Chemical Selection; Selection And Evolution At The Nanoscale

[HydrogenBond]

In the theory of Evolution and Natural Selection, the environment plays an important role in the selection processes of evolution. The needs of evolution are different whether we are at the Arctic Circle or at the Equator. The type of life selected will be optimized to potentials set by the environment. The polar bear is perfectly designed for the Arctic but would not be selected at the equator since it is not optimized for the heat. 

 

The goal of this topic is to extrapolate Evolution and Natural Selection to life at the nanoscale; chemicals. In the case of life on earth, the nanoscale environment, for chemical selection and nanoscale evolution, is based on water. As a visual, the organics of life are analogous to the animals, which can undergo changes, while the water is the environment which ultimately does the selecting. This topic will discuss why water is the perfect environment for selecting chemicals all the way to life and beyond. 

 

The goal is not to scare people so they circle the wagons for protection from the bogey man. However, part of the goal is to dispel key myths of science. Selection is not random at the macro-scale, nor is it random at the nanoscale. It is defined by the potentials of the environment. Once we know these about water, you can make predictions about chemical selection. 

 

 

[A-wal]

I'd like to know what it is that makes water so special. There is life on this planet that doesn't need the sun at all but as far as I know all life on Earth needs water, no exceptions.

 

Is the hunt for alien life by searching for water because biologists believe that the need for water would be universal to all life or simply because it is here so it's the most logical place to start?

[exchemist]

I'd like to know what it is that makes water so special. There is life on this planet that doesn't need the sun at all but as far as I know all life on Earth needs water, no exceptions.

 

Is the hunt for alien life by searching for water because biologists believe that the need for water would be universal to all life or simply because it is here so it's the most logical place to start?

I think it goes something like this:

 

1) for biochemistry you need chemical reactions proceeding at a temperature that is not too cold (everything too slow) and not too hot (large molecules shake themselves to pieces due to thermal motion). Something in the range 200-400K or so seems most likely to be suitable.

 

2) everyone envisages that a solvent would be needed for any kind of biochemistry we can conceive of. For cell membranes, a lipid bi-layer or some analogue of that appears to be important, so a polar solvent would seem to have possible advantages (to allow a suitably insoluble liquid phase to be constructed to make the layer).

 

3) water is such a solvent, it is made of elements with widespread abundance and it has an unusually wide temperature range in its liquid phase.   

 

So, while I have not read that anyone thinks water is definitely essential to any conceivable biochemistry, it looks like a good candidate. There are thought to be oceans of liquid methane on Jupiter's moons, which could possibly be a solvent for some alternative low temperature biochemistry. But it is not polar, so any life chemistry based on methane would look very different. Liquid ammonia is another rather good polar solvent, made from abundant elements. But I don't know of any place where this has been found to date. (The liquid range of methane is only 20K and that of ammonia is only 44K, vs. 100K for water.)

Edited December 9, 2016 by exchemist

[A-wal]

Ah, not the actual water so much as the temperature range of water as a liquid. That makes perfect sense.

 

That kind of answers the OP's post. There probably was life that evolved to use other liquids at the very beginning but it couldn't compete with much more versatile water based life in terms of temperature differences.

 

I was going to mention the liquid methane lakes on Titan. In the absence of water surely life is likely to use the next most suitable liquid so maybe only looking for water isn't the best method?

 

Interesting side note. I think it's generally accepted that life has to be either carbon or silicone based because they're the only two elements 'sticky' enough to store complex information.

[exchemist]

Ah, not the actual water so much as the temperature range of water as a liquid. That makes perfect sense.

 

That kind of answers the OP's post. There probably was life that evolved to use other liquids at the very beginning but it couldn't compete with much more versatile water based life in terms of temperature differences.

 

I was going to mention the liquid methane lakes on Titan. In the absence of water surely life is likely to use the next most suitable liquid so maybe only looking for water isn't the best method?

 

Interesting side note. I think it's generally accepted that life has to be either carbon or silicone based because they're the only two elements 'sticky' enough to store complex information.

Yes, I think you refer to carbon's unique propensity for what chemistry calls "catenation", which means the ability of one carbon atom to bond to others to form long chains. This stable chaim-forming ability is not only needed to "store information" as in DNA, but also to enable other crucial biochemicals to form in a stable manner, such as polymers of amino acids (proteins), polymers of sugars (starch, cellulose and other carbohydrates), lipids (fatty acid esters) and so on. 

 

Silicon (not silicone), which lies immediately below carbon in the Periodic Table, has something of the same tendencies.  However the snag with silicon is that it also has other bonding options (due to the presence of low energy 3d orbitals, which carbon lacks) which compete with catenated structures. I may be rusty on this but I rather think one particular problem is that compounds with Si-H bonds can more easily oxidise to SiO2 (sand, basically) than C-H compounds. That would create major problems for life based on Si in an environment with free oxygen (though, as we know it is possible to have life without that.) At any event, on Earth, Si barely appears in biochemistry, in spite of its enormous abundance: it is almost all bound to oxygen, in the form of the huge range of silicates that comprise the rocks. 

[A-wal]

Silicon (not silicone)

:) As opposed to silicone based life that lives mostly in California.

[OceanBreeze]

 

Silicon (not silicone), which lies immediately below carbon in the Periodic Table, has something of the same tendencies.  However the snag with silicon is that it also has other bonding options (due to the presence of low energy 3d orbitals, which carbon lacks) which compete with catenated structures. I may be rusty on this but I rather think one particular problem is that compounds with Si-H bonds can more easily oxidise to SiO2 (sand, basically) than C-H compounds. That would create major problems for life based on Si in an environment with free oxygen (though, as we know it is possible to have life without that.) At any event, on Earth, Si barely appears in biochemistry, in spite of its enormous abundance: it is almost all bound to oxygen, in the form of the huge range of silicates that comprise the rocks. 

 

I wonder why silica-based life is so rare? I have seen these in the oceans and they are remarkable creatures.

 

The glass spicules are as efficient at transmitting light as the best fiber optic cables, and the glass is formed biologically at room temperature; something our scientists have yet to achieve in the lab.

[exchemist]

I wonder why silica-based life is so rare? I have seen these in the oceans and they are remarkable creatures.

 

The glass spicules are as efficient at transmitting light as the best fiber optic cables, and the glass is formed biologically at room temperature; something our scientists have yet to achieve in the lab.

I think it is probably for the sorts of chemical reasons I indicated, viz. the instability of long chains of Si atoms, compared to alternatives, including oxidation to SiO2 - which is the Si compound shown in your picture.   

[CraigD]

I wonder why silica-based life is so rare? I have seen these in the oceans and they are remarkable creatures.

Silica-based life on Earth isn’t just rare, it’s non-existent or undiscovered.

 

The metabolism of the

 

 

 

The glass spicules are as efficient at transmitting light as the best fiber optic cables, and the glass is formed biologically at room temperature; something our scientists have yet to achieve in the lab.

E. aspergillum not only has a transparent and refractive glass skeleton, like other Hexactinellid sponges, it's electrically conductive. Learning to engineer these animals to make engineering materials would be a major accomplishment, and seems to have attracted a lot of interest.

 

Another cool feature of E. aspergillum is its symbiosis with a species of small shrimp (I think they’re Caridina spongicola, but couldn’t quickly find an authoritative reference), which enter it’s basket-shaped body when they are small, then grow to be too big to escape, living their lives there and producing offspring that leave and colonize other E. aspergillum. These mated pairs of shrimp are what give the sponge its common name, Venus' flower basket.

 

I’d never heard of these amazing animals, OceanBreeze – thanks for the introduction! :thumbs_up

[OceanBreeze]

Silica-based life on Earth isn’t just rare, it’s non-existent or undiscovered.

 

The metabolism of the euplectella aspergillum sponge is the usual carbon-based DNA and protein kind. It uses silicon in the same way animals like us humans use calcium, to form a sturdy skeleton to support its other tissues. E. aspergillum’s skeleton is made mostly of SiO₂ (silica) vs ours, which are made mostly of Ca₁₀(PO4)₆(OH)₂ (hydroxylapatite, also called bone mineral).

 

E. aspergillum not only has a transparent and refractive glass skeleton, like other Hexactinellid sponges, its electrically conductive. Learning to engineer these animals to make engineering materials would be a major accomplishment, and seems to have attracted a lot of interest.

 

Another cool feature of E. aspergillum is its symbiosis with a species of small shrimp (I think they’re Caridina spongicola, but couldn’t quickly find an authoritative reference), which enter it’s basket-shaped body when they are small, then grow to be too big to escape, living their lives there and producing offspring that leave and colonize other E. aspergillum. These mates pairs of shrimp are what give the sponge its common name, Venus' flower basket.

 

I’d never heard of these amazing animals, OceanBreeze – thanks for the introduction! :thumbs_up

 

 

I am not a chemist or a biologist, just a mariner who was involved in collecting them as part of a research project in the Andaman Sea.

 

While technically not silica-based lifeforms; their skeletons are 99.9% glass, I believe the exact chemical composition is (SiO₂·nH₂O).

 

They are absolutely amazing organisms. These animals represent the oldest, still extant metazoan taxon.

 

The emergence of these animals could be calculated back to 650–665 million years ago [Mya], a date that was confirmed by fossils records [11]. Hence the Porifera must have lived already prior to the Ediacaran-Cambrian boundary, 542 Mya.

 

I’m glad you find them interesting. This is a nice informative video:

[HydrogenBond]

If you compare the boiling points of methane CH4 (-161C), Ammonia NH3 (-33C) and water H2O (+100C), although they all have the same molecular weights, the boiling point of water is extremely high for something so small and light. This tells us that the binding forces within liquid water; between water molecules, are much stronger than either methane or ammonia. The difference between methane and ammonia can be explained by the hydrogen bonding of ammonia.

 

Both ammonia and water can form hydrogen bonds, with ammonia having an extra hydrogen bonding hydrogen, relative water. However, water has a symmetry in terms of two donator hydrogens and two receiver groups. This allows water to bond with up to four other water and polymerize, using secondary bonding, loosely analogous to carbon does with primary bonding, to form extended structuring.

 

In terms of water at the nanoscale, water tends to self aggregate based on these favorable secondary bonding energetics. The self bonding of water tends to cause organic materials to phase separate. The cell is full of distinct phases; organelles, induced by exclusion by water. Ammonia is a good organic solvent and can be use to dissolve grease and oil. It lacks the extended structuring of water, causing it to emulsify, instead of differentiate organic phases. 

 

The term hydrophobic is sort of a misnomer. Organics are not afraid of water, since water can form hydrogen bonds with most organics and organic surfaces, via van der Waals interactions. However, water can do much better, energetically, by hydrogen bonding to other water. Therefore water tends to segregate and self aggregate, causing organics to cluster and phase separate. 

 

One feature of hydrogen bonding, that water can achieve, is called cooperate hydrogen bonding. This is type of resonance, loosely analogous to what happens in benzene. In the cases of water, the 3-D clustering allows the hydrogen bonding network and symmetry to delocalize electrons; resonance stabilization. The hydrogen bonding along the DNA double helix is also able to form cooperative hydrogen bonding, something it learned from water; evolved to do this. 

[HydrogenBond]

Water has the highest heat capacity of any liquid

Heat capacity is the number of heat units required to heat a body one degree. It take more energy to heat water, one degree, than any other liquid. This is also connected to hydrogen bonding. Water will form hydrogen bonds, with up to four neighbors. The symmetry of two donor and two acceptors groups allows water to polymerize into clusters, with the clusters able to form cooperative hydrogen bonding; resonance for added stability. As we add heat, all these layers of hydrogen bonding stability, have a lot of capacity to absorb energy. First, the cooperative resonance will become more and more limited, then larger clusters will become smaller, until finally local hydrogen bonds begin to break and reform.

One of the values of water being able to absorb so much energy; heat, is this helps to regulate the entropy of the organics of life. Entropy needs heat; waste heat, for entropy to increase. The high heat capacity of water absorbs much of the waste heat. This makes it harder for the organic structures to gain entropy, thereby allowing order to persist over a wide range of temperature.

For example, when proteins fold in water, they fold with very specific folds. This is due to the energy needs of 3-D hydrogen bonding of water. Water wants to go all the way to cooperative resonance. This need will first cause the hydrophobic groups to phase separate, one by one, based on their energy potential with the water. The water then also causes the hydrophilic groups to populate the surface, with water hydrogen bonded to these and to other surface water, forming a girdle around the surface of the protein. This girdle is under tension; surface tension. Protein can maintain their exact folds due to the water girdle. 

Proteins will begin to denature in water at about 41C or 105.8F. Denaturation is a process in which proteins or nucleic acids lose the quaternary structure, tertiary structure and secondary structure which is present in their native state. As we increase temperature from 98.6F (human body temperature), the high heat capacity of water is absorbing the heat energy. This is causing the cooperative resonance and larger scale clustering to diminish to some degree. The protein remains stable, since it can't gain enough entropy to denature. When we reach 105.8 F, the water has absorbed sufficient energy to where the larger scale 3-D girdle begins to split at the seams; smaller scale hydrogen bonding, and we get a protein muffin top.

[exchemist]

Water has the highest heat capacity of any liquid

Heat capacity is the number of heat units required to heat a body one degree. It take more energy to heat water, one degree, than any other liquid. This is also connected to hydrogen bonding. Water will form hydrogen bonds, with up to four neighbors. The symmetry of two donor and two acceptors groups allows water to polymerize into clusters, with the clusters able to form cooperative hydrogen bonding; resonance for added stability. As we add heat, all these layers of hydrogen bonding stability, have a lot of capacity to absorb energy. First, the cooperative resonance will become more and more limited, then larger clusters will become smaller, until finally local hydrogen bonds begin to break and reform.

 

One of the values of water being able to absorb so much energy; heat, is this helps to regulate the entropy of the organics of life. Entropy needs heat; waste heat, for entropy to increase. The high heat capacity of water absorbs much of the waste heat. This makes it harder for the organic structures to gain entropy, thereby allowing order to persist over a wide range of temperature.

 

For example, when proteins fold in water, they fold with very specific folds. This is due to the energy needs of 3-D hydrogen bonding of water. Water wants to go all the way to cooperative resonance. This need will first cause the hydrophobic groups to phase separate, one by one, based on their energy potential with the water. The water then also causes the hydrophilic groups to populate the surface, with water hydrogen bonded to these and to other surface water, forming a girdle around the surface of the protein. This girdle is under tension; surface tension. Protein can maintain their exact folds due to the water girdle. 

 

Proteins will begin to denature in water at about 41C or 105.8F. Denaturation is a process in which proteins or nucleic acids lose the quaternary structure, tertiary structure and secondary structure which is present in their native state. As we increase temperature from 98.6F (human body temperature), the high heat capacity of water is absorbing the heat energy. This is causing the cooperative resonance and larger scale clustering to diminish to some degree. The protein remains stable, since it can't gain enough entropy to denature. When we reach 105.8 F, the water has absorbed sufficient energy to where the larger scale 3-D girdle begins to split at the seams; smaller scale hydrogen bonding, and we get a protein muffin top.

Actually it is not quite true that water that the highest specific heat of any liquid, though it is the highest among commonly occurring liquids. Molten lithium, for instance, has a higher spec heat.: https://en.wikipedia.org/wiki/Heat_capacity

Edited December 23, 2016 by exchemist

[HydrogenBond]

Actually it is not quite true that water that the highest specific heat of any liquid, though it is the highest among commonly occurring liquids. Molten lithium, for instance, has a higher spec heat.: https://en.wikipedia.org/wiki/Heat_capacity

 

 

 

That is true for heat capacity per unit of mass; gram; 4.379 versus 4.1813. However, if we do this per mole  (atoms Lithium versus H2O molecules), water is number one; 75.327 versus 30.33. It has to do with the hydrogen bonding of H2O.  

 

 

Lithium at 181 °C^[33] liquid 4.379 30.33 Water at 25 °C liquid 4.1813 75.327

 

 

Water expands when it freezes. 

Water expands when it freezes due to special features of hydrogen bonding. Hydrogen bonding in water is primarily an electrostatic attraction, between the positive charge of the hydrogen protons and the negative charges on the oxygen of water. The electrostatic potential lowers as distance decreases; hydrogen and oxygen get closer. Yet, water expands when it freezes, giving off energy. When water freezes and expands the electrostatic attraction is going the wrong way  This should be endothermic, yet it is exothermic.

 

The reason has to do with hydrogen bonding also showing partial covalent bonding character. For proper covalent bonding, the oxygen and hydrogen need to align and separate, somewhat, so there is proper wave addition of the molecular bonding orbitals.

 

In liquid water, hydrogen bonds exist in both states; polar and covalent, and can easily switch back and forth, since there is only a small energy difference between the two states. The average life of a H2O molecule in liquid water is about 1 millisecond before it break covalent bonds and switch hydrogen, all at room temperature. The hydrogen bonds starts as the polar state. It can then switch to the covalent state. The accepting water, shifts one of its other hydrogen bonds from covalent to polar. The result is a balance of forces and new hydrogen partners. This helps with the cooperative resonance as well as quantum tunneling.

 

The value of this is every hydrogen bond in the 3-D water matrix, is a binary switch. The dual nature of hydrogen bonding allows the switch to flip, without having to break the hydrogen bonding. Water can be attached to an enzyme; girdle, and by flipping the switch, change the local surface potentials, while retaining sufficient girdle strength. 

 

The polar hydrogen bonding benefits by minimizing distance, to minimize charge potential. The covalent aspect of hydrogen bonding is slightly more stable. It has to align and expand, relative to the polar state, to get proper orbital overlap. The net result is the binary switch is not just an on-off (P-C switch), but each switch setting has four different physical potentials. The covalent setting is more expanded (adds volume), which can add pressure to the local surroundings, contains less internal energy (enthalpy) and contains less entropy. While the polar setting exerts a negative pressure on the surroundings (contracts), occupies less volume, contains more enthalpy and also exhibits more entropy. If we have an enzyme girdle and we switch the setting, we can add or take away free energy, as well as pull or push the enzyme. Or if we wish to shut off an enzyme, we only need the flip the water switch one setting and leave it there.

 

Picture the water of the cell forming it own structuring, due to the hydrogen bonding of water, while also phases separating organelles and others features as separated things in the cell. These organelles have their unique surfaces with the water, which impact the aqueous hydrogen bonding girdle. Since these surfaces are unique and different, they will have different impacts on the water. Each girdle can have a unique combination of switch settings, that define the surface locally and globally. 

[HydrogenBond]

The potential in the water is equal to the sum of its dissolved and surface interface parts. 

If we have pure water, the water molecules will hydrogen bond forming extended water structures. These can also form cooperative resonance for added stability. As we add materials to the water, different materials will impact water differently. The water will alter its structuring, to minimize energy, based on the material and the concentration, and how these impact the water.

As an example, although sodium; Na+ and potassium; K+, cations both have a single positive charge, water responds differently to each cation in terms of its structuring. Sodium ions will bind to the oxygen of water stronger than the hydrogen of water can bind via hydrogen bonding. The impact of sodium is to create more order in water; kosmotropic. Potassium ions, although they also having a single positive charge, bind to the oxygen of water weaker than water binds to itself. This tends to disrupt the structures of water; chaotropic, adding potential energy.

When cells pump and exchange sodium and potassium cations, the sodium ions accumulate on the outside and potassium ions accumulate on the inside. The purpose of this is to set up two distinct aqueous environments; with a water potential gradient between the two zones (order and disorder). The exterior sodium cation induction makes water more friendly to organic food materials. The reduced food material will add energy to water, due to the induction of surface tension. This is compensated by the order in water, induced by the sodium. Inside the cell, the potassium ions, by created chaos in water structuring, helps to loosen up the protein girdles, so the protein are more bioactive; move between conformations.

If you remove the outer membranes from modern cells, so there is no cationic pumping mechanism, the naked interiors of the cell, will still concentrate potassium ions. They will extract potassium from the environment, up to normal cell concentrations. This is due to the potassium ions and the protein surfaces, balancing each other out, relative to minimizing water potential. The water is able to lower potential, due to the protein surfaces, by drawing in potassium ions.

In terms of evolution (blue sky theory), if you had an empty volume, surrounded by a simple membrane with cation pumping and exchange, one could use this to extract specific protein from the environment, selected to compensate for the interior K+. The K+ and protein will form a team needed to minimize water potential. This is not random but based on energy in the water.

Many scientists believe the cation pumps are no longer needed, but are there simply as a failsafe. However, active cationic pumping, by increasing the membrane potential higher, is still helpful for driving extractions in both directions; inputting and exporting materials.

[HydrogenBond]

Merry Christmas!

 

I have been trying to show how water is not an ideal solvent. Water is very unique and anomalous, exhibiting extreme properties relative to all materials. Water has the ability to self bond in ordered clusters, which can also form cooperative resonance. This stability makes water exclusionary in terms of many of the organic materials of life; water and oil affect. The organics of life tend to form separated phases, surrounded by water attached to their surfaces. Natural selection will follow the lead of water; minimize potential of each surface. At minimum potential protein are perfectly packed and stable without any variation.  

 

The hydrogen bonding within water, by being a binary switch, with each switch setting having four potential aspects, not only allows water to define any surface or solute with detailed binary information, but the four switch potentials for each binary setting, become involved in the energetics of the surface. The water can push or pull and change enthalpy and entropy on the surface. 

 

Water is the great integrator of the cell, using its binary language to communicate and influence, near and far.  

 

The DNA is the most hydrated material in the cell, needing about 30% water by weight to maintain its native b-DNA structure in the crystalize state. The amount of water is higher in the active state. The value of this high level of hydration, is the DNA is the sweet spot in the cellular water. It is the place of lowest water potential. The highest energy place in the cell, relative to water, is the cellular membrane. These two zones set up a gradient in the water. 

 

As an analogy say you added ice to a warm beverage. There will be not only be heat transfer; heat communication between the hot and cold zones, but also a material conviction will be set up where cold water from the ice sinks and warm water rises up to the ice. In the cell, the latter is reflected by material fluxes from the DNA into the rest of the cell, and from the membrane into the cell toward the DNA. These fluxes attempt to help the water lower the gradient. 

 

However, this gradient is semi-perpetual because it is based on sturdy surfaces held together by primary chemical bonding. The DNA double helix is very stable and does not degrade in the water. Instead, its secondary, tertiary and quaternary bonding is in constant flux, reflecting the changes on the surfaces needed to lower the gradients. Instead of ice in the beverage, that can melt and disappear, we have a heat exchanger that are always cold, so there is perpetual convection. 

 

Cell cycles reflect the membrane side of the gradient getting the better of the DNA side; accumulate food materials. The food materials are reduced and will increase the water potential. This will cause increased activity on the DNA. RNA has more hydrogen bonded water than does DNA, per unit length, due to its sugar moiety. However the RNA is smaller than the DNA, so the total hydrated water is less. The DNA is more hydrated due to its huge size. The higher production of RNA, observed during cell cycles, cranks up the chiller side, so the DNA zone can lower water potential.

 

The duplication of the DNA, creates a second chiller in the cell. This causes the water, near the DNA to lower potential. Now the cellular gradient is being driven from the DNA side, causing changes in the membrane. For example, the osmotic input of water, to expand the cell, reflects higher entropy water entering. The doubled DNA is encouraging extra covalent switches in the water surfaces, which is too much for pure water. One solution is osmosis, to add entropy to the water; implicit of more polar switches. The division into two daughter cells reflects higher entropy; less order. This places the water back within its natural range. 

 

 

[CraigD]

Actually it is not quite true that water that the highest specific heat of any liquid, though it is the highest among commonly occurring liquids. Molten lithium, for instance, has a higher spec heat.: https://en.wikipedia.org/wiki/Heat_capacity

That is true for heat capacity per unit of mass; gram; 4.379 versus 4.1813. However, if we do this per mole (atoms Lithium versus H2O molecules), water is number one; 75.327 versus 30.33. It has to do with the hydrogen bonding of H2O.

I’d like the input of someone with practical, working knowledge of chemistry (I had the 4 hrs lecture + 4 hrs lab I was advised was the minimum for a well-rounded undergrad science education, and so long ago I’ve forgotten even the few essentials I learned then), but isn’t heat capacity per mol as much a measure of the size of the molecule as its heat capacity, so not very useful in comparing the gross thermal properties of different substances?

 

For example, from the table in the linked Wikipedia article, the heat capacity of a big hydrocarbon like C₂₅H₅₂ (paraffin wax) is about 900 J/mol/K, while C₈H₁₈ (octane), which has a similar specific heat (2.22 vs 2.5 J/g/K) , has 228 J/mol/K. Both are much greater than 75.327 for H₂O, but neither are as good as a always-liquid-phase heat carrier than H₂O.

 

From the Wikipedia table, I also noticed that liquid H₃N (ammonia) has a higher specific heat than liquid H₂O, 4.7 vs 4.1813 J/g/K. Ammonia is an amazingly versatile molecule. Though clearly not as versatile and essential as water in biological organism (it plays a major role as a plant nutrient component, minor roles in animal protein synthesis and metabolism, but is familiar to physiologists and medical people mostly as a symptom and cause of disease), it not only a versatile solvent, but it burns powerfully (4 NH₃ +3 O₂ → 2 N₂ + 6 H₂O + 2.112 x 10^-18 J). Water is pretty amazing, but ammonia can be used in plant fertilizer, as a refrigerant (the space-side of the ISS’s cooling systems are mainly ammonia-using), and as a rocket fuel (the highest-performance version of the X-15 – the one that could reach space – used an ammonia+oxygen rocket motor)!