Photophysics of some cationic dyes in aqueous micellar dispersions of surfactants and in different solvents

Safranin T- SDS- GO ternary system: A fluorescent pH sensor

Graphene oxide (GO), one of the popular materials in recent years, has been synthesized according to the modified Hummers' method. Stable dispersions of different amounts of negatively charged GO were prepared in aqueous media. The GO/dye composites were prepared in deionized water by a simple method with the positively charged Safranin T compound (SfT), which is known to have strong fluorescence properties. By changing the GO/dye ratio, it was obtained stable composites in aqueous media. It was investigated the interaction of SfT with GO in an aqueous solution under the critical micelle concentration (CMC), at the CMC and above the CMC by adding sodium dodecyl sulfate (SDS). It was clarified the formation of GO-SfT composites by using spectroscopic techniques. In these composites, the effect of GO layers on the SfT's photophysical properties was examined by absorption and fluorescence spectroscopy techniques. The change in the quenching effect of GO was monitored both adding a stabilizing electrolyte (NaCl) to the media and changing the pH of the medium. The evaluation was on the probability of the GO-SfT-SDS ternary system being a pH sensing biological sensor material. As a result of this study, it was thought that the GO-SfT-SDS system could be functionalized as a fluorescent pH sensor by taking advantage of GO's sensitivity to pH.

Photophysical Properties of Some Fluorescent Dyes in SDS Micellar Solutions

Photophysical properties of fluorescent dyes such as Safranin T, Acridine Orange, Pyronin B and Pyronin Y in SDS micelles were examined by using spectroscopic techniques. Firstly, spherical micelles in deionized water were prepared with Sodium Dodecyl Sulfate (SDS) surfactants and they were transformed into their layered structures (lamellar micelles) by the aid of NaCl (sodium chloride). SEM studies confirmed the transformation of SDS micelles from the spherical structures to the lamellar structures. Secondly, absorption and fluorescence characteristics of the dyes in deionized water and the SDS micelles aqueous solutions were characterized in the presence of various NaCl concentrations at above the critical micelle concentration (CMC). Moreover, the photophysical properties of the dyes in various media were discussed by fluorescence quantum yield and fluorescence lifetime data. The micellar structures called a mimetic membrane system changed the photophysical properties of the dyes compared to those in deionized water.

Excitation of triplet states of hypericin in water mediated by hydrotropic cromolyn sodium salt

Hypericin (Hyp) is a hydrophobic pigment found in plants of the genus Hypericum which exhibits low levels of solubility in water. This work shows that the solubility of Hyp can be significantly increased through the addition of cromolyn disodium salt (DSCG). Performed studies using UV-VIS absorption and fluorescence spectroscopies demonstrate that Hyp remains in a predominantly biologically photodynamic active monomeric form in the presence of DSCG at concentrations ranging from 4.6×10^-3 to 1.2×10^-1mol·L^-1. The low association constant between Hyp and DSCG (K_a=71.7±2M^-1), and the polarity value of 0.3 determined for Hyp in a DSCG-water solution, lead to a suggestion that the monomerization of Hyp in aqueous solution can be explained as a result of the hydrotropic effect of DSCG. This hydrotropic effect is most likely a result of interactions between two relative rigid aromatic rings of DSCG and a delocalized charge on the surface of the Hyp molecule. The triplet-triplet (T-T) electronic transition observed in is Hyp in the presence of DSCG suggests a possible production of reactive oxygen species once Hyp is irradiated with visible light in a DSCG aqueous solution.

Interaction of phenazinium-based photosensitizers with the 'N' and 'B' isoforms of human serum albumin: Effect of methyl substitution

The present work is focused on exploring the interaction of two phenazinium-based biological photosensitizers, phenosafranin (PSF) and safranin-O (SO), with human serum albumin (HSA), with particular emphasis on the physiologically significant NB conformational transition of the protein on the dye:HSA interaction. In addition, the presence of methyl substitution on the planar phenazinium ring in SO paves way for looking into the effect of simple chemical manipulation (that is, methyl substitution on the dye nucleus) on the dye:protein interaction behavior as a function of various (pH-induced) isoforms of HSA. Our results reveal a significantly stronger binding interaction of SO with the B isoform of HSA (at pH9.0) compared to that with the N isoform (at pH7.4). On the contrary, the PSF:HSA interaction is found to be reasonably insensitive to the aforesaid conformational transition of HSA. However, the probable binding location of both the dye molecules (PSF and SO) is found to be within the protein scaffolds (domain IB). This is further quantified from the modulation of fluorescence decay behavior of the dyes within the protein scaffolds. It is important to note that the rotational relaxation behavior of the protein-bound dyes reveals an unusual 'dip-rise-dip', an observation not reported earlier. Such unusual anisotropy decay is meticulously analyzed by an associated (or multicomponent) exponential decay model which emphasizes on the fractional contributions from differential classes of fluorophore populations characterized by the fast (due to unbound or solvent exposed part of the fluorophore) and slow (due to embedded or bound part) motions, in combination with their different local mobilities. Furthermore, the translational diffusion of the dye molecules in the presence of the protein in different isoforms (N-form or B-form) at a single molecule level is also measured by Fluorescence Correlation Spectroscopy (FCS).