Solid-state 13C CPMAS Research Articles

Quantitative elemental and structural analysis of dissolved organic carbon fractions from lakes near Sudbury, Ontario

Dissolved organic carbon (DOC) was quantitatively isolated as five separate fractions from two Sudbury area lakes (Ontario, Canada) using the tandem XAD-8/XAD-4 resin technique. Fulvic acids made up ≈ 48% of the total, humic acids ≈ 8%, hydrophobic neutrals ≈ 8%, XAD-4 acids ≈ 11%, and XAD-4 acetonitrile extracts ≈ 13%. Hydrophobic:hydrophilic ratios were about 65:35. Solid-state CPMAS 13C NMR indicated a primarily aliphatic nature in all fractions. Percent aromaticity was in the order humic acids > fulvic acids > XAD-4 acetonitrile extracts ≈ XAD-4 acids ≈ hydrophobic neutrals. Titration analysis showed that the 13C NMR peaks of fulvic acids, humic acids, and XAD-4 acids from 160–190 ppm were primarily carboxyl in nature. The XAD-4 acids were the most acidic, suggesting that they may be important geochemical agents. 13C NMR indicated that polysaccharides formed < 20% of any fraction. The two neutral fractions (hydrophobic neutrals and XAD-4 acetonitrile extracts) had relatively high N contents, possibly due to the acetonitrile used to extract them. However, the 13C NMR spectra did not show significant quantities of acetonitrile. The elemental and structural composition covaries in the three acid fractions, such that if one acid is enriched or depleted, so are the others. This suggests that the humic and non-humic acids form a continuum in which all fractions are affected by the same formative processes. Compared to published data for other freshwater samples, the three acid fractions from the Sudbury area lakes have low or very low aromaticity. This may indicate that the acid and metal loadings in the Sudbury area have affected the structure of the organic acids, despite the circumneutral character of the study lakes. These are the first quantitative 13C NMR results published for the hydrophobic neutrals and XAD-4 acetonitrile extracts, so comparisons are not possible. Key words: aquatic DOC, organic acids, 13C NMR, humic substances, non-humic substances.

13C CPMAS NMR, XRD, d.c. and a.c. electrical conductivity of aromatic acids doped polyaniline

Aromatic acids, para-toluene sulfonic acid (PTSA) and sulfosalicylic acid (SSA), doped polyanilines at different dopant levels and prepared by chemical and electrochemical methods are characterized by the high-resolution solid-state 13C CPMAS NMR technique. X-ray diffraction (XRD) patterns of highly protonated samples show a peak around 24 °. There is increase in crystallinity as the dopant concentration is increased. Temperature dependence of d.c. electrical conductivity measurements suggests that conduction takes place in an inhomogeneous medium consisting of ‘metallic’ polymer particles embedded in an insulating matrix. A.c. electrical conductivity measured on some of these samples shows that σ ac ∝ ω s in the frequency range 10 Hz to 100 kHz, and s is found to decrease as the dopant concentration and the temperature are increased. For higher dopant concentration samples, σ ac is found to be temperature independent in the frequency range 10 Hz–100 kHz. The real part of the dielectric constant showed a steep increase at low frequencies. The results of a.c. transport are discussed in terms of hopping of charges among defect states.

Stannacyclohexanes and spiro-tin compounds with s stannole or a stannolene group

1,1-Diethynyl-1-stannacyclohexane ( 5) was prepared, and its reaction with triethylborane or 9-isobutyl-9-borabicyclo[3.3.1]nonane gave the corresponding spiro-tin compounds 6 and 7 with a stannole fragment. The molecular structure of the derivative 7 was determined by X-ray analysis (triclinic, space group Povbar|1; a=835.2(7), b=1117.5(2), c=1165.6(2) pm; α=72.05(3), β=74.32(3), γ=50.61(3)°). Treatment of 6 with trimethyltin ethoxide gave at first quantitatively the spiro-tin compound 8 with a 2-stannole unit which rearranges upon heating into the spiro-tin compound 9 with a 3-stannole unit. The reaction of 7 with trimethyltin butoxide gave quantitatively another tetracyclic compound 10, analogous to 8. All compounds were characterised by 1H, 11B, 13C and 119Sn NNMR data. Numerous coupling signs nJ( 119Sn 1 H) and 2J( 119sn 117SN) were determined by 2D 13C/ 1H and 119Sn/ 1H heteronuclear shift correlations. Compound 7 was studied by solid-state 13C and 119Sn CPMAS NMR. This revealed the presence of a second crystalline phase in the bulk of the solid material, as confirmed by powder X-ray diffraction data. 119Sn CPMAS NMR spectra of 7 show resolved scalar 1119Sn- 11B coupling ( 3J( 119 Sn 11 B) = 68±5 and 65+-5 Hz ).

Surface Organometallic Chemistry of Tin: Grafting Reactions on Highly Dehydroxylated Silica

Abstract A new grafting method of organotin complexes with the surface of highly dehydroxylated silica is reported. Characterisation was achieved by surface microanalysis, in situ IR, solid state 13C CP-MAS and 119Sn MAS NMR. Bu3Sn-O-SnBu3 reacts with the strained siloxanes and opens these bridges at room temperature. The reaction occurs also with the remaining hydroxyl groups and with less strained siloxane bridges, leading in all cases to the same surface organometallic fragment ≡Si-O-SnBu3.

Solid-state electronic absorption, fluorescence and13C CPMAS NMR spectroscopic study of thermo- and photo-chromic aromatic Schiff bases

Solid-state electronic absorption, fluorescence emission and 13C CPMAS spectroscopies have been applied to a series of aromatic Schiff bases displaying both ground and excited state intramolecular proton transfer phenomena. All the results can be explained on the basis of a thermal equilibrium between enolimine and keto–enamine tautomeric forms in the crystalline state. Most of the studied compounds are thermochromic. However, a few are photochromic. The carbon-13 NMR data in the solid state show, in general, residual (13C, 14N) dipolar coupling effects. In certain cases, however, where fast proton transfer occurs in the ground state, these effects are shown to be self-decoupled.

Solid State 13C CP-MAS NMR Studies of the Crystallinity and Morphology of Poly(l-lactide)

Solid-state 13C CP-MAS NMR spectroscopy has been used to investigate highly crystalline, partially crystalline, and amorphous poly(l-lactide) (PLLA). The amorphous domains have broad resonances with Gaussian line shapes, while the crystalline domains have narrower resonances with a high degree of Lorentzian character. Spectra of highly crystalline PLLA have at least five distinct resonances for the carbonyl and methine functional groups in the polymer, indicating five or more crystallographically inequivalent sites in the crystalline domains of the polymer. For the amorphous polymer, broad Gaussian peaks are observed for each of the methyl, methine, and carbonyl functional groups. Spectra of partially crystalline PLLA contains spectral features of both domains, and furthermore, the spectra appear to be sensitive to both short range (nanometer) and long range (micrometer) order within the polymer. A method to extract the information of crystallinity and morphology from the solid-state CP-MAS NMR spectra of partially crystalline PLLA is discussed.

Variation in reflectance and chemistry of vitrinite and vitrinite precursors in a series of Tertiary Coals, Arctic Canada

A continuous 3300 m thick sequence of coal measures from the Eureka Sound Group, Foshiem Peninsula, Ellesmere Island has been studied in order to document changes in chemistry of coals from 0.17 to 0.56% vitrinite reflectance ( R o) as well as to determine differences in chemistry between collinite and telinite and their precursor macerals. Electron microprobe, micro-FTIR, solid state 13C-CPMAS NMR and reflected light microscopy techniques were applied. For the series of coals studied, collinite has a slightly higher R o than telinite; R o values of both macerals give precise measures of organic maturation. Reflectance is a better maturation parameter than carbon content and aromaticity over the studied maturation range. NMR and FTIR spectra show distinct changes in chemistry between coals with R o below and above 0.2%. In organic matter with R o below 0.2%, distinct differences exist between samples with respect to both the relative proportions of cellulose and lignin and the relative abundance of individual cellulose varieties. Coals with R o above 0.2% do not have measurable amounts of cellulose, and differences between samples are indicated by differences in aromaticity of the lignin component. FTIR spectra show that, in coals with R o < 0.2%, there is more cellulose in telinite than in collinite. Cellulose is not present in coals with R o > 0.2%, and the lignin component is more aromatic in collinite than in telinite. The differences between telinite and collinite are attributed to differences in chemistry of the primary plant material.

Variable-temperature 13C solid-state NMR spectra: Mobility of trimethyltin groups in coordination polymers of the type [(Me 3Sn) 4M(CN) 6]∞ (MFe, Os, Ru)

Solid-state 13C CP MAS NMR studies of compounds [(Me 3Sn) 4M(CN) 6]∞ with MFe, Ru and Os were performed over a temperature range of 80 K in order to understand exchange thermodynamics. For each compound six methyl carbon signals are seen below 240 K, showing there are two non-equivalent Me 3Sn units. Using detailed lineshape analysis the thermodynamic activation parameters for the three samples were obtained. Low-temperature 2-D exchange spectra indicated that exchange occurs between the carbons of each Me 3Sn rotor independently. Therefore in the calculations a model of two independent three-site mutual-exchange processes was used. The effect of 117/119Sn satellites was included.

Micromorphological and 13C NMR characterization of a Humic, Lignic, and Histic Folisol from British Columbia

The thick folic (mainly upland forest) materials (&gt; 40 cm of accumulated organic material) that occur in the Coastal Western Hemlock Biogeoclimatic Zone in British Columbia have not been described with regard to the spatial interrelationships of the soil constituents in context with the chemical composition of the different horizons. Micromorphological assessment and solid-state 13C NMR were used to characterize the accumulated folic materials from a Lignic Folisol (northern Vancouver Island), Histic Folisol (Prince Rupert, BC) and a Humic Folisol (Queen Charlotte Islands, BC). Micromorphology provided information on the spatial relationships of the soil constituents and 13C NMR provided data on the chemical components of the folic materials. Soil faunal activity, primarily from mites, was the dominant soil-forming process observed in the organic horizons of the Folisols, being especially prominent in the Lignic Folisol with the breakdown of woody materials. Solid state 13C CPMAS NMR spectra facilitated distinguishing three main types of horizons: (1) Horizons derived from accumulated residues (L, Fr, and Hr) showing higher carbohydrate-like C and O-alkyl C values and lower total aromatics; (2) Horizons with advanced decomposition (Hr2, Oh1, and Hd) which were higher in alkyl C; and (3) Horizons derived from ligneous material (Fw and Hdw) where carbohydrate-like C was less than total aromatic C. Implications for adequate nutrient content and forest growth were inferred from the observed micromorphology and chemical composition of the folic materials. Key words: Folisol, forest soils, micromorphology, 13C NMR, faunal activity

Hydrocarbon-Bridged Polysiloxane and Polysilsesquioxane Network Materials.

ABSTRACTHexylene-and phenylene-bridged polymethylsiloxane xerogels X-2 and X-4, respectively, were prepared by the sol-gel hydrolysis and condensation of 1, 6-bis(diethoxymethyl-silyl)hexane 1 and 1, 4-bis(diethoxymethysilyl)benzene 2 under acidic and basic conditions. These polymerizations afforded network polymers in the form of wet gels within several hours. The gels were processed to afford xerogels whose characteristics (determined by solid state 13C and 29Si CP MAS NMR spectroscopy and nitrogen sorption porosimetry) were compared and contrasted with those of their analogous polysilsesquioxanes. 29Si CP MAS NMR indicates a high, degree of hydrolysis and polycondensation; porosimetry measurements reveal that the materials have significant surface areas, save for the acid-catalyzed hexylene gels X-2.

Studies of the sorption of triethyl phosphate by ion-exchanged smectite clays

The binding of triethyl phosphate (TEP) to smectites containing Bu4N+, Mg2+ or Al3+ as the counter-ion has been studied. Solid-state 31P and 13C CPMAS and SPE-MAS NMR were used to observe both mobile and motion-restricted phases. Magnesium complexes of TEP and dimethylmethyl phosphonate (DMMP) have been prepared and used as models for the complexes formed in the clay matrix. These compounds were also investigated by solid-state 31P NMR and FTIR spectroscopies. TG, XRD and FTIR spectroscopy have also been used to study the sorbed TEP species. A number of sorption sites have been detected; one important mechanism of sorption involves coordination to the interlamellar cation.

Imidazole and benzimidazole addition to quinones. Formation of meso and d,l isomers and crystal structure of the d,l isomer of 2,3-Bis(benzimidazol-1'-yl)-1,4-dihydroxybenzene

The hydroquinones obtained by addition of imidazole, 2-methylimidazole and benzimidazole to 1,4-benzoquinone and 1,4-naphthoquinone have been isolated and identified. In the case of 1,4-benzoquinone they are monosubstituted hydroquinones 1a - 1e, o-substituted hydroquinones 2a - 2c, and p-disubstituted derivatives 3a - 3c while in the case of 1,4-naphthoquinone, only disubstituted derivatives 5a and 5c have been isolated. In solution, 2,3-bis(2′-methylimidazol-1′-yl)-1,4-dydroxybenzone ( 2b), 2,3-bis (benzimidazol-1′-yl)-1,4-dihydroxybenzene ( 2c) and 2,3-bis(benzimidazol-1′-yl)-1,4-dihydroxynaphthalene ( 5c) exist as mixtures of meso and d,l isomers. NMR spectroscopy (n.O.e. experiments in 1H NMR and solid-state 13C CPMAS spectra) and AM1 semiempirical calculations have been used to establish the structure of the isomers both in the solid state and in solution as well as their interconversion pathways. Compound 2c- d,l crystallizes with two methanol solvate molecules as guests and it has a crystallographic twofold axis through the middle. The host molecules are linked together by means of the methanol molecules through O-H⋯O/N hydrogen bonds giving rise to chains along the c axis centrosymmetrically related.

Solid-state 31P [formula omitted] NMR vs. solution study of bis(tertiary phosphines)

Solid-state 31P and 13C CP MAS results of several diphosphines are compared with solution phase data. Non-equivalence of the P atoms are observed in the solid state for the less flexible derivatives (including all chiral diphosphines studied), whereas the more flexible compounds with a linear alkyl chain such as the 1,2-ethane and the 1,4-butane derivatives give only rise to a single resonance. For the more strained bis(diphenylphosphino)methane contradictory data have been reported. Our experiments confirm the existence of an AB spin system, i.e., two different P atoms in solid state. Substantial chemical shift difference between P atoms have been observed in the solid state but not in solution of the chiral compounds. A possible explanation is suggested in terms of the concerted anisotropic effect of the phenyl rings attached to the phosphorus atom.

CPMAS 13C NMR and pyrolysis-GC-MS studies of structure and liquefaction reactions of Montana subbituminous coal

This paper reports on the application of solid-state CPMAS 13C NMR and flash pyrolysis-GC-MS for characterization of the macromolecular network of a Montana subbituminous coal and its residues from temperature-programmed and non-programmed liquefaction (TPL and N-PL) at final temperatures ranging from 300 to 425°C in H-donor and non-donor solvents. The combined use of 13C NMR and Py-GC-MS revealed that this coal contains significant quantities of oxygen-bearing structures, corresponding to about 18 O-bound C per 100 C atoms and one O-bound C per every five to six aromatic C's. The oxygen-bearing components in the coal include catechol-like structures, which seem to disappear from the liquefaction residues above 300°C; carboxyl groups, which almost disappear after 350°C; and phenolic structures, which are most important in the original coal but diminish in concentration with increasing temperature. These results point to the progressive loss of oxygen functional groups and aliphatic-rich species from the macromolecular network of the coal during programmed heat-up under TPL conditions. The higher conversions in TPL runs in H-donor tetralin (relative to the conventional N-PL runs) suggest that the removal of carboxylic and catechol groups from the coal and the capping of the reactive sites by H-transfer from H-donors at low temperatures (≤350°C) have contributed to minimizing the retrogressive crosslinking at higher temperatures. Quantitative calculation of NMR data and mathematical correlation were also attempted in this work. For 24 liquefaction residues derived under significantly different conditions, linear correlations between C-distribution and reaction temperature (≥ 300°C) have been found, which can be expressed by a simple equation, C i = αf i + βT, where f i and C i, represent content of aromatic, aliphatic, or oxygen-bound carbons in the original coal and residue, respectively; T stands for the reaction temperature; α and β are constants.

Characterization of crosslinked ethylene—Vinylacetate copolymers

AbstractTwo types of ethylene‐vinylacetate copolymers, containing 16% and 9% of vinylacetate, respectively, were crosslinked with dicumyl peroxide in a Brabender plastograf. The time of the torque maximum was proportional to the degree of crosslinking. The degree of crosslinking was determined by extraction and depended on the concentration of the crosslinking agent and of vinylacetate in the copolymer, and on the crosslinking temperature and time. It was found by DSC and by solid‐state CP‐MAS 13C NMR that with the progress of crosslinking the crystalline phase of the copolymers changed to the amorphous phase. Crosslinking took place mostly on the acetate groups.

Proton transfer in rubazoic acid derivatives in solution and in the solid state. An NMR study

Solution 1H and 13C, and solid-state 13C CPMAS NMR data are reported for the rubazoic acid derivatives 4-(5-hydroxy-1,3-dimethylpyrazol-4-ylmethylidene)-1,3-dimethyl-2-pyrazolin-5-one 1, 4-(5-hydroxy-1,3-dimethylpyrazol-4-ylimino)-1,3-dimethyl-2-pyrazolin-5-one 2, 4-(5-hydroxy-1-phenyl-3-aminopyrazol-4-ylmethylidene)-1-phenyl-3-amino-2-pyrazolin-5-one 3, and 4-(5-hydroxy-1-p-sulfophenylene-3-methylpyrazol-4-ylmethylidene)-1-p-sulfophenylene-3-methyl-pyrazolin-5-one 4. Solution 15N NMR chemical shifts have also been measured, lsotopic 2H shifts for the OH signal in CDCI3 for the first two compounds were found to be +0.28 ± 0.03 and +0.40 ± 0.03 ppm respectively. AM1-calculated molecular geometries are also reported. The overall results support the idea of a fast proton transfer equilibrium between two enolic tautomers both in solution and in the solid state. The degeneracy of the tautomers is removed in crystals.

Complexation of 7-azaindole by the methylmercury(II) cation

Complexes of the types [CH3Hg(aza)], [CH3Hg(Haza)]X, and [(CH3Hg)2(aza)]X are obtained by reacting CH3HgOH and/or CH3HgX (X = NO3, ClO4) with 7-azaindole (Haza). The weakly acidic N1-H proton on the pyrrole ring is displaced by the hydroxide, whereas the perchlorate and nitrate salts lead to CH3Hg+ coordination to the N7 lone pair on the pyridine ring. Detailed analysis of the infrared spectra of the complexes and their N-deuterated derivatives provides diagnostic regions for eventual prediction of the coordination mode in other systems. All compounds are characterized by means of 1H, 13C, and 199Hg NMR spectra in DMSO solution and solid-state CP-MAS 13C spectra. Comparison of the solution and solid-state 13C spectra show that the species present in the solids remain undissociated in DMSO. Each type of complex can be identified from a characteristic pattern of large displacements of the ligand 13C signals. The 1H spectra are less informative because substitution of the N1-H proton by CH3Hg+ induces only minor shifts. Metal solvation appears to have a major influence on the 13C and 199Hg chemical shifts of the CH3Hg+ groups.

The significance of solid‐state 13C NMR spectroscopy of whole soil in the characterization of humic matter

Abstract Differences in characteristics of humic matter were investigated by solid‐state CP/MAS 13C NMR spectroscopy of whole (nontreated) materials and their extracted humic fractions. Samples used in the analysis were lignite, a commercial humate AG, and the Bh horizons of a Mascotte and a Lawnwood soil. Humic fractions were extracted by the 0.1 M NaOH or Na4P2O7 (pH 9.8) method. The humic (HA) and fulvic acid (FA) obtained were weighed and analysed for total acidity, carboxyl and phenolic‐OH group contents. Whole lignite, humate AG and soil samples, and the HA and FA fractions were analyzed by solid state CP MAS 13C NMR and infrared spectroscopy. Carbon, H, and N contents were determined by chemical analysis. NMR spectra of the combined HA+FA extracts resembled the spectra of the whole materials. No additional signals were detected, indicating that alien compounds were not produced during the extraction. The best spectra were obtained with HA samples produced by the NaOH method. These spectra closely r...

Asp 85 is the only internal aspartic acid that gets protonated in the M intermediate and the purple-to-blue transition of bacteriorhodopsin A solid-state 13C CP-MAS NMR investigation

High-resolution solid-state 13C NMR spectra of the ground state and M intermediate of the bacteriorhodopsin mutant D 96N with the isotope label at [4- 13C]Asp and [11- 13C]Trp were recorded. The NMR spectra show that Asp 85 is protonated in the M intermediate. The environment of Asp 85 is quite hydrophobic. On the other hand, Asp 212 remains deprotonated and a slight shift to lower field indicates a more hydrophilic environment. Asp 85 also protonates in the purple-to-blue transition or bacteriorhodopsin in the deionized membrane, where it experiences a similar environment to M. The shift of Trp resonances in M reflect a conformational change of the protein in forming the M intermediate.

Solid state 13C CP-MAS NNR and other spectral studies of tradition mental complexes

Solid state 13C CP-MAS NNR and other spectral studies of tradition mental complexes