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Module 1: Chemistry of Carbohydrates

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Hello everybody and welcome back. So, we are discussing the carbohydrates and carbohydratebased molecules that can have various applications. So, basically, I will start today with the importance of the nanomaterials or now, which we can call nanomedicine or nanobiotechnology you can say even nanochemistry. (Refer Slide Time: 01:54) So, that basically covers the area of using or developing new nanomaterials or new nanoparticles or nanomaterials for biological applications such as drug delivery, such as using the molecules themselves as the medicines, such as in order to study several binding property activities inside the cells, taking probe molecules into the cells in a nanoparticle format. And since we are talking about this, the most abundant amount of nanomaterials or a nanoparticle that has gained enormous importance are the metal-based nanoparticles. So, I will just talk very briefly without these metal-based nanoparticles, I think nanobiology or nanobiotechnology or nanomedicine is incomplete so I will very briefly talk about this and then will conclude metal-based nanoparticles have gained a lot of importance nanochemistry in general and particularly nanomedicine. For example, silver nanoparticles. Silver nanoparticles show a very good amount of antibacterial property. Similarly, gold nanoparticles, they have actually, for certain types of cancers, show a pretty good amount of anti-cancer activity. So they are used as therapeutics. So they have a therapeutic activity to kill certain cancer or tumor cells. So, gold nanoparticles in literature, you will find there are many different types of gold nanoparticles that have been synthesized that have been developed and people are doing research on them many of those varieties, so pretty good activity against the tumor cell lines. Similarly, nowadays, copper-mediated nanoparticles. Especially copper-based nanoparticles, especially, the copper nanoclusters, this will very good biological activity. Anti-bacterial anti-tumor or both In general biological activities lot of cellular studies have been performed using the copper nanoclusters. (Refer Slide Time: 07:22) And today a lot of people are trying to develop even iron nanoparticles. Iron nanoparticles have one particular property that they are magnetic in nature. So they are usually called being called magnetic nanoparticles. Magnetic nanoparticles and they are being used to treat certain types of virus to kill the virus. Viruses and bacteria because of this, are magnetic properties they are being used to destroy certain types of viruses that have themselves certain magnetic activity or the bacteria. So, these are some of the examples of the nanoparticles being used in medicinal chemistry or nanobiotechnology. So, now, the question is how these nanoparticles are usually synthesized. So, as I have mentioned nanoparticles usually have the size range 1 nanometer to you can say up to 1000 nanometer for biological good biological activity, it usually should be between 1 to 100- nanometer particle size and nanoclusters have a larger size than 100 nanometers, but they fall within 1000 nanometer maybe 300, 400 nanometers sometimes. So, what you are actually doing here is you are using certain components you are using a chemical, for example, these metal things metal-based compounds and you are reducing the size of the metal that is done usually. So, for example, if you take silver if you consider the synthesis of silver nanoparticles, then initiate, you take salt of silver, maybe a silver nitrate salt. So this is a salt, where silver exists in the +1 oxidation state. Now if you can reduce these under controlled manner reduction, then you form silver 0. And if you have a particular type of environment here environment there that actually forces these particles to reduce their size or to aggregate or disperse, but it will reduce their size and that is when it forms nanoparticles. So, silver 0 oxidation state will exist as silver nanoparticles Ag nanoparticles which will be surrounded by it is the environment and most often the environment is the reducing agent that you have used that is the first environment actually surrounding environment. So, you can use chemicals typically if you want to reduce silver nitrate to silver 0, you can use reducing agents such as sodium borohydride, then it will be surrounded by counter enhance and that will be the first reason for the formation of silver 0 into nanoparticle form or quite often, once these nanoparticles are forming, they are not quite stable. So, you need a certain stabilizing agent and here we usually use large macromolecules so, that will further stabilize the nanoparticles I will show one example. So, this is your stabilized nanoparticles. (Refer Slide Time: 12:30) For example, if you want to synthesize gold nanoparticles typically people start with gold oric chloride. HAUL 4 is a liquid that makes a solution of gold oric chloride and then we use a reducing agent here. Sodium borohydride so you take a test tube add gold oric chloride add sodium borohydride in a formal medium keep on staring for some time, it depends upon your reaction conditions, it can take from minutes to hours, but it finishes usually typically either half an hour to 1 hour it will be done most of the times then you will have gold 0. And then if you use a certain stabilizing agent, the most common stabilizing agent people use is citrate. Citrate base basically cyclic acid structure, this is OH COO-COO - I think, COO minus. So that way you can surround the gold with the charge density and here you will have all the negative charges on the surface because of the carboxylate enhance and that is the reason why gold nanoparticles are formed and gold nanoparticles have usually very small size. You can even purchase nowadays golden nanoparticles from 5 nanometers of to 20 nanometers or maybe 50 nanometers. So, it can be as small as 5 nanometers it can go large also. (Refer Slide Time: 14:39) So, I will show you this is how it looks like, but this is not citrate stabilized this is another gold nanoparticles we have synthesized in our laboratory. This is basically we have done using the polymer-like chitosan we have used. So, this is how it looks like when the nanoparticles are synthesized this pink color actually demonstrates that you nanoparticles have been formed. And in this case, the nanoparticles are dispersed well dispersed in the solution and are not precipitated out because this is typical for gold. Because gold nanoparticles are so small that you cannot usually precipitate it out they are dispersed in solutions and they are so, color. The reason for this color is you can read a little bit that is surface plasmon resonance because of a particle, particle interactions basically, surface plasmon resonance is the reason why the nanoparticles so colors and you can pretty much see them in if you take and if you are visible spectroscopy. You can see where before gold oric chloride does not show any we went. Once you started synthesizing then the nanoparticles are new nice bend will come up that is the responsible for this color and this bend is because of the surface plasmon resonance bend. So, the problem here is if you want to use these nanoparticles for biological purposes, then these nanoparticles have to be nontoxic. That is the first criteria and when as I have said when you using the reducing agent, the reducing agent stays on the nanoparticles it provides an environment it provides an interaction factor. So, it stays with the nanoparticle that is synthesized and these reducing agents are toxic. These are pure chemicals. So, ideally, the nanoparticles that are being developed using the chemicals as the reducing agent are not good for application into biology. So, nowadays that is why people use natural products such as chitosan such as Aloe Vera such as silk such as citrate. Cyclic acid is also a natural product often and does not source much toxicity. So the use of those materials is as reducing agent and they also act as a stabilizing agent also. So I will show you just for example if you take the example of a chitosan reducing agent plus stabilizing agent both. So, if this is your chitosan you have amine roof here, amine group there and here you have the hydroxyl groups as well. So, those hydroxyl groups are also responsible for reducing your nanoparticles. If you use; gold oric chloride and without the reducing agent you can develop a method without using another chemical as reducing agents. It will you have to do such certain kinds of optimization to use this then you will have gold nanoparticles surrounded by chitosan here would be amine he would be amine so, positives. Basically, when you are using this acid, the chloride basically has an H + also. So, that will protonate amine into an NH3 +. And those captions are responsible for stabilizing the nanoparticles for stabilizing that forces the particles to be in the nanoparticle form. And on the surface, you can have the other ones on the unreacted amines can be there hydroxyls that are present they can be there. So, depending upon what agent what polymeric component you are using, it can be chitosan. It can be PEG which is polyethylene glycol. There are many it can be peptides you can synthesize nanoparticles with a stabilizing agent and they are supposed to be nontoxic in nature because you whatever you have used throughout is kind of natural units and such kind of nanoparticles have advantages. Number 1 is, of course, I have talked about the nanoparticle itself, for example, gold has antitumor activity. So, you can use this itself to kill the tumor cells. Number 2, since you have stabilized or since you have recovered your nanoparticles or nanoparticle are merged with the macromolecular structures. You can do a lot of chemistries on the surface of the nanoparticles. So, here you have hydroxyl if you use something else, you can have carboxylic acid and here you have already amines it is here. So you can attach the targeting moieties or other kinds of components that you want, you can add as peptide here, you can change its viscosity, you can change its solubility property by adding either the hydrophobic group if you want it to be more insoluble, you can add the more hydrophilic group in order to make it more dispersed or more soluble you can add DNA to it lot of studies have been done a lot of nanoparticles have been synthesized. Where DNA is attached to study different activities, which is including the single point mutations. Gold nanoparticles have been enormously used and very nicely used actually, to find out the presence of a single base mutation in DNA. (Refer Slide Time: 21:54) And gold has another kind of property that when they are in dispersed mode hold 0 nanoparticles, not silver gold. So, gold nanoparticles in disperse they are so pink color as you have seen this color. So, that is the dispersed nanoparticles pretty transparent you can see now if you vary the concentration and make it denser this is also gold nano but aggregation because of high concentrations the atoms aggregate the nanoparticles aggregate. So, this is aggregation the reason for aggregation is various it can be automatic interactions or it can be the interaction between the surfaces the functional groups present in the surface can interact with each other also. So, these are the functional groups present on the surface. So, depending upon your choice you can make your surface in such a way that it will facilitate aggregation. So, for example, those who are biologics maybe knowing that biotin-avidin binding is very strong and people in biotechnology in bio in chemical biology, this is one of the oldest techniques if you want to study binding between 2 components, one component is attached with the biotin other component is attached with it avidin so, that you will know that they will come instantly closer together. So, here also such kinds of tricks have been used to make the aggregation so, if you have a mixture of biotin stabilized gold and another one is avidin stabilized gold then if you mix them together they will immediately form aggregation. So, you will have gold aggregation and this aggregated gold has a color of intense blue, intense blue color you will get. So, this change of color you can measure of course using spectroscopic techniques using the UV. This change of color is also a way to study different biological aspects. And this is what has been used very nicely to find out the presence of a single-base mismatch in DNA. For example, if one gold nanoparticle you attach with a single-stranded DNA and another golden nanoparticle you attach with another SS DNA single-stranded DNA. If these 2 are complimentary then you will have hybridization perfect hybridization and that will give you aggregation. So, it will show you blue color this is pink, this is pink gold mixed together that will give you a blue color. If these are not matched properly, if there is a single presence of mutation here, then they will not aggregate. So, and you will not see the blue color. So, like that this is the plant I have explained, there are a lot of tricks in it. So, these kinds of phenomena have been used very nicely to study a lot of biological activities a lot of chemical activities as well. So, like that, you can develop many nanoparticle materials. And one important thing I forgot to mention I should mention is that you have stabilized these with the polymorphic metrical another reason of using such bulky large structured material is that because of their hydrophobic filling property or sometimes they have hydrophobic property, you can make use of them to encapsulate or to trap small molecules, such as drugs. I have talked about using only the nutrition or only the macromolecule and the drug. Now I am talking about using the metal nanoparticles stabilized by this macromolecule and encapsulated drugs. This is where most of the drug delivery applications came. So, you can have if you have your drug hydrophilic, then it can easily be entrapped on the surface because these are hydrophilic in nature now, to some extent, so your drugs can be encapsulated here, and then the whole thing as a nanoparticle form will get into the cell. If your drug is hydrophobic, then you can make these things hydrophobic by attaching the long carbon chain hydrophobic carbon chain, and then your drugs will be inside will go inside if these are hydrophobic in nature, drugs can be found here. So and the whole thing stays as a nanoparticle kind of form quite stable. And then you can take that into the cell. So drug delivery applications are huge when it comes to metal-based nanoparticles. So, with this, I will conclude this module. (Refer Slide Time: 27:37) This is how the size of the nanoparticles look like. This is the 200 scale. This is called FETEM fuller electron transmitted electron microscopy. Transmitted electron microscopy is TEM and TEM is the Fourier Transform factor. So this is the size of the nanoparticles. This is the size of the nanoparticles, this is some of our pictures actually if you look at a single nanoparticle. This is the size which means this basically is around 50 nanometer. So, this is well within the 100-nanometer range and we have synthesized by modification of the chitosan with the drug there. So, like that it is so if you read it in a high hand machine, it will show you the image like this. So, with this, I will conclude this module. Thank you.