Calendar

• Seminar by Mr. Dinesh Kumar Yadav, Dept. of Chemical Sciences, TIFR, Mumbai on September 16, 2021 at 4.00 pm (via Zoom)

  Title:

  Protein Electrochemistry: Metal Complexes as a Promoters of the Electron Transfer from a Gold Electrode to Cytochrome c

  Abstract:

  Direct protein electrochemistry is an important method to determine the redox potential and electron transfer kinetics of metalloproteins. The bare metal electrode generally causes irreversible adsorption and denaturation of the protein on the electrode surface. There have been extensive studies on modification of the gold electrode using thiol functionalized promoters. We have investigated the effect of metal ion binding to a thiol-based Schiff base complex immobilized on the gold electrode for the electron transfer to cytochrome c. Selfassembled Monolayer (SAM) contains Schiff-Base ligand formed by cysteine and salicylaldehyde on the gold electrode was shown to promote quasi-reversible electrochemistry of cytochrome c. Various transition metal complexes of the Schiff-base ligand immobilized on the gold electrode were also found to promote electrochemistry of cytochrome c. The redox potential of the protein was determined to be 0.05±0.02 V (vs Ag/AgCl), which agrees with the reported value. In heterogeneous electron transfer rates for were determined by analyses of the cyclic voltammetric data using Laviron’s equation. The heterogenous electron rate constant (ks) calculated by Laviron’s equation suggest that there is small increase in the electron transfer rates when metal ion (Cr, Fe, Mn) is coordinated to the Schiff base on the electrode surface, suggesting that metal ion coordination possibly stabilizes the SAM of the Schiff base and favours electron transfer to cytochrome c.

• Seminar by Dr. Ahin Roy, Trinity College Dublin, Ireland on September 8, 2021 at 2.30 pm (via Zoom)

  Title :

  Structure-property Correlation in Oxide Materials through Aberration-corrected Electron Microscopy

  Abstract :

  The unprecedented control of the electron beam in the modern electron microscopes allows diffraction from nanometer regions, and conjunctionally being equipped with spectrometers, they can explore chemical information of the material – establishing much coveted structure-property correlations on-the-go. This can be of great interest to a materials chemist, and I will illustrate a couple of examples in that direction from recent works on oxides.

  Firstly, the talk will focus on WO3, which exists in a plethora of crystallographic phases. With judicious choice of chemistry, hexagonal and orthorhombic phases can be selectively accessed. Detailed conventional TEM coupled with simulations lead to insights on the operative growth mechanism in that process. Moreover, an epitaxial phase transformation, viz. hexagonal to monoclinic has been observed recently, hitherto unknown in literature. This leads to a possibility of phase-selective ion-intercalation in this material, which will be discussed. Such structural changes have pronounced effect on the electrochromic property of the material. In the next part, I will briefly focus on hexagonal perovskite BaMnO3, wherein reduced Mn-states have been observed on the surface and was established as the reason for its catalytic activity.

• Seminar by Dr. Ahin Roy, Trinity College Dublin, Ireland on September 6, 2021 at 4.00 pm (via Zoom)

  Title :

  Atomic and Electronic Structure of Ultrathin Single-crystalline Nanowires from Electron Microscopy and Simulations

  Abstract :

  Being the eye of nanomaterials space with atomic-scale resolution, aberration-corrected (scanning) transmission electron microscopy (AC-(S)TEM) can provide a wealth of structural information in low-dimensional materials. With a judicious choice of system of interest, atomistic simulations can facilitate such microscopy. In this talk, I will discuss a couple of such simulation-aided microscopy experiments for different inorganic nanowires.

  The talk will focus on structural aspect of symmetry-broken single-crystalline ultrathin Au nanowires, wherein simulations predict that the {111} atomic planes of Au undergo wrinkling, leading to formation of saddle surfaces. Detailed AC-TEM on such wires confirms this prediction. Crystallographic arguments pinpoint the nature of surface stress to be the driving factor behind such structural transformation. Recent AC-STEM experiments with similar scale Pt nanowires show that with a priori crystallographic information, it is possible to reconstruct a 3-D structure from a single projection image of the material, paving a way for suitable alternative to conventional electron tomography. Lastly, in terms of electronic properties, I will briefly talk about Te nanowires, wherein simple adsorption of NO2 shows a semiconductor to metal transition- predicted in simulations and verified by experiments.

• Seminar by Dr. Sumit Kumar, Institute of Basic Science CSLM, South Korea on August 31, 2021 at 4.00 pm (via Zoom)

  Title :

  Nano-brick: Designing Nanomaterials for Living system

  Abstract :

  Nanomaterials have been widely explored in the biomedical field, and it is crucial to choose the right material and engineer it appropriately to achieve the desired properties. A variety of natural and synthetic polymers have been investigated in the field, and they can be engineered for different formulations. Here, I will mainly present how biomolecules can be used to engineer the different forms for surface texturing, self-assembling nanoparticles, and creating a confined nanoenvironment. To be effective in medicine, I will introduce new methods for creating diversity in nanostructures to enable seamless integration with living tissue, where the understanding of nanoscale is necessary. These advanced nanomaterials could enable an effective, minimally invasive, personalized healthcare system. Thorough understanding of underlying mechanisms, and advancing to a robust biomedical solution for healthcare, cellular energy generation, and nanobio-manufacturing, could be further translated into commercial products and therapies. These sophisticated nanobio-hybrid platforms with advanced synthetic routes have potential applications in early disease detection and targeted therapy. 

• Seminar by Dr. Sumit Kumar, Institute of Basic Science CSLM, South Korea on August 30, 2021 at 3.00 pm (via Zoom)

  Title:

  Exosome: A Journey from Garbage Bags to Life-Saving Case

  Abstract:

  Biological membranes provide a fascinating example of a separation system that is multifunctional, tunable, and efficient for biocatalytic transformations such as enzyme cascades that involve complex networks proceeding in spatially confined nonreactors. Synthetic mimics of cellular compartments based on real membrane, lack the feasibility to encapsulate desired number of reactants together and precisely control the mixing of reactants during chemical transformation due to its mechanical and chemical fragility. Inspired by multicompartment structures of cellular architectures, we present a novel strategy to encapsulate of multiple enzymes and other reactants, in naturally secreted nanosized extracellular vesicles (EV) that act as nanoreactors for effective biocatalytic cascades in vitro and inside cells, and displays long time stability to work as an artificial organelles (AO). EV membrane proteins are chemically engineered by functionalizing the catechol moiety on the outer surface to drive the fusion of vesicles. This strategy is based on supramolecular metal complex formation that bridges the membrane proteins to allow controlled fusion for encapsulating multiple reactants and mixing them inside the EV. The integration of the multienzyme system inside AO leads to dramatically enhancements in their activity of the catalytic cascades, respectively, compared with the bulk mixture of the catalysts in solution. Importantly, our AO are functional after assembling a minimal electron transport chain capable of adenosine triphosphate synthesis (ATP), combining Escherichia coli F₁F₀ ATP-synthase and the primary proton pump bo₃-oxidase, which demonstrates the feasibility of our method for using this as cellular implants in living organisms. As a programmable tool to work as membrane fusion machinery, catechol-tethers can be further applied to regulate other biological processes where capturing and bridging of two membranes are the prerequisites.