title: Studies of catalysis of the hydrolysis of phenyl glycinate and some related esters

authors: Lee, Lim Eng

abstract: This thesis reports the results and conclusions from the first kinetic studies undertaken of the hydrolysis of phenyl ester of an α-amino acid (glycine), previous studies having been limited to 4-nitrophenyl esters. Some data on 4-methoxyphenyl glycinate are also reported, together with some new data on 4-nitrophenyl esters required for comparison purposes. 
Studies have concentrated on catalysts previously reported as effective in the hydrolysis of 4-nitrophenyl esters of amino acids, the aim being to determine if results for a phenyl ester with a relatively poor leaving group might help in determining mechanisms involved in catalysis. 

(i) HCO₃⁻. Unlike the case for 4-nitrophenyl esters, phenyl glycinate hydrolysis is catalysed in bicarbonate solutions not by CO₂ as previously suggested but by HCO₃⁻, the kinetic form is given by 
Rate= k[neutral ester][HCO₃⁻] 
Kinetically equivalent forms involving CO₂ and CO₃²⁻ terms have been excluded. Comparison of the catalytic effect of HCO₃⁻ with that of imidazole and that of HPO₄²⁻ excludes the possibilities of general base and nucleophilic catalysis by HCO₃⁻ and a mechanism involving initial nucleophilic addition of amine to HCO₃⁻ followed by intramolecular nucleophilic substitution is suggested as most likely.

(ii) 4-nitrobenzaldehyde. Phenyl and 4-methoxyphenyl glycinate show the same kinetic form as 4-nitrophenyl esters but the catalytic effects are much smaller and consistent only with rate-determining attack on ester carbonyl. This supports the concept of rate-determining decomposition of a carbinolamine species, which is also consistent with an observed small effect of temperature on the overall catalytic rate constant.

(iii) Imidazole. Unlike the case for 4-nitrophenyl esters, the kinetics are dominated for both neutral and protonated phenyl glycinate species by a term second order in imidazole, which is consistent with general base catalysis of nucleophilic substitution by imidazole in the formation of an acylimidazole intermediate. A term first order in imidazole makes a minor contribution and probably represents general base catalysis as indicated through comparison of the magnitude of the catalytic effect of imidazole with that of HPO₄²⁻, which is also reported on for the first time in this thesis. 

(iv) N-ethylmorpholine. An unusual non-linear dependence of the observed first order rate constants on catalyst concentration is shown to be consistent with complexing of N-ethylmorpholine and ester prior to reaction. Equilibrium constants for complex formation and rate constants for decomposition are evaluated. However, the effects of model compounds as tests for medium effects of the amine and its cation throw some doubt on the validity of this interpretation. In particular, dioxane, as a model for N-ethylmorpholine, has an inhibitory effect on the hydrolysis of unprecedented magnitude.

(v) Hydroxide. Alkaline hydrolysis of phenyl glycinate  has been studied so as to obtain rate constants for both the neutral and cationic ester species. The latter is about 300 times more reactive.

Studies on 4-nitrophenyl esters have also been advanced in tandem with those of the phenyl and 4-methoxyphenyl esters. The kinetic form for catalysis in bicarbonate solutions has been confirmed as involving CO₂ and not HCO₃⁻, as is consistent with carbamate formation, but whether formation or decomposition of carbamate is rate-determining is still uncertain. The small effect of temperature on reaction rate together with the lack of base catalysis in the reaction support rate-limiting decomposition of carbamate, but the overall rate is close to that predicted by interpolation from other studies for carbamate formation. The possibility of hydrolysis at the zwitterion stage is considered. New data are also reported for 4-nitrobenzaldehyde catalysis for comparison with those of the phenyl and 4-methoxyphenyl esters.

text: Studies of catalysis of the hydrolysis of phenyl glycinate and some related esters This thesis reports the results and conclusions from the first kinetic studies undertaken of the hydrolysis of phenyl ester of an α-amino acid (glycine), previous studies having been limited to 4-nitrophenyl esters. Some data on 4-methoxyphenyl glycinate are also reported, together with some new data on 4-nitrophenyl esters required for comparison purposes. 
Studies have concentrated on catalysts previously reported as effective in the hydrolysis of 4-nitrophenyl esters of amino acids, the aim being to determine if results for a phenyl ester with a relatively poor leaving group might help in determining mechanisms involved in catalysis. 

(i) HCO₃⁻. Unlike the case for 4-nitrophenyl esters, phenyl glycinate hydrolysis is catalysed in bicarbonate solutions not by CO₂ as previously suggested but by HCO₃⁻, the kinetic form is given by 
Rate= k[neutral ester][HCO₃⁻] 
Kinetically equivalent forms involving CO₂ and CO₃²⁻ terms have been excluded. Comparison of the catalytic effect of HCO₃⁻ with that of imidazole and that of HPO₄²⁻ excludes the possibilities of general base and nucleophilic catalysis by HCO₃⁻ and a mechanism involving initial nucleophilic addition of amine to HCO₃⁻ followed by intramolecular nucleophilic substitution is suggested as most likely.

(ii) 4-nitrobenzaldehyde. Phenyl and 4-methoxyphenyl glycinate show the same kinetic form as 4-nitrophenyl esters but the catalytic effects are much smaller and consistent only with rate-determining attack on ester carbonyl. This supports the concept of rate-determining decomposition of a carbinolamine species, which is also consistent with an observed small effect of temperature on the overall catalytic rate constant.

(iii) Imidazole. Unlike the case for 4-nitrophenyl esters, the kinetics are dominated for both neutral and protonated phenyl glycinate species by a term second order in imidazole, which is consistent with general base catalysis of nucleophilic substitution by imidazole in the formation of an acylimidazole intermediate. A term first order in imidazole makes a minor contribution and probably represents general base catalysis as indicated through comparison of the magnitude of the catalytic effect of imidazole with that of HPO₄²⁻, which is also reported on for the first time in this thesis. 

(iv) N-ethylmorpholine. An unusual non-linear dependence of the observed first order rate constants on catalyst concentration is shown to be consistent with complexing of N-ethylmorpholine and ester prior to reaction. Equilibrium constants for complex formation and rate constants for decomposition are evaluated. However, the effects of model compounds as tests for medium effects of the amine and its cation throw some doubt on the validity of this interpretation. In particular, dioxane, as a model for N-ethylmorpholine, has an inhibitory effect on the hydrolysis of unprecedented magnitude.

(v) Hydroxide. Alkaline hydrolysis of phenyl glycinate  has been studied so as to obtain rate constants for both the neutral and cationic ester species. The latter is about 300 times more reactive.

Studies on 4-nitrophenyl esters have also been advanced in tandem with those of the phenyl and 4-methoxyphenyl esters. The kinetic form for catalysis in bicarbonate solutions has been confirmed as involving CO₂ and not HCO₃⁻, as is consistent with carbamate formation, but whether formation or decomposition of carbamate is rate-determining is still uncertain. The small effect of temperature on reaction rate together with the lack of base catalysis in the reaction support rate-limiting decomposition of carbamate, but the overall rate is close to that predicted by interpolation from other studies for carbamate formation. The possibility of hydrolysis at the zwitterion stage is considered. New data are also reported for 4-nitrobenzaldehyde catalysis for comparison with those of the phenyl and 4-methoxyphenyl esters.

year: 1979

title: Variability in the trophic level index in Lake Rotoehu from 1990 to 2021

authors: Woelmer, Whitney

abstract: Setting an appropriate Trophic Level Index (TLI) target for lakes in the Rotorua Te Arawa region is critical for informing short- and long-term management decisions. Due to high variability in the observed TLI of Lake Rotoehu, coupled with contrasting understanding of historical water quality in the lake, the Bay of Plenty Regional Council requested a robust analysis of the drivers of the TLI over time to help inform the suitability of the current TLI target. To undertake this, we first quantified the uncertainty around the TLI in the 1990s, when the current TLI target was set based on the “best” observed water quality within the long-term monitoring program, to understand how a lower sampling frequency from 1990-2000 (~every 2-3 months) impacted TLI estimates. We found that while sampling fewer times in the year in the 1990s increased uncertainty around TLI estimates by 0.2-0.3 TLI units, a marked shift in water quality from a TLI of 3.6 in 1992 to 4.5 in 1993 remained evident.
To understand if the main drivers affecting the TLI were different during the 1990s as opposed to later decades, we calculated the Pearson correlation coefficient between the TLI and several driver variables separately for each decade. Drivers in this analysis included meteorological variables, lake water level, and in-lake water quality not in the TLI calculation (e.g., bottom water nutrients, water temperature, stratification metrics), and the amount of aluminium sulphate dosed to the lake. While several variables were consistently important across all decades (e.g., bottom water nutrients, bottom water temperature, and mean monthly air temperature), average monthly water level and minimum windspeeds were only important in the 1990s, indicating that these variables had been related to major shifts in water quality seen during that time.
Lastly, to better understand the relative importance of multiple drivers of the TLI and whether this importance changes over time, we conducted a moving window analysis. We fit autoregressive models, meaning the models included the previous month’s TLI estimate, as well as a single driver variable over a moving window of ~8 years, where each window moved forward one month at a time. We found that air temperature, bottom water temperature, and bottom water dissolved reactive phosphorus (DRP) were most often the top predictors of the TLI. However, the relative importance of average monthly water level increased sharply to the most important driver during a time period which also corresponded to very high water levels. Additionally, examination of model parameters over the simulation period demonstrated that the strength and magnitude of the relationship between the TLI and individual drivers changed over time, indicating that that relationships are not fixed through time.
Overall, this work highlights the importance of re-evaluating the underlying relationships between the TLI and drivers over time, emphasising the dynamic nature of Lake Rotoehu. We demonstrate a clear shift in water quality between 1992 and 1993, likely driven by low water levels and windspeeds, which may have induced a pattern of increased external loading that still exists. Importantly, many of the variables which emerged as important for the TLI (water level, windspeed) will continue to vary with changing climate and are outside of the control of management. In light of this, while the current TLI target (3.9) may be feasible for Lake Rotoehu given historical observations and possible reference conditions, achieving this target consistently may be very difficult going forward due to catchment and climate pressures which have put Lake Rotoehu outside of an undisturbed reference state. This work can be built upon through future analyses which continue quantifying the changing relationships between the TLI and drivers over time, increasing the use of high-frequency buoy data to better inform water quality dynamics at shorter time scales, and testing our understanding of the drivers of water quality through predictions. The overall aim for future research would therefore be to establish water quality targets that not only align with community aspirations but are also technically feasible, especially in light of global change.

text: Variability in the trophic level index in Lake Rotoehu from 1990 to 2021 Setting an appropriate Trophic Level Index (TLI) target for lakes in the Rotorua Te Arawa region is critical for informing short- and long-term management decisions. Due to high variability in the observed TLI of Lake Rotoehu, coupled with contrasting understanding of historical water quality in the lake, the Bay of Plenty Regional Council requested a robust analysis of the drivers of the TLI over time to help inform the suitability of the current TLI target. To undertake this, we first quantified the uncertainty around the TLI in the 1990s, when the current TLI target was set based on the “best” observed water quality within the long-term monitoring program, to understand how a lower sampling frequency from 1990-2000 (~every 2-3 months) impacted TLI estimates. We found that while sampling fewer times in the year in the 1990s increased uncertainty around TLI estimates by 0.2-0.3 TLI units, a marked shift in water quality from a TLI of 3.6 in 1992 to 4.5 in 1993 remained evident.
To understand if the main drivers affecting the TLI were different during the 1990s as opposed to later decades, we calculated the Pearson correlation coefficient between the TLI and several driver variables separately for each decade. Drivers in this analysis included meteorological variables, lake water level, and in-lake water quality not in the TLI calculation (e.g., bottom water nutrients, water temperature, stratification metrics), and the amount of aluminium sulphate dosed to the lake. While several variables were consistently important across all decades (e.g., bottom water nutrients, bottom water temperature, and mean monthly air temperature), average monthly water level and minimum windspeeds were only important in the 1990s, indicating that these variables had been related to major shifts in water quality seen during that time.
Lastly, to better understand the relative importance of multiple drivers of the TLI and whether this importance changes over time, we conducted a moving window analysis. We fit autoregressive models, meaning the models included the previous month’s TLI estimate, as well as a single driver variable over a moving window of ~8 years, where each window moved forward one month at a time. We found that air temperature, bottom water temperature, and bottom water dissolved reactive phosphorus (DRP) were most often the top predictors of the TLI. However, the relative importance of average monthly water level increased sharply to the most important driver during a time period which also corresponded to very high water levels. Additionally, examination of model parameters over the simulation period demonstrated that the strength and magnitude of the relationship between the TLI and individual drivers changed over time, indicating that that relationships are not fixed through time.
Overall, this work highlights the importance of re-evaluating the underlying relationships between the TLI and drivers over time, emphasising the dynamic nature of Lake Rotoehu. We demonstrate a clear shift in water quality between 1992 and 1993, likely driven by low water levels and windspeeds, which may have induced a pattern of increased external loading that still exists. Importantly, many of the variables which emerged as important for the TLI (water level, windspeed) will continue to vary with changing climate and are outside of the control of management. In light of this, while the current TLI target (3.9) may be feasible for Lake Rotoehu given historical observations and possible reference conditions, achieving this target consistently may be very difficult going forward due to catchment and climate pressures which have put Lake Rotoehu outside of an undisturbed reference state. This work can be built upon through future analyses which continue quantifying the changing relationships between the TLI and drivers over time, increasing the use of high-frequency buoy data to better inform water quality dynamics at shorter time scales, and testing our understanding of the drivers of water quality through predictions. The overall aim for future research would therefore be to establish water quality targets that not only align with community aspirations but are also technically feasible, especially in light of global change.

year: 2025

title: Mouri matters Contextualizing mouri in Māori health discourse

authors: Penehira, Mera

abstract: The vision statement of Te Reo o Taranaki, “Tuku reo, tuku mouri: language, culture, crossing generations”, embodies the essence of an understanding of mouri which goes beyond the simple dictionary translations of “life force” or “life essence”. Indeed, there are numerous oral narratives—whakataukī (proverbs), waiata (songs), haka (dance), karanga (ceremonial call), whaikōrero (formal speech), karakia (prayers and incantations)—from the present day to our earliest records of Māori history that engage the notion of mouri. The purpose of this paper is to examine current understandings of mouri and, by linking the concept with linguistic, cultural and intergenerational terms—as in the Taranaki example—it will be argued that mouri is something of significance to our “being” and to our wellbeing.

text: Mouri matters Contextualizing mouri in Māori health discourse The vision statement of Te Reo o Taranaki, “Tuku reo, tuku mouri: language, culture, crossing generations”, embodies the essence of an understanding of mouri which goes beyond the simple dictionary translations of “life force” or “life essence”. Indeed, there are numerous oral narratives—whakataukī (proverbs), waiata (songs), haka (dance), karanga (ceremonial call), whaikōrero (formal speech), karakia (prayers and incantations)—from the present day to our earliest records of Māori history that engage the notion of mouri. The purpose of this paper is to examine current understandings of mouri and, by linking the concept with linguistic, cultural and intergenerational terms—as in the Taranaki example—it will be argued that mouri is something of significance to our “being” and to our wellbeing.

year: 2011