A simple handheld device based on the fluorescence analysis of 3,6-bis(1-methyl-4-vinylpyridinium) carbazole diiodide ( BMVC) stained cells was established for routine screening and potentially for early detection of cancer cells at extremely low cost. Flow cytometry assay further supported the utility of this simple device, where a preliminary study of tissue biopsy showed highly encouraging results.

We have introduced a G-quadruplex-binding ligand, 3,6-bis(1-methyl-4-vinylpyridinium)carbazole diiodide (BMVC), to verify the major structure of d(T2AG3)4 (H24) in potassium solution and examine the structural conversion of H24 in sodium solution upon potassium titration. The studies of circular dichroism, induced circular dichroism, spectral titration and gel competition have allowed us to determine the binding mode and binding ratio of BMVC to the H24 in solution and eliminate the parallel form as the major G-quadruplex structure. Although the mixed-type form could not be eliminated as a main component, the basket and chair forms are more likely the main components of H24 in potassium solution. In addition, the circular dichroism spectra and the job plots reveal that a longer telomeric sequence d(T2AG3)13 (H78) could form two units of G4 structure both in sodium or potassium solutions. Of particular interest is that no appreciable change on the induced circular dichroism spectra of BMVC is found during the change of the circular dichroism patterns of H24 upon potassium titration. Considering similar spectral conversion detected for H24 and a long sequence H78 together with the G4 structure stabilized by BMVC, it is therefore unlikely that the rapid spectral conversion of H24 and H78 is due to structural change between different types of the G4 structures. With reference to the circular dichroism spectra of d(GAA)7 and d(GAAA)5, we suggest that the spectral conversion of H24 upon potassium titration is attributed to fast ion exchange resulting in different loop base interaction and various hydrogen bonding effects.

We have used the combination of the coupling-constant integration procedure and the variational quantum Monte Carlo method to study the exchange-correlation (XC) interaction in small molecules: Si-2, C2H2, C2H4, and C2H6. In this paper we report the calculated XC energy density, a central quantity in density functional theory, as deduced from the interaction between the electron and its XC hole integrated over the interaction strength. Comparing these "exact" XC energy densities with results using the local-density approximation (LDA), one can analyze the errors in this widely used approximation. Since the XC energy is an integrated quantity, error cancellation among the XC energy density in different regions is possible. Indeed we find a general error cancellation between the high-density and low-density regions. Moreover, the error distribution of the exchange contribution is out of phase with the error distribution of the correlation contribution. Similar to what is found for bulk silicon and an isolated silicon atom, the spatial variation of the errors of the LDA XC energy density in these molecules largely follows the sign and shape of the Laplacian of the electron density. Some noticeable deviations are found in Si-2 in which the Laplacian peaks between the atoms, while the LDA error peaks in the regions "behind" atoms where a good portion of the charge density originates from an occupied 1 sigma(u) antibonding orbital. Our results indicate that, although the functional form could be quite complex, an XC energy functional containing the Laplacian of the energy is a promising possibility for improving LDA.

A study of ion equilibration in annular regions of ultracold strontium plasmas is reported. Plasmas are formed by photoionizing laser-cooled atoms with a pulsed dye laser. The experimental probe is spatially-resolved absorption spectroscopy using the S-2(1/2)-P-2(1/2) transition of the Sr+ ion. The kinetic energy of the ions is calculated from the Doppler broadening of the spectrum, and it displays clear oscillations during the first microsecond after plasma formation. The oscillations, which are a characteristic of strong coulomb coupling, are fit with a simple phenomenological model incorporating damping and density variation in the plasma.

Surface-supported planar clusters can sprout active research and create numerous applications in the realm of nanotechnology. Exploitation of these clusters will be more extended if their properties on a supported substrate are thoroughly apprehended, and if they can be fabricated in a controllable way. Here we report finding the magic numbers in two-dimensional Ag clusters grown on Pb quantum islands. We demonstrate, with the images and energy spectra of atomic precision, the transition from electronic origin to a geometric one within the same system. Applying the magic nature, we can also produce a large array of planar clusters with well-defined sizes and shapes.

We present a first-principles investigation of the lattice dynamics and thermodynamical properties of a complex hydride NaAlH(4), a promising material for hydrogen storage. The calculations are performed within the density-functional-theory framework and using a linear response theory. Calculations of the phonon spectrum, Born effective charges Z(*), and dielectric constants in high and low frequency limits are reported. The mode characters of the zone-center phonons, including the LO-TO splitting, are identified and compared to the experiment. The quasiharmonic approach is used to study thermal expansion as well as the mean square displacement of each atom as a function of temperature. A connection is established between the latter and the melting point. The inclusion of the zero-point motion leads to an expanded lattice compared to the static lattice, while the low frequency oscillations are found to play an important role in the melting and decomposition of NaAlH(4).

Fluorescence studies of 3,6-bis(1-methyl-4-vinylpyridinium) carbazole diiodide (BMVC) in glycerol/water mixtures allow us to elucidate the photophysical behavior of BMVC upon interaction with different DNA structures. The very weak fluorescence emission of BMVC in highly polar solvents of water is attributed to an increase in nonradiative decay due to the intramolecular twist of the vinyl group induced by charge transfer. Increasing the solvent viscosity and rigidity could lead to large changes in the barrier height and substantial effects on relaxation processes, and result in an enhancement of the fluorescence quantum yield. Similarly, different binding interactions of BMVC with various DNA could perturb the frictions of the reorientation of the vinyl group. We suggest that the intramolecular twist of the vinyl group of BMVC is mainly responsible for the distinct fluorescence emissions under different local environments. (c) 2006 Elsevier B.V. All rights reserved.

By using a low temperature scanning tunneling microscope we have probed the superconducting energy gap of epitaxially grown Pb films as a function of the layer thickness in an ultrathin regime (5-18 ML). The layer-dependent energy gap and transition temperature (T-c) show persistent quantum oscillations down to the lowest thickness without any sign of suppression. Moreover, by comparison with the quantum-well states measured above T-c and the theoretical calculations, we found that the T-c oscillation correlates directly with the density of states oscillation at E-F. The oscillation is manifested by the phase matching of the Fermi wavelength and the layer thickness, resulting in a bilayer periodicity modulated by a longer wavelength quantum beat.

A CE-resonance Raman spectroscopy (CE-RRS) method based on MEKC and sweeping-MEKC modes is described. A nonfluorescent compound, malachite green (MG), and a doubled Nd:YAG laser (532 nm, 300 mW) were selected as model compound and light source, respectively. In order to carry out a quantitative analysis of MG, a monochromator (effective bandwidth, 0.4 nm) was used to collect the specific Raman line at 1616 cm(-1) (N-phi and C-C stretch, corresponding to 582 nm when the wavelength of the exciting source was 532 nm). As a result, the LOD for MG was 10 ppm, based on the MEKC/RRS mode. This could be improved to 5 ppb when the sweeping-MEKC/RRS mode was applied. Furthermore, with the addition of nano-size silver colloids to the CE buffer the detection limits can be further improved, but the data obtained with surface-enhanced resonance Raman spectroscopy (SERRS) are less useful for quantitative purposes.

We have used ab initio methods to study the possible transition between icosahedral (ico) and cuboctahedral (fcc) structures in lead nanoclusters of sizes up to 309 atoms. Spontaneous fcc-to-ico transition in Pb-13 was observed in the ab initio molecular dynamics (MD) simulations at various temperatures. The transition path can be described predominantly by an angular variable s, which can, generally be applied to the similar transitions in clusters of larger sizes and was observed to follow the Mackay model. We have calculated the two-dimensional energy surface that describes the transition in Pb-13 and found a barrierless fcc-to-ico transition path, which is consistent with the observed spontaneous transition in the ab initio MD simulations. The atomic displacements in the transition were identified as one of the vibrational eigenmodes of these two Pb-13 clusters. For clusters of larger sizes (Pb-n, where n = 55, 147, and 309), the possible transitions following similar paths were determined not to be barrierless and the sizes of the barriers were determined by the ab initio elastic band method.

Different G-quadruplex structures for the human telomeric sequence d(T(2)AG(3))(4) in vitro have been documented in the presence of sodium and potassium. Verification of the G-quadruplex structures in human telomeres in vivo is the main issue in establishing the biological function of the G-quadruplex structures in telomeres as well as the development of anticancer agents. Here we have applied two-photon excitation fluorescence lifetime imaging microscopy to measure the fluorescence lifetime of the BMVC molecule upon interaction with various DNA structures. The distinction in lifetime measured with submicrometer spatial resolution in two-photon excitation fluorescence lifetime imaging microscopy provides a powerful approach not only to verify the existence of the antiparallel G-quadruplex structure in human telomeres but also to map its localizations in metaphase chromosomes.