Heteronuclear Multiple Quantum Correlation Spectroscopy Research Articles

Heteronuclear Correlation Experiments Such as Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC), Heteronuclear Multiple-Quantum Correlation Spectroscopy (HMQC) and Heteronuclear Multiple-Bond Correlation Spectroscopy (HMBC) Comparative Study On Malignant and Benign Human Endocrinology and Thyroid Cancer Cells and Tissues Under Synchrotron Radiation

Heteronuclear Correlation Experiments Such as Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC), Heteronuclear Multiple-Quantum Correlation Spectroscopy (HMQC) and Heteronuclear Multiple-Bond Correlation Spectroscopy (HMBC) Comparative Study On Malignant and Benign Human Endocrinology and Thyroid Cancer Cells and Tissues Under Synchrotron Radiation

Two-dimensional NMR spectroscopy reveals cation-triggered backbone degradation in polysulfone-based anion exchange membranes

Anion exchange membranes (AEMs) find widespread applications as an electrolyte and/or electrode binder in fuel cells, electrodialysis stacks, flow and metal-air batteries, and electrolyzers. AEMs exhibit poor stability in alkaline media; their degradation is induced by the hydroxide ion, a potent nucleophile. We have used 2D NMR techniques to investigate polymer backbone stability (as opposed to cation stability) of the AEM in alkaline media. We report the mechanism behind a peculiar, often-observed phenomenon, wherein a demonstrably stable polysulfone backbone degrades rapidly in alkaline solutions upon derivatization with alkaline stable fixed cation groups. Using COSY and heteronuclear multiple quantum correlation spectroscopy (2D NMR), we unequivocally demonstrate that the added cation group triggers degradation of the polymer backbone in alkaline via quaternary carbon hydrolysis and ether hydrolysis, leading to rapid failure. This finding challenges the existing perception that having a stable cation moiety is sufficient to yield a stable AEM and emphasizes the importance of the often ignored issue of backbone stability.

Investigation of Cation Degradation in Anion Exchange Membranes Using Multi-Dimensional NMR Spectroscopy

Low temperature anion exchange polymer electrolyte membrane (AEM) based fuel cells and electrolyzers have been successfully shown to convert hydrogen and oxygen to electricity (and vice-versa) with high efficiencies and energy densities with non-precious group metals. However, a significant challenge to realizing these technologies is the poor alkaline stability of the AEMs. In this work, we present the results of our multi-faceted approach to better understand AEM degradation in alkaline media. Several two-dimensional (2D) NMR techniques were applied to comprehensively elucidate cation degradation in polysulfone-based AEMs exposed to alkaline solutions. The 2D NMR tools utilized were: a) homonuclear correlation spectroscopy (COSY), b) 1H-X (X = 13C or 31P) heteronuclear multiple quantum correlation spectroscopy (HMQC), and c) 1H-13C heteronuclear multiple bond correlation spectroscopy (HMBC). Analysis of the 2D NMR spectra enabled precise identification of the degradation products for several different cation chemistries (quaternary ammonium, imidazolium, and phosphonium types). The observation of multiple degradation products highlighted the fact that the cation groups degraded through fundamentally different mechanisms. A clear understanding of the degradation mechanism is a critical requirement in the process of selecting or designing alternate cation chemistries for alkaline resilient AEMs.

STRUCTURAL ELUCIDATION OF A NEUTRAL WATER-SOLUBLE α-D-GLUCAN FROM THE FUNGUS OF HERICIUM ERINACEUS

ABSTRACT A new α-D-glucan (HEPF5), with a molecular weight of 4.23 × 105 Da as determined by high-performance liquid chromatography, was isolated from the water extract of the fruiting bodies of Hericium erinaceus. Its chemical structure was characterized by sugar and methylation analysis along with infrared (IR), 1H and 13C nuclear magnetic resonance spectroscopy, including correlated spectroscopy, total correlation spectroscopy, heteronuclear multiple quantum correlation spectroscopy and nuclear Overhauser enhancement spectroscopy experiments for linkage and sequence analysis. The polysaccharide is composed of a multibranch tetrasaccharide repeating unit with the following structure: PRACTICAL APPLICATIONS Mushroom-derived polysaccharides have emerged as an important class of bioactive substances, to which numerous medicinal and therapeutic properties have been attributed. Hericium erinaceus is a traditional Chinese medicinal fungus distributed throughout China. It is used to treat gastric ulcers, chronic gastritis and other digestive tract-related diseases. As the function is intimately related to the structure, characterization of highly complex and diverse polysaccharides is highly desirable. Despite the large amount of knowledge on the structure of polysaccharide, elucidation of the fine structures of heteropolysaccharide from varied sources and diverse conditions still remains as a matter of immense interest and importance. This paper describes the structure of a novel water-soluble heteropolysaccharide isolated from the fruiting bodies of H. erinaceus. It should help in correlating the structure and function relationship, which is significant for its utilization both in pharmaceutical and food industries.

Complete assignment of1H and13C NMR spectra of vinflunine

A new family of fluorinated Vinca alkaloids was synthesized in superacidic media. Superacidic media were obtained by mixing a strong Bronsted acid, such as anhydrous hydrogen fluoride, with a strong Lewis acid, such as antimony pentafluoride. Thus vinflunine was obtained when vinorelbine was treated in HF–SbF5 at −40 °C in the presence of a chlorinated solvent such as CH2Cl2, CHCl3 or CCl4. Vinflunine was characterized by superior in vivo activity to vinorelbine in preclinical tumor models. The chemical structure of vinflunine was been examined using NMR spectrometry. Taking into account the complexity of the NMR spectra, the total assignment of the 1H and the 13C spectra required experiments using homonuclear (1H–1H) and heteronuclear (1H–13C) correlations such as gradient-selected COSY (gs-COSY), double-quantum filtered COSY (DQFCOSY), heteronuclear multiple quantum-correlation spectroscopy (HMQC) and heteronuclear multiple bond correlation spectroscopy (HMBC). We also undertook a comparative structural analysis between vinflunine base and vinflunine ditartrate in acetone solution. The conformation of the vinflunine base molecule in acetone solution was studied with a NOESY experiment. The structure of vinflunine was thus determined without ambiguity, and its conformation was verified by a single-crystal x-ray diffraction study. The results indicated that the conformation in the solution state was analogous to that observed in the solid state. Copyright © 2001 John Wiley & Sons, Ltd.

Soft metal ions, Cd(II) and Hg(II), induce triple-stranded alpha-helical assembly and folding of a de novo designed peptide in their trigonal geometries.

We previously reported the de novo design of an amphiphilic peptide [YGG(IEKKIEA)4] that forms a native-like, parallel triple-stranded coiled coil. Starting from this peptide, we sought to regulate the assembly of the peptide by a metal ion. The replacement of the Ile18 and Ile22 residues with Ala and Cys residues, respectively, in the hydrophobic positions disrupted of the triple-stranded alpha-helix structure. The addition of Cd(II), however, resulted in the reconstitution of the triple-stranded alpha-helix bundle, as revealed by circular dichroism (CD) spectroscopy and sedimentation equilibrium analysis. By titration with metal ions and monitoring the change in the intensity of the CD spectra at 222 nm, the dissociation constant Kd was determined to be 1.5 +/- 0.8 microM for Cd(II). The triple-stranded complex formed by the 113Cd(II) ion showed a single 113Cd NMR resonance at 572 ppm whose chemical shift was not affected by the presence of Cl- ions. The 113Cd NMR resonance was connected with the betaH protons of the cysteine residue by 1H-113Cd heteronuclear multiple quantum correlation spectroscopy. These NMR results indicate that the three cysteine residues are coordinated to the cadmium ion in a trigonal-planar complex. Hg(II) also induced the assembly of the peptide into a triple-stranded alpha-helical bundle below the Hg(II)/peptide ratio of 1/3. With excess Hg(II), however, the alpha-helicity of the peptide was decreased, with the change of the Hg(II) coordination state from three to two. Combining this construct with other functional domains should facilitate the production of artificial proteins with functions controlled by metal ions.

Mycobacterium smegmatis Phosphoinositols-Glyceroarabinomannans: STRUCTURE AND LOCALIZATION OF ALKALI-LABILE AND ALKALI-STABLE PHOSPHOINOSITIDES

Lipoarabinomannans from fast growing Mycobacterium sp., namely AraLAMs, stimulate the early events of macrophage activation. The immunological activities of all of these AraLAMs drastically decrease with the loss of the mild alkali groups, which were believed to be restricted to the fatty acid residues from the phosphatidyl-myo-inositol anchor. This report reveals the presence and the structure of mild alkali-labile phosphoinositide units linked via the phosphate to the C-5 of the beta-D-Araf in the AraLAMs of Mycobacterium smegmatis, a fast growing mycobacterial species. Their structure was unambiguously established with a strategy based on both one-dimensional 31P and two-dimensional 1H-31P heteronuclear multiple quantum correlation spectroscopy (HMQC) and HMQC-homonuclear Hartmann-Hahn spectroscopy NMR experiments applied to native AraLAMs and to AraLAMs treated in mild alkali conditions. Next to these alkali-labile phosphoinositides estimated at three per molecule, two other mild alkali-stable phosphoinositide units were identified: the expected (myo-inositol-1)-phosphate-(3-glycerol) unit typifying the well known glycosylphosphatidylinositol anchor of the mannan core and, more surprisingly, one (myo-inositol-1)-phosphate-(5-beta-D-Araf) unit having the same structure as the alkali-labile ones. Moreover, these four phosphoinositide units were found capping the arabinan side chains. Thus, their different behavior toward mild alkaline hydrolysis was explained according to their accessibility to the alkali reagent. This novel class of LAMs, namely phosphoinositols-glyceroarabinomannans (PI-GAMs), are characterized by their phosphoinositide units but also by the absence of fatty acid residues. These PI-GAMs were found to elicit the secretion of tumor necrosis factor-alpha, suggesting that phosphoinositides are the major PI-GAM epitope involved in this process.

Lipooligosaccharidic antigen containing a novel C4-branched 3,6-dideoxy-alpha-hexopyranose typifies Mycobacterium gastri.

Lipooligosaccharides (LOSs) have recently been proposed as markers of mycobacterial avirulence. They have been characterized in Mycobacterium kansasii cell wall and were investigated in Mycobacterium gastri since the distinction between the two mycobacterial species remains in some question. A set of unknown LOSs was isolated from M. gastri W471. The highly antigenic lipooligosaccharide, LOS-III, was purified and appeared in all the M. gastri strains investigated regardless of their morphology. Moreover, by enzyme-linked immunosorbent assay and chromatographic approaches, it was found that LOS-III unambiguously distinguished M. gastri from the opportunistic pathogen M. kansasii. The LOS-III structure was established from its native form using NMR spectroscopy. This strategy revealed the presence of a supplementary monosaccharide (X) which was not characterized by routine carbohydrate analysis. Its core structure, 3,6-dideoxy-alpha-hexopyranose, was established from the complete assignment of the 1H and 13C spectra by two-dimensional homonuclear (COSY, HOHAHA) and heteronuclear 1H-13C heteronuclear multiple quantum correlation spectroscopy (HMQC) and HMQC-HOHAHA spectroscopy. Due to the absence of a proton at C4, the key data of the C4 side chain structure came from the heteronuclear multiple bond correlation spectroscopy (HMBC) spectrum. It was revealed to be a C-alkyl chain of partial structure 1,3-dimethoxypropyl. From the HMBC spectrum, this novel C-branched monosaccharide was located at the nonreducing end of the LOS, while the putative reducing end was found to consist of a 2',4,6-triacylated alpha-alpha-trehalose. The following structure, based on the evidence presented in this paper, is proposed for LOS-III: Xp alpha(1-->3)[L-Xylp beta(1-->4)](6)3-O-Me-Rhap alpha(1-->3)D- Galp beta(1-->3)-D-Glcp beta(1-->4)2-O-acyl-D-Glcp-alpha(1<==>1)alpha 4,6-di-O- acyl-D-Glcp.