Dataset Information

Water-Soluble Colorimetric Amino[bis(ethanesulfonate)] Azobenzene pH Indicators: A UV-Vis Absorption, DFT, and ¹H-¹⁵N NMR Spectroscopy Study.

ABSTRACT: Water-soluble azobenzene derivatives containing amino[bis(ethanesulfonate)] groups are demonstrated as colorful pH indicators in water and on filter paper. Vibrant color changes were observed from yellow/orange to pink between pH 1 and 4, which are attributed to an intramolecular charge-transfer mechanism. The pK _as of the indicators range from 2.1 to 2.6. ¹H/¹H-¹⁵N NMR studies in deuterium oxide reveal that the protonation of the azobenzene pH indicators occurs predominantly at the ?-azo nitrogen atom, in agreement with the density functional theory calculations. Excellent selectivity for protons was confirmed in water over common biologically relevant metal ions. Studies in methanol, however, indicate that the pH indicator with a methoxy group ortho to the amino[bis(ethanesulfonate)] group facilitates the selective coordination of Cu²⁺ with a binding constant p?_Cu2+ of 4.6 ± 0.1. The indicators complement the existing library of azobenzene indicator dyes and may be useful for measuring the environmental pH at higher proton concentrations.

SUBMITTER: Cardona MA

PROVIDER: S-EPMC6644513 | biostudies-literature | 2017 Sep

REPOSITORIES: biostudies-literature

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Publications

Water-Soluble Colorimetric Amino[bis(ethanesulfonate)] Azobenzene pH Indicators: A UV-Vis Absorption, DFT, and 1H-15N NMR Spectroscopy Study.

Cardona Maria A MA Makuc Damjan D Szaciłowski Konrad K Plavec Janez J Magri David C DC

ACS omega 20170926 9

Water-soluble azobenzene derivatives containing amino[bis(ethanesulfonate)] groups are demonstrated as colorful pH indicators in water and on filter paper. Vibrant color changes were observed from yellow/orange to pink between pH 1 and 4, which are attributed to an intramolecular charge-transfer mechanism. The pK as of the indicators range from 2.1 to 2.6. 1H/1H-15N NMR studies in deuterium oxide reveal that the protonation of the azobenz ...[more]

PMID: 31457862

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Project description:A methodological survey of density functional theory (DFT) methods for the prediction of UV-visible (vis)-near-infrared (NIR) spectra of phthalocyanines is reported. Four methods, namely, full time-dependent (TD)-DFT and its Tamm-Dancoff approximation (TDA), together with their simplified modifications (sTD-DFT and sTDA, respectively), were tested by using the examples of unsubstituted and alkoxy-substituted metal-free ligands and zinc complexes. The theoretical results were compared with experimental data derived from UV-visible absorption and magnetic circular dichroism spectroscopy. Seven popular exchange-correlation functionals (BP86, B3LYP, TPSSh, M06, CAM-B3LYP, LC-BLYP, and ωB97X) were tested within these four approaches starting at a relatively modest level using 6-31G(d) basis sets and gas-phase BP86/def2-SVP optimized geometries. A gradual augmentation of the computational levels was used to identify the influence of starting geometry, solvation effects, and basis sets on the results of TD-DFT and sTD-DFT calculations. It was found that although these factors do influence the predicted energies of the vertical excitations, they do not affect the trends predicted in the spectral properties across series of structurally related substituted free bases and metallophthalocyanines. The best accuracy for the gas-phase vertical excitations was observed in the lower-energy Q-band region for calculations that made use of range-separated hybrids for both full and simplified TD-DFT approaches. The CAM-B3LYP functional provided particularly accurate results in the context of the sTD-DFT approach. The description of the higher-energy B-band region is considerably less accurate, and this demonstrates the need for further advances in the accuracy of theoretical calculations. Together with a general increase in accuracy, the application of simplified TD-DFT methods affords a 2-3 orders of magnitude speedup of the calculations in comparison to the full TD-DFT approach. It is anticipated that this approach will be widely used on desktop computers during the interpretation of UV-vis-NIR spectra of phthalocyanines and related macrocycles in the years ahead.

Dataset Information

Water-Soluble Colorimetric Amino[bis(ethanesulfonate)] Azobenzene pH Indicators: A UV-Vis Absorption, DFT, and ¹H-¹⁵N NMR Spectroscopy Study.

Publications

Water-Soluble Colorimetric Amino[<i>bis</i>(ethanesulfonate)] Azobenzene pH Indicators: A UV-Vis Absorption, DFT, and <sup>1</sup>H-<sup>15</sup>N NMR Spectroscopy Study.

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