Condensation Pathway Research Articles

Condensation methodology for quantification of Polymyxin B fluorimetrically: application to pharmaceutical formulations and greenness assessment

The appearance of multidrug-resistant Gram-negative bacterial infections, along with the lack of newly discovered antibiotics, resulted in the return to old antimicrobial medications like Polymyxins. As a result, the suggested technique aims to develop a fast, environmentally friendly, and sensitive fluorimetric method for quantifying Polymyxin B. The investigated approach depends on generating a highly fluorescent derivative by a condensation pathway between the studied drug and ninhydrin in the presence of phenylacetaldehyde and then estimated spectrofluorimetrically. After the reaction conditions were well optimized, the fluorescent product was estimated at emission wavelength (λem) = 475.5 nm (following excitation at a wavelength (λex) = 386 nm. The developed calibration plot displayed rectilinear throughout the following range (0.2-3 µg mL− 1), and the calculated limit of detection and quantification were 0.062 µg mL− 1 and 0.187 µg mL− 1, respectively. As a consequence, the drug’s ophthalmic and intravenous pharmaceutical forms were both successfully quantified with an excellent degree of recovery. Finally, the methodology’s greenness was assessed utilizing Analytical Eco-Scale scores.

Influence of precursor aging and condensation progression on silica thin films grown by electrochemically induced sol-gel deposition

Electrochemically induced sol-gel enables the fast synthesis of functional oxide coatings. In the case of silica, the condensation reaction can be catalysed by electrogenerated hydroxides. Using this technique, highly organized nanostructured thin films can be deposited onto conductive substrates by combining structure-directing templates with the electrochemically induced silica sol-gel process that occurs locally at the electrode surface. This specific template-directed process, called electrochemically assisted self-assembly (EASA), utilizes a sol-gel precursor solution optimized for a minimal spontaneous condensation (and gelation) rate in the absence of an electrochemical trigger. Despite the slow kinetics of the condensation reaction, the solution remains unstable and some incipient condensation reactions will still occur over time, continuously modifying the Si(IV) precursor solution. In this work, we discuss how precursor's aging affects the deposition rate and the properties of the deposited coatings. Two distinct aging effects are observed: an aging effect which occurs over time and an aging effect which occurs through electrochemical activation during preceding depositions. Both these aging effects result in accelerated film growth rates, up to 200 × faster than the deposition rate from a fresh precursor solution. Additionally, it was observed that time aging yields less resistive, weaker films, while electrochemical aging leads to films which retain similar properties as films grown using fresh precursor solutions. The time aging effect could be inhibited by storing the precursor solution at -35 °C. These observations are explained based on the different condensation pathways during acidic and alkaline condensation, which is known to yield inherently different silica oligomer products. The results and insights described here contribute to upscaling the electrochemical sol-gel process for mesoporous silica films and provides further fundamental insights into the underlying silica condensation reactions.

The bioaugmentation effect of microbial inoculants on humic acid formation during co-composting of bagasse and cow manure

The effective degradation of recalcitrant lignocellulose has emerged as a bottleneck for the humification of compost, and strategies are required to improve the efficiency of bagasse composting. Bioaugmentation is a promising method for promoting compost maturation and improving the quality of final compost. In this study, the bioaugmentation effects of microbial inoculants on humic acid (HA) formation during lignocellulosic composting were explored. In the inoculated group, the maximum temperature was increased to 72.5 °C, and the phenol-protein condensation and Maillard humification pathways were enhanced, thus increasing the HA content by 43.85%. After inoculation, the intensity of the microbial community interactions increased, particularly for fungi (1.4-fold). Macrogenomic analysis revealed that inoculation enriched thermophilic bacteria and lignocellulose-degrading fungi and increased the activity of carbohydrate-active enzymes and related metabolic functions, which effectively disrupted the recalcitrant structure of lignocellulose to achieve a high humification degree. Spearman correlation analysis indicated that Stappia of the Proteobacteria phylum, Ilumatobacter of the Actinomycetes phylum, and eleven genera of Ascomycota were the main HA producers. This study provides new ideas for bagasse treatment and recycling and realizing the comprehensive use of resources.

Selective Partial Reduction of Nitroarenes to the Hydrazoarene Catalyzed by Amine‐Modified Ordered Mesoporous Silica Immobilized Ionic Liquid (OMSIIL) Stabilised RuNPs

AbstractRuthenium nanoparticles stabilised by an amine‐modified Ordered Mesoporous Silica Immobilized Ionic Liquid (OMSIIL) are efficient catalysts for the partial reduction of nitrobenzene to hydrazobenzene with 100 % selectivity as well as the complete reduction to aniline. High selectivity for the partial reduction of nitrobenzene to hydrazobenzene was obtained when the reaction was conducted in ethanol with 0.5 mol% catalyst and NaBH4 as the hydrogen donor whereas aniline was obtained as the sole product in water when dimethylamine borane (DMAB) was used as the hydrogen donor. Interestingly, while a range of electron poor nitroarenes were reduced to the corresponding hydrazoarene with high selectivities and good conversions, nitroarenes substituted with electron donating groups resulted in complete reduction to the aniline. Composition‐time profiles suggest that reductions conducted in ethanol with sodium borohydride occur via the condensation pathway while those conducted in water using dimethylamine borane as the hydrogen source may well go via the direct pathway. This is the first example of the selective reduction of nitrobenzene to hydrazobenzene using a ruthenium nanoparticle‐based catalyst and the initial TOF of 320 mol nitrobenzene converted mol Ru−1 h−1 for the partial reduction of nitrobenzene to hydrazobenzene is markedly higher than previous literature reports. A study of the catalyst performance as a function of the surface modification revealed that each component has a direct and dramatic effect on the efficacy as RuNPs stabilised by COK‐12 modified with imidazolium‐based ionic liquid and a primary amine gave the highest conversion while selective removal of either component or replacement of the primary amine with a tertiary amine resulted in a marked reduction in efficiency.

Statistically driven automated method for catalytic glucose conversion optimisation.

A statistically driven, automated approach to optimize glucose transformations to platform chemicals, methyl lactate and levulinic acid, is reported. The combination of a robotic synthesis platform with design of experiments methods enabled efficient and precise modelling of glucose conversion catalysed by SnCl4·5H2O with 0-100% H2O and methanol as a cosolvent. Using this strategy, optimal reaction conditions within the available reaction space were identified in 58 runs, showcasing the excellent efficiency of this method in producing high yields of methyl lactate (75.9%) and levulinic acid (64.5%) in independent reactions via distinct retro-aldol condensation and dehydration pathways, respectively.

Influence of Water Concentration on High-Temperature Reactive Condensation of Chromium Vapors Generated in 800 °C Air

Reactive evaporation of chromium (Cr) from stainless steels used in solid oxide electrochemical systems, such as solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) systems, is well-documented. However, the condensation and interactions of volatilized Cr species onto and with surrounding interfaces during complex and dynamic system exposures is less understood. Understanding these interactions during operation is critical for improving system performance and safeguarding environmental, health and safety, as some condensed species contain toxic hexavalent Cr (Cr(VI)). The objective of this study is to investigate the condensation pathways of Cr vapors within representative high-temperature system environments. To accomplish this objective, Cr vapors, produced by high-temperature (800 °C) air exposures of trivalent chromium (Cr(III)) oxide (Cr2O3) powder with variable moisture content, were condensed onto various ceramic materials at lower temperatures (<400 °C). The total amount of Cr and ratios of oxidation states were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES) and diphenyl carbazide (DPC) colorimetric/direct UV–vis spectrophotometer analyses. Increased Cr condensation was observed with increased water content, with similar Cr(VI) to total Cr ratios. Results and interpretations are discussed in context of improving understanding of Cr reactive condensation in SOFC/SOEC and related high-temperature materials and systems.

Reactive Condensation of Cr Vapor on Aluminosilicates Containing Alkaline Oxides

The research presented herein is part of a larger project delving into the mechanisms and pathways for reactive condensation of Chromium (Cr) vapors in high-temperature (>500o C) environments. The overall goal of this research project is to improve fundamental understanding of reactive condensation pathways for chromium (Cr) vapors generated in high-temperature systems such as exhaust manifolds, steam turbines, boilers, or solid oxide fuel cells (SOFCs). Reactive evaporation of Cr from stainless steels commonly used in these systems is well-documented; however, the interactions between volatilized Cr species and surrounding interfaces during complex and dynamic system exposures is poorly understood. Understanding the interactions between volatilized Cr species and downstream components during operation is critical for improving system performance, environmental health, and safety as some condensed Cr forms toxic hexavalent Cr(VI) species. The focus of this study is on the effects of alkaline oxides present within the substrate material on reactive condensation mechanisms of Cr vapors. Studying the reaction mechanisms between Cr vapors and ceramic surfaces has direct application to SOFCs as these materials are widely used in the field. For example, alumina-silica glass-ceramics are used as sealants in SOFCs. These materials belong to the SiO2–Al2O3 system and contain different compositions of oxides including CaO, Na2O, MgO, K2O, B2O3, Y2O3, and BaO. Another sealing material used in SOFCs is mica, a class of silicate minerals that forms into distinct layers. Two types of mica commonly used in SOFC applications are muscovite (potassium aluminum silicate hydroxide fluoride, KAl2(AlSi3O10)(F,OH)2), and phlogopite (potassium magnesium aluminum silicate hydroxide, KMg3(AlSi3O10)(OH)2). The specific research objective is to explore the effects of alkaline oxide additives in aluminosilicates on Cr collection and speciation. To accomplish this objective, an experimental platform was designed to assess interactions between samples of high-temperature steel alloys or Cr oxide (Cr2O3) powder with ceramic insulating materials. The chemical composition of the insulating materials used in this study range from pure silica (SiO2) and alumina (Al2O3) to combinations thereof with and without inclusions of alkaline earth metals (e.g., Ca, Mg). Preliminary results show three- to four-fold increases in Cr(VI) formation on silica fibers with weight percentages of ~30 and ~40 percent alkaline oxides (CaO and MgO), respectively, after exposure to volatile Cr species, relative to low-alkaline silica. Figure 1 presents an overview of the experimental concept, Cr(VI) test kit, and preliminary results for dependency on alkaline oxide content. Figure 1

Significance of pH and iron-sulfur chemistry for molybdenum sequestration under sulfidic conditions

Molybdenum (Mo), a redox-sensitive trace metal, plays an important role in recording ancient oxygenation and deoxygenation events as a paleoredox proxy. The mobility and reactivity of Mo in aqueous conditions are closely tied to the chemistry of reduced sulfur and iron species. However, our current knowledge on the formation, structure, stability, and condensation pathways of FeMoS clusters in aqueous settings remains limited, which has driven the current study. In this study, we conducted systematic experiments investigating the interactions between dissolved Mo (initially introduced as molybdate, MoO42−, or tetrathiomolybdate, MoS42−), ferrous iron (Fe2+), and sulfide (ΣH2Saq) in variously defined abiotic sulfidic systems to determine the external conditions (i.e., pH, and reactant concentrations and ratios) necessary for the formation of solid-phase Fe-Mo sulfides. Solution samples of each system were monitored using ultraviolet-visible spectroscopy (UV–vis) to track the degree of thiolation of dissolved Mo species. Precipitates were analyzed using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) to determine their elemental compositions and valences, and structure (i.e., crystalline or amorphous), respectively. All FeMoS precipitates were amorphous and contained 76–90% Mo(IV) and 10–24% Mo(V) with a trend toward lower Mo(IV):Mo(V) ratios with increasing pH. The degree of Mo thiolation, which was strongly dependent on solution pH and Fe2+ concentrations, greatly affected the amount of Mo sequestered (i.e., an increased degree of Mo thiolation in solution led to an increased amount of Mo in the final FeMoS precipitate). These findings suggest that changes in pH and Fe2+ concentrations may be responsible for the sulfide-independent variations in Mo behavior observed in euxinic basins.

The Influence of Water Concentration on High-Temperature Reactive Evaporation and Condensation of Cr in 800°C Air

Deleterious reactive evaporation of chromium from stainless steels commonly used in solid oxide electrochemical systems is well-documented; however, interactions between Cr vapor species and surrounding interfaces during complex and dynamic system exposures is poorly understood. Understanding the interactions between Cr vapor species and downstream components during operation is critical for improving system performance and safeguarding environmental, health and safety, as many condensed Cr compounds contain toxic and carcinogenic hexavalent chromium Cr(VI). Furthermore, the interactions between volatilized Cr species and surrounding interfaces are dependent upon dynamic chemical environments. The objective of this study is to systematically investigate and report on condensation pathways of Cr vapors within representative system environments with variable water concentrations. To accomplish this objective, an experimental platform was designed to generate Cr vapor species from the reactive evaporation of chromia (Cr2O3) powder with high-temperature (>1100 K) air/H2O mixtures, and expose downstream ceramic insulation materials (e.g., aluminosilicate fibers) at reduced temperatures (<600 K). Insulation material chemical compositions investigated include pure silica (SiO2) and alumina (Al2O3) to combinations thereof with and without inclusions of alkaline earth metals (e.g., Ca, Mg, Sr). Materials are studied as a function of exposure conditions using complementary materials characterization tools such as SEM-EDX, XPS, and diphenyl carbazide reactions to assess Cr(VI) concentrations. Reactive evaporation of Cr from chromia occurs in the presence of oxygen and/or water vapor to form various Cr-containing vapor species. Thermodynamic data reveals an equilibrium partial pressure increase of several orders of magnitude at elevated (>500 K) temperatures for all Cr vapor species. In the presence of water vapor, the partial pressure of Cr oxyhydroxide (CrO2(OH)2(g)) is greater by many several orders of magnitude and becomes the dominant species up to ~1500 K. The research objective is to explore effects of water vapor in air on Cr condensation and speciation on different ceramic insulation materials. The experimental setup thus far has exposed aluminosilicate fibers to volatilized Cr species from Cr oxide powder at 1100 K for 150 hours under varying water vapor conditions: 0 vol%(dry), 3 vol%, and 10 vol% H2O. Preliminary results show an increase in Cr(VI) formation on fibers exposed to volatile Cr species as water vapor content increases. See Figure 1 for an overview of the experimental concept, Cr(VI) test kit, and preliminary results for dependency on water vapor. Analyses of these results will be presented and discussed in context of potential implications for SOFC/SOEC systems. Figure 1

The Influence of Water Concentration on High-Temperature Reactive Evaporation and Condensation of Cr in 800°C Air

Reactive evaporation of Cr from stainless steels used in solid oxide electrochemical systems, such as solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) systems, is well-documented as the cause of Cr poisoning; however, the condensation and interactions of volatilized Cr species onto and with surrounding interfaces during complex and dynamic system exposures is less understood. Understanding these interactions during operation is critical for improving system performance and safeguarding environmental, health and safety, as some condensed Cr forms toxic hexavalent chromium (Cr(VI)) species. The objective of this study is to investigate and report on condensation pathways of Cr vapors within representative high-temperature system environments. To accomplish this objective, Cr vapors, produced by high-temperature (800°C) air exposures of trivalent chromium (Cr(III)) oxide (Cr2O3) powder with variable moisture content, were condensed onto various ceramic materials at lower temperatures (<400°C). Both the total amount of Cr and ratios of oxidation states were measured using ICP-MS and colorimetric analyses. An increase of Cr condensation was observed with increased water content, with similar Cr(VI) to Cr(III) ratios. Results and interpretations are discussed in context of improved understanding of Cr reactive evaporation and condensation in SOFC/SOEC and related high-temperature materials and systems.

Over-expression of RRM2 predicts adverse prognosis correlated with immune infiltrates: A potential biomarker for hepatocellular carcinoma.

Ribonucleotide reductase regulatory subunit M2 (RRM2) has been reported to be an oncogene in some malignant tumors, such as lung adenocarcinoma, oral squamous cell carcinoma, glioblastoma, and breast cancer. However, the clinical significance of RRM2 in hepatocellular carcinoma has been less studied. The aim of this study was to assess the importance of RRM2 in hepatocellular carcinoma (HCC) based on the Cancer Genome Atlas (TCGA) database. The RRM2 expression levels and clinical features were downloaded from the TCGA database. Immunohistochemistry results between tumor tissues and normal tissues were downloaded from the Proteinatlas database. Meanwhile, the expression levels of RRM2 in tumor and paraneoplastic tissues were further verified by qRT-PCR and Western Blotting. Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG) and protein-protein-interactions (PPI) network were constructed to analyze RRM2-related downstream molecules. In addition, RRM2 expression-related pathways performed by gene set enrichment analysis (GSEA). Association analysis of RRM2 gene expression and immune infiltration was performed by single-sample GSEA (ssGSEA). The RRM2 expression level in tumor tissues was higher than normal tissues (P <0.001). The elevated expression of RRM2 in HCC was significantly correlated with T stage (P <0.05), pathologic stage (P <0.05), tumor status (P <0.05), histologic grade (P<0.001), and AFP (P <0.001). HCC with higher RRM2 expression was positively associated with worse OS (overall survival), PFS (progression-free survival), and DSS (disease-specific survival). In the univariate analysis, the expression of RRM2, T stage, M stage, pathologic stage, and tumor status were negatively correlated with OS (P <0.05). Further analysis using multivariate Cox regression showed that tumor status (P<0.01) and RRM2 expression (P<0.05) were independent prognostic factors of OS in HCC. GO/KEGG analysis showed that the critical biological process (chromosome condensation and p53 signaling pathway) might be the possible function mechanism in promoting HCC. Moreover, GSEA showed that several pathways were enriched in RRM2 high-expression samples, including PD-1 signaling, cell cycle, P27 pathway, and T cell receptor signaling pathway. RRM2 was significantly correlated with the infiltration level of CD8 T cells, Cytotoxic cells, DCs, Neutrophils, NK cells, and T helper cells (P <0.05). Over-expression of RRM2 predict adverse prognosis and is correlated with immune infiltrates in HCC. RRM2 may be a significant molecular biomarker for HCC diagnosis and prognosis.

Site-directed double monoubiquitination of the repeat domain of the amyloid-forming protein tau impairs self-assembly and coacervation

In Alzheimer’s disease and related disorders called tauopathies, the microtubule-associated protein tau accumulates in the brain in the form of amyloid-like supramolecular filaments. As an intrinsically disordered protein, tau undergoes many post-translational modifications, including ubiquitination. Alterations to the levels of ubiquitination of tau have been observed at various stages of neurodegenerative conditions.We focus on proteoform-specific interrogations to obtain mechanistic insight into the effects of ubiquitination on disease-related conformational transitions of tau. Single and double ubiquitination of tau at residues Lys311 and Lys317 is strongly associated with pathological conditions. In this study, we leveraged disulfide-directed chemistry to install ubiquitin at one or both of those positions in the isolated microtubule-binding repeat domain of tau. We obtained homogeneously modified tau proteins and observed that they retained disordered character in solution.We found that ubiquitination in position 317 (with or without ubiquitination in position 311) impaired the formation of ordered fibrillar structures via oligomeric intermediates. Since the transition to fibrillar species may proceed via an alternative condensation pathway involving liquid droplet intermediates, we further tested the ability of the ubiquitinated proteoforms to phase separate. Single monoubiquitinated tau species were able to coacervate, however no liquid droplets were observed for the double ubiquitinated form.Taken together, the data indicate that double ubiquitination in the third repeat of tau disfavors the formation of amyloid aggregates by distinct mechanisms, suggesting that the presence of ubiquitinated residues 311 and 317 in insoluble tau may result from modifications in advanced stages of aggregation. These findings contribute to our understanding of the influence of site-specific ubiquitination on the pathological conformational transitions of a prototypical intrinsically disordered protein.

11B NMR Spectroscopy: Structural Analysis of the Acidity and Reactivity of Phenyl Boronic Acid-Diol Condensations.

Phenyl boronic acids are valuable for medical diagnostics and biochemistry studies due to their ability to readily bind with carbohydrates in water. Incorporated in carbohydrates are 1,2-diols, which react with boronic acids through a reversible covalent condensation pathway. A wide variety of boronic acids have been employed for diol binding with differing substitution of the phenyl ring, with the goals of simplifying their synthesis and altering their thermodynamics of complexation. One method for monitoring their pKa's and binding is 11B NMR spectroscopy. Herein, we report a comprehensive study employing 11B NMR spectroscopy to determine the pKa of the most commonly used phenyl boronic acids and their binding with catechol or d,l-hydrobenzoin as prototypical diols. The chemical shift of the boronic acid transforming into the boronate ester was monitored at pHs ranging from 2 to 10. With each boronic acid, the results confirm (1) the necessity to use pHs above their pKa's to induce complexation, (2) that the pKa's change in the presence of diols, and (3) that 11B NMR spectroscopy is a particularly convenient tool for monitoring these interconnected acidity and binding phenomena.

Exploring the internal driving mechanism underlying bacterial community-induced organic component conversion and humus formation during rice straw composting with tricarboxylic acid cycle regulator addition

The aim of this study was to investigate the effect of tricarboxylic acid (TCA) cycle regulators on CO2 emissions, the conversion of organic components and humus formation during composting. The addition of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NADH) reduced CO2 emissions during rice straw composting. According to co-occurrence networks results, ATP enhanced the connectivity and complexity of the network; NADH enhanced microbial interactions. The different kind of TCA cycle regulators had different effect on humus formation pathway. The structural equation model showed that ATP might promote lignin transformation into humus via the sugar-amine condensation pathway and lignin-protein pathway while NADH may promote cellulose degradation into soluble sugar and organic matter, which are transformed into humus. This work will provide valuable guidance for exploring the mechanism of TCA cycle regulators in promoting organic carbon fixation and reducing inorganic carbon mineralization.

The neglected effects of polysaccharide transformation on sludge humification during anaerobic digestion with thermal hydrolysis pretreatment

Humus accumulation during sludge stabilization is attracting increasing attention because of its land use potential. This study investigated the effects of thermal hydrolysis pretreatment (THP) on sludge humification and the related regulatory mechanisms during anaerobic digestion (AD). The sludge subjected to AD with THP at 160 °C (AnD-160) exhibited 7.3% and 8.5% higher total extractable carbon (TEC) and humic acid carbon (HAC) concentrations than the unpretreated sludge, respectively, while the sludge subjected to AD with THP at 180 °C (AnD-180) exhibited 1.4% and 7.0% lower concentrations. Humification of AnD-160 and AnD-180 were enhanced and inhibited, respectively. THP influenced sludge humification during AD through both intracellular polyphenol synthesis and extracellular humus condensation pathways related to polysaccharide metabolism. The 160 °C-pretreated sludge exhibited higher polysaccharide availability (more soluble polysaccharides and reducing sugars) than the other samples and thus had more active intracellular polyphenol metabolism during AD. The polyphenol accumulation stimulated the synthesis of related condensation enzymes (polyphenol oxidase and quinone oxidoreductases), facilitating extracellular HA production during AD. However, THP at 180 °C resulted in the highest production of melanoidins with CO-C heterocycles through C = O and CH sites of polysaccharides (778.46 vs. 193.87 R.U. nm2-mL/g for the unpretreated sample). This heterocyclization decreased the polysaccharide availability and inhibited intracellular polyphenol synthesis, consequently inhibiting condensation enzymes supply and extracellular HA production during AD. Overall, this study highlights the crucial but neglected role of polysaccharides in sludge humification during AD: the availability of polysaccharides affected by their occurrence state and molecular structure could determine the humification, which can be regulated by THP at different temperature.

Comparative analysis of the white rot fungus Trametes hirsuta 072 laccases ability to modify 17β-oestradiol in the aqueous medium

A comparative study of the ability of Trametes hirsuta laccase isoenzymes to biotransform 17β-oestradiol (3,17β-dihydroxyestra-1,3,5(10)-triene, E2) was carried out. Native major LacA and recombinant minor isoenzymes (rLacC, rLacD, and rLacF) obtained in Penicillium canescens were used. It was found that all the studied isozymes are capable of catalysing the oxidative coupling of E2 in an aqueous medium (22 ± 2 °C, pH 4.5) with the formation of predominantly dimers and trimers. Other concurrently formed products were detected by high-pressure liquid chromatography – high-resolution mass spectrometry (HPLC–HRMS) and characterized, summarizing the overall condensation pathway of E2 in laccases. The highest catalytic activity was observed for major LacA. For other laccases, the activity decreased in the following sequence rLacF > rLacD > rLacC. Utilization of T. hirsuta enzymatic variety of laccases can be of benefit for detoxification of phenol-like steroid compounds in the environment.

The importance of four-membered NHCs in stabilizing Breslow intermediates on benzoin condensation pathway.

N-heterocyclic carbenes (NHCs) have been established to be effective organocatalysts for facilitating the benzoin condensation and many other reactions. These reactions involve the formation of a Breslow intermediate (BI), which exhibits umpolung chemistry. To facilitate organocatalysis, several new cyclic carbenes are being introduced, four-membered NHCs are of special interest. Whether these NHCs can exhibit catalytic influence or not, can be evaluated by exploring the potential energy surface (PES) of the benzoin condensation reaction. Quantum chemical analysis has been carried out to compare the PES of these four-membered NHCs with that of standard five-membered NHCs to explore their catalytic ability. The barrier for the first step of the reaction for the formation of BI is comparable in all the cases. But the barrier for the second step of the reaction leading to the benzoin formation from BI is estimated to be very high for the four membered NHCs. These results indicate that the probability of identifying and isolating the BI is very high in comparison to the completion of benzoin condensation reaction in the case of the four-membered NHCs.

Xanthohumol targets the JNK1/2 signaling pathway in apoptosis of human nasopharyngeal carcinoma cells.

Nasopharyngeal carcinoma (NPC) is one of the most aggressive malignant tumors of the head and neck. Xanthohumol (Xn) is a compound extracted in a high concentration from the hard resin of hops (Humulus lupulus L.), the basic raw material of beer. This study investigated the apoptotic effect and anticancer properties of Xn in human NPC cell lines. Our study demonstrated that at the concentration 40 μM, Xn significantly reduced cell viability and promoted cell cycle arrest in the G2/M phase in two cell lines. The results indicated that Xn induced apoptosis in NPC cell lines through annexin V/propidium iodide staining, chromatin condensation, and apoptosis-related pathways. Xn upregulated the expression of apoptosis-related proteins, namely DR5, cleaved RIP, caspase-3, caspase-8, caspase-9, PARP, Bim, and Bak, and it downregulated the expression of Bcl-2. Xn upregulated the c-Jun N-terminal kinase (JNK) in the mitogen-activated protein kinase (MAPK), and the inhibition of JNK clearly resulted in decreasing expression of Xn-activated cleaved caspase-3 and PARP. Our research provides sufficient evidence to confirm that Xn induces the MAPK JNK pathway to promote apoptosis of NPC and is expected to become a safe and acceptable treatment option for human NPC.

Unravelling the kinetics of α-synuclein aggregation via the condensation pathway

Aggregation of α-synuclein is the main hallmark of Lewy bodies which are implicated in Parkinson’s disease. New evidence suggests that α-synuclein aggregation nucleates through liquid-liquid phase separation. By developing a quick and reliable ThT-based liquid-liquid phase separation maturation assay, at physiological concentrations and conditions, we can qualitatively and quantitatively assess the relative amyloid formation within liquid droplets/condensates over time. We also show that α-synuclein aggregation within condensates is likely to follow a secondary nucleation-dominated model with fibril fragmentation.

Azo(xy) vs Aniline Selectivity in Catalytic Nitroarene Reduction by Intermetallics: Experiments and Simulations

Intermetallic nanoparticles are promising catalysts in hydrogenation and fuel cell technologies. Much is known about the ability of intermetallic nanoparticles to selectively reduce nitro vs alkene, alcohol, or halide functional groups; less is known about their selectivity toward aniline vs azo or azoxy condensation products that result from the reduction of a nitro group alone. Because azo(xy)arenes bear promise as dyes, chemical stabilizers, and building blocks to functional materials but can be difficult to isolate, developing high surface area nanoparticle catalysts that display azo(xy) selectivity is desirable. To address this question, we studied a family of nanocrystalline group 10 metal (Pd, Pt)- and group 14 metal (Ge, Sn, Pb)-containing intermetallics─Pd2Ge, Pd2Sn, Pd3Sn2, Pd3Pb, and PtSn─in the catalytic reduction of nitroarenes. In contrast to monometallic Au, Pt, and Pd nanoparticles and ″random″ PdxSn1 – x nanoalloys, which are selective for aniline, nanoparticles of atomically precise intermetallic Pd2Ge, Pd2Sn, Pd3Sn2, and PtSn prefer an indirect condensation pathway and have a high selectivity for the azo(xy) products. The only exception is Pd3Pb, the most active among the intermetallic nanoparticles studied here, which is instead selective for aniline. Employing a novel application of molecular dynamics─based on machine learned potentials within a DeePMD framework─to heterogeneous catalysis, we are able to identify key reaction species on the different types of catalysts employed, furthering our understanding of the unique selectivity of these materials. By demonstrating how intermetallic nanoparticles can be as active yet more selective than other more traditional catalysts, this work provides new physical insights and opens new opportunities in the use of these materials in other important chemical transformations and applications.