[CCoE Notice] Cullen College Dissertation Defense Announcement - Aman Agrawal - ChBE

[Hutchinson, Inez A]

[Dissertation Defense Announcement at the Cullen College of Engineering]

The Roles of Rainwater, Electric Field, and Polymer Charge Density in the Formation and Organization of Coacervate Protocells



Aman Agrawal

September 6, 2023;   12:00 Noon

Room: Agrawal Building, AERB 320



                                             MS TEAMS: Click here to join the meeting<https://urldefense.com/v3/__https://teams.microsoft.com/l/meetup-join/19*3ameeting_MDFlOTI2NTMtZDVjYy00Y2U5LWJiY2YtYzkxOTIwM2MzYzc1*40thread.v2/0?context=*7b*22Tid*22*3a*22170bbabd-a2f0-4c90-ad4b-0e8f0f0c4259*22*2c*22Oid*22*3a*229a68cf44-744e-46c1-b1fd-8a7ecad722f6*22*7d__;JSUlJSUlJSUlJSUlJSUl!!LkSTlj0I!Fr1wYXMQADxhFHBQ454lgdkN9kFQCh2PPi67YA53Eks7C2Cx5yxQIKJ01wnlefDypF3sMUawVMobGZg8y-AeHrTkbj4$ >

                                                            Meeting ID: 254 327 422 502

                                                            Passcode: kN87hx





Committee Chair:
Alamgir Karim, PhD

Committee Members:

Jacinta Conrad, Ph.D. | Peter Vekilov, Ph.D. | Jack Douglas, Ph.D. |

Christine Keating, Ph.D. | Sarah Perry, Ph.D

Abstract

The compartmentalization of RNA is an essential aspect of protocells for Darwinian evolution in the context of the origin of life. Membraneless coacervate droplets, such as those formed by polycation and nucleotide, have long been proposed as model protocells due to their excellent ability to concentrate RNA by natural partitioning without any transport barrier. However, the high rate of exchange of RNA between these membraneless protocells, along with their rapid fusion with each other, have proven them ineffective for any functional spatiotemporal compartmentalization. Furthermore, there is a lot of interest in manipulating colloidal particles using external fields, but the research has mostly been limited to solid particles. It is becoming apparent that manipulating liquid droplets at the microscale using external fields could be useful in forming 3D assemblies without changing the density of the solvent that is required for solid particles. However, recent research showed that coacervates are unstable under external fields and tend to vacuolate and explode.

            In this thesis, we show experimentally how coacervate droplets can be stabilized against coalescence by sheering them in distilled water. We found that the droplets gain interfacial elasticity, possibly due to the formation of ionic crosslinks as a consequence of the ejection of interfacial counterions. We hypothesized that rainwater, which is essentially distilled water, could have helped the formation of crosslinks on the interface of coacervate droplets that not only suppress their fusion but also allow small RNA oligonucleotides (6-8 nt) to exchange at a short timescale while keeping the longer ones (35-nt or higher) compartmentalized for days. Such a size-based trafficking genetic material could have formed the basis of chemical communication between evolving protocells.

            Next, using these stable droplets, we showed that we can precisely control the positions of individual droplets and arrays of them with relatively low-voltage electric fields (on the order of 10 V/cm) and that the imposition of an oscillatory field gives rise to chain formation with coarsening of these chains into long fibers. Such a phase–separation–like process is generally observed in electrorheological fluids of solid colloidal particles subjected to much larger field strengths. Since many different molecular payloads can be incorporated into these stable droplets, we anticipate many applications.

            Finally, we showed how multi-compartment coacervate protocells can be made using polymers of different charge densities. By synthesizing polyelectrolyte chains with a varying fraction of charged to uncharged monomers, we studied multicomponent phase separation of a homologous series of polyelectrolytes to understand the nuances of multiphase separation.

[Engineered For What's Next]


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