Electrochemical generation-collection sensors for bioanalysis

Electrochemical generation-collection devices have potential for application in a wide range of analytical devices, both as free standing sensor systems and as components in analytical systems such as high performance liquid chromatography (HPLC) or flow injection analysis (FIA). The underlying principle is that an electrochemical reaction on one element is used to generate some chemical species which is then transported by diffusion or diffusion and convection to a second electrode where the electrochemical reaction is reversed. The fraction collected is a function of device geometry, operating conditions, any reaction of the generated species in bulk solution and mass transport. This thesis describes the construction of generation-collection sensors comprising coplanar inlaid microelectrodes of different size and shape: ring-disc and disc-disc in sizes ranging from 10 m to 100 m. Fabrication techniques including sputter-coating and embedding of wires were developed and are described. The sensors were characterised using scanning electron microscopy and their electrochemical characterisation was achieved using reversible outer sphere redox couples including ferrocene derivatives, ruthenium hexaammine (III/II) and ferro/ferricyanide. Experimental data are given for the effects of geometry, size and generator current density, particularly where this would affect the uniformity of the flux. Tests were also undertaken in specially built flow cells to assess their viability for application in FIA and LC detection. Where possible, performance in both the steady state and transient mode were compared with numerical and analytical models. Three specific bioanalytical applications were investigated and are described: (i) detection of peptides and amino acids using electrochemically generated bromine/ hypobromite (ii) electrochemical biuret detection and (iii) determination of titratable acidity and alkalinity (buffer capacity). Results for (i) showed more complex behaviour with the Pt-Pt dual microelectrode than that has been reported for macroelectrodes under similar system. Voltammetric results are reported. Electrochemical biuret systems showed less improvement in sensitivity with the generation-collection mode to small peptide molecules. For the buffer capacity sensor, both disc-disc and ring-disc geometries were investigated in a range of sizes 25 to 75 m for the disc and approximately 1 m for the ring. A pH sensitive surface was prepared by the deposition of hydrated iridium oxide on gold. Local pH changes were effect by electrolysis of the buffer solution. Experimental works emphasised the importance of controlling the current density to ensure that buffer capacity was not exceeded. An analytical model was of great use in optimising the device. Results are reported for various buffer systems comparing experiments with steady-state theory.Open Acces

Molecular systematics in Gossypium and its relatives

Gossypium L. is an economically important genus as it harbors four species that provide the cotton of commerce. Although many aspects of the evolution and taxonomy of Gossypium are well understood, there has been little work devoted to assessing relationships among Gossypium and its allied genera. In addition, newly discovered species, of Gossypium sect. Grandicalyx from Australia, have prompted a need for more research into the phylogeny of these new species and their relationships to other Gossypium taxa. Multiple data sets were used to address questions regarding (1) phylogenetic relationships among Gossypium and its relatives, and (2) the phylogeny and evolution of Gossypium sect. Grandicalyx. A protocol for handling multiple and sometimes competing data sets was developed, and was applied in the first study. This same protocol was not applicable for the second study, where amounts of sequence divergence were too low. Phylogenetic analyses of Gossypium and its allies indicated that Gossypium is a monophyletic group and that it is closely related to a clade represented by the Hawaiian genus Kokia and the east African/Madagascan genus Gossypioides. Phylogenetic inferences also suggested that Cienfuegosia may represent the first group to diverge during tribal radiation, and that Thespesia is not monophyletic. Studies of the Australian Gossypium sect. Grandicalyx showed that sect. Grandicalyx is monophyletic, with divergences inferred to be relatively recent. Molecular data sets provide little resolution with respect to the relationship among species within the section. Species are suggested to have radiated in the late Pliocene or Pleistocene after a much earlier (Miocene) divergence from the other extant Australian cottons. The palaeoclimatic record, sequence divergence estimates and phylogenetic data are congruent in suggesting a phytogeographic scenario for the diversification of species in sect. Grandicalyx, through range fragmentation of a more widely distributed ancestor or ancestors. This evolutionary history was accompanied by the development of a prostrate to reclining herbaceous habit, adaptation to seasonal fires, and a suite of features associated with myrmecochory

Notes on Discriminating Morphological Characters for Generic and Sectional Classification of Musaceae in Thailand

ABSTRACTMorphological characters have been used effectively in classification of the banana family, Musaceae. Most taxonomic features are qualitative characters which require experience in evaluation and are subjected to individual opinions. On the other hand, though not many, quantitative characters can be directly measured on sites or from photographs. The objective of this study was to evaluate efficiency of these quantitative features in the classification of the banana family in Thailand. A total of 16 quantitative morphological characters of 143 accessions from 10 native taxa and one introduced Musella species were assessed. All quantitative data were evaluated by box-plot analysis, principal component analysis and discriminant analysis. It was found that the quantitative data are useful in the classification at the generic level in Musaceae and at the sectional level of Musa. All three genera can be distinguished by pseudostem height, number of sucker plants and fruit pedicel length. At sectional level, number of fruit rows on mid hand can separate the sections Rhodoclamys and Callimusa from Musa and leaf blade length can differentiate Rhodoclamys from Callimusa. Interestingly, fruit pedicel length and fruit apex length which were used in Musa acuminata descriptors at subspecific level were not significantly different in this study.Keywords: Characterization, Morphometrics, Musaceae, Numerical Taxonomy, Phenetic analysi

Molecular and morphological characterization of Pyricularia and allied genera

The phylogenetic relationships of Pyricularia species and species from related genera were established from sequences of the internal transcribed spacer ribosomal RNA gene. Phylogenetic analysis disclosed a consistent correlation with spore morphology. Most Pyricularia species studied, and two species of Dactylaria that have obpyriform conidia, fell within the Magnaporthaceae cluster with high bootstrap support. Pyricularia variabilis was more related to Dactylaria, Tumularia or Ochroconis species than to the Magnaporthaceae. Dactylaria and species of Nakataea, Ochroconis, Pyriculariopsis and Tumularia were distinct from the Magnaporthaceae, and the genus Dactylaria is polyphyletic. The combination of morphological and molecular characters, such as spore morphology and ITS ribosomal DNA sequences data, suggested that conidial shape could be a primary character to distinguish Pyricularia from related genera.published_or_final_versio

High-Resolution Multiproxy Record of Environmental Changes and Anthropogenic Activities at Unguja Ukuu, Zanzibar, Tanzania during the Last 5000 Years

A high-resolution multiproxy sedimentary record comprising pollen, charcoal, trace element, stratigraphy and particle size data is used to reveal environmental changes from the mangrove ecosystem at Unguja Ukuu, Zanzibar, Tanzania, over the last 5000 years. Historical human–environment interactions over the last millennia are explored by a comparison of the stratigraphic and archaeological data. The area was characterised by a mixture of mangrove forest and beaches, indicating a low level of tidal inundation to at least 3300 BCE. From 2750 BCE, mangrove forest expanded as the area experienced sea-level rise. Further sea-level rise is recorded between 600 and 1100 CE, indicated by the pollen record, particle size analysis and the presence of shell fragments. After 1100 CE, mangrove forest decreased with back mangrove species increasing, indicating a falling sea level. Cocos nucifera decreased after 1900 CE, which reflects a recent sea-level rise and possibly a phase of exploitation. Cereal pollen shows a high presence at around 1500 CE, which coincided with the arrival of the Portuguese on Zanzibar and the transition to Omani colonisation. The sedimentation rate in the core top indicates that mangroves in Unguja Ukuu cannot keep pace with the current rate of sea-level rise

Unveiling 4500 years of environmental dynamics and human activity at Songo Mnara, Tanzania

Coastal East Africa has undergone massive transformations through the Late Holocene, with a combination of changes in sea level, increasing human settlement, and ensuing use of coastal resources. A comprehensive multi-proxy analysis, including pollen, phytolith, charcoal, stratigraphy, particle size, and geochemical data from sedimentary cores extracted from mangrove ecosystems combined with soils from archaeological contexts, provided valuable insights into vegetation dynamics, environmental changes, and human interactions within the mangrove ecosystem of Songo Mnara Island, Tanzania over the last 2590 BCE (4540 cal yr BP). The bottommost layers indicate a lack of vegetation, as deduced from the presence of coral rags and high calcium and carbonate content, possibly due to high mid-Holocene sea-level. Evidence of mangrove taxa suggests a decrease in sea level, enabling the establishment of mangroves from around 2590 BCE. A brief period of sea-level rise occurred between 90 BCE and 320 CE before sea-level fell until 1570 CE. Significant evidence of human activity is recorded from around 1400 CE indicated by increased charcoal, crop phytoliths, and evidence of marine resource utilisation. The timing of this human-environment interaction is also linked to the time of lower sea level. However, there was evidence suggesting human abandonment of the island from around 1500 CE. This coincided with a subsequent rise in sea levels and potentially prolonged drought conditions spanning from 1570 to 1700 CE. These factors likely contributed to a shortage of food resources in the area, impacting both agricultural practices due to the scarcity of natural freshwater and the accessibility of marine food resources. From 1700 CE to the present, fluctuations in sea level have been observed, with a signal of recent sea-level rise in tandem with shifts in mangrove, terrestrial herbaceous taxa and fire activity. The low sedimentation rates within mangrove areas suggest that the mangroves on Songo Mnara Island may not keep pace with the current rate of sea-level rise

Phylogenetic position and revised classification of Acacia s.l. (Fabaceae: Mimosoideae) in Africa, including new combinations in Vachellia and Senegalia

Previous phylogenetic studies have indicated that Acacia Miller s.l. is polyphyletic and in need of reclassification. A proposal to conserve the name Acacia for the larger Australian contingent of the genus (formerly subgenus Phyllodineae) resulted in the retypification of the genus with the Australian A. penninervis. However, Acacia s.l. comprises at least four additional distinct clades or genera, some still requiring formal taxonomic transfer of species. These include Vachellia (formerly subgenus Acacia), Senegalia (formerly subgenus Aculeiferum), Acaciella (formerly subgenus Aculeiferum section Filicinae) and Mariosousa (formerly the A. coulteri group). In light of this fragmentation of Acacia s.l., there is a need to assess relationships of the non-Australian taxa. A molecular phylogenetic study of Acacia s.l and close relatives occurring in Africa was conducted using sequence data from matK/trnK, trnL-trnF and psbA-trnH with the aim of determining the placement of the African species in the new generic system. The results reinforce the inevitability of recognizing segregate genera for Acacia s.l. and new combinations for the African species in Senegalia and Vachellia are formalized.Web of Scienc