Now showing 1 - 10 of 34
  • Placeholder Image
    Publication
    Molecular tilt-dependent and tyrosine-enhanced electron transfer across ITO/SAM/[DPPC–Au NP–Tyrosine] Janus nanoparticle junction
    (01-09-2016)
    Sarangi, Nirod Kumar
    ;
    Abstract: Enhanced interfacial electron transfer (ET) across the otherwise insulating indium tin oxide/alkanethiol self-assembled monolayer (SAM)/redox molecule junction was accomplished when a Janus gold nanoparticle (JNP) protected by bioinspired phosphatidylcholine (DPPC) lipid and tyrosine amino acid ligands was anchored on it. In addition to the most theoretical and experimental investigations on the distance-dependent ET across Metal–Organic SAM–Nanoparticle (NP) architectures, the current results succinctly illustrate molecular tilt angle of the SAM and the characteristic of JNP as key factors in expediting the ET rate via electron tunneling. In the absence of JNP, electron tunneling with a tunneling factor β = 1.1 Å−1 across the SAM was the rate-limiting step, evidenced from electrochemical impedance spectroscopy (EIS). The apparent electron transfer rate constant (kapp0) for anchored SAM was enhanced by at least one order of magnitude than the DPPC-only protected nanoparticle, suggesting the potential role of tyrosine towards the enhanced ET. The asymmetric and biogenic nature of the construct sheds light on a potential bioelectronic device for novel electronic attributes. Graphical abstract: Entry of TOC [Figure not available: see fulltext.].
  • Placeholder Image
    Publication
    Establishing the ellipsoidal geometry of a benzoic acid-based amphiphile via dimer switching: Insights from intramolecular rotation and facial H-bond torsion
    (02-05-2013)
    Ramesh, Nivarthi
    ;
    Sarangi, Nirod Kumar
    ;
    Soft molecular ellipsoids conceived from 3,4-di(dodecyloxy)benzoic acid (DDBA) amphiphile draw attention to monomer structure design, intramolecular -COOH headgroup twist and cyclic-acyclic dimer switching through facial H-bond torsion (ψ). Generically, precipitation in hydrogen bonded systems has been the prime phenomenon once the critical aggregation concentrations were reached in the bulk solution. DDBA was no exception to this generalization. It formed precipitates in chloroform and methanol with no specific geometry but with cyclic dimer motifs in them. On the contrary, surface pressure modulated interfacial aggregation with ellipsoidal geometry followed acyclic dimerization (catemer motif) with various levels of headgroup torsion, established through real-time polarization modulated infrared reflection-absorption spectroscopy (IRRAS) and density functional theory (DFT) calculations, that estimated the energy costs for these unexplored pathways. The reaction coordinates and ψ in consonance with 2D surface pressure modulation thus directed the shape anisotropy during the dynamic self-assembly of DDBA. Changes in subphase pH and metal ionic environment had a derogatory effect on the ellipsoid formation, the structural requirement for which strictly followed a stringent need for twin alkyl chains in an asymmetric unit cell, as 4-dodecyloxybenzoic acid (MABA) with a single alkyl chain formed exclusively spherical assemblies with no dimer modulation. The investigation thus reports unexplored energy pathways toward ellipsoidal geometry of the amphiphile in the course of its interfacial aggregation. © 2013 American Chemical Society.
  • Placeholder Image
    Publication
    Design of Dual Hybrid Network Natural Rubber-SiO2 Elastomers with Tailored Mechanical and Self-Healing Properties
    (24-06-2019)
    Sattar, Mohammad Abdul
    ;
    Gangadharan, Shyju
    ;
    The preparation of natural rubber (NR)-silica (SiO2) elastomeric composites with excellent mechanical properties along with better self-healing ability remains a key challenge. Inspired by the energy dissipation and repairability of sacrificial bonds in biomaterials, a strategy for combining covalent and noncovalent sacrificial networks is engineered to construct a dual hybrid network. Here, the approach used to fabricate the composites was self-assembly of NR, bearing proteins and phospholipids on its outer bioshell, with SiO2 via metal-ion-mediated heteroaggregation effected by reversible electrostatic and H-bonds. Further, covalent cross-links were incorporated by a silane coupling agent, bis [3-(triethoxysilyl) propyl] tetrasulfide. The intrinsic self-healing ability of the composite at the molecular level was studied by broadband dielectric spectroscopy that unraveled the mechanism of the healing process. The synergistic effect between the molecular interdiffusion of the cross-linked NR chains and the electrostatic and H-bonding interactions imparted an exceptional self-healing characteristic to the liquid-liquid-mixing-prepared NR-SiO2 composites with improved mechanical performance. Specifically, the segmental relaxation dynamics of the healed composite was largely restricted due to increased number of ion-dipole interactions and S-S cross-links at the junction of the cut surface. We envisage that this extraordinary healing property, unreported yet, would be of great importance toward the design of novel NR-SiO2 elastomeric hybrids with superior mechanical properties.
  • Placeholder Image
    Publication
    A new fullerene-C60 – Nanogold composite for non-enzymatic glucose sensing
    (31-03-2017)
    Sutradhar, Sanjeeb
    ;
    A new functionalized fullerene C60 – thiol capped gold nanoparticle based nanocomposite using 3-amino-5-mercapto-1,2,4-triazole as the ligand was designed and synthesized following electronic structure calculation via DFT formalism. The electrostatic potential map from the DFT optimized geometry implied C60 core of the composite to remain electron deficient, and a much reduced HOMO-LUMO energy gap for the composite towards enhanced electron-transport ability was noted. Experimentally, first, fullerene-C60 was functionalized with the multipolar group containing ligand 3-amino-5-mercapto-1,2,4-triazole, making it hydrophilic and its aqueous dispersion was subsequently used to make a composite with in-situ prepared aqueous phase gold nanoparticles. The composite modified glassy carbon electrode showed electrocatalytic behaviour towards sensing of glucose, studied via cyclic voltammetry and electrochemical impedance spectroscopy. Thus, the highly stable and low onset potential non-enzymatic sensor exhibited high electro-catalytic activity and effective electron transfer from the electro-catalyst to the substrate electrode in a linear concentration range spanning over 0.025–0.8 mM and a higher sensitivity response of 1.2 μA mM−1 cm−2 with good reproducibility, long term stability, anti-interference ability and chloride poisoning resistance.
  • Placeholder Image
    Publication
    Unraveling tryptophan modulated 2D DPPC lattices: An approach toward stimuli responsiveness of the pulmonary surfactant
    (24-11-2011)
    Sarangi, Nirod Kumar
    ;
    A molecular understanding on the preferential and selective interactions of L-tryptophan, a major component of surfactant proteins, with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) is important in the metabolic cycle of the pulmonary surfactant. In view of this, interfacial signals of interest in real time were tapped with aligned DPPC monolayers over a physiological tryptophan subphase using extremely surface sensitive 2D vibrational spectroscopy. Polarization-modulated and angle dependent Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) of DPPC monolayers on water and L-tryptophan subphases depicted fine structure/conformation differences in the interaction modes, evidenced from changes in the vibrational band intensities and frequencies under conditions of controlled 2D surface pressure. The computed 1:1 adducts of DPPC/H2O and DPPC/tryptophan in support of FT-IRRAS fine structure characteristics demonstrated binding in interfacial DPPC-tryptophan adducts to be driven by cation - π interactions alongside hydrogen bonding of carbonyl and phosphate groups of the lipid with NH3+ of the zwitterionic tryptophan. In situ spectroscopy enabled assignment of relative orientations of the equivalent - CH2 functional groups from the polarized XY plane transition moments with component intensities of the split orthorhombic CH 2 mode. A larger molecular tilt of 37° for the DPPC monolayer over tryptophan subphase in comparison with that over water (26°) substantiated the DPPC headgroup interaction with tryptophan, complemented through δ (N+(CH3)3), νas (PO2-), νs (PO2-), νas (C - N+ - C), and ν (C=O) vibrational features. The IRRAS spectral features of the DPPC 2D condensed phase showed distinct tryptophan-induced temperature dependent lattice phase transitions: hexagonal → orthorhombic → triclinic → hexagonal packing of the hydrocarbon chains was noted over a subphase temperature range from 20 to 43 °C. The temperature dependent 2D DPPC lattice characteristics cited in this work will aid in understanding the impact of a temperature pulse toward the membrane functionality. © 2011 American Chemical Society.
  • Placeholder Image
    Publication
    One pot hemimicellar synthesis of amphiphilic Lanus gold nanoclusters for novel electronic attributes
    (07-09-2010)
    Biji, P.
    ;
    Sarangi, Nirod K.
    ;
    A one-pot hemimicellar synthesis of oriented, amphiphilic, and fluorescent Janus gold clusters, establishing the Janus character in terms of ligand asymmetry and distribution, has been demonstrated. The method was based on the efficient Langmuir strategy, where the in situ two-dimensional (2D) reduction of Au3+ in the sprayed micellar electrostatic complex, TO A+-AuCl4 -, was accomplished by subphase tryptophan that acted as the hydrophilic protecting ligand on one hemisphere of the spherical gold cluster. In contrast to the reported micelle-assisted Janus cluster formation, here the cluster growth occurred inside the surface pressure driven hemimicelles, which rapidly formed 2D cluster arrays without any interfacial reorientation. The Janus structure was validated using angle dependent polarized Fourier Transform Infrared Reflection-Absorption Spectroscopy (FT-IRRAS), where orientation dependent vibrational changes in the adsorbed ligand functionalities were detected. Electrochemical impedance measurements of the transferred Janus layers onto hydrophobized ITO revealed the heterogeneous electron transfer rate constant kET to show a clear orientational odd-even parity effect with the odd layers showing much higher rates. Isobaric area relaxation investigations further evidenced toward a hemispherical instantaneous nucleation with edge growthmechanismof the nanoclusters formed at the tryptophan subphase. Surface pressure as a thermodynamic variable effectively controlled the interparticle separation; intercluster electron coupling exhibited insulator-metal transition in the Janus cluster monolayers through scanning electrochemical microscopy investigations. © 2010 American Chemical Society.
  • Placeholder Image
    Publication
    Proton switching as a driving force for the metal-organic complex-mediated growth of gold colloids
    (01-01-2016)
    Jacob, Geevarghese Vadakken
    ;
    Sutradhar, Sanjeeb
    ;
    A mono-protonated (bis(4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine)iron(ii)) complex [[Fe(ptpy)(Hptpy)](PF6)3] acts as a structure directing agent for larger gold colloids in the present investigation. We report here a H-bonded [Fe(ptpy)(Hptpy)](PF6)3 complex acting as an inter-linker for the complex-mediated growth of gold nanoparticles. This exploration discusses the possibility of proton switching in [Fe(ptpy)(Hptpy)](PF6)3, which can interconvert the oxidation state of Fe between +2 and +3 at the interface of citrate-capped gold nanoparticles, enabling the complex-mediated growth of geometry-specific, large size gold colloids.
  • Placeholder Image
    Publication
    L-tryptophan-induced electron transport across supported lipid bilayers: An alkyl-chain tilt-angle, and bilayer-symmetry dependence
    (21-12-2012)
    Sarangi, Nirod Kumar
    ;
    Molecular orientation-dependent electron transport across supported 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers (SLBs) on semiconducting indium tin oxide (ITO) is reported with an aim towards potential nanobiotechnological applications. A bifunctional strategy is adopted to form symmetric and asymmetric bilayers of DPPC that interact with L-tryptophan, and are analyzed by surface manometry and atomic force microscopy. Polarization-dependent real-time Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) analysis of these SLBs reveals electrostatic, hydrogen-bonding, and cation-π interactions between the polar head groups of the lipid and the indole side chains. Consequently, a molecular tilt arises from the effective interface dipole, facilitating electron transport across the ITO-anchored SLBs in the presence of an internal Fe(CN)64-/3- redox probe. The incorporation of tryptophan enhances the voltammetric features of the SLBs. The estimated electron-transfer rate constants for symmetric and asymmetric bilayers (ks=2.0×10 -2 and 2.8×10-2 s-1) across the two-dimensional (2D) ordered DPPC/tryptophan SLBs are higher compared to pure DPPC SLBs (ks=3.2×10-3 and 3.9×10-3 s-1). In addition, they are molecular tilt-dependent, as it is the case with the standard apparent rate constants kapp0, estimated from electrochemical impedance spectroscopy and bipotentiostatic experiments with a Pt ultramicroelectrode. Lower magnitudes of ks and kapp0 imply that electrochemical reactions across the ITO-SLB electrodes are kinetically limited and consequently governed by electron tunneling across the SLBs. Standard theoretical rate constants k th0 accrued upon electron tunneling comply with the potential-independent electron-tunneling coefficient β=0.15 Å-1. Insulator-semiconductor transitions moving from a liquid-expanded to a condensed 2D-phase state of the SLBs are noted, adding a new dimension to their transport behavior. These results highlight the role of tryptophan in expediting electron transfer across lipid bilayer membranes in a cellular environment and can provide potential clues towards patterned lipid nanocomposites and devices. Turn up the transport: Molecular orientation-dependent electron transport across symmetric and asymmetric supported lipid bilayers (SLBs) in the presence of transport-active L-tryptophan is reported (see picture). In spite of tryptophan expediting electron-transfer rates across the SLBs, kinetic limitations effectuate electron tunnelling with a potential-independent tunnelling coefficient β=0.15 Å-1. A novel two-dimensional phase-dependent transport with an insulator- semiconductor transition is highlighted. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Placeholder Image
    Publication
    Tailoring recognition clefts from non-specific recognition matrices in mixed molecular arrays
    (15-10-2014)
    Ramesh, Nivarthi
    ;
    Multi-component organic interfaces with molecular-level mixing were prepared by integrating benzoic acid appended thiophene amphiphile [4-(6-(thiophene-3-carbonyloxy)hexyloxy)benzoic acid] (T6BA) and (±)-α-lipoic acid onto the Au surface. On a flat surface with infinite radii of curvature, T6BA and (±)-α-lipoic acid, endowed with chemically distinct end-groups, provided sufficient length mismatch to gain conformational entropy leading to stripe-like patterns when the immiscible ligands co-adsorbed. Good quality multi-component organic interfaces and molecular islands could be fabricated via composition variation of the participating ligands. Host–guest chemistry between benzoic acids and β-cyclodextrin was used to confirm the molecular-level mixing. T6BA and (±)-α-lipoic acid, each being a non-specific recognition matrix for dopamine, could thus be organized into mixed molecular arrays having well defined cavities for guest inclusion. This mixed molecular array behaved as a ‘recognition matrix’ for dopamine (DA, 15 nm) in the presence of ascorbic acid (AA). The surface patterns described here on a flat surface should in principle be applicable to other geometrical structures like spheres and cylinders. Further, charge transfer through the T6BA self-assembled monolayers depended on the anion type present in the supporting electrolyte, monitored through cyclic voltammetry. © 2014 the Partner Organisations.
  • Placeholder Image
    Publication
    Fibrous gels of cetylpyridinium chloride in binary solvent mixtures: Structural characteristics and phase behaviour
    (14-09-2012)
    Ramakanth, Illa
    ;
    Ramesh, Nivarthi
    ;
    Molecular gels of cetylpyridinium chloride (CPC) in binary solvent mixtures have been investigated. CPC formed a turbid gel at a critical solvent composition of 3:1 v/v CHCl 3:H 2O. The gelation ability was evaluated in various other organic solvents in the presence of water and the phase evolution was studied. The microstructure of the CPC gel was proposed based on spectroscopic, microscopic and small-angle X-ray scattering (SAXS) techniques. A detailed molecular level investigation using SAXS and molecular modelling demonstrated the gel to assemble as a lamellar organization maintaining a highly interdigitated bilayer structure with CPC molecules. Concentration dependent hierarchical self-assembly from micelles to fibrous gels was thus elucidated with highly interdigitated lamellar gel organization resulting from intense hydrophobic interactions in the tail-to-tail arranged bilayers. The stimuli responsiveness of the gel was elucidated with pH dependent entrapment of Congo Red. © 2012 The Royal Society of Chemistry.