Effects of saturation on optical bistability with coupled surface plasmons

We present exact numerical results for a symmetric layered medium (prism/Ag film/nonlinear dielectric/Ag film/prism) where the middle dielectric slab is assumed to have a saturation-type nonlinearity. We show bistable behaviour in the power dependence of the reflectivity ofp-polarized light under the condition when coupled surface modes are excited in the structure. Moreover, we study the effect of saturation on the bistable behaviour to show that multivalued character is inhibited by saturation effects. The field distributions corresponding to the minimum reflectivity states of the nonlinear structure are also presented.     

Dielectric studies of binary mixtures of n -propyl alcohol and ethylenediamine

Dielectric constant (ε’) and dielectric loss (ε") of n-propyl alcohol (PA), ethylenediamine (EDA) and their binary mixtures, for different mole fractions of ethylenediamine have been experimentally measured at 11.15 GHz microwave frequency. Values of density (ρ), viscosity (η) and square refractive index (n _D ² ) of binary mixtures as well as those of pure liquids are reported. Excess square refractive index, viscosity and activation energy of viscous flow have also been estimated. These parameters have been used to explain the formation of complexes in the system.     

The thiazolium-catalyzed Sila-Stetter reaction: conjugate addition of acylsilanes to unsaturated esters and ketones

A new acyl anion addition reaction between acylsilanes and alpha,beta-unsaturated conjugate acceptors promoted by a nucleophilic organic catalyst has been disclosed. The 1,4-dicarbonyl products produced in this reaction are highly useful synthons. Neutral carbenes (or zwitterions) generated in situ from commercial thiazolium salts are used as effective catalysts for the reaction which is in contrast to established anionic catalysts typically employed to promote the required Brook rearrangement (1,2-silyl shift from carbon to oxygen) involved in the reported reaction. This process successfully utilizes acylsilanes as tunable acyl anion progenitors and is tolerant of a wide range of structural diversity on the acylsilane or the conjugate acceptor.     

Spectrophotometric determination of thiourea in microgram quantities

Summary Copper(II) forms a stable colourless complex with thiourea. This property has been utilized to develop a Spectrophotometric method for the determination ofg quantities of thiourea. The complex absorbs in ultraviolet region and the determinations are carried out at 250 nm. The method permits the determination of thiourea from 10–60g with error not exceeding ± 1.0%.

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Zusammenfassung Kupfer(II) bildet mit Thioharnstoff eine farblosa Komplexverbindung, die sich auf Grund ihrer Absorption bei 250 nm zur spektrophotometrischen Bestimmung von Mikrogrammengen Thioharnstoff eignet. 10 bis 60g Thioharnstoff lassen sieh mit einem Fehler von höchstens ± 1,0% bestimmen.

     

Analytical aspects of some organic acids Part III

Summary m-Phenylenedioxydiacetic acid gives a white precipitate with thorium even in the absence of an electrolyte which is quantitative up toph 4. Be²⁺, Mg²⁺, Ca²⁺, Zn²⁺, Pb²⁺ and Mn²⁺ ions are removed by single precipitation and Al³⁺, UO₂ ²⁺ and trivalent cerite earth ions are removed by double precipitation. Sn²⁺, Sn⁴⁺ and Cr³⁺ ions interfere.Part II: See. Z. analyt. Chem.165, 343 (1959).     

New designs for inhibitors of the NF-κB: DNA binding

We present a series of new inhibitors of the association between nuclear factor kappa B (NF-B) and the corresponding B site in DNA. They were designed using the lead compound 15-deoxy-^12,14 -prostaglandin J₂ (PGJ2), which is a natural product with demonstrated inhibitory efficiency for this system. First, the binding mode of PGJ2 to NF-B was unraveled by GOLD docking calculation. Subsequently, substitutions were made to PGJ2 to optimize its association with NF-B. Care was taken not to strongly increase the reactivity of the new compounds, and to keep the overall shape, size and hydrophilicity of the lead compound, which should render them a similar bioavailability. Molecular mechanics calculations were performed to decide on the suitability of the substitutions, and to evaluate the energies of association with NF-B. Density functional theory calculations were performed also to study the overall reactivity of the substituted drugs towards NF-B. Important general conclusions were obtained, concerning the improvement of these natural inhibitors; namely, a set of rational methodologies were deduced to improve the association between the PGJ2 derivatives and NF-B, and their efficiency demonstrated by generating a set of substituted complexes, some of them with a very much increased affinity for NF-B, opening new doors to enlarge the therapeutic capabilities of this class of drugs.     

Analytical aspects of some organic acids

Summary A direct titrimetric method for the estimation of iron(III) has been developed, which involves the adjustment of concentration of iron(III) andPh, dilution, addition of 1 ml of 2% indicator solution and titration with EDTA (30° to 35° C). It is based on the fact that the iron(III) forms a blue coloured complex which is destroyed at the 11 molar ratio making the end-point of the titration. Quantity of iron(III) as small as 23.2 mg can be titrated accurately when present in a volume of 100 ml. Study of interferences revealed that quite a number of elements like Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, UO₂ ²⁺ and Mn²⁺ does not interfere, whereas much interference is caused by Cu²⁺, Zn²⁺, Pb²⁺, Fe²⁺, Co²⁺, Ni²⁺, ZrO²⁺, V0²⁺, Al³⁺, Cr³⁺, Ti⁴⁺, Ce⁴⁺ and Th⁴⁺. The method proposed for iron(III) is selective and should be of considerable use in many cases.Part III: See Z. analyt. Chem. 167, 332 (1959).     

Length dependent folding kinetics of phenylacetylene oligomers: structural characterization of a kinetic trap

Using simulation to study the folding kinetics of 20-mer poly-phenylacetylene (pPA) oligomers, we find a long time scale trapped kinetic phase in the cumulative folding time distribution. This is demonstrated using molecular dynamics to simulate an ensemble of over 100 folding trajectories. The simulation data are fit to a four-state kinetic model which includes the typical folded and unfolded states, along with an intermediate state, and most surprisingly, a kinetically trapped state. Topologically diverse conformations reminiscent of alpha helices, beta turns, and sheets in proteins are observed, along with unique structures in the form of knots. The nonhelical conformations are implicated, on the basis of structural correlations to kinetic parameters, to contribute to the trapped kinetic behavior. The strong solvophobic forces which mediate the folding process and produce a stable helical folded state also serve to overstabilize the nonhelical conformations, ultimately trapping them. From our simulations, the folding time is predicted to be on the order of 2.5-12.5 mus in the presence of the trapped kinetic phase. The folding mechanism for these 20-mer chains is compared with the previously reported folding mechanism for the pPA 12-mer chains. A linear scaling relationship between the chain length and the mean first passage time is predicted in the absence of the trapped kinetic phase. We discuss the major implications of this discovery in the design of self-assembling nanostructures.     

Asymmetric synthesis of functionalized trans-2,6-disubstituted piperidines with N-sulfinyl delta-amino beta-ketoesters. Synthesis of (-)-lasubine I

[reaction: see text] The hydroxy-directed reduction of 1,2-dehydropiperidines with the "ate" complex of DIBAL-H and n-BuLi affords functionalized trans-2,6-disubstituted piperidines. This methodology was employed in the asymmetric synthesis of the quinolizidine alkaloid (-)-lasubine I.