bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of 1H NMR selective and biselective relaxation times. III—conformational analysis of quinidine in solution
Authors: Sai Torei , Takao Narao , Sugiura Makiko
Published: May 2005

A relaxation method was applied to quinidine (1) where cross‐relaxations (σij) were obtained by 1H selective and biselective T1 measurements and correlation times for molecular reorientation (τc) were evaluated from the frequency dependence of the non‐selective T1. The interproton distances (rij) were estimated using these σij and τc values, and the conformation of 1 was determined by comparing the estimated rij values with those calculated from the molecular model. The resulting proposed conformation had the following dihedral angles: ∠ C‐11C‐10C‐3–C‐4 = 150°, ∠ C‐4′C‐9C‐8C‐7 = 50° and ∠ C‐9′C‐4′C‐9C‐8 = 70°. The conformation of the side‐chain (∠ C‐11C‐10C‐3C‐4) is different from the results for the crystal by x‐ray analyses.
Electron spin resonance study of spin‐trapped radicals from gamma irradiation of fructans
Authors: Triolet J. , Raffi J. , Agnel J‐P. , Battesti C. , Thiery C. , Vincent P.
Published: May 2005

Fructans (GFn) are important constituents of some plants. A study of the radiolysis of fructans in solution was performed using the spin‐trapping method. Electron spin resonance, combined with high‐performance liquid chromatography and followed by spectral analysis with the simulation program Voyons, showed three main trapped radical species in fructans GF2 to GF4. Similar trapped radical species have already been identified in irradiated sucrose using the same experimental methods, and their structures have been established. A study of the individual contribution of each radical to the global spectra of fructans confirms previous results on the localization of the unpaired electron; the broadening of the radical line widths with the increase of the fructan chain length also shows that radical formation occurs without depolymerization of the parent oligomer. Sucrose therefore provides a good model for a radiolysis study of fructans, at least for low n values.
Hoechst 33258 and its complex with the oligonucleotide d(CGCGAATTCGCG) 2: 1H NMR assignments and dynamics
Authors: Parkinson John A. , Barber Jill , Buckingham Beverley A. , Douglas Kenneth T. , Morris Gareth A.
Published: May 2005

The 1H NMR assignments of the 1:1 complex between d(CGCGAATTCGCG)2 and the minor‐groove Hoechst 33258 ligand and the activation energy for the dissociation of the complex have been determined.
NMR of terminal oxygen. 9—17O NMR of the PO ‘double bond’: Phosphine oxides, phosphinates, phosphonates, acylphosphonates and related compounds
Authors: Dahn Hans , Van Toan Vien , Ung‐Truong My‐Ngoc
Published: May 2005

The 17O NMR spectra of phosphorus‐bound oxygen atoms in secondary phosphine oxides (R2HPO, 1), alkyl phosphinates [RHP(O)OR′, 2 and R2P(O)OR′, 3], dialkyl phosphonates [RP(O)(OR′)2, 4], dialkyl acylphosphonates [RCOP(O)(OR′)2, 5] and some related compounds were measured. The signals of terminal O appear at high field, only slightly downfield from those of bridge O. Compared with carbonyl O, terminal PO shows lower sensitivity to structural variations, notably to geminal groups (with the exception of Cl and Br), and a very low sensitivity to arene ring substituents. The difference is discussed in terms of π‐bond character; the carbonyl oxygen of RCOP(O)OR′)2 is sensitive to variations in structure.
Carbon‐13 NMR spectra of 1‐substituted prop‐2‐ynes and 1,4‐bis‐derivatives of but‐2‐yne
Authors: Banerji Avijit , Saha (Née Sengupta) Piyali , Majumdar Krishna C. , Choudhury Prabir K.
Published: May 2005

13C NMR data for several 1‐substituted prop‐2‐ynes and 1,4‐bis derivatives of but‐2‐yne are reported with full assignments. Substituent effects of —X—aryl groups (X = O, S, NMe, SO2) at the propargylic position on the chemical shifts of the acetylenic carbons were determined.
A pulse sequence for T1 measurement by inversion–recovery in the presence of acoustic ringing
Authors: Bagno Alessandro
Published: May 2005

A pulse sequence is presented which allows one to perform an inversion–recovery experiment for T1 determination on quadrupolar nuclei in the presence of acoustic ringing. The sequence is based on a modification of the reference baseline subtraction −90° pulse sequence. Some examples of 17O and 14N and relaxation are presented, including spectra with overlapping peaks from which T1 values cannot be simply extracted from line widths.
Proton NMR studies of syn‐ and anti‐tricyclo [5.1.0.03,5]octanes and their dichloromethyl derivatives
Authors: Xu Linxiao , Brinker Udo H. , Smith William B.
Published: May 2005

The carbon and proton NMR spectra of syn‐ and anti‐tricyclo[5.1.0.03,5]octanes and their dichlorocarbene CH bond insertion products were determined by conventional 1D and 2D methods. Partially relaxed proton spectroscopy was carried out in some instances to aid in the separation of badly overlapped multiplets. A detailed analysis of the spectra was carried out with the aid of a new equation relating both the torsion angles and the CCH angles to the vicinal proton coupling constants. These values were combined with molecular modeling to draw conclusions regarding the conformational preferences for these molecules.
Application of the topological analysis of 13C chemical shifts to the elucidation of the electronic and steric features of polyoxygenated benzenes with different substituents. Simulation of the 13C NMR spectra
Authors: Dostovalova Valentina I. , Fedorov Lev A.
Published: May 2005

A novel topological method was developed for the analysis of 13C chemical shifts in polyoxygenated benzenes, C6H6‐n(OY)n, where Y = H, Me and Ph. Carbon chemical shifts were described with individual and collective increments for oxygen itself and for oxygen substituents. The oxygens themselves have only one two‐particle increment (1,4‐dioxy interaction) in addition to the individual positional increments (ipso, ortho, meta, para). The 1,2‐dioxy interaction exerts no influence on any ring carbon chemical shifts, and thus the 1,2‐di‐ortho‐subgraphs were connected with the steric properties of the oxygen substituents. The results are in agreement with molecular mechanics calculations and NMR data in the solid state. Hydrogen bonding with specific solvents deshielded the ipso and ortho carbons by about 1.5 ppm. This predictive set completely described the 13C NMR spectra of all the polyoxygenated benzenes studied within the experimental accuracy (RRMS = 0.6 ppm). The incremental scheme will be predictive and useful for PC programming.
1H and 13C NMR studies on the antidepressant drug tianeptine
Authors: Platzer N. , Bouchet J. P. , Malen C. , Labrid C. , Mocaer E.
Published: May 2005

The conformational behaviour of 7‐[(3‐chloro‐6,11‐dihydro‐6‐methyldibenzo[c, f][1,2]thiazepin‐11‐yl)amino] heptanoic acid 5,5 dioxide (tianeptine), a new antidepressant drug, was studied by means of 1H and 13C NMR. The ring skeleton exhibits two distinct conformations at low temperature. The conformational exchange is still restricted at room temperature, particularly in the solvents D2O and CDCl3, where significant aggregation of the molecules occurs. The side‐chain seems to adopt a preferential conformation where it is bent over the unsubstituted aromatic ring. This conformational preference in the biologically active structure might be related to the observed loss of activity when substituents are introduced on the aromatic rings.
Use of two‐dimensional NMR and molecular modelling for the structure determination of novel cyclophosphamide derivatives: Diastereomers of 1‐aza‐2‐bis(2‐chloroethyl)‐ amino‐3‐oxa‐2‐oxo‐2‐phospha‐7‐thia‐bicyclo‐ [4.4.0]decane and [4.3.0]nonane
Authors: Schmidt Brigitte F. , Tang Wei‐Ci , Eisenbrand Gerhard , Von Der Lieth Claus‐Wilhelm , Hull William E.
Published: May 2005

High‐field NMR studies at 11.7 T of newly synthesized diastereomeric 1‐aza‐2‐bis(2‐chloroethyl)amino‐3‐oxa‐2‐ oxo‐2‐phospha‐7‐thia‐bicyclo[4.4.0]decanes (4, 5) and the corresponding [4.3.0]nonanes (6, 7) were carried out by employing a combination of one‐ and two‐dimensional homo‐ and heteronuclear methods. Unambiguous 31P, 1H and 13C chemical shift assignments for these bicyclic derivatives of cyclophosphamide were obtained, and the spin–spin couplings involving 1H, 13C and 31P were analysed in detail to determine the stereochemistry. Particularly useful were 1H J‐resolved experiments, which separated phosphorus–proton couplings from proton–proton couplings, and 1H13C shift‐correlation experiments, which resolved the carbon–phosphorus couplings and provided information on the relative signs of J(P, H) and J(P,C). In addition, extensive molecular modelling calculations using various force‐field (ALCHEMY, DISCOVER) and molecular orbital methods (MNDO, AM1, PM3) were carried out, and improved parameters for cyclophosphamides were developed for ALCHEMY. The diastereomeric pairs 4, 5 and 6, 7 differ in the axial vs. equatorial orientation of the sulphur substituent on the oxazaphosphorinane ring, which is itself exclusively in a chair conformation with axial PO for all substances.
Structural studies on clarithromycin (6‐O‐methylerythromycin A): Assignments of the 1H and 13C NMR spectra in organic and aqueous solutions
Authors: Awan Abida , Barber Jill , Brennan Richard J. , Parkinson John A.
Published: May 2005

Full assignments of the 1H and 13C NMR spectra of clarithromycin (6‐O‐methylerythromycin A) in CDCl3 and buffered D2O were carried out. In contrast to erythromycin A, clarithromycin exists as a single isomer, the 9‐ketone, in aqueous solution.
NMR study of complex triquinanes and bulleranes derived from photoisomerization of aryl‐substituted norbornan‐2‐ones
Authors: De Keukeleire Denis , He Shu‐Lin , De Bruyn André
Published: May 2005

Analysis of 1H and 13C NMR data by 2D NMR techniques was used for the structural identification of triquinanes and bulleranes considered as precursors of complex natural products such as (+)‐cerapicol. The polycyclic molecules are derived from a tandem Norrish Type I photoreaction and intramolecular arene–alkene meta photocycloaddition of aryl‐substituted norbornan‐2‐ones.
Strategies for the phase editing of relayed responses in 2D HMQC‐TOCSY spectra
Authors: Crouch Ronald C. , Spitzer Timothy D. , Martin Gary E.
Published: May 2005

An NMR technique for the determination of proton vicinal couplings relayed at the carbon chemical shift is presented. With this technique, which is an extension of DEPT‐HMQC‐TOCSY, it is possible to generate phaseedited 2D NMR data in which the 1H13C relayed responses differ in phase as a function of the proton multiplicity of the carbon from whose proton(s) the response originates. A simple pulse scheme is presented to allow further simplification of the spectrum by eliminating the direct 1H13C correlations. Thus, responses arising from methines or methyls will be of opposite phase from responses originating from methylenes; direct correlations are eliminated to minimize congestion. An example is presented with the cardiac drug digoxin.
Conformation and dynamics of glycoprotein oligosaccharides as studied by 1H NMR spectroscopy
Authors: Van Halbeek Herman , Poppe Leszek
Published: May 2005

Most complex carbohydrates can take a large number of shapes in solution. Determining the favored solution conformations and characterizing the internal motions of complex carbohydrates is essential to understanding their biological function, particularly their interactions with proteins. This paper describes an NMR spectroscopic study of the internal dynamics of a mucin glycoprotein‐derived di‐antennary octasaccharide,

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1H NMR spectra of this oligosaccharide in D2O and H2O were completely assigned by the combination of TOCSY, ROESY and triple‐quantum spectroscopy experiments. Specific {1H,1H} cross‐relaxation rates and 1H longitudinal relaxation times were measured at various temperatures and magnetic field strengths. The data show that the NeuAcα(2 → 3)Galβ arm of the octasaccharide can adopt two conformations around the (2 → 3)‐bond. Most important, the NeuAcα(2 → 3)Galβ and Galα(1 → 4)Galβ linkages both have pronounced conformational flexibility; their rearrangements are fast on the time scale of the overall molecular tumbling.
Sign determination of coupling constants nJ(M, 13C) (n = 1, 2, 3), nJ(M, 1H)(n = 3, 4), for M = 29Si, 119Sn, 207Pb, 195Pt and 199Hg and 3J(195Pt, C  CM) (M = 29Si, 119Sn and 207Pb) in representative alkynyl‐silicon, ‐tin, ‐lead, ‐platinum and ‐mercury compounds
Authors: Wrackmeyer Bernd , von Locquenghien Klaus Horchler , Kupče Ēriks , Sebald Angelika
Published: May 2005

Heteronuclear double and triple resonance experiments of the type 1H{X} (X = 31P, 199Hg, 207Pb), 13C{1H, 31P}, 29Si{1H, 31P}, 207Pb{1H, 31P}, pseudo‐triple resonance experiments [e.g. 13C{1H(199Hg)}, 207Pb{1H(13C)}], together with two‐dimensional (2D) 13C/1H heteronuclear shift correlations, were carried out to determine the signs of various coupling constants [1J(M13C), 2J(MC13C), 3J(MCC13C), 3J(MCC1H), 4J(MCCC1H); M = 29Si, 119Sn, 207Pb, 195Pt, 199Hg; 3J(195PtCCM); M = 29Si, 119Sn, 207Pb] in 17 alkynyl metal compounds. In all compounds studied, the sign of the reduced coupling constants nK(M13C) (n = 1, 2, 3) is positive. The same is true for 3K(MCC1H) and 3K(195PtCCM) (M = 29Si, 119Sn, 207Pb), whereas a negative sign was found for all 4K(MCCC1H) values.
183W–1H long‐range shift correlation and 1H NOESY studies on tungsten(II) hydrido–pyrazolylborate complexes
Authors: Templeton Joseph L. , Philipp Craig C. , Pregosin Paul S. , Rüegger Heinz
Published: May 2005

183W NMR spectra for several tungsten carbonyl complexes were recorded using heteronuclear multiple‐quantum spectroscopy. The measurements involved the use of both one‐bond and long‐range coupling constants, with the latter technique demonstrating a general approach to obtaining 183W spectra in Tp′ [Tp′ = tris(3,5‐dimethylpyrazolyl)borohydride] and Cp tungsten compounds. Differences in the 183W chemical shifts between the Tp′ and Cp complexes are explained in terms of σ‐donor and π‐acceptor capabilities of the ligands. It is suggested that the very small 1J(183W,1H) value of 7 Hz in WH(Tp′)(CO)3 arises from an interaction of an H+ with a [W(Tp′)(CO)3]− orbital with a relatively large d‐component. For WH(Tp′)(CO)(PHCCMe) (3), the very lowfield hydride chemical shift, δ = 10.8, is suggested to arise, in part, from anisotropic effects. 1H NOESY measurements on 3 show that the hydride lies in a deshielding region with respect to both the acetylene and two pyrazolylborate rings, the acetylene is bent such that the CH3 and Ph groups move toward one another and there is a second isomer of 3, presumably related to the geometry of the coordinated acetylene with respect to the WCO bond.
13C NMR assignments of brassinosteroids by two‐dimensional techniques
Authors: Ando Tetsu , Aburatani Masakazu , Koseki Nozomu , Asakawa Seiichi , Mouri Takehito , Abe Hiroshi
Published: May 2005

1H NMR spectra of eight naturally occurring brassinosteroids, plant hormones with a steroid skeleton, and five synthetic analogues were analysed by COSY and long‐range COSY measurements. Based on the 1H resonances, the 13C signals were assigned by a combination of CH COSY and long‐range CH COSY spectra detecting 13C nuclei, or by HMQC and HMBC spectra detecting 1H nuclei. Although the steroids showed complex 1H signals around 1–2 ppm, the resonances for the two angular methyl groups and the other methyl groups in the side‐chain could be assigned unambiguously and used as a reference point for the other assignments. Strong correlation peaks between the methyl protons and carbons connected with the protons through two or three bonds were observed in the long‐range CH COSY or the HMBC spectra. These spectra provide valuable information for assigning the 13C NMR resonances of this class of compounds.
13C NMR spectroscopic study of diphenyl ether and 28 of its polychlorinated derivatives
Authors: Nevalainen Tapio , Kolehmainen Erkki , Säämänen Marja‐Leena , Kauppinen Reijo
Published: May 2005

The 13C NMR chemical shifts and coupling constants for diphenyl ether and 28 environmentally interesting polychlorinated diphenyl ethers were measured and analysed.
1H, 13C and 19F NMR spectral data for fifteen fluorinated steroids
Authors: Nelson Janis T. , Kurz Lilia J.
Published: May 2005

Analyses of the 1H, 13C and 19F NMR spectra of 15 mono‐, di‐, tri‐ or tetrafluoro‐substituted steroids were carried out by two‐dimensional 1H1H and 1H13C shift correlation experiments.
Assignment of the 1H and 13C NMR spectra of the C21 steroids 12‐β‐O‐acetyltenacigenin A and tenacigenin A by two‐dimensional NMR techniques and computer modeling
Authors: Luo Si‐Qi , Lin Long‐Ze , Cordell Geoffrey A. , Xue Liang , Johnson Michael E.
Published: May 2005

Stereochemical assignments of the C21 steroids 12‐β‐O‐acetyltenacigenin A and tenacigenin A were performed by use of two‐dimensional phase‐sensitive COSY, ROESY, 1H and 13C shift correlation spectroscopy (HETCOR and FLOCK), and ambiguous assignments were resolved through molecular modeling comparisons. This combination of techniques is applicable for the assignment of the highly overlapped 1H signals of these steroids.
13C and2H NMR studies of the molecular flexibility of phenylethylamine and amphetamine derivatives
Authors: Border Corinne L. , Craik David J. , Shehan B. Philip
Published: May 2005

A series of phenylethylamine and amphetamine derivatives were synthesized in order to determine the nature of the internal and overall molecular dynamics in these systems.13C and2H NMR relaxation times were measured. For the latter measurements, compounds specifically deuteriated in the side‐chains were synthesized. The relaxation data were analysed via a computer model incorporating the spectral density function for axially symmetric anisotropic motion. The motion of these molecules was found to be substantially anisotropic, with rotation about the symmetry axis of the molecule being at least twice as fast as rotation normal to the symmetry axis. The results of more complex models of axially symmetric anisotropic molecular motion, involving internal rotation or conic diffusion of the side‐chains, were found to be sensitive to variation of the input data, but the correlation times for internal rotation of the ring—C‐β bond were longer than might have been expected. Similarly, owing to its flexibility, the effective correlation times of atoms in the side‐chain were found to be faster than those of the ring carbons, but did not always decrease along the side chain. Intermolecular interactions or aggregation states in CDCl3may reduce segmental motion of side‐chains. A particular feature of the current study is that it was demonstrated that deuteriation of the side‐chain gives a unique opportunity to determine independently side‐chain correlation times via the quadrupolar relaxation times of the2H nucleus, and to compare these results with those of the carbon atoms. These correlation times were found to be in very good agreement with those obtained from the13C data.
Principal component analysis of the 13C NMR shifts of norbornyl derivatives. II—tetracyclic dodecane derivatives
Authors: Tostes José Glauco Ribeiro , Seidl Peter Rudolf , Leal Kátia Zaccur , Bruns Roy Edward
Published: May 2005

Principal component analysis is applied to the 13C NMR chemical shifts of 29 tetracyclic dodecane derivatives, the spectra of most of which have been recently assigned. These derivatives are subdivided into three classes: exo‐endo, exo–exo and endo–endo. Only the seven 13C shifts of one of the two norbornyl moieties of these derivatives are used in the construction of the data matrix, the other moiety being considered as a ring substituent. This data treatment allows these 29 systems to become a test system for a previously worked (through principal component analysis) standard or training set of 13C shifts of 55 substituted norbornanes. Only one two‐dimensional principal component projection is necessary for identifying the main structural effects in the chosen norbornyl moiety of the test system, highlighting trends in the 13C data of these test derivatives and confirming their recent 13C spectral assignments.
Interconversion of diastereomeric complexes involved in Rh(I)‐catalyzed asymmetric hydrogenation: A (31P, 31P) EXSY NMR study
Authors: Bircher Hansruedi , Bender Bruce R. , von Philipsborn Wolfgang
Published: May 2005

Rhodium(I) complexes containing chiral chelating diphosphines, e.g. R,R‐dipamp [(R,R)‐1,2‐bis(o‐methoxy‐phenylphenylphosphino)ethane] or S,S‐chiraphos [(2S,3S)‐bis(diphenylphosphino)butane] and a prochiral olefin, e.g. methyl (Z)‐α‐acetamidocinnamate (mac), form diastereomeric complexes which differ only in which enantiotopic face of the olefin is bound to rhodium and can be observed by 31P NMR. The interconversion of the two diastereomers has been observed with (31P,31P)‐{1H} 2D EXSY techniques for various mixing times, Tm, and in three different solvents (CD2Cl2, CD3OD and CD3COCD3). The results clearly demonstrate that both inter‐ and intramolecular ligand exchange processes are occurring, and that diastereomeric interconversion cannot proceed exclusively by complete mac dissociation followed by readdition to the opposite enantiotopic olefin face. The new results are consistent with previous DANTE NMR experiments. The differing results in CD2Cl2, CD3OD and CD3COCD3 solutions suggest the possibility of solvent involvement in the rate‐limiting step of ligand exchange. The 2D EXSY method appears to be the method of choice for elucidating the qualitative exchange pathway of this complex system.
Measurement of the paramagnetic intramolecular contribution to the spin–lattice relaxation time in a nitroxide‐labelled glucoside
Authors: Cinget Francis , Gagnaire Didier , Houdier Stephan , Vottéro Philippe J. A.
Published: May 2005

Doubly labelled 2,2,6,6‐tetramethylpiperidinyl‐1‐oxyl‐4‐yl 2′,3′,4′,6′‐tetra‐O‐acetyl‐β‐D‐glucopyranoside, 2,2,6,6‐tetramethylpiperidinyl‐1‐oxyl‐4‐yl β‐D‐glucopyranoside and 1′,2′‐O‐[1‐(2,2,6,6,‐tetramethyl‐4‐oxy‐1‐oxylpiperidinyl)ethylidene]‐3′,4′,6′‐tri‐O‐acetyl‐α‐D‐glucopyranose (13C and NO⋅) were used as model compounds to study the paramagnetic intramolecular contribution (1/T1e)intra to the 13C longitudinal relaxation rate caused by the unpaired electron of the nitroxide radical. It is shown that measurement of (1/T1)intra is possible on the assumption that the electron–nucleus dipole–dipole interaction dominates the other terms contributing to 1/T1 in the case of paramagnetic substances, and by extrapolating the experimental value of 1/T1 to infinite dilution.
Studies of cis‐[PtCl2(PPh2nPr) (BzS{O}Bz)] by solid‐state CP/MAS 31P NMR spectroscopy, single‐crystal X‐ray diffraction and X‐ray powder diffraction: Investigation of a question concerning polymorphism versus space group ambiguity
Authors: Davies Julian A. , Dutremez Sylvain G. , Pinkerton A. Alan
Published: May 2005

The 31P CP/MAS NMR spectrum of cis‐[PtCl2(PPh2 nPr)(BzS{O}Bz)] was found to exhibit two central resonances with appropriate couplings to 195Pt, despite the fact that a single‐crystal x‐ray diffraction study indicated that the complex crystallized in the monoclinic space group P21/n with Z = 4, i.e. that there is only a single crystallographically unique phosphorus atom. The possibility that the 21 screw axis was absent (i.e. that the space group was actually Pn) was examined by a reinvestigation of the original x‐ray data, but no definitive evidence for the alternative space group could be obtained. An examination of a bulk sample of cis‐ [PtCl2(PPh2nPr)(BzS{O}Bz)] by x‐ray powder diffraction and comparison of the results with data from the single‐crystal x‐ray diffraction experiment revealed that the crystal selected for diffraction studies was a different polymorph from the bulk of the sample which was used for the 31P CP/MAS NMR measurements. X‐ray powder diffraction is thus shown to provide a valuable bridge between solid‐state CP/MAS NMR measurements and single‐crystal x‐ray diffraction data.
Effect of carbonyl substituents on the barrier to rotation in N‐ethyl‐N‐methylamides
Authors: Bonacorso Helio G. , Caro Miguel S. B. , Zanatta Nilo , Martins Marcos A. P.
Published: May 2005

The barriers to rotation about the C(O)N bond for 13 α‐alkyl‐ and α‐halo‐substituted N‐theyl‐N‐methylamides were determined by 1H NMR spectroscopy at coalescence temperature. Plots of Gibbs free energy (ΔG°) and Gibbs energy of activation (ΔG‡) values against Charton's electronic and steric parameters of the α‐carbonyl groups allows the conclusion that both the isomeric preference and the barrier to rotation about the C(O)N bond of the N‐ethyl‐N‐methylamides depend mainly on the steric effect of the α‐carbonyl group.
13C NMR spectra of a series of 2′,3′,4′‐trimethoxyflavones. Reinvestigation of signal assignment in 13C NMR spectra of flavones
Authors: Wallet J.‐C. , Gaydou E. M.
Published: May 2005

13C NMR chemical shifts of a series of 2′,3′,4′‐trimethoxylated flavones are reported. The 13C NMR chemical shifts of 2′,3′, 4′‐trimethoxyflavone was reinvestigated by 2D NMR. It is shown that two signals which were assigned by the lanthanide shift reagent method in an earlier study must be reversed.
Explicit formulae for MQ‐filtered COSY of an arbitrary number of magnetically equivalent sets of spin‐1/2 nuclei
Authors: Shekar S. C. , Krishnan V. V.
Published: May 2005

Expressions for the density matrix and the observable spectra are explicitly presented for multiple quantum (MQ) filtered correlation spectroscopy pertaining to weakly coupled spin‐½ nuclei. A feature of most general nature is preserved throughout the calculations, namely arbitrary number of magnetically equivalent sets, with no restriction on the number of spins contained in a given set. The equations have been encoded in a modular fashion into the code PQFCOSY in Fortran language for ease of computation.
Pair‐induced chemical shifts (pairwise corrections) and an additivity scheme for the estimation of aromatic 1H NMR shifts in polysubstituted benzenes with two or more vicinal substituents
Authors: Guy Robert G.
Published: May 2005

The aromatic 1H NMR shifts of ortho‐disubstituted benzenes were used to derive 285 pair‐induced chemical shifts (pairwise corrections) for vicinal pairs of the substituent set (F, Cl, Br, I, NH2, NHCOMe, NO2, OH, OMe, Me, CHO, COMe, CN, Ph). Using these parameters and a simple additivity scheme, 617 ring 1H shifts in polysubstituted benzenes with two or more vicinal substituents were reliably predicted with an average standard deviation of 0.08 ppm.
Conformational behaviour of some trifluoroenaminones by multinuclear magnetic resonance
Authors: Wöjcik Jacek , Domalewski Wojciech , Kamieńska‐Trela Krystyna , Stefaniak Lech , Vdovienko Siergiej I. , Gerus Igor. I. , Gorbunova Marina G.
Published: May 2005

The structures of 4‐N‐methylamino and 4‐N,N‐dimethylamino‐1,1,1‐trifluorobut‐3‐en‐2‐one (1, 2) were solved by means of an analysis of 1H, 1H and 1H, 13C coupling constants. NOE measurements, 13C, 1H heteronuclear correlation and selective decoupling. The spectra of 1 are strongly solvent dependent. Variable‐temperature experiments indicated that in these compounds the double bond character of the CN bond is fairly pronounced and that the p‐electrons from the nitrogen atom are engaged in the conjugated π‐electron system. 14N, 15N, 17O and 19F chemical shifts for 1 are reported.
Reorientational dynamics and internal mobility of the mixed agonist‐antagonist opioid narcotic cyclazocine by 13C NMR relaxation times
Authors: Carbone Domenica , Grassi Antonio , Pappalardo Giuseppe C. , Radics Lajos
Published: May 2005

The motional behaviour of the mixed agonist‐antagonist opioid narcotic cyclazocine (2‐cyclopropylmethyl‐2′‐hydroxy‐5,9‐dimethyl‐6,7‐benzomorphan) as a cationic species (CLZH +) was analysed by 13C NMR spin–lattice relaxation times (T1). Both AM1 and MM2 theoretical calculations were performed to predict the preferred conformations and torsional energetics of CLZH+ in the vapour phase. The analysis of the experimental T1 data (in aqueous solution) was performed by using an analytical model to describe the overall and internal motions of the molecule. The best fit of the relaxation times allowed the detection, in the liquid phase, of effective solute‐solvent interactions and the fully anisotropic diffusive process of the molecule. The motional parameters obtained indicated an increased retational anisotropy of CLZH+ on passing from the gas phase to the solution state. Different activation energies arising from separate solvation effects were found for the motion of the 10‐Me and 11‐Me groups. The fitted energies and transition energies matrix relative to the internal motion of the N‐cyclopropylmethyl group indicated that the preferred conformational states are not isolated and that the overall and internal motions are of the same order of magnitude.
Diazo compounds stabilized, by keto and/or sulphonyl groups. A comparative study by 17O NMR spectroscopy
Authors: Cerioni Giovanni , Culeddu Nicola , Saba Antonio
Published: May 2005

Comparison of the 17O NMR chemical shifts for the keto and the sulphonyl group when stabilizing the carbanionic centre of aliphatic diazo compounds allowed the exclusion for the sulphonyl group, a stabilizing effect through resonance.
13C NMR data for abieta‐7,13‐diene diterpenoids
Authors: Feliciano A. San , del Corral J. M. Miguel , Gordaliza M. , Salinero M. A.
Published: May 2005

13C NMR data for several abieta‐7,13‐diene diterpenoids are reported. The most significant effects caused by the change in the stereochemistry at C‐4 and other structural modifications are discussed.
NMR studies on conformational and N‐configurational interconversion in 3‐methyl derivatives of the non‐narcotic analgesic drug nefopam
Authors: Glaser Robert , Blumenfeld Jeanine , Geresh Shimona
Published: May 2005

Two different N‐configurations and two different eight‐membered ring conformations were found in the diastereomeric crystalline (1R,3S)/(1S,3R)‐ and (1S,3R)/(1S,3S)‐3‐methylnefopam hydrochloride salts. 1H and 13C NMR spectroscopy showed that both crystalline epimers undergo N‐configurational and eight‐membered ring conformational equilibria on dissolution in a solvent (e.g. CD2Cl2). Observation of N‐H proton vicinal coupling in both the solution‐state major and minor species for each epimer signifies slow exchange limit kinetic regimes for N‐configurational interconversion via a prototropic shift‐nitrogen inversion. Since previous studies have shown 2,5‐benzoxazocine ring inversion to be unfavourable, the finding of weighted time‐average vicinal coupling constants for the OCH(CH3)CH2NH(CH3)CH2 moiety is interpreted in terms of a fast exchange limit (and in some cases fast magnetic site exchange broadening) kinetic regime for eight‐membered ring conformational change. For each C‐3 epimer; a quantitative estimation was made for the 2n = 4 solution‐state diastereomeric forms resulting from the two stereogenic elements of N‐configuration and ring conformation. Comparisons were made with the parent nefopam hydrochloride, N‐desmethylnefopam hydrochloride metabolite and the nefopam methiodide quaternary ammonium salt.
Inverse‐detected two‐dimensional NMR experiments on a system undergoing chemical exchange near coalescence
Authors: Robinson Valerie J. , Bain Alex D.
Published: May 2005

In systems undergoing intermediate chemical exchange, observation of carbon NMR signals by standard onedimensional methods is often hampered by severe line broadening accompanied by reduced sensitivity. In contrast, the HMQC inverse‐detected heteronuclear chemical shift correlated experiment detects the 13C satellites of the proton lines. If the proton exchange is fast, the width of the satellites is independent of the intramolecular carbon exchange, and hence the carbons are more efficiently detected. The carbon spectrum of 1‐tert‐butoxycarbonyl‐N‐tert‐butyloctahydro‐1H‐indole‐2‐carboxamide serves to demonstrate this phenomenon. Carbons severely broadened in the 1D experiment appear largely unaffected when detected in the HMQC experiment. A straightforward explanation for this observation is presented together with a preliminary discussion of the carbon (F1) line widths in the HMQC spectra of exchanging systems.
NMR studies on natural all‐trans‐(9′Z,11′Z)‐(3R,3′S,5′R,6′R)‐pyrrhoxanthin, an acetylenic C37‐skeletal nor‐carotenoid butenolide
Authors: Englert Gerhard , Aakermann Torunn , Liaaen‐Jensen Synnøve
Published: May 2005

All‐trans‐(9′Z,11′Z)‐(3R,3′S,5′R,6′R)‐Pyrrhoxanthin was isolated from a natural bloom of dinoflagellates (mainly Ceratium spp.) and submitted to detailed 1H NMR and 13C NMR analysis, including homonuclear COSY (2D), ROESY (1D and 2D), TOCSY (1D) and 1H‐detected one‐bond and multiple‐bond 1H, 13C COSY. All chemical shifts and coupling constants in the 1H NMR spectrum and all carbons in the 13C NMR spectrum were assigned. The result is consistent with the structure, previously deduced, including relative configuration. A recently proposed variant of the ROESY pulse sequence, called T‐ROESY, claimed to suppress undesired TOCSY transfer, provided excellent results free of TOCSY artifacts caused by coherent magnetization transfer via J coupling pathways independent of the choice of the position of the carrier frequency.
Multinuclear 195Pt and 15N magnetic resonance spectroscopic studies of the reaction of K[PtCl3(NH3)] with KI and amines
Authors: Qu Y. , Farrell N. , Valsecchi M. , de Greco L. , Spinelli S.
Published: May 2005

Reaction of the platinum complex K[PtCl3(NH3)] with NH3 or NH2(CH2)nNH2 in the presence of I− gives the mixed chloroiodoamine complexes cis‐[PtCl3(NH3)2] and [{cis‐Pt(Cl)3(I)(NH3)2}2μNH2(CH2)nNH2], respectively. These findings prompted an examination of the nature of the reaction of K[PtCl3(NH3)] with I− in detail. Rapid displacement of two chlorides to give the trans‐[Pt(I)2Cl(NH3)]− anion is observed with a subsequent slow displacement of the third chloride to give the [PtI3(NH3)]− anion. Concomitant with the formation of the triiodo anion, dimerization occurs, giving the iodo‐bridged compound [PtI2(NH3)]2. Correlation of δ(195Pt) and δ(15N) chemical shifts and 1J(195Pt,15N) coupling constants was made with literature values, allowing a complete set of data for the series [PtXn(NH3)4 − n](2 − n)+ with systematic variation of X (Cl,I) to be presented.
1H and 13C NMR studies of E/Z 2‐hydroxyindolenines
Authors: Morales‐Ríos Martha S. , Bucio M. Alvina , Joseph‐Nathan Pedro
Published: May 2005

The 1H NMR spectra of E/Z 2‐hydroxyindolenines are reported in both CDCl3 and DMSO‐d6 solvents. The data suggest a preferred conformation of the heterocyclic ring, which is slightly distorted from planarity, in agreement with the x‐ray crystallographic data of one of the isomers. The 13C NMR spectra for the Z‐hydroxyindolenines are also described. Substituent effects on E/Z isomerism about the exocyclic CC bond are discussed.
Residual dipolar splittings in, 13C MAS NMR arising from interactions with chlorine nuclei
Authors: Harris Robin K. , Sünnetçioǧlu M. Maral , Cameron Kenneth S. , Riddell Frank G.
Published: May 2005

Residual dipolar splittings in 13C cross‐polarization magic‐angle spinning spectra arising from coupling to chlorine nuclei are reported for the three chloroacetanilide isomers, using several spectrometers. At medium to high magnetic field doublets are seen for CCl carbon resonances. Perturbation theory explains the appearance of the spectra qualitatively but is inadequate quantitatively.
Full assignments of proton and carbon signals of picrasidine‐G by 1D and 2D NMR methods
Authors: Liu Jian , Davidson R. Stephen , Howarth Oliver W.
Published: May 2005

The alkaloid picrasidine‐G was isolated from Picrasma quassioides. This alkaloid has previously been reported as a new natural product, but its 13C NMR signals still remain unassigned and some ambiguities remains in the proton assignments. Analysis of the 1H and 13C NMR spectra and 1 D NOE and 2D NMR spectra led to the unambiguous assignment of the 1H and 13C signals of picrasidine‐G.
1H nuclear magnetic resonance studies of the reaction of iron(III) porphyrin cation radical with aryl Grignard reagents
Authors: Chmielewski Piotr J. , Latos‐grażyński Lechoslaw , Rachlewicz Krystyna
Published: May 2005

Addition of aryl Grignard reagents to an iron(III) tetraphenylporphyrin π cation radical, [(TPP⋅)FeIIICl] (SbCl6), in dichloromethane solution at 202 K yields a mixture of σ‐phenyl iron(IV) tetraphenylporphyrin, [(TPP)FeIV(Ph)] (SbCl6), and σ‐phenyl iron(III) tetraphenylporphyrin, (TPP)FeIIICl. A σ‐phenyliron(III) complex is also formed by nucleophilic addition to the tetraphenylporphyrin macrocycle accompanied by σ‐phenyl axial coordination. The complexes formed were identified by 1H NMR spectroscopy. A new route for generating σ‐aryl iron(IV) porphyrin species from the iron(III) porphyrin π cation radical was established. The characteristic 1H NMR pattern of the low‐spin iron(III) porphyrin ring modified species reflects its Cs symmetry and includes four upfield‐shifted pyrrole resonances (2.31, −10.40, 20.39 and −20.87 ppm, 202 K) accompanied by a set of σ‐phenyl resonances (ortho, −188.4; p‐H, −102.5; p‐CH3 for σ‐p‐tolyl, 162.3 ppm). Analysis of the paramagnetic shifts of the σ‐phenyl (σ‐p‐tolyl) ligand of the new species indicates a high π spin density consistent with the electronic structure of low‐spin iron(III) and the contribution of a σ‐delocalization mechanism via donation from a filled σ‐phenyl orbital to an empty dz2; orbital. The formation of a low‐spin σ‐phenyliron(III) isoporphyrin or low‐spin σ‐phenyl N‐arylporphyrin is considered. The meso substitution can be accounted for by a mechanism which emphasizes the radical nature of the reaction substrate and involves the formation of σ‐transient forms.
Characterization of hyperfine‐shifted 1H resonances in oxidized and reduced putidaredoxin, an Fe2S2 ferredoxin from Pseudomonas putida
Authors: Ratnaswamy Gayathri , Pochapsky Thomas C.
Published: May 2005

Hyperfine‐shifted 1H resonances in the two accessible oxidation states of putidaredoxin (Pdx), an Fe2S2 ferredoxin from Pseudomonas putida, were observed and their temperature dependence and relaxation times measured using rapid‐recycle NMR methods. As with other Fe2S2 ferredoxins, the hyperfine‐shifted resonances observed in oxidized (Fe3+−Fe3+) Pdx exhibit anti‐Curie behavior, their signals moving away from the diamagnetic region with increasing temperature. The hyperfine‐shifted resonances of reduced Pdx (Fe3+−Fe2+) exhibit Curie‐type behavior, and closely resemble the appearance and behavior of the hyperfine shifted resonances of human ferredoxin (HFdx), with which Pdx shares significant sequence and functional homology. Electron self‐exchange is slow on the 1H chemical shift time‐scale, as half‐reduced samples of Pdx exhibit hyperfine‐shifted resonances characteristic of both forms.
Two‐dimensional 1H NMR spectroscopy of paramagnetic haem models of the cytochromes: Successes, failures and unanswered questions
Authors: Simonis Ursula , Lin Qing , Tan Helming , Barber R. Andrew , Walker F. Ann
Published: May 2005

As part of an effort to assign completely the1H resonances of the pyrrole protons of model haems, the NOESY spectra of a series of unsymmetrically phenyl‐substituted derivatives of a low‐spin paramagnetic haem model complex tetraphenylporphyrinatoiron (III)bis(N‐methylimidazole), [TPPFe(N‐Meim)2]+, for which the COSY spectra have been reported previously, were recorded in CD2Cl2 or CDCl3 at temperatures of 30 to −35°C using a variety of mixing times. Fourphenomena of importance to the understanding of the cross‐correlation patterns obtained in the NOESY spectra of these paramagnetic complexes were observed: (1) NOE cross peaks can be detected for these intermediate molecular weight complexes, even in non‐viscous solvents; (2) for some complexes only one set of NOE cross peaks different from those previously observed in the COSY maps were obtained, whereas for other complexes two sets were observed; (3) cross correlations between protons in the same pyrrole ring (i.e. cross peaks previously observed in the COSY maps) were observed in the NOESY spectra of some complexes, but not of others; and (4) at ambient temperature, where axial ligand exchange is detectable through cross peaks between the methyl resonances of free and coordinated N‐methylimidazole, additional sets of cross correlations between pairs of pyrrole protons, not observed at −35°C, were detecte d. Each of these phenomena is discussed and questions are raised concerning the cross‐relaxation pathways leading to the observed NOESY maps of these paramagnetic complexes. At the present state of development of two‐dimensional NMR studies of these paramagnetic model haem complexes, the electron density distribution in the orbital utilized for spin delocalization can be delineated (with some cautionary notes), but there still remains some ambiguity in the assignment of the fourpyrrole proton resonances of these mono‐ortho‐substituted tetraphenylporphyrinatoiron(III)complexes.
Investigation of the dynamics of cyclodextrins and their inclusion complexes in water by deuterium NMR
Authors: Azaroual‐Bellanger Nathalie , Perly Bruno
Published: May 2005

Deuterium NMR and relaxation data are presented to investigate the state of β‐cyclodextrin in aqueous solution and to derive dynamic parameters for inclusion complexes. Labelled host and guest molecules were used, and dedicated pulse sequences are proposed for improving the deuterium spectra in terms of reduction of artifacts and of solvent peak(s) and also in terms of total duration of the experiments. This technique was used to investigate the state of β‐cyclodextrin in aqueous solution and to derive important information regarding the degree of dynamic coupling between host and guest in inclusion complexes.
Determination of the quadrupole coupling from featureless line shapes
Authors: Hepp M. A. , Man P. P. , Trokiner A. , Fraissard J.
Published: May 2005

NMR nutation and quadrupole echo experiments were used to determine the quadrupole frequency (ωQ) of 87Rb (I = 3/2) in a single crystal of RbCaF3. Since RbCaF3 has a cubic unit cell above 195 K, there is no second‐order quadrupole shift and the spectrum is rather featureless. By fitting the response of 87Rb, as a function of pulse duration, to the predicted response we were able to determine that the average ωQ/2π = 4.5 kHz in this sample. Discrepancies in the agreement between the theory and the experiment for the echo response were attributed to differential relaxation of the central and satellite transitions.
Determination of three‐dimensional structure of nervosin in solution by two‐dimensional nuclear magnetic resonance spectroscopy
Authors: Yang Yanwu , Xu Xiaolong , Wang Dehua , Qian Baogong
Published: May 2005

Two‐dimensional NMR techniques were used to obtain a complete proton spectral assignment of nervosin, a natural product with medicinal interest isolated from a Chinese herbal medicine. The full relaxation matrix analysis method was used to process the NOE matrix of nervosin. The three‐dimensional structure in solution was calculated by the combination of the WUPH and WUPH‐S methods, based on NMR experimental data, with molecular mechanics energy minimization calculation. The result indicated that the solution structure of nervosin is similar to the x‐ray structure.
Identification of modified natural porphyrin isomers: 1H and 13C NMR assignments by NOESY and reverse heteronuclear shift correlation
Authors: Bondon Arnaud , Autret Marie , Simonneaux Gérard
Published: May 2005

The efficiency of two‐dimensional homonuclear 1H1H NOE spectroscopy in characterizing and fully assigning the 1H NMR spectra of several isomers of meso‐ or ring‐substituted deuteroporphyrins is demonstrated. The carbon resonances of the skeleton and the substituents were fully assigned using two‐dimensional reverse heteronuclear shift correlation spectroscopy.
NMR conformational analysis of complexes of the carboxylic ionophore nigericin with Na+ and K+
Authors: Beloeil Jean‐Claude , Biou Valérie , Dauphin Gérard , Garnier Jean , Morellet Nelly , Vaufrey Françoise
Published: May 2005

The conformations of the complexes formed by the ionophore nigericin with Na+ and K+ in CDCl3 solution determined by ROESY NMR and distance geometry computations are in good agreement with the X‐ray crystallographic data. The structures with the Na+ ion are more compact than those with the K+ ion, as the latter have a wider cage for the ion.
Stereospecific assignment of exocyclic methylene protons in panose by 13C‐filtered 1D TOCSY
Authors: Poppe Leszek , Sheng Shuqun , van Halbeek Herman
Published: May 2005

The C‐6‐methylene protons in the internal glucosyl unit of panose, D‐Glc‐α(1 → 6)‐D‐Glc‐α(1 → 4)‐D‐Glc(α,β), were stereospecifically assigned. The assignment strategy involved the measurement of the long‐range 3J(C‐4, H‐6R) and 3J(C‐4,H‐6S) coupling constants for this residue in panose, with natural 13C isotope abundance, using a newly designed 13C‐filtered 1D TOCSY experiment.
Variable‐temperature 13C CP/MAS study of (Me3Sn)2CO3
Authors: Kümmerlen Jörg , Sebald Angelika
Published: May 2005

Solid (Me3Sn)2CO3, 1, forms polymeric zig‐zag chains were bidentate magnified image units (containing a tetrahedral Me3Sn group) connect trigonal‐bipyramidal Me3SnO2 units which form the polymeric backbone. Both the tetrahedral and the trigonal‐bipyramidal Me3Sn moiety in solid 1 undergo 2π/3 reorientation around their respective SnO bonds at ambient temperature. Although 13C cross‐polarization magic angle spinning (CP/MAS) spectra of 1 are strongly temperature dependent in the temperature range 160–383 K, neither lineshape analysis of these exchange‐broadened 13C spectra nor 13C 2D exchange spectroscopy allows the extraction of meaningful kinetic data for solid 1. Owing to severe overlap problems in the various 13C CP/MAS spectra and because of the apparent vastly different 2π/3 jump rates for the two different Me3Sn units in solid 1, only combined information from variable‐temperature/variable‐r.f. irradiation strength 13C CP/MAS experiments in conjunction with consideration of geometric information from single‐crystal x‐ray diffraction yields an estimate of the respective activation energies for the 2π/3 jump processes of the trigonal‐bipyramidal Me3Sn(1) unit (Ea = 22.1 ± 2.4 kJ mol−1) and of the tetrahedral Me3Sn(2) unit (Ea ≈︁ 50 kJ mol−1) in solid 1.
13C NMR spectra of allosteric effectors of hemoglobin
Authors: Ostrowski Stanislaw , Priebe Waldemar , Burke Thomas G.
Published: May 2005

Carbon‐13 NMR studies were performed for a series of allosteric effectors of hemoglobin. Spectral assignments were made by comparison of 1H‐decoupled 13C spectra; for selected cases, 2D HETCOR experiments were applied. High regularity in the chemical shifts of the similar fragments of these structures was found.
NMR spectra and configuration of biochromophoric compounds with norbornylogue spacer
Authors: Touillaux R. , Jiwan J.‐L. Habib , Soumillion J.‐Ph.
Published: May 2005

The determination of the structure and configuration of bichromophoric compounds with a norbornylogue spacer is presented on the basis of the 1H and 13C chemical shifts and vicinal HH coupling constants.
Methoxy group conformation effects on 13C NMR parameters in 1‐cis‐methoxy‐ and 1‐trans‐methoxy‐1,3‐trans‐butadiene
Authors: Esteban Angel L. , Galache Maria P. , Diez Ernesto , Biekofsky Rodolfo R. , Contreras Rubén H.
Published: May 2005

The proton‐coupled 13C NMR spectra of 1‐trans‐methoxy‐ (2) and 1‐cis‐methoxy‐1,3‐trans‐butadiene (3) are consistent with a methoxy heavy atom planar conformation with s‐syn and s‐anti orientations, respectively. Ab initio 6–31G* calculations confirmed such conformations. They were taken as model compounds to determine the influence of electrostatic interactions on the methoxy 13C NMR parameters. A shielding increase of 4 ppm is observed in 2, with respect to 3, for the OMe 13C chemical shift in an s‐syn conformation and is ascribed to the attraction between the methyl and vinyl moieties as proposed by Li and Chesnut. The methyl 1J(C,H) coupling is not affected by this interaction, showing that the carbon 2p electrons are more polarizable than those in the 2s orbital.