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Priyam Kumar De
Priyam Kumar De
Non Adiabatic Dynamics Near Metal Surface
Molecular Dynamics simulation of Molecules near metal surface is theoretical challenge. Semi classical molecular dynamics is based on Born-Oppenheimer aprroximation. But when molecules come near the metal surface, non adiabatic coupling between states appear and hence BO approximation fails. For simulations beyond BO approximation, non adiabatic coupling has to be included explicitely. For doing such dynamics several methods are present. FSSH, IESH, SHME. In these methods, system hops from one state to another state depending on the non adiabatic coupling. For NO scattering over gold surface, vibrational relaxation of NO occurs through non adiabatic coupling. In my poster, I will talk about these methods and how these methods can be improved fo NO scattering over Gold surface system. One important thing missing in these approaches is Quantum Nuclear Effect, that is treating nuclei quantum mechanically. This poster has a very brief discussion about QNE.
Ishita Sengupta
Ishita Sengupta
Introducing elementary NMR concepts through simple interactive Python programs
In this in-house symposium, I will present a Jupyter notebook, to highlight a set of simple interactive Python programs to introduce elementary concepts of nuclear magnetic resonance spectroscopy to a beginner, with no knowledge of the Python programming language. In particular, these scripts allow the beginner with basic knowledge of quantum mechanics to grasp important concepts like precession, nutation, laboratory and rotating frames, on and off-resonance RF pulses through user input and graphical and terminal output of results. This interactive graphical platform can greatly aid in demonstrating key concepts, supplementing traditional theoretical approaches of teaching NMR.
Anjana Menon
Anjana Menon
Effect of Anti-Tubercular Drug on the Biophysical Characteristics of Mycomembrane at Different Growth Stages
Mycobacterial species possess a dynamic cell envelope consisting of an array of unique lipids, [1] which contributes to the differential interaction with various therapeutic agents. Moreover, as bacterial lipidome varies considerably in the early and late infection stages [2] , it is critical to analyse its ability to tolerate antibiotic treatments under these conditions. Knowledge of the lipid structure and its spatial organization is inescapable to predict the specific drug-membrane interactions that would lead to the passive drug diffusion across the membrane. In this regards, model membranes recontituted by the core lipids present in the mycobacterial membranes is an attractive scaffold to screen for potential drug candidates [3] and to project plausible antibiotic variations needed to beat the growing resistance. Studies on the changes of the membrane biophysical parameters by the anti-tubercular drugs could also predict or fine-tune the structural efficiency of membrane active drugs. Extending these studies to a complete-lipid scaffold of mycobacterium species could pilot the designing of effectual drugs for the therapeutic eradication of mycobacterial species.
Praveen Kumar (RC)
Praveen Kumar (RC)
Transport of probe particles in a polymer network: effects of probe size, network rigidity and probe–polymer interaction
There are several numbers of transport processes in biology, chemistry, and materials science that occur in a crowded medium such as diffusion of proteins in the biological hydrogel, mucus membrane, polymer thin film, etc. Diffusion of probe particles (like protein, colloidal bead, or nanoparticle) inside the crowded medium (gel-like medium) is strongly affected by the size of the probe particle, probe-polymer interaction, and the stiffness of the polymer. We use molecular dynamics simulations to investigate the dynamics of the probe in a polymer network on the diamond lattice to mimic the crowded environment (cellular environment). Our study shows that the dynamics of the probe particle inside the gel-like medium become restricted, non-Gaussian, and subdiffusive on increasing the probe size, network rigidity, and probe-polymer interactions as observed in experiments. Interestingly, the bigger probe easily stretches (cannot break) the more flexible network but on increasing the rigidity of the network, the bigger probe cannot efficiently push. Additionally, in the short time, the velocity autocorrelation functions have negative dips owing to caging of the probe, where FBM (fractional Brownian motion) and CTRW (continuous time random walks) both contribute.
Vijay Tripati
Vijay Tripati
Is the origin of blue emission really characteristic of a material?
Does real graphene quantum dots emit is still an unsatisfactorily answered question? Creating graphene quantum dots, with less or no functional groups, can answer this question. We know that metallic objects create arcs under microwaves. We have used this phenomenon to generate pristine graphene quantum dots with no functional groups, which are hydrophobic. We see no emission from them. Surprisingly, they started emitting in the blue region after ageing in an organic solvent for a few days. The blue emission has vibronic features. Unfortunately, similar emission is reported in various nanomaterials including doped ZnO, GaN nanoparticles, even in metallic Zn nanoparticles. The cause of emission in most of the case are attributed to cation vacancies in some cases are supported by theoretical calculations. After careful studies, we have found that the blue emission with vibronic features is coming from the sample vail itself that are normally used in every chemistry laboratory.
Sharmistha Das
Sharmistha Das
Interplay of Multiexciton Relaxation and Carrier Trapping in Photoluminescent CdS Quantum Dots prepared in Aqueous Medium
A comprehensive understanding of exciton dynamics of water soluble quantum dots (QDs), especially those synthesized directly in aqueous media, is critical for devising their applications. Trapping processes are expected to play a pivotal role here, as surface trap states are abundant in such QDs. The present study, based on ultrafast transient absorption, provides an insight into exciton dynamics in PEI-capped CdS QDs synthesized by a one-pot reaction in water. They are robust and strongly photoluminescent (PL), unlike many other aqueous QDs. Excitation energy dependence of PL and the underlying mechanisms have been investigated. Analysis of fluence dependent transient absorption bleach and photoinduced absorption is performed to deconvolute contributions from multiexciton recombination and carrier trapping. A simple kinetic model is used to quantify the rate constants associated with intraband relaxation of hot excitons and hot carrier trapping. Similar magnitudes observed for the two pathways highlights the competitive kinetics between them, which is responsible for a drastic decrease in PL quantum yields for excitation above band gap. Such efficient hot carrier trapping in these QDs may possibly foreshadow ultrafast trap mediated electron transfer and thus render them suitable for redox sensing and photocatalysis.
Amitava Giri
Amitava Giri
In search of minimalistic network motif to achieve complex dynamical features in Bio-chemical system
Dynamics of biological systems are highly complex due to multiple nonlinear interactions prevailing in the biochemical and gene regulatory network. However, the decision making events (e.g. cell division, differentiation, cells migration etc.) for any biological phenomena happens in a robust manner as a function of specific external or internal signalling cue. Most of the time, this robustness is achieved by maintaining a complex dynamical behaviour of the steady state levels of extremely important regulatory genes in the form of bi-stability (cell division or cell migration), tri-stability (epithelial to mesenchymal transition) or mushroom kind bifurcations (stem cell differentiation into definite cell type). In literature, mathematical modelling studies revealed that bi-stable dynamics can be achieved from network motifs giving rise to auto positive, double negative or double positive feedback interactions. In this regard, studies on tri-stable and mushroom bifurcation kind of dynamical system in the context of robust biological decision making event still remain elusive. Here, we employ a combination of theory and simulations to figure out the appropriate network motifs that are responsible for orchestrating such complex decision making events in biological systems. Not only that, we are able to measure the relative effectiveness of a particular network motif to produce such bifurcation features, but it also provide us the necessary clues to fine tune the dynamics of these network motifs to optimize the biological systems. Thus, it helps us to understand how to control the biological networks governing various biological phenomenon much precisely.
Surya K
Surya K
Palladium-Catalyzed meta-C−H Allylation of Arenes: Molecular Role of a Pyrimidine Based Template and Hexafluoroisopropanol
Controlling remote selectivity and delivering novel functionalities at distal positions in arenes are an important endeavour in contemporary organic synthesis. Maiti and coworkers achieved a meta-C−H allylation of arenes with the aid of a palladium catalyst, pyrimidine-based auxiliary, and allyl phosphate.1 In continuation of our interests in exploring the mechanism of catalytic reactions,2 we became curious to learn more this catalytic example consisting of Pd(OAc)2 and N-acetyl glycine ligand, along with NaOTf and AgOAc in HFIP as the solvent. We carried out a detailed density functional theory computation by using the B3LYP-D3 functional. We found that the reaction is catalysed by an active species wherein the Pd(II) is a chelated to N-acetyl glycinyl ligand, an acetic acid, and an HFIP. Our results suggested that the reaction proceeds through a ligand-assisted meta-C−H activation, allyl addition to form a Pd-π-allyl species, which is then followed by the turnover determining the C−C bond formation, leading to the meta-allylated arene as the product. The role of HFIP and that of silver additive throughout the catalytic cycle has been systematically studied. A greater number of noncovalent interactions between the HFIP molecule with both the substrate and the catalyst in the lower energy meta-C-H activation transition state was found compared to similar transition states with no or lesser number of explicit HFIP molecules. While HFIP lowers the energy of transition states and intermediates, the MPAA ligand N-Ac-Gly-OH helps in the C−H activation. The computational results were in agreement with the experimentally observed meta regioselectivity.
Chidambar Kulkarni
Chidambar Kulkarni
Dynamic reconfiguration of functional polymer films by light
Controlling molecular motion at the nano-, meso- and macroscopic length scale is actively pursued to create next generation materials that can perform intricate functions such as motors, ratchets and machines.1 The pioneering work on molecular motors2 and other photoactive systems provide an excellent platform to control motion at the molecular level. However, translating such a motion to meso- or macroscopic length scale is often challenging in condensed phases due to the restricted motion of molecules/polymers. In this talk I will discuss our recent work in which we show dynamic control over polymer chain motion and organization in thin film by using a combination of supramolecular plasticizers and polarization of the incident light. Intriguingly, we observed a molecular motor like behavior at the mesoscopic level due to the chirality of the polymer and the incident light. Our work demonstrates that even functional polymers can exhibit emergent molecular motor like behavior at the mesoscopic scale.
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