Additive effect on the dimer formation of thiazine dyes

Nanoporous hybrid core–shell nanoparticles for sequential release

Silica inside – organosilica outside, and nanoporous throughout: Drug molecules to be released sequentially from novel core–shell nanoparticles select their location (core/shell) autonomously.

Modulation of release mechanisms of methylene blue (MB) monomers and dimers from silica-MB@shellac synthesized by antisolvent crystallization

Release behaviors of drugs from drug deliveries are crucial for the enhancement of therapy efficiency, reduction of toxicity and patient compliance. Herein, antisolvent crystallization is employed to coat methlyene blue (MB)-loaded silica by shellac precipitation (silica-MB@shellac), which is simultaneously induced by outward diffusion of H⁺ ions from particular silica-MB. The encapsulation of shellac shell on silica-MB modulates the aggregation state of MB, which endows silica-MB@shellac a decreased MB's thermal stability, enhanced photoluminescence intensity, improved stability against in vitro reduction by ascorbic acid and retained photodynamic therapy activity. From the absorbance of MB supernatant obtained during incubation, the concentrations of MB monomers and dimers are determined via a non-linear regression analysis to investigate the influence of shellac coating on MB's release mechanisms from silica-MB@shellac. According to the simulated models, small diffusion constants of MB are caused by limited diffusion through shellac shells with high compaction degrees. These are observed for samples synthesized under high supersaturation degree during antisolvent crystallization. High degree of supersaturation is achieved through increasing shellac concentration, additive amount and dropping rate of antisolvent, as well as decreasing pH values of aqueous buffers as antisolvent. Furthermore, a combined mechanism of Fickian diffusion and Case-IΙ relaxation is proposed to describe the release behaviors of MB monomer and dimers from silica-MB@shellac. Therefore, this work may shed light on the encapsulation method of polymer on drug-loaded powders and the control of aggregation states of photosensitizers to promote the photoluminescence intensity, photodynamic therapy efficiency and controlled release behaviors.

Additive-induced aggregate changes of two structurally similar dyes in aqueous solutions: A comparative photophysical study

Absorption and emission spectral characteristics of the two structurally similar phenothiazine dyes, azure B and toluidine blue, in aqueous solutions of the two sets of molecular additives (ureas and monosaccharides) were studied as a function of the dye and additive concentrations. The absorption spectra of the dyes were also studied in pure tetramethylurea with an aprotic nature. The spectral data were analyzed using DECOM Program. The dimer structure of the interacting molecules in these dyes was discussed using the exciton model. The urea class of additives was found to act as water structure-breakers over the range of studied concentration. The carbohydrate additives were found to act as water structure-breakers at low concentrations. However, the water structure breaking process may be disfavored by the additive-additive interactions at higher concentrations. It can be concluded that at low additive concentrations, the main driving force for breaking the dye association is water-additive interaction, which disrupts the water hydrogen bonds induced by the additives. However, at the high additive concentrations, the different phenomena including additive-additive and additive-dye interactions can change the structure, strength, and aggregative properties of the dyes. Finally, the urea in water induces noticeably fluorescence quenching in emission spectra of both the dyes.

A comparative spectroscopic study of thiourea effect on the photophysical and molecular association behavior of various phenothiazine dyes

This paper describes the role of a structure breaking additive (thiourea) on the photophysical and molecular association of a series of phenothiazine dyes in aqueous media using the absorption and fluorescence spectroscopic methods for the first time. The studied dyes were thionine, azure A, azure B, toluidine blue, and methylene blue. The spectral data were analyzed using DECOM program. Relevant spectral parameters in the dye solutions were estimated and discussed based on the chemical structure of the additive and excitonic treatment. The observation of spectral changes in the spectral data of the (water-additive-dye) system indicates the possible structure formation between the dye and additive molecules. However, it is found that in the high concentrations of thiourea the dimer geometries (H- and J-type dimers) are influenced by the dye-additive interactions. As a result, a competition between the dye-additive and dye-dye interactions was also observed.

Thionine–graphene oxide covalent hybrid and its interaction with light

Quenching of the thionine singlet excited state in covalently functionalized graphene oxide with an efficient back electron transfer process.

Thiazine dyes: Evaluation of monomeric and aggregate forms

The aggregation phenomenon of Azure B, monobrominated Azure B, Thionine and Methylene Blue was studied by UV-Visible spectrophotometry in different media as a function of dye concentration and temperature variations. The tests carried out in organic solvents allowed the identification of monomeric species of these compounds, which have not been reported in literature and have been wrongly assigned for years. The results obtained in water allowed demonstrating that different kinds of aggregates are present in this medium. In addition, the aggregation tendency of these dyes in organic solvent and aqueous media was established. Several parameters such as lipophilicity, effect of bulky substituents and interactions with media were considered to interpret the aggregation behavior of thiazine dyes.