Synthesis and physical behavior of amphiphilic dendrimers with layered organization of hydrophilic and hydrophobic blocks

Amphiphilic carbosilane dendrimers with novel architectural layout have been synthesized. These dendrimers contain peripheral groups consisting of covalently bound promesogenic fragments and hydrophilic (oligoethyleneglycolic) linkages which are connected to a carbosilane core in two distinct ways: as spacer or as tail arrangement. Such molecules have a block structure where the hydrophilic and hydrophobic blocks are distributed within the dendrimer forming layers of different polarity. The hydrophilic layer is either enclosed between two hydrophobic parts of the molecule or is situated on the periphery. The synthetic strategy for achieving these structures is described. The interfacial properties of the dendrimers were studied and the influence of the dendritic structure’s organization on the Langmuir film formation process is assessed.     

Nanocomposites and Blends of Biocatalytically Synthesized Organosilicone Co-Polymers for Flame Retardant Applications

The great synthetic flexibility of organosilicone polymers, their ease of processing, low cost, and nontoxic nature present an attractive alternative solution over current flame retardant materials. Novozyme-435 catalyzed amidation reaction with silicone-based oligomer was carried out to scale up the synthesis of co-polymer which was fully characterized from its detailed spectroscopic studies. Synthesized co-polymer was compounded in polyolefins for flame retardant applications. Nanoclay [Cloisite 20A, 2C₁₈ MMT (dimethylditallowammonium-/dimethyldioctadecylammonium-modified montmorillonite)] was used as a potential additive in co-polymer, which was then blended with polyolefins to improve their thermal as well as flame retardant properties. The present work provides an initial exciting basis for the enzymatic synthesis of silicon based co-polymers in bulk and their flame retardant applications.     

Mayer sampling: calculation of cluster integrals using free-energy perturbation methods

Free-energy simulation methods are applied toward the calculation of cluster integrals that appear in diagrammatic methods of statistical mechanics. In this approach, Monte Carlo sampling is performed on a number of molecules equal to the order of the integral, and configurations are weighted according to the absolute value of the integrand. An umbrella-sampling average yields the value of the cluster integral in reference to a known integral. Virial coefficients, up to the sixth for the Lennard-Jones model and the fifth for the SPCE model of water, are calculated as a demonstration.     

Thermal expansion behavior of silicon at low temperatures

Lattice parameters, thermal expansion coefficients and Grüneisen parameters of silicon are determined by an X-Ray diffraction method in the temperature range of 180–40 K without the use of liquid gases. Thermal expansion of silicon becomes negative below 120 K which is discussed in terms of its lattice vibrations and crystal structure.     

Enzymatic synthesis of multi-component copolymers and their structural characterization

The use of enzymes in synthetic applications has increased dramatically in the recent years and the field of polymer science is part of this trend. Synthesis of a variety of polymers using lipase catalyzed (Candida antarctica) polymerization reactions has led to a variety of new materials with interesting properties in our laboratories. This paper describes the synthesis of multi-component polyesters and mixed polymers having polyester and polyamide linkages under solvent-less conditions using Candida antarctica lipase B. The effect of a third component, i.e. a series of 1,omega-alkanediols (1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, 1,14-tetradecanediol and 1,16-hexadecanediol) on the copolymerization reaction of dimethyl 5-hydroxyisophthalate with poly(ethylene glycol 600) has been studied and the mechanism for the incorporation of the third component is proposed. We have also studied the effect of different functional groups during terpolymerization reaction of dimethyl 5-hydroxyisophthalate with poly(ethylene glycol) by adding a third component having different functionalities (1,6-hexanediol, 1,6-hexanediamine or 1,6-hexanedithiol) and compared the effect of hydroxyl, amine and thiol groups on the polymerization reactions.     

Low temperature lattice parameters and expansion coefficients of AI2Au and LiF Gruneisen constants of LiF

There is no difference in the thermal expansion behavior of an intermetallic compound (Al₂Au) and of an ionic (LiF), except in the magnitude of the expansion coefficients, which for both compounds upon cooling below 40°K approach zero. The lattice parameters of the two compounds mentioned decrease uniformly and without anomalies with lowering the temperature, approaching a constant value below 40°K. The a–T relationship between 40 and 180° is given in form of equations. A pump working on the Joule-Thomson principle was used for cooling. The GRÜNEISEN parameter, γ, of LiF between 40 and 180°K is a constant, contrary to theoretical prediction. The values of a, α and γ agree well with previous measurements, where liquid gases were used for cooling and lattice parameter determinations and a dilatometer for expansivity measurements.     

On algorithm portfolios and restart strategies

We consider two parallel strategies for randomized restart algorithms. Given a set of available algorithms, one can either choose the best performing algorithm and run multiple copies of it in parallel (single algorithm portfolio), or choose some subset of algorithms to run in parallel (mixed algorithm portfolio). It has been previously shown in the literature that the latter approach may provide better results. In this paper we investigate the extent of such improvement.     

Supramolecular assemblies based on copolymers of PEG600 and functionalized aromatic diesters for drug delivery applications

A chemoenzymatic approach has been developed to synthesize poly(ethylene glycol)-based amphiphilic copolymers under mild reaction conditions that self-assemble in aqueous media to form polymeric nanomicelles in the range of 20-50 nm. The supramolecular organization of polymeric nanomicelles was studied by 1H NMR longitudinal relaxation time (T1) and light scattering techniques (static and dynamic). Interestingly, the enzyme novozyme-435 plays an important role in controlling the polymerization and distribution of polymer chains, which is critical for the formation of nanomicelles with unimodal distributions. The methodology developed is highly flexible as it allows the introduction of various functionalities in the polymeric nanomicelles. These self-organized nanomicelles are highly efficient drug delivery vehicles for hydrophobic and partially hydrophilic drugs, both transdermally and orally, as they have the ability to encapsulate guest molecules during self-organization. In vivo studies by encapsulating anti-inflammatory agents (aspirin and naproxen) in these polymeric nanomicelles and by applying topically resulted in significant reduction in inflammation. The % reduction in inflammation using polymeric nanomicelles containing aspirin and naproxen was 62 and 64%, respectively.     

Selective separation of pyrite and chalcopyrite by biomodulation

Selective separation of pyrite from other associated ferrous sulphides at acidic and neutral pH has been a challenging problem. This paper discusses the utility of Acidithiobacillus ferrooxidans for the selective flotation of chalcopyrite from pyrite. Consequent to interaction with bacterial cells, pyrite remained depressed even in the presence of potassium isopropyl xanthate collector while chalcopyrite exhibited significant flotability. However, when the minerals were conditioned together, the selectivity achieved was poor due to the activation of pyrite surface by the copper ions in solution. The selectivity was improved when the sequence of conditioning with bacterial cells and collector was reversed, since the bacterial cells were able to depress collector interacted pyrite effectively, while having negligible effect on chalcopyrite. The observed behaviour is analysed and discussed in detail. The separation obtained was significant both at acidic and alkaline pH. This selectivity achieved was retained when the minerals were interacted with both bacterial cells and collector simultaneously.