June 26, 2019 at 2.30 pm in AG-69
Visible light driven carbon dioxide reduction on plasmonic catalyst
Direct conversion of solar to chemical energy has gained renewed interest in the recent years. Plants uptake atmospheric CO2 to produce sugar by the process of photosynthesis. Recreating this process requires materials which can absorb light and convert it into energy. Plasmonic nanoparticles of silver and gold are excellent candidates for photocatalysis due to their high absorption cross section. In my talk, I will show that under light irradiation, silver nanoparticles catalyze CO2 reduction reaction. Spatially resolved single particle surface enhanced Raman spectroscopy shows formation of intermediate such as HOCO* as well products such as carbon monoxide and formic acid. Further, binding geometry of HOCO* plays decisive role in directing the reaction either towards carbon monoxide or formic acid.
Although catalytic reaction on plasmonic nanostructures is fairly well studied, the fate of metal nanoparticles post photocatalysis is largely unknown. We found that plasmon-assisted CO2 reduction reaction induces significant directional restructuring on catalyst surface. In the second part of the talk, I will show you how these structural changes in plasmonic catalysts also gives an insight into the mechanism of photocatalytic activation, the distribution of active sites on nanoparticle surface and the definite role of light.
1.G. Kumari, X. Zhang, D. Devasia, J. Heo, P. K. Jain. ACS Nano 2018, 12, 8330−8340.
2.S. Yu, A. J. Wilson, G. Kumari, X. Zhang, P. K. Jain. ACS Energy Lett. 2017, 2, 2058-2070.
3.X. Zhang, G. Kumari, J. Heo, P. K. Jain. Nat. Commun. 2018, 9, 3056
June 25, 2019 at 2.30 pm in AG-69
Carbon dioxide capture: Insights from Raman spectroscopy
Increasing carbon dioxide levels stemming from various anthropogenic sources have led to adverse climatic conditions. CO2 sequestration becomes vital to mitigate global warming. Metal organic frameworks (MOFs) have immense potential to sequester CO2 owing to their porous and flexible architecture exhibiting high guest selectivity. While the as-synthesized structure can be predicted by X-ray diffraction, knowing in-situ structural dynamics during gas adsorption is a challenge. In the first part of the talk, I will discuss how adsorption or desorption of gases modulates the structure of MOFs. Investigating these dynamics frameworks are crucial for designing new materials with higher CO2 uptake.
Furthermore, it is necessary to reduce captured CO2 into fuels and one of the ways to achieve this is by using metal nanostructures. In addition to catalysing chemical reaction, plasmonic nanoparticles also amplify the signal of adsorbed molecules enabling their detection via surface enhanced Raman spectroscopy (SERS). In the second half of the talk, I will show different types of plasmonic nanostructures and further illustrate that silver nanoparticles exhibit high SERS enhancement and hence is a suitable catalyst for studying single molecule reaction.
1.P. Kanoo, S. K. Reddy, G. Kumari, R. Haldar, C. Narayana, S. Balasubramanian, T. K. Maji. Chem. Commun. 2012, 48, 8487-8489.
2.G. Kumari, K. Jayaramulu, T. K. Maji, C. Narayana. J. Phys. Chem. A 2013, 117, 11006-11012.
3.G. Kumari, C. Narayana. J. Phys. Chem. Lett 2012, 3, 1130-1135.
June 18, 2019 at 2.30 pm in AG-80
Organometallic Catalysis for Energy & Environment: What we have achieved
Catalysis plays a major role in the production of food, pharmaceuticals and energy. We have been working in the area of green homogeneous catalysis using pincer complexes of transition-metals. We have developed several interesting methods that are environmentally-benign and sustainable for the production of industrially useful chemicals from the cheap and inexpensive starting materials using pincer complexes of earth-abundant metals such as manganese. These methods are based on hydrogenation or dehydrogenation reactions which makes the overall process highly atom-economic. Utilization of manganese in place of precious metals such as ruthenium makes the overall process cheaper and more sustainable. Some of these examples will be discussed in the lecture, such as:
1.We reported the first example of the direct synthesis of amides by the dehydrogenative coupling of amines with either alcohols or esters using an earth-abundant metal catalyst.
2.We reported the first example of the direct hydrogenation of organic carbonates to methanol using an earth-abundant metal catalyst. As organic carbonates can be readily prepared from CO2 and alcohols, this method can be utilized as an alternative route for the conversion of low-pressure CO2 to methanol.
3.We discovered a fundamentally new Liquid Organic Hydrogen Carrier (LOHC) based on coupling of diols and diamines for the development of a reversible hydrogen storage material.
1.(a) A. Kumar, N. A. E. Jalapa, G. Leitus, Y. Diskin Posner and D. Milstein, Angew. Chem. Int. Ed., 2017, 56, 14992. (b) N. A. E. Jalapa, A. Kumar, G. Leitus, Y. Diskin Posner and D. Milstein, J. Am. Chem. Soc., 2017,139, 11722.
2.A. Kumar, T. Janes, N. A. E. Jalapa, D. Milstein, Angew. Chem. Int. Ed., 2018, 57, 12076.
3.A. Kumar, T. Janes, N. A. E. Jalapa, D. Milstein, J. Am. Chem. Soc., 2018, 140, 7453.
On June 19, 2019 at 2.30 pm in AG-80
Organometallic Catalysis for Energy & Environment: What we can achieve
We are living in the age where we have witnessed critical rise in all types of pollution and the depletion of limited supply of fossil fuel. A lot of it is caused by the way our industries manufacture their products and our dependence on fossil fuel for the production of energy. In order to restore the balance of clean environment we need to develop production methods that are environmentally-benign, atom-economic and sustainable. This lecture will focus on some of the strategy in Green Catalysis that can be utilized for the production of industrially useful chemicals and energy storage materials from inexpensive and readily available starting materials. For example: (a) Based on our recent discovery,1 utilization of alkali or alkaline earth-metal catalysts instead of transition-metal catalysts can make the overall process cheaper and sustainable. (b) Development of reversible chemical hydrogen storage materials such as those based on glycerols or amine-boranes2. (c) Chemical recycling of robust plastics such as nylons, polycarbonates and polyurethanes using ruthenium catalyzed hydrogenative depolymerization method.
1.A. Kumar, T. Janes, S. Chakraborty, P. Daw, N. von Wolff, R. Carmieli, Y. Diskin-Posner, D. Milstein, Angew. Chem. Int. Ed., 2019, 58, 3373.
2.A. Kumar, N. Beatie, S. A. Macgregor, A. S. Weller, Angew. Chem. Int. Ed., 2016, 55, 6551.
June 7, 2019 at 2.30 pm in AG-69
Microsecond conformational dynamics of biopolymers studied by two-dimensional fluorescence lifetime correlation spectroscopy
Many biological functions of biopolymers (protein/DNA/RNA) are realized with their spontaneous structural fluctuation. Therefore, the elucidation of the energy landscape of biopolymers and their structural dynamics is essential. Single molecule spectroscopy is a powerful tool to investigate this problem, and the single molecule Förster resonance energy transfer (smFRET) technique is widely utilized. However, conventional smFRET detects only millisecond and slower dynamics. In this presentation, I’ll introduce recently developed two-dimensional fluorescence lifetime correlation spectroscopy (2D FLCS)1,2 that distinguishes the conformers by their fluorescence lifetime and detects their interconverstion dynamics with a microsecond time resolution. Next, I will introduce a new method that combines dynamic fluorescence quenching (DQ) and 2D FLCS. In comparison to FRET which detects relatively large structural change, DQ is more sensitive to the local solvent accessibility of the attached dye. A major advantage of this method is that it requires only single-dye labeling compared to FRET which requires double-labeling. By applying this DQ 2D FLCS to a singly-labeled DNA hairpin, we succesfully resolved the open and closed forms in the equilibrium and detected their microsecond interconversion dynamics. I’ll also show the application of 2D FLCS on preQ1 riboswitch, an important antibiotic drug target, to resolve its heterogeneous folding dynamics and distinct ligand binding mechanisms.
[1, 2] Ishii, K. & Tahara, T. Journal of Physical Chemistry B, 2013 117, 11414 & 11423.