Reversible photomagnetic properties of the molecular compound [{Cu(bipy)2}2{Mo(CN)8}]·9H2O·CH3OH

The optical and photomagnetic properties of [{Cu^II(bipy)₂}₂{Mo^IV(CN)₈}]·9H₂O·CH₃OH (1) have been reinvestigated. A comparison between spectra in solution and in the solid state revealed the presence of an intervalence band (or Metal–Metal Charge Transfer, hereafter noted MMCT) at 570 nm. The photomagnetic properties have been performed in a Superconducting QUantum Interference Device at 10 K with irradiation in the range of the MMCT: 488 nm, 520 nm and 647 nm at 10 K. An important increase of the magnetic signal has been measured after 1 h of irradiation at 488 nm, whereas a weaker increase has been obtained for the irradiation at 520 nm in the same conditions. Moreover, after an excitation at 488 nm, an irradiation at 647 nm has induced a decrease of the magnetic moment, which corresponds to a partial deexcitation. The complete characterization of the photoproduct has been realised after an irradiation of 4 h at 488 nm. The photomagnetic properties have shown an increase of the paramagnetism of 1 at low temperature. After a thermal heating at 300 K, the material goes back to its initial state before irradiation. It is the first time that a fully reversible photomagnetic behaviour for the compound [{Cu^II(bipy)₂}₂{Mo^IV(CN)₈}]·9H₂O·CH₃OH has been described. The observed properties have been discussed in terms of an electron transfer mechanism Mo → Cu.     

A regiodivergent synthesis of ring a C-prenylflavones

Capitalizing on the use of orthogonal protecting groups and the development of a modified Robinson flavone synthesis that avoids harsh acidic conditions, a regioselective synthesis of 6- and 8-prenylflavones from the same prenylated disilylated phloracetophenone (9) has been developed, targeting cannflavin B (1d), the COX-inhibiting principle of marijuana, and its unnatural isomer isocannflavin B (1e) as model compounds.     

Dynamic near three-to-one internal resonance in composite stiffened panels

Nonlinear dynamic of composite stiffened panels to parametric and three-to-one internal resonances is investigated. The ordinary differential equation of two mode shapes is established by using Galerkin method and the condition of three-to-one internal resonance between the first mode (1,3) and the second mode (3,1) is examined near the principal resonance 2:1 of the first mode. Then, the nonlinear behavior of the two buckling mode shapes is analyzed using a perturbation analysis. We show the existence of jump phenomena for the two modes indicating a complex dynamic of the structure near the three-to-one internal resonance for the HM Graphite/epoxy materials.     

Novel pyrazoline and pyrazole porphyrin derivatives: synthesis and photophysical properties

2-Vinyl-5,10,15,20-tetraphenylporphyrinatozinc(II) reacts with nitrile imines, generated in situ from ethyl hydrazono-α-bromoglyoxylates, affording the corresponding pyrazolines in good to excellent yields. Treatment of pyrazoline derivatives with DDQ affords the corresponding pyrazole derivatives with moderate to excellent yields. When the hydrolysis of ester group in the pyrazoline derivatives was considered, it was observed the concomitant oxidation of the heterocyclic unit, which allowed directly obtaining porphyrin-pyrazole derivatives with a carboxylic group, in very good yields.The photophysical properties of the pyrazoline and pyrazole porphyrin derivatives show that the influence of the heterocyclic substituents is limited by the tendency of these molecules to aggregate. All other properties and especially the triplet kinetics remain unaffected. The adducts with low tendency to aggregate showed very high singlet oxygen yield, which makes these compounds interesting for their use as photosensitizers for PDT.     

A DFT calculation of electronic structures,magnetic, and thermoelectric properties of the new equiatomic quaternary Heusler alloy RuTiCrSi

The stabilities, mechanical, electronic, and magnetic properties of the new equiatomic quaternary Heusler alloy (EQHA) RuTiCrSi were investigated using the Kohn-Sham DFT (KS-DFT) calculations within the generalized gradient approach (GGA), the modified version of the exchange potential introduced by Becke and Johnson in addition to the GGA (mBJ-GGA), and Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional. The ground-state equilibrium energy reveals that the ferromagnetic with type 2 structure is the more stable. The RuTiCrSi is energetically, mechanically, and dynamically stable. The calculated self-consistent total magnetic moment is 2 μB and agrees well with the Slater-Pauling rule of $M_{\mathrm{t}}=\left|Z_{\mathrm{t}}-24\right|$. The electronic structure results from mBJ-GGA and HSE06 functionals show a half-metallic behavior. A high Curie temperature is obtained using the mean-field approximation. The thermoelectric response was calculated using the semi-classical Boltzmann transport equation under constant relaxation time. The maximum value of Seebeck coefficient is observed at the ambient temperature of $741\mathrm{\mu V}{\mathrm{K}}^{-1}$. It was also observed that the power factor increases significantly as temperature rises. Therefore, the new EQHA RuTiCrSi seems to be a potential candidate for spintronic thermoelectric applications.     

Behavioral and Antennal Responses of Tribolium confusum to Varronia globosa Essential Oil and Its Main Constituents: Perspective for Their Use as Repellent

Essential oils of aromatic plants represent an alternative to classical pest control with synthetic chemicals. They are especially promising for the alternative control of stored product pest insects. Here, we tested behavioral and electrophysiological responses of the stored product pest Tribolium confusum, to the essential oil of a Brazilian indigenous plant, Varronia globosa, collected in the Caatinga ecosystem. We analyzed the essential oil by GC-MS, tested the effects of the entire oil and its major components on the behavior of individual beetles in a four-way olfactometer, and investigated responses to these stimuli in electroantennogram recordings (EAG). We could identify 25 constituents in the essential oil of V. globosa, with anethole, caryophyllene and spathulenole as main components. The oil and its main component anethole had repellent effects already at low doses, whereas caryophyllene had only a repellent effect at a high dose. In addition, the essential oil abolished the attractive effect of the T. confusum aggregation pheromone. EAG recordings revealed dose-dependent responses to the individual components and increasing responses to the blend and even more to the entire oil. Our study reveals the potential of anethole and the essential oil of V. globosa in the management of stored product pests.     

Efficiency of succinylated-olive stone biosorbent on the removal of cadmium ions from aqueous solutions

Chemical functionalization of olive stone wastes with succinate linkers can potentially improve the performance of wastewater treatment technologies via enhanced adsorption and high affinity of the covalently attached succinate groups for heavy metals. In this study, a novel reusable adsorbent material based on agricultural waste has been synthesized by esterifying the lignocellulosic matrix of olive stones with succinic anhydride in toluene under basic conditions. Characterization of the as-prepared material by FTIR and solid-state MAS ¹³C NMR spectroscopies and TGA confirmed that the heterogeneous esterification has proceeded very efficiently to yield the succinylated-olive stone (S–OS). Subsequent alkaline treatment of S–OS with saturated NaHCO₃ aqueous solution led to the resulting sodic material (NaS–OS), which was subjected to batch experiments in order to evaluate its cadmium-removing efficiency from aqueous solutions at realistic concentrations of cadmium found in industrial effluents. The results obtained from the sorption characteristics have revealed that NaS–OS material is highly effective in removing cadmium from aqueous solutions, with a maximum uptake capacity of 200 mg g⁻¹ (1.78 mmol g⁻¹). The Langmuir isotherm model was found to fit adequately the equilibrium isotherm data. Cadmium adsorption occurs rapidly and the adsorption mechanism is a chemical sorption via ionic exchange between the adsorbate and adsorbent. Thermodynamic parameters were also evaluated from the effect of temperature studies. Regenerability of NaS–OS material was ascertained by quantitative desorption of cadmium with 1 M aqueous NaCl and the reusability of the matrix after five repeated cycles led to nearly no attenuation in its performance (less than 2% in the sorption capacity), indicating that repeated use of NaS–OS is quite feasible. Compared to other low-cost adsorbents utilized for the removal of Cd(II) from water/wastewater, NaS–OS shows higher sorption capacity. These results have important implications for the design of low-cost adsorbents based on agricultural wastes.     

Orientation and mechanical properties of PBT and its blends with a liquid-crystalline copolyester

Blends of poly (butylene terephthalate) (PBT) and a liquid-crystalline copolyester (60 mol % poly(p-hydroxy benzoic acid)/40 mol % polyethylene terephthalate) (LCP) were prepared in the melt state. The investigation of mechanical properties indicated that, for the processing conditions used, neither the addition of up to 30 wt % LCP to PBT nor the cooling history affected significantly the tensile modulus E. For oriented specimens, a marked improvement of E was obtained for all the blends, and increased with the LCP content. This improvement was more marked for slowly cooled samples. X-ray diffraction was used to quantify the orientation of the crystalline PBT and liquid-crystalline LCP phases. It was shown that neither the thermal history nor the presence of up to 30 wt % LCP affected the orientation behavior of the PBT crystalline phase. For the LCP phase, measurements were not possible for concentrations lower than 10 wt %, and were more difficult and less precise than for PBT. Nevertheless, it was possible to show that a better orientation was obtained for the slowly cooled samples and for higher concentrations of LCP in the blends. This correlated with the enhancement of mechanical properties observed for the oriented samples.     

Quantum Screening Operators and Canonical q-de Rham Cocycles

In this paper a close connection is established between certain cohomology spaces of representations of the quantum affine algebra , and a twisted $q$-de Rham (Jackson–Aomoto) cohomology of configuration spaces using the quantum screening operators. Received: 24 December 1997 / Accepted: 2 April 1998