Correlation NMR Spectroscopy Research Articles

Pulse design for broadband correlation NMR spectroscopy by multi-rotating frames

We present a method for designing radio-frequency (RF) pulses for broadband or multi-band isotropic mixing at low power, suitable for protein NMR spectroscopy. These mixing pulses are designed analytically, rather than by numerical optimization, by repeatedly constructing new rotating frames of reference. We show how pulse parameters can be chosen frame-by-frame to systematically reduce the effective chemical shift bandwidth, but maintain most of the effective J-coupling strength. The effective Hartmann-Hahn mixing condition is then satisfied in a multi-rotating frame of reference. This design method yields multi-band and broadband mixing pulses at low RF power. In particular, the ratio of RF power to mixing bandwidth for these pulses is lower than for existing mixing pulses, such as DIPSI and FLOPSY. Carbon-carbon TOCSY experiments at low RF power support our theoretical analysis.

Solid-state tautomeric structure and invariom refinement of a novel and potent HIV integrase inhibitor

The conformation and tautomeric structure of (Z)-4-[5-(2,6-difluorobenzyl)-1-(2-fluorobenzyl)-2-oxo-1,2-dihydropyridin-3-yl]-4-hydroxy-2-oxo-N-(2-oxopyrrolidin-1-yl)but-3-enamide, C27H22F3N3O5, in the solid state has been resolved by single-crystal X-ray crystallography. The electron distribution in the molecule was evaluated by refinements with invarioms, aspherical scattering factors by the method of Dittrich et al. [Acta Cryst. (2005), A61, 314-320] that are based on the Hansen-Coppens multipole model [Hansen & Coppens (1978). Acta Cryst. A34, 909-921]. The β-diketo portion of the molecule exists in the enol form. The enol -OH hydrogen forms a strong asymmetric hydrogen bond with the carbonyl O atom on the β-C atom of the chain. Weak intramolecular hydrogen bonds exist between the weakly acidic α-CH hydrogen of the keto-enol group and the pyridinone carbonyl O atom, and also between the hydrazine N-H group and the carbonyl group in the β-position from the hydrazine N-H group. The electrostatic properties of the molecule were derived from the molecular charge density. The molecule is in a lengthened conformation and the rings of the two benzyl groups are nearly orthogonal. Results from a high-field (1)H and (13)C NMR correlation spectroscopy study confirm that the same tautomer exists in solution as in the solid state.

A comparison of the properties of two structurally equivalent but regiochemically different mono‐alkylated polybithiophenes prepared through AABB‐type stille polycondensation

AbstractPrevious routes to polymers with mono‐alkylated bithiophenes have proceeded through polymerization of monoalkyl‐2,2′‐bithiophene monomers through oxidative or AB‐type cross‐coupling polymerizations. The resulting polymer regiochemistry affects both the location and orientation of the polymer side‐chains. In contrast, AABB‐type cross‐coupling polymerizations can control the location and in some cases the orientation of the side‐chains. To study how this control can impact polymer properties, two poly(monodecyl‐2,2′‐bithiophene) polymers have been synthesized through Stille AABB‐type polycondensations of 2,5‐bis(trimethylstannyl)thiophene with different monomers. The alkyl side‐chains are located on every other thiophene, but polymer 1 consists of both head‐to‐tail and head‐to‐head dyads, whereas polymer 2 is made up of only head‐to‐head dyads. 1H NMR, 13C NMR, and heteronuclear single quantum correlation spectroscopy are used to confirm and contrast the polymer regiochemistries. The physical properties of the two polymers are analyzed using UV–vis spectroscopy, differential scanning calorimetry, and grazing‐incidence X‐ray diffraction. Polymer 2 is found to display significantly more aggregation in solution than 1, and it displays different thermal properties. The film properties of polymers 1 and 2, however, are very similar, with nearly identical UV–vis profiles and d‐spacing values as determined by grazing incidence X‐ray diffraction. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Elaiomycins K and L, new azoxy antibiotics from Streptomyces sp. Tü 6399*

Elaiomycins K and L, two new azoxy-type antibiotics, were detected by HPLC-diode array screening in the culture filtrate extract of Streptomyces sp. Tü 6399. The structures were determined by high-resolution MS and 2-dimensional (1)H and (13)C correlated NMR spectroscopy including (15)N-NMR experiments and established these compounds as new members of the elaiomycin family. Both metabolites show a weak antibacterial activity against Bacillus subtilis and Staphylococcus lentus as well as against the phytophathogenic strain Xanthomonas campestris.

Synthesis and Characterization of New 5-Linked Pinoresinol Lignin Models

Pinoresinol structures, featuring a β-β'-linkage between lignin monomer units, are important in softwood lignins and in dicots and monocots, particularly those that are downregulated in syringyl-specific genes. Although readily detected by NMR spectroscopy, pinoresinol structures largely escaped detection by β-ether-cleaving degradation analyses presumably due to the presence of the linkages at the 5 positions, in 5-5'- or 5-O-4'-structures. In this study, which is aimed at helping better understand 5-linked pinoresinol structures by providing the required data for NMR characterization, new lignin model compounds were synthesized through biomimetic peroxidase-mediated oxidative coupling reactions between pre-formed (free-phenolic) coniferyl alcohol 5-5'- or 5-O-4'-linked dimers and a coniferyl alcohol monomer. It was found that such dimers containing free-phenolic coniferyl alcohol moieties can cross-couple with the coniferyl alcohol producing pinoresinol-containing trimers (and higher oligomers) in addition to other homo- and cross-coupled products. Eight new lignin model compounds were obtained and characterized by NMR spectroscopy, and one tentatively identified cross-coupled β-O-4'-product was formed from a coniferyl alcohol 5-O-4'-linked dimer. It was demonstrated that the 5-5'- and 5-O-4'-linked pinoresinol structures could be readily differentiated by using heteronuclear multiple-bond correlation (HMBC) NMR spectroscopy. With appropriate modification (etherification or acetylation) to the newly obtained model compounds, it would be possible to identify the 5-5'- or 5-O-4'-linked pinoresinol structures in softwood lignins by 2D HMBC NMR spectroscopic methods. Identification of the cross-coupled dibenzodioxocin from a coniferyl alcohol 5-5'-linked moiety suggested that thioacidolysis or derivatization followed by reductive cleavage (DFRC) could be used to detect and identify whether the coniferyl alcohol itself undergoes 5-5'-cross-linking during lignification.

Enhanced Solid-State NMR Correlation Spectroscopy of Quadrupolar Nuclei Using Dynamic Nuclear Polarization

By means of a true sensitivity enhancement for a solid-state NMR spectroscopy (SSNMR) experiment performed under dynamic nuclear polarization (DNP) conditions, corresponding to 4-5 orders of magnitude of time savings compared with a conventional SSNMR experiment, it is shown that it is possible to record interface-selective (27)Al-(27)Al two-dimensional dipolar correlation spectra on mesoporous alumina, an advanced material with potential industrial applications. The low efficiency of cross-polarization and dipolar recoupling for quadrupolar nuclei is completely negated using this technique. The important presence of pentacoordinated Al has not only been observed, but its role in bridging interfacial tetra- and hexacoordinated Al has been determined. Such structural information, collected at low temperature (∼103 K) and 9.4 T with the use of DNP, would have been impossible to obtain under standard conditions, even using a higher magnetic field. However, here it is demonstrated that this information can be obtained in only 4 h. This work clearly opens a new avenue for the application of SSNMR to quadrupolar nuclei and notably the atomic-scale structure determination of catalysis materials such as mesoporous alumina.

A set of triple-resonance nuclear magnetic resonance experiments for structural characterization of organophosphorus compounds in mixture samples

The 1H, 13C correlation NMR spectroscopy utilizes JCH couplings in molecules, and provides important structural information from small organic molecules in the form of carbon chemical shifts and carbon-proton connectivities. The full potential of the 1H, 13C correlation NMR spectroscopy has not been realized in the Chemical Weapons Convention (CWC) related verification analyses due to the sample matrix, which usually contains a high amount of non-related compounds obscuring the correlations of the relevant compounds. Here, the results of the application of 1H, 13C, 31P triple-resonance NMR spectroscopy in characterization of OP compounds related to the CWC are presented. With a set of two-dimensional triple-resonance experiments the JHP, JCH and JPC couplings are utilized to map the connectivities of the atoms in OP compounds and to extract the carbon chemical shift information. With the use of the proposed pulse sequences the correlations from the OP compounds can be recorded without significant artifacts from the non-OP compound impurities in the sample. Further selectivity of the observed correlations is achieved with the application of phosphorus band-selective pulse in the pulse sequences to assist the analysis of multiple OP compounds in mixture samples. The use of the triple-resonance experiments in the analysis of a complex sample is shown with a test mixture containing typical scheduled OP compounds, including the characteristic degradation products of nerve agents sarin, soman, and VX. The viability of the approach in verification analysis is demonstrated in the analysis of the 30th OPCW Proficiency Test sample.

Co-polymerization analysis of thermosetting resins using1H-15N-13C triple resonance NMR spectroscopy

1H-15N-13C correlation NMR spectroscopy techniques developed to identify and characterize co-polymer fragments in melamine-urea-formaldehyde (MUF) and phenol-urea-formaldehyde (PUF) model systems have been applied to industrially prepared MUF, PUF, and phenol-melamine-formaldehyde (PMF) resins. The NMR data confirm that co-polymers form in a commercially prepared MUF resin manufactured by Momentive Specialty Chemicals Pty. Ltd. Spectra from PUF model reactions were compared with those from a PUF resin and it was determined that PUF co-polymers did not form in the resin prepared using typical temperature and pH. Finally, NMR spectroscopy was used to identify and characterize PMF co-polymer bonds in a phenol-melamine-urea-formaldehyde (PMUF) resin prepared using a procedure from Momentive Specialty Chemicals Pty. Ltd. With these NMR techniques in hand, it is now possible to relate co-polymer structures to properties of commercial thermosets. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Metabolic response to exogenous ethanol in yeast: An in vivo statistical total correlation NMR spectroscopy approach

In vivo NMR spectroscopy, together with selectively 13C-labelled substrates and 'statistical total correlation spectroscopy' analysis (STOCSY), are valuable tools to collect and interpret the metabolic responses of a living organism to external stimuli. In this study, we applied this approach to evaluate the effects of increasing concentration of exogenous ethanol on the Saccharomyces cerevisiae fermentative metabolism. We show that the STOCSY analysis correctly identifies the different types of correlations among the enriched metabolites involved in the fermentation, and that these correlations are quite stable even in presence of a stressing factor such as the exogenous ethanol.

η3-Furfuryl and η3-Thienyl Complexes of Palladium and Platinum of Relevance to the Functionalization of Biomass-Derived Furans

A number of cationic and neutral η3-furfuryl complexes of palladium and platinum were prepared, including one with a ligand derived from fructose, 5-chloromethylfurfural. The complexes were studied by variable-temperature and heteronuclear correlation NMR spectroscopy, as well as single-crystal X-ray crystallography. Analogous η3-thienyl complexes could be prepared and detected in solution by NMR, but could not be isolated due to facile decomposition.

Solid-State MAS NMR Studies of Brønsted Acid Sites in Zeolite H-Mordenite

(17)O-(1)H double resonance NMR spectroscopy was used to study the local structure of zeolite H-Mordenite. Different contact times were used in cross-polarization magic angle spinning (CPMAS) NMR, CP rotational-echo double resonance (CP-REDOR) NMR, and heteronuclear correlation (HETCOR) NMR spectroscopy to distinguish between Brønsted acid sites with different O-H distances. The accessibility of the various Brønsted acid sites was quantified by adsorbing the basic probe molecule trimethylphosphine in known amounts. On the basis of these experiments, locations of different Brønsted acid sites in H-Mordenite (H-MOR) were proposed. The use of (17)O chemical shift correlations to help assign sites is discussed.

Poly(isobornyl methacrylate-co -methyl acrylate): Synthesis and stereosequence distribution analysis by NMR spectroscopy

Copolymerization of isobornyl methacrylate and methyl acrylate (I/M) is performed by atom transfer radical polymerization using methyl-2-bromopropionate as an initiator and PMDETA/CuBr as catalyst under nitrogen atmosphere at 70 °C. The copolymer compositions determined from 1H NMR spectra are used to determine reactivity ratios of the monomers. The reactivity ratio determined from linear Kelen–Tudos method and non-linear error-in-variable method, are rI = 1.25 ± 0.10, rM = 0.84 ± 0.08 and rI = 1.20, rM = 0.82, respectively. 1D, distortion less enhancement by polarization transfer and 2D, heteronuclear single quantum coherence, and total correlation spectroscopy NMR experiments are employed to resolve highly overlapped and complex 1H and 13C{1H} NMR spectra of the copolymers. The carbonyl carbon of I and M units and methyl carbon of I unit are assigned up to triad compositional and configurational sequences, whereas β-methylene carbons are assigned up to tetrad compositional and configurational sequences. Similarly, methine carbon of I unit is assigned up to triad level. The couplings of carbonyl carbon and quaternary carbon resonances are studied in detail using 2D hetero nuclear multiple bond correlation spectra. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Electron spray ionization mass spectrometry and 2D 31P NMR for monitoring 18O/16O isotope exchange and turnover rates of metabolic oligophosphates.

A new method was here developed for the determination of (18)O-labeling ratios in metabolic oligophosphates, such as ATP, at different phosphoryl moieties (α-, β-, and γ-ATP) using sensitive and rapid electrospray ionization mass spectrometry (ESI-MS). The ESI-MS-based method for monitoring of (18)O/(16)O exchange was validated with gas chromatography-mass spectrometry and 2D (31)P NMR correlation spectroscopy, the current standard methods in labeling studies. Significant correlation was found between isotopomer selective 2D (31)P NMR spectroscopy and isotopomer less selective ESI-MS method. Results demonstrate that ESI-MS provides a robust analytical platform for simultaneous determination of levels, (18)O-labeling kinetics and turnover rates of α-, β-, and γ-phosphoryls in ATP molecule. Such method is advantageous for large scale dynamic phosphometabolomic profiling of metabolic networks and acquiring information on the status of probed cellular energetic system.

ChemInform Abstract: Resolving the Different Silicon Clusters in Li12Si7 by 29Si and 6,7Li Solid‐State NMR Spectroscopy.

AbstractDifferent Si clusters in Li12Si7 are resolved and their individual connectivities are analyzed by 29Si correlation NMR spectroscopy.

High‐Pressure Synthesis and Structural Investigation of H3P8O8N9: A New Phosphorus(V) Oxonitride Imide with an Interrupted Framework Structure

The first crystalline phosphorus oxonitride imide H(3)P(8)O(8)N(9) (=P(8)O(8)N(6)(NH)(3)) has been synthesized under high-pressure and high-temperature conditions. To this end, a new, highly reactive phosphorus oxonitride imide precursor compound was prepared and treated at 12 GPa and 750 °C by using a multianvil assembly. H(3)P(8)O(8)N(9) was obtained as a colorless, microcrystalline solid. The crystal structure of H(3)P(8)O(8)N(9) was solved ab initio by powder X-ray diffraction analysis, applying the charge-flipping algorithm, and refined by the Rietveld method (C2/c (no. 15), a=1352.11(7), b=479.83(3), c=1820.42(9) pm, β=96.955(4)°, Z=4). H(3)P(8)O(8)N(9) exhibits a highly condensed (κ=0.47), 3D, but interrupted network that is composed of all-side vertex-sharing (Q(4)) and only threefold-linking (Q(3)) P(O,N)(4) tetrahedra in a Q(4)/Q(3) ratio of 3:1. The structure, which includes 4-ring assemblies as the smallest ring size, can be subdivided into alternating open-branched zweier double layers {oB,2(2)(∞)}[(2)P(3)(O,N)(7)] and layers containing pairwise-linked Q(3) tetrahedra parallel (001). Information on the hydrogen atoms in H(3)P(8)O(8)N(9) was obtained by 1D (1)H MAS, 2D homo- and heteronuclear (together with (31)P) correlation NMR spectroscopy, and a (1)H spin-diffusion experiment with a hard-pulse sequence designed for selective excitation of a single peak. Two hydrogen sites with a multiplicity ratio of 2:1 were identified and thus the formula of H(3)P(8)O(8)N(9) was unambiguously determined. The protons were assigned to Wyckoff positions 8f and 4e, the latter located within the Q(3) tetrahedra layers.

One Metabolite, Two Pathways: Convergence of Polypropionate Biosynthesis in Fungi and Marine Molluscs

Structural similarity or even the identity of polyketide compounds does not necessarily imply unique biosynthesis. Feeding experiments with a (13)C labeled precursor establish that the C(3) units in 7-methyl-cyercene-1 (1) are derived from intact propionate in the marine mollusc Ercolania funerea. The same compound in the terrestrial fungus Leptosphaeria maculans/Phoma lingam is synthesized by an acetate/SAM pathway thus proving for the first time metabolic convergence of polyketide biosynthesis in eukaryotes. Traditional (1)H-(13)C NMR correlation spectroscopy has been successfully applied to estimate (13)C incorporation in biosynthetic experiments.

An Amyloid Organelle, Solid-state NMR Evidence for Cross-β Assembly of Gas Vesicles

Functional amyloids have been identified in a wide range of organisms, taking on a variety of biological roles and being controlled by remarkable mechanisms of directed assembly. Here, we report that amyloid fibrils constitute the ribs of the buoyancy organelles of Anabaena flos-aquae. The walls of these gas-filled vesicles are known to comprise a single protein, GvpA, arranged in a low pitch helix. However, the tertiary and quaternary structures have been elusive. Using solid-state NMR correlation spectroscopy we find detailed evidence for an extended cross-β structure. This amyloid assembly helps to account for the strength and amphiphilic properties of the vesicle wall. Buoyancy organelles thus dramatically extend the scope of known functional amyloids.

Characterization and Scope of S-layer Protein O-Glycosylation in Tannerella forsythia

Cell surface glycosylation is an important element in defining the life of pathogenic bacteria. Tannerella forsythia is a Gram-negative, anaerobic periodontal pathogen inhabiting the subgingival plaque biofilms. It is completely covered by a two-dimensional crystalline surface layer (S-layer) composed of two glycoproteins. Although the S-layer has previously been shown to delay the bacterium's recognition by the innate immune system, we characterize here the S-layer protein O-glycosylation as a potential virulence factor. The T. forsythia S-layer glycan was elucidated by a combination of electrospray ionization-tandem mass spectrometry and nuclear magnetic resonance spectroscopy as an oligosaccharide with the structure 4-Me-β-ManpNAcCONH(2)-(1→3)-[Pse5Am7Gc-(2→4)-]-β-ManpNAcA-(1→4)-[4-Me-α-Galp-(1→2)-]-α-Fucp-(1→4)-[-α-Xylp-(1→3)-]-β-GlcpA-(1→3)-[-β-Digp-(1→2)-]-α-Galp, which is O-glycosidically linked to distinct serine and threonine residues within the three-amino acid motif (D)(S/T)(A/I/L/M/T/V) on either S-layer protein. This S-layer glycan obviously impacts the life style of T. forsythia because increased biofilm formation of an UDP-N-acetylmannosaminuronic acid dehydrogenase mutant can be correlated with the presence of truncated S-layer glycans. We found that several other proteins of T. forsythia are modified with that specific oligosaccharide. Proteomics identified two of them as being among previously classified antigenic outer membrane proteins that are up-regulated under biofilm conditions, in addition to two predicted antigenic lipoproteins. Theoretical analysis of the S-layer O-glycosylation of T. forsythia indicates the involvement of a 6.8-kb gene locus that is conserved among different bacteria from the Bacteroidetes phylum. Together, these findings reveal the presence of a protein O-glycosylation system in T. forsythia that is essential for creating a rich glycoproteome pinpointing a possible relevance for the virulence of this bacterium.

Solvation and Crystal Effects in Bilirubin Studied by NMR Spectroscopy and Density Functional Theory

The open-chain tetrapyrrole compound bilirubin was investigated in chloroform and dimethyl sulfoxide solutions by liquid-state NMR and as solid by (1)H, (13)C, and (15)N magic-angle spinning (MAS) solid-state NMR spectroscopy. Density functional theory (DFT) calculations were performed to interpret the data, using the B3LYP exchange-correlation functional to optimize geometries and to compute NMR chemical shieldings by the gauge-including atomic orbital method. The dependence of geometries and chemical shieldings on the size of the basis sets was investigated for the reference molecules tetramethylsilane, NH(3), and H(2)O, and for bilirubin as a monomer and in clusters consisting of up to six molecules. In order to assess the intrinsic errors of the B3LYP approximation in calculating NMR shieldings, complete basis set estimates were obtained for the nuclear shielding values of the reference molecules. The experimental liquid-state NMR data of bilirubin are well reproduced by a monomeric bilirubin molecule using the 6-311+G(2d,p) basis set for geometry optimization and for calculating chemical shieldings. To simulate the bilirubin crystal, a hexameric model was required. It was constructed from geometry-optimized monomers using information from the X-ray structure of bilirubin to fix the monomeric entities in space and refined by partial optimization. Combining experimental (1)H-(13)C and (1)H-(15)N NMR correlation spectroscopy and density functional theory, almost complete sets of (1)H, (13)C, and (15)N chemical shift assignments were obtained for both liquid and solid states. It is shown that monomeric bilirubin in chloroform solution is formed by 3-vinyl anti conformers, while bilirubin crystals are formed by 3-vinyl syn conformers. This conformational change leads to characteristic differences between the liquid- and solid-state NMR resonances.

Synthesis, characterization and antitumor activity study of some cyclometalated organoplatinum(II) complexes containing aromatic N-donor ligands

A general approach has been designed to synthesize some mononuclear and binuclear cyclometalated platinum(II) complexes, containing aromatic N-donor ligands with the presence of one Cl − trans to carbon. In this way, cyclometalated platinum(II) complex [Pt(C^N)Cl(dmso)], 1, C^N = N(1),C(2′)-chelated, deprotonated 2-phenylpyridine and dmso = dimethylsulfoxide, was used as a precursor to react with imidazole derivatives (1-methylimidazole, 2a, imidazole, 2b,), monodentate pyridine derivatives (4-methylpyridine, 2c, pyridine, 2d,) and bidentate pyridine derivative (4,4′-bipyridine, 3 and 4,). Synthesized complexes were fully characterized by using multinuclear NMR spectroscopy ( 1H, 13C{ 1H} and 195Pt), correlation NMR spectroscopy ( 1H- 1H COSY, 13C{ 1H}- 1H Heteronuclear Multiple Quantum Correlation, HMQC, Heteronuclear Multiple Bond Correlation, HMBC, 15N- 1H HETCOR), elemental analysis, X-ray crystallography and ESI-Mass spectrometry. Antitumor effects of mononuclear cyclometalated platinum(II) complexes 2a, 2c, 2d and 3 were determined on Jurkat, K562, and Raji cell lines and results showed reasonable cytotoxicities.