Listeria monocytogenes in Milk Products

peer-reviewedMilk and milk products are frequently identified as vectors for transmission of Listeria monocytogenes. Milk can be contaminated at farm level either by indirect external contamination from the farm environment or less frequently by direct contamination of the milk from infection in the animal. Pasteurisation of milk will kill L. monocytogenes, but post-pasteurisation contamination, consumption of unpasteurised milk and manufacture of unpasteurised milk products can lead to milk being the cause of outbreaks of listeriosis. Therefore, there is a concern that L. monocytogenes in milk could lead to a public health risk. To protect against this risk, there is a need for awareness surrounding the issues, hygienic practices to reduce the risk and adequate sampling and analysis to verify that the risk is controlled. This review will highlight the issues surrounding L. monocytogenes in milk and milk products, including possible control measures. It will therefore create awareness about L. monocytogenes, contributing to protection of public health

A chemical kinetic interpretation of the octane appetite of modern gasoline engines

Fuel anti-knock quality is a critical property with respect to the effective design of next-generation spark-ignition engines which aim to have increased efficiency, and lower emissions. Increasing evidence in the literature supports the fact that the current regulatory measures of fuel anti-knock quality, the research octane number (RON), and motor octane number (MON), are becoming decreasingly relevant to commercial engines. Extrapolation and interpolation of the RON/MON scales to the thermodynamic conditions of modern engines is potentially valuable for the synergistic design of fuels and engines with greater efficiency. The K-value approach, which linearly weights the RON/MON scales based on the thermodynamic history of an engine, offers a convenient experimental method to do so, although complementary theoretical interpretations of K-value measurements are lacking in the literature. This work uses a phenomenological engine model with a detailed chemical kinetic model to predict and interpret known trends in the K-value with respect to engine intake temperature, pressure, and engine speed. The modelling results support experimental trends which show that the K-value increases with increasing intake temperature and engine speed, and decreases with increasing intake pressure. A chemical kinetic interpretation of trends in the K-value based on fundamental ignition behaviour is presented. The results show that combined experimental/theoretical approaches, which employ a knowledge of fundamental fuel data (gas phase kinetics, ignition delay times), can provide a reliable means to assess trends in the real-world performance of commercial fuels under the operating conditions of modern engines. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.Funding from the European Commission Marie Curie Transfer of Knowledge Scheme (FP7) pursuant to Contract PIAP-GA-2013-610897 GENFUEL is greatly acknowledged. KPS would like to thank Dr. Ultan Burke and Dr. Colin Banyon for fruitful discussions on the topic.peer-reviewed2020-06-2

The Amyloidogenic Peptide Amyloid Beta(16–22) Displays Facet Dependent Conformation on Metal Surfaces

Currently, it is not understood how metal nanoparticles influence the formation of protein fibrils, although recent literature highlights that the shape and chemical composition of such nanoparticles can strongly influence the process. Understanding this process at a fundamental level can potentially unlock routes to the development of new therapeutics, as well as novel materials for technological applications. This requires a microscopic picture of the behaviour of amyloidogenic proteins on metal surfaces. Using replica exchange molecular dynamics simulations, we investigate the conformation of the model amyloidogenic peptide, Aβ(16–22), on different gold and silver surfaces. The conformation of the peptide on gold surfaces also shows a strong facet dependence, with fibril-like conformations being promoted in the 100 surface and inhibited on the 111 surface. A smaller degree of facet dependence is seen for silver with the peptide behaving similar on both of these. The difference in the facet dependence can be related to the difference between direct adsorption onto the gold 111 surface, with a preference towards indirect (water mediated) adsorption onto the other surfaces. This new information on the behaviour of an amyloidogenic peptide on metal surfaces can give insight into the size-dependent effect of nanoparticles on fibril formation and the use of surfaces to control fibrillation

A chemical kinetic interpretation of the octane appetite of modern gasoline engines

Fuel anti-knock quality is a critical property with respect to the effective design of next-generation spark-ignition engines which aim to have increased efficiency, and lower emissions. Increasing evidence in the literature supports the fact that the current regulatory measures of fuel anti-knock quality, the research octane number (RON), and motor octane number (MON), are becoming decreasingly relevant to commercial engines. Extrapolation and interpolation of the RON/MON scales to the thermodynamic conditions of modern engines is potentially valuable for the synergistic design of fuels and engines with greater efficiency. The K-value approach, which linearly weights the RON/MON scales based on the thermodynamic history of an engine, offers a convenient experimental method to do so, although complementary theoretical interpretations of K-value measurements are lacking in the literature. This work uses a phenomenological engine model with a detailed chemical kinetic model to predict and interpret known trends in the K-value with respect to engine intake temperature, pressure, and engine speed. The modelling results support experimental trends which show that the K-value increases with increasing intake temperature and engine speed, and decreases with increasing intake pressure. A chemical kinetic interpretation of trends in the K-value based on fundamental ignition behaviour is presented. The results show that combined experimental/theoretical approaches, which employ a knowledge of fundamental fuel data (gas phase kinetics, ignition delay times), can provide a reliable means to assess trends in the real-world performance of commercial fuels under the operating conditions of modern engines. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.Funding from the European Commission Marie Curie Transfer of Knowledge Scheme (FP7) pursuant to Contract PIAP-GA-2013-610897 GENFUEL is greatly acknowledged. KPS would like to thank Dr. Ultan Burke and Dr. Colin Banyon for fruitful discussions on the topic.2020-06-2

Benchmarking Compound Methods (CBS-QB3, CBS-APNO, G3, G4, W1BD) against the Active Thermochemical Tables: A Litmus Test for Cost-Effective Molecular Formation Enthalpies

The theoretical atomization energies of some 45 C_<i>x</i>H_<i>y</i>O_<i>z</i> molecules present in the Active Thermochemical Tables compilation and of particular interest to the combustion chemistry community have been computed using five composite model chemistries as titled. The species contain between 1–8 “heavy” atoms, and a few are conformationally diverse with up to nine conformers. The enthalpies of formation at 0 and 298.15 K are then derived via the atomization method and compared against the recommended values. In general, there is very good agreement between our averaged computed values and those in the ATcT; those for 1,3-cyclopentadiene exceptionally differ considerably, and we show from isodesmic reactions that the true value for 1,3-cyclopentadiene is closer to 134 kJ mol^–1 than the reported 101 kJ mol^–1. If one is restricted to using a single method, statistical measures indicate that the best methods are in the rank order G3 ≈ G4 > W1BD > CBS-APNO > CBS-QB3. The CBS-x methods do on average predict Δ_f<i>H</i>^⊖(298.15 K) within ≈5 kJ mol^–1 but are prone to occasional lapses. There are statistical advantages to be gained from using a number of methods in tandem, and all possible combinations have been tested. We find that the average formation enthalpy coming from using CBS-APNO/G4, CBS-APNO/G3, and G3/G4 show lower mean signed and mean unsigned errors, and lower standard and root-mean-squared deviations, than any of these methods in isolation. Combining these methods also leads to the added benefit of providing an uncertainty rooted in the chemical species under investigation. In general, CBS-APNO and W1BD tend to underestimate the formation enthalpies of target species, whereas CBS-QB3, G3, and G4 have a tendency to overestimate the same. Thus, combining CBS-APNO with a G3/G4 combination leads to an improvement in all statistical measures of accuracy and precision, predicting the ATcT values to within 0.14 ± 4.21 kJ mol^–1, thus rivalling “chemical accuracy” (±4.184 kJ mol^–1) without the excessive cost associated with higher-level methods such as W1BD

An ab initio/transition state theory study of the reactions of Ċ5H9 species of relevance to 1,3-Pentadiene, Part II: Pressure dependent rate constants and implications for combustion modeling

The temperature- and pressure-dependence of rate constants for several radicals and unsaturated hydrocarbons reactions (1,3-C5H8/1,4-C5H8/cyC(5)H(8) + (H)over dot, C2H4 + (C)over dot(3)H5-a, C3H6 + (C)over dot(2)H(3)) are analyzed in this paper. The abstraction reactions of these systems are also calculated and compared with available literature data. (C)over dot(5)H(9) radicals can be produced via (H)over dot atom addition reactions to the pentadiene isomers and cyclopentene, and also by H-atom abstraction reactions from 1- and 2-pentene and cyclopentane. Comprehensive (C)over dot(5)H(9) potential energy surface (PES) analyses and high-pressure limiting rate constants for related reactions have been explored in part I of this work (J. Phys. Chem. A 2019, 123 (22), 9019-9052). In this work, a chemical kinetic model is constructed based on the computed thermochemistry and high-pressure limiting rate constants from part I, to further understand the chemistry of different C5H8 molecules. The most important channels for these addition reactions are discussed in the present work based on reaction pathway analyses. The dominant reaction pathways for these five systems are combined together to generate a simplified (C)over dot(5)H(9) PES including nine reactants, 25 transition states (TSs), and nine products. Spin-restricted single point energies are calculated for radicals and TSs on the simplified PES at the ROCCSD(T)/aug-cc-pVTZ level of theory with basis set corrections from MP2/aug-cc-pVXZ (where X = T and Q). Temperature- and pressure-dependent rate constants are calculated using RRKM theory with a Master Equation analysis, with restricted energies used for minima on the simplified (C)over dot(5)H(9) PES and unrestricted energies for other species, over a temperature range of 300-2000 K and in the pressure range 0.01-100 atm. The rate constants calculated are in good agreement with those in the literature. The chemical kinetic model is updated with pressure-dependent rate constants and is used to simulate the species concentration profiles for H. atom addition to cyclopentane and cyclopentene. Through detailed analyses and comparisons, this model can reproduce the experimental measurements of species qualitatively and quantitatively with reasonably good agreement.This study is supported by Science Foundation Ireland and the China Scholarship Council (CSC). The authors want to acknowledge the financial support of Science Foundation Ireland under Grant No. 15/IA/3177 and 16/SP/3829, and the provision of computational resources from ICHEC under the NUI Galway shared condominium accounts. The Computational resources are provided by the Irish Centre for High-End Computing (ICHEC), under project number ngche063c, ngcom006c and ngche058c. The authors are grateful to Stephen Klippenstein for the help with MESS code study. Chong-Wen Zhou acknowledges the support from National Science and Technology Major Project (2017-III-0004-0028) and Beihang University under the Fundamental Research Funds.2021-05-1

An ab initio/transition state theory study of the reactions of Ċ5H9 species of relevance to 1,3-Pentadiene, Part II: Pressure dependent rate constants and implications for combustion modeling

The temperature- and pressure-dependence of rate constants for several radicals and unsaturated hydrocarbons reactions (1,3-C5H8/1,4-C5H8/cyC(5)H(8) + (H)over dot, C2H4 + (C)over dot(3)H5-a, C3H6 + (C)over dot(2)H(3)) are analyzed in this paper. The abstraction reactions of these systems are also calculated and compared with available literature data. (C)over dot(5)H(9) radicals can be produced via (H)over dot atom addition reactions to the pentadiene isomers and cyclopentene, and also by H-atom abstraction reactions from 1- and 2-pentene and cyclopentane. Comprehensive (C)over dot(5)H(9) potential energy surface (PES) analyses and high-pressure limiting rate constants for related reactions have been explored in part I of this work (J. Phys. Chem. A 2019, 123 (22), 9019-9052). In this work, a chemical kinetic model is constructed based on the computed thermochemistry and high-pressure limiting rate constants from part I, to further understand the chemistry of different C5H8 molecules. The most important channels for these addition reactions are discussed in the present work based on reaction pathway analyses. The dominant reaction pathways for these five systems are combined together to generate a simplified (C)over dot(5)H(9) PES including nine reactants, 25 transition states (TSs), and nine products. Spin-restricted single point energies are calculated for radicals and TSs on the simplified PES at the ROCCSD(T)/aug-cc-pVTZ level of theory with basis set corrections from MP2/aug-cc-pVXZ (where X = T and Q). Temperature- and pressure-dependent rate constants are calculated using RRKM theory with a Master Equation analysis, with restricted energies used for minima on the simplified (C)over dot(5)H(9) PES and unrestricted energies for other species, over a temperature range of 300-2000 K and in the pressure range 0.01-100 atm. The rate constants calculated are in good agreement with those in the literature. The chemical kinetic model is updated with pressure-dependent rate constants and is used to simulate the species concentration profiles for H. atom addition to cyclopentane and cyclopentene. Through detailed analyses and comparisons, this model can reproduce the experimental measurements of species qualitatively and quantitatively with reasonably good agreement.This study is supported by Science Foundation Ireland and the China Scholarship Council (CSC). The authors want to acknowledge the financial support of Science Foundation Ireland under Grant No. 15/IA/3177 and 16/SP/3829, and the provision of computational resources from ICHEC under the NUI Galway shared condominium accounts. The Computational resources are provided by the Irish Centre for High-End Computing (ICHEC), under project number ngche063c, ngcom006c and ngche058c. The authors are grateful to Stephen Klippenstein for the help with MESS code study. Chong-Wen Zhou acknowledges the support from National Science and Technology Major Project (2017-III-0004-0028) and Beihang University under the Fundamental Research Funds.peer-reviewed2021-05-1