Cu(I)-catalyzed oxidative cyclization of alkynyl oxiranes and oxetanes

In the presence of a Cu(I) catalyst and a pyridine oxide, alkynyl oxiranes and oxetanes can be converted into functionalized five- or six-membered α,β-unsaturated lactones or dihydrofuranaldehydes. This new oxidative cyclization is proposed to proceed via an unusual allenyloxypyridinium intermediate.     

Reverse engineering from spectrophotometric measurements: performances and efficiency of different optimization algorithms

A large number of parameters is often required to describe optical dispersion laws, and it is only through the use of an appropriate global optimization procedure that an accurate thin-film index determination can be achieved. In this paper, we propose to investigate the respective performances of three different optimization algorithms, namely Simulated Annealing, Genetic Algorithm and Clustering Global Optimization and compare results with a commercial software dedicated to thin-film index determination. This study is restricted to the single-layer thin-film index determination of transparent and absorbing materials. It includes the theoretical study of simulated reflection and transmission spectra, and the experimental characterization of Ta₂O₅ and Si layers.     

Surfactant (bi)layers on gold nanorods

Gold nanorods in aqueous solution are generally surrounded by surfactants or capping agents. This is crucial for anisotropic growth during synthesis and for their final stability in solution. When CTAB is used, a bilayer has been evidenced from analytical methods even though no direct morphological characterization of the precise thickness and compactness has been reported. The type of surfactant layer is also relevant to understand the marked difference in further self-assembling properties of gold nanorods as experienced using 16-EO(1)-16 gemini surfactant instead of CTAB. To obtain a direct measure of the thickness of the surfactant layer on gold nanorods synthesized by the seeded growth method, we coupled TEM, SAXS, and SANS experiments for the two different cases, CTAB and gemini 16-EO(1)-16. Despite the strong residual signal from micelles in excess, it can be concluded that the thickness is imposed by the chain length of the surfactant and corresponds to a bilayer with partial interdigitation.     

Lamellarins as Inhibitors of P‐Glycoprotein‐Mediated Multidrug Resistance in a Human Colon Cancer Cell Line

Chemical analysis of a Didemnum sp. (CMB‐01656) collected during scientific Scuba operations off Wasp Island, New South Wales, yielded five new lamellarins A1 ( 1 ), A2 ( 2 ), A3 ( 3 ), A4 ( 4 ) and A5 ( 5 ) and eight known lamellarins C ( 6 ), E ( 7 ), K ( 8 ), M ( 9 ), S ( 10 ), T ( 11 ), X ( 12 ) and χ ( 13 ). Analysis of a second Didemnum sp. (CMB‐02127) collected during scientific trawling operations along the Northern Rottnest Shelf, Western Australia, yielded the new lamellarin A6 ( 14 ) and two known lamellarins G ( 15 ) and Z ( 16 ). Structures were assigned to 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 on the basis of detailed spectroscopic analysis with comparison to literature data and authentic samples. Access to this unique library of natural lamellarins ( 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ) provided a rare opportunity for structure–activity relationship (SAR) investigations, probing interactions between lamellarins and the ABC transporter efflux pump P‐glycoprotein (P‐gp) with a view to reversing multidrug resistance in a human colon cancer cell line (SW620 Ad300). These SAR studies, which were expanded to include the permethylated lamellarin derivative ( 17 ) and a series of lamellarin‐inspired synthetic coumarins ( 19 , 20 , 21 , 22 , 23 , 24 ) and isoquinolines ( 25 , 26 ), successfully revealed 17 as a promising new non‐cytotoxic P‐gp inhibitor pharmacophore.     

Atmospheric fate of methacrolein. 1. Peroxy radical isomerization following addition of OH and O2

Peroxy radicals formed by addition of OH and O(2) to the olefinic carbon atoms in methacrolein react with NO to form methacrolein hydroxy nitrate and hydroxyacetone. We observe that the ratio of these two compounds, however, unexpectedly decreases as the lifetime of the peroxy radical increases. We propose that this results from an isomerization involving the 1,4-H-shift of the aldehydic hydrogen atom to the peroxy group. The inferred rate (0.5 ± 0.3 s(-1) at T = 296 K) is consistent with estimates obtained from the potential energy surface determined by high level quantum calculations. The product, a hydroxy hydroperoxy carbonyl radical, decomposes rapidly, producing hydroxyacetone and re-forming OH. Simulations using a global chemical transport model suggest that most of the methacrolein hydroxy peroxy radicals formed in the atmosphere undergo isomerization and decomposition.     

Atmospheric fate of methacrolein. 2. Formation of lactone and implications for organic aerosol production

We investigate the oxidation of methacryloylperoxy nitrate (MPAN) and methacrylicperoxy acid (MPAA) by the hydroxyl radical (OH) theoretically, using both density functional theory [B3LYP] and explicitly correlated coupled cluster theory [CCSD(T)-F12]. These two compounds are produced following the abstraction of a hydrogen atom from methacrolein (MACR) by the OH radical. We use a RRKM master equation analysis to estimate that the oxidation of MPAN leads to formation of hydroxymethyl-methyl-α-lactone (HMML) in high yield. HMML production follows a low potential energy path from both MPAN and MPAA following addition of OH (via elimination of the NO(3) and OH from MPAN and MPAA, respectively). We suggest that the subsequent heterogeneous phase chemistry of HMML may be the route to formation of 2-methylglyceric acid, a common component of organic aerosol produced in the oxidation of methacrolein. Oxidation of acrolein, a photo-oxidation product from 1,3-butadiene, is found to follow a similar route generating hydroxymethyl-α-lactone (HML).     

Near-infrared dual luminescence from an extended zinc porphyrin

The photophysical characterization of an extended zinc porphyrin is reported. Fusion of bis-tetraazaanthracene on the porphyrin ring causes an unusual dual luminescence ascribed to two non-equilibrated singlet excited states.     

Heuristics for the multi-depot petrol station replenishment problem with time windows

In the multi-depot petrol station replenishment problem with time windows (MPSRPTW), the delivery of petroleum products stored in a number of different petroleum depots to a set of petrol distribution stations has to be optimized. Each depot has its own fleet of heterogeneous and compartmented tank trucks. Stations specify their demand by indicating the minimum and maximum quantities to be delivered for each ordered product and require the delivery within a predetermined time window. Several inter-related decisions must be made simultaneously in order to solve the problem. For this problem, the set of feasible routes to deliver all the demands, the departure depot for each route, the quantities of each product to be delivered, the assignment of these routes to trucks, the time schedule for each trip, and the loading of the ordered products to different tanks of the trucks used need to be determined. In this paper, we propose a mathematical model that selects, among a set of feasible trips, the subset that allows the delivery of all the demands while maximizing the overall daily net revenue. If this model is provided with all possible feasible trips, it determines the optimal solution for the corresponding MPSRPTW. However, since the number of such trips is often huge, we developed a procedure to generate a restricted set of promising feasible trips. Using this restricted set, the model produces a good but not necessarily optimal solution. Thus the proposed solution process can be seen as a heuristic. We report the results of the extensive numerical tests carried out to assess the performance of the proposed heuristic. In addition, we show that, for the special case of only one depot, the proposed heuristic outperforms a previously published solution method.     

Photoinduced electron transfer in Os(terpyridine)-biphenylene-(bi)pyridinium assemblies

A series of linearly arranged donor-spacer-acceptor (D-S-A) systems 1-3, has been prepared and characterized. These dyads combine an Os(II)bis(terpyridine) unit as the photoactivable electron donor (D), a biphenylene (2) or phenylene-xylylene (3) fragment as the spacer (S), and a N-aryl-2,6-diphenylpyridinium electrophore (with aryl = 4-pyridyl or 4-pyridylium in 1 or 2/3, respectively) as the acceptor (A). Their absorption spectra, redox behavior, and luminescence properties (both at 77 K in rigid matrix and at 298 K in fluid solution) have been studied. The electronic structure and spectroscopic properties of a representative compound of the series (i.e., 2) have also been investigated at the theoretical level, performing Density Functional Theory (DFT)-based calculations. Time-dependent transient absorption spectra of 1-3 have also been recorded at room temperature. The results indicate that efficient photoinduced oxidative electron transfer takes place in the D-S-A systems at room temperature in fluid solution, for which rate constants (in the range 4 × 10(8)-2 × 10(10) s(-1)) depend on the driving force of the process and the spacer nature. In all the D-S-A systems, charge recombination is faster than photoinduced charge separation, in spite of the relatively large energy of the D(+)-S-A(-) charge-separated states (between 1.47 and 1.78 eV for the various species), which would suggest that the charge recombination occurs in the Marcus inverted region. Considerations based on superexchange mechanism suggest that the reason for the fast charge recombination is the presence of a virtual D-S(+)-A(-) state at low energy--because of the involvement of the easily oxidizable biphenylene spacer--which is beneficial for charge recombination via superexchange but unsuitable for photoinduced charge separation. To further support the above statement, we prepared a fourth D-S-A species, 4, analogous to 2 but with a (hardly oxidizable) single phenylene fragment serving as the spacer. For such a species, charge recombination (about 3 × 10(10) s(-1)) is slower than photoinduced charge separation (about 1 × 10(11) s(-1)), thereby confirming our suggestions.     

A generalised 17-state vibronic-coupling Hamiltonian model for ethylene

In a previous work [B. Lasorne, M. A. Robb, H.-D. Meyer, and F. Gatti, "The electronic excited states of ethylene with large-amplitude deformations: A dynamical symmetry group investigation," Chem. Phys. 377, 30-45 (2010); and ibid. 382, 132 (2011) (Erratum)], we investigated the electronic structure of ethylene (ethene, C(2)H(4)) in terms of 17 dominant configurations selected at the multiconfiguration self-consistent field level of theory. These were shown to be sufficient to recover most of the static electron correlation among the first valence and Rydberg states at all geometries. We also devised a strategy to build a 17-quasidiabatic-state matrix representation of the electronic Hamiltonian for curvilinear coordinates using dynamical symmetry. Here, we present fitted surfaces in the form of a generalised vibronic-coupling Hamiltonian model for two nuclear coordinates, CC bond stretching and torsion. Dynamic electron correlation is included into the electronic structure to improve the energetics of the Rydberg states at the multireference configuration interaction level of theory. The chemical interpretation of the adiabatic states of interest does not change qualitatively, which validates our choice of underlying quasidiabatic states in the model. The absorption spectrum is calculated with quantum dynamics and partially assigned. This first two-dimensional model shows a surprisingly good agreement with the experimental spectrum.