scholarly journals Factorial Design of Experiments for Optimization of Photocatalytic Degradation of Tartrazine by Zinc Oxide (ZnO) Nanorods with Different Aspect Ratios

2020 ◽  
Author(s):  
Andrew Skinner ◽  
Anthony DiBernardo ◽  
Arvid Masud ◽  
Nirupam Aich ◽  
Alexandre Pinto
Keyword(s):  
Zinc Oxide ◽  
Aspect Ratio ◽  
Photocatalytic Degradation ◽  
Factorial Design ◽  
Removal Efficiency ◽  
Rate Constant ◽  
Zno Nanorods ◽  
Order Rate Constant ◽  
Order Rate ◽  
Initial Ph

The photocatalytic degradation of the azo dye tartrazine using zinc oxide (ZnO) as photocatalyst under ultraviolet light was investigated using a 2<sup>4</sup> factorial design. The variables studied were the aspect ratio of ZnO nanorods, the ZnO load, the initial pH of tartrazine solution, and the H<sub>2</sub>O<sub>2</sub> volume. These variables were studied aiming to maximize the tartrazine removal efficiency and the pseudo-1<sup>st</sup>-order rate constant of the removal process. The ZnO aspect ratio was tuned by varying the Lewis base during the synthesis, hexamethylenetetramine (HMTA) was used to prepare ZnO with low aspect ratio (ZnO_LowAR), and NaOH was used to prepare ZnO with high aspect ratio (ZnO_HighAR). The microstructural characterizations indicated that ZnO_LowAR and ZnO_HighAR nanorods have similar structural, textural and optical properties. The only exception was the dimensions of the nanorods obtained, which could result in differences in the facets exposed on each type of nanorod surface. The factorial design revealed that ZnO aspect ratio, the initial pH of tartrazine solution, and the H<sub>2</sub>O<sub>2</sub> volume all have primary significant effects, whereas the ZnO load is not significant neither in the tartrazine removal efficiency nor in the pseudo-1<sup>st</sup>-order rate constant. Statistical models considering the coefficients of the significant interactions were obtained, leading to reasonable predicted results in comparison to the results experimentally obtained. The conditions leading to highest removal efficiency (~92%) and pseudo-1<sup>st</sup>-order rate constant (3.81 x 10<sup>-2</sup> min<sup>-1</sup>) were carried out with ZnO_HighAR, initial pH 7, and without H<sub>2</sub>O<sub>2</sub>, which outperformed the TiO<sub>2</sub> P-25 under the same conditions.

scholarly journals Factorial Design of Experiments for Optimization of Photocatalytic Degradation of Tartrazine by Zinc Oxide (ZnO) Nanorods with Different Aspect Ratios

2020 ◽  
Author(s):  
Andrew Skinner ◽  
Anthony DiBernardo ◽  
Arvid Masud ◽  
Nirupam Aich ◽  
Alexandre Pinto
Keyword(s):  
Zinc Oxide ◽  
Aspect Ratio ◽  
Photocatalytic Degradation ◽  
Factorial Design ◽  
Removal Efficiency ◽  
Rate Constant ◽  
Zno Nanorods ◽  
Order Rate Constant ◽  
Order Rate ◽  
Initial Ph

The photocatalytic degradation of the azo dye tartrazine using zinc oxide (ZnO) as photocatalyst under ultraviolet light was investigated using a 2<sup>4</sup> factorial design. The variables studied were the aspect ratio of ZnO nanorods, the ZnO load, the initial pH of tartrazine solution, and the H<sub>2</sub>O<sub>2</sub> volume. These variables were studied aiming to maximize the tartrazine removal efficiency and the pseudo-1<sup>st</sup>-order rate constant of the removal process. The ZnO aspect ratio was tuned by varying the Lewis base during the synthesis, hexamethylenetetramine (HMTA) was used to prepare ZnO with low aspect ratio (ZnO_LowAR), and NaOH was used to prepare ZnO with high aspect ratio (ZnO_HighAR). The microstructural characterizations indicated that ZnO_LowAR and ZnO_HighAR nanorods have similar structural, textural and optical properties. The only exception was the dimensions of the nanorods obtained, which could result in differences in the facets exposed on each type of nanorod surface. The factorial design revealed that ZnO aspect ratio, the initial pH of tartrazine solution, and the H<sub>2</sub>O<sub>2</sub> volume all have primary significant effects, whereas the ZnO load is not significant neither in the tartrazine removal efficiency nor in the pseudo-1<sup>st</sup>-order rate constant. Statistical models considering the coefficients of the significant interactions were obtained, leading to reasonable predicted results in comparison to the results experimentally obtained. The conditions leading to highest removal efficiency (~92%) and pseudo-1<sup>st</sup>-order rate constant (3.81 x 10<sup>-2</sup> min<sup>-1</sup>) were carried out with ZnO_HighAR, initial pH 7, and without H<sub>2</sub>O<sub>2</sub>, which outperformed the TiO<sub>2</sub> P-25 under the same conditions.

scholarly journals The reactivities and ionization properties of the active-site dithiol groups of mammalian protein disulphide-isomerase

1991 ◽  
Vol 275 (2) ◽  
pp. 335-339 ◽  
Author(s):  
H C Hawkins ◽  
R B Freedman
Keyword(s):  
Rate Constant ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Second Order ◽  
Native Enzyme ◽  
Liver Protein ◽  
Thiol Groups ◽  
Protein Disulphide Isomerase ◽  
Order Rate ◽  
Reactive Groups

1. The number of reactive thiol groups in mammalian liver protein disulphide-isomerase (PDI) in various conditions was investigated by alkylation with iodo[14C]acetate. 2. Both the native enzyme, as isolated, and the urea-denatured enzyme contained negligible reactive thiol groups; the enzyme reduced with dithiothreitol contained two groups reactive towards iodoacetic acid at pH 7.5, and up to five reactive groups were detectable in the reduced denatured enzyme. 3. Modification of the two reactive groups in the reduced native enzyme led to complete inactivation, and the relationship between the loss of activity and the extent of modification was approximately linear. 4. Inactivation of PDI by alkylation of the reduced enzyme followed pseudo-first-order kinetics; a plot of the pH-dependence of the second-order rate constant for inactivation indicated that the essential reactive groups had a pK of 6.7 and a limiting second-order rate constant at high pH of 11 M-1.s-1. 5. Since sequence data on PDI show the presence within the polypeptide of two regions closely similar to thioredoxin, the data strongly indicate that these regions are chemically and functionally equivalent to thioredoxin. 6. The activity of PDI in thiol/disulphide interchange derives from the presence of vicinal dithiol groups in which one thiol group of each pair has an unusually low pK and high nucleophilic reactivity at physiological pH.

The Dephosphorylation of Adenosine 5′ -Triphosphate in a Binary and Ternary Zn2+ Complex

1974 ◽  
Vol 29 (11-12) ◽  
pp. 680-682 ◽  
Author(s):  
Peter Amsler ◽  
David Buisson ◽  
Helmut Sigel
Keyword(s):  
Rate Constant ◽  
Ternary Complex ◽  
Order Rate Constant ◽  
Reactive Species ◽  
Ph Optimum ◽  
First Order ◽  
Order Rate

The dephosphorylation of ATP was characterized by determining the dependence of the first-order rate constant on pH in the absence and presence of Zn2+ and together with Zn2+ and 2,2′-bipyridyl. The Zn2+-accelerated reaction passes through a pH optimum at about 8. The decrease in the rate at higher pH is due to the formation of Zn(ATP) (OH)3-; this species is relatively insensitive towards dephosphorylation. It is concluded that Zn(ATP)2- is the reactive species and that the interaction between N (7) and Zn2+ in this complex is crucial for its reactivity. In the presence of 2,2′-bipyridyl (Bipy) the ternary complex, Zn (Bipy) (ATP)2-, is formed which is rather stable towards dephosphorylation. It is suggested that the described effects of acceleration and inhibition are helpful for understanding the recycled processes in nature.

Kinetics of reconstitution of apotyrosinase by copper

1990 ◽  
Vol 68 (2) ◽  
pp. 476-479
Author(s):  
Donald C. Wigfield ◽  
Douglas M. Goltz
Keyword(s):  
Rate Constant ◽  
Copper Concentration ◽  
Copper Ions ◽  
Copper Ion ◽  
Order Rate Constant ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Rate Limiting ◽  
Kinetics Of

The kinetics of the reconstitution reaction of apotyrosinase with copper (II) ions are reported. The reaction is pseudo first order with respect to apoenzyme and the values of these pseudo first order rate constants are reported as a function of copper (II) concentration. Two copper ions bind to apoenzyme, and if the second one is rate limiting, the kinetically relevant copper concentration is the copper originally added minus the amount used in binding the first copper ion to enzyme. This modified copper concentration is linearly related to the magnitude of the pseudo first order rate constant, up to a copper concentration of 1.25 × 10−4 M (10-fold excess), giving a second order rate constant of 7.67 × 102 ± 0.93 × 102 M−1∙s−1.Key words: apotyrosinase, copper, tyrosinase.

DFP (Dilsopropylfluorophosphate) Studies on Molecular Mechanisms of Surface-Dependent Activation of Prekallikrein(PK) and Factor XII(Hageman Factor, HF)

1979 ◽  
Author(s):  
J.H. Griffin ◽  
G. Beretta
Keyword(s):  
Enzymatic Activity ◽  
Rate Constant ◽  
Active Sites ◽  
Molecular Mechanisms ◽  
Order Rate Constant ◽  
Factor Xii ◽  
Single Chain ◽  
Hageman Factor ◽  
Order Rate ◽  
Coagulant Activity

Previous 3H-DFP studies showed that HF binding to kaolin does not result in formation of new active sites. New studies show that single chain zymogen HF, in solution or surface bound, reacts slowly with DFP causing loss of coagulant activity and uptake of 1 mol DIP/mol HF with a 2nd order rate constant, k2=0.4 M-1 min-1. High MW kininogen (HMWK) did not affect the rate constant for this reaction. PK reacts with DFP causing loss of coagulant activity with k2=0.6 M-1min-1. These values are ~103lower than for the activated enzymes (160 and 500 M-1 min-1 for HFa and kallikrein respectively) and are similar to values for trypsinogen that exhibits weak enzymatic activity. HF, PK, HMWK, and kaolin were separately preincubated with 40mM DFP for 5 min to inhibit traces of active enzymes. Then, mixing of these reagents in the presence of 40mM DFP caused a burst of cleavage of 131I-HF and 125I-PK, the extent of which depended on the amount of HMWK. To avoid reciprocal proteolysis of HF and PK, “killed” zymogens (DIP-HF or DIP-PK formed by 48 hr incubation with 40mM DFP) were used in place of HF or PK. Controls showed that PK and DIP-PK were similarly cleaved by purified HFa. If DIP-131I-HF or DIP-125I-PK was substituted for HF or PK in mixtures of HF, PK, HMWK, and kaolin, no detectable cleavage occurred. These data allow that inherent activity of single chain forms of HF or PK may trigger-surface dependent reactions, but the vast majority of molecules are activated by reciprocal proteolysis between HF and PK with HMWK as a cofactor.

scholarly journals MWCNTs/Ag-ZnO nanocomposite for efficient photocatalytic degradation of congo red

2020 ◽  
Vol 34 (1) ◽  
pp. 55-66
Author(s):  
Amogne W. Yibeltal ◽  
Belete B. Beyene ◽  
Shimelis Admassie ◽  
Abi M. Taddesse
Keyword(s):  
Zinc Oxide ◽  
Visible Light ◽  
Rate Constant ◽  
Congo Red ◽  
Organic Pollutant ◽  
Order Rate Constant ◽  
Multi Walled Carbon Nanotubes ◽  
Walled Carbon Nanotubes ◽  
Role Of Light

Three nanomaterials namely, zinc oxide (ZC), silver-doped zinc oxide (AZ) and multi-walled carbon nanotubes coupled with silver doped zinc oxide nanocomposite (MWAZ) were synthesized, characterized and employed for photo degradation of an organic pollutant, congo red (CR). The photocatalytic activity study showed efficient degradation of CR upon irradiation with UV and visible light in the order of MWAZ > AZ > ZC > Commercial ZnO (ZCO). Percentage photodegradation of 99% and a pseudo 1st order rate constant of 2.3 x 10-2 min-1 were achieved by MWAZ as a catalyst under visible light irradiation, implying photo- sensitizing ability of MWCNTs and the capability of MWCNTs to hinder recombination of photogenerated holes and electrons. The control experiment in the dark condition gave only 7.9% of degradation efficiency and 5.56 x 10-4 min-1 rate constant, implying the significant role of light source for catalytic degradation of CR.   Bull. Chem. Soc. Ethiop. 2020, 34(1), 55-66. DOI: https://dx.doi.org/10.4314/bcse.v34i1.5

The mechanisms of hydrolysis of alkyl N-alkylthioncarbamate esters at 100 °C

2005 ◽  
Vol 83 (9) ◽  
pp. 1483-1491 ◽  
Author(s):  
Eduardo Humeres ◽  
Maria de Nazaré M. Sanchez ◽  
Conceição ML Lobato ◽  
Nito A Debacher ◽  
Eduardo P. de Souza
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Base Catalysis ◽  
Hydrolysis Rate ◽  
Negative Slope ◽  
General Base ◽  
Order Rate ◽  
Basic Hydrolysis ◽  
Rate Profile ◽  
Hydrolysis Of

The hydrolysis of ethyl N-ethylthioncarbamate (ETE) at 100 °C was studied in the range of 7 mol/L HCl to 4 mol/L NaOH. The pH–rate profile showed that the hydrolysis occurred through specific acid catalysis at pH < 2, spontaneous hydrolysis at pH 2–6.5, and specific basic catalysis at pH > 6.5. The Hammett acidity plot and the excess acidity plot against X were linear. The Bunnett–Olsen plot gave a negative slope indicating that the conjugate acid was less hydrated than the neutral substrate. It was concluded that the acid hydrolysis occurred by an A1 mechanism. The neutral species hydrolyzed with general base catalysis shown by the Brønsted plot with β = 0.48 ± 0.04. Water acted as a general base catalyst with (pseudo-)first-order rate constant, kN = 3.06 × 10–7 s–1. At pH > 6.5 the rate constants increased, reaching a plateau at high basicity. The basic hydrolysis rate constant of ethyl N,N-diethylthioncarbamate, which must react by a BAc2 mechanism, increased linearly at 1–3 mol/L NaOH with a second-order rate constant, k2 = 2.3 × 10–4 (mol/L)–1 s–1, which was 10 times slower than that expected for ETE. Experiments of ETE in 0.6 mol/L NaOH with an excess of ethylamine led to the formation of diethyl thiourea, presenting strong evidence that the basic hydrolysis occurred by the E1cb mechanism. In the rate-determining step, the E1cb mechanism involved the elimination of ethoxide ion from the thioncarbamate anion, producing an isothiocyanate intermediate that decomposed rapidly to form ethylamine, ethanol, and COS.Key words: alkylthioncarbamate esters, ethyl N-ethylthioncarbamate, ethyl N,N-diethylthioncarbamate, hydrolysis, mechanism.

scholarly journals Inactivation of the endogenous argininosuccinate lyase activity of duck δ-crystallin by modification of an essential histidine residue with diethyl pyrocarbonate

1993 ◽  
Vol 293 (2) ◽  
pp. 537-544 ◽  
Author(s):  
H J Lee ◽  
S H Chiou ◽  
G G Chang
Keyword(s):  
Enzyme Activity ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Histidine Residue ◽  
Argininosuccinate Lyase ◽  
First Order ◽  
Diethyl Pyrocarbonate ◽  
Order Rate ◽  
Lyase Activity ◽  
Pseudo First Order

The argininosuccinate lyase activity of duck delta-crystallin was inactivated by diethyl pyrocarbonate at 0 degrees C and pH 7.5. The inactivation followed pseudo-first-order kinetics after appropriate correction for the decomposition of the reagent during the modification period. The plot of the observed pseudo-first-order rate constant versus diethyl pyrocarbonate concentration in the range of 0.17-1.7 mM was linear and went through the origin with a second-order rate constant of 1.45 +/- 0.1 M-1.s-1. The double-logarithmic plot was also linear, with slope of 1.13, which suggested a 1:1 stoichiometry for the reaction between diethyl pyrocarbonate and delta-crystallin. L-Arginine, L-norvaline or L-citrulline protected the argininosuccinate lyase activity of delta-crystallin from diethyl pyrocarbonate inactivation. The dissociation constants for the delta-crystallin-L-arginine and delta-crystallin-L-citrulline binary complexes, determined by the protection experiments, were 4.2 +/- 0.2 and 0.12 +/- 0.04 mM respectively. Fumarate alone had no protective effect. However, fumarate plus L-arginine gave synergistic protection with a ligand binding interacting factor of 0.12 +/- 0.02. The double-protection data conformed to a random Uni Bi kinetic mechanism. Fluorescence-quenching studies indicated that the modified delta-crystallin had minimum, if any, conformational changes as compared with the native delta-crystallin. Inactivation of the enzyme activity was accompanied by an increasing absorbance at 240 nm of the protein. The absorption near 280 nm did not change. Treatment of the modified protein with hydroxylamine regenerated the enzyme activity to the original level. These results strongly indicated the modification of an essential histidine residue. Calculation from the 240 nm absorption changes indicated that only one histidine residue per subunit was modified by the reagent. This super-active histidine residue has a pKa value of approximately 6.8 and acts as a general acid-base catalyst in the enzyme reaction mechanism. Our experimental data are compatible with an E1cB mechanism [Raushel (1984) Arch. Biochem. Biophys. 232, 520-525] for the argininosuccinate lyase with the essential histidine residue close to the arginine-binding domain of delta-crystallin. L-Citrulline, after binding to this domain, might form an extra hydrogen bond with the essential histidine residue.

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