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during this presentation i will be

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talking about the possibility for

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spontaneous peptide bond formation at

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the water surface

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specifically i'm interested in this type

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of chemistry for its potential relevance

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to prebiotic chemistry and the origins

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of life

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i've put my email here on this first

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slide please feel free to email me with

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any questions or just to follow up and

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see where this research has gone

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to begin i want to share the three

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assumptions that we make about prebiotic

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earth

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first we assume that liquid water would

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have been present

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second we assume that the small monomers

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necessary for the formation of life

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including amino acids would have been

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present

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and third we assume that at least to

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some degree

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these small monomers would have been in

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the liquid water

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one of the questions that we have

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however about the origins of life is how

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we would have gone

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from these simple monomers to the more

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complex oligomers and biopolymers that

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would have been necessary for the

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origins of life

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as i mentioned earlier the small

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monomers present on early earth likely

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would have been in the liquid water of

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the earth this is really problematic for

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condensation chemistries like i've drawn

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here where you have a monomer a and

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monomer b

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combining to form some sort of larger

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more complex molecule a b

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and the reason that this is

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prohibitive to this type of chemistry is

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that when

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these two monomers combine

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very often they also eliminate a water

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molecule now

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eliminating a water molecule into bulk

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water is thermodynamically prohibitive

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meaning that a lot of these types of

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chemistries would have had difficulties

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occurring without some sort of

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help so in modern biology of course we

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have enzymes but that would not have

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been present on early earth

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peptide bond formation as i will be

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talking about today is a great example

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of one of these types of chemistries

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that is thermodynamically unfavorable in

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bulk water so as i've drawn here

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two amino acid monomers combining to

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make a peptide releases water

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this reaction has a small equilibrium

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constant in bulk solution as depicted by

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the arrows in the middle

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so as shown by the big arrow on top it

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is much more likely that these amino

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acids would stay as their individual

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monomer form

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however there's a very interesting

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emerging body of research that shows

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chemistries that are prohibited in bulk

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water

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interface

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first i want to mention that many

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organic molecules are found at the water

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surface and this does include even the

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small amino acids that are necessary for

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peptide bond formation

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at the air water interface

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molecules are in contact with bulk water

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but they are also in contact with the

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vapor phase where the concentration of

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water would be much lower

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this makes it much more likely that

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condensation reactions

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can easily eliminate water molecules

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into the vapor phase and makes the air

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water interface a very interesting

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environment for peptide bond formation

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in fact our group released a study in

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2012 that did show that peptide bond

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formation can occur spontaneously at the

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water interface

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when using activated amino acid esters

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and a transition metal

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so first the amino acid esters formal

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complex with the transition metal at the

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water interface

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this aligns the amino acids in a way

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that is favorable for

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peptide bond formation

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an ethanol molecule is subsequently

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released and then the dipeptide shown on

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the right is formed and with the new

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peptide bond as i've circled

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this study used the surface-specific

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technique infrared reflection absorption

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spectroscopy also known as iris

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iris works by reflecting light off of

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the water surface and obtaining a

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reflection absorption spectrum

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these spectra are very similar to

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vibrational spectra that you might have

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seen in the gas phase

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however they give us structural

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information for molecules that

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specifically sit at the water surface

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here i'm showing the results from this

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study

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in box a is the iris spectrum for the

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transition metal complex and in box b is

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the spectrum of the water surface after

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the solution has been allowed to sit on

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the trough overnight

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specifically i'd like to point out this

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red dash line which corresponds to a new

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peak that grew in overnight

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this peak corresponds to the amide one

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band of a peptide bond so on the right

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i'm showing you the molecule that we

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believe was produced and i've circled

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the specific bond that we're detecting

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with this new p

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while this study is exciting as it

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showed spontaneous peptide bond

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formation at the water surface

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it did use activated amino acids

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so now the question is can the water

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surface promote peptide bond formation

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as many of you will be aware there have

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been many interesting studies coming out

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of the georgia pec group recently

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specifically i'd like to discuss this

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one by forsyth at all that came out in

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2015

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so they used mixtures of

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lactic acid and various amino acids and

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they found that by wet dry cycling these

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mixtures

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as you can see in this graph

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after just one cycle they already saw

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some mi bond yield and with subsequent

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cycling they see more and more percent

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they proposed that this happens by a

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two-step mechanism first the lactic acid

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monomers oligomerized to form an ester

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and then the trailing lactic acid

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monomer is replaced by an amino acid

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monomer

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this forms what's called a pepsi peptide

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and interestingly as cycling continues

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the amino acids will continue to add to

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the end of the chain forming longer and

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longer peptides

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this is particularly interesting in

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light of a study that we released

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earlier this year this study was looking

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at solutions of pyruvic acid however we

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noticed that pyruvic acid seemed to be

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spontaneously forming lactic acid at the

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water surface

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and then those lactic acid monomers

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appear to be forming lactic acid

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oligomers

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this study was performed in a languare

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trough which maximizes the surface area

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to volume ratio of the solution

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and a blodget attachment which allows us

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to collect molecules specifically from

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the surface

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whenever surface molecules are collected

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we simultaneously collect molecules from

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the bulk solution

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and then both surface and bulk samples

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are run through esi mass spectrometry to

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identify the species present

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here i'm showing some of the results

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from this study in red are the bulk

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results and in blue are the

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surface results and the darker color is

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after three hours of the solution

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sitting on the trough and the lighter

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color is immediately after the solution

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this peak in particular is interesting

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as the mass to charge ratio corresponds

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to a molecule that could be formed by

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two lactic acids combining

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and releasing a water molecule so

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potentially this peak corresponds to the

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esters that we may need to form depth

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peptides

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to summarize everything that i've just

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talked about

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we know that the water surface can

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promote peptide bond formation under

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certain circumstances

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we know that wet dry cycling of lactic

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acid amino acid mixtures forms depth c

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peptides

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and we know that lactic acid appears to

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form esters at the air water interface

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combining all of this

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it's reasonable to ask well can the

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water surface promote deficient

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formation

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from lactic acid and amino acid mixtures

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without the need for wet dry cycling

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going forward we plan to study mixtures

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of alpha hydroxy acids and amino acids

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at the water surface using both our iris

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and logic collection techniques

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we have also obtained and planned to use

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a series of alpha hydroxy acids with

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changing tail length

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longer molecules more surface active

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thereby allowing us to select for

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surface specific chemistry

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we have been able to obtain ira spectra

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of the series of hydroxy acids

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both lactic acid and hydroxyactinoic

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acid are soluble so they're placed on

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the trough in solution

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while hydroxy stearic acid is insoluble

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so it's placed on top of a clean water

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surface by way of chloroform which is

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subsequently evaporated leaving a

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disordered monolayer of these molecules

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here i'm showing the carbonyl section of

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the iris spectrum for the series of

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hydroxy acids

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on top we have lactic acid in black and

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then hydroxyoptinoic in blue that

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clearly show the carbonyl stretch

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on the bottom in green i have hydroxy

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stearic acid which does not show the

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carbonyl stretch

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however given that the

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hydrochloric acid is a disordered

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monolayer

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it is reasonable to assume that there

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are fewer molecules

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in the sample pathway

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so that we may not see the carbonyl

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stretch for hydroxy stearic acid

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now i'm showing the ch stretch region of

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the spectrum for all three molecules the

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lactic acid does not show signals in

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this region about the hydroxyactinoic

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acid

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starts to show signal and the hydroxyl

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steric acid has quite strong signals

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and this makes sense just due to the

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shear number of ch stretches that the

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hydroxy stearic acid has in comparison

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with say lactic acid

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additionally we've modified our iris

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setup and we've added

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a polarizer this polarizer allows us to

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get orientation in addition to

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structural information

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so briefly the s polarized light will

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tell us

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which bonds are sitting parallel to the

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surface and the p-polarized light will

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tell us which bonds are sitting

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not parallel to the surface

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here's a quick depiction of what the

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hydroxy stearic acid molecules might

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look at the surface we are in a

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disordered regime so we would expect

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these tails to be quote unquote floppy

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and not necessarily

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perpendicular to the surface

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and this is exactly what we see in the

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polarized spectrum for

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hydroxy steric acid on top i'm showing

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00:11:14,710 --> 00:11:13,120
the p polarized light in dark green so

289
00:11:17,190 --> 00:11:14,720
these are the

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00:11:18,949 --> 00:11:17,200
bonds that are sitting not parallel to

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00:11:21,590 --> 00:11:18,959
the surface and on the bottom i'm

292
00:11:23,350 --> 00:11:21,600
showing the s-polarized results

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00:11:24,949 --> 00:11:23,360
which show the bonds that are sitting

294
00:11:25,829 --> 00:11:24,959
parallel to the surface and we have a

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00:11:28,710 --> 00:11:25,839
mix

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00:11:31,590 --> 00:11:28,720
which is exactly what we expect for a

297
00:11:34,550 --> 00:11:31,600
disordered monolayer

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00:11:36,870 --> 00:11:34,560
now that we have been able to obtain the

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00:11:38,550 --> 00:11:36,880
iris spectra for the hydroxy acids we

300
00:11:41,110 --> 00:11:38,560
will be moving on to

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00:11:43,269 --> 00:11:41,120
mixtures of hydroxiasis with the amino

302
00:11:44,470 --> 00:11:43,279
acids and looking for pepsi peptide

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00:11:48,230 --> 00:11:44,480
formation

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00:11:51,829 --> 00:11:50,230
finally i'd like to acknowledge our

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00:11:54,949 --> 00:11:51,839
funding sources and the mass

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00:11:56,790 --> 00:11:54,959
spectrometry facility at cu boulder