The <Emphasis Type="Italic">p</Emphasis>-Adic order of the <Emphasis Type="Italic">k</Emphasis>-Fibonacci and <Emphasis Type="Italic">k</Emphasis>-Lucas numbers

Let (F _k,n ) _n and (L _k,n )n be the k-Fibonacci and k-Lucas sequence, respectively, which satisfies the same recursive relation a _n+1 = ka _n + a _n?1 with initial values F _k,0 = 0, F _k,1 = 1, L _k,0 = 2 and L _k,1 = k. In this paper, we characterize the p-adic orders ν _p (F _k,n ) and ν _p (L _k,n ) for all primes p and all positive integers k.     

Determining the properties of pulsed laser deposited thin films by controlling the kinetic energy of the film-forming particles

The deposition of Al₂O₃ thin films by pulsed KrF excimer laser radiation (248 nm) on fused silica substrates is investigated as a function of the processing variables: laser fluence, processing gas pressure and target-to-substrate distance. The kinetic energy of the Al species in the laser-generated plasma, as measured by time-of-flight optical emission spectroscopy and time-of-flight quadrupole mass spectrometry, is described as a function of the type and pressure of the processing gas, the distance from target, and the laser fluence. The influence of the kinetic energy of the film-forming particles on the density and the refractive index of the resulting films, determined by ellipsometry, is investigated. The densification of the Al₂O₃ thin films to 94% of the bulk value is achieved by film-forming Al particles impinging on the growing surface with mean kinetic energies of about 25 eV.     

Expanding the Scope of 2′‐SCF3 Modified RNA

The 2′‐trifluoromethylthio (2′‐SCF₃) modification endows ribonucleic acids with exceptional properties and has attracted considerable interest as a reporter group for NMR spectroscopic applications. However, only modified pyrimidine nucleosides have been generated so far. Here, the syntheses of 2′‐SCF₃ adenosine and guanosine phosphoramidites of which the latter was obtained in highly efficient manner by an unconventional Boc‐protecting group strategy, are reported. RNA solid‐phase synthesis provided site‐specifically 2′‐SCF₃‐modified oligoribonucleotides that were investigated intensively. Their excellent behavior in ¹⁹F NMR spectroscopic probing of RNA ligand binding was exemplified for a noncovalent small molecule–RNA interaction. Moreover, comparably to the 2′‐SCF₃ pyrimidine nucleosides, the purine counterparts were also found to cause a significant thermodynamic destabilization when located in double helical regions. This property was considered beneficial for siRNA design under the aspect to minimize off‐target effects and their performance in silencing of the BASP1 gene was demonstrated.     

A Mini‐Twister Variant and Impact of Residues/Cations on the Phosphodiester Cleavage of this Ribozyme Class

Nucleolytic ribozymes catalyze site‐specific cleavage of their phosphodiester backbones. A minimal version of the twister ribozyme is reported that lacks the phylogenetically conserved stem P1 while retaining wild‐type activity. Atomic mutagenesis revealed that nitrogen atoms N1 and N3 of the adenine‐6 at the cleavage site are indispensable for cleavage. By NMR spectroscopy, a pK_a value of 5.1 was determined for a ¹³C2‐labeled adenine at this position in the twister ribozyme, which is significantly shifted compared to the pK_a of the same adenine in the substrate alone. This finding pinpoints at a potential role for adenine‐6 in the catalytic mechanism besides the previously identified invariant guanine‐48 and a Mg²⁺ ion, both of which are directly coordinated to the non‐bridging oxygen atoms of the scissile phosphate; for the latter, additional evidence stems from the observation that Mn²⁺ or Cd²⁺ accelerated cleavage of phosphorothioate substrates. The relevance of this metal ion binding site is further emphasized by a new 2.6 Å X‐ray structure of a 2′‐OCH₃‐U5 modified twister ribozyme.