An ab initio valence bond study on cyclopenta-fused naphthalenes and fluoranthenes

To probe the effect of external cyclopenta-fusion on a naphthalene core, ab initio valence bond (VB) calculations have been performed, using strictly atomic benzene p-orbitals and p-orbitals that are allowed to delocalize, on naphthalene (1), acenaphthylene (2), pyracylene (3), cyclopenta[b,c]acenaphthylene (4), fluoranthene (5), and cyclopenta[c,d]fluoranthene (6). For the related compounds 1-4 and 5,6 the total resonance energies (according to Pauling's definition) are similar. Partitioning of the total resonance energy in contributions from the possible 4n + 2 and 4n pi-electron conjugated circuits shows that only the 6pi-electron conjugated circuits (benzene-like) contribute to the resonance energy. The results show that cyclopenta-fusion does not extend the pi system in the ground state; the five-membered rings act as peri-substituents. As a consequence, the differences in (total) resonance energy do not coincide with the differences in thermodynamic stability. Notwithstanding, the relative energies of the Kekule structures can be estimated using Randic's conjugated circuits model.     

Spin polarization in the lowest triplet state of chlorophyll

Chlorophyll-b in glassy solution has a spin-polarized lowest triplet state at and above 77 K. The magnitude of the effect is different for MTHF and ethanol as solvents, in contrast to what is found for the porphin free base. Chlorophyll-a does not exhibit spin-polarization under identical conditions as for chlorophyll-b. Zero-field parameters are found to be:chlorophyll-a (MTHF) D = (281 ± 6) × 10^?4 cm^?1; E = (39 ± 3) × 10^?4 cm^?1;chlorophyll-b (MTHF) D = (289 ± 4) × 10^?4 cm^?1; E = (49 ± 3) × 10^?4 cm^?1,From ESR signal kinetics it follows that for chlorophyll-b, population and depopulation mainly involve the spin level y?, describing a spin moving in a plane perpendicular to the molecular plane:P_y ? P_x ? P_z; k_x = 240 ± 40 s^?1; k_y = 600 ± 120 s^?1; k_z ? 75 s^?1,where P_i and k_i denote populating and decay rates. Thus, the kinetic scheme for the chlorophyll triplet is different from that of porphyrins with heavier metal ions, but very similar to that of the porphin free base. The spin-lattice relaxation time is found to be anisotropic and shorter than the decay rates of individual spin levels. Nevertheless, spin polarization can be observed, essentially because the ESR signal amplitude depends on population differences.     

Polymorph formation studied by 3D nucleation simulations. Application to a yellow isoxazolone dye, paracetamol, and L-glutamic acid

Knowledge of the nucleation and growth behavior of polymorphs is vital in a variety of industrial applications. With the aid of the growth probability method the nucleus size is obtained as a function of the driving force for crystallization by simulating the growth probability of clusters of various sizes. From these values the cluster interfacial energy can be computed, allowing for the determination of the nucleation rate. The simulations show that nucleation of the metastable form of a yellow isoxazolone dye dominates at higher driving forces while below a certain driving force the stable form nucleates. Two other compounds show dominant nucleation of their stable form, even at extreme driving forces. This is in accordance with experimental findings for all these compounds. The growth probability method is therefore a promising indicator for polymorph nucleation behavior.     

Simultaneous Determination of 4‐Chlorophenol and Oxalic Acid Using an Expanded Graphite‐Epoxy Composite Electrode

An expanded graphite‐epoxy composite electrode (EG‐Epoxy) was employed for the simultaneous determination of 4‐chlorophenol (4‐CP) and oxalic acid (OA) by using cyclic voltammetry (CV), chronoamperometry (CA), and differential pulse voltammetry (DPV). The results indicated that OA could be determined in the presence of the same concentrations of 4‐CP within the concentration range of 0.1 mM to 0.5 mM with a relative standard deviation (RSD) smaller than 5%. Electrode fouling occurred during CA for 4‐CP concentrations larger than 0.5 mM. The DPV method was used for the simultaneous determination of 4‐CP and OA before and after electrochemical oxidation by chronopotentiometry under galvanostatic conditions (j=0.04 mA cm^?2, t=2 h) of a tap water sample spiked with 0.19 mM 4‐CP and 0.1 M Na₂SO₄.     

Addition of carbon to anatase TiO2 by n-hexane treatment—surface or bulk doping?

Anatase TiO₂ can be sensitized to visible light by adding carbon as a dopant. Towards this end, TiO₂ photoelectrodes were subjected to a thermal treatment in a hexane-rich environment. By comparing the optical and photoelectrochemical characteristics of both thin film and nanocrystalline nanoporous photoelectrodes, carbon is found to be located mainly at the surface of the TiO₂. The amount of carbon that diffuses into the bulk of the material is too small to significantly enhance the visible light response and only a small shift of the absorption edge towards higher wavelengths is observed. The presence of carbon in TiO₂ shifts the anatase-to-rutile transformation temperature beyond 800 °C, and X-ray diffraction shows that spray deposition of TiO₂ under a CO₂ atmosphere results in a higher bulk carbon concentration than a post-deposition thermal treatment in a hexane-rich environment.     

Western blot detection of brain material in heated meat products using myelin basic protein and neuron-specific enolase as biomarkers

An assay based on Western blotting and detection of central nervous system (CNS)-specific antigens was developed to detect brain tissue in processed (heated) meat products. Bands of antigen-bound primary antibodies were visualised through secondary anti-antibodies labelled with peroxidase, which generated chemiluminescence documented by a photographic film. Ponceau-S staining before antibody incubation and molecular mass information on detected antigens after immunoreactions added information supporting correct identification of brain tissue in the meat products. In this approach B50/growth-associated protein (B50), glial fibrillary acidic protein (GFAP), myelin basic protein (MBP), neurofilament (NF), neuron-specific enolase (NSE) and synaptophysin (Syn) proteins were detected in raw luncheon meat and a liver product enriched with brain tissue at a level of 5% (m/m). Only MBP and NSE were considered suitable biomarkers for detection of 1% (m/m) brain tissue in meat products pasteurised at 70 °C or sterilised at 115 °C. The use of an anti-monkey MBP instead of anti-human MBP enabled speciation of the CNS material whether from bovine and ovine brains or from porcine brain tissue. This immunoblot assay potentiates the analysis of approximately 70 samples within 8 h, including sample preparation and the simultaneous probing of NSE and MBP target antigens.     

On the rapid evaluation of cofactors in the calculation of nonorthogonal matrix elements

The calculation of matrix elements involving nonorthogonal orbitals is speeded up by recognizing the orthogonalities between orbitals, leading to generalized Slater rules. The block structure present in the overlap matrix makes an efficient evaluation of its cofactors possible. These cofactors are calculated per subblock, each with its own parity sign. An adjustment parity sign has to be evaluated, which is added to the combined local signs, to give the correct total sign for the matrix element. An algorithm for the evaluation of this adjustment sign has been developed, making an easy and correct evaluation possible. The current scheme is shown to be very efficient, but possibilities for further improvement remain. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 77–83, 1998     

Removal of dependencies from nearly complete basis sets. Calculations on the helium dimer

A method is devised for dealing with almost linearly dependent basis sets that contain large sets of bond functions. Using the largest of such basis sets, LARSAT, the second-order Møller-Plesset polarization dispersion energy of the helium dimer is calculated to be - 17.08 K at R = 5.6 bohrs. MR-SDCI calculations, employing a set of 37 reference configurations, were performed for the helium dimer with several basis sets at 4.0 and 5.6 bohrs. Size-extensivity corrections were included to take into account the R dependency of the size-extensivity error in MR-SDCI calculations. The He₂ interaction energies computed with basis LARSAT are - 10.92 K at 5.6 bohrs and 295.1 K at 4.0 bohrs. The 37-MR-SDCI calculations with basis LARSAT almost reproduce the He₂ full configuration interaction (CI) interaction energies computed with the same basis, at notably smaller cost. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 805–815, 1997     

Software news and updates

A parallel version of the valence bond program TURTLE has been developed. In this version the calculation of matrix elements is distributed over the processors. The implementation has been done using the message‐passing interface (MPI), and is, therefore, portable. The parallel version of the program is shown to be quite efficient with a speed‐up of 55 at 64 processors. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 665–672, 2001