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991.
We employ the simulated annealing algorithm to optimize totally quantized Fourier diffractive elements, whose phase modulation is constrained by a symmetry similar to that of the desired diffraction pattern. Elements optimized under this restriction, show better performance than the conventionally optimized ones, for which the object phase function is randomly modified. In addition, the elements constrained by spatial symmetry are optimized with relatively low computational efforts. 相似文献
992.
Jos Luis Palacios 《International journal of quantum chemistry》2001,81(2):135-140
We find closed‐form expressions for the resistance, or Kirchhoff index, of certain connected graphs using Foster's theorems, random walks, and the superposition principle. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 135–140, 2001 相似文献
993.
994.
995.
We use equivariant bifurcation theory to show the existence of infinite sequences of isometric embeddings of tori with constant mean curvature (CMC) in Euclidean spheres that are not isometrically congruent to the CMC Clifford tori, and accumulating at some CMC Clifford torus. 相似文献
996.
Jean-Pascal Bourgeois Luis Echegoyen Monia Fibbioli Ern Pretsch Franois Diederich 《Angewandte Chemie (International ed. in English)》1998,37(15):2118-2121
Regioselective Bingel macrocyclization of C60 with a bis-malonate containing a novel dibenzo[18] crown-6 tether provides a versatile access to trans-1 fullerene bis-adducts such as (±)- 1 . Complexation of a potassium ion by (±)- 1 has a pronounced effect on the redox properties of the carbon sphere as a result of the close proximity of the fullerene surface to the crown ether bound cation, which is enforced by the double bridging. 相似文献
997.
Luis Miguel Buelvas-Puello Gabriela Franco-Arnedo Hugo A. Martínez-Correa Diego Ballesteros-Vivas Andrea del Pilar Snchez-Camargo Diego Miranda-Lasprilla Carlos-Eduardo Narvez-Cuenca Fabin Parada-Alfonso 《Molecules (Basel, Switzerland)》2021,26(24)
Phenolic compounds from mango (M. indica) seed kernels (MSK) var. Sugar were obtained using supercritical CO2 and EtOH as an extraction solvent. For this purpose, a central composite design was carried out to evaluate the effect of extraction pressure (11–21 MPa), temperature (40–60 °C), and co-solvent contribution (5–15% w/w EtOH) on (i) extraction yield, (ii) oxidative stability (OS) of sunflower edible oil (SEO) with added extract using the Rancimat method, (iii) total phenolics content, (iv) total flavonoids content, and (v) DPPH radical assay. The most influential variable of the supercritical fluid extraction (SFE) process was the concentration of the co-solvent. The best OS of SEO was reached with the extract obtained at 21.0 MPa, 60 °C and 15% EtOH. Under these conditions, the extract increased the OS of SEO by up to 6.1 ± 0.2 h (OS of SEO without antioxidant, Control, was 3.5 h). The composition of the extract influenced the oxidative stability of the sunflower edible oil. By SFE it was possible to obtain extracts from mango seed kernels (MSK) var. Sugar that transfer OS to the SEO. These promissory extracts could be applied to foods and other products. 相似文献
998.
Jos Luis Alcntara‐Flores Sylvain Berns Yasmi Reyes‐Ortega Rafael Zamorano‐Ulloa 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(3):m79-m81
The title compound, [ZnBr2(C15H26N2)], when synthesized starting from Zn0, is obtained in two polymorphic forms, one belonging to space group P212121 and one to P1. The present contribution deals with the triclinic phase, which is isostructural with the orthorhombic form but presents a larger metal–metal intermolecular separation; the Zn⃛Zn distance is 7.4715 (6) Å for the triclinic polymorph as opposed to 6.534 Å for the orthorhombic polymorph. 相似文献
999.
Jeanne Crassous Jos Rivera Nicolette S. Fender Lianhe Shu Luis Echegoyen Carlo Thilgen Andreas Herrmann Franois Diederich 《Angewandte Chemie (International ed. in English)》1999,38(11):1613-1617
The pure enantiomers of D 2 -C 84 as well as a third constitutional isomer of this higher fullerene were produced by a retro-Bingel reaction on the first organic derivatives of C84 (see scheme). These derivatives were synthesized by Bingel cyclopropenation of C84, separated, and unambiguously structurally characterized. 相似文献
1000.
Jean-Pascal Bourgeois Paul Seiler Monia Fibbioli Ern Pretsch Franois Diederich Luis Echegoyen 《Helvetica chimica acta》1999,82(10):1572-1595
The fullerene-crown ether conjugates (±)- 1 to (±)- 3 with trans-1 ((±)- 1 ), trans-2 ((±)- 2 ), and trans-3 ((±)- 3 ) addition patterns on the C-sphere were prepared by Bingel macrocyclization. The trans-1 derivative (±)- 1 was obtained in 30% yield, together with a small amount of (±)- 2 by cyclization of the dibenzo[18]crown-6(DB18C6)-tethered bis-malonate 4 with C60 (Scheme 1). When the crown-ether tether was further rigidified by K+-ion complexation, the yield and selectivity were greatly enhanced, and (±)- 1 was obtained as the only regioisomer in 50% yield. The macrocyclization, starting from a mixture of tethered bis-malonates with anti ( 4 ) and syn ( 10 ) bisfunctionalized DB18C6 moieties, afforded the trans-1 ((±)- 1 , 15%), trans-2 ((±)- 2 , 1.5%), and trans-3 ((±)- 3 , 20%) isomers (Scheme 2). Variable-temperature 1H-NMR (VT-NMR) studies showed that the DB18C6 moiety in C2-symmetrical (±)- 1 cannot rotate around the two arms fixing it to the C-sphere, even at 393 K. The planar chirality of (±)- 1 was confirmed in 1H-NMR experiments using the potassium salts of (S)-1,1′-binaphthalene-2,2′-diyl phosphate ((+)-(S)- 19 ) or (+)-(1S)-camphor-10-sulfonic acid ((+)- 20 ) as chiral shift reagents (Fig. 1). The DB18C6 tether in (±)- 1 is a true covalent template: it is readily removed by hydrolysis or transesterification, which opens up new perspectives for molecular scaffolding using trans-1 fullerene derivatives. Characterization of the products 11 (Scheme 3) and 18 (Scheme 4) obtained by tether removal unambiguously confirmed the trans-1 addition pattern and the out-out geometry of (±)- 1 . VT-NMR Studies established that (±)- 2 is a C2-symmetrical out-out trans-2 and (±)- 3 a C1-symmetrical in-out trans-3 isomer. Upon changing from (±)- 1 to (±)- 3 , the distance between the DB18C6 moiety and the fullerene surface increases and, correspondingly, rotation of the ionophore becomes increasingly facile. The ionophoric properties of (±)- 1 were investigated with an ion-selective electrode membrane (Fig. 2 and Table 2), and K+ was found to form the most stable complex among the alkali-metal ions. The complex between (±)- 1 and KPF6 was characterized by X-ray crystal-structure analysis (Figs. 3 and 4), which confirmed the close tangential orientation of the ionophore atop the fullerene surface. Addition of KPF6 to a solution of (±)- 1 resulted in a large anodic shift (90 mV) of the first fullerene-centered reduction process, which is attributed to the electrostatic effect of the K+ ion bound in close proximity to the C-sphere (Fig. 5). Smaller anodic shifts were measured for the KPF6 complexes of (±)- 2 (50 mV) and (±)- 3 (40 mV), in which the distance between ionophore and fullerene surface is increased (Table 3). The effects of different alkali- and alkaline-earth-metal ion salts on the redox properties of (±)- 1 were investigated (Table 4). These are the first-ever observed effects of cation complexation on the redox properties of the C-sphere in fullerene-crown ether conjugates. 相似文献