title: Further studies on the chemistry of molybdenyl adducts of [Pt₂(μ-S)₂(PPh₃)₄]: Hydrolysis, condensation and ligand exchange processes

authors: Henderson, William

subjects: platinum complexes

abstract: Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with [MoO₂(acac)₂] in methanol gives the known five-coordinate Mo(VI) adduct [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OMe)]⁺ isolated as its PF₆⁻, BPh₄⁻ and [Mo₈O₂₆]₄⁻ salts; the latter was structurally characterised, the polymolybdate anion being the uncommon γ form. Hydrolysis of [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OMe)]⁺ in wet dichloromethane initially produces [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OH)]⁺ and subsequently the bright yellow oxo-bridged dimolybdenum species [{Pt₂(μ-S)₂(PPh₃)₄MoO₂}₂O]₂⁺, structurally characterised as its tetraphenylborate salt, and found to contain two five-coordinate molybdenum centres. [{Pt₂(μ-S)₂(PPh₃)₄MoO₂}₂O]₂⁺ can be prepared directly from [Pt₂(μ-S)₂(PPh₃)₄] and [MoO₂(acac)₂] in wet MeCN. Slow reconversion to [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OMe)]⁺ occurs when [{Pt₂(μ-S)₂(PPh₃)₄MoO₂}₂O]₂⁺ is dissolved in methanol. [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OMe)]⁺ undergoes alkoxide exchange in dichloromethane-alcohol solutions to give [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OR)]⁺ species (R = e.g. n-octyl). These reactions are easily monitored using electrospray ionisation mass spectrometry.

text: Further studies on the chemistry of molybdenyl adducts of [Pt₂(μ-S)₂(PPh₃)₄]: Hydrolysis, condensation and ligand exchange processes Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with [MoO₂(acac)₂] in methanol gives the known five-coordinate Mo(VI) adduct [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OMe)]⁺ isolated as its PF₆⁻, BPh₄⁻ and [Mo₈O₂₆]₄⁻ salts; the latter was structurally characterised, the polymolybdate anion being the uncommon γ form. Hydrolysis of [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OMe)]⁺ in wet dichloromethane initially produces [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OH)]⁺ and subsequently the bright yellow oxo-bridged dimolybdenum species [{Pt₂(μ-S)₂(PPh₃)₄MoO₂}₂O]₂⁺, structurally characterised as its tetraphenylborate salt, and found to contain two five-coordinate molybdenum centres. [{Pt₂(μ-S)₂(PPh₃)₄MoO₂}₂O]₂⁺ can be prepared directly from [Pt₂(μ-S)₂(PPh₃)₄] and [MoO₂(acac)₂] in wet MeCN. Slow reconversion to [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OMe)]⁺ occurs when [{Pt₂(μ-S)₂(PPh₃)₄MoO₂}₂O]₂⁺ is dissolved in methanol. [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OMe)]⁺ undergoes alkoxide exchange in dichloromethane-alcohol solutions to give [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OR)]⁺ species (R = e.g. n-octyl). These reactions are easily monitored using electrospray ionisation mass spectrometry.

year: 2011

title: A novel drifter designed for use with a mounted Acoustic Doppler Current Profiler in shallow environments

authors: Mullarney, Julia C.

subjects: Acoustic Doppler Current Profiler

abstract: We present a novel design for a surface drifter, mounted with a pulse-coherent Acoustic Doppler Current Profiler (ADCP) for measuring near-surface (depths 0.18-1 m) flows. During repeated drifter deployments over the tidal flats of Skagit Bay, the mounted ADCP recorded high quality and high resolution profiles of velocity in depths as shallow as 0.4 m. Depth-dependent velocities revealed regions of vertically sheared currents and wave motions not resolved by surface drifters alone. Although the cost of ADCPs is substantial, the drifter bodies were low cost, robust, and of simple construction.

text: A novel drifter designed for use with a mounted Acoustic Doppler Current Profiler in shallow environments We present a novel design for a surface drifter, mounted with a pulse-coherent Acoustic Doppler Current Profiler (ADCP) for measuring near-surface (depths 0.18-1 m) flows. During repeated drifter deployments over the tidal flats of Skagit Bay, the mounted ADCP recorded high quality and high resolution profiles of velocity in depths as shallow as 0.4 m. Depth-dependent velocities revealed regions of vertically sheared currents and wave motions not resolved by surface drifters alone. Although the cost of ADCPs is substantial, the drifter bodies were low cost, robust, and of simple construction.

year: 2013

title: Elucidating the origin and transmission of tetrodotoxin in New Zealand bivalves

authors: Biessy, Laura

subjects: Tetrodotoxin

abstract: Tetrodotoxin (TTX) is a potent neurotoxin that acts by selectively targeting sodium channels, blocking propagation of action potentials and causing paralysis. It has been responsible for countless human intoxications and deaths around the world, particularly in Japan, from consumption of pufferfish. The distribution of TTX and its analogues is remarkably diverse, and the toxin has been detected in organisms from marine, freshwater and terrestrial environments. Increasing detections of TTX in aquaculture species not typically associated with TTX, such as edible bivalves and gastropods, has drawn considerable attention to the toxin, reinvigorating scientific interest and regulatory concerns. There have been reports of TTX in 18 species of edible shellfish species from ten countries since the 1980’s, with some reports above the safe threshold established by the European Food Safety Authority (EFSA) of 44 μg of TTX per kg of shellfish.
Despite decades of research, the exact origin of TTX remains a mystery. Current literature supports three hypotheses: endogenous production, symbiotic bacteria, or direct bioaccumulation through a dietary source. In 2009, the sea slug Pleurobranchaea maculata was found to contain high concentrations of TTX in New Zealand and an extensive research programme to explore the origin of TTX in P. maculata in New Zealand was launched. During this research, Paphies australis, an endemic clam, was found to accumulate high concentrations of TTX (800 μg kg⁻¹). The aim of this thesis was to elucidate the source of TTX in these clams that are a common food source and are culturally important in New Zealand. Paphies australis are largely sessile and found in subtidal habitats making them a highly amedable organisms to investigate the source of TTX.
In this thesis, I used a multiple line of evidence approach to investigate potential TTX producers. This included histological and analytical techniques to explore the micro-distribution of TTX within the organs of P. australis, aquaria studies to investigate the depuration and uptake of TTX, field studies to explore the variations in TTX concentrations from different P. australis populations and other bivalve species in New Zealand, and molecular analyses. Immunohistological analysis of
P. australis tissues employing a TTX monoclonal antibody demonstrated that TTX was present in the outer cells of the siphons, but also in their digestive system, foot and gill tissues. These results were also supported by chemical analysis using liquid chromatography with tandem mass spectrometry. Observing TTX in organs involved in feeding provided initial evidence to support the hypotheses of an exogenous source in P. australis and presence in siphon tips supports the hypothesis that TTX is used as a chemical defence against predators.
The TTX depuration rate in P. australis was then assessed by maintaining TTX-bearing individuals in captivity and feeding them a non-toxic diet for 150 days. The bivalves significantly depurated the toxin (0.4% of total toxin content per day) and there was a rapid decline of the toxin in their digestive glands with only traces amounts remaining after 21 days. This result provides evidence to support the hypothesis that P. australis do not endogenously produce TTX.
During field surveys, P. australis from 10 different sites around New Zealand were harvested and tested for TTX. There were significant differences in TTX concentrations from the different sites. All P. australis contained TTX but bivalves from the warmer North Island sites contained significantly higher concentrations than those from the South Island. These results provided further evidence to support the proposition that the source of TTX in P. australis is likely exogenous, varying in abundance by location. I hypothesised that the source is a warm-water-adapted TTX producer that is mostly present or more prevalent in warmer climates, or that TTX production is triggered by warmer temperatures.
To explore this possibility further, I used metabarcoding to investigate the bacteria present in the digestive glands and siphons of P. australis from the 10 sites with different TTX concentrations and collected monthly over a year from one site with high TTX concentrations. Marine cyanobacteria, in particular picocyanobacteria (e.g., Cyanobium, Synechococcus, Pleurocapsa, and Prochlorococcus), were found in all samples collected from sites containing the highest amount of TTX and were present in the core microbiome of TTX-bearing P. australis. Cyanobacteria are well known for producing a wide range of marine and freshwater toxins and this finding warrants further investigation.
Lastly, I assessed if wild P. australis could sequester and accumulate TTX from a dietary source. I developed a novel method to artificially feed a controlled amount of TTX to bivalves. The micro-encapsulation method incorporated humic acid so that the water-soluble TTX bound to a solid substance. The main finding from this study was that P. australis can rapidly accumulate of TTX from an external dietary source and concentrations were much higher (> 100 μg kg⁻¹) than the safe threshold in bivalves established by the EFSA (44 μg kg⁻¹) in under two weeks. This further strengthens the hypothesis that bivalves most likely accumulate TTX from their diet.
This thesis has addressed several critical knowledge gaps in our understanding of the source of TTX in bivalves, particularly in the clam P. australis. A detailed account of each study is presented in this thesis and future research to elucidate the origin of TTX in bivalves are suggested.

text: Elucidating the origin and transmission of tetrodotoxin in New Zealand bivalves Tetrodotoxin (TTX) is a potent neurotoxin that acts by selectively targeting sodium channels, blocking propagation of action potentials and causing paralysis. It has been responsible for countless human intoxications and deaths around the world, particularly in Japan, from consumption of pufferfish. The distribution of TTX and its analogues is remarkably diverse, and the toxin has been detected in organisms from marine, freshwater and terrestrial environments. Increasing detections of TTX in aquaculture species not typically associated with TTX, such as edible bivalves and gastropods, has drawn considerable attention to the toxin, reinvigorating scientific interest and regulatory concerns. There have been reports of TTX in 18 species of edible shellfish species from ten countries since the 1980’s, with some reports above the safe threshold established by the European Food Safety Authority (EFSA) of 44 μg of TTX per kg of shellfish.
Despite decades of research, the exact origin of TTX remains a mystery. Current literature supports three hypotheses: endogenous production, symbiotic bacteria, or direct bioaccumulation through a dietary source. In 2009, the sea slug Pleurobranchaea maculata was found to contain high concentrations of TTX in New Zealand and an extensive research programme to explore the origin of TTX in P. maculata in New Zealand was launched. During this research, Paphies australis, an endemic clam, was found to accumulate high concentrations of TTX (800 μg kg⁻¹). The aim of this thesis was to elucidate the source of TTX in these clams that are a common food source and are culturally important in New Zealand. Paphies australis are largely sessile and found in subtidal habitats making them a highly amedable organisms to investigate the source of TTX.
In this thesis, I used a multiple line of evidence approach to investigate potential TTX producers. This included histological and analytical techniques to explore the micro-distribution of TTX within the organs of P. australis, aquaria studies to investigate the depuration and uptake of TTX, field studies to explore the variations in TTX concentrations from different P. australis populations and other bivalve species in New Zealand, and molecular analyses. Immunohistological analysis of
P. australis tissues employing a TTX monoclonal antibody demonstrated that TTX was present in the outer cells of the siphons, but also in their digestive system, foot and gill tissues. These results were also supported by chemical analysis using liquid chromatography with tandem mass spectrometry. Observing TTX in organs involved in feeding provided initial evidence to support the hypotheses of an exogenous source in P. australis and presence in siphon tips supports the hypothesis that TTX is used as a chemical defence against predators.
The TTX depuration rate in P. australis was then assessed by maintaining TTX-bearing individuals in captivity and feeding them a non-toxic diet for 150 days. The bivalves significantly depurated the toxin (0.4% of total toxin content per day) and there was a rapid decline of the toxin in their digestive glands with only traces amounts remaining after 21 days. This result provides evidence to support the hypothesis that P. australis do not endogenously produce TTX.
During field surveys, P. australis from 10 different sites around New Zealand were harvested and tested for TTX. There were significant differences in TTX concentrations from the different sites. All P. australis contained TTX but bivalves from the warmer North Island sites contained significantly higher concentrations than those from the South Island. These results provided further evidence to support the proposition that the source of TTX in P. australis is likely exogenous, varying in abundance by location. I hypothesised that the source is a warm-water-adapted TTX producer that is mostly present or more prevalent in warmer climates, or that TTX production is triggered by warmer temperatures.
To explore this possibility further, I used metabarcoding to investigate the bacteria present in the digestive glands and siphons of P. australis from the 10 sites with different TTX concentrations and collected monthly over a year from one site with high TTX concentrations. Marine cyanobacteria, in particular picocyanobacteria (e.g., Cyanobium, Synechococcus, Pleurocapsa, and Prochlorococcus), were found in all samples collected from sites containing the highest amount of TTX and were present in the core microbiome of TTX-bearing P. australis. Cyanobacteria are well known for producing a wide range of marine and freshwater toxins and this finding warrants further investigation.
Lastly, I assessed if wild P. australis could sequester and accumulate TTX from a dietary source. I developed a novel method to artificially feed a controlled amount of TTX to bivalves. The micro-encapsulation method incorporated humic acid so that the water-soluble TTX bound to a solid substance. The main finding from this study was that P. australis can rapidly accumulate of TTX from an external dietary source and concentrations were much higher (> 100 μg kg⁻¹) than the safe threshold in bivalves established by the EFSA (44 μg kg⁻¹) in under two weeks. This further strengthens the hypothesis that bivalves most likely accumulate TTX from their diet.
This thesis has addressed several critical knowledge gaps in our understanding of the source of TTX in bivalves, particularly in the clam P. australis. A detailed account of each study is presented in this thesis and future research to elucidate the origin of TTX in bivalves are suggested.

year: 2021