Poster Session 1

2:00-3:00 PM

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This poster includes the development of redox mediated unprecedented heterometallic coordination polymer {[RuIII(acac)2(-bis-1-N,1-N))2AgI(ClO4)]ClO4}n (3) via the oxidation of monomeric building block cis-[RuII(acac)2(1-N-BTD)2] (1) by AgClO4 (BTD= exodentate 2,1,3-benzothiadiazole, acac=acetylacetonate). Monomeric cis-[RuII(acac)2(1-N-BTD)2] (1) and [RuII(acac)2(1-N-BTD)(CH3CN)] (2) are simultaneously obtained from the reaction of electron deficient BTD heterocycle and electron rich metal precursor RuII(acac)2(CH3CN)2 in refluxing CH3CN. Molecular identities of 1-3 are authenticated by their single crystal X-ray structures as well as by solution spectral features. It also reflects elusive trigonal planar geometry of Ag ion in Ru-Ag derived polymeric 3. Ru(III) (S=1/2) derived 3 displayed metal based anisotropic EPR with <g>/g=2.12/0.56 and paramagnetically shifted 1H NMR. The drastic decline in emission intensity and quantum yield but insignificant change in lifetime of 3 with respect to 1 can be addressed in terms of static quenching and/or paramagnetism induced phenomenon. Homogeneously dispersed dumbbell shaped morphology and particle diameter of 3 are established by microscopic (TEM-EDX/SEM) and DLS analysis, respectively. Moreover, dynamic nature of polymeric 3 is highlighted by its degradation to 1-N-BTD coordinated monomeric fragment 1, which can also be followed spectrophotometrically in polar protic EtOH. Interestingly, both monomeric 1 and polymeric 3 exhibit efficient electrocatalytic activity towards water oxidation processes (OER, HER), which also divulge better intrinsic water oxidation activity of 3 over 1. The work therefore highlights a new direction in the specific domain of metal-redox mediated polymer formation and its efficient application in electrochemical water splitting for sustainable energy conversion.

Applications of Olefin-Metathesis in Polyquinanes Synthesis

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The synthesis of complex molecules such as polyquinanes is a difficult task for synthetic chemists due to their fascinating molecular architecture include (i) contiguous stereocenters, (ii) all-carbon quaternary centers, and (iii) dense functional groups. In this context, the cascade olefin-metathesis is proved as the most prominent process to create highly complex systems by minimizing the total number of linear steps. The ring-rearrangement metathesis (RRM) and ring-closing metathesis (RCM) processes are explored for the synthesis of several natural products skeletons such as cameroonanol, subergorgic acid, isocomene, silphinene, arnicenone, crinipellin, and presilphiperfolanol from a less explored exo-dicyclopentadiene-1-one. Our strategies involve readily available starting materials, operationally simple reactions, and produces the highly congested polycyclic frameworks containing up to nine contiguous stereogenic centers which include up to two all-carbon quaternary centers. Hence, these strategies are useful to design medicinally important “drug-like molecules”.

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Macromolecular crowding and preferential exclusion counteract the effect of protein denaturant: Biophysical aspects

Biological macromolecules like nucleic acids, proteins, lipids, carbohydrates, ribosomes etc. function under intracellular crowded environment. The crowded environment alters the structural, functional and thermodynamic properties of the macromolecules in contrast to normal conditions which are commonly used in experimental studies. In this work, we examine the effect of molecular crowding and preferential exclusion on stability of a model protein, lysozyme. The work was performed using a combination of spectroscopic and calorimetric approach. We employed gaunidinium hydrochloride as protein denaturant and molecular crowders like PEG 600, Dextran 40 and osmolytes like glycine, proline, sorbitol and sarcosine individauuly and in mixture. Our results provide quantitative assessment of stabilization offered by these molecules and mechanistic insights into counteraction mechanism. PEG600 itself destabilized the protein while, sorbitol did not show any effect on protein stability. All other stabilizing agents studied here, offered a partial counteraction of denaturation. Our results suggest that chemical interactions of the stabilizing agents with the denaturants play a minimal role in prevention or reversal of denaturation while volume exclusion is the main cause for the protein stability offered.

MD studies to probe the effects of chemical modifications on pseudoknot of cas12a- CRISPR guide RNA

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CRISPR is an adapted immune mechanism in the bacteria applied to the eukaryotes as a powerful genome-editing technique. CRISPR-cas12a is known for its specificity and the ability to edit sequences that were challenging to target. Cas12a-guide RNA has a conserved pseudoknot structure towards the 5ʹ-handle. Chemically modified CRISPR systems have been shown to increase efficiency and reduce off-target editing activity. Experiments revealed that the DNA modifications in the pseudoknot RNA of cas12a affected the editing activity considerably. To rationalize these findings, we have employed Gaussian accelerated MD simulations. Our studies reveal the structural and functional requirements of Cas12a-CRISPR system, and provide guidelines to rationally modify guide RNAs for developing CRSIPR therapeutics.

Synthetic Utility of Sugar-Derived Cyclic Nitrones: A Diastereoselective Synthesis of 5-5 and 5-6 Fused Bicyclic Ureas via Cross-Metathesis/Aza-Michael Reaction Strategy

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Cyclic and bicyclic ureas are common subunits that are found in many biologically active molecules and natural products, including HIV protease inhibitors. Chiral imidazolin-2-ones have also been widely utilized as chiral auxiliaries in organic synthesis. In addition, cyclic or bicyclic ureas have been utilized as intermediates in the synthesis of cyclic guanidines, which are also found in a number of biologically active compounds and natural products. Herein, we describe our chiral pool approach towards the synthesis of 5-5 and 5-6 fused bicyclic ureas using sugar-derived cyclic nitrones as the starting material. Products were obtained in moderate to good yields with high diastereoselectivity up to a 9:1 ratio. Chirality in bicyclic ureas was preserved by using sugar-derived cyclic nitrone derived from various sugars. Key transformations in our synthesis are cross-metathesis between different urea derivatives with methyl acrylate followed by intramolecular aza-Michael addition reactions.

Poster Presentation Link

The concurrent existence of Ferromagnetic and Ferroelectric properties in the same material gives rise to ‘Multiferroic systems’ which are widely popular due to their extended range of applications like Multiple-state memory, electric field controlled ferromagnetic resonance devices, sensors, transducers, actuators, storage devices etc. Inorganic bulk multiferroic systems (Perovskites, Ceramics), despite offering greater polarization and Curie temperature values with wider Hysteresis loops, suffer through the long-standing problems like less controllable properties (e.g. magnetic ordering), involvement of toxic heavy metals, costly high temperature method of preparation and extremely low mechanical flexibility. All of these can be easily overcome by discrete organic-inorganic hybrid systems. By proper ligand design strategy and right combination of metal (either 3d and/or 4f) ions, we can not only control both ferroelectric and ferromagnetic properties but also facilitate them to exist simultaneously. Keeping this in mind, we intend to develop 3d or 3d-4f chiral metal complexes for two reasons- 1) there are very few systematic study on the multiferroic property of the discrete molecular systems although they are very advantageous, 2) Existence of multiferroic property will pave the way to realize molecular-based information storage devices, sensors, energy harvesting, etc.

Biomimetic Ion Transport of Dipeptides having Lipid like Structure

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Synthetic peptides capable of biomimetic ion transport are emerging as useful materials and therapeutics.1-2 Herein, we have synthesized three dipeptide derivatives with varying alkyl side chains in order to mimic the structure of lipid. Systematic studies show that the peptide having the closest structure with lipid having maximum ion transport rate. The peptides having shortest and longest hydrophobic tails have no transport and moderate ion transport activity, respectively.3 This observation suggests that peptides with correct balance between hydrophobicity and hydrophilicity act as best ion transporters. U tube experiment also confirms the transporters may form a mononuclear or supramolecular channel to transport ions through lipid bi-layer.

Doorway Mechanism for Electron Attachment Induced DNA Strand Breaks

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We report a new doorway mechanism for the dissociative electron attachment to genetic materials. The dipole-bound state of the nucleotide anion acts as the doorway for electron capture in the genetic material. The electron gets subsequently transferred to a dissociative σ*-type anionic state localized on a sugar-phosphate or a sugar-nucleobase bond, leading to their cleavage. The electron transfer is mediated by the mixing of electronic and nuclear degrees of freedom. The cleavage rate of the sugar-phosphate bond predicted by this new mechanism is higher than that of the sugar-nucleobase bond breaking, and both processes are considerably slower than the formation of a stable valence-bound anion. The new mechanism can explain the relative rates of electron attachment induced bond cleavages in genetic materials.

Investigating the interplay between chirality and spins in conjugated polymers.

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Ordered thin-films of chiral organic molecules/polymers on surfaces act as electron spin filters at room temperature, an effect that is termed as chiral-induced spin selectivity (CISS). Organic semiconductors and organic-inorganic hybrids are promising materials for spintronic-based memory devices. When electrons pass through a chiral supramolecular self-assembled material, mainly one type of the electrons spin is preferentially transferred through the helical system. So far, the CISS effect is studied in closed shell systems (paired electrons). Here we aim to study the influence of chirality on unpaired electrons in open-shell systems. We choose a fluorene-based π-conjugated polymer that contains both chiral and pendent persistent radical moiety. Here chiral side-chains induce handedness to the polymer chain at the supramolecular level, and the radical attached as a pendent group experiences the chiral field. We plan to test how a radical or open-shell system affects the spin selectivity of electron transport.

A Binary Matrix Method to Enumerate, Hierarchically Order and Structurally Classify Peptide Aggregation

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Protein aggregation is a common and complex phenomenon in biological processes, yet a robust analysis of this aggregation process remains elusive. The commonly used methods such as centre-of-mass to centre-of-mass (COM–COM) distance, the radius of gyration (Rg), hydrogen bonding (HB) and solvent accessible surface area (SASA) do not quantify the aggregation accurately. Herein, a new and robust method that uses an aggregation matrix (AM) approach to investigate peptide aggregation in a MD simulation trajectory is presented. A nxn two-dimensional aggregation matrix (AM) is created by using the inter-peptide Cα–Cα cut-off distances which are binarily encoded (0 or 1). These aggregation matrices are analysed to enumerate, hierarchically order and structurally classify the aggregates. Moreover, the comparison between the present AM method and the conventional Rg, COM–COM and HB methods shows that the conventional methods grossly underestimate the aggregation propensity. Additionally, the conventional methods do not address the hierarchy and structural ordering of the aggregates, which the present AM method does. Finally, the present AM method utilises only nxn two-dimensional matrices to analyse aggregates consisting of several peptide units. To the best of our knowledge, this is a maiden approach to enumerate, hierarchically order and structurally classify peptide aggregation.