Artarborol, a nor-caryophyllane sesquiterpene alcohol from Artemisia arborescens. stereostructure assignment through concurrence of NMR data and computational analysis

A nor-caryophyllane derivative, artarborol, has been isolated from wormwood (Artemisia arborescens) and its stereostructure established by using a combination of chemical derivatization, NMR data, molecular modeling, and quantum-mechanical calculations. In particular, comparison of experimental 13C NMR data with a Boltzmann-weighed average of 13C NMR chemical shifts, calculated by ab initio DFT method, supported the stereochemical assignment.     

Combinatorial synthesis of isoxazole library and their liquid crystalline properties

Six types of isoxazoles including 60 molecules were synthesized using combinatorial synthesis on solid support in a parallel fashion. Highly regioselective 1,3-dipolar cycloaddition of the nitrile oxides to the triple bond of the solid-attached ethynylbenzamides gave isoxazoles on solid support in good yield. Thirty molecules of them exhibited mesomorphic properties. The combination of molecular mechanics calculations and X-ray diffraction experiments of 2g and 3g revealed that the smectic phase of 2g had a bilayer structure, whereas 3g showed a monolayer liquid crystalline phase. These are supported in comparison with the single crystal structures of 2g and 3g.     

Electron affinities of heavier phosphoryl and thiophosphoryl halides APX3 (A = O, S and X = Br, I)

We carried out computational studies of OPX₃ and SPX₃ (X = Br and I) molecules and their corresponding anions using density functional theory, Møller‐Plesset, and CCSD(T) methods with newly developed model core potentials (MCP). Reliabilities of the MCP were demonstrated by comparing experimental and calculated results. We computed the geometric structure, electron affinities, and electrostatic moments using systematic sequences of the dzp‐, tzp‐, and qzp‐quality basis sets. Both C_3v and C_s symmetries were assumed to ascertain that minima on the potential energy surface were found. Infrared and Raman frequencies were calculated and compared with available experimental data. Natural population analyses were performed and used to determine distribution of the extra electron in anions. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007     

Revised model core potentials of s-block elements

We developed new model core potentials (MCPs) for s-block elements from Na to Ra, in which the outer core (n-1)s and (n-1)p electrons are treated explicitly together with the ns electrons. By adding suitable correlating functions, we demonstrated that the present MCP basis sets show excellent performance in describing the electronic structures of atoms and molecules, bringing about accurate ionization potentials of atoms and very good spectroscopic constants of ionic and covalent molecules. The results obtained with the new MCPs are very close to the ones obtained using the all-electron correlation consistent basis sets of Dunning.     

The chemical effects of molecular sol-gel entrapment

Chemical conversions within the cages of doped sol-gel porous oxides take place with unique advantages over reactions in solution as the glassy matrix has tremendous effects on the reactivity of the entrapped molecules. The chemical properties of sol-gel materials can be tailored in an immense range of values and chemists are increasingly achieving control on reactions taking place within these matrices, including crucially important photovoltaics. Highlighting recent major advancements, we show in this tutorial review how this is actually taking place.     

Protein nanopores with covalently attached molecular adapters

Molecular adapters are crucial for the stochastic sensing of organic analytes with alpha-hemolysin (alphaHL) protein nanopores when direct interactions between analytes and the pore cannot readily be arranged by conventional protein engineering. In our earlier studies, cyclodextrin adapters were lodged noncovalently within the lumen of the alphaHL pore. In the present work, we have realized the controlled covalent attachment of a beta-cyclodextrin (betaCD) adapter in the two possible molecular orientations inside alphaHL pores prepared by genetic engineering. There are two advantages to such a covalent system. First, the adapter cannot dissociate, which means there are no gaps during stochastic detection, a crucial advance for single-molecule exonuclease DNA sequencing where the continuous presence of a molecular adapter will be essential for reading individual nucleotides. Second, the ability to orient the adapter allows analytes to bind through only one of the two entrances to the betaCD cavity. We demonstrate that the covalently attached adapters can be used to alter the ion selectivity of the alphaHL pore, examine binding events at elevated temperatures, and detect analytes with prolonged dwell times.     

Existence of solutions for a perturbed Dirichlet problem without growth conditions

We present some results on the existence and multiplicity of solutions for boundary value problems involving equations of the type −Δu=f(x,u)+λg(x,u), where Δ is the Laplacian operator, λ is a real parameter and , are two Carathéodory functions having no growth conditions with respect to the second variable. The approach is variational and mainly based on a critical point theorem by B. Ricceri.     

Optimal control for the thermistor problem with a current limiting device

Email: cimatti{at}dm.unipi.it Received on September 26, 2005; Accepted on August 2, 2006 The problem of finding in the thermistor problem the optimaldifference of applied potential in order to minimize a suitablecost functional involving the temperature is studied. We findthe optimal system in the elementary case of constant electricconductivity. In addition, a theorem of existence of the optimalsolution is given in the general case of conductivities dependingon the temperature.