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[Music]

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I'm gonna be talking about prebiotic

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photochemistry today and we've actually

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heard quite a bit about photochemistry

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sauce one of the benefits of going

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towards the end of the conference I get

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to invoke a lot of what other people

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have already discussed and in particular

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I'm going to be talking about how we can

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use photo chemistry to build bigger

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molecules we've talked a lot about photo

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stability and how that can be really

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important so we don't break up molecules

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but I'm gonna be talking more about how

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we can make bigger molecules using photo

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chemistry so I think it's important to

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define what I mean when I'm talking

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about molecular complexity you can think

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about complexity as just having a large

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mixture of lots of molecules but in this

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case I really do mean forming bigger

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molecules so how do we form covalent

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bonds without biology in a prebiotic

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setting and so if you have simple

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molecules like our favorite fatty acids

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we've been talking about a lot how did

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we get from those simple prebiotic

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available molecules to the more complex

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biomolecules that are actually needed

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for life and so I'll be talking about

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quite a bit this model system for making

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simple double tailed lipids where we

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sort of are in an intermediate region of

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chemical space between these simple

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single tailed fatty acids and the much

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more complex phospholipids that are in

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modern cells and so there's a way of

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doing this photochemically using a very

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simple system but before I get into the

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specifics I want to step back a little

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bit and talk about both prebiotic

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chemistry and photo chemistry in general

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and so again we've heard a lot about how

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prebiotic chemistry is sort of how you

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go from simple systems to complex

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systems and that's great except that

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there's always the back reaction of

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going back from a complex system to a

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more simple one and so if we're thinking

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about a system that isn't being driven

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in some sense there's always going to be

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an equilibrium and even if your

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equilibrium is thermodynamically

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favoring this more complex system you're

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still kind of going to be stuck in this

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equilibrium state and so you generally

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need

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a driving force to maintain

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disequilibrium which is often an input

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of energy and so if you just think about

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going from simple processes to the more

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complex things including life you're

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maintaining disk equilibrium and so when

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we need to think about energy sources

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there are lots of different prebiotic

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energy sources you can pick and we've

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we've heard a lot about a lot of these

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but solar radiation is a really

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attractive energy source for a couple of

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different reasons one of which it's just

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a much larger energy source than

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anything else that would have been

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available this particular study was only

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looking at UV light that was less than

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250 nanometers which is clearly not all

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of the light in the system but even that

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is over a couple over magnitude more

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energy from the Sun than the other

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sources and it's also important to think

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about photo chemistry and light from the

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Sun because photo chemistry is

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fundamentally different than thermal

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chemistry thermo chemistry you have a

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bath of molecules in say an aqueous

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environment and you heat it up and

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you're all just jostling around the

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whole system is moving and it's

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generally not particularly specific

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whereas with photo chemistry you have a

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specific molecule that absorbs light at

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a certain energy range and you can

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excite a single molecule or a single

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type of molecule in a solution while the

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bath remains low and the other molecules

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are not necessarily excited and

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photochemistry is also sort of

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inherently a non equilibrium system

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because you're exciting the molecule and

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it's also very dependent on which

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molecule you choose what chemistry are

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going to get out if you're going to get

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out any chemistry all right so we've

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seen a plot from Parker that was based

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on a lot of the same data but what

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conditions are we talking about when

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we're talking about the young son during

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the prebiotic conditions so we have a

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few things on here so we have the sort

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of modern extraterrestrial solar

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spectrum outside the atmosphere and then

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we have this model of the young son of

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about 3.8 billion years ago and then

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I've also put the current surface

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spectrum on here so it's this

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son but looking at it sort of on the

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surface so what light is making it

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through and of course we see this really

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distinct cutoff at 290 nanometers which

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is where ozone is cutting off the UV

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light but you notice the changes we're

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seeing in the solar spectrum due to the

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atmosphere are sort of of the same order

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of magnitude for lack of a better word

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as the changes of several billion years

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of solar evolution and so it's really

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important to think about what prebiotic

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atmospheric filters we're going to have

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and the we have guesses for what the

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prebiotic atmosphere was and what

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filters there would be they're not I

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would say particularly well constrained

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but most people agree that most of the

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wavelengths of light at about less than

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200 nanometers would be pretty much

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filtered by the time you get to the

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surface of the earth and that there

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would be some attenuation between 200

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and 250 nanometers so we've heard a lot

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about sort of the more UV that's given

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off by the younger son but most of that

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it really is out in this higher UV range

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that wouldn't necessarily make it all

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the way down to the surface of the earth

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where we're at least considering doing

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useful photo chemistry but there is sort

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of this almost hundred nanometer range

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of sort of quote unquote useful UV near

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UV radiation that can do that can help

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build chemical complexity and so as I

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was saying photochemistry is molecule

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specific but it's also very

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environmental environmentally specific

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and so we were saying we don't

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necessarily know a lot about the early

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Earth conditions during this period of

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prebiotic chemistry I think we're all

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pretty well agreed that there were

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oceans or water of some variety we have

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guesses with nitrogen and co2 for what

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the atmosphere was there are different

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estimates of whether there would have

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been say organic Hayes's to help filter

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some of the UV light out and then other

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people have estimated sort of what

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minerals and land there would be but for

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our purposes we generally try to keep it

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really simple so we use aqueous

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environments and

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use sunlight and so one of the molecules

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we use is pyruvic acid here it's an oXXO

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acid and so it's got a carboxylic acid

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and then a ketone and most of your photo

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chemistry and where you absorb light is

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going to be controlled by what

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functional groups are in your molecule

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so here we see the absorption spectrum

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for the gas phase pyruvic acid and you

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notice that the aqueous phase pyruvic

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acid is blue shifted so where these

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electronic states are lying really does

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change as to whether it's a gas phase

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species or an aqueous phase species but

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if we use this longer tailed alkyl lock

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so acid - oh a it really hasn't changed

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much from the aqueous phase pyruvic acid

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so the alkyl tail isn't changing much of

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the electronic structure here and we got

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a good overview of your Blonsky diagrams

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earlier today so I won't have to go into

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it in too much detail but this is for

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pyruvic acid it's just a cartoon sketch

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of what goes on with the photo chemistry

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here but basically you absorb a light

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you go up to this singlet and PI star

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manifold and then in the gas phase you

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the molecule falls apart into methyl

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hydroxy carbon and then can go on to

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make small molecule products but as soon

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as you're in aqueous phase you now can

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inter system cross to this triplet state

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via a conical intersection and you can

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get really interesting products and so

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when we're talking about what the

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triplet state is doing it interacts with

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another pyruvic acid in this case this

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is the dial but there's an equilibrium

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between the pyruvic acid and the dial

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and equation and it D carboxylates and

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it generates two organic radicals and

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the organic radicals can go on to make a

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number of products but the one we're

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going to focus on in particular is this

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this is dimethyl tartaric acid so by

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absorbing light and a three carbon

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molecule decarboxylated and then making

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a radical we can recombine two of these

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radicals to form a six carbon molecule

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so you're making a carbon-carbon bond

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and you're you know essentially

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dimerizes a molecule and so that's cool

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for a lot of reasons but it's especially

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interesting if you stick alkyl tails on

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here instead of methyls

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because then suddenly you have a way of

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going from a simple single tailed

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surfactant that's prebiotic lee possible

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to a simple double tailed surfactant

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which is really interesting from because

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generally there hasn't been a great

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abiotic way of making double tailed

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lipids it's not a phospholipid but it's

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sort of in this region of chemical space

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in between the single tailed carboxylic

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acids and the phospholipids it's also

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really interesting because we start well

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below the aggregation concentration of

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the single tailed lipid the 208

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but upon fatah lysis and no further

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perturbation of the system you actually

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see this the solution turned cloudy and

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so we're getting self-assembly of these

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we're getting self-assembly as the

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photolysis proceeds as reforming these

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double tailed molecules because double

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tailed molecules generally have a lower

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critical sort of aggregation

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concentration and we've done a little

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bit of initial characterization of these

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guys they are pretty mono dispersed in

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size at about a hundred nanometers in

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radius and we can tell that they are

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spherical so basically they're too big

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to be micelles we haven't definitively

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proven that they're vesicles but they're

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of the correct size to be vesicles and

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even if they are just sort of ordered

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aggregates that's a really interesting

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phase of self-assembly to get something

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that's so mono dispersed in size so

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we're still working to characterize this

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but in the next couple of minutes I want

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to talk about this other chemistry or

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using the same idea of chemistry that

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we're really excited about right now so

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again we've got these organic radicals

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and when you're in a solution of pyruvic

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acid it makes sense that these two are

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going to recombine to make the molecules

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come together but in a prebiotic system

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you're not just going to have a single

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molecule floating around doing chemistry

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with itself and so if we can come up

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with

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way to use these photoactive organic

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radicals as drivers for further

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chemistry that's really interesting and

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so these are initial results that were

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we're finishing up right here but

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basically we can take pyruvic acid it

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also works for 200 a and we can take a

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short-tailed carboxylic acid so in this

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case hexanoic acid and we can hydrogen

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abstract from the hexanoic acid to form

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a radical here and then we do see it's a

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minor product given how our experimental

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constraints but we do see both the

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pyruvic and the hexanoic acid these

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radicals coming together and we see a

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mixed product between the two and so if

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that's the case then we really have

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developed sort of a primitive or a

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fairly robust system for generating

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primitive lipids double tailed lipids

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both with two oxoacids coming together

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but also being able to take a molecule

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like a carboxylic acid that it's not

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itself photo active and can't do photo

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chemistry but we can use the photo

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active species as drivers for further

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chemistry and with that I just want to

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thank everybody you've seen this picture

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so work better on ourselves or in both

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quit well yeah so I didn't talk about

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that today but so these molecules are

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surfactant molecules they are going to

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partition to the surface and we in our

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group an atmospheric chemistry group

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really like to think about aerosols

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which have a very large surface area to

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volume ratio and so you can get a much

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higher relative concentration in these

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little aerosols that have so much

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surface area and so probably I mean it's

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a surface area argument if you're

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fitting a you know concentration things

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so we would love to do it on their cells

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but this was all studies actually I'm

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used to seeing aerosols from your group

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all right another ferris wheel