Acenaphthoquinoxaline Derivatives as Dental Photoinitiators of Acrylates Polymerization

A series of dyes based on the acenaphthoquinoxaline skeleton was synthesized. Their structure was modified by introducing electron-withdrawing and electron-donating groups, increasing the number of conjugated double bonds and the number and position of nitrogen atoms, as well as the arrangement of aromatic rings (linear or angular). The dyes were investigated as a component in the photoinitiating systems of radical polymerization for a potential application in dentistry. They acted as the primary absorber of visible light and the acceptor of an electron, which was generated from a second component being an electron donor. Thus, the radicals were generated by the photoinduced intermolecular electron transfer (PET) process. Electron donors used differed in the type of heteroatom, i.e., O, S and N and the number and position of methoxy substituents. To test the ability to initiate the polymerization reaction by photoinduced hydrogen atom transfer, we used 2-mercaptobenzoxazole as a co-initiator. The effectiveness of the photoinitiating systems clearly depends on both the modified acenaphthoquinocaline structure and the type of co-initiator. The lower amount of heat released during the chain reaction and the polymerization rate comparable to this achieved for the photoinitiator traditionally used in dentistry (camphorquinone) indicates that the studied dyes may be valuable in this field.

Recent Advances in Electrochemiluminescence and Chemiluminescence of Metal Nanoclusters

Metal nanoclusters (NCs), including Au, Ag, Cu, Pt, Ni and alloy NCs, have become more and more popular sensor probes with good solubility, biocompatibility, size-dependent luminescence and catalysis. The development of electrochemiluminescent (ECL) and chemiluminescent (CL) analytical methods based on various metal NCs have become research hotspots. To improve ECL and CL performances, many strategies are proposed, from metal core to ligand, from intermolecular electron transfer to intramolecular electron transfer. Combined with a variety of amplification technology, i.e., nanostructure-based enhancement and biological signal amplification, highly sensitive ECL and CL analytical methods are developed. We have summarized the research progresses since 2016. Also, we discuss the current challenges and perspectives on the development of this area.

Carnitine metabolism in the human gut: characterization of the two-component carnitine monooxygenase CntAB from Acinetobacter baumannii

Bacterial formation of trimethylamine (TMA) from carnitine in the gut microbiome has been linked to cardiovascular disease. During this process, the two-component carnitine monooxygenase (CntAB) catalyzes the oxygen-dependent cleavage of carnitine to TMA and malic semialdehyde. Individual redox states of the reductase CntB and the catalytic component CntA were investigated based on mutagenesis and electron paramagnetic resonance (EPR) spectroscopic approaches. Protein ligands of the flavin mononucleotide (FMN) and the plant-type [2Fe-2S] cluster of CntB and also of the Rieske-type [2Fe-2S] cluster and the mononuclear [Fe] center of CntA were identified. EPR spectroscopy of variant CntA proteins suggested a hierarchical metallocenter maturation, Rieske [2Fe-2S] followed by the mononuclear [Fe] center. NADH-dependent electron transfer via the redox components of CntB and within the trimeric CntA complex for the activation of molecular oxygen was investigated. EPR experiments indicated that the two electrons from NADH were allocated to the plant-type [2Fe-2S] cluster and to FMN in the form of a flavin semiquinone radical. Single-turnover experiments of this reduced CntB species indicated the translocation of the first electron onto the [Fe] center and the second electron onto the Rieske-type [2Fe-2S] cluster of CntA to finally allow for oxygen activation as a basis for carnitine cleavage. EPR spectroscopic investigation of CntA variants indicated an unusual intermolecular electron transfer between the subunits of the CntA trimer via the “bridging” residue Glu-205. On the basis of these data, a redox catalytic cycle for carnitine monooxygenase was proposed.

Role of N,N-Dimethylglycine and Its Catabolism to Sarcosine in Chromohalobacter salexigens DSM 3043

ABSTRACT Chromohalobacter salexigens DSM 3043 can grow on N,N-dimethylglycine (DMG) as the sole C, N, and energy source and utilize sarcosine as the sole N source under aerobic conditions. However, little is known about the genes and enzymes involved in the conversion of DMG to sarcosine in this strain. In the present study, gene disruption and complementation assays indicated that the csal_0990, csal_0991, csal_0992, and csal_0993 genes are responsible for DMG degradation to sarcosine. The csal_0990 gene heterologously expressed in Escherichia coli was proven to encode an unusual DMG dehydrogenase (DMGDH). The enzyme, existing as a monomer of 79 kDa with a noncovalently bound flavin adenine dinucleotide, utilized both DMG and sarcosine as substrates and exhibited dual coenzyme specificity, preferring NAD+ to NADP+. The optimum pH and temperature of enzyme activity were determined to be 7.0 and 60°C, respectively. Kinetic parameters of the enzyme toward its substrates were determined accordingly. Under high-salinity conditions, the presence of DMG inhibited growth of the wild type and induced the production and accumulation of trehalose and glucosylglycerate intracellularly. Moreover, exogenous addition of DMG significantly improved the growth rates of the four DMG– mutants (Δcsal_0990, Δcsal_0991, Δcsal_0992, and Δcsal_0993) incubated at 37°C in S-M63 synthetic medium with sarcosine as the sole N source. 13C nuclear magnetic resonance (13C-NMR) experiments revealed that not only ectoine, glutamate, and N-acetyl-2,4-diaminobutyrate but also glycine betaine (GB), DMG, sarcosine, trehalose, and glucosylglycerate are accumulated intracellularly in the four mutants. IMPORTANCE Although N,N-dimethylglycine (DMG) dehydrogenase (DMGDH) activity was detected in cell extracts of microorganisms, the genes encoding microbial DMGDHs have not been determined until now. In addition, to our knowledge, the physiological role of DMG in moderate halophiles has never been investigated. In this study, we identified the genes involved in DMG degradation to sarcosine, characterized an unusual DMGDH, and investigated the role of DMG in Chromohalobacter salexigens DSM 3043 and its mutants. Our results suggested that the conversion of DMG to sarcosine is accompanied by intramolecular delivery of electrons in DMGDH and intermolecular electron transfer between DMGDH and other electron acceptors. Moreover, an unidentified methyltransferase catalyzing the production of glycine betaine (GB) from DMG but sharing no homology with the reported sarcosine DMG methyltransferases was predicted to be present in the cells. The results of this study expand our understanding of the physiological role of DMG and its catabolism to sarcosine in C. salexigens.

In Search for Effective and Safe Drugs Against SARS-CoV-2: Part III] the Electronic Factors of Remdesivir and the Naturally Extracted Aspirochlorine Drugs

This report is associated with an ongoing coronavirus outbreak. We selected Remdesivir (used in the treatment of Ebola) and Aspirochlorine (a natural product found in <i>Aspergillus oryzae)</i>, and their binding to specific peptide sequences of the coronavirus S-protein: ACE2 interface-drug binding adduct were calculated. The stable intermolecular adducts between the chosen drug molecules with the S protein and ACE2 result in limited host-virus interactions. The electrophilicity and nucleophilicity indices of the drugs showed that both drugs act as electron sinks to shield ACE2 from interacting with the S protein. Aspirochlorine acts as an electron acceptor (electrophile) toward both individual targets, the ACE2, and S proteins (nucleophiles). Aspirochlorine electronically shields ACE2 from the interaction with S protein by sinking the electronic charge of the S protein. The electrophilicity and nucleophilicity parameters of Remdesivir were higher than those of ACE2, and both molecules were bound via hydrogen bonding intermolecular interactions without intermolecular electron transfer. Remdesivir also shields ACE2 from the S protein. The results obtained strongly suggest the beneficial use of both drugs. The results reported indicate that the association of remdesivir with the target proteins was exothermic, while it was endothermic in the case of Aspirochlorine. Both drugs offer protection and/or treatment against the coronavirus S-protein COVID-19.

In Search for Effective and Safe Drugs Against SARS-CoV-2: Part III] the Electronic Factors of Remdesivir and the Naturally Extracted Aspirochlorine Drugs

This report is associated with an ongoing coronavirus outbreak. We selected Remdesivir (used in the treatment of Ebola) and Aspirochlorine (a natural product found in <i>Aspergillus oryzae)</i>, and their binding to specific peptide sequences of the coronavirus S-protein: ACE2 interface-drug binding adduct were calculated. The stable intermolecular adducts between the chosen drug molecules with the S protein and ACE2 result in limited host-virus interactions. The electrophilicity and nucleophilicity indices of the drugs showed that both drugs act as electron sinks to shield ACE2 from interacting with the S protein. Aspirochlorine acts as an electron acceptor (electrophile) toward both individual targets, the ACE2, and S proteins (nucleophiles). Aspirochlorine electronically shields ACE2 from the interaction with S protein by sinking the electronic charge of the S protein. The electrophilicity and nucleophilicity parameters of Remdesivir were higher than those of ACE2, and both molecules were bound via hydrogen bonding intermolecular interactions without intermolecular electron transfer. Remdesivir also shields ACE2 from the S protein. The results obtained strongly suggest the beneficial use of both drugs. The results reported indicate that the association of remdesivir with the target proteins was exothermic, while it was endothermic in the case of Aspirochlorine. Both drugs offer protection and/or treatment against the coronavirus S-protein COVID-19.