"Laser flash spectroscopy of photosystem II" Photosystem II (PS II) of plants and cyanobacteria oxidizes water in a light-powered reaction. Thereby, this protein is the ultimate source of the atmospheric oxygen. The capacity to oxidize water is owed to two properties of PS II: (i) The midpoint potential of the oxidizing chlorophyll moiety is increased by 0.6 V compared to photosystem I or photochemical reaction centers of anoxygenic bacteria, and (ii) the energy requirements of the four steps needed for the tetravalent oxidation of water are adapted to the energy of red light quanta. This thesis deals with two particular aspects, namely: 1. The coupling of the electron transfer from tyrosine Z (YZ) to the primary donor (P680+) to proton transfer, and an inquiry on the role of a positive charge on YZox (plus base cluster) in increasing the oxidizing potential at the catalytic site. 2. The localization of the electron hole, P680+, among the excitonically coupled four inner chlorophyll a molecules, and an estimation of the midpoint potential differences between them. Electron-proton-coupling by YZ This study was carried out with PS II core complexes from spinach or pea with a deactivated (removed) manganese cluster. The reduction of P680+ was investigated as a function of pH by detecting the laser flash induced absorption changes with nanosecond resolution. Two kinetic components were found with different pH-dependence and activation energies. The alteration of kinetic parameters by H/D isotope substitutions or by addition of divalent cations implied two different types of YZ-oxidation: At acidic pH the electron transfer was coupled with proton transfer, whereas in the alkaline region it was more rapid and no longer controlled by proton transfer. The conversion between both mechanisms occured at pH 7.4. This value corresponds either to the apparent pK of YZ itself (i.e. of the hydroxy group of the phenol ring) or to the pK of an acid-base-cluster, which includes YZ. Independent measurements of pH-transients by following the absorption changes of hydrophilic proton indicators corroborated this notion. The data were interpreted as indicating that the phenolic proton of YZ was released into the medium at acidic, but not at alkaline pH. The electron transfer and proton release characteristics of intact, oxygen-evolving PS II resembled those in deactivated samples kept at alkaline pH. We concluded that the electron transfer from YZ to P680+ in the native system was not coupled with proton transfer into the bulk. This has shed doubt on a popular hypothesis on the role of YZ as 'hydrogen abstractor' from bound water. On the other hand, the energetic constraints of water oxidation could be eased by the positive upcharging during oxidation of YZox plus its base cluster. On the localization of the electron hole of P680+ Photooxidation of PS II oxidizes the set of four innermost chlorophyll a molecules giving rise to the only spectroscopically defined species P680+. The deconvolution of difference spectra into bands of pigments is ambiguous. By using photoselective excitation of antennae, i.e. chl a molecules with site specific energies at the long wavelength border of the mean Qy-band, and by polarized detection, it was possible to tag P680+QA-/P680QA and 3P680/P680 difference spectra with a further parameter, the (wavelength-dependent) anisotropy r. Results obtained at liquid nitrogen temperature (77 K) can be clearly interpreted in terms of two chl a monomer bands. The two main components of the P680+QA-/P680QA difference spectrum were marked by two distinct values of the anisotropy and could be interpreted in a straightforward manner: the bleaching of a band at 675 nm belonging to the charged species (chl a+) and an electrochromic blue-shift of a nearby chl a from 684 to 682 nm. The main bleaching band of the 3P680/P680 spectrum (at 77 K) can be apparently attributed to a third (or several) chl a component(s). The analysis of the P680+QA-/P680QA spectrum at cryogenic temperature is compatible with monomeric chl a bands. On the other hand, one could assume a system of excitonically coupled core pigments, as it was recently introduced in the literature on the basis of energy transfer studies ('multimer model'). However, in view of the clear indications for an electrochromic band shift and the location of the bleaching band, which absorbs in a wavelength region of monomeric chl a, one assumption of the 'multimer model' should be questioned. Presumably, the excitonic couplings are rather weak, in particular between each of the two central chl a-molecules (PA/PB) and its respective accessory chl a (BA/BB), because of (i) the distances and (ii) different site energies of the monomeric chromophores. At room temperature, the absorption difference and anisotropy spectra of P680+QA-/P680QA were clearly altered. The anisotropy data indicated that the changes could no longer exclusively be ascribed to thermal broadening of individual bands. The localization of the positive charge on one pigment, analogous to the situation at 77 K, was now unlikely. Hence, the midpoint potential differences between the inner four chlorophyll a molecules were small and were estimated as approximately 15 meV.

Les détails du mécanisme d’une réaction acidobasique sont encore nébuleux au sein de la communauté scientifique. Les résultats présentés dans cet ouvrage suggèrent un modèle mécanistique général basé sur la théorie de l’état de transition pour une réaction acidobasique en milieu aqueux. Ce modèle est proposé après l’analyse méticuleuse de 56 simulations mettant en avant-plan une réaction de transfert de proton entre le phénol et l’acétate dans l’eau. Cette réaction passe par différents nombres d’acteurs, incluant l’acide, la base et le nombre de molécules d’eau impliquées dans le transfert. Ce modèle général regroupe de nombreux mécanismes par lesquels le transfert de proton survient. Il s’agit notamment de procédés impliquant différents nombres de molécules d’eau intermédiaires (1, 2, 3, 4 ou 5), mais aussi des cas où l’acide entre en contact direct avec la base et des cas où la déprotonation de l’acide semble indépendante de la base. Cette proposition présente aussi une nouvelle définition quantitative des mécanismes concerté et séquentiel jusqu’ici différenciés qualitativement dans la littérature. / The details of the acid-base reaction mechanism are still rather vague among the scientific community. The results shown in this document suggest a general mechanism predicated on the transition state theory for the acid-base reaction in an aqueous environment. This model is offered after a meticulous analysis of 56 computational simulations presenting a proton transfer reaction between a phenol derivative and the acetate ion in water. The number of actors greatly varies from one reaction to another, including the acid, the base and the numerous water molecules engaged in the transfer. This general model encompasses many sub-mechanisms leading to the proton transfer completion. Mostly, the processes involve different amounts of bridging water molecules (1, 2, 3, 4 or 5). Yet, it also showcases scenarios where the acid interacts directly with the base and some situations where the acid deprotonation seems to behave independently from the base. This proposal further offers a new, quantitative distinction between the concerted and sequential mechanisms rather than the until-now qualitative description in the literature.

No description available.

Anthropogenic emissions into the troposphere can impact air quality, leading to poorer health outcomes in the affected areas. Volatile organic compounds (VOCs) are a group of chemical compounds, including some which are toxic, that are precursors in the formation of ground-level ozone and secondary organic aerosols. VOCs have a variety of sources, and the distribution of atmospheric VOCs differs significantly over time and space. Historically, the large number of chemical species present at low concentrations (parts-per-trillion to parts-per-billion by volume) have made VOCs difficult to measure in ambient air. However, with improvements in analytical instrumentation, these measurements are becoming more common place. Direct mass spectrometry (MS), such as membrane introduction mass spectrometry (MIMS) and proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) facilitate real-time, continuous measurements of VOCs in air, with full scan mass spectral data capturing changes in chemical composition with high temporal resolution. Operated on-road, mobilized direct MS has been used for quantitative mapping of VOCs at the neighborhood scale, but identifying VOC sources based on the observed mixture of molecules in the full scan MS dataset has yet to be explored. This dissertation describes the use of chemometric techniques to interrogate full scan MS data, and the progression from discriminating VOC samples of known chemical composition based on full scan MIMS data through to the apportionment of VOC sources measured continuously with a PTR-ToF-MS system operating in a moving vehicle. Lab‐constructed VOC samples of known chemical composition and concentration demonstrated the use of principal component analysis (PCA) to discriminate, and k-nearest neighbours to classify, samples based on normalized full scan MIMS data. Furthermore, multivariate curve resolution-alternating least squares (MCR-ALS) was used to resolve mixtures into molecular component contributions. PCA was also used to discriminate ‘real-world’ VOC mixtures (e.g., woodsmoke VOCs, headspace above aqueous hydrocarbon samples) of unknown chemical composition measured by MIMS. Using vehicle mounted MIMS and PTR-ToF-MS systems, full scan MS data of ambient atmospheric VOCs were collected and PCA was applied to the normalized full scan MS data. A supervised analysis performed PCA on samples collected near known VOC sources, while an unsupervised analysis using PCA followed by cluster analysis was used to identify groups in a continuous, time series PTR-ToF-MS dataset measured between Nanaimo and Crofton, British Columbia (BC). In both the supervised and unsupervised analysis, samples impacted by emissions from different sources (e.g., internal combustion engines, sawmills, composting facilities, pulp mills) were discriminated. With PCA, samples were discriminated based on differences in the observed full scan MS data, however real-world samples are often impacted by multiple VOC sources. MCR-weighted ALS (MCR-WALS) was applied to the continuous, time series PTR-ToF-MS data from three field campaigns on Vancouver Island, BC for source apportionment. Variable selection based on signal-to-noise ratios was used to reduce the mass list while retaining the observed m/z that capture changes in the mixture of VOCs measured, improving model results, and reducing computation time. Both point (e.g., anthropogenic hydrocarbon emissions, pulp mill emissions) and diffuse (e.g., VOCs from forest fire smoke) VOC sources were identified in the data, and were apportioned to determine their contributions to the measured samples. The data analyzed captured fine scale changes in the ambient VOCs present in the air, and geospatial maps of each individual source, and of the source apportionment were used to visualize the distribution of VOC sources across the sampling area. This work represents the first use of MCR-WALS to identify and apportion ambient VOC sources based on continuous PTR-ToF-MS data measured from a moving vehicle. The methods described can be applied to larger scale field campaigns for the source apportionment of VOCs across multiple days to capture diurnal and seasonal variations. Identifying spatial and temporal trends in the sources of VOCs at the regional scale can help to identify pollution ‘hot spots’ and inform evidence-based public policy for improving air quality. / Graduate / 2022-08-17

<p>This study is focused on the design, production, and operation of a controlled environmental olfaction chamber to evaluate human physiological and emotional response to volatile chemical emissions (VCPs) from scented household products in addition to careful characterization of the volatile organic compounds (VOCs) present in these product emissions. Utilizing proton transfer reaction time-of-flight mass spectrometry, the chamber can collect VCP emissions and identify VOCs present to complete an accurate chemical profile of household and common product emissions not previously known. This instrument is one of the first of its kind and will serve as a key element in understanding the relationship between human physical and cognitive health and the built environment.</p>

多数の溶媒分子に取り囲まれている溶液中において溶質分子の化学反応素過程を考える場合、溶媒分子による反応の平衡論的、動的な効果を考える必要がある。本研究では、ユニークな反応場として水や有機溶媒とは区別される、超臨界流体とイオン液体をとり上げ、溶質分子のプロトン移動反応、光解離反応について、時間分解レーザー分光と分子動力学計算、理論的解析を行い、その現象を明らかにする試みをおこなった。 / In solution, solvent molecules involve chemical reaction of solute molecules and could alter both reaction yield and kinetics. In this thesis, the author focused on fundamental chemical reactions (intermolecular proton transfer and photodissociate reaction) in a unique class of solvents, supercritical fluids and ionic liquids. By measuring time-resolved fluorescence spectrum and transient absorption spectrum of solutes, the author discusses how the reaction yield and kinetics are described by solvent physicochemical properties. / 博士(理学) / Doctor of Philosophy in Science / 同志社大学 / Doshisha University