MICROHYDRATION OF DOPAMINE
Quantum-Mechanical Simulation in Gas Phase
Manuel Mateus Ventura
Professor Emeritus(Biophysics), Universidade de Brasilia,Brazil
ABSTRACT
Microhydration of DOPAMINE (neutral and protonated) is studied with the computing of interaction energies in the microhydrates, in gas phase. Quantum chemical method (DFT/HF) is used: B3lyp/ 6-31++G** (for neutral dopamine) and B3lyp/ 6-311++G**/ cc-pVDZ (for protonated DOPAMINE). The results indicate strong stabilization for microhydrates, chiefly in the case of the DOPAMINE+.
INTRODUCTION
Dopamine is an important hormone and neurotransmitter. Chemically it is 3,4-dihdroxiphenethylamine (C8 H11 N O2) or 4-(2-aminoehyl)benzene-1,2-diol (UPAC)related to other structures biologically actives (1,2). From its molecular structure ( with two phenolic hydroxyls and amino-group) it is possible to assume interaction of dopamine with molecules of water. This interaction is more intense com ( … –NH3+. That interaction has been studied in alanine (in gas phase)(3-8). In the present paper, results of quantum-chemical computing of dopamine microhydrates, for dopamine ( non-protonated and protonated ) in gas phase, are showed and discussed.
COMPUTATIONAL PROCEDURES
Molecular structure models were build and geometry pre-optimized (MM) using HyperChem orArgusLab(AM1). Optimization of molecular geometries and energy minimizations (single points) were performed with Q-Chem (v 4.0.1.0). Molecular Interaction energies were computed by means of the expression
n = 0, 1, 2, … (1)
where E(int) indicates energy of molecular interaction , E(complex)is the molecular energy
of the complex, and the last term is the energy of the sum of the n component parts of the complex . Expression (1) does not take into account the error resulting of orbital superposition(BSSE). Theory levels: a) b3lyp/ 6-311++G** for computing non-protonated dopamine and its hydrates, b) b3lyp/ 6-311++G**/ cc-pVDZ for protonated dopamine and hydrates.
RESULTS
TABLE I – Energies of DOPAMINE (neutral) in interaction com water molecules (in gas phase)
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DOPAMINE(H2O)n = 0 – 2 hydratecomponents INTERACTION ENERGY(dopamine -
(energy , kJ/mol)* water molecules) kJ/mol*
n = 2 - 1757596.417064 - 8.659825762
H2O(a)+H2O(b) - 401386.1582251
n=1 H2O (a) - 200692.4356765 - 12.07189409
n=1 H2O (b) - 200692.4223065 - 13.65695964
H2O (a) <-> H2O(b) + 2.85546045
DOPAMINE(n=0) - 1356181.599066
*Q-Chem computes energy output results in atomic units ( eqvalent to Hartree) which has
been converted to kJ/mol ( 1 a.u. = 1 hartree = 2625.5000 kJ/mol.
TABLE II - Energies of DOPAMINE-NH3+ and its microhydrates ( in gas phase ).
[DOPAMINE-NH3+] (H2O)n = 0- 4 Molecular Energy (kJ/mol) InteractionEnergy(kJ/mol)
n = 0 - 1357220.149061
n =1 (d) - 1557884.692511 - 63.9071220
n= 2 (cd) - 1758334.316114 -136.1617771
n = 3 (bcd) - 1959183.515841 -186.3275311
n = 4 -2159802.960766 -229.3247760
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Distances between N+ and water molecules in microhydrates were measured as 2.6885, 2.85355, 2.94698, 2.914889, in A, for WI, WII, WIII, WIV, respectively. In the tetrahydrate, 5 hydrogen bonds were detected: WI …O (of the phenolic hydroxyl), WI … N+, WI … WII, WII … WIII, W3 … N+ .
Figure 1 – Model of( DOPAMINE+)tetrahydrate.
Water molecules WI, W2, W3, W4 areindicated
up -> down.
CONCLUSIONS
Energies of interaction of dopamine (neutral and protonated) and water molecules ( in gas phase) indicate strong stabilization of of the hydrates, particularly for dopamine protonated hydrates (hydrogen bonds and electrostatic interactions ).That hydration may have functional signification.
REFERENCES
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