[poonilization]

Hello, I need some help with a 4 page review I am doing, the topic title is "The Importance of Tunnelling in Enzymatic Proton Transfer". I submitted a plan to the topic lecturer and mentioned Heisenberg's uncertainty principle and wave/particle duality and when he provided feedback he told me I need to reference it.

I'm a little confused, I've been struggling to find Heisenberg's original paper on the uncertainty principle, and even if i were to find it, wouldn't it be written in german? How would i know if im referencing the correct paper if i can't read or understand it?

Also any help on the topic of "The Importance of Tunnelling in Enzymatic Proton Transfer" is greatly appreciated.

[Irlanur]

I assume that what you've learned about Heisenbergs Principle is not from any original paper, so just cite the book/script where you learned it. But I guess you could actually see that as "common knowledge". e.g. It's not that every chemistry paper with some NMR spectra cites the whole history (Uhlenbeck and Goudsmith, Bloch, Hahn, Ernst...).

[Corribus]

Probably referencing a physical chemistry or physics textbook is adequate. I don't know the paper where the uncertainty principle was first formulated, but you're probably right that it's in German, and you'll find that a lot of the famous principles or equations that we know today didn't have an obvious initiation point in the literature. (I.e., there may not be a single paper where Heisenberg came out and said, 'Ok, so there's this new uncertainty principle thing that I've been thinking about...'). It's a good question though. I have a nice collection of classic papers from the 20s through 40s (many in languages I cannot read)... and I do not believe I have one of Heisenberg's. Maybe I'll have to rectify that!

As for tunnelling in biological proton transfer reactions, one of the classic cases is Vitamin E. (See, e.g., Ouchi, J Phys Chem B, 2010, 114, 6601). For more relevant enzymatic reactions, here are a few promising references that might help get you started.

http://pubs.acs.org/doi/abs/10.1021/ja037233l
http://www.sciencemag.org/content/303/5655/186
http://www.nature.com/nature/journal/v399/n6735/full/399496a0.html
http://iopscience.iop.org/1367-2630/12/5/055002
http://www.pnas.org/content/94/23/12360.full

You should also look into the kinetic isotope effect, which is a common experiment used to measure tunnelling contributions in these kinds of systems.

[poonilization]

thanks for the reply, i really appreciate the help and the references were really useful

[Babcock_Hall]

http://www.annualreviews.org/doi/abs/10.1146/annurev-biochem-051710-133623

A recent review article from one well-known researcher in the field.

[poonilization]

I would just like to say thanks for the help everyone, all the links to papers have given me a great basis to learn what quantum tunnelling is. I was just wondering if someone could explain a point that is mentioned across multiple papers, ill quote from one i am reading now "Detailed temperature dependent measurement of isotope effects in soybean lipoxygenase-1 (SLO) revealed a large kinetic isotope effect. The transfer rate of hydrogen is typically 2 orders of magnitude larger than that of deuterium. Arrhenius plots of the isotope effect lead to an activation energy which is far too small to account for the large isotope effect, which is almost temperature independent. This almost immediately suggests that the hydrogen transfer mechanism is dominated by tunneling. As is well understood, tunneling rates are exponentially sensitive to the mass of the tunneling particle."

Could someone elaborate as to why a reaction rate that is independent of temperature is an indicator of tunnelling? Also another thing I see mentioned is the lower the temperature the more likely it is proton tunnelling occurs "reaction rate becomes temp independent below 40K" why is this?

[Corribus]

Are you familiar with R. P. Bell's tunneling factor modification of the Arrhenius equation?
Wikipedia actually has a nice entry on this, including temperature effects.

http://en.wikipedia.org/wiki/Kinetic_isotope_effect

(See section on Tunneling, subsection on temperature effects)

Note that tunneling isn't actually independent of temperature, because temperature does impact the population of thermally excited-vibrational states, which have a shorter barrier widths to tunnel through than colder states (imagine trying to dig a hole through a hill that is roughly conical-shaped when you're near the top of it versus near the bottom, which is thicker).

[Irlanur]

simplified: there are two ways a proton can get away from one bond and form another. One is the "classical" pathway, where the proton just "walks over the potential energy barrier". The rate where a proton takes this pathway is obviously temperature dependant because at higher temperature it is more likely that the proton has sufficient energy.

On the other hand, because the proton mass is quite small, a proton can also tunnel through the potential energy barrier, which means that it classically does not have enough energy. at very low temperatures, where only the vibrational ground state is populated, this is sometimes the only relevant pathway. at high temperature, where the classical pathway dominates, tunneling is often neglectible

[poonilization]

Thanks for breaking it down, i understand it much better