Enzymatic Method for the Synthesis of Long DNA Sequences with Multiple Repeat Units

A polymerase chain reaction (PCR) derived method for preparing long DNA, consisting of multiple repeat units of one to ten base pairs, is described. Two seeding oligodeoxynucleotides, so‐called oligoseeds, which encode the repeat unit and produce a duplex with 5′‐overhangs, are extended using a thermostable archaeal DNA polymerase. Multiple rounds of heat–cool extension cycles, akin to PCR, rapidly elongate the oligoseed. Twenty cycles produced long DNA with uniformly repeating sequences to over 20 kilobases (kb) in length. The polynucleotides prepared include [A]_n/[T]_n, [AG]_n/[TC]_n, [A₂G]_n/[T₂C]_n, [A₃G]_n/[T₃C]_n, [A₄G]_n/[T₄C]_n, [A₉G]_n/[T₉C]_n, [GATC]_n/[CTAG]_n, and [ACTGATCAGC]_n/[TGACTAGTCG]_n, indicating that the method is extremely flexible with regard to the repeat length and base sequence of the initial oligoseeds. DNA of this length (20 kb≈7 μm) with strictly defined base reiterations should find use in nanomaterial applications.     

Influence of molecular weight upon drag reduction by polymers

Summary Drag reduction measurements have been made with samples of polyethyleneoxide and polyacrylamide with relatively narrow molecular weight distributions obtained by fractionation of commercial polymers. Relationships between the polymer molecular weight and the concentration required to give the same drag reduction have been determined. The influence of polymer degradation upon these relationships has been investigated.Molecular weight distributions of commercial polymers have been determined and their influence upon the drag-reducing properties is noted.The influence of wall shear stress has been investigated over the range 1.0 × 10² - 4.5 × 10³ dyn/cm². The results with unfractionated polymers were found to be consistent with other results in the literature.     

Palladium-catalyzed Coupling between Aryl Halides and Trimethylsilylacetylene Assisted by Dimethylaminotrimethyltin

Palladium‐catalyzed coupling between aryl halides, especially less reactive ones or N‐heteroaryls, and trimethylsilylacetylene in the presence of dimethylaminotrimethyltin generated the coupled products in high yields. The reaction does not need CuI and base as auxiliary agents.     

Edge searching weighted graphs

In traditional edge searching one tries to clean all of the edges in a graph employing the least number of searchers. It is assumed that each edge of the graph initially has a weight equal to one. In this paper we modify the problem and introduce the Weighted Edge Searching Problem by considering graphs with arbitrary positive integer weights assigned to its edges. We give bounds on the weighted search number in terms of related graph parameters including pathwidth. We characterize the graphs for which two searchers are sufficient to clear all edges. We show that for every weighted graph the minimum number of searchers needed for a not-necessarily-monotonic weighted edge search strategy is enough for a monotonic weighted edge search strategy, where each edge is cleaned only once. This result proves the NP-completeness of the problem.     

Structure and emission spectra of dinuclear lanthanide(III) β-diketonate complexes with a bridging 2,2′-bipyrimidine ligand

The 2,2′-bipyrimidine (bpm) adducts of the β-diketonate complexes of Eu(III), Sm(III), or Yb(III) with 2,2′,6,6′-tetramethyl-2,4-heptanedione (tmhd) resulted in the formation of dinuclear species. The synthesis and X-ray structure of these three new dinuclear lanthanide complexes are found to be similar. Each lanthanide ion is eight coordinate, bound to six O-atoms from the β-diketonates and 2N atoms from the bridging bpm ligand. They exhibit Ln–Ln distances (Sm(III): 6.935 Å, Eu(III): 6.901 Å, Yb(III): 6.679 Å) and Ln–ligand distances that are consistent with the decrease in radii across the lanthanide series. Absorption spectra of the complexes are dominated by ligand absorptions. Both the solution and solid state emission spectra of the complexes resemble ordinary monomeric lanthanide species, indicating independent ions in the dinuclear species. Cyclic voltammetry of all the complexes appear almost identical with discernable ligand centered redox reactions. The complex with Eu(III) ions, having the lowest possible lanthanide redox potential, was not found to display a signal corresponding to metal reduction.     

Templating Ag on DNA/polymer hybrid nanowires: Control of the metal growth morphology using functional monomers

Ag nanowires and nanoparticles have been formed on hybrid λ-DNA/conducting polymer templates. The strong, but non-covalent, interaction of the conducting polymer with the double helix allowed us to incorporate chemical functionalities (alkynyl) into the DNA/conducting polymer strands by synthesis of functional monomers. Oxidative polymerisation of alkynyl-thienylpyrrole in the presence of λ-DNA produced conductive nanowires bearing alkyne groups; we show, using a combination of AFM, cAFM and EFM phase measurements that the alkyne functionality strong influences the subsequent templating reaction of Tollens’ reagent to produce uniform conductive nanowires comprised of many connected Ag clusters.     

Twisted Frobenius Extensions of Graded Superrings

We define twisted Frobenius extensions of graded superrings. We develop equivalent definitions in terms of bimodule isomorphisms, trace maps, bilinear forms, and dual sets of generators. The motivation for our study comes from categorification, where one is often interested in the adjointness properties of induction and restriction functors. We show that A is a twisted Frobenius extension of B if and only if induction of B-modules to A-modules is twisted shifted right adjoint to restriction of A-modules to B-modules. A large (non-exhaustive) class of examples is given by the fact that any time A is a Frobenius graded superalgebra, B is a graded subalgebra that is also a Frobenius graded superalgebra, and A is projective as a left B-module, then A is a twisted Frobenius extension of B.