Surface modification of titanium dioxide nanoparticles (TiO2 NPs) with the biologically active molecule pyridoxine hydrochloride (vitamin B6) was found to alter the optical properties. Microstructural characterization involving transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis revealed that the anatase TiO2 NPs had a narrow size distribution with an average diameter of 45 ?. The absorption onset of the surface-modified TiO2 samples was red-shifted by about 0.4 eV compared to the unmodified particles. The mode of binding between vitamin B6 and the surface Ti atoms was investigated by Fourier transform infrared spectroscopy (FTIR). From the Benesi? Hildebrand plot, the stability constant of the surface complex was found to be of the order 102 M-1. The experimental findings were supported by detailed quantum chemical calculations based on the density functional theory (DFT). Agreement was found between the experimentally measured absorption spectra of the TiO2 NPs surface-modified with vitamin B6 and the theoretically calculated electronic excitation spectra of the corresponding model system.