title: Derivatisation of Polyphenols

authors: Bridson, James Hadley

subjects: tannin

abstract: Polyphenols, such as tannins, offer potential as a bio-derived chemical feedstock.  Their present utilisation is limited mainly to leather tanning and wood panel adhesives.  However, appropriate derivatisation may alter both the chemical and physical properties and thereby allow further utilisation of polyphenols.

Derivatisation of polyphenols was achieved by esterification and etherification of the phenol groups.  Esterification was achieved by alcoholysis of acid chlorides and transesterification with vinyl esters, while etherification was achieved by the ring opening of propylene oxide.  The polyphenols used were resorcinol, catechin, Pinus radiata bark tannin, and Schinopsis lorentzii tannin.  The products were characterised using a range of techniques including NMR (1H, 13C and 2D NMR in both the solution and solid state), ESI-MS, GPC, DSC, TGA, and rheology.

The preparation of polyphenolic esters by alcoholysis provided model compounds to establish the key chemical, spectroscopic, and physical features.  A range of simple polyphenol esters such as resorcinol dilaurate and catechin pentalaurate were prepared using lauroyl chloride.  Furthermore, tannin lauroyl esters were prepared with varying degrees of substitution.  A transesterification method was developed for the preparation of polyphenol esters.  Ester interchange occurred effectively in the presence of base catalyst in aqueous solution or dimethyl sulfoxide with short or long chain vinyl esters.  This included the first report of the base-catalysed transesterification of flavonoids by vinyl esters to give products such as catechin mono- and di-laurate.  Transesterification occurred preferentially at the B-ring as shown by NMR spectroscopy.  Subsequently, this transesterification procedure was used to prepare tannin esters.  The chemical and physical properties of polyphenol esters were assessed using thermal, antioxidant, and UV/VIS light absorption analysis.  Thermal analysis indicated melt/flow properties for some of the polyphenol esters.  In some cases, the thermal stability was also shown to increase upon esterification.  The antioxidant activity was shown to decrease upon transesterification of pine bark tannin with vinyl laurate, while the UV/VIS absorption was shown to increase.  These properties may lend the products towards applications as polymer additives or pharmaceuticals.    

Polyphenol ethers were prepared by the Williamson ether synthesis and ring opening of propylene oxide.  However, the Williamson ether synthesis, a common route to prepare ethers, proved unsuitable for flavonoids.  Catechin and tannin hydroxypropyl ether derivatives of varying substitution were prepared by the ring-opening of propylene oxide in the presence of triethylamine.  Upon hydroxypropylation the thermal properties of the polyphenol were altered.  For example, catechin hydroxypropyl ethers showed a glass transition, which was dependent upon the molar substitution, while rheology showed melt behaviour for several of the tannin hydroxypropyl ethers.

text: Derivatisation of Polyphenols Polyphenols, such as tannins, offer potential as a bio-derived chemical feedstock.  Their present utilisation is limited mainly to leather tanning and wood panel adhesives.  However, appropriate derivatisation may alter both the chemical and physical properties and thereby allow further utilisation of polyphenols.

Derivatisation of polyphenols was achieved by esterification and etherification of the phenol groups.  Esterification was achieved by alcoholysis of acid chlorides and transesterification with vinyl esters, while etherification was achieved by the ring opening of propylene oxide.  The polyphenols used were resorcinol, catechin, Pinus radiata bark tannin, and Schinopsis lorentzii tannin.  The products were characterised using a range of techniques including NMR (1H, 13C and 2D NMR in both the solution and solid state), ESI-MS, GPC, DSC, TGA, and rheology.

The preparation of polyphenolic esters by alcoholysis provided model compounds to establish the key chemical, spectroscopic, and physical features.  A range of simple polyphenol esters such as resorcinol dilaurate and catechin pentalaurate were prepared using lauroyl chloride.  Furthermore, tannin lauroyl esters were prepared with varying degrees of substitution.  A transesterification method was developed for the preparation of polyphenol esters.  Ester interchange occurred effectively in the presence of base catalyst in aqueous solution or dimethyl sulfoxide with short or long chain vinyl esters.  This included the first report of the base-catalysed transesterification of flavonoids by vinyl esters to give products such as catechin mono- and di-laurate.  Transesterification occurred preferentially at the B-ring as shown by NMR spectroscopy.  Subsequently, this transesterification procedure was used to prepare tannin esters.  The chemical and physical properties of polyphenol esters were assessed using thermal, antioxidant, and UV/VIS light absorption analysis.  Thermal analysis indicated melt/flow properties for some of the polyphenol esters.  In some cases, the thermal stability was also shown to increase upon esterification.  The antioxidant activity was shown to decrease upon transesterification of pine bark tannin with vinyl laurate, while the UV/VIS absorption was shown to increase.  These properties may lend the products towards applications as polymer additives or pharmaceuticals.    

Polyphenol ethers were prepared by the Williamson ether synthesis and ring opening of propylene oxide.  However, the Williamson ether synthesis, a common route to prepare ethers, proved unsuitable for flavonoids.  Catechin and tannin hydroxypropyl ether derivatives of varying substitution were prepared by the ring-opening of propylene oxide in the presence of triethylamine.  Upon hydroxypropylation the thermal properties of the polyphenol were altered.  For example, catechin hydroxypropyl ethers showed a glass transition, which was dependent upon the molar substitution, while rheology showed melt behaviour for several of the tannin hydroxypropyl ethers.

year: 2007

title: Nonlinear adjustments of volatility expectations to forecast errors: Evidence from Markov-Regime switches in implied volatility

authors: Nishina, Kazuhiko

subjects: economic analysis

abstract: This paper tests for nonlinearities in the behavior of volatility expectations based on model-free implied volatility indices. Using Markov regime-switching models, the empirical evidence from the German, Japanese and U.S. markets suggests that there are indeed regime-specific levels of volatility expectations. Whereas the regimes seem to be governed by the degree of serial correlation and adjustment to forecast errors, there is no evidence of significant leverage effects. The frequency of regime shifts in volatility expectations is affected by the onset of financial crises, which have the effect of increasing the likelihood of regimes driven by lower autoregressive effects and faster speeds of adjustment. The evidence suggests that despite the heterogeneous beliefs of market participants, implied volatility indices provide a measure of consensus expectations that can be useful in understanding the nonlinear behavior of volatility expectations during periods of financial instability

text: Nonlinear adjustments of volatility expectations to forecast errors: Evidence from Markov-Regime switches in implied volatility This paper tests for nonlinearities in the behavior of volatility expectations based on model-free implied volatility indices. Using Markov regime-switching models, the empirical evidence from the German, Japanese and U.S. markets suggests that there are indeed regime-specific levels of volatility expectations. Whereas the regimes seem to be governed by the degree of serial correlation and adjustment to forecast errors, there is no evidence of significant leverage effects. The frequency of regime shifts in volatility expectations is affected by the onset of financial crises, which have the effect of increasing the likelihood of regimes driven by lower autoregressive effects and faster speeds of adjustment. The evidence suggests that despite the heterogeneous beliefs of market participants, implied volatility indices provide a measure of consensus expectations that can be useful in understanding the nonlinear behavior of volatility expectations during periods of financial instability

year: 2012

title: A population-based study of traumatic brain injury incidence and mechanisms in New Zealand: 2021–2022 compared with 2010–2011

authors: Jones, Kelly

subjects: Traumatic brain injury

abstract: Background: Monitoring traumatic brain injury (TBI) incidence and epidemiological patterns is important for evidence-based strategic planning, policy, prevention, and resource allocation. We revisited population-based estimates and examined patterns of TBI incidence (all ages, severities) in 2021–2022 compared with 2010–2011 in New Zealand (NZ). Methods: Examining an urban (Hamilton) and rural (Waikato District) region in NZ (May 2021–April 2022, unintentionally following the start of the COVID-19 pandemic), we calculated crude annual age-, sex-, ethnic-, urban/rural area- and mechanism-specific TBI incidence per 100,000 person-years with 95% Confidence Intervals (CI). Poisson regression was used to derive adjusted Risk Ratios (aRRs) to compare age-standardised rates between sex, ethnicity, and area groups. Direct standardisation was used to age-standardise rates to the world population. We calculated Incidence Rate Ratios (IRRs) with 95% CI to compare 2021–2022 with 2010–2011 age-standardised rates. Findings: Total TBI incidence per 100,000 person-years was 852 cases (95% CI 816–890), including 791 cases (756–828) of mild TBI, and 61 cases (52–72) of moderate to severe TBI. TBI affected males more than females (IRR 1.31, 95% CI 1.29–1.33), and urban more than rural residents (IRR 1.57, 1.43–1.73). Most TBI (61%) occurred in people aged 15–64 years and were due to falls (48%). European and Asian peoples had lower risk of TBI than Māori (aRRs 0.68, 0.31 respectively). Compared to 2010–2011, total TBI incidence and rates among Māori were stable; TBI incidence was greater among females, urban residents, and adults aged ≥34 years; and TBI due to falls significantly increased (IRR 1.20, 95% CI 1.03–1.40). Interpretation: Noting increased risks for underestimation due to COVID-19, findings suggest overall TBI incidence rate in NZ was similar in 2021–2022 to 2010–2011, while highlighting changes in TBI distribution. Age-, sex-, area-, ethnic-, and mechanism-specific distributions should be considered when revisiting prevention strategies to reduce TBI incidence. Funding: Health Research Council of New Zealand of NZ.

text: A population-based study of traumatic brain injury incidence and mechanisms in New Zealand: 2021–2022 compared with 2010–2011 Background: Monitoring traumatic brain injury (TBI) incidence and epidemiological patterns is important for evidence-based strategic planning, policy, prevention, and resource allocation. We revisited population-based estimates and examined patterns of TBI incidence (all ages, severities) in 2021–2022 compared with 2010–2011 in New Zealand (NZ). Methods: Examining an urban (Hamilton) and rural (Waikato District) region in NZ (May 2021–April 2022, unintentionally following the start of the COVID-19 pandemic), we calculated crude annual age-, sex-, ethnic-, urban/rural area- and mechanism-specific TBI incidence per 100,000 person-years with 95% Confidence Intervals (CI). Poisson regression was used to derive adjusted Risk Ratios (aRRs) to compare age-standardised rates between sex, ethnicity, and area groups. Direct standardisation was used to age-standardise rates to the world population. We calculated Incidence Rate Ratios (IRRs) with 95% CI to compare 2021–2022 with 2010–2011 age-standardised rates. Findings: Total TBI incidence per 100,000 person-years was 852 cases (95% CI 816–890), including 791 cases (756–828) of mild TBI, and 61 cases (52–72) of moderate to severe TBI. TBI affected males more than females (IRR 1.31, 95% CI 1.29–1.33), and urban more than rural residents (IRR 1.57, 1.43–1.73). Most TBI (61%) occurred in people aged 15–64 years and were due to falls (48%). European and Asian peoples had lower risk of TBI than Māori (aRRs 0.68, 0.31 respectively). Compared to 2010–2011, total TBI incidence and rates among Māori were stable; TBI incidence was greater among females, urban residents, and adults aged ≥34 years; and TBI due to falls significantly increased (IRR 1.20, 95% CI 1.03–1.40). Interpretation: Noting increased risks for underestimation due to COVID-19, findings suggest overall TBI incidence rate in NZ was similar in 2021–2022 to 2010–2011, while highlighting changes in TBI distribution. Age-, sex-, area-, ethnic-, and mechanism-specific distributions should be considered when revisiting prevention strategies to reduce TBI incidence. Funding: Health Research Council of New Zealand of NZ.

year: 2026