Organosulfur chemistry | EPFL Graph Search

Organosulfur chemistry is the study of the properties and synthesis of organosulfur compounds, which are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulfur is vital for life. Of the 20 common amino acids, two (cysteine and methionine) are organosulfur compounds, and the antibiotics penicillin and sulfa drugs both contain sulfur. While sulfur-containing antibiotics save many lives, sulfur mustard is a deadly chemical warfare agent. Fossil fuels, coal, petroleum, and natural gas, which are derived from ancient organisms, necessarily contain organosulfur compounds, the removal of which is a major focus of oil refineries. Sulfur shares the chalcogen group with oxygen, selenium, and tellurium, and it is expected that organosulfur compounds have similarities with carbon–oxygen, carbon–selenium, and carbon–tellurium compounds

Hydrothermally Stable Sulfonated Carbons as Solid Acid Catalysts for the Hydrolysis of Lignocellulose

David Ferdinand Scholz

The recycling of homogeneous acids imposes great challenges to the feasibility of lignocellulose hydrolysis processes. Although heterogeneous catalysts would offer a perspective to circumvent these challenges, conventional solid acids are instable under the hydrothermal conditions typical of hydrolysis processes. In this regard, acid functionalized carbons appear as auspicious alternatives due to the higher perseverance of carbon frameworks. The strong Brønsted acid sites in sulfonated carbons would be particularly well suited to catalyze the hydrolysis of cellulosic biomass. The utilization of these materials has so far been impeded by the controversy regarding the stability of sulfonic acid groups in carbons. Furthermore, it remains uncertain how the constraints imposed on the reaction system by the insolubility of lignocellulose influence the ability of solid acids to function as hydrolysis catalysts. This thesis shows that hydrothermally stable sulfonated carbons can be prepared by utilizing the structure-stability dependence of sulfonic acid groups in carbonaceous materials. The sulfonation of materials featuring a low degree of graphitization resulted in active solid Brønsted acid catalysts that however deactivated through the leaching of sulfonic acid groups. An in-depth physicochemical characterization of the catalysts paired with a systematic study of the stability of model sulfonic acids, revealed that the leaching-tendency is defined by substituent effects. Activating/deactivating substituents control the hydrothermal stability of aryl sulfonic acids by decreasing/increasing the tendency of the carbon-sulfur bond to undergo solvolysis. The presence of stabilizing and destabilizing substituents was found to be tunable by the temperature dependent decomposition of oxygen containing surface groups. Sulfonation of cellulose carbonized at 350°C resulted in a catalyst with 850 µmol g-1 hydrothermally (180 °C) stable sulfonic acid groups. Additionally, a hitherto unknown mode of deactivation was identified that proceeds by the ion-exchange of cationic impurities with protons of the active sites. This mode of deactivation can be fully overcome by implementing countermeasures to reverse or suppress ion-exchange processes. To tackle the limitations of homogeneous acids, the stable sulfonated carbons were used as catalysts in a semi-batch based lignocellulose hydrolysis process. It was found that the chemical recalcitrance and the insolubility of the substrate imposed strong limitations on the reaction with the catalyst and that soluble product formation occurred predominantly via auto-hydrolysis. The propensity of cellulose to undergo auto-hydrolysis could be enhanced by amorphizing its crystal structure through mechanical pretreatment in ball-mill. A heterogeneously catalyzed hydrolysis was achieved through mechanocatalytic processes facilitated by the concerted ball-milling (CBM) of the sulfonated carbon with the substrate. Sulfonic acid groups were pinpointed as active sites during the mechanocatalytic formation of soluble oligosaccharides. The secondary hydrolysis to monosaccharides in the semi-batch reactor was no longer constrained by the insolubility of the substrate. The combination of CBM pretreatment and hydrolysis in the semi-batch reactor was successfully extrapolated to the conversion of spruce fir wood to achieve yields in C5 and C6 derived products that are competitive with state-of-the-art diluted acid processes.

EPFL2019

Versatile Route to trans-Platinum(II) Complexes via Manipulation of a Coordinated 3-(Pyridin-3-yl)propanoicAcid Ligand

Paul Joseph Dyson, Marta Maroto Diaz, Tina Riedel

We describe the direct coupling of alcohols and amines to a 3-(pyridin-3-yl)propanoic acid ligand coordinated to a Pt(II) to afford ester and amide derivatives. Using this approach, a family of trans-Pt(II) compounds with amine ligands bearing long perfluorinated chains was prepared, as these chains potentially endow the complexes with thermoactivatable properties. Related compounds with alkyl chains in place of the perfluorinated chains were also prepared as controls using the same direct coupling method. The stability of the complexes in solution, their reactivity with DNA and proteins, and their antiproliferative activity evaluated in tumorigenic (A2780 and A2780cisR) and nontumorigenic (HEK293) cells at 37 degrees C and following exposure to elevated temperatures (that mimic the temperatures employed in thermotherapy) were also studied to assess their utility as putative (thermoactivated) anticancer agents.

2019

Application of Hypervalent Iodine Reagents for Novel Cysteine Labeling

Romain Gaëtan Tessier

Selective functionalization of peptides and proteins has always been a valuable tool for the study and manipulation of biological processes. In this context, cysteines are of particular interest. Their intrinsic high nucleophilicity makes these amino acids excellent targets for peptides and proteins modification. As a result, cysteine labeling techniques have been extensively investigated. Nevertheless, while bioconjugation requires high efficiency, selectivity and kinetic under mild and aqueous conditions, most of the reported methodologies exhibit significant limitations. For instance, lack of chemoselectivity, as well as low or uncontrolled reactivity, are frequently reported. Furthermore, many of these methods rely on reagents challenging to prepare, store and use. In this regard, hypervalent iodine reagents are attractive. Heterocyclic Î»3-iodanes demonstrated high reactivity and selectivity, together with great stability and low toxicity. Nevertheless, applications to peptides and proteins modification remain rare. Employing ethynylbenziodoxolone reagents (EBXs), we previously described an efficient and chemoselective alkynylation of organosulfur compounds. The process was performed under âopen-flaskâ conditions, at room temperature, without any metal- or additive-assistance. In collaboration with Dr. Adibekian and co-workers, we then employed this methodology to intracellular proteomic profiling of cysteine residues. Nevertheless, only the most reactive cysteines were efficiently labeled. Accordingly, the goal of my thesis was to investigate the reactivity between any cysteine residues and EBX reagents, under mild and aqueous conditions. We started our investigations with treatment of glutathione, a naturally occurring tripeptide, with an azide-containing EBX reagent. Although a complete conversion of the starting material was observed, the corresponding thioalkyne product was not formed. Instead, we observed thiol-yne reactivity and selective thiol trans-addition in Î²-position of the EBX reagent, leading to vinylbenziodoxolone product (VBX). This efficient cysteine labeling exhibited high selectivity, fast kinetic and great robustness. Various cysteine-containing peptides and proteins, along with diverse EBX reagents, were well tolerated. When an azide-containing EBX reagent was employed, strain-promoted azide-alkyne cycloadditions (SPAAC) were successfully achieved. Alternatively, the hypervalent iodine function was engaged in aqueous Suzuki-Miyaura cross-couplings. Various boronic acids, containing electron-rich and âdeficient aryls, heteroaryls and vinyls, were successfully subjected to this palladium-promoted process. Remarkably, both SPAAC and cross-coupling were orthogonal to each other. We then investigated the singular reactivity of the TMS-EBX reagent. Under basic aqueous conditions, we observed fast desilylation of the hypervalent iodine reagent. Upon glutathione treatment, the resulting EBX substrate was engaged in a thiol-yne reaction. Nevertheless, the corresponding VBX product exhibited a low stability and led to alkynylated glutathione. Further optimization furnished an efficient, selective and rapid ethynylation of numerous cysteine-containing peptides.

EPFL2019

Hydrothermally Stable Sulfonated Carbons as Solid Acid Catalysts for the Hydrolysis of Lignocellulose

David Ferdinand Scholz

EPFL2019

Application of Hypervalent Iodine Reagents for Novel Cysteine Labeling

Romain Gaëtan Tessier

EPFL2019