A New Bioactive Complex between Zn(II) and a Fluorescent Symmetrical Benzanthrone Tripod for an Antibacterial Textile

Round 1

Reviewer 1 Report

 

The authors describ a new fluorescent Zn(II) complex of symmetric tripod based on a 3-substituted 16 benzanthrone. Spectral characterization is well established and also photophysical properties of this new metal complex, where they have used sophisticated analytical techniques such as NMR, SEM and X-ray photoelectron spectroscopy. The complexe possesses good antimicrobial activity against the Gram-positive bacteria. The article is well written with a comprehensive English.

I recommend for publication in its current form.

Author Response

We thank the reviewer for the positive comment of our work.

Reviewer 2 Report

In the manuscript, a synthesis and characterization of a novel fluorescent Zn(II) complex is described and discussed. Furtherly, it was applied on cotton in order to obtain antibacterial activity of the fabric. Besides yellow coloration of the modified cotton was also presented. The manuscript is well designed and in the experimental all necessary analysis were obtained. However, my main consideration is the main aim of the paper, as only poor antibacterial activity was obtain on cotton fabric. Accordingly, I would suggest major revision of the paper, including application of higher concentration of Zn(II) complex to obtain better antimicrobial activity. Please see comments bellow.

 

Why applying newly synthetized fluorescent Zn(II) complex to cotton cellulose fibres, if only moderate antibacterial activity was obtain (64 % growth reduction of only one, among three tested bacteria)? Namely, there are many antibacterial substances, reflecting higher growth reduction of bacteria. Accordingly, better explanation of the purpose of the research should be included in the introduction. Is it simultaneous coloration and bacteriostatic activity of the cotton fabric? If so, this should be emphasized in the introduction part. As seen in Fig. 6 the antibacterial activity of novel Zn(II) complex is concentration depended. Thus higher concentration of the Zn(II) complex should be applied on cotton in order to obtain antibacterial textile as claimed in the title. Additionally, the add on (i.e. increase of the dry mass of the fabric after deposition of Zn(II) complex) should be included in order to provide amount of the Zn(II) complex on the fabric. Please explain why so small samples were taken in the application process. Namely, handling with so small samples (e.g. 1g in mass) hardly reflects representative results. What is washing durability of the functionalized cotton fabric in terms of antimicrobial activity and colour fastness? Figure 6. Please explain the units “mkg/ml”. Figure 7. The results for P. aeruginosa are not seen in the figure. Besides, also the legend is not completely seen. I would recommend to present the results in terms of “growth reduction”.

Author Response

Why applying newly synthetized fluorescent Zn(II) complex to cotton cellulose fibres, if only moderate antibacterial activity was obtaining (64 % growth reduction of only one, among three tested bacteria)? Namely, there are many antibacterial substances, reflecting higher growth reduction of bacteria. Accordingly, better explanation of the purpose of the research should be included in the introduction. Is it simultaneous coloration and bacteriostatic activity of the cotton fabric? If so, this should be emphasized in the introduction part.

Done in the text

As seen in Fig. 6 the antibacterial activity of novel Zn(II) complex is concentration depended. Thus higher concentration of the Zn(II) complex should be applied on cotton in order to obtain antibacterial textile as claimed in the title.

A concentration of 0.5 wt% is sufficient to produce a saturated color, and on the other hand, the deposited amount of tripod is greater than than that at which highest antibacterial effect was obtained.

Additionally, the add on (i.e. increase of the dry mass of the fabric after deposition of Zn(II) complex) should be included in order to provide amount of the Zn(II) complex on the fabric.

The explanation was added in the text p3 row96

Please explain why so small samples were taken in the application process. Namely, handling with so small samples (e.g. 1g in mass) hardly reflects representative results.

In our studies, we usually use samples of 1 gram of cotton cloth. In our opinion, this is not a small sample, given that the weight of the fabric is 140 g / square meter. Basically, these are 3.5 / 4 cm samples, which are completely sufficient for this type of testing.

What is washing durability of the functionalized cotton fabric in terms of antimicrobial activity and colour fastness?

In this study we have not investigated the washing durability and colour fastness of the functionalized cotton fabric, because our idea was to use this materials as disposable gauzes, bandages, etc., in the clinical practice.

Figure 6. Please explain the units “mkg/ml”.

In Fig. 6, “mkg” means micrograms – is changed to “µg/ml”.

Figure 7. The results for P. aeruginosa are not seen in the figure. Besides, also the legend is not completely seen. I would recommend to present the results in terms of “growth reduction”.

Figure 7 is changed as recommended

Reviewer 3 Report

Staneva et al. have reported the synthesis of zinc-benzanthrone complex which was evaluated for antimicrobrial activity in solution state and also after impregnation on cotton fabric.

The solution state antimicrobial activity was modest against B. cereus and provides an interesting starting point but a structure activity study would improve the significance of this work.  Similarly, it would be of value to determine the amount of complex on the fabric, or if different preparation conditions could improve the loading and antimicrobial activity.  In both instances, it would be beneficial to include BT as a control.  Claims that the complex does not leach should be support with evidence such as absorption spectra of the supernatant.

Figure 8 requires further discussion, preferably highlighting details in the images which support the claims.

It wasn't clear what information is provided by the SEM characterisation.  Is this related to the antimicrobial activity?  Does this data need to be included?

At this stage I think more work is required before the manuscript can be accepted for publication.  

 

Author Response

 

 

The solution state antimicrobial activity was modest against B. cereus and provides an interesting tarting point but a structure activity study would improve the significance of this work. Similarly, it would be of value to determine the amount of complex on the fabric, or if different preparation conditions could improve the loading and antimicrobial activity. 

The amount of deposited zinc complex on the cotton fabric is given in the experimental part. P3 row 96

In both instances, it would be beneficial to include BT as a control.  Claims that the complex does not leach should be support with evidence such as absorption spectra of the supernatant.

Figure 8 requires further discussion, preferably highlighting details in the images which support the claims. It wasn't clear what information is provided by the SEM characterisation.  Is this related to the antimicrobial activity?  Does this data need to be included?

Answer: SEM analysis presented in Figure 8 clearly shows that the bioactivity of the tripod on the cotton fabric is expressed in its inhibition of bacterial biofilm formation and therefore its inclusion in the manuscript is required. Information is provided in the paper.

Round 2

Reviewer 2 Report

The authors have addressed all comments appropriately, thus I recommend the publication of the manuscript. However, before that minor correction of Fig. 7 is needed; i.e. there is no need to show control (blue coloured bar). Namely as it is, it means that control fabric demonstrated 100% growth inhibition of the tested bacteria.

Author Response

The authors have addressed all comments appropriately, thus I recommend the publication of the manuscript. However, before that minor correction of Fig. 7 is needed; i.e. there is no need to show control (blue coloured bar). Namely as it is, it means that control fabric demonstrated 100% growth inhibition of the tested bacteria.

Figure 7 has been modified.

Reviewer 3 Report

The experimental section does provide the amount of zinc complex used to functionalise the cotton fabric, however this is not quantitive evidence of incorporation.

The absence of bacteria in Figure 8 panel C is clear, but I still think it would be beneficial to further explain the observations for the non-specialist reader.  Particularly as this work is multidisciplinary and directed at a broad audience.

I would reconsider the inclusion of Figure 4.

Author Response

The absence of bacteria in Figure 8 panel C is clear, but I still think it would be beneficial to further explain the observations for the non-specialist reader.  Particularly as this work is multidisciplinary and directed at a broad audience.

Additional explanation has been done in the text.

 

I would reconsider the inclusion of Figure 4.

Figure 4 has been removed from the text.