NMR elucidation of some ligands derived from the pentacycloundecane skeleton

The complete NMR elucidation of three novel pentacycloundecane (PCU)-derived ligands is reported. 2D NMR techniques are used to overcome the problem of major overlapping of methine signals on the cage skeleton. The compounds were synthesized as potential ligands to be used in asymmetric catalysis. They represent the first instance where aromatic moieties have been attached directly to the cage skeleton using lithiation techniques. The X-ray crystal structure of one of the ligands was obtained. The X-ray structure was helpful in determining the potential NOESY interactions within the set of molecules. For the other ligands a high level Density Functional Theory (DFT) optimization was performed [B3LYP/6-31+g(d)] to visualize possible NOE interactions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A new polymorph of a cobalt(III) Schiff base complex exhibits a one‐dimensional C—H⋯O hydrogen‐bonded extended structure with helical 21 symmetry

In a new polymorph of acetato(2,2′‐{imino­bis[(E)‐propane‐3,1‐diylnitrilo­methyl­idyne]}diphenol­ato)­cobalt(III), [Co(C₂₀H₂₃N₃O₂)(C₂H₃O₂)], in the space group P2₁/c, the Co^III ion is six‐coordinate, with unequal Co—O_phenolate distances that average 1.908 (12) Å and more similar Co—N_imine distances averaging 1.937 (4) Å. The acetate ion occupies the sixth coordination site and forms an intra­molecular hydrogen bond (H⋯O = 1.95 Å) with the Co‐bound NH group of the penta­dentate chelate. The extended structure is a one‐dimensional (aryl)C—H⋯O(carbonyl) hydrogen‐bonded polymer with 2₁ (helical) symmetry and is thus distinct from the simple hydrogen‐bonded stack of the P2₁/n polymorph [Matsumoto, Imaizumi & Ohyoshi (1983). Polyhedron, 2 , 137–139].     

Linear stability of solutal convection in solidifying mushy layers: permeable mush–melt interface

The linear stability theory is used to investigate analytically the effect of a permeable mush–melt boundary condition on the stability of solutal convection in a mushy layer of homogenous permeability at the near eutectic (solid) limit. The results clearly show that, in contrast to the impermeable mush–melt interface boundary condition, the application of the permeable mush–melt interface boundary condition destabilizes the convection in a mushy layer.     

Iridium-catalyzed asymmetric hydrogenation of olefins using TIQ phosphine–oxazoline ligands

A novel family of tetrahydroisoquinoline (TIQ) phosphine–oxazoline ligands and four corresponding iridium complexes have been developed and applied to the asymmetric hydrogenation of unfunctionalized olefins. The results showed that the best conversion rates were observed in up to 99% with an enantiomeric excess of 91%.     

An improved synthesis of Fmoc-N-methyl-alpha-amino acids

A highly efficient and environmentally more benign synthesis of Fmoc-N-methyl-alpha-amino acids from the corresponding Fmoc-amino acid, via intermediate 5-oxazolidinones, has been developed by using Lewis acid catalysis for the reductive opening of the oxazolidinone ring.     

A robust approach to studying the adsorption of Pluronic F108 on nonporous membranes

A method for poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) desorption from synthetic nonporous polymeric membranes, using hexane:isopropanol treatment and subsequent colorimetric quantification, is described. The polymers polysulfone, poly(vinyldiene fluoride), and poly(ether imide) were used to fabricate solid adsorption matrices. The desorbed Pluronic F108 forms a color complex with ammonium ferrothiocyanate (NH4FeSCN) and is based on partitioning of a chromophore present in NH4FeSCN from an aqueous phase to a chloroform phase in the presence of Pluronic. The protocols for Pluronic desorption and detection are simple, sensitive, inexpensive, rapid, and reproducible over a wide range of Pluronic coating concentrations and membrane surface chemistries. A linear response over the concentration range from 3 to 130 microg ml(-1) is obtained. The adsorption isotherms for flat sheet membranes are also described and the Langmuir equation provides the best fit for the adsorption data obtained within the concentration range studied. The absence of any significant interference from certain proteins, vitamins, carbohydrates, plasma, and halogenated derivatives makes the assay equally suitable for the estimation of Pluronic F108 in the attendant Pluronic conjugates or in biomedical applications. Using nonporous hollow fine fibers and capillary membranes as model curved substrates we were also able to correlate an increase in the radius of curvature with a corresponding increase in the surface interfacial adsorption of Pluronic F108.     

Kinetics and mechanism of hydroboration of oct-1-and-4-ene by dimeric dialkylboranes

The kinetics and mechanism of hydroboration of oct-1-and-4-ene with a series of dimeric dialkylboranes was investigated. The kinetic results showed that the hydroboration of terminal olefins proceeds via a three-halves-order mechanism, first-order with respect to the olefin and one-half-order with respect to the dimer. Using dicyclohexylborane, diisopinocamphenylborane, and 3,6-dimethylborepane the observed rate constants for the hydroboration of oct-4-ene were approximately 6 times smaller than those for oct-1-ene. Supporting computations showed that both steric and electronic effects influence the rate of hydroboration of both internal and terminal olefins. A model computational study of the isomerization of oct-4-ene with di(prop-2-yl)borane showed that formation of the terminal hydroborated complex is thermodynamically favored over the internal complex.     

Bidirectional racemic synthesis of the biologically active quinone cardinalin 3

Readily available 2,2',6,6'-tetramethoxy-1,1'-biphenyl was transformed in 14 synthetic steps into the natural product cardinalin 3 using a bidirectional approach. One of the key steps was the formation of the cis-1,3-dimethylnaphtho[2,3-c]pyran ring. (+/-)-1,1'-[6,6'-Diallyl-5,5'-bis(benzyloxy)-1,1',3,3'-tetramethoxy-2,2'-binaphthalene-7,7'-diyl]diethanol was treated with O(2) in the presence of CuCl(2) and catalytic PdCl(2) to afford 5,5'-bis(benzyloxy)-7,7',9,9'-tetramethoxy-1,1',3,3'-tetramethyl-1H,1'H-8,8'-bibenzo[g]isochromene. Hydrogenation of this compound afforded 7,7',9,9'-tetramethoxy-cis-1,3-cis-1',3'-tetramethyl-3,3',4,4'-tetrahydro-1H,1'H-8,8'-bibenzo[g]isochromene-5,5'-diol in quantitative yield, which was converted in 3 steps to cardinalin 3.     

On the Effect of Anisotropy on the Stability of Convection in Rotating Porous Media

We investigate natural convection in an anisotropic porous layer subjected to centrifugal body forces. The Darcy model (including centrifugal and permeability anisotropy effects) is used to describe the flow and a modified energy equation (including the effects of thermal anisotropy) is used in the current analysis. The linear stability theory is used to evaluate the critical Rayleigh number for the onset of convection in the presence of thermal and mechanical anisotropy. It is found that the convection is stabilized when the thermal anisotropy ratio (which is a function of the thermal and mechanical anisotropy parameters) is increased in magnitude.     

Radiating fluid sphere immersed in an anisotropic atmosphere

We model a radiating star undergoing dissipative gravitational collapse in the form of radial heat flux. The exterior of the collapsing star is described by the generalised Vaidya solution representing a mixture of null radiation and strings. Our model generalises previously known results of constant string density atmosphere to include inhomogeneities in the exterior spacetime. By utilising a causal heat transport equation of the Maxwell–Cattaneo form we show that relaxational effects are enhanced in the presence of inhomogeneities due to the string density.