Lights, Clicks, Action: The Science Behind Photo Click Chemistry

                                                        

                                     Photoclick Chemistry

          Good Afternoon, Folks! Last week, we skimmed the top of the vast ocean of Click Chemistry; today, we will dive deeper into a fascinating branch known as PhotoClick Chem. This chemistry combines the simplicity of Click Chemistry with the wonders of light to create unique yet straightforward reactions. This type of reaction is yet another example of how Click Chemistry has influenced all lengths of science. So, without further ado, let's get into it.

    We previously discussed what Copper-Catalyzed azide-alkyne cycloaddition (CuAAC) is. We also discussed the benefits of the reaction but not the disadvantages of it. The main component of this, which takes away from its overall remarkable nature, is the copper. The very substance that allows the reaction to begin is also the substance that causes it to be harmful. Copper has detrimental effects on human and environmental health. Because of that, the widespread use of this reaction has often been prohibited for fear of causing issues as a result of it. It wasn't until the strain-promoted azide-alkyne cycloaddition (SPAAC) was discovered that this issue was resolved. This reaction is incredibly similar to CuAAC, except for one key difference—the catalyst. In SPAAC, the catalyst used is Cyclooctene. Cyclooctyne is a compound containing an eight-membered ring with a triple bond between two of the carbon atoms. This compound is incredibly strained, meaning it has to be tight and compact to store all the carbon atoms. Atoms typically enjoy being at specific angles to allow themselves comfort, but this molecule, has too many carbon atoms to be at that angle. Imagine a ruler; you can bend it if you try, but it doesn't want to be bent, and the second it can release, it does. The same applies to this reaction, except its "release" is bonding with another molecule, which, in this case, would be the Azide. That is what makes this reaction so effective. Due to the amount of reactivity in Cyclooctynes, they work perfectly to have a chemical bond without any metal catalyst involved. This also makes them much safer, more reliable, and available for wider use. However, one vital variable remains that limits both of these reactions' abilities: control. While this reaction could be done under milder conditions with more control, complete control still wasn't possible. Nonetheless, what if there was a reaction that could be activated with just the flip of a switch?

Ladies and gentle scientists, I present to you... photoclick chemistry. PhotoClick Chemistry is the process by which a chemical reaction is formed simply by shining light on a molecule. Scientists attempted to use photons to activate certain inactive molecules at a specific time in a precise place. This type of reaction was beneficial in all sorts of fields, from drug delivery to 3D printing of biomaterials. However, let's descend deeper into each type of Photoclick Chem.

    Type 1: This reaction starts with light, triggering the breakdown of a precursor molecule (the starting molecule), which then proceeds to release certain groups like N2, CO2, or a photo-protecting group, creating a reactive intermediate (a highly reactive molecule). Once this molecule forms, it can react selectively with a cognate reaction partner (a reaction partner that bonds well with it) or revert to its original state. If it chooses to react, it leads to the formation of new products. The key part of this reaction is the stability of the reactive intermediate. If it has too long of a half-life (the amount of time a molecule stays intact), it will not have a proper response to bonding with other atoms and may produce harmful side effects. However, this reaction is incredibly beneficial when the reactive intermediate has a short half-life.

    Type 2: This is where a molecule absorbs light and changes its structure. From there, it forms a reactive intermediate that is incredibly unstable. The final step of this reaction either involves reacting with another molecule or reverting to its original form.

    Type 3: The final type of Photoclick reaction requires a catalyst and is only aided by Photoclick Chem rather than enabled by it.

    

    These three types of PhotoClick reactions describe the majority of these reactions. This provides a basic overview of PhotoClick Chem, so now to wrap up this blog—my thoughts. PhotoClick Chem is fascinating to me because of how easily a reaction can be made. Often when chemistry is described, you imagine beakers filled with strange liquids and difficult lab experiments, but PhotoClick Chem is just flipping a switch. It's fascinating to think of how much work goes into making something that is so simple and how it is all intentional. I may be incorrect in saying this, but I feel as though photons may soon take over chemistry. After all, they have already snuck into one of the most revolutionizing branches of science. I am also starting to notice a pattern where I am particularly attracted to reactions involving radiation or photons. I'm not entirely sure why, but they just seem the most interesting type of chemistry.

    Anyway, I don't have a lot to say about PhotoClick Chemistry. These first two posts haven't been terrific since I'm still new to this. However, I enjoy doing this, and I'm excited to continue this journey. I hope to develop my skills in the future (and maybe start to comprehend this jargon). For those who got through this painstaking article, I applaud you and thank you for reading. To end this off, a quick question: What ways could you apply PhotoClick Chem to your daily life? I hope you learned something new today, and I will see you next week!