Approximate MCSCF optimization for multiconfigurational spin‐tensor electron propagator method (MCSTEP): The vertical ionization potentials of CO,HCN, HNC,H2CO,and O3

The multiconfigurational spin tensor electron propagator method (MCSTEP) was developed as an implementation of electron propagator/single particle Green's function methods. MCSTEP was specifically designed for open shell and highly correlated (nondynamically correlated) initial states. The initial state used in MCSTEP is typically a small complete active space (CAS) with multiconfigurational self‐consistent field (MCSCF) state. In some cases, because of our use of a small CAS in MCSTEP, the Lagrangian eigenvalues of the MCSCF reference state are in an undesired order (u). The desired order (d) can usually be obtained by excluding one or more orbital rotations in MCSCF optimization between the doubly occupied and partially occupied orbitals. We systematically examine several cases where the undesired order occurs for the low‐lying vertical MCSTEP ionization potentials (IPs) of the molecules CO, HCN, HNC, H₂CO, and O₃ with our recently established CAS choices for MCSCF/MCSTEP. By excluding one or more orbital rotations between the partially and doubly occupied orbitals, an approximate MCSCF reference state with the same CAS choice is obtained for use in standard MCSTEP calculations that, in general, gives more reliable vertical MCSTEP IPs. © 2007 Wiley Periodicals, Inc. J Quantum Chem, 2008     

A novel 3D mammalian cell perfusion-culture system in microfluidic channels

Mammalian cells cultured on 2D surfaces in microfluidic channels are increasingly used in drug development and biological research applications. These systems would have more biological or clinical relevance if the cells exhibit 3D phenotypes similar to the cells in vivo. We have developed a microfluidic channel based system that allows cells to be perfusion-cultured in 3D by supporting them with adequate 3D cell-cell and cell-matrix interactions. The maximal cell-cell interaction was achieved by perfusion-seeding cells through an array of micropillars; and 3D cell-matrix interactions were achieved by a polyelectrolyte complex coacervation process to form a thin layer of matrix conforming to the 3D cell shapes. Carcinoma cell lines (HepG2, MCF7), primary differentiated (hepatocytes) and primary progenitor cells (bone marrow mesenchymal stem cells) were perfusion-cultured for 72 hours to 1 week in the microfluidic channel, which preserved their 3D cyto-architecture and cell-specific functions or differentiation competence. This transparent 3D microfluidic channel-based cell culture system also allows direct optical monitoring of cellular events for a wide range of applications.     

Determination of molar absorptivity coefficients for major type-B trichothecenes and certification of calibrators for deoxynivalenol and nivalenol

This paper presents results from the European Commission-funded project Doncalibrant, the objective of which was to produce calibrators with certified mass fractions of the Fusarium toxins deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-Ac-DON), 15-acetyldeoxynivalenol (15-Ac-DON), and nivalenol (NIV), in acetonitrile. The calibrators, available in ampoules, were sufficiently homogeneous, with between-bottle variations (s _bb) of less than 2%. Long-term stability studies performed at four different temperatures between −18 and 40 °C revealed no significant negative trends (at a confidence level of 95%). Molar absorptivity coefficients (in L mol⁻¹ cm⁻¹) were determined for all four toxins (DON: 6805 ± 126, NIV: 6955 ± 205, 3-Ac-DON: 6983 ± 141, 15-Ac-DON: 6935 ± 142) on the basis of a mini-interlaboratory exercise. The overall uncertainty of the calibrators’ target values for DON and NIV were evaluated on the basis of gravimetric preparation data and include uncertainty contributions from possible heterogeneity, storage, and transport. The Doncalibrant project resulted in the production of calibrators for DON (IRMM-315) and NIV (IRMM-316) in acetonitrile with certified mass fractions of 25.1 ± 1.2 μg g⁻¹ and 24.0 ± 1.1 μg g⁻¹, respectively. Both CRMs became commercially available from the Institute for Reference Materials and Measurements (IRMM, Geel, Belgium) at the beginning of 2007.     

Scaling in nonstationary voltammetry representations

Despite the widespread use of voltammetry for a range of chemical, biological, environmental, and industrial applications, there is still a lack of understanding regarding the functionality between the applied voltage and the resulting patterns in the current response. This is due to the highly nonlinear relation between the applied voltage and the nonstationary current response, which casts a direct association nonintuitive. In this Article, we focus on large-amplitude/high-frequency ac voltammetry, a technique that has shown to offer increased voltammetric detail compared to alternative methods, to study heterogeneous electrochemical reaction-diffusion cases using a nonstationary time-series analysis, the Hilbert transform, and symmetry considerations. We show that application of this signal processing technique minimizes the significant capacitance contribution associated with rapid voltammetric measurements. From a series of numerical simulations conducted for different voltage excitation parameters as well as kinetic, thermodynamic, and mass transport parameters, a number of scaling laws arise that are related to the underlying parameters/dynamics of the process. Under certain conditions, these observations allow the determination of all underlying parameters very rapidly, experiment duration typically相似文献   

Chemical screening of olive biophenol extracts by hyphenated liquid chromatography

Chemical screening using reversed phase HPLC-photodiode array detection (RPLC-DAD) and RPLC-electrospray ionisation mass spectrometry (RPLC-ESI-MS) is widely applied as an approach to streamline natural products research. The full potential of this approach is demonstrated in this paper by application to the chemical screening of olive products including olive mill waste (OMW). Out of 100 biophenols previously reported in olive products, the on-line RPLC-DAD-ESI-MS was able to confirm the presence of 52 compounds in OMW. This included a number of simple phenols, flavonoids and secoiridoids. By careful examination of the combined DAD and ESI-MS data, extra information was elucidated including: the site of glycosidation on the phenol ring of hydroxytyrosol; the identity of the other luteolin-glucoside isomer as luteolin-4′-O-glucoside; identifying rutin rather than the previously reported hesperidin (and the reasons for possible mis-assignment); and the detection of diastereomers of 4-hydroxyphenylethyl alcohol-deacetoxy elenolic acid dialdehyde (4-HPEA-DEDA) and 3,4-dihydroxyphenylethyl alcohol-deacetoxy elenolic acid dialdehyde (3,4-DHPEA-DEDA).     

Essential concepts in the optical properties of quantum dot molecules

Here we review the basic optical spectra of quantum dot molecules. We apply a simple and straightforward model to calculate charge stability regions in vertically coupled double dot molecules that are embedded in a Schottky diode. This model allows us to relate features in the optical spectrum to the diode structure. The underlying concepts allow one to design quantum dot molecules functionalized for optical operations.     

Nucleophilic displacements of non-racemic α-trifluoromethyl benzylic triflates

Effective protocols for the introduction of chiral α-trifluoromethyl benzyl moieties by nucleophilic displacement of enantiomerically enriched α-trifluoromethyl benzylic triflates are presented. The effects of substrate electronics, solvent polarity, temperature, and base are studied by measuring the diastereomeric or enantiomeric excesses of the displacement products formed by coupling a variety of α-trifluoromethyl benzylic triflates with a range of nucleophiles including amines, carboxylates, thiols, and malonates. Preliminary investigations to elucidate the mechanism(s) involved in the loss of stereochemical integrity at the benzylic center in the nucleophilic displacement reactions are also reported.     

Edge searching weighted graphs

In traditional edge searching one tries to clean all of the edges in a graph employing the least number of searchers. It is assumed that each edge of the graph initially has a weight equal to one. In this paper we modify the problem and introduce the Weighted Edge Searching Problem by considering graphs with arbitrary positive integer weights assigned to its edges. We give bounds on the weighted search number in terms of related graph parameters including pathwidth. We characterize the graphs for which two searchers are sufficient to clear all edges. We show that for every weighted graph the minimum number of searchers needed for a not-necessarily-monotonic weighted edge search strategy is enough for a monotonic weighted edge search strategy, where each edge is cleaned only once. This result proves the NP-completeness of the problem.