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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.


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pH dependence of the thermal rate constants ko (a), kc (b), kh (c), and k–h (d).Data shown for 1 (■), 5 (●),and 6 (▼). The data is collected in Table S1 inthe Supporting Information.
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fig4: pH dependence of the thermal rate constants ko (a), kc (b), kh (c), and k–h (d).Data shown for 1 (■), 5 (●),and 6 (▼). The data is collected in Table S1 inthe Supporting Information.

Mentions: The experiments and thedata analysis procedure at pH 7 described above were performed alsoat pH 5–10. Figure 4 shows the pH dependenceof the rate constants ko, kc, kh, and k–h for 1, 5, and 6. The extracted rate constants reflect the kinetic modelshown in eq. 1, i.e., none of the protonatedspecies SPH+ or MCH+ were considered. For 1, this is a good approximation over the entire pH interval5–10 as pKaII = 3.7for this derivative, and hence, less than 5% exists as MCH+ at pH 5. For 5 and 6, the correspondingpKa-values are 4.5 and 4.4. This impliesthat around 25% MCH+ is present at pH 5, why the data isonly shown between pH 6 and pH 10.


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)

pH dependence of the thermal rate constants ko (a), kc (b), kh (c), and k–h (d).Data shown for 1 (■), 5 (●),and 6 (▼). The data is collected in Table S1 inthe Supporting Information.
© Copyright Policy
Related In: Results  -  Collection

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

fig4: pH dependence of the thermal rate constants ko (a), kc (b), kh (c), and k–h (d).Data shown for 1 (■), 5 (●),and 6 (▼). The data is collected in Table S1 inthe Supporting Information.
Mentions: The experiments and thedata analysis procedure at pH 7 described above were performed alsoat pH 5–10. Figure 4 shows the pH dependenceof the rate constants ko, kc, kh, and k–h for 1, 5, and 6. The extracted rate constants reflect the kinetic modelshown in eq. 1, i.e., none of the protonatedspecies SPH+ or MCH+ were considered. For 1, this is a good approximation over the entire pH interval5–10 as pKaII = 3.7for this derivative, and hence, less than 5% exists as MCH+ at pH 5. For 5 and 6, the correspondingpKa-values are 4.5 and 4.4. This impliesthat around 25% MCH+ is present at pH 5, why the data isonly shown between pH 6 and pH 10.

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.


Related in: MedlinePlus