TIFR
Department of Chemical Sciences
School of Natural Sciences

Calender

April 4, 2019 at 4.00 pm in AG-80

Title :

Probing Singlet Fission on all-trans Lycopene Aggregates

April 2, 2019 at 2.30 pm in AG-80

Title : 

Computational Descriptions of Bis-terpyridine Based Molecular Breadboard Circuits and their Single-Molecule Break Junction Conductance

April 1, 2019 at 4.00 pm in AG-69

Title :

Designing Protein-Specific Folding Catalysts

March 28, 2019 at 2.30 pm in D-406

Title :

Design and Synthesis of Conjugated Molecules for Band Gap Engineering and Photostability of OPVs

Abstract :

             Organic photovoltaic (OPV) modules are flexible, light weight, transparent and thin compared to other emerging photovoltaic technologies, making them well-suited for applications ranging from solar windows to fabrics. A large number of polymer semiconducting materials of Donor-Acceptor–Donor (D-A-D) architecture have been synthesized and used in OPV devices in recent times reaching remarkable power conversion efficiencies up to 15%. However, the diversity of monomeric units and the numerous available reports in the structural complexity of D-A-D conjugated p-type polymers indicate that there is scope for new materials which can further improve the performance of OPV devices based on D-A-D polymers. In this seminar presentation, I will discuss briefly about my Ph.D. thesis work. The first part of work explores structural level architecturing of conjugated small molecules and polymers to modify the performance of the OPVs. Demonstrate the effect of molecular level modification on frontier molecular energy levels, planarity, absorption spectra and device performance. 

             Additional to the development in power conversion efficiency of the OPVs, the cost of large area OPV device manufacture continues to decrease with improvements in roll-to-roll manufacturing processes. However, while these advances in efficiency and cost will ultimately the key to the success of the technology, the long term stability of OPV devices under illumination still remains an obstacle to their industrial viability. While the thermal and oxidative-stability of contacts and interfaces in an OPV device can contribute to a decrease in its performance with time, a leading contributor to device decay is photo-oxidation of the active layer itself. 

 

             Hence in the second part of the work, a series of chalcogen based polymers have been synthesized and the photostability of the unencapsulated active layers and the device life time has been monitored over a period of time. The thesis work has further investigated the photostability of several combinations of fluorinated and non-fluorinated high-performance donor polymers with both traditional and fluorinated fullerenes. The miscibility of the active layer component is probed with time-resolved photoluminescence (TRPL). The miscibility of the polymers and the fluorinated fullerenes were improved by the strategic fluorination of the polymers, by new synthesis routes. These results ultimately suggest that appropriate fluorination strategies applied to both the donor and acceptor can be a viable route toward a new model of intrinsically photo- and phase-stable OPV active layers.

 

March 25, 2019 at 4.00 pm in AG-69

Title :

Fluorescent Sensors for Imaging Signal Mediating Phospholipids

March 7, 2019 at 2.30 pm in AG-80

Title :

Functional Bridged Silsesquioxanes and applications

Abstract :

Click here

March 5, 2019 at 2.30 pm in AG-69

Title :

Tuning Photo-functionalization of sp2 Carbon-Hydrogen Bond Inside Water Soluble Supramolecular Nanocage

February 28, 2019 1t 4.00 pm in AG-80

Title :

Electron Tunneling Barriers in Marcus Theory and Floppy Molecular Breadboard

February 26, 2019 at 2.30 pm in AG-69

Title :

Solvated Metal Atom Dispersion and Digestive Ripening – Duo par excellence for Diverse Nanostructured Materials

Abstract :

The properties of nanostructured materials strongly depend on their size, shape, interparticle distance, and the surrounding environment which could be tuned precisely by controlling the particle size of the material. Size dependent property of a polydisperse sample is an average effect due to the presence of different sized particles in the system. The property exhibited by a monodisperse sample however, could be ascribed as emerging from a single entity. Control over size and size distribution is indispensible for attaining a desired property. A lot of attention is focused on developing synthetic strategies leading to monodispersity and those that are simple to manipulate, easy to scale up and highly reproducible.

We have been using the Solvated Metal Atom Dispersion (SMAD) method for the synthesis of colloids of metal nanoparticles. The as-prepared colloid from this method consists of polydisperse metal nanoparticles. In a process termed as digestive ripening, addition of a surfactant to the as-prepared sample renders it highly monodisperse. This combination, SMAD and digestive ripening has recently been extended to obtain nearly monodisperse semi-conductor nanostructured materials as well. In this talk, the power of the SMAD and the (co)digestive ripening processes will be demonstrated toward the synthesis of highly monodisperse metal, core-shell, alloy, intermetallic, and composite nanostructured materials. Additionally, applications of some of the materials synthesized using this methodology in the fields of hydrogen storage and generation, magnetism, catalysis, and surface enhanced Raman scattering will also be discussed.

 

February 21, 2019 at 12.15 pm in AG-69

Title :

[FeFe] Hydrogenase H-cluster Biosynthesis

Abstract :

Radical SAM enzymes (1) use a [4Fe-4S] cluster to cleave S-adenosylmethionine to generate the 5’-deoxyadenosyl radical, which in turn abstracts an H-atom from a given rSAM enzyme’s substrate to initiate catalysis. As an example, the RS enzyme HydG lyses tyrosine to generate the CO and CN ligands of the H-cluster of [FeFe] hydrogenase, building an organometallic Fe(CO)2CN(cysteine) moiety that incorporates an iron atom derived from a unique 5-Fe Fe-S cluster (2-7).  We have recently characterized the first organometallic intermediate of this catalytic cycle (8) (figure panel).  This presentation will focus on the use of EPR spectroscopy to interrogate the geometrical and electronic stuctures of such rSAM enzyme intermediates. Additionally, using HydG along with two other Fe-S maturase enzymes HydE and HydF, we can use cell free synthesis to precisely isotope-edit the H-cluster, which can then be fruitfully probed via EPR spectroscopy targeting its paramagnetic intermediates in the hydrogen oxidation or proton reduction catalytic cycle. New cell free synthesis experiments exploring the effects of deleting subsets of the maturases or adding synthetic analogs in the assembly process are giving new insights into the overall bioassembly of this important metallo-cofactor.

 

1.Horitani et al., Science (2016) 6287:822-825

2.Myers  et al., J. Am. Chem. Soc. (2014) 136:12237-12240.

3.Kuchenreuther et al., Science (2013) 342:472-475

4.Kuchenreuther et al., Science (2014)  343:424-427

5.Dinis et al., Proc. Natl. Acad. Sci. U.S.A.  (2015) 112:1362-1367.

6.Suess et al.,  Proc. Natl. Acad. Sci. U.S.A. (2015) 112:11455-11460. 

7.Suess, et al., J. Am. Chem. Soc. (2016) 138:1146-1149. 

 

8.Rao et al., Nat. Chem. (2018) 10:555-560.

Pulse EPR Characterization of the first organometallic intermediate in Fe-Fe hydrogenase bioassembly  formed by the radical SAM enzyme  HydG (ref 8)

February 21, 2019 at 11:30 am in AG-69

Title :

Activity-Based Sensing Approaches to Decipher Transition Metal Signaling

Abstract :

Traditional strategies for development of chemoselective imaging reagents rely on molecular recognition and static lock-and-key binding to achieve high specificity. We are advancing an alternative approach to chemical probe design, termed activity-based sensing (ABS), in which we exploit inherent differences in chemical reactivity as a foundation for distinguishing between chemical analytes that are similar in shape and size within complex biological systems. This presentation will focus on ABS approaches to develop new fluorescent probes for transition metals and reactive oxygen, sulfur, and carbon species and their signal/stress contributions to living systems, along with activity-based proteomics to identify novel targets and pathways that these emerging classes of chemical signals regulate.

February 20, 2019 at 3.15 pm in AG-69

Title :

Renewable Carbon Engineering Confluence of Modern Biological & Chemical Sciences

Abstract :

World depends heavily on non-renewable fossil products for its energy, materials and chemical needs. Climate trends over past two decades necessitate an aggressive path towards reducing carbon emissions and increasing use of renewable carbon. The total of available renewable carbon is likely to be a combination of first generation (food derived), second generation (non-food derived), third generation (non-land use change) and fourth generation (CO2) carbon. Mankind generates substantial quantities of under-utilized surplus agricultural wastes as also other wastes such as municipal solid wastes, municipal liquid waste and industrial wastes. All these put together have the potential to fully substitute petroleum fuel and materials requirements of the world. Thus there is a need to be able to engineer the available renewable carbon to the products in use today. 

Renewable carbon however presents itself in varied and complex forms, and novel science and technology platforms are needed in order to derive desired products from these at reasonable costs. Sustainable and scalable technology platforms are being conceptualised, designed and scaled up at the DBT-ICT Centre for Energy Biosciences using combinations of chemical and biological processes that can convert carbonaceous wastes into products that are today derived from petroleum. The presentation shall broadly discuss these platforms that are likely to have impact on designing sustainable economies.

 

February 20, 2019 at 2.30 pm in AG-69

Title :

Probing Ultrafast Chemical Dynamics Inspired by the Rhythms of Fireflies

Abstract :

Coherence phenomena arise from interference, or the addition, of wave-like amplitudes in phase [1]. While coherence has been shown to yield transformative new ways for improving function, advances have been limited to pristine matter, as quantum coherence is considered fragile. Here I will discuss how vibrational and vibronic wavepackets entrain ensembles of molecules, like the synchronized flashing of fireflies. I will discuss how this can be used to probe mechanisms of ultrafast dynamics and how in-step vibrational motion might be employed to control function on ultrafast timescales. I will give examples that include light-harvesting in photosynthesis, energy flow in organometallic molecules that is ‘wired’ by Fermi resonance, and ultrafast electron transfer in molecular systems. 

[1] Scholes, et al. “Optimal Coherence in Chemical and Biophysical Dynamics” Nature 543, 647–656 (2017).

February 19, 2019 at 2.30 pm in AG-69

Title :

Photodissociation of Acetylacetone:  Photoionization and Threshold Photoelectron Spectroscopy Reveal Much More Than OH Radicals

Abstract :

The absorption of light by an organic molecule, and the subsequent pathways for energy transformation and release, are fundamental process governing life on earth.  Two of the most important electronic chromophores in organic systems are C=O bonds (carbonyl molecules) and C=C bonds (alkenes and polyenes).  Carbonyl molecules, such as acetaldehyde (CH3CHO) also have enol tautomers (H2C=CHOH, vinyl alcohol).  This tautomerization converts the weakly absorbing C=O chromophore to a strongly absorbing C=C chromophore.  We have studied the photodissociation of acetylacetone (AcAc), which exists at 300 K in the gas phase mostly as the enolone tautomer, rather than the diketo tautomer (see figure).  The enolone tautomer is stabilized by both  conjugation and an internal hydrogen bond.  Previous studies have concluded that OH loss is the dominant (or only) channel when AcAc is excited in the ultraviolet at 266 or 248 nm.  However, truly universal detection techniques have not been used in these studies.  By combining multiplexed photoionization mass spectrometery (MPIMS), threshold photoelectron photoion coincidence spectroscopy (TPEPICO), and time-resolved infrared absorption spectroscopy of OH radicals, we have discovered that photodissociation of AcAc is much richer than previously presumed, and that OH production is not even energetically allowed following one-photon excitation at 266 or 248 nm.  This work demonstrates the power of multiplexed, universal detection of charged particles in photodissociation studies, and lifts the veil on the photodissociation of a molecule that is both an enol and a ketone.

February 14, 2019 at 4.00 pm in AG-80

Title :

Development of Alkane hydroxylating Biocatalyst using Cytochrome P450 enzyme