(E/Z)‐Isomerization of 3′‐Epilutein

3′‐Epilutein (=(all‐E,3R,3′S,6′R)‐4′,5′‐didehydro‐5′,6′‐dihydro‐β,β‐carotene‐3,3′‐diol; 1 ), isolated from the flowers of Caltha palustris, was submitted to both thermal isomerization and I₂‐catalyzed photoisomerization. The structures of the main products (9Z)‐ 1 , (9′Z)‐ 1 , (13Z)‐ 1 , (13′Z)‐ 1 , (15Z)‐ 1 , and (9Z,9′Z)‐ 1 were determined based on UV/VIS, CD, ¹H‐NMR, and MS data.     

Effect of feed zone width on product purity in preparative-scale,continuous free-flow isoelectric focusing separation of enantiomers

The effects of the increased width of the sample feed stream upon the purity of the collected fractions were examined in the continuous free-flow isoelectric focusing separation of the enantiomers of dansyl-tryptophan. Compared to the reference separation obtained with a narrow feed stream introduced through the central sample feed port of the continuous free-flow isoelectric focusing separation unit, the final pH gradient, the position of the enantiomer band centroids and the values of the cumulative product recoveries and cumulative product purities remained essentially identical as the width of the feed band of the racemic sample dissolved in the carrier ampholyte was increased up to the full width of the separation chamber suggesting that the current, limiting practice of narrow, central feed bands can be safely abandoned and dilute feedstock solutions can be utilized in preparative-scale isoelectric focusing enantiomer separations.     

Subgroup 4 (Ti,Zr, Hf) derivatives of Cobalt Carbonyls

Bimetallic and trimetallic compounds containing unsupported bonds of subgroup 4 metals (M = Ti, Zr, Hf) and Co were prepared by hydride elimination (A) from RM derivatives (R¹ = PhCH₂; RN; R² = Me, Et)) and by salt elimination (B) from RMX (X = Cl, Br; R.¹ = PhCH₂, RN and R³O; R³= i-Pr, n-Bu)) by reaction with HCo(CO)₄ and Na[Co(CO)₄], respectively. Compounds RMCo(CO)₄ with R¹ = PhCH₂, RM[Co(CO)₄]₂ R.¹ = PhCH₂, were prepared both by methods A and B, while (R³O)₄-n Ti[Co(Co)₄]n (n = 1, 2) compounds were obtained by reaction B. Several tertiary phosphine and phosphite derivatives of the former two types were obtained by substitution of a carbonyl group by PR ligand or by A type reaction of HCo(CO)³(PR with RM compounds.     

The relationship between the structures of Cu(II) complexes and their chemical transformations

The structures of compounds M ₂ ^I M^II(SEO₄)₂ (M^I=K, Tl; M^II=Cu and Ni), were studied using IR, electronic and EPR spectra. The results indicate a hexacoordination of both central atoms, and a bridging function of selenato groups, the mode of their coordination varies with M^I and M^II. The compound Tl₂Cu(SeO₄)₂ was prepared also in the amorphous glassy form, although with partial decomposition. It is presumed that in the homogeneous smaragd-green material -Cu-O-Cu-, -Cu-OSeO₂-Cu- and -Cu-OSeO₃-Cu- bridges are present simultaneously. The course of the thermal decomposition of the studied compounds depends on the nature of the M^I and M^II cations. According to powder X-ray patterns, the decomposition products do not contain individual oxides. Nearly complete removal of selenium was observed in the decomposition of hydrated ammonium double selenates of Ni(II) and Cu(II).

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Zusammenfassung Mittels IR-, Elektronen- und EPR-Spektren wurden die Strukturen der Verbindungen M ₂ ^I M^II (SeO₄)₂ mit M^I=K und Tl sowie M^II=Cu and Ni bestimmt. Die Ergebnisse zeigen eine Hexakoordination beider Zentralatome und eine Brückenfunktion der Selenatgruppen, deren Koordination sich mit M^I und M^II ändert. Die Verbindung Tl₂Cu(SeO₄)₂ wurde, wenn auch unter geringen Zerfalles, auch in einer amorphen Glasform hergestellt. Es wird angenommen, daß in den Smaragdgrün-Stoffen gleichzeitig-Cu-O-Cu-, -Cu-OSeO₂-Cu- und -Cu-OSeO₃-Cu- Brücken vorkommen. Der Verlauf der thermischen Zersetzung der untersuchten Verbindungen hängt von der Art der M^I und M^II-Kationen ab. In Bezugnahme auf Röntgenpulverdiffraktionsaufnahmen enthalten die Zersetzungsprodukte keine getrennten Oxide. Beim Zerfall von hydratierten Ammoniumdoppelselenaten von Ni(II) und Cu(II) wurde eine fast vollständige Abgabe von Selen beobachtet.

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M ₂ ^I Mⁱⁱ(SeO₄)₂, ⁱ — , , ⁱⁱ , - , . , - ^{i ii}. Tl₂Cu(SeO₄)₂ , . , ----, --OSeO₂- -Cu-OSeO₃-u-. ^{i ii}. , . .

     

Maximization of separation efficiency in capillary electrophoretic chiral separations by means of mobility-matching background electrolytes

It has been predicted, both theoretically and by computer simulation, that in capillary electrophoresis the electromigration-dispersion-induced peak broadening can be eliminated by matching the mobilities of the analyte and the background electrolyte co-ion. Though mobility matching can be achieved by invoking multiple secondary chemical equilibria in the background electrolyte — such as protonation or complexation - to change the mobility of the co-ion, this approach is not feasible when the composition of the background electrolyte is dictated by the need to achieve a certain separation selectivity. In this paper, a background electrolyte preparation principle is outlined which decouples the dual roles of the background electrolyte, namely the buffering function and the mobility matching function, by ascribing the buffering function solely to the counter-ion (a conjugate acid or conjugate base) and the mobility matching function solely to the co-ion (a strong electrolyte). The power of this approach is demonstrated by solving difficult enantiomer separations.     

Flavonoids. 41. Stereospecific synthesis of 2,3-dihydro-c-3-substituted-t-3-methyl-r-2-phenyl-4H-1-benzopyran-4-ones

The synthesis of 2,3-dihydro-t-3-mesyloxy-c-3-methyl-r-2-phenyl-4H-1-benzopyran-4-one (1) is described. The reaction of mesylate 1 with various nucleophiles, first of all O- and N-nucleophiles, yields the corresponding 2,3-dihydro-c-3-substituted-t-3-methyl-r-2-phenyl-4H-1-benzopyran-4-ones 2b, 7b, 9, 10, 12, 14 and 18 . Azide 14 is a useful intermediate for the synthesis of flavonoids 15–17 .     

Photo-induced disproportionation of iodomalonic acid

The stoichiometry, equilibrium, and kinetics of the photo-induced disproportionation of iodomalonic acid to I^?, I₂, and tartronic acid have been studied by means of spectrophotometry and iodide selective electrode at 20.0 ± 0.2°C, pH 2.0–4.0. At pH > 2.9, only I^? and HOCH(COOH)₂ are detected as major products and the reaction reaches 100% conversion. At pH < 2.9, I₂ and malonic acid are also formed and the reaction stops at a conversion rate less than 100%. Both UV (band with a peak at 360 nm) and visible light (480 nm) have been found to be effective. Two primary photochemical processes are identified: While both reactions are sensitive to UV light, only (M2) can be affected by visible light. (M1) and (M2) are considered to initiate a chain reaction sequence in which I^· radicals oxidize iodomalonic acid. Dual effects of reaction products on the reaction rate have been observed: while iodine increases the efficiency of visible light and accelerates the reaction, malonic acid inhibits the photo-decomposition by mediating the recombination of I^· radicals to I₂. © 1995 John Wiley & Sons, Inc.     

Analog of heat equation for gaussian measure of a ball in Hilberrt space

If _a,T is a Gaussian measure on a Hilbert space with meana and covariance operatorT, andr is a fixed positive number, then the functiong(a,T)= _a,T {xr} satisfies the equation

Random field forward interest rate models,market price of risk and their statistics

In this paper we consider discrete time forward interest rate models. In our approach, unlike in the classical Heath–Jarrow–Morton framework, the forward rate curves are driven by a random field. Hence we get a general interest rate structure. Our aim is to give an overview of our results in such a model on the following questions: no-arbitrage conditions, maximum likelihood estimation of the volatility, as well as the joint estimation of the parameters and the asymptotic behaviour of the estimators, relationship with continuous models. Finally we give discussion on the practical problems of the estimation and we show several numerical results on the statistics of such models. This research has been supported by the Hungarian Scientific Research Fund under Grants No. OTKA–F046061/2004 and OTKA–T048544/2005.