An ester bond underlies the mechanical strength of a pathogen surface protein

Gram-positive bacteria can resist large mechanical perturbations during their invasion and colonization by secreting various surface proteins with intramolecular isopeptide or ester bonds. Compared to isopeptide bonds, ester bonds are prone to hydrolysis. It remains elusive whether ester bonds can completely block mechanical extension similarly to isopeptide bonds, or whether ester bonds dissipate mechanical energy by bond rupture. Here, we show that an ester-bond containing stalk domain of Cpe0147 is inextensible even at forces > 2 nN. The ester bond locks the structure to a partially unfolded conformation, in which the ester bond remains largely water inaccessible. This allows the ester bond to withstand considerable mechanical forces and in turn prevent complete protein unfolding. However, the protecting effect might be reduced at non-physiological basic pHs or low calcium concentrations due to destabilizing the protein structures. Inspired by this design principle, we engineer a disulfide mutant resistant to mechanical unfolding under reducing conditions.

Cunninghamella spp. produce mammalian-equivalent metabolites from fluorinated pyrethroid pesticides

Cunninghamella spp. are fungi that are routinely used to model the metabolism of drugs. In this paper we demonstrate that they can be employed to generate mammalian-equivalent metabolites of the pyrethroid pesticides transfluthrin and β-cyfluthrin, both of which are fluorinated. The pesticides were incubated with grown cultures of Cunninghamella elegans, C. blakesleeana and C. echinulata and the biotransformation monitored using fluorine-19 nuclear magnetic resonance spectroscopy. Transfluthrin was initially absorbed in the biomass, but after 72 h a new fluorometabolite appeared in the supernatant; although all three species yielded this compound, it was most prominent in C. blakesleeana. In contrast β-cyfluthrin mostly remained in the fungal biomasss and only minor biotransformation was observed. Gas chromatography-mass spectrometry (GC–MS) analysis of culture supernatant extracts revealed the identity of the fluorinated metabolite of transfluthrin to be tetrafluorobenzyl alcohol, which arose from the cytochrome P450-catalysed cleavage of the ester bond in the pesticide. The other product of this hydrolysis, dichlorovinyl-2,2-dimethylcyclopropane carboxylic acid, was also detected by GC–MS and was a product of β-cyfluthrin metabolism too. Upon incubation with rat liver microsomes the same products were detected, demonstrating that the fungi can be used as models of mammalian metabolism of fluorinated pesticides.

Thermal (In)stability of Atropine and Scopolamine in the GC-MS Inlet

The intoxication due to unintentional or intentional ingestion of plant material containing tropane alkaloids is quite frequent. GC-MS method is still widely used for the identification of these toxicologically important substances in human specimen. During general unknown analysis, high temperature of inlet, at least 270 °C, is commonly used for less volatile substances. Unfortunately, both tropanes are thermally unstable and could be overlooked due to their degradation. The temperature-related degradation of tropanes atropine and scopolamine was systematically studied in the inlet of a GC-MS instrument in the range 110–250 °C by increments of 20 °C, additionally also at 275 °C, and in different solvents. At inlet temperatures not higher than 250 °C, the degradation products were formed by elimination of water and cleavage of atropine’s ester bond. At higher temperatures, elimination of formaldehyde became predominant. These phenomena were less pronounced when ethyl acetate was used instead of methanol, while n-hexane proved unsuitable for several reasons. At an inlet temperature of 275 °C, tropanes were barely detectable. During systematic toxicological analysis, any tropanes’ degradation products should indicate the possible presence of atropine and/or scopolamine in the sample. It is not necessary to prepare thermally stable derivatives for confirmation. Instead, the inlet temperature can be decreased to 250 °C, which diminishes their degradation to a level where their detection and identification are possible. This was demonstrated in several case studies.

Thermal and Mechanical Characterisation of Poly(ω -Hydroxy Pelargonate): A Preliminary Study for Bioplastic

Poly(ω-hydroxy pelargonate) or P(ω-OHP) is a potential biodegradable plastic which was prepared by melt condensation of its monomer (ω-hydroxy pelargonic acid). In this study, the performances of P(ω-OHP) in thermal and mechanical aspects, as well as the method employed for the monomer preparation was presented. Although this type of monomer is well established for pharmaceutical and cosmetic application, its possibility to be applied in bioplastic has not been extensively studied. Previous research also showed that the monomer preparation was rather complicated, expansive, and hazardous. Thus, this study offers the safe method through chemical modification which conducted in mild condition. The monomer structure was verified by using ESI-MS at 173.1 m/z with 92% purity. After melt-condensation process was carried out at 190 °C for 4 h, the formation of P(ω-OHP) was identified by the present of methylene ester bond indicated on 1H NMR peak at 4.05 ppm. The thermal properties were analyzed by DSC, TGA,and rheometer. P(ω-OHP) was melted at 72.8 °C and start to degrade at 220 °C with rheology analysis represented Newtonian flow at 80 and 180 °C.P(ω-OHP) contains 73.5% degree of crystallinity as determined by XRD with fewer amorphous area has affecting low mechanical value in hardness (31) and compressive strength (modulus 47.3 MPa, yield 1.03 MPa). The results suggest that P(ω-OHP) is thermally stable and physically hard and brittle. The findings have implications for bioplastic custom and subjected to improvement via polymer blending or block co-polymerization for application flexibility.

Self-assembled 5-fluorouracil-cinnamaldehyde nanodrugs for greatly improved chemotherapy in vivo

The preferred cancer treatment is to achieve a high therapeutic effect as well as reduce side effects. In this study, we developed carrier-free nano drugs based on 5-fluorouracil (5FU) and cinnamaldehyde (CA) to meet the above goals. Two model drugs were spliced by acetal linkage and ester bond, which could self-assemble into nano drug particles (5FU–CA NPs) with a size of ∼170 nm. In vitro cell experiments showed 5FU–CA NPs were efficiently internalized by HepG2 cells. They then quickly exerted dual drug activities by the cleavage of acetal and ester bond, resulting in enhanced cell-killing efficacy and apoptosis. Synergistic mechanisms were achieved via the anti-metabolic effects mediated by 5FU–COOH and the oxidative damage induced by CA. In vivo anti-tumor evaluation further indicated that 5FU–CA NPs had higher tumor growth inhibition than 5FU–COOH/CA mixture (5FU–COOH + CA) and exhibited lower systemic toxicity under the same reducing dose of each drug. Overall, this is a successful synergistic anti-tumor attempt through rational self-assembly of drugs with different mechanisms and it can be extrapolated to other agents.