Photopatterning in poly-L-lysine thin films using UV-enhanced hydrophilicity

Deep UV lithography on poly-L-lysine thin films was used to generate microarrays with enhanced hydrophilicity. This was manifested as adsorption of ambient humidity from air by areas exposed to UV fluence around 5 J/cm2 and was made visible by phase-contrast microscopy. Kinetics of adsorption was investigated by a novel technique involving fabrication of submicrometer hydrophilicity grating by two-beam UV interferometry. In an aqueous colloidal medium, gold and polystyrene microspheres preferentially attach to areas that are relatively less hydrophilic, i.e., those areas not exposed to UV light. This observation provides a method for fabricating micro- and nanoporous arrays with controlled porosity. The technique is demonstrated with microspheres of sizes between 250 nm and 10 microm.     

12/10- and 11/13-mixed helices in alpha/gamma- and beta/gamma-hybrid peptides containing C-linked carbo-gamma-amino acids with alternating alpha- and beta-amino acids

New classes of alpha/gamma- and beta/gamma-hybrid peptides have been synthesized with novel 12/10- and 11/13-mixed helical patterns, respectively. The alpha/gamma-peptides were derived from the dipeptide repeats with alternating arrays of l-Ala and gamma-Caa((l)) (C-linked carbo-gamma-amino acid from d-mannose), which generated a new 12/10-mixed helix, for the first time, without a beta-amino acid. The beta/gamma-peptides made from an alternating arrangement of beta-Caa((x)) (C-linked carbo-beta-amino acid) and gamma-Caa((x)) (C-linked carbo-gamma-amino acid from d-xylose), on the other hand, resulted in an unprecedented 11/13-helix. The secondary structures in these peptides have been ascertained from detailed NMR studies, and CD spectroscopy and molecular dynamics investigations provided additional support for the structures derived.     

Sensitization of cancer cells to DNA damaging agents by imidazolines

Apoptosis, or programmed cell death, is a cellular mechanism used to regulate cell number and eliminate damaged or mutated cells. Concomitant with the initiation of the apoptotic cell signal, chemotherapeutic agents also induce anti-apoptotic factors, such as NF-kappaB, which compromise the overall efficacy of chemotherapeutic anticancer treatment. Here we describe an adjuvant therapy in which a small molecule is used to sensitize cancer cells toward apoptosis induced by chemotherapeutics. Our results indicate that the imidazoline 1d modulates the pro-survival NF-kappaB pathway and selectively sensitizes cancer cells toward DNA damaging agents, thus enhancing the overall efficacy of the treatment. Pretreatment of cancer cells with the noncytotoxic imidazoline 1d (10 nM) resulted in a significant increase in apoptosis and anticancer efficacy of the clinically significant DNA damaging agents camptothecin and cisplatin. Noncancerous cells remained unaffected during this regimen.     

Synthesis of novel bis‐condensed heterocyclic ring assembly systems

The novel bis‐condensed heterocyclic systems with ring assemblies based on peripheral barbituric acid rings and central pyran, pyridine and thiine rings have been generated by the reaction of terephthalaldehyde and isophthalaldehyde with barbituric acid for comparison with the analogous systems generated with said dialdehydes and 1,3‐cyclohexanedione.     

Interactions between anionic mixed micelles and α-cyclodextrin and their inclusion complexes: conductivity, NMR and fluorescence study

Mixed micelle formation of anionic surfactants sodium dodecyl sulfate (SDS) and sodium lauroyl sarcosine (SLAS) have been studied in water and in 5, 10, and 15 mM concentrations of α-cyclodextrin (α-CD) over mole fraction range of α _SDS from 0 to 1. From the conductivity curves, the critical micellar concentration (CMC) for the pure and binary mixtures were evaluated. The degree of counterion association (χ) or counterion dissociation (δ), the equivalent ionic conductivities of the monomeric species (Λ _m), the associated species (Λ _assc), and the micelle (Λ _mic) were evaluated from the slope of the conductivity vs concentration plots. The CMC values have been used to calculate the thermodynamic parameters such as the standard free energy of micelle formation and a transfer of standard free energy of micelle from the aqueous medium to additive medium computed. The apparent CMC of the surfactants varies linearly with α-CD concentrations. From the dependence of CMC of the surfactants on α-CD concentration, we are able to determine the association constant (K) of surfactant-α-CD inclusion complexes assuming 1:1 stoichiometry. Mixed micelle behaves ideally in the pure water as well as at the different concentrations of α-CD, which was evaluated by using the Clint equation, the regular solution approximation, and Motomura’s formulation. Self-diffusion coefficients of the micelle increased upon the induction of SDS into the micelle. 2D-rotating frame Overhauser effect spectroscopy spectra of SDS and SLAS were recorded in the presence of α-CD to investigate the interaction between H-atoms of the alkyl chain of the surfactants and H-atoms of the hydrophobic cavity of α-CD indicating multiple complexation. The fluorescence anisotropy of rhodamine B has been measured to observe the structural behavior of mixed micelle.     

An intriguing empirical rule for computing the first normal stress difference from steady shear viscosity data for concentrated polymer solutions and melts

The Cox–Merz rule and Laun’s rule are two empirical relations that allow the estimation of steady shear viscosity and first normal stress difference, respectively, using small amplitude oscillatory shear measurements. The validity of the Cox–Merz rule and Laun’s rule imply an agreement between the linear viscoelastic response measured in small amplitude oscillatory shear and the nonlinear response measured in steady shear flow measurements. We show that by using a lesser-known relationship also proposed by Cox and Merz, in conjunction with Laun’s rule, a relationship between the rate-dependent steady shear viscosity and the first normal stress difference can be deduced. The new empirical relation enables a priori estimation of the first normal stress difference using only the steady flow curve (i.e., viscosity vs shear rate data). Comparison of the estimated first normal stress difference with the measured values for six different polymer solutions and melts show that the empirical rule provides values that are in reasonable agreement with measurements over a wide range of shear rates, thus deepening the intriguing connection between linear and nonlinear viscoelastic response of entangled polymeric materials.     

Theoretical Study of Screening Dependence of Aluminium Doped MgB_2

The screening dependence of superconducting state parameters(λ, μ*, T_c, and N_0V(1) of six alloys of aluminium doped Mg B2 systems are studied in the BCS–Eliashberg–Mc Millan framework by employing five forms of dielectric screening function, viz. random phase approximation(RPA), Harrison, Geldart and Vosko(GV), Hubbard and Overhauser in conjunction with Ashcroft's potential. It is observed that electron-phonon coupling strength λ and Coulomb pseudopotential μ*are quite sensitive to the form of dielectric screening, whereas transition temperature T_c, isotope effect exponent α and effective interaction strength N_0V(1 show weak dependence on the form of dielectric screening function. It is found that the RPA form of dielectric screening function yields the best results for transition temperature T_c for all alloys of the Mg-Al-B system. The results obtained using GV screening are much higher than the experimental results. This shows that all the four dielectric screenings used here almost describe superconductivity in all the alloys of the Mg-Al-B system, but the GV screening is not suitable for such an alloy system.     

First order transition to oscillation death through an environment

The emergence of dynamical abrupt transitions for the first time in an ensemble of identical limit-cycle and chaotic oscillators coupled via a common environment is reported. The transition from the oscillatory state to the death state and vice versa, in these networks of oscillators are found not only discontinuous as well as irreversible in the parameter space. This first order phase transition in these systems is termed as Explosive Death. The occurrence of such transition is studied in details by using an appropriate order parameter for both limit-cycle and chaotic oscillators, in particular, Stuart–Landau and Rössler oscillators. The backward transition point for this phenomenon is obtained analytically using linear stability analysis and is found to be consistent with the numerical results.     

Electronic transport across a junction between armchair graphene nanotube and zigzag nanoribbon

Based on the well known nearest-neighbor tight-binding approximation for graphene, an exact expression for the electronic conductance across a zigzag nanoribbon/armchair nanotube junction is presented for non-interacting electrons. The junction results from the removal of a half-row of zigzag dimers in armchair nanotube, or equivalently by partial rolling of zigzag nanoribbon and insertion of a half-row of zigzag dimers in between. From the former point of view, a discrete form of Dirichlet condition is imposed on a zigzag half-line of dimers assuming the vanishing of wave function outside the physical structure. A closed form expression is provided for the reflection and transmission moduli for the outgoing wave modes for each given electronic wave mode incident from either side of the junction. It is demonstrated that such a contact junction between the nanotube and nanoribbon exhibits negligible backscattering, and the transmission has been found to be nearly ballistic. In contrast to the previously reported studies for partially unzipped carbon nanotubes (CNTs), using the same tight binding model, it is found that due to the “defect” there is certain amount of mixing between the electronic wave modes with even and odd reflection symmetries. But the junction remains a perfect valley filter for CNTs at certain energy ranges. Applications aside from the electronic case, include wave propagation in quasi-one-dimensional honeycomb structures of graphene-like constitution. The paper includes several numerical calculations, analytical derivations, and graphical results, which complement the provision of succinct closed form expressions.     

Analysis of fiber optic SPR sensor utilizing platinum based nanocomposites

SPR based fiber optic sensor using nanocomposite is presented. Nanocomposites comprising of Pt nanoparticles with various volume fractions embedded in dielectric matrices of TiO₂ and SnO₂ are considered. Sensitivity enhances with increase in thickness of nanocomposite and volume fraction of nanoparticles for both nanocomposites. Optimized thicknesses are obtained to be 40 and 50 nm for Pt–TiO₂ and Pt–SnO₂ nanocomposites respectively while optimized volume fraction is found to be 0.85 for both nanocomposites. 40 nm thick Pt–TiO₂ nanocomposite based sensor with 0.85 volume fraction possesses utmost sensitivity.