Facilely Prepared Cl-Doped Graphene as an Efficient Anode for the Electrochemical Catalytic Degradation of Acetaminophen

The application of electrochemical catalytic oxidation in wastewater treatment with powerful Cldoped graphene as an anode has been discussed as a novel approach to degrade acetaminophen effectively. The characteristics of Cl-doped graphene that were related to Cl loading content and microscopic morphology were analyzed by using several instruments, and the defects created by Cl doping were identified. Quenching experiments and electron paramagnetic resonance detection were proposed to clarify the mechanism underlying the production of active free radicals by Cldopedgraphene. The degradation results indicated that efficiency increased with the percentage of Cl atoms doped into the graphene. The best degradation efficiency of acetaminophen could reach 98% when Cl-GN-12 was used. In the process of electrocatalytic oxidation, O•−2, and active chlorine, as the main active species, persistently attacked acetaminophen into open-ring intermediates, such as 4-chlororesorcinol, and finally into CO2 and H2O.

Aqueous chemical bleaching of 4-nitrophenol brown carbon by hydroxyl radicals; products, mechanism and light absorptivity

The reaction of hydroxyl radicals (OH) with 4-nitrophenol (4-NP) in the aqueous solution was investigated at pH = 2 and 9. As a result, the molar yield of the phenolic products was measured to be 0.20 ± 0.05 at pH = 2 and 0.40 ± 0.1 at pH = 9. The yield of 4-nitrocatechol (4-NC) was higher at pH = 9; at the same time, a lower number of phenolic products was observed due to the hydrolysis and other irreversible reactions at pH > 7. Mineralization investigated with total organic carbon (TOC) technique showed that after 4-NP was completely consumed approx. 85 % of the organic carbon remained in the aqueous solution. Hence, up to 65 % of the organic carbon that remained in the aqueous solution accounted for the open-ring non-phenolic products. The light absorptivity of the reaction solution between 250 and 600 nm decreased as a result of OH reaction with 4-NP. At the same time, 4-NP solution showed some resistance to chemical bleaching due to the formation of the light-absorbing by-products. This phenomenon effectively prolongs the time-scale of chemical bleaching or 4-NP via reaction with OH by a factor of 3–1.5 at pH 2 and 9, respectively. The experimental data acquired indicated that both photolysis and reaction with OH can be important removal processes of the atmospheric brown-carbon from the aqueous particles containing 4-NP.

Rad24-RFC loads the 9-1-1 clamp by inserting DNA from the top of a wide-open ring, opposite the mechanism of RFC/PCNA

ABSTRACTIn response to DNA damage, the ring-shaped 9-1-1 clamp is loaded onto 5’ recessed DNA to arrest the cell cycle and activate the DNA damage checkpoint. The 9-1-1 clamp is a heterotrimeric ring that is loaded in S. cerevisiae by Rad24-RFC, an alternative clamp loader in which Rad24 replaces the Rfc1 subunit in the RFC1-5 clamp loader of PCNA. Unlike RFC that loads the PCNA ring onto a 3’-ss/ds DNA junction, Rad24-RFC loads the 9-1-1 ring onto a 5’-ss/ds DNA junction, a consequence of DNA damage. The underlying 9-1-1 clamp loading mechanism has been a mystery. Here we report two 3.2-Å cryo-EM structures of Rad24-RFC bound to DNA and either a closed or 27 Å open 9-1-1 clamp. The structures reveal a completely unexpected mechanism by which a clamp can be loaded onto DNA. The Rad24 subunit specifically recognizes the 5’-DNA junction and holds ds DNA outside the clamp loader and above the plane of the 9-1-1 ring, rather than holding DNA inside and below the clamp as in RFC. The 3’ ssDNA overhang is required to obtain the structure, and thus confers a second DNA binding site. The bipartite DNA binding by Rad24-RFC suggests that ssDNA may be flipped into the open 9-1-1 ring, similar to ORC-Cdc6 that loads the Mcm2-7 ring on DNA. We propose that entry of ssDNA through the 9-1-1 ring triggers the ATP hydrolysis and release of the Rad24-RFC. The key DNA binding residues are conserved in higher eukaryotes, and thus the 9-1-1 clamp loading mechanism likely generalizes.

Wideband monopole antenna with dual band rejection characteristics

A wideband printed monopole antenna with two rejection bands is proposed in this article. The antenna provides a wideband from 5.4 GHz to 17.2 GHz with two rejection bands covering 6.9 to 7.4 GHz and 8.3 to 9.2 GHz with two peak notch frequencies of 7.2 GHz and 8.6 GHz respectively. Tested peak gain at two peak notch frequencies of 7.2 GHz and 8.6 GHz are 2.5 dBi and −1.5 dBi respectively. These two rejection bands are effectively used to avoid undesired intrusion from the C band and the X band. The lower rejection band has been realized by cutting an open ring circular slot on the metal patch whereas U like slot has been inserted on the ground plane just beneath the feed line to achieve the upper rejection band. Simulated and tested S 11 parameter, gain, radiation efficiency, E-H radiation patterns, and surface currents of the antenna are presented here. The antenna uses small dimensions and it is very simple to design. The proposed antenna confirms that it is useful for short-range and fast data communication systems.

The Role of Non-Enzymatic Degradation of Meropenem—Insights from the Bottle to the Body

Several studies have addressed the poor stability of meropenem in aqueous solutions, though not considering the main degradation product, the open-ring metabolite (ORM) form. In the present work, we elucidate the metabolic fate of meropenem and ORM from continuous infusion to the human bloodstream. We performed in vitro infusate stability tests at ambient temperature with 2% meropenem reconstituted in 0.9% normal saline, and body temperature warmed buffered human serum with 2, 10, and 50 mg/L meropenem, covering the therapeutic range. We also examined meropenem and ORM levels over several days in six critically ill patients receiving continuous infusions. Meropenem exhibited a constant degradation rate of 0.006/h and 0.025/h in normal saline at 22 °C and serum at 37 °C, respectively. Given that 2% meropenem remains stable for 17.5 h in normal saline (≥90% of the initial concentration), we recommend replacement of the infusate every 12 h. Our patients showed inter-individually highly variable, but intra-individually constant molar ORM/(meropenem + ORM) ratios of 0.21–0.52. Applying a population pharmacokinetic approach using the degradation rate in serum, spontaneous degradation accounted for only 6% of the total clearance.

A Metabolomics and Molecular Networking Approach to Elucidate the Structures of Secondary Metabolites Produced by Serratia marcescens Strains

An integrated approach that combines reverse-phase high-performance liquid chromatography (RP-HPLC), electrospray ionization mass spectrometry, untargeted ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MSE) and molecular networking (using the Global Natural Products Social molecular network platform) was used to elucidate the metabolic profiles and chemical structures of the secondary metabolites produced by pigmented (P1) and non-pigmented (NP1) Serratia marcescens (S. marcescens) strains. Tandem mass spectrometry-based molecular networking guided the structural elucidation of 18 compounds for the P1 strain (including 6 serratamolides, 10 glucosamine derivatives, prodigiosin and serratiochelin A) and 15 compounds for the NP1 strain (including 8 serratamolides, 6 glucosamine derivatives and serratiochelin A) using the MSE fragmentation profiles. The serratamolide homologues were comprised of a peptide moiety of two L-serine residues (cyclic or open-ring) linked to two fatty acid chains (lengths of C10, C12, or C12:1). Moreover, the putative structure of a novel open-ring serratamolide homologue was described. The glucosamine derivative homologues (i.e., N-butylglucosamine ester derivatives) consisted of four residues, including glucose/hexose, valine, a fatty acid chain (lengths of C13 – C17 and varying from saturated to unsaturated) and butyric acid. The putative structures of seven novel glucosamine derivative homologues and one glucosamine derivative congener (containing an oxo-hexanoic acid residue instead of a butyric acid residue) were described. Moreover, seven fractions collected during RP-HPLC, with major molecular ions corresponding to prodigiosin, serratamolides (A, B, and C), and glucosamine derivatives (A, C, and E), displayed antimicrobial activity against a clinical Enterococcus faecalis S1 strain using the disc diffusion assay. The minimum inhibitory and bactericidal concentration assays however, revealed that prodigiosin exhibited the greatest antimicrobial potency, followed by glucosamine derivative A and then the serratamolides (A, B, and C). These results provide crucial insight into the secondary metabolic profiles of pigmented and non-pigmented S. marcescens strains and confirms that S. marcescens strains are a promising natural source of novel antimicrobial metabolites.