EFFECTS OF IONIC STRENGTH and pH ON THE BINDING OF SANGUINARINE TO DEOXYRIBONUCLEIC ACID

Abstract— The interaction of sanguinarine with DN A has been studied in buffers of various ionic strengths and pH values where the physicochemical properties of DNA remain unchanged. Spectrophotometric analysis using absorption and fluorescence techniques indicates that the complex formed between sanguinarine and DNA is a function of ionic strength and pH. Increasing the salt concentration minimizes the importance of intercalator charge and extrapolation to 1 M [Na+] salt reveals the intercalative abilities, as reflected in binding constants, to be of the same order of magnitude as that of ethidium bromide. The fluorescence of sanguinarine bound to DNA is quenched and can be decreased by [Na +], [Mg²+] and [Ca²+] ions. The influence of pH on the fluorescence spectrum of sanguinarine with increasing concentration of DNA was studied. It is concluded that the binding of sanguinarine to DNA contains a large favourable non-electrostatic interaction and the alkaloid binds more DNA in buffer of low ionic-strength and acidic pH.     

Surface functionalized nano‐objects from oleic acid‐derived stabilizer via non‐polar RAFT dispersion polymerization

Surface functionalization in a nanoscopic scaffold is highly desirable to afford nano‐particles with diversified features and functions. Herein are reported the surface decoration of dispersed block copolymer nano‐objects. First, side‐chain double bond containing oleic acid based macro chain transfer agent (macroCTA), poly(2‐(methacryloyloxy)ethyl oleate) (PMAEO), was synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization and used as a steric stabilizer during the RAFT dispersion block copolymerization of benzyl methacrylate (BzMA) in n‐heptane at 70 °C. We have found that block copolymer morphologies could evolve from spherical micelles, through worm to vesicles, and finally to large compound vesicles with the increase of solvophobic poly(BzMA) block length, keeping solvophilic chain length and total solid content constant. Finally, different thiol compounds having alkyl, carboxyl, hydroxyl, and protected amine functionalities have been ligated onto the PMAEO segment, which is prone to functionalization via its reactive double bond through thiol‐ene radical reactions. Thiol‐ene modification reactions of the as‐synthesized nano‐objects retain their morphologies as visualized by field emission‐scanning electron microscopy. Thus, the facile and modular synthetic approach presented in this study allowed in situ preparation of surface modified block copolymer nano‐objects at very high concentration, where renewable resource derived oleate surface in the nanoparticle was functionalized. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 263–273     

Kinetics and mechanism of the oxidation of ethylene glycol, 2,3-butanediol and pinacol by hexachloroiridate(IV)

Summary The kinetics of oxidation of ethylene glycol, 2,3-butanediol and pinacol have been studied spectrophotometrically under different experimental conditions. The reactions seem to occur through the formation of an intermediate complex between each diol and iridium(IV). The complexes decompose through intermediate free radicals to form formaldehyde, acetaldehyde and acetone, respectively. Thermodynamic parameters have been calculated.     

Absorption and emission of light in red emissive carbon nanodots

The structure–function relationship, especially the origin of absorption and emission of light in carbon nanodots (CNDs), has baffled scientists. The multilevel complexity arises due to the large number of by-products synthesized during the bottom-up approach. By performing systematic purification and characterization, we reveal the presence of a molecular fluorophore, quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA), in a large amount (∼80% of the total mass) in red emissive CNDs synthesized from o-phenylenediamine (OPDA), which is one of the well-known precursor molecules used for CND synthesis. The recorded NMR and mass spectra tentatively confirm the structure of QXPDA. The close resemblance of the experimental vibronic progression and the mirror symmetry of the absorption and emission spectra with the theoretically simulated spectra confirm an extended conjugated structure of QXPDA. Interestingly, QXPDA dictates the complete emission characteristics of the CNDs; in particular, it showed a striking similarity of its excitation independent emission spectra with that of the original synthesized red emissive CND solution. On the other hand, the CND like structure with a typical size of ∼4 nm was observed under a transmission electron microscope for a blue emissive species, which showed both excitation dependent and independent emission spectra. Interestingly, Raman spectroscopic data showed the similarity between QXPDA and the dot structure thus suggesting the formation of the QXPDA aggregated core structure in CNDs. We further demonstrated the parallelism in trends of absorption and emission of light from a few other red emissive CNDs, which were synthesized using different experimental conditions.

Herein we unveil the presence of a molecular fluorophore quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA) in a colossal amount in red emissive CNDs synthesized from o-phenylenediamine, a well-known precursor molecule used for CND synthesis.     

Perfect fluid dark matter

Taking the flat rotation curve as input and treating the matter content in the galactic halo region as perfect fluid we obtain a space–time metric at the galactic halo region in the framework of general relativity. We find that the resultant space–time metric is a non-relativistic dark matter induced space–time embedded in a static Friedmann–Lemaître–Robertson–Walker universe i.e. the flat rotation curve not only leads to the existence of dark matter but also suggests about the background geometry of the universe. Within its range of validity the flat rotation curve and the demand that the dark matter to be non-exotic together indicate for a (nearly) flat universe as favored by the modern cosmological observations. We obtain the expressions for energy density and pressure of dark matter there and consequently the equation of state of dark matter. Various other aspects of the solutions are also analyzed.     

Non-renormalizable Yukawa interactions and Higgs physics

We explore a scenario in the Standard Model in which dimension-four Yukawa couplings are forbidden by a symmetry, and the Yukawa interactions are dominated by effective dimension-six interactions. In this case, the Higgs interactions to the fermions are enhanced in a large way, whereas its interaction with the gauge bosons remains the same as in the Standard Model. In hadron colliders, Higgs boson production via gluon-gluon fusion increases by a factor of nine. Higgs decay widths to fermion-antifermion pairs also increase by the same factor, whereas the decay widths to photon-photon and γZ are reduced. Current Tevatron exclusion range for the Higgs mass increases to ∼146-222 GeV in our scenario, and new physics must appear at a scale below a TeV.     

Solvatochromic behavior of dyes with dimethylamino electron‐donor and nitro electron‐acceptor groups in their molecular structure

Six dyes with N,N‐dimethylaminophenyl and 4‐nitrophenyl or 2,4‐dinitrophenyl groups in their molecular structures were prepared and characterized. These compounds have different conjugated bridges (C?C, C?N, and N?N) connecting the electron‐donor and the electron‐acceptor groups. All compounds are solvatochromic, with reverse solvatochromism occurring. The solvatochromic band observed in each spectrum for the dyes is due to a π ? π* transition, of an intramolecular charge transfer nature, which occurs from the electron‐donor N,N‐dimethylaminophenyl group to the electron‐acceptor group in the molecules, which is reinforced by the structures of the compounds optimized by applying density functional theory, which exhibit high planarity. The reverse solvatochromism was explained considering two resonance structures. The benzenoid form is better stabilized in less polar solvents and characterizes the region displaying positive solvatochromism, while the dipolar form is better stabilized in more polar solvents, in the region of negative solvatochromism. The Catalán multiparametric approach was used to study the contribution of solvent acidity, basicity, dipolarity, and polarizability to the solvatochromism exhibited by the compounds. These compounds are good candidates for the investigation of the polarizability and, to a lesser extent, the dipolarity of the medium, with very little interference from specific interactions of the solvent through hydrogen bonding. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermoreversible polyaniline gels

Polyaniline (PANI) forms thermoreversible gels in different sulphonic acids e.g. dinonyl napthalene sulphonic acid (DNNSA), dinonylnapthalene disulphonic acid (DNNDSA), ± camphor ‐ 10 ‐ sulphonic acid (CSA) and dodecyl sulphonic acid (DSA) when processed from the formic acid medium. The surfactant concentration has been varied from weight fraction of PANI (W_PANI)=0.05−0.60. In most cases at W_PANI=0.05−0.40 compositions fibrillar network structures are observed from SEM study. They also exhibit reversible first order phase transition during both heating and cooling in DSC. The melting temperature and the gelation temperature increases with increase in surfactant concentration of the gel. From the WAXS pattern it is concluded that crystallization of the surfactant tails anchored from the nitrogen atom of PANI through its SO₃ H head group is responsible for gelation. The conductivity of all the gels with increase in PANI concentration showed a maximum with composition. The maximum conductivity is ∼0.01 S/cm, for W_PANI=0.22. The conductivity variation has been explained by considering it as a function of both interchain and intrachain contributions.     

On the gelation rate of thermoreversible poly(vinylidene fluoride) gels in glyceryl tributyrate

The gelation rate of poly(vinylidene fluoride) (PVF₂)/glyceryl tributyrate (GTB) system has been measured. It has been analysed with the help of an equation which contains φⁿ and f(T) term where φ is a reduced overlapping concentration and n is analogous to the percolation exponent β in a three-dimensional lattice. f(T) is related to the temperature function of the coil-to-helix transition. Analysis of the gelation rates supports that the three-dimensional percolation is a suitable mechanism in this gelation process and it also indicates that the gelation is caused by coil-to-helix transition followed by their association.