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[Music]

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[Applause]

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Thank You Michel cassava I'm gonna talk

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about biomolecular synthesis again but

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from a quantum chemical perspective so

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we all first let me let me acknowledge

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my collaborators my theoretical

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collaborators here dr. Jim Lee proposed

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the Martin had gotten professor Thomas

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Tyne and my collaborators at NASA Ames

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experimental side notice Scott Sanford

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Michele Louisville and Chris matarese

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and funding from NASA Astrobiology

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Institute as well so we all know by now

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that that that biomolecules are organic

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molecules are formed on the surfaces of

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on the surfaces of are found in the

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services of meteorites and bodies that

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have are extraterrestrial in origin I

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stick to we stick to answering questions

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of how they're formed and why their form

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and by which processes so here is a

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cartoon of what may be molecular

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synthesis in the gas phase which may

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then be incorporated into into parent

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bodies such as meteor as such as you

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know grains or it could be formed on the

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surface of the grains or on the surfaces

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of the grains that is covered with a

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little bit of ice and we know these

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molecules can be as complex as sugars

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nuclear bases alcohols etc we try to

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look at what physical processes that

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that create the reactants what reactions

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are possible what's not possible what

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products are more likely to happen what

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what is less likely to happen

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so this is again in sort of motivated by

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and in collaboration with experiments

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where Michelle Kristin and Scott has

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done this and others have many others

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have done this they'd looked at Isis

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that in the laboratory and then exposed

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the ISIS with UV light and seen organic

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at low temperature deposited on aluminum

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foil ionized with or irradiated with UV

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lamp and and and experimented with HPLC

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and GCMs and found all sorts of

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interesting molecules including hypo

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xanthine adenine guanine I saw burn in

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xanthine and and so on and so we tried

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to understand what might have happened

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in between in between between depositing

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and and identifying the molecules so

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what might have happened was you have

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about ten point two five little folds of

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energy that may break water into

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hydroxyl may break or ammonia into amino

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group it does not iein eyes water

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because two point six electron volt is

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not available but it can ionize ammonia

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it can break ammonia or and it can even

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ionize and break purine into their

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components so all these reactants are

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are available in this and the sister

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said for h2o radical cation they then go

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on to react in various ways so here is a

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just a few of those and we look at each

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one of these but I'm going to point out

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just couple of them so here's a neutral

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purine reacting with water or ammonia

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neutral peirong reacting with a hydroxyl

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or ammonium or amino group radical

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reacting with the radical radical cation

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of purine reacting with hydroxyl or

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amino group and so on so I'm going to

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stick to this and for a good reason

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should be clear later stick to reactions

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between purine cation and and hydroxyl

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and amino radicals these are radical

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radical reactions so easier but there's

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a good reason for it but all these

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reactions we have actually explored and

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is available in our papers you can

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always go and look at those we use

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[Applause]

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primarily for these work density

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functional theory using one of the most

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modern density functions called Omega B

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97

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viii along with a large enough basis set

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and for condensed phase calculations we

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do a conductor like polarized continuum

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models so these are two sets of

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calculations between gas phase and

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explicitly condensed phase calculations

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and sometimes we use molar + @

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perturbation theory as well depending on

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the need so what we really do we try to

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explore the mechanism of these reactions

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so here is purine cation for you

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reacting with a hydroxyl radical giving

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you an intermediate that needs to then

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lose a proton to give you the product

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the products in this case is two

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hydroxyl two hydroxy purine it can

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happen in a different way as well

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feeding cattle reacting with water give

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you in between a few steps giving you

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the same thing and those same reaction

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scanning even happen with amino group

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and many other many other reactants so

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if we look at each one of these

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reactions let's look at the amino

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reaction first it is a reaction diagram

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so the x-axis is your reaction

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coordinate unitless and y axis is energy

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in kilocalories per mole here's the the

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reactants you have the purine cation the

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amino group and and the water and the

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intermediates here and the products

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there now the intermediates form in this

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case without any barrier because you

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have a reaction between a radical and a

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radical and that gives you the covalent

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bond formation here but that this this

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these molecules still need to lose a

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proton and that proton is lost because

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of the because of the water around it

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the water water's proton affinity

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actually pulls the proton out and gives

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you these products if you didn't include

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this water in this in this equation

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these energies for the products would be

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somewhere around here

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which means the reactions will not be

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favorable you need to include at least

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one water actually more than one water

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but in this case with even with one

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water the reaction main energies become

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favorable this already tells you that

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pure gas phase reaction

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is kind of difficult pure gas phase

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reaction between this radical cation and

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a radical will give you the intermediate

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but not the products because the protons

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still going to be stuck there and you

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need something to pull that proton out

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water does that right here you can show

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this using condensed phase calculations

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explicitly here

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so these RC PCM calculations and again

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we make the reactants 0 arbitrarily and

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and see the what happens to

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intermediates and products here you see

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that the the effect of the condensed

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phase clearly it pulls the energy is

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down further and makes a reaction go

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better similar things you can now start

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now the other point I want to make from

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this is that that you have two products

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that is six amino purine and two men

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amino purine that is the most likely

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what's most stable products in this six

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I mean appear in is nothing but adenine

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adenine is your most favorable product

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if you take one of these two and or both

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and do the next step that is an addition

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of either amine group amino group or a

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hydroxyl group you would find something

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like this

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so here's an example of adenine reacting

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with hydroxyl and and you have the

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reactants their intermediates and

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products here so if you start from

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adenine you get to I so guanine if you

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start from too high to amino purine you

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get to go on in

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here's going in and again you see the

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same thing happening this is a pure gas

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phase calculation in in black and blue

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you see the reactants of the

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intermediates forming the products for

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me in the product intermediates are

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still a little bit lower in energy so

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that the reaction shouldn't go if you

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actually include the condensed phase and

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the condenses calculations clearly

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showed that that the reactions go in in

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the products direction so so you have

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you need the matrix you need the water

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matrix these reactions do not go in the

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gas phase so gasp your gas phase

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formation oxidation or amino ammunition

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of purines to adenine or guanine is

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unlikely but condensed phase

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with covered with ice phase followed by

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ionization formation is very likely so

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we may ask why I work with cation all

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the time so here's the pure in cation

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and seen pigeon cations before it's a

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good reason for it now and it became

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clear later so here's an example that

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has is out of place here's an example of

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an experiment that Chris and Michelle

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did where they deposited I was time to

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have okay okay so I mean a purine in

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pure ammonia and ionized and right

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followed by radiation and we did the

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calculations ensure that you should be

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able to make adenine from it because you

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know I mean any NEC has strong enough

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return affinity to pull that proton out

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so you should you should get adenine and

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and all other amino purine products

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except when they do the experiments they

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don't see any now this this is an

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interesting case it became clearer later

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when we found this paper by quill ethyl

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where they make this observation that

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the ice matrix acts as an electronic

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solitaire switch where the relative

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amount of water and ammonia determines

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whether the positively or the negatively

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charged PA is in this case but in our

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case purine is formed so in pure water

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you have cations and in pure ammonia you

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have a neurons produced that's because

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of the low ionization energy of ammonia

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and hire an additional energy of water

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low ionization of energy of ammonia

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makes ammonium cat or ammonia cation

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plus an electron electron is captured by

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the the purine or the pH and you have

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the anion so when you have the Anna and

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the reactions don't go go like the way I

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should and you don't see any product

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that kind of proves the cationic

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mechanism because the moment you have

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the water water helps create the cations

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of the purine or the pyrimidine or

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whatever you have working with

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the cationic reaction goes forward this

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is kind of the proof of the cationic

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mechanism that's why we chose the

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cationic mechanism of all the of the

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mechanisms here so now going forward we

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just can do the same experiment in

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Reverse you say how about the hydroxyl

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if the hydroxyl attaches first you see

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the same thing in this case you would

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see hypose Anthon instead of amino

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purines and then those can then take in

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each amino group later and we'll give

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you the similar products basically

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guanine I said one in and see similar

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ordering of energy but now what is

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available will be important at the first

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step so if you started from purine if

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your first step was an amino group

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addition then you expect to find

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adenine if your first step was a

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hydroxyl group addition you expect to

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make hypose and thin but this actually

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makes a very interesting case if water

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is more abundant so if you make hypo

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Santi and you expect that in the next

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step if it is a amination then you would

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expect to form guanine and if it is a

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hydroxylation then you expect to forms

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xanthine on the other hand if you if

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your first step was an ammunition then

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you make adenine and then the next step

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would takes you takes you to I so

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guanine all these products are possible

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it just depends on what is available at

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the NIR environment and what reaction is

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statistically more feasible so with all

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these I'm just going to skip next few

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slides and come to my broad conclusions

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is that that the that the cationic

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mechanism is likely the way this these

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reactions go it needs the presence of

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the water matrix for for two reasons

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water actually plays the devil and and

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the do-gooder here is a catalyst because

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it helps create the cations it provides

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a matrix for the reaction and also

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provides the hydroxyl radicals for for

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the reaction so it provides the

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reactants to but also acts as a as a

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competitor because once the hydroxyl is

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produced it attacks everything in the

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amino group does not have the

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opportunity to to

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sort of a catalyst and a competitor and

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from our other experiments we found that

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that the uracil adenine and guanine are

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kind of easily formed but timing is not

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so easily formed and that's the part I

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skip but you can always go back and read

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the papers previous papers and so which

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is kind of goes along with the absence

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of timing in the meteorite examples thus

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far so with that I'm just going to skip

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next few slides and come to and say

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thank you and take any questions you may