Formation Of Acid Research Articles

Spectrophotometric and HPLC analysis of amoxicillin trihydrate in presence of acetaminophen in different pH media

BackgroundThis study is aimed to develop a simple, effective and economic method for the UV spectrophotometric analysis of amoxicillin trihydrate in the presence of acetaminophen. The Beer–Lambert law was obeyed in the concentration range of 2–10 µg/ml for amoxicillin trihydrate, acetaminophen and combinations, in all the different pH media: pH 1.2, 6.8, 7.4 and neutral (double-distilled water). For the simultaneous equation method, the absorbance maxima of amoxicillin trihydrate was found at 228 nm, and for acetaminophen, it was found at 243 nm, after scanning the solutions in respective buffers.ResultThe standard curve of amoxicillin trihydrate and acetaminophen was plotted, and the correlation coefficient (R2) value was found to be in the range of 0.991–0.994 and 0.993–0.999, respectively. These two drugs were combined in a ratio of 5:3 (amoxicillin trihydrate: acetaminophen), and its absorbance maxima was discovered at 232 nm (isoabsorptive point), where its correlation coefficient was calculated from the standard curve which is in range of 0.993–0.996. The above-mentioned method was found to comply all the validation parameters as per the ICH guidelines such as accuracy, precision, linearity, LOD, LOQ, reproducibility and recovery. This method is successfully applied to estimate the combination of these two drugs in their pharmaceutical dosage forms without and interaction of their excipients. This method is based on to check the stability of amoxicillin trihydrate in different pH media in the presence of acetaminophen.ConclusionHydrolysis of beta-lactam ring of amoxicillin trihydrate occurs in acidic pH (below 2) which causes the formation of amoxicilloic acid which may cause reduction in its microbial activity but neither shifting of wavelength nor appearance of extra peak occurred in UV spectroscopy. Although some changes of % area of amoxicillin trihydrate is observed in acidic media in HPLC method, there are no significant changes observed among the amoxicillin trihydrate solutions with acetaminophen prepared in different pH media, when using UV spectrophotometric method.

Improving SO2 Tolerance and Low-Temperature Denitrification Performance in NH3-SCR Catalysis: A Comprehensive Study on Nb and Mn Modified CeO2 Catalysts

In pursuit of improving the performance of MnCe-based catalysts in NH3-assisted selective catalytic reduction (NH3-SCR) of NOx technology, particularly their SO2 resistance and low-temperature activity, a series of NbMnCeOx catalysts were synthesized. Results reveal that the Nb0.1Mn2Ce5Ox catalyst provides the most excellent SO2 resistance and SCR catalytic activity. Incorporating Nb into the MnCeOx structure enriches the formation of additional chemisorbed oxygen species and surface acidity, promoting NO2 production while effectively preventing the over-oxidation of NH3 to produce N2O. The incorporation of Nb and Mn into CeO2 improves the content of Brønsted- and Lewis-acid sites, facilitating the NH3 capture and NH4+ generation, thus enabling the NH3-SCR process via both Eley-Rideal (E-R, Mechanism S1) and Langmuir-Hinshelwood (L-H, Mechanism S2) mechanisms, with the latter dominating at low temperatures. Nb doping considerably reduces the sulfate formation and the initial SO2 adsorption on the NbMnCeOx surface, while decreasing the average oxidation state of Mn and shielding it from electronic attack from S4+ in SO2. This study highlights the synergistic effect of Nb and Mn in bolstering acidic sites in CeO2-based catalysts and proposes the reaction mechanisms for improving the low-temperature and sulfur-resistant NH3-SCR performance.

A new trend in combustion engine’s deep waste heat recovery by application of condensing economizers in exhaust boilers

Waste heat recovery technologies to remove heat and harmful pollution from exhaust gas–vapor mixtures remain a general trend in enhancing the efficiency of power plants. The exhaust gases from combustion engines when water-fuel emulsion (WFE) combustion contain a large amount of solid particles, deposition of which on the heating surfaces of the exhaust gas boilers (EGB) can degrade their heat transfer performance and shorten the service life. The processes of pollution deposition from exhaust gases on the economizer condensing heat exchange surface (CHES) of the EGB were studied, and their effect on the CHES heat and mass transfer characteristics was assessed. It is found that increasing the water content in the WFE to 30 % enhances the intensity of acid mass transfer due to decreasing the low-temperature corrosion rate with reaching the maximum-intensity at wall temperatures of 110…120 °C against 140…150 °C in conventional practice, which allows deeper exhaust heat utilization and increasing boiler heat productivity by about 30 %. At a water content of 30 % the sulfuric acid concentration was 57 %, which confirms the hypothesis about the passage of the nitrous mechanism of sulfuric acid formation in the condensate on CHES. The optimized CHES cleaning periodicity values corresponding to the smallest fouling coefficient and the highest heat transfer were determined. The correlations for determining the fouling, heat transfer and thermal efficiency coefficients for the CHES of the EGB when WFE combustion are provided. They are helpful for designing the economizer CHES of EGB.

The Influence and Mechanisms of Natural Plant Polysaccharides on Intestinal Microbiota-Mediated Metabolic Disorders

Natural plant polysaccharides are renowned for their broad spectrum of biological activities, making them invaluable in both the pharmaceutical and food industries. Their safety, characterized by low toxicity and minimal side effects, coupled with their potential therapeutic properties, positions them as crucial elements in health-related applications. The functional effectiveness of these polysaccharides is deeply connected to their structural attributes, including molecular weight, monosaccharide components, and types of glycosidic bonds. These structural elements influence how polysaccharides interact with the gut microbiota, potentially alleviating various metabolic and inflammatory disorders such as inflammatory bowel disease, diabetes, liver-associated pathologies, obesity, and kidney diseases. The polysaccharides operate through a range of biological mechanisms. They enhance the formation of short-chain fatty acids, which are pivotal in keeping intestinal health and metabolic balance. Additionally, they strengthen the intestinal mucosal barrier, crucial for deterring the ingress of pathogens and toxins into the host system. By modulating the immune responses within the gut, they help in managing immune-mediated disorders, and their role in activating specific cellular signaling pathways further underscores their therapeutic potential. The review delves into the intricate structure–activity relationships of various natural polysaccharides and their interactions with the intestinal flora. By understanding these relationships, the scientific community can develop targeted strategies for the use of polysaccharides in therapeutics, potentially leading to innovative treatments for a range of diseases. Furthermore, the insights gained can drive the advancement of research in natural polysaccharide applications, providing direction for novel dietary supplements and functional foods designed to support gut health and overall well-being.

Simplified Meteorite Parent Body Alteration of Amino Acids by Hydrothermal Processes.

Amino acids have been identified in extraterrestrial materials such as meteorites and returned samples from asteroids and comets. Some of these amino acids or their precursors may have formed on icy interstellar dust grains or at a later phase when these grains became incorporated into larger parent bodies. In this work, we simulated parent body aqueous alteration of the residues from irradiated interstellar ice analogs in the presence of relevant minerals (pulverized serpentinite and Allende meteorite). We tracked the change in amino acid abundances as a function of hydrothermal processing time and examined how these differed based on the presence of minerals. We find that the presence of minerals and their mineralogy can have a significant impact on the formation and destruction of amino acids during simulated aqueous alteration experiments.

Isolation and Identification of Effective Probiotics on Staphylococcus epidermidis Strains Isolated from Urine Sample

Background: The increasing prevalence of antibiotic-resistant Staphylococcusepidermidis strains underscores the urgent need for alternative therapeutic approaches. Probiotics, known for their ability to competitively exclude pathogens and modulate host immune responses, present promising potential in combating S. epidermidis infections. Objectives: This study aimed to evaluate the effectiveness of probiotics in inhibiting the growth of S.epidermidis. Methods: Staphylococcus epidermidis was isolated from urine samples of hospitalized patients in Isfahan, Iran. Probiotics were isolated from yogurt and milk. The antibacterial activity of these probiotics was assessed using agar well diffusion and broth microdilution methods. Time-kill assays and acid tolerance tests were also conducted. Anti-biofilm effects were evaluated, and the potential inhibitory mechanisms were explored through chemical analysis using high-performance liquid chromatography (HPLC). Cytotoxicity was assessed via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Results: Two probiotic strains, Streptococcus lutetiensis OR496927.1 and Lactiplantibacillus plantarum OR496928, were successfully isolated from dairy products. Both strains exhibited cytotoxic effects on S. epidermidis isolates, with S. lutetiensis demonstrating significant activity at 1/2 minimum inhibitory concentration (MIC) and L. plantarum at 1/4 MIC. L. plantarum thrived at pH 3, while S. lutetiensis exhibited growth at both pH 3 and 4. Both probiotics showed anti-biofilm activity, though L. plantarum demonstrated stronger effects overall. The strains produced lactic, formic, and acetic acids, which were key factors in their inhibitory effects. Toxicity was observed at a concentration of 50% after 24 hours, while cell viability remained unaffected at lower concentrations. Conclusions: The findings highlight the potential of probiotics to address antibiotic-resistant S. epidermidis infections. Further research is necessary to explore their therapeutic applications and optimize treatment strategies.

Prebiotic formation of enantiomeric excess D-amino acids on natural pyrite

D-amino acids, found in excess in a minority of organisms and crucial for marine invertebrates, contrast with the more common L-amino acids in most life forms. The local prebiotic origin of D-amino acid enantiomeric excess in natural systems remains an unsolved conundrum. Herein, we demonstrate the formation of enantiomeric excess (ee) D-amino acids through photocatalytic reductive amination of α-keto acids on natural pyrite. Various amino acids with ee values in the range of 14.5–42.4%, are formed. The wavy arrangement of atoms on the surface of pyrite is speculated to lead to the preferential formation of D-amino acids. This work reveals the intrinsic asymmetric photocatalytic activity of pyrite, which could expand understandings on mechanism of asymmetric catalysis and chirality of inorganic crystals. Furthermore, it provides a plausible pathway for the prebiotic formation of D-amino acids, adding further evidence to the origin of D-amino acids enantiomeric excess in natural systems.

Novel technology of electric combustion of pulverized coal and prospects of its use with small additions of hydrogen to ensure ignition of low-grade fuels

Coal-fired generation has long been, and still is, one of the leaders in global power generation. According to the International Energy Agency at the moment the share of coal-fired generation is about 39%.Despite the global trend of decarbonization, global coal-fired power generation is steadily growing. In 2019, coal-fired generation grew by about 1.5%. As of 2019, the world's proven coal reserves are concentrated in the United States (23%), the Russian Federation (15%), Australia (14%), and China (13%), amounting to about 1070 billion tons. In 2020, due to the pandemic of a new coronavirus infection, coal-fired power generation has been slightly reduced. Low-grade coals such as brown coals or lignite make up more than 40% of the world's reserves [4–6]. Which suggests the need to switch to burning these types of coals. Consumption of high-sulfur viscous fuel oils as starting, reserve or main fuel leads to emissions of such harmful substances as benz(a)pyrene and vanadium pentoxide in addition to toxic sulfur oxides, nitrogen and carbon. When sulfur oxides are formed, the dew point temperature of flue gases increases, which leads to the formation of sulfuric acid and, as a consequence, to frequent repairs of tail parts of boiler units due to their corrosion. Composition of flue gases at oil combustion also depends on its quality: its content of sulfur, nitrogen, metals, polycycloarenes, etc. The same replacement of liquid fuel at start-ups of pulverized coal-fired boiler units and maintenance of pulverized coal flare combustion will reduce the fire hazard of the production process, the operating costs of TPP, the environmental hazards of gaseous products of co-combustion of liquid and solid fuels. The article presents a review of modern technologies for firing up pulverized coal-fired boiler units, as well as presents the original technology of electric ignition and the results of tests on the laboratory bench.

Proposed Importance of HOCO Chemistry: Inefficient Formation of CO2 from CO and OH Reactions on Ice Dust

With the advent of JWST ice observations, dedicated studies on the formation reactions of detected molecules are becoming increasingly important. One of the most interesting molecules in interstellar ice is CO2. Despite its simplicity, the main formation reaction considered, CO + OH → CO2 + H through the energetic HOCO* intermediate on ice dust, is subject to uncertainty because it directly competes with the stabilization of HOCO as a final product, which is formed through energy dissipation of HOCO* to the water ice. When energy dissipation to the surface is effective during the reaction, HOCO can be a dominant product. In this study, we experimentally demonstrate that the major product of the reaction is indeed not CO2, but rather the highly reactive radical HOCO. The HOCO radical can later evolve into CO2 through H-abstraction reactions, but these reactions compete with additional reactions, leading to the formation of carboxylic acids (R-COOH). Our results highlight the importance of HOCO chemistry and encourage further exploration of the chemistry of this radical.

Mechanistic insight into the catalytic activities of metallic sites on nitrogen-doped graphene quantum dots for CO2 hydrogenation

The origin of selectivity and activity of the CO2 hydrogenation reaction on single-atom catalysts composed of three adjacent 3d transition metals (Fe, Co, and Ni) supported on N-doped graphene quantum dots were systematically investigated and compared using density functional theory (DFT) calculations, natural bond orbital (NBO), and quantum theory of atoms in molecules (QTAIM) analysis. This study reveals that π-backbonding between the metal and CO2* does not occur and [CO2]δ+ species drive the reaction. The CO2* reacts with H2 via the Eley-Rideal (ER) mechanism by using the synergistic effects of the N site. The higher the partial positive charge on the C atom, the lower the Ea of the reaction. Subsequently, a tautomerization reaction, which is facilitated by hydrogen bonding, occurs and hydrogen is transferred to HCOO* resulting in the formation of CHOOH*. This study shows the selective formation of formic acid from CO2 is accessible on these SACs and Fe-SAC is the best one between these three catalysts. Although CO2 is more inert than formic acid the H2 molecule reacts with the adsorbed formic acid more difficult than the adsorbed CO2. It is because the hydrogenation of formic acid causes C-H bond formation resulting in failure of the coordinated O atom's octet and the unstable H2COOH* is formed. This step is the rate-determining step of HOCH2OH formation from CO2, with Ea of 1.94, 2.03, and 2.23 eV for Fe, Co, and Ni, respectively. Finally, the system undergoes another tautomerization reaction resulting in the formation of HOCH2OH (formaldehyde monohydrate).

Growth dynamics, antagonistic activity and acid production of Lactiplantibacillus (=Lactobacillus) plantarum KT-L18/1 and Bacillus subtilis BPT-B1 inoculants in alfalfa silage

Aim. To study growth dynamics, antagonistic activity and acid formation of two inoculant strains, Lactiplantibacillus (=Lactobacillus) plantarum КТ-L18/1 and Ваcillus subtilis ВРТ-В1, that were introduced into alfalfa silage, up to 30 days of fermentation. Methods. A streptomycin-resistant strain of both above-mentioned organisms, obtained in earlier research, was used to achieve the research aims. Alfalfa was artificially wilted and dried to a dry matter content of 39–40 %. Fermentation was conducted under anaerobic conditions in polyethylene bags. Inoculant was added at a concentration of 108 CFU/kg alfalfa. The resulting 12 × 3 = 36 bags were kept at room temperature in a dark place for 30 days. At each examination date one sample per treatment was used and examined after cultivation of the two inoculants on elective De Man-Rogosa-Sharpe (MRS) agar and meat infusion agar (MIA), containing streptomycin. The antibacterial (ABA) and antifungal activities (AFA) were studied by the agar diffusion method. Results. After 30 days of ensiling the alfalfa samples, L. plantarum КТ-L18/1str and В. subtilis ВРТ-В1str were still present at levels of 9.2 lg CFU/g and 6.9 lg CFU/g respectively. In the natural population of LAB, L. plantarum КТ-L18/1str had a dominant position. After 30 days of the alfalfa fermentation L. plantarum КТ-L18/1str and В. subtilis ВРТ-В1str maintained ABA and AFA to the PPB strains (S. aureus, P. aeruginosa, S. typhimurium) and fungal strains tested. However, the antagonistic activities of the two inoculant strains decreased during the fermentation, for L. plantarum КТ-L18/1str from 7–21 %, and for В. subtilis ВРТ-В1str from 16–21 %. Compared to the uninoculated control treatment, the inoculated silage treatments had a lower pH level (5.2–5.3), an increased number of lactic acid bacteria (LAB) (by 32 %), and clostridia were no longer detected. The inoculation impacted fungi down to a level of 102–103 CFU/g that can ensure the aerobic stability of the feed. Conclusions. The inoculant strains and L. plantarum КТ-L18/1str and Ваcillus subtilis ВРТ-В1str showed a high competitiveness with background microbiota in an ensiling experiment with alfalfa. The antagonistic activity of the two strains to PPB after fermentation was preserved at a high level, albeit with a decrease of 7–21 %. Ваcillus subtilis ВРТ-В1str kept its AFA against all three fungal strains tested during the 30 days of fermentation. For L. plantarum КТ-L18/1str this was true for a strain of the Penicillium chrysogenum only. The inoculation of and L. plantarum КТ-L18/1str and Ваcillus subtilis ВРТ-В1str caused a decrease in pH of 8–9 % at the end of the fermentation period, an accumulation of LAB with 32 %, and the inhibition of the growth of clostridia up to undetectability in the fermented alfalfa. For both inoculants, compared to uninoculated control variant, fungi decreased down to 102–103 CFU/g of the feed, which can ensure the aerobic stability of the feed.

Association Between Type 1 Diabetes Mellitus and Dental Caries in Children: A Systematic Review

Background: Diabetes mellitus is one of the diseases with chronic prevalence. Keep going increased, not only in adults but also in children. Diabetes mellitus type 1, the most common, occurs in children. Dental caries is an infection caused by metabolizing bacteria Streptococcus mutans, and Lactobacilli that convert carbohydrates into acid that damages tooth enamel. Diabetes can cause changes in saliva composition and flow. Saliva is vital in guarding a healthy tooth by neutralizing acid and providing minerals for remineralizing tooth enamel. Method: A systematic review was done by reviewing research through English data sources Pub Med, Proquest, Cochran, and Wiley. Four studies were included according to the inclusion criteria. Result: The results of a review of these four journals showed that children aged 6-18 who have type 1 or type 2 diabetes mellitus have a higher risk of developing dental caries or dental diseases. Children with diabetes are predisposed to have more glucose in their saliva. High glucose can become a source of nutrition for bacteria cariogenic, which contributes to the formation of plaque and acids that damage teeth. Conclusion: Diabetes mellitus is a risk factor for oral health. Diabetes Mellitus had a significant correlation with dental caries in children. Keywords: Diabetes Mellitus, Children.

Live-Cell Imaging of RNA G-Quadruplex with a Dual-Color Fluorescence Switch-on Probe.

In-cell imaging of the G-quadruplex (G4) formation of nucleic acids remains challenging for revealing G4's functions in cells. This study describes the cell imaging method of G4 nucleic acids using our unique tripodal quinone-cyanine fluorescent dye, QCy(MeBT)3, whose 600nm and 700nm fluorescence is enhanced independently upon the binding with double-stranded DNA and G4-DNA/RNA, respectively. The use of QCy(MeBT)3 enables us to visualize cytosolic G4 RNAs in fixed and living HeLa cells with near-infrared 700nm fluorescence.

Silver Electrodes Are Highly Selective for CO in CO2 Electroreduction due to Interplay between Voltage Dependent Kinetics and Thermodynamics.

Electrochemical reduction is a promising way to make use of CO2 as feedstock for generating renewable fuel and valuable chemicals. Several metals can be used as the electrocatalyst to generate CO and formic acid, but hydrogen formation is an unwanted side reaction that can even be dominant. The lack of selectivity is, in general, a significant problem, but silver-based electrocatalysts have been shown to be highly selective, with faradaic efficiency of CO production exceeding 90%, when the applied voltage is below -1 V vs RHE. In this voltage range, only a small amount of hydrogen and formate is formed. We present calculations of the activation free energy for the various elementary steps as a function of applied voltage at the three low index facets, Ag(111), Ag(100) and Ag(110), as well as experimental measurements on polycrystalline electrodes, to identify the reason for this high selectivity. The formation of formic acid is suppressed, even though it is thermodynamically favored, because of the low coverage of adsorbed hydrogen and kinetic hindrance to the formation of the HCOO* intermediate, while *COOH, a key intermediate in CO formation, is thermodynamically unstable until the applied voltage reaches -1 V vs RHE, at which point the kinetics for its formation are more favorable than for hydrogen. The calculated results are consistent with experimental measurements carried out for acidic conditions and provide an atomic scale insight into the high CO selectivity of silver-based electrocatalysts.

Ore sulfur of Golovnin Volcano, Kunashir Island

Research subject. Hydrothermal deposits of Golovnin Caldera. Aim. To study the epithermal volcanogenic ore formation. Key points. Until now, there has been a consensus on the exogenous sedimentary (colloidal) genesis of sulfur in volcanic lakes. Our observations and microstructure studies indicate the presence of sulfur melt at the bottom of Kipyaschee Lake. Drops of this melt are carried to the surface of the lake as part of a light gray foam. The significant differences of sulfur spherules in the concentration of sulfide mineralization, in its composition, as well as in the presence or absence of numerous opal inclusions are most simply explained by the capture of droplets in various parts of the sulfur melt and their subsequent movement by a gas stream passing through the melt. Elemental sulfur condensate is formed in bottom sediments as a result of forced cooling of endogenous gas flows by lake water. The main condensation of sulfur occurs here (96% or more of the total potential of fluid sulfur). Residual condensation of sulfur occurs in the aquatic environment. Finely dispersed sulfur condensate in a mixture with water is unstable and breaks down over time with the release of hydrogen sulfide and the formation of sulfurous and sulfuric acids. The activity of bottom hydrotherms and coastal unrest prevents the formation of colloidal sulfur sediment at the bottom of lakes. In the crater depressions at the bottom of the lakes of the Golovnin Caldera, sulfidization of its melt occurs simultaneously with the condensation of sulfur itself. Gravitational deposition of sulfides in the sulfur melt leads to their enrichment of the root parts of crater depressions, where pyrite ore bodies are formed in real time. Terrestrial sulfur deposits, together with the modified rocks overlying them, demonstrate the full profile of endogenous apical oxidation under gas-hydrothermal action: sulfur and sulfur-opal rocks up the section are replaced by gypsum-jarosite rocks and, further, by an “iron hat” of limonite-cemented breccias of the dome mantle. Conclusions. Observations, microstructure studies and molecular chemical modeling indicate the endogenous condensate origin of ore sulfur in the Golovnin Caldera and exclude its exogenous sedimentary genesis.

Fungal Extracellular Enzymes from Aspergillus spp. as Promising Candidates for Extra-Heavy Oil Degradation and Enhanced Oil Recovery.

Heavy crude oil (HCO) and extra-heavy crude oil (EHCO) with high viscosity and density pose enormous challenges to the exploitation of oil reserves. While bacteria are increasingly used in biocatalytic upgrading of HCO and EHCO, less attention has been paid to the potential of fungi. The aim of this study was to ascertain the role of fungal extracellular enzymes from Aspergillus spp. In the biodegradation of EHCO and their application potential for enhanced oil recovery. A. terreus HJ2 and A. nidulans HJ4 with the ability to biodegrade HCO were previously isolated from bitumen enrichment cultures. Both strains grew well on EHCO agar plates supplemented with a small amount of soluble starch (0.2%) and yeast extract (0.3%). Extracellular enzymes from each strain separately, as well as mixtures of the enzymes, exhibited EHCO degradation activity, leading to redistribution of hydrocarbons with substantial formation of biogases and organic acids in a 7-day period. Enzymatic degradation resulted in decreased contents of resins and asphaltenes, accompanied by increased contents of saturates and aromatics. Gas chromatography-mass spectrometry revealed distinct redistribution patterns of n-alkane in the biotreated oil. Enzymatic degradation additionally caused considerable reduction in oil viscosity (by 12.7%) and heavy metal concentrations (Ni, by 44.1%; Fe, by 54.0%; V, by 31.6%). The results provide empirical evidence for the application potential of fungal extracellular enzymes from Aspergillus spp. in EHCO recovery and biocatalytic upgrading of EHCO.

Carbamic acid and its dimer: A computational study.

A recent work by Marks et al. on the formation of carbamic acid in NH -CO interstellar ices pointed out its stability in the gas phase and the concomitant production of its dimer. Prompted by these results and the lack of information on these species, we have performed an accurate structural, energetic and spectroscopic investigation of carbamic acid and its dimer. For the former, the structural and spectroscopic characterization employed composite schemes based on coupled cluster (CC) calculations that account for the extrapolation to the complete basis set limit and core correlation effects. A first important outcome is the definitive confirmation of the nonplanarity of carbamic acid, then followed by an accurate estimate of its rotational and vibrational spectroscopy parameters. As far as the carbamic acid dimer is concerned, the investigation started from the identification of its most stable forms. For them, structure and vibrational properties have been evaluated using density functional theory, while a composite scheme rooted in CC theory has been employed for the energetic characterization. Our results allowed us to provide a better interpretation of the feature observed in the recent experiment mentioned above.

Environmental pH and compound structure affect the activity of short-chain carboxylic acids against planktonic growth, biofilm formation, and eradication of the food pathogen Salmonella enterica.

Short-chain carboxylic acids (SCCAs) that are naturally produced by microbial fermentation play an essential role in delaying microbial spoilage. SCCAs are structurally diverse, but only a few of them are routinely used in food biopreservation. This study investigated the effects of environmental pH and intrinsic properties of 21 structurally different SCCAs on the antimicrobial and antibiofilm activity against Salmonella enterica. Inhibition of SCCA toward planktonic and biofilm growth of S. enterica was higher in an acidic environment (pH 4.5) that is common in fermented products, and for SCCA that possessed both a high acid dissociation strength (pKa) (>4.0) and a positive hydrophobicity [octanol/water partition coefficient (log Kow)]. Crotonic and caproic acids were identified as SCCAs with potential as biopreservatives even at near-neutral pH. SCCA with hydrophilic groups such as lactic acid did not inhibit S. enterica at concentrations up to 50 mM, while SCCA with benzene or methyl groups or a double bond prevented S. enterica growth and biofilm formation. Stimulation of biofilm formation was observed for formic, acetic, and propionic acid close to the minimum inhibitory concentration to reduce 50% of cell density (MIC50) of planktonic cells, and for citric and isocitric acid with an MIC50 of ≥50 mM. The presence of low concentrations of formic and propionic acids during biofilm formation conferred protection during eradication possibly due to a pre-adaptation effect, yet two consecutive acid treatments were successful in eradicating biofilms if the first acid treatment was two- to threefold of the MIC50.IMPORTANCEThis study provides a systematic comparison on the antimicrobial and antibiofilm activity of more than 20 structurally different SCCAs against a common food pathogen. We tested the antimicrobial activity at controlled pH and identified the structure-dependent antimicrobial effects of SCCA without the confounding influence of acidification. The combined effect of pKa and log Kow was identified as an important feature that should be considered when deciding for a specific SCCA in the application as antimicrobial. Our results imply that additional phenomena such as the use of SCCA as substrate and cellular pre-adaption effects have to be taken into consideration. We finally present a two-step treatment as an efficient approach to eradicate biofilms, which can be applied for the disinfection of contact surfaces and manufacturing equipment. Results obtained here can serve as guidelines for application of SCCA to avoid the growth of food pathogens and/or to develop biopreserved food systems.

Substrate specificity and kinetic mechanism of 3β-hydroxy-[formula omitted]5-C27-steroid oxidoreductase

Cholesterol is a key sterol whose homeostasis is primarily maintained through bile acid metabolism. Proper bile acid formation is vital for nutrient and fat-soluble vitamin absorption and emulsification of lipids. Synthesis of bile acids occurs through two main pathways, both of which rely on 3-hydroxy-5-C27 steroid oxidoreductase (HSD3B7) to begin epimerization of the 3β hydroxyl of cholesterol into its active 3α conformation. In this sequence HSD3B7 catalyzes the dehydrogenation of the 3β-hydroxy group followed by isomerization of the Δ5-cholestene-3-one. These reactions are some of the many steps that transform cholesterol for either storage or secretion. HSD3B7 has distinct activity from other 3β-HSD family members leaving significant gaps in our understanding of its mode of catalysis and substrate specificity. Additionally, the role of HSD3B7 in health and disease positions it as a metabolic vulnerability that could be harnessed as a therapeutic target. To this end, we evaluated the mechanism of HSD3B7 catalysis and reveal that HSD3B7 displays activity towards diverse 7α-hydroxylated oxysterols. HSD3B7 retains its catalytic efficiency towards these substrates, suggesting that its substrate binding pocket can withstand changes in polarity upon alterations to this hydrocarbon tail. Experiments aimed at determining substrate order are consistent with HSD3B7 catalyzing a sequential ordered bi bi reaction mechanism with the binding of NAD+ followed by 7α-hydroxycholesterol to form a central complex. HSD3B7 bifunctional activity is dependent on membrane localization through a putative membrane-associated helix giving insight into potential regulation of enzyme activity. We found strong binding of the NADH product thought to activate the isomerization reaction. Homology models of HSD3B7 reveal a potential substrate pocket that allows for oxysterol binding and mutagenesis was utilized to support this model. Together these studies offer an understanding of substrate specificity and kinetic mechanism of HSD3B7 which can be exploited for future drug development.

Insights into the enhancement of trace level NO2− on 2,4,6-tribromophenol degradation in UV/PS process: Experimental study and theoretical calculation

Sulfate radical (SO4−)-based UV/persulfate (PS) process is extensively studied to remove organic pollutants in water, while the wide presence of nitrite (NO2−) in natural water can quickly react with SO4− and hydroxyl radicals (OH) to form reactive nitrogen species (RNS). In this study, the degradation of 2,4,6-tribromophenol (TBP) in UV/PS process in the presence of low concentration of NO2− was systematically investigated through experimental studies and theoretical calculations. The introduction of trace NO2− enhanced the TBP degradation by UV/PS process due to the formation of RNS (such as NO2 and BrNO2) and both RNS and SO4− played the important role in the pH range of 6.0–8.0. TBP was more easily photolyzed under alkaline conditions due to higher photodegradation coefficient at pH 8.0. When TBP underwent deprotonation, the reaction energy barrier of TBP with SO4−, OH and NO2 significantly decreased and subsequent debromination may be more likely to occur. Additionally, NO2 attacked ionized TBP at relatively high rate mainly through electron transfer. The degradation pathways of TBP mainly involved in the debromination, hydroxylation and nitrosylation and the generated products all presented lower toxicity than TBP. Moreover, the effects of PS dosage, NO2− concentration, humic acid, bicarbonate and chloride on TBP elimination also were thoroughly assessed. The presence of low concentration of NO2− reduced the toxicity risk caused by the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) during the chlorination process after UV/PS pre-oxidation. This study broadens the knowledge of trace NO2− enhancing organic pollutants degradation by UV/PS process.