Further results on the euler and Genocchi numbers

Summary We characterize the ordinary generating functions of the Genocchi and median Genocchi numbers as unique solutions of some functional equations and give a direct algebraic proof of several continued fraction expansions for these functions. New relations between these numbers are also obtained.     

DFT investigation of the formation of linear aminols as the first step toward the induction of oxidatively generated interstrand cross-link DNA lesions

Apyrimidinic/apurinic sites feature among the most prevalent DNA lesions. If not repaired, it has been recently evidenced that they are prone to react in situ with vicinal nucleobases, evolving toward more complex and highly mutagenic interstrand cross-links. Information concerning the structure and the multi-step reactivity leading to such clustered defects is scarce due to their low formation yield. This study reports a DFT exploration of the condensation reaction between a ketoaldehyde (derived from an oxidized C4’ abasic site) and three nucleobases featuring an amino group. They are found to present a very similar intrinsic reactivity, indicating in turn that differences of reactivity arise more from the relative positioning of the two reactive fragments within a flexible B-DNA. We also probe the role of a vicinal water molecule for the formation of the aminol and the requirements to reach an adequate estimate of this strongly exothermic reaction, which drives the DNA damage process.     

Modular engineering of H-bonded supramolecular polymers for reversible functionalization of carbon nanotubes

A H-bond-driven, noncovalent, reversible solubilization/functionalization of multiwalled carbon nanotubes (MWCNTs) in apolar organic solvents (CHCl(3), CH(2)Cl(2), and toluene) has been accomplished through a dynamic combination of self-assembly and self-organization processes leading to the formation of supramolecular polymers, which enfold around the outer wall of the MWCNTs. To this end, a library of phenylacetylene molecular scaffolds with complementary recognition sites at their extremities has been synthesized. They exhibit triple parallel H-bonds between the NH-N-NH (DAD) functions of 2,6-di(acetylamino)pyridine and the CO-NH-CO (ADA) imidic groups of uracil derivatives. These residues are placed at 180° relative to each other (linear systems) or at 60°/120° (angular modules), in order to tune their ability of wrapping around MWCNTs. Molecular Dynamics (MD) simulations showed that the formation of the hybrid assembly MWCNT?[X?Y](n) (where X = 1a or 1b -DAD- and Y = 2, 3, or 4 -ADA-) is attributed to π-π and CH-π interactions between the graphitic walls of the carbon materials and the oligophenyleneethynylene polymer backbones along with its alkyl groups, respectively. Addition of polar or protic solvents, such as DMSO or MeOH, causes the disruption of the H-bonds with partial detachment of the polymer from the CNTs, followed by precipitation. Taking advantage of the chromophoric and luminescence properties of the molecular subunits, the solubilization/precipitation processes have been monitored by UV-vis absorption and luminescence spectroscopies. All hybrid MWCNTs-polymer materials have been also structurally characterized via thermogravimetric analysis (TGA), transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS).     

Unraveling gold(I)-specific action towards peptidic disulfide cleavage: a DFT investigation

Ground-state disulfide dissociation is a target of prime importance in structural biochemistry. A main difficulty consists in avoiding competition with carbon–sulfur and backbone scission pathways. In tandem mass spectrometry, such selectivity is afforded using transition elements or coinage-metal ions as catalyst. Yet, the underlying gas-phase mechanistic details remain poorly understood. Gold(I)-assisted disulfide cleavage is investigated by means of DFT calculations, to elucidate the highly selective and specific catalytic action of this transition-metal cation, a most promising one in tandem mass spectrometry. The preferential cleavage of sulfur–sulfur versus carbon–sulfur linkages on dimethyldisulfide, taken as a prototypical aliphatic compound, is rationalized on the basis of molecular orbital arguments. Secondly, it is revealed that the disulfide dissociation profile is dramatically impacted by a peptidic environment. Calculations on L,L-cystine derivatives show two main factors: the topological frustration for an embedded -CH(2)-S-S-CH(2)- motif induces a 5 kcal mol(-1) penalty, whereas electrophilic assistance via complexation of nitrogen and oxygen atoms lowers activation barriers by a factor of 3. S-S weakening is both thermodynamically and kinetically driven by the versatile coordination mode of gold(I). The influence of amine-terminus group protonation is finally sketched: it gives rise to an intermediate reactivity. This study sheds lights on the key action of the peptidic environment in tuning the dissociation profile in the presence of this transition-metal monocation.     

Mindlin??s Problem for a Halfspace Indented by a Flexible Plate

The paper deals with a contact problem for an isotropic elastic halfspace indented by a flexible circular plate and simultaneously subjected to a Mindlin-type axial force. The approach adopted is to solve the contact problem for the flexible circular plate and the elastic halfspace; this serves as the auxiliary solution to examine, via the Maxwell-Betti reciprocal theorem, the influence of the internal Mindlin force. The contact between the flexible plate and the elastic halfspace is solved using a variational approach. The net displacement of the flexible circular plate and the internal Mindlin force can be evaluated in analytical form. The result has applications to the in situ evaluation of the deformability characteristics of geologic media.     

Cleavage of the C---Se bond of cyclic selenoacetals derived from 4-t-butyl cyclohexanone with butyllithiums and tin and silyl hydrides

Selenoacetals derived from 1,3-propanediselenol and 1,2-ethanediselenol are much less prone to be cleaved by butyllithiums than their open chain analogues. The stereochemistry of the products resulting from these reactions as well as from the cleavage of the C---Se bond under radical conditions is disclosed.     

Diastereoselective addition of silyl- and stannyl metals to γ-alkoxy-alkylidene malonates

Stereochemical control of the addition of silyl- and stannyl metals to chiral γ-alkoxy-alkylidene malonates proved to be dependant on the nature of the counter ion and of the solvent but in an unpredictable way.     

Comments on “theory of oscillatory oxidation of carbon monoxide over platinum” by R.E. Lagos,B.S. Sales and H. Suhl

The position of the thermochemical surface oscillation (TCSO) model applied to the CO oxidation on supported Pt pellets is tentatively specified.     

Absolute residue cross sections for 46–50Ti + 13C reactions at 36, 46 and 56 MeV

Absolute cross sections for nuclei produced in the reactions ^46–50Ti + ¹³C at 36, 46 and 56 MeV (lab) were measured. Complete identification in mass and atomic number for the evaporation residues was obtained by means of in-beam γ-ray spectroscopy techniques. In the entire energy range, an overall satisfactory account of the observed product nuclei is given by the predictions of the fusion-evaporation model. Direct channels like inelastic scattering and n-transfer appear to be noticeable and contribute ~ 15 % to the total cross section.     

The decay of neutron deficient97Ag,98Ag,and99g,m Ag

The decays of neutron-deficient 21-sec⁹⁷Ag, 44.5-sec⁹⁸Ag, 15-sec^99mAg, and 124-sec^99gAg nuclides have been investigated with the LISOL facility. Sources were produced by the⁹²Mo(¹⁴N, ypxn) reactions on an enriched⁹²Mo target. Positron-, x-, and γ-ray singles spectra have been performed on mass separated samples. The results are consistent with 9/2⁺ ground state in⁹⁹Ag and a high (6⁺ or 7⁺) spin and parity for⁹⁸Ag.