Well, I was looking for a Eutectic mix to use for the upper bound of a “Smith Scale” thermometer (as I mentioned in the Degrees of Degrees posting) and got side tracked by a very interesting thing…
First, a digression on Eutectic Metal mixtures:
A Eutectic is a mixture of things that melts / solidifies at one particular point. It is typically significantly lower temperature than either part alone. So mix some lead and some tin and start cooling it, one or the other will form crystals first and leave the solution. Gradually what is left approaches the Eutectic Point, when the temperature stops dropping until the whole mass solidifies.
BTW, I sort of like Eutectic Solder, at Tin 63% / Lead 37% mix with 183 C / 361.4 F melt, or Rose’s Metal, a eutectic mix of Bismuth 50%, Lead 25% and Tin 25%, but have not yet settled… Rose’s metal is listed as having a melt point of 98 C / 208 F in one page and 100C / 212 F melt point in another, so needs more research. I kind of like the Eutectic Solder as it is now readily available, but could even have been made in ancient Egyptian times. It also gives about 360 degrees above 0 F, so using the ammonium salt mix for one end and Eutectic Solder for the other gives 360 degrees of almost the same size as an F degree ;-) But being that close it’s kind of hard to claim it as ‘new’ and not just ‘close but slightly off’…
So this same eutectic idea has a lot of uses. A nice solder that does not have a pasty stage, so far fewer cold soldered joints. Eutectic salts that hold a constant temperature as heat is added or removed (commonly used for storing solar energy overnight while keeping temperatures in a range you like. 68-72 F for passive room temperature stabilizing. In the very high hundreds to thousands of degrees for storing solar thermal at concentrating solar thermal electric facilities.
Sodium Chloride and Ice form a Eutectic Mixture at temperatures below the freezing point of water. That is why putting salt on ice causes it to melt. The water is pulled out of the ice into the eutectic solution until it reaches that stable, lower, temperature. Then with excess ice you can make ice cream. With excess salt you can clear frozen roads.
So there are many eutectic metal alloys, but only a few commonly used and well documented. Field’s Metal and Wood’s Metal are (or were) used in things like fire sprinklers. At a specific temperature, they melt, and let the water run… Wood’s Metal is 158 F / 70 C (but has lead and cadmium in it – so is now considered evil). Lead 26.7% Tin 13.3% Cadmium 10%. Cadmium is a fairly horrid toxin. Lead is toxic, but not to the degree that would warrant the present paranoia about it.
Field’s Metal is a safer replacement. It melts at 144 F / 62 C and has Bismuth 32.5% Tin 16.5% Indum 51%. Other than Indium being a bit rare and Bismuth not being in the local hardware store it’s a great idea for anywhere that people might occupy. OTOH, anywhere that the fire is burning up is likely to have a fair amount of lead in the electronics anyway so I’m not seeing all that much advantage…
Part of the reason we had a Bronze Age was that mixing copper and tin or copper and zinc gives an alloy that melts at a lower temperature, so is easier to create and work.
But more to the point: One can find all sorts of eutectic mixes, be they metals, salts, organics.
On To Organics
So, while wandering around looking for an interesting Eutectic Mix that would make for a nice upper calibration point of a thermometer, I ran into a bit of Unsettling Science. (That’s my neologism for what happens to “Settled Science” when it runs into something closer to the truth / newer and more complete ;-)
For many years I’d sporadically wondered why certain compounds kept showing up in biochemistry. It was not a very important nagging… just a slightly unsettled feeling. A ‘something is not complete there’ feeling. Citric Acid. Malic Acid. Lactic Acid is just about everywhere and I have some making Sourdough as I type. (and some other organic acids) Along with all those sugars. Glucose, sucrose, fructose, etc. It just seemed like there were a few more loose ends than ought to be. In particular, the way Maple Sap is such a sugar rich solution. It just seemed like the tree was being ‘wasteful’ of it’s energy stores leaving them in solution when they could be stuck away as starches.
I’d basically decided to just classify them as “sloppy nature” and not worry about it (but still it was a bit of a bother…) I mean, really. WHY have so many plants got sugars all over. They can just leak out when in solution. WHY have so many plants got various organic acids laying all over. Again they can just be lost from solutions. The amount of Citric Acid needed for the Krebs / Citric Acid cycle is way smaller than what you find in your Citrus Fruits…
But life is not long enough to follow EVERY loose end to a conclusion. You need to pick the ones that are interesting and let the others go. For the others, you can either accept a “forever nagging spot” or paper over it with a “plausible even if I don’t like it”. Rather than go insane from too many unsatisfied itches, I chose to paper over with “well, there must be a good reason and the plant knows.” And moved on.
Now it looks like some clever folks have found out what the ‘good reason’ is, and it has the potential to open whole new areas of chemical synthesis and whole new understandings of how life works. Heck who knows, there might even be some applicability to things like eutectic mixes in ice cores… As various biological dusts get added to ice, what happens to solubilities again?…
The first paper I ran into had a Greenwash flavor to it. Wandering past that I found the original PDF version:
Are Natural Deep Eutectic Solvents the Missing Link in Understanding Cellular Metabolism and Physiology?[W]
Young Hae Choi1, Jaap van Spronsen1, Yuntao Dai, Marianne Verberne, Frank Hollmann, Isabel W.C.E. Arends, Geert-Jan Witkamp and Robert Verpoorte*
we asked ourselves why a few very simple molecules are always present in considerable amounts in all microbial, mammalian, and plant cells. It seems that these compounds must serve some basic function in living cells and organisms. These compounds include sugars, some amino acids, choline, and some organic acids such as malic acid, citric acid, lactic acid, and succinic acid. With the exception of sugars, which may serve as storage products and a source of energy, the other compounds are present in such large amounts that it does not make sense to consider them as only intermediates in metabolic pathways.
Here, we develop a novel theory about the role of these compounds, which may explain many questions in the biochemistry of cells and organisms. The theory is based on analogy with green chemistry, where in past years various synthetic ionic liquids (ILs) have been developed for chemical and enzymatic reactions as well as for the extraction of natural products.
So these folks looked in more depth, saw that there wasn’t a simple answer and discovered some really interesting things. It’s at times like this that I regret not scratching some itches… Then I remember that trying to keep all the itches leads to insanity and figure I’m better off reading about it now from someone else ;-)
But it is only in recent years that ILs and deep eutectic solvents (DES) have been revisited by chemical engineering, because such solvents can replace conventional organic solvents. Mixing salts and/or organic compounds may cause a considerable reduction of the melting point, turning them into liquids even at very low temperatures. Using the liquids made from synthetic chemicals, ILs and DES now have many different applications such as dissolving polymers and metals and as media for biotransformation (Welton, 1999; Wasserscheid and Keim, 2000; Abbott et al., 2004; Gorke et al., 2008). In fact, many of the synthetic ILs contain choline and in some cases also natural organic acids.
In analogy with the synthetic ILs, we hypothesized that the metabolites that occur in large amounts in cells may form a third type of liquid, one separate from water and lipids. Taking the plant metabolomics data we have collected over recent years into consideration, we saw a clear parallel with the synthetic ILs. The above-mentioned major cellular constituents seemed perfect candidates for making ILs and DES. As the first step, we made various combinations of these candidates, thereby discovering more than 30 combinations that form viscous liquids (Table I). Here, we will use “natural deep eutectic solvents” (NADES) as a common term for these mixtures. The preparation of NADES and NMR measurements are described in Supplemental Materials and Methods S1.
The article goes on to show various mixes of organic acids and sugars and choline and some other bits can make rather nice ionic liquids that enable various interesting biochemical reactions. Often giving a different mix of products or giving some interesting selectivity options over the products.
The bottom line is that they found a variety of things in living cells dissolve into those DES better than into water or lipids and that even things like starches and cellulose have some greater activity. So if you want to create starches or cellulose, or move it around, it looks like these Deep Eutectic Solvents have a great deal to offer.
Suddenly it makes a lot more sense why Citrus Fruit are full of Citric Acid, why Yogurt makes a lot of Lactic Acid (why our muscles do too, when we exert too fast… it isn’t an inefficiency, it’s a step…) and even why so many fruits are filled with both sugars and organic acids. Heck, even corn in the milk stage has them. Where there is a lot of biochemistry happening, there are a lot of the Eutectic Solvent ingredients around.
That sugars in sap also help prevent freeze damage may be secondary to assisting in materials transport and to assisting in metabolic processes.
Plants in particular have a bunch of things in them that don’t dissolve all that well in water (vis trees not washing away in the rain) nor in lipids. Yet a mushroom can liquefy and absorb it easily. Somehow all sorts of living things can pick up and move all sorts of molecules that are not all THAT easily dissolved in water or lipids. (And besides, lipids are not all that well mixed with the water based parts, so you have a solvent barrier between the two that has to be bridged…)
This raises the question of how these compounds are biosynthesized and stored. For example, the flowers of Sophora species contain between 10% and 30% dry mass of the sparsely water-soluble flavonoid rutin (Paniwnyk et al., 2001). In biosynthesis, it is generally thought that the enzyme-mediated reactions in cells occur in water. However, this raises questions of how these reactions function with substrates and products that are poorly soluble in water. In addition, the biosynthesis of water-insoluble polymers such as cellulose, amylose, and lignins probably needs a stage of the macromolecule being dissolved to enable the further addition of building blocks.
To assess the possibility of NADES being the third liquid phase in organisms in which certain biosynthetic steps or storage of products may occur, the solubility of some common natural products in NADES was measured. For example, we found that the solubility of the flavonoid rutin in various NADES was 50 to 100 times higher than in water (Fig. 2). Moreover, the completely water-insoluble paclitaxel and ginkgolide B showed high solubility: 0.81 and 5.85 mg mL−1, respectively, in Glc-choline chloride. Considering macromolecules, DNA (from male salmon), albumin, and amylase did show good solubility in some of the NADES tested. The solubility of the salmon DNA was shown to be 39.4 mg mL−1 in malic acid:Pro (1:1) compared with 26.9 mg mL−1 in water. The albumin solubility was 30.6 mg mL−1 in Fru:Glc:Suc (1:1:1) and 235.0 mg mL−1 in water. Even the non-water-soluble polysaccharide, starch, showed a solubility of 17.2 mg mL−1 in Glc:choline chloride (1:1).
There is a whole lot more in the paper, so hit the link. It covers things like freeze protection and dessication protection and a variety of ways this can enhance survival in difficult conditions.
For me, one of the more interesting potentials (though NOT said in the article) is that it seems to serve as an alternative Ionic Solvent to water. This implies it might be possible to form life without water at all. Purely based on DES / Lipid chemistry. That, at least for now, has to stay in the realm of Science Fiction… But it does present the potential to have a life form evolve on a hydrocarbon / CO2 rich world without a lot of water present.
So to handle those hard to handle biochemicals, it looks like Nature’s Trick is to use a Eutectic Mix of sugars and organic acids. The “Deep”part refers to how deep the melt temperature is depressed.
A deep eutectic solvent or DES is a type of ionic solvent with special properties composed of a mixture which forms a eutectic with a melting point much lower than either of the individual components. The first generation eutectic solvents were based on mixtures of quaternary ammonium salts with hydrogen donors such as amines and carboxylic acids. The deep eutectic phenomenon was first described in 2003 for a mixture of choline chloride (2-hydroxyethyl-trimethylammonium chloride) and urea in a 1:2 mole ratio, respectively. Choline chloride has a melting point of 302 °C and that of urea is 133 °C. The eutectic mixture melts as low as 12 °C. There are four types of eutectic solvents:
That is one heck of a lot of melt point depression. It also explains why so many sugary things end up sticky ;-)
It looks to me like water is needed mostly to make things liquid at ‘closer to zero’ and that a non-water life form at, say, 100 C could be a theoretical possible… Though they might find water caustic and dissolve in it !
There isn’t a whole lot more in the wiki, so I’m just going to quote the whole thing here. Not surprising for a field that looks like it has all of about 8 years of significant interest under it’s belt. (Probably a good field for new students to head into. Lots of room for discovery / Thesis Topics…)
The DESs have been studied for their applicability in industry at lab level, and the DES described above was found to be able to dissolve many metal salts like lithium chloride (solubility 2.5 mol/L) and copper(II) oxide (solubility 0.12 mol/L). In this capacity these solvents are used for metal cleaning prior to electroplating. Because the solvent is conductive it also has a potential application in electropolishing. Organic compounds such as benzoic acid (solubility 0.82 mol/L) also have great solubility and this even includes cellulose. Compared to ordinary solvents, eutectic solvents also have a very low VOC and are non-flammable. Other deep eutectic solvents of choline chloride are formed with malonic acid at 0 °C, phenol at -40 °C and glycerol at -35 °C. Compared to ionic liquids which share many charactistics but are ionic compounds and not ionic mixtures, deep eutectic solvents are cheaper to make, much less toxic and sometimes biodegradable.
Some have suggested the possibility that carboxylic acids in conjunction with compounds such as sugar alcohols show promise and potential as a DES. A small group of undergraduate researchers at a small college in middle Tennessee have reportedly formulated a solvent that shows potential for having practical applications in green chemistry and could possibly have commercial applications in varying fields. They have not released their formulations or ratios, however it has been rumored the solvent was derived from some combination of carboxylic acid and an unknown sugar alcohol.
Due to the increase in research activities on DESs and their applications, it was necessary to characterize them (measure their physical properties and establish a database). So far, one research only published by American Chemical Society/Journal of Chemical and Engineering Data, had dealt with the task of the characterization of these solvents. That research took DESs based on Phosphonium salts as a subject to its study, because this type of salts was yet to be studied.
The applicability of DESs in industry is still subject to a wide study. A search on the internet for “Deep Eutectic Solvents” can return lot of results, but a specific search with proper keywords can lead to the exact research groups that are researching on DESs. Few papers are already published on DESs’ applications, and it is expected that this will change dramatically in the near future.
So a “watch this space” seems in order.
New industrial chemistry.
New understandings of biochemistry.
New applications in organic chemistry.
And maybe, just maybe, some new planets to look at as potential places to find life. Those a bit shy on water, but rich in organics. Both higher temperature (water vaporized) or potentially lower temperature where liquid hydrocarbons could provide the freeze depression while the organic acids provide the ionic solvent character.
I wonder if anyone has studied Liquid Methane / Ethane / Propane DES mixes?…