pH And Coacervates: Is There Evidence That Acidic Environments Increase Coacervate Formation?

Introduction

While coacervates are not alive, they are good representations of how early life may have formed from simple organic substances under the right conditions, which eventually led to the formation of prokaryotes. Under suitable conditions, life-like structures can form naturally from relatively simple materials. In the 1920’s, a scientist named Oparin predicted that biological molecules would form in an acidic mixture of inorganic molecules. In the 1950’s, the Miller-Urey experiment demonstrated that biological molecules could develop from inorganic molecules of methane, ammonia, and hydrogen in liquid water, and Sidney Fox went on to show that Miller-Urey product molecules would form more complex polymers if clay was present. (Daintith, 2009)

Evolution, which provides an explanation for the diversity of life, has left fossil indicators of past lives, and gives us a good predictor for events from the past, going into the future. Evolution is much easier to study than the origin of life itself, which is why a good model for the study of life-like structures is important.

Coacervates may have formed from simple organic substances under the right conditions, which eventually led to the formation of prokaryotes. The study of coacervates are crucial in this experiment, because they mimic life by creating vacuoles and movement. Not only are coacervates good representations of how early life may have formed, they are easy to produce, and data can be easily re-tested to verify its validity. Proteins, carbohydrates and other materials in a solution can be mixed to form droplets composed of different types of molecules, bounded by a membrane-like interface to the surrounding medium. (Weinbreck, Tromp, de Kruif, 2004)

Hypothesis

If the pH of the solution decreases as a result of adding HCl, the number of coacervates formed will increase. The data will support the experimental hypothesis because early life tended to form under more acidic conditions (Mellersh and Smith, 2010), and later evolved to expand into environments with alkaline surroundings. We can reasonably infer that coacervate formation should increase with decreasing pH.

Confounding Variables

A significant confounding variable that we encountered was drop size from using the plastic pipettes. We controlled this confounding variable by ensuring that every drop of HCl was approximately the same volume. If we did not ensure that this confounding variable had not been controlled, we could have been confounded by outliers and a significant deviation in our data. This obstacle could have been solved by using a pipette with a higher accuracy, or even a machine to add droplets.

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A not-so significant but possible confounding variable was the repeated use of the same pipettes. The reuse of pipettes, particularly tips, have been shown to affect measurement accuracy by up to 4% (Sartorious, 2002). While not particularly significant given the scope of this experiment, and the use of transfer pipettes instead, the accuracy, when trying to determine an exact value such as the pH, will not be high. It is advisable to follow standard laboratory procedures and use a new pipette or pipette tips each time a volumetric measurement needs to be made.

Results

When no HCl was added to the solution, the pH was 6.4 and the mixture was clear. 10 coacervates could be seen growing. After adding 1 drop of HCl into the gelatin solution and mixing slightly, the solution became cloudy, and the pH decreased to 6.1. When placed under a microscope, we could see more coacervates than before, at 17 coacervates. After adding HCl drop by drop, at 4 drops of HCl, the gelatin solution became clear again and the pH had decreased to 5.4. The solution had four times more coacervates than at the beginning.

The data shown in Figure 1 shows that the data follows a gradual, decreasing trend. The trendline drawn in Figure 2 has a slope of -32, which is interpreted such that for every increase in pH of 1, there will likely be around 32 more coacervates that have formed. It is observed from the data that a decrease in pH (adding hydrochloric acid) results in a higher number of coacervates observed to have formed.

Discussion

Coacervates emulate, albeit a very primitive level, the structure and function of living cells necessary to biological fitness, in that they are capable of absorbing nutrition and grow under a proper physically and chemically suitable environment. As our results portrayed, we successfully created coacervates by combining simple organic compounds: gelatin, emulating protein, gum arabic, emulating carbohydrates, and hydrochloric acid, which would produce more coacervates. Our experiment showed a congregation of 'proteins' and 'carbohydrates' binding together to form protobionts, or in this case, coacervates. We observed the cell-like structures that formed under a microscope, and it can be concluded that a lower pH is more favorable for coacervate formation. As you can see in Figure 2, the negative slope of the trendline shows that a decrease in pH yields a higher number of coacervates. Although the coacervates displayed properties typical of living cells, such as the capability to absorb nutrition and growth, the coacervates were not living entities and could not display properties such as homeostasis and reproduction through mitosis or meiosis.

Conclusion

The purpose of this lab was to see how coacervates are created, how they model living cells, and the effect of pH on their formation. We know that combining a variety of organic compounds, coacervates can form an outer layer, similar to the cell wall/membrane of living cells. We can tentatively conclude that a decreasing pH results in a higher number of coacervates formed, which will allow future experimental studies, such as observing coacervate formation under more extreme pHs, to be much more refined. Coacervates are considered to be the building blocks of early life, and by analyzing the effect of pH on their formation, we can see that their evolution may have occurred by using chemical processes in order to produce organic compounds retrieved from oceans for food, given that early oceans were acidic (Weizmann Institute of Science, 2017).

References

1. Sartorious group (2002). “Piston-operated volumetric apparatus — Part 2: Piston pipettes”. Retrieved from http://www.sartorius.co.rs/contentFiles/files/ISO_8655-2_2002.pdf.
2. Weinbreck, F., & Tromp, R.H., & de Kruif, C.G. (2004). “Composition and Structure of Whey Protein/Gum Arabic Coacervates”. Retrieved from https://pubs.acs.org/doi/abs/10.1021/bm049970v.
3. Daintith, J. (2004). “Biographical Encyclopedia of Scientists”. (pp. 259). CRC Press.
4. Weizmann Institute of Science. (2017). 'First oceans may have been acidic.' ScienceDaily. Retrieved from http://www.sciencedaily.com/releases/2017/04/170410095624.htm.
5. Mellersh, A.R., & Smith, P.M. (2010). 'The Alkaline World and the Origin of Life'. School of Sciences, University of Derby. Retrieved from http://journalofcosmology.com/Abiogenesis102.html.