NMR Investigations (nmr + investigation)

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of NMR Investigations

  • solid-state nmr investigation


  • Selected Abstracts


    Mixed-Ligand Oxidovanadium(V) Complexes with N, -Salicylidenehydrazides: Synthesis, Structure, and 51V Solid-State MAS NMR Investigation,

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2008
    Simona Nica
    Abstract The synthesis and spectroscopic characterization of a series of three oxidovanadium(V) complexes with 8-hydroxyquinoline and Schiff-base ligands derived from salicylaldehyde and ,-hydroxy-functionalized carbohydrazides with different chain lengths are reported. The complex with the hydrazone ligand containing the shortest chain length was crystallographically characterized. This complex crystallizes in the triclinic space group P with two structurally similar but crystallographically independent oxidovanadium(V) complexes. Each vanadium atom is six-coordinate in a distorted-octahedral geometry. The two molecules are assembled through hydrogen-bonding interactions between the hydroxyl groups of the side-chain substituted Schiff-base ligand and the oxido group of one of the two complexes. Electrochemical measurements performed in acetonitrile solution reveal two reversible one-electron reduction steps. The observed pre-wave feature of the second reduction step indicates the presence of dissociation equilibria related to the 8-hydroxyquinoline coligand. Magic-angle spinning solid-state 51V NMR spectroscopy allowed to characterize the full series of complexes with alkyl and hydroxy alkyl-substituted hydrazone ligands that were used. The quadrupolar coupling constants are small with a value of about 4 MHz and show little variation within the series. The asymmetry of the chemical shift tensor indicates a rather axial symmetric environment around the vanadium(V) center. The isotropic chemical shifts observed in the solid state occur at about 30 ppm, which is in the same order of magnitude as the solvent induced variations, about 10 ppm, found for different solvents.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


    NMR Investigation of the Bound Conformation of Natural and Synthetic Oligomannosides to Banana Lectin

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2007
    Caroline Clavel
    Abstract The conformational behaviour of three mannose-containing oligosaccharides, namely, the ,1,3[,1,6] trisaccharide, a heptasaccharide with ,1,2, ,1,3 and ,1,6 linkages and a tetrasaccharide consisting of ,1,3 and ,1,2 linkages, when bound to banana lectin (BanLec) has been evaluated by trNOE NMR methods and docking calculations. It was found that the molecular recognition event involves a conformational selection process with only one of the conformations present in the free state of the sugar being recognised at the lectin binding site. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]


    Partially versus Exhaustively Carbamoylated Cyclodextrins: NMR Investigation on Enantiodiscriminating Capabilities in Solution

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2003
    Gloria Uccello-Barretta
    Abstract The enantiodiscriminating efficiency of exhaustively carbamoylated, mixed carbamoylated/silylated, and partially carbamoylated cyclodextrins in solution has been compared by NMR spectroscopy. Investigation of the origin of the observed chiral discrimination was also carried out. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


    The Stereostructure of Porphyra-334: An Experimental and Calculational NMR Investigation.

    HELVETICA CHIMICA ACTA, Issue 3 2007
    Evidence for an Efficient, Proton Sponge'
    Abstract The mycosporine-like amino acid (MAA) porphyra-334 (1) is subjected to extensive 1H- and 13C-NMR analysis as well as to density-functional-theory (DFT) calculations. All 1H- and 13C-NMR signals of 1 are assigned, as well as the resonances of prochiral proton pairs. This is achieved by 500-MHz standard COSY, HMQC, and HMBC experiments, as well as by one-dimensional (DPFGSE-NOE) and two-dimensional (NOESY) NOE experiments. Diffusion measurements (DOSY) confirm that 1 is monomeric in D2O solution. DFT Calculations yield 13C-NMR chemical shifts which are in good agreement for species 6 which is the imino N-protonated form of 1. An exceptionally high proton affinity of 265.7,kcal/mol is calculated for 1, indicating that 1 may behave as a very powerful ,proton sponge' of comparable strength as synthetic systems studied so far. Predictions of 13C-NMR chemical shifts by the ,NMRPredict' software are in agreement with the DFT data. The absolute configuration at the ring stereogenic center of 1 is concluded to be (S) from NOE data as well as from similarities with the absolute configuration (S) found in mycosporine-glycine 16. This supports the assumption that 1 is biochemically derived from 3,3- O -didehydroquinic acid (17). The data obtained question the results recently published by a different research group claiming that the configuration at the imino moiety of 1 is (Z), rather than (E) as established by the here presented study. [source]


    GC-MS and 13C NMR Investigation of Lead Zirconate Titanate Precursor Sols for Fiber Preparation

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2007
    Mei Zhang
    Different macroscopic properties of PZT fibers have been obtained when using acetic acid and methacrylic acid to modify the PZT precursor. In order to clarify the role of the acids the molecular structure of the acidified PZT precursors was investigated and compared by gas chromatography-mass spectrometry, Fourier transform infrared, 13C nuclear magnetic resonance (NMR) spectroscopy (solution and solid state 13C NMR) and the reason for obtaining long PZT fibers is discussed. The results indicate that when methacrylic acid was used, long gel and ceramic fibers have been obtained because strongly co-ordinating carboxylate groups of methacrylic acid were formed. Linear chains, like those of methacrylic acid propyl ester and methacrylic acetate, have been formed in the PZT precursor sols. In addition, after heat treatment the polymer decomposed quickly so that pure perovskite could be obtained at low temperature in the PZT fibers. When acetic acid was used short fibers were obtained. Acetic acid may act as chelate agent to form oxo acetate in the precursors; this oxo acetate nature also resulted in PZT fibers drawing. However, the longest gel and ceramic fibers have been prepared from precursors with methacrylic acid. [source]


    Synthesis of a Single Four-Ring (S4R) Molecular Zinc Phosphate and Its Assembly to an Extended Polymeric Structure: A Single-Crystal and in situ MAS NMR Investigation.

    CHEMINFORM, Issue 51 2003
    Srinivasan Natarajan
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]


    Isotopically Labeled and Unlabeled ,-Peptides with Geminal Dimethyl Substitution in 2-Position of Each Residue: Synthesis and NMR Investigation in Solution and in the Solid State.

    CHEMINFORM, Issue 2 2003
    Dieter Seebach
    No abstract is available for this article. [source]


    Solid-State NMR Investigations of the Unusual Effects Resulting from the Nanoconfinement of Water within Amphiphilic Crosslinked Polymer Networks

    ADVANCED FUNCTIONAL MATERIALS, Issue 21 2009
    Ryutaro Ohashi
    Abstract Two types of solid-state 19F NMR spectroscopy experiments are used to characterize phase-separated hyperbranched fluoropolymer,poly(ethylene glycol) (HBFP,PEG) crosslinked networks. Mobile (soft) domains are detected in the HBFP phase by a rotor-synchronized Hahn echo under magic-angle spinning conditions, and rigid (hard) domains by a solid echo with no magic-angle spinning. The mobility of chains is detected in the PEG phase by 1H,,,13C cross-polarization transfers with 1H spin-lock filters with and without magic-angle spinning. The interface between HBFP and PEG phases is detected by a third experiment, which utilized a 19F,,,1H,(spin diffusion),1H,,,13C double transfer with 13C solid-echo detection. The results of these experiments show that composition-dependent PEG inclusions in the HBFP glass rigidify on hydration, consistent with an increase in macroscopic tensile strength. [source]


    , -Peptide Conjugates: Syntheses and CD and NMR Investigations of ,/, -Chimeric Peptides, of a DPA- , -Decapeptide, and of a PEGylated , -Heptapeptide

    HELVETICA CHIMICA ACTA, Issue 12 2009
    James Gardiner
    Abstract ,3 -Peptides consisting of six, seven, and ten homologated proteinogenic amino acid residues have been attached to an , -heptapeptide (all d- amino acid residues; 4), to a hexaethylene glycol chain (PEGylation; 5c), and to dipicolinic acid (DPA derivative 6), respectively. The conjugation of the , -peptides with the second component was carried out through the N-termini in all three cases. According to NMR analysis (CD3OH solutions), the (M)- 314 -helical structure of the , -peptidic segments was unscathed in all three chimeric compounds (Figs.,2, 4, and 5). The , -peptidic section of the ,/, -peptide was unstructured, and so was the oligoethylene glycol chain in the PEGylated compound. Thus, neither does the appendage influence the , -peptidic secondary structure, nor does the latter cause any order in the attached oligomers to be observed by this method of analysis. A similar conclusion may be drawn from CD spectra (Figs.,1, 3, and 5). These results bode well for the development of delivery systems involving , -peptides. [source]


    Synthesis and Conformational Switching of Partially and Differentially Bridged Resorcin[4]arenes Bearing Fluorescent Dye Labels.

    HELVETICA CHIMICA ACTA, Issue 6 2003
    Preliminary Communication
    We report the synthesis of modified Cram -type cavitands bearing one or two fluorescent labels for single-molecule spectroscopic studies of vasekite conformational switching (Scheme,3). Syntheses were performed by stepwise bridging of the four couples of neighboring H-bonded OH groups of resorcin[4]arene bowls (Schemes,2 and 3). The new substitution patterns enable the construction of a large variety of future functional architectures. 1H-NMR Investigations showed that the new partially and differentially bridged cavitands feature temperature- and pH-triggered vasekite conformational isomerism similar to symmetrical cavitands with four identical quinoxaline bridges (Table). It was discovered that vasekite switching of cavitands is strongly solvent-dependent. [source]


    ChemInform Abstract: Single-Crystal Structure Determination and Solid-State NMR Investigations of Lithium Nitridosilicate Li2SiN2 Synthesized by a Precursor Approach Employing Amorphous "Si(CN2)2".

    CHEMINFORM, Issue 28 2009
    Sandro Pagano
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    Solid-State NMR Investigations on Si,B,C,N Ceramics Derived from Boron-Modified Poly(allylmethylsilazane).

    CHEMINFORM, Issue 16 2005
    Frank Berger
    No abstract is available for this article. [source]


    17O NMR investigation of phosphite hydrolysis mechanisms

    MAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2007
    Sarah K. McIntyre
    Abstract The use of solution 17O NMR spectroscopy in verifying the mechanism of trialkyl phosphite hydrolysis is presented. Trimethyl phosphite was reacted with 17O-labeled H2O at different temperatures and two reactant concentrations, with the reaction being monitored by 17O NMR. Kinetic details elucidated from the NMR spectra are also discussed. Copyright © 2007 John Wiley & Sons, Ltd. [source]


    Xyloccensin X and Y, two new limonoids from xylocarpus molluccensis: NMR investigation in mixture,

    MAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2006
    Abhijeet Deb Roy
    Abstract Two new limonoids, xyloccensin X (1) and xyloccensin Y (2), have been identified in mixture using NMR spectroscopy. Both limonoids were isolated in mixture from the fruit of the plant Xylocarpus molluccensis. The structures of these were proposed after extensive 2D NMR analyses in mixture. Copyright © 2006 John Wiley & Sons, Ltd. [source]


    A solid-state NMR investigation of the structure of nanocrystalline hydroxyapatite

    MAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2006
    Christian Jäger
    Abstract Nanocrystalline hydroxyapatite (HAp) prepared by a precipitation route was investigated. The X-ray diffraction (XRD) powder patterns of the elongated nanocrystals with a typical diameter of about 10 nm and length of 30,50 nm (by transmission electron microscopy (TEM)) revealed the presence of HAp with significantly broadened XRD reflections. However, Ca deficiency was found, as the Ca/P ratio was 1.5 only (so-called calcium-deficient hydroxyapatite (CDHA)), and not 1.67. This Ca deficiency of nanocrystalline HAp is explained using NMR. It is shown unambiguously that (i) the nanocrystals consist of a crystalline core and a (disordered) surface region with a relative phosphate content of about 1:1, (ii) the crystalline core is HAp, and (iii) the surface region is dominated by hydrogen phosphate anions (with no hydroxyapatite-like structural motif) and structural water (hydrate). From the relative phosphate content and taking into account the crystal shape, the thickness of the surface layer along the main crystal axis could be estimated to be about 1 nm, and the average chemical composition of the surface layer has been determined. Finally, a Ca/P ratio of 1.52 was estimated from the NMR data that compares well with the value of 1.51 from chemical analysis. The important consequences are that the surface of nanocrystalline HAp has nothing in common with the bulk composition and that the chemistry of such materials (e.g. the binding of protein molecules to phosphate surfaces) must be reconsidered. Copyright © 2006 John Wiley & Sons, Ltd. [source]


    Theoretical and experimental 13C and 15N NMR investigation of guanylhydrazones in solution

    MAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2003
    Tales L. C. Martins
    Abstract Experimental and theoretical 15N and 13C NMR data for the three nitrobenzaldehyde guanylhydrazones are reported. The theoretical data were obtained using sequential molecular dynamics/quantum mechanics methodology for the calculation of flexible molecules in a condensed phase, followed by the use of the GIAO/DFT method with the 6,311G** basis set. The experimental 15N chemical shifts for the guanylhydrazones are compared with the calculated shifts. Copyright © 2003 John Wiley & Sons, Ltd. [source]


    Pulsed field gradient NMR investigation of solubilization equilibria in amino acid and dipeptide terminated micellar and polymeric surfactant solutions

    MAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2002
    Robin S. Hickok
    Abstract Pulsed field gradient NMR spectroscopy was used to investigate the association of toluene, chlorobenzene and benzyl alcohol with amino acid and dipeptide terminated polymerized surfactants (PS). The diffusion coefficient for each probe was measured in the presence and absence of the polymers and the mole fraction of bound probe molecules, fb, was calculated. For all solutions investigated, the probes associated more strongly with unpolymerized surfactant micelles than with corresponding PS. For example, the toluene fb values for association with sodium undecanoyl valinate micelles and the PS poly(sodium undecanoyl valinate) were 0.88 and 0.15, respectively. The relatively weak probe,polymer association was attributed to the polarity and fluidity of the polymers' hydrocarbon cores and to the fact that these PS have smaller aggregation numbers than the corresponding unpolymerized surfactant micelles. Copyright © 2002 John Wiley & Sons, Ltd. [source]


    Aluminium-27 NMR investigation of the influence of cation type on aluminosilicate solutions

    MAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2002
    Naser Azizi
    Abstract The effects of tetraalkylammonium (TAA) and alkali metal cations on the equilibrium distribution of aluminosilicate oligomers in aqueous alkaline aluminosilicate solutions were investigated using 27Al NMR spectra and their evolution with time. The results indicate that there are no differences in the initial equilibria involving solutions containing both TAA and alkali metal cations on the one hand and those containing alkali metal cations only. However, re-equilibration of the aluminosilicate species for TAA/Na aluminosilicates is slow (usually not detectable on the time-scale of the experiments), whereas when purely alkali metal cations are used, the spectra alter over a period of ,1 h, such that resolution is degraded substantially. In the latter case, it is suggested that the anions aggregate into larger systems, although the solutions are still clear. 29Si NMR evidence for slow equilibration of silicate and aluminosilicate solutions at higher concentrations is also discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source]


    Synthesis and Crystallographic Characterisation of the Heterodimetallic Complex [(Dibenzo-18-crown-6)K(,-Cl)3Ru(,6 - p -cymene)]

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2007
    Carsten A. Vock
    Abstract The triple-chlorido-bridged heterodimetallic dinuclear complex [(dibenzo-18-crown-6)K(,-Cl)3Ru(,6 - p -cymene)] containing an (,6 -arene)RuII fragment and a Group 1 metal crown ether fragment was synthesized and characterized by spectroscopy and X-ray crystallography. The solid-state structure clearly reveals the presence of the triple-chlorido-bridged dinuclear complex, whereas NMR investigations in different deuteriated solvents reveal the presence of an essentially 1:1 mixture of 1 and starting materials, indicating the presence of a dynamic equilibrium. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]


    Electronic Control of the Rotational Barrier in ,2 -Alkyne-1-thio Complexes

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2007
    Wolfram W. Seidel
    Abstract A family of thio-alkyne complexes [Tp,Mo(CO)(L)(BnSC2S)] {Bn = benzyl, Tp, = hydrotris(3,5-dimethylpyrazolyl)borate, L = carbonyl (2), 2,6-dimethylphenyl isocyanide (7), tert -butyl isocyanide (8), 4-(dimethylamino)pyridine (9)} was prepared by reductive removal of a benzyl group in the corresponding bis(benzylthio)acetylene complexes [Tp,Mo(CO)(L)(BnSC2SBn)](PF6) (1 -PF6, 4 -PF6, 5 -PF6 and 6 -PF6). All complexes were characterized by IR, 1H, 13C spectroscopy and cyclic voltammetry. X-ray diffraction studies of 5 -PF6, 8 and 9 were carried out. The alkyne ligand is bound symmetrically to molybdenum in 5 -PF6 and unsymmetrically in 8 and 9. The trend in the ,-acidity of ligand L is reflected in the spectroscopic and electrochemical data as well as in the molecular structures. Variable temperature 1H NMR investigations with 7, 8 and 9 disclosed that the barrier of the alkyne rotation at molybdenum decreases in the order of rising electron density at the metal center while the steric demand increases. Therefore, electronic control of the barrier by the specific character of the ligand L is evident.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]


    NMR T1 -Relaxation Measurements on Paramagnetic Organolanthanides:An Alternative Tool for Structure Determination in Solution

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005
    Laurent Brachais
    Abstract 1H NMR investigations were conducted on four paramagnetic organolanthanides, all bearing the tetraisopropylcyclopentadienyl ligand Cp4i (HC5iPr4) in order to verify whether or not interactions observed in the solid state are maintained in solution. In some cases variable-temperature experiments were necessary to enhance the resolution and determine the best conditions for the study. The 1D NMR spectrum could be interpreted in every case. Complementary 2D COSY experiments allowed the full attribution of the signals. T1 (1H) relaxation values were determined for all the paramagnetic complexes at the most suitable temperature, and compared with those of the diamagnetic KCp4i. The same tendency was observed, with particular features concerning the isopropyl groups. Among the four methyl groups, one exhibits a much higher T1 value and one a much lower value; the two others are intermediate. This was interpreted as the result of a privileged conformation of the Cp4i ligand: the two ,-isopropyl groups take up a spatial orientation with one methyl group in the exo position, opposite to the metal atom, whereas the methyl groups of the two ,-isopropyl groups are equidistant from the metal atom. Whatever the nature of the metal (Nd, Sm), the oxidation state (SmII, SmIII) or the temperature (298, 363 K), this conformation is retained. The structure in solution seems to be different from that previously determined in the solid state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]


    NMR investigations of subunit c of the ATP synthase from Propionigenium modestum in chloroform/methanol/water (4 : 4 : 1)

    FEBS JOURNAL, Issue 7 2002
    Ulrich Matthey
    The subunit c from the ATP synthase of Propionigenium modestum was studied by NMR in chloroform/methanol/water (4 : 4 : 1). In this solvent, subunit c consists of two helical segments, comprised of residues L5 to I26 and G29 to N82, respectively. On comparing the secondary structure of subunit c from P. modestum in the organic solvent mixture with that in dodecylsulfate micelles several deviations became apparent: in the organic solvent, the interruption of the ,,helical structure within the conserved GXGXGXGX motif was shortened from five to two residues, the prominent interruption of the ,,helical structure in the cystoplasmic loop region was not apparent, and neither was there a break in the ,,helix after the sodium ion-binding Glu65 residue. The folding of subunit c of P. modestum in the organic solvent also deviated from that of Escherichia coli in the same environment, the most important difference being that subunit c of P. modestum did not adopt a stable hairpin structure like subunit c of E. coli. [source]


    Composition of the essential oil of flowers of Chloranthus spicatus (Thunb.) Makino

    FLAVOUR AND FRAGRANCE JOURNAL, Issue 4 2006
    Hailemichael Tesso
    Abstract The composition of the essential oil of the flowers of Chloranthus spicatus (Thunb.) Makino (Chloranthaceae) was investigated using capillary GC-GC/MS, preparative GC and NMR techniques. Forty-seven compounds were identified either by comparing their retention indices and mass spectra with a library of authentic samples established under identical experimental conditions or, by isolating the compounds and deriving their structures by one- and two-dimensional NMR investigations. Thus, four minor components, viz. chloranthalactone A (0.5%), isogermafurenolide (0.7%), eudesma-4(15),7(11),9-trien-12-olide (0.5%), and 7, -hydroxyeudesm-4-en-6-one (3.3%), were isolated for the first time as constituents of the essential oil of the flowers of C. spicatus and their structures established. The major components of the oil include (Z)- , -ocimene (6.3%), allo-aromadendrene (6.2%), sarisane (2-allyl-4,5-methylenedioxyanisol, 4.2%) and selina-4(15),7(11)-diene (6.4%). Copyright © 2006 John Wiley & Sons, Ltd. [source]


    A verticillane-type diterpene from Boswellia carterii essential oil

    FLAVOUR AND FRAGRANCE JOURNAL, Issue 5 2001
    Simla Basar
    Abstract The essential oil of Boswellia carterii resinoid (olibanum) was investigated by GC,MS. In addition to known compounds, a new verticillane-type diterpene was isolated and identified by NMR investigations as verticilla-4(20),7,11-triene. Copyright © 2001 John Wiley & Sons, Ltd. [source]


    Chemical Approach for the Study of the ,Kissing Complex' of Moloney murine leukaemia Virus

    HELVETICA CHIMICA ACTA, Issue 7 2008
    Sébastien Porcher
    Abstract The replication of Moloney murine leukaemia virus relies on the formation of a stable homodimeric ,kissing complex' of a GACG tetraloop interacting through only two C,G base pairs flanked of 5,-adjacent unpaired adenosines A9. Previous NMR investigations of a model stem loop 1 has not permitted to reveal the origin of this interaction. Therefore, with the aim of deeper comprehension of the phenomena, the model sequence 10 was prepared where position 9 has been substituted for a nucleoside offering a wider , -stacking. In this context, the wyosine phosphoramidite building block 2 was prepared and incorporated by adapting the conditions of the automated synthesis and developing original templated enzymatic ligation. However, no ,kissing interaction' has been observed for this model sequence 10 due to steric hindrance as confirmed by computational simulation. Consequently, several other model sequences, 18, 23,26, containing modified nucleosides were prepared. Finally, the importance of the cross-loop H-bond between G8 and G11 nucleobases was revealed by preparing a 18mer RNA hairpin 27, where the guanosine G8 has been substituted for inosine. The latter, which does not possess a C3 amino function compared to guanosine, is unable to form any ,kissing complex' demonstrating the importance of this secondary interaction in the formation of the complex. [source]


    Effect of non-exponential and multi-exponential decay behavior on the performance of the direct exponential curve resolution algorithm (DECRA) in NMR investigations

    JOURNAL OF CHEMOMETRICS, Issue 11 2003
    Todd M. Alam
    Abstract The effect of non-exponential and multi-exponential decay or relaxation behavior on the performance of the direct exponential curve resolution algorithm (DECRA) is investigated through a series of numerical simulations. Three different combinations of decay or relaxation behavior were investigated through DECRA analysis of simulated pulse gradient spin echo (PGSE) NMR diffusion spectra that contained the combination of two individual components. The diffusion decay behavior of one component was described by a single-exponential decay, while the second component was described by either (1) a multi-exponential decay, (2) a decay behavior described by the empirical Kohlrausch,Williams,Watts (KWW) relation or (3) a multi-exponential decay behavior correlated with variations in the NMR spectral line shape. The magnitudes and types of errors produced during the DECRA analysis of spectral data with deviations from a pure single-exponential decay behavior are presented. It is demonstrated that the deviation from single-exponential decay impacts the resulting calculated line shapes, the calculated relative concentrations and the quantitative estimation of the decay or relaxation time constants of both components present in the NMR spectra. Copyright © 2004 John Wiley & Sons, Ltd. [source]


    A type-II , -turn, proline-containing, cyclic pentapeptide as a building block for the construction of models of the cleavage site of pro-oxytocin

    JOURNAL OF PEPTIDE SCIENCE, Issue 7 2001
    Monica Dettin
    Abstract Previous studies have indicated that proteolytic activation of pro-hormones and pro-proteins occurs most frequently at the level of basic amino acids arranged in doublets and that the dibasic sites are situated in or next to , -turns. Investigations utilizing synthetic peptides reproducing the N -terminal processing domain of pro-oxytocin-neurophysin have suggested a close relationship between the secondary structure of the cleavage locus and enzyme recognition, the minimal recognized sequence being the -Pro-Leu-Gly-Gly-Lys-Arg-Ala-Val-Leu- segment of the native precursor. NMR investigations and energy minimization studies have demonstrated that this sequence is organized in two type-II , -turns involving the -Pro-Leu-Gly-Gly- and -Lys-Arg-Ala-Val- sequences. To further strengthen the above reported hypothesis and to study the role of turn subtypes, a new proline containing cyclic substrate of the processing enzyme, in which the N -terminal side that comes before the Lys-Arg pair is constrained to adopt a type-II , -turn, has been synthesized. The presence of a type-II , -turn structure in this cyclic peptide model has been demonstrated by a combined NMR, CD and FT-IR absorption investigation. A preliminary study shows that PC1 is able to recognize and process our constrained substrate. Copyright © 2001 European Peptide Society and John Wiley & Sons, Ltd. [source]


    Phase Biaxility in Smectic-A Side-Chain Liquid Crystalline Elastomers

    MACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2009
    Rebekka Storz
    Abstract 2H NMR investigations on the biaxial phase behavior of smectic-A liquid crystalline side-chain elastomers are presented. Biaxiality parameters were determined by measuring the quadrupolar splitting of two spin probes, namely benzene-d6 and hexamethylbenzene-d18, at various angles between the principal director and the external magnetic field: while for a uniaxial sample the angular dependence can be described by the second Legendre polynomial, an additional asymmetric term needs to be included to fit the data of the two investigated biaxial systems. Two elastomers synthesized from mesogens that differ in the molecular geometry in order to study the molecular origin of biaxiality were compared. Biaxiality is observed for both elastomers when approaching the glass transition, suggesting that the network dynamics dominate the formation of the biaxial phase. [source]


    N-terminal extension changes the folding mechanism of the FK506-binding protein

    PROTEIN SCIENCE, Issue 9 2001
    Alla Korepanova
    Abstract Many of the protein fusion systems used to enhance the yield of recombinant proteins result in the addition of a small number of amino acid residues onto the desired protein. Here, we investigate the effect of short (three amino acid) N-terminal extensions on the equilibrium denaturation and kinetic folding and unfolding reactions of the FK506-binding protein (FKBP) and compare the results obtained with data collected on an FKBP variant lacking this extension. Isothermal equilibrium denaturation experiments demonstrated that the N-terminal extension had a slight destabilizing effect. NMR investigations showed that the N-terminal extension slightly perturbed the protein structure near the site of the extension, with lesser effects being propagated into the single ,-helix of FKBP. These structural perturbations probably account for the differential stability. In contrast to the relatively minor equilibrium effects, the N-terminal extension generated a kinetic-folding intermediate that is not observed in the shorter construct. Kinetic experiments performed on a construct with a different amino acid sequence in the extension showed that the length and the sequence of the extension both contribute to the observed equilibrium and kinetic effects. These results point to an important role for the N terminus in the folding of FKBP and suggest that a biological consequence of N-terminal methionine removal observed in many eukaryotic and prokaryotic proteins is to increase the folding efficiency of the polypeptide chain. [source]


    High Resolution 1H NMR investigations of the oxidative consumption of salivary biomolecules by ozone: Relevance to the therapeutic applications of this agent in clinical dentistry

    BIOFACTORS, Issue 1-4 2006
    Martin Grootveld
    Abstract High resolution proton (1H ) nuclear magnetic resonance (NMR) spectroscopy was employed to simultaneously evaluate the oxidising actions of ozone (O3) towards a wide range of salivary biomolecules in view of its applications in dental practices, which may serve as a viable and convenient means for the treatment of dental caries. Treatment of supernatants derived from unstimulated human saliva specimens (n=12) with O3 (4.48 mmol) revealed that this reactive oxygen species gave rise to the oxidative consumption of pyruvate (generating acetate and CO2 as products), lactate (to pyruvate and sequentially acetate and CO2), carbohydrates in general (a process generating formate), methionine (giving rise to its corresponding sulphoxide), and urate (to allantoin). Further, minor O3 -induced modifications included the oxidation of trimethylamine and 3-D-hydroxybutyrate, the fragmentation of salivary glycosaminoglycans to NMR-detectable saccharide fragments, and the conversion of polyunsaturated fatty acids to their ozonides. Moreover, evidence for the ability of O3 to induce the release of selected low-molecular-mass salivary biomolecules from macromolecular binding-sites was also obtained. Since many of the oxidation products detectable in O3 -treated samples are identical to those arising from the attack of ,OH radical on biofluid components, it appears that at least some of the modifications observed here are attributable to the latter oxidant (derived from O generated from the single electron reduction of O3). [source]