NMR Study of the Tautomerism of Porphyrin Including the Kinetic HH/HD/DD Isotope Effects in the Liquid and the Solid State

Braun, J.; Koecher, Martin; Schlabach, Martin; Wehrle, Bernd; Limbach, Hans−Heinrich; Vogel, Emanuel

doi:10.1021/ja00094a014

Cited by 194 publications

(202 citation statements)

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“…For example, the experimental rate at 300 K is k exp Z2!10 4 s K1 [7], and we calculate k ISM Z1. 4 .…”

Section: Resultsmentioning

confidence: 99%

“…The thermal tautomerism rates of the simplest member of this family, the free-base porphyrin (H 2 P), and its deuterated analogue (D 2 P), have been studied in the 95-309 K temperature range [6,7], and recently attracted considerable theoretical interest [8][9][10]. These data offer the opportunity to test the role of tunnelling in a thermal H-atom transfer reaction studied over a large range of temperatures.…”

Section: Introductionmentioning

confidence: 99%

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Tunnelling in low-temperature hydrogen-atom and proton transfers

Arnaut

Formosinho

Barroso

2006

Journal of Molecular Structure

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The reaction path of the interacting-state model with the Lippincott-Schroeder potential for hydrogen bonds, is used in transition-state theory calculations with the semiclassical correction for tunnelling (LS-ISM/scTST) to estimate proton and hydrogen-atom transfer rates at low temperatures. Down to 100 K, the semiclassical correction leads to semi-empirical rates and isotope effects that are in good agreement with the thermal tautomerism of porphine, and the excited-state tautomerisms of salicylideneanilines and 2-(2 0 -hydroxyphenyl)benzoxazole. For lower temperatures, the tunnelling corrections become extremely high and unreliable. It is shown that the permeability of an Eckart barrier fitted to the curvature of the LS-ISM reaction path leads to good estimates of these reaction rates down to 2 K. q

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“…For example, the experimental rate at 300 K is k exp Z2!10 4 s K1 [7], and we calculate k ISM Z1. 4 .…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Tunnelling in low-temperature hydrogen-atom and proton transfers

Arnaut

Formosinho

Barroso

2006

Journal of Molecular Structure

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“…However, the presence of metastable intermediates -the cis structures, where the protons occupy the positions on the adjacent nitrogen atoms (lb in Fig. 1) was also postulated [21,30]. Moreover, the experimental data suggest that the shape of the potential energy surface need not remain the same in different electronic states.…”

Section: Introductionmentioning

confidence: 96%

“…Only the ground state tautomerization rates have been so far carefully measured for 1 [6,13,15,18,[20][21][22][29][30]. The reaction proceeds in So as a thermally activated tunnelling process, involving two successive single-hydrogen transfers.…”

Section: Introductionmentioning

confidence: 99%

Light-Induced Tautomerization in Porphyrin Isomers

Waluk

1999

Acta Phys. Pol. A

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Double proton tautomerization occurring in porphyrin and its structural isomers represents a special case of a chemical transformation in which the substrate and the product are formally the same. The methods used for the investigation of this kind of processes are based on polarized spectroscopy and high-resolution techniques, such as matrix isolation. Their combined use results in obtaining information pertinent to the mechanism of proton transfer, regarding e.g., the values of proton transfer rates, structure of the tautomeric forms or the shape of the potential energy surfaces. In addi-• tion, these procedures provide a way of obtaining spectral, photophysical and structural data that would be otherwise difficult to gain. The examples include determination of transition moment directions, assignment of electronic and vibrational states, elucidation of the character of the substitutional replacement of the rare gas matrix atoms by the chromophore, and the analysis of the nature of the symmetry lowering due to the matrix cage.

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“…3) An understanding of the mechanism of the inner-hydrogen tautomerization process is mandatory for potential technological application of porphyrins. For this reason, tautomeric exchange of the inner hydrogens of a porphyrin free base has been the subject of numerous theoretical [4][5][6][7][8][9] and experimental [10][11][12][13][14][15][16][17][18][19] studies. Most of the theoretical studies have attempted to establish a comprehensive mechanistic and kinetic basis for NH tautomerization by means of various molecular orbital calculations.…”

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confidence: 99%