pH-Dependent electronic and spectroscopic properties of pyridoxine (Vitamin B6).
The key electronic and spectroscopic properties of vitamin B(6) (pyridoxine) and some of its main charged and protonated/deprotonated species are explored using hybrid density functional theory (DFT) methods including polarized solvation models. It is found that the dominant species at low pH is the N(1)-protonated form and, at high pH, the O(3)(')-deprotonated compound. Computed and experimental UV-spectra for these species (experimental spectra recorded at pH 1.7 and 11.1, respectively) show a very close resemblance. At pH 4.3, the protonated species dominates, but with onset of the zwitterionic oxo form which is also the dominant species at neutral pH. The computational studies furthermore show that neither a polarized continuum model of the polar aqueous solvent or explicit hydrogen bonding through additional water molecules are sufficient to describe accurately the spectrum at physiological pH. Instead, Na(+) and Cl(-) counterions were required to give a blue-shift of approximately 0.15 eV.
Ristilä
Mikael
M
Department of Natural Sciences and Orebro Life Science Center, Orebro University, S-701 82 Orebro, Sweden.
Matxain
Jon M
JM
Strid
Ake
A
Eriksson
Leif A
LA
D004583:Electrons; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D011736:Pyridoxine / Q000737:chemistry*; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry; D013057:Spectrum Analysis; D013816:Thermodynamics; D025101:Vitamin B 6 / Q000737:chemistry*; D014803:Vitamin B Complex / Q000737:chemistry; D014867:Water / Q000737:chemistry
D012997:Solvents; D014867:Water; D014803:Vitamin B Complex; D025101:Vitamin B 6; D011736:Pyridoxine