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The replacement of oxygen by sulfur atoms of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes is an efficient way to adjust the photophysical properties (sulfur tuning). While previously developed S-4-DBD dyes exhibit considerably red-shifted absorption and emission wavelength, the heavy atom effect of four sulfur atoms cause low fluorescence quantum yields and short fluorescence lifetimes. Herein, we demonstrate that the replacement of less than four sulfur atoms (S-1-DBD, 1,2-S-2-DBD, and 1,4-S-2-DBD dyes) permits a fine-tuning of the photophysical properties. In some cases, a similar influence on the wavelength without the detrimental effect on the quantum yields and lifetimes is observed. Furthermore, the synthetic accessibility of S-1- and S-2-DBD dyes is improved, compared with S-4-DBD dyes. For coupling with biomolecules a series of reactive derivatives of the new dyes were developed (azides, OSu esters, alkynes, maleimides).
The reliance on fossil fuels has resulted in an abnormal increase in the concentration of greenhouse gases, contributing to the global climate crisis. In response, a rapid transition to renewable energy sources has begun, particularly lithium-ion batteries, playing a crucial role in the green energy transformation. However, concerns regarding the availability and geopolitical implications of lithium have prompted the exploration of alternative rechargeable battery systems, such as sodium-ion batteries. Sodium is significantly abundant and more homogeneously distributed in the crust and seawater, making it easier and less expensive to extract than lithium. However, because of the mysterious nature of its components, sodium-ion batteries are not yet sufficiently advanced to take the place of lithium-ion batteries. Specifically, sodium exhibits a more metallic character and a larger ionic radius, resulting in a different ion storage mechanism utilized in lithium-ion batteries. Innovations in synthetic methods, post-treatments, and interface engineering clearly demonstrate the significance of developing high-performance carbonaceous anode materials for sodium-ion batteries. The objective of this dissertation is to present a systematic approach for fabricating efficient, high-performance, and sustainable carbonaceous anode materials for sodium-ion batteries. This will involve a comprehensive investigation of different chemical environments and post-modification techniques as well.
This dissertation focuses on three main objectives. Firstly, it explores the significance of post-synthetic methods in designing interfaces. A conformal carbon nitride coating is deposited through chemical vapor deposition on a carbon electrode as an artificial solid-electrolyte interface layer, resulting in improved electrochemical performance. The interaction between the carbon nitride artificial interface and the carbon electrode enhances initial Coulombic efficiency, rate performance, and total capacity. Secondly, a novel process for preparing sulfur-rich carbon as a high-performing anode material for sodium-ion batteries is presented. The method involves using an oligo-3,4-ethylenedioxythiophene precursor for high sulfur content hard carbon anode to investigate the sulfur heteroatom effect on the electrochemical sodium storage mechanism. By optimizing the condensation temperature, a significant transformation in the materials’ nanostructure is achieved, leading to improved electrochemical performance. The use of in-operando small-angle X-ray scattering provides valuable insights into the interaction between micropores and sodium ions during the electrochemical processes. Lastly, the development of high-capacity hard carbon, derived from 5-hydroxymethyl furfural, is examined. This carbon material exhibits exceptional performance at both low and high current densities. Extensive electrochemical and physicochemical characterizations shed light on the sodium storage mechanism concerning the chemical environment, establishing the material’s stability and potential applications in sodium-ion batteries.
In this paper, we report X-ray absorption and core-level electron spectra of the nucleobase derivative 2-thiouracil at the sulfur L1- and L2,3-edges. We used soft X-rays from the free-electron laser FLASH2 for the excitation of isolated molecules and dispersed the outgoing electrons with a magnetic bottle spectrometer. We identified photoelectrons from the 2p core orbital, accompanied by an electron correlation satellite, as well as resonant and non-resonant Coster–Kronig and Auger–Meitner emission at the L1- and L2,3-edges, respectively. We used the electron yield to construct X-ray absorption spectra at the two edges. The experimental data obtained are put in the context of the literature currently available on sulfur core-level and 2-thiouracil spectroscopy.
This study introduces a method for multiparallel analysis of small organic compounds in the unicellular green alga Chlamydomonas reinhardtii, one of the premier model organisms in cell biology. The comprehensive study of the changes of metabolite composition, or metabolomics, in response to environmental, genetic or developmental signals is an important complement of other functional genomic techniques in the effort to develop an understanding of how genes, proteins and metabolites are all integrated into a seamless and dynamic network to sustain cellular functions. The sample preparation protocol was optimized to quickly inactivate enzymatic activity, achieve maximum extraction capacity and process large sample quantities. As a result of the rapid sampling, extraction and analysis by gas chromatography coupled to time-of-flight mass spectrometry (GC-TOF) more than 800 analytes from a single sample can be measured, of which over a 100 could be positively identified. As part of the analysis of GC-TOF raw data, aliquot ratio analysis to systematically remove artifact signals and tools for the use of principal component analysis (PCA) on metabolomic datasets are proposed. Cells subjected to nitrogen (N), phosphorus (P), sulfur (S) or iron (Fe) depleted growth conditions develop highly distinctive metabolite profiles with metabolites implicated in many different processes being affected in their concentration during adaptation to nutrient deprivation. Metabolite profiling allowed characterization of both specific and general responses to nutrient deprivation at the metabolite level. Modulation of the substrates for N-assimilation and the oxidative pentose phosphate pathway indicated a priority for maintaining the capability for immediate activation of N assimilation even under conditions of decreased metabolic activity and arrested growth, while the rise in 4-hydroxyproline in S deprived cells could be related to enhanced degradation of proteins of the cell wall. The adaptation to sulfur deficiency was analyzed with greater temporal resolution and responses of wild-type cells were compared with mutant cells deficient in SAC1, an important regulator of the sulfur deficiency response. Whereas concurrent metabolite depletion and accumulation occurs during adaptation to S deprivation in wild-type cells, the sac1 mutant strain is characterized by a massive incapability to sustain many processes that normally lead to transient or permanent accumulation of the levels of certain metabolites or recovery of metabolite levels after initial down-regulation. For most of the steps in arginine biosynthesis in Chlamydomonas mutants have been isolated that are deficient in the respective enzyme activities. Three strains deficient in the activities of N-acetylglutamate-5-phosphate reductase (arg1), N2 acetylornithine-aminotransferase (arg9), and argininosuccinate lyase (arg2), respectively, were analyzed with regard to activation of endogenous arginine biosynthesis after withdrawal of externally supplied arginine. Enzymatic blocks in the arginine biosynthetic pathway could be characterized by precursor accumulation, like the amassment of argininosuccinate in arg2 cells, and depletion of intermediates occurring downstream of the enzymatic block, e.g. N2-acetylornithine, ornithine, and argininosuccinate depletion in arg9 cells. The unexpected finding of substantial levels of the arginine pathway intermediates N-acetylornithine, citrulline, and argininosuccinate downstream the enzymatic block in arg1 cells provided an explanation for the residual growth capacity of these cells in the absence of external arginine sources. The presence of these compounds, together with the unusual accumulation of N-Acetylglutamate, the first intermediate that commits the glutamate backbone to ornithine and arginine biosynthesis, in arg1 cells suggests that alternative pathways, possibly involving the activity of ornithine aminotransferase, may be active when the default reaction sequence to produce ornithine via acetylation of glutamate is disabled.