Suppression of electron-hole correlations in 3D polymer materials

We present an ab initio study of the optical absorption spectra of isolated as well as crystalline trans-polyacetylene. We include excitonic effects by solving the Bethe-Salpeter equation for the electron-hole two-particle correlation function. We observe that the strength of the electron-hole interactions drastically reduces when going from an isolated polymer chain to a crystalline arrangement. This is not only a result of enhanced screening in the 3D material, but also of the increased spatial extent of the exciton perpendicular to the polymer chains. We point out that these findings apply to crystalline phases of conjugated polymers and molecular crystals in general.     

Inadequacy of perfect-reflector models in cavity QED for systems with low-frequency excitations

It is shown that the model of perfectly reflecting boundaries widely employed in cavity QED is unsuitable for systems that have long-wavelength excitations. A prime example is a free charged particle near a reflecting wall. Modeling the wall as perfectly reflecting from the outset ignores evanescent waves that couple to the particle through virtual excitations at low energies, which can lead to errors in order of magnitude and even sign. The example of a free electron near an imperfectly reflecting wall characterized by a constant frequency-independent refractive index n is investigated in detail by determining its energy shift relative to an electron in vacuum through both nonrelativistic and relativistic calculations.     

QALE analysis of CO dissociative kinetics of Ru(CO)4L (L = P-donor ligands): accelerating effects of hydrogen in PHnR(3 - n) ligands (n = 1-2)

Studies of CO-dissociative substitution reactions of the complexes Ru(CO)4L (L = a wide variety of P-donor ligands) have been extended and analysis of the results by the QALE methodology has been refined (QALE = quantitative analysis of ligand effects). Rates increase substantially with increasing size of L, mainly as a consequence of increasingly favourable activation entropies. These can be associated with increasing Ru-CO bond breaking that is compensated enthalpically by increasing Ru-P bond making allowed by release of steric strain. Explicit allowance for pi-acidity shows that these effects are just significant while sigma-donor and aryl effects are negligible. However, pendent hydrogen atoms, attached directly to the phosphorus atoms, have a pronounced and unique positive effect on the rates, with significant kinetic isotope effects (KIE). This is associated with the novel occurrence of direct Ru-H or incipient Ru-(eta2-P-H) agostic bond making as the CO ligand departs.     

Introduction of 4(S)-oxazolidineacetic acid, 2-oxo (D-Oxac) motif in a polypeptide chain: synthesis and conformational analysis

A four step synthesis of 4(S)-oxazolidineacetic acid, 2-oxo benzyl ester (D-Oxac-OBn) from L-Asp-OH in 45% overall yield is reported. The formation of by-products is completely avoided, by microwave irradiation and by the use of caesium carbonate as base. Moreover the synthesis and IR and 1H NMR conformational analysis of the tetramers Boc-L-Val-D-Oxac-L-Ala-OBn and Boc-L-Val-D-Oxac-Aib-L-Ala-OBn in solution is reported.     

Core of projective dimension one modules

The core of a projective dimension one module is computed explicitly in terms of Fitting ideals. In particular, our formula recovers previous work by R. Mohan on integrally closed torsionfree modules over a two-dimensional regular local ring. The first author was partially supported by a Faculty Research Fellowship from the University of Kentucky. The second and third authors gratefully acknowledge partial support from the NSF.Mathematics Subject Classification (2000):Primary 13A30, 13B21; Secondary 13C99     

Acridinone-based anion receptors and sensors

The interaction of a variety of acridinone derivatives containing hydrogen-bond donor groups in the 4- and 5-positions with anions demonstrate the potential of this new scaffold in anion receptor and sensor design.     

Effect of Extraction Methods and In Vitro Bio-Accessibility of Microencapsulated Lemon Extract

The extraction of bioactive compounds from fruits, such as lemon, has gained relevance because these compounds have beneficial properties for health, such as antioxidant and anticancer properties; however, the extraction method can significantly affect these properties. High hydrostatic pressure and ultrasound, as emerging extraction methods, constitute an alternative to conventional extraction, improving extractability and obtaining extracts rich in bioactive compounds. Therefore, lemon extracts (LEs) were obtained by conventional (orbital shaking), ultrasound-assisted, and high-hydrostatic-pressure extraction. Extracts were then microencapsulated with maltodextrin at 10% (M10), 20% (M20), and 30% (M30). The impact of microencapsulation on LEs physicochemical properties, phenolics (TPC), flavonoids (TFC) and relative bio-accessibility (RB) was evaluated. M30 promoted a higher microencapsulation efficiency for TPC and TFC, and a longer time required for microcapsules to dissolve in water, as moisture content, water activity and hygroscopicity decreased. The RBs of TPC and TFC were higher in microcapsules with M30, and lower when conventional extraction was used. The data suggest that microencapsulated LE is promising as it protects the bioactivity of phenolic compounds. In addition, this freeze-dried product can be utilized as a functional ingredient for food or supplement formulations.