Remote stereoselective deconjugation of α,β-unsaturated esters by simple amidation reactions

The thermodynamically disfavored isomerization of α,β-unsaturated esters to deconjugated β,γ-unsaturated analogues occurs readily when coupled to an amidation. Within the framework of macrocyclic derivatives, it is shown that 15, 16, and 18 membered macrocycles react with tBuOK and anilines to generate, in one-pot, β,γ-unsaturated amides (yields up to 88%). Importantly, single (chiral) diastereomers are isolated (d.r. > 49 : 1, ¹H NMR) irrespective of the size and nature of the rings, showing an effective transmission of remote stereochemistry during the isomerization process. CSP-chromatographic resolution and absolute configuration determination by VCD are achieved.     

A H, C and N NMR spectroscopic and GIAO DFT study of ethyl 5-oxo-2-phenyl-4-(2-phenylhydrazono)-4,5-dihydro-1H-pyrrole-3-carboxylate

¹⁵N-Labelled ethyl 5-oxo-2-phenyl-4-(2-phenylhydrazono)-4,5-dihydro-1H-pyrrole-3-carboxylate was synthesized by azo-coupling of diazotized aniline (using Na¹⁵NO₂ , 99% ¹⁵N) with ethyl 4,5-dihydro-5-oxo-2-phenyl-(1H)-pyrrole-3-carboxylate. The product was formed as a tautomeric hydrazone mixture as confirmed by ¹³C and ¹⁵N chemical shifts, and was obtained as a mixture of E and Z isomers according to ⁿJ(¹⁵N, ¹³C). A comparison of the ¹H NMR data with GIAO DFT calculations enabled determination of the configuration of the carboxy ester group in both isomers.     

Exploration of the electrophoretic behaviour of borane cluster anions and of the capability of capillary electrophoresis to separate them chirally

Mobilities of investigated boron cluster compounds in 3-(N-morpholino)propanesulfonic and phosphate buffers adjusted to pH 7 either with sodium hydroxide or with tris(hydroxymethyl)aminomethane depend on both buffer ions. The zone width and zone asymmetry, which are usually markedly higher than those of organic or common inorganic ions of comparable size, depend on the type of the borane cluster anion. Unusual shapes of zones of two investigated compounds have been found in tris phosphate buffer. Acetonitrile was superior to methanol as an organic additive to separation systems from the viewpoint of the zone symmetry and separation speed. Narrow trigonal zones, typical of organic ions non-interacting with the capillary wall, have been observed for some bridged sandwich cobalt complexes in run buffers with the addition of acetonitrile. The interaction of borane cluster anions with beta-cyclodextrin cavity is excessively strong in purely aqueous solutions. Methanol and acetonitrile, which generally weaken the interaction, sometimes affect the separation enantioselectivity of various compounds in different ways in addition to the weakening effect. Chiral discrimination was reached for all ten investigated anions, which belong to four different structural types of cluster boranes. Stability constants estimated for some analyte-beta-cyclodextrin complexes range between 100 and 1800 l/mol in acceptable separations. The relative difference of the constants was from 3 to 20%.     

Experimental demonstration of continuous variable quantum erasing

We experimentally demonstrate the concept of continuous variable quantum erasing. The amplitude quadrature of the signal state is labeled to another state via a quantum nondemolition interaction, leading to a large uncertainty in the determination of the phase quadrature due to the inextricable complementarity of the two observables. We show that by erasing the amplitude quadrature information we are able to recover the phase quadrature information of the signal state.     

Shear wave dispersion and attenuation in periodic systems of alternating solid and viscous fluid layers

The attenuation and dispersion of elastic waves in fluid-saturated rocks due to the viscosity of the pore fluid is investigated using an idealized exactly solvable example of a system of alternating solid and viscous fluid layers. Waves in periodic layered systems at low frequencies are studied using an asymptotic analysis of Rytov’s exact dispersion equations. Since the wavelength of shear waves in fluids (viscous skin depth) is much smaller than the wavelength of shear or compressional waves in solids, the presence of viscous fluid layers necessitates the inclusion of higher terms in the long-wavelength asymptotic expansion. This expansion allows for the derivation of explicit analytical expressions for the attenuation and dispersion of shear waves, with the directions of propagation and of particle motion being in the bedding plane. The attenuation (dispersion) is controlled by the parameter which represents the ratio of Biot’s characteristic frequency to the viscoelastic characteristic frequency. If Biot’s characteristic frequency is small compared with the viscoelastic characteristic frequency, the solution is identical to that derived from an anisotropic version of the Frenkel–Biot theory of poroelasticity. In the opposite case when Biot’s characteristic frequency is greater than the viscoelastic characteristic frequency, the attenuation/dispersion is dominated by the classical viscoelastic absorption due to the shear stiffening effect of the viscous fluid layers. The product of these two characteristic frequencies is equal to the squared resonant frequency of the layered system, times a dimensionless proportionality constant of the order 1. This explains why the visco-elastic and poroelastic mechanisms are usually treated separately in the context of macroscopic (effective medium) theories, as these theories imply that frequency is small compared to the resonant (scattering) frequency of individual pores.     

Water‐Soluble Polymeric Carbon Nitride Colloidal Nanoparticles for Highly Selective Quasi‐Homogeneous Photocatalysis

Heptazine‐based polymeric carbon nitrides (PCN) are promising photocatalysts for light‐driven redox transformations. However, their activity is hampered by low surface area resulting in low concentration of accessible active sites. Herein, we report a bottom‐up preparation of PCN nanoparticles with a narrow size distribution (ca. 10±3 nm), which are fully soluble in water showing no gelation or precipitation over several months. They allow photocatalysis to be carried out under quasi‐homogeneous conditions. The superior performance of water‐soluble PCN, compared to conventional solid PCN, is shown in photocatalytic H₂O₂ production via reduction of oxygen accompanied by highly selective photooxidation of 4‐methoxybenzyl alcohol and benzyl alcohol or lignocellulose‐derived feedstock (ethanol, glycerol, glucose). The dissolved photocatalyst can be easily recovered and re‐dissolved by simple modulation of the ionic strength of the medium, without any loss of activity and selectivity.     

Fuzzy equational logic

Presented is a completeness theorem for fuzzy equational logic with truth values in a complete residuated lattice: Given a fuzzy set Σ of identities and an identity p≈q, the degree to which p≈q syntactically follows (is provable) from Σ equals the degree to which p≈q semantically follows from Σ. Pavelka style generalization of well-known Birkhoff's theorem is therefore established. Received: 15 March 2000 / Revised version: 20 September 2000 Published online: 12 December 2001     

Capillary electrophoresis of boron cluster compounds in aqueous and nonaqueous solvents

The electrophoretic properties of boron cluster compounds were determined in water, methanol and ACN as solvents of the BGE and discussed based on the principles of ion migration. Two types of boron cluster compounds were investigated. One type consisted of derivatives of the nido-7,8-dicarbaundecaborate cluster, the other types are derivatized cobalt bis(dicarbollide) ions (COSANs) whose central cobalt atom is sandwiched by two 7,8-dicarbaundecaborate clusters. The BGE in all solvents was acetate/acetic acid buffer with pH 4.75 in water, 9.7 in methanol and 22.3 in ACN, respectively, at different ionic strength between 5 and 30 mM. The dependence of the mobility on ionic strength could not be explained by the theory of Debye, Hückel and Onsager, but good agreement was found upon considering an ion size parameter. Limiting mobilities were derived by curve fitting, and by the aid of the solvent viscosities the hydrodynamic radii of the analyte anions were calculated. They are between 0.25 and 0.48 nm, and were nearly independent of the solvent. Electrophoresis of the analytes in a BGE consisting of 6 mM perchloric acid in ACN allows the conclusion that the present boron cluster compounds behave as stronger acids than perchloric acid.     

Alkyl glycosides as potential anti-<Emphasis Type="Italic">Candida albicans</Emphasis> growth agents

Candida infections are becoming increasingly prevalent and many clinical isolates are resistant to common azole derivatives treatment. Accordingly, the capacity of a series of 19 alkyl glycosides, mainly mannosides and glucosides but also a cellobioside with aglycone chain-length from C-6 to C-20, to inhibit the growth of laboratory and clinically isolated strains of Candida albicans, was investigated. The study showed that only glycosides with the C-10 and C-12 aglycones were effective growth inhibitors of both types of Candida, strains, whose metabolic activity was also significantly reduced as revealed by an XTT assay.