PONE-D-22-05311Oxidation-reduction and photophysical properties of isomeric forms of SafraninPLOS ONE

Dear Dr. Koder,

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Additional Editor Comments:

Editor’s comments Ms. # PONE-D-22-05311

Corrections needed:

Table 1 -- 2,8-diamino-3,7-dimethyl-10

Figs. as displayed in Ms. copy that I received did not appear to be of a quality to reproduce sufficiently well in the final publication.

p. 20, L10: “why the redox potential of II is slightly lower than II as well.” Needs to be clarified??

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Reviewers' comments:

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Comments to the Author

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Reviewer #1: Yes

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: N/A

Reviewer #2: N/A

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

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Reviewer #1: This manuscript is clearly written and describes the careful characterization of commercially prepared Safranine O, which is commonly used as a mediator in electrochemistry. Specifically, they note that during synthesis, two distinct molecules are produced with unique spectral and electrochemical properties. Given that these compounds are widely used and the mixture of compounds complicates their application, it is important that this work be published.

Experiments are well described and the data is clearly presented. Only one minor issue - a relict from a previous submission:

"The reduction potential of Safranine O at pH 7.0 was first reported by Prince et al. *in this journal*

in 1981 to be −280 mV vs the Standard Hydrogen Electrode (SHE) as determined by polarography [9]"

Reviewer #2: This manuscript by Andersen et al describes an analysis of two commercial preparations of safranin, revealing it to be made up of a number of isomers with varying optical and redox properties. The findings will be of interest to users of safranine as a mediator or dye.

The research has been conducted to a high standard and the conclusions drawn seem reasonable. The manuscript is mostly well written and clear, but would benefit from a thorough proof-read.

It would have been helpful for the authors to have included page numbers in their manuscript. In the absence of these the following refers to page numbers in the pdf document

Page 8, second line from bottom – random use of italics

Page 9, line 9 – the authors write “in this journal in 1981”. Does this betray a previous, unsuccessful submission to BBA?

Page 14, Figure legend. Some additional punctuation would be helpful here.

Page 14, last line and Page 15, first line - what does “Figure 3c and 3d” refer to here?

Page 21. All references should be in a consistent format.

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Reviewer #1: No

Reviewer #2: No

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Oxidation-reduction and photophysical properties of isomeric forms of Safranin

PONE-D-22-05311R1

Dear Dr. Koder,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements. Please note that an error on p.13, line 12 of the revised Ms. was found (should read: why the redox potential of II is slightly lower than III as well.) that can be corrected in the galley proofs.

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Kind regards,

Robert A. Niederman, Ph.D

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Please note that an error on p.13, line 12 of the revised Ms. was found (should read: why the redox potential of II is slightly lower than III as well.) that can be corrected in the galley proofs.