Oxidoreductase Catalyzed Polymerization of 3-Methylpyrrole

A one-pot, environmentally friendly enzymatic method is described for the synthesis a polypyrrole derivative, poly(3-methylpyrrole) (poly(3-MP)) in an aqueous solvent system. The enzyme, soybean peroxidase (SBP), was shown to successfully polymerize the beta functionalized pyrrole monomer. The resulting polymer was semiconducting, thermally stable, and exhibited bipolaron absorptions when synthesized in the presence of poly(sodium 4-styrenesulfonate) (PSS). Polymers synthesized in the presence of 10-camphor sulfonic acid (CSA) were found to exhibit slightly higher conductivity values, but were less thermally stable compared to poly(3-MP) polymerized in the presence of PSS. This work should stimulate further interest in expanding the use of enzymes as catalysts for the polymerization of other pyrrole derivatives, as well as other classes of conjugated polymers.     

On bounding Hecke-Siegel eigenvalues

We use the action of the Hecke operators (1≤j≤n) on the Fourier coefficients of Siegel modular forms to bound the eigenvalues of these Hecke operators. This extends work of Duke-Howe-Li and of Kohnen, who provided bounds on the eigenvalues of the operator T(p).     

Symbolic Covariance Principal Component Analysis and Visualization for Interval-Valued Data

This article proposes a new approach to principal component analysis (PCA) for interval-valued data. Unlike classical observations, which are represented by single points in p-dimensional space ?^p, interval-valued observations are represented by hyper-rectangles in ?^p, and as such, have an internal structure that does not exist in classical observations. As a consequence, statistical methods for classical data must be modified to account for the structure of the hyper-rectangles before they can be applied to interval-valued data. This article extends the classical PCA method to interval-valued data by using the so-called symbolic covariance to determine the principal component (PC) space to reflect the total variation of interval-valued data. The article also provides a new approach to constructing the observations in a PC space for better visualization. This new representation of the observations reflects their true structure in the PC space. Supplementary materials for this article are available online.     

An oscillating plate in a binary mixture of hemihedral fluids

Summary The sinusoidal oscillations of an infinite plate in a mixture of two incompressible Newtonian hemihedral fluids are investigated. The solution is compared with the previously derived corresponding one for holohedral fluids.

---

Zusammenfassung Es werden die sinusförmigen Schwingungen einer unendlichen Platte in einer Mischung von zwei inkompressiblen Newtonschen hemiedrischen Flüssigkeiten untersucht. Die Lösung wird mit der früher erhaltenen entsprechenden Lösung für holoedrische Flüssigkeiten verglichen.

     

Absolute free energy calculations by thermodynamic integration in four spatial dimensions

An optimized technique for calculating the excess chemical potential of small molecules in dense liquids and the binding affinity of molecular ligands to biomolecules is reported. In this method, a molecular species is coupled to the system of interest via a nonphysical fourth spatial dimension w through which insertion or extraction can be carried out [R. Pomes, E. Eisenmesser, C. B. Post et al., J. Chem. Phys. 111, 3387 (1999)]. Molecular simulations are used to compute the potential of mean force (PMF) acting on the solute molecule in the fourth dimension. The excess chemical potential of that molecule is obtained as the difference in the PMF between fully coupled and fully decoupled systems. The simplicity, efficiency, and generality of the method are demonstrated for the calculation of the hydration free energies of water and methanol as well as sodium, cesium, and chloride ions. A significant advantage over other methods is that the 4D-PMF approach provides a single effective and general route for decoupling all nonbonded interactions (i.e., both Lennard-Jones and Coulombic) at once for both neutral and charged solutes. Direct calculation of the mean force from thermodynamic integration is shown to be more computationally efficient than calculating the PMF from umbrella sampling. Statistical error analysis suggests a simple strategy for optimizing sampling. The detailed analysis of systematic errors arising from the truncation of Coulombic interactions in a solvent droplet of finite size leads to straightforward corrections to ionic hydration free energies.     

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.     

A neutron diffraction and 170Yb Mössbauer investigation of the perovskite ytterbium titanium oxide

A phase with the perovskite structure (Pbnm) and a composition YbTiO_2.95 has been prepared by a high-temperature carbothermic method. Neutron diffraction shows a colinear ferrimagnetic structure at 7 K with Yb and Ti moments antiparallel along the c-axis of the orthorhombic cell and an Yb moment of 1.8(3)μ_B. ¹⁷⁰Yb Mössbauer measurements find a more precise and accurate value of 2.0(1)μ_B from the maximum hyperfine field. From the temperature dependence of the hyperfine field a T_c = 42(1) K is found. The Yb sublattice magnetization below T_c follows a Brillouin function. At low temperature a distribution of hyperfine fields is observed which is attributed to a random distribution of defects surrounding the Yb sites. The magnetic structure is discussed in relation to possible values for the crystal field parameters, especially B²₀.     

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.