The preparation of carbocyclic medium rings by two electron processes is reviewed with particular reference to the synthesis of natural products. The formation of medium rings by oxidative and homolytic methods is also reviewed. The synthesis and behaviour of both cis- and tran- ring expansion precursors is described. The 1,4-addition of tributylstannyl lithium to a range of cyclic α,β-unsaturated ketones was performed and procedures found whereby the so-formed enolates could be alkylated with a variety of electrophiles. Using these procedures a range of trans- ring expansion precursors were obtained in moderate to good yield. By the 1,4-addition of tributylstannyl lithium to 2-(ω-phenylselenoalkyl)-cyclohexenones, followed by enolate quenching with either water or methyl iodide, a range of cis- ring expansion precursors were produced. Homolytic ring expansion by either one, three, or four carbon atoms was shown to be possible, producing, respectively, seven, nine, or ten membered functionalised cycloalkenones in high yield except in cases where intramolecular reductive elimination was also possible. Attempts to extend this methodology to the synthesis of exomethylene cycloalkanones is described. The 3-tributylstannyl-3-(ω-phenylselenoalkyl)-cyclohex-2-enone precursors were found not to be successful substrates for ring expansion. The regiospecific alkylation of 2-(tributylstannylmethyl)-cyclohexanone with l-chloro-4-iodo-butane, followed by conversion of the chloride moiety to iodide led to a precursor which, on exposure to homolysis conditions, fragmented to produce the desired exomethylene cyclodecanone in high yield. Work directed towards the synthesis of medium ring cycloalkynones is described. Procedures were developed whereby 2-alkylated cyclohexan-l,3-dione derivatives could be obtained cleanly and in excellent yield on a large scale. The conversion of these derivatives to potential cycloalkynone precursors is described. It is shown that the products obtained after exposure of these precursors to homolysis conditions could, in principle, be derived from the putative cycloalkynones and mechanisms are suggested to explain the formation of these compounds. The homolytic ring expansion reaction was also performed on a substrate possessing an acyl radical precursor in the hope that a medium ring 1,2-dione would be produced. The synthesis of this substrate and its behaviour towards ring expansion is described. It is shown that, again, radical reaction was successful (to the medium ring dione) however subsequent reactions of this product led to the isolation and characterisation of a number of compounds . Attempts to extend this methodology to the synthesis of the natural products curdione and neocurdione is also described. Model reactions with 2,6-dimethylcyclohex-2-enone as the 1,4-addition precursor and 1,4-di-iodobutane as the electrophile led to a ring expansion substrate which fragmented to two ring contracted isomeric compounds in addition to the ring expanded material. Approaches to the preparation of suitable electrophiles for the natural product synthesis are described and their proposed use in subsequent conversion to curdione and neocurdione given.

A study was carried out on phosphatase activity, phosphate uptake and its relationship to hair formation in the Rivulariaceae. The Rivulariaceae was chosen as it is a widespread taxon, where hair formation is a common occurrence, and previous studies indicated that they originate from environments where a large proportion of the phosphorus (P) is present as organic P. It seems possible that hair-forming Rivulariaceae are especially well adapted to utilize organic P. Initially 51 axenic cyanobacterial strains, from 10 genera, were screened for yields using organic P sources and for cell-bound and extracellular phosphomonoesterase (PMEase) and phosphodiesterase (PDEase) activities. All strains exhibited detectable inducible PMEase activities, and highest cell-bound PMEase activities were in hair-forming Rivulariaceae. Synechococcus had significantly low cell-bound phosphatase activities and five strains were unable to hydrolyze phytic acid. PDEase activities were lower compared to PMEase activities in all strains. Strains isolated from deepwater rice habitats had significantly higher levels of PDEase activity. In the three Calothrix strains tested, Calothrix 202, 550 and 603, inducible phosphatase activities were similar whether the P source was inorganic or organic. PMEase synthesis in these strains began when cellular P (% dry wt) values were in the range 0.60 - 1.0%. Differences in the influence of environmental variables on cell-bound and extracellular PMEase activities in hair-forming Calothrix 550 were slight, suggesting that PMEases in the two fractions had a common origin. Of the eleven ions tested Ca had the most pronounced stimulatory effect on PMEase activity. Localization of enzyme activity in Calothrix 550 suggested that the enzyme was bound to a surface. Partial purification of an extracellular PMEase fraction detected four bands of PMEase activity on a non-denaturing polyacrylamide gel. Three of the four bands were associated with carbohydrate and the bands were not extractable by mechanical means. Localization of PMEase activity in hair-forming strains by azo dye (naphthol AS-MX) and 5-bromo-4-chloro-3-indolyl phosphate (BCIP) showed that PMEase activity was associated with hair cells. Phosphate uptake experiments with Calothrix 253 and 550 suggested that uptake at high external phosphate concentrations was located in hair cells. NaCl, above 67.5 mM, inhibited hair formation and subsequently phosphatase activity in Calothrix 253 and 690. Addition of mannitol or sorbitol had no effect on hair formation, suggesting inhibition of hair formation was not an osmotic effect. Removal of P-deficient cultures from saline to freshwater media led to a marked synchronization of hair formation (in 90% of trichomes) and increase in cell-bound PMEase activity. Localization of cell-bound PMEase activity by light microscopy, using naphthol AS-MX, detected activity in the hair cells.

In this work a review of many of the current theories of star formation as it is understood today is presented. New polarimetric observations of three cometary nebulae, RMon/NGC2261, RCr A/NGC6729 and the Chamaeleon Infrared Nebula are presented and discussed. It is shown how previous polarimetric measurements of the illuminating source of Hubble's variable nebula (NGC2261) have often produced results which increase in error with increasing wavelength. The reason for this is that previous authors have used an aperture size for measurements of R Mon which includes effects of a highly polarized feature ~ 5" north of RMon. Though this phenomenon has been seen before by other observers, its effect on polarimetric measurements of R Mon has not been recognised before despite tests to check for this. The data presented here agree with the interpretation that this feature is the northern-lobe of a mini-bipolar nebula, and it is further suggested that this is a manifestation of episodic mass outflow from R Mon. Previous explanations for the polarization of R Mon and RCr A cannot explain the rapid change in polarization and position angle that these young stellar objects are seen to undergo. Models of these objects which assume that they appear as polarized sources are used to explain the polarizations and are discussed. These models are not only able to produce the level of polarization seen at the source, but they are also currently the best models for explaining the rapid changes in polarization that are observed. A jet-like feature is seen to the south-west of the main nebulosity in the Chamaeleon IRN for the first time in observations presented in this thesis. A similar jet seen emerging from RCr A has been explained as being an emission feature collimated by an inner-circumstellar disc by previous authors. Evidence presented in this work for the jets seen emanating from both RCr A and the Chamaeleon IRN, suggests that these features are merely the preferentially illuminated rims of one of the outflow cavities, seen mainly by reflection of light from the source. Further evidence is provided to show that NGC2261 and NGC6729 are illuminated by RMon and RCr A respectively. In the case of the Chamaeleon IRN new evidence is provided to show that the nebula is illuminated by a heavily obscured infrared source located midway between the two outflow cavities.

No description available.

No description available.

Pyrite is a ubiquitous mineral in shales. It results from the bacterial reduction of seawater sulphate to sulphide and the reaction of that sulphide with iron to form iron sulphides and subsequently pyrite. Five Jurassic shales were examined. 1 The Upper Oxford Clay (Oxfordian) Warboys Cambridgeshire. 2 The Dunans Clay (Callovian-oxfordian) Isle of Skye. 3 The Lower Oxford Clay (Callovian) East midlands. 4 The Posidonia Shales (Lias ε) Southern Germany. 5 The Dunans Shale (Callovian) Isle of Skye. The five shale units are divisible into three major biofacies "Normal" (Units 1& 2), "Restricted" (3) and "Bituminous" (4 & 5), which show varying pyrite contents and isotopic compositions, that reflect the changing influence of the three limiting factors of pyrite formation (sulphate, organic carbon, and iron). Samples of shale were analysed for fine grained pyrite content and isotopic composition, organic and carbonate carbon, and hydrochloric acid soluble iron. The Normal shales showed low pyrite sulphur (<1.3%) and organic carbon (<2%), degree of pyritization (D. O. P. ) (<0.5) and negative (<-28%o) δ34S values. These are consistent with the formation of pyrite near the sediment surface, limited by organic carbon. In the Restricted shales higher pyrite sulphur (av. 1.4%) and organic carbon (av. 5%), degree of pyritization (0.5 to 0.7) and less negative (>-28%o, <-9%o) δ34S values indicate the continuation of pyrite formation deeper into the sediment, where it is limited by sulphate diffusion. High D. O. Ps in the Posidonia Shales (>0.8) suggest that pyrite formation is limited by the availability of iron in Bituminous shales. Heavier δ34S values (>-28%o) in the Posidonia Shale suggest limitation of sulphate reduction by sulphate diffusion, and lighter values in the Dunans Shale (<-28%o) suggest limitation by organic matter. Petrographic and isotopic studies of shell replacement and associated concretionary pyrite from the Lower Oxford Clay show types of replacement related to the differences between the porewaters within the shell and those of the shale, particularly as regards iron supply.

No description available.

There are three related studies within this thesis that examine the relationships between the properties of coals and the characteristics of the chars produced during rapid pyrolysis in a laboratory based Entrained Flow Reactor (EFR) which simulates the rapid rates of heating (104 to 105 °C s-1 ) typical of pulverised fuel boilers. The first study, using a suite of nine coals, investigates the influence of coal rank upon the generation of specific types of char, their respective physical and structural characteristics and their relative combustabilities. The second study, using a suite of twenty-two coals, examines various coal characterisation techniques and the correlations between those techniques and the associated char, and specifically investigates petrographic techniques as a means of characterising coal feedstock. The third study, using freshly mined coals, investigates the effects of oxidation (100°C, air) and weathering (ambient) upon standard analytical techniques and relates such changes to the physical, structural and combustion characteristics of the associated char. There is a common relationship between the elemental oxygen content of the parent coal and the generation of specific types of char for both vitrinite rich coals of differing coal rank and for the oxidised or weathered coals. There is also an inverse relationship (R 2 = 0.97) between the elemental oxygen content of a vitrinite rich coal and the proportion of cenospheres generated by pyrolysis at 1000°C using the EFR. Furthermore, the enhancement of char combustion at 1000°C (in an EFR) is related to the physical and structural characteristics of the char, i.e. the presence or absence of porosity (visible using SEM and TEM), the CO2 surface area and optical texture. A relationship exists (R2 = 0.83) between the morphology of a char (1000°C / N2) and the petrographic composition of the parent coal. The new term microlithotype, is an amalgamation of various vitrinite rich microlithotype classes that simplifies the nomenclature. A combination of calorific value, microlithotype, and coal rank (vitrinite reflectance) illustrates the influence of petrographic composition upon calorific value and also suggests a 'Province' dependency amongst the Cretaceous/Tertiary and Carboniferous coals studied. The coal properties calorific value, microlithotype, and coal rank can be related (R 2 = 0.91) to the proportion of porous chars for the Cretaceous/Tertiary suite of coals, illustrating the use of multivariate analyses when characterising coal feedstock. The effects of oxidation and weathering upon vitrinite fluorescence is also reported. The oxidation of coal at 100°C produces rims of quenched fluorescence which are not apparent within the weathered coals. Furthermore, the intensity of fluorescence at 650 nm (1650) decreases due to progressive oxidation or weathering, but decreases at a rate that is dependent upon the severity (temperature) of the conditions employed. The proposed oxidation quotient (0/Q = I65W%Romax) is a sensitive indicator of the oxidative conditions up to 100°C.

No description available.

No description available.