Chloride Binding Properties of a Macrocyclic Receptor Equipped with an Acetylide Gold(I) Complex: Synthesis, Characterization, Reactivity, and Cytotoxicity Studies
Round 1
Reviewer 1 Report
The paper by prof Ballester et al. describe the synthesis and studies of a new “two wall” calixpyrrole bearing on one aromatic arm an acetylide gold moity and on the other arm an iodo group. The iodo group of molecule 2 replace the alkyne group from molecule 1 to achieve different binding properties for chloride anion as TBA salt.
The work is well executed and the characterization of recognition event between calixpyrroles and chloride well documented by 1H NMR titration in dichloromethane and acetone and ITC the same solvents. Theorical calculations were also undertaken to understand how this receptor works.
I recommend publication of this work and I provide below some suggestion to improve the reader experience:
- Line 62: it would be interesting to describe the weak emission upon excitation at 300 nm. Is it fluorescence or/and phosphorescence like the one described in ref 12?
- Scheme 1 b), scheme 2, scheme S6: can you please check the angle of the alkyne. It seems that it is not exactly 180°
- On figure 2, it would be great to indicate on the figure what NCH2 refer to (maybe “TBA region”?).
- Scheme S5 : is there a reason why ethynyltoluene is not in the plan?
- Figure S48 + S50: on my screen, it is difficult to differentiate black number from blue one (in fact blue one are purple on my screen). Maybe it could be interesting to use primed number (4’).
Comments for author File: 
Comments.pdf
Author Response
Line 62: it would be interesting to describe the weak emission upon excitation at 300 nm. Is it fluorescence or/and phosphorescence like the one described in ref 12?
Answer: We want to clarify that line 62 is indeed describing the results of 1Au included in reference 12. We added the name of the compound in line 62 for clarification.
Scheme 1 b), scheme 2, scheme S6: can you please check the angle of the alkyne. It seems that it is not exactly 180°.
Answer: We have checked the angle in all the schemes and it is certainly 180º. Most likely, the conversion of the image to pdf has distorted a bit this angle. As suggested by the editor we have not changed these chemdraw structures.
On figure 2, it would be great to indicate on the figure what NCH2 refer to (maybe “TBA region”?).
Answer: We have included a clarification of the TBA region in the caption of Figure 2.
“Figure 2. Selected downfield and upfield regions (aromatic and TBA regions, respectively) of the 1H NMR spectra (400 MHz, CD2Cl2, 298 K) acquired during the titration of the mono-nuclear 2Au calix[4]pyrrole receptor ([2Au]=1.9 mM) with TBACl: a) 0 b) 1 c) 4.5 d) 10.5 e) 21 and f) 27 equiv. added. See Scheme 1a for proton assignment. The scale of the aromatic region is increased 16 times with respect to the upfield TBA region in order to show the presence of the second set of aromatic proton signals.”
Scheme S5: is there a reason why ethynyltoluene is not in the plan?
Answer: We think that the reviewer refers to why ethynyl toluene is not in the plane. We have modified Scheme S5 in order to avoid confusions and it is now included in the revised version of the SI document.
Figure S48 + S50: on my screen, it is difficult to differentiate black number from blue one (in fact blue one are purple on my screen). Maybe it could be interesting to use primed number.
Answer: We thank the reviewer for the comment. As suggested, we have changed the blue colors by primed numbers in the revised version of the Supporting Information.
Reviewer 2 Report
The article is well written, it is clear in the exposition of its objectives and in the work carried out.
Congratulations for the work presented.
Author Response
We thank the reviewer for the comments. No changes were requested by this reviewer.
Reviewer 3 Report
Ballester et al have reported the synthesis and extensive characterization of a mono-nuclear ‘’two wall’’ aryl-extended Calix [4] pyrrole receptor (2Au) with an acetylide-gold(I)-PTA complex. They have described the results of the 1H NMR titration experiment of the macrocyclic gold complex with TBACl (tetrabutylammonium chloride) in dichloromethane and acetone solution. The authors have performed ITC (isothermal titration calorimetry) and pair-wise binding experiments to accurately characterize the gold complex in acetone. Finally, They have evaluated the anticancer activity of the gold macrocyclic acetylide complex, and its relative acetylide complex 6Au (Scheme1) against three human cancer cell lines (MIA-PaCa-2, A549, HeLa).
The paper is well written, and thoroughly presented, and it deserves to be published in inorganics. However, some observations require the attention of the authors:
1. Scheme 1a is not very clear and not easy to understand, I suggest the authors improve it.
2. The authors have reported the synthesis of oligomeric gold complex 5 (Scheme 1a), using chloro (tetrahydrothiophene)gold (I), freshly prepared. Why haven’t the authors used chloro gold(I) dimethylsulfide, commercially available?
3. The authors have reported the anticancer activity of gold 2Au macrocyclic complex, and it was compared with macrocyclic compound. Has the cytotoxic activity of complex 1Au (Figure1, Sun, Q.; Aragay, G.; Pinto, A.; Aguiló, E.; Rodríguez, L.; Ballester, P., Influence of the Attachment of a Gold(I) Phosphine Moiety at the Upper Rim of a Calix[4]pyrrole on the Binding of Tetraalkylammonium Chloride Salts. Chem.--Eur. J. 2020, 26 (15),3348-3357), been evaluated/compared?
4. In section 2.7, The authors can include the status of macrocyclic gold(I) complexes (e.g., stabilized by NHC, phosphine, etc..) as antitumoral compounds.
Author Response
1) Scheme 1a is not very clear and not easy to understand, I suggest the authors improve it.
Answer: We thank the reviewer for this suggestion. We realized that there was an arrow missing in Scheme 1 and some reaction conditions/reagents were missing in the Scheme. We have improved it and included in the revised version of the manuscript.
2) The authors have reported the synthesis of oligomeric gold complex 5 (Scheme 1a), using chloro (tetrahydrothiophene)gold (I), freshly prepared. Why haven’t the authors used chloro gold(I) dimethylsulfide, commercially available?
Answer: We used freshly prepare chloro (tetrahydrothiophene)gold (I) following the procedure described in the literature for other alkynyl gold(I) compounds (see ref 17 of the original manuscript). We thank the reviewer for the comment and we will consider this alternative in future preparations of alkynyl gold(I) complexes.
3) The authors have reported the anticancer activity of gold 2Au macrocyclic complex, and it was compared with macrocyclic compound. Has the cytotoxic activity of complex 1Au (Figure1, Sun, Q.; Aragay, G.; Pinto, A.; Aguiló, E.; Rodríguez, L.; Ballester, P., Influence of the Attachment of a Gold(I) Phosphine Moiety at the Upper Rim of a Calix[4]pyrrole on the Binding of Tetraalkylammonium Chloride Salts. --Eur. J. 2020, 26 (15),3348-3357), been evaluated/compared?
Answer: We have not evaluated the cytotoxic activity of complex 1Au. We did not consider this comparison relevant for the aim of this work.
4) In section 2.7, The authors can include the status of macrocyclic gold(I) complexes (g., stabilized by NHC, phosphine, etc..) as antitumoral compounds.
Answer: Section 2.7. in the original version of the manuscript already includes some references related to the status of organo-gold and specially alkynyl gold complexes as antitumoral compounds (see references 41 and 43). In the revised version of the manuscript we have specified that these compounds can be NHC and phosphine derivatives.
"Organo-gold and gold coordination-based complexes (e.g. stabilized by NHC, phosphine ligands, etc.) have been described to show cytotoxic activity"
Moreover, we added one more recent reference related to the use of these complexes as potential anticancer agents (see reference 44 in the revised version of the manuscript).
Ref 44: “Yang, Z.; Jiang, G.; Xu, Z.; Zhao, S.; Liu, W., Advances in alkynyl gold complexes for use as potential anticancer agents. Coord. Chem. Rev. 2020, 423, 213492.”
