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Asked by QLF to Freddie, Jena, Kirsten, Kon, Zarah on 15 Nov 2016.
Hi, this is a cool question but quite complex, so bear with me as I go through the answer! 🙂
I think there are two parts to this question: how to extract chemicals from plants, and how to show their effects, and I am going to focus on the big chemical that most people think of when talking about Nicotiana, which is a genus of plants in the Solanaceae family, nicotine!
Extracting chemicals is often dangerous, and with something like Nicotiana (and Solanaceae more generally – think about the nightshade plants!) the scientist would need to be very careful as some of the substances are extremely toxic. Nicotine in purified form for example is skin absorbent and high dangerous in raw form. So this is NOT an experiment to try at home. That said, to see what chemicals a plant has, a scientist might first do chromotography, to separate out the different types of chemicals present. In the case of Nicotiana, and several other plants especially in the Solanaceae family, the interesting ones are the alkaloids. Because there are so many with a lot of different structures there is no single method for extracting them, but most methods exploit the fact that most alkaloids tend to be soluble in organic solvents but not in water. They are present in the form of organic acid salts (mainly) which can stay that way or change to bases. Scientists can use base extraction by processing with an alkaline solution and organic solvent, or they could use an acidic extraction using a weak acid, adding a base to convert the alkaloid to basic forms to be extracted by an organic solvent. Alkaloids are separated from the mixture using their different solubility with solvents and reactivity with reagents or through simple distillation.
The second part is about the effects of chemicals (alkaloids like nicotine) found in Nicotiana. Moving away from carcinogenic properties for a moment, we know that nicotine has a lot of harmful properties, including being a potential lethal poison if handled incorrectly in pure form (but to put your mind at rest – you will never see it in pure form outside extremely controlled lab conditions, it is always diluted and safe to handle when purchased in the form of nicotine patches for example – panic not!). Experiments on mice and rats (and sometimes humans as well) with dilute/non-pure nicotine show that it can bind to nicotinic acetylcholine receptors in the brain and create a psychoactive effect, as well as impacting other receptors in the brain and central nervous system. It can increase the amount of adrenaline in the system by binding to the ganglion type nicotinic receptors in the adrenal medulla.
Now, nicotine and cancer – well there is a big debate on this. Is it a carcinogen? Test-tube studies (in vitro studies) say yes, living experiments (in vivo studies) say no, so far anyway. Some scientists have suggested that other things in cigarettes are more important causes of cancer like acetaldehyde, isoprene and acrolein, and have pointed out that there have been no adverse effects reported yet from nicotine replacement patches. BUT while the relationships between humans, nicotine and cancer are still a controversial topic, some studies of animal cells and cell cultures have shown nicotine’s role in cancer formation, including promoting tumour growth, encouraging cells to not die off when they are supposed to (preventing apoptosis), and in one study even increased tumour size in mice (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2759510/).
If you’ve got this far with reading my answer, thanks, and I hope this helps a bit. It’s a really interesting question and one thing I would encourage you to think about is, if there are harmful alkaloids in some plants, then maybe there are useful chemicals in others, and if so, how would you plan a project to find/explore those? 🙂
Hi! Thanks you so much for your answer, i work on the worst effects of smoking. Moreover, i find tars (not in the plant) which can be very carcinogenic, and toxic gases like mercure! It’s really shocking and you help me a lot!
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