Synthesis of (±) lupinifoun, di-o-methyl xanthohumol and isoxanthohumol and related compounds

Nuclear prenylation of naringenin (7) with 2-methylbut-3-en-2-ol in the presence of boron trifluoride etherate gives a mixture of 6-C-prenyl-(11), 8-C-prenyl-(15) and 6,8-di-C-prenyl-(8) derivatives. On formic acid cyclisation, 11 yielded two monodihydropyrans (12 and 13), but 15 afforded only one viz 16; similarly 8 formed the bisdihydropyran 10. Methylation of 8-C-prenyl naringenin (15) with Me₂SO₄ resulted in the formation of di-O-methyl derivatives of xanthohumol (22) and isoxanthohumol (23).

Cyclodehydrogenation of 6,8-di-C-prenyl-naringenin (8) with DDQ gave a mono-C-prenyl-2,2-dimethylpyran (1) corresponding to (±) lupinifolin. The angular isomer (2) was also formed. The structure of natural flemichin-B therefore needs further consideration. Similarly, cyclodehydrogenation of 6-C-(11)- and 8-C-prenyl-(15) naringenins afforded the corresponding linear (24) and angular (25) derivatives which have been characterized by conversion into known chalcones 26 and 27 by O-methylation.     

INDUCED DEACTIVATION OF NAPHTHALENE TRIPLETS BY CIS-PIPERYLENE

Abstract— Interaction of naphthalene triplets with trans -piperylene leads to triplet energy transfer with unit efficiency. When cis -piperylene is used as a quencher of naphthalene triplets, the efficiency of triplet energy transfer is found to be 0–76 ± 004. The rest of the quenching encounters in this case lead to deactivation of naphthalene triplets, without energy transfer.     

On a class of nonlinear integral equations of Urysohn's type

In this paper we study an interesting class of nonlinear integral equations of Urysohn's type, namely,

$\text{u(x) +}\text{∑}\text{j=l}\text{n}\text{∫}{}_{\mathrm{\Omega }}\text{k}{}_{\mathrm{j}}\text{(x,y)f}{}_{\mathrm{j}}\text{(y, u(y)) dy= v(x)}\text{(x ∈ Ω)}$

. It is shown that such an equation can be considered as a nonlinear operator equation of Hammerstein type in an appropriate Banach space. One can in this way extend the theory of nonlinear operator equations of Hammerstein type (except for the part which uses variational methods) to this class of equations.     

Generalized prolate spheroidal wave functions

The following equation $$(1 - x^2 )d^2 y/dx^2 + [(\beta - \alpha - (\alpha + \beta + 2)x]dy/dx + (\chi (c) - c^2 x^2 )y = 0$$ has been solved wherex(c) a separation constant is the characteristic value and is a function ofc. This solution is a generalization of spheroidal wave function into the series form ofP _n ^α;β (x),α andβ both separately are greater than ?1. The finite transform and its properties have been defined and a boundary value problem has been solved applying these tools.     

Electrophoresis simulations using Chebyshev pseudo-spectral method on a moving mesh

We present the implementation and demonstration of the Chebyshev pseudo-spectral method coupled with an adaptive mesh method for performing fast and highly accurate electrophoresis simulations. The Chebyshev pseudo-spectral method offers higher numerical accuracy than all other finite difference methods and is applicable for simulating all electrophoresis techniques in channels with open or closed boundaries. To improve the computational efficiency, we use a novel moving mesh scheme that clusters the grid points in the regions with poor numerical resolution. We demonstrate the application of the Chebyshev pseudo-spectral method on a moving mesh for simulating nonlinear electrophoretic processes through examples of isotachophoresis (ITP), isoelectric focusing (IEF), and electromigration-dispersion in capillary zone electrophoresis (CZE) at current densities as high as 1000 A/m. We also show the efficacy of our moving mesh method over existing methods that cluster the grid points in the regions with large concentration gradients. We have integrated the adaptive Chebyshev pseudo-spectral method in the open-source SPYCE simulator and verified its implementation with other electrophoresis simulators.     

Kinetik der Entladung von Zn2+ und Ni2+ an der Quecksilbertropfelektrode in einem Thiomalatmedium

Zusammenfassung Wir untersuchten auf polarographischem Wege die Kinetik der Entladung von Zn²⁺ und Ni²⁺ an der Quecksilbertropfelektrode in einem Thiomalatmedium konstanter Ionenstärke (=0,5). Wir stellten fest, daß die Reduktion von Zn²⁺ und Ni²⁺ irreversibel verläuft und berechneten daher die kinetischen Parameter (Übertragungskoeffizient , Geschwindigkeitskonstante der HinreaktionK _f,h ^o ) nach dem theoretischen Verfahren vonKoutecky in der vonMeites undIsrael erweiterten Form.

---

Kinetics of discharge of Zn²⁺ and Ni²⁺ at the D.M.E. in thiomalate media

Kinetics of discharge of Zn²⁺ and Ni²⁺ have been studied polarographically in thiomalate media of constant ionic strength (=0.5) at the dropping mercury electrode. The reduction of both Zn²⁺ and Ni²⁺ was found to be irreversible. Hence, the kinetic parameters (transfer coefficient , and forward rate constantK _j,h ^o ) have been calculated byKoutecky's theoretical treatment as extended byMeites andIsrael.

---

---

Mit 2 Abbildungen     

Investigation of electronic structure and associated nuclear quadrupole interaction of adsorbed fluorine atoms on silicon surface

The electronic energy levels and wave functions of fluorine and chlorine atoms adsorbed at the <111> surface of silicon are obtained by the Hartree-Fock procedure applied to clusters simulating the surface structure. Minimising the total energy with respect to the positions of the halogen atoms, the Si-Cl distance in the adsorbed system was found to be in good agreement with that from a recent SEXAFS measurement, there being no corresponding data presently available for fluorine on silicon surface. The calculated¹⁹ f ^* nuclear quadrupole coupling constants using the electronic wave functions for SiH₃F and the larger cluster Si₄H₉F, simulating the surface, differed substantially in contrast to the situation for the Si-F distance, indicating that the quadrupole coupling is a more sensitive indicator of the adequacy of the cluster chosen to represent the surface system. Experimental results for the coupling constants are awaited for comparison with theory.     

(+)-Trans-chrysanthemic acid from (+)-Δ3-carene

A new and more efficient route for the conversion of the readily available (+)-Δ³-carene into (+)-trans-chrysanthemic acid is described.     

o-Iodosobenzoate as an oxidimetric titrant

o-Iodosobenzoate has been used as a titrant at pH 7 with potassium iodide and starch as indicator, under Andrews' titration conditions with iodine monochloride as preoxidant, and in acid medium with potassium bromide and Methyl Red as indicator. Methods are described for the determination of tetrathionate (through disulphide cleavage by cysteine), hydrogen sulphite, thiosulphate, xanthates, cysteine and glutathione in certain combinations (involving masking of sulphite and thiols with acrylonitrile). Hexacyanoferrate(II) is determined in the presence of arsenic(III), antimony(III) and thallium(I). Sulphathiazole, sulphadiazine and sulphamerazine consume six equivalents of bromine per mole, but phthalation or diazotization of the aromatic amino group prevents disubstitution of bromine in the benzene ring. Chloramphenicol is determined by reduction of its aromatic nitro group to an amino group, followed by bromination. Rutin and vitamin C react with eight and two equivalents of bromine per mole respectively.