Quantum Crystallography: A charge density route to understand molecular interactions

High resolution X-ray diffraction data analysis is established to provide extensive quantitative inputs to evaluate the electron density distribution in molecular crystals. Theoretical approaches have been designed in recent years to obtain inputs at the same level of reliability and sophistication and hence it has become possible to obtain interesting features of atoms in molecules and molecules in crystals. In this talk the identification of s- and p- holes and their role in directing intermolecular interactions, particularly involving the elements of the groups 14-17, will be outlined and new types of bonding will be characterized.

Nature and Strength of Non-Covalent Interactions

Historically, the deviation from Ideal Gas law in the case of real gases was the first realization of intermolecular interactive forces. This was attributed to weak van der Waal’s forces (or London forces) that exist in all atomic and molecules gases. Later, in 1937 Linus Pauling based on the empirical observations available by thenintroduced another type of interaction, namely, hydrogen bonding interaction. In the last several decades a number of different types of weak interactions and their influence on dictating the properties of substances, influences on the activities have been reported. Our group has been working on experimental characterization of hydrogen bonding interaction prevalent in biological milieu. In this talk I will focus mainly on our work on unconventional hydrogen bonding interactions involving sulfur and carbon atoms.

Probing the Anticancer Potential of Curcumin Metal Complexes

Curcumin is the active ingredient of turmeric (Haldi) which exhibits cancer preventive properties. Its utility is, however, severely limited due to its hydrolytic instability and poor bio-availability. It is listed in this year (2017) under PAINS (pans-assay interference compounds) and IMPs (invalid metabolic panaceas) thus negating the beneficial biological effects of this important natural product [1]. It has been observed that metal complexes of curcumin are stable and less susceptible from its hydrolytic degradation in a cellular medium. Coordination of curcumin to a metal ion in its enolic form significantly enhances its stability and activity. Curcumin dye being a fluorescent molecule allows one to do imaging studies on the cellular uptake of the complexes in different organelles of the cells. The efficacy of curcumin can be augmented on its photo-activation using it as a photosensitizer like Photofrin used in Photodynamic therapy (PDT) of cancer [2]. Photo-activation of a PDT drug results in the selective damage of the cancer cells by producing reactive oxygen species (ROS) at the photo-exposed cancer cells leaving the unexposed healthy cells minimally affected. The utility of curcumin based metal complexes as PDT agents is relatively new and unexplored. Recent work from our group has shown that 3d/4f-metal complexes of curcumin (Hcur) in the presence of different ancillary ligands in a ternary structure exhibit significant PDT effect in visible light. Recent developments in this chemistry will be presented highlighting the light-induced anticancer activity [3].

[1] K. M. Nelson, J. L. Dahlin, J. Bisson, G. F. Pauli and M. A. Walters, J. Med. Chem. 2017, 60, 1620.
[2] D. E. J. G. J. Dolmans, D. Fukumura, R. K. Jain, Nat. Rev. Cancer 2003, 3, 380.
[3] S. Banerjee, A. R. Chakravarty, Acc. Chem. Res. 2015, 48, 2075; U. Bhattacharyya, B. Kumar, A. Garai, A. Bhattacharyya, A. Kumar, S. Banerjee, P. Kondaiah and A.R. Chakravarty, Inorg. Chem. 2017, 56, 12457; K. Mitra, S. Gautam, P. Kondaiah and A.R. Chakravarty, Angew Chem. Int. Ed. 2015, 54, 13989.

Assembly of Nanoparticles and Single Molecule Raman Spectroscopy

It can be argued that Nature’s greatest gifts to living beings are the molecules. The chemical bonds ‘connecting’ the atoms in three dimensions define the nature of the molecule. On the other hand, an imagination, this is persistent amongst the scientists practicing nanoscale science and technology, is to be able to organize nanoscale particles in one, two and three dimensions in a programmed manner. This is to achieve new properties in the organized structures, in addition to those available with the constituent units. We work on the development of principles to systematically organize nanoscale particles using molecules as the ‘bonds’. This is based on chemical reactions in the liquid medium. Our current focus is to find ways of organizing metal nanoparticles, quantum dots and atomic clusters. For example, we discovered that complexation reaction on the surface of quantum dots leads to a new species the physical properties of which are more than simple combinations of those of the quantum dot and the complex.1 The approach may also lead to obtaining higher order structures of the combined constituents. On the other hand, we observe that organization of organic ligand-stabilized atomic clusters is rather facile if pursued via the formation of inorganic complexes. For example, zinc ion mediated assembly of gold clusters produced nanoscale particles, which could be used for the reversible storage of gaseous hydrogen or for chiral recognition and separation of molecules.2,3 Further we find that the formation assembly of noble metal nanoparticles - using molecules - is more challenging with the presence of zero valent metal atoms on the surface. Howbeit, use of a new inorganic complex helped form dimers of gold nanoparticles with considerable yield.2 The plasmonic ‘hot spot’ in between the dimer provided eminent opportunity to pursue Raman spectroscopy of single molecule.4

1. Pramanik, S.; Bhandari, S.; Roy, S.; Chattopadhyay, A. Synchronous Tricolor Emission-Based White Light from Quantum Dot Complex. J. Phys. Chem. Lett. 2015, 6, 1270-1274.
2. Basu, S.; Paul, A.; Chattopadhyay, A. Zinc Mediated Crystalline Assembly for Expedient Hydrogen Storage and Sensing. J. Mater. Chem. A 2016, 4, 1218-1223.
3. Basu, S.; Paul, A.; Chattopadhyay, A. Zinc-Coordinated Hierarchical Organization of Ligand-Stabilized Gold Nanoclusters for Chiral Recognition and Separation. Chem. Eur. J. 2017, 23, 9137-9143.
4. Dutta, A.; Chattopadhyay, A. Surface and Tip Enhanced Raman Spectroscopy at the Plasmonic Hot Spot of a Co-Ordination Complex Conjugated Gold Nanoparticle Dimer. J. Phys. Chem. C 2017; DOI: 10.1021/acs.jpcc.7b07301.

Molecular Assemblies for Predictive Responses

Purpose-built molecules that are capable of functioning in a predictive manner in the presence of a certain external stimulation is an important area of contemporary research and has significance for chemistry, clinical biology, diagnostic and photoactive smart material. Various photo-induced responses are being utilized for designing such photoactive molecules. Derivatives of BODIPY or Rhodamine derivatives with varying photo-induced responses have been extensively used by researchers active in these areas. Rich photophysical properties, the stability of the photoinduced excited states and reversible redox behavior are crucial parameters that need to be considered while designing a receptor specific for each of these various applications. Our research interests include harnessing both coordinative interactions as well as various nonbonding interactions for realizing our goal. Non-invasive imaging approach is preferred for observing individual events in cells, as imaging studies are performed in physiologically authentic environments and have relevance for cell/molecular biology for studying biochemical processes. There are significant activities in designing appropriate imaging reagent for visualization of specific organelles with organelle-selective dyes in the membrane-enclosed intracellular structures, as this helps in gaining insight for monitoring important biological processes. Stability towards photo-bleaching, cell membrane permeability, nominal cytotoxicity and luminescence in the longer wavelength following excitation with non-harmful visible light are some of the essential criteria for any such efficient imaging reagents. Some of our recent efforts in addressing these issues the area of cellular imaging and photo-induced toxicity shall be discussed.

Molecules with Celebrity Status

Nature, through biosynthetic pathways, generates simple to architecturally very complex carbon frameworks which have medicinal value to cure diseases. Despite great progress made in the health care, the mortality rate globally is still at a very high rate. There are several diseases for which the root cause needs to be understood well before discovering drugs. These include Cancer, CNS and infection disorders. Natural Products have been a source of inspiring starting molecules in early drug discovery. Several natural products and synthetic molecules have attained the status of "True Celebrity".Our research group has been engaged in both total synthesis of bioactive natural products and their synthetic analogs towards identifying newer drug leads.

The lecture will highlight our contributions in the synthesis of natural products, which have relevance in identifying leads in Cancer, CNS and infection disorders. Some background on the molecules, which have changed the world with wonder properties, will also be discussed.

Molecular Modelling: Applications to Gas Storage, Self Assembly & Ion Transport

Accurate molecular modelling methods have evolved over the last few decades to such an extent that it is possible to predict properties of matter quite reliably. The techniques range from quantum chemical approaches, atomistic simulations, coarse grained and mesoscale methods and offer considerable insights into microscopic phenomena which determine the behavior of materials under any condition or form. The talk will cover basic aspects of modelling methods and will illustrate them with examples which include: Storage of carbon dioxide in porous materials, supramolecular polymerization in non-polar solvents, and room temperature ionic liquids.

From mud cracks to Optoelectronic devices- Our efforts in translating Invention to Technology

Visibly transparent yet electrically conducting materials are rare. Conventionally used tin doped indium oxide (ITO)glass plates are not only expensive but are also not suitable for flexible displays due to brittle nature of the coating itself. In recent years, many alternative transparent conductors are being developed, someimportant ones beingdoped ZnO and conducting polymer films, graphene, carbon nanotube networks, metal nanowire networks and lithographic patterns.Replacing the well established ITO foundry is not all that trivial [1-3].In the recent past, we have developed a method which makes use ofcrack network in desiccated colloidal layer as template for growing metal nanowires [4]. From early efforts of optimizing the method [5,6] to fabricatingand successfullydemonstrating almost all optoelectronic devices without the aid of ITO, has been a journey filled withexcitements and challenges. The recipe has been extended to many other devices, essentially realizing a world of transparent electronics; themost recent example is a transparent and flexible supercapacitor [7]. The presentation will begin with an introduction to the topic providing an overview of the efforts being made in the literature to replace ITO. This will be followed bya description of the various results obtained from the laboratory including theoretical understanding of the process.The presentation will also bring out our herculean efforts in translating this invention intoa technology potentially attractive to industry.

References
1. G. U. Kulkarni, S. Kiruthika, R. Gupta, K. D. M. Rao, Curr. Opin. Chem. Eng. 2015, 8, 60.
2. D. S. Hecht, L. Hu and G. Irvin, Adv. Mater.,2011, 23, 1482.
3. S. Ye, A. R. Rathmell, Z. Chen and I. E. Stewart, B. J. Wiley,Adv. Mater.,2014, 26, 6670.
4. S. Kiruthika, R. Gupta, K. D. M. Rao, S. Chakraborty, N. Padmavathy, G. U. Kulkarni, J. Mater. Chem. C 2014, 2, 2089
5. K. D. M. Rao, G. U. Kulkarni, Nanoscale2014, 6, 5645
6. K. D. M. Rao, R. Gupta, G. U. Kulkarni, Adv. Mater. Interfaces 2014, 1.
7. S. Kiruthika, C. Sow, G. U. Kulkarni, Small, 2017, Just accepted.