Molecular structure and reversible photodegradation in anthraquinone dyes

Excited-State Intramolecular Hydrogen Transfer of Compact Molecules Controls Amyloid Aggregation Profiles

Developing chemical methodologies to directly modify harmful biomolecules affords the mitigation of their toxicity by persistent changes in their properties and structures. Here we report compact photosensitizers composed of the anthraquinone (AQ) backbone that undergo excited-state intramolecular hydrogen transfer, effectively oxidize amyloidogenic peptides, and, subsequently, alter their aggregation pathways. Density functional theory calculations showed that the appropriate position of the hydroxyl groups in the AQ backbone and the consequent intramolecular hydrogen transfer can facilitate the energy transfer to triplet oxygen. Biochemical and biophysical investigations confirmed that these photoactive chemical reagents can oxidatively vary both metal-free amyloid-β (Aβ) and metal-bound Aβ, thereby redirecting their on-pathway aggregation into off-pathway as well as disassembling their preformed aggregates. Moreover, the in vivo histochemical analysis of Aβ species produced upon photoactivation of the most promising candidate demonstrated that they do not aggregate into oligomeric or fibrillar aggregates in the brain. Overall, our combined computational and experimental studies validate a light-based approach for designing small molecules, with minimum structural complexity, as chemical reagents targeting and controlling amyloidogenic peptides associated with neurodegenerative disorders.

Imaging studies of photodegradation and self-healing in anthraquinone derivative dye-doped PMMA

We study photodegradation and self-healing of nine different anthraquinone-derivatives doped into PMMA using transmission imaging microscopy in search of structure-property relationships of the underlying mechanisms. We find that seven of the nine anthraquinone derivatives display partially reversible photodegradation, with 1,8-dihydroxyanthraquinone (Dantron/Chrysazin) having the best photostability and recovery characteristics of all dyes tested in this study. Based on these measurements we predict that a sample of 1,8-dihydroxyanthraquinone doped into PMMA with a concentration of 9 g l-1 will have a record setting irreversible inverse quantum efficiency of Bε = 4.56 × 109. Additionally, by considering the performance of the different anthraquinone derivatives and their structures, we develop three rules-of-thumb to qualitatively predict the photostability and recovery characteristics of anthraquinone derivatives. These rules-of-thumb will help guide future experiments and molecular modeling in discerning the underlying mechanisms of reversible photodegradation. Finally, we compare our results for disperse orange 11 dye-doped PMMA to the extended Correlated Chromophore Domain Model (eCCDM). While the eCCDM correctly predicts the behavior of the reversible decay component, it fails to correctly predict the behavior of the irreversible degradation component. This implies further modifications to the eCCDM are required.

BiVO4/WO3 nano-composite: characterization and designing the experiments in photodegradation of sulfasalazine

A BiVO₄-WO₃ nano-composite (NC) was hydrothermally prepared and characterized by different techniques including X-ray diffraction (XRD), scanning electron microscope equipped with an energy-dispersive X-ray (EDX) analyzer, X-ray mapping, UV-Vis reflectance spectroscopy (DRS), and photoluminescence spectroscopy (PL). The average crystallite size of 8.5 nm was estimated for the composite by the Williamson-Hall equation. The band gap energies of 2.46, 3.02, and 2.95 eV were obtained for the direct electronic transitions of BiVO₄, WO₃, and the composite, respectively. The point of zero charges (pHpzc) of the composite was also estimated at 5. The composite was then used in the photodegradation of sulfasalazine (SSZ). When the moles of WO₃ was four times greater than BiVO₄, the best photocatalytic activity and the lowest PL intensity were obtained. The simultaneous effects of the experimental variables on the boosted photocatalytic activity of the composite (to the single semiconductors) were studied by the response surface methodology (RSM). A significant quadratic model was confirmed for processing the data based on the F value of a model F value of 63.55 > F_{0.05, 14, 13} = 2.55. This was also confirmed by LOF F value of 2.56 < F_{0.05, 10, 3} = 8.79. Besides, the multiple correlation coefficients R² (R² = 0.9856), adjusted R² (adj-R² = 0.9701), and predicted R² (pred-R² = 0.9098) confirm the goodness of the model. The optimal run included C_SSZ 9 mg/L, pH 4, 40 min irradiation time, and 0.8 g/L of the composite under the visible light irradiation.

Recovery of photodegraded rhodamine 6g in ester-containing polymer matrices

Self-healing, rhodamine 6g, dye-doped polymers are reported. The amplified spontaneous emission (ASE) photodegrades after repeated exposure to 532 nm laser light at 10 Hz. Recovery of the ASE signal is observed in dye-doped thermoplastic polyurethane and glycol-modified poly(ethylene terephthalate); both polymers contain repeating ester groups in their backbone. The polymer ester groups are hypothesized to mediate the full recovery of rhodamine 6g from a photodegraded state. A small amount of ASE recovery after photodegradation is observed in dye-doped poly(vinyl alcohol), >98% hydrolyzed, where conversion of rhodamine 6g from a long-lived dark state contributes to the majority of the increased ASE signal in poly(vinyl alcohol) while small amounts of recovery from interactions with residual acetate groups are also possible.

Nitrogen-containing organic compounds: Origins, toxicity and conditions of their photocatalytic mineralization over TiO2

Sustainable water management remains a global concern to meet the food needs of industrial and agricultural activities. Therefore, pollution abatement techniques, cheap and environmentally, are highly desired and recommended. The present review is devoted to the origin and the toxicity of nitrogen-containing organic compounds in water. The progress made in removing these pollutants, in recent years, is addressed. However, a prominent place is given to the photocatalytic degradation process using the TiO₂ as a semiconductor, the conditions for good mineralization and especially the factors influencing it. The parameters that impact the performance of this method are the pH, the temperature, the reactor used, the light, the concentration of the pollutant, the amount of catalyst, etc. Up to now, the importance of one parameter relative to another has not been established because in the context of the photocatalytic degradation, certain parameters are often tightly coupled. Consequently, the mineralization is dependent on the initial degree of oxidation of nitrogen atom contained in the pollutant to be degraded. The hydroxyl nitrogen is primarily converted into nitrate ions (NO₃^-), while the amides and the primary amines are converted into ammonium ions (NH₄⁺).

Imaging studies of temperature dependent photodegradation and self-healing in disperse orange 11 dye-doped polymers

Using confocal transmission imaging microscopy, we measure the temperature dependence of photodegradation and self-healing in disperse orange 11 (DO11) dye-doped (poly)methyl-methacrylate (PMMA) and polystyrene (PS). In both dye-doped polymers, an increase in sample temperature results in a greater photodegradation rate and degree of degradation, while also resulting in a slower recovery rate and larger recovery fraction. These results confirm the temperature dependence predictions of the modified correlated chromophore domain model (mCCDM) [B. R. Anderson and M. G. Kuzyk, Phys. Rev. E 89, 032601 (2014)]. Additionally, using quantitative fitting of the imaging data for DO11/PMMA, we determine the domain density parameter to be ρ = 1.19 (±0.25) × 10(-2) and the domain free energy advantage to be λ = 0.282 ± 0.015 eV, which are within the uncertainty of the values previously determined using amplified spontaneous emission as the probe method [S. K. Ramini et al., Polym. Chem. 4, 4948 (2013)]. Finally, while we find photodegradation and self-healing of DO11/PS to be qualitatively consistent with the mCCDM, we find that it is quantitatively incompatible with the mCCDM as recovery in DO11/PS is found to behave as a stretched (or double) exponential as a function of time.