TIFR
Department of Chemical Sciences
School of Natural Sciences

Calender

May 19, 2015 at 2.30 pm in AG-80

Title :

Grafting High Affinity Metal Coordination to Design Artificial Metalloproteins

Abstract :

Metalloproteins represent some of the best-known inorganic catalysts in nature, catalyzing difficult and important reactions with exceptional efficiency. 1 Design of artificial metalloproteins allows us to understand the critical features required for their structure and function. Equipped with this knowledge it is possible to engineer novel structures and functions not found in nature. In the first part of this talk I will focus on our efforts in de novo metalloprotein design to build self-assembling polypeptide systems capable of sequestering toxic heavy metals (Cd, Pb, Hg) with exceptionally high affinity and site-selective molecular recognition properties, and highlight the factors that control these properties. 2 In the second part I will describe a biosynthetic metalloprotein design approach to successfully engineer artificial biocatalysts mimicking a complex metalloenzyme involved in biological denitrification (nitric oxide reductases that reduce NO to N 2 ). 3 I will discuss how these model systems help us delineate the likely mechanisms by which this enzyme catalyzes this
environmentally important reaction.

(1) a)Chakraborty, S.; Hosseinzadeh, P.et al. In Encyclopedia of Inorganic and Bioinorganic Chemistry; John Wiley & SonsLtd: 2011; b)Liu, J.; Chakraborty, S.et al. Chem. Rev. 2014, 114, 4366; c) Lu, Y.; Chakraborty, S.et al. In Comprehensive Inorganic Chemistry II (Second Edition); Reedijk, J., Poeppelmeier, K., Eds.; Elsevier: Amsterdam, 2013; Vol. 3, p 565.
(2) a)Chakraborty, S.; Iranzo, O.et al. J. Am. Chem. Soc. 2012, 134, 6191; b) Chakraborty, S.; Kravitz, J. Y.et al. Angew. Chem. Int. Ed. 2011, 50, 2049; c) Chakraborty, S.; Touw, D. S.et al. J Am. Chem. Soc. 2010, 132, 13240; d) Iranzo, O.; Chakraborty, S.et al. J. Am. Chem. Soc. 2011, 133, 239.
(3) a) Chakraborty, S.; Reed, J.et al. Angew. Chem. Int. Ed. 2014, 53, 2417; b) Matsumura, H.; Hayashi, T. et al. J. Am. Chem. Soc. 2014, 136, 2420

May 18, 2015 at 4.00 pm in AG-69

Title :

Designing Nanostructures in Reaction Flask

Abstract :

How to architect different nanosutuctures in solution?  From the literature survey, one can understand that all the reaction processes in designing different kinds of nanostructures are simple and handy. Just add precursors along with few specific stabilizing ligands dissolved in appropriate solvent in the reaction flask, set the reaction temperature as per their reactivity and timely harvest; this remains the main theme of the reaction for almost all nanostructures synthesis. However, on the other side, chemists always think differently and the main goal remains on understanding the crystal growth and to induce new functional properties in the designed materials. Hence, apart from the injections of the precursors and cooking in a reaction flask, the physics and chemistry involved in the nanomaterials synthesis puzzle the chemists. However, it is really exciting to find peculiar kinds of nanostructures under the microscope, and that again boosts up when the shape evolution is tagged with the reaction chemistry followed in the reaction flask. In last thirty years, the field has improved tremendously and a wide variety of nanomaterials are already designed and reported. But, while functional materials are concerned, as per the development of new technology, developments of new materials with improved materials properties are always in demand. Keeping this view in mind, this talk would present the state of art in development of chemical synthesis of one of the most demanding functional materials, Heterostructured nanomaterials. A detail study on the physics and chemistry of designing such materials with semiconductor-semiconductor and semiconductor-noble metal hetero-junctions would be discussed. In addition, the formation mechanism in bringing two dissimilar materials with different physical/chemical properties together and the tuning of materials properties through hetero-structure formation would be presented.

May 14, 2015 at 2.30 pm in AG-80

Title :

Probing Excited State Redox Reactions Inside Molecular Containers

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.