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DOI:
https://doi.org/10.34804/supra.20210928398 Cc Cc by 4.0
Title:
Host−Guest Complexation of Neutral Red with Macrocyclic Host Molecules:  Contrasting pKa Shifts and Binding Affinities for Cucurbit[7]uril and β-Cyclodextrin
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Description:
The photophysical properties of the phenazine-based dye neutral red were investigated in aqueous solution in the presence of the macrocyclic host molecule cucurbit[7]uril (CB7) using ground-state absorption as well as steady-state and time-resolved fluorescence measurements. The results are contrasted to those previously obtained for β-cyclodextrin (β-CD; Singh et al. J. Phys. Chem. A 2004, 108, 1465). Both the neutral (NR) and cationic (NRH+) forms of the dye formed inclusion complexes with CB7, with the larger binding constant for the latter (K = 6.5 × 103 M-1 versus 6.0 × 105 M-1). This result differed from that for β-CD, where only the neutral form of the dye was reported to undergo sizable inclusion complex formation. From the difference in binding constants and the pKa value of protonated neutral red in the absence of CB7 (6.8), an increased pKa value of the dye when complexed by CB7 was projected (∼8.8). This shift differed again from the behavior of the dye with β-CD, where a decreased pKa value (ca. 6.1) was reported. The photophysical properties of both NR and NRH+ forms showed significant changes in the presence of CB7. Fluorescence anisotropy studies indicated that the inclusion complexes of both forms of the dye rotate as a whole, giving rotational relaxation times much larger than that expected for the free dye in aqueous solution. The thermodynamic parameters for the NRH+·CB7 complex were investigated in temperature-dependent binding studies, suggesting an entropic driving force for complexation related to desolvation of the cation and the removal of high-energy water molecules from the CB7 cavity.
Citation:

H. Pal, W. M. Nau, J. Mohanty, A. C. Bhasikuttan, SupraBank 2025, Host−Guest Complexation of Neutral Red with Macrocyclic Host Molecules:  Contrasting pKa Shifts and Binding Affinities for Cucurbit[7]uril and β-Cyclodextrin (dataset). https://doi.org/10.34804/supra.20210928398

Link: https://doi.org/10.34804/supra.20210928398
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Citation:

J. Mohanty, A. C. Bhasikuttan, W. M. Nau, H. Pal, J. Phys. Chem. B 2006, 110, 5132–5138.

Link: https://doi.org/10.1021/jp056411p
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Creators:
Orcidid | Ror | J. Mohanty
Orcidid | Ror | A. C. Bhasikuttan
Orcidid | Ror | W. M. Nau
Orcidid | Ror | H. Pal
Contributers:
Orcidid | Ror | Changming Hu | DataManager
Orcidid | Ror | Anxhela Zhiti | DataManager

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