bluuebunny/crossref_metadata_2025 huggingface dataset:
13C NMR studies of the solution molecular dynamics of tricyclic antidepressants
Authors: Casarotto Marco G. , Craik David J. , Munro Sharon L. A.
Published: May 2005

13C NMR spin–lattice relaxation times (T1s) and nuclear Overhauser enhancements (NOE's) were measured for a series of clinically used tricyclic antidepressants (TCAs), imipramine (1), amitriptyline (2), doxepin (3) and dothiepin (4), at two magnetic field strengths (corresponding to 13C frequencies of 75 and 100 MHz). The measurements were carried out at a range of solution concentrations in CDCI3 and D2O in order to determine the factors that influence overall and internal molecular dynamics in these systems. Both the hydrochloride salts and free bases were examined. For solutions in CDCI3 over a range of concentrations, or for low‐concentration (0.03 M) solutions in D2O, T1 and NOE measurements were independent of magnetic field strength, indicating that motion of the TCAs was in the ‘extreme narrowing limit.’ In contrast, for 0.3 M solutions of the hydrochloride salts in D2O, T1 and NOE measurements were field dependent, indicating the presence of significantly slower molecular mobility. It is proposed that micelles are present at this concentration and are responsible for reduced overall tumbling of the TCAs. Several degrees of internal motion were detected by the relaxation and T1 measurements, viz. rapid flexing motion of the benzylic bridging carbons in the central seven‐membered ring and segmental motion of the side‐chain. From an examination of the effect of solvent, concentration and protonation state of the side‐chain on the latter motion, it was possible to derive information on side‐chain conformations and interactions.
Study of the frozen water–poly(vinyl alcohol) system by 2H and 13C NMR spectroscopy
Authors: Gusev D. G. , Lozinsky V. I. , Vainerman E. S. , Bakhmutov V. I.
Published: May 2005

2H and 13C NMR techniques were used to investigate the thermodynamic state of water molecules and of poly(vinyl alcohol) (PVA) chain segments in frozen 10% PVA solutions in 99.8% and 8.5% 2H2O in the ‐66 to 3°C temperature range. The minimum amount of water not entering into the structure of ice is shown to correspond to a ratio of three water molecules to four PVA hydroxyl groups. The quantity of unfrozen water in the investigated systems was observed to change in the 5‐6°C range next to the melting point of pure water. The measurements show that, within the same temperature interval, the temperature decrease is accompanied by a sharp decrease in the 2H spin‐lattice relaxation time T1, whereas 13C T1 and the width of the 13C NMR signals increase up until the resolved PVA signals disappear. The correlation time of the motion of water deuterons and the PVA chain segments was calculated from the 2H and 13C T1 data. The interrelation between the data obtained and the cryostructurization processes leading to the formation of gels in frozen aqueous PVA solutions is discussed.
Two‐dimensional homonuclear and heteronuclear correlation NMR studies of diprenorphine: A prototypic 6α, 14α‐endo‐ethanotetrahydrothebaine
Authors: Mazza Samuel M. , Erickson Ronald H. , Blake Paul R. , Lever John R.
Published: May 2005

Analysis of the 1H–1H COSY, 13C–1H HETCOR and NOESY spectra of diprenorphine, a prototypic 6α, 14α‐endo‐ethanotetrahydrothebaine, yielded 1H NMR and 13C NMR assignments which should aid in spectral studies of structural congeners from this class of opioid ligands. 13C NMR assignments were in accord with those previously reported, with the exception of the C‐17 and C‐18 carbon resonances, which were shown to be reversed. Specific assignments for the non‐equivalent C‐20 and C‐21 methyl groups were possible through NOESY due to intramolecular hydrogen bonding between the 19‐hydroxy and the 6‐methoxy groups. The piperidyl ring presented a chair conformation, similar to that of morphine, with an equatorial N‐cyclopropylmethyl moiety.
Tumour inhibitory triazenes. 5—15N NMR study of 1‐aryl‐3,3‐dialkyltriazenes
Authors: Wilman Derry E. V.
Published: May 2005

The variation of the 15N chemical shifts with substitution for a series of 1‐aryl‐3,3‐dialkyltriazenes is decribed. Good correlations were found between the relative chemical shifts at all three nitrogen sites and the electronic properties, as measured by the substituent coefficient, coefficient, σ, for the meta and para substituents in the aryl group. No such correlations were evident for variations in the 3‐alkyl substituents.
Amended heteronuclear correlations by multiple‐quantum evolution. Stereosequence assignments of polymers with improved sensitivity
Authors: Kövér K. E. , Borbély J. , Batta Gy.
Published: May 2005

It is demonstrated that the Müller and Bolton type of multiple‐quantum heteronuclear shift correlation is a promising tool for stereosequence assignments of polymers. Slight modification of the basic MQ pulse sequence results in a 2–3‐fold gain in sensitivity compared with the conventional single‐quantum spectra while retaining the one‐quantum frequency scale in the F1 dimension.
Structures of zearalenone and zearalanone in solution: A high‐field NMR and molecular modelling study
Authors: Cordier Christine , Gruselle Michel , Jaouen Gérard , Hughes Donald W. , McGlinchey Michael J.
Published: May 2005

The complete 1H and 13C NMR spectra of the mycotoxin zearalenone are described. An analysis of all the vicinal proton–proton coupling constants, together with molecular modelling results, leads to a three‐dimensional structure very similar to those observed x‐ray crystallographically for related systems. Analogous data on zearalanone reveal that whereas the overall molecular geometry is similar to that of zearalenone, the alkyl terminus of the 12‐membered bridging moiety is now oriented almost orthogonally to the aromatic ring plane.
DNMR of small ring paracyclophanes
Authors: Sternhell S. , Tansey C. W. , Tobe Y. , Kakiuchi K. , Kobiro K.
Published: May 2005

The fluxional behaviour of 4‐methyl[2] paracyclo[ 2] (2,5)furanophane, [6] paracyclophane, 8‐methyl[6]‐paracyclophane and 8‐hydroxymethyl[ 6] paracyclophane was studied by dynamic NMR spectroscopy to yield kinetic parameters which were compared with available data for related compounds.
Miscibility of polymer blends investigated by 1H spin diffusion and 13C NMR detection
Authors: Schmidt‐Rohr Klaus , Clauss Joachim , Blümich Bernhard , Spiess Hans Wolfgang
Published: May 2005

The miscibility of two high‐performance polymers, an aromatic poly(ether‐imide) and a poly(aryl‐ether‐ketone), was investigated by a novel combination of solid‐state NMR techniques. This involves a new type of selection of 1H magnetization based on chemical shift differences, 1H spin diffusion during the mixing time and high‐resolution 13C detection. Mixing of components on a molecular scale is proved directly.
Passive observation of 15N satellites in two‐dimensional heteronuclear X–1H shift‐correlated spectra via a Hahn spin–echo extended pulse sequence
Authors: Kupče Ēriks , Wrackmeyer Bernd
Published: May 2005

The application of a Hahn spin–echo extended X–1H shift‐correlated (X = 13C, 29Si, 119Sn, 207Pb) two‐dimensional NMR technique to carbon–, silicon–, tin– and lead–nitrogen compounds is described. This allows complete suppression of the central line (representing the isotopomer with 14N), leaving solely the 15N satellites in the two‐dimensional spectrum leading both to accurate measurement of long‐range 15N1H spin–spin coupling constants and to the determination of the relative signs of the 15NX and 15N1H couplings. 15N/14N isotope effects on 119Sn and 207Pb chemical shifts were measured apparently for the first time.
Fluorine deshielding in the proximity of a methyl group. An experimental and theoretical study
Authors: Gribble Gordon W. , Keavy Daniel J. , Olson Erik R. , Rae Ian D. , Staffa Alfred , Herr Tomas E. , Ferraro Marta B. , Contreras Rubén H.
Published: May 2005

19F chemical shifts are reported for a series of alkyl‐substituted fluoronaphthalenes and related compounds that exhibit steric crowding around the fluorine atom due to the proximity of methyl groups. Comparisons of these chemical shifts with others measured in similar compounds but without the corresponding methyl groups show that this crowding effect produces a large low‐field shift of the 19F signal. Similar effects, but with an even larger sensitivity to the steric crowding, were recently reported for 17O chemical shifts. The electronic origin for this proximity effect on 19F chemical shifts is analyzed within the molecular orbital theory, at the INDO level, using the inner projections of the polarization propagator technique. It is found that the presence of the methyl group produces an increase in the absolute value of the paramagnetic term of the magnetic shielding constant.
NMR lipid profiles of cells, tissues and body fluids. I— 1D and 2D Proton NMR of lipids from rat liver
Authors: Casu Mariano , Anderson Graeme J. , Choi Gregory , Gibbons William A.
Published: May 2005

A combination of established lipid extraction procedures and high‐resolution 1D and 2D NMR spectroscopic methods has been used to analyse qualitatively and quantitatively the lipid composition of rat liver. The major lipids present in each structural class were identified and quantified. Considerable information on the composition of the different classes of structural and unsaturated fatty acid chains were obtained for the intact lipids without resort to hydrolysis. Significantly, the relative amounts of cholesterol, glycerophospholipids, ether lipids, sphingolipids and glycerides were shown to be in agreement with previous determinations by high‐performance liquid and other chromatographic procedures.
NMR spectroscopic properties of heptakis(2,6‐di‐O‐pentyl)‐β‐cyclodextrin: Two‐dimensional NMR spectra of a key intermediate in preparing chiral stationary phases for enantioselective capillary gas chromatography
Authors: Meier‐Augenstein Wolfram , Burger Barend V. , Spies Hendrik S. C.
Published: May 2005

The 1H and 13C NMR spectra of heptakis(2,6‐di‐O‐pentyl)‐β‐cyclodextrin in deuteriochloroform have been fully and unambiguously assigned. Several methods, including homo‐ and heteronuclear spin decoupling, two‐dimensional homo‐ and hetero‐nuclear correlation NMR spectroscopy, spectral simulation and the measurement of relaxation times were used for chemical shift assignments.
Nuclear quadrupole resonance in chloromethylphenols
Authors: Kalathimattam Roy Sebastian , Bai Amitha , Uchil Jayagopal
Published: May 2005

The temperature dependences of the 35Cl nuclear quadrupole resonance (NQR) frequencies of 4‐chloro‐3‐methyl‐, 2‐chloro‐5‐methyl‐ and 4‐chloro‐2‐methyl‐phenol were studied in the temperature range from 77 K up to the respective melting points. 4‐Chloro‐2‐methylphenol undergoes a phase transition at ca 185 K, and the presence of trans–cis isomeric forms is inferred. The NQR frequencies of molecules at absolute zero temperature were evaluated.
Stereochemistry of 3‐arylideneflavanones and their thio analogues by the use of 3J(CH) couplings
Authors: Tóth Gábor , Szöllösy Åron , Lévai Albert , Oszbach György , Dietrich Wolfgang , Kühne Harald
Published: May 2005

The application of the 3J(HCXC) couplings in 3‐arylideneflavanones and 3‐arylidenethioflavanones allows a semi‐quantitative estimation of the conformational equilibrium.
NMR and conformational studies of the cyclobutane ring involved in the bicyclo [4.2.0]octane system of a tetracyclic diterpene structure
Authors: Manh Duc Do Khac , Fetizon Marcel , Prévost Chantal , Roy Pierre
Published: May 2005

Conformational studies were performed on the bicyclo [4.2.0] octane system of a series of related tetracyclic diterpenes, using molecular mechanics and 1H NMR. Both methods gave compatible results, but did not permit the deduction of any quantitative relationship linking the vicinal coupling constants to the cyclobutane dihedral angles. Nevertheless, the Karplus relationship allowed a qualitative interpretation of the coupling constants in terms of conformation. A set of characteristic 1H NMR coupling constants was obtained which allows the interpretation of the 1H NMR spectrum of any compound presenting a similar system.
Inclusion complexes between β‐cyclodextrin and β‐benzyloxy‐α‐propionic derivatives of paramagnetic DOTA‐ and DPTA‐Gd(III) complexes
Authors: Aime Silvio , Botta Mauro , Panero Maurizio , Grandi Maurizio , Uggeri Fulvio
Published: May 2005

The addition of β‐cyclodextrin to a solution containing β‐benzyloxy‐α‐propionic‐substituted DOTA‐ and DTPA‐Gd(III) complexes leads to the formation of inclusion compounds whose equilibrium constants have been determined by NMR titrations. The main effect associated with the formation of this ‘host‐uest’ interaction is a marked elongation of the molecular reorientational time, τr, which in turn results in increased solvent proton relaxation rates.
Intermolecular and intramolecular effects on the 1H and 13C shielding in some gaseous hydrocarbons at various temperatures—experimental results
Authors: Bennett Brian , Raynes William Thomas
Published: May 2005

The proton and 13C shielding constants in CH4, C2H6, C3H8, and some other gaseous hydrocarbons have been studied as functions of density at temperatures in the range 180–370 K. The linear coefficients describing the density dependence of the shielding, after correcting for bulk susceptibility, increase substantially as the temperature is reduced, indicating stronger intermolecular interactions. (Some of the required magnetic susceptibilities were determined in this work by an NMR method). The 13C measurements for CH4 are close to those of an earlier study; the results for the other gases are new. The linear coefficient is substantially greater for the carbon shielding of the methyl group in propane than for the methylene group at any temperature, but there is virtually no distinction between the linear coefficients for the proton shielding in this gas. Values for do0/dT, the temperature dependence of the shielding extrapolated to zero density, are also presented for both proton and 13C shielding in the hydrocarbons. They are positive and negative in different instances. It is shown from this and earlier gas‐phase studies that standard literature values of the methane 13C shielding relative to the 13 shielding in the other hydrocarbons are in error.
Quantitative empirical treatment of 13C NMR chemical shifts of aliphatic halides
Authors: Suryanarayana Iragavarapu , Gasteiger Johann
Published: May 2005

The 13C NMR chemical shifts of the α, β, γ and δ carbons of aliphatic fluorides, chlorides, bromides and iodides can be reproduced by a four‐parameter equation; the charge Q on the carbon atom, the number of hydrogen atoms three bonds away, N3H, the interactions of the polarizabilities of the halogen atoms one bond away with the hydrogens present in the first sphere, as represented by PXN1H, and the polarizabilities of halogens in the second sphere, PX(2). A regression coefficient of 0.9714 and a standard deviation of 4.85 ppm are obtained for all aliphatic halides in which the R skeleton includes alkyl, acyclic and bicyclic rings. For alkyl compounds only the correlation is of the order of R = 0.997 and the standard deviation is less than 2 ppm. Here the influence of C, H, F, Cl, Br and I are reproduced quantitatively.
Complete 1H and 13C NMR assignments of ruthenium(II) complexes with two new 2‐pyridylquinoline ligands
Authors: Finocchiaro Paolo , Mamo Antonino , Tringali Corrado
Published: May 2005

The complete assignment of the proton and carbon spectra for two new 2‐pyridylquinoline ligands, 4‐phenyl‐2‐(2′‐pyridyl)quinoline (Ph‐pq) and 2,6‐di(4′‐phenylquinol‐2′‐yl)pyridine (Ph‐dqp), and their ruthenium(II) complexes [Ru(bpy)2(Ph‐pq)](PF6)2 and [Ru(Ph‐dqp)2](PF6)2 has been accomplished using a combination of one‐ and two‐dimensional NMR techniques, including COSY, NOESY, one‐bond and long‐range HETCOR and selective INEPT spectra. The J(H,H) and J(C,H) values have been determined for the majority of the resonances.
Structure of [RhH2(PPh3)2(bipy)]Cl (bipy = 2,2′‐bipyridyl) from multinuclear NMR studies
Authors: Heaton B. T. , Jacob C. , Heggie W. , Page P. R. , Villax I.
Published: May 2005

By the use of the INEPT pulse sequence it has been possible to obtain 15N and 103Rh NMR data on [RhH2(PPh3)2(bipy)]Cl (bipy = 2,2′‐bipyridyl) containing natural abundance 15N and prove the stereochemistry; 1H and 31P NMR data are also reported for [RhH2(PPh3)2(bipy)]Cl which can be easily prepared in the pure state by the reaction of [RhCl(PPh3)3] or [Rh2Cl2(PPh3)4] with bipy ([Rh]: [bipy] = 1:1) under an H2 atmosphere.
Variable‐pressure oxygen‐17 NMR study of water exchange on hexaaquarhodium(III)
Authors: Laurenczy Gábor , Rapaport Irina , Zbinden Donald , Merbach André E.
Published: May 2005

Rate constants and activation parameters for water exchange on hexaaqua‐ and monohydroxypentaaquarhodium(III) were determined by 17O NMR as a function of temperature (323–364 K) and pressure (up to 210 MPa, at 323 K) at several acidities (1.0–5.0 molal HClO4). The observed rate constant was of the form kex = k1 + k2/[H+], where the subscripts 1 and 2 refer to the exchange pathways on Rh(H2O)63+ and Rh(H2O)5(OH)2+, respectively. The kinetic parameters are as follows: k1298 = 2.2 × 10−9 s−1, ΔH1‡ = 131 ± 23 kJ mol−1, ΔS1‡ = + 29 ± 69 J K−1 mol−1, ΔV1‡ = −4.2 ± 0.6 cm3 mol−1; k2298 = 1.5 × 10−8 m s−1, ΔH2‡ = 136 ± 7 kJ mol−1, ΔS2‡ = + 61 ± 21 J K−1 mol−1, ΔV2‡ = + 1.3 ± 0.3 cm3 mol−1. The thermodynamic parameters for the acid dissociation reaction of Rh(H2O)63+ were determined potentiometrically and spectrophotometrically: pKa298 = 3.45 and ΔVa0 = −0.2 ± 0.5 cm3 mol−1. Values were estimated for the first‐order rate constant (using the relationship k2 = kOHKa) and the corresponding activation volume for Rh(H2O)5(OH)2+: kOH298 = 4.2 × 10−5 s−1 and ΔVOH‡ = + 1.5 cm3 mol−1. The kinetic results imply an associative interchange mechanism Ia for Rh(H2O)63+ and an interchange mechanism I with a slight dissociative character for the strongly OH labilized Rh(H2O)5(OH)2+ species.
13C and 1H NMR chemical shift assignments of 1‐ and 2‐alkylnaphthalenes (R = Me, Et, i‐Pr, t‐Bu) and determination of substituent effects on 13C and 1H chemical shifts
Authors: Ernst Ludger , Schulz Petra
Published: May 2005

Complete 13C spectral assignments were made for 1‐ and 2‐R‐naphthalenes (R = Me, Et, i‐Pr, t‐Bu) in CDCl3 solution (5 mol%) by the use of 2D techniques including 2D INADEQUATE. Contradictory assignments from the literature were clarified and incomplete data completed. Substituent effects on 13C shifts are briefly discussed. 1H chemical shifts were determined by 13C/1H shift correlation.
Second‐order regression of 13C substituent chemical shifts with Taft's sigma constants
Authors: Holik Miroslav
Published: May 2005

In addition to Taft's dual substituent parameter (DSP) and DSP–non–linear resonance (DSP–NLR) models, and Charton's triple substituent parameter (TSP) equation, two second‐order regression models were tested using published data for 13C substituent chemical shifts of the C‐4 atom in 1,4‐disubstituted benzenes. The complete data matrix consisted of 14 series with a fixed Y (C‐4) substituent, each with 14 variable X (C‐1) substituents. Second‐order (in the σ parameter or in a combination of the σ1 and σ constants) models gave results as good as, and in some cases even better than, the DSP–NLR equation; the results of the TSP model were always worse. The whole data matrix was submitted to principal component analysis. Target testing has shown vectors of σ, (σ)2 and σI constants as ‘real’ principal components.
Phosphorus‐31 NMR studies of polymer‐supported highly reactive copper reagents
Authors: O'Brien R. A. , Gupta A. K. , Rieke R. D. , Shoemaker R. K.
Published: May 2005

The chemistry of highly reactive zerovalent copper species represents an active area of research. Recently, active metal chemistry has been successfully accomplished using polymer‐supported triphenylphosphine–copper(I) coordination complexes as precursors. Since the materials are solids, detailed examination of the reagents at vaious stages of chemical reaction can be problematic, since the primary means of examination has historically been proton, 13C and 31P NMR methods. In this study, cross‐polarization magic angle spinning (CPMAS) experiments, combined with 31P T1 relaxation measurements (via proton cross‐polarization), provided data which allowed the determination of the role of the phosphine species in the overall chemistry of these materials. Although it is known that the type of phosphine affects the chemistry, it was found here that there is no observable interaction between the reduced copper species and the polymer‐supported triphenylphosphine.
Nuclear magnetic resonance evidence for radiation damage of saturated phosphatidylcholine in bilayers
Authors: Casu Mariano , Lai Adolfo , Erriu Gianni , Onnis Salvatore , Zucca Nazario
Published: May 2005

Multilayer membranes of 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphorylcholine were prepared in D2O and exposed to γ‐radiation. Changes in the chemical structure due to irradiation were studied by 1H, 13C and 31P NMR after lyophilization and dissolution in chloroform‐methanol (1 : 2, v/v). One‐ and two‐dimensional techniques were used. 1‐Palmitoyl‐sn‐glycero‐3‐phosphorylcholine, 2‐palmitoyl‐sn‐glycero‐3‐phosphorylcholine, glycero‐3‐phosphorylcholine and palmitic acid were identified as new components. Their development during irradiation was quantitatively determined. The results were discussed in terms of possible reaction steps responsible for the radiolytic decomposition.
1H and 13C NMR studies of substituted isoquinolinium derivatives in different solvents
Authors: Werra W. , Heber D. , Holzgrabe U.
Published: May 2005

1H and 13C NMR data for 1‐cyano‐, 4‐cyano‐, 4‐bromo‐ and 4‐bromo‐5‐nitro‐substituted isoquinolines, isoquinoline N‐oxides and N‐methoxy and N‐ethyl salts in different solvents are reported. The substituent chemical shifts are discussed with regard to the reactivity of the N‐methoxy compounds in the presence of nucleophilic reagents.
Complete assignment and conformational studies of tomatine and tomatidine
Authors: Willker W. , Leibfritz D.
Published: May 2005

Heteronuclear correlation techniques and homonuclear E.COSY spectra were used to obtain a complete assignment of the 13C and 1H NMR spectra of the aglycone tomatidine. In addition, 1D/2D TOCSY, NOESY and ROESY spectra allowed the assignment of the sugar moiety in tomatine. The procedure used is of general applicability for the structural elucidation of sugars and glycosidic biomolecules.
Determination of the resonance frequency ratio of the 31P and 1H NMR resonance shift standards 85% orthophosphoric acid and tetramethylsilane
Authors: Edzes Hommo T.
Published: May 2005

The NMR resonance frequency ratio of the 31P NMR resonance shift standard 85% orthophosphoric acid (H3PO4) and the 1H standard tetramethylsilane (TMS) was determined by means of the ‘dispersed phase’ method. The Ξ value, equal to 108 times the resonance frequency ratio, was 40480737.0 ± 0.2 Hz at 25°C. A small dependence on temperature (−0.11 Hz °C−1) and on phosphoric acid concentration (−0.50 Hz %−1) was observed around 25°C. Traces of iron in phosphoric acid were found to have a negligible effect on Ξ values, although line widths increased. The determination of Ξ allows accurate referencing of 31P NMR spectra relative to the 1H resonance of internal TMS or of a secondary 1H shift standard. The accuracy of the 31P NMR resonance shift scale is primarily limited by the uncertainty of solvent‐induced 1H resonance shifts of TMS.
Conformational analysis 18—lanthanide‐induced shift (LIS) investigation of some 2‐substituted 1,3‐dioxanes
Authors: Abraham Raymond J. , Wallace Kerry , Wilkins Suzanne , Sancassan Fernando
Published: May 2005

A LIS analysis of 2‐isopropyl‐1,3‐dioxane (1) and 2‐methyl‐2‐phenyl‐1,3‐dioxane (2) is reported. The monodentate complexing model gives good agreement with the observed shifts in both compounds, whereas the bidentate model (lanthanum binding to both oxygens) does not give an acceptable solution. In 1 the lanthanide complexes almost exclusively (90%) with the axial lone pair of the oxygen atom. The four‐site binding model gives excellent agreement with the observed shifts (Rx 3.5%). In 2 a similar lanthanide binding is found, and the analysis of the LIS allows both the deduction of the molecular conformation (C‐2‐methyl equatorial, C‐2‐phenyl axial) and also the orientation of the phenyl group (perpendicular).
Unambiguous structure determination of some pyrazolo [1,5‐a]pyrimidine derivatives by multinuclear NMR spectroscopy
Authors: Chimichi Stefano , Cosimelli Barbara , Bruni Fabrizio , Selleri Silvia
Published: May 2005

The condensation of 3(5)‐aminopyrazole and 5‐amino‐3‐phenylpyrazole with ethyl 2,4‐dioxopentanoate and 2‐ethoxymethylidene‐3‐oxobutyrate has been re‐investigated. Contrary to previos reports, the former reaction gives rise to both regioisomeric pyrazolo [1,5‐a]pyrimidines (5‐carbethoxy‐7‐methyl‐and 7‐carbethoxy‐5‐methyl‐), the structures of which were determined by 1H and 13C NMR spectroscopy. The 6‐carbethoxy‐7‐methyl‐regioisomer is shown to be the only product in the reaction of the same aminopyrazoles with 2‐ethoxymethylidene‐3‐oxobutyrate; the regiochemical assignment was independently achieved by multimuclear (13C and 15N) NMR spectroscopy.
Characterization of aluminium complexes in tea extract. Part I—27Al NMR studies
Authors: Mhatre S. N. , Iyer R. K. , Moorthy P. N.
Published: May 2005

The high‐field 27Al NMR spectrum of aqueous tea extract contained two narrow resonances at 9.85 and 16.15 ppm. The spectra of aluminium chelates with a number of model ligands (catechol, pyrogallol, catechin, kojic acid, protocatechuic acid, ascorbic acid and salicylic acid) containing chelating moieties present in the constituents of tea showed broad resonances in the range 8–36 ppm. Potentiometric and NMR studies indicate the formation of a monohydroxo 1:1 Al‐catechin chelate (δ 8.3 ppm) with highly distorted symmetry. From a comparison of the NMR spectra of tea infusions at different pH values with those of aluminium chelates with malic acid and oxalic acid (minor constituents in tea), the resonance at 16.15 ppm was assigned to the highly symmetric octahedral anionic chelate trisoxalatoaluminium, [Al(C2O4)3]3−. This was confirmed by anion‐exchange separation of the chelate and its identification by 27Al NMR spectroscopy. The signal at 9.8 ppm could be due to a mixed ligand chelate containing oxalate. In the case of the aluminium‐malate system, the resonance at 20 ppm was assigned to a 1:2 chelate in which malate functions as a tridentate resulting in five‐ and six‐membered chelate rings.
NMR Study of isolobal N‐CH3+, N‐BH3 and N‐BF3 imidazole derivatives
Authors: Padilla‐Martínez Itzia Irene , Ariza‐Castolo Armando , Contreras Rosalinda
Published: May 2005

Some N‐BH3, N‐BF3, N+‐CH3 and N+‐H imidazole derivatives have been prepared and their 13C, 11B and 1H NMR spectra studied. The effect of the different substituents was analysed. The isolobal character of the N‐BH3 and N‐CH3 derivatives is reflected in their spectra. In the 13CH coupled spectra of N‐borane adducts, the hydrides appear to be coupled with the heterocyclic carbon atoms. The C‐4 chemical shift value is indicative of the nature of the N‐substitution: lone pair (128–130 ppm), BH3 (126–128 ppm), BF3 and [CH3]+ (122–124 ppm) or [H]+ (117–119 ppm). The latter values allowed the chemical shifts of frozen imidazole to be estimated: 128 ppm for C‐4 and 117 for C‐5.
Carbon–carbon and proton–proton coupling constants in tetramethyl 9aH‐quinolizine‐1,2,3,4‐tetracarboxylate and its alkyl derivatives
Authors: Kamieńska‐Trela Krystyna , Kania Lidia , Bednarek Elżbieta
Published: May 2005

The 1H and 13C NMR spectra of the parent tetramethyl 9aH‐quinolizine‐1,2,3,4‐tetracarboxylate and 20 of its alkyl‐substituted derivatives were obtained and analysed. The study included measurements of one‐bond carbon–carbon and also proton–proton coupling constants across three, four, five and six bonds. An analysis of the data allowed an estimation of electron distribution and steric requirements in this group of compounds. No correlation was observed between 1J(C,C) values and the corresponding bond lengths.
1H NMR spectra of nitrated aminopyridines
Authors: Ritter Helmut , Kaiser M.
Published: May 2005

The 1H NMR spectra of 26 nitrated aminopyridines were measured and interpreted. Chemical shift assignments were based on existing chemical shift rules for substituted pyridines and spectral comparison with compounds of similar structure. Some o‐aminonitropyridines were found to give a splitting of the amino signals due to intermolecular hydrogen bonding; steric hindrance is shown to influence this bonding.
Carbon‐13 NMR spectra of bile acid derivatives. Part III. Unsaturated 5β‐cholanoic acids
Authors: Iida Takashi , Goto Junichi , Nambara Toshio
Published: May 2005

13C NMR signals were assigned for 18 methyl 5β‐cholenoates with a double bond in ring A, B, C or D (Δ2, Δ3, Δ5, Δ6, Δ7, Δ8(14), Δ9(11), Δ11 or Δ14). The double bond substituent effects on the 13C NMR chemical shifts of the parent 5β‐cholanoates were clarified.
Investigation of solvation effects on the solid‐state 31P NMR spectra of tertiary phosphine derivatives and metal complexes
Authors: Davies Julian A. , Dutremez Sylvain G.
Published: May 2005

An investigation of bis(diphenylphosphino)methane dioxide (dppm dioxide), cis‐[PtCl2(PPh3)2] cis‐[PtCl2{P(p‐C6H4Cl)3}2] and cis‐[PtBr2(PPh3)2] by solid‐state CP/MAS 31P NMR spectroscopy, x‐ray powder diffraction and 1H, 13C{1H} and 31P{1H} solution NMR methods illustrates the sensitivity of the appearance of solid‐state NMR spectra to solvation effects in crystalline solids. The presence or absence of solvent of crystallization and the slow loss of solvent of crystallization from a sample over time are clearly manifested in the solid‐state NMR spectra as the local site symmetry in the solid is changed. These effects have led workers to report different data for a given compound when, in fact, different types of solvates were investigated.
Observation of 201Hg NMR spectra for solid K2Hg(CN)4
Authors: Wu Gang , Wasylishen Roderick E.
Published: May 2005

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

119Hg NMR chemical shifts of the stable mercury species HgCl with n = 0–4 were determined by a least‐squares algorithm from 199Hg chemical shifts measured in 50 mM aqueous mercury solution as a function of the chlorine concentration at 25°C. The concentrations of the corresponding mercury species in the solutions necessary in this special procedures were calculated by using published equilibrium constants. The results relative to dimethyl‐mercury are −2256 ppm (Hg2+), −1897 ppm (HgCl+), −1560 ppm (HgCl2), −1436 ppm (HgCl3−) and −1152 ppm (HgCl) with maximum errors of ±5 ppm.
Multinuclear (1H, 13C, 15N, 19F, 31P) one‐ and two‐dimensional magnetic resonance study of tert‐butylamino‐tert‐butyl‐fluorophosphane, tert‐butylimino‐tert‐butylphosphane and of its dimer formed by [1 + 2] cycloaddition
Authors: Wrackmeyer Bernd , Köhler Christian
Published: May 2005

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

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

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

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

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

Pelargonidin‐3‐O‐β‐glucopyranoside was isolated from an acidified methanolic extract of frozen strawberries, purified by several chromatographical techniques and subjected to homo‐ and heteronuclear proton and carbon NMR analysis, including selective decoupling, DQF‐COSY, NOESY, SEFT, HMQC and HMBC. Several strategies for the unambiguous assignment of the aglycone H‐6 and H‐8 resonances are discussed. Secondary isotope effects and different deuterium exchange rates of the protons were found.
3D H, C, P correlation: A new application of 3D NMR spectroscopy
Authors: Berger Stefan , Bast Peter
Published: May 2005

The first example of 3D NMR spectroscopy involving 1H, 13C and 31P nuclei is described. The use of this technique for difficult signal assignments in organophosphorus chemistry is demonstrated.
Pyramidal nitrogen inversion hindered by a strong intramolecular hydrogén bond in 2‐diethylaminomethylphenols
Authors: Denisov G. S. , Gindin V. A. , Golubev N. S. , Koltsov A. I. , Smirnov S. N. , Rospenk Koll Sobczyk M. A. And L.
Published: May 2005

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

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

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

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

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

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

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

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

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

Magnetic field gradients were incorporated into the selective COSY experiment. The new gradient‐selected experiment has the expected advantages of significantly improved spectral quality resulting from better artifact suppression and the capacity to acquire spectra using fewer scans. A sample of brucine was used to evaluate the experiment and the resulting spectra were of excellent quality. These experiments may be implemented on commercial instrumentation.