Faculty Publications (CPMU)

Allosteric Transition Induced by Mg2+ Ion in a Transactivator Monitored by SERS

Wed, 01 Jan 2014 00:00:00 GMT

Allosteric Transition Induced by Mg2+ Ion in a Transactivator Monitored by SERS Kundu, Partha P.; Bhowmick, Tuhin; Swapna, Ganduri; Kumar, G. V. Pavan; Nagaraja, V.; Narayana, Chandrabhas We demonstrate the utility of the surface-enhanced Raman spectroscopy (SERS) to monitor conformational transitions in protein upon ligand binding. The changes in protein's secondary and tertiary structures were monitored using amide and aliphatic/aromatic side chain vibrations. Changes in these bands are suggestive of the stabilization of the secondary and tertiary structure of transcription activator protein C in the presence of Mg2+ ion, whereas the spectral fingerprint remained unaltered in the case of a mutant protein, defective in Mg2+ binding. The importance of the acidic residues in Mg2+ binding, which triggers an overall allosteric transition in the protein, is visualized in the molecular model. The present study thus opens up avenues toward the application of SERS as a potential tool for gaining structural insights into the changes occurring during conformational transitions in proteins. Restricted Access

Porous polyimides from polycyclic aromatic linkers: Selective CO2 capture and hydrogen storage

Wed, 01 Jan 2014 00:00:00 GMT

Porous polyimides from polycyclic aromatic linkers: Selective CO2 capture and hydrogen storage Rao, K. Venkata; Haldar, Ritesh; Maji, Tapas Kumar; George, Subi Jacob Porous polyimides are important class of macromolecules owing to their excellent redox behaviour, efficient capture of CO2 and H-2 gases, interesting photocatalytic properties and superior thermal and chemical stabilities. Here we describe in detail, the synthesis and gas storage properties of a series of porous polyimides (Tr-NPI, Tr-PPI, Tr-CPI, Td-PPI and Td-CPI) with various network topologies derived from polycyclic aromatic hydrocarbon linkers. These polyimides are synthesized in a single step by the condensation of corresponding polycyclic aromatic dianhydrides (NDA, PDA and CDA) with structure directing amine (TAPA and TAPM) monomers, having trigonal and tetrahedral geometry. The structure of all the polymers was fully characterized by various techniques. The present work also introduces for the first time porous polyimides containing rigid polycyclic aromatic compounds such as coronene. All the polyimides presented here exhibit high thermal stability and show selectivity towards CO2 uptake at room temperature (293 K), due to the presence of aromatic clouds and CO2 phillic oxygen and nitrogen functionalities on their pore surface. Moreover these polymers also showed significant uptake of H-2 gas (77 K). The present work has significant implications on the design of robust porous organic solids from small molecules for efficient capture of CO2 and H-2 gases. 2014 Elsevier Ltd. All rights reserved. Restricted Access

Supramolecular Gating of Ion Transport in Nanochannels

Wed, 01 Jan 2014 00:00:00 GMT

Supramolecular Gating of Ion Transport in Nanochannels Kumar, B. V. V. S. Pavan; Rao, K. Venkata; Sampath, S.; George, Subi Jacob; Eswaramoorthy, Muthusamy Several covalent strategies towards surface charge-reversal in nanochannels have been reported with the purpose of manipulating ion transport. However, covalent routes lack dynamism, modularity and post-synthetic flexibility, and hence restrict their applicability in different environments. Here, we introduce a facile non-covalent approach towards charge-reversal in nanochannels (< 10 nm) using strong charge-transfer interactions between dicationic viologen (acceptor) and trianionic pyranine (donor). The polarity of ion transport was switched from anion selective to ambipolar to cation selective by controlling the extent of viologen bound to the pyranine. We could also regulate the ion transport with respect to pH by selecting a donor with pH-responsive functional groups. The modularity of this approach further allows facile integration of various functional groups capable of responding to stimuli such as light and temperature to modulate the transport of ions as well as molecules. Restricted Access

Amine-Responsive Adaptable Nanospaces: Fluorescent Porous Coordination Polymer for Molecular Recognition

Wed, 01 Jan 2014 00:00:00 GMT

Amine-Responsive Adaptable Nanospaces: Fluorescent Porous Coordination Polymer for Molecular Recognition Haldar, Ritesh; Matsuda, Ryotaro; Kitagawa, Susumu; George, Subi Jacob; Maji, Tapas Kumar Flexible and dynamic porous coordination polymers (PCPs) with well-defined nanospaces composed of chromophoric organic linkers provide a scaffold for encapsulation of versatile guest molecules through noncovalent interactions. PCPs thus provide a potential platform for molecular recognition. Herein, we report a flexible 3D supramolecular framework {[Zn(ndc)(o-phen)]center dot DMF}(n) (o-phen= 1,10-phenanthroline, ndc=2,6-napthalenedicarboxylate) with confined nanospaces that can accommodate different electron-donating aromatic amine guests with selective turn-on emission signaling. This system serves as a molecular recognition platform through an emission-readout process. Such unprecedented tunable emission with different amines is attributed to its emissive charge-transfer (CT) complexation with o-phen linkers. In certain cases this CT emission is further amplified by energy transfer from the chromophoric linker unit ndc, as evidenced by single-crystal X-ray structural characterization. Restricted Access