Electrochemical and electron spin resonance studies of selected benzazolo[3,2-a]quinolinium salts

The electrochemical reduction of the chloride or perchlorate salts of benzazolo[3,2-a]quinolinium ion and several of its analogues is reported. The compounds studied are the perchlorate salt of 3-nitrobenzothiazolo-and 3-nitro-9-methoxybenzothiazolo[3,2-a]quinolinium, and the chloride salts of 7-ethyl-, 3-nitro-7-methyl-, 3-nitro-7-ethyl-, 3-nitro-7-isopropyl-, 3-nitro-7-butyl- and 3-nitro-7-benzylbenzimidazolo[3,2-a]-quinolinium, respectively. Cyclic voltammetry of the corresponding 3-nitrobenzothiazolo[3,2-a]quinolinium derivatives in N,N-dimethylformamide shows an irreversible peak potential at -0.6 and a quasi-reversible peak at -(1.2–1.3) volts, respectively, relative to the standard calomel electrode. In contrast, the corresponding 3-nitrobenzimidazolo[3,2-a]quinolinium derivatives show, in general, reversible peaks at near -0.8 and -(1.2–1.4) volts, respectively. Upon electrolytic reduction, only the nitro-substituted derivatives produced observable electron paramagnetic resonance electron spin resonance spectra. This observation is explained in terms of the stabilization of the radicals produced by the nitro group. Theoretical MM+/AM1/UHF calculations support the idea that the larger nitrogen splitting is caused by N-12 and the minor splittings by N-7 in the benzimidazolo[3,2-a]quinolinium ion series.     

Darboux transformations for Lamé potentials

Irreducible second order Darboux (SUSY) transformations are applied to Lam periodic Hamiltonians in order to find physically acceptable partner potentials with the same band structure. The main differences with the usual SUSY approach of potentials allowing for a discrete spectrum are pointed out. Presented at the 9th Colloquium “Quantum Groups and Integrable Systems”, Prague, 22–24 June 2000. This work has been partially supported by CONACyT (project 32086-E) Mxico, DGES (PB98-0370) from MEC (Spain), Junta de Castilla y Len (CO2/199), and Universidad de Valladolid.     

Optimization of quantized diffractive elements with symmetry constraints

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.     

Closed‐form formulas for Kirchhoff index

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     

Supercritical Fluid Extraction of Phenolic Compounds from Mango (Mangifera indica L.) Seed Kernels and Their Application as an Antioxidant in an Edible Oil

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.     

Bifurcation of Constant Mean Curvature Tori in Euclidean Spheres

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.     

Regioselective Synthesis of trans-1 Fullerene Bis-Adducts Directed by a Crown Ether Tether: Alkali Metal Cation Modulated Redox Properties of Fullerene–Crown Ether Conjugates

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.     

The triclinic polymorph of di­bromo[(–)‐sparteine‐κ2N,N′]­zinc(II)

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.