Weak Base Conditions Research Articles

Synthesis of S-Allyl-O, O′-Dibutyl Phosphorodithioate and Its Adsorption Mechanism on Chalcopyrite Surface

The demand for non-ferrous copper metals has increased dramatically with the development of the global economy; accordingly, some refractory copper sulfide ores with low grade and their associated minerals are beginning to be utilized, making the flotation separation of copper concentrates exceptionally difficult, especially the separation of chalcopyrite and pyrite. In this paper, S-allyl-O, O′-dibutyl phosphorodithioate (ADTP) was synthesized by a one-pot method and used as a chalcopyrite collector in the flotation separation of chalcopyrite and pyrite. Flotation experiments results have shown that ADTP exhibits better selectivity and greater collecting power for chalcopyrite under neutral or weak base conditions. The 95% recovery of chalcopyrite can be achieved at pH 8.0 and 8.0 mg/L ADTP. From the analysis results of the contact angle, the SEM-EDS spectrogram, and elemental mapping, it was found that ADTP adsorbed uniformly on a chalcopyrite surface and made a significant contribution to the hydrophobicity of the surface. Confirmed by FTIR and XPS analysis, ADTP was able to form P–S–Cu bonds on a chalcopyrite surface, proving that it was adsorbed on the chalcopyrite surface in the form of chemisorption.

Bidentate Ru(II)‐NC Complexes as Catalysts for Transfer Hydrogenation of Ketones with Ethanol

AbstractIn this study, we developed a bidentate Ru(II)‐NC‐catalyzed transfer hydrogen reaction of ketones using ethanol (EtOH) as the hydrogen source under weak base conditions. The control experiments suggested that the reaction proceeded via a Ru‐H mechanism, yielding ethyl acetate as the only byproduct. The deuterium‐labeling experiments showed that hydrogen evolved from the CH2 and OH groups. These results provide a new weak base system for the transfer hydrogen reaction of ketones using EtOH as the hydrogen donor.

Synthesis of Alkyl Aryl Ethers by O-Arylation of Alcohols with Diaryliodonium Salts: Scope, Limitations, and Mechanism

AbstractWe describe the development of a C–O coupling reaction between aryl(2,4,6-trimethoxyphenyl)iodonium salts and aliphatic alcohols under weak base conditions. The scope of the reaction is presented, with 16 examples ranging in yield from moderate to high (54–96%). The limitations of the reaction are also presented. Mechanistic experiments reveal a complex network of reactions that include side reactions that generate arynes and oxidize the alcohol nucleophile.

A Facile Synthesis Route to AuPd Alloys for the Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid.

Synthesis of 2,5-furandicarboxylic acid (FDCA) can be achieved via catalytic oxidation of 5-hydroxymethylfurfural (5-HMF), in which both base and catalyst play important roles. This work presents the development of a simple synthesis method (based on a commercial parent 10 wt.% Pd/C catalyst) to prepare the bimetallic AuPd alloy catalysts (i. e., AuPd/C) for selective 5-HMF oxidation to FDCA. When using the strong base of NaOH, Pd and Au cooperate to promote FDCA formation when deployed either separately (as a physical mixture of the monometallic Au/C and Pd/C catalysts) or ideally alloyed (AuPd/C), with complete 5-HMF conversion and FDCA yields of 66 % vs 77 %, respectively. However, NaOH also promoted the formation of undesired by-products, leading to poor mass balances (<81 %). Comparatively, under weak base conditions (using NaHCO3 ), an increase in Au loading in the AuPd/C catalysts enhances 5-HMF conversion and FDCA productivity (due to the enhanced carbonyl oxidation capacity) which coincides with a superior mass balances of >97 %. Yet, the excessive Pd content in the AuPd/C catalysts was not beneficial in promoting FDCA formation.

Ru(II)-Catalyzed N-Methylation of Amines Using Methanol as the C1 Source.

Four ruthenium complexes were used as catalysts for the N-methylation of amines using methanol as the C1 source under weak base conditions. The (DPEPhos)RuCl2PPh3(1a) catalyst showed the best catalytic performance (0.5 mol %, 12 h). The deuterium labeling and control experiments suggested the reaction via the Ru-H mechanism. This study provides a new ruthenium catalyst system for N-methylation with methanol under weak base conditions.

N,N-Dialkylation of Acyl Hydrazides with Alcohols Catalyzed by Amidato Iridium Complexes via Borrowing Hydrogen

Direct N,N-dialkylation of acyl hydrazide catalyzed by a series of amidato iridium complexes bearing an electron-donating group in the ligand using methanol or ethanol as the alkyl reagent under weak base conditions (10 mol % KHCO3) is described. A wide range of acyl hydrazide derivatives are converted to the corresponding N,N-dialkylated products in excellent yields (38 examples, yields of ≤96%). On the basis of the control experiments and nuclear magnetic resonance studies, a plausible mechanism was proposed. The experimental results indicate that ortho electron-donating groups on the phenyl moiety of the picolinamide ligand play a crucial role in catalytic activity.

SiQDs/Cu-β-CD nanoclusters: A fluorescence probe for the mutual non-interference detection of uric acid and l-cysteine under alkaline conditions

l -Cysteine can enhance the fluorescence of SiQDs/Cu 2 -β-CD nanoclusters at pH 8; uric acid can attenuate their fluorescence at pH 13. SiQDs = silicon quantum dots ; Cu 2 -β-CD = Cu-modified- β -cyclodextrin; l -Cys = l -cysteine. • SiQDs/Cu 2 -β-CD nanoclusters were prepared via coordination-driven self-assembly. • N anoclusters had distinct fluorescence responses for l -cysteine and uric acid. • N anoclusters can achieve the mutual non-interference detection of uric acid and l -cysteine. The fluorescence probes based on quantum dots (QDs) have been widely used in the detection of uric acid (UA), but other biomolecules such as biothiols, ascorbic acid and dopamine have interference with the detection result due to their similar chemical properties. Herein, SiQDs/Cu 2 -β-CD nanoclusters were prepared via coordination-driven self-assembly between Cu 2 -β-CD and –NH 2 on the surface of SiQDs , and UA could attenuate the fluorescence of the nanoclusters under strong alkali conditions, while l -cysteine ( l -Cys) had no effect. Under the optimum conditions, the decreased fluorescence intensity is linearly proportional to the concentration of UA in the range of 0.025–0.15 mM with a detection limit of 4.9*10 -3 mM. Furthermore, under neutral or weak base conditions, l -Cys could improve the fluorescence of the nanocluster, but UA had no effect, which could also be used to detect l -Cys. This work provides a sensitive, selective and convenient fluorescence method for UA and l -Cys detection in the present of another interfering biomolecule.

Calcium-chelated nanosystem reversing cancer chemoresistance via replenishing intracellular calcium ions

Chemoresistance is the major reason for the failure of chemotherapy, which is a major cause of death in patients with advanced cancer. However, the current approach to reversing cancer chemoresistance is limited. Calcium ions are indispensable for all physiological activities of the body. Because a calcium concentration was reduced in chemoresistant cancer cells, we fabricated calcium-chelated nanoparticles upon self-assembly to replenish intracellular calcium ions in the cells. Through employing an amphipathic polyethylene glycosylated (PEGylated) lipids covalent bonding chelator molecule to bind calcium ions, the chelate calcium ions are used for the first time to reverse the chemoresistance of cancer cells. This nanoparticle released calcium ions more rapidly in a weakly acidic environment than in neutral and weak base conditions, which ensures the effective release of calcium ions in the acidic microenvironment of tumors. As assessed by in vitro and in vivo experiments, this calcium-chelated nanoparticle indeed restored calcium homeostasis and reversed chemoresistance in a variety of chemoresistant cancer cells, whereas calcium chloride solution did not increase the concentration of calcium ions in chemoresistant cancer cells. Furthermore, the mechanism study showed that calcium-chelated nanoparticles affected the expression of chemoresistant genes and promoted cancer cell apoptosis by inhibiting the NF-κB signaling pathway. In conclusion, our data provide direct insight into an effective approach for the reversal of chemoresistance and calcium-chelated nanoparticles may have potential applications for treating chemoresistant patients.

DIPEA-induced activation of OH- for the synthesis of amides via photocatalysis.

The development of green protocols for photocatalysis where water acts as a nucleophile, induced by a weak organic base, is difficult to achieve in organic chemistry. Herein, an efficient light-mediated strategy for the synthesis of amides in which a weak organic base acts as a reductant to induce the formation of OH– from water under metal-free conditions is reported. A mechanistic study reveals that the generation of an N,N-diisopropylethylamine (DIPEA) radical via single electron transfer (SET), with the assistance of photocatalyst, that increases the nucleophilicity of the water molecules with respect to the cyanides is essential. Moreover, the removal rate of nitrile in wastewater can be as high as 83%, indicating that this strategy has excellent potential for nitrile degradation.

MORPHOPHYSIOLOGICAL STATUS OF SIMMENTAL BREED CATTLE IN YAKUTIA

The authors argue the impact of environmental stress factors on physiological status of Simmental cattle of local selection, adapted to conditions of breeding in Arctic zone, characterized by weak forage base and unfavorable extreme natural conditions. They found out the total number of red blood cells and the level of hemoglobulin in the investigated animals in the peripheral blood is 14.55% lower than the standard values on the average. The granulocyte concentration in the leukocyte formula exceeds the standard by 1.2%. The level of total protein in the blood serum is significantly higher than the standard one: in calves - by 38.01, in cows - by 17% (P0.001). In peripheral blood, dysproteinemia is observed in the animals. The impact of environmental stress factors on neutrophil opsonophagocytic reaction (ORP) parameters, such as phagocytic activity of neutrophils (FA), phagocytic number (FN), phagocytic index (PI), in vitro, has been determined. The greatest growth of phagocytic activity was observed in the winter stable period, which exceeded the physiological standard by 5.99%. The FA is relatively high in other seasons and corresponds to the upper limit values of the multiyear average. When studying the qualitative characteristics of microphages - phagocytic number - it was revealed that the maximum values are observed in cows in winter-spring period (10,3±1,6 and 10,0±0,7 m.t.), and the minimum - in summer (7,9±0,9 m.t.). When estimating the phagocytic index in the opsonophagocytic reaction, the authors revealed the profound growth of PI values in winter (8.1±1.4 m.t.), which is 34.56% higher than in summer. The data obtained confirm the severity of the impact of environmental conditions, in particular, seasonal changes that play specific role in the adaptive response and in the preservation of the overall organism resistance.

Enzyme cum pH dual-responsive controlled release of avermectin from functional polydopamine microcapsules

Novel enzyme cum pH dual-responsive microcapsule were prepared with an aim to enhance the utilization of pesticides and reduce environmental pollution. The synthetic procedure involved the introduction of urea bonds by forming a covalent bond between isocyanate–functionalized polydopamine (PDA) microcapsules and polyethyleneimine (PEI). The prepared AVM@PDA-IPTS-PEI microcapsules could effectively protect avermectin (AVM) from ultraviolet radiation, and thus decelerate the decomposition rate; the cumulative release showed positive correlations with pH and the urease activity. The AVM release rate was highest at pH 10. At pH 7, the release rate was enhanced after addition of urease, showing improved urease-responsive property under neutral or weak base condition. Especially at pH 7 in presence of urease, the release behavior was in agreement with the Logistic model and able to describe the S-shaped/sigmoidal release profiles, whereas Korsmeyer–Peppas model was better suited in the absence of urease, as the value of K1 was smaller than 0.45, suggesting that the behavior was controlled by Fick’s diffusion. AVM@PDA-IPTS-PEI displayed better adhesion property than AVM, and the microcapsule ameliorated foliage wettability. AVM@PDA-IPTS-PEI exhibited the insecticidal property similarly with AVM, which can be used for reducing the applied quantity of pesticides and improving their efficacy.

Desilylation-Triggered Degradable Silylacetal Polymers Synthesized via Controlled Cationic Copolymerization of Trimethylsilyl Vinyl Ether and Cyclic Acetals.

Silylacetal was demonstrated to function as a promising cleavable moiety for preparing polymers degradable via desilylation under diverse, mild conditions. The silylacetal moieties were installed in the main chain of the polymers via the controlled cationic copolymerization of trimethylsilyl vinyl ether (TMSVE) and a cyclic acetal under appropriately designed conditions. Importantly, desilylation reactions of the silylacetal units occurred under weak acid, base, or fluoride ion conditions, which triggered the degradation of the polymer via the spontaneous cleavage of the unstable hemiacetal moieties generated by the desilylation. Moreover, silylacetal moieties were successfully incorporated at the desired positions in the main chain via the addition of a small portion of TMSVE during the controlled cationic copolymerization of a vinyl ether and cyclic acetal. The strategy devised in this study will allow the design of elaborate polymers that undergo degradation triggered by various stimuli.

Co(cyclam) alkynyl complexes of gem-DEE-aryl: Synthesis, molecular and electronic structures

Reported in this contribution are the syntheses of mono-alkynyl complexes [Co(cyclam)(gem-DEE-Ar)Cl]Cl (cyclam = 1,4,8,11-tetraazacycloctetradecane; gem-DEE = geminal-diethynylethene) with Ar as either –C6H4-4-NO2 (1) or –C6H4-4-NMe2 (2) from the reactions between [Co(cyclam)Cl2]Cl and H-gem-DEE-Ar under weak base conditions. Further reaction between compound 1 and Li-gem-DEE–C6H4–4-NMe2 at −78 °C afforded the unsymmetric complex trans-[Co(cyclam)(gem-DEE–C6H4–4-NO2)(gem-DEE–C6H4–4-NMe2)]Cl (3). Providing structural features observed for other Co(cyclam) alkynyls, X-ray diffraction study also reveals the influence of the aryl substituent on the first coordination sphere of the Co(III) center. The presence of an aryl substituent also shifts the Co-based redox couples, and enables intense LMCT transitions that are absent in complexes of unsubstituted gem-DEE. These contrasts can be rationalized based on DFT calculations.

Highly efficient triazolone/metal ion/polydopamine/MCM-41 sustained release system with pH sensitivity for pesticide delivery.

MCM-41 was prepared through the sol–gel method and encapsulated by polydopamine (PDA) before being coordinated with metal ions to form a highly efficient sustained release system (M-PDA–MCM-41) for triazolone delivery. The characterization results confirmed the existence of the coordination bond between the PDA layer and triazolone through the bridge effect from metal ions, which enhanced the interaction between PDA–MCM-41 and triazolone. The adsorption capacity of Fe-PDA–MCM-41 increased up to 173 mg g–1, which was 160% more than that of MCM-41. The sustained release performance of M-PDA–MCM-41 in different pH values was investigated. Under the conditions of pH ≤7, the release speed of triazolone increased with pH decreasing, whereas its release speed in the weak base condition was slower than in the neutral condition. Therefore, the as-synthesized system showed significant pH-sensitivity in the sustained release process, indicating that the sustained release system can be well stored in the neutral or basic environment and activated in the acid environment. Their sustained release curves described by the Korsmeyer–Peppas equation at pH 7 showed the same behaviour, indicating that PDA decoration or metal ion coordination only increases the steric hindrance and the interaction between carrier and triazolone instead of changing the original structure of the pure MCM material in accordance with X-ray diffraction and Brunauer-Emmett-Teller analysis results.

Nanoscale center-hollowed hexagon MnCo2O4 spinel catalyzed aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

A series of bimetallic Mn-Co-O catalysts were synthesized by a simple hydrothermal method, and the catalytic performance was evaluated. Among these catalysts, center-hollowed hexagon MnCo2O4 exhibited excellent catalytic effect in aerobic oxidation of 5-hydroxymethylfurfural (5-HMF) to 2,5-furandicarboxylic acid (FDCA). A 99.5% 5-HMF conversion and 70.9% FDCA yield can be obtained under molecular oxygen and weak base condition. The efficient catalytic performance was attributed to the Mn3+ ions on the surface of MnCo2O4 catalyst, and its high oxygen mobility and reducibility. Furthermore, this simple synthesis process of non-precious metal catalyst is beneficial to the production of FDCA.

Crystal structures of 5,12-dimethyl-1,4,8,11-tetra-aza-cyclo-tetra-decane cobalt(III) mono-phenyl-acetyl-ide and bis-phenyl-acetyl-ide.

Reported in this contribution are the synthesis and crystal structures of new mono- and bis-phenyl-acetyl-ides based on CoIII(DMC) (DMC is 5,12-dimethyl-1,4,8,11-tetra-aza-cyclo-tetra-deca-ne). Chlorido-(5,12-dimethyl-1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)(phenyl-ethyn-yl)cobalt(III) chloride-aceto-nitrile-methanol (1/1/1), [Co(C8H5)Cl(C12H28N4)]Cl·CH3CN·CH3OH, 1, and (5,12-dimethyl-1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)bis-(phenyl-ethyn-yl)cobalt(III) tri-fluoro-methane-sulfonate-di-chloro-methane (2/1), [Co(C8H5)2(C12H28N4)]2(CF3SO3)2·CH2Cl2, 2, were prepared under weak-base conditions in satisfactory yields. Single-crystal X-ray diffraction studies revealed that both 1 and 2 adopt a pseudo-octa-hedral symmetry in which the Cl-Co-C angles of 1 and C-Co-C of 2 range from 177.7 (2) to 178.0 (2)° and from 177.67 (9) to 179.67 (9)°, respectively. In both structures, the CoIII metal center is coordinated in the equatorial plane by four N atoms, in which the N-Co-N angles range from 85.6 (3) to 94.4 (3)°. The structure of 1 features two crystallographically independent mol-ecules in its triclinic cell (Z' = 2), which are related to each other by pseudo-monoclinic symmetry. The crystal investigated was twinned by a symmetry operator of the approximate double-volume C-centered cell (180° rotation around [201] of the actual triclinic cell), with a refined twin ratio of 0.798 (3) to 0.202 (3). Both methanol solvent mol-ecules in 1 are disordered, the major occupancy rates refined to 0.643 (16) and 0.357 (16). Compound 2 also contains two mol-ecules in the asymmetric unit, together with two tri-fluoro-methane-sulfonate anions [of which one is disordered; occupancy values of 0.503 (16) and 0.497 (16)] and a disordered di-chloro-methane [occupancy values of 0.545 (12) and 0.455 (12)].

Volatile Fatty Acid Accumulation by Alkaline Control Strategy in Anaerobic Fermentation of Primary Sludge

Abstract Effects of pH (5–12) on primary sludge (PS) fermentation and volatile fatty acid (VFA) accumulation were studied in batch experiments. Results showed that under strong alkaline conditions (pH 10–12), hydrolysis could be accelerated and high soluble chemical oxygen demand (SCOD) produced, but acidification was inhibited, resulting in a decrease of VFA production; whereas in weak base (pH 8, 9) conditions, more VFAs accumulated, although less SCOD was produced. Optimal conditions for PS to accumulate VFAs in this study were pH 9 and a fermentation time of 10 days. The study also revealed that protein degradation played an important role in VFA production. More protein was hydrolyzed and acidified at pH 9 than at pH 10 in the system, although protein content at pH 10 was higher. Acetic and propionic acids were the dominant acid species. Furthermore, a comparison of VFAs, NH4+, and pH relationships in pH 9 and pH-uncontrolled systems showed that weak base conditions could significantly enhance the pr...

Triclosan removal from surface water by ozonation - Kinetics and by-products formation

Removal of triclosan from surface water by ozonation was investigated. The results showed that complete elimination of triclosan from a surface water bearing 1–5 mg/L triclosan via continuous ozonation at 5 mg/L, require an ozonation time of 20–30 min depending on pH. Triclosan oxidation followed pseudo-first order kinetics with an apparent reaction rate constant varying from 0.214 min−1 to 0.964 min−1 depending on pH, initial triclosan concentration and water composition. Although the effect of pH was complex due to possible existence of different moieties, higher TCS removal efficiencies were obvious at weak-base conditions. Experiments performed to identify degradation by-products showed the formation of four by-products, namely, 2,4-dichlorophenol, 4-chlorocatechol and two unidentified compounds. Additionally, 2,4-dichloroanisole was detected when a methyl moieties exist in water. By-products were found to be eliminated upon further ozonation. The required exposure time varied from 20 to 30 min depending on pH of water. The ozone demand exerted for the complete oxidation of triclosan and its by-products was calculated as 13.04 mg ozone per mg of triclosan. A triclosan degradation pathway, which was found to be highly pH dependent, was proposed.

An Aerobic Synthetic Approach toward Bis-Alkynyl Cobalt(III) Compounds.

Reported herein is an expanded investigation into a new method for the preparation of Co(III) cyclam bis-alkynyls (cyclam = 1,4,8,11-tetraazacyclotetradecane) under aerobic, weak base conditions. Treatment of trans-[Co(cyclam)(C2Ar)Cl]Cl-type complexes (Ar = C6F5 (1a), 4-C6H4NMe2 (1b)) with AgOTf in MeCN resulted in the doubly charged complexes [Co(cyclam)(C2Ar)(NCMe)](OTf)2 (Ar = C6F5 (2a), 4-C6H4NMe2 (2b)). These solvento complexes 2a,b undergo rapid alkynylation under aerobic conditions in the presence of an organic base and HC2Ar' to form the symmetrical or unsymmetrical bis-alkynyl complexes trans-[Co(cyclam)(C2Ar)(C2Ar')](OTf) (Ar/Ar' = C6F5 (3a), 4-C6H4NMe2 (3b); Ar = C6F5 and Ar' = 4-C6H4NMe2 (3c), C2Ph (3d)) in good yields. Molecular structures of the new compounds were established using single-crystal X-ray diffraction. Structural studies revealed a notable trans influence for the Co-Cα bond lengths in the unsymmetrical complex 3c with a bond length of 1.929(7) Å for the electron-withdrawing -C2C6F5 ligand and 1.944(7) Å for -C2-4-C6H4NMe2. The optical HOMO-LUMO gaps for the bis-alkynyl complexes follow the trend 3a (2.83 eV) > 3d (2.77 eV) > 3c (2.70 eV) > 3b (2.64 eV). Although [Co(cyclam)(C2R)2]+ type complexes typically have irreversible electrochemical reductions, reversibility of the Co(+3/+2) couple improves in Co(III) cyclam complexes bearing more electron withdrawing substituents. Voltammetric analysis also revealed a modest NMe2/NMe2 coupling across the Co-alkynyl backbone in 3b, while DFT calculations identified the HOMO in 3b as the superexchange pathway for such coupling.

Development of Novel Urease-Responsive Pendimethalin Microcapsules Using Silica-IPTS-PEI As Controlled Release Carrier Materials

Microcapsules are highly desirable for attaining the most effective utilization of the pesticide as well as reducing environmental pollution. In this work, a novel urease-responsive system was prepared using isocyanate-functionalized silica cross-linked with polyethylenimine (silica–IPTS–PEI) via urea bonds. The results demonstrated that the silica–IPTS–PEI microcapsules had a high pendimethalin loading efficiency (approximately 30% w/w) and could effectively enhance the thermal and light stability of pendimethalin. The release curves agreed with the Ritger and Peppas equation, and the release of pendimethalin was diffusion-controlled. The release rates of synthesized silica-IPTS-PEI microcapsules showed positive correlation with the temperature. In weak acid and base conditions, the pendimethalin release rates were higher than under neutral conditions, and the silica–IPTS–PEI microcapsules displayed excellent urease-responsive property with controlled release performance. Compared with pendimethalin emul...