mild acid
Recently Published Documents

The general stress response (GSR) in Listeria monocytogenes plays a critical role in the survival of this pathogen in the host gastrointestinal tract. The GSR is regulated by the alternative sigma factor B (σB), whose role in protection against acid stress is well established. However, the mechanisms leading to its activation by low pH are unknown. Here, we investigated the involvement of the stressosome, a sensory organelle, in transducing low pH signals to induce the GSR. Mild acid shock (15 min at pH 5.0) activated σB and conferred protection against a subsequent lethal pH challenge. A mutant strain where the stressosome subunit RsbR1 was present but its remaining paralogues were genetically inactivated retained the ability to induce σB activity at pH 5.0. The role of stressosome phosphorylation in signal transduction was investigated by mutating the putative phosphorylation sites in the core stressosome proteins RsbR1 (rsbR1 T175A, T209A, T241A) and RsbS (rsbS S56A), or in the active site of the stressosome kinase RsbT (rsbT N49A). The rsbS S56A and rsbT N49A mutations abolished the response to low pH. The rsbR1 T175A variant, retained a near-wild type phenotype. The rsbR1 T209A and rsbR1 T241A mutants displayed constitutive σB activity. Mild acid shock upregulates invasion genes and stimulates epithelial cell invasion, effects that were abolished in mutants with an inactive or overactive stressosome. Overall, the results show that the stressosome is required for acid-induced activation of σB in L. monocytogenes. Furthermore, RsbR1 can function independently of its paralogues and that signal transduction requires RsbT-mediated phosphorylation of RsbS on S56 and RsbR1 on T209. These insights shed light on the mechanisms of signal transduction that activate the GSR in L. monocytogenes in response to acidic environments, and highlight the role this sensory process in the early stages of the infectious cycle.

Two mono meso-functionalized [20]di-[Formula: see text]-benzihomoporphyrins containing [Formula: see text]-formylphenyl and [Formula: see text]-iodophenyl groups at meso-position respectively were synthesized by condensing one equivalent of appropriate tetrapyrrane with one equivalent of [Formula: see text]-formyl benzaldehyde/[Formula: see text]-iodo benzaldehyde in CH2Cl2 under mild acid catalyzed conditions. The meso-formylphenyl and meso-iodophenyl functionalized di-[Formula: see text]-benzihomoporphyrins were used to synthesize two covalently linked di-[Formula: see text]-benzihomoporphyrins-BODIPY conjugates. The meso-formylphenyl-functionalized di-[Formula: see text]-benzihomoporphyrin was converted to corresponding meso-dipyrrolyl substituted di-[Formula: see text]-benzihomoporphyrin by treating with excess pyrrole under acid catalyzed conditions. In the next step, the meso-dipyrrolyl di-[Formula: see text]-benzihomoporphyrin was subjected to oxidation followed by BF2 complexation to afford the directly linked di-[Formula: see text]-benzihomoporphyrin-BODIPY conjugate. The meso-iodophenyl functionalized di-[Formula: see text]-benzihomoporphyrin was coupled with ethynyl-functionalized BODIPY under mild Pd(0) coupling condition to synthesize diphenylethyne-bridged di-[Formula: see text]-benzihomoporphyrin-BODIPY conjugate. The two conjugates were characterized by HR-MS, NMR, absorption, electrochemical, fluorescence and DFT studies. The spectral and electrochemical studies indicated that the two constituents, di-[Formula: see text]-benzihomoporphyrin and BODIPY units in the conjugates interact weakly and retain their individual characteristic features. DFT studies indicated a possibility of charge transfer between di-[Formula: see text]-benzihomoporphyrin and BODIPY units in conjugates.

The moderately halophilic strain Salinivibrio sp. EG9S8QL was isolated among 11 halophilic strains from saline mud (Emisal Salt Company, Lake Qarun, Fayoum, Egypt). The lipopolysaccharide was extracted from dried cells of Salinivibrio sp. EG9S8QL by the phenol–water procedure. The OPS was obtained by mild acid hydrolysis of the lipopolysaccharide and was studied by sugar analysis along with 1H and 13C NMR spectroscopy, including 1H,1H COSY, TOCSY, ROESY, 1H,13C HSQC, and HMBC experiments. The OPS was found to be composed of linear tetrasaccharide repeating units of the following structure: →2)-β-Manp4Lac-(1→3)-α-ManpNAc-(1→3)-β-Rhap-(1→4)-α-GlcpNAc-(1→, where Manp4Lac is 4-O-[1-carboxyethyl]mannose.

Abstract In horizontal open hole wells, the formation of filter cake while drilling the open hole section of the well is desirable. This filter cake serves the purpose of forming a semi-impervious layer around the reservoir drain-hole. This layer helps reduce losses considering the overbalance required for well control during drilling. It also serves as an additional structural support to keep the open hole stable when the drilling bottom hole assembly (BHA) is pulled out of hole and the screens and lower completions accessories are being run in hole. However, when thewell is put into production, the filter cake becomes a contributor to skin and poor reservoir productivity. It is therefore required to get rid of the filter cake after running the screens and the lower completion. Having procured and prepared the sand screens for deployment after drilling the open hole section, it is important that they are run to the bottom successfully with minimal damage and plugging. Usually, the open hole section of the horizontal well is drilled with specially formulated drill-in-fluids (DIF). Since this section is drilled in over balanced mode, the exerted pressure keeps the hole open so that the sand screen can be run successfully. The DIF replaces the drilling mud used to drill the earlier hole section(s) but in addition to providing well control via overbalance and transporting cuttings from the hole to surface, it also minimizes invasion damage to the reservoir pay zone. A commonly used weighing material when densities up to 11.5ppg are required for well control is calcium carbonate (CaCO3). When densities above 11.5ppg are required (for deeper, abnormally pressured reservoirs), it becomes necessary to weight up the mud with a heavier material, usually barite + CaCO3. During the drilling process, this overbalance pressure exerted on the reservoir forces the CaCO3 out of the DIF solution and it forms a semi-impervious filter cake on the sand face of the reservoir. This desirable filter cake helps minimize excessive fluid losses into the reservoir hence limiting invasion and damage. It also contributes to the structural integrity of the open hole, keeping it stable prior to running of the screens. Depending on the weighting material used in the drilling of the reservoir drain-hole, the micro-emulsion breaker (MEB) can be designed to break down the filter cake and any undisolvedparticulates can be mobilized and water-wetted and can be then flowed during production or injection. The challenge is that depending on the lower completion configuration, it may take some time to get the wash pipe and work string out of the lower completion and close the formation isolation device. In some cases, it is possible for the formation isolation device to fail. If the Micro-emulsion Blend (MEB) is quick acting, any of these scenarios can lead to uncontrollable losses and serious difficulties in continuing the completion operation. This elucidates the need for a delayed acting MEB treatment. Lab tests and analysis involving the exact DIF /filter cake and various compositions of the MEB at downhole conditions to arrive at the required delay in action. It is critical to ensure that the delayed action does not result in reduced efficacy of the treatment. Hence, the MEB is not diluted for slow action but rather it is engineered combinatorially with a retarder and downhole mild acid generating microemulsion chemistry that gradually generates the necessary mild acid that will slowly dissolve the bridging materials (eg. calcium carbonate) in the mud withtime and allows the full strength of the MEB to take effect after the stipulated delay period. This paper will focus on the lab analysis and iterations to arrive at an optimal MEB blend.

High-tech applications require increasing amounts of rare earth elements (REE). Their recovery from low-grade minerals and their recycling from secondary sources (as waste materials) are of critical importance. There is increasing attention paid to the development of new sorbents for REE recovery from dilute solutions. A new generation of composite sorbents based on brown algal biomass (alginate) and polyethylenimine (PEI) was recently developed (ALPEI hydrogel beads). The phosphorylation of the beads strongly improves the affinity of the sorbents for REEs (such as La and Tb): by 4.5 to 6.9 times compared with raw beads. The synthesis procedure (epicholorhydrin-activation, phosphorylation and de-esterification) is investigated by XPS and FTIR for characterizing the grafting route but also for interpreting the binding mechanism (contribution of N-bearing from PEI, O-bearing from alginate and P-bearing groups). Metal ions can be readily eluted using an acidic calcium chloride solution, which regenerates the sorbent: the FTIR spectra are hardly changed after five successive cycles of sorption and desorption. The materials are also characterized by elemental, textural and thermogravimetric analyses. The phosphorylation of ALPEI beads by this new method opens promising perspectives for the recovery of these strategic metals from mild acid solutions (i.e., pH ~ 4).

<p>The recovery of PO<sub>4</sub> from wastewaters by using biochar proves not to be completely satisfactory. The surface of the biochar is typically negatively charged, which prevents the adsorption of PO<sub>4</sub>. For this reason, mixtures of biochar and natural carbonate materials have been tested as a novel sorbent material for PO<sub>4 </sub>recovery from both synthetic-and waste- water. The goal of the research is to obtain a PO<sub>4 </sub>based complex starting from natural second-generation materials such as food industry byproducts, plants and other residues to prepare fertilisers compliant to the component material category CMC 6 defined in the Regulation <strong>(</strong>EU) 2019/1009/EU It has to be noted that natural carbonate materials are not pure CaCO<sub>3</sub>, but present small impurities that contribute to modify their properties. Therefore, the use of carbonate materials obtained from different sources can lead to different performances when it comes to PO<sub>4</sub> removal from wastewaters.</p><p>In this work we present results of PO<sub>4</sub> removal obtained from a mixture of biomass and different carbonate materials. The mixture has been treated through a specific thermal protocol to obtain two different calcium-oxide rich charcoals here named composites C1 and C2. Initially, each composite was added to synthetic waters with different PO<sub>4 </sub>concentration, with a composite:water ratio of 1:1000. The initial concentrations of PO<sub>4 </sub>were 10, 100 and 1000 mg/l. After treatment with the composite, regardless of whether C1 or C2 was used, the PO<sub>4 </sub>concentration in the waters with initial concentration of 10 and 100 mg/L was nearly zero, with pH values at equilibrium around 11.9. The treatment of the water with initial PO<sub>4 </sub>concentration of 1000 mg/l shows a reduction of 20% and 40% with C1 and C2, respectively, with final pH values around 7.8.</p><p>After addition of the composites to the water, the solutions present very high pH values except for the water with the highest concentration. Although this is an optimal situation for the removal of PO<sub>4</sub>, it leads to two problems. First, the filtered water is not suitable for direct disposition in sewers, since the pH is higher than the limit established by the wastewater legislation (9.5). Second, a pH value larger than 9 determines the precipitation of PO<sub>4 </sub>regardless of the presence of the composite, which suggests that the PO<sub>4</sub> is not adsorbed by the composites, thus not leading to the desired complex</p><p>In order to quantify the exact amount of PO<sub>4</sub> adsorbed by the composite, the experiments have been repeated under controlled pH, keeping it around a value of 7 by the use of a mild acid. In this condition, after 1h treatment, 50% of phosphate was removed and bound to the composite</p><p>The work intends to present the results at laboratory scale and next steps at higher TRL.</p>