TIFR
Department of Chemical Sciences
School of Natural Sciences

Calender

February 19, 2018 at 4.00 pm in AG-69

Title :

Breaking the RET barrier using metamaterials

Abstract :

Resonance Energy Transfer (RET) is a form of direct energy transfer between two dipoles. It has a very precise distance dependence that has allowed the technique to be widely used in particular for determining complex molecular structures. However, it is only effective over ˜ 15 nm separations. I will discuss our proof-of-principle experiments which extend the RET range of effectiveness by an order-of-magnitude and show RET between a donor-acceptor pair separated by 160 nm. This increase is facilitated by using metamaterials a class of custom-made nanophotonic structures that are designed to have unique optical properties, specifically, a topological transition from a closed to an open form which can be tuned for individual RET pairs. We will go over the design of the metamaterial for our experiment and also discuss the experimental demonstration of long distance RET using time resolved and steady state spectroscopy.

February 13, 2018 at 2.30 pm in AG-66

Title :

Nonadiabatic Reaction Dynamics at Conical Intersection

Abstract :

Excited-state reactions take place via couplings among near-lying electronic states. These electronic state couplings are mediated by nuclear momenta associated with vibrational motions and become most efficient at conical intersections where two or more electronic states are degenerate at the same nuclear configuration. Thereafter, nonadiabatic reaction pathways are open so that chemical reactions are driven into particular reaction outcomes. Even though conceptual description for nonadiabatic reactions as above is nicely conceived, actual experimental evidences are quite rare. Here, we present experimental cases where conical intersections are spectroscopically characterized and associated nonadiabatic dynamic pathways are identified in energy and time domains. Specifically, predissociation dynamics of thioanisoles in the supersonic jet are thoroughly investigated to unravel detailed mechanism involved in nonadiabatic transitions taking place in the vicinity of the conical intersection encountered along the reaction coordinate.

References :

K.C. Woo, D. H. Kang, and S. K. Kim, J. Am. Chem. Soc. 139, 17152 (2017).

H. S. You et. al., Int. Rev. Phys. Chem. 34, 429 (2015).

H. S. You, S. Han, J. S. Lim, S. K. Kim, J. Phys. Chem. Lett. 6, 3202 (2015).

J. S. Lim, S. K. Kim, Nat. Chem. 2, 627 (2010).

 

February 12, 2018 at 4.00 pm in AG-69

Title :

Tracking Phospholipid Induced Coil-Helix Transitions in Phosphoinositide-binding Motifs of Actin Binding Proteins

February 5, 2018 at 4.00 pm in AG-69

Title :

Exploring the mechanical properties of Ubiquitin-CUE2 complex

January 29, 2018 at 4.0 pm in AG-69

Title :

Elucidating the Reaction Coordinate for Charge Transfer Dynamics in Organic Donor-Acceptor Frameworks

January 25, 2018 at 2.30 pm in AG-80

Title :

Chaperonin nano-machines: allostery and function

Abstract :

Chaperonins are nano-machines that are built of two back-to-back stacked heptameric rings.  They assist protein folding by undergoing large conformational changes that are controlled by ATP binding and hydrolysis.  In the E. coli cell, only about 60 different proteins require GroEL for efficient folding.  In the first part of the talk, I will describe work that was aimed at determining the properties that distinguish GroEL clients from non-clients.  In the second part of the talk, I will describe new approaches for establishing allosteric mechanisms.  Using these approaches, it was possible to show that the chaperonin GroEL from E. coli undergoes concerted intra-ring conformational changes whereas its eukaryotic homologue CCT/TRiC undergoes sequential intra-ring conformational changes.  The impact of these different allosteric mechanisms on the folding functions of GroEL and CCT/TRiC will be discussed.

January 24, 2018 at 2.30 pm in AG-69

Title :

From destructive to constructive – Using energy to strengthen polymeric materials

Abstract :

In this talk, I will present my plans to design polymers with new capabilities – ones that improve their performance as a response to distinct energy inputs. I will discuss my proposals to develop: 1) polymers that can undergo autonomous strengthening when they experience mechanical force; and 2) polymerization methods that are self-catalyzed and require less energy to perform without sacrificing the material strength of resulting polymer. The former will be achieved by designing synthetic polymers containing mechanoresponsive functional groups that can rearrange to generate strong bases under mechanical actuations. The base in turn will trigger the formation of new polymer chains leading to strengthening of the overall polymeric material. The later project aims at designing new class of phthalonitrile based polymeric resins that undergo self-catalyzed crosslinking or curing. The first generation of these phthalonitrile monomers will contain masked phenolic curing promoters that can be unmasked under mild heating in the presence of suitable additives and then trigger a self-catalyzed polymer curing process.

January 23, 2018 at 2.30 pm in AG-69

Title :

Mechanochemical strengthening of polymeric materials using piezoelectric nanoparticles

Abstract :

Mechanical actuation of synthetic polymers usually results in bond breakage leading to eventual failure. In contrast, biological systems use mechanical force for constructive purposes. For example, bones and muscles heal and become stronger under moderate levels of stress often encountered during exercise. In this talk, I will present my work towards developing synthetic polymeric materials that grow stronger under mechanical activation.

Mechanical force can be harnessed for performing constructive chemistry using the piezoelectric effect. Mechanical activation of piezoelectric nanoparticles generates several volts of electrochemical potential on the nanoscale. I present a method to harness this electro-mechanical reaction to enable polymerization reactions such as atom-transfer radical polymerization (ATRP) and copper-catalyzed azide-alkyne ‘click’ (CuAAC) using piezo reduction to generate a Cu(I) based catalysts. This research project is an entirely new area of polymer mechanochemistry and we were the first to demonstrate piezochemically-activated polymerization reactions. We are now starting to develop polymeric systems in which mechanical stress plays a constructive role. 

 

January 8, 2018 at 4.00 pm in AG-69

Title :

Organic Photocatalysis inside Water-Soluble Supramolecular Cages

January 5, 2018 at 2.30 pm in AG-69

Title :

Making and Breaking of Chemical Bonds with Visible Light

Abstract :

In the recent past visible light photoredox catalysis has gained enormous attention as an energy-efficient and versatile method for chemical synthesis.(1, 2) In my presentations, I will mainly talk about our recent work on visible light photoredox catalysis using stable radical anions of commercially available inexpensive organic dyes.(3-7) The applications of bioinspired consecutive photoinduced electron transfer (conPET)(3, 4, 6, 7) and sensitization initiated electron transfer (SenI-ET)(5) processes will be discussed in the context of breaking and making of stable chemical bonds for useful synthetic transformations.

 

References: 

 

1.  B. Konig, Eur. J. Org. Chem., 1979-1981 (2017).

2.  I. Ghosh, L. Marzo, A. Das, R. Shaikh, B. Konig, Acc. Chem. Res. 49, 1566-1577 (2016).

3.  I. Ghosh, T. Ghosh, J. I. Bardagi, B. Konig, Science 346, 725-728 (2014).

4.  I. Ghosh, B. Konig, Angew. Chem. Int. Ed. 55, 7676-7679 (2016).

5.  I. Ghosh, R. S. Shaikh, B. Konig, Angew. Chem. Int. Ed. 56, 8544-8549 (2017).

6.  A. Das, I. Ghosh, B. Konig, Chem. Commun. 52, 8695-8698 (2016).

7.  L. Marzo, I. Ghosh, F. Esteban, B. Konig, ACS Catal. 6, 6780-6784 (2016).

 

January 4, 2018 at 2.30 pm in AG-80

Title :

Stable Radical Anions in Photocatalysis

Abstract :

In the recent past visible light photoredox catalysis has gained enormous attention as an energy-efficient and versatile method for chemical synthesis.(1, 2) In my presentations, I will mainly talk about our recent work on visible light photoredox catalysis using stable radical anions of commercially available inexpensive organic dyes.(3-7) The applications of bioinspired consecutive photoinduced electron transfer (conPET)(3, 4, 6, 7) and sensitization initiated electron transfer (SenI-ET)(5) processes will be discussed in the context of breaking and making of stable chemical bonds for useful synthetic transformations.

 

References: 

 

1.  B. Konig, Eur. J. Org. Chem., 1979-1981 (2017).

2.  I. Ghosh, L. Marzo, A. Das, R. Shaikh, B. Konig, Acc. Chem. Res. 49, 1566-1577 (2016).

3.  I. Ghosh, T. Ghosh, J. I. Bardagi, B. Konig, Science 346, 725-728 (2014).

4.  I. Ghosh, B. Konig, Angew. Chem. Int. Ed. 55, 7676-7679 (2016).

5.  I. Ghosh, R. S. Shaikh, B. Konig, Angew. Chem. Int. Ed. 56, 8544-8549 (2017).

6.  A. Das, I. Ghosh, B. Konig, Chem. Commun. 52, 8695-8698 (2016).

7.  L. Marzo, I. Ghosh, F. Esteban, B. Konig, ACS Catal. 6, 6780-6784 (2016).

 

December 21, 2017 at 2.30 pm in AG-80

Title :

The electron’s spin and molecular chirality - How are they related and how can they be utilized?

Abstract :

Spin based properties, applications, and devices are commonly related to magnetic effects and to magnetic materials. However, we found that chiral organic molecules act as spin filters for photoelectrons transmission,1  in electron transfer,2 and in electron transport.3

 

The new effect, termed Chiral Induced Spin Selectivity (CISS),4,5  was found, among others, in bio-molecules and in bio-systems. It has interesting implications for the production of new types of spintronics devices,6,7 and on electron transfer in biological systems.8  The basic effect will be explained and various applications and implications will be discussed.

 

References 

 

1.Göhler, B.; Hamelbeck, V.; Markus, T.Z.; Kettner, M.; Hanne, G.F.; Vager, Z.; Naaman, R.; Zacharias,  H. Science 2011, 331, 894.

2.Mishra, D.; Markus, T.Z.; Naaman, R.; Kettner, M.; Göhler, B.; Zacharias, H.; Friedman, N.; Sheves, M.; Fontanesi, C. PNAS,   2013, 110, 14872.

3.Xie, Z.; Markus, T. Z.; Cohen, S. R.; Vager, Z.; Gutierrez, R.; Naaman, R. Nano Letters, 2011, 11, 4652.

4.Naaman, R.; Waldeck, D.H. J. Phys. Chem. Lett. (feature) 2012, 3, 2178.

5.R. Naaman, D. H. Waldeck, Spintronics and Chirality: Spin Selectivity in Electron Transport Through Chiral Molecules, Ann. Rev. Phys. Chem. 2015, 66, 263–81. 

6.O. Ben Dor,  S. Yochelis, A. Radko, K. Vankayala, E. Capua, A. Capua, S.-H. Yang, L. T. Baczewski, S. S. P. Parkin, R. Naaman, and Y. Paltiel, Nat. Comm. 8:14567 (2017).

7.K. Michaeli, V.  Varade, R. Naaman, D. Waldeck, Journal of Physics: Condensed Matter, 29, 103002 (2017) 

8.I. Carmeli, K. S. Kumar, O. Hieflero, C. Carmeli, R. Naaman,  Angew. Chemie  2014, 53, 8953 –8958.

 

December 18, 2017 at 4.00 pm in AG-69

Title : 

Synthesis of TEMPO linked Chromophore Molecules and Their Photophysical Quenching

December 14, 2017 at 2.30 pm in B-333

Title :

Computational Material Design of Two Dimensional Materials and Their Energy Applications

Abstract :

Two-dimensional materials have attracted attention from both fundamental aspects and application. In this work, we will present some of our recent effort to using first-principles based computational tools to design two-dimensional materials for energy applications. We have explored new possible ionic two dimensional materials and discover some that have not been synthesized yet1. Furthermore, their potential applications to adsorption of Li (for battery and hydrogen storage)2 and hydrogen evolution reactions3 are also examined.

 

References :

 

1.Chung-Huai Chang, Xiaofeng Fan, Shi-Hsin Lin, J-L Kuo, Phys. Rev. B, 88, 195420 (2013)

2.S-H Lin, and J-L Kuo, Phys. Chem. Chem. Phys., 16, 20763 (2014)

3.Yun-Wen Chen, Yaojun Du, and J-L Kuo, J. Phys. Chem. C, 118, 20383 (2014)

4.D. B. Putungan, S-H Lin, and J-L Kuo, Phys. Chem. Chem. Phys., 17, 11367 (2015)

 

December 13, 2017 at 11.30 am in AG-66

Title

Vibrational Anharmonicity and IR Spectra of Hydrogen Bonded Clusters

Abstract :

Structure of hydrate proton is typically classified into Eigen (H3O+) and Zundel (H5O2+) forms. While this is a textbook knowledge, it remains very challenging to keep track of their vibrational signatures owing to the strong vibrational coupling. We have developed several computational scheme to reveal the vibrational couplings (from strong to weak) with the hope to link vibrational spectra and the structure of these clusters. Gas-phase ionic spectra collected over the last two decades have provided plenty of experimental vibrational spectra that allow us to examine the vibrational motion of proton in H-bonded cations. In this talk, we will present our recent systematic theoretical studies both different types of Zundel1,2 and H3O+ under different solvation environments3,4. Our theoretical studies engage ab initio treatment on a selected set of quantum degrees of freedom and treat their vibrational anharmonicity/coupling explicitly. If time permits, we will also access the performance of a few approximate treatments on vibrational coupling/anharmonicity to treat larger hydrogen-bonded molecular clusters5

 

References 

 

1.J.A. Tan and J.-L. Kuo. J. Phys. Chem. A., 119, 11320 (2015)

2.J.A. Tan and J.-L. Kuo. Phys. Chem. Chem. Phys., 18, 14531 (2016)

3.J-W Li, M. Morita, T. Takahashi, and J-L Kuo, J. Phys. Chem. A, 119, 10887 (2015)

4.J. Tan, J-W Li, C-c Chiu, H. Huynh, H-Y Liao, and J-L Kuo, Phys. Chem. Chem. Phys., 18, 30721 (2016)

 

5.K-L Ho, L-Y Lee, M. Katada, A. Fujii, and J-L Kuo, Phys. Chem. Chem. Phys., 18, 30498 (2016)