Tautomeric and conformational equilibria of tyramine and dopamine in aqueous solution

Peter I. Nagy, Gergely Völgyi, K. Takács-Novák

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

The protonation macro- and microconstants have been measured for tyramine at three temperatures using potentiometry combined with UV spectroscopy. The experimentally determined zwitterion/neutral tautomerization equilibrium constant for tyramine in aqueous solution decreases with increasing temperature from log kz = 1.03 at Τ= 287 K to log kz = 0.39 at Τ= 310 K. Using the van't Hoff isochore, the tautomerization enthalpy was calculated as -9.3 to -13.4 kcal mol-1 in the indicated temperature range. Theoretical calculations on the solvent effects have been performed using the PCM polarizable continuum dielectric solvent approach at the B3LYP/6-31G* level, and by performing Monte Carlo simulations utilizing the free energy perturbation method. The applied PCM approach, including B3LYP/6-311++G** and MP2/6-31G* single point calculations, as well, consistently favours the neutral form in aqueous solution both for tyramine and dopamine. In contrast, Monte Carlo simulations predict solvent effects that are too large and favour the zwitterionic form both for tyramine and dopamine. Neither method can predict the experimental finding that the prevalent tautomer is the zwitterion for tyramine but is the neutral form for dopamine in aqueous solution. The Monte Carlo results could be improved by finding new, appropriate net atomic charges. The present charge sets derived by fits to the PCM/B3LYP/6-31G* and PCM/B3LYP/6-311++G**//PCM/ B3LYP/6-31G* molecular electrostatic potentials provide structures for the zwitterionic solutes that are too polar.

Original languageEnglish
Pages (from-to)1589-1601
Number of pages13
JournalMolecular Physics
Volume103
Issue number11-12
DOIs
Publication statusPublished - 2005

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dopamine
Tyramine
Pulse code modulation
Dopamine
zwitterions
aqueous solutions
potentiometric analysis
tautomers
Temperature
trucks
Isochores
temperature
Potentiometry
solutes
simulation
enthalpy
free energy
electrostatics
continuums
Protonation

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Tautomeric and conformational equilibria of tyramine and dopamine in aqueous solution. / Nagy, Peter I.; Völgyi, Gergely; Takács-Novák, K.

In: Molecular Physics, Vol. 103, No. 11-12, 2005, p. 1589-1601.

Research output: Contribution to journalArticle

Nagy, Peter I. ; Völgyi, Gergely ; Takács-Novák, K. / Tautomeric and conformational equilibria of tyramine and dopamine in aqueous solution. In: Molecular Physics. 2005 ; Vol. 103, No. 11-12. pp. 1589-1601.
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