Structural Comparison of Oligoribonucleotides and Their 2′-Deoxy-2′-fluoro Analogs by heteronuclear NMR spectroscopy

1-(2′-Deoxy-2′-fluororibofuranosyl)pyrimidines were synthesized and incorporated into an RNA oligonucleotide to give 5′-r[C_fGC_f(U_fU_fC_fG)GC_fG]-3′ (C_f: short form of C = 2′-deoxy-2′-fluorocytidine; U_f: short form of U = 2′-deoxy-2′-fluorouridine). The oligomer was investigated by means of UV, CD, and NMR spectroscopy to address the question of how F-labels can substitute ¹³C-labels in the ribose ring. Through-space (NOE) and through-bond (scalar couplings) experiments were performed that make use of the ameliorated chemical-shift dispersion induced by ¹⁹F as an alternative heteronucleus. A comparison of the structures of fluorinated vs. unmodified oligomer is given. It turns out that the fluorinated oligonucleotide exists in a 14:3 equilibrium between a hairpin and a duplex conformation, in contrast to the unmodified oligonucleotide which predominantly adopts the hairpin conformation. Furthermore, the fluorinated hairpin structure adopts two distinct conformations that differ in the sugar conformation of the U and C nucleoside units, as detected by the ¹⁹F-NMR chemical shifts. The role of the 2′-OH group as stabilizing element in RNA secondary structure is discussed.     

Die Kristallstrukturen von Rh10Ga17 und Ir3Ga5

Zusammenfassung Die Kristallstrukturen von Rh₁₀Ga₁₇ und Ir₃Ga₅ werden bestimmt und mittels zweidimensionalerFourier-Synthesen verfeinert. Die beiden Verbindungen gehören zu einer Gruppe von TiSi₂-Abkömmlingen der allgemeinen Formel T _n B_2n-m (TB_2-x ). Die Gitterkonstanten betragen für Rh₁₀Ga₁₇ a=5,813;c=47,46 und für Ir₃Ga₅ a=5,823;c=14,20 Å.

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The crystal structures of Rh₁₀Ga₁₇ and Ir₃Ga₅ have been determined by means of two-dimensionalFourier syntheses. The crystal structure of the two compounds of the general formula T _n B_2n-m (TB_2-x ) can be derived from the TiSi₂-type. The lattice parameters were found to be: Rh₁₀Ga₁₇ a=5,813;c=47,46 and Ir₃Ga₅ a=5,823;c=14,20 Å.

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Mit 2 Abbildungen     

Die Verbindungen 2SiO2·P2O5 und 2GeO2·P2O5

Zusammenfassung Bei röntgenographischen Untersuchungen im System GeO₂-P₂O₅ wird eine Verbindung der Zusammensetzung 2 GeO₂·P₂O₅ aufgefunden. Einkristallaufnahmen ergeben eine hexagonale (trigonale) Elementarzelle mita=7,99₈ undc=24,8₆ Å. Die schon beschriebene Verbindung 2 SiO₂·P₂O₅ erweist sich als isotyp:a=7,86₂ undc=24,1₃ Å.     

I(+1) transfer from diiodomalonic acid to malonic acid and a complete inhibition of the CO and CO2 evolution in the Briggs-Rauscher reaction by resorcinol

A recent report on an intense CO 2 and CO evolution in the Briggs-Rauscher (BR) reaction revealed that iodination of malonic acid (MA) is not the only important organic reaction in the classical BR oscillator. To disclose the source of the gas evolution, iodomalonic (IMA) and diiodomalonic (I2MA) acids were prepared by iodinating MA with nascent iodine in a semibatch reactor. The nascent iodine was generated by an iodide inflow into the reactor, which contained a mixture of MA and acidic iodate. Some CO2 and a minor CO production was observed during these iodinations. It was found that in an aqueous acidic medium the produced I2MA is not stable but decomposes slowly to diiodoacetic acid and CO2. The first-order rate constant of the I 2MA decarboxylation at 20 degrees C was found to be k1 = 9 x 10(-5) s(-1), which is rather close to the rate constant of the analogous decarboxylation of dibromomalonic acid under similar conditions (7 x 10(-5)s(-1)). From the rate of the CO2 evolution, the I2MA concentration can be calculated in a MA-IMA-I2MA mixture as only I2MA decarboxylates spontaneously but MA and IMA are stable. Following CO2 evolution rates, it was proven that I2MA can react with MA in the reversible reaction I2MA + MA <--> 2 IMA. The equilibrium constant of this reaction was calculated as K = 380 together with the rate constants of the forward k 2 = 6.2 x 10 (-2) M (-1)s(-1) and backward k-2 = 1.6 x 10(-4) M(-1)s(-1) reactions. The probable mechanism of the reaction is I(+1) transfer from I2MA to MA. The presence of I(+1) in a I2MA solution is demonstrated by its reduction with ascorbic acid. To estimate the fraction of CO2 coming from the decarboxylation of I2MA in an oscillatory BR reaction, the oscillations were inhibited by resorcinol. Unexpectedly, all CO2 and CO evolution was interrupted for more than one hour after injecting a small amount of resorcinol (10(-5) M initial concentration in the reactor). Finally, some implications of the newly found I(+1) transfer reactions and the surprisingly effective inhibition by resorcinol regarding the mechanism of the oscillatory BR reaction are discussed. The latter is explained by the ability of resorcinol to scavenge free radicals including iodine atoms without producing iodide ions.     

Structure and properties of semicrystalline polymers via high-frequency acoustic and x-ray measurements. I. Ferroelectric P(VDF/TrFE) copolymer

Acoustic, opto-acoustic, and x-ray investigations have been performed in order to study the influence of irradiation, electrical poling, and mechanical orientation on the morphology of ferroelectric random copolymers of vinylidene fluoride and trifluorethylene {P[VDF/TrFE] (70/30)}. The influences of these different treatments on the molecular orientation distribution of the amorphous and crystalline phases are discussed, as well as their influences on the crystallinity of the material. The elastic stiffness and the related viscosity tensors of P[VDF/TrFE] (70/30), the elastic stiffness modulus of the amorphous matrix, and the hierarchy of stiffness constants of the crystalline state have been determined. © 1993 John Wiley & Sons, Inc.     

Polymer decoration: The orientation of polymer folds as revealed by the crystallization of polymer vapors

A new technique of decoration of the fold surface of polymer crystals is described. It is similar in methodology to gold decoration, but makes use of vapors of crystallizable polymers, principally polyethylene, as decorating material. Upon condensation and crystallization, the highly anisometric decorating molecules become oriented parallel to the fold direction. They build up small crystalline lamellae which, seen edge-on, appear as elongated rods and can be easily observed by conventional transmission electron microscopy. This decoration technique reveals the sectorization of polymer single crystals grown from solution. It can be used to determine the local fold orientation (with a resolution of ca. 10 nm) of polymers crystallized under a wide range of conditions, including crystallization from the bulk. The technique reveals that under all crystallization conditions so far investigated the outermost part of the polymer fold surface is relatively ordered, and the folds and/or loops are, as a rule, oriented nearly parallel to the macroscopic growth front.     

Efficiency scale for polymer nucleating agents

Nucleation of crystallizable polymers is quantified through an efficiency scale obtained and calculated using differential scanning calorimetry (DSC). This scale, defined in self-nucleation experiments, is a simple, convenient and reliable calorimetric efficiency scale. Typical nucleating agents for isotactic polypropylene are evaluated; they rate at best at 60 to=70% on this efficiency scale.

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Zusammenfassung Anhand einer unter Einsatz von DSC erhaltenen und berechneten Effizienzskale wurde eine Quantifizierung der Keimbildung bei kristallisierbaren Polymeren vorgenommen. Diese in selbstkeimbildenden Experimenten definierte Skale ist eine einfache, praktische und sinnvolle kalorimetrische Effizienzskale. Für isotaktisches Polypropylen wurden typische Keimbildungsagenzien entwickelt, deren Bestgeschwindigkeit auf dieser Effizienzskale bei 60 bis 70% liegt.

     

Zur Chemie der vicinalen Triketone, 4. Mitt.

o-Halogenated (o,o-dihalogenated) anilines react with phenalenetrione (PT) in boiling xylene or acetic acid to give 7H,8H-naphtho[1.8–bc]phenoxazin-7-one derivatives. The analogous reaction with 2.6-dimethyl-or 2.6-diethyl-aniline in xylene gives oxazepines, while in acetic acid preferential addition of the aniline with the para position to the NH₂-group to the central C=O-group ofPT occurs. It can be shown, that the first step in the ring closure reaction is the formation of semiaminales.Es wird gezeigt, daß Aniline, die in 2-bzw. 2,6-Stellung halogensubstituiert sind, mit Phenalentrion (PT) in Xylol oder Eisessig zu den entsprechenden 7H,8H-Naphtho[1,8–bc]-phenoxazin-7-on-derivaten reagieren. Die analoge Umsetzung mit 2,6-Dimethyl-bzw. 2,6-Diäthyl-anilin in Xylol führt zu Oxazepinen, während in Eisessig bevorzugt Addition des zur NH₂-Gruppe in p-Stellung befindlichen H-Atoms an die mittelständige C=O-Gruppe desPT stattfindet. Es wird experimentell bewiesen, daß diese Ringschlußreaktion über primär gebildete Halbaminale abläuft.

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Herrn Prof. Dr.O. Kratky, Graz, mit besten Wünschen zum 70. Geburtstag gewidmet.