Proton Nuclear Magnetic Resonance Characterization Research Articles

Controllable Polymerization of N -Substituted β-Alanine N -Thiocarboxyanhydrides for Convenient Synthesis of Functional Poly(β-peptoid)s

Controllable Polymerization of <i>N</i> -Substituted β-Alanine <i>N</i> -Thiocarboxyanhydrides for Convenient Synthesis of Functional Poly(β-peptoid)s

Oxygen-Tolerant RAFT Polymerization Catalyzed by a Recyclable Biomimetic Mineralization Enhanced Biological Cascade System.

An enzyme cascade system including glucose oxidase (GOx) and iron porphyrin (DhHP-6) is encapsulated in a metal-organic framework called zeolitic imidazolate framework-8 (ZIF-8) through one-step facile synthesis. The composite (GOx&DhHP-6@ZIF-8) is then used to initiate oxygen-tolerant reversible addition-fragmentation chain-transfer polymerization for different methacrylate monomers, such as 2-diethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, and poly(ethylene glycol) methyl ether methacrylate (Mn = 500g mol-1 ). The composite shows the robustness toward solvent and temperatures, all polymerizations using above monomers and catalyzing by GOx&DhHP-6@ZIF-8 exhibits high monomer conversion (>85%) and narrow molar mass dispersity (<1.3). Besides, acrylic and acrylamide monomers such as 2-hydroxyethyl acrylate and N,N-dimethylacrylamide are also carried to demonstrate the broad applicability. Proton nuclear magnetic resonance characterization and chain extension experiments confirm the retaining end groups of the resultant polymers, which is a significant feature of living polymerization. More importantly, the process of recycling the composite through a centrifuge is simplistic, and the composite still maintains similar activity compared to the original composites after five times. This low-cost and easily separated composite catalyst represents a versatile strategy to synthesize well-defined functional polymers suitable for industrial-scale production.

C4H8SO3Hmim]HSO4 as an efficient catalyst for direct liquefaction of bagasse lignin: Decomposition properties of the inner structural units

Catalytic valorization of renewable aromatic lignin is attracting increasing attention. In this study, an efficient method for direct liquefaction of sugarcane bagasse lignin using acidic ionic liquid (IL) 1-(4-sulfobutyl)-3-methyl imidazolium hydrosulfate ([C4H8SO3Hmim]HSO4) is presented. The relationships between catalyst dosage, reaction condition parameters and degree of liquefaction, and the structure and elemental composition of liquefaction residue were investigated. The transformation performances of three molecular structural units (guaiacyl, syringyl, and hydroxyphenyl units) of bagasse lignin were also intensively examined using gas chromatography-mass spectrometry, elemental analysis, Fourier transform infrared spectrometry, and proton nuclear magnetic resonance characterization. The results demonstrated that the dual-functionalized acidic IL exhibited excellent catalytic performance in the direct liquefaction process. More than 65% degree of liquefaction was achieved under optimized conditions, yielding 13.5% of useful aromatic fine chemicals such as phenol, 4-ethylphenol, and guaiacol. The p-hydroxyphenyl unit of lignin was the most flexible, followed by the guaiacyl unit, whereas the syringyl group was the most refractory. Furthermore, the catalytic mechanism was proposed.

Proton NMR characterization of gasoline–ethanol blends

Nuclear magnetic resonance (NMR) can be conveniently used for accurate measurement of water and ethanol concentrations in gasoline–ethanol fuel blends. The spectra also contain information on proton exchange rates. In addition, NMR pulsed-field-gradient diffusion measurement allows estimation of ethanol–water clusters and viscosity of the fuel blends.

Proton Nuclear Magnetic Resonance Characterization of Resins from the Family Pinaceae

Proton magnetic resonance spectra were recorded for solutions of resinous materials harvested from 82 species in seven genera of the gymnospermous plant family Pinaceae. Data were recorded in both one and two (COSY) dimensions. Approximately 11 peaks in the 1D spectra and 10 cross-peaks in the 2D spectra were present in almost all pinacean spectra, providing a familial diagnostic. Some 40 1D peaks or peak clusters and 60 2D cross-peaks or clusters were considered significant and are reported, when present, for all species. Whereas previous solid-state 13C data were diagnostic primarily at the family level, the patterns of 1D and 2D peaks may provide diagnostic information at the genus and species levels. These spectra constitute the first broad use of 1H NMR to study plant exudates in general and to provide taxonomic characterization in particular.

Liquid Chromatography–Mass Spectrometry and Proton Nuclear Magnetic Resonance Characterization of Trace Level Condensation Products Formed Between Lactose and the Amine‐Containing Diuretic Hydrochlorothiazide

Trace levels of condensation products between lactose and the amine‐containing diuretic hydrochlorothiazide are formed when a mixture of the two solids containing 30% weight water is heated at 60 °C for 2 weeks. The two most abundant condensation products were characterized by liquid chromatography‐mass spectrometry (LC‐MS) and proton nuclear magnetic resonance (1H NMR) spectroscopy. Under these relatively mild conditions of formation, the amine–lactose reaction products are limited to those involving the elimination of only a single molecule of water, rather than the multiple‐water eliminations associated with later stages of the Maillard reaction. The spectroscopic data clearly show that the primary condensation products are cyclic N‐substituted glycosylamines rather than Schiff base, 1,2‐enolic forms, or Amadori rearrangement products of identical mass. In solution, the two most abundant N‐substituted glycosylamines are shown to be in a kinetically slow equilibrium with each other, most likely through a mutarotation involving the intermediate formation of the acyclic Schiff base. © 2000 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 89: 920–929, 2000

Liquid chromatography–mass spectrometry and proton nuclear magnetic resonance characterization of trace level condensation products formed between lactose and the amine‐containing diuretic hydrochlorothiazide

Liquid chromatography–mass spectrometry and proton nuclear magnetic resonance characterization of trace level condensation products formed between lactose and the amine‐containing diuretic hydrochlorothiazide

High-resolution proton nuclear magnetic resonance characterization of seminolipid from bovine spermatozoa.

The high-resolution one- and two-dimensional proton nuclear magnetic resonance (1H-NMR) characterization of seminolipid from bovine spermatozoa is presented. The 1H-NMR data was confirmed by gas-liquid chromatography-mass spectrometric analysis of the partially methylated alditol acetates of the sugar unit, mild alkaline methanolysis of the glyceryl ester, mobility on normal phase and diphasic thin-layer chromatography (HPTLC), and fast atom bombardment mass spectrometry (FAB-MS). The structure of the molecule corresponds to 1-O-hexadecyl-2-O-hexadecanoyl-3-O-beta-D-(3'-sulfo)-galactopyranosyl- sn-glycerol.

Proton nuclear magnetic resonance characterization of the aromatic residues in the variant-3 neurotoxin from Centruroides sculpturatus Ewing.

The amino acid sequence for the variant-3 (CsE-v3) toxin from the venom of the scorpion Centruroides sculpturatus Ewing contains eight aromatic residues. By use of 2D NMR spectroscopic methods, the resonances from the individual protons (NH, C alpha H, C beta H',H", and the ring) for each of the individual aromatic residues have been completely assigned. The spatial arrangement of the aromatic ring systems with respect to each other has been qualitatively analyzed by 2D-NOESY techniques. The results show that Trp-47, Tyr-4, and Tyr-42 are in close spatial proximity to each other. The NOESY contacts and the ring current induced shifts in the resonances of the individual protons of Tyr-4 and Trp-47 suggest that the aromatic ring planes of these residues are in an orthogonal arrangement. In addition, the spatial proximity of the rings in the pairs Tyr-4, Tyr-58; Tyr-42, Tyr-40; and Tyr-40, Tyr-38 has also been established. A comparison with the published crystal structure suggests that there is a minor rearrangement of the aromatic rings in the solution phase. No 2D-NOESY contacts involving Phe-44 and Tyr-14 to any other aromatic ring protons have been observed. The pH dependence of the aromatic ring proton chemical shifts has also been studied. These results suggest that the Tyr-58 phenolic group is experiencing a hydrogen-bonding interaction with a positively charged group, while Tyr-4, -14, -38, and -40 are experiencing through-space interactions with proximal negatively charged groups. The Trp-47 indole NH is interacting with the carboxylate groups of two proximal acidic residues. These studies define the microenvironment of the aromatic residues in the variant-3 neurotoxin in aqueous solution.

Characterization by nuclear magnetic resonance of the concanavalin A binding oligosaccharide on the beta b chain of placental beta-hexosaminidase B: lectin binding to the separated polypeptide chains of hexosaminidases A and B.

The type and distribution of the oligosaccharides on each polypeptide of human placental beta-hexosaminidases A (alpha (beta a beta b)) and B (2(beta a beta b)) were examined. The denatured polypeptides were separated by isoelectric focussing in a polyacrylamide slab gel and each gel was then overlaid with 125I-labelled lectins. The study indicated that the beta a chain contains negligible carbohydrate, the beta b chain contains both the high-mannose and a complex type oligosaccharide, and the alpha chain contains predominantly high-mannose or hybrid type moieties. Two asparagine-linked high-mannose type oligosaccharides present on the beta b polypeptide of beta-hexosaminidase B were isolated by concanavalin A chromatography and by reverse-phase high pressure liquid chromatography. Proton nuclear magnetic resonance characterization of the oligosaccharides revealed an equimolar glycan mixture of the high-mannose type structure Man5 and Man6.

Proton nuclear magnetic resonance characterization of chloro(N-methyl-5,10,15,20-tetraphenylporphyrinato)nickel(II) and chloro(N-methyloctaethylporphyrinato)nickel(II) complexes

Proton nuclear magnetic resonance characterization of chloro(N-methyl-5,10,15,20-tetraphenylporphyrinato)nickel(II) and chloro(N-methyloctaethylporphyrinato)nickel(II) complexes

NMR studies of the variant-3 neurotoxin from Centruroides sculpturatus Ewing.

We report a preliminary high-resolution proton nuclear magnetic resonance characterization of the variant-3 toxin from the scorpion Centruroides sculpturatus Ewing (range Southwestern USA). This toxin assumes a well defined folded conformation in aqueous solutions at room temperature and undergoes reversible thermal denaturation. A number of amide hydrogens exhibit exchange life times varying from several minutes to several hours. A few tentative assignments of the low field aromatic CH resonances has been made on the basis of 2D-COSY and NOE experiments. The upfield shifts exhibited by Trp-47 suggest a unique microenvironment for this residue. The NMR data suggest that there is some degree of correlation between the solution structure of the variant-3 toxin and its crystallographic structure. Our studies provide a basis for a detailed elucidation of the structure-function relationships of these interesting scorpion toxins which bind to the sodium channels of excitable membranes and delay sodium current inactivation.

Molecular flexibility in microtubule proteins: proton nuclear magnetic resonance characterization.

Bovine microtubule protein preparations have been examined by proton nuclear magnetic resonance (1H NMR) spectroscopy at 270 MHz. Sharp resonances have been identified as deriving from microtubule-associated proteins. These resonances persist after self-assembly of microtubule protein. Brief tryptic treatment of assembled microtubules, specifically cleaving the microtubule-associated protein HMW2 (Mr = 270 000), releases the pendant portion of HMW2 (Mr = 240 000), three-quarters of which is in a flexible conformation. Isolated tau protein and HMW2 protein both show substantial flexibility; on recombination with tubulin dimer, tau shows considerable decrease in flexibility whereas HMW2 is unaffected. The observations may have important implications for the interactions between microtubules and other cytoskeletal structures.

Proton nuclear magnetic resonance characterization of the oxidized intermediates of cytochrome c peroxidase.

Oxidation of cytochrome c peroxidase with hydrogen peroxide to form the initial oxidized intermediate, cytochrome c peroxidase compound I, drastically alters the proton hyperfine nmr spectrum. In contrast to studies of horseradish peroxidase, where the spectrum of horseradish peroxidase compound I is similar to that of the native protein, cytochrome c peroxidase compound I exhibits only broad resonances near 17 and 30 ppm from 2,2-dimethyl-2-silapentane-5-sulfonate. No unique resonances attributable to cytochrome c peroxidase compound II could be identified. These results define the molecular conditions for which resolved hyperfine resonances of the iron(IV) states of heme proteins may be observed when the data presented here are compared with the data from horseradish peroxidase. Oxidation of cytochrome c peroxidase while it is complexed to ferricytochrome c reveals that the heme resonances of cytochrome c are not influenced by the oxidation state of cytochrome c peroxidase.

Proton nuclear magnetic resonance characterization of the electronic structure of horseradish peroxidase compound I

Proton nuclear magnetic resonance characterization of the electronic structure of horseradish peroxidase compound I

Proton nuclear magnetic resonance characterization of heme disorder in hemoproteins.

A proton NMR method is described for determining the orientation of a porphyrin within the heme pocket of a hemoprotein. The pattern of the hyperfine-shifted heme methyl resonances in low-spin ferric model compounds is demonstrated to characteristically reflect the position of a localized low-symmetry perturbation on the pi system. The specific assignments via deuteration of the two interconvertible sets of methyl resonances observed for deuteroporphyrin-reconstituted sperm whale metmyoglobin cyanide lead to the conclusion that the low-symmetry perturbations on the heme due to the apo-protein contacts differ for the two protein components by a 180 degrees rotation about the alpha-gamma meso axis. Hence the heme in the reconstituted myoglobin is "disordered" in solution, and the altered functional properties of the reconstituted protein cannot be simply attributed to the local effect of the heme substituent. This NMR technique has applicability for determining the relative heme orientation in related hemoproteins, and may clarify the origin of doubling of heme resonances observed in several native hemoproteins.