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Correlation Experiments (correlation + experiment)
Selected AbstractsLong-range JCH heteronuclear coupling constants in cyclopentane derivatives.MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2007Part II Abstract Here we report the detailed measurement of long-range heteronuclear spin,spin coupling constants, especially 2, 3JCH spin,spin couplings for eight different cyclopentane derivatives. These 2, 3JCH constants were shown to be a useful tool in the determination of the relative stereochemistry in these rings. The coupling constant measurements reported here are based on two different experiments: a 2D heteronuclear correlation experiment named G-BIRDR, X -CPMG-HSQMBC and the 2D-coupled gHSQC {1H- 13C} experiment Copyright © 2006 John Wiley & Sons, Ltd. [source] Methyl TROSY: explanation and experimental verificationMAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2003Jason E. Ollerenshaw Abstract In TROSY experiments, relaxation interference effects are exploited to produce spectra with improved resolution and signal-to-noise. Such experiments cannot be explained using the standard product operator formalism, but must instead be analyzed at the level of individual density matrix elements. Herein we illustrate this point using an example from our recent work on a TROSY 1H,13C correlation experiment for methyl groups in large proteins. Methyl groups are useful spectroscopic probes of protein structure and dynamics because they are found throughout the critical core region of a folded protein and their resonances are intense and well dispersed. Additionally, it is relatively easy to produce highly deuterated protein samples that are 1H,13C labeled at selected methyl positions, facilitating studies of high molecular weight systems. Methyl groups are relaxed by a network of 1H,1H and 1H,13C dipolar interactions, and in the macromolecular limit the destructive interference of these interactions leads to unusually slow relaxation for certain density matrix elements. It is this slow relaxation that forms the basis for TROSY experiments. We present a detailed analysis of evolution and relaxation during HSQC and HMQC pulse schemes for the case of a 13C1H3 spin system attached to a macromolecule. We show that the HMQC sequence is already optimal with respect to the TROSY effect, offering a significant sensitivity enhancement over HSQC at any spectrometer field strength. The gain in sensitivity is established experimentally using samples of two large proteins, malate synthase G (81.4 kDa) and ClpP protease (305 kDa), both highly deuterated and selectively 1H,13C-labeled at isoleucine , methyl positions. Copyright © 2003 John Wiley & Sons, Ltd. [source] An accessible two-dimensional solution nuclear magnetic resonance experiment on human ubiquitin,BIOCHEMISTRY AND MOLECULAR BIOLOGY EDUCATION, Issue 2 2005David Rovnyak Abstract Solution-state nuclear magnetic resonance (NMR) is an invaluable tool in structural and molecular biology research, but may be underutilized in undergraduate laboratories because instrumentation for performing structural studies of macromolecules in aqueous solutions is not yet widely available for use in undergraduate laboratories. We have implemented an experiment that is ideal for more commonly available 4.8,7.0 Tesla, double-channel NMR instruments that would not usually be used for biomolecular NMR work. We analyzed a commercially available, 15N-enriched human ubiquitin sample with a two-dimensional correlation experiment using indirect 1H evolution and direct 15N detection, which produced spectra with high resolution on a spectrometer operating at 7.0 Tesla (300 MHz 1H resonance frequency). The simplicity of the experiment makes it possible to be configured by undergraduate students with minimal supervision from the instructor. Students gain experience in acquiring multidimensional biomolecular NMR experiments, confirm that ubiquitin is stably folded, and observe the correspondence between specific signals and individual amino acids in ubiquitin. [source] Syntheses and Coordination Chemistry of Aminomethylphosphine Derivatives of AdenineEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2003Qingzhi Zhang Abstract Two aminomethylphosphane derivatives of adenine 9-(2-{bis[(diphenylphosphanyl)methyl]amino}ethyl)adenine (La) and 9-(3-{bis[(diphenylphosphanyl)methyl]amino}propyl)adenine (Lb) were synthesised. Oxidation of La and Lb with H2O2, elemental sulfur or elemental selenium led to the corresponding oxidized products 4a/b,6a/b. Both La and Lb behave as didentate ligands towards late transition metals. Reaction of La or Lb with [MX2(cod)] (M = Pd, Pt; X = Cl, Me) gave chelate complexes 7a/b,10a/b. Reaction of La or Lb with [AuCl(tht)] or [{RuCl(,-Cl)(p -MeC6H4iPr)}2] gave the didentate bridging complexes 11a/b and 12a. All compounds have been fully characterised by microanalysis, IR, 1H and 31P{1H} NMR spectroscopy, and EI/CI/FAB mass spectrometry. 1H{31P} NMR and 1H- 13C correlation experiments were used to confirm the spectral assignments where necessary. Two compounds were structurally characterised by X-ray crystallographic analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Testosterone 1,-hydroxylation by human cytochrome P450 3A4FEBS JOURNAL, Issue 19 2004Joel A. Krauser Human cytochrome P450 3A4 forms a series of minor testosterone hydroxylation products in addition to 6,-hydroxytestosterone, the major product. One of these, formed at the next highest rate after the 6,- and 2,-hydroxy products, was identified as 1,-hydroxytestosterone. This product was characterized from a mixture of testosterone oxidation products using an HPLC-solid phase extraction-cryoprobe NMR/time-of-flight mass spectrometry system, with an estimated total of ,,6 µg of this product. Mass spectrometry established the formula as C19H29O3 (MH+ 305.2080). The 1-position of the added hydroxyl group was established by correlated spectroscopy and heteronuclear spin quantum correlation experiments, and the ,-stereochemistry of the added hydroxyl group was assigned with a nuclear Overhauser correlated spectroscopy experiment (1,-H). Of several human P450s examined, only P450 3A4 formed this product. The product was also formed in human liver microsomes. [source] Indirect detection of the 183W and 57Fe nuclei using 119Sn-relayed 1H,X correlation spectroscopyMAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2010T. Andrew Mobley Abstract Recently reported triple-resonance Y-relayed 1H,X correlation experiments have been utilized to characterize 183W and 57Fe chemical shifts using 119Sn as the Y-relaying nucleus instead of the previously used 31P. Application of an adaptation of Gudat's original INEPT/HMQC sequence results in a significant enhancement of the signal-to-noise (S/N) ratio for two-dimensional 119Sn-relayed 1H,183W and 1H, 57Fe correlation spectra with efficient detection of the transition metal nucleus in tungsten and iron complexes lacking an observable direct scalar coupling between the transition metal and any hydrogen nuclei. Strengths and shortcomings of the novel sequence and the original sequences reported by Gudat are discussed in the context of 119Sn-relayed proton detection of very low frequency transition metal nuclei. Copyright © 2010 John Wiley & Sons, Ltd. [source] High-resolution NMR correlation experiments in a single measurement (HR-PANACEA)MAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2010riks Kup Abstract Three important NMR pulse sequences, INADEQUATE, HSQC and three-dimensional HMBC have been combined into a single entity called high-resolution Parallel Acquisition NMR: an All-in-one Combination of Experimental Applications (HR-PANACEA) to provide reliable structural information about a small molecule in a single measurement. This exploits a recent instrumental development that permits simultaneous acquisition of signals from several nuclear species, using multiple receivers. Where high-precision values of the long-range heteronuclear splittings are important, selected regions of a large experimental data matrix are extracted and examined with the highest possible resolution. The J -doubling technique is then applied to derive precise values for these couplings. As proof of principle, the method is applied to the molecule of methyl salicylate, confirming the expected conformation of the COH moiety. Copyright © 2010 John Wiley & Sons, Ltd. [source] Complete multinuclear magnetic resonance characterization of a set of polyfluorinated acids and alcoholsMAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2009Alexander A. Marchione Abstract A complete 1H, 19F, and 13C NMR assignment of a homologous series of polyfluorinated acids and alcohols is reported. These assignments were obtained chiefly through single and multiple-bond 1H,13C and 19F,13C correlation experiments (HSQC, HMBC). 19F NOESY experiments were required for assignment of two compounds with diastereotopic 19F nuclei in the CF2chain of the molecule. Copyright © 2008 John Wiley & Sons, Ltd. [source] Isoquinoline alkaloids: a 15N NMR and x-ray study.MAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2002Part Abstract Continuing our systematic 15N NMR study of isoquinoline alkaloids, we report a contribution extending our previous paper. The 15N NMR chemical shifts and 15N,1H long-range coupling pathways of tertiary and quaternary isoquinoline alkaloids of several constitutional types are presented. The selected compounds belong to the protoberberine, proaporphine, pavinane, rhoeadine and phtalideisoquinoline classes of alkaloids and were investigated by gradient-selected inverse-detected multiple bond correlation experiments (GHMBC and GSQMBC). In addition, x-ray data and the principal geometric parameters of stylopine, mecambridine, norchelerythrine, isothebaine and mecambrine are reported and discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Structural investigations of isomeric oxidised forms of hyperforin by HPLC-NMR and HPLC-MSnPHYTOCHEMICAL ANALYSIS, Issue 5 2003J.-L. Wolfender Abstract The prenylated phloroglucinol hyperforin, thought to be an essential component for the anti-depressant activity of St. John's Wort (Hypericum perforatum), is unstable. The facile oxidative degradation of hyperforin poses serious problems for standardisation, and may also dramatically affect the pharmacological activity of the extracts. Hyperforin was dissolved in hexane and stored at room temperature for 3 days and yielded various closely related degradation products which, although dif,cult to isolate on the preparative scale, have been analysed by on-,ow and stop-,ow HPLC-NMR and HPLC-MS/MS. From on-line spectroscopic data, and with the aid of complementary in-mixture standard NMR two-dimensional correlation experiments, the different oxidised forms of hyperforin were found to be phloroglucinol derivatives in which a hydroxy-dihydrofuran ring is formed involving the enol OH at C-7 or C-9 (tautomeric form) and the prenyl chain at C-8 of the core nucleus of hyperforin. The strategy followed for the on-line identi,cation of these constituents is discussed. Copyright © 2003 John Wiley & Sons, Ltd. [source] Chemical shift assignment of the transmembrane helices of DsbB, a 20-kDa integral membrane enzyme, by 3D magic-angle spinning NMR spectroscopyPROTEIN SCIENCE, Issue 2 2008Ying Li Abstract The Escherichia coli inner membrane enzyme DsbB catalyzes disulfide bond formation in periplasmic proteins, by transferring electrons to ubiquinone from DsbA, which in turn directly oxidizes cysteines in substrate proteins. We have previously shown that DsbB can be prepared in a state that gives highly resolved magic-angle spinning (MAS) NMR spectra. Here we report sequential 13C and 15N chemical shift assignments for the majority of the residues in the transmembrane helices, achieved by three-dimensional (3D) correlation experiments on a uniformly 13C, 15N-labeled sample at 750-MHz 1H frequency. We also present a four-dimensional (4D) correlation spectrum, which confirms assignments in some highly congested regions of the 3D spectra. Overall, our results show the potential to assign larger membrane proteins using 3D and 4D correlation experiments and form the basis of further structural and dynamical studies of DsbB by MAS NMR. [source] Structure of an elastin-mimetic polypeptide by solid-state NMR chemical shift analysisBIOPOLYMERS, Issue 2 2003M. Hong Abstract The conformation of an elastin-mimetic recombinant protein, [(VPGVG)4(VPGKG)]39, is investigated using solid-state NMR spectroscopy. The protein is extensively labeled with 13C and 15N, and two-dimensional 13C- 13C and 15N- 13C correlation experiments were carried out to resolve and assign the isotropic chemical shifts of the various sites. The Pro 15N, 13C,, and 13C, isotropic shifts, and the Gly-3 C, isotropic and anisotropic chemical shifts support the predominance of type-II ,-turn structure at the Pro-Gly pair but reject a type-I ,-turn. The Val-1 preceding Pro adopts mostly ,-sheet torsion angles, while the Val-4 chemical shifts are intermediate between those of helix and sheet. The protein exhibits a significant conformational distribution, shown by the broad line widths of the 15N and 13C spectra. The average chemical shifts of the solid protein are similar to the values in solution, suggesting that the low-hydration polypeptide maintains the same conformation as in solution. The ability to measure these conformational restraints by solid-state NMR opens the possibility of determining the detailed structure of this class of fibrous proteins through torsion angles and distances. © 2003 Wiley Periodicals, Inc. Biopolymers 70: 158,168, 2003 [source] Boomerang-Type Substitution Reaction: Reactivity of Fullerene Epoxides and a HalofullerenolCHEMISTRY - AN ASIAN JOURNAL, Issue 2 2007Zhenshan Jia Abstract The Cs -symmetric fullerene chlorohydrin C60(Cl)(OH)(OOtBu)4 reacts with 4-dimethylaminopyridine (DMAP) and 1,4-diazabicyclo[2.2.2]octane (DABCO) to yield two isomers with the formula C60(O)(OOtBu)4 in good yields. These isomers differ with respect to the location of the epoxy functionality. The one from DMAP is Cs symmetric, whereas that from DABCO is C1 symmetric with the epoxy group on the central pentagon. Two different mechanisms are proposed to explain the chemoselectivity of these reactions. The reaction with DMAP involves single-electron transfer as the key step; DMAP acts as the electron donor. A combination of an oxygen-atom shift and SN2,, processes (boomerang substitution) are responsible for the formation of isomer with DACBO. Various related reactions support the proposed mechanisms. The structures of new fullerene derivatives were determined by spectroscopy, single-crystal X-ray analysis, and chemical correlation experiments. [source] | ||||||||||