Photochemical Transformations of Chalcone-Vitamin E Hybrids

Chalcone-vitamin E hybrids 6’-O-tosyl-3,4,5-trimethoxy-δ-tocopherol-chalcone (1), 3,4,5-trimethoxy-δ-tocopherol-chalcone (2), 6’-O-tosyl-3,4,5-trimethoxy-δ-tocopherol-retrochalcone (3) and 3,4,5-trimethoxy-δ-tocopherol-retrochalcone (4) were synthesized as part of a search for new biological activities in these types of derivatives. We report herein on the photoisomerization products of hybrids 1-4, and the effects of the solvent and substitution patterns in producing secondary products such as flavanone 6, 3-deoxyanthocyanidin 8, and hemiketal 10. Photochemically-induced changes are considered important since structural modifications and/or the presence of additional products can affect the biological activity of this type of semisynthetic hybrids. Resumen. Los híbridos de chalcona-vitamina E, 6’-O-tosil-3,4,5-trimetoxi-δ-tocoferol-chalcona (1), 3,4,5-trimetoxi-δ-tocoferol-chalcona (2), 6’-O-tosil-3,4,5-trimetoxi-δ-tocoferol-retrochalcona (3) y 3,4,5-trimetoxi-δ-tocoferol-retrochalcona (4), fueron sintetizados como parte de la búsqueda de nuevos perfiles de actividad biológica para este tipo de derivados. En este trabajo reportamos los productos de fotoisomerización de los híbridos 1-4, y los efectos del disolvente, así como de distintos patrones de sustitución en la generación de productos secundarios como la flavanona 6, la 3-deoxiantocianidina 8, y el hemicetal 10. Los cambios fotoinducidos son considerados de gran importancia debido a que la modificación en la estructura y/o la presencia de productos adicionales puede afectar la actividad biológica de este tipo de híbridos semisintéticos.

A General Approach for All-visible-light Switching of Diarylethenes through Triplet Sensitization using Semiconducting Nanocrystals

Coupling semiconducting nanocrystals (NCs) with organic molecules provides an efficient route to generate and transfer triplet excitons. These excitons can be used to power photochemical transformations such as photoisomerization reactions using low energy radiation. Thus, it is desirable to develop a general approach that can efficiently be used to control photoswitches using all-visible-light aiming at future applications in life- and material sciences. Here, we demonstrate a simple ‘cocktail’ strategy that can achieve all-visible-light switchable diarylethenes (DAEs) through triplet energy transfer from the hybrid of CdS NCs and phenanthrene-3-carboxylic acid, with high photoisomerization efficiency and improved fatigue resistance. The size-tunable excitation energies of CdS NCs make it possible to precisely match the corresponding energy of the relevant DAE photoswitch. We demonstrate reversible all-visible-light photoisomerization of a series of DAE derivatives both in the liquid and solid state, even in the presence of oxygen. Our general strategy is promising for fabrication of all-visible-light activated optoelectronic devices as well as memories, and should in principle be adaptable to photopharmacology.

Synthesis of photochemical transformations of oil in the sea

In this presentation and article, we synthesize findings from a workshop about our understanding of the interplay between crude oil photochemical oxidation and oil spill response, emphasizing how this understanding has evolved since the 2010 DWH spill. Our discussion is guided by one overarching questions: what role does photochemical oxidation play towards informing effective oil spill response operations? We show that prior to the DWH spill, our understanding of the relative importance of oil weathering processes, specifically photochemical weathering, was incomplete. We further explore how accounting for photochemical changes to oil's properties (physical and chemical) could improve the effectiveness of oil spill response operations, specifically chemical dispersant applications. Lastly, we identify priority knowledge gaps related to this guiding research question.

Sensitized Photolysis of Thioglycolic Acid in Aquatic Environment

The photochemical transformations of thioglycolic acid using model systems was studied by varying the irradiation sources and the kinetic parameters were determined. It was found that thioglycolic acid undergoes destruction on induced photolysis in the presence of humic substances, and its half-life can be estimated as 10-14 days, depending on weather conditions (cloudiness, time of day, season etc.). Results obtained in the course of this study on model systems were transferred to natural waters, and it was concluded that thioglycolic acid has a positive influence on the chemical self-purification processes of water, in the natural aquatic environment. This is manifested by increasing the self-purification capacity of water, due to the generation of active oxygen species, which lead to the degradation not only of this thiol, but of other pollutants present in aquatic environment, as well. At the same time, the products of the transformations are harmless to the aquatic environment and hydrobionts.

Predicting wavelength-dependent photochemical reactivity and selectivity

Predicting the conversion and selectivity of a photochemical experiment is a conceptually different challenge compared to thermally induced reactivity. Photochemical transformations do not currently have the same level of generalized analytical treatment due to the nature of light interaction with a photoreactive substrate. Herein, we bridge this critical gap by introducing a framework for the quantitative prediction of the time-dependent progress of photoreactions via common LEDs. A wavelength and concentration dependent reaction quantum yield map of a model photoligation, i.e., the reaction of thioether o-methylbenzaldehydes via o-quinodimethanes with N-ethylmaleimide, is initially determined with a tunable laser system. Combined with experimental parameters, the data are employed to predict LED-light induced conversion through a wavelength-resolved numerical simulation. The model is validated with experiments at varied wavelengths. Importantly, a second algorithm allows the assessment of competing photoreactions and enables the facile design of λ-orthogonal ligation systems based on substituted o-methylbenzaldehydes.