Chitin and Silk Fibroin Biopolymers Modified by Oxone: Efficient Heterogeneous Catalysts for Knoevenagel Reaction

Round 1

Reviewer 1 Report

The manuscript proposed by Neves et al. presents the development of new chitin and silk biopolymers modified for heterogeneous catalytic application. The work is of appropriate quality and the scientific contribution will be of great interest for the readers in Catalysts. Therefore, I recommend its publication after the following minor corrections:

1. Update the references in the introduction (20222 year).

2. Improve the quality and presentation of the figures. E.g. increase the resolution and the font size.

3. Figure 1b. Include the error bars.

4. Discuss the stability of the catalysts after several cycles of use and include the characterization of the materials after different cycles.

5. Figure 5. Please explain why the thermogravimetric curve exceeds the 100% at several temperatures.

6. For the discussion of figure 5, include the process of decomposition in the main steps observed in the thermogravimeric curve.

Author Response

Dear Editor-in-Chief

Prof. Dr. Keith Hohn

Catalysts

We are very pleased to know that our submitted manuscript entitled “Chitin and Silk Fibroin Biopolymers Modified by Oxone: Efficient Heterogeneous Catalysts for Knoevenagel reaction. We appreciate the time and effort that you and the reviewers dedicated to providing feedback on our manuscript and are grateful for the insightful comments on and valuable improvements to our paper. We have incorporated all of the suggestions made by the reviewers. Those changes are highlighted within the manuscript. Please see below, in green, for a point-by-point response to the reviewers’ comments and concerns

1. Update the references in the introduction (2022 year).

R = The references in the introduction were update.

• Chakraborty, S.; Paul, A.R.; Majumdar, S. Base and metal free true recyclable medium for Knoevenagel condensation reaction in SDS-ionic liquid-aqueous miceller composite system. Results in Chemistry 2022, 4, 100294–100232, doi: 1016/j.rechem.2022.100294.
• Bi, S.; Meng, Fancheng.; Wu, D.; Zhang, F. Synthesis of vinylene-linked covalent organic frameworks by monomer Self-catalyzed activation of Knoevenagel condensation. Journal of American Chemical Society 2022, 8, 3653–3659, doi: 1021/jacs.1c12902.
• Tran, V. A.; Quynh, L.T.N.; Vo, T.T.; Nguyen, P.A.; Don, T.N.; Vasseghian, Y.; Phan, H.; Lee, S.W. Experimental and computational investigation of a green Knoevenagel condensation catalyzed by zeolitic imidazolate framework-8. Environmental Research 2022, 204, 112364–112374, doi: 1016/j.envres.2021.112364.
• Lv, H.; Zhang, Z.; Fan, L.; Gao, Y.; Zhang, X. A nanocaged cadmium-organic framework with high catalytic activity on the chemical fixation of CO₂ and deacetalization-knoevenagel condensation. Microporous and Mesoporous Materials 2022, 335, 111791-–111800, doi: 1016/j.micromeso.2022.111791
• Madkour, M.; Khalil, K.D.; Al-Sagheer, F.A. Heterogeneous Hybrid Nanocomposite Based on Chitosan/Magnesia Hybrid Films: Ecofriendly and Recyclable Solid Catalysts for Organic Reactions. Polymers 2021, 13, 3583–3597, doi: 3390/polym13203583.
• Abrantes, P.G.; Costa, I.F.; Falcão, N.K.S.M.; Ferreira, J.M.G.O.; Junior, C.G.L.; Teotonio, E.E.S.; Vale, J.A. The Efficient Knoevenagel Condensation Promoted by Bifunctional Heterogenized Catalyst Based Chitosan-EDTA at Room Temperature. Catalysis Letters 2022, 1, 1–11, doi: 10.1007/s10562-022-04034-y.

2. Improve the quality and presentation of the figures. E.g. increase the resolution and the font size.

R= The quality of the figures was modified.

3. Figure 1b. Include the error bars.

R = The error bars were incluied in the Figure 1.

4. Figure 5. Please explain why the thermogravimetric curve exceeds the 100% at several temperatures.

R= Thermogravimetric curves do not exceed 100%. In all analyzed samples, there is a temperature range in which the mass did not change because there was no physical, chemical or physico-chemical phenomenon to result in mass loss, so in this range the mass remains 100%. When the samples begin to be influenced by temperature, mass loss begins and the curve leaves its plateau and begins a downward movement. The percentages correspond to mass loss during

this entire process.

However, the CH-Ox curve seems to be slightly above 100%, in this special sample 2.3675mg was weighed and this value rises to 2.38mg probably because of a slight shake of the balance.

When the curve of this sample is placed together with the curve of the CH, there is the false impression that the curve starts above 100%, but this is not real, there is no diagnosed mass gain, just a slight vibration of the balance.

To complement, it should be noted that the equipment used in the analysis is a TGA-50 Shimadzu, in this model the scale is suspended by a rod and vibrations are common, the analysis begins after the complete stabilization of the scale, but it is still possible to have some movement that results in a false slight increase in mass. The distinction between a true increase in mass and a shake of the balance occurs because there is no unevenness in the curve, it remains straight until the temperature at which mass loss begins. If there had been a gain in mass, we would have noticed a slight rise in the curve and its subsequent return to the baseline.

5. For the discussion of figure 5, include the process of decomposition in the main steps observed in the thermogravimeric curve.

The process of decomposition in the main steps observed in the thermogravimetric curve was

explained in the pg 10, lines 270- 289.

The thermal behavior of the pure SF and SF-Ox was analyzed by thermogravimetric analysis (TGA). The degradation temperature, known to be a criterion of thermal degr1adation, was calculated based on differential TGA curves (Figure 5). The fibroin TG curve showed a single mass loss step at a temperature of 266.6 °C. From this point (266.66 ºC) the fibroin TG curve descends, implying a progressive loss of mass until the end of the analysis at 600 ºC. The thermal decomposition of fibroin is related to the breakdown of side chain groups of amino acid residues, as well the cleavage of the peptide bonds [30]. In addition, the thermal decomposition of fibroin at temperatures above 300 ºC is associated with the thermal degradation of silk fibroin with a β-

sheet structure oriented along the fiber [11]. The chitin TG curve exhibited a mass loss of 32.124% in the range of 243°C-422 °C (Figure5B). The thermal decomposition of chitin is related to the depolymerization/decomposition of polymeric chains through deacetylation and the cleavage of the glycosidic bonds, in addition to the destruction of the pyranose ring [15]. Figures 5A and 5B show the TG curves of fibroin and chitin after treatment with Oxone ® salt. In both curves it can be seen that the polymers present greater thermal stability after treatment with Oxone ® . SF-Ox presents a mass loss range of between 288.15 ºC and 432.5 ºC, with a 20% mass loss. While CT-Ox presents a mass loss range of between 166.96 ºC and 485 ºC, with 23% mass loss. SF-Ox exhibits a residue of 80%, and CT-Ox exhibits a residue of 77%, with a larger residue a signifying a greater resistance to thermal decomposition, as is the case with CT-Ox and SF-Ox, depending on the mineralization provided by Oxone ® [10].

Best regards,

Prof. Dr. Irlon M. Ferreira

Universidade Federal do Amapá

Grupo de Biocatálise e Síntese Orgânica Aplicada
http://lattes.cnpq.br/9897023410899133

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors of the publication "Chitin and Silk Fibroin Biopolymers Modified by Oxone: Effi-2 cient Heterogenous Catalysts for Knoevenagel response "presented the results of new materials of silk fibroin (FS-Ox) and chitin (CT-Ox) functionalized with Oxone® salt used in the synthesis of Knoevenagel adducts. The experiments were made using benzaldehyde derivatives, malononitrile and a mixture of water and ethanol as green solvents. The efficiency of conventional and microwave radiation as a heat source for this the reaction was also tested. When reactions were run for 60 min under optimized the twelve Knoevenagel adducts were obtained under conventional heating conditions. When microwave radiation is used, reaction periods were shortened twelve times, with the same Knoevenagel adducts with good CT-24 In most cases, Ox (39-99%) and FS-Ox (35-99%) yields were achieved. Each part of the publication has been described in detail, and each of them brings great substantive value in the subject matter presented by the authors. The conclusions are consistent and closely related to the research topic. As a reviewer of this work, I do not make any comments as to the substantive and experimental content, nor do I have any additional questions as to the content of the publication. I believe that the authors have exhausted all the topics in the reviewed work.

Comments for author File: Comments.pdf

Author Response

Dear Editor-in-Chief

Prof. Dr. Keith Hohn

Catalysts

We are very pleased to know that our submitted manuscript entitled “Chitin and Silk Fibroin Biopolymers Modified by Oxone: Efficient Heterogeneous Catalysts for Knoevenagel reaction. We appreciate the time and effort that you and the reviewers dedicated to providing feedback on our manuscript and are grateful for the insightful comments on and valuable improvements to our paper. We have incorporated all of the suggestions made by the reviewers. Those changes are highlighted within the manuscript. Please see below, in green, for a point-by-point response to the reviewers’ comments and concerns

1. Update the references in the introduction (2022 year).

R = The references in the introduction were update.

• Chakraborty, S.; Paul, A.R.; Majumdar, S. Base and metal free true recyclable medium for Knoevenagel condensation reaction in SDS-ionic liquid-aqueous miceller composite system. Results in Chemistry 2022, 4, 100294–100232, doi: 1016/j.rechem.2022.100294.
• Bi, S.; Meng, Fancheng.; Wu, D.; Zhang, F. Synthesis of vinylene-linked covalent organic frameworks by monomer Self-catalyzed activation of Knoevenagel condensation. Journal of American Chemical Society 2022, 8, 3653–3659, doi: 1021/jacs.1c12902.
• Tran, V. A.; Quynh, L.T.N.; Vo, T.T.; Nguyen, P.A.; Don, T.N.; Vasseghian, Y.; Phan, H.; Lee, S.W. Experimental and computational investigation of a green Knoevenagel condensation catalyzed by zeolitic imidazolate framework-8. Environmental Research 2022, 204, 112364–112374, doi: 1016/j.envres.2021.112364.
• Lv, H.; Zhang, Z.; Fan, L.; Gao, Y.; Zhang, X. A nanocaged cadmium-organic framework with high catalytic activity on the chemical fixation of CO₂ and deacetalization-knoevenagel condensation. Microporous and Mesoporous Materials 2022, 335, 111791-–111800, doi: 1016/j.micromeso.2022.111791
• Madkour, M.; Khalil, K.D.; Al-Sagheer, F.A. Heterogeneous Hybrid Nanocomposite Based on Chitosan/Magnesia Hybrid Films: Ecofriendly and Recyclable Solid Catalysts for Organic Reactions. Polymers 2021, 13, 3583–3597, doi: 3390/polym13203583.
• Abrantes, P.G.; Costa, I.F.; Falcão, N.K.S.M.; Ferreira, J.M.G.O.; Junior, C.G.L.; Teotonio, E.E.S.; Vale, J.A. The Efficient Knoevenagel Condensation Promoted by Bifunctional Heterogenized Catalyst Based Chitosan-EDTA at Room Temperature. Catalysis Letters 2022, 1, 1–11, doi: 10.1007/s10562-022-04034-y.

2. Improve the quality and presentation of the figures. E.g. increase the resolution and the font size.

R= The quality of the figures was modified.

3. Figure 1b. Include the error bars.

R = The error bars were incluied in the Figure 1.

4. Figure 5. Please explain why the thermogravimetric curve exceeds the 100% at several temperatures.

R= Thermogravimetric curves do not exceed 100%. In all analyzed samples, there is a temperature range in which the mass did not change because there was no physical, chemical or physico-chemical phenomenon to result in mass loss, so in this range the mass remains 100%. When the samples begin to be influenced by temperature, mass loss begins and the curve leaves its plateau and begins a downward movement. The percentages correspond to mass loss during

this entire process.

However, the CH-Ox curve seems to be slightly above 100%, in this special sample 2.3675mg was weighed and this value rises to 2.38mg probably because of a slight shake of the balance.

When the curve of this sample is placed together with the curve of the CH, there is the false impression that the curve starts above 100%, but this is not real, there is no diagnosed mass gain, just a slight vibration of the balance.

To complement, it should be noted that the equipment used in the analysis is a TGA-50 Shimadzu, in this model the scale is suspended by a rod and vibrations are common, the analysis begins after the complete stabilization of the scale, but it is still possible to have some movement that results in a false slight increase in mass. The distinction between a true increase in mass and a shake of the balance occurs because there is no unevenness in the curve, it remains straight until the temperature at which mass loss begins. If there had been a gain in mass, we would have noticed a slight rise in the curve and its subsequent return to the baseline.

5. For the discussion of figure 5, include the process of decomposition in the main steps observed in the thermogravimeric curve.

The process of decomposition in the main steps observed in the thermogravimetric curve was

explained in the pg 10, lines 270- 289.

The thermal behavior of the pure SF and SF-Ox was analyzed by thermogravimetric analysis (TGA). The degradation temperature, known to be a criterion of thermal degr1adation, was calculated based on differential TGA curves (Figure 5). The fibroin TG curve showed a single mass loss step at a temperature of 266.6 °C. From this point (266.66 ºC) the fibroin TG curve descends, implying a progressive loss of mass until the end of the analysis at 600 ºC. The thermal decomposition of fibroin is related to the breakdown of side chain groups of amino acid residues, as well the cleavage of the peptide bonds [30]. In addition, the thermal decomposition of fibroin at temperatures above 300 ºC is associated with the thermal degradation of silk fibroin with a β-

sheet structure oriented along the fiber [11]. The chitin TG curve exhibited a mass loss of 32.124% in the range of 243°C-422 °C (Figure5B). The thermal decomposition of chitin is related to the depolymerization/decomposition of polymeric chains through deacetylation and the cleavage of the glycosidic bonds, in addition to the destruction of the pyranose ring [15]. Figures 5A and 5B show the TG curves of fibroin and chitin after treatment with Oxone ® salt. In both curves it can be seen that the polymers present greater thermal stability after treatment with Oxone ® . SF-Ox presents a mass loss range of between 288.15 ºC and 432.5 ºC, with a 20% mass loss. While CT-Ox presents a mass loss range of between 166.96 ºC and 485 ºC, with 23% mass loss. SF-Ox exhibits a residue of 80%, and CT-Ox exhibits a residue of 77%, with a larger residue a signifying a greater resistance to thermal decomposition, as is the case with CT-Ox and SF-Ox, depending on the mineralization provided by Oxone ® [10].

Best regards,

Prof. Dr. Irlon M. Ferreira

Universidade Federal do Amapá

Grupo de Biocatálise e Síntese Orgânica Aplicada
http://lattes.cnpq.br/9897023410899133