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Characterization of the thermal and photoinduced reactions of photochromic spiropyrans in aqueous solution.

Hammarson M, Nilsson JR, Li S, Beke-Somfai T, Andréasson J - J Phys Chem B (2013)

Bottom Line: The experimental studies on the hydrolysis reaction mechanism were supplemented by calculations using quantum mechanical (QM) models employing density functional theory.The results show that (1) the substitution pattern dramatically influences the pKa-values of the protonated forms as well as the rates of the thermal isomerization reactions, (2) water is the nucleophile in the hydrolysis reaction around neutral pH, (3) the phenolate oxygen of the merocyanine form plays a key role in the hydrolysis reaction.Hence, the nonprotonated merocyanine isomer is susceptible to hydrolysis, whereas the corresponding protonated form is stable toward hydrolytic degradation.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biological Engineering, Physical Chemistry, Chalmers University of Technology , 412 96 Göteborg, Sweden.

ABSTRACT
Six water-soluble spiropyran derivatives have been characterized with respect to the thermal and photoinduced reactions over a broad pH-interval. A comprehensive kinetic model was formulated including the spiro- and the merocyanine isomers, the respective protonated forms, and the hydrolysis products. The experimental studies on the hydrolysis reaction mechanism were supplemented by calculations using quantum mechanical (QM) models employing density functional theory. The results show that (1) the substitution pattern dramatically influences the pKa-values of the protonated forms as well as the rates of the thermal isomerization reactions, (2) water is the nucleophile in the hydrolysis reaction around neutral pH, (3) the phenolate oxygen of the merocyanine form plays a key role in the hydrolysis reaction. Hence, the nonprotonated merocyanine isomer is susceptible to hydrolysis, whereas the corresponding protonated form is stable toward hydrolytic degradation.

No MeSH data available.


Selected critical points along the minimum energy path startingfrom the TTC conformer with the nucleophilic watermolecule coordinated on the molecule (MC). The obtainedcritical points were qualitatively the same for the QM(1w) and ONIOM(6w)models. Relevant distances of the atoms participating in the hydrolysisare displayed for the QM(1w) and in parentheses for the ONIOM(6w)with values in Ångströms. For more details, see Tables 3 and 4, and Figures S6 andS7 in the Supporting Information.
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fig7: Selected critical points along the minimum energy path startingfrom the TTC conformer with the nucleophilic watermolecule coordinated on the molecule (MC). The obtainedcritical points were qualitatively the same for the QM(1w) and ONIOM(6w)models. Relevant distances of the atoms participating in the hydrolysisare displayed for the QM(1w) and in parentheses for the ONIOM(6w)with values in Ångströms. For more details, see Tables 3 and 4, and Figures S6 andS7 in the Supporting Information.

Mentions: Priorto addressing the reaction steps, the initial “reactant”conformer of MC was selected based on considering the four differentrelative orientations of the p-nitro-phenolate andthe indolenium groups. Based on previous results48 and on our analysis (see SupportingInformation), we concluded that the TTC conformeris the major initial reactant and, hence, was used in the calculations.The initial TTC conformer was optimized with fouralternative water positions close to CA and the lowestenergy conformer was selected to be the reactant state (MC) as shown in Figure 7. A similar analysiswas performed for the protonated form, MCH+, where theenergetic distribution of the conformers showed that the TTT conformer is somewhat more stable than the TTC conformer.However, the two conformers are separated by only a low energy transitionstate (TS) as detailed in the Supporting Information, why we addressed the reaction paths starting from both TTC and TTT conformers for MCH+.


Characterization of the thermal and photoinduced reactions of photochromic spiropyrans in aqueous solution.

Hammarson M, Nilsson JR, Li S, Beke-Somfai T, Andréasson J - J Phys Chem B (2013)

Selected critical points along the minimum energy path startingfrom the TTC conformer with the nucleophilic watermolecule coordinated on the molecule (MC). The obtainedcritical points were qualitatively the same for the QM(1w) and ONIOM(6w)models. Relevant distances of the atoms participating in the hydrolysisare displayed for the QM(1w) and in parentheses for the ONIOM(6w)with values in Ångströms. For more details, see Tables 3 and 4, and Figures S6 andS7 in the Supporting Information.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3814652&req=5

fig7: Selected critical points along the minimum energy path startingfrom the TTC conformer with the nucleophilic watermolecule coordinated on the molecule (MC). The obtainedcritical points were qualitatively the same for the QM(1w) and ONIOM(6w)models. Relevant distances of the atoms participating in the hydrolysisare displayed for the QM(1w) and in parentheses for the ONIOM(6w)with values in Ångströms. For more details, see Tables 3 and 4, and Figures S6 andS7 in the Supporting Information.
Mentions: Priorto addressing the reaction steps, the initial “reactant”conformer of MC was selected based on considering the four differentrelative orientations of the p-nitro-phenolate andthe indolenium groups. Based on previous results48 and on our analysis (see SupportingInformation), we concluded that the TTC conformeris the major initial reactant and, hence, was used in the calculations.The initial TTC conformer was optimized with fouralternative water positions close to CA and the lowestenergy conformer was selected to be the reactant state (MC) as shown in Figure 7. A similar analysiswas performed for the protonated form, MCH+, where theenergetic distribution of the conformers showed that the TTT conformer is somewhat more stable than the TTC conformer.However, the two conformers are separated by only a low energy transitionstate (TS) as detailed in the Supporting Information, why we addressed the reaction paths starting from both TTC and TTT conformers for MCH+.

Bottom Line: The experimental studies on the hydrolysis reaction mechanism were supplemented by calculations using quantum mechanical (QM) models employing density functional theory.The results show that (1) the substitution pattern dramatically influences the pKa-values of the protonated forms as well as the rates of the thermal isomerization reactions, (2) water is the nucleophile in the hydrolysis reaction around neutral pH, (3) the phenolate oxygen of the merocyanine form plays a key role in the hydrolysis reaction.Hence, the nonprotonated merocyanine isomer is susceptible to hydrolysis, whereas the corresponding protonated form is stable toward hydrolytic degradation.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biological Engineering, Physical Chemistry, Chalmers University of Technology , 412 96 Göteborg, Sweden.

ABSTRACT
Six water-soluble spiropyran derivatives have been characterized with respect to the thermal and photoinduced reactions over a broad pH-interval. A comprehensive kinetic model was formulated including the spiro- and the merocyanine isomers, the respective protonated forms, and the hydrolysis products. The experimental studies on the hydrolysis reaction mechanism were supplemented by calculations using quantum mechanical (QM) models employing density functional theory. The results show that (1) the substitution pattern dramatically influences the pKa-values of the protonated forms as well as the rates of the thermal isomerization reactions, (2) water is the nucleophile in the hydrolysis reaction around neutral pH, (3) the phenolate oxygen of the merocyanine form plays a key role in the hydrolysis reaction. Hence, the nonprotonated merocyanine isomer is susceptible to hydrolysis, whereas the corresponding protonated form is stable toward hydrolytic degradation.

No MeSH data available.