Calendar

• Annual Works Seminar by Dr. Abhisek Ghosal, Dept. of Chemical Sciences, TIFR Mumbai, on May 23, 2022 at 4.00 pm in AG-69

  Title :

  Modelling optical properties of f-centre defects: A generalised KS semicanonical projected RPA perspective

  Abstract :

  Defects can dominate the electronic and optical properties in materials, thus play a vital role in the performance of many technological applications. Among various defects, our primary focus is on f-centre defects which can act as a strong local-reduction site in the chemical processes. The experimental measurement of such defects are usually hampered by their low concentration. Therefore, theoretical studies of defect sites are of major importance for a deeper understanding of how defects might work. Theoretical studies based on periodic supercell model can be a method of choice, but encounters higher defect concentration. It is also computationally demanding using quantum chemistry (QC) methods. On the other hand, embedded cluster model is capable of describing isolated point defects along with the highlevel QC methods. In this direction, we present periodic electrostatic embedding cluster model (PEECM) in which the quantum mechanical part is treated with the recently developed generalised Kohn-Sham semicanonical projected RPA (GKS-spRPA) theory. A detailed systematic assessment of properties towards the bulk limit is presented here on a representative f-center LiF. In all instances, these results are excellent agreement with the available theoretical and experimental results. At the end, I will discuss about the importance of surface defects as well as major challenges to model such defect within the PEECM-GKS-spRPA framework.

  In the second part of my presentation, I will discuss about metastable systems which are observed in radioactive decays, dissociative electron attachment, stark ionisation, even in biomolecules like DNA base pairs, etc. These states are characterised by complex energy, the real part of which is the resonance energy and the imaginary part is associated with its lifetime. The GKS-spRPA can be a method of choice for such problems, but it requires the analytical continuation of real energy to complex domain. Here, a non-Hermitian analogue of adiabatic connection is derived. Further, it has been shown that it is same as the Hermitian approach as long as the non-Hermitian part is symmetric and local. Finally, the ongoing work and future direction is discussed.

• Annual Works Seminar by Mr. Shreyas Vaidya, Dept. of Chemical Sciences, TIFR, Mumbai on May 19, 2022 at 4.00 pm in AG-80

  Title :

  Towards Bleomycin-Platinum Glycoconjugates for Targeted Chemotherapy: An Odyssey in Carbohydrate Chemistry

  Abstract :

  Cancer is the second leading cause of fatalities worldwide. The serendipitous discovery of anticancer activity of Cisplatin in 1965 by Prof. Rosenberg ushered in a new era of cancer chemotherapy. It is the preferred choice of treatment against a large variety of cancers. Despite its clinical success, cisplatin treatment has some drawbacks. Adverse side effects like nephrotoxicity, ototoxicity, anaemia are commonly observed in patients undergoing chemotherapy.

  In this context, the selective accumulation of the cytotoxic drug at the tumor site is highly desirable to achieve improved efficacy and minimal side-effects. Glucose metabolism is typically upregulated in cancer cells as compared to the normal cells (Warburg Effect). An overexpression of Glucose Transporter (GLUT) family of proteins is observed in the cancer cells. GLUTs have emerged as an attractive target for a large number of targeted anticancer strategies.  Recently, the disaccharide moiety of anticancer drug Bleomycin A₅ has been reported to exhibit preferential uptake in cancer cells ^[1,2]. However, there is contradiction in the chemical literature about the minimal epitope of this disaccharide which is necessary and sufficient for imparting the observed selectivity ^[3]. We have therefore decided to investigate this problem by carrying out a structure-activity relationship study on the bleomycin disaccharide. In this talk I will discuss about the synthetic problems faced during the journey from the starting molecules to the target sugar-platinum conjugates.

   

  References:

  1. Zhiqiang Yu.; Ryan M. Schmaltz.; Trevor C. Bozeman.; Rakesh Paul.; Michael J. Rishel.; Krystal S. Tsosie.; Sidney M. Hecht. Am. Chem. Soc. 2013, 135, 2883−2886
  2. Benjamin R. Schroeder.; M. Imran Ghare.; Chandrabali Bhattacharya.; Rakesh Paul.; Zhiqiang Yu.; Paul A. Zaleski.; Trevor C. Bozeman.; Michael J. Rishel.; Sidney M. Hecht. Am. Chem. Soc. 2014, 136, 13641−13656
  3. Zhou Cui.; Ye Wenchong.; Wang Xiaoyang European Journal of Medicinal Chemistry. 2021, 226, 112866.
• Annual Works Seminar by Mr. Rohit, Dept. of Chemical Sciences, TIFR, Mumbai on May 17, 2022 at 4.00 pm in AG-69

  Title :

  Harvesting and storing solar energy

  Abstract :

  Solar energy is the cleanest renewable source of energy. Currently, coupling of photovoltaic (PV) devices with batteries and/or supercapacitors harvest and store this energy. However, coupling these devices usually involves multiple interfaces through which the generated excited carriers have to traverse. To mitigate the problem of efficiency losses through multiple interfaces, an approach of capturing and storing solar energy simultaneously in a single material (bi-functional material) has been put forward very recently in the literature. The talk will present the understanding we build through an electrochemical approach on how a single material is capable of harvesting and storing solar energy simultaneously. The talk will also exploit the variety of parameters that include tuning of structural and external parameters, leading to increasing the charge storage amount and prolonging its duration.

• Annual Works Seminar by Mr. Kishan Kumar Yadav, Dept. of Chemical Sciences, TIFR, Mumbai on May 12, 2022 at 4.00 pm in AG-66

  Title :

  Photoredox C-C Coupling Reactions inside Supramolecular Cavities

  Abstract :

  Enzymes act as nano-vessels which can selectively catalyze chemical reactions by confinement and controlled activation of substrates.^[1] Chemists have designed supramolecular cavities to mimic enzymes and demonstrated selective product formation. ^[2] Recently it was shown that the photoactivation of weakly polarized sp³ C-H bonds in water can be selectively done using water-soluble octahedral Pd₆L₄¹²⁺ nano-cage. ^[3] However, these cages sometime suffer from low catalytic turnover due to product trapping inside the nano-cages. ^[4] In order to solve this issue we have tried photocatalysis via charge transfer mediated pathways inside a square pyramidal Pd₆L₄¹²⁺ nano-bowl ^[5] which is formed by self-assembly of [Pd(en)(ONO₂)₂] complex with triazine based ligands as the cavity walls.  In this seminar, I will discuss our ongoing efforts to optimize and characterize the photocatalytic inter- and intra-molecular C-C coupling reactions between carbon centres having either sp or sp³ hybridization leading to selective C-C bond formation in water using steady-state and transient absorption spectroscopy. Subsequently, I will show that how the tuning of shape of confinement from octahedral to square pyramidal is leading to different selectivity and faster kinetics.

     References

  1. Rittle J., et. al, Science 2010, 330, 933–937
  2. Zhang, Q., et. al, Chem. 2015, 7, 197–202
  3. Das A., et. al, Adv. 2019, 5, eaav4806
  4. Yoshizawa M., et. al, Science 2006, 312, 251-254.
  5. Fujita M., et. al, Chem. Int. Ed. 1998, 37, No. 15
• Annual Works Seminar by Mr. Saideep Singh, Dept. of Chemical Sciences, TIFR, Mumbai on May 9, 2022 at 4.00 pm in AG-69

  Title :

  Plasmonic Metal Nitrides for Transforming CO₂ to CO using Solar Energy

  Abstract :

  Metal nitrides are evolving as promising photocatalysts owing to their exquisite plasmonic features. Recently, Molybdenum nitrides (MoN) nanosheets show plasmonic behavior that allowed the material as a light harvester. We are searching for various stable, and good lightharvesting metal nitrides, that are highly active and selective for CO₂ hydrogenation reactions.

  In this work, we have designed and synthesized nanosheets of Nickel Nitride (Ni₃N) using the solvothermal process. Material characterizations were carried out using various techniques such as SEM, TEM, HRTEM, XRD, XPS, UV-DRS, N₂ sorption etc. It has a broad optical spectrum and absorbs well in the visible region. EELS spectroscopy indicated the plasmonic character of the material. Ni₃N was then studied for CO₂ hydrogenation to CO using hydrogen under light. The photocatalytic CO production rate was (713 ± 40 mmol g^-1 h ^-1 ) with 100 % CO selectivity. Notably, the reaction was carried out in a flow reactor at low temperature (50-110 °C) and atmospheric pressure without external heating. Linear dependence of CO production rate on light intensity indicated the non-thermal hot-electron mediated CO₂ reduction. Fe³⁺ to Fe²⁺ one-electron reduction reaction also indicated electron transfer mechanism. Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that CO₂ hydrogenation took place by direct dissociation path via linearly bonded Ni-CO intermediates.

  References:

  1. Bailera, M.; Lisbona, P.; Romeo, L. M.; Espatolero, S. Renew. Sustain. Energy Rev, 2017, 69, 292–312.

  2. Jia, J.; Qian, C.; Dong, Y.; Li, Y. F.; Wang, H.; Ghoussoub, M.; Butler, K. T.; Walsh, A.; Ozin, G. A. Chem. Soc. Rev. 2017, 46, 4631–4644

  3. H.S. Gujral et al. Sci. Technol. Adv. Mater., 2022, 23, 77

  4. Guan, H., Yi, W., Li, T. et al. Nat Commun, 2020, 11, 3889

  5. D. Fomra, M. Mamun, K. Ding, V. Avrutin, Ü. Özgür, N. Kinsey, Opt. Express, 2021, 29, 19586-19592