title: The kinetics of the dissociation of dihydroxyacetone dimer in aprotic media

authors: Owens, Adrian

subjects: Dihydroxyacetone

abstract: The dissociation of the dihydroxyacetone (DHA) dimer in mānuka honey has previously been proposed to be the rate determining step in the overall conversion of DHA to methylglyoxal, the agent reported to be responsible for the non-peroxide anti-bacterial activity displayed by mānuka honey.

The ¹H and ¹³C NMR spectra for the DHA dimer and the DHA monomer in DMSO-d6 were assigned using 1D and 2D NMR spectroscopy.

¹H and ¹³C NMR spectroscopy were utilised to investigate the kinetics of the dissociation of the DHA dimer in DMSO-d6, an anhydrous solvent chosen to mimic the dehydrating conditions present in the honey matrix.

Four series of kinetic experiments were conducted, one without catalysis, one with D₂O catalysis, one with CD₃COOD catalysis and one with CD₃COOD/CD₃COOD catalysis. Each of these experiments obtained the equilibrium constant, K and the rate constants k, k₁ and k₋₁ for the dissociation of the DHA dimer under different conditions that may be present in the honey matrix, with the exclusion of the CD₃COOD/CD₃COOD catalysed experiments which were conducted as part of the investigation to determine a proposed reaction mechanism.

Two reaction intermediates were observed in the CD₃COOD catalysed experiments, they were characterised and provided supporting evidence for a proposed acid-catalysed reaction mechanism for the DHA dimer dissociation. The absence of reaction intermediates in the D₂O catalysed experiments provided supporting evidence for a proposed base-catalysed reaction mechanism for the DHA dimer dissociation.

Reaction mechanisms for the DHA dimer dissociation in DMSO-d6 and mānuka honey were proposed based on the findings of previous studies and the findings associated with the kinetic experiments conducted in this study.

text: The kinetics of the dissociation of dihydroxyacetone dimer in aprotic media The dissociation of the dihydroxyacetone (DHA) dimer in mānuka honey has previously been proposed to be the rate determining step in the overall conversion of DHA to methylglyoxal, the agent reported to be responsible for the non-peroxide anti-bacterial activity displayed by mānuka honey.

The ¹H and ¹³C NMR spectra for the DHA dimer and the DHA monomer in DMSO-d6 were assigned using 1D and 2D NMR spectroscopy.

¹H and ¹³C NMR spectroscopy were utilised to investigate the kinetics of the dissociation of the DHA dimer in DMSO-d6, an anhydrous solvent chosen to mimic the dehydrating conditions present in the honey matrix.

Four series of kinetic experiments were conducted, one without catalysis, one with D₂O catalysis, one with CD₃COOD catalysis and one with CD₃COOD/CD₃COOD catalysis. Each of these experiments obtained the equilibrium constant, K and the rate constants k, k₁ and k₋₁ for the dissociation of the DHA dimer under different conditions that may be present in the honey matrix, with the exclusion of the CD₃COOD/CD₃COOD catalysed experiments which were conducted as part of the investigation to determine a proposed reaction mechanism.

Two reaction intermediates were observed in the CD₃COOD catalysed experiments, they were characterised and provided supporting evidence for a proposed acid-catalysed reaction mechanism for the DHA dimer dissociation. The absence of reaction intermediates in the D₂O catalysed experiments provided supporting evidence for a proposed base-catalysed reaction mechanism for the DHA dimer dissociation.

Reaction mechanisms for the DHA dimer dissociation in DMSO-d6 and mānuka honey were proposed based on the findings of previous studies and the findings associated with the kinetic experiments conducted in this study.

year: 2016

title: Identifying temporal and spatial variations in the binding properties of transition metal-organic ligand complexes in cave waters using organic inclusions in speleothem calcite: Implications for paleoclimate research.

authors: Brodnax, Robert

subjects: speleothems

abstract: Speleothems such as stalagmites, stalactites and flowstones, contain paleoclimate information encoded in their geochemical properties. One of these properties, transition metal abundance in speleothem calcite, is tightly controlled by complexation reactions in cave water with dissolved organic matter (DOM). Organic compounds are also preserved in speleothem deposits. DOM structure varies from cave system to cave system and over time, but whether these structural variations meaningfully alter the way DOM controls trace metal incorporation into calcite is unclear. This is relevant to the development of speleothem transition metal content as a paleoclimate proxy, particularly over large spatial and temporal scales where DOM structure variations are likely. This study identifies variations in the binding properties of DOM preserved in speleothem calcite over time and space by extracting organic compounds of known age and origin from speleothems collected from New Zealand, Niuean, British, and Australian cave systems. The kinetic properties of DOM complexes from these extracts were measured using small volume diffusive gradients in thin films (SV-DGT) and the variation in the binding strength of complexes with Cu, Co, and Ni was compared across time and space. DOM binding of Cu and Co were found to vary significantly depending on the cave system from which the DOM originated. Whether this variation was linked to climate changes represented in the age of the DOM or to changes in system characteristics related to geographical setting was unclear. Despite this, it is apparent that there are factors related to the origin of DOM in cave systems that influence the kinetic restrictions applied to transition metals in cave water. This variability should be considered when linking trace element contents in cave precipitates to paleoclimate change.

text: Identifying temporal and spatial variations in the binding properties of transition metal-organic ligand complexes in cave waters using organic inclusions in speleothem calcite: Implications for paleoclimate research. Speleothems such as stalagmites, stalactites and flowstones, contain paleoclimate information encoded in their geochemical properties. One of these properties, transition metal abundance in speleothem calcite, is tightly controlled by complexation reactions in cave water with dissolved organic matter (DOM). Organic compounds are also preserved in speleothem deposits. DOM structure varies from cave system to cave system and over time, but whether these structural variations meaningfully alter the way DOM controls trace metal incorporation into calcite is unclear. This is relevant to the development of speleothem transition metal content as a paleoclimate proxy, particularly over large spatial and temporal scales where DOM structure variations are likely. This study identifies variations in the binding properties of DOM preserved in speleothem calcite over time and space by extracting organic compounds of known age and origin from speleothems collected from New Zealand, Niuean, British, and Australian cave systems. The kinetic properties of DOM complexes from these extracts were measured using small volume diffusive gradients in thin films (SV-DGT) and the variation in the binding strength of complexes with Cu, Co, and Ni was compared across time and space. DOM binding of Cu and Co were found to vary significantly depending on the cave system from which the DOM originated. Whether this variation was linked to climate changes represented in the age of the DOM or to changes in system characteristics related to geographical setting was unclear. Despite this, it is apparent that there are factors related to the origin of DOM in cave systems that influence the kinetic restrictions applied to transition metals in cave water. This variability should be considered when linking trace element contents in cave precipitates to paleoclimate change.

year: 2024

title: The use of Māori mythology in clinical settings: Training issues and needs

authors: Cherrington, Lisa

subjects: Maori

abstract: Within therapeutic settings, narrative
approaches are increasingly being used as a
way of creating new understandings and
new stories. This paper discusses the use of
purakau as a Māori focused intervention
when working with Māori tangata whaiora
(clients) and their whānau. This paper will
outline the rationale and relevance of using
purakau with Māori. However, the
emphasis is on the training provided to
clinicians in the use of purakau. An outline
of the training process is provided. In
doing so, issues regarding the use of these
taonga (treasures) in clinical psychology
will be raised. It will be argued that Māori
mythology must have a place in the kete of
Māori psychology.

text: The use of Māori mythology in clinical settings: Training issues and needs Within therapeutic settings, narrative
approaches are increasingly being used as a
way of creating new understandings and
new stories. This paper discusses the use of
purakau as a Māori focused intervention
when working with Māori tangata whaiora
(clients) and their whānau. This paper will
outline the rationale and relevance of using
purakau with Māori. However, the
emphasis is on the training provided to
clinicians in the use of purakau. An outline
of the training process is provided. In
doing so, issues regarding the use of these
taonga (treasures) in clinical psychology
will be raised. It will be argued that Māori
mythology must have a place in the kete of
Māori psychology.

year: 2003