 Turn off your video and stay muted during the talk. The way the talk is going to work is that the speaker has 15 minutes for the presentation. I will then give a five minute warning to the speaker. That means you have five minutes to finish up. So that's be a total of 20 minutes. And then the last five minutes are meant for discussions and question answer. So without further ado, Jart, I hope I'm pronouncing your name correctly. The virtual floor is yours. Okay, thank you very much, Ali. Yes, I'm Jart Kruger from the Department of Physics, Victoria in South Africa. Ali, before I start, I just want to make sure my talk at 25 minutes. So I prepared for 20 minute talk. That's correct. 20 minute talk is correct. I will give you a warning when you're at 15 minutes. That's all. Okay, perfect. Yeah, so thank you very much for the kind invitation to give a lecture at this conference, and it's a privilege for me to actually give the opening lecture at this conference. I'm looking forward to participating in three days of stimulating science from African scientists because I believe that Africa has a lot of potential and there's a lot of potential that we are going to show in these two days. Okay, right. So since biophysics is a relatively foreign concept to most physics students in Africa, I wanted to give some introduction to this exciting field of research. In particular, I'll give a brief introduction to quantum biology and nano biophysics, which are relatively new research fields considered by many. I will focus mostly on quantum biology, which can consider the subdomain of nano biophysics. After a fairly brief introduction, I will give some examples for my own research in the context of photosynthesis and do this mainly from an experimental point of view. Okay, I guess that most of you might be asking what exactly is quantum biology. Quite simply, it's the application of quantum mechanics to biology. That is, quantum biology is the field of study that investigates processes in living organisms that cannot be accurately described by the classical laws of physics. And the emphasis here is on non-trivial quantum effects. Because obviously, at the molecular and atomic scales, all types of matter in animate or animate is governed by quantum mechanics. So we focus here on the special case of non-trivial quantum effects. The renowned science writer Philip Ball from England has declared some nine years ago in a nature news feature that quantum biology is a new field of science. And it may be key to practical quantum computing and high efficiency solar cells. This research field actually started much earlier. In fact, it developed more or less alongside quantum mechanics. And here are just three of numerous interesting historical highlights. In 1932, Niels Bohr delivered his famous Light and Life lecture at the International Congress on Light Therapy in Copenhagen in Denmark. And then, eight years later in 1944, Schrodinger published his well-known little book, What is Life? And then let's skip a few decades. And interestingly, Roger Penrose, whom you'll recognize as one of this year's Nobel laureates in physics, published a pretty controversial book in 1989, where he stated that consciousness is described by more than classical rules. In other words, it must involve quantum mechanics. Now, after 30 years of scientific advances, we know that this idea stated by Roger Penrose may be not so outrageous at all. I would then also highly recommend this headline review article, which reflects a little bit on the history of the field, but much more on the current state of the art and also the predicted future of cosmology. Here are a few examples of processes featuring non-trivial quantum effects in biology. And there are perhaps many more similar processes in biological systems. So far, it's been very difficult to verify experimentally the existence of non-trivial quantum effects in most of these processes, not for photosynthesis. These processes in photosynthesis, the primary processes of which I'm going to talk about today, they are the most vivid and convincing illustrations of quantum biology. Since these processes feature on the macro molecular scale, quantum biology can potentially have a huge impact on numerous technologies. What's very interesting is the fact that most of the key enabling technologies that the EU is seeking to realize are based on quantum mechanical phenomena, and they find examples in nature. In other words, mankind is desperately seeking technological solutions which already exist in nature. Here are a few examples of what life can do that we cannot do yet. To the time limit, I'm only going to flash this information to you, but you're probably aware of the fact that these presentations are available on the ICTP YouTube channel and on a conference page, or otherwise, if you want to have more information, please don't hesitate to contact me and I'll be glad to do so. Okay, let's go to the next slide. This slide shows a scheme of different hierarchies in biology, which I've shown here for plungs. You can see the plant cells here, and these green dots are the chloroplasts, and remember that from your biology classes, school, and then each of these chloroplasts. So there's an electron micrograph of such a chloroplast and a stacked membrane. And inside such a chloroplast and inside these membranes are the photosystems, which are collections of proteins occurring inside these membranes, and so on. So you see that these processes cover a typical length scale of about 10 orders of magnitude, and time scales ranging of 15 orders in magnitude. So this is already very interesting from a physics point of view, there's very broad range of spatial and time scales that can be accessed experimentally and by these simulations. And even more from the viewpoint of a physicist, proteins are extremely interesting molecules because they are situated right here on the border between the classical and the quantum regimes. Proteins feature very interesting objects for studies of quantum biology. And it's not very much interest to know how these quantum properties of them give rise to differences. Okay, let's now have a brief look at the proteins in plants, which are involved with the first steps of photosynthesis. Here is the photosystem one of plants viewed from the top, on top of the membrane. And for clarity, the proteins have been removed, and you see only the chlorophyll pigments here in green. They also round a reaction center in the middle. And the purpose of this so-called antenna system is to any large reaction center absorption cross section by two orders of magnitude. So after absorption of a photon, the excitation energy is first transferred amongst the pigments within the light harvesting antenna network. Then it's transferred to the pigments in the reaction center. And finally, the energy is trapped in the reaction center by means of charge separation. So let's now rotate the photosystem to 90 degrees to look at it along the membrane. And you see that the initial absorbed photo energy has been converted into a charge gradient or a potential difference across the membrane, which drives the rest of the energy fixation. And this whole process happens very rapidly within about 20 picoseconds in order to prevent charge recombination. And the quantum efficiency of this process is remarkably high, close to 100%, which means that the energy of every absorbed photon is used for photosynthesis. So when this process is repeated many times, you end up with an extremely powerful nanoscale by a battery. Students can calculate the electric field that is caused by four nanometers, the width of the membrane, and 300 millivolts. This is an extremely powerful electric field that is created through this process, just by means of a single charge separated event. Okay, these extremely high pigment densities in these photosystems give rise to so-called molecular excitons, which are excitations that are coherently delocalized over a few pigments. We have two coupled two-level systems. In this case, we have two identical parallel dipoles with identical energies. When the interaction between these two dipoles is much stronger than their interaction with a phonon environment, this gives rise to energy splitting. And when this system is excited by a photon, so when it absorbs a photon, the photo energy will be coherently shared by both states, as shown by the wave function of the product state. The physiological benefits of this phenomenon or the formation of molecular excitons is far superior to the best man-made solar energy materials. For example, molecular excitons give rise to more efficient light absorption, faster energy funneling, which is faster conversion from short to long-wave and spectral bands, faster energy transfer, and it increases the irreversible trapping of the excitations by the reaction center. In other words, the overall efficiency of photosynthesis is increased dramatically by the formation of these molecular excitons. Let me give you an example of excitons in the context of diatoms, which are beautiful unicellular organisms, which are amongst the most common types of phytoplankton, which you get in all types of water environments. So using synomolecule spectroscopy in combination with simulations and comparing the results with those of similar proteins in clones, we managed to demonstrate that these organisms use a much reduced exciton coupling string between three key chlorophyll pigments inside this light harvesting complex despite an extremely high pigment density. And this is done in order to enhance the light harvesting efficiency. This is quite remarkable that it's done by the system in this way because reduced exciton coupling, reduction of exciton coupling, specifically at this site within the protein system, should actually render the proteins more sensitive to disorder, and one would therefore expect their efficiency to drop, the light harvesting efficiency one expects to drop. But instead, these proteins are designed in a special way, a very special way as to utilize this reduced exciton coupling to actually enhance the light harvesting efficiency. Really remarkable what they are doing. Okay, in a second example, this is on a topic of great interest in the field. So when you consider that these parasitic systems are wet noisy environments, you would not expect any long term quantum coherence in these systems. But actually, there have been observations of long terms of several picoseconds actually of quantum coherence during the processes of energy transfer and child separation. And this type of quantum coherence is a different type of quantum coherence than the exciton states. So it's actually a quantum coherence of exciton states, or in other words, quantum coherence of quantum coherence, if you like. In the interest of time, I'm not going to dwell on this topic, but please do contact me if you'd like to know more because a lot of research has been done on this and there's a lot of interesting things that come into these processes. Okay, another topic we have embarked on is to coherently control excitation energy by using a pulse shaper to shape the intensity and amplitude of ultra short laser pulses. Now this works is that we use two pulses to laser pulses in a scheme known as pump probe spectroscopy. The first laser pulse excites the carotenoid molecule inside the main light obviously complex of plants, and then immediately after photo absorption two things can happen with the excitation. One is internal conversion, so just non-radiator decay of the excitation. The other is energy transfer to a chlorophyll, to chlorophyll A in this case. So now by shaping the first pulse, such that it interacts with the molecules for an extended time, this branching ratio can be controlled. And the two resulting states can then be proved by the second pulse to determine which state has been populated more. So the probe for the energy transfer to the chlorophyll is by means of ground state absorption and the probe for the internal conversion pathway is excited state absorption. So here are the two signals in a typical transient absorption spectrum. And when you now take the ratio between these two signals. And that the ratio between the amplitudes and you can calculate the fitness and we've managed to enhance this fitness of this ratio energy transfer over internal conversion by more than 20%. And the optimized pulse, the one which give rise to the maximum amount of fitness in this case is the one. Actually has a very interesting structure. So here is shown the intensity of this pulse as a function of time. And it consists of seven sub pulses separated by 180 femtoseconds. What this suggests is that one or two slow vibrational modes of the carotenoid which is excited. And so some of these vibrational modes are used to control the branching ratio between the two processes, the two states that can populate it. Okay, in the last few minutes, I'll give a very brief introduction to nanobiophysics. So what is nanobiophysics. This protein basically said it all, it consists of something nano something bio and some physics. Since proteins are both bio and nano, when we studied them using some physical tools we are actually practicing nanobiophysics. In fact, all the examples I've shown so far were examples of nanobiophysics so it's a pretty broad field. It's a strong fundamental scientific component to this research field and often also technological incentive. And then nano dimension is often strengthened by using metallic or semiconductor nanoparticles, such as what I'll show in the next example. So metallic nano nano rods specifically have two surface glass. Okay, thank you. Yeah, so metallic nano rods have two surface plasma modes, one along the long axis and one along the short axis. When you change the length of the nano rod, the absorption and emission spectra can be shifted quite substantially. In our recent projects, we have chemically synthesized gold nano rods, and spin coated them on a glass substrate. And on top of this LHG2, which is the main light opposite complex of plants, was spin coated. And the dimensions of the gold nano rods were chosen such that the absorption band, also longitudinal plasma mode, overlap strongly with the absorption and emission bands of LHG2 to ensure optimal interaction or resonance between them. We then investigated the distance dependent interactions between a single nano rod and a single LHG2 complex. And the physics behind these ideas as follows, when you excite a metallic nanoparticle, the electromagnetic field is confined to the near field. So the nanoparticle effectively concentrates the light to within tens of nanometers from the surface, forming a so-called plasmonic hot spot. So when we now put a single protein like LHG2 in this example, in or near the plasmonic hot spot at the tip of a gold nano rod, the photoluminescence got enhanced by two orders of magnitude, as shown here on the right, compared to the case where a single protein LHG2 protein was far from a nanoparticle. And this raisins enhancement is accompanied by a significant reduction in the raisins emission lifetime. So in other words, both the radiator and the non-radiative rates can be drastically tuned by using these surface plasmones. And the raisins enhancement is a product of excitation enhancement and emission enhancement. Parameters that can be separately tuned, for example, by changing the nanoparticle size, its relative orientation, and its distance from the LHG2 protein. In other words, these nanoparticles enable us to accomplish on-demand control of photosynthetic light harvesting. Right, in the last example, I'll show you really a cool experiment. We used light to switch a small protein called the orange carotenoid protein, OCP, to a photoactive state, which then allowed the protein to bind to a very large multi-subunit protein called pycabilisone to switch off its photosynthetic activity. All of this was done at the single protein level. Let me first demonstrate this at the bulk level. So OCP here inside a cuvette is first activated by blue light from an inactive orange form to a photoactivated red form. And this allows it to bind to the core of the pycabilisone complex. So let's look at the spectrum of the active state without the OCP unbound, but when the OCP binds to the core, this presence is quenched dramatically. So basically the photosynthetic activity switch off completely. So let's now illustrate this process at the single protein level by binding a single OCP complex to a single pycabilisone complex. Now using wild type OCP, we have managed to see in real time that upon blue light illumination how the presence is switched off completely. Now by using a mutant of OCP with a low binding affinity, we see not only how the presence is switched off, but also the full recovery after the presence in real time. So this is really fascinating. And what is even more fascinating is the fact that we can see a short living intermediate state between the active and the quenched state, both when the fluorescent switches off and when it recovers. And the spectrum of this intermediate state shown here in blue contains two bands, one very blue shifted band and one very red shifted band. On the right, I compare that I can pay two properties of this blue band. The degree of quenching and the amount of blue ship I can pay this with simulations of this process to get an idea of what would have happened. And what this shows the experimental comparison with the simulations shows that when the OCP couples to the pycabilisone core, the coupling between the subunits of the pycabilisone core significantly decreases. In other words, this process signifies a docking mechanism of OCP upon binding and unbinding from pycabilisone. And how this docking mechanism works is that after blue light activation of OCP when encounters of pycabilisone complex, at least one of the pycabilisone rods temporarily weakens its coupling to the core, possibly by rotating or physically slightly moving away from the core, in order to create space for this small protein OCP to bind to the core of pycabilisone. Okay, so let me wrap this up. And I have some take home messages, in particular for the students here. The experimental and theoretical tools offered by physics are leading to ground breaking discoveries in biology, so I hope that you have recognized this to talk. And quantum biology is an excellent example of how the tools of physics lead to a paradigm shift in our understanding of some biological processes. Then nanobiophysics is another emerging field with tremendous potential for fundamental scientific, as well as disruptive technological advances. And then this was shown in the context of photosynthesis, and I hope that I managed to convince you that photosynthetic proteins are extremely interesting systems from a physics point of view. So if I have another minute left, I just want to acknowledge everyone who has contributed to this work, the first of postgraduate students in my group, and some of them actually those who contributed to this specific work, and also the collaborators below. Some of the experimental work was done in Amsterdam, the pycabilisone and OCP samples were prepared in this lab in France, and the item samples were provided by Claudio Buchhol, and the LH2 samples were provided by Erika Belger from Alcatel. And of course, I would also like to acknowledge all the funders that were involved. And finally, the group members. And thank you very much for listening. I'm very glad to answer any questions. Thank you very much, Jart, for your very interesting talk. I have a virtual clap for you right there. Okay, so we have a better time for some questions. Remember that at the end of the session there's also going to be an extended longer time to ask questions but so the floor is open for questions. You can either. Okay, so there are a couple of questions rolling in from the chat. I'll start with the first one if I understand correctly. There was there was a picture you showed of a graph that looked symmetric intensity versus time. And yes, what the explanation is for that. Tensity versus. Oh, yeah, that one for the current control. Sorry, so the question was to explain more of what's going on there. Right, so yeah, it's very interesting that a symmetric graph was obtained. This was obtained from a so-called frog trace where you can see the full spectrum of the optimal pulse as a function of time. So basically, the whole pump pulse, so this is a two pulse experiment. The first pulse is the pump pulse. And the pulse which gave rise to an optimal fitness as you can see here is fixed out in time. So if we take this from this point to that point it's fixed out in about 1.2 femtoseconds, and it is symmetric about times zero, and it consists of seven sub pulses. The frequency of these sub pulses is 120 femtoseconds, more or less exactly, which means that what is actually happening during this process is that vibrational mode is driven. And since we have excited carotenoid, it must be a vibrational mode within this molecule, and 120 femtoseconds is relatively slow for vibrational mode. So these are vibrational modes in the backbone of the carotenoid. So somehow we are still doing more research on this. So somehow these slow vibrational modes give rise to the fact that the conical intersection between the two states into which this excited state can relax. This conical intersection is tuned by these vibrational modes. In other words, there must be some type of vibrational coupling with the excited states. And why it's so very symmetric, I think that is just very interesting from a physics point of view. And probably just because your most most process in nature are symmetric. And this is just a substantially the fact that symmetry plays a very important role in nature. I hope that this gives adequate information about this. If not, please contact me and I will definitely give you more information on this. Thank you. There's maybe time for just one more question. Omololo asks for an example in quantum biology where quantum coherence slash incoherence is important. Okay, I suppose that is referring to this long living quantum coherence between exit on states. I think we could go back there. It's a bit earlier. I'm sorry, let me quickly go to that slide. It's this one. Yeah, so I suppose that this process is referred to. So, um, okay, there's been a lot of hype in the beginning. I would say just after publication of this, this very first paper, and a lot of experimental and critical studies and that the current consensus in the field is that there is no such thing as long living quantum coherence of electronic of the electronic type. This coherence is of a vibrational nature. So actually, Raman type of vibration ground state vibrations, which is not interesting at all, but there is some indication of coupling between these vibration states and electronic states leading to so called electronic coherence, also extending to a few hundreds of 50 seconds or even bigger seconds. And this has been shown for excitation energy transfer inside this light obviously antenna complexes in all sorts of positive organisms ranging from plants to LG cyanobacteria or almost any type of system. And it has also been shown for the reaction center. So these are the biological systems in which this type of long term coherence has been observed, but they are also theoretical studies, which hypothesize that similar behavior must take place in some other systems that are typical in in my protubules. And there's also another type of process in in magneto resection and where the vibrational modes of environment also plays a very important, very important role to give orientation to a bird during long, long time flights for example from the northern MSP to the southern MSP. And there are a lot of these cases where the very specific vibrational mode of phone on modes in the environment, coupled to electronic modes and give a definite indication of physiological benefit to these organisms. Okay, thank you very much. We'd love to continue this discussion. We will leave it to the end of the session. Thank you again chart was very interesting talk. The next speaker is