Biogenic storage: New progess in glucose metabolism

[PB666]

CO2 to fuel

So before start what is a fuel - classically its something that can burn in an oxidation/reduction reaction. The classic oxidant is oxygen, but it can be NO₂, SO₃, N₂0₅ or any number of compounds that have oxidation states in excess of those in the fuel. In rockets you want oxidants that are dense, but also have a high oxidative capacity to weight ratio, So for insance using S₈ or S0₂ is not particularly wise when one considers that the sulfer has high atomic weight.

Likewise the reductant in the reactant, which on earth since O2 is widely available and non-limiting the reductant is considered classically the fuel. H2 has the highest energy to mass ratio, but it is also the hardest to pack and requires another gas to deliver. The next highest is lithium hydride and beryllium hydrides which are very unstable. Then there is Lithium borohydride LiBH4, this is very useful in chemical synthesis, and it is rather unstable around water. Finally there is CH₄, CH₃OH, CH₂0, CH₃CH₂OH, CH₂=CH₂ (Methane, Methanol, Formaldehyde, and ethanol, acetylene gas), NH₃ can also be a fuel and it can be tightly packed as a solid monopropellant as NH3NO3 (classic fertilizer, cause also of the largest non-wartime man-made disaster). The carbon compounds can also be used to make other fuels and to make other components of rockets. For example denatured cellulose is used to make coal, which is used to make carbon steel.

The basic problem lies in the fact that we rely very heavily on phototrophs to build these fuels. The reaction, of course requires a source of hydrogen

The reaction involves Chlorophyll and Nicotine adenine dinucleotide phosphate (NADP+)

2H₂0 + 2NADP+ -----> 2NADPH + 2H+ + O2

ATP is also generate and I will basically remove these two from view with the abbreviation AN to signify the simple reductant and energy sources.

And thus in this simple step we have part of the fuel, oxygen. The reductant will also work, but it would be very inefficient. We need to take that energy

In the calvin cycle, the NADPH and ATP are added to append CO₂ to an organic compound (below designated R), but unlike in chemical synthesis the natural cycle is pretty much a stepwise reduction and elongation which can be basically simplified to the understanding (with Calvin of course rolling over in his grave, heh-heh). Each step requires a combination of AN.

CO₂-R -------------------> HCO-R ---------> H₂CO-R --------> H₃C-R.

[acetate-carboxyl] [glucose aldehyde] [glucose hydroxyl] [fat terminal]

Each step adds electrons and protons via AN and specialized enzymes, two of the steps loose oxygen.

The more hydrophobic compounds difficult to deal with outside of storage (fat) and cellular structures (cell membranes, aliphatic amino acids), so there is a preference in nature to used oxidized compounds. Note that two of these are components of glucose, in fact glucose is basically composed of 1 aldehyde and 5 hydroxyl groups. The primary end product of photosynthesis. Any compound of N carbons with one aldehyde or ketone and N-1 hydroxyl groups is a sugar.

To make oil is very simple take a the first compound, undergo a dehydration reaction with the second compound and you have an ester.

If the ester has a long enough fat terminal on either end you have oil.

e.g. CH₃CH₂CH₂CO₂CH₂CH₃ Ethyl butryate - A fairly simple and fruity smelling oil that can be used as a condensed fuel. If we take the trios sugar and reduce it one more time we have glycerol. If we dehydrate it with 3 carboxylic acid (acetic acid, butric acid, palmitic acid, steric acid, and/or etc) we get oil and fat that is commonly found in fat cells and can be burned anywhere oil can be burned (Diesel engine for instance). These oils are very energy rich but have a lower density than water or methanol.

To describe the basic problem. To make fuel you can either

1. Make lots of solar panels (rare earth dependency) and create hydrogen and oxygen from electrolysis. very material intensive and inefficient. This may change, and electrolysis may become so efficient that other pathways would be useless. But still hydrogen storage is problematic because it requires the reduction of temperature to near absolute 0 and or significant pressurization, and this is also wasteful.

2. Break light prismatically into the photosynthetic spectrum and photosynthetically fix CO2 and use the rest to heat and electrify the operation. If you have a fusion engine you also may have a source of power in which LEDs provide optimal growth for plants.

To do this we have to know what we need. CO₂ (lots of that in deep space), H₂0 (also lots of this), and a selection of minerals. If we choose 2 we can devise strategies to compact oxygen (e.g. O₈) and increase its storability and so that the storage space issue is effectively dealt with.

But trios sugars can be useful in other ways, for example you can make citrate, and it is relatively easy to rip the protons off of citrate and have a compound with 3 or 4 negative charges on it, and because of its mass and charges its relatively easy to control its position in space, so for instance if you want to acceleration something to say 0.1c as a reaction mass. The great thing about citrate is that it has alot of C and O and very little H, so if you have alot of CO2 and only a little water, but alot of hv and a good accelerator, you can toss these little buggers out with 100 times the reaction mass per moleculer (far fewer erosive collisions with your accelerator). You can do something even more clever, you can take heavy metals that might be availabe in some alien soil, and chelate them to citrate or compounds like EDTA and have an excess of positive charge sticking out in space, and in doing so you can increase the reaction mass per particle to say 300, 500 or 1000 daltons. IN doing so you can completely solve the charge imbalance problem that occurs with ION drives (electrons and protons are discharged at different speeds)

Instead of having something with all the positional certainty of a bag of gnats, you can pretty much linearly accelerate your mass in a strait line. You could even do one step better than this, you could covelantly link naturally magnetic compounds in a magnetic field and essentially create a molecular rail gun, balancing the charge in reaction masses so that charges do not accumulate.

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OK so if we choose #2 we simplify have the following

2 Trios sugars + AN ----------> glucose

N glucose -----------> cellulose_len=n + (N-1) H₂0 (alternatively glycogen)

just about every organism does this, and plants are really good at it, So for instance the tallest natural object in the world is largely composed of cellulose and water.

And cellulose stores very nicely, you can dehydrate it (e.g. kiln dried wood), you can emulsify it with oil, you can hydrate it to form fiber. You can place it in a denaturing oven without oxygen and create charcoal, pure cellulose can result in graphene. Denatured cellulose is the primary fuel of the early industrial age, and it is also the primary cause of respiratory death in China (4000 estimated per day).

So cellulose is useful, but also problematic. To get around the problem cellulose needs to be converted back to glucose, and this is where the problem for biogenic fuels lie. For example most of the energy in a corn plant is not in the corn, but in the vegetative part of the plant. In fact if a plant wastes alot of energy and water growing seed, it could spend that energy growing more cellulose which ultimately has more energy. Cellulose is useful in nature, because it lifts and separates the soils and provides avenues for growth and hydration, but in space, these are not really necessary or desirous, because denaturation of soil in a closed system creates molds, smells and CO2 (several times more than the CO2 produced by the people that eat the food the plant produces). An example is a compost heap of weight 400 lbs and roughly loose half its weight at the same level of hydration within a couple of weeks.

Also once in space and traveling you need the CO2 to make more cellulose, but you do not need C neccesarily to store fuel, since storage can be in H-H form, you can crack hydrocarbons to form hydrogen, releasing CO2 to be used again. But even if this is not desired, you can convert a two carbon sugar to methane, releasing one CO2 and increase the reductant energy per gram and a get one CO2 for recycling.

So the basic holy grail of biorenewable fuel industry is efficient cellulose catabolism. Simply - to get bugs to break it to glucose and give it to us before they eat it and make waste heat and more bugs. But heres the catch, the bugs are a means to an end, the bugs produce enzymes, which is really what is wanted. They carry the blueprint and we humans want to do that task and leave the bugs in the compost heap.

If you can get to glucose, you can essentially split glucose, remove 2 useless carbon dioxides, and arrive at ethanol, which is storable, not corrosive, and particularly useful on special occasions.

The problems is that the bacteria that convert to cellulose to glucose are kind of selfish, they want to use the glucose for themselves after investing the energy (i.e. why cows produce methane). So basically the DOE in the US and other organizations are looking for a magic creature that will take cellulose and for a small price convert it to glucose for us, which we will then send to the fermentor for alcohol production.

One of the places they have been looking are in hotsprings and deep ocean vents. The reason for this is that an increasing number of industrially useful enzymes have been engineered from these sources of exotic microbes. Industry likes enzymes that work at high temperature because at lower temperatures enzymes are often slow, don't interact with compounds specifically as we like or because the reaction energy profile can replace the need for AN or other energy with kinetic energy (maybe more sloppy but rate of biological reactions increase 2 fold for each 10'C thats a 100 fold increase in reaction rate.

The 1,4 linkage that defines cellulose is for whatever reason particularly stable to enzyme activity, and at high temperatures at least one of the sugars can undergo linearization to form a free aldehyde, and this can lower the stability of the bond, making it easier to break.

One clever bug Caldicellulosirupteor bescii may have evolved a Tungsten-hydrolase that uses the element to do this more effectively than all other enzymes, and at high temperature. Many enzymes have metal cofactors, zinc is particularly common cofactor in DNA regulation, molybdemum is found in other cellulases, but typically exotic metals like Tungsten are not used in enzymatic reactions, and the fact this bug seeks it out and incorporates is potentially evidence for it specialization toward high temperature catabolism. Afterall the microbes in a compost heap become more effective at high temperatures and these things can bake very close to the boiling point of water before they start to slow down.

http://www.asm.org/index.php/journal-press-releases/93631-unlikely-element-turns-up-in-enzyme-commercial-renewable-fuels-might-ultimately-result

So the one thing that humans can do is put this into an a protein that is essentially silenced, express it in a bug, such as e. coli or a cell free expression system, use an enzyme like pepsin or trypsin to cut of the appended ends in the presence of tungsten, then purify the enzyme to crystalline form and walla you have s bug-free cellulose converting concentrate suitable for space travel. By being able to work at elevated temperature means that one does not need to add AN to get the hydrolysis to work, which means you can use waste heat to cocatalyze the reaction and make it fast.

Seems far-fetched, actually no, the enzymes you add to your private cesspool or grease trap, crystallized enzymes.

Glucose anabolism can be seen as advantageous if we can solve the catabolism problem with cellulose.

1. Storage options - glucose, cellulose (dehydrated), ethanol, ethane, methane, H2 are all potential products derived from photosynthesis.

2. Complexity options - Larger and more controllable reaction masses for ion drives and mass accelerators.

3. Widely available starting materials in deep space - Asteroids and planetoids are loaded with the basic starting materials CO2 and H20.

4. Photosynthetic spectrum - is in the peak range of sunlight, but also can be duplicated with LEDs and small power in basically a water tank with proper nutrients.

5. Storage density, much easier to store oil than hydrogen and other alternative fuels.

How useful cellulose might be for interstellar travel, during space flight you are traveling for a very long period to your destination, once you arrive there you need to grow and expand into a space colony which then eventually terraforms a planets and then colonizes the planet. But once the ship gets there it is essentially drained of reaction mass. But with cellulose you can essentially solve the problem without initially creating more space ship. Cellulose can be made into long molecules, 100s of feet long, and linked to each other to create large self-reinforced structures that are compatible with space, bundled in smaller and larger units until you essentially have a log tied to the vessel but essentially floating in space. No need to store them on board, cellulose is not volatile and it is solid, to argue that you need to tie it to the ship with something, well rope is also cellulose. When you need to slow down, bring a structure on board, convert it to alcohol. And use if for whatever. So for instance CO2 is abundant in the outer stellar system, but not wear you need it, with PV usable light. So basically build cellulose storage units and use the nuclear engine and reaction mass to get to the interior system build a new station (carbon fiber would be a good choice, with an aluminum coating on the surface). You could even use cellulose to coat the ship to control temperature (insulative properties of cellulose, one of the oldest insulators) and resist the effects of radiation (lead embedded cellulose) and deal with some of the cosmic radiation and high velocity bolloids by providing a means of embedding other solids into a matrix.

Then return to interstellar ship to the outer system to collect more raw materials.

Edited August 16, 2015 by PB666

[More Boosters]

Read all of this, but I can't say I would be confident to summarize it if I were asked. Interesting stuff though, thought this place really needed more attention.