Patrick J. Barrie

The Composition of Sporopollenin and its use in Living and Fossil Plant Systematics

Abstract Previous investigations of sporopollenin using 13C Solid State Nuclear Magnetic Resonance have demonstrated differences between the major groups of plants in the composition of this acetolysisresistant biomacromolecule. The work presented here corroborates these results and suggests that sporopollenin obtained from seed megaspore-membranes differs slightly from that of pollen from the same plant group. Spectra obtained using NMR have been subjected to multivariate analysis. This approach has provided information which may be interpreted in phylogenetic terms. A number of fossil sporopollenins have also been investigated. These all show considerable degradation through diagenesis but retain certain characteristics of the original sporopollenin composition. Microspores and megaspores from the same species of Carboniferous arborescent lycopsid have also been investigated with a view to discerning any differences in composition that may exist between these sources of sporopollenin in the fossil recor...

CHEMICAL AND MICROSCOPIC CHARACTERIZATION OF OUTER SEED COATS OF FOSSIL AND EXTANT WATER PLANTS

Sclerotic outer seed coat layers (testae) of three fossil and two extant water plant species were analyzed using scanning electron and light microscopy in addition to Curie-point pyrolysis, solid state 13C NMR, and CuO oxidation. Comparison between the chemical results from the fossil and extant samples reveals that the original resistant constituents in the sclerotic testae are native lignin-celluloses which are transformed to polyphenol macromolecules recognized in the fossil samples. The combination of microscopic and chemical data provides new insights regarding the early diagenetic processes by which lignin-cellulose-containing plant remains may have been transformed. In particular, the unaltered morphology in combination with major chemical modifications is used as the basis to postulate the timing and nature of lignin transformations. The combination of pyrolysis, solid state 13C NMR, and CuO oxidation is shown to be a powerful tool to characterize the chemical structure of testae of fossil and extant water plants.

Double-rotation 27Al NMR studies of the aluminophosphate molecular sieve AlPO4-11

Abstract 27Al double-rotation (DOR) NMR experiments have been performed on the hydrated and dehydrated molecular sieve AlPO4-11. In combination with MAS NMR and X-ray diffraction, DOR indicates the nature of the phase transition observed when water is adsorbed. In hydrated AlPO4-11, water is strongly attached to approximately 1 5 of the framework aluminium, producing 6-coordinated Al. All five suggested crystallographic sites are hydrated to an equal extent. Because of this, the 27Al NMR signal due to the 6-coordinated species does not completely narrow upon double-rotation.

The chemical composition of Upper Carboniferous pteridosperm cuticles

Abstract Microscopically well-preserved leaf cuticles from four Upper Carboniferous pteridosperm (seed fern) genera have been analyzed using solid state 13 C NMR and Curie-point pyrolysis. The chemical analyses reveal the presence of highly aliphatic macromolecules, comparable with cutan. Cutan production is considered to be responsible for the preservation of these plant structures, and hence for the abundance of well-preserved medullosan pteridosperm foliage in the Upper Carboniferous. Based on a comparison of data from the literature, and these new results, it is suggested that the resistant constituents of these cuticles may serve as an additional source of n -alkanes on diagenesis and catagenesis.

Coking and deactivation during n-hexane cracking in ultrastable zeolite Y

A multi-technique approach has been used to investigate coke formation and the effects of coke formation during n-hexane cracking on ultrastable zeolite Y. The product analysis reveals that propane and propene are the major products, and this suggests that the reaction initiation step may be direct protonation at very strong Bronsted acid sites. The coke formed does not change in composition significantly over the course of the reaction. Infrared spectroscopy reveals that the vast majority of Bronsted and Lewis acid sites are still present in the catalyst, even when the catalyst activity has become low. Diffusion measurements using pulsed field gradient (PFG) NMR show that the mobility of adsorbed n-butane or n-hexane is not affected by the presence of the coke, and so shows that pore blockage is not a significant factor. Based on the experimental results, it is argued that selective site poisoning of a few very strong acid sites is the main deactivation mechanism for this reaction under the conditions employed.

Distorted powder lineshapes in 27 Al CP / MAS NMR spectroscopy of solids

Abstract 27Al CP / MAS NMR spectra of aluminium acetylacetonate show distinct lineshapes depending on the experimental conditions as the different orientations within the powder cross-polarize with differing efficiencies. Selective polarization transfer to the 1 2 ↔ −1 2 transition occurs at rf power levels corresponding to 3ωAl=ωH, while non-selective polarization transfer can occur at higher27 Al rf powers. Two-dimensional quadrupole nutation spectra show that the cross-polarization lineshapes arise principally because the different orientations have different 27 Al nutation frequencies. The results obtained highlight the caution needed in the interpretation of CP/MAS NMR spectra of quadrupolar nuclei.

A Fourier transform infrared spectroscopic and solid-state NMR study of bone mineral in osteogenesis imperfecta

Abstract Fourier transform infrared spectroscopy and 31P solid-state nuclear magnetic resonance spectroscopy were used to determine if any structural or compositional differences in osteogenesis imperfecta (OI) bone mineral could be detected that might help to explain the bone fragility observed in this disease. A previous study by Cassella et al. used an electron probe X-ray microanalytical technique to compare the calcium to phosphorus (Ca/P) molar ratios in normal bone and bone from patients with OI. It was demonstrated that bone from OI patients had a lower Ca/P molar ratio. This study demonstrated that OI bone mineral had a general hydroxyapatite structure and that isomorphous substitutions in the carbanoapatite lattice could account for the low Ca/P molar ratio.

13C solid-state n.m.r. spectroscopy of fossil sporopollenins. Variation in composition independent of diagenesis

Abstract 13 C solid-state nuclear magnetic resonance of sporopollenin from extant and extinct lycopods and gymnosperms shows that this material differs in composition between these major groups. The relative amounts of unsaturated carbon species are lower in the gymnosperms than in the lycopods in both the modern and fossil material. This suggests that the proportion of unsaturated carbon species present in the fossils is related to that of the original material. Since the fossil material used in this study was obtained from single rock samples, this largely eliminates the possibility that the observed differences in n.m.r. characteristics in fossil spore exines from different species can be attributed to different diagenetic histories.

TEOM analysis of the equilibria and kinetics of n-hexane and n-heptane adsorption on FCC catalyst/silicalite

Abstract A tapered element oscillatory microbalance is used for the measurement of uptake rates of n -hexane and n -heptane on fluid catalytic cracking catalyst and silicalite adsorbent. Investigations are considered over the temperature range of 373 to 513 K , and adsorbate partial pressures up to 0.12 bar . Based on measured adsorption isotherms, and through mechanistic descriptions of the diffusion process, a mathematical model is developed to describe the transient response of the microbalance, and subsequently the kinetics of adsorption and desorption. For example, for the hexane-silicalite system at a temperature of 473 K , the diffusion coefficient at zero-surface coverage is estimated as 2.9×10 −11 m 2 / s , with an activation energy of 17 kJ / mol . This is consistent with published data based on other transient analysis methods. At relatively low temperatures of operation, i.e. less than 450 K , a single resistance model for mass transfer failed to accurately predict the desorption profiles for hexane on silicalite. As a means of quantifying the observed desorption rates, a dual-resistance model is introduced in which two different diffusion rates are assumed to take place above and below a threshold value of adsorbate concentration. Such a model may be used to account for silicalite phase transitions at high adsorbate loading.

Solid-state 27Al NMR studies of aluminophosphate molecular sieves: Enhanced resolution by quadrupole nutation and double-rotation

Solid-state 27Al NMR spectra of several aluminophosphate molecular sieves have been recorded with conventional magic-angle spinning (MAS), double-rotation (DOR) and quadrupole nutation with fast MAS. Enhanced resolution was obtained in the quadrupole nutation experiment at certain radiofrequency pulse strengths. This extra resolution can be comparable to that attainable using DOR, and does not introduce spinning sidebands.