TIFR
Department of Chemical Sciences
School of Natural Sciences

Calender

May 12, 2015 at 2.30 pm in AG-69

Title :

Studies in Visible Light Photocatalysis

May 11, 2015 at 4.00 pm in AG-69

Title :

Shape and Morphology Controlled Catalysis by Al-BTC Metal Organic Framework (MOF)

May 4, 2015 at 11.00 am in AG-80

Title :

Real time Small Angle X-ray Scattering at High Flux Synchrotrons Reveals Entropy Driven Multistate Ubiquitin Unfolding Reaction

April 30, 2015 at 4.00 pm in AG-80

Title :

Sequence- and Complexation-dependent Modulation in Equilibrium Flexibility of Ubiquitin and SUMO proteins

April 20, 2015 at 4.00 pm in AG-69

Title :

An Unusual EF-hand Ca2+-binding protein: Structure, Dynamics and Ca2+-binding properties

April 16, 2015 at 2.30 pm in AG-80

Title :

Immobilization of Metal Complexes (Pd, Mn) Over Mesoporous Materials: Synthesis, Characterization and Application for Oxidation, Hydrogenation and C-C Coupling Reactions

Abstract :

The surface modification of M41S type mesoporous materials by transition metal complexes or reactive organic functional groups allows the preparation of multifunctional heterogeneous catalysts with desired catalytic properties. Taking into account of environmental consideration the hetrogenization of organo-catalyst of transition metal complex over organic-inorganic hybrid mesoporous support such as PMO and SBA-15 are focused. The mesoporosity and very high surface area of the surface-functionalized mesoporous materials can also be exploited for the immobilization of different catalytically reactive species. The principal aim of my research is to investigate the approach of heterogenization of various transition metals complex over solid mesoporous supports (SBA-15) and organic-inorganic hybrid mesoporous materials (PMO) for oxidation, hydrogenation and C-C coupling reactions, under different reaction conditions.

 

          Mesoporous silica materials represent a unique class of silica and organic-inorganic hybrid based materials viz; SBA-15 and PMO act as a support which have received much attention because of their uniform hexagonally ordered two dimensional mesoporous channels structure, high specific surface area, large pore volume, uniform pore size (between 2-50 nm), high hydrothermal stability and rich surface chemistry allowing ready diffusion of reactants to the active sites located in the nanopores. Homogeneous catalyst can be immobilized by different ways such as electrostatic interaction, covalent bonding and simply physical adsorption over support etc. Among the various types of immobilization covalent interaction is superior, which involve direct bonding between organic moieties with heterogeneous support through linker group. The recent discovery of the Cu(I)-catalyzed 1, 3-dipolar cycloaddition of organic azides to alkynes has provided the most powerful “click chemistry” tool for conjugation between appropriately functionalized binding partners via an 1, 2, 3-triazole linkage. Additionally, the surface modification of the synthesized mesoporous materials were done by using various organic and organo silane groups, such as 3-aminopropyltrimethoxysilane (3-APTMS), 3-mercaptopropyltrimethoxysilane (3-MPTMS), 3-azidopropyltrimethooxysilan (3-Az-PTMS) (click reaction) for transition metal complexes anchoring by post synthetic route to develop new class of mesoporous catalysts. In-depth characterizations of all synthesized catalyst systems are highlighted to understand the mode of interaction of the active sites in transition metal complex with the mesoporous silicate network and to evaluate the structure-catalytic activity relations and stability of the mesoporous solids for oxidation, hydrogenation and C-C coupling reactions.

April 13, 2015 at 4.00 pm in AG-69

Title :

Adaptive Pores: Reversible Pore Engineering of Mesoporous Silica

Abstract :

Non-covalent and dynamic covalent methods were used to reversibly modify the pore size and philicity of mesoporous silica. In the non-covalent approach, the strong, charge-transfer interactions between pyranine and viologen moieties were usedfor reversible pore engineering.The fast binding of donors enabled quick and facile functionalization at room temperature. The viologen based charge transfer modules were employed in electrostatic gating of ion transport through the nanochannels (<10 nm)  in mesoporous silica. The polarity of ion transport was switched from anion selective to cation selective through ambipolar stage by controlling the extent of pyranine bound to the viologen. Further, the ion transport could be regulated with respect to pH by selecting a donor (coronenetetracarboxylate) with pH responsive functional groups. In the dynamic covalent approach, the reversible bonding between amine and aldehyde has been utilized to reverse the pore properties of silica. The modularity of the approach enables modification of nanopores with custom designed compositions, components and functions.

References:

1.  B. V. V. S. Pavan Kumar, K. V. Rao, T. Soumya, S. J. George

    and M. Eswaramoorthy, ,J. Am. Chem. Soc.,  135, 10902 -

    10905 (2013)

2. B. V. V. S. Pavan Kumar, K. Venkata Rao, S. Sampath,

   S. J. George and M. Eswaramoorthy,  Angew. Chem. Int. Ed.,

   53, 13073-13077  (2014). 

April 6, 2015 at 4.00 pm in AG-69

Title :

Molecular Basis for Optimizing Organic Photovoltaics

March 30, 2015 at 4.00 pm in AG-69

Title :

Selective C-H Functionalization Reaction

Abstract :

Palladium catalyzed coupling between aryl halides and alkenes (Mizoroki-Heck reaction) is one of the most popular reactions for synthesizing complex organic molecules. The limited availability, problematic synthesis, and higher cost of aryl halide precursors (or their equivalents) have encouraged exploration of direct olefination of aryl carbon-hydrogen (C–H) bonds (Fujiwara-Moritani reaction). Despite significant progress, the restricted substrate scope, in particular noncompliance of unactivated aliphatic olefins, has discouraged the use of this greener alternative. Overcoming this serious limitation, a palladium-catalyzed chelation-assisted ortho-C–H bond olefination of phenyl acetic acid derivatives with unactivated, aliphatic alkenes in good to excellent yields with high regio- and stereoselectivities has been reported. The versatility of this operationally simple method has been demonstrated through drug diversification and for synthesizing divinyl benzene derivatives.

March 23, 2015 at 4.00 pm in AG-69

Title :

Spectroscopic and Ab-initio Studies of OH---S and CH---Y(Y=O,S) H-bonded Systems

March 18, 2015 at 2.30 pm in AG-69

Title :

Modeling the Metabolic Pathways

March 11, 2015 at 2.30 pm in AG-69

Title :

Stability, metastability and aggregation in Prion proteins: Importance of capturing the rare events

Abstract :

In contrast to the molecular machinery where nature performs fascinatingly well, there are many examples where things may go terribly wrong leading to life-threatening diseases! In this talk we shall try to understand the elusive problem of “prion propagation” and their aggregation into insoluble fibrils that cause a multitude of neurodegenerative disorders. I shall talk about our recent efforts in identifying the mysterious misfolded scrapie (PrPSc) form of a prion protein that is considered to infect the healthy cellular prions (PrPC) by inducing misfolding in them. Using extensive Replica Exchange Molecular Dynamics (REMD) simulations we have been able to identify many low-lying transient misfolded states that might catalyze the aggregation pathway through hydrophobic interactions. We also speculate that the secondary structural elements in a cellular Prion are in fact stabilized by weak tertiary contacts leading to very low barrier towards misfolding.

We shall also discuss our futuristic ideas about understanding the hydrophobic effects around a complex molecular surface (e.g. proteins), which seem to play a very important role in various self-assembly, aggregation and binding processes. Our long term goal would be to build a computationally efficient, yet quantitative implicit solvation model that would give us solvation thermodynamics of any arbitrary molecular surface.

 

March 10, 2015 at 2.30 pm in AG-69

Title :

The curious case of Cytochrome c Oxidase: Role of protein electrostatics in biomolecular structure-function correlation

Abstract :

Nature has created a wide array of fascinating molecular machinery, and their efficiency is unparalleled when compared to their man-made counterparts. Be it photosynthesis (conversion of light into chemical energy), or enzyme catalysis (speeding up difficult chemical reactions), or ion channels (filtration device with high degree of specificity), or self-assembly of small molecules into organized structures, we have a lot to learn from biology! The need for a molecular level understanding of nature has been dramatically asserted by Richard Feynman: Everything that living things do can be understood in terms of the jiggling and wiggling of atoms. Following this ambitious approach, my goal is to understand the complex biomolecular functions and properties from a molecular point of view. Using statistical mechanics based computational techniques, we are able to connect the molecular interactions (energetics) to their structural, thermodynamic and kinetic properties. The ultimate challenge is to obtain the underlying free energy surfaces for any (bio)chemical processes with quantitative accuracy and computational efficiency.

In this talk, I shall take up the example of the fascinating molecular machinery involved in the proton transport processes in a trans-membrane enzyme Cytochrome c Oxidase (CcO), which reduces oxygen (O2) to water in our respiratory cycle and uses the released energy to pump protons across the membrane. I shall discuss the importance of electrostatic interactions, the role of dielectric heterogeneity of the protein interior in affecting the pKa and protonation state of the key ionizable residues, and the role of internal water molecules therein. We shall demonstrate how molecular thermodynamics can provide physical insights into the function of complex biomolecules.

 

March 9, 2015 at 4.00 pm in AG-69

Title :

Fluorescent Sensors for Signaling Phospholipids

March 5, 2015 at 4.00 pm in AG-80

Title :

Elucidating the Structural Basis of Substrate Recognition by the Proteasomes: A Global Approach

Abstract :

PSMD9, a non-ATPase subunit of the 19S regulatory complex of the 26S proteasome harbours an uncharacterized PDZ-like domain which is well known for protein-protein interaction. PDZ domains interact with C-terminal residues of the interacting partner. In quest for partners of PSMD9, we performed C-terminal tetrapeptide screen representing the C-termini of proteins of human proteome to test the ability of these peptides to bind to PSMD9 and consequently demonstrate that proteins harbouring those C-terminal residues interact with PSMD9. Here, we report that PSMD9 interacts with the C-terminal residues of hnRNPA1, S14, a ligand growth hormone and IL6 receptor via its PDZ-like domain. Studies in our lab have also shown that PSMD9-hnRNPA1 interaction is important for NF-κB signaling. Through homology modeling, docking studies, site directed mutagenesis and simulation, we provide an insight into the probable structure of PDZ domain of PSMD9 and the residues important for the interaction and functions of PSMD9.