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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.


Experimentallyrecorded absorbance traces for 1MC and 1MCH+ at 25 °C at pH 2 (dash-dot, recordedat 410 nm, MCH+), pH 3 (dashed, recorded at 410 nm, MCand MCH+), and pH 4 (dotted, recorded at 512 nm, MC). Thecorresponding normalized traces derived from a simulation using thekinetic model in Scheme 2 and the rate constantsat pH 5 are also shown (solid lines). Note that kh and k–h were slightlyadjusted from the values determined at pH 5 (see text for details).
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fig6: Experimentallyrecorded absorbance traces for 1MC and 1MCH+ at 25 °C at pH 2 (dash-dot, recordedat 410 nm, MCH+), pH 3 (dashed, recorded at 410 nm, MCand MCH+), and pH 4 (dotted, recorded at 512 nm, MC). Thecorresponding normalized traces derived from a simulation using thekinetic model in Scheme 2 and the rate constantsat pH 5 are also shown (solid lines). Note that kh and k–h were slightlyadjusted from the values determined at pH 5 (see text for details).

Mentions: At pH 2–4,a full kinetic model including all species and processes shown inScheme 2 has to be applied. We could not findthe analytic expression for this kinetic situation by the Laplacetransformation method. Instead we used the experimental rate constantsderived at pH 5 and the respective pKa-values to simulate the concentration profiles versus time for allrelevant species by numerical means. These concentration profileswere compared with the experimentally recorded absorption traces ofMC and MCH+ at pH 2–4. While the experimentallyobtained values of ko and kc at pH 5 together with pKaI and pKaII wereused in the simulations, the values of kh and k–h were slightly adjustedfor each pH-value to improve the goodness of fit (the experimentalvalues at pH 5, kh = 1.8 × 10–3 min–1, k–h = 6.6 × 10–5 min–1, werevaried in the intervals 1.8 × 10–3 min–1 – 2.6 × 10–3 min–1 and 0 – 6.6 × 10–5 min–1, respectively). Note that these adjustments are nolarger than the variations in the experimentally obtained values of kh and k–h between pH 5 and pH 10. The results for 1 are shownin Figure 6 and the corresponding data for 5 and 6 is shown in Figure S4 in the Supporting Information. The results clearly showthat the kinetic model holds also at pH values where the interconversionsbetween all five species have to be taken into account.


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)

Experimentallyrecorded absorbance traces for 1MC and 1MCH+ at 25 °C at pH 2 (dash-dot, recordedat 410 nm, MCH+), pH 3 (dashed, recorded at 410 nm, MCand MCH+), and pH 4 (dotted, recorded at 512 nm, MC). Thecorresponding normalized traces derived from a simulation using thekinetic model in Scheme 2 and the rate constantsat pH 5 are also shown (solid lines). Note that kh and k–h were slightlyadjusted from the values determined at pH 5 (see text for details).
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Related In: Results  -  Collection

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fig6: Experimentallyrecorded absorbance traces for 1MC and 1MCH+ at 25 °C at pH 2 (dash-dot, recordedat 410 nm, MCH+), pH 3 (dashed, recorded at 410 nm, MCand MCH+), and pH 4 (dotted, recorded at 512 nm, MC). Thecorresponding normalized traces derived from a simulation using thekinetic model in Scheme 2 and the rate constantsat pH 5 are also shown (solid lines). Note that kh and k–h were slightlyadjusted from the values determined at pH 5 (see text for details).
Mentions: At pH 2–4,a full kinetic model including all species and processes shown inScheme 2 has to be applied. We could not findthe analytic expression for this kinetic situation by the Laplacetransformation method. Instead we used the experimental rate constantsderived at pH 5 and the respective pKa-values to simulate the concentration profiles versus time for allrelevant species by numerical means. These concentration profileswere compared with the experimentally recorded absorption traces ofMC and MCH+ at pH 2–4. While the experimentallyobtained values of ko and kc at pH 5 together with pKaI and pKaII wereused in the simulations, the values of kh and k–h were slightly adjustedfor each pH-value to improve the goodness of fit (the experimentalvalues at pH 5, kh = 1.8 × 10–3 min–1, k–h = 6.6 × 10–5 min–1, werevaried in the intervals 1.8 × 10–3 min–1 – 2.6 × 10–3 min–1 and 0 – 6.6 × 10–5 min–1, respectively). Note that these adjustments are nolarger than the variations in the experimentally obtained values of kh and k–h between pH 5 and pH 10. The results for 1 are shownin Figure 6 and the corresponding data for 5 and 6 is shown in Figure S4 in the Supporting Information. The results clearly showthat the kinetic model holds also at pH values where the interconversionsbetween all five species have to be taken into account.

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.