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Waves are oscillatory motions. You can't have all the particles just leave and create a vacuum. So when the wave enters the lower impedance area there is low pressure in the high impedance area, and so particles must be drawn back in to balance it out forming a new reflected wave.

The flash freezing certainly/hopefully offers a path to capturing many intermediate states for proteins as they Bind small molecules

A big issue is the lack of data. There are lots of crystal structures of proteins and lots of structures with ligands bound but very little data of the intermediary states along the way to binding.

So when going from a high impedance medium to a low impedance medium, shouldn’t all that energy be transmitted into the particle motion? How can a reflected wave be generated?

Sound results from a combination of particle motion and pressure. The motion changes the pressure, the pressure changes the motion. Impedance is how those two are related; a high impedance means that acoustic waves have higher pressure with lower motions, low impedance means low pressures and high motions. With the exception of things like firm barriers (which can be seen as regions with infinite impedance), neither pressure not motion can make a discontinuous jump.

When a wave encounters a barrier, waves face a dilemma. First, since impedance is changing, and impedance is the relationship between motion and pressure, one or both of those must change. Second, neither can change suddenly. The solution to this is that the discontinuity applies to the wave as a whole, not one particular ray, so if you have two waves within the two different mediums (Ie one reflected and one transmitted), there is a wave combination that satisfies both requirements.

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A more physics based answer: Consider the case of an open-closed tube. You are intuitively seeing why the sound bounces off the closed end, because the particles cannot physically move through that barrier. That barrier will provide an additional pressure to ensure that the motion at that point goes to zero. If you send a wave pulse to that end of the tube, the back of the tube will push back hard enough to stop the displacement of the particles, but it cannot do that without also pushing back hard enough for the velocity of those particles to go back, causing a reflected wave pulse going the other way. The open end would seem to let particles move freely, but the open end is fixed to atmospheric pressure*, so the (gauge) pressure of the wave at that point will have to be zero*. The wave pulse sent that direction will not have the expected resistance to its motion that it had in the tube, and as a result the air will move in mass out of the tube, but will do so in the form of a pulse traveling back into the tube. The pulse traveling back into the tube will have the same direction of particle motion, opposite direction of pressure.

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*In reality the atmosphere does not have zero impedance, just a lot less than the air in the tube, which is why mouth effects comes up when trying to apply this

Great addition?? Thanks.

To add to this, there’s an iterative set of interactions where ligand binding induces conformational changes on the receptor, which induces some conformational change on the ligand, and so on. That’s why in silico docking that assumes a rigid receptor often gives spurious results that don’t line up with experimentally measured binding affinities. It’s problematic since reductions in receptor degrees of freedom can impose a significant entropic cost, which can have a major influence on the Gibb’s free energy of the binding event.

We’re getting better at modeling those interactions than we used to be, but it’s still extremely challenging. The best efforts start with a large collection of known binding affinities with different ligands, which can be used to constrain the system.

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Good addition, I'll add a clarifying note to my post. I have a neuroscience background so all the receptor stuff I learned about was based on structural change.

Importantly, physical chemistry helped me to understand how protein protein interactions are essentially creating an energy 'well' that molecules and protein fall into.

It's why superoxide dismituase reached diffusion limited efficiency (let that boggle your noodle for a sec) whereas other more complex interactions are such that they occur less frequently.

I didn't ask this for sodium hydroxide. Anyway, thx

Here’s hoping for further developments with cryo-electron microscopy. The largest benefit imo being it doesn’t require lengthy crystallization waiting periods.

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I don't think we'd regard proteins as rigid bodies. Lots of what makes working with protein structure hard is that we don't have a good way of modelling the dynamics of proteins. The hydrogen bonding network is quite flexible.

Ligand induced structural change is indeed an important type of ligand binding but there are many examples of binding without structural shifts.

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Ouch. I wasn't aware of OP's prior question.

I absolutely agree. Don't be messing around with sodium hydroxide if you don't know what you're doing...and your question demonstrates that you don't.

Contact with NaOH will eat through your skin, or blind your eyes. It'll chew through many things you might use to hold it.

Buy some silica gel packs if you want to dry an area. They're cheap and safe.

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Yeah I mean technically we can't say anything is actually zero but the lower bound is pretty low.

Lots of good answers already, so I'm suggesting a couple of resources instead of answering. Check out the protein database to see the different known shapes of proteins: https://www.rcsb.org/ This is a bit old, but here is a talk about visualizing protein dynamics: https://m.youtube.com/watch?v=t3uQDL-GdLM.

According to some studies, long-term cannabis abuse may cause abnormal brain structure and poor memory, especially in people who have or are at risk of developing schizophrenia. Cannabis, particularly THC (the main psychoactive component of cannabis), may also reduce REM sleep, which is the stage of sleep when we do our most active dreaming, processing emotions, and cementing new memories. Decreasing REM sleep may have some benefits for people with PTSD, since nightmares are a common and disturbing symptom. However, for most people, poor sleep may impair cognitive performance and focus, and increase the risk of cognitive decline and dementia in the long term. Therefore, it is possible that years of poor sleep due to cannabis abuse would contribute to some brain damage.

However, these effects may depend on several factors, such as the dose, frequency, duration, age of onset, and individual susceptibility of cannabis use. Some studies have found no significant effects of cannabis on brain structure or cognition after controlling for confounding variables. More research is needed to establish a causal link between cannabis abuse and brain damage.

I've been quite enjoying these very short "nutshell" explanations of all sorts of science topics. They simplify and barely scratch the surface but give you a hint that you can follow up on. All of them are quite fun: Kurzgesagt The Most Complex Language in the Universe https://youtu.be/TYPFenJQciw