Synthesis and triplex forming properties of pyrrolidino pseudoisocytidine containing oligodeoxynucleotides

Pyrrolidino pseudo-C-nucleosides are isosteres of natural deoxynucleosides which are protonated at the pyrrolidino ring nitrogen under physiological conditions. As constituents of a triplex forming oligodeoxynucleotide (TFO), the positive charge is expected to stabilise DNA triple helices via electrostatic interactions with the phosphodiester backbone of the target DNA. We describe the synthesis of the pyrrolidino isocytidine pseudonucleoside and the corresponding phosphoramidite building block and its incorporation into TFOs. Such TFOs show substantially increased DNA affinity compared to unmodified oligodeoxynucleotides. The increase in affinity is shown to be due to the positive charge at the pyrrolidino subunit.     

Constructing Hierarchical Set Systems

In this note, it is shown that by applying ranking procedures to data that allow, for any three objects a₁, a₂, b in a collection X of objects of interest, to make consistent decisions about which of the two objects a₁ or a₂ is more similar to b, a family of cluster systems can be constructed that start with the associated Apresjan Hierarchy and keep growing until, for k = #X–1, the full set of all subsets of X is reached. Various ideas regarding canonical modifications of the similarity values so that these cluster systems contain as many clusters as possible for small values of k (and in particular for k := 0) and/or are rooted at a specific element in X, possible applications, e.g. concerning (i) the comparison of distinct dissimilarity data defined on the same set X or (ii) diversity optimization, and new tasks arising in ranking statistics are also discussed.Received November 15, 2003     

S-Adapted Oligopoly Equilibria and Approximations in Stochastic Variational Inequalities

This paper deals with a class of dynamic games that are used for modelling oligopolistic competition in discrete time with random disturbances that can be described as an event tree with exogenously given probabilities. The concepts of S-adapted information structure and S-adapted equilibrium are reviewed and a characterization of the equilibrium as the solution of a variational inequality (VI) is proposed. Conditions for existence and uniqueness of the equilibrium are provided. In order to deal with the large dimension of the VI an approximation method is proposed which is based on the use of random sampling of scenarios in the event tree. A proof of convergence is provided and these results are illustrated numerically on two dynamic oligopoly models.     

A Theoretical Investigation of Enantioselectivity: Michael Reaction of Secondary Enamines with Enones

A theoretical study of the enantioselective Michael-type addition of chiral secondary enamines to enones has been achieved. In a first step, the structures of various free enamines have been investigated at the ab initio and MNDO levels. The results clearly show that upon substitution of the prototype vinylamine, the N-center is pyramidalized. The study of enamines with chiral N-substituents such as (S)-Ph(Me)CH or (S)-cyclohexyl(Me)CH reveals a very complex pattern, where up to 8 local energy minimums are characterized whose examination shows that no prediction can be. done regarding the final enantioselectivity of their reaction with enones. These sets of conformers can be regarded as nearly energetically degenerate, at least for the three or four ones of lowest energy. The study of the compact complexes formed between the latter optimal conformers and acrylaldehyde shows that: (i)syn complexation with respect to the N lone pair is the only one which remains possible for steric reason, (ii) small geometrical rearrangements take place as the complexation proceeds, (iii) no clear-cut correspondence exists between the relative sequence of the low-energy conformers of the free enamines and the sequence of the low-energy complexes, (iv) the examination of the relative gradients of the complexation energies provides an index for predicting the relative facilities of the enantiometric pathways, in good agreement with the experimental facts. Our study emphasizes the great complexity of systems of realistic size and brings about critical conclusions regarding classical ad hoc models.     

ESR-spektroskopische Untersuchung des Photoabbaues von Poly(vinyl-2-pyridin) und des Copolymeren Vinyl-2-pyridin/Methylmethacrylat

Ohne Zusammenfassung     

N-H..S hydrogen bonds

Infrared spectra of some compounds containing weak and medium-strong NH..S hydrogen bonds have been investigated. Spectroscopic and structural data have been correlated and compared with those obtained for NH..O and NH..N systems. At the same strength, the N..S distance is 0.51 and 0.36 Å longer than the corresponding N..O and N..N distances, respectively.     

Example of diffusion in a disordered Lorentz gas

We prove a diffusion law for a disordered Lorentz gas obtained by modification of a model of Gates, Gerst, Kac in Ref. 1, even though the motion is not a Markovian one in the technical sense of the word.     

Polarisation remanente dans les varietes de basse temperature de (NH4) 3AlF6 ET (NH4) 3FeF6

Dielectric and thermocurrent measurements have been carried out on (NH₄) ₃AlF₆ and (NH₄) ₃FeF₆ ceramic samples. A maximum of permittivity is observed close to the transition temperature (T_{T(NH4) 3AlF6} = 217K; T_T(NH43FeF6 = 264K. In the low-temperature phase a polarization current of about 10^-9A is obtained and can be reversed when the sign of the polarization field is changed, a property which could correspond to a ferroelectric behavior. However, no pyroelectric current is detected when the temperature decreases from T_T. Another hypothesis, based on a field-induced polarization, has been considered : the depolarization current could be due to charge displacements from potential minima favored by rising temperature. In any way, the low-temperature phase is characterized by a remanent polarization.