High-field NMR Spectroscopy Research Articles

Impact of wettability on moisture transport at mesoscale in porous materials

A multiscale NMR method is used for probing the proton dynamics in control pore glasses (CPG) standing in the meso and macro scale ranges. The porous material has been synthetized in our laboratory following the sol–gel route as well as spinodal decomposition. Special heat treatment has modified the proton species at the pore surface. 1H high field NMR spectroscopy has been realized under controlled relative humidity conditions. This has allowed a clear identification of the different proton species present during the kinetics of hydration from RH=0% up to 98%. We focused on the nuclear magnetic relaxation dispersion experiments to probe specifically the proton dynamics in CPG pores with and without methyl groups at the surface. A detailed analysis of the frequency dependences of the longitudinal relaxation rates in these two materials evidences the impact of microscopic wettability on moisture transport in meso- and macro-porous materials. The surface modification has allowed a frequency rescaling such that different regimes of relaxation dependence can be fully explored in a larger frequency range than that explored by FFC relaxometry. We believe that such an NMR study realized on model porous materials is of particular importance for studying the moisture transport between the meso- and macro-porous networks of cement-based materials.

Probing multi-dynamics of crude oils by high field 2D NMR DOSY and relaxometry

We propose using a set of non-invasive multiscale NMR techniques for probing the structure and dynamics of bulk and confined crude oils with and without asphaltene. High field NMR spectroscopy identifies the proton species. 2D NMR DOSY spectra for bulk crude oils in presence or absence of asphaltene favor an interpretation of two populations of hydrocarbon aliphatic chains in two environments. In the presence of asphaltene, an analysis of the distributions of longitudinal relaxation time, T1, in terms of a bimodal log-normal distribution, confirms the two environments clearly evidenced by varying the Larmor frequency. The remarkable features of the nuclear magnetic relaxation dispersion (NMRD) of 〈1/T1〉 for bulk and confined crude oils with and without asphaltene have been interpreted with an original model of intermittent surface dynamics of proton species at proximity of the surface of asphaltene nanoaggregates and bulk dynamics in between the clusters of these nanoaggregates.

Peach Fruit: Metabolic Comparative Analysis of Two Varieties with Different Resistances to Insect Attacks by NMR Spectroscopy

The metabolite profile of aqueous extracts of two peach varieties, Percoca Romagnola 7 and Flaminia, with different susceptibilities to Ceratitis capitata attack was investigated by means of 1D and 2D high-field NMR spectroscopy. Water-soluble metabolites belonging to different classes such as organic acids (citric, fumaric, malic, quinic, shikimic, and succinic acids), sugars (fucose, fructose, fructose-6-phosphate, glucose, glucose-6-phosphate, rhamnose, sucrose, and xylose), amino acids (alanine, asparagine, isoleucine, threonine, and valine) and other metabolites such as myo-inositol, choline, trigonelline, catechin, chlorogenic and neochlorogenic acids, orthophosphate, and α-l-glycerophosphorylcholine were identified. The metabolite profile together with a suitable statistical analysis was used to make a comparison between the two varieties. The levels of glucose, xylose, myo-inositol, choline, isoleucine, and valine were found to be higher in Flaminia than in Percoca Romagnola 7 samples, whereas the levels of fumaric acid, alanine, quinic acid, sucrose, fucose, and chlorogenic and neochlorogenic acid were found to be higher in Percoca Romagnola 7 than in Flaminia samples.

Metabolic Profiling and Outer Pericarp Water State in Zespri, CI.GI, and Hayward Kiwifruits

The metabolic profiling of aqueous extracts of Zespri Gold ( Actinidia chinensis ) and CI.GI (a controlled crossbreed from different species of Actinidia deliciosa ) kiwifruits and the water state of the outer pericarp of entire fruits were monitored over the season by means of high-field NMR spectroscopy and T(2) relaxation time measurements, respectively, and compared with the corresponding ones of Hayward kiwifruits previously investigated. A more complete assignment of the (1)H spectrum with respect to that obtained previously was reported: histidine, phenylalanine, quercetin 3-rhamnoside, and epicatechin were identified. Metabolic profiling confirmed Zespri's earlier maturation compared with the two other varieties. The water state of entire kiwifruits was measured nondestructively on fruits attached to the plants or detached from the plants. T(2) relaxation times were found to be sensitive to the kiwifruit developmental stage.

Structural characterisation of a complex heteroglycan from the cyanobacterium Nostoc commune

An alkali-extractable O-methylated ribofuranose-containing heteroglycan, Nc-5-s, was isolated from wild-growing field colonies of the cyanobacterium Nostoc commune collected in Iceland, using ethanol fractionation and anion-exchange chromatography. The average molecular weight was estimated to be 1500kDa. Structural characterisation of the heteroglycan was performed by high-field NMR spectroscopy (1D proton, 2D-COSY, 2D-NOESY, 2D-TOCSY, 1H 13C-HSQC, HMBC, H2BC and HSQC-NOESY) as well as monosaccharide analysis after methanolysis by GC and supported by linkage analysis by GC–MS.According to the data obtained, the structure of Nc-5-s is composed of repeating units of 1, 1a, 1b and 2 and 2a in approximate molar ratio of (10:25:50:5:10). [Display omitted]

Nature and Structure of Aluminum Surface Sites Grafted on Silica from a Combination of High-Field Aluminum-27 Solid-State NMR Spectroscopy and First-Principles Calculations

The determination of the nature and structure of surface sites after chemical modification of large surface area oxides such as silica is a key point for many applications and challenging from a spectroscopic point of view. This has been, for instance, a long-standing problem for silica reacted with alkylaluminum compounds, a system typically studied as a model for a supported methylaluminoxane and aluminum cocatalyst. While (27)Al solid-state NMR spectroscopy would be a method of choice, it has been difficult to apply this technique because of large quadrupolar broadenings. Here, from a combined use of the highest stable field NMR instruments (17.6, 20.0, and 23.5 T) and ultrafast magic angle spinning (>60 kHz), high-quality spectra were obtained, allowing isotropic chemical shifts, quadrupolar couplings, and asymmetric parameters to be extracted. Combined with first-principles calculations, these NMR signatures were then assigned to actual structures of surface aluminum sites. For silica (here SBA-15) reacted with triethylaluminum, the surface sites are in fact mainly dinuclear Al species, grafted on the silica surface via either two terminal or two bridging siloxy ligands. Tetrahedral sites, resulting from the incorporation of Al inside the silica matrix, are also seen as minor species. No evidence for putative tri-coordinated Al atoms has been found.

19F NMR spectroscopy study of the metabolites of flucloxacillin in rat urine.

19F NMR spectroscopy was used to monitor the metabolites of flucloxacillin in the urine of a rat dosed with its sodium salt. 19F NMR signals were detected and quantified from flucloxacillin and three metabolites. The 19F NMR method involves minimal sample preparation and is free from interference by endogenous urine components. High-field spin-echo 1H NMR spectroscopy and HPLC were used to confirm the results.

Multinuclear NMR study of silica fiberglass modified with zirconia

Silica fiberglass textiles are emerging as uniquely suited supports in catalysis, which offer unprecedented flexibility in designing advanced catalytic systems for chemical and auto industries. During manufacturing fiberglass materials are often modified with additives of various nature to improve glass properties. Glass network formers, such as zirconia and alumina, are known to provide the glass fibers with higher strength and to slow down undesirable devitrification processes. In this work multinuclear 1H, 23Na, 29Si, and 91Zr NMR spectroscopy was used to characterize the effect of zirconia on the molecular-level fiberglass structure. 29Si NMR results help in understanding why zirconia-modified fiberglass is more stable towards devitrification comparing with pure silica glass. Internal void spaces formed in zirconia–silica glass fibers after acidic leaching correlate with sodium and water distributions in the starting bulk glass as probed by 23Na and 1H NMR. These voids spaces are important for stabilization of catalytically active species in the supported catalysts. Potentials of high-field 91Zr NMR spectroscopy to study zirconia-containing glasses and similarly disordered systems are illustrated.

Guaianolides from Crepis dioscoridis L.

The genus Crepis L. is well known for its abundance in sesquiterpene lactones, the majority of which belong to the costunolide type guaianolides [1]. Due to the pharmacological and chemosystematic interest of these compounds, we investigated the chemical profile of C. dioscoridis L. collected in W. Greece. Air-dried and macerated aerial parts were extracted with a mixture of cyclohexane, diethyl ether and methanol (1:1:1). The extract was concentrated in vacuo and fractioned by V.L.C. followed by repeated CC on silicagel using mixtures of DM:MeOH of increasing polarity. The fractions were monitored by TLC and 1H-NMR. 8-Epigrosheimin and 11βH-11,13-dihydrointegrifolin [2] were yielded by RP18-HPLC (MeOH:H2O 3:2), while three costus type and two hieracin type glucosides were isolated by RP18-HPLC (MeOH:H2O 9:11). The structures of the isolated compounds were elucidated by high-field NMR spectroscopy (1H-NMR, 1H-1H COSY, NOESY, HSQC and HMBC).

ChemInform Abstract: Synthesis and Conformational Analysis of Phosphate-Methylated RNA Dinucleotides.

Synthesis of RNA dimers having a methyl phosphotriester group as the internucleoside linkage is reported; six pairs of diastereoisomerically pure system were prepared, Le., r(CpU) (151, r(ApU) (16), r(CpC) (17), r(ApC) (18), r(CpG) (19), and r(ApG) (20). Compounds 15-20 are stabilized by a 2’-0-methyl group in the 5’-terminal residue. The present systems represent the third class of backbone-modified RNA oligomers, following the 2’-O-methylribonucleotide phosphorothioates and the 2’-O-methylribonucleotide methyl phosphonates. Our synthetic approach comprises the use of 9-fluorenylmethoxycarbonyl (Fmoc) groups for transient protection of the exocyclic NH, groups of the bases A, C, and G, levulinoyl (Lev) groups for the transient protection of the 2’and 3’-OH groups of the 3’-terminal residues, methanolic K2C03 for the simultaneous removal of Fmoc and Lev groups with full preservation of the methyl phosphotriester function, and finally reversed-phase HPLC separation of the Sp and Rp diastereoisomers. The availability of the six dimers in diastereoisomerically pure form enabled us to examine the molecular conformations using high-field NMR and circular dichroism (CD) spectroscopy. These studies led to the following conclusions: (i) NMR J-coupling analysis: the central C I A 5 $ (y) and C d 5 , (j3) bonds in 15-20 show lesa preference for the y+ and @ rotamers, in comparison with their natural analogues, Le., base stacking is diminished upon introduction of the two methyl groups on Or and on the phosphate group; (ii) CD analysis: 15-20 show substantially reduced molecular ellipticities when compared to the natural counterparts, which also reveals that base stacking is reduced; (iii) UV and variable-temperature ‘H NMR measurements: (Sp)and (Rp)-19 show self-association, via the formation of a right-handed miniduplex with two C-G base pairs ((Sp)-l9, T, = 9.3 O C , concn = 36.6 pM; (Rp)-19, T, = 8.7 O C , concn = 48.1 pM). The present conformatipnal data on (Rp)and (Sp)-15-20 are in agreement with literature data on other phosphate-triesterified oligonucleotides, e.g., the trimer d(TwmGpomG) and the tetramer d(TpoaTwmCp0mA). While the latter systems also showed little base-base stacking, it was established that they readily form a local duplex with a complementary natural RNA sequence. Hence we anticipate that phosphate-methylated 2’-O-methyl-RNA oligomers, longer than the dimer svstems described in the Dresent work, will also hybridize easily with complementary natural RNA.

ChemInform Abstract: Electrochemical Property and Formation of the Cation Radical and Dication of Dinaphtho(1,8-b,c)-1,5-dithiocin.

A new symmetrical dithio peri-bridged naphthalene, dinaphtho[l,8-b,c]-1,5-dithiocin (1) has been synthesized. The cyclic voltammogram of 1 showed one reversible oxidation peak. ESR spectrum of the coned H2SO4 solution of 1 showed the formation of the cation radical. The formation of the dication of 1 was observed in the reaction of the corresponding monosulfoxide with concd D2SO4 by both high-field 1H and 13C NMR spectroscopy.

ChemInform Abstract: Diterpenes from Haplopappus chrysanthemifolius.

Three new diterpenes were isolated from the aerial part of Haplopappus chrysanthemifolius and assigned the structures 6α-hydroxy-ent-labd-8(17)-en-15-oic acid, 3β-acetoxy-ent-labd-8(17)-en-15-oic acid and 18α-acetoxylabd-8(17)-en-15-oic acid. The structures were elucidated by high field NMR spectroscopy.

Structural characterisation of a new O-methylated heteroglycan, colleman, from the cyanolichen Collema flaccidum

An alkali-extractable heteroglycan, colleman, was isolated from the cyanolichen Collema flaccidum, using ethanol fractionation and anion-exchange chromatography. The average molecular weight was estimated to be 360 kDa. Structural characterisation of the heteroglycan was performed by high-field NMR spectroscopy (1D proton, 2D-COSY, NOESY, 2D-TOCSY, 1H 13C-HSQC, HMBC, H2BC and HSQC-NOESY). According to the data obtained, the structure of colleman is composed of repeating units of A, B, C and D in approximate molar ratio 5:5:2:1; ▪

Assessing the mechanism of the synergistic action of calixarenes and Co-dicarbollides in lanthanide extractions

The extraction pathway of lanthanide ions from simulated nuclear waste solutions and the synergistic effects of a calixarene and a cobalt dicarbollide anion (CD) have been investigated on a model system by the combined use of electrospray ionization MS, FTMS ICR, together with 1H and 11B high field NMR spectroscopy techniques. Moreover, the extracting capabilities of the calixarene/BrCD mixture were determined by liquid–liquid extraction tests. An enhanced extraction efficiency of the calixarene/BrCD mixture with respect to the calixarene alone was observed. MS analysis allowed the assessment of a supramolecular ternary association, while the NMR data gave information on the calixarene binding sites for lanthanide ions. Herein, we report the experimental evidence of the formation of a ternary lanthanide/calixarene/Co-dicarbollide aggregate, which allowed us for the first time to assess the mechanism of the synergistic action of calixarenes and CD anions in lanthanide ion extraction.

Well‐Defined Silica‐Supported Calcium Reagents: Control of Schlenk Equilibrium by Grafting

Calcium reagents Ca(alpha-Me(3)Si-2-Me(2)N-benzyl)(2) x 2 thf (1) and Ca[N(SiMe(3))(2)](2) x 2 thf (2) reacted with silica partially dehydroxylated at 700 degrees C to afford materials that bear ([triple bond]SiO)Ca(alpha-Me(3)Si-2-Me(2)N-benzyl) x 1.6 thf (SiO(2)-1) and ([triple bond]SiO)Ca [N(SiMe(3))(2)] x 1.3 thf (SiO(2)-2) fragments, respectively. Due to the bulk of the supported complexes, the silanol groups are only partially metalated: 50% in SiO(2)-1 and 70% in SiO(2)-2. In the case of SiO(2)-2, a parallel SiMe(3)-capping side reaction affords in fine a silanol-free surface. The materials were characterized by IR spectroscopy, 1D and 2D solid-state high-field NMR spectroscopy, and elemental analysis. Reaction of 2 with one equivalent of the bulky silanol (tBuO)(3)SiOH, a silica-surface mimic, afforded the homoleptic bis-silyloxide calcium derivative through ligand exchange (Schlenk equilibrium), and a derivative was isolated and structurally characterized. Preliminary studies have shown that both grafted benzyl and amide derivatives are active in olefin hydrosilylation, intramolecular hydroamination, and styrene polymerization, with evidence showing that catalysis occurs through supported species. In styrene polymerization, a marked influence of the surface acting as a ligand on the stereoselectivity of the reaction was observed, as syndiotactic-rich polystyrene (88% of r diads) was obtained. These results illustrate that grafting of calcium benzyl or amide compounds on a silica surface is a new concept to prevent ligand exchange through the Schlenk equilibrium. Heteroleptic calcium complexes that cannot be synthesized as stable molecular species in solution can be obtained as silica-supported species which have been shown to be catalytically active.

Identification of metabolites in human hepatic bile using 800 MHz 1H NMR spectroscopy , HPLC-NMR/MS and UPLC-MS

The first application of high field NMR spectroscopy (800 MHz for (1)H observation) to human hepatic bile (as opposed to gall bladder bile) is reported. The bile sample used for detailed investigation was from a donor liver with mild fat infiltration, collected during organ retrieval prior to transplantation. In addition, to focus on the detection of bile acids in particular, a bile extract was analysed by 800 MHz (1)H NMR spectroscopy, HPLC-NMR/MS and UPLC-MS. In the whole bile sample, 40 compounds have been assigned with the aid of two-dimensional (1)H-(1)H TOCSY and (1)H-(13)C HSQC spectra. These include phosphatidylcholine, 14 amino acids, 10 organic acids, 4 carbohydrates and polyols (glucose, glucuronate, glycerol and myo-inositol), choline, phosphocholine, betaine, trimethylamine-N-oxide and other small molecules. An initial NMR-based assessment of the concentration range of some key metabolites has been made. Some observed chemical shifts differ from expected database values, probably due to a difference in bulk diamagnetic susceptibility. The NMR spectra of the whole extract gave identification of the major bile acids (cholic, deoxycholic and chenodeoxycholic), but the glycine and taurine conjugates of a given bile acid could not be distinguished. However, this was achieved by HPLC-NMR/MS, which enabled the separation and identification of ten conjugated bile acids with relative abundances varying from approximately 0.1% (taurolithocholic acid) to 34.0% (glycocholic acid), of which, only the five most abundant acids could be detected by NMR, including the isomers glycodeoxycholic acid and glycochenodeoxycholic acid, which are difficult to distinguish by conventional LC-MS analysis. In a separate experiment, the use of UPLC-MS allowed the detection and identification of 13 bile acids. This work has shown the complementary potential of NMR spectroscopy, MS and hyphenated NMR/MS for elucidating the complex metabolic profile of human hepatic bile. This will be useful baseline information in ongoing studies of liver excretory function and organ transplantation.

A new sesquiterpene lactone from the aerial parts of Anthemis melanolepis L

Continuing our research on the chemical constituents from the aerial parts of Anthemis melanolepis L., a Greek endemic species belonging to the section Cota [1], we report here the isolation and identification of a new sesquiterpene lactone. The isolation was proceeded according to the Bohlmann isolation method, slightly modified [2]. The structure of the isolated compound 1 was elucidated by spectroscopic methods, particularly high-field NMR spectroscopy (1H-NMR, 1H-1H COSY, NOESY, HSQC, HMBC). Compound 1, namely anthemin C, is a new naturally occurring eudesmanolide. Besides compound 1, there were also isolated twelve known sesquiterpene lactones, one terpene, one triterpene, eight flavonoids and three phenolic acids.

Effects of pH and temperature on the stability of sesquiterpene lactones

As part of a series of our research on sesquiterpene lactones, we report here on the stability of different sesquiterpene lactones, isolated from the species Anthemis melanolepis [1] and Centaurea spinosa [2], under various pH and temperature conditions. The stability of five sesquiterpene lactones bearing or not a side chain was calculated at pH 5.5, 7.4 (buffer solutions) and RPMI 5% and at temperatures 25 0C and 37 0C for 96 hours. Sesquiterpene lactones bearing a side chain lost this side chain at pH 7.4 and 37 0C, while they were stable at pH 5.5. Sesquiterpene lactones not bearing a side chain seemed to be stable at all conditions. The structure of the products was elucidated by spectroscopic methods, particularly high-field NMR spectroscopy (1H-NMR).

Analysis of in vitro 2D-COSY on Human Brain Metabolites for Molecular Stereochemistry

To investigate the 3-bond connectivity of human brain metabolites by scalar coupling interaction through 2D-correlation spectroscopy (COSY) techniques using high field NMR spectroscopy. All NMR experiments were performed at 298K on Unity Inova 500 or 600 (Varian Inc.) equipped with a triple resonance probe head with z-shield gradient. Human brain metabolites were prepared with 10% <TEX>$D_2O$</TEX>. Two dimensional 2D COSY spectra were acquired with 4096 complex data points in <TEX>$t_2$</TEX> and 128 or 256 increments in <TEX>$t_1$</TEX> dimension. The spectral width was 9615.4 Hz and solvent suppression was achieved using presaturation using low power irradiation of the water resonance during 2s of relaxation delay. NMR data were processed using VNMRJ (Varian Instrument) software and all the chemical shifts were referenced to the methyl resonance of N-acetyl aspartate (NAA) peak at 2.0 ppm. Total 10 metabolites such as N-acetyl aspartate (NAA), creatine (Cr), choline (Cho), glutamine (Gln), glutamate (Glu), myo-inositol (Ins), lactate (Lac), taurine (Tau), <TEX>${\gamma}$</TEX>-aminobutyricacid (GABA), alanine (Ala) were included for major target metabolites. Symmetrical 2D-COSY spectra were successfully acquired. Total 14 COSY cross peaks were observed even though there were parallel/orthogonal noisy peaks induced by water suppression. Except for Cr, all of human brain metabolites produced COSY cross peaks. The spectra of NAA methyl proton at 2.02 ppm and Glu methylene proton (<TEX>$CH_2(3)$</TEX>) at 2.11 ppm and Gln methylene proton (<TEX>$CH_2(3)$</TEX>) at 2.14 ppm were overlapped in the similar resonance frequency between 2.00 ppm and 2.15 ppm. The present study demonstrated that in vitro 2D-COSY represented the 3-bond connectivity of human brain metabolites by scalar coupling interaction. This study could aid in better understanding the interactions between human brain metabolites in vivo 2D-COSY study. Also it would be helpful to determine the molecular stereochemistry in vivo by using two-dimensional MR spectroscopy.

Improving resolution in proton solid-state NMR by removing nitrogen-14 residual dipolar broadening

Residual dipolar coupling between quadrupolar and other nuclei under MAS has not usually been thought to be important in high field NMR spectroscopy. We show that coupling to 14N broadens 1H lineshapes significantly even at 11.7 T, and that we can decouple 14N from 1H during 1H homonuclear decoupling to successfully improve 1H resolution. The method used for decoupling is the application of evenly spaced pulses to the quadrupolar nucleus.