bluuebunny/crossref_metadata_2025_split huggingface dataset:
Substituent‐dependent conformational changes in 6β‐substituted codeine derivatives
Authors: Szilágyi László , Makleit Sándor , Hosztafi Sándor , Simon Csaba 
Published: May 2005

AbstractComplete 1H and 13C NMR data are reported for eleven isocodeine and seven dihydroisocodeine derivatives bearing various substituents at position 6. In isocodeines having bulky succinimido or phthalimodo groups at C‐6 ring C adopts a half‐boat conformation, characterized by the quasi‐equatorial orientation of the C‐6N bond. The distortion from the usual boat form is due to steric interactions between C‐14 and β‐substituents at C‐6, and it is greater in 14‐hydroxy derivatives than in isocodeines unsubstituted at this position. In dihydroisocodeines the conformation of ring C is close to a chair, irrespective of the steric demand of the substituent at C‐6.
13C nuclear magnetic resonance studies on pyrano‐ and dihydropyrano‐1,3‐ diphenylprop‐2‐enones
Authors: Parmar V. S. , Sharma S. K. , Vardhan A. , Sharma R. K. , Gupta S. , Malhotra S. , Boll P. M. 
Published: May 2005

AbstractThe 13C NMR spectra of 19 differently substituted pyrano‐ and dihydropyrano‐1,3‐diphenylprop‐2‐enones were recorded and the results are discussed. The data will be useful in the identification of new and natural chalcones.
Region‐selective inverse‐detected long‐range heteronuclear chemical shift correlation using shaped pulses
Authors: Crouch Ronald C. , Spitzer Timothy D. , Martin Gary E. 
Published: May 2005

AbstractF1 region‐selected variants of the HMBC experiment were compared and evaluated. In particular, a significant advantage was demonstrated for an E‐BURP‐2 pulse over a Gaussian 270° pulse for region‐selected applications. The Gaussian 270° pulse would still, however, be the preferred pulse for use in single‐resonance, on‐resonance selective excitation. Data are presented from NMR spectrometers both equipped and not equipped with programmable pulse modulators (waveform generators). Pulse evaluations were performed using the simple heteroaromatic alkaloid quindoline; application of the technique to the important immunosuppressive cyclic peptide cyclosporin‐A is also presented and discussed.
Concerted use of homo‐ and heteronuclear 2D NMR in the elucidation of the structure of a novel pentaester of 19‐hydroxyingol from Euphorbia marginata seeds
Authors: Branch Sarah K. , Rowan Michael G. 
Published: May 2005

AbstractHomo‐ and heteronuclear 2D NMR techniques were used to elucidate the structure of a novel pentaester of 19‐hydroxyingol from Euphorbia marginata seeds. The diterpene skeleton was identified by 1H 1D and 2D COSY spectra. Heteronuclear 2D 13C1H shift correlation spectroscopy was used to assign the 13C signals. The position of the esterified hydroxymethyl group at C‐10 was identified by NOE difference spectroscopy. The nature of the five ester groups and their corresponding positions on the diterpene skeleton were identified by a combination of long‐range 2D 13C1H correlation experiments and 13C spectra with 1H selective decoupling.
High‐resolution solid‐state 195Pt nuclear magnetic resonance in hexachloroplatinates(IV)
Authors: Hayashi Shigenobu , Hayamizu Kikuko 
Published: May 2005

AbstractHigh‐resolution solid‐state 195Pt NMR spectra of ammonium, potassium and sodium hexachloroplatinate(IV) and its hydrate were investigated using magic angle spinning of the sample. The isotropic part of the spectra has fine structure originating from dipole–dipole interaction and indirect spin coupling between platinum and chlorine nuclei. The fine structure was analysed theoretically, yielding the indirect spin coupling constants and their anisotropies.
Study of the dynamics of ferrocene enclathrated in β‐ and γ‐cyclodextrins by one‐dimensional switching‐angle sample spinning NMR spectroscopy
Authors: Imashiro Fumio , Kuwahara Daisuke , Kitazaki Nobuyuki , Terao Takehiko 
Published: May 2005

Abstract13C chemical shift powder patterns of ferrocene enclathrated in β‐ and γ‐cyclodextrins were measured by one‐dimensional switching‐angle sample spinning NMR spectroscopy. The ferrocene molecules were found to precess with a precession angle of 69° in γ‐cyclodextrin. In β‐cyclodextrin the ferrocene molecules I–III, in different motional states, were enclathrated with populations of 0.42, 0.32 and 0.26, respectively; ferrocene I is tightly enclathrated and rotates around its fivefold axis, whereas ferrocenes II and III precess with precession angles of 30° and 42°, respectively.
Ab initio study of the 13C NMR chemical shifts for some polyene compounds as models for the chromophore of rhodopsin
Authors: Wada M. , Sakurai M. , Inoue Y. , Chûjô R. 
Published: May 2005

AbstractAb initio NMR shieldings, based on the Hansen and Bouman theory, were calculated for some polyene compounds in order to apply the method to retinal proteins. It is shown that the ab initio results reproduce well the magnetic properties peculiar to the polyene 13C chemical shifts. In addition, the 13C and 15N shieldings were calculated for several amines as model compounds of the retinal moiety located in bacteriorhodopsin, and the effect on the chemical shifts of the syn–anti orientation about the CN double bond and the protonation of the Schiff base was investigated.
6Li15N heteronuclear multiple quantum correlation (HMQC) spectroscopy: Application to the structure determination of lithium 2,2,6,6‐tetramethylpiperidide mixed aggregates
Authors: Gilchrist James H. , Harrison Aidan T. , Fuller David J. , Collum David B. 
Published: May 2005

AbstractA heteronuclear multiple quantum correlation (HMQC) experiment was used to correlate the 6Li and 15N chemical shifts of mixed aggregates of [6Li, 15N]lithium 2,2,6,6‐tetramethylpiperidide with [6Li]LiBr, [6Li]LiCl, and [6Li]lithium cyclohexenolate. Optimization of the experiment to spin systems containing more than one weak spin is discussed. The two‐dimensional correlations represent a substantial improvement in sensitivity and resolution relative to one‐dimensional methods.
1H‐detected studies of geminal 29Si13C couplings: Dependence of coupling sign and magnitude on molecular structure
Authors: Kupč Ēriks , Wrackmeyer Bernd 
Published: May 2005

AbstractThe magnitude and signs of geminal 29SiZ13C coupling constants were determined for nine derivatives of representative organosilicon compounds [Z = C(sp2, sp3), N, O, (two‐ and three‐coordinate), Si, S] from 1H‐detected two‐dimensional (2D) Ψ‐BIRD‐HSQC and Ψ‐BIRD‐HMQC pseudo‐triple resonance 1H29Si(13C) and 1H13C(29Si) experiments. The high sensitivity of the method allowed the measurements to be carried out in less than 1 h using 2–10 mg of the respective compound. Couplings as small as 0.45 Hz have been resolved. The couplings ranged from −21.4 to +2.2 Hz, showing regular dependence on the nature, hybridization and coordination of the intervening Z atom.
Flip angle calibration of NMR pulses
Authors: Goez Martin 
Published: May 2005

AbstractDifferent one‐dimensional methods for the measurement of the effective flip angles of NMR observation pulses are discussed, and their stability against the noise of the experimental input data is compared. A new multipulse scheme is presented which is much better suited for the determination of small flip angles. Effects of dipolar interactions in a solid on the accuracy of the results are estimated. Experimental tests are given, showing the feasibility of the proposed calibration method.
Natural abundance 17O NMR spectra of some sulphinylimines and isocyanates
Authors: Vedova C. O. Della , Duddeck H. , Praas H.‐W. 
Published: May 2005

AbstractThe 17O chemical shifts of nine sulphinylimines and isocyanates are reported and discussed in terms of electronic and mesomeric effects. Unusually large values were found for the sulphinylimines. The differences in acyl fluorides compared with acyl chlorides are rationalized on the basis of a mesomeric form, implying an increase of the carbonyl bond order.
Assignment of proton NMR resonances and conformational analysis of the K13CK cystatin‐like peptide
Authors: Samsoen Catherine , Lebrun Evelyne , Van Rapenbusch Roland , Davoust Daniel , Lalmanach Gilles 
Published: May 2005

AbstractThe assignments of the proton NMR signals and the conformational analysis of the cystatin‐mimicking peptide K13CK (Lys‐Val‐Gly‐Gly‐Gln‐Val‐Val‐Cys‐Gly‐Ala‐Pro‐Trp‐Lys) in aqueous solution at pH 3.2 have been achieved using two‐dimensional DQF‐COSY, HOHAHA and ROESY nuclear magnetic resonance techniques. The chemical shifts, the magnitudes of the coupling constants, the temperature dependences of the amide protons and the intramolecular NOEs were used to obtain information on the conformation. The NMR spectra of cysteine proteinase inhibitor K13CK demonstrate a cis‐trans isomerism at the Ala10Pro11 peptide bond.
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

AbstractA 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

AbstractFructans (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

AbstractThe 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

AbstractThe 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

Abstract13C 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

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractHigh‐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

AbstractFull 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

AbstractAnalysis 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

AbstractAn 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

AbstractMost 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

AbstractHeteronuclear 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

Abstract183W 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.