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- ItemDNAzymes as Catalysts for l-Tyrosine and Amyloid β Oxidation(Washington, DC : ACS Publications, 2020) Köhler, Tony; Patsis, Panagiotis A.; Hahn, Dominik; Ruland, André; Naas, Carolin; Müller, Martin; Thiele, JulianSingle-stranded deoxyribonucleic acids have an enormous potential for catalysis by applying tailored sequences of nucleotides for individual reaction conditions and substrates. If such a sequence is guanine-rich, it may arrange into a three-dimensional structure called G-quadruplex and give rise to a catalytically active DNA molecule, a DNAzyme, upon addition of hemin. Here, we present a DNAzyme-mediated reaction, which is the oxidation of l-tyrosine toward dityrosine by hydrogen peroxide. With an optimal stoichiometry between DNA and hemin of 1:10, we report an activity of 101.2 ± 3.5 μUnits (μU) of the artificial DNAzyme Dz-00 compared to 33.0 ± 1.8 μU of free hemin. Exemplarily, DNAzymes may take part in neurodegeneration caused by amyloid beta (Aβ) aggregation due to l-tyrosine oxidation. We show that the natural, human genome-derived DNAzyme In1-sp is able to oxidize Aβ peptides with a 4.6% higher yield and a 33.3% higher velocity of the reaction compared to free hemin. As the artificial DNAzyme Dz-00 is even able to catalyze Aβ peptide oxidation with a 64.2% higher yield and 337.1% higher velocity, an in-depth screening of human genome-derived DNAzymes may identify further candidates with similarly high catalytic activity in Aβ peptide oxidation.
- ItemAerobic iron-catalyzed site-selective C(sp3)–C(sp3) bond cleavage in N-heterocycles(Amsterdam : Elsevier, 2021) Leonard, David K.; Li, Wu; Rockstroh, Nils; Junge, Kathrin; Beller, MatthiasThe kinetic and thermodynamic stability of C(sp3)–C(sp3) bonds makes the site-selective activation of these motifs a real synthetic challenge. In view of this, herein a site-selective method of C(sp3)–C(sp3) bond scission of amines, specifically morpholine and piperazine derivatives, using a cheap iron catalyst and air as a sustainable oxidant is reported. Furthermore, a statistical design of experiments (DoE) is used to evaluate multiple reaction parameters thereby allowing for the rapid development of a catalytic process. © 2021
- ItemEvaluation of Sonocatalytic and Photocatalytic Processes Efficiency for Degradation of Humic Compounds Using Synthesized Transition-Metal-Doped ZnO Nanoparticles in Aqueous Solution(New York, NY [u.a.] : Hindawi, 2021) Maleki, Afshin; Seifi, Mehran; Marzban, NaderThe existence of a humic substance in water causes the growth of microorganisms and reduces the quality of water; therefore, the removal of these materials is crucial. Here, the ZnO nanoparticles doped using transition metals, copper (Cu) and manganese (Mn), were used as an effective catalyst for photocatalytic removal of humic substances in an aqueous environment under ultraviolet, visible light, and light-emitting diode irradiations. Also, we study the effect of the sonocatalytic method. A solvothermal procedure is used for doping, and the Cu- and Mn-doped ZnO nanocatalyst were characterized by means of FTIR, XRD, AFM, SEM, and EDAX analyses. We investigate the effect of operational variables, including doping ratio, initial pH, catalyst dose, initial HS content, and illuminance on the removal efficiency of the processes. The findings of the analyses used for the characterization of the nanoparticles illustrate the appropriate synthesis of the Cu- and Mn-doped ZnO nanocatalysts. We observe the highest removal efficiency rate under acidic conditions and the process efficiency decreased with increasing solution pH, when we tested it in the range of 3–7. Photocatalytic decomposition of HS increases with a rise in catalyst dose, but an increase in initial HS content results in decreasing the removal efficiency. We observe the highest photocatalytic degradation of humic acid while using the visible light, and the highest removal efficiency is obtained using Cu.ZnO. The Cu.ZnO also shows better performance under ultraviolet irradiation compared to other agents.
- ItemMedical gas plasma promotes blood coagulation via platelet activation(Amsterdam [u.a.] : Elsevier, 2021) Bekeschus, Sander; Poschkamp, Broder; van der Linde, JuliaMajor blood loss still is a risk factor during surgery. Electrocauterization often is used for necrotizing the tissue and thereby halts bleeding (hemostasis). However, the carbonized tissue is prone to falling off, putting patients at risk of severe side effects, such as dangerous internal bleeding many hours after surgery. We have developed a medical gas plasma jet technology as an alternative to electrocauterization and investigated its hemostatic (blood clotting) effects and mechanisms of action using whole human blood. The gas plasma efficiently coagulated anticoagulated donor blood, which resulted from the local lysis of red blood cells (hemolysis). Image cytometry further showed enhanced platelet aggregation. Gas plasmas release reactive oxygen species (ROS), but neither scavenging of long-lived ROS nor addition of chemically-generated ROS were able to abrogate or recapitulate the gas plasma effect, respectively. However, platelet activation was markedly impaired in platelet-rich plasma when compared to gas plasma-treated whole blood that moreover contained significant amounts of hemoglobin indicative of red blood cell lysis (hemolysis). Finally, incubation of whole blood with concentration-matched hemolysates phenocopied the gas plasmas-mediated platelet activation. These results will spur the translation of plasma systems for hemolysis into clinical practice.
- ItemThe Importance of the Representation of DMS Oxidation in Global Chemistry‐Climate Simulations(Hoboken, NJ : Wiley, 2021) Hoffmann, Erik Hans; Heinold, Bernd; Kubin, Anne; Tegen, Ina; Herrmann, HartmutThe oxidation of dimethyl sulfide (DMS) is key for the natural sulfate aerosol formation and its climate impact. Multiphase chemistry is an important oxidation pathway but neglected in current chemistry-climate models. Here, the DMS chemistry in the aerosol-chemistry-climate model ECHAM-HAMMOZ is extended to include multiphase methane sulfonic acid (MSA) formation in deliquesced aerosol particles, parameterized by reactive uptake. First simulations agree well with observed gas-phase MSA concentrations. The implemented formation pathways are quantified to contribute up to 60% to the sulfate aerosol burden over the Southern Ocean and Arctic/Antarctic regions. While globally the impact on the aerosol radiative forcing almost levels off, a significantly more positive solar radiative forcing of up to +0.1 W m−2 is computed in the Arctic (>60°N). The findings imply the need of both further laboratory and model studies on the atmospheric multiphase oxidation of DMS.
- ItemRuthenacycles and Iridacycles as Transfer Hydrogenation Catalysts(Basel : MDPI, 2021) Ritleng, Vincent; de Vries, Johannes G.In this review, we describe the synthesis and use in hydrogen transfer reactions of ruthenacycles and iridacycles. The review limits itself to metallacycles where a ligand is bound in bidentate fashion to either ruthenium or iridium via a carbon-metal sigma bond, as well as a dative bond from a heteroatom or an N-heterocyclic carbene. Pincer complexes fall outside the scope. Described are applications in (asymmetric) transfer hydrogenation of aldehydes, ketones, and imines, as well as reductive aminations. Oxidation reactions, i.e., classical Oppenauer oxidation, which is the reverse of transfer hydrogenation, as well as dehydrogenations and oxidations with oxygen, are described. Racemizations of alcohols and secondary amines are also catalyzed by ruthenacycles and iridacycles.