Toluidine blue: aggregation properties and structural aspects

Abstract

The toluidine blue (TB) aggregation phenomenon in water solutions was investigated by UV-Vis absorption spectroscopy in a wide range of concentrations, from 10−9 to 10−2 M. The experimental data were fitted by assuming that the spectrum was due to the overlapping of the bands of six different aggregation species simultaneously present in solution. The model and the peak centres of the different species were hypothesized on the basis of exciton theory. All the spectra obtained were simultaneously processed thus allowing the derivation of the K constant, which was assumed to be the same for all the equilibria and which was found equal to 10 500. The ε spectra of the different aggregation species were also obtained. The overall TB spectrum may be mainly attributed to the H-type aggregation, although some of the species also show the J type bands. The structural features of TB and its dimeric aggregate were also investigated by means of molecular mechanics semi-empirical potential energy calculations. The results obtained for the dimer confirm the H type aggregation and show that the lowest energy model of the four possible is the one obtained by a mirror plane of symmetry containing the aromatic rings, in agreement with the x-ray diffraction data which will be presented in a forthcoming paper.

Raman spectroelectrochemical study of Toluidine Blue, adsorbed and electropolymerized at a gold electrode

“…The absorption peak maximum is shifted to lower wavelength values as compared with TB monomers ($610 nm) in aqueous solutions [29]. It was demonstrated that TB dimers exhibit absorption peak near 580 nm [29]. Thus presented data suggest dimerization of TB species upon adsorption on Au electrode surface.…”

“…2 shows the electronic absorption spectrum of TB adsorbed on semitransparent (20 nm thick) gold layer in pH 7.0 solution. The absorption peak maximum is shifted to lower wavelength values as compared with TB monomers ($610 nm) in aqueous solutions [29]. It was demonstrated that TB dimers exhibit absorption peak near 580 nm [29].…”

Real‐Time Visualization of Lysosome Destruction Using a Photosensitive Toluidine Blue Nanogel

“…[12] The aggregated TB within the nanogel led to a weaker ability to generate singlet oxygen molecules under LED light (633 nm) when compared to free TB (Figure 1e). The reduction of photosensitivity could be compensated when TB is released and accumulate within the lysosome following the degradation of HA.…”

Letter to the Editor: Re: Decontamination of Anodized Implant Surface With Different Modalities for Peri‐Implantitis Treatment: Lasers and Mechanical Debridement With Citric Acid

“…There are two pathways for the reaction associated with PDT: the Type I reaction involves generation of hydroxyl radicals (OH·), while the Type II reaction involves generation of singlet state oxygen 2 . However, toluidine blue has peak absorption at a 635‐nm wavelength, while its complete absorption spectrum ranges from wavelengths of 609 to 668 nm 3 . Moreover, while the ascending part of the absorption curve shows a low slope trend, the descending part drops abruptly 3 , 4 .…”

“…However, toluidine blue has peak absorption at a 635‐nm wavelength, while its complete absorption spectrum ranges from wavelengths of 609 to 668 nm 3 . Moreover, while the ascending part of the absorption curve shows a low slope trend, the descending part drops abruptly 3 , 4 . On these grounds, in the above study the authors used a 830‐nm‐wavelength low‐level diode laser to perform the “photodynamic” treatment, but in fact, with the reported irradiation conditions, toluidine blue photoactivation will not take place nor exert antibacterial effects.…”