Assembly of Nanoparticles and Single Molecule Raman Spectroscopy
It can be argued that Natureâ€™s greatest gifts to living beings are the molecules. The chemical bonds â€˜connectingâ€™ 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 â€˜bondsâ€™. 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 â€˜hot spotâ€™ 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.
September 22, 2017
Amitava Das, Director, CSIR-Central Salt & Marine Chemicals Research Institute; G.B. Marg, Bhavnagar: 364002, Gujarat, India
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.
September 15, 2017
S Chandrasekhar, Director, CSIR-Indian Institute of Chemical Technology, Hyderabad
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.
August 18, 2017
Balasubramanian Sundaram, Chemistry & Physics of Materials Unit, JNCASR, Bangalore
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.
August 04, 2017
Prof. S. Natarajan, Solid State Structural Chemistry Unit, IISc., Bangalore
Venue & Time: C V Raman Hall at 4-00 PM - 5.30 PM.
Interplay of Coordination Geometry, Structure and d â€“ d Transitions in the Design of New Chromophores in the Solid State
Crystalline inorganic oxides displaying bright colours attracted much attention from early days for application as gemstones and pigments. Ruby (Cr3+ doped Al2O3) and Emerald (Cr3+ doped Be3Al2(SiO3)6) and Azurite (Cu3(CO3)2(OH)2), Han blue (BaCuSi2O6) and Turquoise (CuAl6(PO4)4(OH)8â€¢4H2O) for example found application as gemstones and pigments since ancient times. In addition to the naturally occurring gemstones and pigments, several man-made (synthetic) coloured solids were also developed to meet the demand. Thus, hydrated chromium oxide (Viridian), cobalt aluminate (Thernardâ€™s blue) and various cadmium sulphides (Cadmium Yellow, Cadmiun Red) as well as anhydrous Fe2O3 (Red ochre) are some of the early synthetic pigments for green, blue, yellow and red colours respectively. Y2BaCuO5, copper substituted apatites, Mn(III) substituted YInO3 and CaTaO2N â€“ LaTaON2 pervoskites are some of the more recent pigment materials for green, blue, red-yellow colours.[2-5] A scientific inquiry into the origin of colours of inorganic solids is essential for a rational design and synthesis of coloured materials. While there are several causes for the colour of solids, the main factor that causes colour in an inorganic oxide containing transition metal ion is the electronic transitions within the partially filled d-states arising from the ligand field effects around the transition metal ion. Octahedral and tetrahedral are the most common geometries where the colour and optical absorption spectra of all the transition metal ions have been well-documented. Transition metal ions in less symmetric geometries such as distorted octahedral and five-fold coordinated (square pyramidal and trigonal bipyramidal) geometries produce colours different from those in regular octahedral and tetrahedral geometries in materials. The present talk would address some of these issues and our efforts towards identifying new chromophores employing transition metal chemistry.[6-12]
1. P. Ball, Bright Earth: Art and the Invention of Color, The University of Chicago Press, Chicago, 2001.
2. P.E. Kazin, M.A. Zykin,Y.V. Zubavichus, O.V. Magdysyuk, R.E. Dinnebier, and M. Jansen, Chem. â€“European J., 2014, 20,165 â€“ 178.
3. J. K. Kar, R. Stevens, C. R. Bowen, J. Alloys Compd. 2008, 455, 121-129.
4. A. E. Smith, H. Mizoguchi, K. Delaney, N. A. Spaldin, A. W. Sleight, M. A. Subramanian, J. Am. Chem. Soc., 2009, 131, 17084-17086.
5. M. Jansen, H. P. Letschert, Nature, 2000, 404, 980-982.
6. S. Tamilarasan,D. Sarma, S. Natarajan and J. Gopalakrishnan, Inorg. Chem., 2013, 52, 5757 â€“ 5763.
7. S. Tamilarasan, D. Sarma, M.L.P. Reddy, S. Natarajan, J. Gopalakrishnan, , RSC Advances, 2013, 3, 3199 â€“ 3202.
8. S Tamilarasan, S Laha, S Natarajan, J Gopalakrishnan, J. of Mater. Chem. C, 2015, 3(18), 4794-4800.
9. S. Tamilarasan, S. Laha, S. Natarajan and J. Gopalakrishnan, Eur. J. Inorg. Chem., 2016, 288 â€“ 293.
10. S. Laha, S. Tamilarasan, S. Natarajan and J. Gopalakrishnan, Inorg. Chem., 2016, 55, 3508 â€“ 3514.
11. S. Laha, S. Natarajan and J. Gopalakrishnan, Eur. J. Inorg. Chem., 2016, 288 â€“ 293.
12. A. Bhim, J. Gopalakrishnan and S. Natarajan, Eur. J. Inorg. Chem., 2017 (submitted)
July 28, 2017
Prof. G.U. Kulkarni, Centre for Nano and Soft Matter Sciences, Bangalore
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 . 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 . 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.
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.