TIFR
Department of Chemical Sciences
School of Natural Sciences

Calender

June 25, 2019 at 2.30 pm in AG-69

Title :

Carbon dioxide capture: Insights from Raman spectroscopy

Abstract :

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. 

References. 

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. 

On June 19, 2019 at 2.30 pm in AG-80

Title :

Organometallic Catalysis for Energy & Environment: What we can achieve

Abstract :

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 18, 2019 at 2.30 pm in AG-80

Title :

Organometallic Catalysis for Energy & Environment: What we have achieved

Abstract :

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.

 

June 10, 2019 at 4.00 pm in AG-69

Title :

Defect Engineering in Dendritic Fibrous Nano Silica-based Material for CO2 Methanation

June 7, 2019 at 2.30 pm in AG-69

Title :

Microsecond conformational dynamics of biopolymers studied by two-dimensional fluorescence lifetime correlation spectroscopy

Abstract :

 

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.

 

June 3, 2019 at 4.00 pm in AG-69

Title :

Stability Aspects and Optoelectronic Properties of Hybrid Perovskites

May 16, 2019 at 4.00 pm in AG-80

Title :

Role of Salt Bridges in Thermodynamic Stability of Ubiquitin

May 14, 2019 at 2.30 pm in AG-69

Title :

In Search of New Materials for Electrical Energy Storage

 

May 13, 2019 at 4.00 pm in AG-69

Title :

Effect of Temperature and Circular Permutation on the Mechanical Stability of Proteins

May 9, 2019 at 4.00 pm in AG-80

Title :

Unfolding of Proteins in Solution Under External Electric Field

May 8, 2019 at 2.30 pm in AG-80

Title :

Using Microwave Pulses to Expand the Scope of DNP Enhanced Solid-State NMR Spectroscopy

Abstract :

 

Dynamic nuclear polarization has revolutionized the field of solid-state NMR by providing the sensitivity enhancement of orders of magnitude. Currently, most DNP experiments are performed using continuous-wave (CW) microwave irradiation near EPR frequency of the polarizing agents using dedicated gyrotrons. The CW-DNP mechanisms, i.e. solid-effect (SE), cross-effect (CE) and thermal mixing (TM) become less efficient at higher magnetic fields due to inefficient state mixing caused by large Zeeman splitting. Therefore, the signal enhancements achieved at high magnetic fields are well below the theoretical maximum of 658.
 
An alternative approach, which is recently gaining foothold, will be discussed. In this approach, microwave pulses with varying phase, length, amplitude and frequency are employed to obtain field independent electron-nuclear polarization transfer by fulfilling the required matching condition. Such methods require microwave irradiation with low duty cycle, which minimized the problem of sample heating that is prominent is CW-DNP experiments. Moreover, the paramagnetic effects, i.e. NMR line-broadening, signal quenching and relaxation enhancement, caused by the presence of a paramagnetic center can also be reversed using microwave pulses with frequency switching capabilities. I will show experimental evidences of reversal of paramagnetic effects at a magnetic field of 6.9 T and 4K temperature. 
 
At the end, I will talk about my future research plans focusing at developments and applications of the magnetic resonance techniques (NMR and DNP) to study materials and biological samples.  

May 7, 2019 at 2.30 pm in AG-80

Title :

Advancing the Magnetic Resonance Frontiers for the Study of Complex Molecules and Active Materials

Abstract :

Nuclear Magnetic Resonance (NMR) is a spectroscopic method that provides atomically resolved structural and dynamical information of systems from a vast category including organic and inorganic chemistry, materials and biology. The technique offers unique capabilities to study complex molecules that are insoluble and non-crystalline such as amyloid fibrils, membrane proteins, amorphous polymers, catalytic compounds, and battery materials etc. A major challenge in the applications of solid-state NMR spectroscopy is the intrinsically low sensitivity of the technique that practically restricts its use to a limited number of NMR active isotopes such as 1H, 19F, 31P, 13C, and 15N. Therefore, a number of practically relevant systems that in principle can be studied using solid-state NMR, remain out of its reach. 
 
I will present two approaches to address the problem of sensitivity in solid-state NMR. The first approach is development of new methods, i.e., radio frequency (RF) pulse sequences to probe NMR isotopes like 2H, 14N, 7Li etc.  that are difficult due to their less sensitivity (low gyromagnetic ration and/or less natural abundance) and large anisotropic interaction like quadrupolar coupling and chemical shift anisotropy. A new RF pulse sequence and its applications to biological and material samples with various challenging NMR isotopes will be discussed, demonstrating the versatility of the new method and its impact.  
 
In the second approach, I will discuss a rapidly emerging hyperpolarization technique known as dynamics nuclear polarization (DNP), which can enhance the sensitivity of NMR by orders of magnitude. DNP has already made a paradigm shift in solid-state NMR spectroscopy by enabling studies of systems like proteins in physiological conditions and materials with extremely insensitive NMR isotopes like 17O. However, the state-of-the-art DNP methods rely on exogenously added source of paramagnetic centers (typically stable nitroxide or carbon-based radicals) for the polarization. The scope of DNP can be further expanded by performing endogenous DNP using paramagnetic metal centers as the source of polarization to enhance sensitivity of the surrounding nuclear spins. Such metal centers are intrinsically present in systems like metalloproteins, metalloenzymes, energy harvesting materials and battery compounds. More importantly, endogenous DNP is a critical step towards performing “hyperfine DNP spectroscopy” to extract the local structural information directly from the electron-nuclear hyperfine interaction while detecting sensitivity enhanced NMR signal. Recent results using V4+ centers for the first time to enhance polarization of protons in the sample will be shown to illustrate the concept of hyperfine DNP spectroscopy.

May 3, 2019 at 2.30 pm in AG-69

Title :

Sensors and Chelators for Essential Transition Metal Ions

May 2, 2019 at 4.00 pm in AG-80

Title :

How membrane characteristics influence membrane protein conformation

Abstract :

Cell membranes not only maintain cell integrity, but possibly also influence the functioning of membrane proteins. Local membrane order and cholesterol content are two important factors, but they remain poorly understood.  Here, I have probed how the mode of interaction of Amylin (a disease causing peptide oligomer with high membrane affinity) is controlled by the nature of membrane. For this purpose, we have built a combined AFM-Confocal-FLIM-FCS set up and probed the accessibility of the terminals (N and C) and the extent of insertion in different membrane environments. We find that these parameters are highly dependent on the local lipid order. We also monitored the extent of depletion of cholesterol in presence and absence of amylin, and found that amylin resists the changes caused by cholesterol depletion and helps the membrane to retain its integrity. Thus, our study quantifies the strong reciprocal influence between membrane proteins and membranes, which has possible biological consequences.

May 1, 2019 at 2.30 pm in AG-69

Title :

Buoyant Microcapsules: Simple motility to Complex Autonomous Behavior

Abstract :

Nature has always been a great source of inspiration for the design of artificial materials with improved hierarchical organization, superior properties and smart functions. In this age of artificial intelligence and smart systems, chemists are increasingly looking to design active and adaptive materials taking inspiration from the various biological processes and their self-regulatory mechanisms which make ‘life’ possible. In this talk, I will illustrate with an example of a microcapsule with an entrapped gas bubble whose motility is governed by buoyancy forces, how we can design complex autonomous behavior into relatively simple systems. Our results show that microcapsules can be propelled by an active control of buoyancy forces and this buoyant motility can be used to trigger chemical reactions, simulate self-sorting behavior in microcapsule communities and achieve complex oscillatory motility.

References:

  1. B. A. Grzybowski & W. T. S. Huck, The Nanotechnology of Life-inspired Systems, Nat. Nanotechnol. 2016, 11, 585.
  2. B. V. V. S. P. Kumar, A. J. Patil & S. Mann, Enzyme-powered motility in buoyant organoclay/DNA protocells, Nat. Chem. 2018, 10, 1154.
  3. L. Rodriguez-Arco, B. V. V. S. P. Kumar, M. Li, A. J. Patil & S. Mann, Modulation of Higher-order Behaviour in Model Protocell Communities by Artificial Phagocytosis, Angew. Chem. Int. Ed. 2019, DOI: 10.1002/ange.201901469.