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Two-dimensional NMR Spectroscopy (two-dimensional + nmr_spectroscopy)
Selected AbstractsBasic One- and Two-Dimensional NMR Spectroscopy.CHEMPHYSCHEM, Issue 6 2005Completely Revised, Fourth, Updated Edition. No abstract is available for this article. [source] Transient complexes of redox proteins: structural and dynamic details from NMR studiesJOURNAL OF MOLECULAR RECOGNITION, Issue 6 2004Miguel Prudêncio Abstract Redox proteins participate in many metabolic routes, in particular those related to energy conversion. Protein,protein complexes of redox proteins are characterized by a weak affinity and a short lifetime. Two-dimensional NMR spectroscopy has been applied to many redox protein complexes, providing a wealth of information about the process of complex formation, the nature of the interface and the dynamic properties of the complex. These studies have shown that some complexes are non-specific and exist as a dynamic ensemble of orientations while in other complexes the proteins assume a single orientation. The binding interface in these complexes consists of a small hydrophobic patch for specificity, surrounded by polar, uncharged residues that may enhance dissociation, and, in most complexes, a ring or patch of charged residues that enhances the association by electrostatic interactions. The entry and exit port of the electrons is located within the hydrophobic interaction site, ensuring rapid electron transfer from one redox centre to the next. Copyright © 2004 John Wiley & Sons, Ltd. [source] SPEED: single-point evaluation of the evolution dimensionMAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2007Eriks Kup Abstract Two-dimensional NMR spectroscopy can be speeded up by orders of magnitude by severely restricting the number of sampling operations in the evolution dimension,we demonstrate that just a single measurement may suffice. The frequencies evolving in the indirect dimension (t1) are deduced from the amplitudes of the signals acquired in the direct dimension (t2). Prior measurements of the one-dimensional spectra are required. Results are presented for the two-dimensional 13C-HSQC spectrum of 2-ethylindanone recorded at a single fixed setting of the evolution time, demonstrating a speed advantage of 120. The method can be extended to multidimensional spectra, with correspondingly greater gains in speed. Copyright © 2007 John Wiley & Sons, Ltd. [source] NMR studies of chiral organic compounds in non-isotropic phasesCONCEPTS IN MAGNETIC RESONANCE, Issue 3 2008Marek J. Potrzebowski Abstract In this article, new applications and perspectives of one- and two-dimensional NMR spectroscopy for study of chiral organic compounds in the non-isotropic phases (solid state and liquid crystals) are presented. The review is organized into five sections. In the first part, theoretical background and short introduction to solid state NMR are shown. The second part presents how NMR isotropic chemical shift can be used for distinguishing of racemates and enantiomers. In the third section, the power of the ODESSA pulse sequence for investigation of racemates, enantiomers and establishing of enantiomeric excess are discussed. The fourth part shows the application of analysis of principal elements of chemical shift tensors obtained by means of 2D NMR techniques for searching of absolute configuration and conformational changes in the solid state. The final part presents recent achievements of chiral liquid crystals NMR methodology for study of chiral compounds. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A:201,218, 2008. [source] Isolation and structural characterization of an R-form lipopolysaccharide from Yersinia enterocolitica serotype O:8FEBS JOURNAL, Issue 3 2001Clemens Oertelt The lipopolysaccharide (LPS) of strain 8081-c-R2, a spontaneous R-mutant of Yersinia enterocolitica serotype O:8, was isolated using extraction with phenol/chloroform/light petroleum. Its compositional analysis indicated the presence of d -GlcN, d -Glc, lglycerodmanno - and dglycerodmanno -heptose, 3-deoxy- dmanno -oct-2-ulosonic acid (Kdo) and phosphate. From deacylated LPS obtained after successive treatment with hydrazine and potassium hydroxide, three oligosaccharides (1,3) were isolated using high-performance anion-exchange chromatography, the structures of which were determined by compositional analysis and one- and two-dimensional NMR spectroscopy as in which all sugars are pyranoses, and R and R, represent ,- d -Glc (in 1 and 2) and ,- d -GlcN (in 1 only), respectively. d -,- d -Hep is dglycero -,- dmanno -heptose, l -,- d -Hep is lglycero -,- dmanno- heptose, Kdo is 3-deoxy- dmanno -oct-2-ulosonic acid, and P is phosphate. The liberated lipid A was analyzed by compositional analyses and MALDI-TOF MS. Its ,- d -GlcN4P-(1,6)-,- d -GlcN-1,P backbone is mainly tetra-acylated with two amide- and one ester-linked (at O3 of the reducing GlcN) (R)-3-hydroxytetradecanoic acid residues, and one tetradecanoic acid that is attached to the 3-OH group of the amide-linked (R)-3-hydroxytetradecanoic acid of the nonreducing GlcN. Additionally, small amounts of tri- and hexa-acylated lipid A species occur. [source] Reduction of cis - and trans -1,2-epithio- p -menth-8-ene: preparation of new fragrant terpenoid thiolsFLAVOUR AND FRAGRANCE JOURNAL, Issue 1 2003Karine Candela Abstract The synthesis of 2-mercapto- p -menth-8-ene (3) and 1-mercapto- p -menth-8-ene (4) are described, starting, respectively, from thioepoxydation of (+)- trans -limonene 1,2-epoxide (1a) and (+)- cis -limonene 1,2-epoxide (1b) via hydride reduction of episulphides 2a and 2b. Structural determination of these sulphur-containing terpenoids was achieved by one- and two-dimensional NMR spectroscopy. The odours of these two new monoterpene thiols were described, respectively, as reminescent of grapefruit juice and as being typically alliaceous. Copyright © 2002 John Wiley & Sons, Ltd. [source] Structure determination of oligomeric alkannin and shikonin derivativesBIOMEDICAL CHROMATOGRAPHY, Issue 7 2005Apostolos Spyros Abstract Monomeric alkannin and shikonin (A/S) are potent pharmaceutical substances with a wide spectrum of biological activity and comprise the active ingredients for several pharmaceutical preparations. Therefore, the determination of the impurities, degradation products or byproducts in alkannin and shikonin samples is of great importance. Oligomeric alkannin and shikonin are formed during biosynthesis of these bioactive secondary metabolites in Boraginaceaous root plants, during tissue culture production of A/S, during alkaline hydrolysis of A/S esters and also thermal treatment of A/S. In the present study, a dimeric alkannin/shikonin compound was isolated by size exclusion chromatography from alkannin and shikonin commercial samples and its structure was determined by one- and two-dimensional NMR spectroscopy. The structure of the most abundant oligomeric species in these samples, a dimeric naphthoquinone, was established for the ,rst time, indicating that coupling of the side chain of one naphthoquinone unit with the aromatic ring of a second naphthoquinone leads to dimer formation. This type of coupling allows further oligomerization by leaving one isohexenyl side chain available at the second monomer unit. Copyright © 2005 John Wiley & Sons, Ltd. [source] Full Structure of the Carbohydrate Chain of the Lipopolysaccharide of Providencia rustigianii,O34CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2008Abstract A lipopolysaccharide isolated from an opportunistic pathogen of the Enterobacteriaceae family Providencia rustigianii,O34 was found to be a mixture of R-, SR-, and S - forms consisting of a lipid moiety (lipid,A) that bears a core oligosaccharide, a core with one O-polysaccharide repeating unit attached, and a long-chain O-polysaccharide, respectively. The corresponding carbohydrate moieties were released from the lipopolysaccharide by mild acid hydrolysis and studied by sugar and methylation analyses along with one- and two-dimensional NMR spectroscopy and high-resolution electrospray ionization mass spectrometry. As a result, the structures of the core and the O-polysaccharide were established, including the structure of the biological repeating unit (an oligosaccharide that is preassembled and polymerized in biosynthesis of the O-polysaccharide), as well as the mode of the linkage between the O-polysaccharide and the core. Combining the structure of the carbohydrate moiety thus determined and the known structure of lipid,A enabled determination of the full lipopolysaccharide structure of P. rustigianii,O34. [source] Face-Selective [2]- and [3]Rotaxanes: Kinetic Control of the Threading Direction of CyclodextrinsCHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2007Tomoya Oshikiri Abstract New [2]- and [3]pseudorotaxanes containing ,-cyclodextrin (,-CDs) molecules as rotors and alkyl pyridinium derivatives as axles were prepared by a slipping process. The inclusion behavior of these rotaxanes was investigated by using one- and two-dimensional NMR spectroscopy. The methyl group at the 2-position of the pyridinium moiety at the end of each axle molecule was found to control the rates of threading of the ,-CD onto the axle molecules. ,-CD can approach axle molecules from a particular direction to form inclusion complexes. Axle molecules that contain a 2-methylpyridinium moiety at one end and a bulky stopper at the other end can regulate the direction of approach to give a [2]pseudorotaxane such as 2,b,,-CD. A [3]pseudorotaxane in which two ,-CD molecules are arranged facing in the same direction at two stations of the tetracationic axle molecule was also obtained. These face-selective behaviors are dominated by kinetic processes rather than thermodynamic processes. [source] A [3]Rotaxane with Three Stable States That Responds to Multiple-Inputs and Displays Dual Fluorescence AddressesCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2005Da-Hui Qu Abstract A [3]rotaxane molecular shuttle containing two ,-cyclodextrin (,-CD) macrocycles, an azobenzene unit, a stilbene unit, and two different fluorescent naphthalimide units has been investigated. The azobenzene unit and the stilbene unit can be E/Z -photoisomerized separately by light excited at different wavelengths. Irradiation at 380 nm resulted in the photoisomerization of the azobenzene unit, leading to the formation of one stable state of the [3]rotaxane (Z1- NNAS-2CD); irradiation at 313 nm resulted in the photoisomerization of the stilbene unit, leading to the formation of another stable state of the [3]rotaxane (Z2- NNAS-2CD). The reversible conversion of the Z1 and Z2 isomers back to the E isomer by irradiation at 450 nm and 280 nm, respectively, is accompanied by recovery of the absorption and fluorescence spectra of the [3]rotaxane. The E isomer and the two Z isomers have been characterized by 1H NMR spectroscopy and by two-dimensional NMR spectroscopy. The light stimuli can induce shuttling motions of the two ,-CD macrocycles on the molecular thread; concomitantly, the absorption and fluorescence spectra of the [3]rotaxane change in a regular way. When the ,-CD macrocycle stays close to the fluorescent moiety, the fluorescence of the moiety become stronger due to the rigidity of the ,-CD ring. As the photoisomerization processes are fully reversible, the photo-induced shuttling motions of the ,-CD rings can be repeated, accompanied by dual reversible fluorescence signal outputs. The potential application of such light-induced mechanical motions at the molecular level could provide some insight into the workings of a molecular machine with entirely optical signals, and could provide a cheap, convenient interface for communication between micro- and macroworlds. [source] Enantioselective Fluorescence Sensing of Amino Acids by Modified Cyclodextrins: Role of the Cavity and Sensing MechanismCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2004Sara Pagliari Dr. Abstract Two selectors based on modified cyclodextrins containing a metal binding site and a dansyl fluorophore,6-deoxy-6- N -(N, -[(5-dimethylamino-1-naphthalenesulfonyl)aminoethyl]phenylalanylamino-,-cyclodextrin,containing D -Phe (3) and L -Phe (4) moieties were synthesized. The conformations of the two selectors were studied by circular dichroism, two-dimensional NMR spectroscopy and time-resolved fluorescence spectroscopy. Cyclodextrin 4 was found to have a predominant conformation in which the dansyl group is self-included in the cyclodextrin cavity, while 3 showed a larger proportion of the conformation with the dansyl group outside the cavity. As a consequence, the two cyclodextrins were found to bind copper(II) with different affinities, as revealed by fluorescence quenching in competitive binding measurements. Addition of D - or L -amino acids induced increases in fluorescence intensity, which were dependent on the amino acid used and in some cases on its absolute configuration. The cyclodextrin 4 was found to be more enantioselective than 3, suggesting that the self-inclusion in the cyclodextrin cavity strongly increases the chiral discrimination ability of the copper(II) complex. Accordingly, a linear fluorescent ligand N, -[(5-dimethylamino-1-naphthalenesulfonyl)aminoethyl]- N1 -propyl-phenylalaninamide, which has the same binding site and absolute configuration as 4, showed very low chiral discrimination ability. The enantioselectivity in fluorescence response was found to be due to the formation of diastereomeric ternary complexes, which were detected by ESI-MS and by circular dichroism. Time-resolved fluorescence studies showed that the fluorescence of the dansyl group was completely quenched in the ternary complexes formed, and that the residual fluorescence was due to uncomplexed ligand. [source] Structure of an Extracellular Polysaccharide from a Strain of Lactic Acid BacteriaCHINESE JOURNAL OF CHEMISTRY, Issue 12 2003Xiao-Mei Gu Abstract A new extracellular polysaccharide (EPS-I) isolated and purified from Z222, a strain of Lactic acid bacteria has been investigated. Sugar composition analysis, methylation analysis and 1H NMR and 13C NMR spectroscopy reveal that the EPS-I is composed of a pentasaccharide repeating unit. The sequence of sugar residue was determined by using two-dimensional NMR spectroscopy, including heteronuclear multiple-bond correlation (HMBC) and nuclear overhauser effect spectroscopy (NOESY). [source] | ||||||||||||||||||||||