Abstract
Carboxylic acids conjugated with 4,5-dimethoxy-2-nitrobenzyl photoremovable protecting group are well known and widely used for biological studies. In this paper, we study the photolysis of likewise “caged” acetic, caprylic and arachidonic acids. Unexpectedly, we observed huge growth of fluorescence emission at ~430 nm during photolysis. Following further UV irradiation, a product with fluorescence at longer wavelength was formed (470 nm excitation / ~500–600 nm emission). While it may be used to monitor the “uncaging”, these fluorescent products may interfere with widespread dyes such as fluorescein in biomedical experiments. This effect might be negligible if the photolysis products dissolve in the medium. On the other hand, we observed that arachidonic and caprylic acids derivatives self-organize in emulsion droplets in water environment due to long lipophilic chains. Illumination of droplets by UV rapidly induces orange fluorescence excited by 488 nm light. This fluorescence turn-on was fast (~0.1 s) and apparently caused by the accumulation of water-insoluble fluorescent residuals inside droplets. These self-organized lipophilic structures with fluorescence turn-on capability may be of interest for biomedical and other application. We have identified and hypothesized some compounds which may be responsible for the observed fluorescense.
Highlights
Light is used in different aspects of our life, from natural photosynthesis and to artificial photonic networks
We describe arachidonic and caprylic acids conjugated with 4,5-dimethoxy-2-n itrobenzyl-based protecting group
Besides the fluorescence excited by ~355 nm, which is present for usual nitrobenzol protecting group, DMNB version produces some compound whose fluorescence is significant under 488 nm excitation
Summary
Light is used in different aspects of our life, from natural photosynthesis and to artificial photonic networks. Lipo- or amphiphilic molecules conjugated with nitrobenzyl-based moieties have been used for preparation of photosensitive liposomes[11,12]. In such self-organized structures, light may be used to modify the properties of particles, for instance, destabilize the surface inducing cargo release. We describe arachidonic and caprylic acids conjugated with 4,5-dimethoxy-2-n itrobenzyl-based protecting group (so called “dimethoxynitrobenzyl-caged” or “DMNB-caged”). We show that these compounds form emulsions in water (with small fraction of DMSO), in contrast to acetic acid modified in the same way. The possibility to switch on fluorescence might be useful in imaging applications[25]
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