TIFR
Department of Chemical Sciences
School of Natural Sciences

Calender

April 20, 2021 at 5.00 pm (Via Zoom)

Title :

Ultrastable organic fluorophores for single-molecule research: part II

Abstract :

Single-molecule Förster resonance energy transfer (smFRET) imaging is an integral tool for examining conformational and compositional processes critical to the functions of biological systems. Robustness of smFRET imaging and reproducibility of smFRET efficiencies are increased through photostabilization of fluorophores, state-of-the-art instrumentation, data analysis, and stringent data correction procedures [1,2]. Here, we report that small molecule photostabilizing agents in imaging buffers are although important for photostabilization of fluorophores, they can be bottlenecks for quantitative smFRET imaging due to their varied photophysical and photochemical impacts on fluorophores. To mitigate these problems, we provide a simple strategy of using ‘self-healing’ organic fluorophores that are intramolecularly photostabilized by cyclooctatetraene (COT) as a triplet state quencher. COT-mediated self-healing mechanism enables robust determination of true smFRET efficiency of organic fluorophores on both nucleic acids and proteins in oxygenated as well as in deoxygenated imaging buffers. These findings conceptually advance our understanding of smFRET and provide strategies for robust, quantitative smFRET imaging [3].

[1] Hellenkamp et al., Nat. Methods, 15, 669–676 (2018).

[2] Lerner et al., eLife, 10:e60416 (2021).

 

[3] Pati et al., manuscript to be submitted.

 

April 19, 2021 at 5.00 pm (Via Zoom)

Title :

Ultrastable organic fluorophores for single-molecule research: part I

Abstract :

Photophysical performances of organic fluorophores in modern imaging applications, including single-molecule and super-resolution fluorescence microscopy, are compromised by their transient excursions to dark triplet and radical states causing stochastic photo blinking and irreversible photobleaching. To circumvent these problems, we develop and study “self-healing” organic fluorophores, in which the dark triplet states are intramolecularly quenched by triplet state quenchers [1,2]. This intramolecular photostabilization approach dramatically increases fluorophore brightness, signal-to-noise ratio, and photostability, while simultaneously reduces phototoxicity by decreasing the generation of reaction oxygen species. The performance enhancements of the fluorophores enable us to achieve robust, submillisecond recordings of protein dynamics using wide-field illumination and camera-based single-molecule Förster resonance energy transfer (smFRET) techniques reaching the theoretical speed limit of camera-based detections [3]. These findings extend the potential to image single molecules in vitro and in live-cell applications in the absence of solution-based photostabilizers at physiological oxygen concentrations in the kilohertz regime [3,4] and shed important light on the multivariate parameters critical to self-healing organic fluorophore design.

[1] Altman et al., Nat. Methods, 9, 68–71 (2011).

[2] Zheng et al., Chem. Soc. Rev., 43, 1044–1056 (2014).

[3] Pati et al., PNAS, 117, 24305–24315 (2020).

 

[4] Asher et al., Nat. Methods, doi:10.1038/s41592-021-01081-y (2021).

 

April 9, 2021 at 6.00 pm (Via Zoom)

Title :

Mechanistic investigations of high-valent metal intermediates of biomimetic non-heme model systems

Abstract :

Metalloenzymes are known to play pivotal role in catalysing a plethora of biological and biochemical reactions. These transformations are directed by a variety of high-valent reactive intermediates that undergo crucial redox reactions by atom-transfer or electron-transfer or radical reaction pathways. These high-valent reactive intermediates of non-heme model systems are known to be influenced by factors like coordination motifs and topology, ligand architecture, pH, spin states of metal ions, solvation and temperature.1 The factors that govern the reactivity profiles are often associated with the mechanistic pathways followed. Hence, it is important to dig deep into the mechanistic details of the reactions performed by these model systems.

Non-heme iron-oxo intermediates have been identified as potential reactive intermediates in a variety of electrophilic reactions. It can catalyse C-H activation reactions and can also undergo heteroatom oxidation. Subtle modifications in a ligand skeleton can be seen to hugely accelerate reaction rates catalysed by non-heme iron-oxo complexes.2 Also, with the help of a series of structurally tweaked ligand frameworks, the governing factors that orchestrate the eccentric reactivity trends of iron-oxo moieties have been brought to the forefront.3 With the help of a couple of isomeric bispidine Mn(III)-peroxo complexes, a new mechanism for aldehyde deformylation reaction has been established. Keto-enol tautomerism in the reaction mechanism can be seen to trigger an electrophilic pathway instead of the commonly portrayed nucleophilic mechanism.4 Another intended engineering in the bispidine framework resulted in stabilizing a metastable non-heme iron(III)-alkylperoxo complex. These complexes are generally non-reactive. Surprisingly, however, versatile reactivity towards both electrophiles and nucleophiles have been observed for the same.

References:

1. Mukherjee, G.; Sastri, C. V. Isr. J. Chem. 2020, 60, 1032-1048.

2. Mukherjee, G.; Lee, C. W. Z.; Nag, S. S.; Alili, A.; Cantú Reinhard, F. G.; Kumar, D.; Sastri, C. V.; de Visser, S. P. Dalton. Trans. 2018, 47, 14945-14957.

3. Mukherjee, G.; Alili, A.; Barman, P.; Kumar, D.; Sastri, C. V.; de Visser, S. P., Chem. Eur. J. 2019, 25, 5086-5098.

 

4. Cantu Reinhard, F. G.; Barman, P.; Mukherjee, G.; Kumar, J.; Kumar D.; Kumar D.; Sastri, C. V.; de Visser, S. P. J. Am. Chem. Soc. 2017, 139, 18328-18338.

April 6, 2021 at 4.30 pm (Via Zoom)

Title :

π-Conjugated functional materials: design, synthesis and potential application

Abstract :

Electronics industries are highly dominated by Si and other inorganic semiconductor. After the discovery of conducting polymers there is enormous hope on carbon-based materials as future electronics. Recent research advancement in this area is highly promising but yet to go a long way. Organic materials as semiconductor have several advantages, such as easier designing and synthesis, better batch to batch reproducibility, cheap and most important one is flexibility which can fulfil the dream of future flexi-electronics. Relatively lower performance and stability than that of inorganic semiconductors are the major issues to be fixed. So designing of new efficient materials is on high demand.

So here in this seminar, I will discuss my contribution towards designing and synthesizing new -conjugated functional materials for potential application in organic electronics. The packing pattern in solid state is very vital which controls the performance of the resulting device, so during my PhD I worked with -conjugated oligomers to understand their intra and inter-molecular non-bonding interaction which control the packing pattern in solid state. Also π-conjugated polymers were developed from these oligomers and their electrochromic behaviours were studied. Graphene has evolved an important class of carbon-based materials as future electronics but zero band-gap and difficult synthetic accessibility is the major problem. Whereas nano-graphene, a smaller unit of graphene is an important alternative class of materials, I will discuss design and synthesis of new nano-graphene moiety. 

In the second half of my seminar I will discuss my future research proposal. Designing of new carbon-rich materials is my primary goal as an independent researcher. To execute the synthesis of these designed materials we will follow some established synthetic strategy or will introduce modified synthetic pathways. Of course the materialistic properties of those new materials will be explored through fabricating devices such as organic field effect transistors (OFETs), organic light emitting diodes (OLEDs) and organic spintronics. Also these materials will be explored in the area of artificial photosynthesis for solar light storage. 

Reference

1) H. Shirakawa, et al. J. Chem. Soc., Chem. Commun., 1977, 578.

2) a) M. Stępień et al. Chem. Rev., 2017, 117, 3479; b) J. Wu et al. Chem. Rev., 2007, 107, 718.

3) P. B. Pati et al., Angew. Chem. Int. Ed., 2020, 59, 14891. 

4) P. B. Pati et al., ACS Appl. Mater. Interfaces, 2013, 5, 12460. 

 

5) P. B. Pati et al., Cryst. Growth Des., 2014, 14, 1695. 

 

April 5, 2021 at 4.30 pm (Via Zoom)

Title :

Solar energy conversion to storage: my journey

Abstract :

For long sustainable human civilization we have to reduce our ecological footprint and that can only be done by minimizing the impact on the environment without compromising the current process of modernization. Out of several challenges to mankind, source of energy is the major one. In current time we are very much dependent on our fuel bank i.e. fossil fuels. The stored fossil fuels will not run for ever, sooner or later we will run out of this. The other aspect is that burning fossil fuels generate CO2 which is the one of the main culprits for global warming and related environmental disbalance. So there is a basic need to search for alternative renewable energy sources. One good way is to utilize the solar energy that can be done either conversion of solar energy into electrical energy or storing as fuels. 

So here in this seminar I will discuss my contribution towards these goals. A part of my PhD thesis deals with solar energy conversion and to do that I designed several series of organic dyes for dye sensitized solar cells (DSSC). DSSC is a nice technique for converting solar energy into electrical energy but ˜ 20% of total consumption of energy is consumed as electrical energy and rest as fuels. Alternative and effective way to contribute towards the renewable energy research area is to think about storing solar energy as fuel. To fulfil that goal we can mimic natural photosynthesis. So I will discuss some of my works during postdoctoral study which were focused in the area of solar light utilization to do some chemical reactions such as water and CO2 reduction and alcohol oxidation by either heterogeneous photocatalysis or photo-electrocatalysis through photo-electrochemical cells (PEC).

 

Reference

1) M. Grätzel et al. , Nature, 2001, 414, 338.

2) A. Fujishima et al., Nature, 1972, 238, 37.

3) P. B. Pati et al., Tetrahedron, 2013, 69, 2167. 

4) P. B. Pati et al., Energy Environ. Sci., 2017, 10, 1372.

 

5) P. B. Pati et al., Nat. Commun., 2020, 11, 3499.

 

March 30, 2021 at 2.30 pm (Via Zoom)

Title :

Molecular dynamics simulation studies of Antigen-Antibody interactions

Abstract :

Antigen-Antibody interactions are an important area of research in biophysical chemistry and structural biology. The availability of an increasing amount of structural data of antigens and antibodies allows a better understanding of their interactions and dynamics. The binding of an antibody to the antigen involves a combination of weak non-covalent interactions. This binding may cause significant conformation changes in both antibody and antigen and these changes may involve both structural and dynamical changes. In our study, we have identified the key residues involved in hydrogen-bonding interactions and salt-bridges in Ag-Ab complex by taking an example of HIV-1 protease and F11.2.32 mAb raised against the protease. We also examined the role of CDR flexibility in binding different conformations of the same epitope sequence in peptide and protein antigens. Our results provide the basis for understanding the cross-reactivity observed between the antibody with protease and the epitope peptide from it. We also studied the role played by dynamics in the function of the protease and how control of flexibility through Ab binding and site specific mutations can inhibit its activity. The study points to a plausible method for allosteric drug control. We believe this work is of value to the existing literature on Antigen-Antibody interactions and novel drug discovery methods that involve the modulation of the dynamics of an enzyme. 

March 25, 2021 at 10.00 am (Via Zoom)

Title :

Non-Macrocyclic Chelators for Metal-based Radiopharmaceuticals

Abstract :

Radiopharmaceuticals are a class of drug that relies on the physical decay of a radionuclide to elicit a diagnostic or therapeutic purpose. While organically derived radiotracers, which employ non-metal radionuclides (e.g., 18F, 11C, 123I), have received considerable attention in the field of nuclear medicine, metal-based radiopharmaceuticals are undoubtedly more versatile and hold great promise for the future. The availability of diverse medicinally useful radiometals with varying physical (half-life, specific activity, emission type) and chemical (hardness, oxidation state, acidity) properties has stimulated research interest in harnessing the potential of radiometals for diagnostic imaging as well as use of the emitted particles “millions of tiny bullets of energy” (α- particles, β - particles and Auger electrons) for therapy to kill welltargeted cancerous cells. Contemporary inorganic radiopharmaceuticals often follow a fourcomponent design and are comprised of a radiometal, bifunctional chelator, linker and targeting vector. This talk will focus on the role of coordination chemistry in the development of chelators for their application in nuclear medicine. The synthesis and detailed studies of three new chelators for hexa- and octa-coordinated (radio)metal ions (e.g., Sc3+, Ga3+, In3+, Lu3+) will be discussed

March 23, 2021 at 4.30 pm (Via Zoom)

Title :

Chemical Control of Defects for Optimizing Thermoelectric Performance of Lead Telluride

Abstract :

A surprisingly large portion of energy is lost as waste heat every year due to inefficient utilization.1 Thermoelectric (TE) materials may increase the overall efficiency of our energy utilization by directly converting waste heat to electricity.2 It is essential to have high efficiency in both p and n type semiconducting materials to achieve a high performance in thermoelectric generators. However, the efficiency of a TE material depends on the dimensionless figure of merit that involves a complex relation between the electronic and thermal properties as stated by the Wiedemann-Franz law.2 This presents a serious roadblock in the optimization of thermoelectric performance of any material.

In this seminar, I will present effective strategies to circumvent this problem in lead telluride (PbTe) which is a benchmark thermoelectric material via chemical control of point defects in the matrix. I will discuss the mechanisms to decouple the electronic and thermal properties of this system. I will further elaborate how these defects affect the electronic band structure of p and n type PbTe leading to modulation of the carrier concentration over a broad temperature range to facilitate high thermoelectric performance.3,4 

In the later part of the seminar, I will discuss my future research plans related to thermal energy harvesting using environment friendly materials and the study of their structure-property correlations. 

References

1. Rattner, A. S.; Garimella S. Energy 2011, 36(10), 6172–6183

2. He, J.; Tritt, T. M. Science 2017, 357 (6358), eaak9997

3. Sarkar, S.; Zhang, X.; Hao, S.; Hua, X.; Bailey, T. P.; Uher, C.; Wolverton, C.; Dravid, V.; Kanatzidis, M. G. ACS Energy Lett. 2018, 3 (10), 2593–2601 

4. Sarkar, S.; Hua, X.; Hao, S.; Zhang, X.; Bailey, T. P.; Slade, T. J.; Yasaei, P.; Korkotz, R.; Tan, G.; Uher, C.; Wolverton, C.; Dravid, V. P.; Kanatzidis, M. G. Chem. Mater. 2021, 33, 5, 1842–1851

 

March 22, 2021 at 4.30 pm (Via Zoom)

Title :

Influence of Lattice Ordering on the Catalytic Activity of Bimetallic Nanoparticles: Structure Matters!

Abstract :

With rising fossil fuel prices and worsening air quality, scientific research for alternative and sustainable energy conversion techniques has become an imminent necessity. Among these techniques, fuel cells that convert chemical energy into electricity have emerged as one of the most prominent options owing to high energy efficiency, low emissions and noise levels, as well as modular structure.1 Electrochemical oxidation of fuels such as methanol, ethanol, formic acid, etc. (referred to as small organic molecules or SOMs) needs a stable and highly active catalyst to lower the activation energy that is measured as “overpotential”. Precious metal based bimetallic or multi-metallic nanoparticles are one of the most effective class of catalysts in this respect. However, they suffer from a severe drawback known as “catalyst poisoning” caused by the strong metal-ligand binding with various reaction intermediates.2 Use of various catalyst support may alleviate this problem to a great extent, but homogeneous distribution of an active catalyst on a support may prove to be a challenging task at larger scale.3

In this seminar, I will talk about unsupported intermetallic nanoparticles that have high intrinsic catalytic activity owing to their ordered crystal structure. I will discuss the role of uniform surrounding of the active sites by catalytically “inactive” atoms in two different systems – Ag3In and Pd2Ge nanoparticles used respectively for reduction of an organic molecule and electrochemical oxidation of ethanol.4,5 I will also stress on the importance of lattice defects within the ordered crystal structure of the nanoparticles toward its catalytic activity. 

 

References

 

1. Staffell, I., Scamman, D.; Velazquez, A. A.; Balcombe, P.; Dodds, P. E.; Ekins, P.; Shah, N.; Ward, K. R. Energy Environ. Sci. 2019, 12, 463-491

2. Zhou, M.; Li, C.; Fang, F. Chem. Rev. 2021 121 (2), 736-795

3. Ramani, S.; Sarkar, S.; Vemuri, V.; Peter S. C. J. Mater. Chem. A 2017,5, 11572-11576

4. Sarkar, S.; Balisetty, L.; Shanbogh, P. P.; Peter, S. C. J. catal. 2014, 318, 143-150

5. Sarkar, S.; Jana, R.; Suchitra; Waghmare, U. V.; Kuppan, B.; Sampath, S.; Peter. S. C. Chem. Mater. 2015, 27 (21), 7459-7467

 

March 19, 2021 at 2.30 pm (Via Zoom)

Title :

Investigating Protein-Protein and Protein-Lipid Interaction

Abstract :

Protein-protein and protein-membrane interaction play a major role in various cellular functions. I have probed three such interactions. First, based on protein-protein interactions between SARS-COV-2 and human ACE2, we have designed a detection method that does not require RNA extraction or amplification. We achieve this by measuring FRET (Förster resonance energy transfer), occurring between two appropriately labeled peptides (1,2) bound to the same spike protein. Our initial results show that we do have a weak FRET signal when two peptides bind to the Receptor Binding Domain.  

Another example of protein-protein interaction is amyloid aggregation. It has been a challenge to determine the structure of transient aggregation intermediates. We plan to use optical pH recycling using a photoacid to hold the system indefinitely in the transient state. I will describe our preliminary characterization of the reversibility of a photoacid molecule synthesized by us and its effect on the aggregation kinetics of the amyloid-beta peptide.

Protein lipid interaction plays a major role in the toxicity of amyloid. However, the location and arrangement of amyloid oligomers in the membrane is unknown. We probe this by following the distance-dependent modulation of triplet state relaxation dynamics of fluorescent probes (placed on the peptide) by lipids labeled with radical at different sites. Our results show that amyloid-beta inserts in lipid vesicles at a specific location that is consistent with it forming a specific structure in the membrane. I will show the results of our computational investigation of the stability of antiparallel beta-hairpin conformation, which we have earlier shown to be the relevant structure for small oligomers (3,4), in the solution phase as well as in the lipid membrane. 

References.

1)Cao et. al., Science, 2020, 370, 426-431

2)Pomplun et. al., ACS Cent. Sci., 2021, 7, 156−163

3)Chandra et. al., Biophysics J, 2017, 113, 805-816

 

4)Chandra et. al., Chem. Commun., 2018, 113, 7750-7753

 

March 16, 2021 at 4.30 pm (Via Zoom)

Title :

Interface-selective Time-resolved Nonlinear Spectroscopy at Aqueous Interface

Abstract :

Aqueous interfaces play key roles in a wide variety of fields including atmospheric and environmental chemistry, “on-water” catalysis, electrochemical reactions and biochemical processes. These interfacial reactions are governed by elementary processes involving transfer of energy and electron, making and breaking of bonds as well as conformational transformations which occur on the ultrafast time scale. Although there are spectroscopic techniques that can track down the dynamics of these elementary processes in the bulk, it is extremely challenging to measure these dynamical processes at the interface because its typical thickness is only a few nanometer.

In this seminar, I will talk about interface-selective time-resolved- (TR-) and two-dimensional (2D-) heterodyne-detected vibrational sum frequency generation (HD-VSFG) techniques, which have been pioneered by our group1 for observing the ultrafast dynamics at aqueous interfaces. During my postdoctoral research in Tahara group for the last five years, I have been actively involved in the development of two-dimensional (2D) HD-VSFG setup. I will discuss application of this novel technique to unravel the hitherto unknown dynamics of water at the biological lipid-water2 and charged hydrophobe-water interfaces3 as well as the vibrational relaxation of topmost water (free OH) at the air-water interface4

At the end, I will discuss my future research plans to address important issues relevant to chemical and biological phenomena at interfaces.

 

1 S. Nihonyanagi, S. Yamaguchi, and T. Tahara, Chem.Rev. 117, 10665 (2017).

2 K. Inoue, M. Ahmed, S. Nihonyanagi, and T. Tahara, ‎J. Chem. Phys. 150, 054705 (2019).

3 M. Ahmed, K. Inoue, S. Nihonyanagi, and T. Tahara, Angew. Chem. Int. Ed. 59, 9498 (2020).

4 K. Inoue, M. Ahmed, S. Nihonyanagi, and T. Tahara, Nat. Commun 11, 5344 (2020).

 

 

 

March 15, 2021 at 4.30 pm (via Zoom)

Title :

Interface-selective Nonlinear Spectroscopy at Aqueous Interface

Abstract :

Aqueous interfaces are ubiquitous and play vital roles in a variety of processes relevant to heterogeneous catalysis, electrochemistry, atmospheric, environmental chemistry, and biological self-assembly. Nevertheless, molecular-level understanding of aqueous interfaces is very limited compared to that of the corresponding bulk media. A huge challenge in investigating the aqueous interface is to selectively observe few molecular layer thick interface in the presence of surrounding more plentiful bulk. Due to lack of interface-selectivity, most of the spectroscopic techniques are inadequate for probing aqueous interfaces. Moreover, unlike a solid, water has substantial vapor pressure, which makes it difficult to probe the water surface by conventional spectroscopy such as X-ray photoelectron spectroscopy (XPS). Thus, it is essential to utilize spectroscopic techniques that can selectively detect interfacial molecules and directly reveal the structure and properties of the interface at the molecular level.

In this seminar, I will introduce interface-selective nonlinear spectroscopy technique called heterodyne-detected vibrational sum frequency generation (HD-VSFG), which I have been actively developing during my PhD and postdoctoral research. HD-VSFG can selectively probe the aqueous interfaces via the vibration of the interfacial molecules1. In fact, HD-VSFG provides the accurate vibrational spectra of interfacial molecules that are comparable to the IR/Raman spectra for the bulk. Moreover, the sign of HD-VSFG spectrum (i.e., positive or negative amplitude of the signal) reveals the absolute orientation of interfacial molecules. As typical examples, I will discuss the application of HD-VSFG that addresses the hydrogen bonding and orientation of water molecules at the air/water interface2, properties of osmolyte and denaturant at water surface3. Furthermore, I will discuss my recent HD-VSFG study that resolved the controversy on the origin of SFG signal for the bend vibration of interfacial water4. The presented results highlight the importance of interface-selective molecular information obtainable with HD-VSFG and its potential application to explore interfacial phenomena in more complex chemical and biological systems.

 

1 S. Nihonyanagi, J. A. Mondal, S. Yamaguchi, and T. Tahara, Annu. Rev. Phys. Chem. 64, 579 (2013).

2 M. Ahmed, Y. Nojima, S. Nihonyanagi, S. Yamaguchi, and T. Tahara, ‎J. Chem. Phys. 152, 237101 (2020).

3 M. Ahmed, V. Namboodiri, P. Mathi, A. K. Singh, and J. A. Mondal, ‎J. Phys. Chem. C 120, 10252 (2016).

4 M. Ahmed, S. Nihonyanagi, A. Kundu, S. Yamaguchi, and T. Tahara, ‎J. Phys. Chem. Lett. 11, 9123 (2020).

March 12, 2021 at 2.30 pm (Via Zoom)

Title :

Design and Synthesis of Fluorescent Probes for Selective Detection of Thiols

Abstract :

Cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) are three major low molecular weight biothiols that perform and regulate crucial physiological processes including proteins folding, biological redox homeostasis, intracellular signal transduction and gene regulation. Alterations in plasma and intracellular thiols levels have been linked to various diseases including Alzheimer’s disease, cardiovascular diseases, cancer and skin lesions. Therefore, selective and quantitative detection of thiols may help in early diagnosis of such diseases, in understanding the roles of biothiols in their onset which may help in preventing onset of the same.

Design principle and outcome: Most biological thiols are not inherently fluorescent and therefore cannot be directly visualized via fluorescence spectroscopy. Hence, in my PhD, I devoted my efforts to development and application of selective fluorescent probes that enables indirect visualization and quantification of specific biothiols in a complex biological environment.

In the design a fluorophore is attached to suitable moiety (quencher) which selectively reacts with biothiols . This state is termed as “Fluorescence-Off” state of the probe. Reaction with thiol results in the strong fluorescence of the resultant species. One strategy of sensing involves thiol mediated cleavage of the quencher releasing free fluorophore. Alternately, chemical reaction of thiol with quencher leads to destruction of its quenching ability. In both processes formation of strong fluorescent product leads to “Fluorescence-On” state of the probe.

For developing fluorescent probes having better photophysical properties such as excitation and emission in visible region, good water solubility and improved cell permeability various fluorophores like NBD chloride, Iminocoumarin, Naphthaleimide, Chromenoquinolines, BODIPY and Fluorescein are used. Cell permeability, selectivity and sensitivity of these probes was demonstrated via cell imaging studies.

 

In the second part of this talk, I will discuss about my future research plans.

March 11, 2021 at 2.30 pm (Via Zoom)

Title :

Developing a General Platform for Long Wavelength and Water Soluble BODIPY Photocages with Tunable Cell Permeability for Controlled Delivery of Biologically Relevant Molecules.

Abstract :

 

Photocages are light-sensitive protecting groups that functionally encapsulate molecule of interest (MOI) in an inactive form. Irradiation with light releases the trapped molecule, permitting targeted perturbation of a biological process. Photocages enable to control the spatial distribution and temporal release of MOI using light as an external, a non-invasive trigger. However, most caging groups available that operate by one-photon are excited with UV light. This results in potential tissue damage, limits tissue penetration and restricts the wavelength-window available for activation of multiple cues.

Recently, Weinstain et al. 1 and others2, introduced a novel photocage, excitable in the visible light range, based on the boron-dipyrromethene (BODIPY) core. In order for BODIPY cages to become more practical and functional for biological applications, three main issues were need to be addressed: (i) improving the photoreaction efficiency (ii) introducing cell organelle specificity and (iii) fine-tuning the structure’s photophysical properties and water solubility as well as controlling cell membrane permeability

During this presentation, I will showcase our efforts and outcome to address above drawbacks. This work combines new synthetic routes to develop highly functionalized BODIPY photocages.

To improve photoreaction efficiency we have investigated a systematic structure activity relationship study on 32 mesomethyl BODIPY photocages and assessed their photophysical and photochemical properties. On the other hand, although photocaging facilitates non-invasive and precise spatio-temporal control over the release of biologically relevant MOI using light, subcellular organelles are dispersed in cells in a manner that renders selective light-irradiation of a complete organelle impractical. Organelle-specific photocages could provide a powerful method for releasing bioactive molecules in subcellular locations. We have developed a general platform for introducing cell organelle targeting groups on 2, 6 methyl groups of BODIPY photocages. To test general applicability, we have developed a general post-synthetic method for the chemical functionalization and the synthesis of endoplasmic reticulum (ER)-, lysosome-, and mitochondria-targeted derivatives. We also demonstrated that 2,4-dinitrophenol, a mitochondrial uncoupler, and puromycin, a protein biosynthesis inhibitor, can be selectively photoreleased in mitochondria and ER, respectively, in live cells by using visible light. We have also extended the application of this methodology to develop water-soluble BODIPY photocages with tunable cellular permeability.

References:

1) N. Rubinstein, P. Liu, E. W. Miller, R. Weinstain, Chem. Commun. 2015, 51, 6369–6372.

2) P. P. Goswami, A. Syed, C. L. Beck, T. R. Albright, K. M. Mahoney, R. Unash, E. A. Smith, A. H. Winter, J. Am. Chem. Soc. 2015, 137, 3783– 3786.

February 25, 2021 at 4.00 pm (Via Zoom)

Title :

Chemical Substitution Based Designs for Bis-terpyridine Molecular Breadboard Circuits: Knobs to Tune Quantum Interference Effects