Recognition of alpha-amino acid derivatives by N,N'-dibenzylated S,S-(+)-tetrandrine

Complexation of free and N-acetylated alpha-amino acid anions (Gly, Ala, Phe) and some structurally related guests by a dicationic cyclophane-type N,N'-dibenzylated chiral derivative of a bisisoquinoline macrocyclic alkaloid S,S-(+)-tetrandrine (DBT) has been studied by (1)H-NMR titrations in D(2)O. In contrast to other macrocyclic hosts like cyclodextrins and calixarenes, DBT shows highest affinity and large enantioselectivity (K(S)/K(R) >/=10) toward smaller N-acetylalanine and binds larger phenylalanine derivatives more weakly and non-selectively. With 1,2,3,4-tetrahydroisoquinoline-3-carboxylate, a rigid analog of phenylalanine, binding again becomes enantioselective with K(S)/K(R)= 3.8. The binding specificity of DBT is rationalized on the basis of molecular mechanics calculations.     

Stripe-geometry lasers and their properties

Design types of the stripe-geometry heterojunction laser are reviewed. Various methods for providing an electrical confinement, and/or optical confinement, are explained. The strong lateral confinement is shown to be important to stabilize the lasing filament in the cavity. Planar stripe-geometry lasers (without strong lateral optical confinement) have sometimes anomalous light output characteristics, containing kinks, discontinuities, or hysteresis loops. These irregularities are discussed in terms of optical nonlinear (self-focusing) mechanism. Problems of the electrical characterization of the continuously operating stripe-geometry lasers are considered.The author sincerely thanks his colleagues M. Osinski, A. P. Bogatov, O. G. Okhotnikov, G. T. Pak and G. G. Kharisov for their cooperation.     

Analysis of laser-structure anisotropic semiconductors by the Bloch-function method

The method of Bloch functions is used to obtain the radiation makeup of a semiconductor laser structure consisting of periodically alternating waveguide and antiguide regions, and the differntial gains for the different modes are determined. Pumping of antiguide regions with different structure parameters makes it possible to obtain the maximum gains of a Bloch mode made up of outflowing waveguide modes at the center of the brillouin lobe. The directivity pattern contains in this case sideband satellites in addition to the central lobe. When the structure is optimized, the intensity of the central lobe amounts to 70% of the total emission intensity.Optoelectronics Laboratory, Lebedev Physics Institute, Academy of Sciences of the USSR. Translated from Preprint. No. 105 of the Lebedev Physics Institute, Academy of Sciences of the USSR, 1989.     

Recent development in heavy paraffin synthesis from CO and H2

A review of recent studies on the Fischer–Tropsch synthesis of heavy paraffins is presented. The effects of temperature, pressure, feed composition, active metal, promoters and carriers on the formation of heavy products are discussed. New approaches to wax-selective processes such as the application of metallic carriers and supercritical fluids are also described.     

Carbonylation of chloroacetone to methyl acetoacetate

Methyl acetoacetate was prepared by the selective carbonylation of chloroacetone in the presence of a homogeneous palladium catalyst at 100 °C and under a CO pressure of 1.5 MPa.     

A New Concept for Time-of-Flight Mass Spectrometry with Slowed-down Short-Lived Isotopes

A new concept for direct mass measurements of short-lived nuclei with an electrostatic time-of-flight mass spectrometer is described. The spectrometer can be coupled to an in-flight separator such as SHIP or FRS via a gas stopping cell and a gas-filled linear Paul trap. The time required for mass measurement is of the order of a few milliseconds allowing one to investigate nuclei with these short half-lives. A mass-resolving-power m/Δm _FWHM=50 000 has been reached. First results of the range-focusing technique are presented, which is under development for the efficient stopping and extraction of relativistic exotic nuclei. This revised version was published online in July 2006 with corrections to the Cover Date.     

2,2′-Dipyridyl-6,6′-dicarboxylic acid diamides: Synthesis,complexation and extraction properties

New ligands for complexing of the post-transition metals – diamides of 2,2′-bipyridyl-6,6′-dicarboxylic acid were developed, synthesised and characterised. They were proposed to be effective extractants towards americium. The structures of the amides were studied in solid as well as in solution. The extraction of Am and lanthanides depending on diamide structure, chlorinated cobalt dicarbollide (CCD) – diamide ratio, type of diluent was studied. The optimal conditions for Am/REE separation were determined. The properties of new potentiometric sensors on the base of 2,2′-dipyridyl-6,6′-dicarboxylic acid diamides were studied. The correlation structure vs. properties of ionophores (i.e. extractants), their sensitivity and selectivity in sensor analysis and extraction are discussed.     

Fungus-resistant fluorosiloxane sealant

The results of the partial substitution of titanium dioxide in the composition of VGF-2 fluorosiloxane sealant for an antiseptic additive of benzoguanamine are presented. It is shown that the incorporation of benzoguanamine as a modifying agent and antiseptic into the formulation of VGF-2 sealant improves its fungus resistance and has hardly any effect on the technological and physicomechanical properties of the sealant. Based on the results of complex investigations, a new fluorosiloxane fungus-resistant sealant of the VGF-2-M trademark is developed.