New In Situ Catalysts Based on Nitro Functional Pyrazole Derivatives and Copper (II) Salts for Promoting Oxidation of Catechol to o-Quinone

Round 1

Reviewer 1 Report (New Reviewer)

This manuscript dealt with the development of catalysts based on copper complexes with pyrazole-based ligands for oxidation of catechol to o-quinone. This reaction can be performed by catecholase enzyme and is often called catalase reaction.  It can be found from the analysis of literature, that the authors sequentially study the catalytic activity of various complexes of copper with nitrogen-containing ligands in this reaction. The new complexes with new ligands were studied and demonstrated activity in the reaction under study. The influence of ligands nature, concentration, solvent and the nature of copper salts used as precursors were studied.

However, the manuscript needs revision.

1.    Firstly, the use of English is very poor. The text needs revision by expert in English writing.

2.    Second, for the Journal like Catalyst I recommend to delete mentioning of catecholase reaction from the title and change it by oxidation of catechol to o-quinone, as this manuscript has no intention to mimic or explain the action of catecholase enzyme, and simply use metallocomplex catalyst to perform oxidation of catechol to o-quinone.

3.    The introduction includes many references to a wide variety of applications of compounds based on pyrazoles, which is completely redundant to describe their use as ligands for copper catalysts, which is the subject of the manuscript. Also the mention of metalloproteinase can be excluded. On the other side, some relevant publications of the authors were not mentioned like Materials Today: Proceedings 13 (2019) 1134–1142,

4.    I was not able to find the formulae which were used to calculate reaction rates (e.g. in Table 1). They have to be presented in the manuscript.

5.    What is the nature of precipitate formed during reaction L1 with two copper salts?

6.    What does it mean (2L/1M) in the title of paragraph 4.1.1? It needs to be explained at first appearance, not in the conclusion section.

7.    In the beginning of paragraph 4 it is said that blank experiment demonstrated that Ab% (what is it? Absorbance? It is not measured in percent) almost unchanged. But in what solvent blank experiment was performed?

8.    In paragraph 4.1.1 the concentration of catechol solution is provided as 10^-1 mol/l, that means 1 mol/l. Why not write 1 mol/l?

9.    Is it possible that some components of the reaction mixture react with methanol used as a solvent?

 In paragraph 4.3 it is said that affinity was strong in MeOH. What does it mean?

I cannot understand the first phrase in paragraph 4.4.

The producers of all used compounds are not named in experimental section.

Author Response

Review 1

However, the manuscript needs revision.

1. Firstly, the use of English is very poor. The text needs revision by expert in English writing.

Native English colleague improved the language of the MS (please see the revised version, the English editing was performed by Prof. Abdullah Y. A. Alzahrani).

2. Second, for the Journal like Catalyst I recommend to delete mentioning of catecholase reaction from the title and change it by oxidation of catechol to o-quinone, as this manuscript has no intention to mimic or explain the action of catecholase enzyme, and simply use metallocomplex catalyst to perform oxidation of catechol to o-quinone.

Was changed as you wish (please see the revised version)

2. The introduction includes many references to a wide variety of applications of compounds based on pyrazoles, which is completely redundant to describe their use as ligands for copper catalysts, which is the subject of the manuscript. Also the mention of metalloproteinase can be excluded. On the other side, some relevant publications of the authors were not mentioned like Materials Today: Proceedings 13 (2019) 1134–1142,

Corrected accordingly (we have inserted the suggested reference above, moreover, the references have enhanced by two works about catechol oxidation have recently published by our team in Catalysts and ACS omega, please see the revised version)

32.Titi, A.; Al‐Noaimi, M.; Kaddouri, Y.; El Ati, R.; Yousfi, E.B.; El Kodadi, M.; Touzani, R. Study of the catecholase catalytic properties of copper (II) complexes prepared in‐situ with monodentate ligands. Materials Today: Proceedings 2019, 13, 1134‐1142.

33.El Boutaybi, M.; Titi, A.; Alzahrani, A.Y.A.; Bahari, Z.; Tillard, M.; Hammouti, B.; Touzani, R. Aerial Oxidation of Phenol/Catechol in the Presence of Catalytic Amounts of [(Cl)2Mn(RCOOET)], RCOOET=Ethyl‐5‐Methyl‐1‐(((6‐methyl‐3‐nitropyridin‐2‐yl)amino)methyl)‐1Hpyrazole‐3‐carboxylate. Catalysts 2022, 12, 1642.

34.Abderrahim Titi, Rachid Touzani, Anna Moliterni, Carlotta Giacobbe, Francesco Baldassarre, Mustapha Taleb, Nabil Al-Zaqri, Abdelkader Zarrouk, and Ismail Warad; Ultrasonic Clusterization Process to Prepare [(NNCO)6Co4Cl2] as a Novel Double-Open-Co4O6 Cubane Cluster: SXRD Interactions, DFT, Physicochemical, Thermal Behaviors, and Biomimicking of  Catecholase Activity

4. I was not able to find the formulae, which were used to calculate reaction rates (e.g. in Table 1). They have to be presented in the manuscript.

We added the formulae of reaction rate of catechol oxidation before the table 1

5. What is the nature of precipitate formed during reaction L1 with two copper salts?.

    -When we used the combination one ligand with two cooper (1L/2M), we have noted many time a black powder precipitate in deep of the cuvette and makes absorbance unstable. In fact, we did not characterized the powder precipitated but, the undesired powder formed during reaction (1L/2M) result of excess of metal so probably the nature of the precipitate is copper Oxide

6. What does it mean (2L/1M) in the title of paragraph 4.1.1? It needs to be explained at first appearance, not in the conclusion section.

 We explained it at the first appearance in the title and we exclude the explication from conclusion

7. In the beginning of paragraph 4 it is said that blank experiment demonstrated that Ab% (what is it? Absorbance? It is not measured in percent) almost unchanged. But in what solvent blank experiment was performed?.

- Abbreviation Ab% is means absorbance (has changed in MS, please see the revised version.

8. In paragraph 4.1.1 the concentration of catechol solution is provided as 10^-1mol/l, that means 1 mol/l. Why not write 1 mol/l?

It is mean 0.1mol/L; we modified it to be clearer than 10^-1 mol/L.

9. Is it possible that some components of the reaction mixture react with methanol used as a solvent?

- Yes, because methanol solvent is a polar and a protic solvent, then it has capabilities to form bonding hydrogen and coordinate with vacuum orbital metal by free pair of oxygen, but it is still quite limited compared with the strongest of the prepared ligands.

 In paragraph 4.3 it is said that affinity was strong in MeOH. What does it mean?

From many works about catalysts, the parameter K_m can inform us about the suitability of solvent used with the combination studied and about the affinity of catalyst for catechol substrate which means the influence of catalyst for catechol substrate

I cannot understand the first phrase in paragraph 4.4.

We change the phrase with another clearer

The producers of all used compounds are not named in experimental section.

We mentioned in experimental section

Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

The reviewed paper reports a simple synthesis of four pyrazole derivatives N-substituted nitroaniline moieties. The authors examined the influence of the obtained pyrazole ligands with four copper (II) salts on the solution autoxidation of catechol. The study's outcome is finding the best-performing set (ligand/Cu salt/solvent) as measured by the formation rate of ortho-benzoquinone.

The investigation was carried out using an appropriate methodology, and the experiments were reported adequately. The presented mechanistic discussion is acceptable. The conclusions mostly correspond to the obtained results. However, the whole work is only loosely related to the enzymatic process. I regard the attempted fitting kinetics to the Michaelis-Menten model as an artificial decoration. Also, the title referring to …" for promoting catecholase reaction" should run …for autoxidation of catechol. The nearly identical pictures (Fig. 2,3) should be moved to the SI. The presented Scheme 3 seems superfluous when referring to the current work. It is unacceptable from the chemical point of view without the necessary details. For instance, what exact structures should appear in the key steps B→C→D. Did you detect hydrogen peroxide?

The English used in the paper deserves the attention of an editor.

Author Response

Review 2

The reviewed paper reports a simple synthesis of four pyrazole derivatives N-substituted nitroaniline moieties. The authors examined the influence of the obtained pyrazole ligands with four copper (II) salts on the solution autoxidation of catechol. The study's outcome is finding the best-performing set (ligand/Cu salt/solvent) as measured by the formation rate of ortho-benzoquinone.

The investigation was carried out using an appropriate methodology, and the experiments were reported adequately. The presented mechanistic discussion is acceptable. The conclusions mostly correspond to the obtained results. However, the whole work is only loosely related to the enzymatic process. I regard the attempted fitting kinetics to the Michaelis-Menten model as an artificial decoration. Also, the title referring to …" for promoting catecholase reaction" should run …for autoxidation of catechol. The nearly identical pictures (Fig. 2,3) should be moved to the SI. The presented Scheme 3 seems superfluous when referring to the current work. It is unacceptable from the chemical point of view without the necessary details. For instance, what exact structures should appear in the key steps B→C→D. Did you detect hydrogen peroxide?

-the superfluous of the figures between supporting information and manuscript have done accordingly.

-The exact proposed structures in the key B, C and D is the same proposed structure of complex A, and its structure was simplified as N2CuN2X2 just for more clarity in cycle mechanism, because the differences have just depended in substituted the counter-anion (X) by the catechol substrate and oxidation numbers (II→I →II).

-For the second remark, unfortunately, we did not detect hydrogen peroxide experimentally, because the detector of H2O2 unavailable in our laboratory.

The English used in the paper deserves the attention of an editor.

Native English colleague improved the language of the MS (please see the revised version, the English editing was performed by Prof. Abdullah Y. A. Alzahrani).

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report (New Reviewer)

Sorry, the Authors didn't respond to my previous remarks (see the comments to the earlier version). I'm afraid the paper on simple chemistry was written by bio-medics (?), and the Authors did not understand chemistry (detection of H2O2!). Still, the results (facts) are worthy of publication. However, all the "decorative" material has nothing to do with the outcomes and should be removed. 

Author Response

Sorry, the Authors didn't respond to my previous remarks (see the comments to the earlier version). I'm afraid the paper on simple chemistry was written by bio-medics (?), and the Authors did not understand chemistry (detection of H2O2!). Still, the results (facts) are worthy of publication. However, all the "decorative" material has nothing to do with the outcomes and should be removed. 

Response

Thanks a lot for your kind remarks

Please we don’t have H2O2 detection system

We remove the part 4.4. Proposed mechanism…..

Please see the revised version (R2)

With regards

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

In the revised version of the manuscript “New in-situ catalysts based on nitro functional pyrazole derivatives and Copper (II) salts for promoting the oxidation of catechol to o-quinone” the authors have addressed some minor issues raised by the reviewers earlier. However, one of the major concerns has not been resolved yet. In order to evaluate the performance of the presented catalysts UV-VIS spectra have been recorded and the increase in absorption attributed to the formation of the quinone. However, the quinone has not been isolated in pure form after the reaction and therefore the yield of the product is not correlated to the UV-VIS spectra. It is possible that the spectra are superpositions of the quinone and complexes of copper with catechol or quinone as ligands. The formation of such complexes has been proposed in the mechanistic rational. This could also explain the difference in maximal absorption at longer reaction times when using different ligands. Furthermore, precipitation could also lead to increased absorption, but does not provide information on catalyst performance. 

A second major concern is the calculation of the reaction rates. In most cases, the first data point is already close to maximal absorptions. Therefore, the reaction rate is correlated to the value of maximal absorption and precise kinetic information cannot be obtained.

Author Response

This work aims to prepared in-situ complexes and evaluated their oxidation activities by using UV-visible. The success of conversion reaction of catechol to quinone determined by two approaches Absorbance vis Time at λ=390nm and Absorbance vis Wavelength at λ=390nm. All results calculated and figured have demonstrated that the conversion reaction done successfully, but some time we have noted precipitation phenomena led to illogical value of absorbance more than four because this solid precipitated stop pass of light. The spectra are the superpositions of the quinone and complexes of copper with catechol or quinone as ligands it impossible, as you know each element has a special wavelength, for example, the quinone product of conversion reaction appear at λ=390nm.

For more information

Please see references below

• De Silva et al., Chemical Reviews, 1997,97(5), pp. 1515-1566
• Saha et al., Chemical Reviews, 2012,112(5), pp. 2739-2779
• Liu, et al., Chemical Reviews, 2014,114(9), pp. 5057-5115.

Author Response File: Author Response.pdf

Reviewer 2 Report

Do not remove the data of the conversion(%) such as Figure 1-3 in previous manuscript, need at least one Figure and others move to supporting information.

I am asking the conversion of the Figure 1-3 in previous manuscript, is it true?

 Conversion is too low.

Please show that the reaction proceeds with more than moderate conversion, including isolation yield or quantitative analysis by nmr. I will review again after the data is reported.

Author Response

Review 2

Do not remove the data of the conversion (%) such as Figure 1-3 in previous manuscript, need at least one Figure and others move to supporting information.

• Corrected accordingly please see the revised version and section information attached

I am asking the conversion of the Figure 1-3 in previous manuscript, is it true?

• Yes, all results are correct and the same data that report in previous and present version, just we have drawn all data by using origin program for more clear and homogeneity.

Conversion is too low.

• In fact, the conversion rate is not too low because we have played on various parameters (ligand combination (1L/1M, 2L/1M), concentration effect, solvent effect and counter anions effect) to improve the conversion rate, for this we have obtained an excellent results of oxidation the catechol to quinone by  using these prepared in-situ complexes. The three complexes  2L₂/Cu(NO₃)_{2  ,} 2L₂/Cu(CH₃COO)₂ , 2L₂/CuSO₄  showed an excellent results of conversion rate with V_max  (32.86, 33.56, 4167 μmol.L^-1.min^-1 ) in polar solvent methanol as tabulated in table 4 (please see in the revised version) at 10min. 

Please show that the reaction proceeds with more than moderate conversion, including isolation yield or quantitative analysis by nmr. I will review again after the data is reported.

• I think we have followed a complete strategy to illustrate the activities catalytic of the prepared complexes.
• For the second point that says, we have to isolate the product and structured by NMR. We cannot make this isolation of quinone precisely, because we have used the smallest quantities who one of the major challenges who complicating this separation and the needs a special condition, in the foreground, the separation must make in absence of oxygen for stop the conversion.
• Uv-visible more easy, accessible and we can have a continuous recording instead of NMR (it’s possible but we don’t have this facility in our department)

Some references supporting our studies

• Rebecchi, M.J., Pentyala, S.N., Physiological Reviews, 2000, 80(4), pp. 1291-1335
• El Ati, et al., Indonesian Journal of Science and Technology, 2022, 7 (1),1–18.
• Bouroumane, et al., Arabian Journal for Science and Engineering, 2022, 47 (1), 269–279
• Titi, et al., Journal of Molecular Structure; 2020, 1217 (2020)128422.

Round 2

Reviewer 1 Report

In the resubmitted version of the manuscript the authors have not addressed the major issues raised before by the reviewers. In particular, there is no unequivocal evidence that the recording of UV/VIS-spectra is a suitable tool for quantification of quinone formation as additional contribution by a copper complex or by increased absorption due to a precipitate may lead to false values. It is therefore required that the formation of quinones is independently quantified by a different method such as isolation in pure form or by NMR spectroscopy using an internal standard. An example for this approach is found in the closely related work by Hamann and Tuczek, Chem. Comm. 2014, 50, 2298-2300, which should be cited as well.

Reviewer 2 Report

Other reviewers have provided rejections, I have given you several chances, but since you will not revise, I cannot continue reviewing. If you do not have NMR then please collaborate with other researchers.