Halofluorination of norbornadiene. Evidence for endo and exo attack by electrophiles

Halofluorination of norbornadiene with N-bromosuccinimide, N-chlorosuccinimide or xenon difluoride in the presence of polyhydrogen fluoride-pyridine resulted in the formation of three products: 3-endo-halo-5-exo-fluoro (2) and 3-exo-halo-5-exo-fluoronortricyclane (3), and 2-exo-fiuoro-7-syn-halo-norbornene-5 (4). The exo-attack of the electrophile on norbornadiene is slightly predominant (65% X = Br, 64% X = Cl, 73% X = F) over the endo-attack. The Meerwein-Wagner rearrangement occurred only in the case of chlorine or fluorine halosubstituents of β-carbonium ions formed by exo attack of the electrophile.     

Poly(styrene sulfonic acid)–poly(vinylidene fluoride) interpolymer ion-exchange membranes. I. Preparation and characterization

Highly porous interpolymer ion-exchange membranes have been prepared from poly(styrene sulfonic acid), PSSA and poly(vinylidene fluoride) PVdF using a casting solvent of dimethylformamide and hexamethylphosphoramide. The membranes have been characterized by their water content, concentration potential, ionic conductivity, and their hydraulic permeability. An estimation of the porosity of the membranes has been made from the relative conductance of the potassium and the tetrabutylammonium ions in the film. This porosity has been compared with that derived from a consideration of the water flux through a Poiseuille-type pore.     

Production of cellulolytic and xylanolytic enzymes during growth of anaerobic fungi from ruminant and nonruminant herbivores on different substrates

Applied Biochemistry and Biotechnology - Three anaerobic fungi, twoNeocallimastix strains isolated from a ruminant (sheep) and onePiromyces strain isolated from a nonruminant (black rhinoceros),...     

The hexaazidosilicate(IV) ion: synthesis,properties, and molecular structure

The reaction of SiCl4 with an excess of (PPN)N3 (PPN+ = [(Ph3P)2N]+) affords selectively (PPN)2[Si(N3)6] (1). Simultaneous thermal analysis (TG-DTA) shows that the hexaazidosilicate salt is remarkably stable, melting at Tonex = 214 degrees C. Melting of 1 is followed by two distinct exothermic decomposition processes at Ton = 256 and 321 degrees C, the first one involving elimination of N2 and the second one degradation of the PPN cations and evolution of Si(N3)4, N2, and some HN3. The crystal structure of 1 consists of discrete PPN+ cations and S2 symmetric [Si(N3)6]2- anions, which have a very rare, octahedral SiN6 framework and the highest nitrogen content (90%) among the hexaazidometallates reported so far. The IR, Raman, 29Si, and 14N NMR spectra of 1 in CH3CN suggest in combination with the calculated spectra the presence of intact [Si(N3)6]2--anions of S6 symmetry in solution. Geometry optimizations with various methods and basis sets show an S6 symmetric structure to be the most stable [Si(N3)6]2- isomer, the calculated bonding parameters comparing well with the experimental values.     

Decomposition of oroidin in DMSO/TFA

Oxidative cyclization of the pyrrole-imidazole alkaloids oroidin and sventrin in DMSO/TFA (1:1) yields oxazolines via nucleophilic attack of the carbonyl oxygen at the alkenyl double bond. Oxidation takes place in the benzylic position of the imidazole ring. On prolonged reaction times, the oxazoline ring is hydrolyzed yielding the corresponding ester of pyrrole-2-carboxylic acid containing a free amino group. Overall, the double bond of oroidin is dioxygenated.     

Protein synthesis at atomic resolution: mechanistics of translation in the light of highly resolved structures for the ribosome

Our understanding of the process of translation has progressed rapidly since the availability of highly resolved structures for the ribosome. A wealth of information has emerged in terms of both RNA and protein structure and the interplay between them. This has prompted us to revisit the astonishing "treasure trove" of functional data regarding the ribosome that has accumulated over the past decades. Here we try a systematic synopsis of these ribosomal functions in light of the cryo-electron microscopic structures (resolution >7 A) and the atomic x-ray structures (>2.4 A) of the ribosome.     

Eine Methode zur präparativen Herstellung markierter Trinukleotide

Zusammenfassung Für ein neues Verfahren zur Untersuchung von Codon—Anticodon-Wechselwirkungen wurden radioaktive Trinukleotide mit möglichst hohen spezif. Aktivitäten im Milligrammaßstab benötigt. Zu ihrer Gewinnung wurde ausE. coli und Bäckerhefe, die in³²P-phosphathältigen Nährmedien gezüchtet worden waren, die Gesamt-RNA isoliert und enzymatisch hydrolysiert. Das dabei entstandene Oligonukleotidgemisch wurde durch Papierchromatographie und Elektrophorese aufgetrennt, wobei elf markierte Trinukleotide in reiner Form erhalten werden konnten.

---

For the study of codon-anticodon interactions radioactive trinucleotides with high specific activities had to be prepared in milligram quantities. Labelled RNA was obtained fromE. coli and baker's yeast grown in a medium containing³²P-phosphate. The RNA was hydrolyzed with enzymes and the resulting oligonucleotide mixture separated by paper chromatography and electrophoresis. Eleven pure, labelled trinucleotides were isolated by this procedure.

---

---

Mit 3 Abbildungen