Varieties and Nilpotent Extensions of Permutative Periodic Semigroups

We investigate certain semigroup varieties formed by nilpotent extensions of orthodox normal bands of commutative periodic groups. Such semigroups are shown to be both structurally periodic and structurally commutative, and are therefore structurally inverse semigroups. Such semigroups are also shown to be dense semilattices of structurally group semigroups. Making use of these structure decompositions, we prove that the subvariety lattice of any variety comprised of such semigroups is isomorphic to the direct product of the following three sublattices: its sublattice of all structurally trivial semigroup varieties, its sublattice of all semilattice varieties, and its sublattice of all group varieties. We conclude, therefore, that to completely describe this lattice, we must first describe completely the lattice of all structurally trivial semigroup varieties, since the other two are well known lattices.     

Molecular elasticity and the geometric phase

We present a method for solving the wormlike-chain (WLC) model for twisting semiflexible polymers to any desired accuracy. We show that the WLC free energy is a periodic function of the applied twist with period 4pi. We develop an analogy between WLC elasticity and the geometric phase of a spin-1 / 2 system. These analogies are used to predict elastic properties of twist-storing polymers. We graphically display the elastic response of a single molecule to an applied torque. This study is relevant to mechanical properties of biopolymers such as DNA.     

High-throughput manual parallel synthesis using SynPhase crowns and lanterns

The high-throughput manual solid-phase parallel synthesis of libraries comprising thousands of discrete samples using pellicular supports (i.e. SynPhase crowns and lanterns) and a suite of novel tools and techniques is described. Key aspects of this approach include the combination of a split-split-split synthesis strategy with spatial encoding to differentiate thousands of crowns, the rapid washing and filtration of up to 48 reaction vessels in parallel, the application of an inexpensive and environmentally friendly technique to remove trifluoroacetic acid from sixteen 96-well plates in parallel, and a high-throughput method for removing cleaved crowns from reusable pin racks. Tens of thousands of discrete samples have been produced in-house using this conceptually and operationally straightforward strategy.     

The B-Alkyl Suzuki-Miyaura Cross-Coupling Reaction: Development,Mechanistic Study,and Applications in Natural Product Synthesis A list of abbreviations can be found at the end of the article

The development of new reactions that facilitate the creative and efficient synthesis of molecular structures with desirable properties continues to fascinate chemists. The test of a significant contribution is its acceptance over time by the scientific community. The B-alkyl Suzuki-Miyaura cross-coupling reaction appears to be one such reaction. Since its disclosure by Suzuki and Miyaura in 1986, this reaction has been an attractive solution to challenging synthetic problems.     

ForceFit: A code to fit classical force fields to quantum mechanical potential energy surfaces

The ForceFit program package has been developed for fitting classical force field parameters based upon a force matching algorithm to quantum mechanical gradients of configurations that span the potential energy surface of the system. The program, which runs under UNIX and is written in C++, is an easy‐to‐use, nonproprietary platform that enables gradient fitting of a wide variety of functional force field forms to quantum mechanical information obtained from an array of common electronic structure codes. All aspects of the fitting process are run from a graphical user interface, from the parsing of quantum mechanical data, assembling of a potential energy surface database, setting the force field, and variables to be optimized, choosing a molecular mechanics code for comparison to the reference data, and finally, the initiation of a least squares minimization algorithm. Furthermore, the code is based on a modular templated code design that enables the facile addition of new functionality to the program. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010