Oligonucleotides Functionalized by Fluorescein and Rhodamine Dyes: Michael Addition of Methyl Acrylate to 2′‐Deoxypseudouridine

The 2′‐deoxypseudouridine ( 5 ) was functionalized at N(1) with methyl acrylate by Michael addition. The resulting methyl 2′‐deoxypseudouridine‐1‐propanoate ( 6 ) was converted to the phosphoramidite 8 and to the amino‐functionalized derivative 9 , which was transformed into the fluorescein‐labeled phosphoramidites 14 and 16 . Fluorescent oligonucleotides were synthesized either from these building blocks or by post‐synthetic modification of oligomers containing 2′‐deoxypseudouridine subunits. The stability of oligonucleotide duplexes was determined from the melting profiles, measured by UV‐ or VIS‐light absorbance, as well as from the fluorescence emission spectra. While small spacer residues did not affect the thermal stability of the 2′‐deoxypseudouridine‐containing duplexes, large dye residues led to destabilization.     

Dichlorocarbene Addition to

In contrast to the terminal phosphinidene complex PhPW(CO)(5) (2), which adds to [5]metacyclophane (1) in a 1,4-fashion, dichlorocarbene preferentially adds in a 1,2-fashion to the formal "anti-Bredt" type double bond of the aromatic ring of 1 to afford the norcaradiene 11b, which immediately rearranges to the bridged cycloheptatriene 12b and further by a [1,5] sigmatropic chlorine migration to the isomeric 13b as the first observable product. More slowly, the latter isomerizes via a dissociative mechanism to give 15b. A computational study supports the notion that the [1,5] chlorine migration in the rearrangement 12b --> 13b, for which an activation barrier of 70.2 kJ mol(-)(1) was calculated, is essentially concerted with minor charge separation. In contrast, the analogous [1,5] chlorine migration in the flat model compound 7,7-dichlorocycloheptatriene (12a) displays features of a dissociative pathway.     

An enantiomerically pure 1,5,7-trimethyl-3-azabicyclo[3.3.1]nonan- 2-one as 1H NMR shift reagent for the ee determination of chiral lactams, quinolones, and oxazolidinones

The chiral lactam 1 (or its enantiomer ent-1) was shown to be an effective (1)H NMR shift reagent for the ee determination of chiral lactams, quinolones, and oxazolidinones. It was successfully employed in many cases in which a detection of enantiomers by chromatographic methods failed. The method was extended to a broader range of simple substrates bearing a lactam moiety to evaluate its scope. The NH signals of the substrate enantiomers showed the strongest separation and were used for (1)H NMR integration. In most cases, compound 1 (1.5 equiv; 0.06 M solution) induced a baseline separation of the NH signals and it can consequently be regarded as a generally applicable shift reagent for chiral products with a lactam moiety.     

113Cd Solid‐State NMR for Probing the Coordination Sphere in Metal–Organic Frameworks

Spectroscopic techniques are a powerful tool for structure determination, especially if single‐crystal material is unavailable. ¹¹³Cd solid‐state NMR is easy to measure and is a highly sensitive probe because the coordination number, the nature of coordinating groups, and the geometry around the metal ion is reflected by the isotropic chemical shift and the chemical‐shift anisotropy. Here, a detailed investigation of a series of 27 cadmium coordination polymers by ¹¹³Cd solid‐state NMR is reported. The results obtained demonstrate that ¹¹³Cd NMR is a very sensitive tool to characterize the cadmium environment, also in non‐single‐crystal materials. Furthermore, this method allows the observation of guest‐induced phase transitions supporting understanding of the structural flexibility of coordination frameworks.     

Comparison of the mass spectra of 6-thiotheophyllines and 6-sulfinytheophyllines

Under electron impact, 6-thiotheophyllines eliminate various fragments from the pyrimidine moiety. In a retro Diels-Alder reaction, they lose the fragment X?C?NCH₃ from positions 1 and 2 of the pyrimidine ring. In 6-sulfinyltheophyllines, the sulfinyl group is the main target for fragmentation; it can lose either oxygen or sulfur, and the abundance of [M—16]⁺ and [M—32]⁺ is much higher than the abundance of the molecular ion. Elimination of the sulfur atom of the 6-sulfinyl substituent, with retention of its oxygen, may be explained by intermediate formation of a ring. All further fragmentations of the 6-sulfinyl derivatives proceed by a primary loss of oxygen or sulfur, followed by elimination of fragments from the pyrimidine moiety, similar to the primary processes, observed in the mass spectra of the 6-thiotheophyllines.     

Investigation of non-isothermal laminar elongation processes in viscoelastic liquids

Laminar elongational flows occurring in the presence of heat transfer processes are analysed. A Jeffrey model with temperature dependent parameters is included in the mathematical model of the coupled process and applied to the elongation of a cylindrical jet and a plane layer. The system of partial differential equations is solved by reducing it to a system of ordinary differential equations. The efficiency of the model is tested by comparison with experimental investigations of the elongation of HPDE melts.     

Electronic shell structure in Cs-O clusters

Unusually high ionization energies have been observed for Cs-O clusters having certain sizes and composition, namely for Cs_2n+zO_n with z=8, 18, 34, 58 and 92. The anomalies are well-defined for clusters containing from 1 to 7 oxygen atoms. The indicated values of z are identical to the number of electrons in closed shells of angular momentum.     

Synthesis and reactions of 18β-glycyrrhetaldehyde

18β-Glycyrrhetaldehyde has been prepared by two methods and its synthetic potential has been studied. In spite of some steric hindrance, it reacts on the whole quite normally. The aldehyde has been used for the preparation of derivatives with side-chains at C-20 which resemble those in the corticoid hormones.