Enantioselective Synthesis of Quaternary α‐Amino Acids Enabled by the Versatility of the Phenylselenonyl Group

A novel Cinchona alkaloid‐catalyzed enantioselective conjugate addition of α‐alkyl substituted α‐nitroacetates to phenyl vinyl selenone was developed. The resulting enantio‐enriched α,α‐dialkyl substituted α‐nitroacetates were subsequently converted to various cyclic and acyclic quaternary α‐amino acids, taking advantage of the rich functionalities of the resulting Michael adducts. Novel protocols allowing chemoselective reduction of phenyl selenone to phenyl selenide and reduction of alkyl phenyl selenones to alkanes are also reported.     

Steady compressible Navier–Stokes equations with large potential forces via a method of decomposition

We investigate the steady compressible Navier–Stokes equations near the equilibrium state v = 0, ρ = ρ₀ (v the velocity, ρ the density) corresponding to a large potential force. We introduce a method of decomposition for such equations: the velocity field v is split into a non-homogeneous incompressible part u (div (ρ₀u) = (0) and a compressible (irrotational) part ∇ϕ. In such a way, the original complicated mixed elliptic–hyperbolic system is split into several ‘standard’ equations: a Stokes-type system for u, a Poisson-type equation for ϕ and a transport equation for the perturbation of the density σ = ρ − ρ₀. For ρ₀ = const. (zero potential forces), the method coincides with the decomposition of Novotny and Padula [21]. To underline the advantages of the present approach, we give, as an example, a ‘simple’ proof of the existence of isothermal flows in bounded domains with no-slip boundary conditions. The approach is applicable, with some modifications, to more complicated geometries and to more complicated boundary conditions as we will show in forthcoming papers. © 1998 B.G. Teubner Stuttgart–John Wiley & Sons Ltd.     

Organostannate derivatives of dicyclohexylammonium hydrogen 2,6-pyridinedicarboxylate: solution/solid-state 13C,119Sn NMR and in vitro antitumour activity of bis(dicyclohexylammonium) bis(2,6-pyridinedicarboxylato)dibutylstannate,and the crystal structure of its monohydrate

Bis(dicyclohexylammonium) bis(2,6-pyridinedicarboxylato)dibutylstannate is assigned seven-fold coordination at tin on the basis of its ¹¹⁹Sn CP/MAS NMR chemical shift (δ=−424.9 ppm). The assignment has been corroborated by a crystal structure determination of its monohydrate, whose tin atom has the trans -C₂SnNO₄ pentagonal bipyramidal [Sn–C=2.040(9), 2.067(8) Å; C–Sn–C =168.9(5)°] geometry. One 2,6-pyridine- dicarboxylato group chelates to the tin atom (Sn–O=2.234(4), 2.260(4); Sn–N =2.279(5) Å) whereas the other binds through only one carboxyl –CO₂ end (Sn–O=2.416(5), 2.441(5) Å). Hydrogen bonds link the cation and the stannate into a linear chain parallel to the b -axis. The lattice water molecule is hydrogen-bonded to the free carboxyl end. The anhydrous compound showed higher in vitro antitumor activity than those of carboplatin and cisplatin when screened against breast (MCF-7, EVSAT), colonic (WiDr), ovarian (IGROV) and renal (A498) carcinoma, and melanoma (M19 MEL) cell lines. © 1997 by John Wiley & Sons, Ltd.     

A multimodal analytical toolkit to resolve correlated reaction pathways: the case of nanoparticle formation in zeolites

Unraveling the complex, competing pathways that can govern reactions in multicomponent systems is an experimental and technical challenge. We outline and apply a novel analytical toolkit that fully leverages the synchronicity of multimodal experiments to deconvolute causal from correlative relationships and resolve structural and chemical changes in complex materials. Here, simultaneous multimodal measurements combined diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and angular dispersive X-ray scattering suitable for pair distribution function (PDF), X-ray diffraction (XRD) and small angle X-ray scattering (SAXS) analyses. The multimodal experimental data was interpreted via multi-level analysis; conventional analyses of each data series were integrated through meta-analysis involving non-negative matrix factorization (NMF) as a dimensional reduction algorithm and correlation analysis. We apply this toolkit to build a cohesive mechanistic picture of the pathways governing silver nanoparticle formation in zeolite A (LTA), which is key to designing catalytic and separations-based applications. For this Ag-LTA system, the mechanisms of zeolite dehydration, framework flexing, ion reduction, and cluster and nanoparticle formation and transport through the zeolite are elucidated. We note that the advanced analytical approach outline here can be applied generally to multimodal experiments, to take full advantage of the efficiencies and self-consistencies in understanding complex materials and go beyond what can be achieved by conventional approaches to data analysis.

Multimodal in situ experimental data probing a complex reaction have been integrated via a multi-level analysis involving non-negative matrix factorization and correlation analysis. This strategy can be applied generally to multimodal experiments.     

Matrices for capillary gel electrophoresis--a brief overview of uncommon gels

This article gives an overview of uncommon replaceable matrices (gels) for capillary gel electrophoresis. This electrophoretic technique is useful mainly for the separation and analysis of biopolymers-nucleic acids and their fragments, and proteins/peptides. Commonly used gels are not reviewed. Those mentioned and discussed here are gels containing saccharides, newly developed acrylamide-based gels and thermoadjustable viscosity polymers, namely triblock copolymers and grafted polyacrylamide.     

Chemical analysis of Gothic mortar from a bridge pier in Roudnice nad Labem (Czech Republic)

In this paper, a Gothic mortar originating from the remains of a bridge pier in Roudnice nad Labem (Czech Republic) was analyzed. The inorganic composition of the mortar showing special mechanical properties was studied using polarizing light microscopy, scanning electron microscopy coupled with energy dispersive X-ray spectrometry, and X-ray diffraction, while the protein content was analyzed by peptide mass mapping using matrix-assisted laser desorption/ionization—time of flight mass spectrometry and nanoliquid chromatography coupled to tandem mass spectrometry. Two types of inorganic binders having a composition similar to mineral wollastonite and hydraulic lime and milk protein additive were detected. We believe that organic and inorganic binders added together to the mortar increase its hardness and firmness in the aquatic environment.     

Multicomponent analysis by off-line combination of synchronous fluorescence spectroscopy and capillary electrophoresis of collagen glycation adducts

Capillary electrophoresis separation and synchronous fluorescence spectral detection was used off-line to reveal the nature of fluorescent adducts formed in vivo in the collagen molecule and their distribution in the molecule. It was shown that by using the delta lamda in the area of the Stokes shift for the analyzed entities (approximately 10 nm for pentosidine, 4,5(E)-epoxy-2(E)-heptenal and 4,5(E)-epoxy-2(E)-decenal lysine adducts) a distinct profile of spectral bands can be obtained allowing for differentiation of the several entities involved. In combination with capillary electrophoretic separation of the CNBr peptides the location of individual adducts was possible: while pentosidine (and, perhaps, pentosidine related compounds K1-K4) is found in the large alpha 1(I)CB6 and alpha 2(I)CB3.5 peptides along with a complete set of the other fluorescent adducts, low-molecular-mass peptides originating from the terminal region of the molecule are devoid of any fluorescence. All other parts of the molecule possess synchronous fluorescence profiles corresponding to the intact molecule except that they are devoid of pentosidine. The results indicate random distribution of fluorescent adducts in the collagen molecule and, in a broader context, indicate the usefulness of multicomponent analysis by means of combining synchronous luminescence spectra and capillary electrophoresis.     

Carbon-Nanotube-Appended PAMAM Dendrimers Bearing Iron(II) α-Keto Acid Complexes: Catalytic Non-Heme Oxygenase Models

Poly(amidoamine) dendrimers grafted on carbon nanotubes have been appended with iron(II)-α-keto acid (benzoylformate) complex of polypyridyl ligand to design artificial non-heme oxygenase model. This nano-enzyme was applied for selective catalytic oxidation of organic molecules. Although the carbon nanotubes serve as a robust heterogeneous platform, the amine terminals of dendrimers provide catalysts binding sites and the amide bonds provide a necessary second coordination sphere similar to the enzymatic polypeptide chains. Such a hybrid design prevented the deactivation of the primary active sites leading to 8 times faster oxidative decarboxylation rates than those of its homogeneous analogue. An electrophilic iron(IV)-oxo intermediate has been intercepted, which catalyzes the selective oxidation of alcohols to aldehydes and incorporates single oxygen atoms into sulfides and olefins by using aerial oxygen with multiple turnover numbers. The catalyst was consecutively regenerated three times by mild chemical treatment and showed negligible loss of activity.     

$C^\infty$ regularity of the free boundary for a two-dimensional optimal compliance problem

We study the regularizing effect of perimeter penalties for a problem of optimal compliance in two dimensions. In particular, we consider minimizers of

Separation of structurally related peptides by open-tubular capillary electrochromatography using (metallo)porphyrins as the adsorbed stationary phase

Several (metallo)porphyrins, particularly the porphyrin derivative tetraphenylporphyrin, and complexes of porphyrin derivatives with metal ions (Zn2+, Cu2+, Ni2+, Co2+, Co3+) have been employed as the stationary phase physically adsorbed onto the inner fused-silica capillary surface for open-tubular capillary electrochromatography, and applied for the separation of structurally related peptides. Four octapeptides, derivatives of the B23-B30 fragment of the B-chain of human insulin with minor changes in their sequences (presence of lysine or ornithine in position B-29, presence or absence of phenylacetyl protecting group on the amino group of lysine/ornithine or N-terminal amino group of glycine), were studied as model analytes. Separations were performed both in alkaline (pH 9.0) and in acidic (pH 2.25) background electrolytes, and the changes in the migration/retention behaviour of the model set of peptides were investigated with respect to the porphyrin periphery/central metal atom and the charge of the octapeptides modified. The key moment of successful separation of these peptides seems to be the accessibility of functional groups of the peptides to the interaction with the modifiers tested herein.