General base-catalyzed hydrolysis and carbonyl-18O exchange of N-(4-nitrobenzoyl)pyrrole

1998 ◽  
Vol 76 (10) ◽  
pp. 1410-1417
Author(s):  
Laurence J Beach ◽  
Raymond J Batchelor ◽  
Frederick WB Einstein ◽  
Andrew J Bennet
Keyword(s):  
Ph Value ◽  
Buffer Concentration ◽  
Hydrolysis Kinetics ◽  
Tetrahedral Intermediate ◽  
Ph Values ◽  
General Base ◽  
Amide Hydrolysis ◽  
Measured Ratio ◽  
Exchange Kinetics

Base-promoted hydrolysis kinetics for N-(4-nitrobenzoyl)pyrrole (1) have been measured as a function of buffer concentration at several pH values at 25°C. In addition carbonyl-18O exchange kinetics have been determined at a single pH value (9.48) as a function of 1,4-diazobicyclo[2.2.2]octane (DABCO) concentration. At zero buffer concentration the measured ratio of 18O exchange to hydrolysis (kex/khyd) is approximately 0.04, and this value increases and finally levels off at about 0.23 as the DABCO concentration is increased. These observations are consistent with the buffer acting as a general-base to catalyze both the attack of water to generate an anionic tetrahedral intermediate (To-) and the breakdown of To- to give hydrolysis products.Key words: amide, hydrolysis, catalysis, general-base, tetrahedral intermediate.

Intramolecular nucleophilic participation by the thiol group during amide hydrolysis. Part 2. The imidazole catalysis dilemma

1992 ◽  
Vol 70 (1) ◽  
pp. 62-67 ◽  
Author(s):  
Robert S. McDonald ◽  
Patricia Patterson ◽  
June Rodwell ◽  
Ann Whalley
Keyword(s):  
Aqueous Solution ◽  
Thiol Group ◽  
Tetrahedral Intermediate ◽  
General Base ◽  
General Acid ◽  
Amide Hydrolysis ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Imidazole Catalysis

Catalysis by imidazole and N-methylimidazole buffers of the intramolecular thiolysis of N-n-propyl 2-mercaptomethylbenzamide (forming 2-thiophthalide) has been studied in aqueous solution at 40.0 °C, μ = 1.0. Unlike other buffers previously studied, imidazole and N-methylimidazole are able to catalyze, by a general base route, formation of neutral tetrahedral intermediate; this pathway is rate limiting at pH ≤ 7.5. At higher pH, the previously reported general acid-catalyzed breakdown of this intermediate is rate limiting. The relevance of these observations to the currently accepted pathway for the acylation of papain by amide substrates is discussed. Keywords: amide hydrolysis, intramolecular, thiol participation, imidazole, papain model.

scholarly journals Bonding of Selected Hardwoods with PVAc Adhesive

2020 ◽  
Vol 11 (1) ◽  
pp. 67
Author(s):  
Ján Iždinský ◽  
Ladislav Reinprecht ◽  
Ján Sedliačik ◽  
Jozef Kúdela ◽  
Viera Kučerová
Keyword(s):  
Adhesion Strength ◽  
Cold Water ◽  
Ph Value ◽  
Water Extract ◽  
Solid Wood ◽  
Contact Angles ◽  
Water Contact ◽  
Ph Values ◽  
Positive Tendency ◽  
The Impact

The bonding of wood with assembly adhesives is crucial for manufacturing wood composites, such as solid wood panels, glulam, furniture parts, and sport and musical instruments. This work investigates 13 hardwoods—bangkirai, beech, black locust, bubinga, ipé, iroko, maçaranduba, meranti, oak, palisander, sapelli, wengé and zebrano—and analyzes the impact of their selected structural and physical characteristics (e.g., the density, cold water extract, pH value, roughness, and wettability) on the adhesion strength with the polyvinyl acetate (PVAc) adhesive Multibond SK8. The adhesion strength of the bonded hardwoods, determined by the standard EN 205, ranged in the dry state from 9.5 MPa to 17.2 MPa, from 0.6 MPa to 2.6 MPa in the wet state, and from 8.5 MPa to 19.2 MPa in the reconditioned state. The adhesion strength in the dry state of the bonded hardwoods was not influenced by their cold water extracts, pH values, or roughness parallel with the grain. On the contrary, the adhesion strength was significantly with positive tendency influenced by their higher densities, lower roughness parameters perpendicular to the grain, and lower water contact angles.

scholarly journals Microstructure and Properties of Self-Assembly Graphene Microcapsules: Effect of the pH Value

Nanomaterials ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 587 ◽  
Author(s):  
Yan-Dong Guo ◽  
Jun-Feng Su ◽  
Ru Mu ◽  
Xin-Yu Wang ◽  
Xiao-Long Zhang ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Photoelectron Spectroscopy ◽  
Self Assembly ◽  
Chemical Engineering ◽  
Ph Value ◽  
Liquid Paraffin ◽  
Energy Dispersive Spectrometer ◽  
Core Material ◽  
Microstructure And Properties ◽  
Ph Values

Graphene has attracted attention in the material field of functional microcapsules because of its excellent characteristics. The content and state of graphene in shells are critical for the properties of microcapsules, which are greatly affected by the charge adsorption equilibrium. The aim of this work was to investigate the effect of pH value on the microstructure and properties of self-assembly graphene microcapsules in regard to chemical engineering. Microcapsule samples were prepared containing liquid paraffin by a self-assembly polymerization method with graphene/organic hybrid shells. The morphology, average size and shell thickness parameters were investigated for five microcapsule samples fabricated under pH values of 3, 4, 5, 6 and 7. The existence and state of graphene in dry microcapsule samples were analyzed by using methods of scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). Fourier Transform Infrared Spectoscopy (FT-IR) and Energy Dispersive Spectrometer (EDS) were applied to analyze the graphene content in shells. These results proved that graphene had existed in shells and the pH values greatly influenced the graphene deposition on shells. It was found that the microcapsule sample fabricated under pH = 5 experienced the largest graphene deposited on shells with the help of macromolecules entanglement and electrostatic adherence. This microcapsules sample had enhanced thermal stability and larger thermal conductivity because of additional graphene in shells. Nanoindentation tests showed this sample had the capability of deforming resistance under pressure coming from the composite structure of graphene/polymer structure. Moreover, more graphene decreased the penetrability of core material out of microcapsule shells.

Study on Influence of Silicate Morphology Based on pH Value

2012 ◽  
Vol 454 ◽  
pp. 324-328
Author(s):  
Yan He ◽  
Ya Jing Liu ◽  
Yong Lin Cao ◽  
Li Xia Zhou
Keyword(s):  
Silicic Acid ◽  
Ph Value ◽  
Colorimetric Method ◽  
Absorption Spectrometry ◽  
Degree Of Polymerization ◽  
Raw Material ◽  
X Ray Diffraction ◽  
X Ray ◽  
Ph Values ◽  
The Stability

Infra-red absorption spectrometry, X-ray diffraction observations and characterization tests based on silicon molybdenum colorimetric method were used to investigate the optimal pH value controlling the stability of the silicic acid form. The experiment process was done by using sodium silicate as raw material. The results showed that the solution of silicate influenced the polymerization. The active silicic acid solution with a certain degree of polymerization was obtained by controlling the pH values.

scholarly journals Oral pH value predicts the incidence of radiotherapy related caries in nasopharyngeal carcinoma patients

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Zheng Li ◽  
Qiuji Wu ◽  
Xiangyu Meng ◽  
Haijun Yu ◽  
Dazhen Jiang ◽  
...  
Keyword(s):  
Nasopharyngeal Carcinoma ◽  
Radiation Dose ◽  
Protective Factors ◽  
Green Tea ◽  
Cox Regression ◽  
Ph Value ◽  
Dynamic Monitoring ◽  
Tea Consumption ◽  
Ph Values ◽  
Kaplan Meier

AbstractRadiotherapy-related caries is a complication of radiotherapy for nasopharyngeal carcinoma; however, factors influencing the occurrence, accurate prediction of onset, and protective factors of radiotherapy-related caries remain unclear. This study analyzed risk factors, disease predictors, and protective factors for radiotherapy-related caries in nasopharyngeal carcinoma. This prospective study included 138 nasopharyngeal carcinoma patients receiving radical radiotherapy at our hospital during June 2012–December 2016 and were followed up for dental caries. Patients’ clinical data on radiotherapy were collected, dynamic monitoring was performed to assess changes in oral pH values, and a questionnaire survey was administered to collect patients’ lifestyle habits. Time-dependent cox regression trees, event-free Kaplan–Meier curve, Mann–Whitely U test were used to analysis the results. The median follow-up time was 30 (12–60) months. Radiotherapy-related caries occurred in 28 cases (20.3%). Univariate analyses showed that radiotherapy-related caries was associated with patient’s age, oral saliva pH value, green tea consumption, and radiation dose to sublingual glands, but not with the radiation dose to the parotid and submandibular glands. Multivariate analysis showed that oral saliva pH value [hazard ratio (HR) = 0.390, 95% confidence interval = 0.204–0.746] was an independent prognostic factor for radiotherapy-related caries. Patients with oral saliva pH values ≤ 5.3 in the 9th month after radiotherapy represented a significantly higher risks for radiotherapy-related caries (p < 0.001). Green tea consumption was associated with the occurrence of radiotherapy-related caries, and oral saliva pH values could predict the occurrence of radiotherapy-related caries. Limiting radiation doses to sublingual glands can reduce the occurrence of radiotherapy-related caries.

Effect of pH Value on the Synthesis of NiO Nanoparticles and Microstructure of NiO Based Composite Anode

2021 ◽  
Vol 317 ◽  
pp. 447-453
Author(s):  
Noor Hidayah Aniza Zakaria ◽  
Nafisah Osman
Keyword(s):  
Ph Value ◽  
Sol Gel ◽  
Secondary Phase ◽  
Average Diameter ◽  
Morphological Observation ◽  
Nio Nanoparticles ◽  
Composite Anode ◽  
Ph Values ◽  
Particle Size Analyzer ◽  
Nio Nps

NiO nanoparticle was synthesized by a sol-gel method with three different pH values namely pH=1, 7 and 11, and then calcined at temperature of 450 ᵒC. The influence of different pH values on the physical properties of NiO nanoparticles were investigated by a particle size analyzer (PSA), field emission scanning electron microscope (FESEM) and X-ray diffractometer (XRD). Structural analysis confirmed that a cubic structure of NiO nanoparticle was obtained without any secondary phase for NiO powders prepared with pH=1, while the peak of secondary phase (Ni) appeared for NiO powders prepared with pH= 7 and 11. Morphological observation showed that the NiO nanoparticles prepared with pH=7 and 11 tend to form more agglomerates compared to one prepared with pH=1. The average diameter of NiO nanoparticles with pH 1, 7 and 11 were approximately in the range of 19-26 nm, 21-28 nm, and 24-30 nm, respectively. NiO powder that was synthesized with pH=1 was further used to prepare composite anode of NiO Nps-BaCe0.54Zr0.36Y0.1O2.95 (BCZY) powder. Unfortunately a composite of NiO Nps-BaCeO3-BaZrO3 was obtained instead of BCZY and governed by agglomerates with size in the range of 70-300 nm.

scholarly journals Evaluation of the pH, calcium release and antibacterial activity of MTA Fillapex

2013 ◽  
Vol 42 (5) ◽  
pp. 330-335 ◽  
Author(s):  
Milton Carlos Kuga ◽  
Gisele Faria ◽  
Paulo Henrique Weckwerth ◽  
Marco Antonio Hungaro Duarte ◽  
Edson Alves De Campos ◽  
...  
Keyword(s):  
Antibacterial Activity ◽  
Calcium Release ◽  
Ph Value ◽  
Diffusion Test ◽  
Evaluation Period ◽  
Ph Values ◽  
Agar Diffusion Test ◽  
Ah Plus ◽  
Endodontic Sealers ◽  
And Staphylococcus Aureus

OBJECTIVE: This study evaluated, in several analysis periods, pH and calcium release and antibacterial activity provided by MTA Fillapex sealer compared to Sealapex and AH Plus sealers. MATERIAL AND METHOD: Polyethylene tubes were filled with a sealer and immersed in distilled water. After 24 hours, 14 and 28 days, pH and calcium release by endodontic sealers were evaluated directly in water which the tubes were stored. Sealers antibacterial activity was evaluated against Enterococcus faecalis and Staphylococcus aureus by means of agar diffusion test. All data were submitted to ANOVA and Tukey tests (α=0.05). RESULT: In all periods evaluated, Sealapex had the highest pH value (p<0.05) in comparison to other sealers and MTA Fillapex provided higher pH values than AH Plus (p<0.05). In 14-days period, MTA Fillapex had greater calcium release value than Sealapex (p<0.05). In 28-days period, Sealapex provided higher calcium release than MTA Fillapex (p<0.05). In all periods, AH Plus provided lower calcium release than other sealers (p<0.05). In relation to E. faecalis, there were no differences among the sealers, in relation to antibacterial activity (p>0.05). In relation to S. aureus, Sealapex presented better antibacterial effectiveness than the MTA Fillapex and AH Plus (p<0.05), which were similar each other (p>0.05). CONCLUSION: In final evaluation period, pH values and calcium release provided by MTA Fillapex were lower than provided by Sealapex and higher than provided by AH Plus. The MTA Fillapex antimicrobial action was similar to other endodontic sealers.

GROWTH OF STAPHYLOCOCCUS AUREUS IN ACIDIFIED PASTEURIZED MILK1

1970 ◽  
Vol 33 (11) ◽  
pp. 516-520 ◽  
Author(s):  
T. E. Minor ◽  
E. H. Marth
Keyword(s):  
Staphylococcus Aureus ◽  
Acetic Acid ◽  
Lactic Acid ◽  
Hydrochloric Acid ◽  
Ph Value ◽  
The Other ◽  
Antagonistic Effects ◽  
Pasteurized Milk ◽  
Ph Values ◽  
Effect On Growth

The effect of gradually reducing the pH of pasteurized milk with acetic, citric, hydrochloric, lactic, and phosphoric acids over periods of 4, 8, and 12 hr on growth of Staphylococcus aureus 100 in this substrate was determined. In addition, 1: 1 mixtures of lactic acid and each of the other acids, and of acetic and citric acids were evaluated for their effect on growth of this organism. To achieve a 90% reduction in growth over a 12 hr period, a final pH value of 5.2 was required for acetic, 4.9 for lactic, 4.7 for phosphoric and citric, and 4.6 for hydrochloric acid. A 99% reduction during a 12 hr period was obtained with a final pH value of 5.0 for acetic, 4.6 for lactic, 4.5 for citric, 4.1 for phosphoric, and 4.0 for hydrochloric acid. A pH value of 3.3 was required for a 99.9% reduction with hydrochloric acid, whereas the same effect was produced at a pH value of 4.9 with acetic acid. Correspondingly lower pH values were required to inhibit growth within 8 and 4 hr periods. Mixtures of acids adjusted to pH values at the borderline for growth (12 hr period) exhibited neither synergistic nor antagonistic effects between two acids.

Study on Decolorization of Wastewater Containing Acid Orange II by Adsorption on Expanded Graphite

2011 ◽  
Vol 183-185 ◽  
pp. 873-876
Author(s):  
Jun Jie Yue ◽  
Xing Long Jin ◽  
Zhao Hui Jin
Keyword(s):  
Ph Value ◽  
Expanded Graphite ◽  
Orange Ii ◽  
Dye Wastewater ◽  
Temperature Level ◽  
Initial Concentration ◽  
Acid Orange ◽  
Ph Values ◽  
Simulated Wastewater ◽  
Acid Orange Ii

In this paper, the adsorption and decolorization capability of expanded graphite (EG) on the simulated wastewater containing Acid Orange Ⅱwere studied. The experimental results show that the initial concentration of wastewater, the dosage of EG, the pH value and the temperature all have greater effects on the decolorization ratio of simulated Acid Orange Ⅱ wastewater. The dye- wastewater containing lower concentration(＜150 mg/L) of Acid Orange Ⅱ is more suitable to be treated by EG, and approximately 100 mg/L is the preferable concentration. The decolorization ratio increases with the increment of the dosage of EG and the temperature level, but the growth rate obviously decreases at the higher initial concentration. All the decolorization ratios under strong acidic (pH<5) and alkalic (pH>11) conditions are higher than that at the range of 5-11 pH values, the highest value even reaches over 94%, while the decolorization ratio under the latter conditions are only between 75% and 85%.

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