Preparation and Fungitoxicity of Some Trichloro-, Tribromo-, Tetrachloro-, and Tetrabromo-8-Quinolinols

 3,5,6-, 3,5,7-, 4,5,7-, and 5,6,7-trichloro- and -tribromo-8-quinolinols as well as 3,5,6,7-tetrachloro- and -tetrabromo-8-quinolinols were prepared and tested against six fungi (Aspergillus niger, Aspergillus oryzae, Myrothecium verrucaria, Trichoderma viride, Mucor cirinelloides, and Trichophyton mentagrophytes) in Sabouraud dextrose broth. The compounds strongly inhibit five fungi but not M. cirinelloides. They are less active than the related dichloro-8-quinolinols which is attributed to steric hindrance.     

Ethylene Polymerization‐Induced Self‐Assembly (PISA) of Poly(ethylene oxide)‐block‐polyethylene Copolymers via RAFT

Poly(ethylene oxide) (PEO) with dithiocarbamate chain ends (PEO–SC(=S)?N(CH₃)Ph and PEO–SC(=S)?NPh₂, named PEO‐1 and PEO‐2 , respectively) were used as macromolecular chain‐transfer agents (macro‐CTAs) to mediate the reversible addition–fragmentation chain transfer (RAFT) polymerization of ethylene in dimethyl carbonate (DMC) under relatively mild conditions (80 °C, 80 bar). While only a slow consumption of PEO‐1 was observed, the rapid consumption of PEO‐2 led to a clean chain extension and the formation of a polyethylene (PE) segment. Upon polymerization, the resulting block copolymers PEO‐b‐PE self‐assembled into nanometric objects according to a polymerization‐induced self‐assembly (PISA).     

Ultrafast energy migration in platinum(II) diimine complexes bearing pyrenylacetylide chromophores

The ultrafast excited-state dynamics of three structurally related platinum(II) complexes has been investigated using femtosecond transient absorption spectrometry in 2-methyltetrahydrofuran (MTHF). Previous work has shown that Pt(dbbpy)(C[triple bond]C-Ph)2 (dbbpy is 4,4'-di(tert-butyl)-2,2'-bipyridine and C[triple bond]C-Ph is ethynylbenzene) has a lowest metal-to-ligand charge transfer (3MLCT) excited state, while the multichromophoric Pt(dbbpy)(C[triple bond]C-pyrene)2 (CC-pyrene is 1-ethynylpyrene) contains the MLCT state, but possesses a lowest intraligand (3IL) excited state localized on one of the CC-pyrenyl units (Pomestchenko, I. E.; Luman, C. R.; Hissler, M.; Ziessel, R.; Castellano, F. N. Inorg. Chem. 2003, 42, 1394-96). trans-Pt(PBu3)2(C[triple bond]C-pyrene)2 serves as a model system that provides a good representation of the CC-pyrene-localized 3IL state in a Pt(II) complex lacking the MLCT excited state. Following 400 nm excitation, the formation of the 3MLCT excited state in Pt(dbbpy)(C[triple bond]C-Ph)2 is complete within 200 +/- 40 fs, and intersystem crossing to the 3IL excited state in trans-Pt(PBu3)2(C[triple bond]C-pyrene)2 occurs with a time constant of 5.4 +/- 0.2 ps. Selective excitation into the low-energy MLCT bands in Pt(dbbpy)(C[triple bond]C-pyrene)2 (lambda(ex) = 480 nm) leads to the formation of the 3IL excited state in 240 +/- 40 fs, suggesting ultrafast wire-like energy migration in this molecule. The kinetic data suggest that the presence of the MLCT states in Pt(dbbpy)(C[triple bond]C-pyrene)2 markedly accelerates the formation of the triplet state of the pendant pyrenylacetylide ligand. In essence, the triplet sensitization process is kinetically faster than pure intersystem crossing in trans-Pt(PBu3)2(CC-pyrene)2 as well as vibrational relaxation in the MLCT excited state of Pt(dbbpy)(C[triple bond]C-Ph)2. These results are potentially important for the design of chromophores intended to reach their lowest excited state on subpicosecond time scales and advocate the likelihood of wire-like behavior in triplet-triplet energy transfer.     

Improvement of Drosophila acetylcholinesterase stability by elimination of a free cysteine

Background

Acetylcholinesterase is irreversibly inhibited by organophosphate and carbamate insecticides allowing its use for residue detection with biosensors. Drosophila acetylcholinesterase is the most sensitive enzyme known and has been improved by in vitro mutagenesis. However, it is not sufficiently stable for extensive utilization. It is a homodimer in which both subunits contain 8 cysteine residues. Six are involved in conserved intramolecular disulfide bridges and one is involved in an interchain disulfide bridge. The 8^th cysteine is not conserved and is present at position 290 as a free thiol pointing toward the center of the protein.

Results

The free cysteine has been mutated to valine and the resulting protein has been assayed for stability using various denaturing agents: temperature, urea, acetonitrile, freezing, proteases and spontaneous-denaturation at room temperature. It was found that the C290V mutation rendered the protein 1.1 to 2.7 fold more stable depending on the denaturing agent.

Conclusion

It seems that stabilization resulting from the cysteine to valine mutation originates from a decrease of thiol-disulfide interchanges and from an increase in the hydrophobicity of the buried side chain.     

Cyclodextrins-Kaempferol Inclusion Complexes: Spectroscopic and Reactivity Studies

The slightly water-soluble flavonoid kaempferol (KAE) and its inclusion complexes with β-cyclodextrin (βCD), hydroxypropyl-β-cyclodextrin (HPβCD) or heptakis-2,6-O-dimethyl-β-cyclodextrin (DMβCD) were investigated. The stoichiometric ratios and association constants describing the extent of the formation of the complexes have been determined. Binding constants, estimated from fluorescence studies at different temperatures, were analyzed so as to gain information about the mechanisms involved in the association processes. The thermodynamic data for the inclusion of KAE in DMβCD and HPβCD indicated that it is mainly enthalpy-driven whereas for βCD it is an entropy-driven process. Complex formation was monitored by two-dimensional ROESY experiments through the detection of intramolecular dipolar interaction. ROESY experiments provided data indicating that the B-ring of kaempferol is immersed in the apolar cavity with the A- and C-ring protruding from the wider rim for the three cyclodextrins studied. The antioxidant studies of KAE and CDs complexes showed an increment in its antioxidant activity. The complexes behave as better antioxidants than kaempferol alone.     

Intertwined Analytical,Experimental and Theoretical Studies on the Formation and Structure of a Copper Dienolate

The reaction of a silyl dienolate, a Cu(II) salt and TBAT yielding the corresponding copper dienolate is addressed. A combined NMR and cyclic voltammetry analysis first highlight the role of TBAT in the Cu(II) to Cu(I) reduction and the structure of the precatalytic species. From these first results a second set of NMR and theoretical studies enable the determination of the structure and the mechanism of formation of the copper dienolate catalytic species. Finally, we showed that that the copper catalyst promote the E/Z s-cis/s-trans equilibration of the silyl dienolate precursor through a copper dienolate intermediate. All of these results unveil some peculiarities of the catalytic and asymmetric vinylogous Mukaiyama reaction.     

A turbulent boundary layer over a two-dimensional rough wall

Particle image velocimetry (PIV) measurements and planar laser induced fluorescence (PLIF) visualizations have been made in a turbulent boundary layer over a rough wall. The wall roughness consisted of square bars placed transversely to the flow at a pitch to height ratio of λ/k = 11 for the PLIF experiments and λ/k = 8 and 16 for the PIV measurements. The ratio between the boundary layer thickness and the roughness height k/δ was about 20 for the PLIF and 38 for the PIV. Both the PLIF and PIV data showed that the near-wall region of the flow was populated by unstable quasi-coherent structures which could be associated to shear layers originating at the trailing edge of the roughness elements. The streamwise mean velocity profile presented a downward shift which varied marginally between the two cases of λ/k, in agreement with previous measurements and DNS results. The data indicated that the Reynolds stresses normalized by the wall units are higher for the case λ/k = 16 than those for λ/k = 8 in the outer region of the flow, suggesting that the roughness density effects could be felt well beyond the near-wall region of the flow. As expected the roughness disturbed dramatically the sublayer which in turn altered the turbulence production mechanism. The turbulence production is maximum at a distance of about 0.5k above the roughness elements. When normalized by the wall units, the turbulence production is found to be smaller than that of a smooth wall. It is argued that the production of turbulence is correlated with the form drag.     

Conserved Forms derived from Symmetries

For first order scalar ordinary differential equations, a well–known result of Sophus Lie states that a Lie point symmetry can be used to construct an integrating factor and conversely. However, there exist higher order equations without Lie point symmetries that admit integrating factors or that are exact. We present a method based on λ-symmetries to calculate integrating factors. An example of a second order equation without Lie point symmetries illustrates how the method works in practice and how the computations that appear in other methods may be simplified. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Non-crossing matchings of points with geometric objects

Given an ordered set of points and an ordered set of geometric objects in the plane, we are interested in finding a non-crossing matching between point–object pairs. In this paper, we address the algorithmic problem of determining whether a non-crossing matching exists between a given point–object pair. We show that when the objects we match the points to are finite point sets, the problem is NP-complete in general, and polynomial when the objects are on a line or when their size is at most 2. When the objects are line segments, we show that the problem is NP-complete in general, and polynomial when the segments form a convex polygon or are all on a line. Finally, for objects that are straight lines, we show that the problem of finding a min-max non-crossing matching is NP-complete.