Reef Chemistry Question of the Day

[Randy Holmes-Farley]

Good work, everyone. Some of them were perfect!

Here's the answer I hoped for:

Vodka contains ethanol (CH3CH2OH)and vinegar contains acetic acid (CH3CO2H). Acetic acid is already partially metabolized (oxidized) relative to ethanol since it has more oxygen and less hydrogen, so ethanol (vodka) should be the winner since one should get energy at each step of oxidation.

Here's the full answer:

When ethanol is metabolized (oxidized), it is first converted into acetaldehyde (CH3CHO) and then into acetic acid. Then the acetic acid is converted into CO2 and water.

I actually didn't know of the intermediary step from ethanol to acetaldehyde when I wrote the question, and especially not that this step actually takes up energy, not releasing it. But then the step from acetaldehyde to acetic acid gives much more energy. So the net step from ethanol to acetic acid gives off energy to the organism doing it.

Then acetic acid is metabolized to CO2 giving off a huge amount of energy.

Since ethanol gives off energy being converted into acetic acid, it is the winner!

For our purposes, the energy from metabolizing them is:

ethanol: 1,540.4 kilojoules per mole
acetic acid: 1,325.3 kilojoules per mole

Ethanol also weighs less per molecule, and since I asked about weight based comparison, it is even more the winner.


Wikipedia has a nice summary on this page:

Ethanol metabolism - Wikipedia, the free encyclopedia

from it:
Energy Calculations
The reaction from ethanol to carbon dioxide and water is a complex one that proceeds in three steps. Below, the Gibbs Free Energy of Formation for each step is shown with ΔGf values given in the CRC.


Complete Reaction: C2H6O(Ethanol)→C2H4O(Acetaldehyde)→C2H4O2(acetic Acid) →Acetyl-CoA→3H2O+2CO2.


ΔGf = Σ ΔGfp − ΔGfo


Step One: Ethanol: −174.8 kJ/mol
Ethanal(Acetaldehyde): −127.6 kJ/mol
ΔGf1 = −127.6 + 174.8 = 47.2 kJ/mol(Endergonic)
ΣΔGf = 47.2 kJ/mol (Endergonic)


Step Two: Ethanal: −127.6 kJ/mol
Acetic Acid: −389.9 kJ/mol
ΔGf2 = −389.9 + 127.6 = −262.3 kJ/mol (Exergonic)
ΣΔGf = −215.1 kJ/mol (Exergonic)


Step Three: (Because the Gibbs energy is a state function, we can skip the Acetyl-CoA (step 3), for which themodynamic values are not known).
Acetic Acid: −389.9 kJ/mol
3H2O+2CO2: −1 500.1 kJ/mol
ΔGf4 = −1 500 + 389.6 = −1 110.5 kJ/mol (Exergonic)
ΣΔGf = −1 325.3 kJ/mol (Exergonic)
[h=4][/h]

 

[cope413]

Awesome. Very cool info. And I still shudder when I think about my first quarter pchem class. It was so brutal I changed my major from chem to philosophy. Had to get out of the college of science completely. Haha.

 

[RedReefer]

Like...

 

[mike007]

Okay Randy this way above my head. So in laymen's terms which is better to dose in our tanks?

 

[cope413]

You get much more out of vodka than vinegar, but both still work in our tanks.

 

[Randy Holmes-Farley]

Okay Randy this way above my head. So in laymen's terms which is better to dose in our tanks?

FWIW, better is unrelated to the energy. Both work well.

I started with vodka and decided it was causing a bit more cyano in my tank, and I switched to vinegar with less of a cyano issue.

Also, vinegar may be more readily used by many organisms, not just bacteria, than is ethanol. So it may feed a wide variety of creatures. It is also a very common part of natural cycling.

Here's a blurb I posted several years ago when asked about the cyano question:

My guess is that the particular cyano species that I have may be a little less able to take up acetate, relative to the other bacteria and other organisms in the tank.


Acetate may just be metabolized faster than ethanol by some of the tank creatures, so is less available to cyano.


I was surprised as we recently dug further into the literatre of acetate in natural systems (in another thread) how fast and widespread it consumption is. For example:


Acetate cycling in the water column of the Cariaco Basin: seasonal and vertical variability and implication for carbon cycling. Ho, Tung-Yuan; Scranton, Mary I.; Taylor, Gordon T.; Varela, Ramon; Thunell, Robert C.; Muller-Karger, Frank. Marine Sciences Research Center, State University of New York at Stony Brook, Stony Brook, NY, USA. Limnology and Oceanography (2002), 47(4), 1119-1128. Publisher: American Society of Limnology and Oceanography,
Abstract


Acetate oxidn. frequently has been used as proxy of org. carbon decompn. in marine anoxic sediments. However, the importance of acetate uptake in carbon cycling in marine anoxic water columns is less well studied. Acetate concns. and uptake rate consts., together with total bacterial nos., primary and chemoautotrophic prodn. rates, and particulate org. carbon (POC) fluxes, were measured in the water column of the Cariaco Basin during upwelling and nonupwelling seasons between Nov. 1995 and May 1999 as part of the international CARIACO (Carbon Retention In A Colored Ocean) program. Acetate uptake was found to vary strongly with depth and season. Zones of elevated acetate uptake were found in the surface waters and near the suboxic/anoxic interface. High acetate uptake in the surface oxic layer suggests that acetate cycling may be an important component of org. carbon oxidn. in oxic environments as well as under anoxic conditions. Depth-integrated acetate uptake rates were correlated with the rates of org. carbon supply in the two zones (r2 = 0.37, P = 0.017). Comparisons of acetate oxidn. rates with rates of primary prodn., chemoautotrophic prodn., and POC flux show that, on av., acetate oxidn. can account for respiration of between 16 and 46% of the org. carbon fixed in the water column.

 

[redfishbluefish]

I approached this problem on the biochemistry side....as mentioned in my first post, ethanol is eventually converted to acetic acid. This results in the production of two NADH....which will go on to produce 6 ATP. So Ethanol produces 6 more ATP than acetic acid.


Ethanol ---------------> Acetaldehyde --------------->Acetate--------------->TCA
..................NAD-->NADH..................................NAD-->NADH

 

[Randy Holmes-Farley]

I approached this problem on the biochemistry side....as mentioned in my first post, ethanol is eventually converted to acetic acid. This results in the production of two NADH....which will go on to produce 6 ATP. So Ethanol produces 6 more ATP than acetic acid.

Yes, exactly.

 

[cope413]

Randy, what is your current vinegar dosing schedule? I know you've tweaked and experimented much over the years... I saw at one point up to 400+ml... And I'm curious as to where you're at now, why, and what your results have been.

 

[marke]

Couple questions :
I have a friend who doses methanol instead of vodka and having success. Any research or thought on methanol as a good carbon source?

Question 2:
Another friend swears by using a blended carbon souce to diversify bacteria? Randy has stated that inevitably one strand dominates the others and you remain with only one bacteria type. But what if these other bacteria strands consume something different and hence beneficial before they become over run by the mono strand dominant bacteria. Hence question is can diversity of Bactria via different carbon sources be beneficial or better than just say vinegar only?

 

[Randy Holmes-Farley]

Randy, what is your current vinegar dosing schedule? I know you've tweaked and experimented much over the years... I saw at one point up to 400+ml... And I'm curious as to where you're at now, why, and what your results have been.

I dose ~110 mL per day, spread over 10 x 1 min periods during the light cycle using a 1.1 mL per min BRS doser.

I'm happy with the results (nice sponge growth, for example, presumably due to the bacteria), but I use a lot of other methods for nutrient export so I cannot ascribe any particular nutrient issue to it. I use skimming, a lot of live rock in refugia, macroalgae, GFO, and GAC.

 

[Randy Holmes-Farley]

Couple questions :
I have a friend who doses methanol instead of vodka and having success. Any research or thought on methanol as a good carbon source?

Question 2:
Another friend swears by using a blended carbon souce to diversify bacteria? Randy has stated that inevitably one strand dominates the others and you remain with only one bacteria type. But what if these other bacteria strands consume something different and hence beneficial before they become over run by the mono strand dominant bacteria. Hence question is can diversity of Bactria via different carbon sources be beneficial or better than just say vinegar only?

I don't have an opinion on methanol except it is not nearly so widely used by organisms nor as natural in the ocean as acetate.

I also have never heard any significant reason to think that multiple sources, which may (or may not) drive multiple bacterial species, is more desirable than a single organic type.

 

[redfishbluefish]

However, methanol is the food source for NatuReef's denitrifier, which claims conversion from nitrate to nitrogen gas. Maybe the strains of bacteria that do this full conversion prefer methanol. Unfortunately very little detail is provided about how their system works.