Nearest Neighbor Method

[@shahdalnashashibi722]

this is the best video i have seen in years i am so happy i came across this

[@dano1208899]

Hi, Quick question. In the chart at 15:09., If these delta G values are established by measurements made at 37 deg C, how can I plug these values into an equation for melt temp that requires delta G naught? e.g. Tm = dG naught/(R ln (Ct/4))? Wouldn't the chart's values have to be measured at 25 deg C for this to work?

[@albertcourey6711]

The equation in your question isn't valid. I'm not sure how you derived it. You can't determine the Tm from the free energy. You need to consider both entropy and enthalpy. We assume the entropy and enthalpy values are independent of temperature, which is only approximately true and is probably a source of error in the calculation. By the way, a standard free energy can be defined for any temperature. It's the free energy change when all reactants and products are present at the standard concentration (1 M in this case) and exhibiting ideal behavior.

[@dano1208899]

​@@albertcourey6711 Ah I see, thank you. Now it makes a bit more sense to me. I was looking at the publication that I believe that your nearest neighbor table came from and I noticed that the delta G is written as dG naught 37 while the enthalpy and entropy are written just as delta H naught and delta S naught. Am I correct in thinking that this is because the measurements were taken at 37 deg but the enthalpy and entropy are assumed constant for all temperatures? I'm no chemist by any means, but I work with DNA daily and I've always wished I had a better understanding of its thermodynamics. Thanks for your response and your video , they were very helpful! By the way, I got that formula off of the Wikipedia page for "Nucleic Acid Thermodynamics"

[@zhichenghuang4159]

really like it!