 Okay, thank you for the introduction first after I successfully managed to show my presentation full screen. I would like to thank the organizers for the efforts they spent to organize this nice event. As you already heard from the introduction, I will going to talk of Docs Rubisin and its interaction with biopolymers. In this particular case, those polymers are alginates. I will briefly introduce each of the components of the simulated systems and I will start with the drug which has been on which we were focused. The drug is Docs Rubisin, which is a member of anticycline class of anti-cancer agents. It shows broad spectrum of anti-cancer activity, but there are some troubles using according to the recent researches. There are some troubles with this drug directly and as a drug, it needs some other transporters or some other systems which controls the availability of the drug in the body. And one of the systems which offer such dosage of the drug and transport of the drug are nanoparticle systems. In this particular case, the nanoparticle systems are chitosain alginate nanoparticles. They are attractive platform for Docs Rubisin loading because those polymers are biocompatible and non-toxic. Because there are also some studies for Docs Rubisin loaded over some other particles, even carbon nanotubes or modified mesoporous silicate materials and stuff like that. But here the studies focus on chitosain alginate nanoparticles. The recent experimental results show that these particles loaded with Docs Rubisin provide better accumulation. Do you see the pointer of it also? Yep. Good. So these nanoparticles also provide better accumulation of the drug and longer solute toxic effect of this encapsulated Docs Rubisin in study of melanoma cell lines compared to the free drug. And here are electron microscopy of such particles loaded with the Docs Rubisin. And now I go to briefly introduce the biopolymers, alginate and chitosain. Those two polymers are biodegradable, bioadhesive. They are having basically very similar chains. Their chain is made of carbohydrate rings of pyranose type. The difference between these two types of pairs comes from the functional groups attached to the chains. In the case of alginates, these are carboxylic groups which at certain conditions may deprotonate and bring a negatively charged, negative charge on the polymer. That's why they are called basically anion. The other side, the chitosain has amino groups attached to the pyranose rings. These amino groups at certain conditions can be protonated and they bear some positive charge on the polymer. The aim of this study was to understand, was actually to understand the interaction between the components of this alginate chitosain nanoparticle and Docs Rubisin drug. In order to achieve our goal, we performed the molecular dynamics simulation with a gross-type force field, a specific version for a 7 which is parameterized in a way that represents better the pyranose conformations of sugars, but also it is parameterized quantum chemical calculations to represent better the function of the polar functional groups attached to the polymer chain. For the long-range interaction, for the long-range electrostatics and Van der Waals interactions, we applied the Particle-Mesh-Everald algorithm. Time step of quantum production runs of 100 nanoseconds was analyzed after that. We started with the investigation of the doxin in water. How does this drug behave and whether we may see some intermolecular interaction between the molecules of the drug. For this purpose, we started a simple system which can taste six drug molecules placed randomly in a box. Then we run the simulation and found actually that at some point, some small aggregates of dimer or trimer started to form. And finally, we found a stable stack of five doxorubicin drug, dox molecule, which you can see also here on the large figure. This stack of doxorubicin molecule is stabilized by pi-pi interaction between the aromatic and the quinone part of the drug, in such a way that the polar group in this stack pointing toward the solid. This is such that the doxorubicin molecules was observed experimentally in 1984 where the with the metroscopy methods was estimated also the dimerization constant of doxorubicin molecules. In this particular case, we observed that the stability of this text is governed by the pi-pi intermolecular interactions. For the biopolymer for alginates, we used oligomers, which contains monosaharite residues, which is shown here on this picture, and we studied several different ratios of doxorubicin drug to alginate molecules in the system. Here are some of the results for the simulation with different doxorubicin to alginate ratio. When we have a three to two ratio here on this figure, we observe the interaction between the drug and the polymer in a way that somehow coordinated to the polymer, and those drugs are spread around among the say they do not see each other, they do not interact each other. This was observed also for the situation where we have a two doxorubicin and one alginate, but if we increase the amount of doxorubicin as in the case of four to three ratio, we already observed the aggregate of doxorubicin, which are surrounded by alginate molecules. And when we increase the number of doxorubicin, it starts also to attach to the surface of the alginate molecules, already one of the stack of the doxorubicin. In this way, we observed this aggregate formation of doxorubicin and the arrangement of the doxorubicin molecule in this aggregate is very similar to the one that we observed in the absence of alginate. In order to clarify or to clarify the contribution of the electrostatic interactions between doxorubicin and alginate, we extracted from the simulation data the interatomic distances between the charged nitrogen centers in the molecule of doxorubicin and negatively charged carboxyl oxygen center from the molecule of alginate. Here we present the results for two systems, four to three ratio doxorubicin to alginate and 12 to three systems. We observe a fraction of distances in the range of 2.9 to 3.9 angstroms, suggesting close location of the charged centers. And from here we may conclude that the electrostatic interactions to the binding of doxorubicin to alginates from those plots and the system with the four doxorubicin molecule the area above the which is shown by the dashed line, this is the integral of the radio distribution functions show that it shows that between two and three of the drug molecules are interacting electrostatically with the alginate while for the higher doxorubicin amount, the amount of those groups increases to five. And this type of electrostatic interaction also is consistent with the observation of decrease of the negative zeta potential of nanoparticles, alginate nanoparticles loaded with doxorubicin and this decrease of the zeta potential is about 33 when the nanoparticle is loaded by doxorubicin. We also check whether the solvent accessible surface area of doxorubicin changes when it is together with alginate or without alginate in the water environment. In this slide here is shown the, okay for this rearrangement here, but on the y axis is shown the solvent accessible surface area with a system containing 12 doxorubicin molecules in the water with a blue line and one can see that upon stacking this surface area accessible surface area. A decreasing and at some point when the stakes are stable, it remains constant. Well, in the case of a system of doxorubicin with alginate, we observe that due to the additional packing of the doxorubicin by alginate the accessible surface area of doxorubicin from the water for the decrease. And this system looks like that here in the middle with the green sticks, green wire are shown the doxorubicin which are surrounded by the alginate oligomers. To simulate the system with all its components, we also added the chitosan to the simulation box and simulate the system which contains three alginate oligomers, six chitosan oligomers, six doxorubicin molecules randomly distributed in a box. To see whether the chitosan or there will be some competition between chitosan and doxorubicin in the binding to alginate because of the electrostatic. It turns out that after the during the production run of the simulation we observe a stable state where doxorubicin stack by doxorubicin molecule represented in red color here are stacked together and packed by alginate molecules, alginate oligomers. The difference is that chitosan molecule, chitosan oligomers stays on the on the on the surface of this stack and actually they bind to the unsaturated by doxorubicin negatively charged carboxyl groups and and they actually do not mix together with the doxorubicin to form the cluster which is surrounded by alginates. The analysis of the stack size of the stack in this simulation after let's say 15 nanoseconds of the simulation we have a stable stack of all molecules in the system. Well, the only the doxorubicin molecule is, I mean, it increases starting from in the beginning, there is a stack of two doxorubicin molecule increases to four, then stays stable to five and with some fluctuation to six. The stack of the doxorubicin, which means that the doxorubicin molecules stacks together and they are surrounded by the other by the biopolymers and if this is for the charged groups, we observe much larger amount of close close contacts between positively charged proclamino groups and carboxyl groups from the alginates and from doxorubicin and chitosan as well. In conclusion, I will say that doxorubicin form clusters, which are stabilized by pi pi interactions, and these are packed by alginate molecule mainly oligomers, mainly due to electrostatic interactions via charged groups in both polymers. The chitosan interacts with the alginate and compensate negative charge of the carboxylic groups in the alginates and the mainly electrostatic interaction between the components, the stability of the doxorubicin and alginate complex depend on the change of the pH. And here, as we can see, the result from doxorubicin release from such nanoparticle in different pH value shows that indeed at lower pH, where the increase, the release doxorubicin is amount of doxorubicin is larger. So pH, where the interaction between the charged group is much stronger. Okay, that was all I wanted to share with you and thank you for your kind attention. Thank you to Professor Apetkov for the informative and interesting lecture. Till now I can't see any question in the chat, but please feel if you have any questions now is the moment to tell them and share the opinion. So now I see a question from Professor Ivanova. Did you observe dissociation of cues from the form clusters? For the time of the simulation we have performed we saw people stack of five to six doxorubicins in the cluster and for this cluster we didn't observe dissociation. For the larger, which are for the larger system where we have a 12 doxorubicin in the box, we observe several cluster, not one cluster of 12 doxorubicin molecules. So there is definitely some size dependence of the cluster with respect to the number of doxorubicin molecules, but we didn't study in detail of this process. Thank you. Any other questions? I don't see any others. So thank you to Professor Apetkov for his present. We can proceed with the next coming, although we have some more minutes.