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so we're going to step back a little bit

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in time and talk about I don't know

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whatever timeline you want to talk about

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but we're talking about prebiotic

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chemistry so before life and I'm going

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to be talking today a little bit about

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how we generate molecular complexity and

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when I'm talking about generating

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molecular complexity I mean going from

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the simple molecules that we know how to

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make either on meteorites or in space or

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with Yuri Miller discharges to going

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towards these more functional

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biomolecules so making proteins or RNA

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but also importantly these membrane

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components and so modern cells are

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really complex and the membranes that

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compose them are also really complex so

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enclosures we recognize that they're

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important for life and modern cells tend

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to use phospholipid molecules as their

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membrane components some such as die

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palmitoyl phosphatidyl choline which is

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a typical lung surfactant and so it's a

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really complicated molecule but

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importantly it's got a phosphate group

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and it has two long hydrocarbon tails

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but if we want to start modeling these

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things prebiotic lee we want to come up

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with a simpler model and so people

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usually talk about vesicles so vesicles

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this is obviously not just you can

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encapsulate some water and then they

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have a bilayer of membranes so you have

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oops head groups and things like that so

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you have surfactant molecules on the

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outside and water on the inside and so

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membrane components are amplifiers

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they're surfactants and so they usually

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have a polar head group and a nonpolar

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tail and that means that if you're in

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water the polar head group is

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hydrophilic it likes water and the tail

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group is hydrophobic so these things

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will partition to the surface of water

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and orient themselves and concentrate

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and lap and we can measure these this

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surface activity using a langmuir trough

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which is just a really simple Teflon

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dish you put an aqueous substrate down

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and then you can deposit a monolayer of

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surfactant on top and then you have

53
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these little Teflon barriers and you can

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squeeze the monolayer on the top and

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measure the surface tension and by doing

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that you can get a lot of the surface

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thermodynamics an orientation of the

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packing of the membrane in sort of a

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two-dimensional

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nonsense so that would be a mano later

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but these molecules also form

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three-dimensional structures they form

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especially once you get above a higher

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constant light enough concentration so

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perhaps the simplest is a micelle where

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you have the polar head groups on the

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outside and the nonpolar tails on the

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inside and that makes and that is

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soluble so it can float around in

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material you can also get the vesicles

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as I said where you have a bilayer with

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the soluble head groups on the outside

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and the tails in the middle and you can

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also get things like reverse micelles or

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oil droplets where the heads are on the

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inside the tails running out and that

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will face separate rather than be

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soluble and so modern biology uses a lot

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of phospholipids and they readily form

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these three-dimensional structures and

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vesicles even at fairly low

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concentrations and they have relatively

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simple phase behavior they're not in

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equilibrium with the monomer and

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solution there kinetically trapped

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structures but as I said these are not

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very prebiotic irrelevant so how do we

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get to a model that is more prebiotic

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irrelevance so one of the most popular

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models that people have used have been

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these fatty acids and specifically like

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decanoic acid and so you've got a single

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hydrocarbon tail instead of the double

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tail and just a very simple carboxylic

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acid head group and they've been used to

96
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great effect as modeling protocells you

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can encapsulate RNA you can do all of

98
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these things with that but there's a

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fair amount about the face behavior I

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would argue that we still don't know so

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the generally accepted picture of the

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decanoic acid phase behavior almost

103
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entirely relies on the protonation state

104
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of that carboxylic head group and so if

105
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you're below some critical concentration

106
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which is referred to as critical vesicle

107
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concentration and critical aggregation

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concentration or critical by layer

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concentration you're just going to have

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the monomer floating around in solution

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but when you get above that critical

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concentration it really depends on the

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head group and so if you're at a really

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high pH where all your carboxylic acid

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head groups are deprotonated those are

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going to repel and you're going to end

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up getting my cells and if you're at a

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really low pH where you're not at all

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where everything is protonated the head

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groups won't repel so you'll tend to get

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phase separation into reverse

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my cells and you get the vesicles in

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this sort of sweet spot in between the

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two when roughly half the head groups

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are protonated half pick head groups rd

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protonated and these are also considered

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to be equilibrium structures so you're

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always at equilibrium with a monomer in

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solution so that's the so that's the

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general picture and sort of one of the

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downsides to these is that you require a

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fairly high concentration but if you

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look at the literature a little bit and

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you try to quantify this more in a phase

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diagram picture than a schematic you run

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into a few issues and so it's sort of

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the same idea you've got my cells at

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high ph oil droplets at low pH and

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there's this really narrow range where

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you have stable vesicles which may be

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limits some of the prebiotic

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applications perhaps a little bit and

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then there also if you look in the

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literature several different critical

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vesicle concentrations that are reported

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anywhere from 10 to 40 millimolar for

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decanoic acid which is a pretty big

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range and when you're making these

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vesicles you usually make them in with

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some salt and some buffer and that's not

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always very well characterized so

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there's a little bit more in the phase

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behavior that I think people tend to

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accept and there's also this range where

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there's this critical vesicle

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concentration but the CRC solubility is

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only about 1 millivolt so there's

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clearly aggregation happening in between

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these two but that's sort of a

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disconnect that people don't necessarily

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talk about that much either yeah and so

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the role of salt and pH perhaps maybe we

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should be talking more about ionic

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strength rather than straight up ph for

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how these things are going to do and

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then just as an additional complication

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I said the CRC solubility was about 1

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millon of it at point eight millimolar

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you end up with a nice crystal at the

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bottom so there's a lot of a lot of

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complications here and so we sort of had

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these two options we've got the fatty

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acids which can make these things but

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they're relatively fragile they require

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very specific environmental conditions

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and if you have too much salt they'll

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fall apart phospholipids on the other

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hand are very robust but they're almost

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too robust because if you don't have the

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biological inclusions of modern life

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you're not going to get much

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permeability and no exchange with

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information in the environment and so we

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kind of want to look for something

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that's an intermedia

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solution between the two so we want to

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balance between robustness and

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permeability and we want a lower

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aggregation concentration than the fatty

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acids had and so to do that we have to

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come up with prebiotic chemical

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synthesis and so when you're thinking

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about making things prebiotic Li you

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need and especially if you want them to

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self-assemble into a vesicle or a

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membrane or an enclosure you need

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favourable conditions for both synthesis

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and self-assembly and so people use an

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energy source hydrothermal vents are

200
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very popular we've used the Sun we use

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photochemistry and environments people

202
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talk a lot about clays and mineral

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surfaces we tend to use the air water

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interface because they were widely

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available in our relatively gentle

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environments and so air water interfaces

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there on the ocean surface lakes rivers

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but also atmospheric aerosols the

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surface area of aqueous atmospheric

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aerosols is about two orders of

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magnitude bigger than the surface area

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of the ocean so it's an important thing

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to remember um and when we're talking

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about photochemistry we've talked about

215
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how the early Sun had more UV radiation

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even though it was less luminous and

217
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there was no ozone shield so people

218
00:07:58,119 --> 00:07:56,599
often think about the UV radiation being

219
00:08:00,610 --> 00:07:58,129
destructive but we would argue that it's

220
00:08:03,279 --> 00:08:00,620
not always destructive pyruvic acid for

221
00:08:05,409 --> 00:08:03,289
instance is a common molecule in today's

222
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atmosphere as well as being pyruvate

223
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metabolites and it absorbs light within

224
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the solar spectrum and we know the

225
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aqueous phase photochemistry really

226
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clearly you're excited goes to a triplet

227
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and pi star state other stuff but the

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main thing is you can make dimethyl

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tartaric acid so you've gone from a

230
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three carbon molecule to a six carbon

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00:08:27,879 --> 00:08:25,250
molecule you've made a carbon-carbon

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00:08:30,760 --> 00:08:27,889
bond which is important and so if we use

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00:08:34,209 --> 00:08:30,770
a longer tailed analog of this to Oxbow

234
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octanoic acid we can then go and do the

235
00:08:38,589 --> 00:08:36,649
same photo chemistry and make a double

236
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tailed surfactant die hexyl tartaric

237
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acid and so with water sun and this

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molecule we've made a double tailed

239
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surfactant which is generally hard to do

240
00:08:50,110 --> 00:08:47,839
not a phospholipid but a double tailed

241
00:08:54,130 --> 00:08:50,120
molecule and we do see that it's quite a

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bit more surface active after em after a

243
00:08:58,240 --> 00:08:56,990
fatalis asst which is good or at least

244
00:08:59,890 --> 00:08:58,250
not at all so proud

245
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because if you have more hydrocarbon

246
00:09:06,520 --> 00:09:02,390
tails it should be more surface active

247
00:09:08,350 --> 00:09:06,530
and yes so the sort of schematic is as

248
00:09:09,400 --> 00:09:08,360
we're doing the photochemistry these

249
00:09:10,600 --> 00:09:09,410
molecules are going to start

250
00:09:15,520 --> 00:09:10,610
partitioning more and more to the

251
00:09:17,620 --> 00:09:15,530
surface and without sort of our solution

252
00:09:19,030 --> 00:09:17,630
starts off clear there no my cells were

253
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below all the critical micelle

254
00:09:22,990 --> 00:09:20,960
concentration and as fatalis asst

255
00:09:25,600 --> 00:09:23,000
proceeds without any further aggregation

256
00:09:27,790 --> 00:09:25,610
or whatever and the solution becomes

257
00:09:30,040 --> 00:09:27,800
cloudy so we're forming self-assembling

258
00:09:33,010 --> 00:09:30,050
three-dimensional structures during our

259
00:09:35,170 --> 00:09:33,020
Fatah lysis and we've worked on

260
00:09:37,150 --> 00:09:35,180
characterizing these and they're quite

261
00:09:38,350 --> 00:09:37,160
monodisperse in size their spherical

262
00:09:40,240 --> 00:09:38,360
which we can see by phase contrast

263
00:09:43,030 --> 00:09:40,250
microscopy they're small they're only

264
00:09:45,400 --> 00:09:43,040
about 200 nanometers in diameter but

265
00:09:48,160 --> 00:09:45,410
they're too big to be my cells and so

266
00:09:49,900 --> 00:09:48,170
and they're very stable with time and so

267
00:09:52,330 --> 00:09:49,910
we've tentatively characterize them as

268
00:09:53,800 --> 00:09:52,340
vesicles electron microscopy will tell

269
00:09:56,170 --> 00:09:53,810
us more we're currently working on that

270
00:09:59,140 --> 00:09:56,180
but in any case they're self-assembling

271
00:10:02,680 --> 00:09:59,150
without further perturbation and so for

272
00:10:04,120 --> 00:10:02,690
us we're quite interested in how the

273
00:10:06,850 --> 00:10:04,130
role of the surface and what is the

274
00:10:08,590 --> 00:10:06,860
mechanism of the self-assembly so the

275
00:10:12,130 --> 00:10:08,600
role of pH is we saw with the fatty

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acids where we're more interested in the

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protonation state our fatalis this

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mixture right now is quite acidic

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because it's just no buffer no nothing

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and so it's about pH two and a half

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which perhaps not realistic and but if

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anything if you believe the model of the

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fatty acid face behavior working at a

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higher pH ought to be more conducive to

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forming vesicles the role of salt is

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also really important and just looking

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at how these guys self-assemble into

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these structures and conceivably if the

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photo chemistry goes better at acidic pH

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is atmospheric aerosols are quite a bit

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more acidic than the ocean and so maybe

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the photo chemistry is going to be more

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favorable in the aerosol but then it

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would get deposited into the ocean and

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self-assemble into these vesicles so

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there are a lot of open questions about

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this but it's kind of a cool model

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system that's somewhere in between the

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two general pictures and so that like to

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questions great I get asked fun so you

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said one of the places I followed this

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that these can form is in aerosols and

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then they drop out of the sky and into

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the ocean is that instead I follow that

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correctly the photochemistry could

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certainly happen there um you do see a

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lot of organic matter and aqueous

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aerosols that will partition to the

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surface usually think about that more as

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being a mono layer partitioning to the

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surface but the aerosols are usually

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micron-sized so it's possible these guys

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are small enough you might have a

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soluble guy in there as well I mean

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that's the speculation but it's just

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interesting that you would get these

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different environments so yes my real

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question is how do you have any idea of

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how photo stable these are once they're

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in the aerosol and exposed to the

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harsher environment of early earth

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before they get shielded by the ocean so

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um the good news I mean I guess I don't

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know if you were had really high UV but

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you've lost all your chroma force here

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okay you're not going to so the key so

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it's this alpha keto acid that's the key

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and so it absorbs at about 320

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nanometers but um but here you've just

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got alcohols and acids and so it's not a

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photo chemically active molecule I mean

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probably lyman-alpha I mean you could

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smash it with something but yeah other

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if you had other organic molecules in

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this mixture to would that inhibit the

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formation of these vesicles they get in

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the way or that's a really good question

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so with fatty acids you can often

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stabilize the vesicle formation if you

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have a mixture so even if you have a

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mixture of like a shorter tailed fatty

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acid that won't form vesicles on its own

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it will stabilize it and certainly

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mixtures are going to be more probiotic

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ly relevant okay um it depends a little

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bit so some people talk about shape

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parameter and so if you have things that

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are of a different shape parameter for

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00:13:26,989 --> 00:13:24,959
the self-assembly that might be bad if

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they're not contributed but one of the

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other cool things were interested in

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doing so it's pyruvic acid it forms this

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radical in the mechanism that I didn't

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00:13:38,090 --> 00:13:36,149
go over and it can actually be used as a

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driver to react with another molecule so

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it's possible to perhaps use the radical

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formed with the two octanoic acid and

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react with another lipid and then get

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even more a mixed double tailed molecule

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or something like so there are a lot of