ⩾ 5 × 108 S−1 and k ⩾ 4 × 108 s−1, to be determined for water exchange rates at 298.15 K on [Nd(H2O)9]3+ and [Pr(H2O)9]3+, respectively. These limits are consistent with our current understanding of water exchange on the lanthanide aqua ions, based on the change of relative stability of the ennea and octa aqua ions across the series.
31P and 77Se CP/MAS and 31P CPECHO solid‐state NMR studies of bis(dineopentoxy‐thiophosphoryl) diselenide and disulphide
Authors: Potrzebowski Marek J.
Published: May 2005

The principal elements δii of 31P and 77Se chemical shift tensors for the structural analogues bis(dineopentoxythiophosphoryl) diselenide (1) and bis(dineopentoxythiophosphoryl) disulphide (2) were calculated from spinning sideband intensities employing the MASNMR program. From analysis of the 31P NMR data it was concluded that replacement of sulphur by selenium has little influence on shielding parameters, anisotropy Δδ and span Ω. The asymmetry η and skew k are very similar if the geometry of SPXXPS unit (X = S, Se) is not changed. 77Se NMR data are discussed in terms of PSeSeP unit geometry. The static spectra were recorded employing the CPECHO pulse sequence. It was found that this technique is useful both for the lineshape analysis and the calculation of the second moment. The experimental values of M2d are 0.387 kHz2 for diselenide 1 and 0.495 kHz2 for disulphide 2. These values are consistent with those calculated from the van Vleck equation for polycrystalline materials.
Oxidation of 4‐methylcatechol by dioxygen studied by ESR spectroscopy. The different regioselectivity of OH− and MeO− nucleophilic attack and kinetic deuterium isotope effects
Authors: Davies Martin S. , Mile Brynmor , Rowlands Christopher C. , Barratt Martin D.
Published: May 2005

The oxidation of 4‐methylcatechol by dioxygen and the subsequent reactions of the two nucleophiles OH− and MeO− with the oxidation products were studied by electron spin resonance (ESR) spectroscopy. These reactions are models for those of skin proteins with substituted 1,2‐dihydroxybenzenes (catechols) which produce the severe allergic contact dermatitis associated with plants such as poison ivy, poison oakd and the Japanese lac tree. The rates of formation of the primary and secondary semiquinone radical anions show a large kinetic deuterium isotope effect (ca 10) at 20°C, which is ascribed to a slow deprotonation of the hydrogen bridged 4‐methylcatechol monoanion. There is a marked difference in regioselectivity for OH− and MeO− substitution of the 4‐methylcatechol monoanione; OH− reacts exclusively at the 3‐position whereas MeO− attacks at the 5‐position. This dissimilarity between two normally similar nucleophiles is also ascribed to the occurrence of hydrogen bridging between the substituting OH− at the 3‐position and the adjacent quinone oxygen at the 2‐position. The expected attack at the more electropositive 5‐position occurs with MeO− because no such hydrogen bonding can occur. Disubstitution occurs for OH− but not for MeO−, probably reflecting the greater nucleophilicity of the former.
ID and 2D 1H NMR studies of iron(III) complexes on geoporphyrins of the deoxophylloerythroetio structural type derived from oil shale
Authors: Wototwiec Stanisaw , Latos‐Gražyński Lechostaw , Serebrennikova Olga V. , Czechowski Franciszek
Published: May 2005

One‐ and two‐dimensional 1H NMR studies of low‐spin iron(III) geoporphyrins derived from the deoxophylloery‐throetioporphyrin series (the oil shale source) resulted in an unambiguous assignment of all resonances. Deoxophylloerythroetioporphyrin (DPEP) and its 17‐desethyl homologue were isolated from dictyonema shale as vanadyl complexes. They were demetallated and subsequently converted into iron(III) porphyrins under mild conditions. The 17‐propionic methyl ester analogue, i.e. deoxophylloerythrin methyl ester, was synthesized for comparative studies. A spectroscopic probe to identify iron(III) isocyclic porphyrins was established. The five‐membered isocyclic ring induced considerable asymmetry in the spin density distribution at the 3eπ bonding orbitals, placing the unpaired electron on the dxz orbital located along the N‐21—N–23 axis. The temperature dependence of the hyperfine shift is consistent with the thermal equilibrium between two non‐degenerated electronic states (dxz)2(dyz)1↔(dxz)1(dyz)2. The new structural factor generating the asymmetric spin density distribution in low‐spin iron(III) porphyrin complex was determined. The hyperfine shift pattern of high‐spin iron(III) isocyclic geoporphyrins provided useful probes for their detection in iron geoporphyrin mixtures by 1H NMR prior to their separation. Valuable information is derived from the number of observed signals of meso‐protons and characteristic, extremely downfield resonances of isocyclic ring hydrogens. Both features may be useful for the spectral identification of iron(III) porphyrins of the DPEP series from geological materials of relatively low purity.
MBOHO calculations of carbon‐nitrogen nuclear spin‐spin coupling constants
Authors: Hu Zhen‐Min , Zhan Chang‐Guo
Published: May 2005

The novel generalized correlation of the nuclear spin‐spin coupling constants with the atomic hybrids and net charges was employed to give two new relationships for calculating the carbon‐nitrogen coupling constants by use of the maximum bond order hybrid orbital (MBOHO) procedure together with the simple CNDO/2 calculation. The calculated coupling constants of carbon‐nitrogen single and triple bonds are all in good agreement with the experimental data, which shows that the new relationships obtained are satisfactory for calculation of carbonnitrogen coupling constants.
Conformations and conformational processes of pelargolactam
Authors: Borgen Gerd , Dale Johannes , Rise Frode , Gundersen Lise‐Lotte
Published: May 2005

Pelargolactam (1‐azacyclodecan‐2‐one) was studied by 1H and 13C NMR spectroscopy in solution between 25 and −145°C. Equilibrium solutions of pelargolactam at 25°C consist mainly of the trans isomer together with 5–10% of the cis isomer. Solid pelargolactam consists of a mixture of cis and trans isomers, the cis form dissolving more rapidly than the trans form at −95°C. At temperatures above 90°C the 13C NMR resonances for the cis and trans amides coalesce to one averaged set. A conformational process with a coalescence temperature of −30 to −50°C and a free energy of activation of ΔG≠ = 46 kJ mol−1 observed in the 1H spectrum of the trans isomer is interpreted as geminal exchange in the methylene groups. A lower barrier process was also observed, with a coalescence temperature of ca −115°C and ΔG≠ = 32 kJ mol−1. Only the latter process was observed in the 13C spectrum, and below −120°C all 13C lines split in two in the proportion 1:2. This process is interpreted as the interconversion between two trans conformers. Four conformational candidates were considered and their relative energies calculated by molecular mechanics.
Dynamic behaviour of fluoro‐substituted 1,8‐diarylnaphthalenes: A 19F,19F and 1,1H 2D EXSY NMR and AM1 computational study
Authors: Annunziata Rita , Ponzini Francesco , Raimondi Laura
Published: May 2005

Interactions between polar groups and π systems were studied for stacked aryls in 1‐fluorophenyl‐8‐arylnaphthalenes, in which an ‘electron‐rich’ aryl ring is forced in a stacked geometry with an ‘electron‐poor’ fluorophenyl ring; the rotation process was examined using different NMR techniques (lineshape analysis, 2D EXSY). The ΔG≠S obtained when considering 1H and 19F nuclei were perfectly comparable. Semi‐empirical calculations (AM1) were performed to evaluate ΔG≠S for the rotation process, and the results are compared with the experimental NMR values.
Selective homonuclear Hartmann—Hahn transfer using two coherent r.f. channels: Application to relaxation time measurements
Authors: Yang Daiwen , Nagayama Kuniaki
Published: May 2005

A method to implement selective homonuclear Hartmann—Hahn transfer by using two coherent r.f. channels has been developed. This new method does not require complex pulse sequences. When this approach is combined with selective relaxation measurements, the proton relaxation times (T1, T2 and T1p) of individual protons can be determined even when the signals are hidden under other resonances. An example of the use of this method for the analysis of ribonuclease H is given.
125Te, 13C and 1H NMR characterization of a series of diorganotellurium(II) and tetraorganotellurium(IV) compounds
Authors: Gedridge Robert W. , Higa Kelvin T. , Nissan Robin A.
Published: May 2005

125Te, 13C and 1H NMR studies on a series of symmetric diorganotellurium(II) [R2 Te, where R = Me, Et, n‐Bu, CH2SiMe3, allyl, vinyl, CCMe, CCEt, CC(n‐Pr), CC(t‐Bu), CC(SiMe3) and CCPh], unsymmetric diorganotellurium(II) (RTeR′) (where R = allyl, R′ = Me, Et, i‐Pr, t‐Bu; R = Me and R′ = benzyl), symmetric bis(alkyltelluro)ethyne (RTeC=CTeR, where R = Me and Et) and symmetric tetraorganotellurium(IV) (R4Te, where R = Me, n‐Bu, CH2SiMe3 and vinyl) compounds are presented. 125Te was acquired under 1H‐decoupled and 1H‐coupled conditions. Whereas the 1H‐decoupled 125Te NMR spectra are extremely useful in identifying low levels of tellurium containing impurities, the 1H‐coupled 125Te experiments allow for structure determination and identification of long‐ and short‐range coupling pathways. 1H and 13C NMR were used to assess purity in terms of organic materials which can include solvents, decomposition byproducts and unwanted organometallic compounds from side reactions occurring during synthesis. 125Te satellites are observed in the 1H and 13C NMR spectra and are useful in resonance assignments and in identification of long‐ and short‐range coupling pathways. The effects of substituents on chemical shifts and coupling constants are discussed.
Use of shaped pulses for semi‐selective excitation of imino 1H resonances in duplex DNA and RNA
Authors: Gmeiner William H. , Sahasrabudhe Parag , Pon Richard T.
Published: May 2005

The application of shaped pulses, e.g. TOPHAT and hyperbolic secant, for the semi‐selective excitation of the imino 1H resonances of duplex DNA and RNA in aqueous solution is explored. The excitation profiles for the shaped pulses are calibrated on a sample containing a mixture of A:U base pairs in deuteriochloroform solution. The data obtained by performing a semi‐selective inversion‐recovery pulse sequence using a TOPHAT waveform for the 90° pulse and a hyperbolic secant waveform for the 180° pulse are fitted well by a single exponential function, are independent of transmitter offset over a 1 kHz bandwidth and are in good agreement with the value obtained with hard rectangular pulses. This approach for measuring T1 values was applied to a 2 mM sample of a self‐complementary oligoribonucleotide containing the nucleoside analogue 5‐fluorouridine in 90% H2O. The T1, values were calculated as a function of Tris concentration, a catalyst added to promote imino hydrogen exchange. The T1, values were obtained by good fits of single exponential functions to the inversion‐recovery data. The T1, values depend on the concentration of added Tris. Shaped pulses provide a convenient alternative to long rectangular pulses and hard pulse trains for the semi‐selective excitation of imino 1H resonances.
Carbon‐13 NMR study of the B9(Asp) mutant of human insulin: Sequence‐specific carbon‐13 assignments and structural information
Authors: Kristensen Søren M. , Led Jens J.
Published: May 2005

The resonances of the proton‐bearing 13C nuclei at natural abundance were assigned for the solution dimer of the B9(Asp) mutant of human insulin. The assignments are based on a combination of direct and relayed 1H13C correlated spectra, i.e. SQC, SQC‐HOHAHA and HMQC‐COSY, and the previously assigned 1H spectrum. The study proves valuable not only because of the 13C assignments, but also because it provides a verification, a completion and a few corrections of the previous 1H assignments. Finally, the obtained 13C assignments support the previously reported correlation between the secondary 13Cα and 13Cβ chemical shifts and the secondary structure of proteins.
Structural elucidation of rokitamycin, midecamycin and erythromycin metabolites formed by pathogenic Nocardia
Authors: Morisaki Naoko , Iwasaki Shigeo , Furihata Kazuo , Yazawa Katsukiyo , Mikami Yuzuru
Published: May 2005

Pathogenic Nocardia spp. converted rokitamycin, midecamycin and erythromycin into inactive metabolites, the structures of which were determined from NMR and mass spectral data. Depending on the species of Nocardia, these macrolides underwent phosphorylation at 2′‐OH, hydrolysis of the 4″‐O‐acyl group, glycosylation at 2′‐OH and/or reduction of the 18‐formyl group. Full 1H and 13C assignments are presented and some solvent effects are described.
Carbon‐13 NMR investigations of three fluorinated steroids
Authors: Carss Steven A. , Harris Robin K. , Fletton Richard A.
Published: May 2005

High‐resolution carbon‐13 NMR spectra were obtained for three solid fluorinated steroids. Assignments were carried out using several approaches, including two‐dimensional spectra of the compounds in solution. Solid‐state and solution‐state chemical shifts are compared. Signals from one of the fluorine‐containing carbons in each compound show the effect of interplay between shielding, dipolar and indirect scalar (J) coupling tensors. One sample is found to be a mixture of two polymorphic forms.
Hyperfine couplings of N‐alkoxy‐N‐polynitrophenylaminyl radicals determined by ENDOR and TRIPLE resonance spectroscopy
Authors: Sumi Teemu J. , Stanciuc Gabriela , Kasa Seppo , Joela Heikki
Published: May 2005

Lead tetraacetate one‐electron oxidation of nine different N‐alkoxy‐2,6‐dinitroanilines substituted with trifluoromethyl, methyl and nitro groups in position 4 yielded aminyl radicals for which hyperfine couplings were measured by ENDOR and TRIPLE resonance spectroscopy. The optimum temperature range for proton ENDOR and general TRIPLE resonance measurements of aminyl radicals was 210–250 K and for nitrogen ENDOR 260 K in toluene. Further lowering for the temperature rapidly decreased the EPR intensity. The concentration of the sample and the amount of oxidant were optimized for obtaining ENDOR spectra. The relative signs of the hyperfine couplings of nitrogens, fluorines and protons were determined in the basis of general TRIPLE resonance experiments. The oxidation of N‐methoxy‐N‐2,6‐dinitrophenylamine and N‐ethoxy‐N‐2,6‐dinitrophenylamine with lead tetraacetate produced first the aminyl radical of the respective 2,6‐dinitro compound at low temperature (below 260 K) and very soon afterwards the aminyl radical of the respective 2,4,6‐trinitro compound, by a route in which hydrogen has to be removed from the system. Rotational correlation times were estimated for N‐methoxy‐and N‐ethoxy‐N‐2,4,6‐trinitrophenylaminyl radicals. Nitroxyl radicals were detected only under conditions where oxygen was present in the solvent.
Multiple‐field carbon‐13 NMR relaxation investigation on melezitose
Authors: Mäler Lena , Lang Jan , Widmalm Göran , Kowalewski Jozef
Published: May 2005

Multiple‐field carbon‐13 relaxation data are reported for melezitose, a trisaccharide consisting of two α‐linked glucose residues attached at positions 2 and 3 to a β‐linked fructofuranose residue. Values for T1 and NOE were measured at 4.7, 9.4, 11.8 and 14.1 T and transverse relaxation rates at 4.7 and 9.4 T. The measurements were carried out by means of standard techniques and by polarization transfer (INEPT) enhanced methods. The relaxation data were interpreted with the Lipari‐Szabo ‘model‐free’ approach. It was found that the relaxation data of the ring carbons can be described by the use of the truncated form of the Lipari‐Szabo equation. The global correlation time and order parameter for melizitose were calculated at two temperatures. For the exocyclic CH2 carbons, fits to obtain a local correlation time are reported. For three out of the four exocyclic carbons, a fast correlation time is obtained and their order parameter is lower than that for the ring carbons. The fructose C‐1 exocyclic carbon does not seem to display the same local motions as the other CH2 groups, and a higher order parameter is obtained indicating hindered local motion of that CH2 group.
Dynamic NMR study of the factors governing nitroso group rotation in p‐nitrosoanilines in the solution and solid states
Authors: Fletcher Daniel A. , Gowenlock Brian G. , Orrell Keith G. , Šik Vladimir
Published: May 2005

The energy barriers associated with NO rotation in a series of p‐nitrosoanilines were measured by the total bandshape NMR method. Energies [ΔG‡ (298.15 K)] are in the range 38–57 kJ mol−1, the magnitudes being lowered appreciably by the presence of methyl substituents flanking the nitroso group on either side. In the case of p‐nitroso‐N,N‐dimethylaniline, NO rotation has been shown to occur also in the solid state with a slightly higher energy barrier to that in the dissolved state. For p‐nitroso‐N‐methylaniline, a combination of 2D‐exchange spectroscopy (EXSY) and 1D‐bandshape analysis NMR methods enabled the barriers to NO rotation and NHMe rotation to be measured separately.
Deuterium isotope effects on 13C chemical shifts of intramolecularly hydrogen‐bonded olefins
Authors: Hansen P. E. , Bolvig S. , Duus F. , Petrova M. V. , Kawecki R. , Krajewski R. , Kozerski L.
Published: May 2005

A series of intramolecularly hydrogen‐bonded enamines, enols and enethiols with ester carbonylic, ketonic carbonylic, thioester carbonylic, nitro and sulphoxide acceptors were investigated to obtain 13C chemical shifts and deuterium isotope effects. Results from 33 new compounds and six remeasurements are compared with already existing data. An important aim was to show that isotope effects on chemical shifts are useful descriptors of hydrogen‐bonded systems and not only a parameter proportional to the 13C chemical shifts. Substituent effects were studied and the donors and acceptors ranked according to their abilities to support hydrogen bonding. Steric effects strengthen the hydrogen bonding in cyclic five‐membered β‐diketones. Plots of two‐bond [2ΔC(OD)] vs. four‐bond isotope effects [4ΔC(OD)] show that 4ΔC(OD) increases with increasing hydrogen bond strength and that large deviations from this relationship can be an indicator of tautomerism.
Substituent shielding parameters of fluorine‐19 NMR on polyfluoroaromatic compounds dissolved in dimethyl sulphoxide‐d6
Authors: Ando Shinji , Matsuura Tohru
Published: May 2005

High resolution fluorine‐19 NMR spectra of polyfluoroaromatic compounds dissolved in deuterated dimethyl sulphoxide were measured and substituent shielding parameters were derived. These parameters were compared with the values observed in deuterated chloroform solutions and used to identify fluoroaromatic compounds related to perfluorinated polyimides and poly(amic acids)s. Average differences of Δδ between the solvents are 1.1, 1.0 and 2.1 ppm for o‐, m‐ and p‐fluorines of monosubstituted pentafluorobenzenes, respectively. The significant difference for p‐fluorine of NH2 is important in identifying perfluorinated diamines because they are source materials for perfluorinated polyimides. Substituent shielding parameters for meta and para substitution increase as the respective Hammett σ constants increase, which indicates that fluorine‐19 NMR chemical shift is primarily determined by electron density.
Complete assignment of the aliphatic chains in dimers, trimers and polymer of 3‐hexylthiophene through 2D‐NMR spectroscopy
Authors: Ferrari M. , Mucci A. , Schenetti L. , Malmusi L.
Published: May 2005

The 1H and 13C signals of the hexyl chains of the title compounds were fully assigned. The regiochemical features of the aliphatic region of proton and carbon spectra were analysed in dimers and trimers. Dimers and trimers proved to be reliable model compounds in the regiochemical assignment of poly(3‐hexylthiophene) even when the aliphatic region of proton and carbon spectra was involved. The chemical shifts of the protons of CH2(α)s and of the hexyl chain as a whole and those of the first three aliphatic carbons appear to be the most significant.