Archita Patnaik

The title compound (C13H30N2O 7S) has been determined from three-dimensional X-ray diffraction data. The crystals are monoclinic, a = 22.654(8) Å, b = 8.652(4) Å, c = 23.925(9) Å, β= 123.880(9)°, V= 3893(3) Å3, Z = 8, Dcalc =1.192 g/cm3, space group C2/c. The structure was solved by direct methods and refined by full-matrix least squares method (R = 0.051). The ammonium cation is displaced by 1.08 Å from the mean plane of the ligand causing hydrogen bonding with the macrocyclic O atoms in a perching arrangement. The thiocyanate anion forms an extended hydrogen bonded chain with the cation via the occluded water molecule. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A novel methanofullerene dyad based on a hydrophobic (acceptor C 60 moiety) -hydrophilic (bridge with benzene and ester functionalities)-hydrophobic (donor didodecyloxybenzene) network is designed and synthesized. Electronic absorption spectral features revealed the molecule to exhibit a strong tendency to self-aggregate in binary solvent mixtures at room temperature, where the dielectric constant exceeds a critical value, ∼30. The dynamic structure factors of these spherical aggregates revealed stretched exponential decay with sizes varying between 110 and 250 nm with an increasing concentration, estimated from the dynamic light scattering experiments. However, a loss of shape selectivity of these aggregates was noted at lower water volume fractions in the binary solvent mixtures. The water-extracted spherical clusters were identified to be fractals with a dimension of 1.85, leading to diffusion-limited cluster aggregation as the mechanistic route for clusterization. © 2005 American Chemical Society.

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.].

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.

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.

The room-temperature electrical conductivity of High Density Polyethylene-Carbon Black (HDPE-CB) switching composites as a function of the conductive filler (CB) content was studied by Positron Annihilation Lifetime Spectroscopy (PALS). The CB, highly structured and porous, imparted high conductivity to its composite, starting at a low level of loading. Deconvolution of the lifetime spectra into 4 components reflected upon 3 different morphologies of the composite structure. The free volume was probed using o-Ps pick-off annihilation lifetime parameter τ4 as a measure of electron density and the mean free volume cavity radius. The probability of o-Ps formation and the concentration of free volume cavities were probed by the o-Ps pick-off intensity I4. In the blended composite of 29 phr (parts per hundred parts of resin), the mean free volume size increased to 3.56 Å from 3.27 Å in the pristine polymer with the corresponding increase in the free volume to 204.5 Å3 from 146.8 Å3. The relative number of free volume cavities (I4) in the composite remained fewer than the host polymer over the CB concentration studied. The changes in the cavity size and concentration, particularly a decrease in the relative intensity I4 by 10.5% resulted in the introduction of enhanced crystallinity into the composite structure which was evidenced from a variation in crystallinity from %75% in the pristine to 85% in the 29 phr CB-HDPE composite in the X-ray diffraction profiles.

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.

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.

This first report on temperature programmed decomposition of C60Br24 and C60Br6 using evolved gas analysis and mass spectrometry (EGA-MS) in the temperature range 323-523 K revealed multiple decomposition routes. The deconvoluted decomposition profiles with bi- and tri-modal features in C60Br24 and C60Br6, respectively, indicated evolution of interstitial bromines at a higher temperature as compared to the release of bonded bromines. C60Br6, on decomposition yields cyclopentadienyl radical intermediate and the overall process was found to be diffusion-reaction limited with a diffusion coefficient associated with the release of the interstitial bromine as 4.3 × 10-19 cm2 s-1. © 2003 Elsevier Science B.V. All rights reserved.

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.