Synthesis,structure, and antiviral properties of novel 2-adamantyl-5-aryl-2H-tetrazoles

Chemistry of Heterocyclic Compounds - The reaction of 5-aryl-NH-tetrazoles with adamantan-1-ol in concentrated sulfuric acid proceeds regioselectively with the formation of the corresponding...     

Nucleoside-5'-phosphorothioate analogues are biocompatible antioxidants dissolving efficiently amyloid beta-metal ion aggregates

Amyloid beta (Aβ) peptide is known to precipitate and form aggregates with zinc and copper ions in vitro and, in vivo in Alzheimer's disease (AD) patients. Metal-ion-chelation was suggested as therapy for the metal-ion-induced Aβ aggregation, metal-ion overload, and oxidative stress. In a quest for biocompatible metal-ion chelators potentially useful for AD therapy, we tested a series of nucleoside 5'-phosphorothioate derivatives as re-solubilization agents of Cu(+)/Cu(2+)/Zn(2+)-induced Aβ-aggregates, and inhibitors of Fenton reaction in Cu(+) or Fe(2+)/H(2)O(2) system. The most promising chelator in this series was found to be APCPP-γ-S. This nucleotide was found to be more efficient than EDTA in re-solubilization of Aβ(40)-Cu(2+) aggregates as observed by the lower diameter, d(H), (86 vs. 64 nm, respectively) obtained in dynamic light scattering measurements. Likewise, APCPP-γ-S dissolved Aβ(40)-Cu(+) and Aβ(42)-Cu(2+)/Zn(2+) aggregates, as monitored by (1)H-NMR and turbidity assays, respectively. Furthermore, addition of APCPP-γ-S to nine-day old Aβ(40)-Cu(2+)/Zn(2+) aggregates, resulted in size reduction as observed by transition electron microscopy (diameter reduction from 2.5 to 0.1 μm for Aβ(40)-Cu(2+) aggregates). APCPP-γ-S proved to be more efficient than ascorbic acid and GSH in reducing OH radical production in Fe(2+)/H(2)O(2) system (IC(50) values 85, 216 and, 92 μM, respectively). Therefore, we propose APCPP-γ-S as a potential AD therapy capable of both reducing OH radical production and re-solubilization of Aβ(40/42)-M(n+) aggregates.     

Self-assembly of (perfluoroalkyl)alkanes on a substrate surface from solutions in supercritical carbon dioxide

Toroidal self-assembled structures of perfluorododecylnonadecane and perfluorotetradecyloctadecane have been deposited on mica and highly oriented pyrolytic graphite surfaces by exposure of the substrates to solutions of the (pefluoroalkyl)alkanes in supercritical carbon dioxide. Scanning force microscopy (SFM) images have displayed a high degree of regularity of these self-assembled nanoobjects regarding size, shape, and packing in a monolayer. Analysis of SFM images allowed us to estimate that each toroidal domain has an outer diameter of about 50 nm and consists of several thousands of molecules. We propose a simple model explaining the clustering of the molecules to objects with a finite size. The model based on the close-packing principles predicts formation of toroids, whose size is determined by the molecular geometry. Here, we consider the amphiphilic nature of the (perfluoroalkyl)alkane molecules in combination with incommensurable packing parameters of the alkyl- and the perfluoralkyl-segments to be a key factor for such a self-assembly.     

Concerning an approach to identifying the Lamé parameters of an elastic functionally graded cylinder

Based on the general linear elasticity relations, an axisymmetric problem on the steady-state oscillations of a functionally graded hollow cylinder is formulated. The Lamé parameters are considered variable in radial coordinate. Oscillations are caused by the distributed load applied to the outer part of the cylinder boundary. Using the variable separation method, the direct problem on determining the radial and longitudinal components of the displacement field is investigated. The influence of the laws of variation for the Lamé parameters on acoustic characteristics is analysed. The inverse coefficient problem on the identification of the variable Lamé parameters from the data on the amplitude-frequency characteristic is stated. Based on the weak formulation of the problem for an elastic inhomogeneous body, a general linearised relation for the desired and given characteristics is obtained. A system of the Fredholm integral equations of the first kind is formulated with respect to two unknown corrections to the restored laws of the Lamé parameters change. The solution is built by means of an iterative process. A reconstruction of various laws of changing the Lamé parameters is carried out. The accuracy of the presented algorithm is estimated, and recommendations for the most efficient implementation of the reconstruction procedure are proposed.     

Cancellative residuated lattices arising on 2-generated submonoids of natural numbers

It is known that there are only two cancellative atoms in the subvariety lattice of residuated lattices, namely the variety of Abelian ?-groups ${\mathcal{CLG}}$ generated by the additive ?-group of integers and the variety ${\mathcal{CLG}^-}$ generated by the negative cone of this ?-group. In this paper we consider all cancellative residuated chains arising on 2-generated submonoids of natural numbers and show that almost all of them generate a cover of ${\mathcal{CLG}^-}$ . This proves that there are infinitely many covers above ${\mathcal{CLG}^-}$ which are commutative, integral, and representable.     

Hamiltonian cycles and paths with a prescribed set of edges in hypercubes and dense sets

This paper studies techniques of finding hamiltonian paths and cycles in hypercubes and dense sets of hypercubes. This problem is, in general, easily solvable but here the problem was modified by the requirement that a set of edges has to be used in such path or cycle. The main result of this paper says that for a given n, any sufficiently large hypercube contains a hamiltonian path or cycle with prescribed n edges just when the family of the edges satisfies certain natural necessary conditions. Analogous results are presented for dense sets. © 2005 Wiley Periodicals, Inc. J Graph Theory     

Frequency stabilization of a frequency-doubled 197.2 THz distributed feedback diode laser on rubidium 5S1/2→7S1/2 two-photon transitions

A 197.2 THz (1520.2 nm) ITU-T grid distributed feedback (DFB) diode laser is frequency stabilized at 197.198 THz by 1ocking its second harmonic (SH) signal on the rubidium 5S_1/2→7S_1/2 two-photon transition at 394.396 THz (760.1 nm). With 100 mW from the DFB diode laser and amplifying by an erbium-doped fiber amplifier, we obtain an SH power of 15 mW using a periodically poled lithium niobate (PPLN) waveguide frequency doubler. The stability was 2×10⁻¹¹ (10 s), corresponding to a frequency variation of 4 kHz at 1520.2 nm. Our scheme provides a compact and high performance frequency reference in the communication band.