title: Kinetic studies of cyclisations of 2'-hydroxychalcones and derivatives

authors: Old, Kenneth Barry

abstract: The rates of cyclisation of various 2'-hydroxychalcones to the equilibrium mixture of chalcone and flavanone have been determined over the pH range in which the chalcones undergo ionisation. The compounds studied were 2'-hydroxy-, 2'-hydroxy-5', 6'-benzo-, 2',4'-dihydroxy-, 2'-hydroxy-4'-methoxy-, 2'-hydroxy-6'-methoxy-, and 2'-hydroxy-4', 6'-dimethylchalcone. In each case the observed first order rate constant has been fitted to a theoretical pH-rate profile based on the equation
kₒbₛ = kfCH + k’fC⁻ + k’’ {OH⁻} 
where k is the rate constant for the cyclisation of neutral chalcone (fCH is the fraction of neutral chalcone), k' is the rate constant for the cyclisation of the ionised chalcone (fC⁻ is the fraction of ionised chalcone), and k" is a measure of the rate in the reverse reaction. The expression implies that the reaction in the forward direction can proceed from neutral or ionised chalcone, and in the reverse direction through the reaction of flavanone with hydroxide ion. In all cases the forward reaction of the ionised chalcone (k') is very much faster than that of the neutral species (k). Weak catalysis by some buffer species has been detected but the origin of this catalysis has not been pursued in detail. Comparisons are made between the forward and reverse rate constants for the different chalcones in order to see how they are affected by different A-ring substituents. It is observed that electron releasing groups at the 4'- or 6'- positions decrease the rate. This diminution in the observed rate is particularly pronounced with 6'-substituents, and is considered as possibly due to the steric and/or electrostatic interaction of this substituent with the carbonyl group an interaction that could force the carbonyl group to lie out of the plane of the A-ring thereby changing rates of reactions by electronic or steric effects.
The first kinetic study of the reactivity of a 2'-hydroxychalcone epoxide is reported. The variation of the rate of cyclisation of the parent epoxide, 2'-hydroxychalcone epoxide, to 3-hydroxyflavanone in water, over the range pH 1 - 6.5, is shown to be consistent with the rate equation.
Rate = 0.235 [Epoxide]{H⁺} + 1.85 x 10⁶ [Expoxide] {OH⁻} mol 1⁻¹s⁻¹
This shows the epoxide to be very unstable at or above neutral pH, and suggests that such compounds, if they do occur, as has often been suggested, as intermediates in flavanoid biosynthesis would probably be very difficult to isolate. Their detection under the basic conditions of either the Algar-Flynn-Oyamada oxidation of 2'-hydroxychalcones, or the formation of aurones from certain 2'-hydroxychalcone dibromides, both reactions in which they have been suggested as intermediates, would be equally unlikely : based on a suggested mechanism, the parent epoxide of this study can be predicted to have a half-life at pH 10 of the order of a few milliseconds.
The first determination of the ratio of E- and Z-2'-hydroxy-α-bromochalcones formed directly from a 2'-hydroxychalcone dibromide is described. Combined kinetic and spectrophotometric measurements give the yield (%) of E- and Z-2'-hydroxy-α-bromochalcone as 35 ± 2 and 63 ± 8 respectively for the reaction of erythro-2'-hydroxychalcone dibromide in 4:1 ethanol-water buffered at pH 7.88 with N-ethylmorpholine. Direct cyclisation of the dibromo compound, if it occurs at all, is only a very minor route to 3-bromoflavanone. The lack of any detected dependence buffer concentrations of the rate constants or of the proportions of the E- and Z-isomers formed suggest, an E1cв mechanism rather than an E2. However, with the particular elimination involved (i.e. a double bond being formed α, β to a carbonyl group) there is precedence for small catalysis by N-alkylmorpholines and therefore, it is not certain that the lack of measurable buffer catalysis does in fact mean a total lack of catalysis. Further, if the elimination is in fact by an E1cв type mechanism, a carbanion is not necessarily involved, as the elimination could proceed from the phenolate ion as conjugate base, the phenoxide group acting in place of an external base. An El mechanism is excluded on kinetic grounds.

text: Kinetic studies of cyclisations of 2'-hydroxychalcones and derivatives The rates of cyclisation of various 2'-hydroxychalcones to the equilibrium mixture of chalcone and flavanone have been determined over the pH range in which the chalcones undergo ionisation. The compounds studied were 2'-hydroxy-, 2'-hydroxy-5', 6'-benzo-, 2',4'-dihydroxy-, 2'-hydroxy-4'-methoxy-, 2'-hydroxy-6'-methoxy-, and 2'-hydroxy-4', 6'-dimethylchalcone. In each case the observed first order rate constant has been fitted to a theoretical pH-rate profile based on the equation
kₒbₛ = kfCH + k’fC⁻ + k’’ {OH⁻} 
where k is the rate constant for the cyclisation of neutral chalcone (fCH is the fraction of neutral chalcone), k' is the rate constant for the cyclisation of the ionised chalcone (fC⁻ is the fraction of ionised chalcone), and k" is a measure of the rate in the reverse reaction. The expression implies that the reaction in the forward direction can proceed from neutral or ionised chalcone, and in the reverse direction through the reaction of flavanone with hydroxide ion. In all cases the forward reaction of the ionised chalcone (k') is very much faster than that of the neutral species (k). Weak catalysis by some buffer species has been detected but the origin of this catalysis has not been pursued in detail. Comparisons are made between the forward and reverse rate constants for the different chalcones in order to see how they are affected by different A-ring substituents. It is observed that electron releasing groups at the 4'- or 6'- positions decrease the rate. This diminution in the observed rate is particularly pronounced with 6'-substituents, and is considered as possibly due to the steric and/or electrostatic interaction of this substituent with the carbonyl group an interaction that could force the carbonyl group to lie out of the plane of the A-ring thereby changing rates of reactions by electronic or steric effects.
The first kinetic study of the reactivity of a 2'-hydroxychalcone epoxide is reported. The variation of the rate of cyclisation of the parent epoxide, 2'-hydroxychalcone epoxide, to 3-hydroxyflavanone in water, over the range pH 1 - 6.5, is shown to be consistent with the rate equation.
Rate = 0.235 [Epoxide]{H⁺} + 1.85 x 10⁶ [Expoxide] {OH⁻} mol 1⁻¹s⁻¹
This shows the epoxide to be very unstable at or above neutral pH, and suggests that such compounds, if they do occur, as has often been suggested, as intermediates in flavanoid biosynthesis would probably be very difficult to isolate. Their detection under the basic conditions of either the Algar-Flynn-Oyamada oxidation of 2'-hydroxychalcones, or the formation of aurones from certain 2'-hydroxychalcone dibromides, both reactions in which they have been suggested as intermediates, would be equally unlikely : based on a suggested mechanism, the parent epoxide of this study can be predicted to have a half-life at pH 10 of the order of a few milliseconds.
The first determination of the ratio of E- and Z-2'-hydroxy-α-bromochalcones formed directly from a 2'-hydroxychalcone dibromide is described. Combined kinetic and spectrophotometric measurements give the yield (%) of E- and Z-2'-hydroxy-α-bromochalcone as 35 ± 2 and 63 ± 8 respectively for the reaction of erythro-2'-hydroxychalcone dibromide in 4:1 ethanol-water buffered at pH 7.88 with N-ethylmorpholine. Direct cyclisation of the dibromo compound, if it occurs at all, is only a very minor route to 3-bromoflavanone. The lack of any detected dependence buffer concentrations of the rate constants or of the proportions of the E- and Z-isomers formed suggest, an E1cв mechanism rather than an E2. However, with the particular elimination involved (i.e. a double bond being formed α, β to a carbonyl group) there is precedence for small catalysis by N-alkylmorpholines and therefore, it is not certain that the lack of measurable buffer catalysis does in fact mean a total lack of catalysis. Further, if the elimination is in fact by an E1cв type mechanism, a carbanion is not necessarily involved, as the elimination could proceed from the phenolate ion as conjugate base, the phenoxide group acting in place of an external base. An El mechanism is excluded on kinetic grounds.

year: 1980

title: Dispersal and remineralisation of biodeposits: Ecosystem impacts of mussel aquaculture

authors: Giles, Hilke

subjects: faeces

abstract: Suspension-feeding bivalves produce biodeposits (faeces and pseudofaeces) that have much higher sinking velocities than their constituent particles. Consequently they cause sedimentation of material that might otherwise not be deposited. The benthic remineralisation of biodeposits increases sediment oxygen demand and nutrient regeneration, thus enhancing the benthic-pelagic coupling of nearshore ecosystems. In New Zealand the mussel Perna canaliculus has a high natural abundance and is also intensively cultured. This thesis examines the dispersal and remineralisation characteristics of mussel P. canaliculus biodeposits and the impacts of sedimentation from a mussel farm in the Firth of Thames on sediment biogeochemistry by combining laboratory, field and modelling studies. 

Dispersal characteristics were examined in the laboratory by measuring sinking velocities and erosion thresholds of biodeposits produced by mussels of a wide size range fed three experimental diets. The results show that biodeposit dispersal is a function of mussel diet and size and thus could differ significantly between locations and seasons. Estimates of dispersal distances based on these results demonstrated that the initial dispersal of biodeposits produced by cultured mussels is not far. Depending on the hydrodynamic conditions, secondary dispersal via resuspension potentially plays a more important role in the dispersal of biodeposits from mussel farms than initial dispersal and almost certainly serves as the major means of transport of biodeposits from natural mussel beds.

Biodeposit mineralisation was studied by incubating coastal sediments with added biodeposits and measuring oxygen and nutrient fluxes as well as sediment characteristics over an 11 d period. Sediment oxygen consumption and ammonium release increased immediately after biodeposit addition and remained elevated compared to control cores without additions for the incubation period. A biodeposit decay rate (0.16 d-1) was calculated by fitting a first-order G model to the observed increase in oxygen consumption. This rate is 1 - 2 orders of magnitude higher than published decay rates of coastal sediments without organic enrichment or plant material. Nutrient fluxes during the incubation period illustrated that biodeposit remineralisation alters the stoichiometry of the nutrients released from the sediments which may potentially be more significant than the changes of the individual fluxes.

To determine the impact of a mussel farm in the Firth of Thames I measured sediment oxygen and nutrient fluxes by deploying benthic chambers, sediment characteristics by collecting sediment cores and sedimentation rates by deploying sediment traps in four seasons. Oxygen consumption and sediment nutrient release rates were generally higher under the farm compared to a reference site, demonstrating the typical response to increased organic input. Unusually low nitrogen release rates measured in summer may indicate enhanced denitrification under the farm. A simple budget demonstrated the importance of benthic nutrient regeneration in maintaining primary production in this region and that mussel culture can lead to a redistribution of nutrients. This study showed that site-specific hydrodynamic and biogeochemical conditions have to be taken into account when planning new mussel farms to prevent excessive modifications of nutrient dynamics.

Results of the laboratory and field studies conducted in this thesis were used to parameterise, calibrate and validate models of mussel biodeposit dispersal and remineralisation. A particle tracking model showed that the maximum initial dispersal of faecal pellets from the mussel farm is approximately 300 m and that pellets can be transported several times this distance via resuspension. The remineralisation model was able to simulate the increased nitrogen fluxes from the sediments well and highlighted the need for thorough calibration and parameterisation of the model. 

This thesis contributed to the current understanding of the ecosystem impacts of mussel culture and provided numerical models and model parameters that will assist in the assessment of mussel culture sustainability and the contribution of mussels to the nutrient cycling in nearshore ecosystems.

text: Dispersal and remineralisation of biodeposits: Ecosystem impacts of mussel aquaculture Suspension-feeding bivalves produce biodeposits (faeces and pseudofaeces) that have much higher sinking velocities than their constituent particles. Consequently they cause sedimentation of material that might otherwise not be deposited. The benthic remineralisation of biodeposits increases sediment oxygen demand and nutrient regeneration, thus enhancing the benthic-pelagic coupling of nearshore ecosystems. In New Zealand the mussel Perna canaliculus has a high natural abundance and is also intensively cultured. This thesis examines the dispersal and remineralisation characteristics of mussel P. canaliculus biodeposits and the impacts of sedimentation from a mussel farm in the Firth of Thames on sediment biogeochemistry by combining laboratory, field and modelling studies. 

Dispersal characteristics were examined in the laboratory by measuring sinking velocities and erosion thresholds of biodeposits produced by mussels of a wide size range fed three experimental diets. The results show that biodeposit dispersal is a function of mussel diet and size and thus could differ significantly between locations and seasons. Estimates of dispersal distances based on these results demonstrated that the initial dispersal of biodeposits produced by cultured mussels is not far. Depending on the hydrodynamic conditions, secondary dispersal via resuspension potentially plays a more important role in the dispersal of biodeposits from mussel farms than initial dispersal and almost certainly serves as the major means of transport of biodeposits from natural mussel beds.

Biodeposit mineralisation was studied by incubating coastal sediments with added biodeposits and measuring oxygen and nutrient fluxes as well as sediment characteristics over an 11 d period. Sediment oxygen consumption and ammonium release increased immediately after biodeposit addition and remained elevated compared to control cores without additions for the incubation period. A biodeposit decay rate (0.16 d-1) was calculated by fitting a first-order G model to the observed increase in oxygen consumption. This rate is 1 - 2 orders of magnitude higher than published decay rates of coastal sediments without organic enrichment or plant material. Nutrient fluxes during the incubation period illustrated that biodeposit remineralisation alters the stoichiometry of the nutrients released from the sediments which may potentially be more significant than the changes of the individual fluxes.

To determine the impact of a mussel farm in the Firth of Thames I measured sediment oxygen and nutrient fluxes by deploying benthic chambers, sediment characteristics by collecting sediment cores and sedimentation rates by deploying sediment traps in four seasons. Oxygen consumption and sediment nutrient release rates were generally higher under the farm compared to a reference site, demonstrating the typical response to increased organic input. Unusually low nitrogen release rates measured in summer may indicate enhanced denitrification under the farm. A simple budget demonstrated the importance of benthic nutrient regeneration in maintaining primary production in this region and that mussel culture can lead to a redistribution of nutrients. This study showed that site-specific hydrodynamic and biogeochemical conditions have to be taken into account when planning new mussel farms to prevent excessive modifications of nutrient dynamics.

Results of the laboratory and field studies conducted in this thesis were used to parameterise, calibrate and validate models of mussel biodeposit dispersal and remineralisation. A particle tracking model showed that the maximum initial dispersal of faecal pellets from the mussel farm is approximately 300 m and that pellets can be transported several times this distance via resuspension. The remineralisation model was able to simulate the increased nitrogen fluxes from the sediments well and highlighted the need for thorough calibration and parameterisation of the model. 

This thesis contributed to the current understanding of the ecosystem impacts of mussel culture and provided numerical models and model parameters that will assist in the assessment of mussel culture sustainability and the contribution of mussels to the nutrient cycling in nearshore ecosystems.

year: 2006

title: Kotahi anō te tupuna o te tangata Māori, ko Ranginui e tū nei, ko Papatūānuku e takato nei. Colonisation through Christianity

authors: Wallace, Ritane

subjects: Christianity

abstract: This thesis will look at the role that Christianity and the missionaries played in the colonisation of Māori during the 1800s. With discussion about the colonisation of Aotearoa, it is generally felt within the Christian community that the work of the missionaries and the Crown are separate and therefore the universal belief is that the missionaries are pardoned from the critique of their work here in Aotearoa. However, Christianity throughout history has always been a doorway for the British Empire to enter land that was not their own.
  
It is widely accepted from the viewpoint of Christianity that it holds a religious superiority over all Indigenous people and their religions dating back to Pope Alexander VI and the issuing of the Papal Bull “Inter Caetera” in 1493 to justify Christian European explorers’ claims on land and waterways they allegedly discovered. Christian hegemony shaped missionary views of the ‘other’ and justified the assimilation of Indigenous people into European Christianity. The negative effects of Christianity on Māori far outweigh the positives as mission stations up and down Aotearoa contributed heavily to the loss of language, religion, and land, the three foundational pillars of Māori and other Indigenous peoples around the world.
   
The thesis seeks to hold the missionaries and Christianity to account for its contribution to the colonisation and religious assimilation of Māori into a foreign and unrelated belief system.

text: Kotahi anō te tupuna o te tangata Māori, ko Ranginui e tū nei, ko Papatūānuku e takato nei. Colonisation through Christianity This thesis will look at the role that Christianity and the missionaries played in the colonisation of Māori during the 1800s. With discussion about the colonisation of Aotearoa, it is generally felt within the Christian community that the work of the missionaries and the Crown are separate and therefore the universal belief is that the missionaries are pardoned from the critique of their work here in Aotearoa. However, Christianity throughout history has always been a doorway for the British Empire to enter land that was not their own.
  
It is widely accepted from the viewpoint of Christianity that it holds a religious superiority over all Indigenous people and their religions dating back to Pope Alexander VI and the issuing of the Papal Bull “Inter Caetera” in 1493 to justify Christian European explorers’ claims on land and waterways they allegedly discovered. Christian hegemony shaped missionary views of the ‘other’ and justified the assimilation of Indigenous people into European Christianity. The negative effects of Christianity on Māori far outweigh the positives as mission stations up and down Aotearoa contributed heavily to the loss of language, religion, and land, the three foundational pillars of Māori and other Indigenous peoples around the world.
   
The thesis seeks to hold the missionaries and Christianity to account for its contribution to the colonisation and religious assimilation of Māori into a foreign and unrelated belief system.

year: 2021