Comparative DNA isolation behaviours of silica and polymer based sorbents in batch fashion: monodisperse silica microspheres with bimodal pore size distribution as a new sorbent for DNA isolation.

Monodisperse silica microspheres with bimodal pore-size distribution were proposed as a high performance sorbent for DNA isolation in batch fashion under equilibrium conditions. The proposed sorbent including both macroporous and mesoporous compartments was synthesized 5.1 µm in-size, by a "staged shape templated hydrolysis and condensation method". Hydrophilic polymer based sorbents were also obtained in the form of monodisperse-macroporous microspheres ca 5.5 µm in size, with different functionalities, by a developed "multi-stage microsuspension copolymerization" technique. The batch DNA isolation performance of proposed material was comparatively investigated using polymer based sorbents with similar morphologies. Among all sorbents tried, the best DNA isolation performance was achieved with the monodisperse silica microspheres with bimodal pore size distribution. The collocation of interconnected mesoporous and macroporous compartments within the monodisperse silica microspheres provided a high surface area and reduced the intraparticular mass transfer resistance and made easier both the adsorption and desorption of DNA. Among the polymer based sorbents, higher DNA isolation yields were achieved with the monodisperse-macroporous polymer microspheres carrying trimethoxysilyl and quaternary ammonium functionalities. However, batch DNA isolation performances of polymer based sorbents were significantly lower with respect to the silica microspheres.

Observations of Co4+ in a higher spin state and the increase in the Seebeck coefficient of thermoelectric Ca3Co4O9.

Ca3Co4O9 has a unique structure that leads to exceptionally high thermoelectric transport. Here we report the achievement of a 27% increase in the room-temperature in-plane Seebeck coefficient of Ca3Co4O9 thin films. We combine aberration-corrected Z-contrast imaging, atomic-column resolved electron energy-loss spectroscopy, and density-functional calculations to show that the increase is caused by stacking faults with Co4+-ions in a higher spin state compared to that of bulk Ca3Co4O9. The higher Seebeck coefficient makes the Ca3Co4O9 system suitable for many high temperature waste-heat-recovery applications.

Atomic scale characterization of the Pt/TiO2 interface.

We present results from an investigation of the Pt/TiO(2) catalyst system using a combination of Z-contrast imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope. Evidence of a strong interaction between the Pt particles and the support is found to be dependent on the Pt cluster size, being manifested either as an encapsulation of the Pt particles by the support or a distortion of the structure of the Pt particles. In the case of clusters that are only a few atoms in size, we show direct evidence of an epitaxial nucleation relationship between Pt and Titania. The results also show unexpectedly that Pt particles exhibit a preferential nucleation on rutile rather than anatase.

Comparison of simulation methods for electronic structure calculations with experimental electron energy-loss spectra.

The electronic structure of hexagonal GaN is studied using two simulation techniques in order to develop a method to interpret the fine-structure of an experimental nitrogen K-edge electron energy loss spectrum obtained using a scanning transmission electron microscope. The application of these simulation methods to the bulk spectrum is a necessary first step in developing a fundamental understanding of the effect of changes in the electronic structure on the properties of defects. It is found here that both of the techniques used, multiple scattering (MS) and density functional theory (DFT), produce excellent agreement with the experimental bulk spectrum. The MS method is limited in accuracy but efficient in time, while the DFT method is more accurate but time consuming. Through the combination of these methods, experimental energy loss spectra can be readily understood, and a means to unravel the complexities of the electronic structure can be determined.

Ab initio absorption spectra and optical gaps in nanocrystalline silicon.

The optical absorption spectra of Si(n)H(m) nanoclusters up to approximately 250 atoms are computed using a linear response theory within the time-dependent local density approximation (TDLDA). The TDLDA formalism allows the electronic screening and correlation effects, which determine exciton binding energies, to be naturally incorporated within an ab initio framework. We find the calculated excitation energies and optical absorption gaps to be in good agreement with experiment in the limit of both small and large clusters. The TDLDA absorption spectra exhibit substantial blueshifts with respect to the spectra obtained within the time-independent local density approximation.

Spectroscopic evidence for the tricapped trigonal prism structure of semiconductor clusters

We have obtained photoelectron spectra (PES) for silicon cluster anions with up to 20 atoms. Efficient cooling of species in the source has allowed us to resolve multiple features in the PES for all sizes studied. Spectra for an extensive set of low-energy Si(-)(n) isomers found by a global search have been simulated using density functional theory and pseudopotentials. Except for n = 12, calculations for Si(-)(n) ground states agree with the measurements. This does not hold for other plausible geometries. Hence PES data validate the tricapped trigonal prism morphologies for medium-sized Si clusters.

DNA photoreactivating enzyme from human tissues.

Photoreactivating enzyme activity has been quantitated in human fetal skin, kidney, lung, liver, brain and intestine, and in neonatal human foreskin. In all the tissues examined there were at least two activities: one nominally greater than 10,000 Da, and one nominally less than 10,000 Da. Both can photolyze pyrimidine dimers in DNA using only light of wavelengths greater than 320 nm, thus excluding tryptophan-mediated dimer splitting as an important mechanism for these activities. The activities are inactivated by digestion with trypsin or pronase, and decreased partially or totally by heating to 65 degrees C. The activities from all six tissues, as well as that from neonatal foreskin, act catalytically in dimer photolysis. The properties of macromolecular size, heat lability, protease sensitivity and catalytic pyrimidine dimer photolysis by a non-tryptophan-mediated mechanism correspond to those of a true photoreactivating enzyme.