Aromaticity of the Bergman, Myers-Saito, Schmittel, and directly related cyclizations of enediynes

Aromaticity criteria (magnetic susceptibility exaltations, nucleus independent chemical shifts (NICS), and aromatic stabilization energy (ASE) evaluations) for enediyne and enyne-allene cyclizations evaluated at (UBS)-BLYP/6-31G* all agree that the degrees of cyclic electron delocalization of the benzenoid systems formed by the Bergman (3) and Myers-Saito reactions (5) are comparable to benzene. The reaction enthalpy differences between the parent cyclizations and their benzannelated analogues are not entirely due to disparities in gained ASE during the reactions. The alternative formation of fulvene biradicals is not accompanied by favorable aromatic effects.     

Micro-bore titanium housed polymer monoliths for reversed-phase liquid chromatography of small molecules

A new method for the fixation of polymethacrylate monoliths within titanium tubing of up to 0.8 mm I.D. for use as a chromatographic column under elevated temperatures and pressures is described. The preparation of butyl methacrylate–ethylene dimethacrylate-based monolithic stationary phases with desired porous structures was achieved within titanium tubing with pre-oxidised internal walls. The oxidised titanium surface was subsequently silanised with 3-trimethoxysilylpropyl methacrylate resulting in tight bonding of butyl methacrylate porous monolith to the internal walls, providing stationary phase stability at column temperatures up to 110 °C and at operating column pressure drops of >28 MPa. The titanium housed monoliths exhibited a uniform and dense porous structure, which provided peak efficiencies of up to 59,000 theoretical plates per meter when evaluated for the separation of small molecules in reversed-phase mode, under optimal conditions (achieved at 15 μL/min and temperature of 110 °C for naphthalene with a retention factor, k = 0.58). The developed column was applied to the reversed-phase isocratic separation of a text mixture of pesticides.     

3′‐Deoxyribopyranose (4′→2′)‐Oligonucleotide Duplexes (=p‐DNA Duplexes) as Substitutes of RNA Hairpin Structures

By automated synthesis, we prepared hybrid oligonucleotides consisting of covalently linked RNA and p‐DNA sequences (p‐DNA=3′‐deoxyribopyranose (4′→2′)‐oligonucleotides) (see Table 1). The pairing properties of corresponding hybrid duplexes, formed from fully complementary single strands were investigated. An uninterrupted π‐π‐stacking at the p‐DNA/RNA interface and cooperative pairing between the two systems was achieved by connecting them via a 4′‐p‐DNA‐2′→5′‐RNA‐3′ and 5′‐RNA‐2′→4′‐p‐DNA‐2′ phosphodiester linkage, respectively (see Fig. 4). The RNA 2′‐phosphoramidites 9 – 12 , required for the formation of the RNA‐2′→4′‐p‐DNA phosphodiester linkage were synthesized from the corresponding, 3′‐O‐tom‐protected ribonucleosides (tom=[(triisopropylsilyl)oxy]methyl; Scheme 1). Analogues of the flavin mononucleotide (=FMN) binding aptamer 22 and the hammerhead ribozyme 25 were prepared. Each of these analogues consisted of two p‐DNA/RNA hybrid single strands with complementary p‐DNA sequences, designed to substitute stem/loop and stem motifs within the parent compounds. By comparative binding and cleavage studies, it was found that mixing of the two complementary p‐DNA/RNA hybrid sequences resulted in the formation of the fully functional analogues 23 ⋅ 24 and 27 ⋅ 28 of the FMN‐binding aptamer and of the hammerhead ribozyme, respectively.     

Fast and Reliable Automated Synthesis of RNA and Partially 2′-O- Protected Precursors (`Caged RNA') Based on Two Novel,Orthogonal 2′-O-Protecting Groups,Preliminary Communication

Two sets of RNA phosphoramidites, carrying the (fluoride-labile) 2′-O-[(triisopropylsilyl)oxy]methyl (=tom) group and the (photolabile) [(R)-1-(2-nitrophenyl)ethoxy]methyl (=(R)-npeom) group, were prepared (see 1 – 4 and 5 – 8 , resp.). The two protecting groups were completely orthogonal to each other. Three ribozyme-substrate constructs, protected each by a (R)-npeom group, were synthesized; on photolysis, efficient cleavage of this remaining protecting group occurred (Scheme 3). It could be demonstrated that the presence of one (R)-npeom group within a RNA strand has only a minor influence on the pairing properties of corresponding duplexes.     

Electronic structures of N- and C-doped NiO from first-principles calculations

The large intrinsic band gap of NiO has hindered severely its potential application under visible-light irradiation. In this Letter, we have performed first-principles calculations on the electronic properties of N- and C-doped NiO to ascertain if its band gap may be narrowed theoretically. It was found that impurity bands driven by N 2p or C 2p states appear in the band gap of NiO and that some of these locate at the conduction band minimum, which leads to a significant band gap narrowing. Our results show that N-doped NiO may serve as a potential photocatalyst relative to C-doped NiO, due to the presence of some recombination centres in C-doped NiO.     

A note on Cesàro-Orlicz sequence spaces

The condition δ₂ in Cesàro-Orlicz sequence spaces equipped with the Luxemburg norm is discussed. The comparison theorem for these spaces is presented. Some counterexamples are provided.     

Cauchy, Ferrers-Jackson and Chebyshev polynomials and identities for the powers of elements of some conjugate recurrence sequences

In this paper some decompositions of Cauchy polynomials, Ferrers-Jackson polynomials and polynomials of the form x ²ⁿ + y ²ⁿ , n ∈ ℕ, are studied. These decompositions are used to generate the identities for powers of Fibonacci and Lucas numbers as well as for powers of the so called conjugate recurrence sequences. Also, some new identities for Chebyshev polynomials of the first kind are presented here.