 Hello and welcome to this next segment of CD spectroscopy and MOSBAR spectroscopy for chemist. My name is Arnab Dutta and I am an associate professor in the department of chemistry IIT Bombay. So, previously we are discussing the different aspects of chirality, we found chirality is being present in nature for long time. And over there we found in biology, chirality comes through the different fundamental molecules that is found in biology. These are amino acids, carbohydrates and nucleic acids. And over there in the previous segment we have discussed how the molecular recognition happens partly through this chirality especially through lock and key mechanism or antigen-antibody interaction. Over there we have found that this chirality controls the extent of different interactions like hydrogen bonding, hydrophobic interaction, salt bridges and weak forces. And this chirality controls it by creating a directionality in this particular molecule. Because over here when you have a chirality you can either have a lamin acid or damin acid and their phases are in differently orientation. So, with that they can create a lot of interactive measures and regulate it which particular system will be much more preferred. And by that they can differentiate out of 100 molecules which of the molecule it would like to interact. So, with all these things coming into the picture now we understand yes chirality is a key tool for biology in terms of molecular recognition. Now, the problem we are facing that to have this fundamental question where and how this chirality become a part of this biological system. That is the question we would like to answer in this particular segment. So, before going into that details let us look into chirality one more time. So, when we say chirality again by definition it is a mirror image of a particular object and it is such that the mirror images are not superimposable indistinguishable. That is what we learnt and from a symmetric point group we know which says that the molecule cannot have any particular Sn axis present in that molecule which bring us down that the molecule should belong to Cn or Dn point group n can be also one for the case of Cn. So, that we have learnt so far and one thing we also found that chirality can be detected only by a chiral environment. Otherwise the two mirror images which are known as enantiomers and say I have two different enantiomers enantiomer A and enantiomer B which are very much similar molecule the only thing different is their stereochemistry their mirror image to each other and that is not superimposable or indistinguishable. Now, along with the properties of this enantiomer A and B all the physical properties will be very much similar all the chemical properties also be very closely similar the only thing is going to be differing when you put them in a chiral environment. So, only chirality can distinguish between this enantiomer A and enantiomer B and that is why even when you actually producing a chemical. So, during the production which typically do not use any chiral environment and what we got is 50 percent enantiomer A and 50 percent enantiomer B. So, you cannot avoid it they will always be present 50-50 and if you are doing that reaction the production in a synthetic system which is a chiral in nature that is not chiral what we are going to get is 0 percent energy excess this is called the enantiomeric express. So, you are not going to get any enantiomeric excess both of them will be same. So, we will get a racemic solution. However, if we create an environment which is chiral in nature then I can distinguish between enantiomer A and enantiomer B. So, now just imagine enantiomer A and enantiomer B both are acidic in nature. So, they are enantiomeric acid now if I put a chiral environment and another enantiomeric base then these two enantiomers will interact with them because the environment or the other components chiral these are also chiral during their interaction they will start differentiating because they are going to form diastereomers as the intermediate and diastereomers as you know differ in the reactivity. So, the chiral environment provides the solution to create the room for generating the diastereomers and with that we can separate out enantiomer A and enantiomer B that means we can actually get an enantiomeric excess at the end. So, that is what is actually done in the actual chemistry we try to create a chiral environment for an example we are actually having enantiomer A and B almost at same level we want to separate them we actually use a chiral column which actually creates the environment. For an example the drug design we have gone through the different drugs like ibuprofen and all those things and over there we found this ibuprofen is chiral in nature but there are two different enantiomers one is the actual drug otherwise remains inactive. So, if I want to separate them we have to go through a chiral environment otherwise we cannot separate the two enantiomers we have to create an diastereomer by creating a room of chirality. So, if that is actually coming into the picture and now if I go back to the environment or I should say nature you will see there is a huge amount of enantiomeric production. Now the question is how it is doing enantiomeric production by the nature and however we found most of the time they have exclusively one isomer or I should say enantiomer is preferred. So, that actually gives an idea that where I am doing these reactions in the nature they are actually creating chiral environment and that is first the reason in the nature when you are doing an experiment we are getting exclusively one particular enantiomer. Now the question is when you are talking about chiral environment in nature it began at one point of time right now it is happening in these metalloenzymes which are chiral because they are made out of amino acids or carbohydrates or the nucleic acids also in certain times they are chiral. So, I know they are going to create a chiral environment and we will be going to get exclusively or preferably one of the enantiomers but the question remains same where it all began. So, one of that idea was this chirality may be triggered by extra terrestrial that means this chirality is actually not from the earth itself it actually has come from outside the world. So, is there any proof? So, one of the proof that we are going to discuss today is known as marcheson meteorite. So, marcheson meteorite is actually a meteorite actually came from outside the world and it actually hits in the place named as marcheson this place is situated in Australia and this particular phenomena that the huge meteorite is hitting on the earth at marcheson it happened in the year of 1969. At that time is huge meteorite hits the overall weight of the meteorite that was intact even after the heating was close to 100 kilo that means quite a large amount of meteorite. Meteorite falls on the earth all the time but most of them are so small that they got vanquished during their coming through our stratosphere. But over here some of them actually survives and large enough quantity so that we can do a lot of experiment marcheson meteorite is one of them. So, when this particular meteorite hits the earth at marcheson it actually got fragmented and some of the fragments are in grams, milligram some of them are larger amounts like 7 to 10 kilos and all together when it combined together it is a 100 kilo mass unit. And this mass unit was collected very nicely without any contamination very quickly and transferred it to a lab and in the lab that is going tested. So, now you will be curious to know what is there present in this particular meteorite. So, other than the common factors like rocks the salts and the alams one important thing comes over there there are a lot of organic chemicals and what are those organic chemicals present over there those are actually serine, glycine, alanine, glutamic acid, leucine, valine. So, those are the different amino acids found to be present in this meteorite and very interestingly what we also found that other than glycine which is a chiral one all the other amino acids which are chiral in nature they are present in enantiomeric excess that means this molecules is preferring one amino acid or the other. When you look closely found there are both L and D amino acids are present but they are favoring the L amino acid. And one of the hypothesis is that millions of years ago some of the meteorite falls on the earth which actually has this L amino acid and at that time earth was a hot soup where we actually having a lot of chemicals around us and they start forming this initial part of the biomolecules. And at that point of time the presence of this chiral amino acid which is present in that system around that time probably coming from other extraterrestrial bodies and that actually creates that chiral environment that we are talking is very much needed to create this enantiomeric differentiation. And this enantiomeric differentiation is then favored and we got as a product one of the enantiomers more than the other. And that is possibly what is happening over here and marcheson meteorite is one of the examples of it. But very interestingly when we are looking into the marcheson meteorite in further details we found these are the amino acids we already found even on earth. So they are all present but additionally there are some other amino acids. So let us take a look what are the other amino acids present in that system. And we found they are majorly hydroxyl group bound system. So there you can say derivatives of serine which actually has a side chain of CH2OH hydroxyl group. So now let us say in this marcheson meteorite which is coming from out of the world they are actually having some amino acid which is typically not found on earth typically not found on the biological form in the world. So what are those? This is a hydroxyl group secondary hydroxyl and this is the alpha carbon the chiral carbon and the name of this system is isoserine. So you can see that over here the amine group is moved one side up and this hydroxyl group comes over there. So amine and OH group you can say they swap the places from the actual serine machine. So it is isomer of serine and it is also having a chiral center over there. Then comes the next one which actually contains the amino acid we know for but instead of CH2OH this molecule is CH2CH2OH. So there are 2 CH2 groups over there and this is the alpha carbon. So let me draw that properly. This is the alpha carbon and over there you can see there is one extra CH2 comes into the picture compared to the serine. So the name of this is homoserine and it has been found also in enantiomeric excess due to the presence of this alpha carbon. So all of them are present in marches and meteorite and not only that they are present enantiomeric excess wise that means one of the enantiomer is favored. The next one is the following CH3 and over here this is the group so NH2 group and OH group are present over there in this molecule and this is you can say a derivative of 309 so we call them iso 309 and then there is another version of this particular molecule is the following very much similar looking structure CH3 over here, CWH over here, OH over here but over here the NH2 group changes position and over here you can see there are 2 different point groups in this molecule. So obviously it is going to be chiral and again this chiral molecules was found in marches and meteorite with the one enantiomeric excess and the name of this particular molecule is allo iso 309. Then we have certain more amino acids present that will you go one by one this is a chiral center over here and this known is 4 amino 2 hydroxybutyric acid. So take the first state of each name and the name comes as 4A2HPA. The name is coming from this way because this is the carbon number 1, 2, 3, 4 so 4 carbon so that is butane chain because it is an acid over there it called the butyric acid number 1 positioning is from carboxylic acid that was the preference then number 2 is this 3 and 4 and over there we just write down the name of the position 4 amino 2 hydroxybutyric acid. And there is another one very similar and over here the position of the OH changes it comes over here so that is the only change. So the name will be very similar it is still 4 amino 3 hydroxybutyric acid in short form 4A3HP. So this is also been found in marches and meteorite. So you can see they are all different versions of hydroxyl base amino acid and there is one other more we can see it over here that will go to the next one is the following carboxylic acid is very much similar to the previous ones but over here OH groups go to the terminal NH to go come into the middle of the molecule and this is still a chiral center and the name of this molecule is beta homosurin. So you can say it is a beta amino acid is presenting alpha beta so beta amino acid. Then comes the other one so over here we are just putting this carboxylic acid in one place or the other and changing where is the chiral carbon the name of this amino acid is 3 amino 2 hydroxy methyl hydroxy methyl because it is a methyl group present over there hydroxy methyl propionic acid in short form 3AHPA. So it is the number one carbon over here then 3 so it is a 3 amino that is why it is a 3 amino 2 position is the hydroxy methyl group over here and the rest of the name is propionic acid 3 membering. So that is what is coming over here there are the other two amino acids you also found over there these are the structures so then these actually alpha amino acid but the name is alpha methyl serine because we have learned that in the amino acid alpha position you have one hydrogen one R group on carboxylic one amine over there is no hydrogen connected to this alpha carbon so it is a little bit modification of that and then comes this one carboxylic acid group then we have an NH2 group over here and there is another carboxylic acid group. So this is a version of succinic acid and the name of that is beta amino methyl succinic acid and over here this is a alpha carbon. So you can see in this meteorite molecule we have samples from different chiral molecules which is mostly the hydroxyl group bound systems which is showing that there is possibly a interaction with the water molecules to create this particular set of molecules and this kind of give us a hint that there is a possibility that yes is a possibility that the first chiral molecule probably came on the earth from as an extra terrestrial source and secondly this probably triggered the prebiotic organic synthesis and it also showed that the initial presence of this chiral molecule creates the chiral environment which possibly lead us to the formation of L amino acids or D carbohydrates. So that is possibly triggered those systems and create this chiral environment around the world. So with that in this particular segment we have shown you that what is the exciting world of chirality and how it has been created and now the question comes how do you monitor them and that is why the circular dichroism come handy and give us an idea how we can monitor the different amounts of chirality if one chiral molecule transfer to the other can we follow that with CD spectroscopy or not. So those are the things we are going to follow in the next coming days and with that we would like to conclude this session over here. Thank you. Thank you very much.