Spectroscopic evidence for polarons in poly(3-methylthiophene)

We present the results of an in-situ spectroscopic study of poly(3-methylthiopene) electrochemically doped with BF₄^?. It is concluded that polarons are the primary elementary excitations in the dilute doping regime.     

Sur la composition de l'arôme de thé

A gas-chromatographic investigation of black tea aroma has revealed, besides 19 known components, the presence of 4 new substances: 1-penten-3-ol, trans-2-hexen-1-ol, α-terpineol and β-ionone. The fragmentation pattern of 1-penten-3-ol has been determined by means of high resolution mass spectrography.     

Automatisierte Jodbestimmung in R?ntgen-Kontrastern

Zusammenfassung Eine neue Dehalogenierungs-Methode mit 0,15% Natriumborhydrid in 1 N Natronlauge und Palladium als Katalysator (2 m mit Palladium beschichtetes Messing-Reaktionsrohr) ermöglicht die Ionisierung des organisch gebundenen Jods in 5 min bei 85° C. Anschließend wird die wäßrige Lösung mit Schwefelsäure angesäuert, das Jodid mit Nitrit zu Jod oxydiert und photometrisch bei 455 nm gemessen. Die Prozedur läuft in einem Technicon AutoAnalyzer.

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Automatic iodine determination in X-ray contrasters

A new dehalogenation method with 0.15% sodium tetrahydroborate in 1 N sodium hydroxide and palladium as a catalyst (2 m Pd coated brass reaction tube) makes possible the ionisation of the organic bound iodine in 5 min at 85° C. Subsequently the aqueous solution is made acidic with sulphuric acid, the iodide oxidized to iodine with the aid of nitrite and then measured photometrically at 455 nm. The procedure is carried out in a Technicon AutoAnalyzer.

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Wir danken Herrn Marcel Bonnafé für seine Mithilfe und die wertvollen Ratschläge bei der Aufstellung der Apparatur.     

Structural rationalization of a large difference in RNA affinity despite a small difference in chemistry between two 2'-O-modified nucleic acid analogues

Chemical modification of nucleic acids at the 2'-position of ribose has generated antisense oligonucleotides (AONs) with a range of desirable properties. Electron-withdrawing substituents such as 2'-O-[2-(methoxy)ethyl] (MOE) confer enhanced RNA affinity relative to that of DNA by conformationally preorganizing an AON for pairing with the RNA target and by improving backbone hydration. 2'-Substitution of the ribose has also been shown to increase nuclease resistance and cellular uptake via changes in lipophilicity. Interestingly, incorporation of either 2'-O-[2-(methylamino)-2-oxoethyl]- (NMA) or 2'-O-(N-methylcarbamate)-modified (NMC) residues into AONs has divergent effects on RNA affinity. Incorporation of 2'-O-NMA-T considerably improves RNA affinity while incorporation of 2'-O-NMC-T drastically reduces RNA affinity. Crystal structures at high resolution of A-form DNA duplexes containing either 2'-O-NMA-T or 2'-O-NMC-T shed light on the structural origins of the surprisingly large difference in stability given the relatively minor difference in chemistry between NMA and NMC. NMA substituents adopt an extended conformation and use either their carbonyl oxygen or amino nitrogen to trap water molecules between phosphate group and sugar. The conformational properties of NMA and the observed hydration patterns are reminiscent of those found in the structures of 2'-O-MOE-modified RNA. Conversely, the carbonyl oxygen of NMC and O2 of T are in close contact, providing evidence that an unfavorable electrostatic interaction and the absence of a stable water structure are the main reasons for the loss in thermodynamic stability as a result of incorporation of 2'-O-NMC-modified residues.     

Crystal structure of a B-form DNA duplex containing (L)-alpha-threofuranosyl (3'-->2') nucleosides: a four-carbon sugar is easily accommodated into the backbone of DNA

(L)-alpha-Threofuranosyl-(3'-->2')-oligonucleotides (TNA) containing vicinally connected phosphodiester linkages undergo informational base pairing in an antiparallel strand orientation and are capable of cross-pairing with RNA and DNA. TNA is derived from a sugar containing only four carbon atoms and is one of the simplest potentially natural nucleic acid alternatives investigated thus far in the context of a chemical etiology of nucleic acid structure. Compared to DNA and RNA that contain six covalent bonds per repeating nucleotide unit, TNA contains only five. We have determined the atomic-resolution crystal structure of the B-form DNA duplex [d(CGCGAA)Td(TCGCG)](2) containing a single (L)-alpha-threofuranosyl thymine (T) per strand. In the modified duplex base stacking interactions are practically unchanged relative to the reference DNA structure. The orientations of the backbone at the TNA incorporation sites are slightly altered in order to accommodate fewer atoms and covalent bonds. The conformation of the threose is C4'-exo with the 2'- and 3'-substituents assuming quasi-diaxial orientation.     

Towards Targeted Drug Delivery by Covalent Ligand-Modified Polymeric Nanocontainers

Here we present a novel strategy for specific cellular targeting of polymeric nanocontainers by using self-assembly of block copolymers consisting of either Polydimethoxysiloxane-b-Polymethyloxazoline-b-Polydimethoxysiloxane (PDMS-b-PMOXA-b-PDMS) or functionalized PDMS-b-PMOXA-b-PDMS. Covalent functionalization of the above copolymer was accomplished using either the fluorescent dye sulforhodamine B or a poly-guanosin ligand, the latter by using the Huisgen 1,3-dipolar cycloaddition. The success of the covalent modification of the block copolymer has been determined by studying functionalized sulforhodamine B by NMR and fluorescence correlation spectroscopy. The covalent click chemistry approach leads to efficiently functionalized polymeric nanocontainers which enables specific uptake by activated macrophages overexpressing the scavenger receptor A1.